Special Issue; Products for Industrial Machinery - NTN

"Hybrid Bearphite" a Sintered Metal Sliding Bearing Inserted with Plastic
Variation in bore diameter m
50
40
30
20
10
0
Bearing bore diameter: 7.5 mm
Resin linear expansion coefficient: 1410 -5 /˚C
Ordinary
resin bearing
Hybrid Bearphite
25 35 45 55 65
Temperature ˚C
Actual measurement
with Hybrid Bearphite
Fig. 12 Dimensional stability of HYBRID BEARPHITE
dimensional variation is governed by the design of the
resin layer thickness. In other words, if the thickness
of a resin layer is determined through consideration of
the dimensional variation of the shaft, and the
clearance between the shaft and the bearing can be
maintained at a constant dimension for a wider
temperature range. This is a revolutionary new feature
for resin bearings. Consequently, our Hybrid Bearphite
can realize higher running accuracy at a wider
temperature range, an achievement not previously
attained with conventional resin bearing technologies.
4.3 Bonding strength of the resin layer
The resin layer must be firmly bonded to the
sintered metal in order to maintain a high level of
dimensional accuracy in a sintered metal sliding
bearing. The results of a heat shock test are
summarized in Table 3 to provide data about the
bonding strength of the resin layer. In this test, the
Hybrid Bearphite sliding bearing was subjected to 100
heating-cooling cycles, with each cycle consisting of 1
hour at -20˚C followed by 1 hour +60˚C. Through this,
the dimensions before and after the heat shock test
and the bonding strengths between the sintered
metals and the resin layers were inspected.
The dimensional variation occurring on our Hybrid
Bearphite sliding bearing after undergoing the test
Table. 3 Inner diameter change of HYBRID BEARPHITE
after 100 cycles of heat shock test
TP
1
2
3
Before test
mm
7.501
7.510
7.508
After test
mm
7.500
7.508
7.504
Variation
m
1
2
3
State of
bonding
No peeling
No peeling
No peeling
was very small. This means that the bonding is very
firm between the sintered metal and the resin material
of our Hybrid Bearphite.
4.4 Chemical attack resistance
Resin materials have been used increasingly on
bearing housings in products such as office
automation equipment. Because of the requirements
for satisfying dimensional accuracy and impact
strength, the resins often used on housings are
amorphous resins that are not sufficiently oil-resistant.
Examples of such resins include polycarbonate (PC)
and acryronitrile-butadiene-stryrene copolymer (ABS).
If an operating resin housing comes into contact with
an inappropriate oil, it can develop cracks. This
problem is known as solvent cracking, and it occurs
when the compatibility of a resin with an oil is high.
This allows the oil to penetrate and disentangle the
polymer molecules that constitute the resin, causing
the resin to develop cracks and/or crazing.
Polycarbonate test pieces measuring 152 mm in
length, 12.5 mm in width and 6.35 mm in thickness
were prepared. Each oil was applied to the area of the
test piece where the maximum tensile stress occurs,
and a bending load was exerted for a specific duration
(Fig. 13). Thus, the chemical attack quality of each oil
was evaluated.
The support distance adopted was 100 mm and the
test temperature was 75˚C. As can be seen in Table
4, silicone oil, which is included in the resin layer of
PC
Fig. 13 Test rig for chemical attack
Table. 4 Chemical attack of oils for polycarbonate
Condition Displacement
(mm) 1.5
Oil type Time (h) 3
No oil
Polyethylene glycol
Polyol ester oil
Ether oil (ADE oil)
Mineral oil
PAO
Silicone oil
Application of oil
Support distance100
3.0
3
3.5
3
Displacement
3.5
196
polyolefin oil
Oil blended in Hybrid Bearphite
Symbols in the table: : no crack occurrence, : crack occurrence
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