Abstract: This article introduces the research status and application of solid lubricating materials for polymer, graphite, and molybdenum disulfide embedded sliding bearings. It focuses on the fact that adding fillers to embedded solid lubricating materials can improve the friction and wear performance and mechanical properties of the materials. However, solid lubricating materials have problems in the use of embedded sliding bearings, such as general lubrication performance of a single material, poor corrosion resistance of the metal matrix, and unsuitability for high-speed, light load, and low-temperature working conditions. And the prospect of using filler blending to synergistically reduce friction is proposed for polymer based embedded solid lubricating materials, and an intelligent lubrication concept is proposed for the improvement of graphite and molybdenum disulfide based embedded solid lubricating materials.

Inlaid bearings have been around since the early 1920s. They refer to pre designed and machined holes or grooves with a certain area ratio on the bearing substrate, in which solid lubricating materials are embedded and combined into a whole through special processes. The solid lubricating material embedded in the bearing during operation can slightly protrude from the surface of the substrate under the action of alternating stress and frictional heat, forming a solid lubrication transfer film on the mating surface, preventing direct contact between the friction pair surfaces and thus playing a role in lubrication and friction reduction. In addition to good self-lubricating performance, embedded bearings also have many unique properties that are significantly superior to other self-lubricating bearings, such as strong load-bearing capacity and wide temperature range. Their application in special environments is increasingly being valued by people. This article introduces the research progress of solid lubricating materials for polymer, graphite, and molybdenum disulfide (MoS2) embedded sliding bearings.

1. Solid lubricating materials for polymer embedded sliding bearings

1.1 Polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) has good chemical resistance, high temperature resistance, and low friction coefficient, and is commonly used in bearings and seals. However, PTFE has poor mechanical properties, high coefficient of linear expansion, and poor creep resistance. The use of pure PTFE in bearings is greatly limited. Therefore, when PTFE is used as a solid lubricating material for bearings, fillers are usually added to modify it. Fill PTFE with graphite, glass fiber, carbon fiber MoS2、 The hardness and wear resistance of metals and metal oxides will increase, and the specific wear rate will decrease to less than 1/100 of unfilled.

A type of embedded water turbine generator bearing is made of PTFE as a solid lubricant matrix, with fillers such as graphite, MoS2, and carbon fiber added. Friction and wear tests and bench tests on the bearing have verified that the embedded bearing can enable the water turbine generator to operate normally under special working conditions such as heavy load and mud water.

A solid lubricating material by compression molding using PTFE and 40 nm alumina (mass fraction of 0-20%) as raw materials. The reciprocating friction and wear test was conducted under a contact pressure of 6.4 MPa, a stroke length of 50 mm, and a sliding speed of 50 mm/s. The results showed that the wear resistance of the composite material increased with the increase of alumina, and the material was most wear-resistant when the mass fraction of alumina was 20%, which was 600 times higher than that without filling. This lubricating material can be used as a self-lubricating material for embedded joint bearings.

PTFE as the lubricating matrix, added 10% by mass of nano montmorillonite for mixing, and embedded it in aluminum alloy by compression molding to produce PTFE aluminum alloy embedded lubricating material, which was then subjected to friction and wear tests. The results showed that the steady-state friction temperature was 51 ° C, the friction coefficient was 0.087, and the wear rate was 0.38 x 10-3 mm3 · N-1 · m-1. Compared with non embedded PTFE based composite materials, it was found that the thermal conductivity and wear resistance were greatly improved, while the friction coefficient did not increase significantly. This composite material has excellent friction and wear performance, high compressive strength, and low density, and can be used as a lubricating material for aerospace embedded bearings.

Copper based embedded joint bearing materials were made by filling PTFE with lead powder, graphite, and glass fiber. The experiment found that the lubricating material composition was 40% PTFE+20% lead powder+20% graphite+20% glass fiber, and the joint bearing had good friction and wear performance.

The new steel based embedded PTFE self-lubricating bearing uses GCr15 bearing steel as the metal matrix, PTFE as the solid lubricating material matrix, and graphite, MoS2, and neutral alumina powder as fillers. Friction tests have shown that the pressure of this new type of bearing can reach 90 MPa, with a friction coefficient below 0.15, meeting the mechanical performance requirements of bearings under harsh working conditions.

By comparing the frictional characteristics of three types of embedded bearings made of graphite based, lead containing PTFE, lead-free PTFE solid lubricants, and copper alloy composites, it was found that the lead-free PTFE embedded bearing formed the most complete and uniform transfer film during operation, and had the best wear resistance. Bench tests showed that the lead-free PTFE embedded bearing is expected to have a safe service life of up to 50 years for hydraulic engineering.

The end face friction and wear tests were conducted on several graphite and PTFE composite solid lubricating materials embedded on copper alloys. The results showed that adding an appropriate amount of graphite can form a uniform transfer film on the friction surface, reduce the exposure of the base copper alloy on the friction surface, and effectively reduce the mechanical destructive wear caused by adhesion at the contact interface of the friction pair in the joint bearing made of this material composite during operation.

1.2 Polyether ether ketone

Polyether ether ketone (PEEK) has excellent mechanical properties, good corrosion resistance, thermal stability, and good friction and wear performance. It is another popular anti friction and wear-resistant material after PTFE, with better bearing capacity and wear resistance compared to PTFE. It can be used in non lubricated and dust-free conditions and can replace many traditional metal materials.

The friction and wear properties of PEEK self-lubricating composite materials filled with PTFE were studied. The results showed that the filling of PTFE reduced the friction of PEEK, but the hardness slightly decreased. When it is used as a solid lubricating material for bearings, PTFE with a filling mass fraction of 10% is the most suitable for achieving the best frictional performance of the bearing.

Inlaid bearings were made by filling PEEK with PTFE, graphite, and other materials. The influence of different fillers and filling amounts on the friction and wear properties of the composite material was studied, and the relationship between the specific wear rate of the material and the working limit PV value was determined. The results showed that the friction coefficient of PEEK at room temperature was 0.48. After making PEEK composite material, with the increase of test temperature, the friction coefficient of the material decreased to about 0.20~0.25, and the filling mass fraction was 15%. The PTFE and 15% graphite PEEK materials have the best friction and wear performance, indicating that this self-lubricating composite material has better performance under high temperature conditions and can be used as a solid lubricating material for self-lubricating embedded bearings.

The friction and wear properties of PEEK and PTFE mixture were studied. The wear rate of PEEK with a mass fraction of 32% was the lowest at 2x 10-9mm3 · N-1 · m-1, which was 0.11% of unfilled PEEK and 0.0004% of unfilled PTFE. This proves that the composite material can be used as a solid lubricating material for embedded bearings.

1.3 Polyimide

Polyimide (PI) is currently one of the organic polymer materials with good thermal stability. PI, as a special engineering plastic with excellent comprehensive performance, has excellent thermal stability, outstanding radiation resistance, and excellent anti friction and wear resistance. It can form a transfer film on the mating surface during dry friction, playing a self-lubricating role. Widely used in high-temperature and high-pressure anti friction and wear-resistant working conditions.

Using PI composite materials to manufacture high-temperature resistant self-lubricating bearing bushings, it has the characteristics of energy saving, no environmental pollution, and can increase the service life by 2-3 times. It can replace various powder metallurgy oil containing bearings, metal sliding bearings, and various rolling bearings, and can meet harsh working conditions such as high temperature, high load, high speed, and high dust.

A solid lubricating material was developed using PI as the matrix and graphite as the filler. The experimental results showed that graphite filling can improve the friction and wear performance of PI. With the increase of graphite filling amount, the friction coefficient decreases, the wear scar width decreases, but the impact strength decreases. When the mass fraction of graphite added to PI is 15%, the friction and wear performance of the lubricating material is optimal, and it can be used as a solid lubricating material for embedded bearings.

1.4 Summary

The research on using polymer based self-lubricating materials instead of ordinary metal products in bearings is becoming increasingly widespread. The friction and wear performance of polymers is related to their ability to form transfer films on mating surfaces and the characteristics of transfer films. Due to the poor performance of a single polymer, its comprehensive performance when directly applied to sliding bearings is generally average. Therefore, scholars focus on studying the interrelationships between various factors in the friction composite system composed of polymers, fillers, and friction pairs, including friction and wear, microscopic mechanisms, as well as the effects of temperature, lubrication, speed, and other conditions.

2. Solid lubricating materials for graphite embedded sliding bearings

Graphite is a crystalline form of carbon with a hexagonal lattice. Due to the small binding force of molecular bonds between layers, it is prone to slip between layers, resulting in low strength and hardness of graphite. However, it has good lubrication performance, low cost, and no harm to the environment. It is widely used in anti friction and wear-resistant materials. In the mechanical industry, general lubricating oils cannot be used under high temperature, high speed, and high pressure conditions, while graphite can be used at -200~2000 ° C and can be applied to high-speed working conditions. Therefore, graphite is often embedded in metal substrates as a lubricating material.

2.1 Copper alloy matrix

Copper alloy graphite composite materials were introduced in the early 20th century, which are composed of pure copper or copper alloy as the matrix embedded with graphite. Copper alloy graphite composite materials not only have the characteristics of good thermal conductivity, electrical conductivity, and high strength of copper alloy matrix, but also have the good lubricity of graphite at both room temperature and high temperature, and are widely used in oil-free or low oil working conditions.

Embedding lubricating materials such as graphite into copper alloys, due to the effects of friction, compression, and heat, can form a relatively stable lubricating film on the sliding surface of the material itself, and rely on continuous outward compression of graphite to repair the damaged lubricating film, playing a role in lubrication and friction reduction. When the volume fraction of graphite exceeds 20%, it is beneficial to form a complete and continuous graphite lubricating film. Research has shown that the friction coefficient of this copper alloy embedded graphite composite material is close to that of graphite and independent of the matrix.

Dry friction comparative tests were conducted on graphite bearing specimens of tin bronze, aluminum bronze, and aluminum brass inlaid type at room temperature on a friction and wear testing machine, exploring the influence of different copper alloy matrices on the friction and wear performance of inlaid type bearings. The results showed that the tin bronze inlaid bearings exhibited excellent friction and wear performance under various test conditions; The friction and wear performance of aluminum brass and aluminum bronze embedded bearings is poor, especially under high loads.

A process of embedding graphite on the surface of copper alloy joint bearings, which uses copper alloy as the substrate to set blind holes or through holes on the surface, heats to enlarge the diameter of the blind holes or through holes on the surface of the copper alloy, then inserts graphite into the manhole with a pressure head, and cools the copper alloy to restore the aperture to its original size, thereby achieving a firm connection between graphite and alloy. The experiment shows that the copper alloy embedded graphite technology has a lower friction coefficient and higher load-bearing capacity compared to the original technology, and can serve for a long time in a larger temperature range.

A inlaid self-lubricating bearing for over 20 types of mechanical equipment has been developed using tin bronze as the metal matrix and a mixture of graphite, MoS2, and other materials as the solid lubricating material. The experiment shows that load, speed, and temperature have no significant effect on the friction coefficient of the bearing, indicating that this embedded self-lubricating bearing can form a lubricating film with anti friction and wear-resistant effects under high temperature conditions. The actual life of this bearing is about 10 times that of a general bearing.

2.2 Iron based matrix

Iron based materials have certain wear resistance, high strength and hardness, easy processing, low cost, and can adjust their mechanical and corrosion resistance properties by adding carbon or other alloy elements according to the preparation process requirements to adapt to different working environments.

Adding copper as the second phase in iron-based graphite embedded joint bearings can improve friction characteristics. The results show that adding appropriate copper can increase the surface hardness of the material, improve the wear resistance of iron-based materials, and reduce the wear rate.

To study the effect of different iron-based materials embedded with graphite, reference [44] conducted dry friction comparison tests on 45 # steel, stainless steel, and cast iron embedded graphite bearing specimens on an end face friction and wear testing machine. The results showed that 45 # steel had the worst wear resistance and load-bearing capacity, with a large amount of wear under heavy load; When the load is high, the friction performance of the stainless steel embedded graphite bearing sample is good, and the wear is small. Although it is prone to biting when the load is small, the friction coefficient is generally stable compared to the other two iron-based materials.

2.3 Summary

At present, copper alloy embedded graphite technology has been widely used in bearings for special working conditions such as nuclear power, aviation, and aerospace due to its excellent mechanical properties and low friction and self-lubricating properties of graphite. In order to achieve optimal mechanical and tribological properties, factors such as graphite content, solid lubricant composition, and copper alloy types should be considered, which is also the main research direction of scholars at home and abroad. The metal matrix of iron-based graphite embedded bearings tends to alloy to improve their friction and wear performance as well as corrosion resistance.

3. Solid lubricating material for MoS2 embedded sliding bearings

MoS2 is a very soft solid that is not easily damaged on metal surfaces and has good stability. MoS2 crystals have a layered structure formed by multiple stacked layers, and each piece is composed of molybdenum atom planes embedded between two sulfur atom planes. S-Mo-S covalent bond in one layer The strength is very high, while the bonding strength between two adjacent layers caused by van der Waals forces is relatively small. Therefore, it is difficult to break the bond between S-Mo-S layers, and layers are prone to sliding. The lubrication mechanism of MoS2 is very similar to that of graphite.

A new type of embedded joint bearing (MoS2 as a solid lubricant) is used to replace the bearings of ship lock gates. The experimental results show that after working for a period of time, the embedded joint bearing forms a solid lubricating film on the contact surface, and the static friction coefficient is significantly reduced.

Through fatigue life tests and examples, it has been demonstrated that MoS2 can reduce the friction generated during the running and operation of embedded joint bearings, thereby extending the service life of the bearings and reducing their noise during operation.

MoS2 is used as a solid lubricating material in embedded sliding bearings, which can form a stable transfer film on the sliding surface, thereby reducing friction and wear resistance. It can meet the use conditions of high temperature and high pressure environments, but is not suitable for high-speed, light load, and low temperature working conditions.

4. Development direction and prospects

With the continuous progress and development of technology, self-lubricating materials for embedded bearings applied in various working conditions are also constantly being researched and explored.

At present, several types of self-lubricating materials will have the following research focuses in the future:

1) In terms of adding filler modification to solid lubricating materials for polymer embedded bearings, high-performance nanolubricants can be developed and their synergistic anti friction effects can be studied; Researching new resins with high temperature resistance, high cost-effectiveness, and low cost, and blending resin matrices to composite fillers, in order to achieve optimal friction reduction and wear resistance effects.

2) Performance of solid lubricating materials for polymer embedded bearings. Under the premise of being able to adapt to special working conditions such as high temperature and high pressure, new preparation processes for lubricating materials can be developed to fully utilize their excellent lubrication, wear resistance, and mechanical properties. For example, layered nano structured anti friction composite materials can be prepared using in-situ polymerization intercalation, melt intercalation, or solution reflux intercalation processes for application in embedded sliding bearings.

3) Nowadays, the concept of intelligent lubrication has entered people's vision, and I believe that this concept has great potential in the future of embedded bearing lubricants. Intelligent lubrication refers to changing the microstructure of lubricants to improve their functionality. The most widely used method for selecting and improving the microstructure of lubricants is core-shell particles. By changing the core-shell ratio, the mechanical and lubrication properties of composite materials can be adjusted. An appropriate core-shell ratio is beneficial for achieving ideal comprehensive performance. The confinement effect and improved dispersion ability conferred by the core-shell structure effectively enhance the dispersibility of the reinforcing phase, improve the adhesion of the transfer film to the friction surface, and block the wear process of polymer composite materials. According to this concept, it is possible to attempt to prepare polymer based, graphite based, and MoS2 based lubricating materials into core-shell materials. By changing the core-shell ratio to control the lubrication performance, high-performance solid lubricating materials can be developed and applied to embedded sliding bearings.

2026 April 4th Week Marginal Product Recommendation

Material Specification Sheet–MG-6:

Material specification sheet – MG-6 is Ball and roller bearing steel according to EN ISO 683-17. Ball and roller bearing steel for balls and rollers of any dimension,rings and discs up to 30mm effective thickness.