DE1527908B2 - Method of forming a sheet metal container - Google Patents

Description

State of the art

In a known method of the type mentioned in the preamble of claim (DE-PS 5 23 111) a flat blank made of tinplate is assumed, which is hot-dip tinned sheet metal acts. The tin layer, which serves on the one hand for corrosion protection and on the other hand as a drawing agent, is relative thick, and due to its smoothness, it accepts liquid lubricant applied before sheet metal forming hardly on. According to this process, sheet metal containers can be produced with Do not produce particularly thin walls and yet perfect corrosion protection.

task

The invention specified in the claim is based on the object of the known method so to train further that produce corrosion-resistant can bodies in a very economical way permit.

advantages

When using the method according to the invention it has surprisingly been found that, despite the choice of particularly thin layer of tin, which, due to its matt structure, is nevertheless suitable for receiving a liquid lubricant is sufficient, a strong wall thinning can be achieved during ironing, in which the thin layer of tin, which initially serves as a lubricant carrier, provides perfect corrosion protection undergoes compaction and surface smoothing. These positive properties such Sheet metal containers are achieved despite a considerable saving in the metal used, in particular tin, especially in the manufacture of beverage cans, which are mass-produced items is essential.

At this point it should be mentioned that after the procedure mentioned at the beginning became known (Technische Rundschau 61 (1969) Issue 23, pp. 25, 27) electrolytically tinned tinplate entrance to the Practice found and that today the vast majority of tinplate produced is electrolytic is tinned. Accordingly, tinplate that is electrolytically tinned is now being used on a large scale Embodiment of the invention

Further details, advantages and features of the invention will become apparent from the following description and the drawing, (expressly referred to for all details not described in the text. It shows

F i g. 1, on an enlarged scale, is a perspective sectional view of a cut open, with on both sides tin-coated steel sheet; F i g. 2 is a sectional view of a molding device with Drawing and ironing tools and one for pressing the sheet metal blank through the device used die;

F i g. 3 to 5 of FIGS. 2 corresponding sectional views of the device and the in the desired shape brought container and

F i g. Figure 6 is a perspective view of the completed container, partially torn away and in section. As illustrated, sheet steel 6 is made from cold

* ~ Rolled, low-carbon steel is used, which is electrolytically provided with a thin layer of tin 7 - in order to obtain a "matt" tin coating, in contrast to the usual tin plating. This process is generally the same as that used in the tin making industry. The initial thickness of the tin layer can vary depending on the length of the strength of the finished wall Behälterseiten- 'and vary greatly desired Zinnstärke of the finished side wall. The final tin thickness must be sufficient to completely cover both surfaces of the finished sidewall. So z. B. in the method according to the invention a coating thickness of about 1 μίτι used when the material thickness is to be reduced by half. Thicker coatings are also possible; For the sake of economy, however, the aforementioned coating thickness is used, which has proven to be sufficient.

After the electrolytically tinned sheet has dried, z. B. with the help of a punch press a round one Blank 8 punched out.

In Figure 2, a generally designated 10 drawing device is shown in a tool holder 12 is arranged. Both the pulling device 10 and the carrier 12 are not in any closer detail illustrated hydraulic press arranged. In the tool holder 12, a drawing ring 14 is initially with an opening 16 is provided. The mold opening 16 has an adjacent the top of the ring 14 rounded pulling edge 18.

Over the pull ring 14 and in axial alignment with the In the mold opening 16, a cylindrical molding die 20 with an underside 22 is arranged so that it can move up and down. The design of the end surface 22 determines the final shape of the container to be formed and can be flat, be conical, spherical, or a combination of these shapes. In the preferred shown in the drawing Embodiment is a flat-ending surface 22 for achieving flat-bottomed containers used.

An oily lubricant that soaks the matt tin layer 7 is applied to the blank 8. Included the blank 8 is placed between the mold 14 and an annular blank holder arranged above the mold 24 used.

During the downward movement, the punch 20 continuously pulls the edge of the blank 8 under the blank holder 24 out and over the drawing edge 18 of the mold 14. The blank is in this way in the shape of a tube brought so that a cup-shaped object with a side wall 40 and a bottom 42 is formed (Fig. 3). At this point, both the side wall 40 and the bottom 42 of the deep drawn Object has a thickness substantially corresponding to the thickness of the blank 8.

During the drawing it is ensured that no wrinkles or folds arise in the blank 8, if its edge is pulled out from under the blank holder 24; however, the hold-down force applied should not be so big that the metal tears apart.

While it is still in engagement with the pulling edge 18, the cup-shaped object enters a Ironing ring 44, which is arranged in the tool holder 12 below the mold 14 (FIG. 4). The ironing ring 44 has an ironing surface 45 which has a smaller diameter than the train of the drawing ring 14. By the Downward movement of the punch 20 becomes the tinned side wall of the cup-shaped article pressed past the ironing surface 45, the thickness of the side wall 40 is reduced and this extended.

During this ironing process, both the tin layer and the oily lubricant are used with the it is impregnated for lubrication during the cold reduction of the cup wall. The one from the matte Oil absorbed by the tin layer remains tougher than with conventional tin plating with a shiny tin surface and exhibits a better lubricating effect under the extreme pressures during ironing. The oil inside and on the tin surface lubricates during ironing and the soft The tin layer itself is stretched on its inside and polished on the outside.

A second ironing ring 48 with an ironing surface 49 is in the same way in the tool holder 12 below of the ironing ring 44 set. The punch 20 brings the cup-shaped during its downward movement Object to 'ironing surface 49, while the side wall is still with the ironing surface 45 of the first ironing ring 44 is engaged. Depending on the distances between the respective ironing surfaces the side wall can also still be in engagement with the pulling edge 18 of the pulling ring 14 when it reaches the ironing surface 49 of the second ironing ring 48. On the downward movement, the side loosens from the drawing edge 18, but still acts with the ironing surfaces 45 or 49 of the ironing rings 46 or 48 together (Fig. 5).

The side wall is smoothed further by the ironing surface 49, whereby its wall thickness is reduced and its length is increased. The bottom 42 of the completely formed, deep-drawn and smoothed container 52 is as thick as the blank 8; its side wall 54, on the other hand, is considerably thinner than the blank 8.

While only two ironing rings are shown in the drawing, each one is desired Side wall length and thickness further ironing rings can be used.

In the described molding process for forming the container 52, the outer layer Ta deforms differently than the inner layer Tb. In each ironing process, the layer Ta is more deformed when it is pressed through between the respective ironing surface and the punch. During this »squeezing through

Schens «effects the oil with which the originally matt Tin layer 7 was impregnated on the container exterior, dip required lubrication.

The hard mechanical loading of the layer Ta not only thins it, but also increases its mirror gloss until it is shinier than the side wall surface of a conventional tin made from tinplate treated with conventional tin plating.

The tin layer Tb on the inside of the container wall is not polished and therefore does not have a glossy surface as the outer layer 7a, but the same gloss as the blank, even though it is considerably thinner due to the stretching and expansion of the side wall.

For this purpose 2 sheets of drawings

Claims (1)

Claim: Method for forming a sheet metal container having a bottom and a cylindrical side wall, one made of low-carbon steel with a tin coating on both sides provided flat blank passed through a drawing ring and thereby preformed into a cup whose bottom and side wall have essentially the same thickness, whereupon the wall the preformed cup is subjected to an ironing process, characterized in that that the tin layer is applied electrolytically matt and at most about 1 μm thick, on the matte tin layer a liquid lubricant is applied and ironing under dilution of the cylindrical side wall of the preformed cup by a total of at least 50% will. used for tin can making; it was made on filing date but not for such thin Sheet metal deep-drawn can body used. Finally, note that electrolytically deposited Tin layers were known as the base of the drawing agent ("Messages from the Research Society for Sheet Metal Processing" 1955, No. 19, p. 230). It should also be mentioned that it is used for the production of baking molds by a Drawing process known without subsequent ironing ίο is (US-PS 28 01604), which is used To provide sheet steel with a tin oxide layer with a thickness of at least 7 μm, the surface of which is therefore not left in a dull state due to the oxidation. On the other hand, it is already part of the stand der Technik ("Sheet Metal Industries" December 1966 and "Die Design Handbook" 1955, pp. 17-9 and 17-11) to produce thin-walled can bodies by multi-stage ironing.