EP0251192A2 - Lubricant for metal formation - Google Patents

Abstract

The aqueous lubricant for metal cold-forming contains 10 to 35% by weight of a thermosetting acrylate-based resin having a glass transition point of -10 to +25 DEG C, 3 to 15% by weight of wax and 0.5 to 5% by weight of a surfactant, the thermosetting resin/wax weight ratio being adjusted to 2-12. Particularly suitable resins are of the general formula -(Ra-Rb-Rc-Rd)n-, Ra, Rb, Rc and Rd being different monomers and "n" being a degree of polymerisation from 1,000 to 50,000. The wax should have a melting point above 45 DEG C. In the process for faciliting the cold-forming of metallic workpieces, the lubricant is applied to the metal surface, dried on in air to form a coating weight from 0.5 to 30 g/m<2>, heated to a temperature of 80 to 120 DEG C (object temperature) and finally cured.

Description

The invention relates to an aqueous lubricant for the cold forming of metals and a method for facilitating the cold forming of metallic workpieces with the aid of this lubricant.

In cold forming, it is customary to provide the workpieces with a lubricant coating in order to reduce the frictional resistance between the metal surface of the workpiece and the forming tool. Basically two methods are used for this. One is to use lubricants with high pressure additives or viscosity regulators when lower degrees of deformation are required. The other provides for a resin-based lubricant film to be applied first from the organic phase and then a lubricating oil if heavy reshaping is intended.

Recently, the use of lubricants for a variety of purposes has been increasing steadily. In the case of severe forming conditions, the aforementioned lubricant systems no longer perform their task satisfactorily. Certain problems with regard to environmental protection and workplace hygiene result from the frequently present content of organic solvents. Aspects of flammability also often play an important role.

Of further importance when using lubricants is the question of whether or not after forming Lubricant film remaining on the workpiece can be removed in a simple manner, for example with the aid of an alkaline cleaner.

The object of the invention is to provide a lubricant for the cold forming of metals, with the aid of which even heavy forming can be carried out in a satisfactory manner, which can do without organic solvents and whose residues can be removed in a simple manner after the forming.

The object is achieved by formulating the aqueous lubricant of the type mentioned at the outset in accordance with the invention in such a way that it contains from 10 to 35% by weight of an acrylic-based thermosetting resin with a glass transition point of from -10 to + 25 ° C 3 to 15% by weight of wax and 0.5 to 5% by weight of surfactant, the weight ratio of thermosetting resin to wax being set to 2 to 12.

Usually, the aqueous lubricant is allowed to air dry, if necessary by additional heating.

According to a preferred embodiment of the invention, a lubricant is used which contains a thermosetting resin of the general formula - (Ra-Rb-Rc-Rd) _n , where Ra, Rb, Rc, Rd represent different monomers and "n" is the degree of polymerization is 1,000 to 50,000.

The order of the individual monomers in the resin is irrelevant. The value for "n" within the limits of 1,000 and 50,000 should be chosen such that a resin with a glass transition point of - 10 ° C to + 25 ° C results. The resin can be prepared by polymerizing a mixture of the monomers at a temperature of 50 to 60 ° C for a period of 5 to 7 hours. The monomers can also be polymerized in solution or dispersion. Depending on the method, solvents other than water, such as ethanol or isopropanol, can be used or co-used.

Further advantageous embodiments of the invention consist in formulating the lubricant with a thermosetting resin,

in which Ra is at least one monomer from the group consisting of vinyl toluene, styrene, methyl methacryl and acrylonitrile and has a share of 20 to 70% by weight of the resin,

- In the Rb at least one monomer from the group of an acrylic ester, obtained by reacting acrylic acid with a primary aliphatic alcohol having 1 to 12 carbon atoms, or a methacrylic ester, obtained by reacting methacrylic acid with a primary aliphatic alcohol having 3 to 12 carbon atoms Is atoms and has a share of 20 to 70% by weight of the resin,

in which Rc is at least one monomer from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid, 2-hydroxyethyl methacrylate phosphoric acid ester or salts thereof and has a share of 1 to 15% by weight of the resin,

- in which Rd is at least one monomer from the group consisting of 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, N-methylolacrylamide or ester thereof, diacetone acrylamide and glycidyl methacrylate and has a share of 1 to 20% by weight of the resin.

Suitable waxes include paraffin wax, animal or vegetable oil, higher fatty acids, higher alcohols, esters of higher fatty acids and higher alcohols, higher fatty acid amides, higher fatty acid amines and the like. In order for the lubricant film to remain firm, it is appropriate according to a further advantageous embodiment to use waxes with a melting point above 45 ° C. One way to increase the melting point of the wax is to add hydrogen to double bonds.

Particularly suitable surfactants are those of the anionic or nonionic type. Examples of anionic surfactants are sodium alkylnaphthyl sulfonate, sodium alkylbenzenesulfonate and Turkish red oil. Examples of nonionic surfactants are polyoxyethylene alkyl ethers with the alkyl group of a higher alcohol, polyoxyethylene nonylphenol ether, polyethylene glycol fatty acid esters and sorbitol fatty acid esters.

The surfactant is particularly responsible for the emulsification or dispersion of the wax in water. For further improvement, mechanical stirring can be carried out with the addition of a homogenizing agent.

Another expedient formulation of the aqueous lubricant consists in an additional content of solid lubricant additive. Examples include graphite, molydand disulfide, talc, Teflon, boron nitride, calcium carbonate, melamine, cyanuric acid adducts and the like.

The advantage of using a thermosetting resin based on acrylate arises from the following facts. The cold forming of metals generates heat that increases the temperature of the workpiece and tool. The heavier the forming, the greater the heat development and thus the higher the temperature. With continuous forming, heat accumulation also occurs. Compared to thermoplastic resins based on acrylate, which soften when heated above the glass transition point and therefore cannot prevent contact between the workpiece and the tool, this contact and consequently corrosion is avoided with certainty with thermosetting resins based on acrylate. Thermosetting resins do not have this advantage par excellence. Many resins harden in such a way that they cannot follow the expansion of the workpiece associated with the deformation. As a result, the film of lubricant tears and there is the aforementioned contact between the workpiece and the tool. Many of the thermosetting resins are also no longer easy to remove after forming, e.g. with the help of an alkaline cleaner.

Surprisingly, in the thermosetting resins based on acrylate with a glass transition point from - 10 ° C to + 25 ° C, the advantages of excellent adhesion on the Metal surface, the flexibility or adaptability to the elongation and the ease of removal of the lubricant film after the forming united. At a glass transition point below - 10 ° C, the lubricant coating becomes too soft so that it can be removed during the forming process. At values above + 25 ° C, the coating becomes too hard and the adaptability to the elongation of the workpiece is no longer sufficient.

In this respect, the best results are achieved if a lubricant is used that contains an acrylic-based resin with a glass transition point from 0 to + 5 ° C.

As extensive studies have shown, the monomer amounts Ra - in the amounts specified in each case - are in particular for the hardness and tensile strength, that of Rb in particular for the extensibility, that of Rc in particular for the adhesion to the metal surface and the dispersibility of the resin and that of Rd in particular responsible for an additional improvement in liability.

If the proportion of the monomer Ra falls below 20% by weight, the lubricant coating can become too soft, if it exceeds 70% by weight it can become too hard. In both cases, a perfect separation effect for the workpiece / tool is not guaranteed with certainty.

If the proportion of the monomer Rb is below 20% by weight, the glass transition point is increased and the coating formation at room temperature can deteriorate. At a If the proportion exceeds 70% by weight, the hardness of the lubricant coating can become too low.

The effect of the proportions of the monomers Ra and Rb is largely opposite, so that their balance is important.

If the proportion of the monomer Rc is outside the prescribed limits, the adhesion of the coating can be too low and the removability of the remaining lubricant film with an alkaline cleaner can be impaired (at less than 1% by weight). On the other hand, the viscosity of the lubricant can increase significantly, which would make it more difficult to apply, and its hygroscopicity may increase, which would be associated with reduced adhesion due to the absorption of water (at more than 15% by weight).

If the monomer content of Rd falls below 1% by weight, the crosslinking of the resin can become unsatisfactory, as a result of which the resistance under the influence of heat could decrease. At values above 20% by weight, the degree of crosslinking can increase so much that the flexibility of the lubricant coating is lost. A proportion of 5 to 15% by weight is optimal for the hydroxyalkyl methacrylate, and a proportion of 1 to 5% by weight is optimal for N-methylolacrylamide or glycidyl methacrylate.

The weight ratio of thermosetting resin to wax is important insofar as the adhesion of the lubricant coating decreases when it falls below 2, so that the coating tears. If l2 is exceeded the lubricating effect after. The preferred range is 4 to 6.

It is important for the surfactant content that the dispersibility decreases too much when the concentrations are too low and that the lubricity of the coating is impaired when the concentrations are too high. In addition to the preferred anionic or nonionic type surfactants, cationic or amphoteric surfactants can also be used.

The lubricant is applied to the cleaned workpieces by dipping, spraying, brushing, pouring or roller application at room temperature. Then it is dried. The mixture is expediently dried in air, then heated to 80 to 120 ° C. and finally hardened. The procedure improves the adhesion of the lubricant coating. The height of the coating weight depends essentially on the intended forming. Among other things, are regulated by the concentration of the lubricant components.

In the case of low degrees of deformation, 0.5 to 5 g / m² are advantageous, in the case of high degrees of deformation 5 to 30 g / m² (indicated as a dry coating).

With the aid of the invention, lubricant coatings with dry weights of 0.5 to 30 g / m 2 can be applied, with which any conventional cold forming can be carried out. The coating has excellent adhesion and release properties. When the coating is heated to 100 to 150 ° C as a result of the formed and Frictional heat follows the shape of the workpiece without breaking the film, effectively preventing it from seizing. After the deformation, the remaining lubricant film can be removed in a simple manner using an alkaline cleaner.

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

Examples 1 to 5

SUS 304 quality stainless steel pipes, pickled and rinsed with water, were lubricated with various lubricants at 20 ° C for a period of 1 min. treated in diving. The components contained in the lubricants with regard to thermosetting resin and wax are described in more detail in Tables 1 and 2 below.

After drying in air for one hour, it was dried further with air at 100 ° C. for 30 minutes. The layer weight produced was within the range from 10 to 15 g / m². The tubes were then drawn on a drawing bench and evaluated for their appearance and the removability of the lubricant film remaining on the surface.

The drawing conditions were

To determine the removability of the lubricant film remaining after drawing, the tubes were immersed in an alkaline solution at 90 ° C. for a period of 1 hour. The solution contained 3% by weight sodium hydroxide, 1.5% by weight sodium tripolyphosphate and surfactant. The degree of removability was assessed visually.

The results are shown in Table 3.

Sheets of the same steel quality with the dimensions 50 × 100 × 0.8 mm were treated with the same lubricants under identical conditions as stated above for the pipes. They were then subjected to the Bauden test to determine the friction coefficient and the sliding number until the occurrence of contact marks.

The test results are set out in Table 4.

Comparative Example 1

Steel pipes with the quality and pretreatment as in Example 1 were provided with an oxalate coating using a commercially available oxalation solution (Ferrbond A; 35 g / l, accelerator l6; lg / l from Nihon Parkerizing Co.) (treatment temperature 90 ° C., treatment time 10 min .). After water rinsing the tubes were at 80 ° C for 3 min. treated in a lubricant solution (Bonderlube 235 from Nihon Parkerizing Co; 70 g / l) and dried. Steel sheets were treated in the same way. The tests described in Example 1 were then carried out.

Tables 3 and 4 contain the results.

Comparative Example 2

Steel pipes of the quality and pretreatment described in Example 1 were min. dipped in a resin diluted with toluene in a ratio of 1: 1 (Hangsterfer III QD from Hangsterfer) and then air-dried for 1 day. The layer weight produced was 10 g / m². After further application of a lubricating oil (J-1 from Hangsterfer), the tubes were drawn and evaluated as indicated in Example 1. Correspondingly treated sheets were subjected to the Bauden test.

The test results are set out in Tables 3 and 4.

Comparative Example 3

The experiment according to Example 1 was repeated with lubricant 1, but the resin no. l not the networking component Rd (HEMA). The layer weight ranged from 10 to 15 g / m².

The test results obtained for tubes and sheets are again shown in Tables 3 and 4.

Comparative Example 4

The test according to Example 1 was carried out with lubricant no. 3 repeated, but the resin contained No. 3 not the cross-linking component Rd (HPA).

The test results obtained for tubes and sheets are set out in Tables 3 and 4.

As Table 3 shows, the lubricant coatings produced with the lubricants according to the invention have excellent lubricating properties. They are significantly better than the lubricant coatings produced using the comparison tests. Furthermore, the lubricant coatings produced according to the invention are far superior to the other lubricant coatings in terms of removability after drawing.

With regard to the Bauden test, Table 4 illustrates the better friction coefficient and the higher resistance to seizure phenomena obtained with the coatings according to the invention compared to known coatings.

Claims (11)

1. Aqueous lubricant for the cold forming of metals, characterized in that it contains 10 to 35% by weight of a thermosetting resin based on acrylate with a glass transition point of - 10 to + 25 ° C, 3 to 15% by weight. Wax and 0.5 to 5 wt .-% surfactant, the weight ratio of thermosetting resin to wax is set to 2 to 12. 2. Lubricant according to claim l, characterized in that it contains a water-curable resin of the general formula - (Ra-Rb-Rc-Rd) _n - where Ra, Rb, Rc, Rd represent different monomers and "n" the degree of polymerization with is 1,000 to 50,000. 3. Lubricant according to claim l or 2, characterized in that it contains a thermosetting resin in which Ra is at least one monomer from the group vinyltoluene, styrene, methyl methacrylate and acrylonitrile and has a proportion of 20 to 70 wt .-% in the resin . 4. Lubricant according to claim 1, 2 or 3, characterized in that it contains a thermosetting resin in which Rb contains at least one monomer from the group of an acrylic ester, obtained by reaction of acrylic acid with a primary aliphatic alcohol having 1 to 12 carbon atoms , or a methacrylic ester, obtained by reacting methacrylic acid with a is primary aliphatic alcohol with 3 to 12 carbon atoms and has a share of 20 to 70 wt .-% in the resin. 5. Lubricant according to one or more of claims 1 to 4, characterized in that it contains a thermosetting resin in which Rc is at least one monomer from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid, 2-hydroxyethyl methacrylate-phosphoric acid ester or salts thereof and has a proportion of 1 to 15% by weight of the resin. 6. Lubricant according to one or more of claims 1 to 5, characterized in that it contains a thermosetting resin, in which Rd at least one monomer from the group 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, N-methylolacrylamide or ester thereof , Diacetone acrylamide and glycidyl methacrylate and has a share of 1 to 20 wt .-% in the resin. 7. Lubricant according to one or more of claims 1 to 6, characterized in that it contains a wax with a melting point above 45 ° C. 8. Lubricant according to one or more of claims 1 to 7, characterized in that it contains an anionic and / or nonionic surfactant. 9. Lubricant according to one or more of claims l to 8, characterized in that it additionally contains a solid lubricant additive. l0. Lubricant according to one or more of claims 1 to 9, characterized in that it contains a thermosetting resin based on acrylate with a glass transition point of 0 to + 5 ° C. 11. A method for facilitating the cold forming of metallic workpieces with the aid of the lubricant according to one or more of claims l to l0, characterized in that the lubricant is applied to the metal surface, in air with the formation of a coating weight of 0.5 to 30 g / m² dries up, heated to a temperature of 80 to 120 ° C (object temperature) and finally hardens.