Special Issue; Products for Industrial Machinery - NTN

"Hybrid Bearphite" a Sintered Metal Sliding Bearing Inserted with Plastic
Fusing section
Photosensitive
drum bearing
Developing section
bearing
Paper stock travel
Transfer section
bearing
Transport roller
Transfer belt
Photosensitive drum
Toner cartridge
Imaging
Imaging
Imaging
Imaging
Fig. 1 Schematic of copying machines and printers
for resin bearings, used in this type of application, can
have disadvantages. During the molding process, their
shrinkage rate and coefficient of linear thermal
expansion are large and, as a result, their dimensional
accuracy and stability are poor.
Mechanisms, such as the photosensitive drum
whose running accuracy greatly affects print quality,
incorporate rolling bearings because rolling bearings
boast better functionality even though they are
relatively expensive. Concequently, there has been a
growing need for a bearing suitable for this application
that are both less expensive and more accurate.
3. Development of Hybrid Bearphite
3.1 Concept for the newly developed bearing
To satisfy the needs described in Section 2 , we
developed the Hybrid Bearphite, based on a concept
that consists of the following parts. 1) An insert
molding technique is used to form a thin resin layer on
the inner bore surface of a metal backing to achieve
better dimensional accuracy. 2) The metal backing is
made of sintered metal alloy to ensure effective
bonding to the resin layer due to its anchoring effect.
3) The resin layer is made of a low friction sliding
material so that the rotational torque with the bearing
is low. The newly developed Hybrid Bearphite bearing
is schematically illustrated in Fig. 2.
A resin layer formed inside the bore surface of a
metal member will usually develop peeling on the
metal-resin interface due to shrinkage occurring from
molding operation with the resin.
With our Hybrid Bearphite sliding bearing, however,
the resin material is allowed to fill the pores in the
sintered metal so that the resultant anchoring effect
helps prevent the resin layer from peeling off the metal
Sintered metal alloy
Resin sliding material
Fig. 2 Concept of HYBRID BEARPHITE
backing. At the same time, through improvement of
the insert molding process, the thickness of the resin
layer is regulated to 0.25 mm so that the resin layer
features good dimensional accuracy and the
dimensional stability of the resin layer is high relative
to temperature variation. If the end faces are each
provided with a resin layer, then the sliding bearing
can bear not only a radial load but also an axial load.
3.2 Development of resin sliding material
Since the main purpose of the Hybrid Bearphite
sliding bearing is the replacement of rolling bearings,
the friction on its sliding surface needs to be low.
However, the friction coefficient of any conventional
resin sliding material is 0.1 or higher, 2) so such a
material would not serve for this sliding bearing. To
address this problem, we attempted to develop a new
resin sliding material with a friction coefficient half that
of conventional resin sliding materials.
The friction-wear characteristics of a resin are
usually improved by blending in oil or a solid lubricant
such as polytetrafluoroethylene (PTFE) or graphite.
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