Bearing Net

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For a copy of the information on this page download the NBC TR Technical catalogue

Mounted ball bearing units...

consist of ball bearings with spherical outer diameter mounted in pressed steel or ductile cast iron housings, and are further categorised by the method of attachment to the shaft

  • Set screw mounting type       - the most popular and most widely used consisting of 2 setscrews 120o apart
  • Adaptor sleeve locking type  - more usually found on large or high speed units
  • Eccentric locking collar          - usually found on units with reversing shafts 

The specially heat treated inner ring is wider than that of a standard ball bearing to increase stability and more effective lockscrew locking.

Limiting speeds

The limiting speed of ball bearing inserts is mainly determined by the quality of fit between the bearing and the shaft. Usually a shaft with h7, h8 or h9 tolerance is recommended for light loads and slow speeds, whilst a tight j7 fit is recommended for higher speeds and heavier loads.

The limiting speeds for a variety of fits are tabulated below. The j7 (h9/IT5) figures apply to adapter mount ball bearing inserts, the others to setscrew and eccentric locking collar type units.

shaft  (mm)
200 Series
300 Series
Shaft tolerance
Shaft tolerance
j7 (h9/IT5)
h7
h8
h9
j7 (h9/IT5)
h7
h8
h9
12
6700
5300
3800
1400
-
-
-
-
15
6700
5300
3800
1400
-
-
-
-
17
6700
5300
3800
1400
-
-
-
-
20
6000
4800
3400
1200
-
-
-
-
25
5600
4000
3000
1000
5000
3600
2600
900
30
4500
3400
2400
850
4300
3000
2200
800
35
4000
3000
2000
750
3800
2800
2000
700
40
3600
2600
1900
670
3400
2400
1700
630
45
3200
2400
1700
600
3000
2200
1500
560
50
3000
2200
1600
560
2600
2000
1400
500
55
2600
2000
1400
500
2400
1800
1300
450
60
2400
1800
1200
450
2200
1700
1100
430
65
2200
1700
1100
430
2000
1500
1100
400
70
2200
1600
1100
400
1900
1400
1000
360
75
2000
1500
1000
380
1800
1300
900
340
80
1900
1400
950
340
1700
1200
850
320
85
1800
1300
900
320
1600
1100
800
300
90
1700
1200
800
300
1500
1100
750
280
95
-
-
-
-
1400
1000
700
260
100
-
-
-
-
1300
950
670
240
105
-
-
-
-
1200
900
630
220
110
-
-
-
-
1200
800
600
200
120
-
-
-
-
1100
750
530
190
130
-
-
-
-
1000
670
480
180
140
-
-
-
-
900
600
430
160

Housing strengths

One of the most common design errors is to base the selection on the bearing strength only. The "tear out strength" of the housing must be considered. The housing strength is a fraction of the bearing insert static capacity, and it is recommended that a safety factor of 6 is applied.

Seals

In general, bearing inserts have a single steel/rubber lipped seal that offers low friction, good grease retention and good protection against external contaminants. However, there is a small clearance between shaft and seal that will inevitably increase after hours of use.

For extreme environmental conditions we recommend use of the triple lip seal arrangement which impinge slightl;y on the shaft forming a tighter seal. A far better barrier to liquid and solid contamination is thus formed. This type of seal is typically found in machinery used in mines and quarries.

Lubrication & Maintenance

Inserts are sealed and factory lubricated with a standard lithium based EP2 grease suitable for operation between -20o C and 120o C, and are generally considered to be sealed for life. However, operation at temperatures > 70o C will seriously reduce grease life and this must be taken into account.

Recommended relubrication intervals take into account the operating speed, operating temperature and the environment.  Some of the grease will find its way into the bearing through the lubrication slot (if provided) and regreasing holes in the outer ring, while some will simply extrude between at the bearing/housing interface.

Note d= (ID+OD)x rpm/2
 

dn value Environment Temp oC Relube  interval
<40 000 Clean

-15 - +65
+65 - +100

6 - 12 months
2 - 6 months

< 70 000 Clean

-15 - + 65
+65 - +100

2 - 6 months
1 month

Any Dirty

< 65
>65

1 week - 1 month
1 day - 2 week

Any Very dirty Any temp 1 day to 1 week
Any Water splash Any Daily

Mounting bolts and shaft mount gribscrews should be checked from time to time as vibration may cause them to loosen in service.

Tolerances for spherical housing bores

The dimensional tolerance for the inner diameter of the sphere is H7 which will normally give a clearance fit with the bearing insert. By special order a tighter tolerance J can be specified which will result in an interference fit.

 Information extracted from TR catalogue E03-1999    

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