1. Purpose of lubrication
The purpose of rolling bearing lubrication is to reduce friction and wear inside the bearing and prevent seizure. Its lubrication effects are as follows.
(1) Reduce friction and wear.
Prevent direct metal contact between the contact parts of the bearing ring, rolling element and retainer, and reduce friction and wear.
(2) Extend fatigue life.
The rolling fatigue life of the bearing will be extended if the rolling contact surface is well lubricated during operation. On the contrary, if the lubricating oil viscosity is low and the lubricating oil film thickness is small, it will be shortened.
(3) Discharge and cooling of friction heat.
For the circulating oil supply method, the heat generated by friction can be discharged by oil, or the heat transmitted from the outside can be cooled. Prevent the bearing from overheating and prevent the deterioration of the lubricating oil itself.
(4) Others.
Prevent foreign matter from invading the inside of the bearing and prevent rust or corrosion.
2. Lubrication method
The lubrication method of the bearing is divided into grease lubrication and oil lubrication. In order to give full play to the performance of the bearing, it is necessary to first select the appropriate lubrication method according to the working conditions and purpose of use. Considering only lubrication, oil lubrication is dominant. However, grease lubrication can simplify the peripheral structure of the bearing.
1. Grease lubrication
(1) The amount of grease filled in the bearing seat
The amount of grease filled in the bearing seat varies depending on the bearing speed, bearing seat structure, space volume, grease brand, and the gas in the operating environment. For machine tool spindle bearings with a small allowable temperature rise, less grease should be filled. The general standards are as follows.
First, fill the inside of the bearing with grease. At this time, the retainer should also be guided and the grease should be inserted. Then, fill the space volume inside the bearing seat outside the shaft and bearing with grease according to the following amount.
1/2~2/3 (when the limit speed is 50% lower)
1/3~1/2 (when the limit speed is 50% higher)
(2) Grease replenishment
Generally, once the grease is filled, it can be used for a long time without replenishment. However, some operating conditions require frequent replenishment or replacement of grease. Therefore, the design of the bearing seat should also take this into consideration. When the replenishment interval is short, the grease filling port and the discharge port should be designed at the appropriate position of the bearing seat. This is to facilitate the replacement of deteriorated grease. For example, the space of the bearing seat on the grease replenishment side is divided into several parts by using a fan-shaped grease replenishment plate, and the grease can flow into the bearing after filling only one part. The grease squeezed out from the inside of the bearing is discharged from the bearing seat by the grease valve. If the grease valve is not used, the space of the bearing seat on the discharge side is enlarged, and the old grease accumulates here, and the cover is removed regularly to remove it.
(3) Grease replenishment interval
Even high-quality grease will deteriorate after a period of use, resulting in reduced lubrication performance. Therefore, grease should be replenished in a timely manner. The grease replenishment interval is expressed in terms of operating time. (1) and (2) in Figure 12.2 are rough standards. Figure 12.2 shows the curve when using high-quality lithium soap mineral grease, temperature 70°C, and standard load (P/C=0.1).
·When the temperature is higher than 70℃, the grease replenishment interval will be halved for every 15℃ increase in bearing temperature.
·Grease Especially when high-quality grease is used for ball bearings, the replenishment interval can be extended. When the temperature is lower than 70℃, mineral oil lithium soap grease or synthetic oil lithium soap grease should be used.
(4) Grease life of sealed ball bearings
The grease life of grease filled in single-row deep groove ball bearings, seals or dust cover seals can be calculated using formula (12.1), formula (12.2) or Figure 12.3.
{General purpose grease (1)}
log t=6.54-2.6(n/Nmax)-[0.025-0.012(n/Nmax)]T-------（12.1）
{High quality grease (2)}
log t=6.12-1.4(n/Nmax)-[0.018-0.006(n/Nmax)]T-------（12.2）
Where t: average grease life (h)
n: bearing rotation speed (rpm)
Nmax: grease lubrication limit speed (rpm) (values for ZZ type and VV type in the bearing size table.)
T: bearing operating temperature (℃)
In addition, the applicable ranges of formula (12.1) and formula (12.2), or Figure 12.3, are as follows.
