US2740729A - Process for coating sheet metal strip - Google Patents

Description

April 3, 1956 R. HODIL 2,740,729

PROCESS FOR COATING SHEET METAL STRIP Filed June 7, 1951 2 Sheets-Sheet 1 April 3, 1956 R. HODIL PROCESS FOR COATING SHEET METAL STRIP 2 Sheets-Sheet 2 Filed June 7, 1951 PNEyj.

United States Patent PROCESS FOR COATING SHEET METAL STRIP Ralph Hodil, Vandergrift, Pa., assignor to Granite City Steel Company, Granite City, 111., a corporation of Delaware Application June 7, 1951, Serial No. 230,307

4 Claims. (Cl. 117-102) having uniform coatings thereon regardless of the speed of travel of the material to be coated. 7

Another object of this invention is toprevent the pumping action caused by high speed rotation of cooperating rolls in a metallic bath thereby providing a more uniform coating across the entire width of the sheet metal strip.

Still another object is to provide a process for making improved coatings on sheet metal strip with more simple and inexpensive apparatus.

A still further object of the invention is to provide a process for galvanizing sheet metal strip at speeds inexc'ess of speeds used in the conventional galvanizing processes.

These and other objects and advantages will become apparent hereinafter.

This invention is embodied in a process which may be standard or conventional up to the point where the sheet metal strip leaves the metallic coating bath, and comprises then passing the metallic sheet metal strip between two non-rotating or very slowly rotating rolls.

The invention further consists in the process hereinafter described and claimed. In the accompanying drawings which form part of this specification and wherein like numerals refer to like parts wherever they occur:

Fig. 1 is a schematic view of this invention embodied in a conventional galvanizing process,

Fig. 2 is an enlarged view of a vertical cross-section taken through the metallic coating kettle,

Fig. 3 is a perspective view of said kettle, and

Fig. 4 is a perspective view of a metal coating kettle having rolls therein which rotate very slowly.

Conventional process It is believed that this invention can best be understood by first briefly describing a conventional galvanizing proc ess. The essential steps of a process commonly practiced are as follows. 7

Referring now to Fig. 1, which is a diagrammatic sketch of a conventional galvanizing line embodying this invention, it will be seen that said lineincludes a roll of sheet metal strip A which is free to rotate in an uncoiler 1. The sheet metal strip A is passed through a cleaning tank 2, which holds a suitable detergent, and an acid tank 3, which contains muriatic acid. The sheet metal strip A is then fed over a roll 4, through a conventional flux 5, into akettle 6 containing a galvanizing bath 7 under a roll 8, and upwardly through said bath 7.

Up to this point, that is, up to the point where the sheet metal strip A begins its upward movement through the zinc bath 7, the conventional process is the same as the new process. In the conventional process, however, exit rolls (not shown) are located in approximately the "ice p same relative position as the rolls 9 shown in the drawings. These conventional gear driven exit rolls are usually 7 /2 inches or more in diameter and rotate at the same peripheral speed as the sheet metal strip A so that said strip A does not slide on the faces of the exit rolls as it passes therebetween.

In the conventional processes, the main limitation on the speed of the sheet metal strip A is that portion ofthe conventional process after the sheet metal strip A begins its upward movement through the bath 7. The speed ofv the sheet metal strip A is limited by the throw ofI of zinc by the exit rolls when said rolls rotate in excess of a certain number of revolutions per minute, and by the fact that heavy coatings are applied to the edges of said sheet metal strip A because of the pumping action resulting from the rapidly rotating cooperating rolls. In some cases, the coating builds up so rapidly on the edges that insufiicient coating material is applied to the center portion of the sheet metal strip A. Furthermore, these exit rolls have a further disadvantage in that they must be removed from the bath andreplaced periodically. In some conventional galvanizing processes, the sheet metal strip A is run at a speed of feet per minute, although speeds nearing 250 feet per minute have been attained. If the conventional exit rolls do not rotate, the design or spangle is always destroyed by the resultant wiping action.

The sheet metal strip A, after it leaves the exit rolls in the metallic bath 7, passes upwardly through a cooling tower 10, over a roll 11, and then downwardly and over suitable-rolls 12 to a power take up reel 13.

New process The process embodying this invention overcomes all of the objectionable features which characterize the conventional galvanizing process and which limit the speed of the sheet metal strip A. At the same time, the process produces a good looking Spangled coating.

As hereinbefore stated, this new process is the same as a conventional process up to the'point where the sheet metal strip A leaves the galvanizing bath 7. In the new process, however, the sheet metal strip A is passed through the rolls 9. The rolls 9, which not not rotate,

are preferably about 3 /2 inches or less in diameter and are made preferably from a hardened abrasion resisting alloy which does not readily combine with zinc. In practice, the rolls 9 should preferably have a diameter in the order of 3 /2 inches which means that arcuate surfaces having a radii of curvature in the order of 1% inches will be presented. Rolls of this type permit little or no zinc alloy build-up at the edges of the sheet metal strip A and present hard arcuate surfaces which linearly contact each surface of the sheet metal strip A.

Eventually, this arcuate surface will wear flat. When this happens, a noncceptable product is produced'because the coated surface is white and non-Spangled. To prevent this, rolls 9 may be rotated sutficiently to present a new arcuate surface to the sheet metal strip A. If desired,-a new arcuate surface can be presented periodically manually or mechanically, or can be presented constantly by rotating the rolls 9 very slowly in the same direction as the travel of the sheet metal strip A. The amount of rotation required to prevent the rolls from wearing fiat varies with the diameter and hardness of the rolls 9 and the speed of the sheet metal strip A and other factors. On some installations this rotation might be of the order of one revolution per hour.

One way of presenting a new arcuate surface to the sheet metal strip A is to provide the rolls 9 with polygonal necks 14, as shown in Fig. 3, which are positioned in a suitable housing comprising pivoted carriages 15 and 16 which pivot along the bars 17 and 18. Pressure, symbolized by a weight 19, is applied to the carriage to force the roll 9 against one surface of the sheet metal strip A. The other carriage 16 is provided with an eyebolt which can be adjusted in accordance with the pressure desired. This arrangement prevents excessive upward movement of the rear of the carriage 16. The pressure of the weight 19 on the carriage 15 causes the r lls 9 to exert pressure on both sides of the sheet metal strip A thereby preventing the passage of excess zinc. This arrangement allows for adjustment of both the weight 19 and eyebolt 20 so that the pressure on each surface of the sheet metal strip A will be substantially the same for producing a uniform coating on both surfaces. When the presented arcuate surfaces of the rolls 9 wear fiat, the rolls 9 are moved so thata new arcuate surface is presented. With the arrangement shown in Fig. 3, the rolls are lifted upwardly, rotated slightly, and lowered.

If desired, a new arcuate surface can be presented to each surface of the strip A by constantly rotating said rolls 9 at a very slow rate. One arrangement for accomplishing this is shown in Fig. 4 wherein one roll 9 is rotatably mounted in a fixed carriage 2i and the other is rotatably mounted in a pivoted carriage 22, which pivots on a bar 23. Pressure, symbolized by a weight 24, is applied to said carriage 22. A motor rotates said rolls 9 very slowly through a suitable reducing gear system 26.

With any of these arrangements, or their equivalents, the weight of the coating applied per square foot of surface can be varied in the same manner as with conventional rolls which rotate with the same peripheral speed as the strip A travels. This can be accomplished by varying the level of the metallic bath in relation to the nip, or point of contact, of the non-rotating rolls 9. As hereinbefore stated, the rolls 9 are non-rotating rolls, but may be rotated periodically or constantly at a very slow rate for the sole purpose of preventing wear at one specific point. As used in the specification and claims, the term non-rotating is used to cover both of these conditions. The term sheet metal strip as used herein is intended to include all continuous sheets or strips regardless of their width.

The use of rolls 9, hereinbefore described, removes the limitation on the speed of the sheet metal strip A. Because the rolls do not rotate, zinc is not thrown from the gears and rolls by centrifugal force, as in the case of conventional rolls rotating at high speeds. Furthermore, a more uniform coating across the entire width of the sheet is produced because there is no pumping action which results from high speed rotation and which causes a build-up of the coating metal at certain points. This results in a more uniform product and in a considerable saving of coating metal. Furthermore, this process eliminates the frequent stoppages for roll changes required in the conventional process, thereby resulting in improved production with less scrap and less maintenance.

What I claim is:

1. The method of producing a spangled galvanized sheet which comprises, introducing a continuous strip of the sheet material into a bath of molten zinc and continuously removing the strip vertically from the bath, passing the vertically progressing strip near its point of emergence from the bath between a pair of opposed arcuate nonrotating surfaces having radii of curvature in the order of 1%" and which are partially submerged in the zinc bath, maintaining the arcuate surfaces in contact with the opposite sides of the strip so that such arcuate surfaces contact the strip along lines substantially directly opposite each other and which lie in a plane parallel to the surface of the molten zinc and which is at substantially right sheet which comprises, introducing a continuous strip of the sheet material into a bath of molten zinc and continuously removing the strip vertically from the bath, passing the vertically progressing strip near its point of emergence from the bath between a pair of opposed nonrotating rollers having a diameter in the order of 3 /2" and which are partially submerged in the zinc bath, maintaining the rollers in contact with the opposite sides of the strip so that such rollers contact the strip along lines substantially directly opposite each other and which lie in a plane parallel to the surface of the molten zinc and which is at substantially right angles to the strip, and maintaining the level of the molten Zinc fixed with relation to the lines of contact between the rollers and the strip so as to obtain a continuously uniform coating upon the strip.

3. The method of producing a Spangled galvanized sheet which comprises, introducing a continuous strip of the sheet material into a bath of molten zinc and continuously removing the strip vertically from the bath, passing the vertically progressing strip near its point of emergence from the bath between a pair of opposed arcuate surfaces having radii of curvature in the order of 1%" and which are partially submerged in the zinc bath, maintaining the arcuate surfaces in contact with the opposite sides of the strip so that such arcuate surfaces contact the strip along lines substantially directly opposite each other and which lie in a plane parallel to the surface of the molten zinc and which is at substantially right angles to the strip, maintaining the arcuate surfaces substantially constantly fixed but periodically rotating them a predetermined amount to present different portions of the arcuate surfaces in contact with the strip, and maintaining the level of the molten zinc fixed with relation to the lines of contact between the arcuate surfaces and the strip so as to obtain a continuously uniform coating upon the strip.

4. The method of producing a Spangled galvanized sheet which comprises, introducing a continuous strip of the sheet material into a bath of molten Zinc and continuously removing the strip vertically from the bath, passing the vertically progressing strip near its point of emergence'from the bath between a pair of opposed rollers having a diameter in the order of 3 /2 and which are partially submerged in the zinc bath, maintaining the rollers in contact with the opposite sides of the strip so that such rollers contact the strip along lines substantially directly opposite each other and which lie in a plane parallel to the surface of the molten zinc and which is at substantially right angles to the strip, maintaining said rollers substantially constantly fixed but periodically rotating them a predetermined amount to present different surface portions of the rollers in contact with the strip, and maintaining the level of the molten zinc fixed with relation to the lines of contact between the rollers and the strip so as to obtain a continuously uniform coating upon the strip.

References Cited in the file of this patent UNITED STATES PATENTS 850,548 Steele Apr. 16, 1907 2,126,578 Roemer et a1. Aug. 9, 1938 2,398,034 Oganowski Apr. 9, 1946 2,598,733 Warner June 3,. 1952

Claims (1)

1. THE METHOD OF PRODUCING A SPANGLED GALVANIZED SHEET WHICH COMPRISES, INTRODUCING A CONTINUOUS STRIP OF THE SHEET MATERIAL INTO A BATH OF MOLTEN ZINC AND CONTINUOUSLY REMOVING THE STRIP VERTICALLY FROM THE BATH, PASSING THE VERTICALLY PROGRESSING STRIP NEAR ITS POINT OF EMERGENCE FROM THE BATH BETWEEN A PAIR OF OPPOSED ARCUATE NONROTATING SURFACES HAVING RADII OF CURVATURE IN THE ORDER OF 1 3/4" AND WHICH ARE PARTIALLY SUBMERGED IN THE ZINC BATH, MAINTAINING THE ARCUATE SURFACES IN CONTACT WITH THE OPPOSITE SIDES OF THE STRIP SO THAT SUCH ARCUATE SURFACES CONTACT THE STRIP ALONG LINES SUBSTANTIALLY DIRECTLY OPPOSITE EACH OTHER AND WHICH LIE IN A PLANE PARALLEL TO THE SURFACE OF THE MOLTEN ZINC AND WHICH IS AT SUBSTANTIALLY RIGHT ANGLES TO THE STRIP, AND MAINTAINING THE LEVEL OF THE MOLTEN ZINC FIXED WITH RELATION TO THE LINES OF CONTACT BETWEEN THE ARCUATE SURFACES AND THE STRIP SO AS TO OBTAIN A CONTINUOUSLY UNIFORM COATING UPON THE STRIP.

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