Rolling bearing in plastic applications in
Rolling mechanical transmission is an important and indispensable part , it is for improving transmission efficiency, reduce energy consumption plays an irreplaceable role.
In modern rolling bearing technology development process , in order to improve the bearing capacity , its optimized design , the use of new materials and new technologies. Plastics, especially plastics and specialty plastics have been increasingly showing their superiority and importance in the bearing industry has.
Plastic proportion of small , wear resistance, corrosion resistance, radiation resistance , good toughness, can be seismic, solid objects can be embedded , and can be targeted accordingly modified to improve its performance based on the design and use requirements , easy processing, direct injection molding complex structures , improved design flexibility and freedom , which provides all the technical and economic feasibility for plastic applications in rolling bearing .
Plastics Application Profiles in Rolling in
Since the bearing 1930 to the first available thermosetting resin , various polymers bearing areas and applications of polymer -based mixtures with the increasing range of applications is expanded .
Plastic bearing retainer to be applied in
After World War II , the Swedish company SKF bearings with PA66 successfully produced a " 0 " class bearing plastic cage ; the 1970s on behalf of the U.S. company Timken bearings tapered bearings for cars front wheel spindle conducted using PA66 cage system trials and studies , more than 160,000 km driving test , nylon cage good lossless prove its performance is better than the life of the steel cage.
Application of plastic cage is the most prominent German . SKF company in the 1980s , had 70 percent of cylindrical roller bearings , and 80% of the new generation of cylindrical roller bearings are used a plastic cage ; FAG Bearings company in more than 50 sets of bearings must provide for it in every car most uses a plastic cage , "E" type symmetrical spherical roller bearings (D ≤ 320mm) 100% using PA66/GF cage, increasing the number of rollers lengthened , so that the bearing load capacity increased by 7 % -37 % temperature of -60 - +120 ℃. SKF company has a high-speed, high temperature , chemical attack requirement, has been widely used PEEK / GF.
In order to satisfy the most demanding automotive applications require , SKF deep groove ball bearing engineers began to turn to the design of high-performance polymeric materials VICTREX PEEK
Application of plastic cage started in the mid- 1960s . In the 1980s , the structure of various types of bearings abroad in plastic cages are widely used in the rise and influence , there are many domestic units carefully conducted research and development and application of plastic cage work , and in the military bearing and some special application of the bearing is preferably obtained . Also in the motor bearings , rolling bearings, freezer bearings, linear motion bearings , bearings and other significant aspects , plastic cage is gradually applied.
Cage is an important part of rolling bearings . It is not only subject to frictional forces , inertial force and the tension of the mechanical stress , but also by certain lubricant or lubricant additive chemical aging products , organic solvents or cooling agents to produce , their impact may be factors such as temperature , shock, vibration , radiation and a combination of factors .
Cage material properties and operational reliability is the key to ensure normal operation of the bearing . Polymer cage strength and flexibility to achieve a perfect combination of lubricated steel surface it has good sliding properties , low friction, wear and heat so that the bearing is maintained at a minimum level. Low inertia material density , even in the absence of the lubricant condition is still plastic cage with excellent operating performance, even when the bearing is therefore no risk that the continuous seizure and secondary injury.
Plastic cage can accommodate in the same cross-sectional dimensions and the number of additional conditions , the size of a larger rolling , thereby increasing the carrying capacity of the bearing, in addition improvement in storage lubricant lubrication conditions , reducing vibration, self-tuning adaptive and save materials, improve production efficiency has obvious advantages. Currently plastic cage main timber is glass fiber reinforced nylon 66 , glass fiber content of 25% -30 %. With the advent of technology, the development of modified plastics and new materials will further expand the plastic used in the bearing cage .
Further expand the application of plastics in Rolling
Plastics are widely used in the bearing retainer holder , has highlighted the advantages of plastic in the rolling bearing applications. With the development of modern technology, the successful development of new materials and plastics extends the scope of application for plastic applications in rolling bearings to further expand the space.
1 ) , has a plastic bearing retainer from PA66/GF, gradually began to use PTFE, PTFE / GF, PEI, PVDF, PEEK / GF, PEEK / CF, PPS, PI, UHMWPE and other materials to adapt to different working conditions . Such as PTFE, PVDF mainly used for anti- corrosion requirements of working conditions ; UHMWPE has good strength , low friction characteristics and low temperature applications (down to -150 ℃), PEEK / GF or CF is mainly used for high-temperature , radiation-resistant , low friction, and working conditions .
2 ) , inner and outer rings are made ??of plastic appears. More types of different purposes.
For example : the inner and outer rings with a POM or PA, the retainer are PA66/GF (wt25%), the rolling body is a glass, stainless steel or ceramic ( zirconia mainly ZrO2, silicon nitride Si3N4, silicon carbide SiC). Such bearings perform well in an alkaline environment , but does not apply to run under acidic corrosive environments.
Inner and outer rings with HDPE, PP , or UHMWPE, cage using HDPE, PP , or UHMWPE bearing , can be used for alternating relatively weak acid environment ( by 30% CuCL2 solution and 30% NaOH solution test ) , applicable to large most acid / base / salt / solvent / oil / gas and seawater corrosion environments.
Inner and outer rings using PEEK / CF, PEEK / GF, PI, PPS and other materials are also used. In POM or PEEK as inner and outer cage of PA66 or PA66/GF or PEEK plastic bearings , precision and tolerance than the usual plastic bearings to improve a lot , suitable for precision machinery, high speed requirements and special conditions occasions.
3 ), is substantially the rolling of stainless steel material , rolling ceramic , glass is also used . In recent years has emerged with PEEK, PI manufacturing rolling .
Bearing main raw material for SiC
4 ), is substantially the rolling of stainless steel material , rolling ceramic , glass is also used . In recent years has emerged with PEEK, PI manufacturing rolling .
Development of plastic, for its application in the bearing to provide a strong technical support
In other countries, plastic bearings developed rapidly, but also a wider range of applications , thanks to the development of plastic in the first place . According to reports, the United States TIMKEN bearing company has developed an advanced bearing material , which is developed after NSK Bearings SKF bearing plastic bearing materials and research and development of high-performance automotive plastic bearing cage and a new development. In 2005 Seiko materials by optimizing the molecular weight of PA , GF GF diameter of the mixing ratio and the like , the rigidity and tensile strength of the material was increased by 70% and 45 % higher than the previously applied material , thereby improving the carrying capacity of the material and creep resistance , which improve bearing performance to provide a strong technical support.
In China, the production of raw materials , especially the development and production of a late start bearing special plastic varieties , there is a big gap with foreign countries . Our engineering plastics and special engineering plastics are also many varieties mainly rely on imports , and some so-called " strategic materials " is still foreign to our blockade , which restricts the development of plastic bearing a certain extent .
Plastic bearings in question must be noted
Many performance characteristics compared to plastic and metal to make it gained widespread use in the bearing , but some of the inherent characteristics of the plastic also makes it shall not be given full consideration in the application of the bearing . As a relatively low intensity , poor hardness, thermal expansion coefficient is much larger than metal , low thermal conductivity, thermal conductivity is poor, heat distortion temperature is low, the relatively poor performance of some plastic acid , as well as high temperature creep and other issues, there are plastic oil resistance and poor , to put forward our views on the following related problems.
With precision
Specifies the level of precision bearings , precision P0 in addition to the ordinary level , there P6, P5, P4 grade, precision in order to improve the GB and ISO standards , this standard applies only to steel bearings and ceramic bearings does not apply to plastic bearings . Precision plastic bearings with relatively low compared to the two types of bearings .
Setting and control clearance value is determined bearing accuracy is very important indicator. Rolling operation the size internal clearance values ??, their fatigue life, vibration and noise , temperature , etc. greatly affect bearing performance . The so-called clearance value refers to the bearing inner (or outer ) side is fixed , the amount of movement of the ferrule and down or left and right direction of the other moves . Clearance values ??for national steel bearings and ceramic bearings with relevant regulations. However, the inner , outer , or inner and outer roller are all made ??of plastic , which is not applicable, it may be because of the poor thermal performance of plastic , so that the clearance is larger reasons and difficult to control.
Similarly , the use of plastic bearings with radial clearance larger than metal bearings . For example, carbon fiber filled PTFE , the gap is usually taken bearing diameter (0.006-0.015) D, D for the shaft diameter (mm). Generally , a total radial clearance of not less than 0.1mm ( when D < 10mm, the value of the gap may be less than 0.1mm), it can avoid the locking of the bearing due to material expansion .
Closely related to the size and precision of the coefficient of thermal expansion of products . Molding shrinkage Average coefficient of thermal expansion of the material will reduce the reduction in accuracy is improved products , so as to reduce the bearing clearance values ??plastic , with improved accuracy, the thermal expansion coefficient of the material is reduced. Also to be noted that the fiber reinforced plastic , since the orientation of the fibers in the flow direction , the thermal expansion coefficient is greater than the flow direction perpendicular to the direction of anisotropy , the article deflection , and dimensional stability .
Relatively moving parts must have a high rigidity and hardness difference
Metal bearings inside, there is a certain difference in hardness between the outer ring and rolling , rolling element and cage material. This plastic bearings , it also has the same requirements .
Closely related to the hardness and rigidity of the plastic . Where measures to improve the rigidity of the material has the effect of increasing the hardness .
Will produce different types of plastics and worn with different materials . When the engagement is made of metal , and hard metal ( e.g., steel ) with the less wear , and the soft metal ( such as brass , aluminum , etc.) with a greater wear . Will produce an uneven surface such as a metal " erosion wear " ; such as metal surface is very smooth , it will produce " adhesive wear ." When engaging material dissimilar resins, adhesive wear generally larger , depending on the extent of its different varieties , such as PBT, PA and POM affinity poor , difficult to produce adhesive wear , and ABS, PP and POM is easy to produce adhesive wear . When the same type of resin material is engaged , the friction and wear characteristics with the dissimilar metal or a resin complex is much worse than the adhesive wear is much greater , due to the difference in hardness in this regard is not , on the other hand because the resin poor heat resistance , thermal conductivity lower than metals and creep occurs , especially at high pressure rolling , sliding surface abnormal high temperature , decrease in hardness , adhesion greatly facilitated , and it is easy to send or locking harsh noise .
No sufficient difference in hardness between similar materials , easily lead to a greater friction relative movement , a large accumulation of frictional heat generated in the friction surface, leaving the resin is softened or molten , so that a frictional resistance to further expand ; resin and the metal of the exists between the hardness difference, while the friction coefficient is small , the thermal conductivity of metal is easy to make savings in reduced friction heat dissipation surface , so that the resin is softened or melted to occur under higher loads or faster .
In the metal bearing , the hardness of the rolling elements is generally higher than the inner and outer rings , it is advantageous to reduce friction and wear, improved bearing life and bearing capacity. Present in the plastic bearing , the rolling little plastic , rigid or not the difference in hardness may be an important reason.
Reduce friction and wear problems
Usually on the friction and wear properties of polymer materials, friction coefficient, specific wear rate , critical PV value and noise indicators to evaluate .
Average wear in plastic POM, PA66, UHMWPE, PTFE, PEEK and other materials is preferably , but using as the friction coupling , is still relatively high coefficient of friction , wear rate greater than the critical PV value is also low, even occur harsh noise.
Coefficient of friction materials generally small , self-lubricating , too. Conditions have self-lubricating cohesion between molecules are smaller , the molecular structure of atoms in a symmetrical arrangement . Another lubricating properties and lubrication conditions.
From the point of view abrasion resistance , UHMWPE, PA, POM, PTFE and other resins are superior to steel and brass.
To reduce the friction coefficient and wear amount of the resin , in addition to the friction coefficient of a resin selected to improve the lubrication conditions, the resin may also be filled by a filler wear , such as PTFE, UHMWPE, graphite , MoS2, oil , powder and bronze a series of measures to enhance the use of modified GF, CF and other fibers.
PV value problem
PV value is a pressure and velocity relative motion between the parts of a very important indicator. The critical limit PV value is about covering layer of plastic and dry friction sliding bearings and lubrication oil pressure ( load ) or speed , which determines the wear resistance of the material, is the life of the product or product use restrictions temperature , this value and friction power loss is proportional to the factors which characterize the heat bearing . The purpose is to limit PV value limit temperature rise to prevent the emergence of high temperature bearings glued destruction.
The size of the PV properties of the matrix resin , the object of friction , lubrication and so on and the operating temperature . PV is such a critical complement each other when POM 0.04-0.09MPa.m / s, followed by self-lubricating modified critical PV value up 0.196MPa.m / s; while POM and 45 # steel with critical PV value up to 0.392-0.588MPa ? m / s. PTFE -based nanocomposites PV value up 1.42-1.49MPa.m / s, temperature up to 230 ℃. Different resins at the same speed , PV different values ??at different temperatures ; same resin at different temperatures PV values ??are different.
CF reinforced PEEK especially the level at 200 ℃, V = 183m/min its PV value of up to 60MPa ? m / min, and low coefficient of friction , low wear rate , so it prospects in the bearing is obvious. GF and CF -reinforced PEEK heat distortion temperature up to 315 ℃, long-term use temperature up to 250-260 ℃; under various pressure, speed , temperature and the roughness of the original conditions exhibit good wear resistance, self -lubricating it applies to a lower coefficient of friction , wear demanding conditions.
PEEK resistance to γ -ray irradiation resistance, chemical peel resistance, fatigue resistance is the best of all resins . It can be used hundreds of hours over 250 ℃ steam or high-pressure water while the performance will not be much change. PEEK in the aerospace , aviation and special conditions using plastic bearings offer great material advantage.
PA66/GF general use at temperatures not exceeding 120 ℃, for some strong aggressive media such as ammonia refrigerant compressor used , it can not be used in more than 70 ℃ operating temperature. SKF companies generally use PEEK / GF in the holder , in order to meet the high-speed, high temperatures and chemical attack , or the stringent requirements of the AC motor or a transformer applications and drinking places .
Anyway , should be a reasonable choice varieties of plastic bearings used in accordance with the critical PV value , temperature fever situation resin used in working conditions .
Good energy conservation
Even with a plastic cage bearing metal structure , in order to further reduce friction and still use a lubricant , and once the internal lubricant is used up, its life will end. Bearing life , the most critical is the starting stage , in the initial stage of operation , the lubricating film is not formed , the bearing tends to run in the dry state , such as bearing lubrication run from the outset , which can solve the lubricating film formed in the hysteresis problems.
American igus series plastic bearings without adding lubricant to achieve environmental protection , and its polymer solid lubricant inside the bearing can also reduce bearing quality , while reducing the consumption of fuel and lubricants to reduce carbon dioxide emissions .
In this regard , for the manufacture of polymers bearing parts should be modified as necessary to resolve the problem of the formation of a lubricating film lag , to minimize the use of industrial lubricants do not even realize energy saving .
Conclusion
Plastics possess its properties, through appropriate and necessary modified , can and has gained in the bearing.
Plastic bearing inner and outer rings of the application has been developing steadily ; their applications on the rolling elements should be treated according to specific circumstances .
According to the critical PV value , the friction and wear characteristics of various plastic properties, the rational use of the application Occasion . Currently PEEK / CF ( or GF) performance of the most prominent.
When the plastic used in the bearing , pay attention to the coordination of technical feasibility, economic viability and environmental nature.
