There are limits to the speed at which INA bearings can reach. It usually depends on the operating temperature at which the lubricant and the material of the bearing components can be used.
The speed at which the bearing reaches the operating temperature limit depends on the amount of heat generated by the friction during rolling (including any other external heat) and how much heat can be carried away from the bearing.
The type and size of the INA bearing, internal structure, load bearing, lubrication and cooling conditions, cage structure, manufacturing accuracy and clearance, etc., have a certain impact on the speed that the bearing can achieve.
Two differently defined rated speeds are usually listed in the relevant product table; reference speed (related to heat) and limit speed (related to physical structure), which are parameters depending on different considerations.
Most INA bearings are damaged for many reasons, such as excessively small bearing clearances caused by previously estimated loads, ineffective seals, and tight fits. Any of these factors have their particular type of damage and leave a special mark of damage. Therefore, inspecting the bearing of the damaged shaft, in most cases, its possible cause can be found.
In general, one-third of INA bearing damage is caused by fatigue damage, the other third is due to poor lubrication, and the other third is due to contaminants entering the bearing or improperly installed. However, these types of damage are also related to industry. For example, the pulp and paper industry is mostly due to bearing damage due to poor lubrication or contamination rather than material fatigue.
2018年12月29日星期六
2018年12月18日星期二
Reasons for SKF bearing damage and how to avoid it
Generally speaking, as long as the SKF imported bearings are in a good working environment, the correct use will not be as damaged as some SKF bearings. But why is this SKF imported bearing that belongs to precision parts damaged?
According to the analysis of the engineers, many SKF bearings are damaged because they exceed the load that SKF bearings can bear or the gaps of SKF bearings are too small due to poor sealing and tight fitting. And different reasons can lead to different SKF imported bearing damage forms or leave traces of different damage. In many cases, we also found that one-third of SKF bearings are damaged due to fatigue, another 1/3 is due to poor lubrication, and one-third is because the working environment is not clean, and it has entered the dirt or device. Incorrect.
In order to reduce the damage of SKF bearings as much as possible, we should pay attention to keep SKF bearings and working environment clean, and do not let dust and other dirt enter SKF bearings. Second, be careful not to apply too much pressure during installation.
According to the analysis of the engineers, many SKF bearings are damaged because they exceed the load that SKF bearings can bear or the gaps of SKF bearings are too small due to poor sealing and tight fitting. And different reasons can lead to different SKF imported bearing damage forms or leave traces of different damage. In many cases, we also found that one-third of SKF bearings are damaged due to fatigue, another 1/3 is due to poor lubrication, and one-third is because the working environment is not clean, and it has entered the dirt or device. Incorrect.
In order to reduce the damage of SKF bearings as much as possible, we should pay attention to keep SKF bearings and working environment clean, and do not let dust and other dirt enter SKF bearings. Second, be careful not to apply too much pressure during installation.
2018年12月14日星期五
Analysis of the influence of ntn thin-wall bearing vibration on service life
In general, rolling bearings in ntn bearings do not generate noise by themselves. The "thin wall bearing noise" that is usually felt is actually the sound effect of the bearing directly or indirectly vibrating with the surrounding structure.
This is why many times noise problems can be considered as vibration problems involving the entire bearing application. Excitation due to the change in the number of rolling elements. When a radial load is applied to a thin-walled bearing, the number of rolling elements carrying the load will change slightly during operation, and the resulting vibration is unavoidable. However, it can be relieved by axial preloading and loaded on all rolling elements.
When the waviness of the component is closely matched between the bearing ring and the bearing housing or the transmission shaft, the ntn bearing ring may be deformed in accordance with the shape of the adjacent component. If deformation occurs, vibration may occur during operation. Therefore, it is important to machine the housing and drive shaft to the required tolerances.
Partial damage Due to handling or installation errors, small portions of thin-walled bearing raceways and rolling elements may be damaged. In operation, rolling a damaged ntn bearing component produces a specific vibration frequency. Vibration frequency analysis identifies damaged bearing components. Vibration Behavior in Applications In many applications, the stiffness of the bearing is the same as the stiffness of the surrounding structure. Due to this feature, it is possible to reduce the vibration in the application by properly selecting the bearings (including preload and clearance) and their configuration in the application.
Whether ntn bearings can judge the degree of damage according to various needs, and the main consideration in this regard is the effect of damage. For mechanical performance, importance, installation conditions are considered, to the next maintenance The effect determined during the period, but for the case where the defect cannot be used, it is necessary to replace the new thin-walled bearing, and it is necessary to pay attention to the crack of any one of the inner ring, the outer ring, the rolling element, and the cage. This is also an effect that is maintained in this regard. So there are also skills in the sense, the following is to introduce the rules from eight.
After the ntn bearing is subjected to a load, plastic deformation occurs at the contact between the rolling element and the raceway. When the load is too heavy, plastic deformation pits will be formed on the surface of the raceway, and the bearing will generate vibration and noise during operation.
Due to the relative movement of the rolling elements and the raceways and the intrusion of dirt and dust, the rolling bodies and the raceway surfaces are subject to wear. When the amount of wear is large, the bearing ntn, noise and vibration of the shaft are increased, which reduces the running precision of the thin-walled bearing, thus directly affecting the accuracy of some main engines. Therefore, for some precision mechanical bearings, the amount of wear can be used to limit the life of the bearing.
This is why many times noise problems can be considered as vibration problems involving the entire bearing application. Excitation due to the change in the number of rolling elements. When a radial load is applied to a thin-walled bearing, the number of rolling elements carrying the load will change slightly during operation, and the resulting vibration is unavoidable. However, it can be relieved by axial preloading and loaded on all rolling elements.
When the waviness of the component is closely matched between the bearing ring and the bearing housing or the transmission shaft, the ntn bearing ring may be deformed in accordance with the shape of the adjacent component. If deformation occurs, vibration may occur during operation. Therefore, it is important to machine the housing and drive shaft to the required tolerances.
Partial damage Due to handling or installation errors, small portions of thin-walled bearing raceways and rolling elements may be damaged. In operation, rolling a damaged ntn bearing component produces a specific vibration frequency. Vibration frequency analysis identifies damaged bearing components. Vibration Behavior in Applications In many applications, the stiffness of the bearing is the same as the stiffness of the surrounding structure. Due to this feature, it is possible to reduce the vibration in the application by properly selecting the bearings (including preload and clearance) and their configuration in the application.
Whether ntn bearings can judge the degree of damage according to various needs, and the main consideration in this regard is the effect of damage. For mechanical performance, importance, installation conditions are considered, to the next maintenance The effect determined during the period, but for the case where the defect cannot be used, it is necessary to replace the new thin-walled bearing, and it is necessary to pay attention to the crack of any one of the inner ring, the outer ring, the rolling element, and the cage. This is also an effect that is maintained in this regard. So there are also skills in the sense, the following is to introduce the rules from eight.
After the ntn bearing is subjected to a load, plastic deformation occurs at the contact between the rolling element and the raceway. When the load is too heavy, plastic deformation pits will be formed on the surface of the raceway, and the bearing will generate vibration and noise during operation.
Due to the relative movement of the rolling elements and the raceways and the intrusion of dirt and dust, the rolling bodies and the raceway surfaces are subject to wear. When the amount of wear is large, the bearing ntn, noise and vibration of the shaft are increased, which reduces the running precision of the thin-walled bearing, thus directly affecting the accuracy of some main engines. Therefore, for some precision mechanical bearings, the amount of wear can be used to limit the life of the bearing.
2018年12月12日星期三
Quality judgment measures for FAG bearing installation
After the FAG bearing is installed in the main machine, if the radial runout of the main shaft is measured, it can be found that the measured value of each revolution has a certain change; when the measurement is continuously performed, it can be found that after a certain number of revolutions, the change will be approximately Repeatedly appear. The index for measuring the degree of such change is the cyclic rotation precision, and the change approximately repeats the required number of revolutions to represent the "quasi-period" of the cycle rotation accuracy. The magnitude of the magnitude change in the quasi-period is large, that is, the cycle rotation precision is poor. .
If the spindle is properly preloaded, the speed is gradually reduced to close to the duty speed to implement the "run-in" function of the bearing, which can improve the cycle rotation accuracy of the spindle.
The main factors used for adjustment are installation, use and maintenance, maintenance, etc. in line with technical requirements. According to FAG bearing installation, use, maintenance, maintenance technical requirements, the bearing contact load, speed, temperature, vibration, noise and lubrication status monitoring and inspection, find the abnormality immediately to find the cause, make adjustments to make it back to normal. The installation condition is one of the factors that use the bearing is the primary factor that often causes the change of state between the various parts of the installation package, the abnormal operation state and the early termination of life
1. Contact fatigue failure
Contact fatigue failure means that the working surface of the FAG bearing is subjected to alternating stress and causes failure. Contact fatigue spalling occurs on the bearing working surface, often accompanied by fatigue cracks, first from the maximum alternating shear stress below the contact surface, and then spread to the surface to form different peeling shapes, such as pitting or pitting. Peeling into small pieces called shallow peeling. Due to the gradual enlargement of the exfoliation surface, it tends to expand deeper and form deep exfoliation. Deep exfoliation is a source of fatigue in contact fatigue failure.
2, wear and tear failure
Wear failure refers to the failure of the relative sliding friction between the surfaces resulting in the continuous wear of the metal on the working surface. Continued wear and tear will cause gradual damage to the bearing components and ultimately lead to loss of FAG bearing dimensional accuracy and other related problems. Wear may affect the shape change, the increase of the clearance and the change of the surface of the working surface may affect the lubricant or cause the pollution to a certain extent, resulting in complete loss of the lubrication function, thus causing the bearing to lose the rotation precision or even the normal operation. Wear failure is one of the common failure modes of various types of bearings. It is usually classified into the most common abrasive wear and adhesive wear according to the form of wear.
1) Instrument detection
Using a spectrometer such as a spectrometer or SPM or a new VIB05 detector to determine the operating state of the bearing to determine whether maintenance or replacement should be performed is the most convenient and reliable method.
For example, when using the VIBO5 detector, this is a microprocessor-based machine state detection instrument with vibration detection, FAG bearing status analysis and infrared temperature measurement. The operation is simple, and the status alarm is automatically indicated. It is very suitable for the field equipment operation and maintenance personnel to detect the equipment status, find problems in time, and ensure the normal and reliable operation of the equipment.
With such an instrument, the bearing working potential can be fully utilized, the bearing warranty can be timely and the failure can be avoided, and it is suitable for young workers to make up for their lack of experience.
2) Manual detection
In places where the above instruments are not available, the equipment can be tested using a medical stethoscope-like monitoring tool. Experienced operators can also use the tools such as round bars or wrenches to resist the outer casing of the machine, and use the ear to monitor through the tool. The sound of the bearing.
The normal FAG bearing operation sound should be uniform, stable and not harsh, and the abnormal bearing operation sound is intermittent, impact or harsh sound.
If the spindle is properly preloaded, the speed is gradually reduced to close to the duty speed to implement the "run-in" function of the bearing, which can improve the cycle rotation accuracy of the spindle.
The main factors used for adjustment are installation, use and maintenance, maintenance, etc. in line with technical requirements. According to FAG bearing installation, use, maintenance, maintenance technical requirements, the bearing contact load, speed, temperature, vibration, noise and lubrication status monitoring and inspection, find the abnormality immediately to find the cause, make adjustments to make it back to normal. The installation condition is one of the factors that use the bearing is the primary factor that often causes the change of state between the various parts of the installation package, the abnormal operation state and the early termination of life
1. Contact fatigue failure
Contact fatigue failure means that the working surface of the FAG bearing is subjected to alternating stress and causes failure. Contact fatigue spalling occurs on the bearing working surface, often accompanied by fatigue cracks, first from the maximum alternating shear stress below the contact surface, and then spread to the surface to form different peeling shapes, such as pitting or pitting. Peeling into small pieces called shallow peeling. Due to the gradual enlargement of the exfoliation surface, it tends to expand deeper and form deep exfoliation. Deep exfoliation is a source of fatigue in contact fatigue failure.
2, wear and tear failure
Wear failure refers to the failure of the relative sliding friction between the surfaces resulting in the continuous wear of the metal on the working surface. Continued wear and tear will cause gradual damage to the bearing components and ultimately lead to loss of FAG bearing dimensional accuracy and other related problems. Wear may affect the shape change, the increase of the clearance and the change of the surface of the working surface may affect the lubricant or cause the pollution to a certain extent, resulting in complete loss of the lubrication function, thus causing the bearing to lose the rotation precision or even the normal operation. Wear failure is one of the common failure modes of various types of bearings. It is usually classified into the most common abrasive wear and adhesive wear according to the form of wear.
1) Instrument detection
Using a spectrometer such as a spectrometer or SPM or a new VIB05 detector to determine the operating state of the bearing to determine whether maintenance or replacement should be performed is the most convenient and reliable method.
For example, when using the VIBO5 detector, this is a microprocessor-based machine state detection instrument with vibration detection, FAG bearing status analysis and infrared temperature measurement. The operation is simple, and the status alarm is automatically indicated. It is very suitable for the field equipment operation and maintenance personnel to detect the equipment status, find problems in time, and ensure the normal and reliable operation of the equipment.
With such an instrument, the bearing working potential can be fully utilized, the bearing warranty can be timely and the failure can be avoided, and it is suitable for young workers to make up for their lack of experience.
2) Manual detection
In places where the above instruments are not available, the equipment can be tested using a medical stethoscope-like monitoring tool. Experienced operators can also use the tools such as round bars or wrenches to resist the outer casing of the machine, and use the ear to monitor through the tool. The sound of the bearing.
The normal FAG bearing operation sound should be uniform, stable and not harsh, and the abnormal bearing operation sound is intermittent, impact or harsh sound.
2018年12月8日星期六
The role of heat treatment of TIMKEN bearing parts
To determine exactly how much it is superheated, the microstructure must be observed. If coarse needle-shaped martensite appears in the quenched structure of GCr15 steel, it is quenched and superheated. The cause of the formation may be excessive heating caused by excessive quenching heating temperature or too long heating and holding time; it may also be due to the serious banding of the original structure, between the two belts.
Quenching cracked bearing parts are called quenching cracks due to internal stress caused by internal stress during quenching and cooling. The causes of such cracks are: due to excessive heating temperature of quenching or too rapid cooling, the microstructure stress when the thermal stress and metal mass volume change is greater than the fracture strength of the steel; the original defects of the working surface (such as surface micro cracks or scratches) Trace) or internal defects of steel (such as slag inclusion, severe non-metallic inclusions, white spots, shrinkage residuals, etc.) form stress concentration during quenching; severe surface decarburization and carbide segregation of TIMKEN bearings; The fire is insufficient or not tempered in time; the cold punching stress caused by the previous process is too large, forging and folding, deep turning tool marks, sharp edges and corners of the oil groove. In short, the cause of the quenching crack may be one or more of the above factors, and the existence of internal stress is the main reason for the formation of quenching cracks. The quenching crack is deep and slender, the fracture is straight, and the fractured section has no oxidation color. It is often a longitudinal straight crack or annular crack on the bearing ring; the shape on the bearing steel ball is S-shaped,
During the heat treatment process of the bearing parts, if it is heated in an oxidizing medium, the surface of the TIMKEN bearing will be oxidized to reduce the mass fraction of carbon on the surface of the part, resulting in surface decarburization. The depth of the surface decarburization layer exceeds the final processing allowance and the part is scrapped. Determining the depth of the surface decarburization layer The metallographic method and the microhardness method can be used in the metallographic examination. The surface layer microhardness distribution curve measurement method shall prevail and the arbitration criterion may be used. The common quality defects of TIMKEN bearing parts after heat treatment include: quenching microstructure overheating, underheating, quenching cracks, insufficient hardness, heat treatment deformation, surface decarburization, soft spots, etc., TIMKEN bearing maintenance and repair methods. Overheating The microstructure after quenching is overheated from the rough mouth of the bearing part.
The importance of the TIMKEN bearing means that when it is damaged, it will cause the equipment to stop. Therefore, it is better to install a temperature detector for this type of bearing. Under normal conditions, TIMKEN bearings will naturally rise in temperature after lubrication or relubrication for one to two days.
Generally, a bearing with a working temperature of 150° or more is called a high-temperature TIMKEN bearing. Since the chrome bearing steel has a temperature drop exceeding 150°, its hardness will drop sharply and the size will be unstable, which will make the TIMKEN bearing not work properly. Therefore, for TIMKEN bearings operating at 150° to 350°, if the ferrule and rolling element are still made of ordinary high carbon chrome bearing steel, the bearing parts must be specially tempered, generally higher than the work. Tempering is carried out at a temperature of 50°. TIMKEN bearing steel that has been tempered according to the above requirements can be used normally at operating temperature. However, due to the decrease in hardness after tempering, the life of TIMKEN bearings has decreased. When the bearing operating temperature is higher than 350 °, it must be made of high temperature resistant TIMKEN bearing steel.
Reasons why TIMKEN bearing temperature is too high:
1. The quality of the bearing lubricant is not good, and the viscosity of the lubricating oil is high;
2, the mechanism assembly is too tight, the gap is insufficient;
3, TIMKEN bearing assembly is too tight;
4. The TIMKEN bearing race rotates on the shaft or inside the casing;
5, the bearing load is too large;
6. TIMKEN bearing cage or rolling element is broken.
Quenching cracked bearing parts are called quenching cracks due to internal stress caused by internal stress during quenching and cooling. The causes of such cracks are: due to excessive heating temperature of quenching or too rapid cooling, the microstructure stress when the thermal stress and metal mass volume change is greater than the fracture strength of the steel; the original defects of the working surface (such as surface micro cracks or scratches) Trace) or internal defects of steel (such as slag inclusion, severe non-metallic inclusions, white spots, shrinkage residuals, etc.) form stress concentration during quenching; severe surface decarburization and carbide segregation of TIMKEN bearings; The fire is insufficient or not tempered in time; the cold punching stress caused by the previous process is too large, forging and folding, deep turning tool marks, sharp edges and corners of the oil groove. In short, the cause of the quenching crack may be one or more of the above factors, and the existence of internal stress is the main reason for the formation of quenching cracks. The quenching crack is deep and slender, the fracture is straight, and the fractured section has no oxidation color. It is often a longitudinal straight crack or annular crack on the bearing ring; the shape on the bearing steel ball is S-shaped,
During the heat treatment process of the bearing parts, if it is heated in an oxidizing medium, the surface of the TIMKEN bearing will be oxidized to reduce the mass fraction of carbon on the surface of the part, resulting in surface decarburization. The depth of the surface decarburization layer exceeds the final processing allowance and the part is scrapped. Determining the depth of the surface decarburization layer The metallographic method and the microhardness method can be used in the metallographic examination. The surface layer microhardness distribution curve measurement method shall prevail and the arbitration criterion may be used. The common quality defects of TIMKEN bearing parts after heat treatment include: quenching microstructure overheating, underheating, quenching cracks, insufficient hardness, heat treatment deformation, surface decarburization, soft spots, etc., TIMKEN bearing maintenance and repair methods. Overheating The microstructure after quenching is overheated from the rough mouth of the bearing part.
The importance of the TIMKEN bearing means that when it is damaged, it will cause the equipment to stop. Therefore, it is better to install a temperature detector for this type of bearing. Under normal conditions, TIMKEN bearings will naturally rise in temperature after lubrication or relubrication for one to two days.
Generally, a bearing with a working temperature of 150° or more is called a high-temperature TIMKEN bearing. Since the chrome bearing steel has a temperature drop exceeding 150°, its hardness will drop sharply and the size will be unstable, which will make the TIMKEN bearing not work properly. Therefore, for TIMKEN bearings operating at 150° to 350°, if the ferrule and rolling element are still made of ordinary high carbon chrome bearing steel, the bearing parts must be specially tempered, generally higher than the work. Tempering is carried out at a temperature of 50°. TIMKEN bearing steel that has been tempered according to the above requirements can be used normally at operating temperature. However, due to the decrease in hardness after tempering, the life of TIMKEN bearings has decreased. When the bearing operating temperature is higher than 350 °, it must be made of high temperature resistant TIMKEN bearing steel.
Reasons why TIMKEN bearing temperature is too high:
1. The quality of the bearing lubricant is not good, and the viscosity of the lubricating oil is high;
2, the mechanism assembly is too tight, the gap is insufficient;
3, TIMKEN bearing assembly is too tight;
4. The TIMKEN bearing race rotates on the shaft or inside the casing;
5, the bearing load is too large;
6. TIMKEN bearing cage or rolling element is broken.
Cross roller bearing introduction and description
Cross-roller bearings, the rollers of which are arranged at right angles to each other at intervals between the inner and outer wheels. They can withstand loads from all directions (such as axial, thrust or momentum loads). Since the roller is in contact with the track surface, the bearing is less likely to be elastically deformed by the load.
This type of bearing is widely used in industrial robots, work machines and medical facilities, where high rigidity, tightness and high speed are required to ensure accuracy.
In the cross-roller bearing, since the cylindrical rollers are vertically arranged by the spacers on the V-shaped groove rolling surface of 90°, one cross roller bearing can withstand radial load and axial load. And load in all directions, such as torque load.
The size of the inner and outer rings is miniaturized to a minimum, and the extremely thin type is a small size close to the limit and has high rigidity, so it is most suitable for a joint portion or a rotating portion of an industrial robot, a rotary table of a machining center, Uses such as robot rotating parts, precision rotary tables, medical equipment, gauges, and IC manufacturing equipment.
This type of bearing is widely used in industrial robots, work machines and medical facilities, where high rigidity, tightness and high speed are required to ensure accuracy.
In the cross-roller bearing, since the cylindrical rollers are vertically arranged by the spacers on the V-shaped groove rolling surface of 90°, one cross roller bearing can withstand radial load and axial load. And load in all directions, such as torque load.
The size of the inner and outer rings is miniaturized to a minimum, and the extremely thin type is a small size close to the limit and has high rigidity, so it is most suitable for a joint portion or a rotating portion of an industrial robot, a rotary table of a machining center, Uses such as robot rotating parts, precision rotary tables, medical equipment, gauges, and IC manufacturing equipment.
2018年12月7日星期五
What is an air bearing?
Air bearing: The air bearing is a sliding bearing that suspends the journal in the bearing ring with high-pressure gas and uses air as a lubricant to completely eliminate the friction between the solids and the heat generated thereby. Air is less viscous than oil, high temperature resistant, and non-polluting, so it can be used in high speed machines, instruments and radioactive devices, but its load capacity is lower than oil.
Under the extremely high rotation of ordinary rolling bearings, the centrifugal force of the rolling elements (balls or rollers) acting on the outer ring raceway is too large to bear. Therefore, the steel rolling elements are replaced by ceramic rolling elements, the former is lighter in weight and the centrifugal force is thus reduced. At the same time, the diameter of the rolling elements is reduced to reduce its centrifugal force. For ultra-high-speed cutting machines, the ideal main bearings are air bearings and magnetic bearings.
Under the extremely high rotation of ordinary rolling bearings, the centrifugal force of the rolling elements (balls or rollers) acting on the outer ring raceway is too large to bear. Therefore, the steel rolling elements are replaced by ceramic rolling elements, the former is lighter in weight and the centrifugal force is thus reduced. At the same time, the diameter of the rolling elements is reduced to reduce its centrifugal force. For ultra-high-speed cutting machines, the ideal main bearings are air bearings and magnetic bearings.
2018年12月5日星期三
Common quality defects of bearing parts after heat treatment
Common quality defects of bearing parts after heat treatment include: quenching microstructure overheating, underheating, quenching cracks, insufficient hardness, heat treatment deformation, surface decarburization, soft spots, etc.
Overheat
Overheating of the microstructure after quenching can be observed from the rough mouth of the bearing part. However, the exact microstructure must be observed to determine the degree of overheating. If coarse needle-shaped martensite appears in the quenched structure of GCr15 steel, it is quenched and superheated. The formation may be caused by excessive overheating of the quenching heating temperature or excessive heating and holding time; or it may be due to the serious banding of the original structure, forming a local martensite needle-like coarseness in the low carbon zone between the two zones. Local overheating caused. The retained austenite in the superheated structure increases, and the dimensional stability decreases. Due to the overheating of the quenched structure, the crystal of the steel is coarse, which leads to a decrease in the toughness of the part, a decrease in the impact resistance, and a decrease in the life of the bearing. Excessive heat can even cause quenching cracks.
2. Underheat
If the quenching temperature is low or the cooling is poor, a tortite structure exceeding the standard is produced in the microstructure, which is called an underheated structure, which lowers the hardness and sharply reduces the wear resistance, which affects the bearing life.
3. Quenching crack
The cracks formed by the internal stress during the quenching and cooling process of the bearing parts are called quenching cracks. The causes of such cracks are: due to excessive heating temperature of quenching or too rapid cooling, the microstructure stress when the thermal stress and metal mass volume change is greater than the fracture strength of the steel; the original defects of the working surface (such as surface micro cracks or scratches) Trace) or internal defects of steel (such as slag inclusion, severe non-metallic inclusions, white spots, shrinkage residuals, etc.) form stress concentration during quenching; severe surface decarburization and carbide segregation; insufficient tempering after quenching of parts Or not tempered in time; the cold punching stress caused by the previous process is too large, forging and folding, deep turning tool marks, sharp edges and corners of the oil groove. In short, the cause of the quenching crack may be one or more of the above factors, and the existence of internal stress is the main reason for the formation of quenching cracks. The quenching crack is deep and slender, the fracture is straight, and the fractured section has no oxidation color. It tends to be a longitudinal straight crack or an annular crack on the bearing ring; the shape on the bearing steel ball is S-shaped, T-shaped or ring-shaped. The microstructure characteristic of quenching cracks is that there is no decarburization on both sides of the crack, and the difference is obvious with forging cracks and material cracks.
4. Heat treatment deformation
When the bearing parts are heat treated, there are thermal stresses and tissue stresses. These internal stresses can overlap or partially cancel each other. It is complex and variable because it can follow heating temperature, heating speed, cooling method, cooling speed, and part shape. And the change in size changes, so heat treatment deformation is inevitable. Knowing and mastering the law of change can make the deformation of the bearing parts (such as the ellipse of the ferrule, the size of the ferrule, etc.) in a controllable range, which is conducive to the production. Of course, mechanical collisions during heat treatment can also deform the part, but this deformation can be reduced and avoided with improved handling.
5. Surface decarburization
During the heat treatment process of the bearing parts, if it is heated in an oxidizing medium, the surface will be oxidized to reduce the mass fraction of carbon on the surface of the part, resulting in surface decarburization. The depth of the surface decarburization layer exceeds the final processing allowance and the part is scrapped. Determining the depth of the surface decarburization layer The metallographic method and the microhardness method can be used in the metallographic examination. The surface layer microhardness distribution curve measurement method shall prevail and the arbitration criterion may be used.
6. Soft point
The phenomenon that the surface hardness of the bearing parts is insufficient due to insufficient heating, poor cooling, improper quenching operation, etc. is called quenching soft point. It can cause a serious drop in surface wear resistance and fatigue strength like surface decarburization.
Overheat
Overheating of the microstructure after quenching can be observed from the rough mouth of the bearing part. However, the exact microstructure must be observed to determine the degree of overheating. If coarse needle-shaped martensite appears in the quenched structure of GCr15 steel, it is quenched and superheated. The formation may be caused by excessive overheating of the quenching heating temperature or excessive heating and holding time; or it may be due to the serious banding of the original structure, forming a local martensite needle-like coarseness in the low carbon zone between the two zones. Local overheating caused. The retained austenite in the superheated structure increases, and the dimensional stability decreases. Due to the overheating of the quenched structure, the crystal of the steel is coarse, which leads to a decrease in the toughness of the part, a decrease in the impact resistance, and a decrease in the life of the bearing. Excessive heat can even cause quenching cracks.
2. Underheat
If the quenching temperature is low or the cooling is poor, a tortite structure exceeding the standard is produced in the microstructure, which is called an underheated structure, which lowers the hardness and sharply reduces the wear resistance, which affects the bearing life.
3. Quenching crack
The cracks formed by the internal stress during the quenching and cooling process of the bearing parts are called quenching cracks. The causes of such cracks are: due to excessive heating temperature of quenching or too rapid cooling, the microstructure stress when the thermal stress and metal mass volume change is greater than the fracture strength of the steel; the original defects of the working surface (such as surface micro cracks or scratches) Trace) or internal defects of steel (such as slag inclusion, severe non-metallic inclusions, white spots, shrinkage residuals, etc.) form stress concentration during quenching; severe surface decarburization and carbide segregation; insufficient tempering after quenching of parts Or not tempered in time; the cold punching stress caused by the previous process is too large, forging and folding, deep turning tool marks, sharp edges and corners of the oil groove. In short, the cause of the quenching crack may be one or more of the above factors, and the existence of internal stress is the main reason for the formation of quenching cracks. The quenching crack is deep and slender, the fracture is straight, and the fractured section has no oxidation color. It tends to be a longitudinal straight crack or an annular crack on the bearing ring; the shape on the bearing steel ball is S-shaped, T-shaped or ring-shaped. The microstructure characteristic of quenching cracks is that there is no decarburization on both sides of the crack, and the difference is obvious with forging cracks and material cracks.
4. Heat treatment deformation
When the bearing parts are heat treated, there are thermal stresses and tissue stresses. These internal stresses can overlap or partially cancel each other. It is complex and variable because it can follow heating temperature, heating speed, cooling method, cooling speed, and part shape. And the change in size changes, so heat treatment deformation is inevitable. Knowing and mastering the law of change can make the deformation of the bearing parts (such as the ellipse of the ferrule, the size of the ferrule, etc.) in a controllable range, which is conducive to the production. Of course, mechanical collisions during heat treatment can also deform the part, but this deformation can be reduced and avoided with improved handling.
5. Surface decarburization
During the heat treatment process of the bearing parts, if it is heated in an oxidizing medium, the surface will be oxidized to reduce the mass fraction of carbon on the surface of the part, resulting in surface decarburization. The depth of the surface decarburization layer exceeds the final processing allowance and the part is scrapped. Determining the depth of the surface decarburization layer The metallographic method and the microhardness method can be used in the metallographic examination. The surface layer microhardness distribution curve measurement method shall prevail and the arbitration criterion may be used.
6. Soft point
The phenomenon that the surface hardness of the bearing parts is insufficient due to insufficient heating, poor cooling, improper quenching operation, etc. is called quenching soft point. It can cause a serious drop in surface wear resistance and fatigue strength like surface decarburization.
Select roll bearing method
The size of the roll bearing is limited by the installation space of the rolling mill (the inner diameter of the bearing and the outer diameter depend on the diameter of the roll neck and the roll body). The bearing has a small cross section and is a thin-walled bearing, and they must also bear a large radial load. Therefore multi-row roller bearings are used.
At present, four-row cylindrical roller bearings and four-row tapered roller bearings are mainly used, and double-row cylindrical roller bearings and double-row tapered rollers are also used. Most of the tapered roller bearings adopt hollow roller and post cage. In order to improve the lubrication condition of the bearing, the outer surface and the end surface of the bearing are respectively provided with oil grooves and oil holes. When the gap is matched with the roll neck, the inner hole surface of the inner ring of the bearing A spiral oil tank is opened on the top.
The structural form of the roll bearing is determined according to different types of rolling mills, different working conditions and different structural configurations. In general, four-row cylindrical roller bearings are easy to obtain high machining accuracy, so they have high-speed rotation characteristics, and are easy to install and disassemble, and can be used to press the inner ring raceway surface and the roll after the inner ring is pressed into the roll neck. Simultaneous grinding, which is beneficial to improve rolling precision. It is mostly used for high-speed, high-precision rolling mill support rolls. Four-row tapered roller bearings have large bearing capacity and can withstand both radial and axial loads. They are suitable for low and medium speed rolling mills. .
At present, four-row cylindrical roller bearings and four-row tapered roller bearings are mainly used, and double-row cylindrical roller bearings and double-row tapered rollers are also used. Most of the tapered roller bearings adopt hollow roller and post cage. In order to improve the lubrication condition of the bearing, the outer surface and the end surface of the bearing are respectively provided with oil grooves and oil holes. When the gap is matched with the roll neck, the inner hole surface of the inner ring of the bearing A spiral oil tank is opened on the top.
The structural form of the roll bearing is determined according to different types of rolling mills, different working conditions and different structural configurations. In general, four-row cylindrical roller bearings are easy to obtain high machining accuracy, so they have high-speed rotation characteristics, and are easy to install and disassemble, and can be used to press the inner ring raceway surface and the roll after the inner ring is pressed into the roll neck. Simultaneous grinding, which is beneficial to improve rolling precision. It is mostly used for high-speed, high-precision rolling mill support rolls. Four-row tapered roller bearings have large bearing capacity and can withstand both radial and axial loads. They are suitable for low and medium speed rolling mills. .
2018年12月4日星期二
Bearing diagnostic management
In order to maintain the performance of the rolling bearing, it can maintain long-term use under good conditions, and the bearing must be inspected and maintained. This kind of inspection and maintenance (see the attached bearing storage before the bearing is installed), it is very good for preventing failure in advance. Importantly, it is desirable to carry out regular inspections and maintenance according to the operating standards that are suitable for the operating conditions of the machine. Generally, the following methods are used: 3.1 Inspection under operating conditions According to the rolling sound, vibration, temperature inspection of the bearing and the nature of the lubricant, the lubricant is checked. The time of supplement or replacement is judged. For details, see item 4: In-service inspection and troubleshooting. 3.2 Bearing inspection Fully observe the periodic inspection and replacement of the machine and remove the bearing. Check the condition of the raceway surface and whether it can be used again. For details, please refer to item 5: Inspection of the bearing.
2018年12月3日星期一
Joint bearing outer ring structure
The joint bearing is divided according to the structure of its outer ring:
a. overall outer ring joint bearing;
b. double semi-outer ring joint bearing;
c. single-slit outer ring joint bearing;
d. Double-slit outer ring (split outer ring) joint bearing.
Third, the joint bearing is divided into the rod end or the rod end:
a. general joint bearing;
b. Rod end joint bearing.
4. The joint bearing is divided into: according to whether it needs to be supplemented with lubricant during work:
a. non-self-lubricating joint bearing;
b. Self-lubricating joint bearings.
5. Joint bearings are classified according to the direction in which they can bear the load, the nominal contact angle and the structural type:
a. radial joint bearing;
b. angular contact joint bearing;
c. thrust joint bearing;
d. Rod end joint bearing.
The joint bearing is widely used in various construction machinery, water conservancy and electric power, and other facilities with steering mechanism.
a. overall outer ring joint bearing;
b. double semi-outer ring joint bearing;
c. single-slit outer ring joint bearing;
d. Double-slit outer ring (split outer ring) joint bearing.
Third, the joint bearing is divided into the rod end or the rod end:
a. general joint bearing;
b. Rod end joint bearing.
4. The joint bearing is divided into: according to whether it needs to be supplemented with lubricant during work:
a. non-self-lubricating joint bearing;
b. Self-lubricating joint bearings.
5. Joint bearings are classified according to the direction in which they can bear the load, the nominal contact angle and the structural type:
a. radial joint bearing;
b. angular contact joint bearing;
c. thrust joint bearing;
d. Rod end joint bearing.
The joint bearing is widely used in various construction machinery, water conservancy and electric power, and other facilities with steering mechanism.
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