EP0200167B1 - Process to facilitate cold forming - Google Patents

Description

The invention relates to a method for facilitating the cold forming of metals by applying a film of lubricant.

To facilitate cold forming, it is known to produce a film of lubricant on the metal surface, thereby reducing wear and friction of workpieces or tools. The lubricant film can e.g. B. by a lubricating oil, which may have added high-pressure additives and / or viscosity regulators, if the workpieces are to be subjected to a relatively slight deformation. In the case of workpieces with intended strong deformation, on the other hand, it is customary to first apply a resin dissolved in organic solvent as a lubricant and then to apply a lubricating oil.

Taking into account the fact that the possible uses of metals are becoming increasingly diverse, certain problems arise when metals provided with conventional lubricating layers are to be subjected to severe deformations in a manner which could not have been predicted beforehand. In addition, the lubricants diluted with usually organic solvents are disadvantageous insofar as, after the reshaping, the residue of the lubricating film cannot be removed in a simple manner with the aid of an alkaline cleaner, but organic solvents which impair the workplace and the environment are required.

The object of the invention is to eliminate the disadvantages inherent in the known, in particular the aforementioned methods for facilitating cold forming, and to provide a method which also allows heavy forming and can be removed from the lubricating film residues in a simple manner using alkaline cleaners.

The object is achieved in that the method of the type mentioned is designed in accordance with the invention in such a way that the surfaces of the metals to be formed are first dried by drying an aqueous solution, the polyethyleneimine with a molecular weight of 1,000 to 100,000 and a thermoplastic water-soluble Contains resin, produces a film with a layer weight of 0.5 - 15 g / m ² (given as dry weight) and then applies a lubricating oil to this film.

The polyethyleneimine to be used in the process according to the invention generally has a branched structure as a result of primary, secondary and tertiary amine groups. If the molecular weight is less than 1,000, the toughness of the film that can be obtained is comparatively low, so that film breakage can occur during cold forming. With a molecular weight of over 100,000, the lubricating properties of the lubricating film are still good, but handling is made more difficult by the high viscosity of the film former. The molecular weight should be in the range of 30,000 to 100,000.

The thermoplastic resin can be, for example, polyacrylic acid ester, polyacrylamide, polyvinylpyrrolidone or a copolymer of ethylene imine and other vinyl compounds such as saponified polyvinyl acetate. Other vinyl compounds copolymerizable with ethyleneimine include vinyl acetate, styrene, methyl vinyl ether, acrylamide, vinyl pyrrolidone and the like. The thermoplastic resin preferably consists of modified polyvinyl acetate, in particular one with a degree of saponification of 70% or more.

Another preferred embodiment of the invention is to produce the lubricant film by drying a solution in which the weight ratio of polyethyleneimine to thermoplastic resin is 1: 4 to 1: 0.67.

Finally, depending on the type of cold forming provided, it may be advantageous to add solid lubricants such as graphite, molybdenum disulfide, talc, Teflon, boron nitride, calcium carbonate, melamine / cyanuric acid adducts and the like to the solution forming the lubricant film.

The film weight obtained in the first stage of the process is important insofar as an inadequate lubricity can be achieved with a layer weight of less than 0.5 g / m ² and seizure between tool and workpiece can occur in extreme cases of deformation. If the layer weight exceeds 15 g / m ² , the lubricant is stripped from the forming tool or the drawing die and the forming device is thereby contaminated.

Particularly favorable results are achieved if, in a further advantageous embodiment of the invention, a film with a layer weight of 0.5 to 3 g / m ² in the case of a subsequent cold forming, e.g. B. by deep drawing or rolling, or from 5 to 10 g / m ² in the case of a subsequent cold forming, for. B. is generated by wire or tube drawing or cold extrusion.

The lubricating film applied in the first stage additionally has the ability to protect the metal surface made of iron or steel from corrosion, so that the articles banded in this way can be stored without hesitation.

The lubricating oil to be applied in the second stage is conventional and can contain greases, oils or mineral oils as a basis. The thickness of the lubricating oil layer should be 0.5 to 5 gMiM2.

According to a preferred embodiment of the invention, a salt of primary, secondary or tertiary amine with high molecular weight organic acid or an organic phosphate ester is applied to the film initially produced as a lubricating oil. In it, the aliphatic amine should have a carbon chain of 8 to 22 carbon atoms. As high molecular acids come in particular fatty acids with 8 to 22 carbon atoms, dicarboxylic acids with 4 to 12 carbon atoms and polymerized fatty acids, eg. B. dimeric fatty acids. The phosphate ester can be an alkyl ester with 12 to 30 C atoms or a polyoxyethylene alkyl phosphoric acid ester. If the cold forming is in the rolling and a cooling effect is desired in addition to the lubricating effect of the lubricating oil, the lubricating oil can be used as an aqueous emulsion.

By adding a barium salt of petroleum sulfonate, the corrosion protection of the Me talles - especially made of iron or steel - continue to be improved.

The aqueous solution according to the first stage can in the usual manner, for. B. by diving, spraying, brushing. Floods or roll application can be applied. Drying takes place in air, expediently with warm air. The lubricating oil is then applied. This is also done in a conventional manner.

In special processes of cold forming, e.g. B. during deep drawing, it is sometimes sufficient to bring only one side of the metal surface into contact with the solution containing polyethyleneimine and thermoplastic resin and consequently to dry a lubricating film only on this surface. The Schrriieröl is applied on both sides.

With the aid of the method according to the invention, it is possible to save energy, to simplify the process of preparing the metal surfaces and to work in an environmentally friendly manner. The film applied in the first stage adheres firmly to the metal surface, so that stripping on contact between the tool and the workpiece does not occur in the first phase of the cold forming process. During the forming process, the workpiece heats up to temperatures of approx. 100 - 150 ° C as a result of forming work and frictional heat. The lubricant film is plasticized and can follow the surface enlargement without breaking the film.

As the experiments preceding the conception of the invention have shown, the advantage achieved with the invention is not achieved if the lubricating oil is added to the aqueous solution of polyethyleneimine and thermoplastic resin. In this case, the adhesion of the film is greatly reduced, with the result that the lubricating film is stripped off during cold forming.

The invention is illustrated by the following examples, for example and in more detail.

Examples 1 to 3

10 wt .-% aqueous solutions of different mixtures of polyethylene imine and modified polyvinyl acetate with mixing ratios according to Table 1 were applied to steel blanks (90 mm diameter; 0.8 mm thickness; steel quality SUS 304) with a doctor blade, so that after drying with hot air of 100 ° C resulted in a layer weight of 5 g _{/ m} ² .

This layer was provided with a lubricating oil which consisted of 90% by weight of mineral oil and 10% by weight of rapeseed oil.

• Faltenhalterdruck: 1 t
• Stempelgeschwindigkeit: 200 mm/min.
• äßerer Stempeldurchmesser: 40 mm
• Schulterradius: 4 x Stempelradius
• das Ziehverhältnis in Prozent = (1-D/Do) x 100 wobei
• D_o der Außendurchmesser der Ronde und
• D der Außendurchmesser nach dem Ziehen ist.

Then the blanks were formed by deep drawing. For this purpose, the test device Model No. TF 102-12 from Tokyo Weighing and Testing Machine Mfg. Co. The test conditions were:

• Fold holder pressure: 1 t
• Stamp speed: 200 mm / min.
• Outer punch diameter: 40 mm
• Shoulder radius: 4 x stamp radius
• the draw ratio in percent = (1-D / Do) x 100 where
• D _o the outer diameter of the round blank and
• D is the outside diameter after drawing.

The results of the deep drawing and the removability of the remaining lubricating film are shown in Table 3. To remove the lubricating film, the drawn workpieces were immersed in a 3% aqueous cleaner (Cleaner 4360 from Nihon Parkerizing Co., Ltd.) heated to 50 ° C. for 20 minutes. The degree of grease film removal was then determined by wetting with water.

Examples 4 to 7

Die erzielten Ergebnisse hinsichtlich Tiefziehbarkeit und Entfernbarkeit des restlichen Schmiermittels sind in Tabelle 3 angegeben.In a further test series, blanks coated with the products and under the conditions of Examples 1 to 3 were tested. Only the ratio of polyethyleneimine and modified polyvinyl acetate was different and corresponded to the information in Table 2.

The results obtained with regard to deep drawability and removability of the remaining lubricant are given in Table 3.

Comparative experiment: The same steel blanks were used as in Examples 1 to 7, but a conventional lubricant was applied. The results for this are also shown in Table 3.

Table 3 shows that the process according to the invention is associated with excellent results compared to the conventional process. The best results were achieved with the procedure according to Examples 1 to 3, in which the ratio of polyethyleneimine to thermoplastic resin is in the preferred range. However, the superiority compared to conventional methods is also clearly visible in the results which were obtained in accordance with Examples 4 to 7 and which did not permit finished drawing. Finally, Table 3 shows that when the method according to the invention was used, the lubricant residues remaining after the shaping could be removed perfectly, whereas it could hardly be removed in the comparison test.

Claims (6)

1. A process to facilitate cold-working of metals by the application of a film of lubricant, characterized in that on the surface of the metals to be worked an aqueous solution, which contains polyethyleneimine having a molecular weight from 1,000 to 100,000 and a thermoplastic water-soluble resin, is dried in situ so as to produce thereon a film having a layer weight of 0.5 to 15 g/m² (stated as dry weight) and a lubricating oil is subsequently applied to that film.

2. A process according to claim 1, characterized in that the film is produced by drying in situ of a solution which contains polyethyleneimine having a molecular weight from 30,000 to 100,000.

3. A process according to claim 1 or 2, characterized in that the film is produced by drying in situ of a solution in which the thermoplastic resin consists of modified polyvinyl acetate which has a degree of saponification of 70 % and more.

4. A process according to any of claims 1 to 3, characterized in that the film is produced by drying in situ of a solution in which the weight ratio of polyethyleneimine to thermoplastic resin is 1 : 4 to 1 : 0,67.

5. A process according to any of claims 1 to 4, characterized in that a film having a layer weight from 0.5 to 3 g/m² is produced in case of a subsequent cold-working by deep-drawing or rolling and a film having a layer weight of 5 to 10 g/m² is produced in case of a subsequent cold-working by wire or tube drawing or by cold extrusion.

6. A process according to any of claims 1 to 5, characterized in that the lubricating oil which is applied to the initially applied film consists of a salt of a primary, secondary or tertiary amine with an organic acid having a high molecular weight or of an organic phosphate ester.