GB1602539A - Process for the production of metal cans - Google Patents

Description

(54) PROCESS FOR THE PRODUCTION OF METAL CANS (71) We, CARNAUD S. A. a French Body Corporate of 65 Avenue Edouard Vaillant, 92103 Boulogne, France, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to the manufacture of metal cans, more particularly to the manufacture of metal cans from circular blanks e.g. blanks which have been cut out from a metal strip. Metal cans of this type are usually called deep drawn bottom cans, and the bottom of such cans is integral with the side walls thereof.

Deep drawn bottom cans in which the ratio of the height to the diameter of the cans is generally from 1 to 1.5 are generally used for the packing of preserves, which may be either fruit or vegetables.

In one known technique for the production of cans of this type, commonly referred to as the "DRD" process, the procedure essentially comprises shaping a blank in one or more passes, e.g. by deep drawing. This results in a single working of the surface of the blank, the thickness of the blank being essentially retained throughout the shaping treatment, with the exception of the thickness which inevitably appears at the top of the resulting shaped blank.

This shaping technique, which has the advantage that it only requires relatively low investment in order to be put into effect, is very suitable where the ratio of height to diameter of the cans to be produced is less than one, as is the case with certain cans used for packing preserves. In addition, with this technique an initial blank of various thickness and/or qualities can be used depending on the requirements for each case. The bottom of the can obtained must be able to follow the deformations produced by the thermal sterilisation treatments which it is customary to apply to such preserves, without thereby impairing the properties of the can bottom.

However the use of this technique to produce cans having a height: diameter ratio greater than one presents certain technical problems which are generally difficult to solve.

For such cans, a plurality of successive shaping passes must be applied, taking into account the limits of surface deformation which each of these passes can individually achieve. In general a blank whose surface has already been provided with a protective coating is used to make a can. The protective coating is one which is capable of constituting the final protective coating ofthe can. Each shaping pass which the protective coating has to undergo can result in its deterioration, this risk being all the greater if the blank has to undergo a succession of such shaping passes.

Furthermore, the rate at which such shaping passes can be applied to one and the same blank is relatively limited.

Finally, since the worked blank practically does not vary in thickness except as stated above, its initial diameter, commonly called the cutting diameter, must be relatively great in order to obtain a given final can diameter. Consequently there will be substantial production of scrap from the strip from which such blanks are cut, and this will result in considerable and therefore relatively expensive consumption of material.

A second known technique for the production of metal cans from circular blanks, commonly referred to as the "DWI" process, comprises applying one or more shaping passes to a circular blank and then applying one or more drawing or stretching passes during which the blank is worked in respect of volume, and not in respect of surface as during the earlier shaping stage, taking into account the reduction of thickness to which it is then subjected.

Although this technique has the disadvantage of requiring relatively heavy investment, nevertheless it provides the advantage of permitting the economical production of cans having particularly thin walls, which are moreover produced from blanks having a relatively small cutting diameter. This has the overall consequence of producing cans of a given diameter with lower consumption of material than in the DRD technique.

Because of its characteristic drawing stage, the DWI technique is particularly suitable for the production of cans in which the ratio of height to diameter is greater than about 1.5, which is the case for example with cans used for the packing of certain beverages, particularly beer.

It is all the more suitable for the manufacture of such cans because an essential feature of these cans is that they should be able to withstand only a relatively moderate internal pressure. Such cans can have relatively small wall thicknesses. This is not the case for the packing of preserves.

Cans used for preserves must be able to withstand not only the pressure but also the internal vacuum to which they are subjected during the cooling which follows the thermal sterilisation process to which they are subjected.

Thus, the DRD technique is more suited for the production of cans in which the height to diameter ratio is lower than one, (i.e. cans suitable for packing preserves), and the DWI shaping-drawing technique is less suitable for such cans because of the need for relatively great wall thicknesses in these cans. For the production of cans in which the height to diameter ratio is higher than 1.5, (i.e. cans intended for packing aerated beverages), the DWI technique is the more suitable and the DRD technique is unsuitable, particularly because of the large consumption of material which it entails and of the difficulties which result from the repeated succession of shaping passes which this technique requires.

This leaves a range of cans in which the height to diameter ratio is from 1 to 1.5. To make such cans a difficult choice has to be made between the DRD and DWI techniques, particularly in cases where cans are intended for the packing of preserves. A technique commonly referred to as the DIR technique has been proposed for making such cans. This technique comprises subjecting a blank to at least one shaping treatment, to a drawing treatment, and to a further shaping treatment. In other words, by applying a combination of the DRD and DWI techniques the working of a blank is completed by a shaping treatment.

However, in the process usually proposed for the application of the DIR technique, e.g. as described in French Patent No.

2,226,227, major importance is attached to the drawing treatment, the drawing rate applied to the blank usually being at least equal to 35 O. Thus this technique is closer to the DWI technique than to the DRD technique.

In practice, because of the major role played by the drawing treatment, the DIR technique like the DWI technique has the advantage of enabling the initial blank to have a relatively small cutting diameter, because the initial thickness is greater, so that the consumption of material is relatively moderate. Generally speaking other conditions being equal, the cutting diameter of a blank when using the DIR technique is close to that required when using the DWI technique, and is therefore smaller than that required when using the DRD technique.

However, the DIR technique like the DWI technique also has the disadvantage of requiring relatively heavy investment.

Similarly, like the DWI technique, the DIR technique has the disadvantage that a blank provided with a protective coating cannot be used because such a coating would inevitably be irreparably damaged during the drawing treatment, and the disadvantage that during this drawing treatment special lubrication of the blank is required, so that it must subsequently be washed, which leads to additional expense.

Finally, in the DIR technique the blank must be able to withstand considerable drawing and therefore the material from which the blank is made must necessarily have a certain malleability. This malleability is difficult to reconcile with the characteristics of elastic flexibility which must be possessed by the bottom of metal cans intended for the packing of preserves.

Thus although the DIR technique is, like the DWI technique, particularly suitable for the production of metal cans in which the height to diameter ratio is higher than about 1.5 (e.g. as in cans normally used for the packing of aerated beverages), it is not as suitable as the DRD technique for the production of cans in which the height to diameter ratio is lower than one and it is not suitable for the production of cans in which the height to diameter ratio is I to 1.5, as is particularly the case with cans intended for packing preserves.

The present invention aims to provide a process for making cans falling within these two latter categories.

Accordingly, the present invention provides a process for the production of a metal can from a circular blank, which process comprises subjecting the blank to at least one shaping treatment, a drawing treatment which is such that the rate of reduction of thickness resulting therefrom is at most 25, and a further final shaping treatment.

Because of this low drawing rate, the process of the invention, which is far closer to the DRD technique than to the DWI technique, permits the use of blanks which are provided with a protective coating, even though for such blanks a slightly larger cutting diameter is needed than that which would be needed when using the DIR technique under the same conditions.

However this diameter is advantageously smaller than that which would be needed if the DRD technique were to be used, other conditions being equal.

Furthermore, since the drawing applied in the present process is slight, it can be performed without special lubrication of the blank and thus there is no need for the drawn blank to be subsequently washed.

Furthermore, the process of the invention provides the advantage of permitting the use of materials of more ordinary quality than those required in the DIR technique and these materials may be identical to those which cdn be worked by the DRD technique.

Finally, the present process does not need particularly large investment, especially since it can easily be performed by the use of a line normally used for the DRD technique by the mere addition to the line of a drawing station.

Because of the low drawing rate applied to the blank, the drawing may also be combined with a shaping treatment, that is to say it may be effected simultaneously with shaping using the same machinery.

Thus the process of the present invention combines the advantages of the DRD technique and the DWI technique, without having their disadvantages.

The present process advantageously permits drawing to be used to make cans usually made in the past by the DRD technique (i.e. cans in which the height to diameter ratio is generally below one), and/or by the addition of a drawing station, conventional equipment can be used to make cans in which the height to diameter ratio is from 1 to 1.5, particularly where such cans are intended for the packing of preserves.

The present invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic section of a circular blank suitable for forming a metal can by the DIR technique; Figures 2 to 4 are diagrammatic sections of the blank of Figure 1 in the course of the successive operations of shaping, drawing, and final shaping which are applied to it, Figure 4 being on a smaller scale than Figures I to 3; Figure 5 shows, on a larger scale, the portion of the blank indicated by V in Figure 4; and Figures 6 to 10 show diagrammatic -sections si ilar-to those of Figures 1 to 5 respectively of a circular blank treated in accordance with an embodiment of the process according to the present invention; and Figure 11 is a partial diagrammatic elevation of the working end of a punch used for the drawing stage of an embodiment of the process according to the present invention.

Referring to Figures 1 to 5, a circular metal blank 10 of a thickness El and of a cutting diameter D1 (Figure 1) is first subjected in accordance with the DIR technique to a shaping treatment which imparts to the blank a configuration in the form of a cup-shaped product 11 having an inside diameter D'1 and a height H1 as shown in Figure 2.

Since a shaping treatment essentially results in surface working of the blank to which it is applied, the wall thickness of the shaped blank 11 thus obtained is generally equal to the thickness El of the initial blank, particularly as regards the bottom 12 of the shaped blank.

In practice a shaping treatment of this kind imparts to the outer surface of the side wall pf a shaped blank 11 of this type a certain conicity which leads to excess thickness at the top of the side wall, but for the sake of simplicity and for greater clarity in the drawings this will be intentionally ignored for the present.

The shaped blank 11 is then subjected to a drawing treatment during which the side wall 13 of the blank passes between an annular die and a punch thereby to reduce the thickness of the side wall.

At the end of this drawing treatment a new cup-shaped rough product 14 is obtained, which as shown in Figure 3 has an inside diameter D'l identical to that of the shaped blank 11 from which it was formed but has a height H' 1 greater than the height Hl of the said shaped blank 11.

The thickness El of the bottom 15 of the cup 14 is equal to the thickness of the bottom 12 of the shaped blank 11 from which it is formed, but because of the drawing to which it has been subjected the thickness el of its side wall 16 is less than the former thickness El of the side wall.

The ratio El -1 El defines the drawing rate applied to the blank of Figure 2.

In the DIR technique such a drawing rate is at least 35% and is usually higher than 35%.

In a final stage, the cup-shaped product 14 is subjected to a final shaping operation at the end of which a can 18 is obtained as shown in Figure 4 which has overall the final desired configuration except for any concentric rings in its bottom wall 19 and/or any annular shaping of its side wall 20 which may be desired.

According to the DIR technique described in French Patent No. 2,226,227 the final shaping phase is carried out with a punch with side walls which have a frustoconical chamfer of small depth situated at a chosen distance from the free end of the punch. The side wall 20 of the resultant can 18 has a corresponding chamfer 21 at an equivalent distance from its bottom 19. The chamfer 21 forms an abrupt transition zone between an upper portion of the can with a side wall 20 of a thickness which is equal to the thickness el of the side wall 16 of the cup-shaped product 14 of Figure 3, and a bottom portion of the can with a side wall 20 which is a continuation of the bottom 19 of the can, the side wall 20 having a thickness equal to the thickness El of the bottom 15 of the said cup-shaped product 14.

The bottom 19 of the resultant can 18 has a thickness generally equal to the thickness El of the original blank 10, its inside diameter corresponds to the desired diameter dl and its height H"1 is greater than the height H'1 of the cup-shaped product 14 from which it was formed.

Preferably, and as illustrated in Figure 4, the final shaping phase also leads to the formation of a collar 22 along the free edge of the resulting can 18. The collar 22 is directed generally radially outwards and to which a turning treatment is applied.

Referring to Figures 6 to 10, the process of the present invention is used for the production of a can 38 having an inside diameter d2, a side wall thickness e2, and a height H"2, these dimensions being equal to the corresponding dimensions of the can 18 obtained with the previous blank 10, i.e.

equal to the diameter dl, the side wall thickness el, and the height H"1 of can 18.

In accordance with the present invention the can 38 of Figure 9 is produced starting from a circular blank 30 which as shown in Figure 6 has a diameter D2 greater then the diameter Dl of blank 10 and a thickness E2 less than the thickness El of blank 10.

As before, the blank 30 is first subjected to a single pass shaping treatment to product a cup-shaped product 31 as shown by the solid lines in Figure 7, or is subjected to two or more passes of a shaping treatment to give the cup-shaped product shown diagrammatically by broken lines in Figure 7. At the end of this stage of the process a cup-shaped blank 31 which has an inside diameter D'2 and a height H2 is obtained.

The shaping process gives a cup-shaped product 31 having a bottom wall 32 and side walls 33 having respective thicknesses which are substantially equal to the thickness E2 of the original blank 30.

In practice, for reasons which will be explained below, for products 31 and 11 having diameters D'l and D'2 which are the same, the height H2 of cup-shaped product 31 is greater than the height H I of the cupshaped product 11 obtained by the shaping of the initial blank 10.

As before, the cup-shaped product 31 is then subjected to a drawing treatment which gives a new cup-shaped product 34 which as shown in Figure 8 has the same inside diameter D'2 as cup-shaped product 31 but has a reduced wall thickness e2.

In the process of the present invention, the theoretical drawing rate or rate of reduction of wall thickness, which is defined as being the ratio E2e2 E2 is less than 25%.

This theoretical drawing rate is preferably from 10 to 20%.

However, in practice this drawing rate may be zero if all that is required is merely the sizing of the shaped product, the purpose of this operation being to bring to the top of the side wall of the cup-shaped product the material which after the shaping treatment forms the gradually increased thickness of the side wall leading to the said conical shape.

In spite of this, the bottom wall 35 of the cup-shaped product 34 still retains a thickness substantially equal to the thickness E2 of the original blank 30 and, because of the reduced drawing, its height H'2 is substantially equal to the height H'l of the corresponding cup-shaped product 14 previously obtained from the blank 10.

However, according to one embodiment of the present invention the punch 37 used for effecting this drawing treatment as shown in Figure 11 has an end with side walls forming a frustoconical shape and, has for example, a 'conicfty" C of from 5 to 30 minutes of arc. This leads to a cup-shaped product 34 having a side wall 39 which has an inside surface which in a lower region adjoining the bottom 35 of the cup is generally frustoconical as shown at 40 in Figure 8. This provides an advantageous gradual transition from the wall thickness e2 of the top portion of the side wall 39 of the cup-shaped product 34 to the wall thickness E2 of the bottom 35 of the cup-shaped product 34.

Cup-shaped product 34 is then subjected to a final shaping treatment, at the end of which, particularly with a procedure comparable to that described previously, a can 38 of desired configuration is obtained (Figure 9). The frustoconical portion 40 of the side wall 39 of the cup-shaped product 34 which is to be subjected to a shaping treatment is favourable for the production of a can 38 having a side wall 42 which is free from any accidental longitudinal creases or incipient creases and having a graduation of thickness which is practically impossible to detect by touch or by eye because it extends over a relatively great height. In Figure 10 this graduation of thickness, which is of generally frustoconical shape, has been intentionally exaggerated as indicated by reference numeral 43. The. frustoconical portion 43 separates an upper portion of the side wall 42 of thickness e2 from a bottom portion of the side wall 42 having a thickness E2.

The base of the side wall 42 of the resulting can 38 is nevertheless advantageously reinforced, particularly at its junction with the bottom 44 of the can and it is thus possible to impress therein a ring of any kind, for example a ring facilitating stacking, that is to say a ring which projects towards the outside and facilitates the stacking of the can on a can of a similar type.

A turning operation is also applied in the same way as before to the collar 41 of the resulting can 38.

The original blank 30 is preferably of a metal which has a protective coating on its surface, since the low rate of drawing to which this blank is subjected in the present process enables the protective coating to retain its properties of flexibility, adhesion, protection, and homogeneity. The blank may, for example, be of tin-plate, black iron, or lacquered iron.

Furthermore, the thickness of the top portion of the side wall of a can obtained by applying the process of the present invention is in practice at least equal to 75% of the thickness of its bottom.

A further advantage of the present process is that when the drawing rate to be used is very low, it is envisaged that the drawing treatment can be carried out simultaneously with the first shaping treatment, and using the same machinery.

WHAT WE CLAIM IS: 1. A process for the production of a metal can from a circular blank, which process comprises subjecting the blank to at least one shaping treatment, a drawing treatment which is such that the rate of reduction of thickness resulting therefrom is at most 25%, and a further final shaping treatment.

2. A process according to Claim 1, wherein said rate of reduction of thickness is from 10 to 20%.

3. A process according to Claim 1, wherein the object of the drawing treatment is merely sizing of the can and the rate of reduction of thickness is zero.

4. A process according to Claim 1, Claim 2 or Claim 3, wherein the drawing treatment is effected with the aid of a punch having an end with an outer surface which is frustoconical.

5. A process according to Claim 4, wherein the frustoconical surface has a conicity of from 5 to 30 minutes of arc.

6. A process according to Claim 1 substantially as hereinbefore described with reference to, and as illustrated in, Figures 6 to 11 of the accompanying drawings.

7. A can obtained by a process as claimed in any one of Claims 1 to 6.

8. A can according to Claim 7, wherein the thickness of the upper portion of the side wall of the can has a thickness which is at least 75% of the thickness of the bottom of the can.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. Cup-shaped product 34 is then subjected to a final shaping treatment, at the end of which, particularly with a procedure comparable to that described previously, a can 38 of desired configuration is obtained (Figure 9). The frustoconical portion 40 of the side wall 39 of the cup-shaped product 34 which is to be subjected to a shaping treatment is favourable for the production of a can 38 having a side wall 42 which is free from any accidental longitudinal creases or incipient creases and having a graduation of thickness which is practically impossible to detect by touch or by eye because it extends over a relatively great height. In Figure 10 this graduation of thickness, which is of generally frustoconical shape, has been intentionally exaggerated as indicated by reference numeral 43. The. frustoconical portion 43 separates an upper portion of the side wall 42 of thickness e2 from a bottom portion of the side wall 42 having a thickness E2. The base of the side wall 42 of the resulting can 38 is nevertheless advantageously reinforced, particularly at its junction with the bottom 44 of the can and it is thus possible to impress therein a ring of any kind, for example a ring facilitating stacking, that is to say a ring which projects towards the outside and facilitates the stacking of the can on a can of a similar type. A turning operation is also applied in the same way as before to the collar 41 of the resulting can 38. The original blank 30 is preferably of a metal which has a protective coating on its surface, since the low rate of drawing to which this blank is subjected in the present process enables the protective coating to retain its properties of flexibility, adhesion, protection, and homogeneity. The blank may, for example, be of tin-plate, black iron, or lacquered iron. Furthermore, the thickness of the top portion of the side wall of a can obtained by applying the process of the present invention is in practice at least equal to 75% of the thickness of its bottom. A further advantage of the present process is that when the drawing rate to be used is very low, it is envisaged that the drawing treatment can be carried out simultaneously with the first shaping treatment, and using the same machinery. WHAT WE CLAIM IS:

1. A process for the production of a metal can from a circular blank, which process comprises subjecting the blank to at least one shaping treatment, a drawing treatment which is such that the rate of reduction of thickness resulting therefrom is at most 25%, and a further final shaping treatment.

2. A process according to Claim 1, wherein said rate of reduction of thickness is from 10 to 20%.

3. A process according to Claim 1, wherein the object of the drawing treatment is merely sizing of the can and the rate of reduction of thickness is zero.

4. A process according to Claim 1, Claim 2 or Claim 3, wherein the drawing treatment is effected with the aid of a punch having an end with an outer surface which is frustoconical.

5. A process according to Claim 4, wherein the frustoconical surface has a conicity of from 5 to 30 minutes of arc.

6. A process according to Claim 1 substantially as hereinbefore described with reference to, and as illustrated in, Figures 6 to 11 of the accompanying drawings.

7. A can obtained by a process as claimed in any one of Claims 1 to 6.

8. A can according to Claim 7, wherein the thickness of the upper portion of the side wall of the can has a thickness which is at least 75% of the thickness of the bottom of the can.