The role of the lubricant is to reduce frictional resistance, reduce wear, cooling and vibration absorption. Lubricants are liquid, solid and gas and semi-solid. Liquid lubricants are called lubricating oils, semi-solid, at room temperature. The grease is grease.
Lubricant
Lubricating oil is the main lubricant. The main physical property index of lubricating oil is viscosity. Viscosity characterizes the internal friction property of liquid flow. The greater the viscosity, the worse the fluidity. Another physical property of the lubricating oil is oiliness, which characterizes the adsorption capacity of the lubricating oil on the metal surface. The greater the oiliness, the stronger the adsorption capacity for the metal, and the easier the oil film is formed. The choice of lubricating oil should take into account factors such as bearing capacity, journal rotation speed, lubrication method, and surface roughness of sliding bearings.
The general principles are as follows:
1. Under high-speed and light-load working conditions, in order to reduce frictional power consumption, a lubricant with a small viscosity can be selected;
2. Under heavy or shock load working conditions, oil with large oiliness and high viscosity should be used to form a stable lubricating film;
3, static pressure or dynamic and static pressure sliding bearings can choose a small viscosity lubricant;
4. Surfaces with rough or unrunned surfaces should be selected with high viscosity lubricants.
The selection of the viscosity of the lubricating oil for hydrodynamically lubricated bearings can be checked by calculation.
Grease
For plain bearings with a journal speed of less than 1 m/s to 2 m/s, grease can be used. The grease is blended with mineral oil, various thickeners (such as calcium, sodium, lithium, aluminum and other metal soaps) and water. The grease has a large consistency (needle penetration) and a large carrying capacity, but its physical and chemical properties are unstable. It should not be used under conditions of large temperature changes, and is often used in low-speed heavy-duty or oscillating bearings.
Solid lubricants and gas lubricants
Solid lubricants include graphite, molybdenum disulfide (MoS2) and polytetrafluoroethylene (PTFE). Generally used under heavy load conditions or under high temperature working conditions. Gas lubricants are commonly used in air, and are used at high speeds and in oils or greases.
Lubrication method
Providing lubricant to the bearing is a necessary condition for forming a lubricating film. The hydrostatic bearing and the hydrostatic bearing continuously supply oil to the bearing bush of the sliding bearing through the oil pump, the throttle and the oil groove, and form an oil film to separate the bearing bush from the journal surface. The oil film of the dynamic pressure sliding bearing is to bring the lubricating oil into the bearing gap by the rotation of the journal, and the oil supply mode includes continuous oil supply and intermittent oil supply.
Intermittent oil supply:
Intermittent oil supply can be oiled by the oil pot and the needle valve can be used to fill the oil through the oil cup. The grease lubrication can only be used intermittently.
Press-fit injection oil cup
Needle valve type oil cup
Continuous oil supply:
Core oil supply oil ring oil supply
Pressure supply
Selection principle:
The lubrication method of the sliding bearing can be determined according to the coefficient k
In the formula:
p=F/(dB)--average pressure (MPa);
V-- journal speed (m/s).
K≤2--lubricated, oil cup lubrication;
k=2—16--needle valve type oil cup lubrication;
k=16-32 oil ring or splash lubrication;
K≥32--pressure cycle lubrication.
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