US3331230A - Method for the manufacture of tin plate - Google Patents

Description

y 1967 R.J. BENTZ ETAL 3,331,230

METHOD FOR THE MANUFACTURE OF TIN PLATE Filed Oct. 13, 1964 DRIER m a 2 a 4 g I I J m PICKLING M AND RINSE ouavcw -7 RINSE PLAT/N6 E I58 I7 INVENTORS. RONALD J. BENTZ and ANER N. LAUBSCHER PERCENT REDUCTION Attorney United States Patent 3,331,230 METHOD FOR THE MANUFACTURE OF TIN PLATE Ronald J. Bentz, Forest Hills Borough, and Aner N.

Laubscher, Penn Hills, Township, Allegheny County,

Pa., assignors to United States Steel Corporation, a

corporation of Delaware Filed Oct. 13, 1964, Ser. No. 403,612 7 Claims. (CI. 72-42) This invention relates to the manufacture of tin plate and in particular to that method of manufacture which is characterized by cold reduction of a tinned steel strip to finish-gage and coating weight.

It has been established that tin plate of exceptional thinness and strength can be produced by rolling low carbon steel strip to an intermediate gage greater than the desired finish-gage, coating the strip with tin and then cold reducing the resulting tinned strip to finish-gage and finish-coating weight. The resulting product has been termed reduced last-tin plate. The final cold reduction step requires the use of a rolling coolant'lubricant which must be removed in order that the tinned surface may be chemically treated to resist staining. And to facilitate handling in subsequent fabricating operations, the chemically treated surface must then be reoiled with a lubricant compatible with the lacquers and enamels used therein. The amount of this lubricant is critical; a film of more than about 2 guns. per base box causes difficulties in soldering and lacquering. Since a base box of tin plate consists of 31,360 sq. in. (217.77 sq. ft.) of plate area, oiling involves spreading extremely minute (less than 2 gms.) quantity of lubricant uniformly over about 435% sq. ft. of surface. While such is accomplished by the foregoing sequence of operations, the costs of cleaning and handling the cold reduced tinned strip through separate chemical treating and oiling facilities are considerable. It has been proposed to avoid these costs by substituting for the conventional coolant-lubricant used in the final cold reduction step an emulsion of the final oiling agent in an aqueous solution of the chemical treating agent. However, the necessary precise control of the oil deposition has never been achieved in such practice.

It is an object of the present invention to provide a method whereby the aforementioned difficulties in the production of reduced last-tin plate may be overcome, and the costs of production greatly reduced.

The accomplishment of this and other objects will be set forth in the following specification to be read in conjunction with the attached drawings wherein:

FIGURE 1 is a diagrammatic showing of the processing steps of the present invention up to the final cold reduction step.

FIGURE 2 is a diagrammatic showing of a cold reduction mill and certain auxiliary equipment essential to completion of processing in accordance with practices of the present invention, and

FIGURE 3 is a graph showing the relative rolling force required in effecting various amounts of cold reduction in a tin coated steel strip. Curve A of this figure obtains when the tinned strip is rolled using the conventional practice of flooding the strip and rolls with a coolantlubricant solution; curves B, C, D, E and F, when the only lubrication provided is a film of 0.20, 0.58, 0.69. 1.0 and 1.2 gmslbb. of cottonseed oil respectively applied to the strip prior to rolling.

We have discovered:

(i) that the presence of an oil film, particularly a film of cottonseed oil or palm oil, of as little as 1 gm. per base box on the surface of a tinned low carbon steel strip provides sufficient lubrication to permit cold re- 3,331,230 Patented July 18, 1967 "ice duction of as much as to to be made in such strip,

(2) hat such a film of oil is reduced in substantially direct proportion to the amount of the cold reduction effected on the strip, and that this result obtains with films up to at least 5 gms./bb. even when the strip and the rolls of the mill are flooded with copious quantities of cooling water, and

(3) that the presence of such films up to at least 5 gms./bb. on the surface of tinned strip does not interfere in the treatment of such surface with the aqueous solutions of chromic acid and/or chromate salts commonly used to impart stain resistance.

These discoveries permit rearrangement of the operational steps in the production of reduced lasttin plate and the elimination of certain troublesome practices heretofore believed necessary.

Referring now to FIGURE 1, the method of the present invention comprises passing a strand of low carbon steel strip of any analysis suitable to the production of tin plate, which has been previously rolled to an intermediate gage, cleaned and annealed, from an uncoiler 1 through conventional pickling and tin plating units 2 and 3 respectively. The tin coated strip is then passed through rinsing and drying units 4 and 5 into a suitable furnace 6 wherein the tin coating is melted and brightened. The strip leaves the furnace through a quench tank 7 and passes to a drier 8. Units 6 and 7 are bypassed if matte-finished tin plate is desired. At this point processing departs from conventional reduced last" practices and the tinned strip is passed through an oiler 9 where a film of either cottonseed or palm oil is applied to its surfaces before rewinding on recoiler 10. Oilcr 9 may be either an electrostatic or an emulsion type of oiler, however, for present purposes it must be operated to apply an oil film of between 1 and 5 gms./bb. If an emulsion oiler is used, a hot air drier, not shown, should be interposed between the oiler and recoiler 10.

As evident from the curves of FIGURE 3, at least 1.0 gm. per base box of oil must be applied to afiord tolerable lubrication during rolling, while a film of about 1.2 gmJbb. provides lubricity fully equivalent of that achieved in conventional rolling ractices. As previously mentioned. the cold reduction reduces this oil film in substantially the same proportion as the strip and the coating. Accordingly, the thickness of oil on the finished product can be controlled by regulating the amount of the oil-precoat in relation to the percent reduction to be effected in the next step of the process. For some products a final oil film of less than 0.5 gm./bb. is sufiicient; for others, a film of as much as 1 gm./bb. may be used. It is important, however. that the final film does not exceed about 2 gms./bb. if difficulties in soldering and lacquering of the product are to be avoided; thus within the range 1 to 5 gms./bb. of oil which can be applied in the pre-oiling step, the maximum will decrease as the amount of reduction to be taken in the subsequent cold reduction step is decreased.

To complete the processing in accordance with present invention, the tinned and pre-oiled strip from recoiler 10 is passed through the cold reduction mill 11 of FIGURE 2. A suitable mill is comprised of two four-high stands 12A and 12B arranged in tandem, an uncoiler 13, a recoiler 20 and the usual fore and aft tensioning devices 14A and B respectively which also serve to maintain a substantially horizontal passline through the mill. Approximately 99% of the reduction necessary to bring the strip to finish gage and coating weight is taken on the first stand 12A; the stand 12B serving mainly as a flattening pass. Reduction can be accomplished in a single pass through a single stand mill; however, two-stage reduction of the above character is preferable since it permits correction of strip shape and surface appearance.

For the purposes of the present invention, a pair of spray pipes A and 15B are provided between stands 12A and B. These pipes are disposed to direct streams of treating solution against the surfaces of the strip as it emerges from the stand 12A. The solution may be any of the aqueous chromium containing solutions commonly used to imp-art stain-resistance to tin plate; a 1 to 2% (by weight) solution of chromic acid being particularly suitable. Tank 16 serves as a reservoir for the solution which is delivered to the sprays by pump 17. Since it is preferable to use a hot (l150 F.) solution the tank 16 is provided with heating means 18 which may be a thermostatically controlled steam heating coil. Excess solution is removed and strip dried prior to entry into stand 128 by hot air drier 19. A conventional chevron type drier is convenient for this purpose. Excess solution driven from the strip by the air blasts of the drier may be collected and returned to the tank 16 by suitable bafiles and conduits, not shown.

The chromate solution applied as described serves the double function of treating the tinned surface and dissipating heat generated in the mill and strip by rolling. Successful treatment requires merely that the top and bottom surfaces of the strip be thoroughly wetted. As previously mentioned, the presence of the oil film does not interfere with action of the solution. nor is the film disturbed by action of the sprays. While the treating sprays have been shown positioned behind st and 12A and this practice is preferred, successful result have also been achieved with sprays located ahead of stand 12A.

The economy of rcducedlast" practices is favored by heavy reductions in the cold reduction step. However, the amount of reduction made in the mill 11 is determined largely by the mechanical properties desired in the finished product. While reductions as high a about 90% can be made, the formability of plate reduced more than 70% is limited. Presently, the most practical operating range is between 30 and 60% with an optimum balance of mechanical properties and economy of operation being achieved at about 50%. The thickness of strip introduced into the process is determined by the ordered gage of the finished product and the amount of reduction to be made in the final rolling step; the latter in combination with the ordered weight of coating determines the amount of tin to be deposited in the coating step.

The preferred practices of our invention are summarized in the following specific example:

Tin plate ordered to lb. basis Weight and 0.25 lb./bb. coating weight and intended for carbonated beverage can bodies is produced by processing a suitable low carbon, low metalloid steel strip through the sequence of operations described above. Since the intended use of this plate requires an optimum balance of strength and formability, the reduction to be taken at mill 11 is set at Accordingly, the trip is initially rolled to 90 lb. basis weight, about 0.010 inch thick, and is electroplated with tin to a nominal coating weight of 0.5 lb./bb. Following plating, and heat-brightening, if the latter step is included, the coated strip is pre-oiled by passing through an electrostatic oiler operated to apply a film of cottonseed oil of between 1.2 and 1.4 gms./bb. Alternatively, this quantity of oil can be applied by treating the strip with a suitable emulsion of cottonseed oil and water. The oiled strip is then cold reduced 50% in a suitable two-stand tandem mil]; about 99.5% of the reduction being taken on the first stand, the remainder on the second stand. The strip is maintained under tension and in a substantially horizontal passline during this operation in accordance with known cold rolling practices.

In the rolling of tin coated strip, it is preferable to use smooth work rolls in the first stand and slightly roughened rolls in the second. As the strip emerges from the first stand of the mill, it is thoroughly wetted with a hot (140 F.) aqueous solution containing 1.75% by weight chromic acid applied to its top and bottom surfaces by sprays at a rate of about 10 gallons per hour. Excess solution is removed and the strip dried before entering the second stand of the mill. The rolling reduces the strip to a finish gage of 45 lb. basis weight (about 0.005 inch) and a finish coating weight of 0.25 lb./bb. Tests have shown the resulting product carries a film of about 0.7 gm./1bb. of cottonseed oil and an underlying film containing from 0.5 to 0.6 mg. per sq. ft. of chromium existing probably as a complex oxide with tin. The latter is sufiicient to maintain the surface substantially free of discoloration during storage and even when baked in air for 20 minutes at 420 F. The lubricity, lacquerability, and solderability of the product are the equivalent of conventional tin plate, while the power requirements in the rolling operation are less than when the steel strip is reduced to finish-gage prior to tinning. Substantially the same results are obtained when palm oil is substituted for cottonseed oil in the pre-oiling step.

The practices of the invention of course are not limited to the grade of plate of the example. Other grades, for example or lb. plate carrying 0.5 or 1.0 lb. of tin per bb., can be produced by adjusting the gage of the entering steel stock and the amount of tin applied in the plating step. The mechanical properties of the steel base can be varied by adjusting the amount of cold reduction; the amount of oil carried on the finished product can be varied by adjusting the film applied in the pre-oiling step as previously explained.

While we have shown and described certain specific embodiments of our invention, it is obvious that modifications can be made without departing from the scope of the appended claims.

We claim:

1. In the method for producing a base box of tin plate characterized by rolling a steel strip to an intermediate gage, coating the steel with tin, and cold reducing the tin coated steel to final gage and coating weight, the improvement comprising applying to the tin coated strip prior to the cold reduction thereof a film of oil in amounts between 1.0 and 5.0 gms. per base box, and treating the oiled surface during said cold reduction with an aqueous chromate containing solution.

2. The method of claim 1 in which the oil applied in the pre-oiling step is selected from the group consisting of palm oil and cottonseed oil.

3. The method of claim 1 in which the treating solution consists of an aqueous solution containing 1 to 2 percent by weight chromic acid.

4. The method of claim 1 in which the tinned and preoiled strip is cold reduced between about 30 and 70 percent.

5. In the method for producing a base box of tin plate characterized by rolling a steel strip to an intermediate gage, coating the steel with tin and cold reducing the tin coated strip to finish gage and coating weight in two stages, the improvement comprising applying between 1.0 and 5.0 gms. per base box of an oil selected from the group consisting of palm oil and cottonseed oil to the tinned strip prior to cold reduction thereof and treating the tinned and pre-oiled strip with an aqueous chromate containing solution after completion of the first stage of said cold reduction.

6. The method of claim 5 in which the treating solution consists of an aqueous solution containing 1 to 2% by weight chromic acid.

7. The method of claim 5 in which the tinned and pre-oiled strip is cold reduced between a total amount of about 30 and 70% with approximately 99% of said total reduction being effected in the first stage of said two stage reduction.

(References on following page) 5 6 References Cited 3,110,413 11/1963 McKay et a1. 29-528 DaVlS 2,850,999 9/1958 Kaplan et a1 29528 CHARLES W. LANHAM, Primary Examiner.

3,050,847 8/1962 Hill 29-5 5 E. M. COMBS, Assistant Examiner.

Claims (1)

1. IN THE METHOD FOR PRODUCING A BASE BOX OF TIN PLATE CHARACTERIZED BY ROLLING A STEEL STRIP TO AN INTERMEDIATE GAGE, COATING THE STEEL WITH TIN, AND COLD REDUCING THE TIN COATED STEEL TO FINAL GAGE AND COATING WEIGHT, THE IMPROVEMENT COMPRISING APPLYING TO THE TIN COATED STRIP PRIOR TO THE COLD REDUCTION THEREOF A FILM OF OIL IN AMOUNTS BETWEEN 1.0 AND 5.0 GMS. PER BASE BOX, AND TREATING THE OILED SURFACE DURING SAID COLD REDUCTION WITH AN AQUEOUS CHROMATE CONTAINING SOLUTION.

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