US3095361A

US3095361A - Method of manufacturing tinplate

Info

Publication number: US3095361A
Application number: US91708A
Authority: US
Inventors: Morris D Stone
Original assignee: United Engineering and Foundry Co
Current assignee: United Engineering and Foundry Co
Priority date: 1961-02-27
Filing date: 1961-02-27
Publication date: 1963-06-25
Anticipated expiration: 1980-06-25
Also published as: DE1296661B; NL125143C; NL273429A; GB1002448A

Description

June 2s, 1963 M. D. STONE 3,095,361

METHOD OF MANUFACTURING TINPLATE Filed Feb. 27, 1961 'l v2a INVENTOR. Q) me/5 a. .sra/v5 ArraQ/vey 3,095,361 Patented June 25, 1963 snee 3,095,361 METHOD OF MANUFACTURING TINPLATE Morris D. Stone, Pittsburgh, Pa., assignor to United Engineering and Foundry Company, Pittsburgh, Pa., a cerporation of Pennsylvania Filed Feb. 27, 1961, Ser. No. 91,708 3 Claims. (Cl. Zim- 28) This invention relates to a method of producing very thin tinplate characterized by a high production capacity and capable of producing tinplate at a substantial saving in manufacturing costs over known methods and wherein the tinplate will have improved metallurgical characteristics.

This economic and metallurgical advancement in the production of tinplate is realized by practicing a method in which the parent strip is reduced to an ultra-thin gauge thereby affording a considerable savings in cost of material, equipment and labor as may be required for producing the tinplate, as well as a marked reduction in scrap losses, while, at the same time, yielding a product having improved hardness and strength characteristics.

In view of the fact that normal gauge tinplate, which falls within the ranges .007 to .011 inch, is not economically suitable for all phases of the container market, the ability of tinplate to maintain and to continue to improve its position in this market depends to an appreciable extent on whether ultra-thin tinplate can be produced more economically. One lof the major problems confronting the economical manufacture of very thin tinplate has to do with whether the tinplate will have the requisite physical properties to enable it to serve its intended purpose. Two other major problems have to do with the additional equipment necessary to produce such tinplate and the considerable scrap losses incident thereto. These scrap losses are brought labout as :a result of the thin strip being damaged during the many processing, handling and transferring steps which are involved in the production of the tinplate. Because of the magnitude of these problems, it has been questioned by some skilled in the art whether very thin tinplate can be economically produced.

In order to better understand the uniqueness and novelty of the present invention, an understanding of the present-day commercial attempts at producing very thin tinplate is believed necessary. At present, there are but two such procedures for making available in limited amounts ultra-thin tinplate lfor use in the manufacture of containers.

One procedure is to utilize the `ordinary processing equipment employed to produce normal gauge tinplate, which consists of reducing the hot rolled and pickled strip in a tandem cold reduction rolling mill where the strip is reduced immediately to its ultra-thin gauge, i.e., to an order of .0045" thick. This `operation is followed by a continuous annealing process, wherein the ultra-thin strip is cleaned and annealed to a soft metallurgical condition. Thereafter, the strip, which is not only very thin but also very soft, both of which factors being conducive to high scrap losses, is transferred to a skin-pass rolling mill for further processing. This operation is designed primarily to develop the desired mechanical properties, along with achieving a smoother and flatter strip surface. The strip, however, retains a considerable degree of softness after the skin-.pass operation.

Subsequent to this skin-pass operation, the ultra-thin strip is transferred for the third time to an electrolytic tinning line. In the tinning line, the strip is rst cleaned, pickled and tinned, after which it is passed through reilowing, passivating or chemical treatment and oiling zones. In this procedure, it is to be appreciated that it is necessary to repeatedly handle, transfer and process the strip in its ultra-thin and soft condition; in which connection when cognizance is taken of the intricacies of the equipment that performs this manner of processing of the very thin strip, it will really be understood why great scrap losses are involved. Moreover, in this procedure it has been found that the strip could only be rolled to the thin desired gauges by overloading the conventional 5-stand tandem cold mill, or by using a 6-stand mill, or alternately by a second succeeding separate rolling step. In this connection, it is to be pointed out that the maximum hardness that has been found practical to achieve in this method has fallen within the range of -6 (T-30 Rockwell of 67 to 73).

With respect to the second procedure currently being used in an attempt to produce ultra-thin tinplate, in order to minimize the necessity of handling, transferring and processing the strip in its ultra-thin and soft condition, the procedure is essentially as follows:

The -hot rolled strip in this case is reduced to approximateiy the order of .020 inch thicker than in the case of the previous explained method, ie., approximately of the order of .100 inch thick. The hot rolled and pickled strip is transferred to a tandem cold reducing mill where the strip is reduced to a thickness of the order of .009 inch, that is, approximately double its final desired thickness. After the cold reduction operation, the strip is transferred in its still relatively thick gauge to an annealing line, where it is cleaned and annealed in the usual manner. From the annealing line, the strip, still in its relatively thick but now soft state, may then be processed in a skin-passing mill, although, in some cases, this step may not be included. The strip is then transferred to a thinning line, where it is cleaned, pickled, tinned, reowed, passivated or chemically treated and oiled. After tinning, the strip is then reduced about 50% in a second cold reduction mill to the iinal desired ultrathin gauge and having the desired hardness. The degrees of hardnesses that are known to be obtained in this method have been lwithin the range of T-7 (T-30 Rockwell of 7l to 78). After the rolling of the tinned strip, it is transferred in its ultra-thin condition to a fourth process line and to its sixth independent processing step where it is cleaned and passivated, and sometimes reflowed for the second time.

In this second procedure, while it has the advantage that the thin product in its soft condition is involved in less handling than in the first procedure, it will be appreciated that to obtain this advantage a substantial increase in equipment and labor force is necessary. Moreover, in view of the `fact that the tinned strip is subjected to a rolling operation in which the surface of the strip may become marred, it is necessary to perform a second reilow operation as well as a chemical treatment and a second cleaning operation. it goes without saying that such an overall process results in increased cost of manufacturing the tinplate.

it is the principal object of the present invention to provide a method of manufacturing tinplate that will be ultra-thin and of low cost, that will keep to a minimum the scrap losses incident to the production thereof, that will require no additional equipment and labor force over the first method described above and Still considerably less with respect to the second aforementioned method, and yet will have the advantage `of a high pardoduction capacity which will not involve additional cleaning, reflowing or chemical 4treating operations to produce tinplate having Ia maximum of hardness and strength as imparted by cold rolling.

This object and the other novel features of the present invention will be more fully appreciated when the fol- 'a a lowing description thereof is read in light of the drawing in which;

FIG.`1 illustrates diagrammatically and in sequence the novel steps of the present invention.

As will be apparent to those skilled in the art, the various processing units illustrated in FIG. l and described hereinafter employed in the herein disclosed rnethod are in themselves well-known elements in the manufacture of steel strip as exemplified in The Making, Shaping and Treating of Steel, United States Steel, 7th edition.

With reference t FIG. l there is shown the last mill stand of a hot strip rolling mill 11 wherein the hot strip is reduced in thickness and following which it is coiled on a mandrel 12. In order to realize the full advantages of the present invention it is recommended that the strip be reduced in the hot rolling imill to a gauge within the range of .080 to .110 inch thick. For the purpose of describing the present invention, it will be assumed that the thickness of the strip issuing from the hot mill is of the order of .100 inch. The hot rolled strip, in the form of a coil, is transferred from the mandrel 12 to a pickling line 13 in which it is, in the usual manner, placed on a pay-off reel 14, joined to the end of a previous strip and fed through the pickling zones, after which it is coiled again on a wind-up reel 15. Of course, the strip during the pickling operation is still in a very thick condition, Ii.e., as previously mentioned .100 inch, so that there will be experienced no scrap losses such as would result if very thin strip were being pickled.

From the pickling line, the pickled strip in coiled form, is transferred to a tandem cold reduction mill 16 where the coil is placed on a pay-off reel 17, fed through each of the five, or as shown in phantom six, stands of the mill and then wound on a tension reel 18. Acconding to the teachings of the present invention, the strip will be reduced in the cold reduction mill to a thickness within the range of .006 to .012 inch. For the purpose of this description, it will be assumed that the thickness of the strip issuing from the cold mill 16 is of the order of .009 inch. This thickness represents approximately double the desired final thickness of the product. In this condition, it is to be observed that the strip will be still relatively thick and by reason of the rolling operation very hard. In view of the fact that the strips thickness -is approximately twice as great as its ultimate desired gauge, the handling, transferring and the immediate subsequent processing thereof will lbe done without experiencing the considerable scrap losses that are inherent in handling very thin material,

After the cold reduction mill operation, the relatively thick hard strip, in coil form, is transferred to an annealing line 19 where it is placed on a pay-off reel 21 and the leading end joined to the trailing end of `a previous istrip, and fed through the annealing line. As is customary, the strip will be cleaned before being annealed lafter which it will pass through the annealing zone and be coiled on a windup rcel 22. It is to be appreciated that at this stage of the operation the strip, as it leaves the annealing line, will be very soft, but at the same time it will have a substantial thickness, and in view of this fact in the further handling, transferring and processing thereof, scrap losses will be minimized.

Following the :annealing operation, the strip -in coiled form, is transferred to :a second cold reduction mill 23 which may consist of either one or two or more stands, a second stand being shown in phantom in the drawing. In this operation the strip, in coiled form, is adapted to be placed on a pay-off reel 24, fed through the mill and wound upon a tension reel 25. As pointed out above, the strip when it is transferred .from the annealing line and during the time it is being handled at the entry side of the second reduction mill 23 will be in a soft condition, but at the same time it will be relatively thick, hence minimizing scrap losses during this phase of the operation. According to the teaching of the present invention, the strip is adapted to be giVeIl its final reduction to its ultra-thin form in the reduction mill Z3 in which the thickness should be within the range of .003 to .006 inch. In this regard, it is important to point out that in order to achieve the full advantage of this invention, the reduction taken in the -rnill 23 should be of the order of from 30 to 60 percent. For the purpose of the description of the present invention, it will be assumed that the final thickness of the strip will be of the order of .0045 inch, which will represent a 50 percent reduction. As mentioned previously, a substantial savings in the overall cost of producing the tinplate is thus realized in reducing the thickness of the strip to Such an extent. It is one of the features of this invention to provide a method wherein such tinplate, resulting from the practice thereof, will have this characteristic. In this connection, it is to be appreciated that not only is the mill 23 employed at this particular stage of the operation to reduce the strip to its final thickness prior to tinning, but just as important and of equal significance is the fact that the reduction taken within the previously mentioned range will impart a substantial hardness to the strip and, in addition, will improve its strength qualities. It is ya feature of the invention herein disclosed that the strip will be given a hardness of the order of T-6 to T-S (T-3O Rockwell of 67 to 83) and that this hardness will be achieved primarily by rolling. It will be appreciated that this degree of hardness will enable the tinplate to be used for the intended purpose, notwithstanding its extreme thinness.

After the second cold reduction operation the strip, in coil form, is transferred in its very thin but very hard condition to an electrolytic thinning line 26 where it is placed on a pay-olf reel 27, joined to the trailing end of a previous strip, and fed through the line, after which it will be coiled upon a windup reel 28. This electrolytic tinning line incorporates the usual equipment adapted to electro-clean, pickle, tin, reow, passivate and oil the strip. It is a feature of this invention to perform all rolling of the strip prior to the tinning operation thereby avoiding the possibility of marring the tinned surfaces. To accomplish this object, the strip, according to the present invention, Will be presented to the thinning line in its nal very thin gauge. However, since by employing the method of the present invention, the strip will have a substantial hardness and improved strength qualities obtained by cold rolling of the strip and as a result scrap losses Iwill be minimized in the further transferring, handling and processing of the strip.

In summarizing the advantages of the present invention over the prior procedures for attempting to produce tinplate more economically, it will be appreciated that the present invention provides a method wherein the resulting tinplate is made very thin with a substantial reduction in the material cost and in the practice of which substantially all of the transferring, handling and processing of the strip are performed, while 4the strip is still in its soft thick condition. Furthermore, when the strip is in its very thin condition, which is only for a small fraction of the overall processing and handling time, this strip is maintained very hard so that a considerable reduction in the scrap losses over the entire processing operation is effected. In addition, the strip not only will be characterized by a substantial hardness and improved strength qualities, which are achieved by rolling, but the strip after tinning will not he subjected to any rolling, thereby resulting in an overall advantage that not only is the product economically produced but it is produced on a line having a very high capacity.

In accordance with the provisions of the patent statutes, I have explained the principle and operation of my invention and have illustrated and described what I consider to represent the best embodiment thereof. However, I desire to have it understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a method of producing tinplate characterized by a high degree of hardness suitable for use in the manufacture of containers, the steps including:

cold reducing the strip to a thickness of at least .006

inch and thicker;

annealing such strip;

cold reducing the annealed strip by an amount of at least 3() percent and greater yto impart to the strip a hardness of at least T-5,

and electrolytically tinning the strip in its thin hard condition.

2. In a method of producing tinplate suitable for use in the manufacture of containers in a minimum number of processing steps and in a manner that scrap losses will be substantially reduced and the strip will be characterized by a high degree of hardness achieved by rolling, the steps including:

reducing this strip in a hot rolling mill to a thickness between the lower and upper limits of .080 to .110 inch, respectively;

further reducing the cold strip in a cold rolling mill to a thickness between the lower and upper limits of .006 to .012 inch, respectively;

annealing said strip as cold reduced;

cold reducing the annealed strip by an amount between the lower and upper limits of 30 to 60 percent, respectively to impart to the strip a hardness between the lower and upper limits of T-6 to T-S, respectively,

and continuously electrolytically tinning the strip in the thin hard condition. 3. In a method of producing very thin tinplate characterized by the fact that when the strip is in a metallurgically soft condition, it is maintained relatively thick, and when in its very thin condition the strip is metallurgically very hard, where-by in both conditions the strip lends itself to ready handling, transferring and processing with minimum losses due to breakage, bending, tearing and the like, and further characterized by the fact that all of the rolling processes are performed prior to the tinning of the strip, the steps including:

cold reducing the strip to a gauge of at least .006 inch and greater which will be relatively thick as compared with the desired final gauge thereof;

continuously annealing the strip while in its relatively thick condition;

cold reducing the soft annealed relatively thick strip at least 30% and greater to its final thin gauge to impart a substantial hardness and strength to the strip,

and as a final step tinning the strip in its thin hard condition.

References Cited in the file of this patent UNITED STATES PATENTS 2,673,836 Vouada Mar. 30, 1954 2,906,652 Kiefer Sept. 29, 1959 FOREIGN PATENTS 1520,373 Australia Sept. 27, 1945 472,120 Canada Mar. 13, 19511

Claims

1. IN A METHOD OF PRODUCING TINPLATE CHARACTERIZED BY A HIGH DEGREE OF HARDNESS SUITABLE FOR USE IN THE MANUFACTURE OF CONTAINERS, THE STEPS INCLUDING: COLD REDUCING THE STRIP TO A THICKNESS OF AT LEAST .006 INCH AND THICKER; ANNEALING SUCH STRIP; COLD REDUCING THE ANNEALED STRIP BY AN AMOUNT OF AT LEAST 30 PERCENT AND GREATER TO IMPART TO THE STRIP A JARDNESS OF AT LEAST T-5, AND ELECTROLYTICALLY TINNING THE STRIP IN ITS THIN HARD CONDITION.