The introduction of self-lubricating spherical plain bearing, bearing structure and solid lubricating materials for inlay
Abstract: The embedded self-lubricating bearing is used to replace the original bearing of the support hinge of the ship lock gate. The inlaid self-lubricating material adopts ultra-fine powder MoS2 as the main component, and the preparation process of inlaid self-lubricating material is introduced. Self-lubricating composite materials have good lubrication performance and can meet the actual needs.
Keywords: Self-lubrication; Joint bearing; MoS2
1. Introduction
The gate is a very important part of the ship lock, sluice and other hydraulic structures, and the support hinge of the gate plays a decisive role in the safe operation of the entire gate. The supporting hinge is used to connect with the supporting end of the radial gate arm, transfer the water pressure of the whole gate and part of the gate weight to the gate pier, and ensure that the gate can rotate around the horizontal axis when it is opened and closed.
The support hinge is generally 6m~12m underwater, and the overhaul is relatively difficult. The water in the sluice must be pumped out before it can be carried out. Therefore, the overhaul period is required to be long, generally 10 years, which requires the support hinge to have good wear resistance. The ship lock gate is very heavy, within the range of 10t~100t. When the ship lock is opened, the swing angle is 70°. These factors make the materials in relative motion easier to wear. At the same time, in order to ensure the smooth opening and closing of the gate, it is required that the friction between the inner sleeve and the outer sleeve of the support hinge is small. In order to meet these requirements, an inlaid self-lubricating sliding bearing for supporting hinges is developed in this paper.
The early self-lubricating spherical plain bearings also prepared lubricating films on sliding surfaces to achieve the effect of friction reduction. H Joint bearings with PTFE coating on the inner surface of outer ring manufactured by Elges Company and KGJ Company have also been studied by NTN Company of Japan. They spray PTFE coating on the inner sliding surface of joint bearings, which has low friction coefficient and high wear resistance. There are many examples of using solid lubricating materials as integral parts, including gears, bearings, cams, rolling bearing cages, etc. made of plastic, and materials with certain characteristics (such as graphite materials with good conductivity, ceramic materials with high hardness, etc.), which can be directly used as parts, such as graphite brushes, electrical contacts, gem bearings, knife edge supports, etc. Embedded self-lubricating bearing is still a blank in China at present. The research on embedded self-lubricating bearing of SKF Company in Sweden is relatively early. In this paper, the structure of self-lubricating spherical plain bearing is designed by imitating the similar bearing structure of SKF Company, and its structure diagram is shown in Figure 1 and Figure 2.
Self-lubricating spherical plain bearings are very important for ship locks and sluices. The gate is a very important part of the ship lock, sluice and other hydraulic structures, and the support hinge of the gate plays a decisive role in the safe operation of the entire gate. The main component of supporting hinge structure is self-lubricating spherical plain bearing. The supporting hinge is used to connect with the supporting end of the radial gate arm, transfer the water pressure of the whole gate and part of the gate weight to the gate pier, and ensure that the gate can rotate around the horizontal axis when it is opened and closed.
2. Bearing Structure
The inner ring sleeve of the bearing is made of iron base alloy, and the outer ring sleeve is made of cast aluminum bronze. It is mainly considered that aluminum bronze material has certain wear resistance and good lubrication performance. The self-lubricating material is embedded on the inner surface of the outer ring. The arrangement of the embedded material is shown in Figure 1. One row is 5 holes, and the other row is 6 holes. The two rows are arranged alternately, and the center of the cylindrical hole is arranged in a square. Each set of bearing has 320 holes in total, and the hole depth is 8mm. The outer ring sleeve of each bearing is composed of two half sleeves. First, the outer ring sleeve of the bearing is cast by centrifugal casting process, then cut into two half sleeves, drill holes on the inner surface of the outer ring sleeve, and inlay solid self-lubricating materials. After each half sleeve is inlaid with solid lubricating materials, the two half sleeves are processed into a complete set of spherical plain bearings. The assembly diagram of the spherical plain bearing is shown in Figure 2. The contact surface of the sliding bearing is spherical. The bearing is suitable for the working condition of low speed rotation. The centerline of the speed shaft can be adjusted by 2 °~3 °. When the spherical plain bearing works, the inner ring sleeve slides relative to the outer ring sleeve, and the solid lubricating material will be transferred to the surface of the inner ring sleeve, forming a very thin layer of solid lubricating film, thus separating the surface of the outer ring sleeve and the inner ring sleeve, and playing a lubricating role at the same time.
Fig. 1 Arrangement of outer ring sleeve and lubricating materials of spherical plain bearing 1
1. Outer ring sleeve 2. Solid self-lubricating material 3. End cap
4. Rubber seal ring 5. Inner ring sleeve 6. Screw
Fig. 2 Assembly Diagram of Spherical Joint Bearing
3. Solid Lubricating Materials for Inlay
The solid lubricating material used is a composite material developed by Tsinghua University and originally used in the aerospace industry. The developed material has very excellent lubrication performance. Generally, the friction coefficient can reach about 0.05. See Figure 3 for the friction coefficient of lubricating material. In the composite solid lubricating materials, there are ultra-fine powder lubricating materials as one of the raw materials, one of which is MoS2 ultra-fine powder. The author once used MoS2 to prepare solid bonded coatings with excellent lubricating properties for the aerospace sector. The test proved that the use of ultra-fine powder materials is one of the important reasons for the low friction coefficient of composite solid lubricating materials.
Parameters of MoS2 ultrafine powder are as follows: average particle size 0.8 μ m. The content is 98.5%, and the other impurities are SiO2, Fe and MoO3.
Before inlaying, the developed solid lubricating materials should go through the following processing stages: mixing, drying, pressing, sintering and turning. If one of these stages is not well controlled, the final prepared materials may not achieve the expected performance.
Mixing is to evenly mix MoS2 ultrafine powder with other solid lubricating materials and additives. At present, the method adopted by the author is to soak the solid materials in industrial alcohol, soak them for a period of time, add zirconia grinding balls, and grind them on the grinding machine for more than 4h. If the mixture is uneven, the appearance quality of the lubricating material is poor and the bonding strength of the material is reduced. After inlaying, when turning the inner surface of the outer ring sleeve, the inlaying material may be broken.
The drying is carried out at 120 ℃, and the temperature is kept in the oven for more than 12h. If the drying is not complete, the material will cause certain difficulties in the subsequent sintering. The liquid component without drying makes the lubricating material flammable during sintering. If the drying time is too long, the performance of the lubricating materials will change, and the prepared lubricating materials will not achieve the expected antifriction effect.
Press forming is carried out on an automatically controlled press. During the pressing process, if the pressure is too large, the material is easy to break or crack inside during sintering.
The sintering of lubricating materials is carried out in a resistance furnace controlled by silicon controlled rectifier. The maximum temperature is 410 ℃ and the total heating time is about 6h.The sintering of lubricating materials is very critical. If the temperature is not well controlled, it is difficult to make the lubricating materials achieve good antifriction effect. When the temperature of the electric furnace exceeds 5 ℃ of the set temperature during sintering, the material is burnt, and most of the materials are oxidized. The sintered material has neither strength nor lubrication performance. If the temperature is slightly lower than the set temperature, some polymer materials in the composition have not been transformed into structures with lubricating properties, and the materials still cannot achieve good lubricating effect.
Fig. 3 Friction coefficient of solid lubricating materials
The preparation of solid lubricating materials is the key to the success of inlaid self-lubricating sliding bearings. The material used in this paper is the formula finally selected after more than two years of experiments, and the ultra-fine powder material is used in lubricating materials for the first time.
4. Discussion
It is found that it is very important to form a thin layer of MoS2 transfer film on the bearing surface for the purpose of reducing friction. When the test starts, the static friction coefficient will be relatively large. If it is measured repeatedly, the static friction coefficient will decrease, and the fluctuation range is very small. At this time, it is found that there is a lubricating film on the bearing surface. MoS2 has excellent adhesion. In industry, there are examples of sliding clean metal on MoS2 to form MoS2 film on metal surface. In this test, MoS2 is made of ultra-fine powder. After several grinding tests, MoS2 is transferred to the surface of the dual pair.
If ultra-fine powder MoS2 is used, the friction coefficient of the coating shall be smaller than that of MoS2 with general particle size. The antifriction effect of MoS2 is due to the layered structure of MoS2. When the (0001) plane of the grain is parallel to the sliding direction, the shear strength between layers is low and they are easy to stagger. The orientation of MoS2 grains changes shortly after the initial sliding, which makes it easier to slip between layers of grains. With ultra-fine powder materials, MoS2 grains are fine, and the orientation of MoS2 grains is easier to change.
If the solid lubricant is properly selected and matched, the solid lubricant coating with excellent performance can be obtained by utilizing their synergistic effect. MoS2 and other solid lubricants have been used jointly as lubricants in inorganic coatings and also in plasma spraying coatings. They can reduce the friction coefficient very well. Generally, solid lubricants have a layered structure and are easy to slide between layers. When other solid lubricants are mixed with MoS2, the content of other non-hexagonal materials between layers can be reduced, so that they can be closely arranged in layers, improve the orientation of grains, and easily produce slip layers.
When MoS2 is used as lubricant alone, when its impurity content is very low, the friction coefficient under vacuum condition is very small, which is in the order of 10-3. If there are some impure substances in MoS2 that are not hexagonal, which destroy the orientation of grains or accelerate the oxidation of MoS2, even if there is MoS2, it will not play a role in lubrication. The lubrication performance of other solid lubricants is also affected by impure substances, and the environment has a great impact. When the solid lubricant contains water, the friction coefficient increases. At the same time, the purity of the solid lubricant cannot be guaranteed during use. Therefore, the friction reduction effect of a single solid lubricant is not obvious. However, the joint action of MoS2 and other solid lubricants is very meaningful, and the friction reduction effect of the prepared coating is obvious.
The self-lubricating sliding bearing is designed by ourselves for the first time, so there are still many problems in the structure.
If the bearing outer ring sleeve has holes, these holes are for inlaying self-lubricating materials in the future. The opening depth is 8mm. Since the cost of self-lubricating materials is high, the deeper the hole is, the more man hours are required to process the hole, and the more self-lubricating materials are used, the higher the cost of the bearing is. From the perspective of practical application, the outer ring sleeve cannot be worn out for 8mm. If it is worn out for 8mm, the bearing has already been scrapped. Therefore, in order to reduce the cost, the opening depth can be reduced. However, in order to prevent the lubricating materials from falling off, the hole depth of the shaft should not be too shallow, and the improved hole depth is set as 4mm.
The size and arrangement of the inner diameter of the hole have not been strictly tested and analyzed, and are designed by the designer based on experience. If the inner diameter of the hole can be reduced and the distribution is more-sparse, the amount of solid lubricating materials can be saved.
More about Jiashan Marginal Filament Wound Plastic Self-lubricating Bearings:
The lubricating layer, which has very low friction coefficient, superior anti-wear feature and scratch resistance, is made by special PTFE fiber and high strength artificial fiber compound. Jiashan Marginal Series bearings are high-load plastic compound bearings with two basic layers. The outside is an enhanced, high-temperature, epoxy resin with wound glass fibers encapsulated within the resin. The inside sliding layer has continuously wound PTFE fibers and a separate special fiber.
We're well-known as one of the leading filament wound plastic self-lubricating bearings manufacturers and suppliers in China for our quality products and customized service. Please feel free to buy or wholesale bulk filament wound plastic self-lubricating bearings in stock here from our factory. Contact us for free sample and pricelist. Filament Wound Plastic Bushes, Plastic Self-lubricating Bearings, Bronze Flange Bushings.
