The characteristics of lubricating grease include:
(1) thixotropy
(2) Viscosity
(3) Strength limit
(4) Low temperature fluidity
(5) Dropping point
(6) evaporation
(7) colloidal stability
(8) Oxidation stability, etc.
There are many kinds and brands of lubricating grease, and there are many classification methods, some of which are classified according to the composition of base oil, such as petroleum-based lubricating grease and synthetic oil lubricating grease; Some are classified by use, such as antifriction grease, protective grease and sealing grease; Some greases are classified according to certain characteristics, such as high-temperature grease, cold-resistant grease and extreme pressure grease. The type of thickener in grease is the main factor that determines the working performance of grease. The characteristics of several lubricating greases are briefly introduced.
(1) hydrocarbon grease
Grease made of base oil thickened with paraffin is called hydrocarbon grease. It has good plasticity, chemical stability and colloidal stability, is insoluble in water and will not emulsify when it meets water. Its disadvantage is its low melting point. Hydrocarbon grease is mainly used for protection.
(2) Soap grease
Soap-based grease accounts for about 90% of grease output and is widely used. The most commonly used greases are calcium-based, sodium-based, lithium-based, calcium-sodium-based and compound calcium-based. Composite aluminum-based and lithium-based greases also account for a certain proportion. These two kinds of greases are promising varieties.
(3) Inorganic grease
There are mainly bentonite grease and silica gel grease. Silicone grease is made of methyl silicone oil thickened by surface modified silica gel, which can be used for electrical insulation and vacuum sealing. Bentonite grease is surface silica gel grease, which is made of organic bentonite treated with surfactant (such as dimethyl octadecyl benzyl ammonium chloride or amino acid amine) and thickened with petroleum lubricating oil or synthetic lubricating oil with different viscosities. Suitable for lubrication of automobile chassis, wheel bearings and high temperature bearings.
(4) Organic grease
Various organic compounds thicken petroleum lubricating oil or synthetic lubricating oil, each with different characteristics, and these greases are mostly used for special purposes. For example, high-temperature grease made of Indanthrene and copper phthalocyanine thickened synthetic lubricating oil can be used at 200~250℃; Grease made of fluorine-containing thickener, such as PTFE-thickened fluorocarbon or perfluoroether, can resist strong oxidant and be used for lubrication of special parts. For example, polyurea grease can be used for bearing lubrication under radiation-resistant conditions.
Intransitive verb solid lubricant
Solid lubrication refers to the use of solid powder, film or whole material to reduce the friction and wear of two relatively moving surfaces and protect the surfaces from damage. According to the tribological terminology formulated by the Organization for Economic Cooperation and Development (OECD), solid lubrication is defined as any solid powder or film used to protect the relatively moving surface from damage and reduce its friction and wear. In the process of solid lubrication, solid lubricant and surrounding media will react physically and chemically with the friction surface to form a solid lubrication film to reduce friction and wear.
The concept of solid lubricant was applied late. 1829, Raney conducted the friction test of graphite and lard composites. Molybdenum disulfide was first used as a lubricant in the 1930s. At present, solid lubricants have been used in many mechanical products, which can effectively lubricate under various special harsh working conditions such as high temperature, high load, ultra-low temperature, ultra-high vacuum, strong oxidizing or reducing atmosphere and strong radiation.
The basic performance of solid lubricant has the following requirements.
(1) can be firmly attached to the friction surface and has the function of protecting the surface.
(2) Low shear strength.
(3) Good stability, including physical thermal stability, chemical thermal stability, aging stability and no corrosion.
(4) Solid lubricants require high bearing capacity.
Because the solid lubricant can't export part of the friction heat on the friction interface like lubricating oil, and it is difficult to supplement it during use, the corresponding remedial measures should be considered according to the characteristics of the solid lubricant when selecting.
At present, there is no unified classification standard for solid lubricants. According to the methods put forward by different scholars and research institutions, solid lubricants can generally be divided into the following categories:
(1) Solid lubricants with layered crystal structure are easily splittable compounds or monomer substances with antifriction effect. According to the combination form, the crystal system and composition can be divided into sulfide, selenide, telluride, fluoride, halide, simple substance (graphite, etc. ), nitride, oxide, organic matter, etc.
(2) Non-layered inorganic substances can be divided into sulfides, tellurides, fluorides, ceramics and superhard alloys.
(3) Soft metal films, such as gold, silver, indium, calcium, cadmium, lead, tin and their alloys.
(4) Polytetrafluoroethylene, polyacetal, nylon, polyamide, polyimide, epoxy resin, phenolic resin, silicone resin and other polymer materials.
(5) Chemically formed films, such as phosphate films.
(6) Chemical synthesis of film, such as introducing sulfur vapor on the surface of molybdenum-plated metal to form MoS2 film.
The use method of solid lubricant is as follows:
(1) Some engineering plastics, such as polytetrafluoroethylene, polyoxymethylene, polyacetal, polyamide, polycarbonate, polysulfone, polyimide, chlorinated polyether, polyphenylene sulfide, polyethylene terephthalate, etc., have low friction coefficient, good moldability and chemical stability, excellent electrical insulation and strong impact resistance, and can be made into integral parts. If glass fiber, graphite fiber and metal fiber are used, gears, bearings, guide rails, cams, rolling bearing cages, etc. with good comprehensive performance. Be widely used. Graphite brush, electric contact, gem bearing, blade support, etc. It is an example of directly manufacturing parts using materials with specific characteristics.
(2) It is one of the common methods to make various covering films by different methods to cover the friction surface of the motion pair with solid lubricant, so as to make it a dry film with certain self-lubricating performance. There are many methods to form films, such as sputtering, electrophoretic deposition, plasma spraying, ion plating, electroplating, chemical generation, impregnation, bonding, extrusion, roll coating and so on.
(3) The so-called composite material is made of composite or composite material, which refers to a material system formed by combining or compounding two or more materials. These substances are different in physical and chemical properties and shapes, and are immiscible with each other. The ultimate goal of combination or compounding is to obtain a new material with better performance, which is generally called composite material. At present, the most widely used composite material is called "metal plastic" (.
Du's bearing material is a metal-plastic bearing formed by plating a layer of 30 ~ 50m bronze on a mild steel plate, then sintering a layer of porous bronze balls, impregnating or roll coating PTFE (polytetrafluoroethylene) to fill the pores, and then sintering and bonding. Its structure is shown in figure 14. It not only keeps the low friction coefficient of PTFE, but also has sufficient mechanical strength, high bearing capacity and heat dissipation.
Figure 14 Structure of Metal Plastics
(4) As a solid lubricating powder, adding a proper amount of solid lubricating powder (such as molybdenum disulfide) into lubricating oil or grease can improve the bearing capacity of lubricating oil and improve the boundary lubrication state, which is also a common use method, such as molybdenum disulfide oil agent, molybdenum disulfide ointment, molybdenum disulfide grease, molybdenum disulfide aqueous solution, etc. When the solid lubricant with particle size less than 0.5m is added to the engine lubricating oil, these small particles can enter the friction surface through the filter. When the friction surface is temporarily short of oil for some reason.
When using solid lubricant, we must understand its characteristics and use it reasonably according to the working conditions, so as to achieve the expected effect.
Several commonly used solid lubricants are as follows:
(1) graphite
(2) Molybdenum disulfide
(3) Polytetrafluoroethylene
(4) nylon