Performance characteristics, application effects and engineering applications of plastics, rubber, ceramics, graphite, metals, metal plastics, plastic alloys and tielimu
Abstract : Development of water lubricated bearings has been in the frontier of scientific research on high effi2 ciency energy saving and environmental protection of mechanical drive system. It becomes a hot spot of study in many countries. The authors systematically studied the materials commonly used in water lubricated bearings. This paper ex2 pounds property characters and engineering application of the materials such as plastic , rubber , ceramics , graphite , mental , mental plastic , plastic alloy and ferreous mesua.
Key words: water lubrication ; sliding bearings; material ; study
0 Introduction
Since water is a low viscosity liquid, the bearing capacity of the lubricating liquid film is directly proportional to the viscosity and inversely proportional to the square of the film thickness; Therefore, when other conditions are the same, in order to obtain equal bearing capacity, the thickness of the water film is only 1% of the thickness of the oil film Π 8. At this time, the water film is difficult to form and cannot produce the fluid lubrication effect, resulting in the low bearing capacity of the water lubricated bearing. Moreover, it may work under the non fluid lubrication condition, and it is easy to produce the mutual contact between the bearing bush and the shaft, resulting in anhydrous lubrication and dry friction Therefore, the performance of water - lubricated bearing material is a major factor to determine its working performance and service life.
Compared with traditional bearings, water lubricated bearings have great difference in material selection, which is mainly due to the great change of working medium The main performance is that the traditional bearing uses oil as lubricant, the corrosion of oil to metal materials is small, and the oil film is easy to form, so its selection range is relatively wide, while the selection of materials for water lubricated bearings must pay more attention to the friction reduction, wear resistance and corrosion resistance of materials In the 1960s, bearing materials made of wood materials, such as iron pear wood and laminate materials, were popular. These materials were very meaningful from the perspective of saving metals, especially non-ferrous metals However, with the development of society and the enhancement of environmental protection awareness, the natural wood resources are also relatively limited, which forces us to use chemical synthetic materials for replacement, so there are some other materials, such as ceramic materials, plastic materials, rubber materials, plastic alloy materials and nylon. Various materials have been used in engineering. The following is a brief comparison of their performance characteristics and use effects.
1 Research on properties of commonly used water lubricated bearing materials
According to the theoretical research and practical application, at present, the wear-resistant materials used to make water lubricated sliding bearings mainly include rubber, plastic, graphite, ceramic, stainless steel, bronze, cermet, metal plastic, iron pear wood and cloth sandwich bakelite. The main performance characteristics are compared and analyzed as follows.
1.1 plastic materials
Due to the versatility of plastics, they are flooding into the mechanical field and are used more and more widely Plastic friction parts are gradually replacing metal friction parts in a wide range At present, phenolic resin and fluorinated ethylene are widely used as plastic materials in water lubricated bearings. In addition, ultra high molecular weight polyethylene, nylon, polytetrafluoroethylene and polyamide are excellent water lubricated bearing materials.
The water lubricated bearings made of these materials have good mechanical properties and wear resistance Plastic is softer than metal. If there are impurities embedded in it, it is not easy to damage the matched shaft. That is to say, plastic has good embedment ability to foreign matters, which is especially suitable for friction parts working under harsh conditions with abrasive particles or impurities, because it can avoid scratching the grinding metal Because of its lubricity, plastics can be used not only for fluid lubrication but also for boundary lubrication However, as a friction pair material, plastic also has its disadvantages, mainly poor heat resistance. As long as the temperature is slightly increased, the mechanical properties will be significantly reduced, and the dimensional stability is also significantly affected by the temperature Many engineering plastics such as phenolic resin have water absorption, and the size increased by water swelling will affect the accuracy In addition, under the action of long - term stress, aging will occur and its performance will deteriorate For these defects of plastics, we can add some additives, improve the processing technology, and optimize the structure to meet the specific performance requirements.
Phenolic resin synthetic materials and polyester resin synthetic materials are internationally commonly used water lubricated (or oil lubricated) bearing materials. The former is represented by the Cylon material made in Canada, while the latter is represented by the weigaoer (also known as versico) material made in South Africa Compared with the two materials, the comprehensive properties of polyester resin are better than that of phenolic resin As bearing material, polyester resin synthetic material has valuable dimensional stability This material has excellent water resistance and does not have the problem of water absorption and expansion. After soaking in water, it still maintains its original strength, hardness and wear resistance, and can operate normally in water containing sediment Phenolic resin composite material has 1.5% water absorption expansion rate In addition, the linear expansion coefficient of polyester resin is smaller than that of phenolic resin, which is 2.5 - 4 times Because the thermal expansion coefficient of phenolic resin composite materials is too large and there is a certain water absorption expansion, a large operating clearance is required in the bearing design so as to leave room for thermal expansion and water expansion in the bearing operation.
Ultra high molecular weight polyethylene (UHMWPE) is a new type of engineering plastic, which has the characteristics of non-toxic, non pollution, recyclable and other environmental protection. It has been widely used and gradually used in water lubricated bearings Its wear resistance is the first of plastics, several times more than carbon steel and brass The impact strength is the highest in the existing plastics, even at - 70 ℃, it still has a high impact strength It has good self - lubricating performance and low friction coefficient, which is comparable to PTFE The water absorption of UHMWPE is the smallest among engineering plastics.
1.2 rubber materials
The idea of rubber as a friction pair material has surprised many experts As a unique material, rubber is characterized by great deformation under certain conditions and almost complete recovery after the deformation force is eliminated. Especially when rubber is lubricated with water, its friction coefficient is greatly reduced Rubber bearing is a kind of non - metallic synthetic material bearing which is used earlier.
Compared with other bearings made of several materials, water lubricated composite rubber bearings have special advantages: first, rubber has good embedment to foreign matters. Under the bad conditions with abrasive particles or impurities, it greatly reduces the wear of rubber bearings, improves its wear resistance, and can prolong the service life of water lubricated bearings Secondly, the rubber bearing has good shock absorption and impact resistance, and can adapt to and slow down the shafting vibration caused by axis runout and offset Third, due to the elastic deformation of the rubber, the contact area between the journal and the bearing can be relatively increased, and the specific pressure of the bearing can be correspondingly reduced Fourth, water is the most ideal lubricant for rubber. This discovery has been successfully applied to the development of water lubricated rubber bearings to replace the traditional metal bearings of marine propulsion systems, and has been widely used in a large number of facilities such as water pumps, water turbines, marine propeller shaft washing machines, irrigation and drainage machinery and marine machinery Fifth, the price of rubber bearing is relatively low, and it is reliable and pollution - free Therefore, the price of rubber bearings has become one of the main bearings used in water - lubricated ships at home and abroad.
However, as a friction pair material, rubber also has its disadvantages, mainly poor dry running performance, and easy to wear and scorch under low speed and frequent startup At the same time, due to the large deformation of rubber material, the running accuracy is not high It has poor high temperature resistance and small bearing capacity, and is generally only suitable for the occasion of conveying normal temperature clean water with small load and complex bearing system stress However, with the progress of material science, the mechanical properties of polymer materials based on rubber materials are gradually improved, and the water lubricated bearings made of rubber materials have gradually been able to be used in medium load conditions BTG plastic alloy material studied in this paper is developed on this basis The affinity between rubber material and water, the bearing capacity and self - lubricating property of rubber material can be improved by adding corresponding additives.
1.3 ceramic materials
Water lubricated bearings made of ceramic and cermet materials such as silicon carbide, silicon nitride and tungsten carbide in ceramics have excellent characteristics such as high hardness, high temperature resistance, wear resistance, chemical corrosion resistance, high strength, oxidation resistance and small thermal expansion coefficient, and have broad application prospects These excellent material properties are not available in common metal materials, polymers and their composites. Therefore, this material is especially suitable for special occasions such as high temperature, high speed, strong magnetic field and corrosive environment, and can also work in special media such as seawater At the same time, it can work normally even without lubrication It has good machinability, which makes its friction surface have good running in It has a high operating temperature, and the applicable temperature can reach 400 ℃ ~ 500 ℃.
However, it is brittle and has poor anti vibration performance, especially its poor embedding performance for abrasive particles. Once the abrasive particles enter between the shaft and the bearing surface, it is easy to cause serious abrasive wear between the shaft and the bearing surface. Because the hardness of ceramics is higher than that of ordinary metals, the wear of the shaft is more serious than that of the bearing, so its application in the bearing is largely limited Brittleness and low impact resistance are the fatal weaknesses of ceramic materials. If this problem can be well solved, it will be an ideal high-temperature structural material, which is known as the "dream of materials".
1.4 graphite materials
Graphite is a kind of material with good self-lubricating performance and low friction coefficient. Under water lubrication, the maximum load can reach 50kgf / cm2 and the sliding speed can reach 4m / s Graphite bearing has high thermal stability and corrosion resistance in acid and alkali solution, and can maintain self-lubricating performance in a wide temperature range from - 100 ℃ to + 600 ℃ The water lubricated bearing is made of graphite impregnated with phenolic resin, which is red sleeved in the thin-walled bushing made of austenitic steel, and forms a bearing pair with the austenitic steel rotating shaft sprayed with hard alloy, so it has a relatively ideal operating performance under the condition that the water temperature does not exceed 80 ℃.
Among the graphite materials, there is a kind of material with better wear resistance - silicified graphite. Silicified graphite is a silicon carbide carbon composite material formed by silicification of carbon graphite matrix material This material not only has the characteristics of self lubrication, good conductivity and thermal conductivity, thermal shock resistance and high temperature strength of carbon graphite material, but also has the advantages of high hardness, oxidation resistance and corrosion resistance of silicon carbide It is suitable for thrust bearing and radial bearing of centrifugal pump, corrosion pump and submersible electric pump.
1.5 metal materials
According to the characteristics of metal materials, the elastic coefficient is large and the hardness is high, so the buffering property to load is poor, and it is difficult to form water film, which is not suitable for fluid lubrication Metal and water react to form oxides, but these oxides not only have no effect on lubrication, but also have adverse effects It is difficult to achieve the purpose of water lubrication only by using single metal However, due to its good wear resistance, it can also be used under the condition of mixed sundries, so this bearing has been widely used under the boundary lubrication conditions of high load and low speed.
Due to the corrosion of metals, most of the metals used as underwater sliding bearings are bronze, high strength brass and aluminum bronze Due to corrosion on the shaft, stainless steel and chrome plated shaft materials must be used Moreover, the electrochemical corrosion caused by the contact of dissimilar metals in water electrolyte must be fully considered.
1.6 metal plastic composite materials
Metal plastic bearing is a new type of water lubricated bearing, which has the advantages of high strength and thermal conductivity of metal, high wear resistance, corrosion resistance and self lubrication of plastic Although it has not been used for a long time, it shows good performance According to different use requirements and environmental conditions, different materials and different manufacturing processes can be used According to the practical results, the metal plastic bearing made of bronze and polytetrafluoroethylene can operate at a water temperature of no more than 250 ℃, a pressure of no more than 3Mpa, and a sliding speed of no more than 12.5m Π It works normally under the condition of S On the premise of correct structural design, the bearing can form a friction pair with the stainless steel shaft surface after chrome plating, nitriding or oxidation treatment, and can obtain better service effect.
1.7 BTG plastic alloy material
BTG plastic alloy material is a new material jointly developed by Chongqing University and Chongqing Pentium science and Technology Development Co., Ltd. to improve the lubrication performance and bearing capacity of water lubricated bearings It is a kind of plastic alloy material based on rubber material, adding various fillers, accelerators and other substances It has excellent vibration absorption performance, good processing performance, good friction and wear performance, anti abrasive wear performance, fatigue wear performance, etc., especially its chemical properties are stable.
1.8 Tieli wood
Tieliwood is a natural tree species originating in South America, with dense, hard and high relative density Tielimu contains 26% resin, 28% resin juice, 1% hard resin and 0.8% bitter sweat The sweat contained in Tieli wood can form emulsion liquid with water due to the friction heat effect, which has self-lubricating effect. However, if this exudate is too much, it will cause bearing adhesion failure It has been widely used in the stern tube bearing of marine ships, but its disadvantage is that it is not suitable for ships that often sail in the waters with more sediment. Because Tieli wood is wood, it has certain water swelling property, so it is necessary to pay attention to the size change caused by swelling Due to the increasing lack of resources, the supply of raw materials of tielimu is very tight and the price is expensive, so countries are trying to find its substitutes.
Tielimu has been used as stern tube bearing material for a long time, and it is still used on small and medium ships of less than 10000 tons It can not operate under the condition of liquid interruption, so it is less used in pumps at present.
2 Application of water lubricated bearing materials
Since the mid-1980s, China has adopted water lubricated bearings in marine centrifugal pumps and axial-flow pumps. At the end of the 1980s, theoretical exploration and experimental research in this field have been carried out From the 1950s to the early 1960s, in the domestic vertical two-stage marine seawater fire-fighting structure, the integral or embedded iron pear wood was used to make water lubricated bearings In the early 1960s, in the structure of marine vertical fire fighting and master pump, integral or embedded nylon 1010 or polytetrafluoroethylene water lubricated bearings were used successively From the early 1960s to the late 1970s, graphite and impregnated stone ink were used to lubricate bearings and thrust bearings in marine pump structures Since the mid-1970s, metal plastic bearings have been widely used and popularized in civil and marine power station boiler feed pump and circulating pump structures and many other marine pump structures Since the mid-1980s, the first Design Institute of the second Machinery Department has designed water lubricated bearings for nuclear pumps, phenolic plastic water lubricated bearings for large vertical axial flow pumps in Jiangdu No.3 station, and water lubricated plastic thrust bearings for submersible electric pumps Some of the thrust bearings and guide bearings of special motors in China also use silicified graphite materials.
As early as the 1970s, in-depth research on water lubricated bearing materials was carried out in Britain, Germany, Japan and many other countries Hayward Taylor company of the United Kingdom has adopted water lubricated sliding bearing in the structure of packless pump. The shaft material is martensitic stainless steel or chrome plated on the surface of carbon steel, and the bearing bush material is asbestos filled phenolic resin. The use effect is good Vickers and Michell of Germany use water lubricated rubber bearings in deep well pumps and submersible pumps, that is, rubber materials are used as bearing shells Thomson golden Co., Ltd. of Canada adopts a water lubrication system in the support of the ship's stern shaft, and a layer of polymer material is compounded on the stainless steel bearing as the bearing bush In Japan, water lubricated bearings are widely used in centrifugal pumps and marine centrifugal pumps, and self-contained water lubricated bearings are used in auxiliary boiler feed pumps for large internal combustion engine tankers. The bearing shells are made of carburized alloys. Toshiba has also developed pump water lubricated bearings for turbo generators and hydro generators Most of the water - lubricated thrust and guide bearings in the main pumps of nuclear power plants in Russia are made of silicified graphite.
3 Concluding remarks
According to the characteristics of water - lubricated bearings, some common structural materials and performance characteristics of water - lubricated bearings are pointed out In order to ensure the normal operation of the bearing and make it have sufficient service life, the bearing material and its surface state should be correctly selected However, any material that can be used can not be perfect and can not fully meet the requirements of water lubricated bearings. Moreover, its applicability is closely related to the specific structure of the bearing, the state of the lubrication system and the working conditions. Therefore, comprehensive analysis and overall consideration should be carried out when selecting.
More about Marginal Self - Lubricating Bearings:
As a specialized manufacturer of self-lubricating bearings & bushings, Marginal Bearing is devoted to researching and producing new self-lubricating bearing materials.
Self-lubricating bearings, as the name suggests, provide their own lubrication during operation without requiring application of grease or oil lubricants. Due to this, self-lubricating bearings are also referred to as maintenance-free or greaseless bearings as they require no relubrication or grease.
An important distinction to make is that self-lubricating bearings are not bearings that come pre-applied with grease or oil lubricant – these bearings are instead referred to as prelubricated bearings. Prelubricated bearings will require relubrication at some point in their service life.
Self-lubricating bearings work by having lubricant impregnated within the sliding layer of the bearing. This lubricant can either be liquid (oil) or solid (graphite, MoS2, lead) based on the requirements of the application (such as operating temperature). As the bearing operates, the lubricant is released through pores in the sliding layer, lubricating the bearing surface. The lubricant is uniformly dispersed throughout the sliding layer and thus there is no reduction in low friction bearing performance, even if the sliding layer becomes worn. A “running-in” surface is also usually included at the top of the sliding layer to provide low friction bearing performance at start up before the impregnated lubricant reaches the bearing surface.
