NO752874L - - Google Patents

Description

Container and method of manufacturing thereof.

The invention relates to containers made from sheet steel, by drawing a bowl which is drawn again.

Beer cans are known which are made of aluminum or tin-coated steel, such as tinplate in the form of sheets, by drawing a bowl which is then reshaped by means of drawing tools, comprising a punch and one or more sinkers, and comprising tools for dimensional drawing. Such boxes have a bottom wall that is essentially the same thickness as the material that is introduced into it. the tool, and side walls that are thinner than the bottom. They are usually internally coated to prevent corrosion, and the outside of the cylindrical side walls are decorated. However, the tin coating is expensive.

According to the invention, a method is provided by drawing a box from a sheet of mild steel or black tin/

and the method is characterized by the fact that the steel surface is treated chemically to produce a surface with a regulated ability to retain lubricants, after which lubricant is applied to the treated surface and a bowl is pulled from the plate and the bowl is lubricated again before any renewed drawing or dimensional deep drawing of the walls .

According to a preferred embodiment of the present method, the chemical treatment is carried out by applying a solid coating containing a phosphate radical to the plate. The coating is preferably chosen from iron phosphate, zinc phosphate, calcium phosphate or manganese phosphate, but it can also be a mixed coating.

The lubricant is a lubricant for press tools and is preferably an emulsion of oil in water.

The invention also provides a box which is characterized by having a bottom wall that is thicker than the side wall, the bottom wall extending downwards and inwards from the side wall to a raised bead and upwards and inwards to a plate which is capable of containing internal pressure.

Various embodiments of the invention will now be described in more detail as examples with reference to the drawings, of which Fig. 1 schematically shows a piece of sheet steel provided with layers for retaining lubricant, Fig. 2 shows a schematic section through the material shown in

Fig. 1 with lubricant added, and

Fig. 3 schematically shows part of a press and tools for

to demonstrate a sequence of manufacturing steps.

According to the embodiment shown in Fig. 1, the plate 1 consists of mild steel of black tin which has been tanned and surface-treated so that it is suitable for drawing. Such a finish is designated as finish 1, finish 2 or finish 3. A suitable surface roughness is approx. 8.89/^m CL.A. The plate is treated chemically to form a solid coating 2 on the steel surface. Suitable coatings include: Iron phosphate present in an amount of 2.15-21.52, preferably 6.46, mg/dm.

Zinc phosphate applied in an amount of 10.76-215.20, preferably 107.60, mg/dm.

Zinc phosphate or calcium phosphate applied in an amount of 5.38-107.60, preferably 26.90, mg/dm.

Manganese phosphate applied in an amount of 10.76-107.60, preferably 32.28/mg/dm

Other phosphate radical containing coatings may be suitable and the coating thickness on one side of the plate may be different from the coating thickness on the other side for reasons explained in more detail below.

The coated plate is then lubricated with a suitable lubricant, examples of which include mineral or vegetable metalworking oils. A suitable example is an emulsion consisting of 10% mineral oil and 2-5% fatty acid in water. Such an emulsion acts as both a lubricant and a cooling agent for tools. However, other emulsions are suitable.

Fig. 2 shows how the lubricant 4 is located on the surface of the coating 2 and penetrates into the spaces between the crystallites of the coating, part of which is indicated by 3. The lubricant can be applied on both sides, but it is advantageous to apply it only on one side for reasons explained in more detail below.

The coated and lubricated steel plate is placed in a press with a tool that punches out a disc which is drawn to a bowl 11 with a larger diameter than the desired final container. The bowl 11 is then transferred to a further press 13 of a known type and with tools which are shown schematically in Fig. 3. These tools comprise a holder 5 for the raw material, a punch 6, a matrix 7, a first deep-drawing ring 8 and another deep-drawing ring 9 and a bottom-forming block 10. If necessary, more than two deep-drawing rings can be used. A line 12 is used for supplying lubricant to the press tool and is provided with three outlets. Through the outlet 12A, lubricant is supplied to the first deep drawing ring, through the outlet 12B to the second deep drawing ring and through the outlet 12C to the bowl 11 and the drawing nozzle 7. The lubricant is continuously circulated through the line and the tool to a storage container 14.

The holder 5 for the raw material is brought down into the bowl 11 and rests against the upper surface of the drawing nozzle 7, whereupon the drawing is started by the punch 6 pushing the bowl 11 through the drawing nozzle 7 to thereby reduce the diameter of the bowl and increase its height. During this operation, the wall thickness of the bowl is kept substantially equal to the thickness of the bottom of the bowl by known means, such as a regulated pressure for the holder for the raw material or by deep drawing in the neck 7A of the nozzle 7. In any of these ways, a bowl is formed which is substantially free of folds and variations in wall thickness.

As the cup emerges from the drawing nozzle 7, it encounters a mist of lubricant which exits through the outlet 12A to lubricate the cup so that it is ready for deep drawing by the punch 6 advancing it to the first deep drawing ring 8.

The wall thickness of the newly drawn bowl is reduced as the punch forces the bowl through the first deep drawing ring 8, due to the fact that the clearance between the punch 6 and the ring 8 is less than the thickness of the metal, and the wall thickness of the bowl is reduced

-1 further in a similar manner when forced through the other

deep drawing ring 9. Further lubricant is supplied between the deep drawing rings 8 and 9 in the form of a mist of lubricant which comes out through outlet 12B.

During deep drawing, the wall material is pulled upwards along the punch so that a frictional engagement between the inside of the bowl and the punch will ease the load on the bottom of the box. This is the reason why it is advantageous to use as little lubrication of the inside of the bowl as possible and to regulate the surface roughness of the steel in contact with the punch. Each nozzle's working surface is exposed to a favorable lubrication by a combination of the processed solid coating and lubricant.

After the deep drawing, the box is guided so that it comes into contact with a bottom shaping block 10. During the withdrawal, the box is removed from the punch 6 in a known manner, such as by means of external mechanical removal devices 15 which can be used together with an ejection device (not shown) in the punch. The box is then degreased and washed. They can be decorated and provided with an upper neck in a known manner.

Cans produced by the described method can be used for a number of different products, including both heat-treated food and drinks. The can HL shown on the block 10 in Fig. 3 is particularly suitable for beverages due to the pressure-resistant end wall comprising a thick, concave raised portion 112 and a peripheral channel 113 connecting the end wall with the thin side wall 114. Cans for heat-treated foodstuffs and which requires an end wall which enables expansion and contraction of the product during processing, is also covered by the invention. Such boxes usually have a main wall with essentially the same thickness as the end wall, and the end wall is divided into fields to enable such movement.

Although the solid coatings described above provide a suitable surface for the application of protective coatings and decorations, a similar result can be achieved with an etching treatment. Such an etching treatment will, however, have to be regulated very carefully to avoid grain boundary cracks in the bowl of the press tool.

With the tool described, the component being processed comes clear of each die before it enters the next, whereby the load on the press is limited to the work to be performed in one step at a time. Tools with nozzles and rings arranged close together are known, but not preferred because this gives less opportunity for heat to be dissipated.

Although the invention has been described in connection with chemically formed coatings with a phosphate radical, certain electrophoretically deposited coatings, such as aluminum coatings, will also provide surfaces with the necessary ability to retain lubricant.

The invention provides a method for the production of seamless cans, where a bowl of black tin with a phosphated surface is formed and drawn and deep drawn using a fluid consisting of (a) an emulsion containing an additive capable of withstanding a very high pressure , or (b) a hydrocarbon containing interfacial lubricants and/or additives capable of withstanding very high pressure.

The invention also provides a method

for the manufacture of seamless cans, where a shell of black tin without a phosphated surface is formed and drawn and deep drawn using a fluid which is a hydrocarbon containing interfacial lubricants and/or additives capable of withstanding very high pressures.

The invention is therefore essentially based on the recognition that a black tin plate can be drawn and the walls deep drawn if the fluid used has the necessary lubrication and cooling properties. Phosphating the black tin facilitates lubrication so that a larger group of fluids can be used, but these must still be of a higher quality than the lubricants used for drawing and deep drawing of white tin.

The metal can be treated e.g. by immersion in an aqueous phosphating solution for 10 -150 s at a temperature of 50-90°C. The metal plate used to form the bowl, or the bowl itself, can be phosphated, preferably the metal plate. It is preferred to phosphatize both the inside and outside of the bowl, although occasionally it may be advantageous to phosphatize only the outside. Suitable cations for the phosphate can be iron, zinc or preferably a combination of zinc and calcium. It is preferred to phosphatize the metal with 5.38-107.60, preferably 10.76-64.56, mg of phosphate per dm<2>surface. It is unnecessary to have a strong phosphating which can even be harmful.

By "emulsion" as used herein is meant an aqueous emulsion of a hydrocarbon oil. The oil can make up 2-30% by weight of the emulsion, and suitable emulsifiers and additives to ensure a stable emulsion can be chosen from materials known in the art.

The hydrocarbon oil can consist of a paraffinic or naphthenic lubricating oil fraction obtained from petroleum and with a viscosity of 15-700, preferably 20-300, est at 38°C. An additive capable of withstanding very high pressures is required if an emulsion is used. The term "additive capable of withstanding very high pressures" as used herein is intended to denote an additive which acts by reacting with the metal surface, e.g. by sulfidation or chlorination. Suitable additives are thus sulphurous fatty oils and acids, chlorinated paraffins and other suitable reactive halogen compounds, sulphated vegetable oils and alkyl and aryl polysulphides. The amount of such an additive can be 0.5-50, preferably 5-40, wt% of the undiluted concentrate.

An alternative and preferred fluid for use with phosphated black tin is a hydrocarbon oil. The superior lubricating properties of hydrocarbon oils compared to emulsions enable a reduction in the amounts of additives used or lead to improved results when using an additive capable of withstanding very high pressures.

The hydrocarbon may be a paraffinic or naphthenic lubricating oil fraction obtained from petroleum and preferably with a viscosity of 100-500, preferably 200-300, est at 100°C. Additives capable of withstanding very high pressures can be used as stated above for the emulsion lubricant, and preferably in an amount of 5-40% by weight of the oil.

Additionally or alternatively, an interface lubricant can be used. By the term "interface lubricant" as used herein is meant a compound, preferably a polar compound, with greater affinity towards metal than the lubricant and therefore capable of acting as an antiwear additive. Examples of suitable additives are organophosphorus salts, e.g. alkyl or aryl phosphates or phosphites, organothiophosphates, e.g. zinc dialkyldithiophosphates, fatty acids or esters, e.g. oleic acid, soaps, e.g. sodium stearate, amines, e.g. oleylamine, and long-chain alcohols, e.g. cetyl alcohol. The antiwear additive may be present in an amount of 0.1-30, preferably 1-10,% by weight of the oil.

For the embodiment where a non-phosphated black tin is used, as indicated above, it is necessary to use a hydrocarbon oil containing an additive which is able to withstand very high pressure. The oil and the additive can be as described above, with the amount of the additive preferably being 5-40% by weight of the oil, but it is also possible to use 100% additives that are able to withstand very high pressures and obtained from natural fats.

One of the fluid's functions is to absorb the significant amount of heat that develops during the draw. Hydrocarbon oils will have a lower heat capacity than emulsion lubricants, and it may: be necessary to take additional precautions to avoid overheating, such as e.g. introduction of known means to improve the heat transfer, such as e.g. aluminum alkoxides.

Each of the below stated combinations of material and lubricant was used for the continuous production of cans using conventional drawing and wall deep drawing equipment for the production of cans.

Example 1

Plate of mild steel with 26.90 mg zinc/calcium phosphate per dm 2and lubricated with 25% of emulsion of a soluble oil containing 20% sulphurous fat.

Example 2

Plate of mild steel with 26.90 mg zinc/calcium phosphate per

dm 2 and lubricated with pure hydrocarbon oil containing 5% oleic acid and with a viscosity of 264 est at 100°C.

Example 3

Plate of mild steel with 26.90 mg zinc/calcium phosphate per

2

dm and lubricated with pure hydrocarbon oil containing 10% sulfur.

fat and with a viscosity of 253 est at 100°C.

Example 4

Plate of mild steel lubricated with a pure hydrocarbon oil containing 40% sulfur-containing grease with a viscosity of 254 est at 100°C.

Claims (8)

1. Procedure for drawing a box from a sheet of mild steel or black tin, characterized in that the steel surface is treated chemically to form a surface with regulated properties to retain a lubricant, after which a lubricant is applied to the treated surface and a cup is withdrawn from the plate and the cup is re-lubricated before any subsequent renewal drawing or.wall deep drawing. 2. Method according to claim 1, characterized by. that at least one wall depth drawing is used after the third drawing. 3. Method according to claim 1 or 2, characterized in that the chemical treatment is carried out by applying a solid coating containing a phosphate radical to the plate. 4. Method according to claim 3, characterized in that iron phosphate, zinc phosphate, calcium phosphate or manganese phosphate is applied as phosphate coating. 5. Method according to claims 1-4, characterized in that a lubricant for press tools is used as lubricant. 6. Method according to claim 5, characterized in that an emulsion of oil in water is used as lubricant. 7. Method according to claim 6, characterized in that an emulsion comprising 10% mineral oil and 2-5% fatty acid is used. 8. Box, characterized in that it has a bottom wall that is thicker than the side wall, the bottom extending downwards and inwards from the side wall to a fixed bead and upwards and inwards to a record that is. isand ti 1 to contain internal pressure.