GB2046298A - Water based hot forging lubricants and process - Google Patents

Abstract

A lubricant composition comprising water, and adipates made by reacting adipic acid with alkali metal or alkali earth metal hydroxide is used for forging operations. Other additives may be present such as thickeners, E.P. additives, suspending agents, germicides, anti-wear agents, pigments, corrosion inhibitors, wetting agents, foam control agents, dyes and perfumes. A hot forging process based on the above lubricant is also disclosed.

Description

SPECIFICATION Water based hot forging lubricants and process Forging is a process by which the shape and physical properties of metal can be changed.

The process involves placing a piece of metal (normally heated) between the halves of a die and forcing the die to close by impact or pressure. The operation causes a controlled plastic deformation of the metal into the cavities of the die. This flow of materials results not only in a change in shape of the metal but also increases the density and uniformity of the metal, improves its grain structure, and causes a shape-conforming grain flow. The resulting workpiece has properties which are superior to those generated by other methods, making forging essential where high performance workpieces are required.

One of the critical components of a forging system is the lubricant which separates the die from the workpiece. As with all lubricating situations, it is essential that this lubricant be effective to minimize wear of the extremely expensive forging dies and minimize expenditure of energy over a wide range of conditions.

The lubricant must also assure a high quality surface on the forging and not leave objectionable residues or corrosion on the dies.

As modern demand for safer and more dependable machine structures increases, the forging art is being applied to more difficult materials, at higher temperatures and pressures to form more complex shapes. Although oil-based lubricating compositions, which are effective under these extreme conditions, have been developed, their properties are found to conflict seriously with national commitments to personal safety and protection of the environment. The oil-based lubricants are normally flammable and can ignite well below common operating temperatures. Normal operation results in billowing carbonaceous smoke which is unpleasant and sometimes toxic. Furthermore, cleaning of the workpieces and dies requires solvent washes that produce large quantities of rinse, which, because of the economics of recycling, and desire to protect the environment can present serious disposal problems.

The ecological problems associated with oilbased hot forging lubricants has led to the development of water-based compositions.

One obvious advantage of a water-based lubricant composition is that die cooling can be accomplished by water evaporation on the hot dies, often making internal cooling of the dies unnecessary. Early attempts directed to waterbased compositions involving graphite, clay minerals iron oxide and molybdenum disulfide E.P. and anti-wear additives were often ineffective because the water did not adequately wet the metal surfaces.

One of the early disclosures of water-based lubricants is U.S. 2,735,814 wherein a die forging lubricant contained fish oil, graphite and water. The patentee in U.S. 2,921,874 found fatty acids, in general, unsuitable as lubricants for forging operations unless they were combined with an organic acid reactant, an organic solvent and water. Fatty acids in excess of 7 carbons were used.

The patentee in U.S. 3,313,729 used a mixture of pyrophosphate, or sodium tetraborate, a fatty acid soap of 8 to 22 carbon atoms, preferably 12 to 18 carbon atoms, to form a dry coating on the metal article prior to cold forging. A similar dry coating lubricant is disclosed in U.S. 3,375,193 based on a water soluble colloid, a fatty acid soap having 12 to 22 carbon atoms, an alkali metal tartrate and inorganic pigments.

A glass-forming lubricant is disclosed in U.S. 3,507,791 comprising an aqueous dispersion of a fatty acid of 10 to 32 carbons, alkanolamine, a water-soluble alcohol and water. The patentee in U.S. 3,983,042 discloses a water-based lubricant for hot forging containing graphite, organic thickener, sodium molybdate and sodium pentaborate.

From the above disclosures, it is apparent that fatty acids and fatty acid soaps have been widely used as an anti-wear and lubricant additive in forging compositions. These fatty acids and soaps have generally been preferred in the C12-C20 range. More recently, the Metalprep Department of Pennwalt Corporation has marketed a hot forging lubricant containing the alkali metal salt of azelaic acid in aqueous solution.

However, there are a number of serious shortcomings in the use of azelaic acid which are not encountered with adipic acid in waterbased lubricants for hot forging. The most serious problem with azelaic acid salts is that it does not wet the forging dies efficiently at elevated temperatures, e.g., 600-800 F.

(316-427 C) whereas adipic acid salts readily wet the dies at these temperatures. Moreover, the azelaic acid salts will smoke in high temperature forgings and have even decomposed before actual forging, whereas the adipic acid salts are relatively free from smoke and fumes and are stable at elevated temperatures.

We have now discovered a lubricant composition and a process of hot forging ferrous and non-ferrous metals based on an aqueous solution of adipic acid salts made reacting adipic acid with alkali metal or alkaline earth metal hydroxide. Conventional lubricating additives are also present. In a dispersion form of this invention, graphite is used in combination with adipic acid salts as the principal lubricating agents.

The lubricating compositions and forging processes of this invention are based on aqueous solutions and dispersions in which adipic acid salts are the principal lubricating agents.

Alkali metal and alkali earth metal hydroxides are used to convert the adipic acid to salts called adipates. Graphite is used in the compositions and processes, in addition to the adipates in those more severe forging operations where additional die life or optimum lubrication may be required. At least one, and generally several conventional lubricating additives, such as organic thickeners, surface active agents including suspending agents, dispersing agents, wetting agents and emulsifying agents, E.P. additives, corrosion inhibitors, germicides, anti-wear agents, foam control agents, pigments, dyes and perfumes are used as required.

The adipic acid is present in the lubricant compositions at a concentration ranging from about 1 to 35% by weight. The alkali metal and alkali earth metal hydroxides will be present at a concentration ranging from about 0.5 to 19% by weight. The conventional lubricating additives will be present at a concentration ranging from about 0.05 to 25% by weight. The balance of the composition is water. When graphite is present in the compositions, it is used at a concentration ranging from 5 to 25% by weight.

Many hot forging lubricants based on oil will flash or cause fire and smoke. Many water-based hot forging lubricants will smoke, cause objectionable odor and toxicity problems, or leave objectional residues on the dies. The compositions and forging process based on adipic acid overcome many of these problems.

The adipic acid is used in the compositions of this invention as the principal lubricating agent. It is present in the form of the alkali or alkali earth metal soap when the water is flashed off in the forging process. The adipic acid is present at a concentration within the range of about 1 to 35% by weight. The adipic acid used is the commercial or technical grade and can be obtained from E. 1.

duPont, Allied Chemical, Celanese and other suppliers.

The aqueous solution and/or dispersion contain alkali metal or alkali earth metal hydroxide in an amount not quite sufficient to convert all of the adipic acid to the corresponding salts, usually called soaps. This facilitates solubilizing the adipic acid. Generally, the alkali metal hydroxide or alkali earth metal hydroxide will be used within the range of about 0.5 to 19% by weight. The actual amount used is determined by chemical control in order to insure that the solution or dispersion remains neutral or slightly alkaline (7.0#8.5pH) and contains no free alkali. Sodium hydroxide is the preferred hydroxide which is conventionally added in the form of an aqueous solution.

When graphite is used in the compositions and processes, it will be present within the range of about 5 to 25% by weight. Graphite is available commercially from a number of suppliers.

At least one conventional lubricating additive will be present in the hot forging compositions, and often several of them will be used as may be required by the particular hot forging operation. The conventional lubricating additive is generally present in the compositions at a concentration ranging from about 0.05 to 25% by weight preferably 0.1 to 10% by weight.

The conventional lubricating additive nearly always used in the compositions and processes of this invention is the class of organic thickeners. The organic thickeners are selected from the class consisting essentially of water dispersable modified celluloses such as, methyl cellulose, water soluble ether cellulose, sodium carboxymethyl cellulose, ammonium carboxyethyl cellulose, methylethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, potassium carboxyhexyl cellulose, sodium cellulose glycollate, carboxypropyl cellulose, and cellulose acetate. Casein and alginates such as sodium alginate are satisfactory thickeners. Bentonite is also a satisfactory thickener.

Other suitable water soluble thickeners include polymethacrylates, polyvinyl alcohol, starch, gelatin, gum arabic and polysaccharides.

The preferred organic thickener is hydroxye thyl cellulose and is commercially available from Hercules Chemical under the trademark Natrosol 250 HR and 250 HHR.

These thickeners assist in solubilizing the other ingredients, enhance adhesion and wetting of the lubricating composition to the forgings. The preferred concentration of the organic thickener in the lubricating composition is about 1 % by weight.

Surace active agents are advantageously employed in the aqueous system to assist in wetting the surfaces of the dies and, in some cases, forgings with the lubricating composition, to disperse, suspend and emulsify the water insoluble components such as, graphite when it is present, and to level the lubricant composition on the forging pieces and dies.

The wetting agents, dispersing agents, emulsifying agents and leveling agents for aqueous systems are well-known in the art. Many examples of each type are disclosed in McCutcheons Detergents and Emulsions, 1978 Edition which is incorporated herein by reference.

Examples of such wetting and dispersing agents are: a polyoxyalkylene derivate of sorbitan monostearate having a molecular weight of about 1300 (Tween 60, manufactured by Atlas Powder Co.) polyoxyethylene sorbitan monooleate (Tween 80, manufactured by Atlas Powder Co.), sorbitan monostearate (Span 60, manufactured by Atlas Powder Co.), sorbitan monooleate (Span 80, manufactured by Atlas Powder Co.), oxyethylene nonylphenol (Tergitol NPX, manufactured by Union Carbide Co., composition approximately one mole of oxyethylene per mole of nonylphenol), polyoxyethylene, nonylphenol (Tergitol NP14, manufactured by Union Carbide Co., composition approximately 14 moles of oxyethylene per mole of nonylphenol); polyoxyethylene nonylphenol (Tergitol NP35, manufactured by Union Carbide Co., composition approximately 35 moles of oxyethylene per mole of nonylphenol), sulfated castor oil (manufactured by Baker Caster Oil Co.), alkyl aryl sulfonate (Duponol G, manufactured by DuPont de Nemours 8 Co.), alkylaryl sulfonate (Textilana MW, manufactured by Textilana Corp.), polyoxypropylene glycol (Pluronic L62, manufactured by Wyandotte Chemicals Corp.), and fatty alkanolamides (Emcol 5100T, manufactured by Witco Chemical Co.). Other similar wetting agents may be used.

As indicated above, in order to achieve a uniform thickness, leveling compounds may be added to the aqueous lubricant to eliminate brush strokes and to provide a smooth, level surface. Examples of such compounds are carboxy-methylcellulose, tricresyl phosphate, glycerine, lecithin, ethylene glycol and sorbitan borate.

Typical emulsifying agents are the olefin oxide-C2 to C3 derivatives of fatty acid partial esters of aliphatic polyhydric alcohol, a fatty alcohol, a fatty acid, an aliphatic amine, and alkyl phenol and mixtures thereof. The fatty acid partial esters include the C8-C24 aliphatic polyhydric alcohols having about 3 to 12, e.g.

3 to 8 carbon atoms, and about 2 to 8 hydroxy groups per molecule. The mono, di.

and tri esters of sorbitol are quite useful. The fatty acids reacted with the C2-C3 olefin oxides include linear aliphatic monobasic acids of C10 to C20. Ethylene oxide derivatives of stearic acid and oleic acid are preferred. The ethoxylated derivatives of the normal C,O to C18 primary alcohols are quite useful. Aliphatic amine derivatives of the linear C19 to C20 are also useful. Alkylphenols which are reacted with ethylene oxide or propylene oxide include the mono and dialkylphenols of about 8 to 12 carbons in the alkyl group such as nonylpheno and di-nonylphenol.

A preferred concentration range of surface active agents in the compositions is about 0.5 to 2.0% by weight.

For difficult forgings under very high pressures, it sometimes is desirable to include E.P.

additives such as molybdenum disulfide, and sodium molybdate.

Pigments may be used in the lubricating compositions to enhance lubrication, to act as a parting compound and to assist in cooling of the dies by acting as an insulator. Graphite is the most commonly used material of this type.

Other suitable pigments which may be used are lithopone, talc, calcium carbonate, zinc oxide, zinc carbonate, mica, magnesium carbonate and titanium dioxide.

Corrosion inhibitors useful in this invention include alkali metal nitrates and alkali metal nitrites. Benzotriazole is effective to prevent copper corrosion. A preferred concentration of corrosion inhibitor is about 0.1 % by weight.

Germicides are desirable in the aqueous systems to prevent the growth of bacteria during storage and shipment of the concentrated aqueous systems, and during storage in the feed tanks of the dilute use solutions.

Dowicil 75, and sodium omadine are satisfactory germicides. A preferred concentration for germicides is about 0.1 % by weight.

Typical foam control agents are the linear aliphatic alcohols of C6 to C12. A preferred concentration of foam control agents is about 0.5% by weight.

Dyes can serve several useful functions in the aqueous lubricants for hot forging. For example, they are an identifying agent to indicate the supplier of the lubricant. Dyes can also be used to indicate the pH of the aqueous solutions where this is important.

Orcoacid alphazurine 2G dye, Blue dye, Medford Chemical's Green dye and Bismark brown dye are satisfactory. The inclusion of perfume is purely for esthetic purposes. Dyes and perfumes are added in amounts to please the senses.

The aqueous hot forging lubricants of the invention are supplied in a concentrated form and the lubricants may be used in the neat concentration for the most difficult forging operations. In other less difficult forgings, the concentrated lubricant may be diluted with water to fit the particular forging needs. The amount of dilution can only be determined by actual operation of the forging press on the particular work piece. Satisfactory forgings have been made with up to 15 volumes of water to 1 of the concentrated lubricant.

The lubricant composition may be formulated as described below. A kettle equipped with stirrer and with either interior or exterior heating and cooling is required. Stainless steel is a preferred metal for the mixing vessel. The vessel is charged with cold water and the organic thickener is added with stirring until dissolved. Next, a portion of the alkali metal hydroxide is added followed by alternate additions of alkali and the adipic acid. The temperature is allowed to rise to about 180 F (82 C). Cooling may be required to keep the solution from boiling. The alkali metal or alkali earth metal hydroxide is added until the acid number is between 0.0 and 0.3. The solution must not contain free alkali.Finally, the dye which has been dissolved in hot water is added as well as any of the other conventional lubricating additives as may be required. The final solution will be a clear liquid with a semi-gel led appearance.

When graphite is used in the lubricant composition, it is preferable to dissolve the adipic acid and alkali metal hydroxide before adding the graphite and organic thickeners.

The surface active agents such as dispersants, wetting agents and emulsifying agents should be added before the graphite and organic thickener.

The best mode of practicing this invention will be apparent from the following examples.

Example 1. An effective lubricating composition in solution form is formulated from the following ingredients given in % by weight.

Organic thickenerA 1 % Caustic soda (50%)solution 13.5% Adipic acid 12.5% Dye 0.05% GermicideB 0.05 Water Balance A-Natrosol 250 H.R. hydroxyethyl cellulose.

B-Dowicil 75.

This composition is quite economical because of the exent it can be diluted with water. It is also biodegradable which greatly facilitates its disposal. It also has the advantage of not being damaged by freezing provided it is thawed prior to use.

Example 2. A graphited form of hot forging lubricant is formulated from the following ingredients given in % by weight: Adipic Acid 15.0% Caustic soda (50% solution) 16.2% Graphite 15.0% GermicideA 0.07% Organic ThickenerB 1.0% Dispersing Agentc 1.0% Water Balance A-Sodium Omadine and Dowicil 75 mixtures.

B-Natrosol 250 HHR.

C-Polywet WD-1.

The lubricant compositions described above can be applied to the forging dies in any convenient manner such as by immersion, by swab, recirculation of the lubricant over the dies or by spraying. Application by spraying is the most efficient application method. The forging process consists of advancing the workpiece into the forging machine, applying an effective amount of the lubricant to the dies, closing the dies, applying pressure to the dies, opening the dies and removing the forging. The effective amount is a lubricating amount. This quantity can only be determined by actual trial conditions since the effective amount of lubricant required will depend on many variables such as temperature level, forging pressure, hardness of the workpiece, degree of difficulty of the forging, the time required for forging and other factors.

Example 3.

The mandrels of a forging press were precoated with the lubricant composition of Example 1 at neat concentration while they were being heated to 1500 F (816on). Three mandrels operated simultaneously. Heavy walled 4"D. (10 16cm) tubing was advanced to the dies while the composition of Example 1, diluted with an equal volume of water, was sprayed on the dies. The dies were closed at 2500 p.s.i.g. (17MN/m2) and 90 long radius elbows were forged.

Continued operation of the forge showed no smoke, no fire and no objectionable odor.

Good wetting and adhesion of the lubricant was obtained while splattering was minimal.

No objectional buildup of the lubricant on the dies occurred. Occasionally, a powdery residue appeared which was easily removed by flushing with steam or hot water. No clogging of the spray nozzles occurred.

Claims (9)

1. An aqueous lubricant composition for metal forging processes, comprising an aqueous solution containing 1-35% adipic acid, 0.5 to 19% of an alkali metal or alkaline earth metal hydroxide, the amount of alkali used being such as to provide a solution having an acid number in the range 0 to 0.3, and 0.05 to 25% of an additive selected from thickeners, surface active agents, suspending agents, germicides, foam control agents, extreme pressure additives, pigments, corrosion inhibitors, dyes and perfumes, all percentages being by weight of the total composition.

2. A lubricant composition according to claim 1 or 2, wherein the additive is present in an amount of from 0.1 to 10% by weight based on the total composition.

3. A lubricant composition according to claim 1 or 2, wherein the additive comprises an organic thickener.

4. A lubricant composition according to claim 3, wherein said thickener is hydroxyethyl cellulose.

5. A lubricant composition according to claim 1, 2, 3 or 4, wherein the composition contains graphite in an amount of from 5-25% by weight based on the total composition.

6. A lubricant composition according to any one of the preceding claims, wherein the alkali metal hydroxide used in the preparation of said salt is sodium hydroxide.

7. A composition according to claim 1, substantially as hereinbefore described in Example 1 or 2.

8. A metalworking process which comprises hot forging a metal in the presence of a hot forging lubricant wherein there is used as said lubricant a composition as claimed in any one of the preceding claims.

9. A metalworking process which comprises hot forging a metal in the presence of a hot forging lubricant wherein there is used as the lubricant an aqueous solution containing 1-35% adipic acid, 0.5 to 19% of an alkali metal or alkaline earth metal hyroxide, the amount of alkali used being such as to provide a solution having an acid number in the range 0 to 0.3.