CA1103569A - Preheat and cleaning system - Google Patents
Preheat and cleaning systemInfo
- Publication number
- CA1103569A CA1103569A CA308,621A CA308621A CA1103569A CA 1103569 A CA1103569 A CA 1103569A CA 308621 A CA308621 A CA 308621A CA 1103569 A CA1103569 A CA 1103569A
- Authority
- CA
- Canada
- Prior art keywords
- strip
- furnace
- gases
- zone
- combustion
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
- C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Heat Treatment Of Strip Materials And Filament Materials (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE A continuous cleaning and preheating system for steel strip to be annealed prior to being coated or otherwise treated wherein controlled reducing steps are employed to remove sur-face contaminants from the strip, which system uses direct flame heating whereby the combustion gases from open flame burners within a closed furnace flow into and along a restric-ted elongated tubular zone so that the gases are in direct contact with the strip as it enters and passes through the tub-ular zone and the furnace in a direction countercurrent to the flow of the said gases.
Description
~ ~3~69 FIELD OF THE INVENTION ~:
This invention relates to the continuous annealing of steel, and more specifically it related to a continuous system for cleaning and preheating steel stxip or the like prior to an-nealing the same in preparation for galvanizing or other opera tions that re~uire a clean surface on the strip which is free of oxides and other residual matter, so as to achieve improved product quality and production efficiency.
In the continuous annealing of steel it is necessary to preheat and clean the steel strip as it comes from the prior fabricating and handIing units because the steel strip frequen- ;
tly has residual rolling oils and other surface con~amlnants which must be removed. To accomplish this, the prior art has first preheated the stxip surface to reduce or oxidize and other-wise process the oils and other contaminants thereon. The strip then enters a hydrogen-rich reducing atmosphere that reacts to completely remove any treated residual contaminants that are on the strip after it has been deposited as the strip travels through the preheat chamber where it has been in flame contact with the furnace heating gases. This cleaning method is often preferred over the practice of removing the surface impurities . .
by contact with a mechanical cleaner. Accordin~ly, the open flame system that will process the surface of the strip pre-paratory to its entering the annealing area of the furnace ; proper has been generally adopte~ by the steel industry. It both clean~ and preheats the strip and thus helps to increase production rates. This invention is concerned with an Lmproved ~-~-i gas preheating and cleaning system.
D~S~ IO~ or ~ r ~-In the prior art continuous annealing systems which are in general use the strip enters from the ambient atmosphere directly into a preheat furnace of a general muffle or oven-: ' ,~
~ ~3~65~
type or of a direct flame contact design through rolls or other seallng means at its entry point, The furnace is inefficient because in order to obtain any degree of effective cleaning and surface preparation of the strip, it is necessary to design the furnace so that it consumes a substantial excess of fuel to provide the heat required to significantly preheat the strip prior to further processing in the annealing system.
The foregoing system has the furt.her disadvantage that when methane or other gaseous hydro carbon fuels are used with mixtures of air in the proportions needed to create the as designed combustion capacity in the preheat furnace, the result-ing products of combustion have expanded many times ~on the order of twenty to twenty-five times). This additional gas volume requires a furnace which must be vented at its top or sides in order to prevent a build-up of pressure from furnace `
gases. Otherwise, the products of combustion seep into the annealing furnace proper which must maintain a hydrogen gas ~.:
~ atmosphere to reduce and remove the residuals as discussed : above. Such preheat furnaces have serious maintenance problems, ; 20 and are thus relatively inefficient because of their excessive use of fuel.
Other examples of prior art systems are shown in U.S.
Patents 1,238,011 to Ellis, 1,310,911 to John, 1,A09,119 to Scanlon et al, 1,716,956 to Hepburn et al, 3,166,304 to Alexeff : and 3,721,520 to Bloom. The Bloom patent discloses a continuous line forgal~anizing wire to protect it from oxidation prior to galvanizing by using a flame burner built into a tube through which the strand is moved.
~ i ~ ~3~
SUMMARY OF THE INVENTION
It is the purpose of this invention to overcome the disadvantages of the prior art by reducing to a substantial exten~t the quantity of combustion gases and fuel required to preheat and clean the strip in the furnace prior to!~continuous annealing, This is accomplished by substantially reducing the flame or combustion area within the prehea~ fuxnace and b~
directing the gases through a confined generally tubular elon gated zone so ~hat ~hey remain in prolonged direct flame contact with the strip during the preheating and cleaning process~ The preheating operation is thus extended over a relatively longer ;~
path of travel while the products ~f combustion contact the strip as they flow countercurrent to the flow of the strip~
This reduces the amount of fuel required to accomplish the required processing.
In the drawings, Figure 1 is a schematic flow sheet of a typical continuous annealing and galvanizing line for steel strip utilizing the preheat furnace o this inven ion;
Figure 2 i~ a horizontal cross-section through one form of urnace embodyin~ the present invention;
Figuxe 3 is a horizontal cross-section of a moclified version of another form of the furnace or practicing the pre-sent invention; and Figure 4 is a horizontal cross-section of a prior art furnace that will be useful for comparison purposes.
DESCRIPTION OF TEIE_INVENTION
Reerring to Figuxe 1~ strip S to be galvanized is `
con~inuously passed through tubular zone 1 and flame furnace
This invention relates to the continuous annealing of steel, and more specifically it related to a continuous system for cleaning and preheating steel stxip or the like prior to an-nealing the same in preparation for galvanizing or other opera tions that re~uire a clean surface on the strip which is free of oxides and other residual matter, so as to achieve improved product quality and production efficiency.
In the continuous annealing of steel it is necessary to preheat and clean the steel strip as it comes from the prior fabricating and handIing units because the steel strip frequen- ;
tly has residual rolling oils and other surface con~amlnants which must be removed. To accomplish this, the prior art has first preheated the stxip surface to reduce or oxidize and other-wise process the oils and other contaminants thereon. The strip then enters a hydrogen-rich reducing atmosphere that reacts to completely remove any treated residual contaminants that are on the strip after it has been deposited as the strip travels through the preheat chamber where it has been in flame contact with the furnace heating gases. This cleaning method is often preferred over the practice of removing the surface impurities . .
by contact with a mechanical cleaner. Accordin~ly, the open flame system that will process the surface of the strip pre-paratory to its entering the annealing area of the furnace ; proper has been generally adopte~ by the steel industry. It both clean~ and preheats the strip and thus helps to increase production rates. This invention is concerned with an Lmproved ~-~-i gas preheating and cleaning system.
D~S~ IO~ or ~ r ~-In the prior art continuous annealing systems which are in general use the strip enters from the ambient atmosphere directly into a preheat furnace of a general muffle or oven-: ' ,~
~ ~3~65~
type or of a direct flame contact design through rolls or other seallng means at its entry point, The furnace is inefficient because in order to obtain any degree of effective cleaning and surface preparation of the strip, it is necessary to design the furnace so that it consumes a substantial excess of fuel to provide the heat required to significantly preheat the strip prior to further processing in the annealing system.
The foregoing system has the furt.her disadvantage that when methane or other gaseous hydro carbon fuels are used with mixtures of air in the proportions needed to create the as designed combustion capacity in the preheat furnace, the result-ing products of combustion have expanded many times ~on the order of twenty to twenty-five times). This additional gas volume requires a furnace which must be vented at its top or sides in order to prevent a build-up of pressure from furnace `
gases. Otherwise, the products of combustion seep into the annealing furnace proper which must maintain a hydrogen gas ~.:
~ atmosphere to reduce and remove the residuals as discussed : above. Such preheat furnaces have serious maintenance problems, ; 20 and are thus relatively inefficient because of their excessive use of fuel.
Other examples of prior art systems are shown in U.S.
Patents 1,238,011 to Ellis, 1,310,911 to John, 1,A09,119 to Scanlon et al, 1,716,956 to Hepburn et al, 3,166,304 to Alexeff : and 3,721,520 to Bloom. The Bloom patent discloses a continuous line forgal~anizing wire to protect it from oxidation prior to galvanizing by using a flame burner built into a tube through which the strand is moved.
~ i ~ ~3~
SUMMARY OF THE INVENTION
It is the purpose of this invention to overcome the disadvantages of the prior art by reducing to a substantial exten~t the quantity of combustion gases and fuel required to preheat and clean the strip in the furnace prior to!~continuous annealing, This is accomplished by substantially reducing the flame or combustion area within the prehea~ fuxnace and b~
directing the gases through a confined generally tubular elon gated zone so ~hat ~hey remain in prolonged direct flame contact with the strip during the preheating and cleaning process~ The preheating operation is thus extended over a relatively longer ;~
path of travel while the products ~f combustion contact the strip as they flow countercurrent to the flow of the strip~
This reduces the amount of fuel required to accomplish the required processing.
In the drawings, Figure 1 is a schematic flow sheet of a typical continuous annealing and galvanizing line for steel strip utilizing the preheat furnace o this inven ion;
Figure 2 i~ a horizontal cross-section through one form of urnace embodyin~ the present invention;
Figuxe 3 is a horizontal cross-section of a moclified version of another form of the furnace or practicing the pre-sent invention; and Figure 4 is a horizontal cross-section of a prior art furnace that will be useful for comparison purposes.
DESCRIPTION OF TEIE_INVENTION
Reerring to Figuxe 1~ strip S to be galvanized is `
con~inuously passed through tubular zone 1 and flame furnace
2 of the preheat section of the line~ It then proceeds :
: 30 through re~ucing furnace 3 into annealing furnace 4. There- -after, it enters cooling section 5 preparatory to treatment in coating bath 6~ All of the foregoinq steps and equipment are
: 30 through re~ucing furnace 3 into annealing furnace 4. There- -after, it enters cooling section 5 preparatory to treatment in coating bath 6~ All of the foregoinq steps and equipment are
-3-- :
3~
conventional except for the treatment in the novel preheat sec-tion and the improved effect which it has on the strip received from it and treated in the remainder of the line.
Figure 2 depicts a preferred form of preheat section of this inven-tion. It will be noted that a furnace of the direct flame contact type is provided which includes burners in only one-~uarter to one-third of its area relative to the prior ;
art design shown in Figure 4. The furnace is entirely closed except for the entry and exit ends thereof as shown in Figure 2 and through which the strip S and combustion gases pass in counter-current direction. Prior to the entry end of the furnace, there is located an elongated horizontally disposed flat tubular or envelope-like unit through which the strip first passes as seen inFigures 1, 2 and 3. It provides a zone which is of substantial length and relatively small height and width, and which advantageously is designed to limit the zone to a height and width to accommodate the strip to be treated therein.
In more detailed explanation of Figure 2, the preheat section includes t~o principal areas, an elongated tubular 20 preheating zone l and a closed muffle-type furnace 2. Tubular ~`
zone 1 has an open-ended entry through which steel strips are introduced to the system. A buffer stack 8, the function of which will be discussed later in more detail, is located im-;mediately adjacent and above the entry or charging end 7.
Tubular zone l is provided with a set of rolls 9, which are substantially the same as those rolls employed in the entire continuous annealing system and which support the strip as it travels horizontally through the various sections of the system.
Tubular zone l is characterized by an elongated area lO the length of which is dependent on the available space in a given mill. The elongated area lO terminates at entry ll to furnace 2. It will be noted that a restricted orifice 12 of heat resistant material is located at entry 11 to inhibit flow of
3~
conventional except for the treatment in the novel preheat sec-tion and the improved effect which it has on the strip received from it and treated in the remainder of the line.
Figure 2 depicts a preferred form of preheat section of this inven-tion. It will be noted that a furnace of the direct flame contact type is provided which includes burners in only one-~uarter to one-third of its area relative to the prior ;
art design shown in Figure 4. The furnace is entirely closed except for the entry and exit ends thereof as shown in Figure 2 and through which the strip S and combustion gases pass in counter-current direction. Prior to the entry end of the furnace, there is located an elongated horizontally disposed flat tubular or envelope-like unit through which the strip first passes as seen inFigures 1, 2 and 3. It provides a zone which is of substantial length and relatively small height and width, and which advantageously is designed to limit the zone to a height and width to accommodate the strip to be treated therein.
In more detailed explanation of Figure 2, the preheat section includes t~o principal areas, an elongated tubular 20 preheating zone l and a closed muffle-type furnace 2. Tubular ~`
zone 1 has an open-ended entry through which steel strips are introduced to the system. A buffer stack 8, the function of which will be discussed later in more detail, is located im-;mediately adjacent and above the entry or charging end 7.
Tubular zone l is provided with a set of rolls 9, which are substantially the same as those rolls employed in the entire continuous annealing system and which support the strip as it travels horizontally through the various sections of the system.
Tubular zone l is characterized by an elongated area lO the length of which is dependent on the available space in a given mill. The elongated area lO terminates at entry ll to furnace 2. It will be noted that a restricted orifice 12 of heat resistant material is located at entry 11 to inhibit flow of
4 -~,s~
combustion gases G from furnace 2 and ther~by provide a positive pressure throughout the furnace 2.
E~urnace ~ is entirely closed except for strip entxy !
ll and strip exit 13. This is in contrast to the prior art system of Figur~ 4 which has a plurality of venting dampers in the furnace roof over each of its multiple flame zones.
Furnace 2 of Figure 2 uses a substantially reduced flame zone and has ~ar fewer open flow burners 14 than hereto-fore required. ~he burners 14 are of conventional design~
and, or example, may correspond to those shown in U.S. Patent 2,933~425 to Hess~
The reduced number of burners needed for generating the combustion gases that provide the total heat xequirements of the furnace is one of the principal novel featuxes of the invention. This is the result of the direct flame contact of the combustion gases G with strip S over the elongated tubular section l wherein the residuals on the surface of strip S are more effectively treated for ultimate processing. The fore-going is in contrast to the furnace section of the prior art which re~uires several controlled heating zones as mentioned above, to achieve satisfactory processing of the residuals on the sur~ace of strip S which in the prior art entered the furnace at ambient temperature.
Figure ~ is in effect an adaptation of the prior art ~;
furnace to the system o~ the invention without rebuilding the furnace and wherein the venting dampers have been eliminated and the roof thus sealed off. Also, by such an arrangement~
several of the combustion zones have been eliminated while at ; the same time a more effective use is made of the reduced emount of heat in the 1esser volume of combustion gases G.
.
' .
~ 5-.,.,.. ". ~ , Among the advantages of the invention are substantial reduction of fuel requirements due to more effective use of heat as previously described, ma-terially reduced furnace main-tenance especially in the furnace roof due to elimination of the venting dampers, increased cleanliness of the strip as indicated by the elimination of virtually all adherence pro- ' blems during subsequent coating operations, and the ability to obtain better heating values on the treated strip.
In the prior art furnace dampers~ i-t is necessary to reline the damper seats several times over any six-month period while during the same time period these areas of the furnace of this invention have not required any relining or other maintenance.
In the present invention the furnace dampers of the prior art are eliminated because the gases exit the furnace through the elongated arealO of tuhular zone 1. At a point immediately adjacent to the entry end of the tubular zone, an appendage zone or stack 8 is installed vertically to a height that is above the highest point of the entire furnace complex. I'his stack unit is rectangular in cross-section and has inside dimensions equal to or greater than the twbular zone 1. The top of the stack 8 is open to the outside atmos-phere where the combustion gases are vented. The unit also acts as a buffer venting unit during the periods immediately following a line stop. The heat transfer conditions in the unit at that time exhaust any encroaching air that may be drawn into the operation 7.
As will be seen by reference to Figure 2, th~ flames produced in the area of the furnace adjacent to the exit from which the strlp passes to the annealing sec-tion are not vented to the outside atmosphere as in the prior art (see Figure 4)~
- but are permitted to travel in a single direction through the ~- 6 ~
~ 3~
.':~, :
furnace and along the length of the zone wherein they are in direct contact with the strip. Although of a lesser volume than the prior art, the gases directly and very effectively preheat and clean the strip surface with a minimum of waste heat. ;~
Figure 3 is a modified version of the preheating and cleaning furnace whereby the size of the closed furnace is substantially reduced and the strip exit is at the immediate end of the burner are so that the flame contact in the con-fined tubular zone begins immediately after the flame zone of the furnace. This design represents a more compact fur-nace in contrast to the system of ~igure 2. Otherwise, the ~`
preheat section of Figure 3 is essentially the same as that of Figure 2 in that it includes tubular zone 1I having an open entry 7', a venting stack 8', conventional rollers 9' for supporting strip S, an elongated area 10', and a restricted exit 12' to inhibit unrestricted flow of gases G from furna~e 2'.
Accordingly, the distinctive feature of the species of the invention of Figure 3 is that the interior of direct flame contact furnace 2l is limited in its dimensions to the space occupied by the burners required to produce the reduced quantityof combustion gases that distinguishes this invention over the prior art/ i.e. the effective size of furnace 2' corresponds to the minor portion of the furnace used as a burner area in furnace 2 of Figure 2.
The reactions of gases G on the surface contaminants (residuals~ of strip S are in general similar to those of the prior art except that the residuals are more effectively pro-cessed because of the more prolonged exposure of strip S to direct flame contact. The combustion gases are of a reducing nature so tkat the contaminants are apparently volati~ed as the ` strip passes through the preheat section. The reducing ~ nature of the gas is enhanced by the hydrogen in the gases ..~
~ ~ ~ 7 ~
: .:
., , , . ' . , ' ~ .. ' .. . . .
~3~i~9 used in the conventional reduction section of the system and which gases flow into the preheat furnace and eY.it the system through the tubular zone.
In actual operation beyond the preheat ~one, any residual coating on the strip is removed in the reducing section so that clean strip enters the annealing furnace. The anneal-ing section of the furnace which i5 of the standard type, is preceded by a reducing section having an atmosphere provided by a hydrogen containing gas (HNX) which reacts to further re-move any residual coating on the strip prior to annealingO Thestandard practice thereafter is to anneal and cool the strip prior to its.exit into the at~,osphere or into a coating unit~ .
EXAMPLE
In a typical operation steel strip enters the system I
in the tu~ular zone at ambient temperature and as it passes through the length thereof into the flame furna.ce, it has gained appreciably higher temperatures.th:an at the same point in prior art operations. The heating continues during the passage of the sheet through the entire preheat urnace, including the combustion zone. The temperature of the combustion gases in the burner area within the preheat furnace are maintained within the range of from about 2000F, to about 2400~F. and directly contact the strip in the furnace and zone. The residue from most rolling oils is volatilized at about 1200~F. to 1400F., so that the remaining heat in the ~urnace goes to preheat the strip S. The strip thereafter passes through the confined passage at the exit end of the preheater and cleaner and into the annealing zone proper. From that point on, the reducin~, ¦
annealing and galvanizing steps are those which are convention-3D ally employed in modern steel plant practices.
: i ,~ , .
~ 8- .
,, , , ~ :
~3~6S~
~he protective atmosphere gases as previously -~
stated flow countercurrent to the strip and r~duce any re-maining residue on the surface thereof as it passes through the annealing system. These protective gases also enter the combustion chamber of the prehea~er furnace and contribute further heat thereto~ The protective ga~es pass along the the combustion gases from the preheater into and through ~he tubular zone and are vented as previously described, Al~hough this invention has been described as part of a continuous galvanizing systemt it can be used effectively in any continuous line where clean strip metal is required, including tin and aluminium coating operations. Also, although it has been described as used in a strip annealing system, it can be applied to other fabricated forms, such as wire, etc., ~;
as well as with other metals.
While in accordance with the provisions of the :~
Statutes I have illustrated and described the best form of ::~
embodiment of my inv~ntion now known to me, it will be apparent to those skilled in the art that changes may be made in the fo~m of the apparatus and process disclosed without departing ~:~
from the spirit and scope of the inv~n~ion set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.
..~ .
~; : :
, ;:
_g;.
combustion gases G from furnace 2 and ther~by provide a positive pressure throughout the furnace 2.
E~urnace ~ is entirely closed except for strip entxy !
ll and strip exit 13. This is in contrast to the prior art system of Figur~ 4 which has a plurality of venting dampers in the furnace roof over each of its multiple flame zones.
Furnace 2 of Figure 2 uses a substantially reduced flame zone and has ~ar fewer open flow burners 14 than hereto-fore required. ~he burners 14 are of conventional design~
and, or example, may correspond to those shown in U.S. Patent 2,933~425 to Hess~
The reduced number of burners needed for generating the combustion gases that provide the total heat xequirements of the furnace is one of the principal novel featuxes of the invention. This is the result of the direct flame contact of the combustion gases G with strip S over the elongated tubular section l wherein the residuals on the surface of strip S are more effectively treated for ultimate processing. The fore-going is in contrast to the furnace section of the prior art which re~uires several controlled heating zones as mentioned above, to achieve satisfactory processing of the residuals on the sur~ace of strip S which in the prior art entered the furnace at ambient temperature.
Figure ~ is in effect an adaptation of the prior art ~;
furnace to the system o~ the invention without rebuilding the furnace and wherein the venting dampers have been eliminated and the roof thus sealed off. Also, by such an arrangement~
several of the combustion zones have been eliminated while at ; the same time a more effective use is made of the reduced emount of heat in the 1esser volume of combustion gases G.
.
' .
~ 5-.,.,.. ". ~ , Among the advantages of the invention are substantial reduction of fuel requirements due to more effective use of heat as previously described, ma-terially reduced furnace main-tenance especially in the furnace roof due to elimination of the venting dampers, increased cleanliness of the strip as indicated by the elimination of virtually all adherence pro- ' blems during subsequent coating operations, and the ability to obtain better heating values on the treated strip.
In the prior art furnace dampers~ i-t is necessary to reline the damper seats several times over any six-month period while during the same time period these areas of the furnace of this invention have not required any relining or other maintenance.
In the present invention the furnace dampers of the prior art are eliminated because the gases exit the furnace through the elongated arealO of tuhular zone 1. At a point immediately adjacent to the entry end of the tubular zone, an appendage zone or stack 8 is installed vertically to a height that is above the highest point of the entire furnace complex. I'his stack unit is rectangular in cross-section and has inside dimensions equal to or greater than the twbular zone 1. The top of the stack 8 is open to the outside atmos-phere where the combustion gases are vented. The unit also acts as a buffer venting unit during the periods immediately following a line stop. The heat transfer conditions in the unit at that time exhaust any encroaching air that may be drawn into the operation 7.
As will be seen by reference to Figure 2, th~ flames produced in the area of the furnace adjacent to the exit from which the strlp passes to the annealing sec-tion are not vented to the outside atmosphere as in the prior art (see Figure 4)~
- but are permitted to travel in a single direction through the ~- 6 ~
~ 3~
.':~, :
furnace and along the length of the zone wherein they are in direct contact with the strip. Although of a lesser volume than the prior art, the gases directly and very effectively preheat and clean the strip surface with a minimum of waste heat. ;~
Figure 3 is a modified version of the preheating and cleaning furnace whereby the size of the closed furnace is substantially reduced and the strip exit is at the immediate end of the burner are so that the flame contact in the con-fined tubular zone begins immediately after the flame zone of the furnace. This design represents a more compact fur-nace in contrast to the system of ~igure 2. Otherwise, the ~`
preheat section of Figure 3 is essentially the same as that of Figure 2 in that it includes tubular zone 1I having an open entry 7', a venting stack 8', conventional rollers 9' for supporting strip S, an elongated area 10', and a restricted exit 12' to inhibit unrestricted flow of gases G from furna~e 2'.
Accordingly, the distinctive feature of the species of the invention of Figure 3 is that the interior of direct flame contact furnace 2l is limited in its dimensions to the space occupied by the burners required to produce the reduced quantityof combustion gases that distinguishes this invention over the prior art/ i.e. the effective size of furnace 2' corresponds to the minor portion of the furnace used as a burner area in furnace 2 of Figure 2.
The reactions of gases G on the surface contaminants (residuals~ of strip S are in general similar to those of the prior art except that the residuals are more effectively pro-cessed because of the more prolonged exposure of strip S to direct flame contact. The combustion gases are of a reducing nature so tkat the contaminants are apparently volati~ed as the ` strip passes through the preheat section. The reducing ~ nature of the gas is enhanced by the hydrogen in the gases ..~
~ ~ ~ 7 ~
: .:
., , , . ' . , ' ~ .. ' .. . . .
~3~i~9 used in the conventional reduction section of the system and which gases flow into the preheat furnace and eY.it the system through the tubular zone.
In actual operation beyond the preheat ~one, any residual coating on the strip is removed in the reducing section so that clean strip enters the annealing furnace. The anneal-ing section of the furnace which i5 of the standard type, is preceded by a reducing section having an atmosphere provided by a hydrogen containing gas (HNX) which reacts to further re-move any residual coating on the strip prior to annealingO Thestandard practice thereafter is to anneal and cool the strip prior to its.exit into the at~,osphere or into a coating unit~ .
EXAMPLE
In a typical operation steel strip enters the system I
in the tu~ular zone at ambient temperature and as it passes through the length thereof into the flame furna.ce, it has gained appreciably higher temperatures.th:an at the same point in prior art operations. The heating continues during the passage of the sheet through the entire preheat urnace, including the combustion zone. The temperature of the combustion gases in the burner area within the preheat furnace are maintained within the range of from about 2000F, to about 2400~F. and directly contact the strip in the furnace and zone. The residue from most rolling oils is volatilized at about 1200~F. to 1400F., so that the remaining heat in the ~urnace goes to preheat the strip S. The strip thereafter passes through the confined passage at the exit end of the preheater and cleaner and into the annealing zone proper. From that point on, the reducin~, ¦
annealing and galvanizing steps are those which are convention-3D ally employed in modern steel plant practices.
: i ,~ , .
~ 8- .
,, , , ~ :
~3~6S~
~he protective atmosphere gases as previously -~
stated flow countercurrent to the strip and r~duce any re-maining residue on the surface thereof as it passes through the annealing system. These protective gases also enter the combustion chamber of the prehea~er furnace and contribute further heat thereto~ The protective ga~es pass along the the combustion gases from the preheater into and through ~he tubular zone and are vented as previously described, Al~hough this invention has been described as part of a continuous galvanizing systemt it can be used effectively in any continuous line where clean strip metal is required, including tin and aluminium coating operations. Also, although it has been described as used in a strip annealing system, it can be applied to other fabricated forms, such as wire, etc., ~;
as well as with other metals.
While in accordance with the provisions of the :~
Statutes I have illustrated and described the best form of ::~
embodiment of my inv~ntion now known to me, it will be apparent to those skilled in the art that changes may be made in the fo~m of the apparatus and process disclosed without departing ~:~
from the spirit and scope of the inv~n~ion set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.
..~ .
~; : :
, ;:
_g;.
Claims (8)
1. In a continuous annealing line system for steel strip comprising in combination preheating and cleaning means for processing residuals on the surface of said strip by direct flame contact at a temperature sufficient to remove residual surface contaminants thereon, means for passing said strip through an annealing zone in the presence of a reducing gas to further remove said residuals and protect the surface of said strip, and means cooling said annealed strip to a temperature suitable for further treatment, the improvement which comprises providing a closed muffle furnace having combustion means for producing flames and combustion gases for heating said furnace and said strip as the same passes through said furnace, and elongated restricted tubular section extending from one end of said furnace and through which said flames and said combustion gases flow for ultimate discharge from said system, means for passing said strip into said tubular section countercurrent to the flow of said gases and flames, means for maintaining said strip in direct contact with said flames and gases as said strip passes through said tubular zone and said furnace, and means for passing said strip from said furnace to said annealing zone.
The continuous annealing line of Claim 1 wherein the combustion means within said closed muffle furnace comprises an arrangement of direct flame burners that occupy a relatively small area within said furnace.
3. The continuous annealing line of Claim 1 wherein the combustion means within said closed muffle furnace comprises an arrangement of direct flame burners that occupy the entire area within said furnace.
4. A process for continuously annealing metal strip comprising;
a) introducing strip to be annealed into an elongated tubular preheat zone and passing it therethrough as said strip contacts hot combustion gases flowing in a direction opposite to the direc-tion of flow of said strip, b) passing said strip into a closed muffle furnace wherein combustion gases are generated for direct flame contact on the surface of said strip to thereby continue the preheating and cleaning thereof to effectively remove surface contaminants therefrom, c) thereafter subjecting said strip to a series of consecutive steps comprising:
i) subjecting said strip to a reducing area within an atmosphere of hydro-gen containing protective gases;
ii) annealing said strip; and iii) cooling said strip to a temperature wherein it is compatible with a subsequent coating operation.
d) permitting said protective gases and said combustion gases to flow countercurrent to the direction of travel of said strip through said furnace and said zone.
a) introducing strip to be annealed into an elongated tubular preheat zone and passing it therethrough as said strip contacts hot combustion gases flowing in a direction opposite to the direc-tion of flow of said strip, b) passing said strip into a closed muffle furnace wherein combustion gases are generated for direct flame contact on the surface of said strip to thereby continue the preheating and cleaning thereof to effectively remove surface contaminants therefrom, c) thereafter subjecting said strip to a series of consecutive steps comprising:
i) subjecting said strip to a reducing area within an atmosphere of hydro-gen containing protective gases;
ii) annealing said strip; and iii) cooling said strip to a temperature wherein it is compatible with a subsequent coating operation.
d) permitting said protective gases and said combustion gases to flow countercurrent to the direction of travel of said strip through said furnace and said zone.
5. The process of Claim 4 wherein the metal strip is steel strip.
6. The process of Claim 4 wherein the coating operation is a zinc galvanizing operation.
7. The method of Claim 4, 5 or 6 wherein the elon-gated tubular zone through which the metal strip is passed is of restricted dimensions generally approximately the shape of said strip whereby said combustion gases and said protective gases are in direct contact with said strip over the length of said zone.
8. The method of Claim 4, 5 or 6 wherein the com-bustion gases from said furnace are of a restricted volume and impinge directly on said strip as they enter said elongated tubular zone.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86322677A | 1977-12-22 | 1977-12-22 | |
| US863,226 | 1977-12-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1103569A true CA1103569A (en) | 1981-06-23 |
Family
ID=25340620
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA308,621A Expired CA1103569A (en) | 1977-12-22 | 1978-08-02 | Preheat and cleaning system |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1103569A (en) |
| GB (1) | GB1604153A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3640213C1 (en) * | 1986-11-25 | 1992-12-10 | Didier Werke Ag | Process for firing molded parts made of coarse ceramic material or oxide ceramic and push-through furnace for the process |
| SE534718C2 (en) * | 2010-04-06 | 2011-11-29 | Linde Ag | Method and apparatus for processing continuous or discrete metal products |
-
1978
- 1978-05-30 GB GB2391178A patent/GB1604153A/en not_active Expired
- 1978-08-02 CA CA308,621A patent/CA1103569A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1604153A (en) | 1981-12-02 |
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| Date | Code | Title | Description |
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| MKEX | Expiry | ||
| MKEX | Expiry |
Effective date: 19980623 |