CA1110120A - Dipless metallizing process and apparatus - Google Patents
Dipless metallizing process and apparatusInfo
- Publication number
- CA1110120A CA1110120A CA305,539A CA305539A CA1110120A CA 1110120 A CA1110120 A CA 1110120A CA 305539 A CA305539 A CA 305539A CA 1110120 A CA1110120 A CA 1110120A
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Abstract
ABSTRACT OF THE DISCLOSURE
Metallic articles, for instance, ferrous strips are metallized, for instance, zinc coated by passing the heated article through a coating chamber and applying thereto a continuous stream of the molten coating metal so as to uni-formly and evenly metallize said article. Thereafter, excess molten coating metal is removed from the coated article by hot gas blasting and the hot gas blasted article leaving the coat-ing chamber is immediately cooled. Wiping means may be provided before applying the molten coating metal so at to deflect any molten coating metal dropping from the metallic article passing therethroughm while rollers may be arranged between the coating metal applying means and the hot gas blasting means. Said rollers serve to remove the major part of excess coating metal from the coated metallic article and to stabilize movement of the metallic article passing through the coating chamber. In contrast to known application of coat-ing metal by atomizing or spraying, no gas is admixed to the continuous stream of the molten coating metal which is, so to say, gently poured onto the surface of the metallic article, Thus coating is effected within a short period of time and a non-porous coating is achieved. Said short period of time of exposure of the steel article to the liquid zinc enables to eliminate the customary addition of aluminum to the spelter, thus permitting the use of steam for the hot blast instead of the more expensive neutral gas for that purpose, likewise eliminating the formation of White rust.
Metallic articles, for instance, ferrous strips are metallized, for instance, zinc coated by passing the heated article through a coating chamber and applying thereto a continuous stream of the molten coating metal so as to uni-formly and evenly metallize said article. Thereafter, excess molten coating metal is removed from the coated article by hot gas blasting and the hot gas blasted article leaving the coat-ing chamber is immediately cooled. Wiping means may be provided before applying the molten coating metal so at to deflect any molten coating metal dropping from the metallic article passing therethroughm while rollers may be arranged between the coating metal applying means and the hot gas blasting means. Said rollers serve to remove the major part of excess coating metal from the coated metallic article and to stabilize movement of the metallic article passing through the coating chamber. In contrast to known application of coat-ing metal by atomizing or spraying, no gas is admixed to the continuous stream of the molten coating metal which is, so to say, gently poured onto the surface of the metallic article, Thus coating is effected within a short period of time and a non-porous coating is achieved. Said short period of time of exposure of the steel article to the liquid zinc enables to eliminate the customary addition of aluminum to the spelter, thus permitting the use of steam for the hot blast instead of the more expensive neutral gas for that purpose, likewise eliminating the formation of White rust.
Description
B~CKGROUND OF THh~ INVENTION
(l) FIELD OF THE INVENTION
The present invention relates to an improved process of providing a metallic article such as a ferrous strip with a coating such as a zinc coating and more partic~
ularly to a "dipless" metallizing process without dipping the article into a molten metallizing bath and to an apparatus for carrying out said process.
' ~'"' '
(l) FIELD OF THE INVENTION
The present invention relates to an improved process of providing a metallic article such as a ferrous strip with a coating such as a zinc coating and more partic~
ularly to a "dipless" metallizing process without dipping the article into a molten metallizing bath and to an apparatus for carrying out said process.
' ~'"' '
(2) DESCRIPTION OF THE PRIOR ART
Modern galvanizing procedures, in spite of recent improvementsl can still be considered in outda-ted inheritance ~ -of the original hot dip galvanizing in which the article to be -~ :
coated was submerged~ while still cold, in a heated zinc pot, thereby passing through a layer of a flux which floats on the molten zinc bath and cleans the article to be coated of any dirt and moisture.
Before galvanizing takes place, the article had to be heated to about the melting point of the zinc. Such heat~
ing, of course, takes some time. During heating a bri-ttle layer of a ferro~zinc aIloy was formed on the interface between the article and the zinc layer~ Said ferro-zinc alloy layer caused the zinc coating to readily flake and peel off the article, thus diminishing considerably the anti-corrosive propert.ies of the galvanized article.
In spite of vast improvements as they are achieved by recent modifications of the known processes, the sheet material~ usually in the form of a continuous strip; is still passed through a molten zinc bath after it has been preheated ~ .
and under the protection o~ a non~o~idi~ing atmosphere.
Thus, it is no more necessary to keep the strip in the molten zinc in order to heat it. However, on account of merely geometrical considerations, the strip must remain in contact with the molten zinc for a longer period of time than required for purely metallurgical consideratlon. As a result of such a prolonged contact of strip and zinc a brittle ferro- :
zinc alloy of greater thickness than desired is formed.
Formation of the ferro-zinc alloy is prevented, at leas-t partly, by the addition of ~luminum or the like to the zinc bath. Such addition, however, reduces to some extent the ductility of the zinc coating in comparison to the ductility of a non-alloyed zinc coating.
It follows that the duration of contact between the article and the zinc bath is determined by the use o~E a zinc bath provided with a sinking drum as well as by the dimensions of such a drum.
` SIIM~RY OF T~IE INVENTION
It is one object of the present invention to over-come the disadvantages of the heretofore used hot dip galvaniz-ing or other metallizing process and to provide a dipless process whereby contact of the ferrous article with the zinc -is of such a short duration that formation of the ferro-zinc alloy layer can be kept under control without having to add aluminum to the spelter.
Another object of the present invention is to provide a simple and effective apparatus to carry out said dipless galvanizing or metallizing process.
~ further ob~ect of the present invention ~s to provide a pure zinc coaked ferrous strip or article with an ~ :
Modern galvanizing procedures, in spite of recent improvementsl can still be considered in outda-ted inheritance ~ -of the original hot dip galvanizing in which the article to be -~ :
coated was submerged~ while still cold, in a heated zinc pot, thereby passing through a layer of a flux which floats on the molten zinc bath and cleans the article to be coated of any dirt and moisture.
Before galvanizing takes place, the article had to be heated to about the melting point of the zinc. Such heat~
ing, of course, takes some time. During heating a bri-ttle layer of a ferro~zinc aIloy was formed on the interface between the article and the zinc layer~ Said ferro-zinc alloy layer caused the zinc coating to readily flake and peel off the article, thus diminishing considerably the anti-corrosive propert.ies of the galvanized article.
In spite of vast improvements as they are achieved by recent modifications of the known processes, the sheet material~ usually in the form of a continuous strip; is still passed through a molten zinc bath after it has been preheated ~ .
and under the protection o~ a non~o~idi~ing atmosphere.
Thus, it is no more necessary to keep the strip in the molten zinc in order to heat it. However, on account of merely geometrical considerations, the strip must remain in contact with the molten zinc for a longer period of time than required for purely metallurgical consideratlon. As a result of such a prolonged contact of strip and zinc a brittle ferro- :
zinc alloy of greater thickness than desired is formed.
Formation of the ferro-zinc alloy is prevented, at leas-t partly, by the addition of ~luminum or the like to the zinc bath. Such addition, however, reduces to some extent the ductility of the zinc coating in comparison to the ductility of a non-alloyed zinc coating.
It follows that the duration of contact between the article and the zinc bath is determined by the use o~E a zinc bath provided with a sinking drum as well as by the dimensions of such a drum.
` SIIM~RY OF T~IE INVENTION
It is one object of the present invention to over-come the disadvantages of the heretofore used hot dip galvaniz-ing or other metallizing process and to provide a dipless process whereby contact of the ferrous article with the zinc -is of such a short duration that formation of the ferro-zinc alloy layer can be kept under control without having to add aluminum to the spelter.
Another object of the present invention is to provide a simple and effective apparatus to carry out said dipless galvanizing or metallizing process.
~ further ob~ect of the present invention ~s to provide a pure zinc coaked ferrous strip or article with an ~ :
-3- ~ ~
intermediate ferro-zinc alloy layer o~ optimum minimum thick--ness.
Other objects of the present invention and advanta-geous features thereof will become apparent as the description proceeds.
In principle the process according to the present invention comprises instantaneous application of molten metal, i.e. fluid zinc to the heated article, i.e. the hot strip, followed immediately thereafter by exposing the zinc-coated article or strip to the action of a hot, non-oxidizing gas blast which removes excess zinc and limits the thickness of the zinc coating. Preferably immediately thereafter the zinc-coated article or strip is rapidly cooled to a temperature below the melting point of the zinc by exposing it to the action of a cooling blast, for instance, by means of jets of a coollng fluid.
According to another embodiment of the present invention a pair of rollers is provided between the appli-cation of molten zinc to the article and the hot gas blast.
These rollers effect better distribution and spreading of the zinc across the entire width of the strip; they will exclude any effect of the hot gas blast on the apparatus and arrange-ments for applying the zinc to the strip; they will cause considerable stabilization of the moving strip thus resulting in greater efficiency of the hot gas blast arrangementsO
The possible geometry of such a process limits the length of contact between ferrous article and zinc to a few inches, compared tc~ several feet as is the case for processes using a zinc bath and a sinking drum~ Thus the duration of the iron-zinc contact according to the present in~ention i9 several times shorter than that of the conventional methods.
,. .
In fact the duration of zinc-to-art~cle contact is limited to less than a second.
As a result thereof, non-alloyed zinc can ~e used in the process of the present invention thus improving the corrosion resistance of the zinc coating ("pure" metal coating~
without undue growth of the brittle intermediate ferro-zinc alloy layer, thus ensuring excellent adherence of the pure zinc coating to the coated article or strip.
Several, but by no means limiting, ways of applying zinc to the strip can be employed. For instance, molten zinc can be poured onto the strip headers equipped with appropriate nozzles through which molten zinc is discharged upon the strip, for instance, i~ediately before it is passed between the above mentioned rollers. According to another embodiment of the 15 present invention, the molten zinc is applied to the bodies of ~ -the rollers and then applied ("printed") onto the strip as lt contacts said rollers. As mentioned above the strip emerging ~rom said rollers undergoes a hot non-oxidizing gas blast followed by a rapidly cooling blast outside of the coating chamber. This blast does not have to be non-oxidizing. An air blast or a water spray or the like are adequate means for cool-ing the coated article.
In a preferredl but by no means limiting, embodiment of the present invention, the strip emerging from a "snout" of a pretreating device, such as a continuous furnace, is conducted around a pulley and rises to the zone of the metallizing process in a substantially vertical direction. The atmosphere surrounding the pulley is substantially the same as is used in the pretreating furnace.
The process chamber has an entry slo~ for the strip by which i-t enters said chamber from the box which carries the ;
: .
strip deflecting pulley. The strip is then taken through "reversed" wiper means contacting the strip under a vexy sli~ht pressure. The purpose of these wiper means is to prevent any excess zinc rolled off the strip by rollerc arranged after the wiper means, from falling down onto the strip deflecting pulley. The major part of the zinc removecl from the strip by the rollers will run down onto the top faces of the wiper means. If part of the zinc runs through the slot of the wiper means, it will, by capillary action, run down the bottom face of the wiper meansO As a result thereof, the rolled-off zinc will drop to the bottom of the process chamber from where it is returned to the zinc melting and de-oxidizing oven~
The molten zinc is supplied ko the zinc application device from a zinc melting oven by means of a zinc pump.
Excess molten zinc which is partly removed by the rollers and finally by subsequent hot blasting, drops to the bottom of the process chamber, from where it is returned, by gravity, to the zinc melting oven for further recirculation. Should any zinc oxide have been formed on the way from the process chamber, it will be de-oxidized to metallic zinc by the floating layer of de-oxidizing agent provided on the molten z~nc surface of the oven.
The zinc applying means are provided between the reversed wiper means and the rollers which serve to remove ~5 most of the excess zinc from the coated strip. Thereafter, the zinc coated strip is sub;ected to a hot blast of a non-oxidizing gas which removes the remainder of the excess zinc. ~ -~
The coated strip passes then from the coating chamber through a narrow slot into the surrounding atmosphere, where it under-goes rapid cooling, i.e. ~uenching.
The combination of said guiding rollers and the immediate quenching of the strip coating at the strip exit ~6-'i, \ .
from the chamber permits to considerably reduce the non guided portion o~ the coated strip, rendering it substantially rigid, when it arrives at the hot blasting zone. Said guiding distance is measured vertically from the bite of said rollers and up to the point where, after being spray cooled, the zinc coating has been sufficiently hard to be mechanically guided by a pulley. Thereby, the strip is kept in a substantially rigid condition so as to ensure optim~ per~ormance of the hot blast. As a result thereof, the nozzles ~or the slot) of the hot blasting unit can be placed much nearer to the strip surface than is possible without the use of the rollers and the rapid cooling means. Thi~ facty in its turn, will result in a lower hot gas pressure and a lower gas consumption.
The resulting "stability" of the travelling strip in the coating chamber also permits to provide narrowing of the strip exit slot therefrom~ A narrow exit slot, of course, allows to operate under a lower pressure of the non-oxidizing atmosphere in the cGating chamber than heretofore possible.
As a result thereof, the gas consumption of the galvanizing unit is considerably reduced.
The short exposure of the metal of the strip to the molten zinc and the almost immediate cool;ng of the zinc coat-ing which takes place when the strip exit~ from the coating chamber render it possible to reduce considerably or to even completely eliminate the addition of aluminum to the spelter.
When aluminum is added to the spelter, the hot blast must be of a non-o~idizing composition or it must even be, for practical reasons, slightly deoxidizing so as not to cause oxidation of the added alumlnum. ~owever, ~hen proceedin~
according to the present invention, the time of contact of the molten zinc with the strip is so short that addition of .
~q~
aluminum can be completely avoided. Therefore, superheated steam can be used for hot blasting because it does not oxidize molten zinc~ Such superheated steam is much cheaper and simpler to produce than a non-oxidizing gas blast.
Besides, should air be mixed with the steam and should some zinc oxide be formed, the de-oxidizing effect of the protective layer provided on the zinc surface in the z:inc melting oven will reduce any formed oxide to metallic zinc. It is, of course, not possible to reduce the aluminum oxide portion of conventional top-dross by the de-oxidizing layer in the 2inc melting ovenO
In view of the fact that the coating of the metallic article can consist of pure zinc when proceeding according to the continuous hot coating process of the presen-t invention, the resulting coating has the best imaginable anti-corrosive properties. Since the coating consists of pure metal, no galvanic effects between the basic zinc and its alloying elements are encountered.
Another advantage of the process according to the present invention is that the coatin~ of pure zinc is more ;~
flexible and ductile than that of its alloys, including alumi-num-zinc alloys~ Thus the pure zinc coated strip can better be subjected to stamping and~or drawing working than products galvanized in the conventional manner. ~ack of aluminum addition to the spelter avoids the unpleasant fea-ture oE
"conventional" continuous galvanizing, namely the formation of "WHITE RUST" which is especially critical in damp a-tmospheres and which is a direct result of the aluminum added to -the spelter. Chromate surface treatment baths, or similar, are used to prevent the formation o~ white rust~ Obviously the present process does not need any such extra treatment.
-While the process according to the present inven-tion has been described hereinabo~e with respect to galvaniz-ing ~errous articles such as stee] strips, lt is, of course, also possible to use said process for applying coatln~s of other metals to metallic articles. Thus the process can be used~ for instance, for coating articles and especially strip with aluminum, tin or tern alloy, or others. Of course, other metallic articles than ferrous articles such as copper strips can also be metallized by the process o~ the present invention.
Likewise, instead of pouring the molten metal through nozzles upon the metallic article or strip or applying it to the article or strip by means, for instance, it can also be applied thereto by other means, ~or instance, by forcing a stream of molten zinc by gravity upon the strip or by any other suitable means. In principle, the molten coating metal is applied to the metallic article by projecting or gently pouring it thereon in the form of a continuous stream.
As mentioned, one of the advantages of using spelter without aluminum alloying is the possibility of using cheap steam for the ho-t blast instead o~ more e~pensive neutral gas, because steam does not oxidize molten zinc (but does, very energetically, aluMinum~ However, it is not possible to have steam of the blast mix with the stationary gas of the pre-treating chamber o~ the furnace. A gas separating means have to be provided, substantially according to the following lines:
as will be described in what ~ollows, a vertical separator is to be located either before the zinc headers and the spreader rolls or at the centerlines plane o~ these rolls. In -the first case the not yet coated strip is exposed to the steam atmo-sphere which is oxidizing to steel; but, for conditions of _9~ : .
. . ~ . . . ~. . . . ..
modern, high strip speed galvaniæing this exposure is of so short a duration that ihis oxidation is not harmful. For lower speed galvanizing, however, the duration is longer and the gas-steam separation wall can be placed over and under the spreader rolls, so ~hat no "rawl' strip is exposed to the steam atmosphereO A possible particularity of such a seal con-sists, for the lower roll, to dip it into a molten-æinc bath which also collects the molten zinc overflow which has been removed by the spreader rolls~ Conventional sealiny and wear elements known to the man skilled in the art are to be used at the split of the "wall" for the high speed type of coating and on the upper roll of the described low speed coating.
Typical examples will be given in connection with the drawings.
In any case, in order to prevent any steam from getting into the neutral gas zone by ]eaks, it is suggested to keep the pressure in the neutral gas zone somewhat higher than in the ':steam" zone~
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, advantages, and uses of the present invention will become apparent ~rom a reading o~ the following specification and claims taken in connection with the attached drawings which form a part of the specifica-tion and wherein:
Fig~ 1 is a vertical cross-sectional view of a dip-less coating apparatus in which molten zinc is applied to the rising strip which is then hot-blasted and quenched;
Fig~ 2 is a cross-sectional view of a similar dipless coating apparatus in which strip movement stabiliæing and excess zinc removing rollers are provided be~ween the zinc applying means and the hot-blasting means;
Fig. 3 is a cross-sectional view o~ a similar dipless , . ~ .
.
coating apparatus in which the molten zinc is applied to the strip by means of a trough~ e distr~buting means;
Fig. 4 i5 a cross-sectional view of a dipless coat-ing apparatus in which the molten zinc is applied to the strip by means of the stabilizing rollers which are partly immersed in an overflowing dipping bath, and Fig. 5 is a cross-sectional view of a dipless coat-ing apparatus similar to the apparatus of Fig. ~ in which the molten zinc is poured on the rollers from a header and i9 applied to the strip by said rollers covered with the molten zinc.
Fig. 6 is a cross-sectional view of a dipless coat-ing apparatus in which the strip is passed through the coating chamber in substantially horizontal direction and, after coat-ing, is deflected upwardly for subsequent treatment.
Fig. 7 is cross-sectional view of a dipless coating ~-apparatus similar to that of Fig. 6 in which the strip is passed substantially horizontally through the coating chamber and also through the subsequent treatment systems.
Fig. 8 is a cross-sectional view of a dipless coat-ing apparatus enabling the use of steam for the hot blast -type, recom~ended for lligh strip velocities.
Fig. 9 is a cross sectional view of a dipless coat-ing apparatus enabling the use of steam for the hot blast ~5 type, recommended for lower strip velocitles.
Fig. 10 shows details of the gas tight seals, applicable to both, the high speed and low speed, systems; it - : . .:
is a section according to X - Y of Figures 8 and 9.
1ike numerals in said drawings indicate li~e parts 3Q of the e~uipment.
:. ' DESCRIPTION OF THE P~EFERRED EMBODIMENTS
. . . ~
In said drawings, F~g. 1 demonstrates the principal features of the present invention.
In said Fig. 1 strip 1 to be coated is passed from the pretreating furnace (not shown) through snout 20 into substantially gas-tight chamber 3 carrying strip deflecting pulley 2. Said pulley 2 deflects strip 1 so that it is conducted vertically upwardly into coating and processing chamber 8 containing and enclosing the various elements of the galvanizing process of the present invention. Strip 1 passes through orifice-like opening 21 into said chamber 8 and is then contacted by the pair of wipers 5. Strip 1 is then contacted by a continuous stream of molten zinc 23 dispensed through headers 4 with nozzle -like openings.
Excess zinc drops onto wipers 5 and is deflected from the strip and collected in return conduit 6 from which the zinc is returned into the zinc melting and regenerating oven (not - -shown). The remainder of excess zinc on the zinc coated strip is removed therefrom by the hot gas blast 22 supplied through hot gas blast header 7. The zinc-coated stxip 1 from which excess zinc has been removed passes through strip exit slot 9 of coating chamber 8 and is conducted to stabiliziny pulley 11 which in co-operation with strip deflecting pulley 2 stabi-lize movement of the strip on travelling through coating chamber 8. Immediately after coated strip 1 has left said chamber 8 through exit slot g, it is rapidly cooled by exposure to a spray of a cooling fluid 24 sprayed thereon by means of header 10~ When operating as shown in Fig. 1~ the strip is passed successively through reverse wipers 5, a stream of molten zinc 23 applied by means of header 4, and hot gas blast 22 applied by means of header 7 all of them enclosed in ~ , ~ . . ' processing chamber 8, and is then rapi~ly cooled by cooling fluid spray 24.
The coating apparatus as illustrated in Fig. 2 differs rom that of Fig. 1 by providing between the appli-cation o the molten zinc stream 23 and the hot gas blast 22, roller means 12 which remove the major part of excess zinc from coated strip 1 passing therethrough. Said roller L
means 12 aid in urther stabili~ing the movement of strip 1 on its travel through coating chamber 8.
In Fig. 3 a modification of the means for applying a continous stream of molten zinc to strip 1 is illustrated while otherwise the apparatus is the same as shown in Fig. 2.
According to this modification the molten zinc 23 is poured : ~.
from header 4 onto deElecting and distributing spreader 13 which applies it to strip lo Another means of applying the molten zinc to strip 1 ~
is illustrated in Fig. 4. According to said modification the ~ ~:
molten zinc 15 is supplied to pans 14 by means o header 4.
Rollers 12, as shown, dip into said pans 14 and carry along the molten zinc for application to strip 1. The rollers 12 ~ -are provided with elongated and inclined slots 17 which carry a journal of the stabiliæing rollers 12 and thus assist in exerting pressure between the rollers 12 but still permit to readily shift the rollers so that a strip threading tool can ~.
be passed therebetween. Dipping pans 14 are provided with a molten zinc overflow 16 allowing the molten zinc 15 in the pans 14 to overflow onto and along the walls of coating chamber 8 and downwardly into the return conduit 6 from where it is returned to the zinc melting oven (not shown).
Another modification of the means for applying .
. ~ . . .
.. , .. , ~ .
molten zinc to the strip 1 is illustrated in Fig. 5, whereby the molten zinc stream 23 is supplied through header ~ to deflector-distributor plate 18 which allows to evenly spread the molten zinc over the surfaces of rollers 12 which apply ("print") the molten zinc onto the surface of strip 1. A
variancy of this consists of spraying the rollers 12 in an anti-rotational direction from headers 4-~ preferably located close to the rollers and to the mounting strip.
It will be noted that in the apparatus illustrated by Figs. 2 to 5 inclusive in which strip stabilizing rollers 12 are used, the exit slots 9 can be made much more narrower than in the apparatus illustrated by Fig. 1, where no stabi-lizing rollers are used~ Since movement of the strip is greatly enhanced by providing rollers 12 as shown in Fig. 2 to 5, the efficiency of the hot blast is considerably improved, so that a reduced hot blast gas consumption is achieved.
Consequently, the hot gas blast headers 7 can be made smaller than the headers 7 to Fig. 1, which shows no stabilizing rollers.
~s stated above, the claimed process permits, according to another embodiment of the present invention, to conduct the hot metallic article to pass substantially hori-zon-tally throu~h coating chamber 3. Thus the procedure per-mits to eliminate the wiper means 5 described hereinabove.
Fig. 6 illustrates in cross-sectional view this procedure. In said Fig. 6 strip 1 to be coated is passed from the pretreating furnace into chamber 3 which carries the strip deflecting pulleys 2 and 2aO ~ulley 2a may e~en be omitted~ Strip 1 passes then substantially horizontally, 3a pre~erably at a small angle downwardly, toward roller 12 which remove the major part of excess zinc from coated strip 1.
~aid rollers pre~erably deflect -the coated strip upwardly to the hot blast means.
~hile passing ~r~m deflecting pulleys 2 and 2a through coating chamber 3, khe strip ~s contacted by a continuous stream of molten zinc 23 dispensed ~hrough headers
intermediate ferro-zinc alloy layer o~ optimum minimum thick--ness.
Other objects of the present invention and advanta-geous features thereof will become apparent as the description proceeds.
In principle the process according to the present invention comprises instantaneous application of molten metal, i.e. fluid zinc to the heated article, i.e. the hot strip, followed immediately thereafter by exposing the zinc-coated article or strip to the action of a hot, non-oxidizing gas blast which removes excess zinc and limits the thickness of the zinc coating. Preferably immediately thereafter the zinc-coated article or strip is rapidly cooled to a temperature below the melting point of the zinc by exposing it to the action of a cooling blast, for instance, by means of jets of a coollng fluid.
According to another embodiment of the present invention a pair of rollers is provided between the appli-cation of molten zinc to the article and the hot gas blast.
These rollers effect better distribution and spreading of the zinc across the entire width of the strip; they will exclude any effect of the hot gas blast on the apparatus and arrange-ments for applying the zinc to the strip; they will cause considerable stabilization of the moving strip thus resulting in greater efficiency of the hot gas blast arrangementsO
The possible geometry of such a process limits the length of contact between ferrous article and zinc to a few inches, compared tc~ several feet as is the case for processes using a zinc bath and a sinking drum~ Thus the duration of the iron-zinc contact according to the present in~ention i9 several times shorter than that of the conventional methods.
,. .
In fact the duration of zinc-to-art~cle contact is limited to less than a second.
As a result thereof, non-alloyed zinc can ~e used in the process of the present invention thus improving the corrosion resistance of the zinc coating ("pure" metal coating~
without undue growth of the brittle intermediate ferro-zinc alloy layer, thus ensuring excellent adherence of the pure zinc coating to the coated article or strip.
Several, but by no means limiting, ways of applying zinc to the strip can be employed. For instance, molten zinc can be poured onto the strip headers equipped with appropriate nozzles through which molten zinc is discharged upon the strip, for instance, i~ediately before it is passed between the above mentioned rollers. According to another embodiment of the 15 present invention, the molten zinc is applied to the bodies of ~ -the rollers and then applied ("printed") onto the strip as lt contacts said rollers. As mentioned above the strip emerging ~rom said rollers undergoes a hot non-oxidizing gas blast followed by a rapidly cooling blast outside of the coating chamber. This blast does not have to be non-oxidizing. An air blast or a water spray or the like are adequate means for cool-ing the coated article.
In a preferredl but by no means limiting, embodiment of the present invention, the strip emerging from a "snout" of a pretreating device, such as a continuous furnace, is conducted around a pulley and rises to the zone of the metallizing process in a substantially vertical direction. The atmosphere surrounding the pulley is substantially the same as is used in the pretreating furnace.
The process chamber has an entry slo~ for the strip by which i-t enters said chamber from the box which carries the ;
: .
strip deflecting pulley. The strip is then taken through "reversed" wiper means contacting the strip under a vexy sli~ht pressure. The purpose of these wiper means is to prevent any excess zinc rolled off the strip by rollerc arranged after the wiper means, from falling down onto the strip deflecting pulley. The major part of the zinc removecl from the strip by the rollers will run down onto the top faces of the wiper means. If part of the zinc runs through the slot of the wiper means, it will, by capillary action, run down the bottom face of the wiper meansO As a result thereof, the rolled-off zinc will drop to the bottom of the process chamber from where it is returned to the zinc melting and de-oxidizing oven~
The molten zinc is supplied ko the zinc application device from a zinc melting oven by means of a zinc pump.
Excess molten zinc which is partly removed by the rollers and finally by subsequent hot blasting, drops to the bottom of the process chamber, from where it is returned, by gravity, to the zinc melting oven for further recirculation. Should any zinc oxide have been formed on the way from the process chamber, it will be de-oxidized to metallic zinc by the floating layer of de-oxidizing agent provided on the molten z~nc surface of the oven.
The zinc applying means are provided between the reversed wiper means and the rollers which serve to remove ~5 most of the excess zinc from the coated strip. Thereafter, the zinc coated strip is sub;ected to a hot blast of a non-oxidizing gas which removes the remainder of the excess zinc. ~ -~
The coated strip passes then from the coating chamber through a narrow slot into the surrounding atmosphere, where it under-goes rapid cooling, i.e. ~uenching.
The combination of said guiding rollers and the immediate quenching of the strip coating at the strip exit ~6-'i, \ .
from the chamber permits to considerably reduce the non guided portion o~ the coated strip, rendering it substantially rigid, when it arrives at the hot blasting zone. Said guiding distance is measured vertically from the bite of said rollers and up to the point where, after being spray cooled, the zinc coating has been sufficiently hard to be mechanically guided by a pulley. Thereby, the strip is kept in a substantially rigid condition so as to ensure optim~ per~ormance of the hot blast. As a result thereof, the nozzles ~or the slot) of the hot blasting unit can be placed much nearer to the strip surface than is possible without the use of the rollers and the rapid cooling means. Thi~ facty in its turn, will result in a lower hot gas pressure and a lower gas consumption.
The resulting "stability" of the travelling strip in the coating chamber also permits to provide narrowing of the strip exit slot therefrom~ A narrow exit slot, of course, allows to operate under a lower pressure of the non-oxidizing atmosphere in the cGating chamber than heretofore possible.
As a result thereof, the gas consumption of the galvanizing unit is considerably reduced.
The short exposure of the metal of the strip to the molten zinc and the almost immediate cool;ng of the zinc coat-ing which takes place when the strip exit~ from the coating chamber render it possible to reduce considerably or to even completely eliminate the addition of aluminum to the spelter.
When aluminum is added to the spelter, the hot blast must be of a non-o~idizing composition or it must even be, for practical reasons, slightly deoxidizing so as not to cause oxidation of the added alumlnum. ~owever, ~hen proceedin~
according to the present invention, the time of contact of the molten zinc with the strip is so short that addition of .
~q~
aluminum can be completely avoided. Therefore, superheated steam can be used for hot blasting because it does not oxidize molten zinc~ Such superheated steam is much cheaper and simpler to produce than a non-oxidizing gas blast.
Besides, should air be mixed with the steam and should some zinc oxide be formed, the de-oxidizing effect of the protective layer provided on the zinc surface in the z:inc melting oven will reduce any formed oxide to metallic zinc. It is, of course, not possible to reduce the aluminum oxide portion of conventional top-dross by the de-oxidizing layer in the 2inc melting ovenO
In view of the fact that the coating of the metallic article can consist of pure zinc when proceeding according to the continuous hot coating process of the presen-t invention, the resulting coating has the best imaginable anti-corrosive properties. Since the coating consists of pure metal, no galvanic effects between the basic zinc and its alloying elements are encountered.
Another advantage of the process according to the present invention is that the coatin~ of pure zinc is more ;~
flexible and ductile than that of its alloys, including alumi-num-zinc alloys~ Thus the pure zinc coated strip can better be subjected to stamping and~or drawing working than products galvanized in the conventional manner. ~ack of aluminum addition to the spelter avoids the unpleasant fea-ture oE
"conventional" continuous galvanizing, namely the formation of "WHITE RUST" which is especially critical in damp a-tmospheres and which is a direct result of the aluminum added to -the spelter. Chromate surface treatment baths, or similar, are used to prevent the formation o~ white rust~ Obviously the present process does not need any such extra treatment.
-While the process according to the present inven-tion has been described hereinabo~e with respect to galvaniz-ing ~errous articles such as stee] strips, lt is, of course, also possible to use said process for applying coatln~s of other metals to metallic articles. Thus the process can be used~ for instance, for coating articles and especially strip with aluminum, tin or tern alloy, or others. Of course, other metallic articles than ferrous articles such as copper strips can also be metallized by the process o~ the present invention.
Likewise, instead of pouring the molten metal through nozzles upon the metallic article or strip or applying it to the article or strip by means, for instance, it can also be applied thereto by other means, ~or instance, by forcing a stream of molten zinc by gravity upon the strip or by any other suitable means. In principle, the molten coating metal is applied to the metallic article by projecting or gently pouring it thereon in the form of a continuous stream.
As mentioned, one of the advantages of using spelter without aluminum alloying is the possibility of using cheap steam for the ho-t blast instead o~ more e~pensive neutral gas, because steam does not oxidize molten zinc (but does, very energetically, aluMinum~ However, it is not possible to have steam of the blast mix with the stationary gas of the pre-treating chamber o~ the furnace. A gas separating means have to be provided, substantially according to the following lines:
as will be described in what ~ollows, a vertical separator is to be located either before the zinc headers and the spreader rolls or at the centerlines plane o~ these rolls. In -the first case the not yet coated strip is exposed to the steam atmo-sphere which is oxidizing to steel; but, for conditions of _9~ : .
. . ~ . . . ~. . . . ..
modern, high strip speed galvaniæing this exposure is of so short a duration that ihis oxidation is not harmful. For lower speed galvanizing, however, the duration is longer and the gas-steam separation wall can be placed over and under the spreader rolls, so ~hat no "rawl' strip is exposed to the steam atmosphereO A possible particularity of such a seal con-sists, for the lower roll, to dip it into a molten-æinc bath which also collects the molten zinc overflow which has been removed by the spreader rolls~ Conventional sealiny and wear elements known to the man skilled in the art are to be used at the split of the "wall" for the high speed type of coating and on the upper roll of the described low speed coating.
Typical examples will be given in connection with the drawings.
In any case, in order to prevent any steam from getting into the neutral gas zone by ]eaks, it is suggested to keep the pressure in the neutral gas zone somewhat higher than in the ':steam" zone~
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, advantages, and uses of the present invention will become apparent ~rom a reading o~ the following specification and claims taken in connection with the attached drawings which form a part of the specifica-tion and wherein:
Fig~ 1 is a vertical cross-sectional view of a dip-less coating apparatus in which molten zinc is applied to the rising strip which is then hot-blasted and quenched;
Fig~ 2 is a cross-sectional view of a similar dipless coating apparatus in which strip movement stabiliæing and excess zinc removing rollers are provided be~ween the zinc applying means and the hot-blasting means;
Fig. 3 is a cross-sectional view o~ a similar dipless , . ~ .
.
coating apparatus in which the molten zinc is applied to the strip by means of a trough~ e distr~buting means;
Fig. 4 i5 a cross-sectional view of a dipless coat-ing apparatus in which the molten zinc is applied to the strip by means of the stabilizing rollers which are partly immersed in an overflowing dipping bath, and Fig. 5 is a cross-sectional view of a dipless coat-ing apparatus similar to the apparatus of Fig. ~ in which the molten zinc is poured on the rollers from a header and i9 applied to the strip by said rollers covered with the molten zinc.
Fig. 6 is a cross-sectional view of a dipless coat-ing apparatus in which the strip is passed through the coating chamber in substantially horizontal direction and, after coat-ing, is deflected upwardly for subsequent treatment.
Fig. 7 is cross-sectional view of a dipless coating ~-apparatus similar to that of Fig. 6 in which the strip is passed substantially horizontally through the coating chamber and also through the subsequent treatment systems.
Fig. 8 is a cross-sectional view of a dipless coat-ing apparatus enabling the use of steam for the hot blast -type, recom~ended for lligh strip velocities.
Fig. 9 is a cross sectional view of a dipless coat-ing apparatus enabling the use of steam for the hot blast ~5 type, recommended for lower strip velocitles.
Fig. 10 shows details of the gas tight seals, applicable to both, the high speed and low speed, systems; it - : . .:
is a section according to X - Y of Figures 8 and 9.
1ike numerals in said drawings indicate li~e parts 3Q of the e~uipment.
:. ' DESCRIPTION OF THE P~EFERRED EMBODIMENTS
. . . ~
In said drawings, F~g. 1 demonstrates the principal features of the present invention.
In said Fig. 1 strip 1 to be coated is passed from the pretreating furnace (not shown) through snout 20 into substantially gas-tight chamber 3 carrying strip deflecting pulley 2. Said pulley 2 deflects strip 1 so that it is conducted vertically upwardly into coating and processing chamber 8 containing and enclosing the various elements of the galvanizing process of the present invention. Strip 1 passes through orifice-like opening 21 into said chamber 8 and is then contacted by the pair of wipers 5. Strip 1 is then contacted by a continuous stream of molten zinc 23 dispensed through headers 4 with nozzle -like openings.
Excess zinc drops onto wipers 5 and is deflected from the strip and collected in return conduit 6 from which the zinc is returned into the zinc melting and regenerating oven (not - -shown). The remainder of excess zinc on the zinc coated strip is removed therefrom by the hot gas blast 22 supplied through hot gas blast header 7. The zinc-coated stxip 1 from which excess zinc has been removed passes through strip exit slot 9 of coating chamber 8 and is conducted to stabiliziny pulley 11 which in co-operation with strip deflecting pulley 2 stabi-lize movement of the strip on travelling through coating chamber 8. Immediately after coated strip 1 has left said chamber 8 through exit slot g, it is rapidly cooled by exposure to a spray of a cooling fluid 24 sprayed thereon by means of header 10~ When operating as shown in Fig. 1~ the strip is passed successively through reverse wipers 5, a stream of molten zinc 23 applied by means of header 4, and hot gas blast 22 applied by means of header 7 all of them enclosed in ~ , ~ . . ' processing chamber 8, and is then rapi~ly cooled by cooling fluid spray 24.
The coating apparatus as illustrated in Fig. 2 differs rom that of Fig. 1 by providing between the appli-cation o the molten zinc stream 23 and the hot gas blast 22, roller means 12 which remove the major part of excess zinc from coated strip 1 passing therethrough. Said roller L
means 12 aid in urther stabili~ing the movement of strip 1 on its travel through coating chamber 8.
In Fig. 3 a modification of the means for applying a continous stream of molten zinc to strip 1 is illustrated while otherwise the apparatus is the same as shown in Fig. 2.
According to this modification the molten zinc 23 is poured : ~.
from header 4 onto deElecting and distributing spreader 13 which applies it to strip lo Another means of applying the molten zinc to strip 1 ~
is illustrated in Fig. 4. According to said modification the ~ ~:
molten zinc 15 is supplied to pans 14 by means o header 4.
Rollers 12, as shown, dip into said pans 14 and carry along the molten zinc for application to strip 1. The rollers 12 ~ -are provided with elongated and inclined slots 17 which carry a journal of the stabiliæing rollers 12 and thus assist in exerting pressure between the rollers 12 but still permit to readily shift the rollers so that a strip threading tool can ~.
be passed therebetween. Dipping pans 14 are provided with a molten zinc overflow 16 allowing the molten zinc 15 in the pans 14 to overflow onto and along the walls of coating chamber 8 and downwardly into the return conduit 6 from where it is returned to the zinc melting oven (not shown).
Another modification of the means for applying .
. ~ . . .
.. , .. , ~ .
molten zinc to the strip 1 is illustrated in Fig. 5, whereby the molten zinc stream 23 is supplied through header ~ to deflector-distributor plate 18 which allows to evenly spread the molten zinc over the surfaces of rollers 12 which apply ("print") the molten zinc onto the surface of strip 1. A
variancy of this consists of spraying the rollers 12 in an anti-rotational direction from headers 4-~ preferably located close to the rollers and to the mounting strip.
It will be noted that in the apparatus illustrated by Figs. 2 to 5 inclusive in which strip stabilizing rollers 12 are used, the exit slots 9 can be made much more narrower than in the apparatus illustrated by Fig. 1, where no stabi-lizing rollers are used~ Since movement of the strip is greatly enhanced by providing rollers 12 as shown in Fig. 2 to 5, the efficiency of the hot blast is considerably improved, so that a reduced hot blast gas consumption is achieved.
Consequently, the hot gas blast headers 7 can be made smaller than the headers 7 to Fig. 1, which shows no stabilizing rollers.
~s stated above, the claimed process permits, according to another embodiment of the present invention, to conduct the hot metallic article to pass substantially hori-zon-tally throu~h coating chamber 3. Thus the procedure per-mits to eliminate the wiper means 5 described hereinabove.
Fig. 6 illustrates in cross-sectional view this procedure. In said Fig. 6 strip 1 to be coated is passed from the pretreating furnace into chamber 3 which carries the strip deflecting pulleys 2 and 2aO ~ulley 2a may e~en be omitted~ Strip 1 passes then substantially horizontally, 3a pre~erably at a small angle downwardly, toward roller 12 which remove the major part of excess zinc from coated strip 1.
~aid rollers pre~erably deflect -the coated strip upwardly to the hot blast means.
~hile passing ~r~m deflecting pulleys 2 and 2a through coating chamber 3, khe strip ~s contacted by a continuous stream of molten zinc 23 dispensed ~hrough headers
4 with nozzle-like openings. Preferably the upper header is provided in the substantially horizontal part of the strip while the lower header is provided underneath rollers 12.
Otherwise the procedure is the same as described hereinabove, except that the wiper or deflecting means 5 are omitted.
Fig. 7 illustrates a further embodiment of the present invention whereby the strip after coating is horizon-tally conveyed past the hot gas blast header 7 through strip exit slot 9 of coating chamber 3 to stabilizing pulleys 11 and lla. Between exit slot 9 and stabilizing pulleys 11 and lla there are arranged two headers 24 spraying cooling fluid upon the coated strip 1 so as to rapidly cool the same.
Coating chambers 3 in Fig. 6 and 7 are provided with outlet 6 for excess molten coatlng metal. The angle of down-ward inclination of strip 1 traveling through coating chamber 3 is indicated by a. Referring to Fig. 8; (30) is the separator wall, of which (31) is its upper part and (32) its lower part. The upper edge ~33) of (32) may be lined with a wear strip (34), adjuskable vertically to compensate for wear. It can be made of relatively soft material like asbes-tos. The passing strip to be galvanized slightly presses onto (33)~ The upper part (31) is slidable in the vertical direction and presses onto strip (1), by ~ts weight, and there-by onto the wear strip (34) or (32). It is shown as a soli~d board maintained in position by appropriate guides on the chamber walls and ceiling extension (35). As ~ill be de-scribed in greater detail in Fig. 10, the upper part ~31) of wall (30) is pressed against a machined pvrtion (42) of ~ -15-,1 .
.
.
~t~
the side wall of the chamber 3 and of the ceiling extension (35). The chamber is split and screwed together by appro-priate flanges (36) on the substantlally vertical planes pass-ing through the center lines of the deflecting pulle~s (2 &
S 2A) and spreading pinch rolls (12 & l~A). The whole system (chamber, rolls, headers, etc.) is inclined somewhat from the horizontal plane to prevent the molten zinc from flowing "upstream" with regard to the movement of the strip, (1).
A bent part (37), forming a "rigidity rib" of the lower part (35) of the separator wall 132), also forms a guide for the strip during the threading of the furnace proper (not shown) and of the metallizing chamber, (3). The pinch rolls (11 ~
llA) catch the quenched strip and deflect it, horizontally or vertically for further processiny.
Fig. 9 showing the separator "on" the spreading pinch rolls, (12 & 12A) of the likewise tilted metallizing chamber (angle slope alpha~, is split on two substantially horizontal planes of the upper and the lower deflector and spreader pinch rolls and screwed toyether by flanges (38).
While the sealing off of the upper spreader pinch roll is achieved by means similar to -those of the wall of the E'ig. 8., that of the lower roll is obtained by dipping it into a pure zinc bath (39) contained in a tank (40). Zinc coming from the headers (4) and partly removed by the spreader pinch rolls, as well as that removed by the hot spray, falls into said tank ~40), overflows its lower edge (48~ and is conducted into the zinc dump (not shown) by pipe (6).
Figr 10 shows a possible embodiment of the seals of the separating walls of the metall~zing chamber aga~nst the side and upper panels of the metallizing chamber. (31) is the --main plate, applied by its smoothed edge (~1) to a machined ~6-,~
face (42) of the side pannel (43 & 3). Spxing (44) forces plate (31) against (42), insuring gas tightness.
The smoothed side (47) of the plate (31) is sealed off by strip (45), the latter being pressed towards (31) by spring (46). Refering to Figs. 1 incl. 7, a man skilled in the art will be able to apply the principle shown in Fi~s. 8, 9, and 10 to be Figures 2 incl. 7~ It will be noted that F~g.
(4 & 5) are appllcable to spreader rolls made of "zinc wettable" materials, like iron or steel, the rest of the figures may be applied to "zinc-unwettable" materials, like silicone-carbon ceramic or composed materials.
~17~19~
/ :
i,,.,, ' ' ~' SUPPLEMENTARY DISCLOSURE
In the principal disclosure the invention is shown in several aspects and shows a process and a system for providing a metallic article with a metallic coating by causing a continuous stream of the molten coating met:al to contact the hot metallic article for a short period of time. Excess coating metal is then removed from the coated metallic article by subjecting it to the action of a hot gas blast. In a preferred embodiment the coated article is subjected to the action of a cooling ~last immediately after the hot gas blast ing.
The hot gas blast provides a means for rapidly removing excess coating metal from the metallic article. The temperature of the hot blast should be hot enough to move excess molten metal from the article, and this may happen when the temperature of the hot blast is somewhat lower than or higher than the melting point of the coating metal.
In this Supplementary Disclosure it is pointed out that in many instances it is advantageous to use a hot blas~
gas temperature lower than the melting point of the coating metal such as zinc. In this way the liquid coating metal is prequenched or prechilled to some extent, thus hastening the solidlfication of the coating when subsequently subjected to a cooling blast. Under such conditions the time of contact of the coated metal with the liquid coating metal is further reduced and the coating process can be controlled more care~ully and closely.
~ he temperature of the "cooler" hot blast may vary according to such factors as -the speed with which the metallic article is being galvanized in the system according to the ''~3 . ', .. . . .. .. . .. .
invention, the desired thickness of the coating, and the condition of the raw material. The temperature o~ the hot blast is preferably from 20 to 80C. below the melting point of the coating material.
Thus the present invention provides a process of providing a metallic article with a metallic coating, in which the steps comprise causing a continuouC; stream of the molten coating metal to contact the hot metallic article for a short period of time, thereby coating the metallic article, and removing excess coating metal from the coated metallic article by subjecting it to the action of a hot, non-oxidizing gas blast, said hot gas blast being at a temperature somewhat lower, preferably between 20 and 80C. lower, than the melting point of the coating rnetal. Preferably, the process also includes the additional step of immediately after hot gas blasting rapidly cooling the coated article by the action of a cooling blast.
In another aspect the invention provides a system for providing a metallic article with a metal coating, said system comprising a coating chamber having an entrance opening for the metallic article to be coated and an exit opening or the metal coated article, said chamber being provided, successively within and enclosed by said chamber; with means for applying a continuous stream of molten metal to the metallic article to be coated so as to uniformly and evenly distribute the coating metal over tne surface of the hot metallic article and to coat the same; and means for subjectin~
the coated metallic article to a hot gas blast at a te~perature somewhat below preferably between 20 and 80C. below, the melting point of the coating metal, so as to remove substan-tially completely excess coating metal from the coated article, and, arranged following the exit opening of said coating chamber; means for rapidly cooling the metal coated article, said cooling means being provided outside the coating chamber.
ZO
IC) : .
Otherwise the procedure is the same as described hereinabove, except that the wiper or deflecting means 5 are omitted.
Fig. 7 illustrates a further embodiment of the present invention whereby the strip after coating is horizon-tally conveyed past the hot gas blast header 7 through strip exit slot 9 of coating chamber 3 to stabilizing pulleys 11 and lla. Between exit slot 9 and stabilizing pulleys 11 and lla there are arranged two headers 24 spraying cooling fluid upon the coated strip 1 so as to rapidly cool the same.
Coating chambers 3 in Fig. 6 and 7 are provided with outlet 6 for excess molten coatlng metal. The angle of down-ward inclination of strip 1 traveling through coating chamber 3 is indicated by a. Referring to Fig. 8; (30) is the separator wall, of which (31) is its upper part and (32) its lower part. The upper edge ~33) of (32) may be lined with a wear strip (34), adjuskable vertically to compensate for wear. It can be made of relatively soft material like asbes-tos. The passing strip to be galvanized slightly presses onto (33)~ The upper part (31) is slidable in the vertical direction and presses onto strip (1), by ~ts weight, and there-by onto the wear strip (34) or (32). It is shown as a soli~d board maintained in position by appropriate guides on the chamber walls and ceiling extension (35). As ~ill be de-scribed in greater detail in Fig. 10, the upper part ~31) of wall (30) is pressed against a machined pvrtion (42) of ~ -15-,1 .
.
.
~t~
the side wall of the chamber 3 and of the ceiling extension (35). The chamber is split and screwed together by appro-priate flanges (36) on the substantlally vertical planes pass-ing through the center lines of the deflecting pulle~s (2 &
S 2A) and spreading pinch rolls (12 & l~A). The whole system (chamber, rolls, headers, etc.) is inclined somewhat from the horizontal plane to prevent the molten zinc from flowing "upstream" with regard to the movement of the strip, (1).
A bent part (37), forming a "rigidity rib" of the lower part (35) of the separator wall 132), also forms a guide for the strip during the threading of the furnace proper (not shown) and of the metallizing chamber, (3). The pinch rolls (11 ~
llA) catch the quenched strip and deflect it, horizontally or vertically for further processiny.
Fig. 9 showing the separator "on" the spreading pinch rolls, (12 & 12A) of the likewise tilted metallizing chamber (angle slope alpha~, is split on two substantially horizontal planes of the upper and the lower deflector and spreader pinch rolls and screwed toyether by flanges (38).
While the sealing off of the upper spreader pinch roll is achieved by means similar to -those of the wall of the E'ig. 8., that of the lower roll is obtained by dipping it into a pure zinc bath (39) contained in a tank (40). Zinc coming from the headers (4) and partly removed by the spreader pinch rolls, as well as that removed by the hot spray, falls into said tank ~40), overflows its lower edge (48~ and is conducted into the zinc dump (not shown) by pipe (6).
Figr 10 shows a possible embodiment of the seals of the separating walls of the metall~zing chamber aga~nst the side and upper panels of the metallizing chamber. (31) is the --main plate, applied by its smoothed edge (~1) to a machined ~6-,~
face (42) of the side pannel (43 & 3). Spxing (44) forces plate (31) against (42), insuring gas tightness.
The smoothed side (47) of the plate (31) is sealed off by strip (45), the latter being pressed towards (31) by spring (46). Refering to Figs. 1 incl. 7, a man skilled in the art will be able to apply the principle shown in Fi~s. 8, 9, and 10 to be Figures 2 incl. 7~ It will be noted that F~g.
(4 & 5) are appllcable to spreader rolls made of "zinc wettable" materials, like iron or steel, the rest of the figures may be applied to "zinc-unwettable" materials, like silicone-carbon ceramic or composed materials.
~17~19~
/ :
i,,.,, ' ' ~' SUPPLEMENTARY DISCLOSURE
In the principal disclosure the invention is shown in several aspects and shows a process and a system for providing a metallic article with a metallic coating by causing a continuous stream of the molten coating met:al to contact the hot metallic article for a short period of time. Excess coating metal is then removed from the coated metallic article by subjecting it to the action of a hot gas blast. In a preferred embodiment the coated article is subjected to the action of a cooling ~last immediately after the hot gas blast ing.
The hot gas blast provides a means for rapidly removing excess coating metal from the metallic article. The temperature of the hot blast should be hot enough to move excess molten metal from the article, and this may happen when the temperature of the hot blast is somewhat lower than or higher than the melting point of the coating metal.
In this Supplementary Disclosure it is pointed out that in many instances it is advantageous to use a hot blas~
gas temperature lower than the melting point of the coating metal such as zinc. In this way the liquid coating metal is prequenched or prechilled to some extent, thus hastening the solidlfication of the coating when subsequently subjected to a cooling blast. Under such conditions the time of contact of the coated metal with the liquid coating metal is further reduced and the coating process can be controlled more care~ully and closely.
~ he temperature of the "cooler" hot blast may vary according to such factors as -the speed with which the metallic article is being galvanized in the system according to the ''~3 . ', .. . . .. .. . .. .
invention, the desired thickness of the coating, and the condition of the raw material. The temperature o~ the hot blast is preferably from 20 to 80C. below the melting point of the coating material.
Thus the present invention provides a process of providing a metallic article with a metallic coating, in which the steps comprise causing a continuouC; stream of the molten coating metal to contact the hot metallic article for a short period of time, thereby coating the metallic article, and removing excess coating metal from the coated metallic article by subjecting it to the action of a hot, non-oxidizing gas blast, said hot gas blast being at a temperature somewhat lower, preferably between 20 and 80C. lower, than the melting point of the coating rnetal. Preferably, the process also includes the additional step of immediately after hot gas blasting rapidly cooling the coated article by the action of a cooling blast.
In another aspect the invention provides a system for providing a metallic article with a metal coating, said system comprising a coating chamber having an entrance opening for the metallic article to be coated and an exit opening or the metal coated article, said chamber being provided, successively within and enclosed by said chamber; with means for applying a continuous stream of molten metal to the metallic article to be coated so as to uniformly and evenly distribute the coating metal over tne surface of the hot metallic article and to coat the same; and means for subjectin~
the coated metallic article to a hot gas blast at a te~perature somewhat below preferably between 20 and 80C. below, the melting point of the coating metal, so as to remove substan-tially completely excess coating metal from the coated article, and, arranged following the exit opening of said coating chamber; means for rapidly cooling the metal coated article, said cooling means being provided outside the coating chamber.
ZO
IC) : .
Claims (34)
1. In a process of coating an elongated metal article with a metal coating, the steps which comprise:
a) continuously heating the metal article to coating temperature;
b) causing a continuous stream of molten coating metal to contact the metal article for a short period of time, thereby coating the metal article;
c) continuously subjecting the coated metal article to the action of a hot non-oxidizing gas blast, whereby to remove excess molten coating metal therefrom.
a) continuously heating the metal article to coating temperature;
b) causing a continuous stream of molten coating metal to contact the metal article for a short period of time, thereby coating the metal article;
c) continuously subjecting the coated metal article to the action of a hot non-oxidizing gas blast, whereby to remove excess molten coating metal therefrom.
2. In the process of Claim 1, the additional step of immediately after hot gas blasting rapidly cooling the coated article by the action of a cooling blast.
3. In the process of Claim 1, the additional step of passing the coated article through means effecting distribution and spreading of the coating metal across the entire surface of the metallic article to be coated and removing the major part of excess coating metal from the coated article said distributing and spreading means being arranged between the means for applying the coating metal to the metallic article and the hot gas blast.
4. In the process of Claim 2, the additional step of passing the coated article through means effecting distribution and spreading of the coating metal across the entire surface of the metallic article to be coated and removing the major part of excess coating metal from the coated article, said distributing and spreading means being arranged between the means for applying the coating metal to the metallic article and the hot gas blast.
5. In the process of Claim 1, the additional step of passing the hot metallic article before coating through wiping means, said wiping means conducting excess molten coat-ing metal away from the metallic article for recovery.
6. In the process of Claim 2, the additional step of passing the hot metallic article before coating through wiping means, said wiping means conducting excess molten coat-ing metal away from the metallic article for recovery.
7. In the process of Claim 3, the additional step of passing the hot metallic article before coating through wiping means, said wiping means conducting excess molten coat-ing metal away from the metallic article for recovery.
8. The process of Claim 1, in which the molten coating metal is continuously applied to the metallic article by means of nozzles adapted to discharge a continuous stream of coating metal onto the hot metallic article.
9. The process of Claim 1, in which the molten coating metal is continuously applied to the metallic article by means of roller means adapted to apply, a con-tinuous layer of coating metal onto the hot metallic article.
10. The process of Claim 1, in which the coating metal is zinc and the metallic article to be coated is a ferrous article.
11. A system for providing a continuous metal article with a metal coating, said system comprising a coating chamber having an entrance opening for the metal article to be coated and an exit opening for the metal coated article, said chamber being provided, successively within and enclosed by said chamber, with means for applying a continuous stream of molten metal to the metal article to be coated so as to uniformly and evenly distribute the coating metal over the surface of the hot metal article and to coat the same, and means for subjecting the coated metal articl.e to a hot gas blast so as to remove substantially com-pletely excess coating metal from the coated article, and, arranged following the exit opening of said coating chamber, means for rapidly cooling the metal coated article, said cooling means being provided outside the coating chamber.
12. The system of Claim 11, in which reverse wiper means opposed to each other are addition-ally provided in advance of the means for apply-ing the coating metal to the metallic article, the hot metallic article to be coated passing between said wiper means, said wiper means serving to deflect excess coating metal from said metallic article.
13. The system of Claim 11, in which the means for applying a continous stream of molten coating metal to the metallic article are headers provided with nozzles discharging said continuous stream of coat-ing metal uniformly and evenly distributed upon the surface of the metallic article.
14. The system of CLaim 12, in which the means for applying a continuous stream of molten coating metal to the metallic article are headers provided with nozzles discharging said continuous stream of coating metal uniformly and evenly distributed upon the surface of the metallic article.
15. The system of Claim 11, in which the means for applying a continuous stream of coating metal to the metallic article are deflecting and distributing spreaders causing the molten coating metal supplied thereto by means of headers to evenly and uniformly contact the metallic article to be metal coated.
16. The system of Claim 12, in which the means for applying a continuous stream of coating metal to the metallic article are deflecting and distributing spreaders causing the molten coating metal supplied thereto by means of headers to evenly and uniformly contact the metallic article to be metal coated.
17. The system of Claim 12, in which the means for applying a continuous stream of molten coating metal to the metallic article are rollers, said rollers dipping into pans arranged thereunder and supplied with molten coating metal, said rollers, on rotation, carrying along molten coating metal and causing said metal to uniformly and evenly contact the metallic article passing between said rollers towards the hot gas blast.
18. The system of Claim 12, in which the means for applying a continuous stream of molten coating metal to the metallic article are rollers, said rollers being supplied by means of a deflector-distributor plate with molten coating metal, said rollers, on rotation, carrying along molten coating metal and causing said metal to uniformly and evenly contact the metallic article passing between said rollers towards the hot gas blast.
19. The system of Claim l1, in which opposed rollers are provided between the molten metal applying means and the hot gas blasting-means, said rollers, on rotation, removing the major part of excess coating metal from the coated metallic article passing through the same.
20. The system of Claim 12, in which opposed rollers are provided between the molten metal applying means and the hot gas blasting means, said rollers, on rotation, removing the major part of excess coat-ing metal from the coated metallic article passing through the same.
21. A system as in Claim 11, for use in applications using metal which will allow the hot blasting gas to be steam instead of neutral or de-oxidizing gas, a separation of the zone in which the application of the molten coating metal is performed from the zone of the hot steam gas blast, which separator will prevent the atmosphere of the coating zone to mix with that of the blasting zone; an atmosphere separator between the coating and blasting zones in which said separator is located in the plane immediately preceding the coating metal distributing means, the general arrangement of the separator, coating and spreading means being such that the not yet coated strip is subjected to the steam atmosphere for less than a second.
22. A system as in Claim 21 in which the separating means are located in or close to the plane of the spreading rollers.
23. A system as in Claim 22, comprising means for sealing of the separator to the lower roll by dipping the said roll in an overflowing bath of molten coating metal.
24. In a process of coating a metal article in strip form with a metal coating, the steps which comprise a) passing the metal strip preheated to a coating temperature into a processing chamber; filled with a non-oxidizing atmosphere, and containing a coating zone; and b) applying by distributing means a continuous stream of the molten coating metal uniformly to both sides of the metal strip for a short period of time so as to minimize the formation of an intermediate alloy layer between the coating metal layer and the surface of the metal article;
c) conducting excess molten coating away from the metal strip by deflecting any excess coating running down-wardly from the article strip, whereby the coating can be recovered and does not interfere with the conveying of successive portions of the strip to the coating zone, and d) subjecting the coated metal strip to the action of a hot, non oxidizing gas blast subsequent to said coating application so as to remove any remaining excess coating metal from the coated metallic article.
c) conducting excess molten coating away from the metal strip by deflecting any excess coating running down-wardly from the article strip, whereby the coating can be recovered and does not interfere with the conveying of successive portions of the strip to the coating zone, and d) subjecting the coated metal strip to the action of a hot, non oxidizing gas blast subsequent to said coating application so as to remove any remaining excess coating metal from the coated metallic article.
25. The process of claim 24 further including the additional step of, immediately after hot gas blasting, rapidly cooling the coated article by the action of a cooling blast.
26. The process of claim 24 further including the step of passing the coated article through means effecting dis-tribution and spreading of the coating metal across the entire surface of the coated metallic article thereby removing the major part of excess coating metal from the coated article and guiding and stabilizing the metallic article on its passing through the coating zone, said distributing and spreading means being arranged between the means for applying the coating metal to the metallic article and the hot gas blast.
27. The process of claim 24, further including the step of continuously applying coating metal to the metallic article by means of nozzles adapted to project a continuous stream of coating metal onto the hot metallic article.
28. The process of claim 24, in which the molten coating metal is continuously applied to the metallic article by means of roller means adapted to apply a continuous layer of coating metal onto the hot metallic article.
29. The process of claim 24, in which the coating metal is zinc and the metallic article to be coated is a ferrous article.
30. In a process of providing a metallic article in strip form with a metallic coating, the steps which comprise a) passing the metallic strip preheated to coating temperature into a processing chamber, with the strip being inclined slightly downwardly with respect to the horizontal;
and containing a coating zone;
b) applying by distributing headers in the coating zone a continuous stream of molten coating metal uniformly to both sides of the metallic strip for a short period of time so as to minimize the formation of an intermediate alloy layer between the coating metal layer-and the surface of the metallic article;
c) conducting excess molten coating away from the metallic strip by means of rollers between which the coated strip passes, said rollers removing the major part of the excess coating from the strip whereby the coating can be recovered and does not interfere with the conveying of successive portions of the strip to the coating zone, and d) subjecting the coated strip to the action of a hot, non-oxidizing gas blast above said rollers, so as to remove any remaining excess coating metal from the coated strip.
and containing a coating zone;
b) applying by distributing headers in the coating zone a continuous stream of molten coating metal uniformly to both sides of the metallic strip for a short period of time so as to minimize the formation of an intermediate alloy layer between the coating metal layer-and the surface of the metallic article;
c) conducting excess molten coating away from the metallic strip by means of rollers between which the coated strip passes, said rollers removing the major part of the excess coating from the strip whereby the coating can be recovered and does not interfere with the conveying of successive portions of the strip to the coating zone, and d) subjecting the coated strip to the action of a hot, non-oxidizing gas blast above said rollers, so as to remove any remaining excess coating metal from the coated strip.
31. The process of Claim 30 in which said molten coating is applied to both sides of the strip in less than 1 second.
32. In a process of providing a metallic article in strip form with a metallic coating, the steps which comprise a) passing the metallic strip preheated to coating temperature in a substantially vertical direction through a processing chamber;
b) passing the metallic strip through a coating zone in said processing chamber and applying a continuous stream of the molten coating metal uniformly to both sides of the metallic strip for less than one second so as to reduce forma-tion of an intermediate alloy layer between the coating metal layer and the surface of the metallic article, c) subsequently passing the coated strip through roller means in said processing chamber effecting distribution and spreading of the coating metal across the entire surface of both sides of the coated strip thereby removing the major part of excess coating metal from the coated strip while simultaneously guiding and stabilizing the coated strip on its passing through the coating zone, d) subjecting the coated metallic strip to the action of a hot, non oxidizing gas blast so as to remove and remaining excess coating metal from the coated metallic article.
e) subjecting the coated metallic strip to energetic cooling means immediately after the strip exit from the coating chamber.
b) passing the metallic strip through a coating zone in said processing chamber and applying a continuous stream of the molten coating metal uniformly to both sides of the metallic strip for less than one second so as to reduce forma-tion of an intermediate alloy layer between the coating metal layer and the surface of the metallic article, c) subsequently passing the coated strip through roller means in said processing chamber effecting distribution and spreading of the coating metal across the entire surface of both sides of the coated strip thereby removing the major part of excess coating metal from the coated strip while simultaneously guiding and stabilizing the coated strip on its passing through the coating zone, d) subjecting the coated metallic strip to the action of a hot, non oxidizing gas blast so as to remove and remaining excess coating metal from the coated metallic article.
e) subjecting the coated metallic strip to energetic cooling means immediately after the strip exit from the coating chamber.
33. In a dipless galvanizing process according to Claim 1, in applications using metal which will allow the hot blasting gas to be steam instead of neutral or de-oxidizing gas, a separation of the zone in which the application of the molten coating metal is performed from the zone of the hot gas blast (steam) which separator will prevent the atmosphere of the coating zone to mix with that of the blasting zone.
34. In a dipless galvanizing process according to Claim 24, 30 or 32, in applications using metal which will allow the hot blasting gas to be steam instead of neutral or de-oxidizing gas, a separation of the zone in which the application of the molten coating metal is performed from the zone of the hot gas blast (steam) which separator will prevent the atmosphere of the coating zone to mix with that of the blasting zone.
SD-35. A process as in Claim 1, 2 or 3 wherein the hot non-oxidizing gas blast is at a temperature somewhat lower than the melting point of the coating metal.
SD-36. A process as in Claim 5, 8 or 9 wherein the hot non-oxidizing gas blast is at a temperature somewhat lower than the melting point of the coating metal.
SD-37. A system as in Claim 11, 12 or 21 wherein the hot gas blast is at a temperature somewhat lower than the melting point of the coating metal.
SD 38. A process as in Claim 24, 30 or 32 wherein the hot non-oxidizing gas blast is at a temperature somewhat lower than the melting point of the coating metal.
SD-39. A process as in Claim 33 wherein the steam is at a temperature somewhat lower than the melting point of the coating metal.
SD-40. A process as in Claim 1, 2 or 3 wherein the hot non-oxidizing gas blast is at a temperature of between 20 and 80°C. below the melting point of the coating metal.
SD-41. A system as in Claim 11, 12 or 21 wherein the hot gas blast is at a temperature of between 20 and 80°C.
below the melting point of the coating metal.
SD-42. A process as in Claim 24, 30 or 32 wherein the hot non-oxidizing gas blast is at a temperature of between 20 and 80°C. below the melting point of the coating metal.
SD-43. A process as in Claim 33 wherein the steam is at a temperature of between 20 and 80°C. below the melting point of the coating metal.
SD-35. A process as in Claim 1, 2 or 3 wherein the hot non-oxidizing gas blast is at a temperature somewhat lower than the melting point of the coating metal.
SD-36. A process as in Claim 5, 8 or 9 wherein the hot non-oxidizing gas blast is at a temperature somewhat lower than the melting point of the coating metal.
SD-37. A system as in Claim 11, 12 or 21 wherein the hot gas blast is at a temperature somewhat lower than the melting point of the coating metal.
SD 38. A process as in Claim 24, 30 or 32 wherein the hot non-oxidizing gas blast is at a temperature somewhat lower than the melting point of the coating metal.
SD-39. A process as in Claim 33 wherein the steam is at a temperature somewhat lower than the melting point of the coating metal.
SD-40. A process as in Claim 1, 2 or 3 wherein the hot non-oxidizing gas blast is at a temperature of between 20 and 80°C. below the melting point of the coating metal.
SD-41. A system as in Claim 11, 12 or 21 wherein the hot gas blast is at a temperature of between 20 and 80°C.
below the melting point of the coating metal.
SD-42. A process as in Claim 24, 30 or 32 wherein the hot non-oxidizing gas blast is at a temperature of between 20 and 80°C. below the melting point of the coating metal.
SD-43. A process as in Claim 33 wherein the steam is at a temperature of between 20 and 80°C. below the melting point of the coating metal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA305,539A CA1110120A (en) | 1978-06-15 | 1978-06-15 | Dipless metallizing process and apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA305,539A CA1110120A (en) | 1978-06-15 | 1978-06-15 | Dipless metallizing process and apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1110120A true CA1110120A (en) | 1981-10-06 |
Family
ID=4111696
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA305,539A Expired CA1110120A (en) | 1978-06-15 | 1978-06-15 | Dipless metallizing process and apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1110120A (en) |
-
1978
- 1978-06-15 CA CA305,539A patent/CA1110120A/en not_active Expired
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