Needle Roller Bearings - Ntn-snr.com

Technical Data
NTN
11. Technical Data
11. 1 HL Bearing
The form of bearing separation life can be mainly
classified into the internal origin type and the surface
origin type. Bearing separation of the surface origin type
is said to occur in an inadequately lubricated area and it
is widely recognized that the bearing separation life
correlates to the oil film parameter that can be determined
by "Elastic Fluid Lubrication Theory (EHL Theory)".
This oil film parameter must be increased for controlling
the surface origin type separation and, for that, the
bearing manufacturers have made possible effort for
better improvement of lubricant and for upgrading of the
bearing rolling raceway surface roughness.
In recent years it has been proposed by the relative
field that the capability of forming an oil film on contact
surfaces could be improved better by changing the form
and directivity of surface roughness of machined parts.
On the other hand, NTN developed successfully long
life HL (High Lubrication) bearings under "Micro EHL
Theory" as one of the countermeasures against surface
origin type separation. And these HL bearings have been
widely used in each field since developed.
11.1.1 Basic concept of HL bearing
Fig. 11.1 illustrates the basic concept of the HL
bearing.
In this Figure, the hatched area shows a contact
portion deformed elastically and the dotted line shows the
lubrication flow, based on "Internal lubrication fluid flow
model in contact portion" disclosed by H.S. Cheng and
others.
Lubricant flow in (B) has a resistance greater than that
in (A). This means that the quantity of a fluid existing
internally in the contact portion increases. In other words,
the thickness of an oil film formed on the rolling contact
surface increases with increase of the fluid quantity.
11.1.2 HL surface
Fig. 11.2 is a magnified photo showing roller surface. In
this Figure the blackened spots are micro recessed spots
and, as seen from this Figure, a number of micro oil pots
of around several tens mm exist at random. The recessed
spots on this surface can be modified into any optional
size and the number of spots by changing the machining
conditions. Fig. 11.3 shows the bus line form of the HL
surface, from which the depth of the micro recessed spots
is nearly 1 mm.
11.1.3 HL bearing application examples
The HL surface-treated bearings are widely used in
various fields. For example, they are used for car
transmission, hydraulic devices, various reduction gears,
etc.
As an example of special application, HL surface
treatment is applied to the special-purposed bearing for
the rocker arm of car engine. This is highly appreciated
as an effective seizure preventive measure.
Fig. 11.2 Magnified photo showing roller surface
A
B
1m
0.1mm
Fig. 11.1 Directivity of finished surface and lubrication fluid
flow model
Fig. 11.3 Bus line form of HL surface
A-52