EP0760784B1 - Stepped fold for a tin - Google Patents

Abstract

PCT No. PCT/DE95/01574 Sec. 371 Date May 13, 1997 Sec. 102(e) Date May 13, 1997 PCT Filed Nov. 14, 1995 PCT Pub. No. WO96/15036 PCT Pub. Date May 23, 1996An improvement in the shape of a fold in a tin can allows the use of sheet metal of lower gauge than that currently used. This is achieved with a fold geometry on a tin can which is closed off with a double fold, such as for a drink or food tin; by providing a continuous or stepped contour on the fold side; and by insuring that the lid hook is clearly in area-contact (positive fit) on its outer side with the free end of the body hook in its lower third. The invention may be applied to standard-gauge as well as thinner-gauge sheet metal, and generally results in a better seal.

Description

The technical field of the invention is the formation of a Fold on a can closed by a lid, such as beverage or Tin can made of tin. Such a fold has the task Lid and can also withstand relatively high forces from outside, for example by pressure or impact, and inside, for Example can be effective through overpressure or underpressure hold together and the interior of the can also compared to the To hermetically seal the outside atmosphere.

While the seam was previously soldered to seal it, a sealing compound has been introduced into the fold for a long time and sealed without a solder connection (cf. DE-A 21 34 034, there Figure 1; EP-A 445 721, there Figure 3; FR-A 2 327 149, there Figure 2; US-A 4,626,158, there Figure 12; US-A 2,327,424, there Figure 6). A double fold is without a compound (sealing material) already described in Fahr 1903, but without a seal To contain compound (see FR-A 334.017, there Figures 8, 9, 10). Such folds are no longer used - in favor of folds with compound used.

It is an object of the invention to improve the properties of a fold with compound, both in terms of its mechanical strength and in terms of a reliable and permanent hermetic seal; consequently, the fold should become more stable, especially when using sheets that are reduced by approximately 0.24 mm compared to sheet thicknesses used today.

This object is according to claims 1, 9 or 11 by a Targeted design of the fold geometry solved. By the according the invention improved folding geometry in the Production of can and / or lid processed thinner sheets be, with the same strength and tightness, or it can - when using the usual sheet thicknesses - a clear one higher strength and an even more reliable hermetic Sealing can be obtained. The high strength is due to a stronger clamping and locking of the folding elements in one limited area of the fold height achieved. This will make the fold more stable, which also leads to the possibility of using in the Thick reduced sheets leads (claim 8).

Due to the stronger clamping, the hermetic seal is also improved.

Because the additional clamping and locking only in the lower Area of the fold is done, the compound material is attached to it prevented from forming the fold from the top To migrate the fold area. Rather, the new fold geometry leads that direct sheet metal contact in the upper edge of the fold is avoided, so that here is under compression Sealant the hermetic sealing function better than at exerts direct sheet metal contact (claim 5).

In the preferred embodiment, the - is in the finished Fold - the area of the lid hook located below and outside with the above the free end of the fuselage hook Surface area in a fixed, preferably form-fitting system, while the upper area of the Cover hook noticeably radially towards the lower area is shifted outside, that is, from the adjacent sheet metal section the fuselage hook is spaced (claim 6). This gives a contoured outer fold surface, the two mentioned upper and lower areas continuously or in a preferably gentle, step into one another (claim 2).

The firm, preferably positive pressure of the Sheet metal areas thus only extend over the lower one Folding area (claim 6). This area is essentially cylindrical (claim 7). It decouples the fold width b from the Length tolerance of the fuselage hook.

The fold geometry can be seen on a cut through the fold seam check and determine a sealed can at any time.

In addition to improving the fold, the invention enables to work with sheet thicknesses below the usual dimensions can. The surface pressure of the sheet metal areas in the lower half to the lower third of the seam go so far that in the area of the lower edge of the fuselage hook mechanical locking occurs. The fold overall is much more stable, both when using conventional Sheets as well as those that, on the other hand, are in their Thickness are reduced.

The flat pressure in the lower fold area (claim 6, Claim 7) can be flanged on the free edge Fuselage hook lead to a level that is in Take over axis holding and locking function can.

The sealing or forming roll with which this fold contour achieved or created has two groove areas that face each other the roller axis have different diameters (claim 11, Claim 12). The two groove areas are mutually axial moved so as to form the transition area. The transition area (or more generally: the annular projection) opens into an approximately cylindrical shape (claim 13) to the lower area when forming the fold (claim 6, claim 7) to give such a shape. In the employed state runs the approximately cylindrical portion of the folding lock roller VR1 parallel to the outer surface of the Capping head VK.

Surprisingly, this not only improves stability lower sheet thickness, but also a decoupling of the Width b of the finished fold from the length tolerance of the Hull hook reached. The fold width b is only one of the used sheet thicknesses, the compound also loses its undesirable influence on the fold width b.

Figur 1

zeigt im Schnitt einen Doppelfalz gemäß dem Beispiel der Erfindung.

Figur 2

ist eine Falzgeometrie nach dem Stand der Technik.

An example of the invention is explained in more detail with reference to schematic drawings.

Figure 1

shows in section a double fold according to the example of the invention.

Figure 2

is a fold geometry according to the state of the art.

In both figures, in addition to the geometry of the fold, the geometry of the sealing head VK and (indicated) also the geometry of the sealing rollers VR and VR1 as a counter-contour to the respective outer contour of the fold are shown. The outer contour of the (inner) closing head VK, as can be seen in the manner shown in FIG. 2, can be used unchanged to achieve the geometry of the fold according to the invention, so that all inner sheet metal layers 2, 1, 2 a, 1 a with the exception of the upper region 2b of the outer layer 2b, 2c of the lid hook, lie flat against one another and are essentially cylindrical or slightly conical to the axis of the container.

Figure 1 shows a double fold according to an example of the invention. The can wall is denoted by 1, the lid with its core wall by 2.

The step 23 of the profile 30, 31 of the indicated fold-closing roller VR1 neutralizes the influence of the fuselage hook length tolerance ΔR _H on the fold width b. Furthermore, the lid hook is better clamped and mechanically locked in its lower region 2c by displaced lid material at 2d. This ensures the tightness of the fold, even with changing can internal pressure.

The sharper shaped lower section 2c of the fold becomes lead to an increase in folding stability in the form that especially with thinner cover and fuselage sheets, rolling up the finished fold is complicated by the inner pressure of the can and so that the use of thinner sheets is possible than is common today.

Figure 2 shows the fold design according to the prior art. Due to the geometries of the sealing head VK and the sealing roller VR (2nd operation) used here, the achievable fold width b is significantly influenced by a change (tolerance in the range R _Hmin <R _Hnom <R _Hmax ) of the trunk hook length R _{H of} the trunk hook 1a. Since the fold width b is an essential measure for evaluating the fold quality and is used for the basic setting of a closing machine, definition problems arise in FIG. 2 which make it impossible to comply with the current fold width tolerance Δb = ± 0.05 mm.

The lid hook is also insufficiently clamped in FIG. 2 , which can lead to leaks in the filled can, particularly in the case of thinner sheets.

In Figure 1 , the closed fold of a tin can is shown (upper, edge-side cutout in cross section), in the contouring according to the example of the invention. The lid hook 2a engages in the body hook 1a. Both lie tightly against each other in the overlap area. In the remaining area, a sealing compound 10 is provided.

To the fluctuation Δb of the fold thickness or fold width b reduce, the fold - the fold geometry - receives a gradation 23 to the lower area 2c. In the example it is the lower third. The step 23 stabilizes the fold. Is that radially inward directed flare pressure high enough, the end region 21 the fuselage hook 1a an additional lock 2d, the stronger seals, but at the same time also holding and compensating function takes over.

The difference dimension d shown in FIG. 2 (as a function of the body hook length R _H ) is replaced in FIG. 1 by a flat pressing of a lower region 2c of the outer cover ring section 2b, 2c on the lower edge region 21 of the body hook 1a. The drawn-in tolerance of ΔR _H no longer produces a difference dimension d (cf. FIG. 2); with d = 0 the influence of ΔR _H on b (the fold width) also becomes zero.

The height of the surface pressure should be equal to or greater than the expected length tolerance ΔR _H , in the example it is about 1.5 times as large. In the example, the fold height is approximately three times larger than the flat contact area 2c with a height of 1.5 · ΔR _H. The step 23 mentioned in the area 2c can be selected gently to more abruptly.

The closing device contains the pressure roller VR1 that with its groove contour 30, 31 the step 23 to the (cylindrical) lower Folding section 2c causes. The step 23 can be introduced immediately when folding (forming the fold); it can also be done in a separate step after Flaring the fold inserted on the outer contour of the fold become.

The corresponding procedure (one-stage or two-stage) is in the capping machine with the VR1 and VK capping head realized. Existing folding machines can be converted easily.

The plane of the fold is the plane that runs perpendicular to the axis of the box and lies approximately in the middle of the fold height that runs in the axis of the box. On average, it is illustrated in FIG. 2 on line b of the fold width.

Claims (13)

1. A configuration of seams on a can, e.g. for drinks or preserves, closed by a double seam, wherein continuous or stepped contouring (23) is provided on the outside (2c, 2b) on the seam and a hook (2a, 2b, 2c) formed on the lid is connected in extremely close-fitting (interlocking) manner to the outside (21) of the free end of a downwardly shaped hook (1a) on the body, characterised in that a sealing-place (20) is formed on the radially outer, axially upper end of the seam by a compound (10), not by contact between metal, the said contact between metal occurring in close-fitting manner in the lower region (2c) of the seam.
2. A seam configuration according to claim 1, wherein the contour (23) is in the form of a smooth or easy step.
3. A seam configuration according to claim 1 or claim 2, wherein the upper region (2b) of the double seam projects radially outwards to an appreciable extent relative to the lower region (2c) of the seam.
4. A seam configuration according to any of the preceding claims, wherein the seam is appreciably asymmetrical relative to the centre plane thereof, especially by about half to the entire thickness of the metal.
5. A seam configuration according to any of the preceding claims, wherein appreciably more compound (10) is provided at the sealing-place (20) above the central plane of the seam than below the said plane.
6. A seam configuration according to any of the claims mentioned, wherein the lower region (2c) of the seam is appreciably narrower than in the region (2b) above and the outer layer (2b, 2c) of the hook shaped on the lid abuts firmly and snugly against only the lower region (2c) of the end region (21) of the hook (1a) on the body, and especially has an approximately cylindrical shape relative to the axis of the can.
7. A seam configuration according to any of the preceding claims, characterised in that the body (1), the inner portion (2a), the region (2c) of the outer layer (2b, 2c) of the lid hook (2a, 2b, 2c) lying under the contouring (23), and the body hook (1a) in the lower region of the seam adjoin one another snugly and extend substantially cylindrically relative to the can axis.
8. A seam configuration according to any of claims 1 to 7, wherein the thickness of the metal is ≤ 0.23 mm, especially 0.22 mm.
9. A method of shaping, forming or contouring the seams of a double-seam closure according to any of the previous claims, wherein the seam formed or already existing in the lower end region (2c, 2d) is shaped more sharply or strongly on the exterior (23) so that owing to contact between metal, it seals more strongly in the lower outer region (2c, 21) than in the upper curved region (2b, 20).
10. A method according to claim 9, wherein, as a result of the sharper shaping, the seam is made asymmetrical relative to its centre plane.
11. A seam-closing roller for a seam-folding machine for applying a double-seam closure to tin cans (1) and lids (2) according to any of the preceding process claims, the roller (VR1) having a peripheral groove (30, 31) formed with a radially inward-extending annular projection (30), the annular projection having a substantially cylindrical shape.
12. A seam-closing roller according to claim 11, characterised in that its inner surface used for shaping is divided by a continuous or stepped transition region (23) into a first smaller-diameter grooved region and a second region having an appreciably larger diameter, measured from the roller axis to the projection or the base of the groove.
13. A seam-closing roller according to claim 11 or claim 12, wherein the annular projection (30) extends approximately parallel to the roller axis or the surface of the closing head (VK).

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