The role of lubricants is to reduce friction resistance, wear, cooling and vibration absorption. Lubricants include liquid, solid, gas and semi-solid. Liquid lubricants are called lubricating oil, and semi-solid, in the form of paste at room temperature, are lubricating grease.
Lubricating oil is the main lubricant. The main physical performance index of lubricating oil is viscosity. Viscosity represents the internal friction performance of liquid flow. The greater the viscosity, the worse its fluidity.Lubrication of Sliding Bearing
Another physical property of lubricating oil is oiliness, which represents the adsorption capacity of lubricating oil on metal surface. The more oily, the stronger the adsorption capacity to metals, and the easier the oil film is to form. The selection of lubricating oil should comprehensively consider the bearing capacity, journal speed, lubrication mode, surface roughness of sliding bearing and other factors.
1. Under the working conditions of high speed and light load, in order to reduce the friction power consumption, the lubricating oil with low viscosity can be selected;
2. Under the working conditions of heavy load or impact load, the lubricating oil with high oil and viscosity shall be used to form a stable lubricating film;
3. The lubricating oil with low viscosity can be selected for static pressure or dynamic and static pressure sliding bearing;
4. Lubricating oil with high viscosity shall be selected for surfaces with rough surface or without running in.
The selection of lubricating oil viscosity of hydrodynamic lubrication bearing can be checked through calculation.
The sliding bearing with journal speed less than 1 m / S ~ 2 m / s can use grease. The grease is mixed with mineral oil, various thickeners (such as calcium, sodium, lithium, aluminum and other metal soaps) and water. The consistency (penetration) of the grease is large and the bearing capacity is large, but the physical and chemical properties are unstable and should not be used under the condition of large temperature change. It is mostly used in low-speed, heavy-duty or swinging bearings.
Solid and gas lubricants
Solid lubricants include graphite, molybdenum disulfide (MoS2) and polytetrafluoroethylene (PTFE). It is generally used under heavy load conditions or high temperature working conditions. Gas lubricants are commonly used in air. They are mostly used at high speed and where lubricating oil or grease cannot be used.
Providing lubricant to the bearing is a necessary condition for the formation of lubricating film. Hydrostatic bearing and dynamic and static pressure bearing continuously supply oil to the bearing bush of sliding bearing through oil pump, restrictor and oil groove to form oil film to separate the bearing bush from the journal surface. The oil film of hydrodynamic sliding bearing brings lubricating oil into the bearing clearance by the rotation of journal. Its oil supply methods include continuous oil supply and intermittent oil supply.
Intermittent oil supply:Lubrication of Sliding Bearing
Intermittent oil supply can be filled by oil pot and lifting needle valve through oil cup. Grease lubrication can only be supplied intermittently.
Press fit type oil filling cup rotary sleeve type oil filling cup
Needle valve type oil filling cup
Continuous oil supply:Lubrication of Sliding Bearing
Core core oil supply ring oil supply
Pressure oil supply
The lubrication mode of sliding bearing can be determined according to the coefficient K
Where:Lubrication of Sliding Bearing
P = f / (DB) — average pressure (MPA);
V — Journal linear velocity (M / s).
K ≤ 2 — lubricated by oil cup;
K = 2-16 — needle valve type oil filling cup lubrication;
K = 16-32 oil ring or splash lubrication;
K ≥ 32 — pressure circulating lubrication.