The influence of cooling process on deformation after metal quenching is also a very important deformation reason. The deformation of hot oil quenching is smaller than that of cold oil quenching, which is generally controlled at 100 ± 20 ℃. The cooling capacity of oil is also crucial to deformation. The stirring mode and speed of quenching affect the deformation.
The faster the cooling speed of metal heat treatment, the more uneven the cooling, the greater the stress, and the greater the variable bearing shape of the die. Pre cooling can be adopted as far as possible on the premise of ensuring the hardness requirements of the die;
The use of staged cooling and quenching can significantly reduce the thermal stress and structural stress during metal quenching, which is an effective method to reduce the deformation of some workpieces with complex shapes; For some workpieces with special complexity or high precision requirements, is other mal quenching can significantly reduce deformation.
On the premise of ensuring the same hardness requirements, try to use oily medium. Experiments and practice have proved that on the premise of no difference in other conditions, the cooling speed of oily medium is slower, while that of aqueous medium is relatively faster. Moreover, compared with oil medium, the change of water temperature has a greater impact on the cooling characteristics of water medium. Under the same heat treatment conditions, the deformation of oil medium after quenching is relatively small compared with that of water medium bearing.
The structure of parts shall be reasonable:preventing bearing
After metal heat treatment, in the cooling process, the thin part always cools fast and the thick part cools slowly. Under the condition of meeting the actual production needs, the great difference between the thickness of the workpiece should be reduced as far as possible, and the section of the part should be uniform as much as possible, so as to reduce the distortion and cracking tendency in the transition zone due to stress concentration;
The symmetry of structure, material composition and structure of the workpiece shall be maintained as far as possible to reduce the distortion caused by uneven cooling; Sharp edges, corners, grooves, etc. shall be avoided as far as possible, and fillet transition shall be provided at the thickness junction and steps of the workpiece; Try to reduce the asymmetry of hole and slot reinforcement structure on the workpiece; The method of reserving processing quantity is adopted for parts with uneven thickness.
Bearing maintenance: in order to maintain the original performance of the bearing in good condition for as long as possible, it must be maintained and overhauled in order to prevent accidents, ensure the reliability of operation and improve productivity and economy.
Maintain the operation standard of corresponding mechanical operation conditions and carry out it regularly. The contents include monitoring the operation status, replenishing or changing the lubricant, and regular disassembly inspection. Maintenance items during operation include bearing rotation sound, vibration, temperature, lubricant state, etc.Maintenance and judgment of preventing bearing heat treatment deformation
Bearing maintenance: bearing cleaning: when disassembling the lower bearing for maintenance, first record the appearance of the bearing, confirm the residual amount of lubricant, and wash the bearing after sampling the lubricant for inspection. As a cleaning agent, gasoline and kerosene are commonly used.Maintenance and judgment of preventing bearing heat treatment deformation
The cleaning of the removed bearing is divided into coarse cleaning and fine cleaning. They are placed in the container respectively. First, put the metal mesh bottom so that the bearing does not directly contact the dirt of the container. During rough cleaning, if the bearing rotates with dirt, it will damage the rolling surface of the bearing, which should be paid attention to. In the coarse cleaning oil, use a brush to remove the grease and adhesion. After it is roughly clean, turn to fine cleaning.Maintenance and judgment of preventing bearing heat treatment deformation
Fine cleaning is to carefully clean the bearing while rotating in the cleaning oil. In addition, the cleaning oil should always be kept clean.Maintenance and judgment of preventing bearing heat treatment deformation
Use reasonable cooling methods preventing bearing heat treatment deformation
Maintenance and judgment of bearing: in order to judge whether the disassembled bearing can be used, it should be checked after the bearing is cleaned. Check the state of raceway surface, rolling surface and mating surface, the wear of cage, the increase of bearing clearance and the damage of irrelevant dimensional accuracy, which are abnormal. Maintenance and judgment of preventing bearing heat treatment deformation
For non separable small ball bearings, support the inner ring horizontally with one hand and rotate the outer ring to confirm whether it is smooth. A large amount of radial or axial movement of one ring while the other ring is fixed. The large amount of activity along the radial direction is called radial clearance, and the large amount of activity along the axial direction is called axial clearance.Maintenance and judgment of preventing bearing heat treatment deformation
Generally speaking, the greater the radial clearance, the greater the axial clearance, and vice versa. According to the state of the bearing, the clearance can be divided into the following three types:
Original clearance
Clearance in free state before bearing installation. The original clearance is determined by the processing and assembly of the manufacturer.Maintenance and judgment of preventing bearing heat treatment deformation
Installation clearance preventing bearing
Also known as fit clearance, it is the clearance when the bearing, shaft and bearing seat are installed but not working. Due to interference installation, either the inner ring is increased, or the outer ring is reduced, or both, the installation clearance is smaller than the original clearance.
Working clearance preventing bearing
The clearance of the bearing in the working state. When working, the temperature rise of the inner ring is large and the thermal expansion is large, which reduces the clearance of the bearing
Bearing clearance; At the same time, due to the load, the contact between the rolling element and the raceway produces elastic deformation, which increases the bearing clearance. Whether the bearing working clearance is larger or smaller than the installation clearance depends on the combined action of these two factors. How to measure and install the size of angular contact bearing
Take of preventing bearing heat treatment deformation
AC contact type: Based on the big end, the preload acts on the big end face of the outer ring, and the actual force is on the other side of the inner ring; On the contrary, taking the big end as the benchmark, the preload acts on the other end face of the inner ring, and the actual force is on the big end face of the outer ring.
BM contact type: similar to the above situation.
Characteristics and application of angular contact ball bearing:
The ultimate speed of angular contact ball bearing is high, which can bear both radial load and axial load, and can also bear pure axial load. Its axial load capacity is determined by the contact angle and increases with the increase of contact angle.
Single row angular contact ball bearings can only bear axial load in one direction. When bearing radial load, additional axial force will be caused, and the corresponding reverse load must be applied. Therefore, this kind of bearings are generally used in pairs. Double row angular contact ball bearing can bear large radial and axial two-way combined load and moment load dominated by radial load. It can limit the two-way axial displacement of shaft or shell, and the contact angle is 30 degrees.preventing bearing
Angular contact ball bearings installed in pairs can withstand radial and axial combined loads dominated by radial loads, as well as pure radial loads. The series configuration can only bear the axial load in a single direction, while the other two configurations can bear the axial load in either direction. This type of bearing is generally selected and combined by the manufacturer and submitted to the user in pairs. preventing bearing
After installation, there is preloading interference, and the ferrule and steel ball are in the axial preload state, which improves the stiffness and rotation accuracy of the whole group of bearings as a single support. Features of articulated bearing:preventing bearing
The articulated bearing can bear large load. According to its different types and structures, it can bear radial load, axial load or combined load of radial and axial at the same time. Because the outer spherical surface of the inner ring is inlaid with composite materials, the bearing can produce self lubrication in operation.
It is generally used for low-speed swing movement and low-speed rotation. It can also make inclined movement within a certain angle range. When the non concentricity between the supporting shaft and the shaft shell hole is large, it can still work normally.preventing bearing
Articulated bearings are widely used in engineering hydraulic cylinders, forging machine tools, engineering machinery, automation equipment, automotive shock absorbers, hydraulic machinery and other industries Introduction and classification of plain bearings plain bearings are spherical plain bearings. The basic type is composed of inner and outer rings with spherical sliding spherical contact surfaces.
According to its structure and type, it can bear radial load, axial load, or combined load acting both radially and axially. Because the spherical sliding contact area of the joint bearing is large and the inclination angle is large, but also because most joint bearings adopt special process treatment methods, such as surface phosphating, galvanizing, chromium plating or outer sliding surface lining, pad inlay, spraying, etc.
It has good anti-wear, self-lubricating ability and anti-corrosion ability even if it is installed with large self lubrication and self-aligning capacity. Bearings are used for a wide range of swinging, tilting and joint movements.
Application scope of articulated bearing
When checking tapered roller bearings, never expose the bearings to pollutants or moisture. If the work is interrupted, the machine shall be covered with oil paper, plastic sheet or similar materials.
If it is possible to clean the naked bearing without disassembly, clean it with a brush coated with white spirit, and then dry it with a piece of lint free cloth or blow dry with compressed air (be careful not to start the rotation of the bearing assembly).Maintenance and judgment of preventing bearing heat treatment deformation
Do not clean the sealed cover or dust-proof bearing; Just wipe the outer surface. If the tapered roller bearing is damaged, it needs to be replaced. It is much more economical to replace the bearing during the regular shutdown and maintenance period than the loss of sudden shutdown due to the damage of the array bearing. Maintenance and judgment of preventing bearing heat treatment deformation
The combined bearing belongs to precision parts, so it is required to be quite cautious in use, that is, the high-performance bearing is used. If it is not used properly, it can not achieve the expected performance effect, and it is easy to damage the bearing.Maintenance and judgment of preventing bearing heat treatment deformation
Without normal lubrication, bearing lubrication has the primary impact on the fatigue life, friction, wear, temperature rise and vibration of rolling bearings. The bearing cannot be obligated.
Analysis of the notice of combined bearing damage shows that 40% of bearing damage is related to poor lubrication. Therefore, the superior lubrication of bearing is an effective way to reduce the friction and wear of bearing.Maintenance and judgment of preventing bearing heat treatment deformation
When replacing the combined bearing, carefully check the new bearing, and carefully check the shaft diameter, bearing seat hole and rotor;
When assembling and disassembling the bearing, strictly implement the maintenance process and operate carefully to avoid bearing damage caused by improper assembly and disassembly;
Refuel and change the oil on time to ensure that the working condition of the bearing is always in good condition;
Check carefully during operation, and eliminate the hidden trouble in time if it is found.Maintenance and judgment of preventing bearing heat treatment deformation
Observation: if the rolling bearing is well lubricated and free of sundries and moisture, it indicates that the oil seal of the bearing is not worn. If the original bearing box is opened, the bearing shall be visually inspected and the oil seal shall be inspected regularly. Maintenance and judgment of preventing bearing heat treatment deformation
Check the condition of the oil seal near the bearing to ensure that they are sufficient to prevent hot liquid, corrosive liquid and gas from penetrating into the bearing along the axis. If the oil seal is damaged, replace it as soon as possible.
Check the automatic lubrication system to ensure that the oil or grease enters the bearing and the correct amount is added. At the same time, check whether the lubricant is discolored or blackened. If so, it usually indicates that the lubricant contains impurities, which is also harmful to the use of the bearing.
Listening: using hearing to identify irregular operation is a very common method. For example, using a screwdriver or electronic stethoscope to detect a simple abnormal noise is a method often used by experienced operators and maintenance personnel. If the bearing is in good operation, it will make a low whine sound. For example, when the bearing makes sharp hiss, squeak and other irregular sounds, it may indicate that the bearing is in poor operation.
Touch: high temperature often indicates that the bearing has been in an abnormal situation, and high temperature is also harmful to the lubricant in the bearing. However, the high temperature of the bearing is caused by the lubricant in the rolling bearing at some times.
If the bearing operates for a long time at a temperature exceeding 120 ℃, the service life of the bearing will be reduced. The causes of bearing high temperature include insufficient or excessive lubrication of lubricant, impurities in lubricant, excessive load, bearing damage, insufficient clearance and friction caused by oil seal. Under normal circumstances, the bearing will have a natural temperature rise just after lubrication or after lubrication, and it will last for one to two days.
The radial clearance of double row deep groove ball bearing refers to the movement amount of one ring fixed and the other ring moving from one extreme position to another in the direction perpendicular to the axis of double row deep groove ball bearing. Whether the selection of bearing clearance is correct or not has a great impact on the mechanical operation accuracy, bearing life, friction resistance, temperature rise, vibration and noise.
If the selection of radial bearing clearance is too small, the number of rolling elements bearing load will increase, the contact stress will decrease, and the operation will be more stable. However, the friction resistance will increase and the temperature rise will also increase. Maintenance and judgment of preventing bearing heat treatment deformation
On the contrary, the contact stress increases, the vibration is large, the friction resistance decreases and the temperature rise is low. Therefore, it is of great significance to select the appropriate clearance value according to the service conditions of the bearing. In fact, when selecting bearing clearance, the following main factors must be fully considered:Maintenance and judgment of preventing bearing heat treatment deformation
The tightness of double row deep groove ball bearing with shaft and shell hole will lead to the change of bearing clearance. Generally, the clearance value will be reduced after the bearing is installed;
During the operation of the double row deep groove ball bearing, due to the different heat dissipation conditions between the shaft and the shell, there is a temperature difference between the inner ring and the outer ring, which will reduce the clearance value;Maintenance and judgment of preventing bearing heat treatment deformation
Due to the different expansion coefficient of shaft and shell materials, the clearance value will be reduced or increased.Maintenance and judgment of preventing bearing heat treatment deformation
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