# What are coefficient of friction, extreme pressure resistance, and load resistance?

There are various functions required of lubricants, such as corrosion prevention to protect against rust, etc. However, as the name implies, a lubricant cannot be called a lubricant unless it has a lubricating function.

### Coefficient of friction

The smaller this coefficient is, the less frictional resistance there is, the less force is required to move the object, and the easier it is for the object to continue to move by inertia once it starts moving. For example, if it is a bearing, the engine connected to the shaft and the shaft to the bearing will have a lighter load, and the bearing will continue to rotate for a longer period of time by inertia even after the input of rotational force is lost.

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### Extreme pressure

When buying lubricants and greases, we often see this term in product descriptions and catch phrases, but few people understand exactly what it means, even if they can vaguely imagine what it means from the lettering.

To put it simply, extreme pressure refers to the point where the oil film is about to run out to the point where the oil film is about to run out. The sliding surfaces of a machine are normally lubricated and protected by an oil film, but when a large amount of pressure is applied, the oil film becomes thin and the sliding surfaces come into direct contact with each other. This large pressure is called extreme pressure. The performance that protects against wear and increased frictional resistance caused by such contact is called extreme pressure performance, or "extreme pressure property" for short.

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This is the over all performance of the other two performance elements. As the name implies, it indicates how much load and pressure the sliding surface can sustain.
It is not simply the total performance of the two, as a very strong oil film, for example, a strong fluid dynamic bearing, may be able to withstand even a low extreme pressure.
However, it is not difficult to imagine that if frictional resistance is low and extreme pressure is high, the allowable load capacity will also be high. Other than the above two factors, there are other factors such as heat, acid, and other factors that cause deterioration of the lubricant and its components.
When load pressure is applied to the sliding surfaces and the oil film can no longer be maintained, the sliding surfaces begin to come into direct contact with each other, and extreme pressure agents work to suppress wear and increase the coefficient of friction.
However, the frictional resistance generates heat on the sliding surfaces and the lubricating oil, and the lubricating oil components are easily affected by thermal decomposition and the atmosphere, making them susceptible to oxidation and degradation caused by acids, moisture, and oxygen. Finally, the parts will seize, break, and stop moving beyond the limit of power.

The dynamic limit is not the same as the load capacity of the lubricant, but it is the resistance to load derived from a variety of compound factors.

Under extreme or near-extreme pressure conditions, the strength of the lubricant itself, such as thermal oxidation resistance and shear resistance, and the additives that support and supplement it, are important.