Plastic (consistent) lubricants. They are oil or synthetic oils with the addition of multifunctional additives and a thickener, which uses soaps of higher grades of fatty acids, solid hydrocarbons (cerasins, paraffins), silica gel and soot, which are classified as heat-resistant thickeners, etc.
Plastic lubricants are used in the following cases:
for heavily loaded sliding bearings operating at low speeds under boundary friction conditions with frequent reversals or in a short-time mode;
In addition to the main purpose, the lubricant is used as a sealant to protect the surface from contamination from the environment;
to create a protective oil film on the friction surface at long stops;
in knots of friction, access to which is difficult or which can work for a long time without replenishing the lubricant;
if it is necessary to simultaneously use the lubricant for preservation and lubrication of the mechanism.
The main characteristics of greases:
ultimate shear strength;
number of penetration.
The viscosity of grease lubricants, unlike lubricating oils, depends not only on temperature, but also on the rate of deformation. The viscosity value of the grease plastic material, determined at a given strain rate and temperature, is constant and is called the effective viscosity.
Ultimate shear strength is the minimum shear stress that causes the lubricant to transfer to its viscous flow. The ultimate shear strength characterizes the ability of the lubricant to be retained on moving parts, to flow out and extrude from unsealed friction units.
Droplet temperature is the temperature at which the lubricant loses its thick consistency and passes into a liquid lubricant state (the temperature at which the first drop falls). Usually, grease is applied at temperatures of 15 … 20 ° C below the dropping point.
The penetration number determines the degree of thickening of the plastic grease, which according to GOST 5346-78 is determined by the depth of immersion in the lubricant of the standard cone penetrometer for 5 s at a temperature of 25 ° C and a total load of 150 g and is expressed in tenths of a millimeter.
For imported plastic lubricants, depending on the penetration range, the concept of the NLGI (National Lubrication Grease Institute-USA) gradient from 000 (liquid grease) and to grade 6 (extremely dense) is established. In most cases, for industrial use, a grease lubrication of the degree of thickening from 000 to 2 is used.