Special Issue; Products for Industrial Machinery - NTN

NTN TECHNICAL REVIEW No. 742006
4.1 Friction-wear characteristics
The Hybrid Bearphite, which is provided with the
insert-molded resin sliding material in its bore surface
was combined with an Ni-plated shaft and was run
under a radial load of 29.6 N and a running speed of
240 min -1 . The resultant friction coefficient is
graphically plotted in Fig. 10. For comparison, the
characteristics of a sintered oil-impregnated bearing
(mineral oil-impregnated copper sintered bearing) are
also plotted in the same diagram.
The friction coefficient of the sintered metal oilimpregnated
bearing was high during the earliest
stage of operation, but eventually decreased as
running-in proceeded, and finally became stable at
0.06. In contrast, the friction coefficient with the Hybrid
Bearphite always remained stable at about 0.06 even
at the earliest stage of operation. The wear with the
sintered metal oil-impregnated bearing after 500 hours
of operation reached 10m while the Hybrid
Bearphite was as small as 6m. This means that the
friction-wear quality of the Hybrid Bearphite sliding
bearing is better than that of the sintered metal oilimpregnated
bearing.
In a test with aluminum shafts, the sintered metal
oil-impregnated bearing caused the aluminum shaft to
be worn rapidly. In contrast, our Hybrid Bearphite
exhibited performance equivalent to that shown in Fig.
10.
Dynamic friction coefficient
0.25
0.20
0.15
0.05
0.00
0
Radial load: 29.6 N
Running speed: 240 min -1
Counterpart shaft: Ni-plated
Hybrid Bearphite
Sintered
oil-impregnated
bearing
100 200 300 400 500
Duration h
Fig. 10 Friction property of HYBRID BEARPHITE
4.2 Dimensional accuracy
The dimensional accuracy data and features of our
Hybrid Bearphite are summarized in Table 2. The
Hybrid Bearphite boasts dimensional accuracy
comparable to that of a sintered oil-impregnated
bearing. Furthermore, since the resin sliding layer on
the Hybrid Bearphite expands and shrinks relative to
the reference surface, it features extremely small
dimensional variation due to temperature variations
(Fig. 11). Note that greater dimensional variation with
a bearing leads to larger shaft clearance, resulting in
greater variation in running accuracy.
For the Hybrid Bearphite with a bore diameter of 7.5
mm, the resin layer thickness was adjusted to 0.25
mm and the linear expansion coefficient of the resin
layer was assumed to be 14 x 10 -5 /˚C. Thus, the
temperature-dependent variation in the bore diameter
of the Hybrid Bearphite was calculated (reference
temperature: 25˚C) and was compared (Fig. 12), with
that obtained from an ordinary resin sliding bearing
comprised solely of resin material. This diagram also
includes the actual measurement data at 60°C. The
steepness of the straight line representing the
Table. 2 Dimensional properties and characteristics of
sliding bearings
Characteristic
Bore diameter
Outside diameter
Bore roundness
Concentricity
Cylindricity
Dimensional variation
Sliding relative
to aluminum
Sliding relative to
SUM + Ni-plating
Hybrid
Bearphite
5m
15m
10m max.
15m max.
10m max.
Low
temperature
Resin sliding
bearing
15m
15m
50m max.
30m max.
40m max.
High
temperature
Sintered metal
oil-impregnated bearing
5m
15m
10m max.
15m max.
10m max.
Reduction in sintered bore
Shrinking of resin layer
Increase in sintered bore
Expansion of resin layer
Interface is firmly bonded
Reference surface for expansion and shrinking
Bearing with smaller change in bore diameter relative to variation in temperature
Fig. 11 Dimensional change of HYBRID BEARPHITE
against temperature change
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