1. The effect of temperature on lubrication
Lubricating oil is the lubrication method of most SKF bearings. The characteristics of the lubricating oil determine its applicable temperature range. Whether it is grease lubrication or oil lubrication, its lubrication performance is affected by temperature changes, mainly as follows: At this time, the lubricating grease will accelerate chemical deterioration and lose its lubricating ability. The viscosity of the lubricating grease will become low and not enough to form a sufficient oil film thickness, resulting in grease leakage and increased vibration and noise.
If the temperature of the SKF bearing rises to the dripping point of the lubricating grease, the grease will become soft, lose the semi-solid nature of the grease, liquefy and lose, and lose its lubricating effect on the bearing. The choice of bearing lubricating grease should be considered from the perspective of temperature changes. For example, the maximum use temperature of lithium-based grease is 100-110℃, and the maximum temperature of lithium-based grease can reach 130-140℃. Excessive temperature rise will bring many destructive results to bearing operation, such as lubrication failure, grease leakage, lower vibration and noise retention, and impact on bearing parts materials.
On the contrary, when the operating temperature of SKF bearing is too low, it will also affect the lubricating function of lubricating grease, which is manifested by the increase of the viscosity and consistency of the grease (the consistency refers to the degree of hardness of the grease), which increases the resistance of the bearing and increases The energy consumption of driving the bearing to run, and the increase in the viscosity and consistency of the lubricating grease, the lubrication point is not timely, the oil film is not repaired in time, the effective lubricating film thickness is reduced, and the bearing working surface is oil-lean.
The main reason for SKF bearing temperature rise
The first is that the friction between the friction pairs of the working surfaces of SKF bearing parts generates heat, and reducing the friction coefficient between the friction pairs through lubricating grease can effectively reduce the temperature rise;
Secondly, the internal friction of the lubricating grease itself generates heat during the operation of the SKF bearing, and reducing the viscosity of the lubricating grease can effectively control this part of the temperature rise.
The increase in temperature and the decrease in the viscosity of lubricating grease are conducive to the cooling and lubrication of the friction pair, but as the viscosity decreases, it is not conducive to preventing the formation of the friction pair from contacting the oil film. In a sense, the two causes and control methods of the temperature rise are sometimes They are contradictory and need to be considered in a balanced manner. According to the different working conditions of the bearing, the lubricating grease of different compositions should be selected reasonably, which can effectively expand the application range of lubricating grease and improve the lubricating effect of lubricating grease. SKF 21313 E bearings online , pls click here :
We usually only pay attention to the lubrication effect of the finished bearing grease under the normal working environment temperature. Due to the temperature rise in the bearing working process, the state of the grease will change. Therefore, in addition to considering the type of bearing grease In addition to the normal operating temperature of the bearing, the impact on the operating temperature rise of the SKF bearing itself cannot be ignored.
2. The effect of speed on lubrication
The lubrication quality of SKF bearings by lubricant is closely related to the working speed of the bearing. When the bearing starts at the early stage of work or when the speed is low, the lubricant cannot form a hydrodynamic lubrication film. At this time, the friction pair is lubricated by the static oil film, so , Lubricants used for bearings with lower speeds should be greases with fillers such as oily agents, friction modifiers, extreme pressure agents, etc. The commonly used lithium-based greases and soap-based greases themselves are oily agents and have a good adsorption function for metals. It is easy to form a static oil film in a non-power state.
When the SKF bearing is in high-speed operation, the grease is thrown away from the position of the friction pair under the action of centrifugal force, causing the working surface to be short of oil. The shear force formed by the high-speed rotation reduces the viscosity and consistency of the grease. At the same time, the high-speed friction of the working surface will increase the temperature of the lubricated part.
Therefore, when determining the bearing lubricating grease under high-speed operating conditions, it is necessary to consider the increased probability of contact fatigue caused by the increase of alternating load, the adhesion of grease at the friction part, and the timely response to the working surface when the temperature rises. Various factors such as oil supply capacity, improvement of grease resistance to shear, reduction of temperature rise or high temperature resistance. In terms of reducing temperature rise, oil and oil mist lubrication can provide better lubrication effect than grease lubrication through timely refuelling of high-speed running friction pairs and flow cooling of friction surfaces.
3. The influence of load on lubrication
The friction between objects is determined by the contact surface pressure and the friction coefficient of the contact surface material. Bearing rings and rolling element materials are generally made of GCr15 steel. It can be considered that the friction coefficient is basically unchanged. Therefore, the main reason for affecting the friction is the load borne by the bearing. When the load is large, it is easy to make the surface of the friction pair lubricate the film Rupture, resulting in adhesive wear on the working surface of the SKF bearing, which can cause severe seizure of the friction pair.
Generally, solid lubricating additives such as molybdenum disulfide, graphite, and polytetrafluoroethylene are used in lubricating grease to improve the lubricating ability of the friction surface. However, the use of solid lubricating additives will increase the noise value of the bearing operation and limit it. Application promotion.
In addition, during the actual operation of the bearing, the actual contact surface area of the friction pair is much smaller than the working area seen from the appearance. Therefore, even if the bearing bears a small load, a larger contact pressure will be formed on the surface of the friction pair. It causes adhesive wear of the friction pair, so although some bearings are not working under higher load conditions, lubricating grease containing extreme pressure agents should also be used.
Although the use of this lubricating grease will increase some costs, but for some special working conditions, from the perspective of improving the service life and reliability of the bearing, the cost performance is still relatively good.
4. The influence of environmental compatibility on lubrication
Generally, the effect of lubricating grease on rubber is often not valued by the bearing manufacturing industry. This is mainly due to the material composition of the commonly used bearing rubber seal ring, which does not damage the lubricating grease and affect the performance of the bearing. However, the possibility of chemical reaction between them should be fully considered when designing and selecting lubricating grease and sealing ring rubber components.
In addition, due to the presence of moisture in the air, there is the possibility of corrosion to steel bearing parts. Preventing corrosion is the basic requirement of lubricating grease. The current lubricating grease can technically guarantee the anti-corrosion requirements of the use environment.
The weakness of anti-corrosion is to resist the attack of chemical substances. This is due to the inaccurate understanding of the chemical composition of the lubricating part when selecting lubricating grease, which results in certain chemical components in the lubricating grease and contact The chemical substances reacted to reduce the corrosion resistance or even fail. However, after understanding the chemical composition of the lubricating part, it is possible to design and select a lubricant that resists chemical corrosion according to the principle of chemical corrosion.