Method of improving the shear stability of lithium soap greases

In a method for preparing a grease containing

• (i) a lubricating oil,
• (ii) a lithium soap of a C.sub.12 -C.sub.24 hydroxy fatty acid,
• (iii) a polyhydric alcohol selected from the group consisting of glycerol, pentaerythritol, and mixtures thereof, and
• (iv) at least two metal hydrocarbylthiophosphate compounds having the formula:
• ##STR3## wherein n is 1-6;
• x is 1-3;
• R.sub.1 and R.sub.2 may each be hydrogen or a hydrocarbyl group having from 1 to 30 carbon atoms;
• and M is a metal selected from the group consisting of aluminum, antimony, cadmium, copper, lead, tin, zinc, and mixtures thereof;
• in which the metal is different in at least two compounds,
• by the steps comprising
• (a) forming a mixture of the lubricating oil and the lithium soap of an hydroxy faty acid at a temperature between about 150.degree. and about 220.degree. F.,
• (b) increasing the temperature of the product from step (a) to between about 350.degree. and about 400.degree. F. for a period of time sufficient to improve dispersion of the lithium soap in the oil,
• (c) cooling the product from step (b) to a temperature between about 150.degree. and about 200.degree. F., and
• (d) adding the polyhydric alcohol and the metal hydrocarbylthiophosphate to the product from step (c),
• the improvement which comprises adding at least a major portion of the polyhydric alcohol to the mixture of lubricating oil and lithium soap of a C.sub.12 -C.sub.24 hydroxy fatty acid before step (b) to increase the shear stability of the grease.

In a method for preparing a grease containing

• (i) a lubricating oil,
• (ii) a lithium soap of a C.sub.12 -C.sub.24 hydroxy fatty acid,
• (iii) a lithium soap of a C.sub.2 -C.sub.12 dicarboxylic acid,
• (iv) from about 0.1 to about 5 wt. % glycerol, and
• (v) from about 0.2 to about 10 wt. % of at least two metal dialkyldithiophosphate compounds in which the metal is different in at least two compounds,
• by the steps comprising:
• (a) forming a mixture of the lubricating oil and the lithium soap of a C.sub.12 -C.sub.24 hydroxy fatty acid at a temperature between about 150.degree. and about 220.degree. F.,
• (b) substantially dehydrating the product from step (a) at a temperature between about 220.degree. and about 350.degree. F.,
• (c) cooling the product from step (b) to a temperature between about 200.degree. and about 260.degree. F.,
• (d) adding a C.sub.2 -C.sub.12 dicarboxylic acid to the product formed in step (c),
• (e) contacting the mixture formed in step (d) with at least a stoichiometric amount of lithium hydroxide, the contacting occurring at a temperature between about 200.degree. and about 240.degree. F.,
• (f) substantially dehydrating the product from step (e) at a temperature between about 220.degree. and about 350.degree. F.,
• (g) increasing the temperature of the product from step (f) to between about 350.degree. and about 400.degree. F. for a period of time sufficient to improve dispersion of the lithium soap in the oil,
• (h) cooling the product from step (g) to a temperature between about 150.degree. and about 200.degree. F., and
• (i) adding the glycerol and the metal dialkyldithiophosphate compounds to the product from step (h),
• the improvement which comprises adding at least a major portion of the glycerol to the mixture formed in step (a), adding at least a major portion of the glycerol to the mixture formed in step (e), or adding at least a major portion of the glycerol to the mixtures formed in steps (a) and (e) to increase the shear stability of the grease.