1, overview of performance characteristics:
Polyimide is a new type of high-temperature engineering plastics, it has unique properties. The domestic bearing to ensure that astronauts may free space movements in modern industry, especially high-tech fields plays an irreplaceable role. Bearing as the basic components, widely used in various fields of national economy, meet the performance requirements of the different conditions of the bearing. Polyimide in the rolling bearing can be used as a cage material can be used as a bearing material in the applications show superior performance and good prospects for development.
Polyimide was first invented by DuPont, USA in the sixties of the last century and put into industrial production. It is a reflection of the dianhydride and diamine, then the imidization of the polymer materials. A large number of benzene rings and double bonds in the molecular chain, the increased rigidity of the molecule, the higher the energy level of the thermal motion of molecular chains, and under it to absorb more energy at higher temperatures to maintain the original shape change, and the molecular chain was broken, which is the underlying reasons of the kinds of materials, high temperature environment.
Very good heat resistance of some varieties of polyimide, the use of temperatures up to 300 ° C, the domestic bearing industry now ranks third in the world at 250 ℃ high temperature environment for long periods. However, the structure of this molecule increase the difficulty of processing the polyimide is a thermoplastic engineering plastics, but it is difficult to use injection molding processing method for molding. Introduce more active ether bond is flexible and forming an effective way to improve its molecular chain of anhydride molecules. Of course, there are many other methods, but also can be synthesized flexible polyimide, the material can be injection molded.
Common forming methods of the polyimide die-casting molding method and injection molding and French, die-casting molding material is heated in the mold cavity pressure, the state of packing material cooling molding. Forming material in this way its mechanical properties is very stable and reliable, the size of the workpiece can be larger, but the efficiency is very low, is not conducive to the industrial production of large quantities of some varieties of polyimide can only use this process. Can be used for small parts or structure of more complex products in order to improve production efficiency, the injection molding process, which requires that the mobility of this material.
A way similar to the powder metallurgy method made of porous materials, the mechanical properties of materials and pore properties of certain indicators to meet the needs of special working conditions. Polyimide because of its unique molecular chain structure, so that it can not significantly reduce the radiation environment of medium-and long-term use of the mechanical properties, which is superior to it compared with other polymer materials. Most of the polymers in the radiation condition will lead to a molecular strand breaks, a significant decline in its performance. No longer even has a mechanical strength, so in some areas of space, the polyimide material properties make it widely used.
The polyimide material with low water absorption, automotive wheel bearing size table for most chemical media can show good stability, it can be long-term use in corrosive environments, a wide field of applications. Its excellent mechanical properties, tensile strength up to 90Mpa, good rigidity, long-term to maintain dimensional stability. Lathing, milling, drilling, processing, general machining way to get better dimensional accuracy and surface quality of products. Excellent insulation, can be used as high-performance electronic components and mechanical parts. Polyimide self-lubricating properties, relative movement between the friction surface, it can be transferred to the grinding surface, the formation of the solid lubricant layer. Dry friction condition, if so, the relative sliding velocity is high, will be generated in the friction surface of a lot of heat, the local temperature can reach the decomposition temperature of polyimide, oxidation in the air environment is inevitable to generate the oxide powder frictional heat softening of the contact parts of the polyimide adhesion off and increases the amount of wear for dry friction state, polyimide materials used in PV value should be controlled to some extent, otherwise it would wear increased, shortened life expectancy . The tests showed that although the polyimide must be self-lubrication, the friction coefficient is not stable, with the extension of the continuous operation time, slowly increasing trend, it should be noted that for some applications with higher requirements on the friction parts . In order to improve the performance and effective way modified polyimide composite. Dispersed the powder lubricant to the materials made of composite materials, maintaining the basic performance of the material on the basis of the friction coefficient decreases, the friction generated heat to reduce.
Usually molybdenum disulfide, graphite, PTFE and other lubricating materials in different proportions with the test results show that the lubrication performance improved significantly. Grease application conditions can be used in high speed state, showing superior performance, its surface adsorption of the lubricant can be used in a high speed state, showing superior performance, its surface The adsorption of lubricants can form a stable and reliable lubricant film, which greatly reduces the coefficient of friction and heat of formation. Its high mechanical properties so that it can maintain a stable size at high speed.
Since the polyimide thermoplastic polymer material, the temperature it was, after more than a certain temperature range, Automobile Clutch Bearing size specifications table first material softening and oxidation and decomposition, the loss of mechanical properties. The temperature of friction part by the combined effect of two factors for ambient temperature and the friction and heat when the ambient temperature when the temperature rises from the frictional heat. Polyimide as the bearings and bearing parts, sports parts of the warming caused by frictional heat. Load and friction coefficient, as well as working time will affect the heat size. Plastic low thermal conductivity, resulting in heat easily gathered in some parts of the local high temperature. Reduce the friction coefficient is an effective means to reduce the heat to increase the cooling speed can effectively reduce face temperature, these factors need to be analyzed according to the use of the environment specific. So the temperature rise, thermal expansion increase, decrease with the gap, and some even a tight fit, so that the friction heat greater, leading to a vicious cycle.
Therefore, the design and processing of polyimide bearing products is equally important. In summary, we can see that, although the polyimide is a good temperature engineering plastics, but the process still to take all possible means to reduce the heat to avoid high temperature damage caused.
2, bearing
Polyimide composite can be used as wear-resistant materials are widely used in high temperature, chemical resistance, radiation resistance, self-lubricating and other field.
Rolling in it mainly as cage material.
The rolling bearing by the inner and outer rings, rolling element and keep the frame four-part composition. Planetary gearbox bearing solution due to the different functions inside and outside the ring and rolling element only by the hardness is high, rigid bearing steel or stainless steel. Raceway and the rolling surface finish is very high, and has very strict technical requirements for the dimensions and tolerances. Cage's role is to separate so that they bear the load bearing, reducing the friction generated by the rolling motion of the rolling body. Polyimide or composite material made of solid lubricating transfer film but also to provide bearing cage.
2.1 polyimide in high-speed bearings
High-speed bearings are generally angular contact ball bearings or deep groove ball bearings. Steel balls as the rolling element contact point, the rolling body is relatively light, can achieve high-speed performance the speed diameter plot of up to one million or more, suitable for high-speed dental drill and high-speed grinding machine spindle bearings. Bearings used in these areas to keep the frame made of polyimide tubing, and then by mechanical processing methods to obtain the required shape and size. Now commonly used dental drill bearing smaller bearing size ? × ? × 4, the cage is very small, within seven ? 1 of the ball. Must reach a speed of 350,000 rev / min in order to play to its performance, with the air turbine dental drill shaft support at the high-pressure air driven turbine high-speed rotation, the head of the dental drill repair teeth. The parts of the bearing working conditions are harsh, first of all brought about by a series of high-speed, high speed, the strength of the cage, apt to rupture and lead to bearing failure.
Bearing lubrication is also more difficult to solve, to extend the hybrid spindle bearing life in accordance with conventional methods, such a high speed bearing oil lubrication device, compressed air atomized lubricant to the bearing lubrication, but because for oral treatment, this method is not allowed, only in the work space using drip a minute amount of lubricant, part of the lubricant in the bearing start-up phase the vast majority were thrown face, so the bearing lubrication conditions very poor.
Fortunately, the bearings of continuous work time is not long, compressed air, take away the heat. These bearings also withstand high-temperature sterilization of about 130 ℃ for four hours, general engineering plastics will soon be aging, so we choose the integrated performance is very good polyimide, polyimide bearings in China the beginning of industrial applications.
The trial work since 1978, was the molding polyimide made from tube-like, and then the size and precision machining for the cage. Its application is successful, the bearing speed is stable at 350 000 rev / min. Noise and life to reach the level of foreign bearings. More processes, the low efficiency of this process made cage costs, and is not suitable for mass production of modern society needs now are also using the injection molding process one-time injection cage, the injection molding process and technology, injection molding raw materials performance in the study.
In addition to the high-speed bearing cage can also be made of polyimide material. Polyimide higher prices, more complex molding process is to limit a lot of promotion. Synthesis technology has improved steadily, and the increase in production, reducing the price of the polyimide, the development of new materials suitable for injection molding and process methods is a necessary condition for the material used widely in the bearing industry. It can replace the current widespread use of Bakelite material for high-speed bearings, improve production efficiency and performance of bearing
2.2 the use of solid self-lubricating bearings
In the space sector, many bearing lubrication can only rely on the solid lubrication solution. Commonly used non-contact seal bearing several technical parameters it is in the rolling surface of the bearing using a variety of methods to form a solid lubricating film, reducing friction.
The solid lubricating film is not renewable one-time film, of the conditions of the bearing, if you can not add lubrication, it may lead to failure. Self-lubricating cage can add the lubricating film.
Made due to the strong radiation in space, and other plastics application is limited, and now polyimide composite cage, the use of polyimide as a body material, inside a molybdenum disulfide solid lubricant. Rolling element bearings with cage pocket holes on the surface contact, relative motion to keep within the framework of the solid lubricant and polyimide transferred to the surface of the rolling element bearing rotation, and then transferred to the channel to supplement the solid lubricating film, achieve the purpose of long-lived. Aerospace and other high-tech field, this type of bearing has been applied more than once, the effect is very satisfactory, satisfactory completion of the work task.
2.3 in the porous oil-bearing frame in
The long and short oil content of polyimide in the gyro motor bearing cage has to solve its long life, high accuracy and reliability problems, the core of the technology that is the preparation of porous cage material.
The gyro motor is a high-precision motors, high-speed rotation of the inertia to determine the baseline direction of the space vehicle, is a crucial component for modern aerospace, aviation and marine areas.
With the advances in technology and requirements, requiring the gyro motor life span is very long, and international gyro motor life up to 80,000 hours. The life of the gyro motor bearing life decided to terminate the life of the motor when the bearing operation failure.
Operation of the process, the lubrication of the parts can not be added only to take a one-time lubrication technology. Apply for the industrialization funding wind power equipment manufacturing enterprises must comply with six conditions have just begun to use grease as a lubricant, grease consistency, leading to increased rotational torque, the quality of offset of the grease will damage the gyro accuracy, while life requirements for grease lubrication can not be achieved. The porous polyimide material is polyimide powder to take special material made of a unique process. It has a certain mechanical strength, the available machining method of forming a cage, interconnected between the internal storage of the lubricant within the porous cage surface, when the bearing operation due to centrifugal force and thermal motion to transfer, to form a complete film. achieve bearing lubrication. Microporous to come into contact with the excess oil to re-adsorbed to the cage, the internal oil to achieve the purpose of long-lived.
Polyimide has excellent overall performance, is an ideal material for production of microporous cage. Stop the force when you install the bearing in the bearing fits perfectly into the correct position of the vast majority of long-life gyro motor bearings are based on the porous polyimide cage, so that the gyro life of 50,000 hours or more, the accuracy and reliability meet the host requirements.
Polyimide as a high performance specialty polymer materials, must have its broader use in wear-resistant structural components, insulation materials, corrosion and other aspects of the application will continue to expand.
Before the onset of the application of the material is limited to high-tech field, the crop is smaller, it is well-known enough, research and production units is limited, many of the technology has not yet reached the level of industrialization, limiting its range of applications.
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