Special Issue; Products for Industrial Machinery - NTN

"Hybrid Bearphite" a Sintered Metal Sliding Bearing Inserted with Plastic
Furthermore, the oil-impregnated silica particles link
with each other and function as passages for the oil.
Through these passages, the oil inside the material is
continuously supplied to the sliding surface, thereby
giving the material a stable low friction coefficient.
The resin sliding material 4 was modified so that its
melted viscosity was suitable for injection molding and
was adopted for the resin layer on the Hybrid
Bearphite.
3.3 Insert injection molding to sintered metal
backing
The factors that help ensure high accuracy with the
Hybrid Bearphite sliding bearing are summarized in
Fig. 7. As already mentioned, if a resin layer is formed
on the bore surface of a conventional metal member,
peeling will unavoidably occur on the metal-resin
interface due to molding-induced shrinking with the
resin material. For our Hybrid Bearphite sliding
bearing design, a resin material is allowed to fill the
pores on the sintered metal so that, due to the
Sintered metal backing
Resin sliding material
Injection-molding conditions
Design
Porosity ratio
Strength and rigidity
Linear expansion coefficient
Melting viscosity
Injection pressure
Die temperature
Die structure (gate)
Resin layer thickness
Fig. 7 Factors to achieve high precision
resultant anchoring effect, the resin layer does not
come off the metal backing. Therefore, we attempted
to optimize the porosity ratio of the surface of the
sintered metal as well as the injection molding
conditions.
Fig. 8 shows an example of optimization of the
surface porosity ratio with a sintered metal backing.
Fig. 8(a) illustrates a standard sintered metal for an
oil-impregnated sliding bearing. Fig. 8(b) provides an
example of optimization of the surface porosity ratio
through adjustment for grain size of the starting metal
powder and molding pressures. Both Fig. 8(a) and
Fig. 8(b) show the surfaces of the sintered metal prior
to insert-molding with a resin material (black areas
denote pores) as well as a view of the surfaces of the
sintered metal after the resin layer formed by insertmolding
had been stripped off by force. The surface
shown in Fig. 8(a) where the resin layer was stripped
off does not show traces of the previously deposited
resin, suggesting that the resin did not fill the pores.
In contrast, with the example in Fig. 8(b), the resin
layer itself was split, and this suggests that the
bonding of the resin layer to the sintered metal was
very strong. As can be understood from this fact, the
bonding strength of the sintered metal backing and
resin layer is very high with our Hybrid Bearphite.
4. Performance of Hybrid Bearphite
Fig. 9 shows the appearance of our Hybrid
Bearphite, which is essentially a sintered metal sliding
bearing with a resin insert. The example in this photo
has a resin layer on its side faces in order to be able
to bear not only a radial load but also an axial load.
The thickness of the resin layers on the bore surface
and end faces is 0.25 mm. The performance of our
Hybrid Bearphite is described below.
Surface of sintered metal
before insert molding
Surface with resin layer
stripped off
(a) Standard sintered metal
Resin
Fig. 9 Appearance of HYBRID BEARPHITE
(b) Optimized sintered metal
Fig. 8 Inner surface of sintered back metal
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