US 2159297 A
Description (OCR text may contain errors)
y 23, 1939- B. RfsHovER APPARATUS FOR COATING METAL Filed July 26, 1932 4 Sheets-Sheet 1 gj iil'p Q l May 23, 1939. B. R. SHOVER APPARATUS FOR COATING METAL Filed July 26, 1932 4 Sheets-Sheet 2 INVE TOR e. fi w y 1939- B. R. SHOVER 2,159,297
APPARATUS FOR COATING METAL Filed July 26, 1952 4 Sheets-Sheet 3 INVENTOR Patented May 23, 1939 UNITED STATES PATENT OFFICE APPARATUS FOR COATING METAL Application June 26, 1932, Serial No. 624,753
This invention relates to apparatus for coating metal. It is described particularly herein as applied to coating strip metal, although it is of general utility for coating sheets, plates, wires and other shapes. In the description and claims, the term strip is used as a term of general definition to include articles in general and is not intended to be restricted to articles of any particular width or length. ln For manyyears tin plate and galvanized sheets have been made by passing a previously cleaned sheet through molten tin or zinc. The base metal to be coated has been carried through the coating bath by rollers and the top of the bath has been covered with a flux. The molten coating metal becomes oxidized to a certain extent in spite of the flux. the oxide formed contaminating the bath. The bath is further contaminated by a dross which is formed by alloyage of the base metal with the coating metal. The dross and oxides sometimes adhere to the strip, causing the coating to be defective. The foreign particles formed by oxidation of the bath or alloyage of the strip with the coating metal have a tendency to collect at the entrance side of the rollers used in conveying the strip through the bath, and after a time these impurities pass through the rolls and collect on the strip, thereby marring the coating.
The disadvantages inherent in the coating methods heretofore employed are eliminated or decreased by the present invention. In the present invention, the coating bath and strip are protected from oxidation by supplying a protective gas such as hydrogen, nitrogen, cracked ammonia or natural gas to the furnace in which the coating metal is contained. The strip is preheated before the coating metal is applied thereto so as to insure the coating metal will take.
The coating metal is applied to the strip in one or more streams and the excess of coating metal, after having been applied to the strip, is collected and again pumped so as to form streams of coating metal which are used to coat subsequent portions of the strip. Other features of the invention are pointed out more particularly hereinafter.
In the accompanying drawings, which illustrate several embodiments of my invention:
Figure 1 is a longitudinal vertical section through the apparatus;
Figure 2 is a transverse vertical section on the line IL-II of Figure 1;
'5 Figure 3 is a partial plan view and partial horizlontal section on the line III-III of Figure Figure 4 is a vertical section taken on the line IV-IV of Figure 3;
Figure 5 is a longitudinal vertical section of a 5 modified form of the invention in which electric resistance heating units are used for preheating the strip;
Figure 6 is an enlarged section on the line VI-VI of Figure 5,'and 10 Figure '7 is a view similar to Figure 6 but illustrating the preheating of the strip by means of a burner instead of electric resistance heating units.
Referring more particularly to the accompanyl5 ing drawings, and especially to Figures 1 through 4, the coating apparatus, which is indicated generally by the reference numeral 2, has a pre heating chamber 3 adjacent its entrance end. The chamber is heated by burners 4 and the 29 products of combustion pass upwardly around a muflle 5 arranged in the preheating chamber 3. The combustion gases then pass through a chamber 6 formed between metal plates 1 and 8 and escape through a stack 9 located adjacent 5 the exit end of the apparatus. If desired, a portion of the combustion gases may be passed directly to a stack 9' located near the entrance end of the apparatus, the stack being controlled by a damper 917. A strip II) which is to be coated 30 is conveyed into the furnace by rollers ll adjacent the entrance end of the furnace, through a gas seal at l2, through the slot l2 in the end of the muffle 5 and is guided by rollers l3, l4 and i5 through a flux pot 16. From the flux pot, 35 the strip passes through the molten coating metal in a container or pot I1 and is then fed upwardly through the coating chamber l9 and the cooling chamber 20. Pinch rolls 2| are used for pulling the strip through the coating apparatus. As the 40 strip passes through the coating chamber 19, streams of coating metal are sprayed against it by nozzles 22 arranged on opposite sides of the strip. The forcible impacting of the molten coating metal against the strip is for the purpose 45 of causing good adherence and a certain amount of alloyage of the coating metal and strip. These nozzles may be arranged to deliver the molten metal at any angle desired. The coating metal flows down over the strip and into the pot ll, from which it is returned to the nozzles by means of a pump 25 and pipe 26.
The dross formed by alloyage of the strip with the coating metal is of only slightly greater specific gravity than the coating metal, and any 5' settling of the dross. In order to prevent agitation of the bath by the coating metal dripping from the sheet, a baiile 2l is provided adjacent the top of the bath. The baille is shaped so as to slope at a slight angle with the surface of the bath, and in this way,any coating metal which may drop oil of the sheet is returned to the bath without agitating it unduly. The suction of the pump is preferably located'only slightly below the surface of the bath so that it will return to the nozzles 22 only pure coating metal and not that which is contaminated by the dross. Since the bath is substantially free from agitation due to the omission of any feed rolls therein, the dross settles to the bottom of the tank and may be withdrawn through a pipe 28.
In the usual type of coating apparatus, the coating pot is heated from the bottom or sides. This causes convection currents to be set up in the bath which prevent rapid settling of the dross. The dross is picked up by the sheet passing through the bath and may form an imperfect coating thereon. Since, according to this invention, the surface of the bath and the strip which is to be coated are protected from oxidation by flowing a protective gas through the coating apparatus, no flux is needed on the top of the bath, and the bath may be heated from the top rather than from the bottom or sides. The heating of the bath surface rather than the bottom or sides thereof decreases the formation of convection currents which would agitate the bath and interfere with the settling of dross. In
this invention, the coating metal in the pot Il may be heated at the start of the operation in order to melt it by means of burners 29, but thereafter during the process these burners are not used, the necessary heat for maintaining the bath molten being provided by other heating means arranged adjacent the top of the bath. In Figure 1, I have shown electric resistance heating elements for this purpose, but burners may be used if desired. The strip itself may also be used to supply heat to the bath metal, the strip being preheated by the heating elements ill and the burners 4 to a temperature higher than the bath prior to the entrance of the strip into the bath.
In order to further guard against agitation of,
the bath metal, a baflle 3! is secured to the side of the pot I l and extends toward the center of the pot a suflicient distance to prevent eddy currents being set up in the bath adjacent the inlet of the pump.
The gas which is used for protecting the surface of the coating metal and the strip from oxidation is supplied through a pipe 32 located adjacent the upper end of the cooling stack 20. The cooling stack and the strip and protective gas flowing therethrough are cooled by means of a cooling coil 33 which may be supplied with water or other cooling fluid through an entrance pipe 34 and anexit pipe 35. The protective gas, after flowing downwardly through the cooling chamber 20, passes through the coating chamber I9, then over the top of the pots I! and I6 and into the muflle 5. It may be conducted to the preheating chamber 3 by a pipe 36, where it may be burned to supplement the heat supplied by the burners l.
The feed rolls Ii are driven from a motor through gearing 4| and the rolls ii are driven from a motor 42 through gearing l3. Pinch rolls 2| are driven by motor 44. The top of the coat- I there is shown a single conveying 2,159,297 agitation of the coating bath tends to prevent ing apparatus adjacent the flux pot l6 is provided with a cover 45 having a seal 46 so that the cover may be removed in order to gain access to the interior of the apparatus. A window 41,
which may be closed by a plug 48, is provided adjacent the lower end of the coating chamber I9 for gaining access to the nozzles '22.
The pump 25 which supplies coating metal to the nozzles 22 is driven by a motor 50. The motor is supported on a removable cover 5| forming a part of the top of the coating apparatus over the coating pot IT. The cover 5| is preferably of such size that when it is removed the motor 50,
pump shaft 52, pump 25, pipe 26 and nozzles 22 may be removed as a unit from the apparatus.
From time to time it is necessary to supply the coating pot with metal to compensate for that used in coating the strip. This is ordinarily done by dumping additional coating metal into the open bath. In the present invention, the oxidation of the bath is reduced when adding coating metal thereto by providing the pot with a conduit which communicates at one end with the bath below the surface thereof and has its other end lying outside of the apparatus. As shown in Figures 3 and 4, the pot I1 is provided at one end with an extension forming a conduit or trough 56 having its lower end 51 communicating with the metal in the pot below the surface thereof. The upper end of the trough lies outside of the coating apparatus and is provided with a cover 58. By means of the feed trough, additional coating metal may be supplied to the pot without exposing the main portion of the bath metal to oxidation. Oxidation of the small portion 59 of the bath surface which lies in the trough may be prevented by supplying protective gas to the space above the bath level through a pipe 60 controlled by a valve 8|. As this space is small, it requires only a very small amount of gas to prevent oxidation of the metal. The valve 6| has a handle 62 which is positioned in the path of movement of the cover 58 so that as the cover is moved into its dotted line position in order to feed additional metal to the bath, it closes the valve, thereby preventing waste of the protective gas during the time that the cover is in open position. A spring 63 opens the valve when the feed trough is closed by the cover.
In Figure 5 there is shown a modified type of apparatus which is generally similar to that described heretofore, but which is heated entirely by electric resistance elements instead of by the combustion of fuel as in the preheating chamber 3 shown in Figure 1. In Figure 5, parts corresponding to those already described have been indicated by the same reference numerals with an 41" aflixed thereto. The strip before entering the flux pot Ito and the coating pot Ila is preheated by passing in contact with pairs of rollers ill which are heated by electric resistance heating elements H mounted in their interiors, as shown in Figure 6. Current is supplied to the heating elements by means of collector rings 12 and lead wires 13. In this construction, the strip is preheated by conduction due to the direct contact of the heated rolls with the strip. This is a more efficient mannerof transmitting heat than by radiation described in the other embodiment. Instead of passing between pairs of rolls, the
and instead of using electric resistance heating units in the interiors of the rolls, the roll interiors may be heated by burners. In Figure '7,
roll 14 over which the strip 10a is conveyed. The interior of the roll is heated by a burner which may be supplied with fuel from any desired source.
In the embodiment shown in Figure 5, the chamber 6 shown in Figure 1 is eliminated and the coating chamber [9a, instead of having its temperature maintained by products of combustion, is heated by electric resistors 16 and the coating chamber is surrounded by a layer 11 of insulating material.
In Figure 1, the strip passes through the bath of coating metal in the pot l1 before the streams of coating metal are applied thereto in the coating chamber l9. In Figure 5, the strip passes directly from the rolls I5a to the nozzles 22a without passing through the bath metal in the pot I121. The strip may or may not pass through the metal in the pot, as desired, whether the preheating be done by electricity or products of combustion. In Figure 5, the coating is accomplished entirely by the streams of coating metal supplied by the nozzles 2211, whereas in Figure 1, the coating is supplemented by the strip first passing through the bath. In those cases where the/strip passes through the bath, it is preferred to maintain the strip adjacent the top of the bath in. order to prevent an undue amount of agitation of the bath, which agitation would decrease settling of the dross. If desired, a pair of conveying rolls may be placed in the coating chamber l9 or [9a to aid in conveying and guiding the strip through the chamber. Although it is preferred to locate the pump 25 in the coating pot, it may be placed outside of the pot, but in communication with the coating metal.
In some cases, it may be found desirable to apply the flux to the strip in stream form, as has been described in connection with the application of coating metal to the strip, instead of passing the strip through the flux bath. Furthermore, in some cases, the flux may be entirely eliminated since the strip and the bath are protected against oxidation due to the use of the protective gas. If desired, the strip, after having been coated and the coating allowed to solidify, may be supplied with an additional coating by conveying it through a second coating chamber which is supplied with protective gas and which has a second set of nozzles for supplying the second coating of metal to the already coated strip.
Although the coating chambers 19 and 19a have been shown and described as provided with means for heating them either by combustion gases or electric resistors, they may be simply heat insulated portions of the stack. Also, cooling coils need not be employed in the cooling chambers 20 and 20a so long as the walls of the cooling chambers have good heat conducting properties.
I have illustrated and described several embodiments of my invention. It is to be understood, however, that the invention may be otherwise embodied or practiced within the scope of the following claims.
1. Apparatus for coating strip metal, comprising a chamber sealed from the atmosphere, means for conveying the strip through the chamber, means for heating the strip while passing through the chamber, a container for a bath of molten coating metal in the chamber, means for supplying a stream of molten coating metal from the container to the strip outside the bath and returning the excess coating metal to the container, means for maintaining that portion of the chamber adjacent the coating means at a temperature at least as high as the melting point of the coating metal, a baffle in the container between the surface of the coating metal bath and the point where the coating metal is applied to the strip, said baflie decreasing agitation of the bath by excess coating metal returned thereto from the strip, and means for supplying protective gas to the chamber to prevent oxidation of the strip and coating metal.
2. Apparatus for coating strip metal, comprising a chamber sealed from the atmosphere, means for conveying the strip through the chamber, means for heating the strip while passing through the chamber, a container for a bath of molten coating metal in the chamber. a pump in the container for supplying a stream of molten coating metal to the strip outside the bath and returning it to the container, a baflie in the coating metal in the container below the pump inlet for decreasing agitation of the bottom of the bath by the pump, and means for supplying protective gas to the chamber to prevent oxidation of the strip and coating metal.
3. In apparatus for coating metal, a container for coating metal, a feed conduit for metal having one end communicating with the interior oi! the container below the bath level and the other end extending outside of the container, 9. cover for the conduit, and means for supplying protective gas to the conduit.
BARTON R. SHOVIR.