FOAM INHIBITION IN GEAR OILS
The rapid movements of gears tend to aerate oils and produce foam. This tendency may be aggravated by the presence of some additives, such as EP agents. Also, the higher the viscosity of the oil the more permanent the foam as a rule. Cases have been noted where foam became so great that it filled the gear case to overflow and long before this the gear teeth failed to obtain sufficient lubricant. While foaming of gear oils might result from vaporization of entrained water or driving of air out of solution, the general cause in gear sets is churning of air into the oil by agitation
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