The installation of SKF bearings must be carried out under dry, clean environmental conditions. Before installation, the machining quality of the mating surfaces of the shaft and housing, the end surfaces of the shoulders, grooves and connecting surfaces should be carefully checked. All mating and connecting surfaces must be carefully cleaned and deburred, and uncast surfaces of castings must be cleaned of molding sand.
SKF bearings should be cleaned with gasoline or kerosene before installation, used after drying, and ensure good lubrication. SKF bearings are generally greased or oil lubricated. When grease lubrication is used, grease with excellent properties such as no impurities, oxidation resistance, rust prevention, and extreme pressure should be selected. The amount of grease filled is 30%-60% of the volume of bearings and bearing boxes, and should not be excessive. The double-row tapered roller bearing with sealing structure and the shaft coupling bearing of the water pump have been filled with grease, and the user can use it directly, and can no longer clean it.
When installing SKF bearings, an equal pressure must be applied to the circumference of the end face of the ring to press the ring in. Do not directly strike the end face of the bearing with a shank or other tools to avoid damage to the bearing. In the case of a small interference, press the end of the SKF bearing ring with a sleeve at room temperature, tap the sleeve with a shank, and press the ring in evenly through the sleeve. If installed in large quantities, a hydraulic press can be used. When pressing in, ensure that the outer ring end face and the shell shoulder end face, the inner ring end face and the shaft shoulder end face are pressed tightly, and no gap is allowed. SKF 22208 EK bearings online , pls click here :
When the interference is large, it can be installed by oil bath heating or inductor heating SKF bearing method. The heating temperature range is 80℃-100℃, and the maximum cannot exceed 120℃. At the same time, nuts or other suitable methods should be used to tighten the SKF bearings to prevent the bearing from shrinking in the width direction and causing a gap between the ring and the shoulder.
Single-row tapered roller bearings should be adjusted for clearance at the end of installation. The clearance value should be specifically determined according to different operating conditions and the amount of interference. If necessary, it should be tested to determine. The double row tapered roller bearing and the pump shaft connection SKF bearing have been adjusted the clearance at the factory, no need to adjust during installation.
After the SKF bearing is installed, a rotation test should be carried out. First, it is used for the rotating shaft or SKF bearing box. If there is no abnormality, the power will be used for unloaded and low-speed operation. If the temperature rises and an abnormality is found, the operation should be stopped and checked. It can be delivered for use only after the normal operation test.
Heat treatment of SKF bearing steel
Bearing steel ingots are generally subjected to diffusion annealing at a high temperature of 1200 to 1250°C for a long time to improve carbide segregation. During hot processing, the atmosphere in the furnace should be controlled. The heating temperature of the billet should not be too high and the holding time should not be too long to avoid serious decarburization. The final rolling (forging) temperature is usually between 800 and 900°C. If it is too high, coarse network carbides are likely to occur, and if it is too low, rolling (forging) cracks are easily formed. The finished rolled (forged) material should be quickly cooled to 650°C to prevent cementite from appearing on the grain boundaries in a network, and the rolling process can be controlled if possible.
In order to obtain good machinability and pre-structure before quenching, the bearing steel for cold working should be completely spheroidized and annealed. Annealing temperature is generally 780 ~ 800 ℃, to prevent decarburization during annealing. If the rolled steel has too coarse mesh cementite, it needs to be normalized before annealing. Chromium bearing steel is usually heated between 830～860℃, oil quenched, and tempered at 150～180℃. In the structure of precision bearings, the amount of retained austenite should be reduced as much as possible or the retained austenite should be kept stable during use, so it is often necessary to perform cold treatment at -80°C (or lower) after quenching and at 120 to 140 Stabilization is carried out for a long time at ℃.
The heat treatment process of bearing steel includes normal heat treatment, annealing and other pre-heat treatment and final heat treatment. GCr15 steel is a kind of high carbon chromium bearing steel with less alloy content, good performance and the most widely used. GCr15 bearing steel has high and uniform hardness, good wear resistance, and high contact fatigue performance after heat treatment.
1.Heat treatment in advance
(1) Normalizing: chrome bearing steel normalizing process, the workpiece is kept warm for 40~60min after diathermy, the cooling needs to be faster, and it is changed to spheroidizing annealing immediately after normalizing.
(2) Spheroidizing annealing: GCr15 chromium bearing steel often adopts isothermal spheroidizing annealing process, 790℃ is considered to be the best spheroidizing heating temperature. It needs to be heated to 900~920℃ before annealing, and normalized after holding 2/3~1h.
The holding time depends on the size of the workpiece, the uniformity of the heating furnace, the method and amount of furnace installation, and the uniformity of the original structure before annealing.
Low temperature spheroidizing annealing is mainly suitable for recrystallization annealing of cold punching balls and cold extrusion ferrules.
Ordinary spheroidizing annealing and isothermal spheroidizing annealing are mainly suitable for the annealing of forged ferrules, hot punching balls and horizontal forging balls. Spheroidizing annealing process of chromium bearing steel.
2.Final heat treatment
(1) Bearing parts: Quenching and low temperature tempering are generally adopted, and its purpose is to improve the strength, hardness, wear resistance and fatigue resistance of steel. The quenching temperature of GCr15 steel is 820~860℃, and the critical diameter of oil quenching is 25mm. Generally, oil cooling quenching is adopted. The heating and holding time is longer than that of alloy tool steel, and the salt bath heating coefficient is 0.8~1.5min/mm. The heating coefficient of the air furnace is 1.5~2min/mm.
Low temperature tempering at 160℃±10℃, tempering time is generally 2~4h.
The precision bearing parts are of stable dimensions. After quenching, they should be cold-treated at -60 to 80°C, and the holding time is 2 to 4 hours. After the cold treatment, the parts are returned to room temperature and tempered within 4 hours to prevent the parts from cracking.
Residual stresses that are not completely eliminated during low temperature tempering will be redistributed after grinding. These two kinds of stress will cause the size of the part to change, and even crack. To this end, supplementary tempering should be performed again, the tempering temperature is 120 ~ 160 ℃, heat preservation 5 ~ 10h or longer.
(2) Tool and mold GCr15 heat treatment: Because this steel is prone to white spot defects, heat treatment of large tool and mold is easy to crack. Slow heating or 690 ℃ long time (more than 5h) section isothermal can reduce the probability of cracking, austenitizing temperature selection 810℃±10℃, heat preservation coefficient a=1.6~0.9min/mm. Workpieces larger than 60mm in diameter require water-oil dual-liquid quenching.