The invention relates to a wall-ironing tool for manu¬ facturing metal containers with a cylindrical body and a bottom by deep drawing, which tool comprises a mandrel and at least one wall-ironing ring unit. Such a wall-ironing tool is known. Known in the prior art is the use of a mandrel and/or a wall-ironing ring of hard-metal. Hard-metal is a comparatively heavy material ha¬ ving a specific mass of 14,000-15,000 kg/m ³ . This results in large inertia forces, particularly for the mandrel recipro- eating at great speed.

A further drawback of the use of hard-metal is limited acid resistance, whereby the relevant surfaces may not be touched with the fingers and it is necessary to rely on spe¬ cial cooling means with a known pH. In order to avoid these drawbacks the invention proposes a wall-ironing tool of the type stated in the preamble which has the characteristic that the mandrel and/or the or each wall-ironing ring, at least the active surfaces thereof, consist of ceramic materi¬ al. Ceramic materials have a specific mass in the order of magnitude of 2,700 kg/m ³ and are therefore about as light as aluminium, and therein have the advantage of possessing ex¬ treme hardness. Hard-metal has a hardness of approximately 1300-1600 Knoop, while the ceramic material aluminium trioxi- de (A1 ₂ 0 ₃ ) for instance has a hardness of 1900-3000 Knoop.

Depending on the desired hardness other materials may also be considered suitable, for example silicon nitride (Si ₃ N ₄ ) which has a hardness in the order of 1400-3400 Knoop. Titanium carbide (TiC) possesses a hardness of approximately 2300- 3500 Knoop. Amorphous boron carbide (ABC) has a hardness of 4000-5000 Knoop. while by way of comparison it is mentioned that diamond has a hardness of between about 5700 and 10400 Knoop.

It will be seen from the above survey that ceramic ma¬ terials are available in extreme hardnesses. This is favoura¬ ble for the tool life of the wall-ironing tool, particularly that of a wall-ironing ring. On average a smaller number of tool changes is hereby necessary, which results in cost sa¬ ving. When after a very large number of operating cycles, for example 500,000, a wall-ironing ring no longer satisfies the required norm, it can be polished again by the manufacturer, whereby it can once again be used, for instance for 500,000 cycles.

It is known to arrange a hard-metal wall-ironing ring in a casing. Usual is a shrinking operation in the order of 0.15 mm. For this purpose the casing, which consists for in¬ stance of tool steel, has to be greatly heated. The drawback here is that the material of the casing can undergo an essen¬ tial change and become softer, whereby a part of its effect is lost. Because of the relatively large shrink it is also possible that the material is loaded to or even beyond the yield point, which is understandably a highly undesirable situation. It has to be understood in this respect that cera¬ mic materials may not be subjected to tensile strain. That is the reason why use has to be made of a casing wherein the wall-ironing ring is arranged through shrinkage. The proper¬ ties of the material of the casing are therefore of decisive importance.

It can occur that as a result of a disturbance a can becomes jammed between a wall-ironing ring and the mandrel. It must then be possible to retract the mandrel without the wall-ironing ring losing its coupling to its casing because of the thus exerted loading. In the case of a wall-ironing ring enclosed exclusively by shrinking the loosening force for a wall-ironing tool for soft-drink containerss dimensioned in typical manner lies in the order of 50,000 N or 5 tons. In the case of a wall-ironing ring unit, wherein the wall-ironing ring and the casing are mutually connected not only by shrinkage but also by adhesive, the loosening force lies at approximately 120,000-130,000 N or 12 tons.

It is important that the adhesive used can grip onto a relatively large surface. To this end the co-operating

surfaces can be cleaned by glass-blasting and thus also be provided with very small pores.

As a suitable adhesive can be considered professional quality Loctite 307. It is noted here that other types of adhesive can also be used, provided they are heatable without degradation to in the order of 100°C-200°C.

The following procedure can be observed for the manu¬ facture of a wall-ironing ring unit. A rough ceramic wall- ironing ring is ground into approximately the desired form. The obtained ring is accurately measured, whereafter a casing is brought to the desired size in exactly the same shape. The co-operating surfaces are subsequently cleaned by sand¬ blasting and a finishing is carried out using a cloth with chlorothene, whereby a very lightly porous, completely grease-free surface is obtained on both sides. The relevant outer surfaces of the ceramic wall-ironing ring are coated with a thin layer of Loctite 307. Ensured in the meantime is that a finished casing is available at an increased temperature, for example 120°C, whereby the inner diameter is enlarged through the thermal expansion. The ceramic ring provided with an adhesive layer is then placed into the central opening of the casing, for example under light pressure, wherein the adhesive is given the opportunity to cure for a period of time. The wall-ironing ring unit is ready for finishing for example after a curing time of one hour. This finishing may consist of a final grinding and polishing operation.

In the drawing: fig. 1 shows a cross section through a wall-ironing ring unit; and fig. 2 shows on enlarged scale the detail II from fig. 1.

A wall-ironing ring 1 of ceramic material is arranged in an annular casing 2 of high-grade tool steel. As shown in fig. 2, the central hole 3 of the casing 2 displays a substantially cylindrical inner surface 4 and a shoulder face 5. The ceramic wall-ironing ring 1 has a posi¬ tioning edge 6 which, in addition to serving for easy posi¬ tioning of the wall-ironing ring 1, also serves to ensure a

reliable locating of the wall-ironing ring 1 against the shoulder face 5. The corner zone 7 might namely still contain a few flaws which could hinder reliable positioning of the wall-ironing ring 1. The wall-ironing ring 1 displays a more or less cylindrical portion 8 and a slightly conically taper¬ ing first portion 9 and connecting thereto a slightly more pronounced conical portion 10. Situated on the downstream side is another conical portion 11.

The surfaces of the wall-ironing ring 1 co-operating with the cylindrical face 4 and the shoulder face 5 are provided beforehand with an adhesive layer.

With respect to the use of ceramic material it is fur¬ ther noted that while a ceramic material is exceptionally hard it is also brittle. One might be inclined to think that, as a result of the shock loading occurring each time a metal cup is introduced for the forming of a can, the material would tend to break. There is no need to fear this danger because of the very precise enclosure resulting from the shrinking operation.

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