GB815874A - Process for preparing mixed-salt grease compositions - Google Patents

Abstract

In the preparation of a grease containing as thickening agent a complex of (1) a metal salt of a low molecular weight acid and (2) a metal salt of a high molecular weight acid and/or an intermediate molecular weight acid prepared by heating a metal base with the acids in the lubricating oil, a slurry of the metal base in at least a portion of the oil is prepared and the low molecular weight acid is intimately dispersed in the slurry in the form of droplets of less than 0.05 mm. diameter, the remaining acids being added prior to or simultaneously with the low molecular weight acid and the mixture heated to form the complex; the intimate dispersion of low molecular weight acid in slurry is preferably achieved by mixing the ingredients in a mixing zone functioning under a shear rate of 5000-100,000 reciprocal seconds and an energy input of 0.1-30 horsepower seconds per pound of material introduced into the zone. The low, high and intermediate molecular weight acids are defined respectively as C1-C6 carboxylic, nitric, hydrochloric, sulphuric or phosphoric acids; C12-C30 fatty acids; and C7-C10 straight-chain, saturated, mono-carboxylic acids. The lubricating oil used may be a mineral base lubricating oil having a viscosity of 30-1000 S.S.U. at 100 DEG F. or a synthetic lubricating oil having a viscosity of at least 30 S.S.U. at 100 DEG F. such as ether alcohols of formula RO(CnH2nO)xH, where R is alkyl, e.g. butyl, n is 2-5 and x is 1-40, esters of monocarboxylic acids totalling 20 to 80 carbon atoms, esters of polyethylene glycols with C8-18 branched chain carboxylic acids, complex esters of polybasic carboxylic acids, polyhydric alcohols and monobasic acids and/or monohydric alcohols, phosphoric acid esters or thioesters of aliphatic alcohols or mercaptans of up to 18 carbon atoms, polymers of chlorofluoroalkylenes, organosiloxanes, sulphite esters, organic carbonates, mercaptals and formals. The grease may contain 50 to 97 weight per cent of such an oil. The remaining 3 to 50 weight per cent of the grease is the complex thickener which may be formed from 1 mol. of the high and/or intermediate molecular weight acid with 3 to 15 mols. of low molecular weight acid and 2 to 8 mols. of metal base; if a mixture of high and intermediate molecular weight acids is used, they may be in any ratio, e.g. between 0.15 to 50 mols. of high per mol. of intermediate molecular weight acid. Suitable metal bases are the oxides, hydroxides and carbonates of calcium, magnesium, strontium and barium. The two streams may be mixed in any machine capable of mixing in less than five seconds and operating at a sufficient rate of shear to reduce the size of the drops of low molecular weight acid to less than 0.05 mm. The grease formed is dehydrated and heated to complex-forming temperatures. In a typical example the slurry comprises by weight 75 per cent of a coastal mineral oil (viscosity 500 S.S.U. at 100 DEG F.), 15 per cent of 98.5 per cent calcium hydroxide, 5 per cent of hydrogenated castor oil and 5 per cent of hydrogenated fish oil acids. This was fed at 75 grams per minute into a centrifugal pump providing a shear rate of 10,000 reciprocal seconds and an energy input of 10 H.P. sec./lb. concurrently with 25 grams per minute of a 60 per cent aqueous acetic acid solution. The grease formed was heated to 300 DEG F. over 50 seconds, diluted with 1 1/2 times its weight of additional mineral oil and 0.5 weight per cent of phenyl alphanaphthylamine added as antioxidant. The product was heated for 1 hour at 460 DEG F. with agitation and cooled; it had a maximum grit diameter of 0.02 mm. compared with 0.1 mm. as when prepared conventionally.