According to the bearing surface grinding metamorphic layer formation mechanism, the impact grinding metamorphic layer of the main factors is the grinding heat and grinding force. The following analysis on the reasons for bearing failure.
1 bearing the grinding heat
The thin bearings grinding, the grinding wheel and the workpiece contact area, consume large amounts of energy, resulting in a large number of grinding heat, causing the local instantaneous grinding zone temperature. Use of linear motion heat transfer theory derivation, calculation or application infrared and thermocouple method measured the instantaneous temperature under experimental conditions can be found in the 0.1 ~ 0.001ms instantaneous temperature within the grinding zone up to 1000 ~ 1500 ℃. Such instantaneous temperature, a certain depth sufficient to work the surface layer of high temperature oxidation, amorphous structure, high-temperature tempering, secondary hardening, cracking and other changes or burns.
(1) the surface oxide layer
The instantaneous high temperature steel surface under the role of oxygen in the air, up into very thin (20 ~ 30nm) thin layer of iron oxide. It should be noted that the oxide layer thickness and the total thickness of the surface layer of grinding deterioration test results showed a corresponding relationship. This shows that the thickness of the oxide layer which is directly related with the grinding process, the grinding quality is an important symbol.
(2) amorphous tissue layer
Instantaneous grinding zone so that the surface temperature reaches a molten state, the molten metal molecular flow has been evenly coated on the work surface, and is the base metal at breakneck speed cooling, forming a thin layer of amorphous tissue layer. It has high hardness and toughness, but it is only about 10nm, it is easy to be removed precision grinding.
(3) high-temperature tempering layer
Instantaneous grinding zone temperature to a certain depth can (10 ~ 100nm) is heated to a temperature above the tempering heating the workpiece. Does not reach the austenitizing temperature in the case, as the heating temperature is increased, the surface layer by layer will be generated corresponding to the temperature of the heating or tempering retempered organizational changes, hardness is decreased. The higher the heating temperature, the hardness decreased also more powerful.
2013年8月27日星期二
Installation of high-speed bearings fit and adjustment
A high speed bearings with clearance and according to both the high-speed precision bearings bearing requirements, but also according to temperature bearing requirements, so consider the coordination and clearance to take account of the following points:
(1) when the temperature rose to high temperature dimensional change and hardness; (2) caused by high speed centrifugal force system change and shape change.
In short, high-speed, high-temperature conditions, coordination and clearance from the choice of the bearing should strive to maintain the accuracy and performance, it is difficult.
In order to ensure the bearing raceway after installation of small deformation, interference fit amount of interference can not get too big, and high speed centrifugal force and high temperature thermal expansion, or offset with the surface normal pressure. Or so with the surface relaxation, so the amount of interference must be considered under the premise of these two factors be carefully calculated, at room temperature constant speed and effective amount of interference for high-speed bearings may be invalid.
If the calculation results of this contradiction is too large (usually only in the ultra high speed only in this case), only by taking the lubrication ring lubrication and hydrostatic lubrication with a double measure, and this solution has the potential to break the bearing dmn value 3 million mark.
In considering the high speed bearing clearance is not only to consider the above factors, but also to consider the thermal elongation axis of the impact on the clearance required bearing in working condition, that there is at operating temperature optimum clearance, which kind of clearance is taken into account, the outer ring ball groove center precise alignment of state formation. As high-speed bearings for lower relative sliding and internal friction, it is best not to use the inner and outer rings relative axial displacement method to adjust the ball bearing clearance.
In considering the amount of interference with the bearing and clearance, to note that materials at high temperatures becomes soft and easily deformed features, as well as many from the room temperature to high temperature changes cause some permanent deformation possibilities.
(2) the requirement for host-related parts
Where the rotational speed bearing system requires precision bearing dynamic balancing shaft and the bearing seat hole installation site should have higher than normal required size and shape precision accuracy, especially for concentricity and retaining shoulder seat hole or journal vertical, and in consideration of these issues, it must also be noted that the high-speed operation of the bearing element and the temperature factor.
Shaft support systems require both high rigidity, and quality requirements as light as possible, in order to overcome this contradiction can be taken, such as reducing the surface roughness and improve surface hardening measures to improve the supporting stiffness, the use of hollow shaft to reduce system quality.
3 high-speed bearings examples of the development hereby HA type with ultra high-speed development of tapered roller bearings for example.
(1) of the problem
In the gas turbine and certain machine tools and construction machinery, high speed and axial load, using the ball bearing is life is too short, use a short cylindrical roller bearing axial load capacity is insufficient, the axial clearance is difficult to adjust, hoping to use cone roller bearings break this problem.
(2) must be solved key technology
Increase speed limit tapered roller bearing technology lies in improving inner ring large rib and roller end lubrication between the state, this area most likely to occur at high speeds severe wear and burns, is the main reason for limiting its high speed.
(3) solution
The general structure of tapered roller bearings, the oil circulation routes in the inner wall with a large roller end contact area is difficult to get oil, and this part of the relative sliding big, precisely needed most lubricants.
Therefore, Japan and other countries have developed HA-type tapered roller bearings, this bearing wall in the outer ring, so that the flow of oil can lubricate the outer ring ribs and roller end contact part, but here even when at rest can also save some oil, to avoid the starting lean burn accidents, but click on the outer wall of the need to create several drain hole to prevent oil discharge passage without, retention caused by certain parts of the oil agitation loss of power and temperature l too high. Since no inner wall, the temperature decreased, thus reducing the mating surface between the inner ring and the shaft occurs between peristaltic possibilities. This structure of the bearing outer ring on the cage used to guide the way, so that the cage can be more smoothly guide roller without askew functioning to avoid vibrations and excessive wear and tear, which will also help speed.
(4) can be achieved
This bearing type HA dmn value up to 200 million, more than triple the normal structure, for example a gas turbine this bearing spindle gear (Model I-IA30205), the axial load 1000N conditions, guarantee There 2L/min the implementation of the bearing to the oil supply of the 4th cycle turbine oil, its working speed of up to 60,000 will not appear in turn burns.
(1) when the temperature rose to high temperature dimensional change and hardness; (2) caused by high speed centrifugal force system change and shape change.
In short, high-speed, high-temperature conditions, coordination and clearance from the choice of the bearing should strive to maintain the accuracy and performance, it is difficult.
In order to ensure the bearing raceway after installation of small deformation, interference fit amount of interference can not get too big, and high speed centrifugal force and high temperature thermal expansion, or offset with the surface normal pressure. Or so with the surface relaxation, so the amount of interference must be considered under the premise of these two factors be carefully calculated, at room temperature constant speed and effective amount of interference for high-speed bearings may be invalid.
If the calculation results of this contradiction is too large (usually only in the ultra high speed only in this case), only by taking the lubrication ring lubrication and hydrostatic lubrication with a double measure, and this solution has the potential to break the bearing dmn value 3 million mark.
In considering the high speed bearing clearance is not only to consider the above factors, but also to consider the thermal elongation axis of the impact on the clearance required bearing in working condition, that there is at operating temperature optimum clearance, which kind of clearance is taken into account, the outer ring ball groove center precise alignment of state formation. As high-speed bearings for lower relative sliding and internal friction, it is best not to use the inner and outer rings relative axial displacement method to adjust the ball bearing clearance.
In considering the amount of interference with the bearing and clearance, to note that materials at high temperatures becomes soft and easily deformed features, as well as many from the room temperature to high temperature changes cause some permanent deformation possibilities.
(2) the requirement for host-related parts
Where the rotational speed bearing system requires precision bearing dynamic balancing shaft and the bearing seat hole installation site should have higher than normal required size and shape precision accuracy, especially for concentricity and retaining shoulder seat hole or journal vertical, and in consideration of these issues, it must also be noted that the high-speed operation of the bearing element and the temperature factor.
Shaft support systems require both high rigidity, and quality requirements as light as possible, in order to overcome this contradiction can be taken, such as reducing the surface roughness and improve surface hardening measures to improve the supporting stiffness, the use of hollow shaft to reduce system quality.
3 high-speed bearings examples of the development hereby HA type with ultra high-speed development of tapered roller bearings for example.
(1) of the problem
In the gas turbine and certain machine tools and construction machinery, high speed and axial load, using the ball bearing is life is too short, use a short cylindrical roller bearing axial load capacity is insufficient, the axial clearance is difficult to adjust, hoping to use cone roller bearings break this problem.
(2) must be solved key technology
Increase speed limit tapered roller bearing technology lies in improving inner ring large rib and roller end lubrication between the state, this area most likely to occur at high speeds severe wear and burns, is the main reason for limiting its high speed.
(3) solution
The general structure of tapered roller bearings, the oil circulation routes in the inner wall with a large roller end contact area is difficult to get oil, and this part of the relative sliding big, precisely needed most lubricants.
Therefore, Japan and other countries have developed HA-type tapered roller bearings, this bearing wall in the outer ring, so that the flow of oil can lubricate the outer ring ribs and roller end contact part, but here even when at rest can also save some oil, to avoid the starting lean burn accidents, but click on the outer wall of the need to create several drain hole to prevent oil discharge passage without, retention caused by certain parts of the oil agitation loss of power and temperature l too high. Since no inner wall, the temperature decreased, thus reducing the mating surface between the inner ring and the shaft occurs between peristaltic possibilities. This structure of the bearing outer ring on the cage used to guide the way, so that the cage can be more smoothly guide roller without askew functioning to avoid vibrations and excessive wear and tear, which will also help speed.
(4) can be achieved
This bearing type HA dmn value up to 200 million, more than triple the normal structure, for example a gas turbine this bearing spindle gear (Model I-IA30205), the axial load 1000N conditions, guarantee There 2L/min the implementation of the bearing to the oil supply of the 4th cycle turbine oil, its working speed of up to 60,000 will not appear in turn burns.
2013年8月24日星期六
Bearing rings of cold treatment method
Quenching the bearing ring to cool to room temperature, immediately placed in an environment below room temperature a certain time, out at room temperature, this is lower than the processing temperature is called cold treatment. Bearing steel cold treatment is often used freezers and dry ice alcohol solution.
1 The role of cold treatment
Precision bearings for higher dimensional stability; ferrule hardened (especially quenching), the internal organization retains more residual austenite, this residual austenite is unstable organization, storage and use of bearings process will continue to change, thus changing the accuracy of the cross bearing. Therefore the use of cold treatment process, it can reduce tissue retained austenite, slightly increase the hardness of parts.
2 Cold Process
Stay at room temperature after quenching: quenching, must make uniform cooling to room temperature inside and outside the ring after the cold treatment, or easy to crack, cooled to room temperature immediately after cold treatment (usually no more than 30min), otherwise it will abort the austenite to martensite changes.
Cold treatment temperature: the temperature of cold treatment based primarily on termination of martensitic transformation temperature of the steel Mf, while also considering the cold treatment on the mechanical properties and process and other factors.
For GCr15 steel, cold treatment selection -70 ℃; accuracy is not very high ferrule or equipment limitations, the cold treatment temperature optionally -40 ~ -70 ℃; super precision bearings in the -70 ℃ ~ -80 ℃ between the cold treatment. Cold temperatures affect the bearing life impact fatigue and exposure.
Cold insulation: Although a large number of martensite is cooled to a certain temperature Tilting moment to complete, but the number of rings to make both surface and core part cold treatment to achieve uniform temperature, requires a certain holding time, usually 1 to 1.5 h.
Cold treatment after tempering: ferrule on the air after the cold treatment, the temperature was slowly warmed to room temperature tempering timely manner. Temperature can not be too fast, or easy to crack; tempering timely, otherwise the internal ferrule large residual stresses can cause cracking rings, generally no more than 2h.
1 The role of cold treatment
Precision bearings for higher dimensional stability; ferrule hardened (especially quenching), the internal organization retains more residual austenite, this residual austenite is unstable organization, storage and use of bearings process will continue to change, thus changing the accuracy of the cross bearing. Therefore the use of cold treatment process, it can reduce tissue retained austenite, slightly increase the hardness of parts.
2 Cold Process
Stay at room temperature after quenching: quenching, must make uniform cooling to room temperature inside and outside the ring after the cold treatment, or easy to crack, cooled to room temperature immediately after cold treatment (usually no more than 30min), otherwise it will abort the austenite to martensite changes.
Cold treatment temperature: the temperature of cold treatment based primarily on termination of martensitic transformation temperature of the steel Mf, while also considering the cold treatment on the mechanical properties and process and other factors.
For GCr15 steel, cold treatment selection -70 ℃; accuracy is not very high ferrule or equipment limitations, the cold treatment temperature optionally -40 ~ -70 ℃; super precision bearings in the -70 ℃ ~ -80 ℃ between the cold treatment. Cold temperatures affect the bearing life impact fatigue and exposure.
Cold insulation: Although a large number of martensite is cooled to a certain temperature Tilting moment to complete, but the number of rings to make both surface and core part cold treatment to achieve uniform temperature, requires a certain holding time, usually 1 to 1.5 h.
Cold treatment after tempering: ferrule on the air after the cold treatment, the temperature was slowly warmed to room temperature tempering timely manner. Temperature can not be too fast, or easy to crack; tempering timely, otherwise the internal ferrule large residual stresses can cause cracking rings, generally no more than 2h.
Bearing basic technical knowledge
Bearing joints: the sliding contact surface of the spherical, mainly applicable to swing movement, tilting movement and rotation of spherical plain bearings.
Bearings: a set of bearing two or more simultaneously by said bearing structure combination of rolling bearings. Such as needle roller and thrust cylindrical roller bearings, needle roller and thrust ball bearings, needle roller and angular contact ball bearings.
Other Bearings: In addition to the above other than the structure of the rolling bearing.
2, the bearing parts
Bearing parts: one consisting of the parts bearing, but does not include all the accessories.
Bearing rings: one or several raceway bearing to the heart of the annular parts.
Bearing washer: with one or several of the thrust bearing raceway ring parts.
Flat ring: a detachable substantially flat washer, use it as an inner or outer part of the radial cylindrical roller bearing outer or inner ring of a wall.
Thrust collar (detachable): a separable with "L" shaped cross-section ring, with the outer part of a radial cylindrical roller bearing inner ring of a wall.
In the ring: having two or more rows of rollers of a roller bearing inner ring separable used to isolate two rollers and guide rollers.
Snap ring: single port having a constant cross-section ring, mounted in a ring ditch, a roller bearing in the housing or shaft axial position.
Lock ring: single port with constant cross-section ring, mounted as a ring in a ring ditch rollers or cage will remain in the bearing.
Spacer: the annular parts, for the two bearing rings or bearing washer, or between the two halves or between the bearing rings between the two halves of the bearing washer, so that they are maintained between the axial distance required.
Seals: formed by one or several parts of the ring cap fixed to the bearing and a ferrule or the gasket ring or gasket in contact with another or to form a narrow gap labyrinth, prevent oil leakage and foreign matter.
Cover: is a ring cover, usually a thin metal plate stamping, a ring fixed to the bearing or washer and extending towards the other ring or gasket, cover bearing internal space, but not with another ring or gasket contacts
Bearings: a set of bearing two or more simultaneously by said bearing structure combination of rolling bearings. Such as needle roller and thrust cylindrical roller bearings, needle roller and thrust ball bearings, needle roller and angular contact ball bearings.
Other Bearings: In addition to the above other than the structure of the rolling bearing.
2, the bearing parts
Bearing parts: one consisting of the parts bearing, but does not include all the accessories.
Bearing rings: one or several raceway bearing to the heart of the annular parts.
Bearing washer: with one or several of the thrust bearing raceway ring parts.
Flat ring: a detachable substantially flat washer, use it as an inner or outer part of the radial cylindrical roller bearing outer or inner ring of a wall.
Thrust collar (detachable): a separable with "L" shaped cross-section ring, with the outer part of a radial cylindrical roller bearing inner ring of a wall.
In the ring: having two or more rows of rollers of a roller bearing inner ring separable used to isolate two rollers and guide rollers.
Snap ring: single port having a constant cross-section ring, mounted in a ring ditch, a roller bearing in the housing or shaft axial position.
Lock ring: single port with constant cross-section ring, mounted as a ring in a ring ditch rollers or cage will remain in the bearing.
Spacer: the annular parts, for the two bearing rings or bearing washer, or between the two halves or between the bearing rings between the two halves of the bearing washer, so that they are maintained between the axial distance required.
Seals: formed by one or several parts of the ring cap fixed to the bearing and a ferrule or the gasket ring or gasket in contact with another or to form a narrow gap labyrinth, prevent oil leakage and foreign matter.
Cover: is a ring cover, usually a thin metal plate stamping, a ring fixed to the bearing or washer and extending towards the other ring or gasket, cover bearing internal space, but not with another ring or gasket contacts
2013年8月23日星期五
Crossed roller bearings composition and characteristics
Crossed roller bearings are divided into two categories, one is a cross cylindrical roller bearings, another is a cross-tapered roller bearings. Cross roller bearings in a foreign country has a long history of application, while in the country is only in recent years before entering the public's sight, with its own characteristics and have other bearings incomparable superiority and well received by everyone be used.
Cross cylindrical roller bearings, having been split inner or outer ring, load rollers and spacer retainer after the Cross-Roller Ring and fastened together to prevent separated from each other, so when you install the cross roller bearing easy to operate. Since the rollers are arranged to cross, so only one set of Cross Roller Ring can bear loads in all directions, compared to conventional models, rigidity increased by 3 to 4 times. Meanwhile, imports bearing Cross cylindrical roller bearings Crossed roller bearings due to inner or outer ring is split in two, the bearing clearance adjustable, even if they are applied preload can be obtained with high precision rotary motion.
Crossed roller bearings Features:
1 operation simplifies installation
Standard cross roller bearing outer ring is divided into two parts, or inner, load roller and cage after being fixed together, you can fine tune the connection when installing bolts and mounting flange to achieve the desired load state Therefore, the installation operation is very simple.
2 bear large axial and radial loads
Because roller at 90 ° to the V-shaped groove raceway via a spacer retainer is arranged perpendicular to each other, this design makes cross roller bearings can withstand greater radial load, axial load and moment load and all the direction of the load.
3 installation space savings
Cross roller bearing outer ring size is minimal miniaturization, especially thin structure is close to the limit of small size, and high rigidity, so the most suitable for industrial robot joints or rotating parts, machining centers of rotation table, manipulator rotating part, precision rotary tables, medical equipment, measuring instruments, IC manufacturing equipment, etc. wide range of applications.
Cross cylindrical roller bearings, having been split inner or outer ring, load rollers and spacer retainer after the Cross-Roller Ring and fastened together to prevent separated from each other, so when you install the cross roller bearing easy to operate. Since the rollers are arranged to cross, so only one set of Cross Roller Ring can bear loads in all directions, compared to conventional models, rigidity increased by 3 to 4 times. Meanwhile, imports bearing Cross cylindrical roller bearings Crossed roller bearings due to inner or outer ring is split in two, the bearing clearance adjustable, even if they are applied preload can be obtained with high precision rotary motion.
Crossed roller bearings Features:
1 operation simplifies installation
Standard cross roller bearing outer ring is divided into two parts, or inner, load roller and cage after being fixed together, you can fine tune the connection when installing bolts and mounting flange to achieve the desired load state Therefore, the installation operation is very simple.
2 bear large axial and radial loads
Because roller at 90 ° to the V-shaped groove raceway via a spacer retainer is arranged perpendicular to each other, this design makes cross roller bearings can withstand greater radial load, axial load and moment load and all the direction of the load.
3 installation space savings
Cross roller bearing outer ring size is minimal miniaturization, especially thin structure is close to the limit of small size, and high rigidity, so the most suitable for industrial robot joints or rotating parts, machining centers of rotation table, manipulator rotating part, precision rotary tables, medical equipment, measuring instruments, IC manufacturing equipment, etc. wide range of applications.
Cross roller bearing surface rust work
Cross roller bearings in the preservation and operation of the process, because of its metal and the external environment, it is easy to produce rust. This not only greatly affect the running properties of the bearing, reduced efficiency. But also to the bearing life greatly reduced. cross roller bearing rust of the surface pretreatment methods:
1 Surface cleaning: cleaning rust must be in accordance with the nature of the surface and the prevailing conditions, select the appropriate method. Commonly used with solvent cleaning, chemical cleaning and mechanical cleaning treatment method.
2 available after the surface is dry clean filtered thrust cylindrical roller bearings drying compressed air, or by 120 ~ 170 ℃ of the drier, can also be wiped clean gauze.
Coated with anti-rust oil Method:
1 immersion method: Some small items using immersion in rust oils, allowed a layer of rust on the surface adhesion grease approach. Antirust film thickness can be controlled by the temperature or viscosity of the oil to achieve.
2 brushing method for NA immersion or spray outdoor construction equipment or special shape products, brush when it is necessary to pay attention not produce accumulation and pay attention coated to prevent leakage.
3 spray some large objects can rust oiled using immersion method, generally about 0.7Mpa pressure filter with compressed air spray cleaner place. Spray application of anti-rust oil or solvent dilution thin rust oil, but must adopt comprehensive fire protection and labor protection measures.
1 Surface cleaning: cleaning rust must be in accordance with the nature of the surface and the prevailing conditions, select the appropriate method. Commonly used with solvent cleaning, chemical cleaning and mechanical cleaning treatment method.
2 available after the surface is dry clean filtered thrust cylindrical roller bearings drying compressed air, or by 120 ~ 170 ℃ of the drier, can also be wiped clean gauze.
Coated with anti-rust oil Method:
1 immersion method: Some small items using immersion in rust oils, allowed a layer of rust on the surface adhesion grease approach. Antirust film thickness can be controlled by the temperature or viscosity of the oil to achieve.
2 brushing method for NA immersion or spray outdoor construction equipment or special shape products, brush when it is necessary to pay attention not produce accumulation and pay attention coated to prevent leakage.
3 spray some large objects can rust oiled using immersion method, generally about 0.7Mpa pressure filter with compressed air spray cleaner place. Spray application of anti-rust oil or solvent dilution thin rust oil, but must adopt comprehensive fire protection and labor protection measures.
2013年8月22日星期四
Bearing inspection and acceptance of the method
Check the bearing, the user must have the following knowledge:
(1) Which of the bearing commodities inspection standards based;
(2) What bearing commodities inspection items, why should test these items;
(3) bearing merchandise conducting quality inspection, you need to do to prepare the work, why should these preparations;
(4) the various test items bearing merchandise under what conditions, with what methods, what equipment to be tested, the test results must be within the tolerances in how to be qualified;
(5) bearing large quantities of goods and sometimes, not one hundred percent inspection, then it should be what kind of sampling plan, what quantity taken for examination in order to more fully with sufficient reliability to represent all the goods bearing the quality and inspection The result has to be measured according to what criteria to determine whether these products are qualified batch should be accepted or rejected should be unqualified approval.
Acceptance inspection of cross roller bearing can generally be divided into three categories, namely:
Routine check - bearing arrives routine general inspection.
Routine examination - of the bearing assembly associated with dimensional accuracy, precision rotation, bearing clearance and the bearing of the residual magnetic intensity of such items to be checked.
Special inspection - the quality of the bearing vibration, noise, quality and other specific requirements of the bearing to be checked.
(1) Which of the bearing commodities inspection standards based;
(2) What bearing commodities inspection items, why should test these items;
(3) bearing merchandise conducting quality inspection, you need to do to prepare the work, why should these preparations;
(4) the various test items bearing merchandise under what conditions, with what methods, what equipment to be tested, the test results must be within the tolerances in how to be qualified;
(5) bearing large quantities of goods and sometimes, not one hundred percent inspection, then it should be what kind of sampling plan, what quantity taken for examination in order to more fully with sufficient reliability to represent all the goods bearing the quality and inspection The result has to be measured according to what criteria to determine whether these products are qualified batch should be accepted or rejected should be unqualified approval.
Acceptance inspection of cross roller bearing can generally be divided into three categories, namely:
Routine check - bearing arrives routine general inspection.
Routine examination - of the bearing assembly associated with dimensional accuracy, precision rotation, bearing clearance and the bearing of the residual magnetic intensity of such items to be checked.
Special inspection - the quality of the bearing vibration, noise, quality and other specific requirements of the bearing to be checked.
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