GB2174713A - Process for lubricating a metal surface - Google Patents

Description

SPECIFICATION Process for lubricating a metal surface When a metal article is subjected to cold working it is necessary to provide it initially with a lubricant coating so asto reduce friction and wear ofthe metal and the working tools. When the degree of cold working is relatively low it is sufficientto form the lubricant coating from a lubricating oil, often including a high pressure additive or other lubricant improver.

When the article is to be subjected to more severe cold working processes it may be necessary to provide a more effective lubricant coating, for instance a twostage coating obtained by applying a resin lubricant from a solution in organic solvent followed bya lubricating oil.

However this system is not always totally effective during severe cold working conditions, the use of an organic solvent can be inconvenient, and it is difficult to remove the lubricant coating with an alkali cleaner after cold working. However for many purposes easy removal of the lubricant coating is necessary.

It is know to improve a lubricant coating by initially providing a chemical conversion coating underneath an upper lubricating layer but it is undesirable to have to rely upon this as it renders the process inadequate when the metal substrate is a metal on which it is difficult to obtain a satisfactory conversion coating, for instance a stainless steel.

It has therefore been ourobjectto provide a lubricant coating that can give satisfactory lubrication propertiesforseverecoldworkingandyetwhich can readily be removed by an alkali cleaner and that preferably does not necessitate the formation of an underlying chemical conversion coating on the metal surface.

In the invention a lubricant coating is formed on a metal surface by applying to the surface an aqueous solution containing a plyethylene-imine and a thermo plastic water-soluble resin and drying the resultant aqueous coating to form a dryfilm having aweightof 0.5to 15 g/m2, and applying a lubricating oil tothefilm.

The polyethylene-imine used in the invention preferably is a branched structure, ratherthan a wholly linear compound, containing primary, secondary or tertiary amino groups. Its molecular weight is preferably in the range 1,000 to 100,000, most preferably 30,000 to 100,000. If the molecular weight is too low, forinstancebelow 1,000, the film may have inadequate toughness forsevere cold working and may be subject two rupture during cold working. If the molecularweight is undesirably high, for instance above 100,000,the lubricating properties may remain satisfactory but the viscosity of the composition may be become undesirably high.

Thethermoplasticresin may be selected from materials such as acrylic ester polymers, polyacrylamide, polyvinyl pyrrolidone, copolymers of ethyleneiminewith othervinyl monomers such as vinyl acetate, styrene, methyl vinyl ether, acrylamide or vinyl pyrrolidone, our a polyvinyl acetate. The preferred thermoplastic resin is a polyvinyl acetate that has a saponification degree of 70% or more.

The ratio ofthe polyethylene-imineto thethermoplasticwater-soluble resin is preferably in the range 1 :4to 3:2.

The aqueous composition may include solid lubri cant,forinstance graphite, molybdenum disulphide, talc, polytetrafluoroethylene (for instance the material sold underthetrade markTeflon), boron nitride, calcium carbonate or melamine/isocyanuric acid adduct.

The dry coating weight of the aqueous composition must be at least 0.5 g/m2 as otherwise the lubricity may be inadequate and even seizure may occur. Ifthe dry coating weight is above 15 g/m2 there is a riskthat the coating will be squeezed offthe metal surface by the working tool or die and this may become plugged with coating material. Preferably the dry coating weight is 0.5 to 3 g/m2when the cold working is press working or rolling and 5 to 10 g/m2 when the cold working is a process such as wire drawing,tube drawing orcoldforging.

In addition to providing a good baseforthe subsequent lubricating oil,the coating over an iron surface can have a rust preventing effect.

Rust preventitive additives may be included to promote this.

The aqueous composition may be applied to the surface by processes such as immersion, spraying, brushing,flowing or roll coating.Thecoating may then be dried, for instance in hot air.

The lubricating oil that is applied overthe dry film may be any conventional fluid lubricant and may be based on, or consist of, one or more fats or oils, including mineral oils. The lubricant is often applied in the form ofan emulsion. Preferably a fatty salt of an aliphatic amine is included in the lubricant. The fatty component may be duetothe aliphaticamine orto the id from which the salt is formed, or both. Preferably the aliphatic amine is a primary, secondary ortertiary amine having 8to 22carbon atoms.The salt-forming acid is preferably a fatty acid having 8to 22 carbon atoms, a dicarboxylic acid having 4to 12 carbon atoms, a dimeric or other polymerised fatty acid, a phosphate ester having 1 to 30 carbon atoms, our a polyoxy ethylene alkyl phosphate ester.

A rust preventive additive such as a barium salt of an oil sulphonate may be incorporated in orderto protect metal surfaces such as iron from corrosion.

Itis necessaryto apply the lubricating oil afterthe aqueous polymer composition because application of a single aqueous composition containing the polymers and the lubricating oil will give inadequate adhesion ofthe polymers, and thus of the lubricant coating, to the metal with the result that the lubricant film is liable to be stripped from the surface during cold working. In the invention however the dried polymericfilm and the lubricant coating adhere satisfactorily to the underlying surface and so metal to metal contact between the article and the working tool are prevented at least in the initial stages of cold working. During the cold working processthetemperature of the metal article may be raised up to, for instance, 100 to 1 500C by the heatofdeformation and friction and yet this does not lead to serious rupture and breakage ofthe underlying polymeric coating.

The application ofthe lubricating oil may be by any convenienttechnique, forinstance any ofthe applica tion methods described above.

When the article is a plate, for instance a steel plate, that is to be subjected to press working it is often sufficient that only one side ofthe plate should be provided with the lubricant coating of the invention, the other side merely being coated with the lubricating oil.

Thethickness ofthe lubricating oil coating in the various processes ofthe invention is preferably in the range 0.5 to S nm.

The invention is of particularvalue on iron and steel articles, especially stainless steel articles. Preferably the metal article has not been given a chemical conversion treatment.

Afterthe cold working process, the lubricant coating can be removed, for instance by a conventional alkaline cleaner.

The process ofthe invention issimpletooperate, does not involve the need for chemical treatments associated with chemical conversion processes, provides a good lubricantfilm, and provides a lubricant film that can easily be removed. In particularthe process lends itself to utilisation atthejob site where the working is conducted.

Example 1 A 10% aqueous solution ofa polyethylene-imine and a modified polyvinyl acetate as given in Table 1 was appliedto onesideofan SUS 304 steel plate of 90 x 0.8tmmwith a bar coater so thatthe dry coating weight was 5 glum2, and the coating was dried with a hot air at 100 C. The film was further coated with a mixed oil of 90% of a machine oil and 10% of a rape oil as a lubricating oil, and then deep draw working was conducted with a deep drawing testing machine. The removability ofthe lubricating film remaining on the steel surface afterworking was tested. The results are shown in Table 3.

Table 1 Example Resin Ingredient 1 2 3 a. Polyethylene-imine 30 Parts 40 Parts 60 Parts b. Modified polyvinyl acetate 70 Parts 60 Parts 40 Parts Compounding ration (b/a) 2.33 1.5 0.67 The polyethylene-imine was EPOMIN P-1 000 (trademark of Nippon Shokubair Kagaku Kogyo Co.

Ltd.), and had a molecularweight of 50,000-60,000 and a viscosity of 400-900 cps (25 C). The modified polyvinylacetatewasGOHSENOLNH 18(trademark of The Nippon Synthetic Chemical IndustryCo. Ltd.) having a polymerisation degree of 1500 or more and a saponification degree of 98-99% and was water soluble.

Example 4-7 A deep drawing test was conducted after coating with the same polyethylene-imine and modified polyvinyl acetate as in Example 1 except using the compounding ratios listed in Table 2, followed by coating with a lubricating oil. The removal test ofthe lubricating film remaining on the steel surface after the deep drawing test were conducted. The results are given inTable3.

Table 2 Example Resin Ingredient 4 5 6 7 a. Polyethylene-imine 5 10 70 95 Parts Parts Parts Parts b. Modified polyvinyl 95 90 30 5 acetate Parts Parts Parts Parts Compounding ratio (b/a) 19 9 0.43 0.04 Comparative Example 7 Using the same stainless steel plate as in Example 1, and NIHON KOHSAKU UY's No.660 commercially available, was applied thereto in a weight of 6 g/m2.

The test plate was subjected to the lubricating test and the removing test of the residual lubricating film in the same fashion as in Example 1. The results are shown in Table 3.

Table 3 Test Lubricating test Removing test of Drawing ratio, % residual lubricating film Example1 drawn off 0 Example2 drawn off 0 Example3 drawn off 0 Example 4 20 0 Example 5 16 0 Example6 14 0 Example7 16 0 Comparative Example 1 9 X 0Completely removed X-Scarcely removed The lubricating test was by a Deep Drawing Testing Machine, Model No.TF 102-12 (manufactured by Tokyo Weighing and Testing Machine Mfg.Co.). The test conditions were: Blankholderpressure 1 ton Punch ascending speed 200 mm/min External diameter of punch 40(p Shoulder radius 4R Drawing ratio % = 1 -D/Do)x1 00 where Do: Outside diameter of blank, D: Outside diameter after drawing.

The removal test ofthe residual lubricating film was performed by immersion in a 3% aqueous solution of FINE CLEANER 4360 (manufactured by Nihon Pa rkerizing Co. Ltd.) at 80 C for 20 minutes and water rinsed. The removability ofthe lubricating film was comparatively evaluated by water-wetting prop erties.

AsapparentfromTable3,the lubricating films formed on the steel surface according to the process for lubricating treatment of this invention exhibited excellent lubricating effects as compared with the film in Comparative Example (conventional lubricating oil) in the deep drawing test. In particular, complete drawing was realised and the best lubricat ingeffectswereexhibitedin Examples 1-3. The draw ratios are shown in Examples 4-7, since complete drawing could not be realised. However, these drawing ratios are higherthanthe ratio in Comparative Example, and thus it may safely be said that the films obtained in Examples 4-7 have better lubricating properties than that obtained in Comparative Example. Moreover, the removability ofthe lubricating films remaining on the steel surface after draw working was excellent since all of them are completely removed. On the other hand, the removability of the film was extremely bad in Comparative Example thus exhibiting a much inferior result.

Claims (9)

1. Aprocessforforminga lubricantcoatingona metal surface comprising applying to the surface an aqueous solution containing a polyethylene-imine and a thermoplasticwater-soluble resin and drying the resultant aqueous coating to form a dry film having a weight of 0.5 to 15 g/m2, and applying a lubricating oil to the film.

2. A process according to claim 1 in which the ratio ofthe polyethylene-imineto the water-soluble resin is between 1:4 and 3:2.

3. A process according to claim 1 or claim 2 in which the lubricating oil is based on or consists of a fat or oil and includes a fatty salt of an aliphatic amine.

4. A process according to any preceding claim in which the lubricating oil is an emulsion of a fatoroil.

5. A process according to any preceding claim in which the polyethylene-imine is a branched polyethyleneimine having an molecularweightof 30,000 to 100,000.

6. A process according to any preceding claim in which the water-soluble resin is a polyvinyl acetate having a saponification degree of 70% or more.

7. A process according to any preceding claim in which the metal surface is of stainless steel.

8. A process according to any preceding claim in which the metal surface carrying the lubricant coating is subjected to cold working.

9. A process according to claim 8 in which the lubricant coating is removed from the metal surface by an alkaline cleanerafterthe cold working.