CA1090684A - Method and an apparatus for cleaning a cold rolled steel sheet - Google Patents
Method and an apparatus for cleaning a cold rolled steel sheetInfo
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- CA1090684A CA1090684A CA273,607A CA273607A CA1090684A CA 1090684 A CA1090684 A CA 1090684A CA 273607 A CA273607 A CA 273607A CA 1090684 A CA1090684 A CA 1090684A
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Abstract
Abstract of the Disclosure A method for cleaning a cold rolled steel sheet which comprises wetting the surface of the cold rolled steel sheet with a wetting agent, jetting a high-pressure fresh water on the wetted surface, forming a continuous water jet curtain in a straight line across the width of the steel sheet, and remov-ing a rolling lubricant and iron powders adhering on the surface simultaneously with the said wetting agent.
Description
-` 1090~
The present invention relates to a method and an -apparatus for cleaning cold rolled steel products such as steel strips, sheets and plates (hereinafter called steel sheet).
In the production of a cold rolled steel sheet, the steel sheet is reduced by the cold rolling to an almost final thickness, and the steel sheet thus cold rolled is very hard, and for applications where good working properties such as bending and drawing are required, it is necessary to annea~
such cold rolled steel sheets appropriately depending on their uses in order to improve mechanical properties. Such annealing is usually done at a temperature ranging from 550C to 800C
in a non-oxidizing gas atmosphere.
However, when the steel sheet is cold rolled, a large amount of mixture of lubricant oil used in the cold rolling and metal powders caused by the friction during the cold rolling remains on the surface of the cold rolled steel sheet, and if the steel sheet with this mixture is annealed, the rolling oil is carbonized and the metal powders are partially carburized and adhere to the steel surface to cause dirty surface and remarkable degradation of surface properties, resulting in loss of commercial value as final steel products and in addition causing considerable hindrance in subsequent workings. For example, when such dirty cold rolled steel sheets are used as p~ating substrates, the residues adhering to the steel surface cannot be removed even by pretreatments for the plating and cause vital surface defects which hinder satisfactory coating so that the surface appearance is deteriorated and the corrosion resistance is remarkably decreased.
Further, when such dirty cold rolled steel sheets are used as substrate for paint coating, pretreatments such as a phosphate coating cannot be performed satisfactorily.
For the reasons set forth above, it is necessary to lOgO~;8~
remove the surface residues by surface cleaning prior to the annealing of the cold rolled steel sheet.
However, the conventional art has been confronted with difficulties in removal of the mixture of the rolling oil and the metal powders sticking to the steel surface after the cold rolling, and the surface cleaning method which can be applied to the cold rolled steel sheet is very limited. This is due to the nature of the surface residues after the cold rolling.
According to the discoveries of the present inventors, main components, such as fatty acids and fatty acid esters, of the rolling oil chemically combines in an iron-soap with a thin iron oxide film covering the steel sheet surface and fine iron powders generated by friction during the rolling so that the iron powders themselves are strongly adhering to each other or they strongly adhere to the steel sheet surface by means of the soap thus formed, and the fine iron powders are less than about 0.1~ in their particle size and are ferromagnetic, easily magnetized and strongly attracted by the steel surface. These facts are considered to cause the difficulties in removing the mixture.
For example, as disclosed by "Tekko Seizo Ho" (Steel Production Process) Section III Workings (2) edited by Japan Iron & Steel Association, an electrolytic method has been esta-blished as a cleaning method for surface cleaning of the steel sheet after the cold rolling, and this method is performed in an electrolytic cleaning line of a total length of about several ten meters, provided separately or as an entry equipment of a continuous annealing furnace. The electroly~ic cleaning line normally comprises four stages of processing, that is, alkali-immersion, brushing, alkali-electrolysis and brushing, wherein the rolling oil is removed by saponification of the alkali while the fine iron powders are removed by action of the brushing.
- 1()90~;8~
For this reason, a longer electrolytic cleaning line is required as the rolling speed of the rolling mill to which the line is adjoined increases, and maintenance of the brushing section, which performs the mechanical removal, is not easy and requires considerable economical cost and consumes a great energy.
Further, from the aspect of efficiency in the rolling oil removal, an alkali solution mainly composed of sodium silicate is used, but during the electrolysis in such a silicate solution, a film mainly composed of silicate is formed on the steel surface being treated if one tries to remove the rolling oil satisfactorily, which film causes vital hindrance against the properties of the final products, such as solderability required for assembling after press-forming, accessibility to phosphate treatment as a pretreatment for paint coating, and qualities required as a plated steel plate such as a tin plate.
In order to overcome the above difficulties, trials .
and proposals for simplifying the surface cleaning step by .
omitting the electrolytic cleaning or, further, eliminating the step have been made for a long time.
One of the proposed methods uses a brushing treatment alone omitting the alkali electrolysis treatment. By the `~ omission of the alkali electrolysis treatment, the degradation of the steel sheet due to the silicate film formation can be prevented, but in turn, the rolling oil removal efficiency decreases, resulting in decreasing of the iron powder removal efficiency, with a large amount of residue unremoved even after ., the annealing, and as a whole degradation of the surface clean-~; ness as compared with the electrolytic cleaning.
Another proposed method is based on the principle of the mill cleaning or detergent rolling, and uses a detergent mainly composed of a surface active agent, and a warm water .
10~
instead of the rolling oil in the final stand of the cold roll-ing mill. According to this method, various modifications and considerations are given to the rolling oil used in all rolling stands except for the last stand, and to the detergent used in the last stand, but in spite of these efforts, the surface cleanness is not improved satisfactorily and the power consump-tion at the last rolling stand increases. Thus, this method has not yet been successful and established.
In spite of various trials and proposals as above for replacing the electrolytic cleaning method, none of them have been successful.
Therefore, the conventional art has not been success-ful in overcoming the problem that the residues produced from the rolling oil and the iron powders, sticking to the steel surface after the annealing, cause vital effects on the quality and properties of the final products. Further, as the surface cléanness of the cold rolled steel sheet has a definite and clear effect on the corrosion resistance after paint coating, and, improvement of the surface cleanness has been always demanded for so that up to now, substantially all of the cold rolled steel sheets are produced using the electrolytic cleaning line in spite of its large power consumption.
Therefore, one of the objects of the present invention is to provide a method and an apparatus which provides a high degree of cleaning efficiency at low cost and save power con-sumption by elimination of the electrolytic cleaning step in the production process of a cold rolled steel sheet.
The term "sheet" used in the present invention includes "foil", "plate", "strip" and "bar".
From the aspect of saving of the energy consumption, the present inventors have made extensive and various studies and experiments for the purpose of obtaining a surface cleanness 1(J90~8~
~imilar or better than that obtainable by the conventional electrolytic cleaning process in spite of the elimination of the electrolytic cleaning step, and have solved the technical incompatibility of the conventional art that if one tries to implify the cleaning step the surface cleanness deteriorates, and if one trie~ to improve the surface cleanness the cleaning step becomes complicated and capital cost and energy consumption increases considerably.
The present inventors have discovered that when a surface of steel sheet after the cold rolling is simply wetted with an organic or inorganic wetting agent (hereinafter called ~imply wetting solution) and then a high-pressure water jet is~
applied thereon, the rolling oil and the iron powders sticking to the steel surface can be easily removed together with the wetting solution by contact with the high-pressure water jet in a very ~hort time, and yet the surface cleanne~s thu~ obtained 18 similar or better than that obtained by cleaning through the electrolytic cleaning line and can be subjected directly to the annealing. By thi Q method, the wetting solution applying device and the high-pressure water jet device can be incorporated a~ a ; very compact equipment in the delivery of the final stand of cold rolling mill or in the entry of a continuous annealing furnace. In this way, the present inventors have succeeded in eliminating the electrolytic cleaning line.
me invention relates to a production process for a cold rolled steel sheet which compri~es a step of cold rolling pickled steel sheet, a step of cleaning a cold rolled sheet and a step of annealing the cleaned steel sheet. The process is characterized by the fact that the cleaning ~tep comprise~
wetting the surface of the cold rolled steel sheet with a wet-ting agent solution in an amount of at least 5 - 10 ml/m2, jetting a high-pres~ure fresh water on the wetted surf-ce, form-ing a continuous water jet curtain in a straight line acros~
the width of the steel sheet and removing a rolling lubricant and iron powders adhering on the surface simultaneously with the said wetting agent.
The present invention will be more clearly understood from the embodiments shown in the attached drawings. It should be understood, however, that the present invention is not limited to these embodiments.
Figures 1 and 2 illu~trate respectively one embodiment of the production proces~ of a cold rolled steel sheet according to the present inven- -tion, ~ .
10'3(~
Figure 3 shows the relation between the water jet energy received by the steel sheet and the jet nozzle pressure for comparison of the water jet according to the present invention with the conventional alkali spray, Figures 4(a), (b) and (c) show schematically various types of jet water curtains; and Figure 5 shows schematically the jet water curtain from a slit nozzle.
Referring to Figure 1, 1 is a pay-off reel, 2 is a guide roll, 3 are rolling mill stands, 3' is a final rolling stand, and 4 is a tension reel. The strip 5 as a coil mounted on the pay-off reel passes through the guide rolls and cold rolled by the work rolls of the rolling stands with application of rolling oil and coiled on the tension reel 4. At the ; delivery of the final stand 3' of the rolling mill stands, there are provided a wetting solution applicator 6, a squeeze roll 7, a high-pressure water jet nozzle 8, a squeeze roll 7' and an air knife 9, which in combination constitutes a cleaning apparatus 10. The surface of the strip 5' coming out of the final stand 3' is contaminated with a large amount of the rolling oil and the fine iron powders.
The strip enters the cleaning apparatus via the guide ; rolls 2', and applied with the wetting solution by the appli-cator 6 ontc the mixture of the rolling oil and the fine iron powders sticking to the steel surface. Then high-pressure water jet is jetted from the high-pressure water jet nozzle 8 onto the strip surface adhered with the mixture of the rolling oil and the fine iron powders and applied with the wetting solution thereon, and after both of the mixture and the wetting solution are removed simultaneously, the water on the strip surface is removed by the squeeze rolls 7' and the air knife 9 and the 10~0684 strip is coiled on the tension reel 4.
Referring to Figure 2 illustrating another embodiment of the present invention where the cleaning apparatus is pro-vided at the entry of a continuous annealing furnace, the strip 5 from No. 1 and No. 2 coil holder 11 passes through a welder 12, a pinch roll 13 and enters a cleaning apparatus similar to that shown in Figure 1 where the surface of the strip 5 is cleaned fully, and then dried by a dryer 14. The cleaned strip 5' is annealed normally by a continuous annealing apparatus 15, and after ordinary after-treatments tnot shown) coiled on No. 1 and No. 2 tension reels 16.
Description will be made on the method according to the present invention.
As for the inorganic wetting agent to be applied onto the cold rolled steel sheet with the mixture of rolling oil and fine iron powders adhering thereon, an aqueous solution mainly `? composed of one or more of sodium silicate, sodium hydroxide (caustic soda), sodium aluminate and sodium phosphate may be used.
,. . . .
i' 20 As for the alkali concentration, 5 - 10 wt.% is preferable. In addition, in order to improve removal efficiency of the various rolling oils, 0.3 to 1 wt.% of a surface active agent, and further, in case when the amount of adhering iron `;
powders is large, 3 to 6 wt.% of an iron-chelating agent may be added. As for the iron-chelating agent, citric acid and its compounds, gluconic acid and its compounds, carbamic acids, ~-!i' hydroxylamines and amines may be used.
' As for the organic wetting agent, organic solvents having a viscosity ranging from 0.5 to 4CP (at 30C), namely a viscosity similar to that of water, are useful.
In order to attain very efficient removal of the rolling oil and the iron powders from the steel surface during ~ .
_, _ .. .. .
0~84 the cold rolling which is normally done at a high speed, it is necessary that the wetting solution, namely the organic solvent in this case, has a high degree of removability by a high-pressure water jet. For this purpose an organic solvent unsusceptible to emulsification or dissolution into the water and having a viscosity similar to or same as that of water is desirable. To satisfy the above requirement, hydrocarbons and halogenated hydrocarbons are suitable, and kerosene, light oil, solvent naphtha, trichloroethylene, perchloroethylene have a viscosity within the above specified range. Therefore, in the present invention, a mixture solvent of one or more of the above hydrocarbons is used.
Regarding the amount of the wetting solution to be applied on the steel sheet, 5 - 10 ml/m2 attainable by the roll squeezing is sufficient. When the amount is less than 5 ml/m2, the removal of the rolling oil and the iron powders is not satisfactory. There is no upper limitation on the applied amount of the wetting solution, but the amounts more than 10 ml/m2 are not economical.
What are important in the combination of the appli-cation of the wetting solution and the high-pressure water jet are, in the first place, that all of the rolling oil, the fine iron powders and the wetting agents are removed altogether at once by one coup of the water jet jetted on the steel surface.
In this case, the work performed by the jet water is determined by the jet water pressure imposed on the steel sheet and the volume of jet water per unit area of the steel sheet surface (hereinafter called flow density), and according to the dis-coveries of the present inventors, the work can be expressed simply by the jet nozzle pressure and the flow density. As shown in Figure 3, it is necessary for obtaining the desired results that the jet nozzle pressure is not less than 5 kg/cm2, preferably not less than 8 kg/cm for any portion of the steel sheet surface and the work expressed by (jet nozzle pressure x flow density) is not less than 0.1 w hr/m2 per unit area of the steel sheet surface.
According to the results of the extensive experiments conducted by the present inventors, a surface cleanness similar to that obtained by the electrolytic cleaning can be obtained in a short time so far as the above conditions are maintained (see Table 2). Therefore, in an actual operation, only by i 10 adjusting the water jet conditions in accordance with a maximum traveling speed of steel sheet, a surface cleanness similar to that obtained by the electrolytic cleaning can be obtained in spite of their variations of the traveling speed. Further, the high-pressure water jet nozzle may be arranged only in a single stage so as to cover the whole width of the steel sheet.
Secondly, as shown in Figure 4(a), it is necessary that the iet water curtain 18 formed is jetted onto the steel sheet ~~
surface 17 in a linear form across the steel width. If the jet water curtain is not formed in a linear form across the sheet width but in a zig-zag form (Figure 4(b)) or a feather-stitch `
form (Figure 4(c)) as commonly done, the jet water does not contact the steel sheet surface at the same time all across the sheet width and the water jetted on the steel surface flows from the portions of the steel surface which have been already struck with the jet water to the portions which have not been struck with the jet water and dilutes or washes off the wetting solu-tion on the surface so that the rolling oil and the fine iron powders are not completely removed when the jet water strikes thereon, leaving stripes 19 parallel to the traveling direction.
Thus, it is important that the jet water curtain strikes on the sheet surface at the same time all across the sheet width.
Therefore, thirdly, it is important to select a nozzle g 1090t;84 for satisfying the above requirement. In order to maintain the required jet water pressure imposed on the steel sheet surface and the required work on the steel surface performed by the jet water and to bring the jet water curtain into contact with the steel sheet surface at the same time all across the sheet width, a slit nozzle as shown in Figure 5 is most desirable. The slit nozzle has a linear slit of a constant width and a length long enough to cover the whole width of the sheet. By using this slit nozzle, it is possible to jet a fresh water at the same time all across the sheet width with a constant jet water pres-sure and a constant flow density at any portion of the sheet surface.
In case of a conventional spray cleaning technique, a number of nozzles are provided in a pressure header so as to spray the fresh water onto the steel sheet surface. However, the cleaning water is sprayed by the nozzles in a divergent form at a certain angle, and presently four types of nozzles having a spray pattern of "full cone", "hollow cone", "square spray" and "flat spray" are commercially available.
When the above commercially available nozzles are used in the present invention, it is necessary that they satisfy the first and second requirements mentioned hereinbefore. The commercially available nozzles of "full cone", "hollow cone" or "square spray" type cannot be used satisfactorily in the present invention because it is difficult for these nozzles to form a jet water curtain in a linear form across the sheet width and to bring the jet water into contact with the sheet surface at the same time all across the sheet width, and the jetted water from these nozzles spreads over a wide area and thus the flow density decreases so that the first requirement cannot easily be satisfied by maintaining the required jet water pressure imposed on the steel sheet.
1090~;84 On the other hand, the commercially available "flat spray" nozzles can be used in the present invention if a number of them are arranged on a header in such a manner that the divergent angle of each water jet is made identical so as to form jet water curtains in a linear form across the sheet width.
In this case, however, it should be noted that both the flow rate of jet water and the jet water pressure imposed on the steel sheet are at their maximum at the center portion of diverging water jet, thus exhibiting their distributions in a mountain-like curve. Therefore, when a number of "flat spray"
nozzles are arranged on a pressure header, it is necessary to -~
adjust the pitch between individual nozzles so as to avoid too much pitch which causes failure to satisfy the first requirement at an intermediate portion between the nozzles. This is the fourth important point.
The fifth important point is the surface temperature of the steel sheet just prior to the application of the jet water -~
thereon and the temperature of the wetting solution applied thereon.
As the cold rolling oil,-oils, such as palm oil and beef tallow, which freezes at ordinary temperatures, are usually used, and in order to remove the rolling oils adhering to the steel surface by a fresh water jet, it is necessary to maintain the adhering rolling oils in a melted state. This is parti-cularly important in cases where the inorganic agents are used for the wetting solution. Results of studies from the above view ; point have revealed that it is desirable to maintain the surface of the steel sheet and the wetting solution at temperatures not lower than 70C. If they are maintained below 70C, desired results in respect of the surface cleanness cannot be obtained.
As for a method for maintaining the surface of-the steel sheet and the wetting solution to be applied thereto at 1090~E~4 70C or higher, it is possi~le to utilize the heat generated in rolling by applying the present invention immediately àfter the cold rolling, because the steel sheet coming out of the cold rolling mill is usually at 100C or higher, or it is possible to pre-heat the steel sheet (as is done for cold strip coils) in cases where the present invention is applied at the entry of a continuous annealing furnace, etc.
As for the pre-heating means, a conventional pre-heating means such as hot-air, steam, hot water, may be used in single or in combination. However, a more desirable method is to immerse the steel sheet in a heated wetting solution so as to perform both the coating of the wetting solution and the pre-` heating of the steel sheet simultaneously.
According to the experiments by the present inventors,the required surface temperature of the steel sheet can be attained by immersion in a hot water heated at 95C in a short time of one second or less in case of a cold rolled steel sheet of an ordinary thickness.
Sixthly, it is important that the rolling oil and the fine iron powders which have been removed will not adhere steel sheet again.
The rolling oil and the fine iron powders adhering to the steel sheet surface are removed altogether from the sheet surface by the jet water according to the present invention and flow as a dirty drainage, and this dirty drainage must be removed quickly from the steel sheet surface, otherwise it remains on the sheet surface and contaminates the surface again.
The drainage can be removed by means of squeeze rolls, an air knife in single or in combination. However, in order to remove it quickly to attain the desired results of the present invention, it is desirable that the above drainage removal means is arranged immediately after the train of the fresh water jet 1090~;84 nozzle. Other than the above removal means, a fresh water jet may be used for removing the dirty drainage.
The present invention is basically different from the conventional art, called alkali spray cleaning method, which is similar to the present invention in respect of the use of alkali.
The surface cleaning according to the alkali spray cleaning method is performed by the combination of the alkali spray and the water rinsing. In this case, the surface dirts are removed in the stage of alkali spray, and water rinsing is necessary to remove the alkali remaining on the steel surface from which the dirts have been removed. Whereas according to the present invention, the wetting solution is merely applied on the surface and thus the dirts are not removed during the stage of the wetting solution application. The removal of the surface dirts or stains, according to the present invention, is performed only by the jet blowing of a high-pressure water after the application of wetting solution, and the wetting solution is also removed together with the dirts. Thus, according to the present invention, the removal of dirts and water rinsing are effected together in a single stage.
Further, in the conventional alkali spray cleaning method, a spray chamber in which a number of spray nozzles are arranged is used, but there is no specific limitation in the selection and arrangement of the nozzles as required in the present invention. Thus, in the present invention, the first and second requirements as mentioned hereinbefore must be satis-fied, while in the alkali spray cleaning method, there is no such requirement, and the nozzles are arranged in the spray chamber in such a manner that the steel sheet surface is brought into contact with the spray liquid repeatedly until the dirts on the steel sheet surface are removed.
The conditions of the water jet in the present - 109()~i84 invention are quite different from the conventional art. For example, according to the disclosure of "Cleaning of Metal" of Modern Engineering Library published by Chijin Shokan, Tokyo, Japan, the spray pressure ranges from 8 to 30 psig, or 2.1 kg/cm2 at maximum, and the spray amount ranges from 60 to 100 1/m2 per minute, and the cleaning is done in about 3 minutes. These conditions may be expressed by the nozzle pressure and the work of water given to the steel sheet as shown in Figure 3 from which it is very clearly understood that the conventional art is done in a completely different zone from that of the present inven-tion. Further, in the present invention, the cleaning is com-pleted in a time shorter than about one second, and thus the cleaning effect is much higher.
The reason why a high-pressure jet, as in the present invention, is not used in the conventional alkali spray method is that there is a problem of foaming due to spraying of the alkali solution. For example, excessive foaming will cause over-flow of the solution from the cleaning device. In case of the conventional alkali spray cleaning method, a nozzle pressure exceeding 20 psig (1.5 kg/cm~) will cause foaming and thus the operation is normally performed with a nozzle pressure below 20 psig. If a higher nozzle pressure is to be applied, it is necessary to use a cleaning agent of less foamability, but such cleaning agent is also low in cleaning power.
This fact has been an important limitation in the conventional alkali-spray cleaning method.
Thus, the present invention is based on a completely different technical thought from that of the alkali spray cleaning method, and is completely free from the foaming problem because the wetting solution is merely applied and the water is jetted under a high pressure. Therefore, in the present invention the wetting solution can be selected without limitations from the 1090~;84 i foaming problem.
As a conventional art similar to the present invention -in that an organic solvent is used for the surface cleaning, there are a method in which adhering oil or grease and metal particles are removed simultaneously by the dissolving power and jet pressure of the solvent, and a UPetroleum Solvent Spray Method" (old U. S. Army Specification MIL-116C). ~;
These methods are limited in the kind of the solvents used because of danger of flaming and explosion induced by the spraying. The present inventors have conducted these spray methods with solvents selected mainly from the aspect of clean-ing effect, but the results as shown in Example 4 have revealed ~ that their cleaning effects are far inferior to that obtained by the present invention. -:
Still further, it has been conventionally practiced --, in various fields to jet a high-pressure water. However, in the field of a steel surface cleaning, a water jet has been used only as a low-pressure spray-rinse for the water washing in the finishing step after the surface cleaning such as alkali clean-ing and emulsion cleaning. This will be clearly understood if one refers to the surface cleaning methods specified by JIS Z
0303 or MIL-P-ll 6D according to which a surface cleaning method only by water jet has not been classified or specified.
, ~ ~
` ~aturally, as the water itself is a polar solvent, it ~i is possible to remove water-soluble dirts by a water jet and some surface cleaning effect can be attained thereby. However, the mixture of rolling oil and fine iron powders sticking to the steel surface after cold rolling, to which the present invention is directed cannot be removed only by water jet as clearly understood in the examples hereinafter set forth. The present invention is based on the discovery that when the wet-; ting solution is applied to the steel sheet as cold rolled and ~.
109~84 the high-pressure water jet strikes on the surface under the ; presence of the wetting solution, the surface stains or dirts can be easily removed, and this discovery is novel in view of ; the conventional steel surface cleaning art.
One may consider to combine the conventional alkali immersion cleaning, the conventional alkali spray cleaning or the solvent degreasing method with a high-pressure water jet, but it leads only to the results that surface stains are removed by the alkali immersion cleaning or alkali spray cleaning and then the spray rinse is done under a high pressure. Such a type of a high-pressure water jet has nothing to do with the present invention as clearly understood from the foregoing descriptions~
The present invention will be more clearly understood from the following embodiments:
Example 1:
A cold rolled steel strip of 200 mm width, 0.8 mm thickness was passed through an experimental cleaning apparatus at traveling speed of 100 m/min. The cleaning apparatus com-prised a wetting agent solution application device of spray androll squeezing type, a single stage high-pressure water jet nozzle and an air knife. The amount of rolling oil and iron powders sticking to the steel surface before the test were in auerage 2 g/m and 900 mg.iron/m2 respectively. The surface cleaning was done by applying to the steel surface 5 ml/m2 of 6% sodium ortho-silicate solution and jetting a high-pressure water jet at 60C onto the surface with a nozzle pressure of 15 kg/cm2 and a flow density of 1 1/m2 according to the present invention (the work done by the jet water was 0.41 w hr/m2) (present invention in Table 1).
For comparison, tests were done on five cases. In the first case (comparison 1 in Table 1), an alkali solution was - 1090~;84 ~. .
applied and water at 60C was jetted with a nozzle pressure of
The present invention relates to a method and an -apparatus for cleaning cold rolled steel products such as steel strips, sheets and plates (hereinafter called steel sheet).
In the production of a cold rolled steel sheet, the steel sheet is reduced by the cold rolling to an almost final thickness, and the steel sheet thus cold rolled is very hard, and for applications where good working properties such as bending and drawing are required, it is necessary to annea~
such cold rolled steel sheets appropriately depending on their uses in order to improve mechanical properties. Such annealing is usually done at a temperature ranging from 550C to 800C
in a non-oxidizing gas atmosphere.
However, when the steel sheet is cold rolled, a large amount of mixture of lubricant oil used in the cold rolling and metal powders caused by the friction during the cold rolling remains on the surface of the cold rolled steel sheet, and if the steel sheet with this mixture is annealed, the rolling oil is carbonized and the metal powders are partially carburized and adhere to the steel surface to cause dirty surface and remarkable degradation of surface properties, resulting in loss of commercial value as final steel products and in addition causing considerable hindrance in subsequent workings. For example, when such dirty cold rolled steel sheets are used as p~ating substrates, the residues adhering to the steel surface cannot be removed even by pretreatments for the plating and cause vital surface defects which hinder satisfactory coating so that the surface appearance is deteriorated and the corrosion resistance is remarkably decreased.
Further, when such dirty cold rolled steel sheets are used as substrate for paint coating, pretreatments such as a phosphate coating cannot be performed satisfactorily.
For the reasons set forth above, it is necessary to lOgO~;8~
remove the surface residues by surface cleaning prior to the annealing of the cold rolled steel sheet.
However, the conventional art has been confronted with difficulties in removal of the mixture of the rolling oil and the metal powders sticking to the steel surface after the cold rolling, and the surface cleaning method which can be applied to the cold rolled steel sheet is very limited. This is due to the nature of the surface residues after the cold rolling.
According to the discoveries of the present inventors, main components, such as fatty acids and fatty acid esters, of the rolling oil chemically combines in an iron-soap with a thin iron oxide film covering the steel sheet surface and fine iron powders generated by friction during the rolling so that the iron powders themselves are strongly adhering to each other or they strongly adhere to the steel sheet surface by means of the soap thus formed, and the fine iron powders are less than about 0.1~ in their particle size and are ferromagnetic, easily magnetized and strongly attracted by the steel surface. These facts are considered to cause the difficulties in removing the mixture.
For example, as disclosed by "Tekko Seizo Ho" (Steel Production Process) Section III Workings (2) edited by Japan Iron & Steel Association, an electrolytic method has been esta-blished as a cleaning method for surface cleaning of the steel sheet after the cold rolling, and this method is performed in an electrolytic cleaning line of a total length of about several ten meters, provided separately or as an entry equipment of a continuous annealing furnace. The electroly~ic cleaning line normally comprises four stages of processing, that is, alkali-immersion, brushing, alkali-electrolysis and brushing, wherein the rolling oil is removed by saponification of the alkali while the fine iron powders are removed by action of the brushing.
- 1()90~;8~
For this reason, a longer electrolytic cleaning line is required as the rolling speed of the rolling mill to which the line is adjoined increases, and maintenance of the brushing section, which performs the mechanical removal, is not easy and requires considerable economical cost and consumes a great energy.
Further, from the aspect of efficiency in the rolling oil removal, an alkali solution mainly composed of sodium silicate is used, but during the electrolysis in such a silicate solution, a film mainly composed of silicate is formed on the steel surface being treated if one tries to remove the rolling oil satisfactorily, which film causes vital hindrance against the properties of the final products, such as solderability required for assembling after press-forming, accessibility to phosphate treatment as a pretreatment for paint coating, and qualities required as a plated steel plate such as a tin plate.
In order to overcome the above difficulties, trials .
and proposals for simplifying the surface cleaning step by .
omitting the electrolytic cleaning or, further, eliminating the step have been made for a long time.
One of the proposed methods uses a brushing treatment alone omitting the alkali electrolysis treatment. By the `~ omission of the alkali electrolysis treatment, the degradation of the steel sheet due to the silicate film formation can be prevented, but in turn, the rolling oil removal efficiency decreases, resulting in decreasing of the iron powder removal efficiency, with a large amount of residue unremoved even after ., the annealing, and as a whole degradation of the surface clean-~; ness as compared with the electrolytic cleaning.
Another proposed method is based on the principle of the mill cleaning or detergent rolling, and uses a detergent mainly composed of a surface active agent, and a warm water .
10~
instead of the rolling oil in the final stand of the cold roll-ing mill. According to this method, various modifications and considerations are given to the rolling oil used in all rolling stands except for the last stand, and to the detergent used in the last stand, but in spite of these efforts, the surface cleanness is not improved satisfactorily and the power consump-tion at the last rolling stand increases. Thus, this method has not yet been successful and established.
In spite of various trials and proposals as above for replacing the electrolytic cleaning method, none of them have been successful.
Therefore, the conventional art has not been success-ful in overcoming the problem that the residues produced from the rolling oil and the iron powders, sticking to the steel surface after the annealing, cause vital effects on the quality and properties of the final products. Further, as the surface cléanness of the cold rolled steel sheet has a definite and clear effect on the corrosion resistance after paint coating, and, improvement of the surface cleanness has been always demanded for so that up to now, substantially all of the cold rolled steel sheets are produced using the electrolytic cleaning line in spite of its large power consumption.
Therefore, one of the objects of the present invention is to provide a method and an apparatus which provides a high degree of cleaning efficiency at low cost and save power con-sumption by elimination of the electrolytic cleaning step in the production process of a cold rolled steel sheet.
The term "sheet" used in the present invention includes "foil", "plate", "strip" and "bar".
From the aspect of saving of the energy consumption, the present inventors have made extensive and various studies and experiments for the purpose of obtaining a surface cleanness 1(J90~8~
~imilar or better than that obtainable by the conventional electrolytic cleaning process in spite of the elimination of the electrolytic cleaning step, and have solved the technical incompatibility of the conventional art that if one tries to implify the cleaning step the surface cleanness deteriorates, and if one trie~ to improve the surface cleanness the cleaning step becomes complicated and capital cost and energy consumption increases considerably.
The present inventors have discovered that when a surface of steel sheet after the cold rolling is simply wetted with an organic or inorganic wetting agent (hereinafter called ~imply wetting solution) and then a high-pressure water jet is~
applied thereon, the rolling oil and the iron powders sticking to the steel surface can be easily removed together with the wetting solution by contact with the high-pressure water jet in a very ~hort time, and yet the surface cleanne~s thu~ obtained 18 similar or better than that obtained by cleaning through the electrolytic cleaning line and can be subjected directly to the annealing. By thi Q method, the wetting solution applying device and the high-pressure water jet device can be incorporated a~ a ; very compact equipment in the delivery of the final stand of cold rolling mill or in the entry of a continuous annealing furnace. In this way, the present inventors have succeeded in eliminating the electrolytic cleaning line.
me invention relates to a production process for a cold rolled steel sheet which compri~es a step of cold rolling pickled steel sheet, a step of cleaning a cold rolled sheet and a step of annealing the cleaned steel sheet. The process is characterized by the fact that the cleaning ~tep comprise~
wetting the surface of the cold rolled steel sheet with a wet-ting agent solution in an amount of at least 5 - 10 ml/m2, jetting a high-pres~ure fresh water on the wetted surf-ce, form-ing a continuous water jet curtain in a straight line acros~
the width of the steel sheet and removing a rolling lubricant and iron powders adhering on the surface simultaneously with the said wetting agent.
The present invention will be more clearly understood from the embodiments shown in the attached drawings. It should be understood, however, that the present invention is not limited to these embodiments.
Figures 1 and 2 illu~trate respectively one embodiment of the production proces~ of a cold rolled steel sheet according to the present inven- -tion, ~ .
10'3(~
Figure 3 shows the relation between the water jet energy received by the steel sheet and the jet nozzle pressure for comparison of the water jet according to the present invention with the conventional alkali spray, Figures 4(a), (b) and (c) show schematically various types of jet water curtains; and Figure 5 shows schematically the jet water curtain from a slit nozzle.
Referring to Figure 1, 1 is a pay-off reel, 2 is a guide roll, 3 are rolling mill stands, 3' is a final rolling stand, and 4 is a tension reel. The strip 5 as a coil mounted on the pay-off reel passes through the guide rolls and cold rolled by the work rolls of the rolling stands with application of rolling oil and coiled on the tension reel 4. At the ; delivery of the final stand 3' of the rolling mill stands, there are provided a wetting solution applicator 6, a squeeze roll 7, a high-pressure water jet nozzle 8, a squeeze roll 7' and an air knife 9, which in combination constitutes a cleaning apparatus 10. The surface of the strip 5' coming out of the final stand 3' is contaminated with a large amount of the rolling oil and the fine iron powders.
The strip enters the cleaning apparatus via the guide ; rolls 2', and applied with the wetting solution by the appli-cator 6 ontc the mixture of the rolling oil and the fine iron powders sticking to the steel surface. Then high-pressure water jet is jetted from the high-pressure water jet nozzle 8 onto the strip surface adhered with the mixture of the rolling oil and the fine iron powders and applied with the wetting solution thereon, and after both of the mixture and the wetting solution are removed simultaneously, the water on the strip surface is removed by the squeeze rolls 7' and the air knife 9 and the 10~0684 strip is coiled on the tension reel 4.
Referring to Figure 2 illustrating another embodiment of the present invention where the cleaning apparatus is pro-vided at the entry of a continuous annealing furnace, the strip 5 from No. 1 and No. 2 coil holder 11 passes through a welder 12, a pinch roll 13 and enters a cleaning apparatus similar to that shown in Figure 1 where the surface of the strip 5 is cleaned fully, and then dried by a dryer 14. The cleaned strip 5' is annealed normally by a continuous annealing apparatus 15, and after ordinary after-treatments tnot shown) coiled on No. 1 and No. 2 tension reels 16.
Description will be made on the method according to the present invention.
As for the inorganic wetting agent to be applied onto the cold rolled steel sheet with the mixture of rolling oil and fine iron powders adhering thereon, an aqueous solution mainly `? composed of one or more of sodium silicate, sodium hydroxide (caustic soda), sodium aluminate and sodium phosphate may be used.
,. . . .
i' 20 As for the alkali concentration, 5 - 10 wt.% is preferable. In addition, in order to improve removal efficiency of the various rolling oils, 0.3 to 1 wt.% of a surface active agent, and further, in case when the amount of adhering iron `;
powders is large, 3 to 6 wt.% of an iron-chelating agent may be added. As for the iron-chelating agent, citric acid and its compounds, gluconic acid and its compounds, carbamic acids, ~-!i' hydroxylamines and amines may be used.
' As for the organic wetting agent, organic solvents having a viscosity ranging from 0.5 to 4CP (at 30C), namely a viscosity similar to that of water, are useful.
In order to attain very efficient removal of the rolling oil and the iron powders from the steel surface during ~ .
_, _ .. .. .
0~84 the cold rolling which is normally done at a high speed, it is necessary that the wetting solution, namely the organic solvent in this case, has a high degree of removability by a high-pressure water jet. For this purpose an organic solvent unsusceptible to emulsification or dissolution into the water and having a viscosity similar to or same as that of water is desirable. To satisfy the above requirement, hydrocarbons and halogenated hydrocarbons are suitable, and kerosene, light oil, solvent naphtha, trichloroethylene, perchloroethylene have a viscosity within the above specified range. Therefore, in the present invention, a mixture solvent of one or more of the above hydrocarbons is used.
Regarding the amount of the wetting solution to be applied on the steel sheet, 5 - 10 ml/m2 attainable by the roll squeezing is sufficient. When the amount is less than 5 ml/m2, the removal of the rolling oil and the iron powders is not satisfactory. There is no upper limitation on the applied amount of the wetting solution, but the amounts more than 10 ml/m2 are not economical.
What are important in the combination of the appli-cation of the wetting solution and the high-pressure water jet are, in the first place, that all of the rolling oil, the fine iron powders and the wetting agents are removed altogether at once by one coup of the water jet jetted on the steel surface.
In this case, the work performed by the jet water is determined by the jet water pressure imposed on the steel sheet and the volume of jet water per unit area of the steel sheet surface (hereinafter called flow density), and according to the dis-coveries of the present inventors, the work can be expressed simply by the jet nozzle pressure and the flow density. As shown in Figure 3, it is necessary for obtaining the desired results that the jet nozzle pressure is not less than 5 kg/cm2, preferably not less than 8 kg/cm for any portion of the steel sheet surface and the work expressed by (jet nozzle pressure x flow density) is not less than 0.1 w hr/m2 per unit area of the steel sheet surface.
According to the results of the extensive experiments conducted by the present inventors, a surface cleanness similar to that obtained by the electrolytic cleaning can be obtained in a short time so far as the above conditions are maintained (see Table 2). Therefore, in an actual operation, only by i 10 adjusting the water jet conditions in accordance with a maximum traveling speed of steel sheet, a surface cleanness similar to that obtained by the electrolytic cleaning can be obtained in spite of their variations of the traveling speed. Further, the high-pressure water jet nozzle may be arranged only in a single stage so as to cover the whole width of the steel sheet.
Secondly, as shown in Figure 4(a), it is necessary that the iet water curtain 18 formed is jetted onto the steel sheet ~~
surface 17 in a linear form across the steel width. If the jet water curtain is not formed in a linear form across the sheet width but in a zig-zag form (Figure 4(b)) or a feather-stitch `
form (Figure 4(c)) as commonly done, the jet water does not contact the steel sheet surface at the same time all across the sheet width and the water jetted on the steel surface flows from the portions of the steel surface which have been already struck with the jet water to the portions which have not been struck with the jet water and dilutes or washes off the wetting solu-tion on the surface so that the rolling oil and the fine iron powders are not completely removed when the jet water strikes thereon, leaving stripes 19 parallel to the traveling direction.
Thus, it is important that the jet water curtain strikes on the sheet surface at the same time all across the sheet width.
Therefore, thirdly, it is important to select a nozzle g 1090t;84 for satisfying the above requirement. In order to maintain the required jet water pressure imposed on the steel sheet surface and the required work on the steel surface performed by the jet water and to bring the jet water curtain into contact with the steel sheet surface at the same time all across the sheet width, a slit nozzle as shown in Figure 5 is most desirable. The slit nozzle has a linear slit of a constant width and a length long enough to cover the whole width of the sheet. By using this slit nozzle, it is possible to jet a fresh water at the same time all across the sheet width with a constant jet water pres-sure and a constant flow density at any portion of the sheet surface.
In case of a conventional spray cleaning technique, a number of nozzles are provided in a pressure header so as to spray the fresh water onto the steel sheet surface. However, the cleaning water is sprayed by the nozzles in a divergent form at a certain angle, and presently four types of nozzles having a spray pattern of "full cone", "hollow cone", "square spray" and "flat spray" are commercially available.
When the above commercially available nozzles are used in the present invention, it is necessary that they satisfy the first and second requirements mentioned hereinbefore. The commercially available nozzles of "full cone", "hollow cone" or "square spray" type cannot be used satisfactorily in the present invention because it is difficult for these nozzles to form a jet water curtain in a linear form across the sheet width and to bring the jet water into contact with the sheet surface at the same time all across the sheet width, and the jetted water from these nozzles spreads over a wide area and thus the flow density decreases so that the first requirement cannot easily be satisfied by maintaining the required jet water pressure imposed on the steel sheet.
1090~;84 On the other hand, the commercially available "flat spray" nozzles can be used in the present invention if a number of them are arranged on a header in such a manner that the divergent angle of each water jet is made identical so as to form jet water curtains in a linear form across the sheet width.
In this case, however, it should be noted that both the flow rate of jet water and the jet water pressure imposed on the steel sheet are at their maximum at the center portion of diverging water jet, thus exhibiting their distributions in a mountain-like curve. Therefore, when a number of "flat spray"
nozzles are arranged on a pressure header, it is necessary to -~
adjust the pitch between individual nozzles so as to avoid too much pitch which causes failure to satisfy the first requirement at an intermediate portion between the nozzles. This is the fourth important point.
The fifth important point is the surface temperature of the steel sheet just prior to the application of the jet water -~
thereon and the temperature of the wetting solution applied thereon.
As the cold rolling oil,-oils, such as palm oil and beef tallow, which freezes at ordinary temperatures, are usually used, and in order to remove the rolling oils adhering to the steel surface by a fresh water jet, it is necessary to maintain the adhering rolling oils in a melted state. This is parti-cularly important in cases where the inorganic agents are used for the wetting solution. Results of studies from the above view ; point have revealed that it is desirable to maintain the surface of the steel sheet and the wetting solution at temperatures not lower than 70C. If they are maintained below 70C, desired results in respect of the surface cleanness cannot be obtained.
As for a method for maintaining the surface of-the steel sheet and the wetting solution to be applied thereto at 1090~E~4 70C or higher, it is possi~le to utilize the heat generated in rolling by applying the present invention immediately àfter the cold rolling, because the steel sheet coming out of the cold rolling mill is usually at 100C or higher, or it is possible to pre-heat the steel sheet (as is done for cold strip coils) in cases where the present invention is applied at the entry of a continuous annealing furnace, etc.
As for the pre-heating means, a conventional pre-heating means such as hot-air, steam, hot water, may be used in single or in combination. However, a more desirable method is to immerse the steel sheet in a heated wetting solution so as to perform both the coating of the wetting solution and the pre-` heating of the steel sheet simultaneously.
According to the experiments by the present inventors,the required surface temperature of the steel sheet can be attained by immersion in a hot water heated at 95C in a short time of one second or less in case of a cold rolled steel sheet of an ordinary thickness.
Sixthly, it is important that the rolling oil and the fine iron powders which have been removed will not adhere steel sheet again.
The rolling oil and the fine iron powders adhering to the steel sheet surface are removed altogether from the sheet surface by the jet water according to the present invention and flow as a dirty drainage, and this dirty drainage must be removed quickly from the steel sheet surface, otherwise it remains on the sheet surface and contaminates the surface again.
The drainage can be removed by means of squeeze rolls, an air knife in single or in combination. However, in order to remove it quickly to attain the desired results of the present invention, it is desirable that the above drainage removal means is arranged immediately after the train of the fresh water jet 1090~;84 nozzle. Other than the above removal means, a fresh water jet may be used for removing the dirty drainage.
The present invention is basically different from the conventional art, called alkali spray cleaning method, which is similar to the present invention in respect of the use of alkali.
The surface cleaning according to the alkali spray cleaning method is performed by the combination of the alkali spray and the water rinsing. In this case, the surface dirts are removed in the stage of alkali spray, and water rinsing is necessary to remove the alkali remaining on the steel surface from which the dirts have been removed. Whereas according to the present invention, the wetting solution is merely applied on the surface and thus the dirts are not removed during the stage of the wetting solution application. The removal of the surface dirts or stains, according to the present invention, is performed only by the jet blowing of a high-pressure water after the application of wetting solution, and the wetting solution is also removed together with the dirts. Thus, according to the present invention, the removal of dirts and water rinsing are effected together in a single stage.
Further, in the conventional alkali spray cleaning method, a spray chamber in which a number of spray nozzles are arranged is used, but there is no specific limitation in the selection and arrangement of the nozzles as required in the present invention. Thus, in the present invention, the first and second requirements as mentioned hereinbefore must be satis-fied, while in the alkali spray cleaning method, there is no such requirement, and the nozzles are arranged in the spray chamber in such a manner that the steel sheet surface is brought into contact with the spray liquid repeatedly until the dirts on the steel sheet surface are removed.
The conditions of the water jet in the present - 109()~i84 invention are quite different from the conventional art. For example, according to the disclosure of "Cleaning of Metal" of Modern Engineering Library published by Chijin Shokan, Tokyo, Japan, the spray pressure ranges from 8 to 30 psig, or 2.1 kg/cm2 at maximum, and the spray amount ranges from 60 to 100 1/m2 per minute, and the cleaning is done in about 3 minutes. These conditions may be expressed by the nozzle pressure and the work of water given to the steel sheet as shown in Figure 3 from which it is very clearly understood that the conventional art is done in a completely different zone from that of the present inven-tion. Further, in the present invention, the cleaning is com-pleted in a time shorter than about one second, and thus the cleaning effect is much higher.
The reason why a high-pressure jet, as in the present invention, is not used in the conventional alkali spray method is that there is a problem of foaming due to spraying of the alkali solution. For example, excessive foaming will cause over-flow of the solution from the cleaning device. In case of the conventional alkali spray cleaning method, a nozzle pressure exceeding 20 psig (1.5 kg/cm~) will cause foaming and thus the operation is normally performed with a nozzle pressure below 20 psig. If a higher nozzle pressure is to be applied, it is necessary to use a cleaning agent of less foamability, but such cleaning agent is also low in cleaning power.
This fact has been an important limitation in the conventional alkali-spray cleaning method.
Thus, the present invention is based on a completely different technical thought from that of the alkali spray cleaning method, and is completely free from the foaming problem because the wetting solution is merely applied and the water is jetted under a high pressure. Therefore, in the present invention the wetting solution can be selected without limitations from the 1090~;84 i foaming problem.
As a conventional art similar to the present invention -in that an organic solvent is used for the surface cleaning, there are a method in which adhering oil or grease and metal particles are removed simultaneously by the dissolving power and jet pressure of the solvent, and a UPetroleum Solvent Spray Method" (old U. S. Army Specification MIL-116C). ~;
These methods are limited in the kind of the solvents used because of danger of flaming and explosion induced by the spraying. The present inventors have conducted these spray methods with solvents selected mainly from the aspect of clean-ing effect, but the results as shown in Example 4 have revealed ~ that their cleaning effects are far inferior to that obtained by the present invention. -:
Still further, it has been conventionally practiced --, in various fields to jet a high-pressure water. However, in the field of a steel surface cleaning, a water jet has been used only as a low-pressure spray-rinse for the water washing in the finishing step after the surface cleaning such as alkali clean-ing and emulsion cleaning. This will be clearly understood if one refers to the surface cleaning methods specified by JIS Z
0303 or MIL-P-ll 6D according to which a surface cleaning method only by water jet has not been classified or specified.
, ~ ~
` ~aturally, as the water itself is a polar solvent, it ~i is possible to remove water-soluble dirts by a water jet and some surface cleaning effect can be attained thereby. However, the mixture of rolling oil and fine iron powders sticking to the steel surface after cold rolling, to which the present invention is directed cannot be removed only by water jet as clearly understood in the examples hereinafter set forth. The present invention is based on the discovery that when the wet-; ting solution is applied to the steel sheet as cold rolled and ~.
109~84 the high-pressure water jet strikes on the surface under the ; presence of the wetting solution, the surface stains or dirts can be easily removed, and this discovery is novel in view of ; the conventional steel surface cleaning art.
One may consider to combine the conventional alkali immersion cleaning, the conventional alkali spray cleaning or the solvent degreasing method with a high-pressure water jet, but it leads only to the results that surface stains are removed by the alkali immersion cleaning or alkali spray cleaning and then the spray rinse is done under a high pressure. Such a type of a high-pressure water jet has nothing to do with the present invention as clearly understood from the foregoing descriptions~
The present invention will be more clearly understood from the following embodiments:
Example 1:
A cold rolled steel strip of 200 mm width, 0.8 mm thickness was passed through an experimental cleaning apparatus at traveling speed of 100 m/min. The cleaning apparatus com-prised a wetting agent solution application device of spray androll squeezing type, a single stage high-pressure water jet nozzle and an air knife. The amount of rolling oil and iron powders sticking to the steel surface before the test were in auerage 2 g/m and 900 mg.iron/m2 respectively. The surface cleaning was done by applying to the steel surface 5 ml/m2 of 6% sodium ortho-silicate solution and jetting a high-pressure water jet at 60C onto the surface with a nozzle pressure of 15 kg/cm2 and a flow density of 1 1/m2 according to the present invention (the work done by the jet water was 0.41 w hr/m2) (present invention in Table 1).
For comparison, tests were done on five cases. In the first case (comparison 1 in Table 1), an alkali solution was - 1090~;84 ~. .
applied and water at 60C was jetted with a nozzle pressure of
2 kg/cm2 and at a flow density of 1 1/m2. Thus, the work was ..
0.05 w hr~m2.
In the second case, no alkali solution was applied, but only water at 60C was jetted with a nozzle pressure of 15 kg/cm2 and a flow density of 1 1/m2. m us, the work of .~ the jet water was 0.41 w hr/m2 (comparison 2 in Table 1).
In the third comparison, no alkali solution was applied, but only a 3% sodium ortho-silicate solution at 60C
was jetted with a nozzle pressure of 15 kg/cm2 at a flowing density of 1 1/m2. Thus, the work was 0.41 w hr/m2 (comparison --
0.05 w hr~m2.
In the second case, no alkali solution was applied, but only water at 60C was jetted with a nozzle pressure of 15 kg/cm2 and a flow density of 1 1/m2. m us, the work of .~ the jet water was 0.41 w hr/m2 (comparison 2 in Table 1).
In the third comparison, no alkali solution was applied, but only a 3% sodium ortho-silicate solution at 60C
was jetted with a nozzle pressure of 15 kg/cm2 at a flowing density of 1 1/m2. Thus, the work was 0.41 w hr/m2 (comparison --
3 in Table 1).
In the fourth comparison, an alkali solution was . applied and then 3% sodium ortho-silicate solution was jetted with a nozzle pressure of 2 kg/cm2 at a flow density of 1 1/m2.
. Thus, the work was 0.05 w-hr/m2 (comparison 4 in Table 1).
In the fifth comparison, no alkali solution was ~ applied, but 3% sodium ortho-silicate solution at 60C was ! jetted with a nozzle pressure of 15 kg/cm and a flow density of 1 1/m2. The work was 0.41 w-hr/m2 (comparison 5 in Table 1).
: The surface cleanness of the steel strips was tested and evaluated into five classes by the wiping method (JIS Z0303) and the water wetting method. The results are shown in Table 1.
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~090~84 m e meaninq of the symbols used in Table 1 and Table 2 are:
~ Excellent 0 Good Fair X Poor XX Very Poor ~"
-18a-~090~84 Surprisingly, the surface cleanness results obtained by the present invention were best. In cases where alkali was used as the jet water, the removal of the residual iron powders was not satisfactory.
Example 2:
The cleaning according to the present invention was performed by a cleaning device arranged at the delivery side of the final stand of a four-stand tand~m cold rolling mill designed for recirculating application rolling lubricant of a beef tallow based oil, as shown in Figure 1. me effective ~ length of the device was 3.5 m.
t During cold rolling a steel strip of 2.3 mm thickness and 1050 mm width into a tin-plate substrate of 0.30 mm thick-¦ ness at a rolling speed of 700 m/min., 10% sodium ortho-silicatesolution was applied at a rate of 7 ml/m onto the surface of the strip from the spray-roll squeezing device provided at the delivery side of the final stand, then fresh water at 60C was jetted on the top and bottom surfaces of strip from high-pressure slit nozzles extending to the total width of the steel strip at a nozzle pressure of 10 kg/cm2 and flow density of 0.5 1/m2 (work of the jet water: 0.13 w-hr/m2) and the water was removed by the roll squeezing and the air knife. The sur-face cleanness of the steel strip thus obtained was 14.1 mg/m2 of residual iron powders as iron, and 4.1 mg/m of residual rolling oil (present invention 1 in Table 2).
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109()~84 For comparison, only 3 wt.% sodium ortho-silicate solution was jetted to the strip surface under the same condi-tions as in the above example, the results were that the amount of the residual iron powder was 134 mg/m2 as iron and the amount of the residual rolling oil was 53 mg/m (comparison 1 in Table 2).
Then, the rolling speed was increased to 850 m/min.
and a solution of l~/o sodium ortho-silicate and 1% sodium glu-conate was applied to the strip surface in an amount of 5 ml/m , and a high-pressure fresh water at 60C was jetted at a nozzle pressure of 10 kg/cm2 and flow density of 0.4 1/m2. The result was that the amount of the residual iron powders was 8.0 mg/m , and the amount of the residual rolling oil was 3.0 mg/m . The work of the jet water was 0.11 w-hr/m (present invention 2 in Table 2).
Meanwhile, when the cleaning according to the present invention was not performed, the resultant surface cleanness after the cold rolling was that the amount of the residual iron powder was 870 mg/m as iron and the amount of the residual rolling oil was 2.4 g/m2 at a rolling speed of 700 m/min. The cold rolled steel strip was passed at a speed of 600 mpm through an electrolytic cleaning line having an effective lèngth of 60 m, and subjected to hot alkali immersion, brushing, alkali electro-lysis and brushing for surface cleaning, and the resultant sur-face cleanness was that the amount of the residual iron powder was 17 mg/m as iron and the amount of the residual rolling oil was 4.6 mg/m (comparison 2 in Table 2).
Further for comparison, the final stand of the cold rolling mill was blocked off so as to be insulated from the recirculation system, and a hot solution at 60C containing 1 wt.% of non-ionic surfactant was jetted to the rolling rolls and the strip with a nozzle pressure of 0.5 kg/cm2 and a flow ~090~4 rate of 2 m3/min. so as to effect the detergent rolling. At a rolling speed of 600 m/min., the roll wearing became more severe as the power consumption required for the final stand increased about 2~/o. The resultant surface cleanness, despite the large amount of detergent, was that the amount of the residual iron powders was 113 mg/m as iron and the amount of the residual rolling oil was 170 mg/m ~ The work of the jet water was 0.2 w-hr/m (comparison 3 in Table 2).
The steel strips thus cleaned by the above treatments were annealed and evaluated for their qualities as an electro-lytic tin-plate, and the results as shown in Table 2 revealed that all of the strips treated by the comparative treatments except for the electrolytic cleaning (comparison 2 in Table 2) were contaminated by dirts after the annealing and their sur-face properties as a cold rolled sheet and as well as a tin-plate substrate were unsatisfactory.
Whereas the results obtained by the present invention were equal to those obtained by the electrolytic cleaning.
Fxample 3:
A cold rolled steel strip of 0.8 mm thickness was divided into eight sheets. Five sheets of them were coated with the wetting solvent specified in the present invention by immersion, and the remaining three sheets for comparison, were coated with wetting solvent outside the scope of the present invention by immersion. The amount of solvent applied was all 10 ml/m and the application was done at 40C.
Onto the surfaces of the wetting solution coated eight steel sheets, water was jetted at a nozzle pressure of 8 kg/cm with a rate of 20 l/min. and a work of the jet water of 0.12 w-hr/m to remove the smudges from the surfaces. The sheet travelling speed was maintained at 200 mpm. The results thus obtained are shown in Table 3.
1090~84 Table 3 } Wetting Viscosity Removal of . . Agents CP (30C) oil and iron powder t%) o _ Spindle Oil 8.3 40 Commercially 39.6 30 available Hydrocarbon cleaning oil ~: 10 _ ~ 4.9 20 -Kerosene 1.18 98 i o Hy~docarbon Light oil 2.86 90 . ~ Solvent 0.56 95 i ~ naphtha . ¦
HTrichloro-:: ~ethylene 0.52 95 Halogenated hydrocarbon Perchloro- . .
_ethylene 0.78 90 -As clearly understood from Table 3, even when the jet- :-ted condition of the jet water is within the scope of the pre-sent invention, the removal of smudges is as low as 4~/O or less -~ if the organic solvent is outside the scope of the present !' invention, According to the present invention, a smudge removal as high as 90% or higher can be obtained.
Example 4:
A cold rolled steel strip of 0.8 mm thickness was div- ~.
ided into four sheets, and one sheet of them was treated for re-moval of smudges according to the present invention and the re-maining three sheets were treated by a comparative method. The ' results are shown in Table 4. The sheet pass speed and the jet ~: water conditions are the same as in Example 3.
, ' , .. ,.~ . . . .
-` 1090~;8~
Table 4 I
Wetting Jet Removal of oil Agents Mediumand iron powder Present invention Kerosene Water 98 none Kerosene 40 spray Comparison Kerosene Steam 55 none Water 5 , Example 5:
The cleaning treatment according to the present inven-tion was performed using an ordinary electrolytic cleaning equip-ment consisting of an alkali hot-dip tank, a first brush scrub-ber, a hot-alkali electrolysis tank, and a second brush scrubber.
A cold rolled steel strip of 0.8 mm and 1,200 mm width was passed through the equipment at a speed of 600 m/sec. The surface con- -dition before the cleaning was that the amount of beef tallow based oil adhering to the surface was 500 - 600 mg/m2, and the amount of iron powders was 300 - 350 mg/m2 as iron.
For starting the treatment, all of the brush rolls of the brush scrubbers were taken off and the hot alkali electro-lysis tank was emptied. The alkali hot-dip tank was filled with fresh water, and heated to 95C by steam. The steel strip pass-; ing through the heated fresh water in 0.7 seconds was heated to a surface temperature of 75C.
A coating device of spray roll squeeze type was pro-vided immediately after the squeeze roll at the delivery side of the hot-dip t~nk, and a solution of 5% caustic soda, 5% sodium ~ .
ortho-silicate, and 2% gluconic acid was coated at 70C on the steel strip in an amount of 10 ml/m2, and a high-pressure water jet was jetted from a fresh water jet nozzle provided at the ; central portion of the first scrubber. Then the dirt drainage ~ -25-~' 1(;~90~8~
was removed from the strip surface by means of the squeeze rolls and the air wiper provided at the outlet side of the scrubber.
~ Present Invention 1: -; A slit nozzle having a linear slit of 1.3 m length ex-tending in the direction of the strip width was provided on a pressure header, and a high-pressure fresh water jet was jetted with a header pressure of 8 kg/cm2 and a flow density of 0.5 1/m2.
The resultant surface was very beautiful and the amount of the residual rolling oil was 2.8 mg/m and the amount of the residual iron powders was 7.3 mg/m . The work of the water jet was 0.11 w hr/m2. ;
Comparison 1:
The similar slit nozzle as used in the "Present Inven-tion 1" but having an expanded slit spacing was used and a fresh water jet was jetted with a header pressure of 1.5 kg/cm , a ~, flow density of 2.7 l/m . The work of the jet water was 0.11 w-hr/m2, but the strip surface thus obtained showed dirts scat-tered all over the surface, and the amount of the residual oil was 83 mg/m and the amount of the residual iron powders was 133 ~-mg/m2, indicating a very unsatisfactory cleaning results.
Comparison 2:
A plural~ity of flat spray nozzles having a diverging angle of 42 were provided with a pitch of 70 mm therebetween in a pressure header, so as to form a jet water curtain in a linear form across the strip width, and a fresh water jet was jetted with a header pressure of 15 kg/cm and a nozzle flow rate of 26 l/min. per nozzle at a distance of 100 mm from the strip sur-face. The average flow density was 0.65 l/m , and the work of the jet water was in average 0.26 w-hr/m . The resultant sur-face showed light strip-like dirts of about 10 mm width with a pitch of 70 mm. This was caused by the improper arrangement of the nozzles in respect of the pitch length which decreased the .
109~i8~
jet water pressure and the flow density at the intermediate portions between the adjacent two nozzles.
~ Present Invention 2:
s Similar flat spray nozzles as in the above Comparison2 were arranged with 50 mm pitches in the pressure header, and a high-pressure fresh water jet was jetted with a header pressure of 15 kg/cm2 and a flow density of 0.9 1/m2. The work of the jet water was in average 0.37 w.hr/m2. The resul-tant surface was beautiful with 3.5 mg/m2 residual rolling oil and 8.7 mg/m residual iron powders.
Next, a high-pressure fresh water jet was jetted with a lowered header pressure of 8 kg/cm2 and a nozzle flow rate of 1 19 l/min. The average flow density was 0.65 l/m and the average work of the jet water was 0.14 w.hr/m . The resultant surface was beautiful with 3.0 mg/m residual oil and 9.3 mg/m2 i residual iron powders.
Comparison 3:
Two pressure headers having each flat spray nozzles arranged with 100 mm pitches as in the above Comparison 2, and the headers were arranged so as to place the nozzles in a triangle zig-zag arrangement with 100 mm pitches, and a high-pressure fresh water jet was jetted with a header pressure of 15 kg/cm and a nozzle flow rate of 26 l/min. per nozzle.
The average flow density was 0.9 l/m and the average work of the jet water was 0.37 w.hr/m2. The resultant surface showed strip-like dirts of about 40 mm width with 100 mm pitches.
This is caused by the fact that the jetted water from the first pressure header flowed around the surface and removed the wet-ting agent coated on the surface portion onto which the water jet is jetted later from the second pressure header, which was caused by the delay of contact of some of the water jet with the strip surface across the strip width.
10~ i8~
As clearly understood from the foregoing descriptions and examples, the present invention has made it possible to remove rollir,g lubricant and iron powders adhering on the steel sheet after cold rolling with a high degree of efficiency by means of a very compact cleaning device arranged with a cold rolling mill or a continuous annealing equipment, and the steel sheet cleaned according to the present invention shows a surface cleanness equal to or better than that of an electro-lytically cleaned steel sheet, and can be directly annealed into a final product. Thus according to the present invention, it is possible to eliminate the electrolytic cleaning step which has been indispensable in the conventional art, and save the power consumption to a great degree.
It should be also understood that the present inven-tion can be applied to sheets of metals other than the steel.
. - 28 -
In the fourth comparison, an alkali solution was . applied and then 3% sodium ortho-silicate solution was jetted with a nozzle pressure of 2 kg/cm2 at a flow density of 1 1/m2.
. Thus, the work was 0.05 w-hr/m2 (comparison 4 in Table 1).
In the fifth comparison, no alkali solution was ~ applied, but 3% sodium ortho-silicate solution at 60C was ! jetted with a nozzle pressure of 15 kg/cm and a flow density of 1 1/m2. The work was 0.41 w-hr/m2 (comparison 5 in Table 1).
: The surface cleanness of the steel strips was tested and evaluated into five classes by the wiping method (JIS Z0303) and the water wetting method. The results are shown in Table 1.
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~ii , i ~ - 17 -1090~84 m ~ o~Do ,0~ ~ ~ X ~) O ~) O r~
~ ~ o C ~
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, ~
a) ~1 ~ ''1'o N ~; ~ ~ u) u) ~ u) ~ ~ h ,l ~ ~ 1 ~ll ~o~ ~r o~
X ~ h rl Ll) r~ r) rl ~a O ~ ~ ~ rl ,~
~ d~ O d~ d~ O ~ ~ ~ ~U rl h Q ~ ~ S-i rl ~1 ', r^l ;3 ~2 ~o o o o o o ~r~ ~ o U ~ h ~ 1 ~ rl q-l h ,~) ,a td r r~ rl ~ Cq O
E-~ ~ 1 3 ~ ~ C 6 3 0 ~ 3 ~~0 ~ Ul a~ 0 3 rl ~ O h ~ rl h0 5~ .5~ ~I r~l S l~
~1 ~ q E~ O R E~ ~a O
v ~ v ~q o oq v Iq v ~qc.) ~q O ~ O ~ O ~ O ~ O a) O a~ . ..
O h O S~ O S~ O h O h O ~ ~J
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O t~) .~ O
~¢ ~ q 2 3 ~ ~ a) ~ o o ~ o U ~:: ~ ~ R R
. ~ ~ ~
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~090~84 m e meaninq of the symbols used in Table 1 and Table 2 are:
~ Excellent 0 Good Fair X Poor XX Very Poor ~"
-18a-~090~84 Surprisingly, the surface cleanness results obtained by the present invention were best. In cases where alkali was used as the jet water, the removal of the residual iron powders was not satisfactory.
Example 2:
The cleaning according to the present invention was performed by a cleaning device arranged at the delivery side of the final stand of a four-stand tand~m cold rolling mill designed for recirculating application rolling lubricant of a beef tallow based oil, as shown in Figure 1. me effective ~ length of the device was 3.5 m.
t During cold rolling a steel strip of 2.3 mm thickness and 1050 mm width into a tin-plate substrate of 0.30 mm thick-¦ ness at a rolling speed of 700 m/min., 10% sodium ortho-silicatesolution was applied at a rate of 7 ml/m onto the surface of the strip from the spray-roll squeezing device provided at the delivery side of the final stand, then fresh water at 60C was jetted on the top and bottom surfaces of strip from high-pressure slit nozzles extending to the total width of the steel strip at a nozzle pressure of 10 kg/cm2 and flow density of 0.5 1/m2 (work of the jet water: 0.13 w-hr/m2) and the water was removed by the roll squeezing and the air knife. The sur-face cleanness of the steel strip thus obtained was 14.1 mg/m2 of residual iron powders as iron, and 4.1 mg/m of residual rolling oil (present invention 1 in Table 2).
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1 1090~84 ,~, , 3~ ~ x~
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109()~84 For comparison, only 3 wt.% sodium ortho-silicate solution was jetted to the strip surface under the same condi-tions as in the above example, the results were that the amount of the residual iron powder was 134 mg/m2 as iron and the amount of the residual rolling oil was 53 mg/m (comparison 1 in Table 2).
Then, the rolling speed was increased to 850 m/min.
and a solution of l~/o sodium ortho-silicate and 1% sodium glu-conate was applied to the strip surface in an amount of 5 ml/m , and a high-pressure fresh water at 60C was jetted at a nozzle pressure of 10 kg/cm2 and flow density of 0.4 1/m2. The result was that the amount of the residual iron powders was 8.0 mg/m , and the amount of the residual rolling oil was 3.0 mg/m . The work of the jet water was 0.11 w-hr/m (present invention 2 in Table 2).
Meanwhile, when the cleaning according to the present invention was not performed, the resultant surface cleanness after the cold rolling was that the amount of the residual iron powder was 870 mg/m as iron and the amount of the residual rolling oil was 2.4 g/m2 at a rolling speed of 700 m/min. The cold rolled steel strip was passed at a speed of 600 mpm through an electrolytic cleaning line having an effective lèngth of 60 m, and subjected to hot alkali immersion, brushing, alkali electro-lysis and brushing for surface cleaning, and the resultant sur-face cleanness was that the amount of the residual iron powder was 17 mg/m as iron and the amount of the residual rolling oil was 4.6 mg/m (comparison 2 in Table 2).
Further for comparison, the final stand of the cold rolling mill was blocked off so as to be insulated from the recirculation system, and a hot solution at 60C containing 1 wt.% of non-ionic surfactant was jetted to the rolling rolls and the strip with a nozzle pressure of 0.5 kg/cm2 and a flow ~090~4 rate of 2 m3/min. so as to effect the detergent rolling. At a rolling speed of 600 m/min., the roll wearing became more severe as the power consumption required for the final stand increased about 2~/o. The resultant surface cleanness, despite the large amount of detergent, was that the amount of the residual iron powders was 113 mg/m as iron and the amount of the residual rolling oil was 170 mg/m ~ The work of the jet water was 0.2 w-hr/m (comparison 3 in Table 2).
The steel strips thus cleaned by the above treatments were annealed and evaluated for their qualities as an electro-lytic tin-plate, and the results as shown in Table 2 revealed that all of the strips treated by the comparative treatments except for the electrolytic cleaning (comparison 2 in Table 2) were contaminated by dirts after the annealing and their sur-face properties as a cold rolled sheet and as well as a tin-plate substrate were unsatisfactory.
Whereas the results obtained by the present invention were equal to those obtained by the electrolytic cleaning.
Fxample 3:
A cold rolled steel strip of 0.8 mm thickness was divided into eight sheets. Five sheets of them were coated with the wetting solvent specified in the present invention by immersion, and the remaining three sheets for comparison, were coated with wetting solvent outside the scope of the present invention by immersion. The amount of solvent applied was all 10 ml/m and the application was done at 40C.
Onto the surfaces of the wetting solution coated eight steel sheets, water was jetted at a nozzle pressure of 8 kg/cm with a rate of 20 l/min. and a work of the jet water of 0.12 w-hr/m to remove the smudges from the surfaces. The sheet travelling speed was maintained at 200 mpm. The results thus obtained are shown in Table 3.
1090~84 Table 3 } Wetting Viscosity Removal of . . Agents CP (30C) oil and iron powder t%) o _ Spindle Oil 8.3 40 Commercially 39.6 30 available Hydrocarbon cleaning oil ~: 10 _ ~ 4.9 20 -Kerosene 1.18 98 i o Hy~docarbon Light oil 2.86 90 . ~ Solvent 0.56 95 i ~ naphtha . ¦
HTrichloro-:: ~ethylene 0.52 95 Halogenated hydrocarbon Perchloro- . .
_ethylene 0.78 90 -As clearly understood from Table 3, even when the jet- :-ted condition of the jet water is within the scope of the pre-sent invention, the removal of smudges is as low as 4~/O or less -~ if the organic solvent is outside the scope of the present !' invention, According to the present invention, a smudge removal as high as 90% or higher can be obtained.
Example 4:
A cold rolled steel strip of 0.8 mm thickness was div- ~.
ided into four sheets, and one sheet of them was treated for re-moval of smudges according to the present invention and the re-maining three sheets were treated by a comparative method. The ' results are shown in Table 4. The sheet pass speed and the jet ~: water conditions are the same as in Example 3.
, ' , .. ,.~ . . . .
-` 1090~;8~
Table 4 I
Wetting Jet Removal of oil Agents Mediumand iron powder Present invention Kerosene Water 98 none Kerosene 40 spray Comparison Kerosene Steam 55 none Water 5 , Example 5:
The cleaning treatment according to the present inven-tion was performed using an ordinary electrolytic cleaning equip-ment consisting of an alkali hot-dip tank, a first brush scrub-ber, a hot-alkali electrolysis tank, and a second brush scrubber.
A cold rolled steel strip of 0.8 mm and 1,200 mm width was passed through the equipment at a speed of 600 m/sec. The surface con- -dition before the cleaning was that the amount of beef tallow based oil adhering to the surface was 500 - 600 mg/m2, and the amount of iron powders was 300 - 350 mg/m2 as iron.
For starting the treatment, all of the brush rolls of the brush scrubbers were taken off and the hot alkali electro-lysis tank was emptied. The alkali hot-dip tank was filled with fresh water, and heated to 95C by steam. The steel strip pass-; ing through the heated fresh water in 0.7 seconds was heated to a surface temperature of 75C.
A coating device of spray roll squeeze type was pro-vided immediately after the squeeze roll at the delivery side of the hot-dip t~nk, and a solution of 5% caustic soda, 5% sodium ~ .
ortho-silicate, and 2% gluconic acid was coated at 70C on the steel strip in an amount of 10 ml/m2, and a high-pressure water jet was jetted from a fresh water jet nozzle provided at the ; central portion of the first scrubber. Then the dirt drainage ~ -25-~' 1(;~90~8~
was removed from the strip surface by means of the squeeze rolls and the air wiper provided at the outlet side of the scrubber.
~ Present Invention 1: -; A slit nozzle having a linear slit of 1.3 m length ex-tending in the direction of the strip width was provided on a pressure header, and a high-pressure fresh water jet was jetted with a header pressure of 8 kg/cm2 and a flow density of 0.5 1/m2.
The resultant surface was very beautiful and the amount of the residual rolling oil was 2.8 mg/m and the amount of the residual iron powders was 7.3 mg/m . The work of the water jet was 0.11 w hr/m2. ;
Comparison 1:
The similar slit nozzle as used in the "Present Inven-tion 1" but having an expanded slit spacing was used and a fresh water jet was jetted with a header pressure of 1.5 kg/cm , a ~, flow density of 2.7 l/m . The work of the jet water was 0.11 w-hr/m2, but the strip surface thus obtained showed dirts scat-tered all over the surface, and the amount of the residual oil was 83 mg/m and the amount of the residual iron powders was 133 ~-mg/m2, indicating a very unsatisfactory cleaning results.
Comparison 2:
A plural~ity of flat spray nozzles having a diverging angle of 42 were provided with a pitch of 70 mm therebetween in a pressure header, so as to form a jet water curtain in a linear form across the strip width, and a fresh water jet was jetted with a header pressure of 15 kg/cm and a nozzle flow rate of 26 l/min. per nozzle at a distance of 100 mm from the strip sur-face. The average flow density was 0.65 l/m , and the work of the jet water was in average 0.26 w-hr/m . The resultant sur-face showed light strip-like dirts of about 10 mm width with a pitch of 70 mm. This was caused by the improper arrangement of the nozzles in respect of the pitch length which decreased the .
109~i8~
jet water pressure and the flow density at the intermediate portions between the adjacent two nozzles.
~ Present Invention 2:
s Similar flat spray nozzles as in the above Comparison2 were arranged with 50 mm pitches in the pressure header, and a high-pressure fresh water jet was jetted with a header pressure of 15 kg/cm2 and a flow density of 0.9 1/m2. The work of the jet water was in average 0.37 w.hr/m2. The resul-tant surface was beautiful with 3.5 mg/m2 residual rolling oil and 8.7 mg/m residual iron powders.
Next, a high-pressure fresh water jet was jetted with a lowered header pressure of 8 kg/cm2 and a nozzle flow rate of 1 19 l/min. The average flow density was 0.65 l/m and the average work of the jet water was 0.14 w.hr/m . The resultant surface was beautiful with 3.0 mg/m residual oil and 9.3 mg/m2 i residual iron powders.
Comparison 3:
Two pressure headers having each flat spray nozzles arranged with 100 mm pitches as in the above Comparison 2, and the headers were arranged so as to place the nozzles in a triangle zig-zag arrangement with 100 mm pitches, and a high-pressure fresh water jet was jetted with a header pressure of 15 kg/cm and a nozzle flow rate of 26 l/min. per nozzle.
The average flow density was 0.9 l/m and the average work of the jet water was 0.37 w.hr/m2. The resultant surface showed strip-like dirts of about 40 mm width with 100 mm pitches.
This is caused by the fact that the jetted water from the first pressure header flowed around the surface and removed the wet-ting agent coated on the surface portion onto which the water jet is jetted later from the second pressure header, which was caused by the delay of contact of some of the water jet with the strip surface across the strip width.
10~ i8~
As clearly understood from the foregoing descriptions and examples, the present invention has made it possible to remove rollir,g lubricant and iron powders adhering on the steel sheet after cold rolling with a high degree of efficiency by means of a very compact cleaning device arranged with a cold rolling mill or a continuous annealing equipment, and the steel sheet cleaned according to the present invention shows a surface cleanness equal to or better than that of an electro-lytically cleaned steel sheet, and can be directly annealed into a final product. Thus according to the present invention, it is possible to eliminate the electrolytic cleaning step which has been indispensable in the conventional art, and save the power consumption to a great degree.
It should be also understood that the present inven-tion can be applied to sheets of metals other than the steel.
. - 28 -
Claims (11)
1. In a production process for a cold rolled steel sheet which comprises a step of cold rolling pickled steel sheet, a step of cleaning a cold rolled sheet and a step of annealing the cleaned steel sheet, a method characterized by said cleaning step which comprises wetting the surface of the cold rolled steel sheet with a wetting agent solution in an amount of at least 5 - 10 ml/m2, jetting a high-pressure fresh water on the wetted surface, forming a continuous water jet curtain in a straight line across the width of the steel sheet and removing a rolling lubricant and iron powders adhering on the surface simultaneously with the said wetting agent.
2. A method according to Claim 1, in which the high-pressure fresh water is jetted with a pressure not less than 5 kg/cm2 of a jet nozzle pressure, and under the condition of (jet nozzle pressure) x (volume of jetted water per unit area of sheet surface) > 0.1 w.hr/m2 - (work done by water jet per unit area of sheet surface) all across the width of the steel sheet.
3. A method according to Claim 1, in which the wetting agent solution is an alkali solution of at least one selected from the group consisting of sodium ortho-silicate, caustic soda, sodium phosphate, and sodium aluminate.
4. A method according to Claim 1, in which the wetting agent is one selected from the group consisting of hydrocarbons and halogenated hydrocarbon having a viscosity from 0.5 to 4CP at 30°C.
5. A method according to Claim 3, in which the wetting agent solution contains 1 to 5 wt.% of an iron-chelating agent.
6. A method according to Claim 3, in which the wetting agent solution contains 0.3 to 1 wt.% of surfactant.
7. A method according to Claim 3, in which the wetting agent solution contains 5 to 10 wt.% of the alkali.
8. A method according to Claim 5, in which the iron chelating agent is at least one selected from the group con-sisting of gluconic acid and its compounds, citric acid and its compounds, carbamic acids, hydroxylamines and amines.
9. A method according to Claim 5, in which the iron chelating agent is sodium gluconate in an amount from 1 to 3 wt.%.
10. A method according to Claim 1, in which the water jet is jetted by a slit nozzle having a width at least larger than the steel sheet width.
11. A method according to Claim 1, in which the water jet is jetted by a plurality of jet nozzles so arranged that one jet curtain from one jet nozzle laps in series with an adjacent jet curtain jetted from an adjacent jet nozzle.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA273,607A CA1090684A (en) | 1977-03-09 | 1977-03-09 | Method and an apparatus for cleaning a cold rolled steel sheet |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA273,607A CA1090684A (en) | 1977-03-09 | 1977-03-09 | Method and an apparatus for cleaning a cold rolled steel sheet |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1090684A true CA1090684A (en) | 1980-12-02 |
Family
ID=4108115
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA273,607A Expired CA1090684A (en) | 1977-03-09 | 1977-03-09 | Method and an apparatus for cleaning a cold rolled steel sheet |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1090684A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111678912A (en) * | 2020-06-18 | 2020-09-18 | 武汉钢铁有限公司 | Method for measuring residual carbon content on surface of cold-rolled sheet |
| CN115613044A (en) * | 2022-09-28 | 2023-01-17 | 湖南金裕环保科技有限公司 | Cold-rolled steel plate oil and dust removing phosphorus-free degreasing agent, and preparation method and application thereof |
-
1977
- 1977-03-09 CA CA273,607A patent/CA1090684A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111678912A (en) * | 2020-06-18 | 2020-09-18 | 武汉钢铁有限公司 | Method for measuring residual carbon content on surface of cold-rolled sheet |
| CN111678912B (en) * | 2020-06-18 | 2023-12-12 | 武汉钢铁有限公司 | Method for measuring residual carbon content on surface of cold-rolled sheet |
| CN115613044A (en) * | 2022-09-28 | 2023-01-17 | 湖南金裕环保科技有限公司 | Cold-rolled steel plate oil and dust removing phosphorus-free degreasing agent, and preparation method and application thereof |
| CN115613044B (en) * | 2022-09-28 | 2024-05-03 | 湖南金裕环保科技有限公司 | Cold-rolled steel plate oil-removing ash-removing phosphorus-free degreasing agent, preparation method and application |
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