Cold forming lubricants and process

Abstract

 A cold forming lubricant and a process for cold forming ferrous and non-ferrous metals such as steel and aluminum utilizes certain sulfur, chlorine and phosphorous compounds, or mixtures thereof, for example sulfurized or chlorinated oleic acids and phosphate esters of polyoxyethylene based non-ionic surfactants, in combination with a dry film lubricant.

Description

Related Application

[0001] This application is a continuation-in-part of copending application SN 294,259 filed August 19, 1981.

Background of the Invention

[0002] This invention relates generally to the cold forming of ferrous and non-ferrous metals such as steel, stainless steel, copper, and aluminium and more specifically to dry film lubricant compositions and processes for severe cold forming operations.

[0003] In the cold extrusion, drawing or forming of metal parts, a current practice is to prepare the parts by . applying a zinc phosphate coating to the parts and then -applying a dry film lubricant or a reactive lubricant to the zinc phosphate coating. Dry film lubricants are products containing soap and borax as their major constituents. Such lubricants are applied from an aqueous solution at high temperatures (greater than 140°F to boiling) and then dried on the metal surface. Dry film lubricants generally are used for mild forming operations.

[0004] Reactive stearate lubricants are also applied from aqueous solution. They consist of solutions of sodium stearate which are controlled in such a way that they react with the zinc phosphate coating to form zinc stearate within the crystal lattice of the coating. This provides a tightly bonded lubricant system which performs well in many severe cold extrusion applications.

[0005] Both lubricant systems offer the advantage of a dry, hard film which is not easily physically removed from the metal surface. This leads to a cleaner and safer work environment because oils tend to run off treated parts and coat the work area. However, there are some severe cold forming applications where neither system will perform adequately. At such times the use of an additional lubricant (such as molybdenum disulfide) or additional processing steps are required, both of which lead to additional expense.

[0006] We have attempted to employ additives to a reactive stearate lubricant which additives included a mica pigment, a dispersant for the mica, sulfurized oleic acid and a phosphate ester to provide a severe cold forming lubricant system. The mica pigment was added to improve the ability of the lubricant to function adequately in a severe cold forming process. However, it was found that in a manufacturing environment, such a lubricant system failed to work satisfactorily due to the settling of the mica from the coating bath and the use of such a system was abandoned.

[0007] We have now found that certain severe cold forming applications can be accomplished without need of a pigment and in some applications the need for a phosphate precoat has been eliminated.

Brief Summary of the Invention

[0008] In accordance with this invention, there is provided a lubricant composition comprising an aqueous, pigment--free bath containing an alkali metal fatty acid soap such as an alkali metal stearate, a compound selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of polyoxyethylene based non-ionic surfactants and mixtures thereof, and a base in an amount to provide a free fatty acid content between about 1.0.

[0009] A process is provided for cold forming metal comprising applying to the metal surface a dry, pigment-free coating of an alkali metal fatty acid soap and a compound selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of polyoxyethylene based non-ionic surfactants and mixtures thereof to form a dry, hard coating and then extruding the metal through a die.

[0010] Also provided is a process for cold forming metal comprising applying to a metal billet a coating of zinc phosphate, applying to the zinc phosphate a second pigment-free coating of an alkali metal stearate and a compound selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of poloxyethylene based non-ionic surfactants, and mixtures thereof so as to form a zinc soap with said zinc phosphate and then extruding said billet through a die.

[0011] Also provided is a dry film lubricant system comprising a zinc phosphate coating reacted with an alkali metal stearate and a compound selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of polyoxyethylene based non--ionic surfactants and mixtures thereof to provide a dry, pigment-free, lubricant film.

Detailed Description

[0012] The lubricant system and process of the invention are suitable for extreme cold forming operations where reductions of 35% or more are necessary in forming metal parts. The metal parts are dipped in a heated aqueous lubricant bath for several minutes, removed and dried to provide a hard dry lubricant film. Optionally, ferrous or aluminum parts are first provided with a zinc phosphate coating having a coating weight of approximately 1500 to 3000'mg/ft² as is conventional. The parts are next dipped in a reactive lubricant bath of the invention which contains an alkali metal stearate, for several minutes. The zinc coating reacts with the bath and, upon drying, a hard, dry lubricant film is formed on the part.

[0013] The lubricant bath of the invention includes an alkali metal (Na, K and Li) soap which upon drying will form a hard, dry lubricant film. Suitable soaps are derived from fatty acids have 12 to 22 carbons and mixtures thereof. Also included is an additive compound selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of poloxyethylene based non-ionic surfactants and mixtures thereof. The sulfurized and chlorinated fatty acids are derived from unsaturated.fatty acids and esters having 12 to 22 carbon atoms in the acid carbon chain, such as oleic, linderic, erucic, linoleic,-linolenic, etc. acids by reacting the unsaturated bonds with sulfur or chlorine. As used herein, the terms chlorinated and sulfurized fatty acids include esters thereof. Such materials are available from Keil Chemical Divison, Ferro Corp. as "sulfur bases" and "chlorinated fatty compounds" and have been traditionally used as additives to fluids for their extreme pressure lubricating properties in metal working applications such as cutting oils, water soluble soaps and drawing compounds but not as lubricant additives for forming dry hard films as in our invention. The phosphate esters are sold as extreme pressure lubricants and are available under the trademark Antara ^@ from GAF Corporation. They comprise a phosphate radical on a polyethyleneoxy non-ionic surfactant base. The non-ionic surfactant base consists of a hydrophobe and polyoxyethylene.

[0014] In one aspect of the invention, it is believed that an important attribute of the additive material is that it has an acid group which can react with the zinc phosphate to form a water insoluble zinc soap which.is chemically bonded to the surface of the metal. The combination of these additives and the stearate provide a dry film with unique lubricating properties which permits the cold extrusion of certain metal parts. The forming temperatures are reduced so that the parts are not heat damaged and the lubricating system avoids various other operating problems such as sticking in the die.

[0015] Because of the added acidity due to the lubricant additives, the free acidity of the bath must be adjusted to assure reaction of the ingredients of the bath with the zinc phosphate coating when a phosphate precoat is - used. The adjustment also is used to control the viscosity of the bath. The "free fatty acid" is adjusted by adding a base such as NaOH so as to be within the range of ± 1.0 with ± 0.5 preferred. Free fatty acid is determined by placing 100 ml of 190 proof ethyl alcohol in a 250 ml. Erlenmeyer flask and adding five drops of phenolphthalein indicator. Sodium hydroxide (0.1N) is added dropwise until a faint pink color develops. A 10 ml. portion of the lubricant bath is pipetted into the alcohol and the alcohol is heated to boiling. While hot, the alcohol solution is titrated to a pink endpoint with the 0.1N NaOH and the amount of NaOH used is recorded as the "free fatty acid points" where 1 ml. = 1.0 point. If the solution is pink after boiling then it is titrated with 0.1N sulfuric acid until the pink color is discharged. The amount of H₂S0₄ used is the "free alkali points" where 1 ml. = 1.0 alkali point or - 1.0 acid point.

[0016] The amount of lubricant additive employed will depend upon the application and generally can range from about 1-30 parts by weight per 100 parts of the total combined weight of fatty acid soap and additive combined. A sufficient amount is used to provide the required lubrication for a given application. Amounts of additive above about 30 parts by weight make the lubricant coating film soft.

[0017] The solution concentration can range from about 2 to 10% by weight and preferably 4 to 8% by weight "total fatty solids". Total fatty solids are determined by pipetting a 20 ml sample of the bath into an 18 gram Babcock type test bottle. A 25 ml. portion of concentrated sulfuric acid is then added and the bottle is shaken until the fatty matter separates. The liquid sample is diluted with 50% aqueous H₂SO₄ until the volume of separated fatty matter can be read on the graduated neck of the botted directly as percent fatty solids.

[0018] The bath of the invention is formed and maintained by adding the ingredients with mixing to hot water (160° or above), otherwise the fatty acid portion will separate.

[0019] The compositions and process of the invention are further illustrated by, but are not intended to be limited to, the following examples wherein parts are parts by weight unless otherwise indicated.

Examples 1-4

[0020] Four different lubricating baths were used to form a hard, dry film lubricant coating on the surface of steel billets to be formed into hose couplings by cold forward extrusion. The billets were cylindrical tubes with a length of about 2k" and a diameter of about ½". The billets were formed into hose couplings by cold forward extrusion where one end of the billet was reduced to provide a 7" long section of 1" in diameter with a wall thickness of about 1/8" extending from about a 1 inch long section of billet of the original dimensions. A zinc phosphate coating was first formed on the billet and then the billets were dipped for 5 minutes in the reactive lubricant bath, which was at a temperature of about 160-170°F, removed and allowed to dry. The bath compositions are given in Table I below:

[0021] The cold forming operation to produce the couplings involved a severe (about a 50%) reduction. Previous attempts to form the part using a standard zinc phosphate coating which had been reacted with sodium stearate were unsuccessful in forming the part. A modified dry film of soap and borax was successful in forming the part without use of phosphate coating but resulted in excessive heat generation and, due to its hygroscopic nature, many operating problems. Each of the compositions shown in Table I allowed the parts to be successfully extruded at lower temperatures (at least 10⁰F) with the compositions of Example 3 and 4 appearing to give the best results.

Example 5

[0022] The composition of Example 4.was used to coat 400 steel billets for deep drawing steel grenades. The billets were cleaned in a caustic solution, rinsed with water, dried, immersed in the lubricant bath at a temperature of 175-180°F for about 5·minutes and then removed from the bath and dried. The bath had a total fatty solids content of 7 to 9% and a free fatty acid content of about 0.5 point. The billets were subjected to four cold forming operations, with cleaning, annealing and lubricant application between each forming operation, to successfully form the grenades. The acceptance rate was 96.5% which is slightly above the normal rate. The process previously used a phosphoric acid reactive oil which was messy to use and corrosive to the skin.

Example 6

[0023] The composition of Example 4 was used to coat aluminum billets for forming fire extinguisher bottles by impact extrusion. The aluminum billets were first cleaned in an alkaline solution, rinsed with water, alkaline etched, and rinsed with water. A number of the billets were coated with zinc phosphate, rinsed with water and an alkaline solution, coated with the lubricant composition of Example 4 at a bath concentration of about 8 percent by weight total fatty solids at temperatures of about 168-180°F and dried. The remaining billets were coated with lubricant without applying the zinc phosphate coating. It was noted that a reaction of the lubricant with the aluminum surface occurred even in the absence of the zinc phosphate undercoat. Both groups of billets were successfully impact extruded. Some die pick up resulted from the phosphate coated parts which could be remedied by lowering the coating thicknesses by adjusting the bath concentrations. The process previously used to form the bottles incuded a zinc phsophate undercoat and a soap type lubricant.

[0024] The process and compositions of the invention thus provide a non-oily, non-hygroscopic, dry, hard lubricant system which permits the severe cold forming of parts without die sticking and without damage or discoloration of the parts due to excessive temperature generation. The lubricant system is so effective that, as illustrated above, the use of a phosphate precoating can be eliminated in certain severe applications which reduces process stops and the possibility of die pick-up of the lubricant.

Claims

1. A lubricant composition comprising an aqueous pigment-free bath containing an alkali metal fatty acid soap and an additive compound selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of polyoxyethylene based non--ionic surfactants and mixtures thereof, said composition having a free fatty acid content of between about ± 1.0 point.

2. The composition of claim 1 wherein the additive is present in about 1-30 parts by weight per 100 parts of total combined weight of additive and fatty acid soap.

3. The composition of claim 1 wherein the bath - contains from about 2 to 10 percent by weight total fatty solids.

4. The composition of claim 1 wherein the fatty acid soap is derived from fatty acids having 12 to 22 carbons and mixtures thereof.

5. The composition of claim 4 wherein the fatty acid soap is an alkali metal stearate.

6. The composition of claim 5 wherein the alkali metal stearate is sodium stearate and the additive is . sulfurized oleic acid.

7. The composition of claim 5 including a phosphate ester of a polyoxyethylene based non-ionic surfactant.

8. A dry film lubricant system comprising a zinc phosphate coating on steel or aluminum which coating has been reacted with an alkali metal stearate and a compound selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of polyoxyethylene based non-ionic surfactants and mixtures thereof to provide a dry, pigment-free lubricant film.

9. A process for cold forming steel or aluminum comprising applying to a steel or aluminum billet a coating of zinc phosphate, applying to the zinc phosphate a second pigment-free coating which includes an alkali metal stearate and an additive selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of- polyoxyethylene based non-ionic surfactants, and mixtures thereof from an aqueous bath so as to form a dry pigment-free lubricant film including a zinc soap and then forming the billet using a die.

10. A process for cold forming metals comprising applying to the metal billet a pigment-free coating which includes an alkali metal fatty acid soap and an additive selected from the group consisting of sulfurized fatty acids, chlorinated fatty acids, phosphate esters of polyoxyethylene based non-ionic surfactants and mixtures thereof from an aqueous bath so as to form a dry, pigment-free lubricant film and then forming the billet using a die.