WO1996017700A2 - Wall thickness distribution in the opening section of cans - Google Patents

Abstract

The invention concerns the field of shaping processes for cans, either made of sheet steel or aluminium sheet or a combined material. In this technical field, ironed can bodies (1) are obtained which are provided with a cover in a closure process, giving rise to closed cans. In this technical field, the object of the invention is to simplify the shaping processes whilst reducing the amount of material required and thus decreasing costs. To this end, a variation in thickness (10, 12, 13) is provided in the upper edge section (A, B) of the ironed can body. The structure of this variation in thickness is such that at least one additional thickness graduation d2, d3 or d4 is permitted. The associated ironing mandrel (100) has a negative contour corresponding to the thickness graduations, when ironing is carried out in the form of a shaping operation.

Description

Wall thickness distribution in the can mouth section

The technical field of the invention is the forming process for tin cans, be they made of sheet steel or aluminum sheet or a combination material. In this technical field, stretched can bodies are created, which are converted into sealed cans with a lid in a closing process. It is an object of the invention to facilitate the forming processes and at the same time save material and thus costs.

This is achieved with the invention in that a thickness variation is carried out in the upper edge portion of the stretched can body (claim 1). The thickness variation is designed in such a way that at least one additional thickness level d ₂ , d ₃ or d ₄ is provided, in addition to a (single) thickness level from d _c to d- _j _ already existing in the prior art (cf. ZB EP- A 59 196).

The ironing mandrel used for forming has gem. the

Invention - in the case of stretching as a forming process - the negative contour corresponding to the thickness gradations (claim 8). In ter en of the process result, the two-part or three-part box with an upper, thickness-varying edge area is obtained (claim 9).

In extension of the principle according to the invention that an additional thickness gradation can make forming processes easier and more efficient, several such thickness gradations can be used to further aspects of the

To positively influence the manufacturing process of can bodies, so the trimming process with the same seaming and closing process. The trimming process is improved if an additional step is provided at the upper edge of the can A, which reduces the sheet to a thickness d ₂ , which is approximately in the order of the wall thickness d, ~. the box lies as it is in the main part of the wall - below the drawn-in area B (claim 6). Both the reshaping behavior when shaping the fold and the reshaping behavior when retracting the upper edge of the can are improved with the proposals according to the invention. In addition, stripping forces from the ironing mandrel are reduced to a particular extent in order to be able to further reduce the sheet thickness in the rest of the trunk area.

The use of lubricants can be avoided due to the improved (easier) forming behavior in order to be able to apply a well-adhering coating after the forming. The coating thus does not take part in the forming process and allows a more corrosion-resistant - because less damaged - surface to be produced.

When trimming, material waste can be reduced and a more precise trimming process of the upper edge of the can can be achieved.

Due to the reduction in axial loads when the upper section of the can is drawn in, a further reduction in thickness can be achieved in the remaining wall area of the can on the basis of the proposals according to the invention, which would be impossible without the invention; the axial forces when pulling in the upper section from the main diameter to a reduced upper edge diameter ("necking") prevents a further reduction in wall thickness in the prior art.

The invention enables such a further development. With the invention, the prerequisites are created to facilitate the forming processes, in particular the drawing in, trimming and forming of the fold edge, and nevertheless the

Opportunity to save material and thus costs. Exemplary embodiments of the invention are intended to explain and supplement their understanding.

Figure la,

Figure lb show a drawn in their neck area

Tin can 1, which has a wall section C, a

Feed section B and a folding section A.

The fold section A becomes one in FIG. 1b

Double fold lock 3 closed.

Figure 2 shows a sheet thickness distribution, as used along the sections A, B and C according to Figures la, lb in the prior art. The sheet thickness d is that which, after the ironing process in the manufacture of the can body in the upper section B, A of

Can wall 1 is present. In the transition section between the feed area B and the wall area C, the sheet tapers to a thickness of d _c due to the ironing process, the transition section is symbolically designated 11 and consists of a light weight

Sloping or ramp.

Figure 3a, Figure 3b, Figure 3c, Figure 3d, Figure 3e show embodiments of

Sheet thickness distributions in section A, B according to Figure la, lb.

Figure 4a,

FIG. 4b schematically shows the manufacturing process of the ironing with a plunger 100 which pushes a bowl la through a "further pull" 20 in order to change the wall thickness d _{Q of} the blank (of the bowl). Behind the

Further ironing rings 21, 22, 23 are provided, through which the plunger 100 passes in order to move to the stop 24 in such a way that the can base 6 is domed 6 and all around receives a bottom profile 5 with which the can is stackable. Because the ram 100 (ironing mandrel) has a certain diameter distribution along its length, the ironed can becomes a certain thickness - or thickness distribution - along its length

Have wall C, B, A. FIG. 4b illustrates the change in the diameter of the plunger 100 by means of a "transition point" 100a rounded without a transition, which leads from a first diameter to a second diameter of the plunger 100.

The forming process with which the neck region B of the can 1 is drawn in in order to make the diameter of the lid smaller and to be able to save material is not shown. It can be carried out as described in the prior art. The starting point for its implementation, however, is a changed thickness distribution d (x) that follows a certain mathematical function (geometry). The thickness distribution d (x) is shown schematically in FIG. 3b, with x = 0 the upper edge of the container wall is located; in the course of the container wall along section C in FIG. 1a, d = dp, - x = h (can height) at the lower end of the can.

If the thickness distribution is carried out as is shown in FIGS. 3a to 3e in individual examples, there are advantages in the reshaping of the feed area B, the axial loads on the can can be reduced in the shaping. Oil can be saved because the axial loads are reduced. Due to lack of

Lubricant also improves the porosity in the can. Finally, there are lower stripping forces of the ironed cup - after the ironing process according to FIG. 4a - when the ironed cup - the container body - is stripped by the ironing mandrel 100. Can continue

Trimmer malfunctions and loss of efficiency can be avoided for the reasons mentioned. The embodiment shown in FIG. 3a in particular allows material to be saved if the upper edge is provided with a thickness d ₂ at x <-0, which section is cut off before the Börde1 process for forming the double seam 3 is formed. Trimmer malfunctions can be avoided if the sheet metal section formed at the upper end at x = 0 is approximately the same as the wall thickness d _c and the fuselage above the trimmer line is cut off. Despite the avoidance of trimmer interference, less material is required. This is ensured by the rising slope 10, which merges into the thickened area d ^ _^ , which in turn merges via the slope 11 into the usual area C of the can wall. The latter has a thickness of d _c . d ₂ is chosen approximately equal to d _c ; d- ^ is about half the initial thickness d _{Q of} the cup before stretching. Figures 2 to 3e are not drawn to scale, the thickness d _c in the wall section C after the ironing process is approximately one third of the initial thickness d _Q. The chosen - not to scale - representation serves to clarify the differences in the mouth section with regard to their thicknesses.

Comparable to FIG. 3a in the end section A, which results in the fold 3 - according to FIG. 1b - is the FIGS. 3c and 3e.

In contrast to the aforementioned figures, the examples according to FIGS. 3b and 3d are those which choose a thickness d ₁ in the end region A, that is to say they do not differ from the usual sheet thickness d- ^ according to FIG. 2 in sections A and B. Instead, a central thickness step 12 is formed in these figures. This central step 12 leads via a further step 11 into the wall section C in FIG. 3b.

The central step 12 has an opposite step or bevel 13 in FIG. 3d, which leads into a renewed sheet metal thickening 11a. Only then is the slope 11 transferred into the wall section C. Common to all examples is at least one (additional) slope or thickness step 10, 12 in the upper end section A, B of the fuselage wall, if one excludes the transition step 11, which is normal in the prior art, from the wall thickness d _c to the end section thickness d- . Taking them into account, there are at least two thickness levels in the upper end section A, B.

According to the sketches of FIGS. 3a to 3e, the ram 100 according to FIG. 4a has the corresponding negative diameter geometry, so that the thickness steps 10, 11, 12, 13 are obtained during the ironing process.

The trimmer line is located between sections A and B, here the wall is cut. The trimmer line is advantageously provided such that it runs to the right of the outermost thickness change step 10 in the figures.

The examples suggest both a one-step sheet thickness step (FIGS. 3a, 3b), a two-step step (FIGS. 3c, 3d) and a three-step step (FIG. 3e). Two stages - stages characterize changes in thickness in section A or B - form a saddle which has a “low point” which corresponds to a ring plane 13a with thickness d ₄ (FIGS. 3d, 3e); the two thickness levels can, however, also lie in relation to one another in such a way that in FIG. 3c a ring hill 10a with the thickness d - _j _ is formed, limited by two bevels 10, 12 leading to thinner sheet thicknesses d ₂ , d ₃ .

All the aforementioned thickness levels are supplemented by a further thickness level 11, which leads into the wall section C with the thickness d, which makes up the largest part of the fuselage wall (x ^ -, ≤ x <h). With all the thickness reductions shown in section A, B corresponding to 0 ≤ x ≤ x _c , it is achieved that further thickness reductions can be carried out in the wall area C or in the bottom area 5, 6 of the can, because the axial forces when the section is drawn in (“snapped in”) B can be reduced.

The ironing mandrel according to FIG. 4b shows one

Transition area 100a, which is clearly shown in Figure 4a. The actual changes in diameter are so small that they would not be recognizable in the schematic image of FIG. 4a, which is why FIG. 4b illustrates a transition area 100a in a (mirror-image) enlargement of the detail.

It consists of a first segment, which is formed by a circular segment in cross-section, a central ramp-shaped area (which, viewed rotationally symmetrically, represents a circumferential surface of a cone) and a third area, which over a (in cross-section) circular segment section turns back into a cylindrical shape of the ironing mandrel 100 passes. The two circle segment transitions at the beginning and at the end of the ramp segment have transitions r1 and r3 (first and third areas) which are shown schematically. The ramp section R running between them corresponds to the ramp section R of FIG. 4a. It runs at a small angle a, which in the example is approximately 2 °. It can be adapted to the thickness geometry to be created according to FIGS. 3a to 3e in such a way that the shorter the corresponding transition 10, 12 or 11 is, the steeper it is and the steeper the greater the change in thickness in the corresponding ramp area R is. It should be borne in mind that the usual sheet thickness is 0.24 mm, i.e. 240 μm, so that the thickness reductions shown macroscopically in the pictures are actually in the order of magnitude mentioned (1/3 to 1/2 of the named thickness).

Claims

Expectations : 1. A method for changing the forming behavior of, in particular, stretched can bodies (1), in which an additional thickness step (10, 12, 13) is introduced into the upper edge region (A, B) of the container body (1). 2. The method according to claim 1, wherein two thickness increments (12, 13; 10, 12) are provided, wherein a thickness increment is a constant to step change in the sheet thickness. 3. The method of claim 1 or 2, wherein the upper end (A) of the fuselage wall (1) is formed into a thickness (d ₂ ) which is significantly less than the largest Sheet thickness (d ₃ , d ₄ , d ₁ ) in the remaining upper edge area (A, B). 4. The method according to any one of the mentioned claims, in which two bevels (10, 12; 12, 13) - which lead to and from different sheet thicknesses (d (x)) - are introduced facing or facing away from each other (Figure 3c, Figure 3d) . 5. The method according to any one of the claims mentioned, in which a thickness gradation (11) from the upper edge region (A, B) to the sheet of the rest of the fuselage (C) takes place during the ironing (100, 20, 21, 22, 23, 24). 6. The method according to any one of claims 3 to 5, wherein the thickness at the end (A) of the fuselage (1) corresponds approximately to the thickness (d _c ) of the wall of the essential part of the fuselage (1). 7. The method according to any one of the claims mentioned, wherein the greatest sheet thickness (d- _j in the upper edge region (A, B) about 1/2 and the sheet thickness of the stretched, remaining wall (C) about 1/3 of the initial thickness (d _Q ) of the sheet before stretching. Ironing mandrel or ironing plunger (100) for a method according to one of the preceding claims, in which more than one change in diameter (100a) is provided in the axially rear ironing region. Body part (1) of a three-part or stretched two-part tin can, which has at least two continuous to step thickness variations (10, 12, 13, 11) in the sheet in the upper edge area (A, B).