Precautions before installation
Preparation of SKF Bearing as SKF Bearing is treated with rust prevention and packaged, do not open the package before installation. In Main Influence addition, the antirust oil coated on SKF Bearing has good lubrication performance. For general-purpose SKF Bearing or SKF Bearing filled with grease, it can be used directly without cleaning.
However, for SKF bearings for instruments or SKF bearings for high-speed rotation, clean cleaning oil shall be used to wash away the antirust oil. At this time, SKF bearings are easy to Main Influence rust and cannot be placed for a long time.
Inspection of shaft and housing clean SKF Bearing and housing to confirm that there are no scars or burrs left by machining. There must be no abrasives (SiC, Al2O3, etc.) molding sand, chips, etc. in the shell. Secondly, check whether the size, shape and processing quality of the shaft and Main Influence shell comply with the drawings.
Before installing SKF Bearing, apply mechanical oil on all mating surfaces of shaft and housing that pass the Main Influence inspection.
Installation method of SKF Bearing
The installation method of SKF Bearing varies according to the type and matching conditions of SKF Bearing.
Since most of them are shaft rotation, the inner ring and outer ring can adopt interference fit and clearance fit Main Influence respectively. When the outer ring rotates, the outer ring adopts interference fit.
(1) Press in installation
Press in installation generally uses press, bolts and nuts, and hand hammer can be used when necessary.
(2) Hot sleeve installation
The hot sleeve method of heating SKF Bearing in oil to expand it and then installing it on the shaft can avoid unnecessary external force and Main Influence complete the installation in a short time.
The early failure forms of rolling SKF bearings mainly include fracture, plastic deformation, wear, corrosion and fatigue. Under normal conditions, it is mainly contact fatigue. In addition to the service conditions, the failure of SKF Bearing parts is mainly restricted by the hardness, strength, toughness, wear resistance, corrosion resistance and internal stress state of steel.
The main internal factors affecting these performances and states are as follows.
Martensite in quenched steel
Retained austenite in quenched steel
Insoluble carbide in quenched steel
Residual stress after quenching and tempering
Impurity content of steel
In order to keep the above material factors affecting the service life of SKF Bearing in a state, it is first necessary to control the original structure of the steel before quenching. The technical measures that can be taken are: austenitizing at high temperature (1050 ℃), rapid cooling to 630 ℃ isothermal normalizing to obtain pseudo eutectoid fine pearlite structure, or cooling to 420 ℃ isothermal treatment to obtain bainite structure.
The fine pearlite structure can also be obtained by rapid annealing with forging and rolling waste heat, so as to ensure the fine and uniform distribution of carbides in the steel. When the original structure in this state is austenitized by quenching and heating, in addition to the carbides dissolved in austenite, the insoluble carbides will aggregate into fine particles.
the carbon content of quenched martensite (i.e. the carbon content of austenite after quenching heating), retained austenite and undissolved carbide mainly depend on the quenching heating temperature and holding time. With the increase of quenching heating temperature (time is certain), the number of undissolved carbide in the steel decreases (the carbon content of quenched martensite increases)
When the amount of retained austenite increases, the hardness first increases with the increase of Main Influence quenching temperature, reaches the peak value, and then decreases with the increase of temperature.
When the quenching heating temperature is constant, with the extension of austenitizing time, the amount of insoluble carbide Main Influence decreases, the amount of residual austenite increases and the hardness increases. When the time is long, this trend slows down.
When the carbide in the original structure is fine, because the carbide is easy to dissolve into austenite, the Main Influence hardness peak after quenching moves to a lower temperature and appears in a shorter austenitizing time.
To sum up, the microstructure of GCrl5 steel after quenching is composed of insoluble carbide of about 7% and retained austenite of about 9% (the average carbon content of cryptocrystalline martensite is about 0.55%).
Moreover, when the carbides in the original structure are fine and evenly distributed, it is conducive to obtain high comprehensive mechanical properties and high service life when the microstructure composition at the above level is reliably controlled. It should be pointed out that for the original structure with fine dispersed carbides, the insoluble fine carbides will aggregate and grow and coarsen when quenching, heating and holding.
Therefore, the quenching and heating time of SKF Bearing parts with this original structure should not be too long. Higher comprehensive mechanical properties can be obtained by rapid heating austenitizing quenching process.
In order to make the surface of SKF Bearing parts remain large compressive stress after quenching and tempering, carburizing or nitriding atmosphere can be introduced during quenching and heating for short-time surface carburizing or nitriding.
Because the actual carbon content of austenite during quenching and heating of this steel is not high, which is far lower than the equilibrium concentration shown in the phase diagram, it can absorb carbon (or nitrogen). When austenite contains high carbon or nitrogen, its MS decreases.
During quenching, martensitic transformation occurs on the surface layer compared with the inner layer and the core, resulting in large residual compressive stress.
After heating and quenching in carburizing atmosphere and non carburizing atmosphere (both tempered at low temperature), the contact fatigue test shows that the service life of surface carburized steel is 1.5 times higher than that of non carburized steel. The reason is that the surface of carburized parts has large residual compressive stress.