LUBRICATION OF BALL BEARING UNITS

LUBRICATION OF BALL BEARING UNITS

1. Permissible speed

Permissible speed of ball bearing is expressed normally in terms of dn value(Bearing bore diameter mm x operating speed r.p.m.), although it is influenced by the shape, size, lubricant type and seal device. The permissible speed can be roughly determined by sliding speed at the friction part of the holding device and rolling body. In the case of ball bearing unit, it is provided with grease sealed by the oil seals and slingers. Accordingly, the friction resistance at seal contact yields also a large influence on the permissible speed.
When such factors are taken into consideration, the permissible speed is given as follows:
                       Dn≤150,000 [dn= d x n]
Whereas,  d: Bearing bore diameter (mm)
         n: Operating speed (r.p.m.)
 

2.  Type of Grease Nipple

3. Lubricant Grease
Ball bearing units adopts the lubrication mechanism by grease. Since the ball bearing itself is required high precision, the grease must be in particularly fine quality.
Various types of grease are sold in the market, each having different combination of mineral oil and metal saponification radical. Among them, lithium saponification radical grease is usually called “Multi-purpose Grease”. It has outstanding properties of heat resistance, low temperature resistance, water expellent and mechanical stability; it is most suitable for a ball bearing unit.
At present, “Gold Pillow Lube” grease is used for the standard product and is lithium saponification radical grease. It is most suitable for the ball bearing.

4. Replenishment of Grease

Since the high quality grease is used for the ball bearing unit, the grease can be used for a considerable time without the grease supply, if the bearing working condition is favorable and the operation temperature is not too high.
However, even if the best quality grease is used, the quality deterioration can not be prevented as the time passes by. When the dust or moisture surrounds the bearing too much or the bearing is subjected to the high temperature, the grease must be supplied periodically according to the grease deterioration.
Our ball bearing unit has such a construction so as to allow the grease replenishment during the use. Grease is injected into the grease nipple by use of the grease gun. Through the oil groove provided in the bearing outer ring and the oil hole, it is supplied to the inside of bearing.
The grease supply interval is dependent on the kind and quality of the grease to be used as well as the operation conditions of the bearing. Under the normal operation condition, however, the value as obtained by the following formula is recommended.
                         N=1010/d
Whereas, N: Total rotation number until the replenishment or replacement
        d: Bearing bore diameter (mm)
If the revolution number per minute constant, the replenishment interval is expressed in terms of the time as follows:
                         H=1x1010 / 60n*d
Whereas,  H: Replenishment interval (hr)
          n: Operating speed (r.p.m.)
Different from the previous calculation data, the following table shows the approximate grease supply interval obtained empirically from various ambient conditions and bearing operation temperatures.

Grease supply period

5.  Range of operating temperature

As bearing units are used not only in normal temperature but also in high or low temperature in many applications.
Bearing units for heat-resistance or cold-resistance application are available by using suitable kind of rubber seal and grease for specific operating temperature as shown in following table.
For heat-resistance application, decrease of load rating of the bearing must be taken into consideration and larger radial internal clearance of the bearing than normal application be taken.
Standard radial internal clearances for heat-resistance application are C4 HT20 for cylindrical bore bearing and tapered bore bearing.
When temperature differential between bearing inner ring and outer ring is extremely large, suitable radial internal clearance must be determined.

Note: For application where operating temperature exceeds 150℃, consult us along with data specification and operating condition.
 

Range of operating temperature

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