If you need to lubricant your machines which operate at high temperatures then you cannot use regular grease. For such applications, you need high-temperature grease. Grease is made up of a base oil, thickener and additives. The raw materials used for the high-temperature grease are different from those of regular grease.
Usually high-temperature grease is made from a synthetic oil base and thickeners like lithium and aluminum complex as these can withstand high temperatures. Grease is used to lubricate the moving surfaces to prevent friction and wear. While selecting a grease for high-temperature application you should check the temperature range, the loading speed and the viscosity of the base oil.
Grease for bearings
When grease is used in bearings that work in high temperatures few points need to be considered. It is important to choose grease based on the operating conditions and the grease filing also should be sufficient. The size of the grease band, open space, home construction, and surroundings all affect how much grease is required.
Filling too much or too little grease can affect the torque and the temperature rise. The low speeds require more grease than the high speeds. The grease should first be filled to an appropriate amount in the bearing and then the free space. When the bearing is operated at a speed of 50% or less then the grease should be filled ½ – ⅔. When the bearing is operated at a speed of 50% or more the grease should be filled ⅓ – ½. However, the amount of grease can be reduced to lower the torque and heat generation.
To ensure the full performance of the bearing sufficient amount of suitable grease has to be used. If the difference between the outside temperature and the bearing temperature is more than maintenance is needed immediately. If the difference in the temperature is less than the grease will work without any problems.
Roller bearings are often lubricated with grease and placed in sealed boxes so that the grease stays close to the bearing for proper lubrication. During the operation, the bearing will come into contact with the rollers and the rings. As the bearings act as a mill the mechanical degradation of the grease will take place. The consistency of grease will weaken and it may flow out of the bearing. Therefore it is important to know the factors that affect the consistency of grease.
If the grease will decrease significantly and will be the reason for failure. Leaded grease was used previously but due to environmental reasons, unleaded grease is used. Depending on the temperature of the bearing the lubrication should be planned.
For example, high-temperature grease is used to lubricate the roller bearings which operate at high speeds and temperatures. The rolling friction of the bearing and the churning of the lubricant can generate heat which can lead to a rise in the temperature. It is important to dissipate this heat to avoid the overheating of bearings. Therefore a high temperature grease should be used. The grease will be stable and effective in such situations as it uses a high-melting point oil. A sufficient lubrication oil film should be maintained to ensure that the bearing operates continuously at high speed.
For example, high-temperature grease is mostly used in the automotive industry as the vehicles are exposed to high amounts of heat. High-temperature grease is best for temperatures reaching 200° C.
Rules for selecting grease
There are different types of grease like general grease, high-temperature grease for bearings and extreme temperature grease. Grease should be evaluated based on its mechanical stability, oxidative stability and thermal stability. Rules for selecting grease:
- The grease should be fully formulated and commercially available.
- It should be recommended for the application by the supplier.
- It should represent a wide range of thickeners and base oil types.
- It should have a national lubricating grease number.
- It should be allowed to be used as per the environmental laws.
Properties
The high-temperature grease can handle higher temperatures than the general grease can handle. It is specially designed to be used at high temperatures. It has unique properties and does not break down as the regular grease at high temperatures. High-temperature grease is of high quality and can work under high temperature conditions. Their properties are as follows:
- It can work under high heat conditions and helps to increase the lifespan of the machines.
- It does not get oxidized when exposed to air which is an important requirement when used in high temperatures.
- It provides protection against rust and corrosion even at high temperatures.
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