How to choose the lubrication method of bearings?

Lubrication methods for bearings are broadly classified into grease lubrication and oil lubrication.

In order to give full play to the function of the bearing, it is important to use the corresponding lubrication method according to the conditions of use of the bearing and the purpose of use.

Bearing grease

Grease is a lubricant consisting of a base oil, a thickener and an additive. When selecting, you should choose a grease that is very suitable for the conditions of use of the bearing. Because the grease trademark is different, there will be a big difference in performance, so you must pay attention when choosing.

Commonly used greases for bearings include calcium-based greases, sodium-based greases, calcium-sodium-based greases, lithium-based greases, aluminum-based greases, and molybdenum disulfide greases.

The amount of grease filled in the bearing is preferably 1/2-1/3 of the internal space of the bearing. It should be reduced to 1/3 at high speed. Excessive grease tends to increase the temperature of the bearing during operation.

Grease selection

  When selecting the grease according to the working temperature, the main indicators should be the dropping point, oxidation stability and low temperature performance. The dropping point can generally be used to evaluate the high temperature performance. The actual working temperature of the bearing should be lower than the dropping point of 10-20 °C.

Synthetic grease should be used at a temperature below the drop point of 20-30 °C. When selecting the grease according to the bearing load, the grease with a small penetration should be selected for the heavy load. When working under high pressure, in addition to the small penetration, it also has a higher oil film strength and extreme pressure performance. When selecting grease according to environmental conditions, calcium-based grease is not easily soluble in water and is suitable for drying and low moisture environments.

Bearing lubricant

Under high-speed and high-temperature conditions, oil lubrication can be used when grease lubrication is not suitable. A large amount of heat can be taken away by the circulation of the lubricating oil. Viscosity is an important characteristic of lubricating oil. The viscosity directly affects the fluidity of the lubricating oil and the thickness of the oil film formed between the friction surfaces. The viscosity of the lubricating oil at the working temperature of the bearing is generally 12-15 cst. The higher the speed, the lower the viscosity, and the heavier the load, the higher the viscosity. Commonly used lubricating oils include mechanical oil, high-speed mechanical oil, turbine oil, compressor oil, transformer oil, and cylinder oil.

Lubrication method

Oil bath lubrication: 油浴润滑是最普通的 Lubrication method ，适于低、中速轴承的润滑，轴承一部分浸在油槽中，润滑油由旋转的轴承零件带起，然后又流回油槽，油面应稍低于最低滚动体的中心。

Drip lubrication: Drip oil lubrication is suitable for bearing parts that need to supply lubricating oil quantitatively. The amount of oil dripping is generally one drop every 3-8 seconds. Excessive oil quantity will cause the bearing temperature to increase.

循环油润滑： The filtered oil is delivered to the bearing components by an oil pump, filtered through the lubricating oil after the bearings, and then cooled and used. Since the circulating oil can take a certain amount of heat to cool the bearing, this method is suitable for bearing parts with a higher rotational speed.

Spray lubrication: The dry compressed air is mixed with the lubricating oil through a sprayer to form an oil mist. In the jet bearing, the air flow can effectively cool the bearing and prevent the intrusion of impurities. This method is suitable for lubrication of high speed and high temperature bearing components.

  Spray lubrication: 用油泵将高压油经喷嘴射到轴承中，射入轴承中的油经轴承另一端流入油槽。在轴承高速旋转时，滚动体和保持架也以相当高的旋转速度使周围空气形成气流，用一般 Lubrication method 很难将润滑油送到轴承中，这时必须用高压喷射的方法将润滑油喷至轴承中，喷嘴的位置应放在内圈和保持架中心之间。

 滚动轴承的润滑剂和润滑方式的选择与轴承的类型、尺寸和运转条件有关，一般情况下滚动轴承采用脂润滑或油润滑，在特殊条件下也可采用固体润滑。在脂润滑和油润滑中，脂润滑用的又最多，约有80%的滚动轴承都是使用脂润滑。

Grease lubrication

The lubrication device is simple. If a sealed bearing or a non-sealed bearing that does not require replenishing grease is used, no additional lubrication is required (in contrast, oil lubrication systems require oil pumps, tubing, fuel tanks, etc.).

润滑脂不易泄漏，轴承的密封结构比较简单，

轴承的维护、保养方便。

润滑脂有密封作用，可防止外部灰尘、水分和其它杂质侵入轴承。

容易提高机械装置的清洁度。

   脂润滑的缺点

轴承磨擦大、散热不好，允许的转速比较低。

脂润滑轴承的dn值一般不能超过3×105mm·r/m·n。

温度很高时，润滑脂的基础油会加快蒸发和氧化变质，润滑脂的胶体结构也会变化而加速分油。

轴承温度每升高10℃—15℃，润滑脂的寿命下降1/2，除特殊的高温润滑脂外，一般润滑脂不能在高温下使用。

适合于高速旋转

高温稳定性好，适合在高温下使用。

   可带走轴承的内部的磨擦热，散热好。当轴承的环境温度高时，油润滑可以起冷却作用。

It is easy to remove wear particles and dust inside the bearing.

It can share a lubricant with parts around the bearing such as gears for common lubrication.

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