Abstract: This article briefly introduces the working principle, preparation process, and installation process of solid self-lubricating bearings. After using this technology on the sintering machine trolley, it greatly reduces the maintenance amount of the trolley, reduces production costs, and achieves good economic benefits.
Keywords: Solid self-lubricating bearings; Sintering trolley
1. Introduction
Mainly reflected in the use of self-lubricating bearings on the trolley. Self lubricating bearings are divided into composite material self lubricating bearings, solid embedded self lubricating bearings, bimetallic material self lubricating bearings, and special material self lubricating bearings. Different self lubricating bearings are selected according to different working conditions. This article mainly introduces the application of solid embedded self-lubricating bearings on trolleys.
The trolley is the main component of the sintering machine, and its main task is to transport materials. Due to the requirements of the sintering process, the working conditions of the sintering machine are extremely harsh. Due to the large and heavy equipment, high environmental temperature, and high dust, the friction and wear of the moving parts of the sintering machine are severe. Lubrication is an effective means to solve equipment wear, but harsh operating conditions bring many problems to equipment lubrication. In order to solve the friction and wear problem of the sintering machine trolley, most domestic enterprises still use traditional oil and grease lubrication. Practice has shown that the existing oil and grease lubrication conditions can no longer meet the operating requirements of the equipment, and the trolley is prone to bite or death of bearings and other friction pair parts, causing serious wear and damage to the sintering machine trolley parts, and ultimately leading to equipment shutdown. Causing a large number of maintenance personnel to invest, reducing productivity, increasing production costs, lubrication has become an important obstacle to the development of production. In order to solve the lubrication problem of the sintering machine trolley, this article designs and adopts a new type of embedded self-lubricating bearing based on the actual working conditions of the trolley, which improves the lubrication conditions, increases its performance, and solves the problems caused by poor lubrication.
2. Design of Solid Self lubricating Bearings
Taking the bearings used for the supporting trolley of the 400m2 sintering machine produced by Tangshan Metallurgical and Mining Machinery Factory as an example, the design of self-lubricating bearings is carried out.
1) Design conditions
Sintering machine specification: 400m2; Trolley specification: 1.5 × 5m;
Working environment: dust; Working temperature: generally within the range of 60-150 ℃, mainly caused by conduction and radiation heat; Trolley running speed: 1.3-3.9m/min.
The rollers that are matched with self-lubricating bearings only rotate relative to the bearings when they are moved by the star gear tooth plates at the head and tail corners of the sintering machine, causing a change in the direction of the trolley's operation.
2) Determination of substrate
When determining the components of the substrate, emphasis should be placed on the bearing capacity and service temperature of the material. Usually, the contact stress of the friction pair is calculated based on the Z-high static load borne by the contact surface to determine the bearing capacity of the substrate. Then select the suitable substrate based on the physical and mechanical properties of various materials.
For the temperature and environment of sintering trolley operation, 40Gr seamless steel pipe is selected as the substrate.
3) Determination of the Ratio of Solid Lubrication Materials
Usually, solid lubricants act as lubricating phases. When selecting lubricating phases, attention should be paid to the reasonable matching between solid lubricants and substrates to improve chemical affinity and increase adhesion. In order to improve lubrication efficiency and reduce wear, a multi-element lubricating phase composed of multiple lubricants is selected. At the same time, the thermal expansion coefficient of the lubricating phase should be slightly greater than the thermal expansion coefficient of the substrate, so that it can effectively reduce friction.
Based on the experimental research results and considering the actual production in the factory, after multiple industrial tests, the composite lubrication material for self-lubricating bearings composed of graphite, molybdenum disulfide, polystyrene resin, and polytetrafluoroethylene suspension resin has been determined through the use of the multiple composite friction reduction and wear resistance benefits of solid lubrication materials. Its ratio is: graphite 48%, molybdenum disulfide 2%, polystyrene ester resin 10%, and polytetrafluoroethylene suspension resin 40%.
4) Determination of the structure and size of self-lubricating bearings
The diagram of the self-lubricating bearing parts is shown in Figure 1. Based on the shaft diameter, its outer diameter is determined to be Å 180 and inner diameter is determined to be Å 160. The tolerance fit is designed according to the fit between the bearing, shaft, and hole, and is determined to be Å 180c11 and 160H7. On the outer surface of the bearing, there is 144- Å 14 embedded bearing self-lubricating material. The structure and dimensions of self-lubricating bearings are shown in Figure 1.
Figure 1 Parts diagram of self-lubricating bearings
3. Manufacturing of Solid Lubricated Bearings
1) Cut the seamless steel pipe according to the dimensions shown in the diagram;
2) On the lathe, first turn the outer circle, inner hole, chamfer, and end face;
3) Drill holes on a drilling machine with a depth of 4.5mm;
4) Mix the lubricant evenly in proportion;
5) Press the mixed powder into a cylindrical shape with a diameter of 14mm and a thickness of 5mm using a press, with a maximum pressure of 200Mpa.
6) Bake the molded lubricating particles in an oven for 10 minutes at a temperature of 300 ℃. The temperature should not be too high, as it will cause polytetrafluoroethylene to melt, leaving only powdered graphite.
7) Hammer the lubricating particles into the holes of the substrate, insert them, and then turn the outer circle according to the drawing requirements, so that the lubricating particles protrude 0.5mm from the surface of the substrate. This way, the bearing rubs against the inner surface of the rolling sleeve, forming a lubricating film with the protruding lubricant.
4. Implementation effect
By comparing the use of self-lubricating bearings on the supporting trolley of the 400m2 sintering machine at Anyang Steel Plant with the original ordinary bearings, the comparison results show that the installation of self-lubricating bearings has achieved good results. The lifespan of using ordinary bearing sleeves and rollers is approximately two years.
After two years of use, the shaft sleeve and roller using self-lubricating bearings have completely worn out, and the expected service life can reach five years. So self-lubricating bearings have excellent lubrication performance and can be widely applied.
5. Working principle of solid self-lubricating bearings
Under ideal fluid lubrication, the surface of relative motion is separated by a layer of lubricating film, and its moving surface is not worn. The sintering machine trolley used to be lubricated with grease. Under high temperature conditions, due to the physical properties of the grease itself, the lubricating film is very easy to be damaged, leading to adhesion and wear on the metal surface of the sintering machine trolley. The lubricant synthesized by using solid lubricating material powder is embedded in the bearing to form a solid lubricating bearing. The solid lubricating powder released during equipment operation covers the friction surface, isolating the contact friction surfaces, and achieving the purpose of reducing friction and anti wear.
The lubricants for metal embedded solid lubrication bearings mainly include solid lubrication materials such as molybdenum disulfide, graphite, and polytetrafluoroethylene. The use of a reasonable ratio has resulted in synergistic effects, leveraging their respective advantages to improve the rigidity, toughness, and heat stability of lubricants. Molybdenum disulfide and graphite both have a layered structure with low friction coefficient. They can transform the friction between two relatively moving surfaces into friction between crystal layers. Micro powder can fill the concave areas on the metal surface, bind with metal molecules, and adhere or penetrate to the metal surface to form a sulfur alloy lubricating film, thereby isolating the friction pair and providing good lubrication. The height of self-lubricating particles in solid self-lubricating bearings exceeds the surface of the steel base by 0.5mm. When working with the friction pair, the higher part is ground flat, forming a lubricating film on the surface of the steel base to reduce the friction coefficient. The total surface area of self-lubricating particles should account for 30% to 50% of the surface area of the steel substrate in order to form an effective lubricating film. Metal embedded solid lubrication bearings not only maintain the strength and "toughness" of steel, but also have the "rigidity" of sulfur alloy on the friction surface. The micro powder of molybdenum disulfide and graphite in the middle of the friction surface has high load-bearing capacity, so it has the dual advantages of good mechanical strength and wear resistance.
6. Conclusion
1) We have developed solid self-lubricating bearings for sintering machine trucks, using seamless steel pipes made of 40Gr steel as the substrate, graphite, molybdenum disulfide, polystyrene ester resin, and polytetrafluoroethylene suspension resin to form a composite lubricating material for self-lubricating bearings.
After practical application verification, this technology is safe and reliable when applied on sintering machine trolleys, and will bring very good economic benefits to the sintering industry.
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