Precautions before installation

Preparation of SKF bearings As SKF bearings are rust-proofed and packaged, do not open the package before installation. In addition, the anti-rust oil coated on SKF bearings has good lubricating properties. For general-purpose SKF bearings or SKF bearings 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 should be used to wash away the anti-rust oil. At this time, SKF bearings are easy to rust and cannot be left for a long time.

Inspection of shaft and housing Clean the SKF bearing and housing to confirm that there are no scratches or burrs left by machining. Abrasives (SiC, Al2O3, etc.) molding sand, cutting chips, etc. must never be inside the shell. Secondly, check whether the size, shape and processing quality of the shaft and the housing conform to the drawings.

Before installing SKF bearings, apply mechanical oil to the mating surfaces of the shaft and the housing that have passed the inspection.

How to install SKF bearings

The installation method of SKF bearings varies with SKF bearing types and matching conditions.

Since most shafts rotate, the inner ring and the outer ring can adopt interference fit and clearance fit respectively. When the outer ring rotates, the outer ring adopts interference fit.

(1) Press-in installation
Press-in installation generally uses a press, bolts and nuts can also be used, and a hand hammer can be used when necessary.

(2) Hot sleeve installation
The heat sleeve method of heating the SKF bearing in oil to expand it and then installing it on the shaft can prevent the SKF bearing from being subjected to unnecessary external forces and complete the installation in a short time.

Material factors affecting SKF bearing life

The early failure modes of rolling SKF bearings mainly include rupture, plastic deformation, wear, corrosion and fatigue. Under normal conditions, they are 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 the steel. The main internal factors affecting these performance and status are as follows.

Martensite in hardened steel
Retained austenite in hardened steel
Undissolved carbides in hardened steel
Residual stress after quenching and tempering
Impurity content of steel

In order to make the above-mentioned material factors that affect the life of SKF bearings in the best condition, the original structure of the steel before quenching needs to be controlled first, and the technical measures that can be taken are: high temperature (1050℃) austenitization, rapid cooling to 630℃, isothermal normalization Pseudo-eutectoid fine pearlite structure, or cold to 420 ℃ isothermal treatment to obtain bainite structure. The forging and rolling waste heat can also be used for rapid annealing to obtain a fine-grained pearlite structure 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 the austenite, the undissolved carbides will aggregate into fine grains.

When the original structure in the steel is constant, the carbon content of quenched martensite (that is, the carbon content of austenite after quenching heating), the amount of retained austenite and the amount of undissolved carbides mainly depend on the quenching heating temperature and holding time As the quenching heating temperature increases (a certain time), the amount of undissolved carbides in the steel decreases (the carbon content of quenched martensite increases) and the amount of retained austenite increases. The hardness first increases with the increase of the quenching temperature. After reaching the peak, it decreases as the temperature increases. When the quenching heating temperature is constant, with the extension of the austenitizing time, the number of undissolved carbides decreases, the number of retained austenite increases, and the hardness increases. When the time is longer, this trend slows down. When the carbides in the original structure are small, the carbides are easily dissolved into austenite, so the hardness peak after quenching shifts to a lower temperature and appears in a shorter austenitizing time.
In summary, the undissolved carbides of GCrl5 steel after quenching are about 7%, and the retained austenite is about 9% (the average carbon content of cryptocrystalline martensite is about 0.55%) is the best structure. Moreover, when the carbides in the original structure are fine and evenly distributed, when the microstructure composition at the above level is reliably controlled, it is beneficial to obtain high comprehensive mechanical properties, thereby having a high service life. It should be pointed out that the original structure with fine and dispersed carbides, when quenching and heating, the undissolved fine carbides will aggregate and grow, making it coarser. Therefore, for SKF bearing parts with this original structure, the quenching heating time should not be too long, and the rapid heating austenitizing quenching process will obtain higher comprehensive mechanical properties.

In order to make the surface of the SKF bearing parts after quenching and tempering have a large compressive stress, a carburizing or nitriding atmosphere can be introduced during the quenching and heating for a short time surface carburizing or nitriding. Since the actual carbon content of austenite during quenching and heating of this steel is not high, which is much lower than the equilibrium concentration shown on the phase diagram, it can absorb carbon (or nitrogen). When austenite contains higher carbon or nitrogen, its Ms decreases, and the surface layer undergoes a martensite transformation after the inner layer and the core during quenching, resulting in greater residual compressive stress. After GCrl5 steel is heated and quenched in a carburizing atmosphere and a non-carburizing atmosphere (both subjected to low temperature tempering), the contact fatigue test shows that the life of surface carburized steel is 1.5 times longer than that of non-carburized steel. The reason is that the surface of carburized parts has large residual compressive stress.