T-227
20.1.3 Forced-Circulation Lubrication
Forced-circulation lubrication applies lubricant to the contact portion of the teeth by
means of an oil pump. There are drop, spray and oil mist methods of application.
1. Drop method:
An oil pump is used to suck-up the lubricant and then directly drop it on the contact
portion of the gears via a delivery pipe.
2. Spray method:
An oil pump is used to spray the lubricant directly on the contact area of the gears.
3. Oil mist method:
Lubricant is mixed with compressed air to form an oil mist that is sprayed against the
contact region of the gears. It is especially suitable for high-speed gearing.
Oil tank, pump, filter, piping and other devices are needed in the forced-lubrication
system. Therefore, it is used only for special high-speed or large gear box applications.
By filtering and cooling the circulating lubricant, the right viscosity and cleanliness can be
maintained. This is considered to be the best way to lubricate gears.
20.2 Gear Lubricants
An oil film must be formed at the contact surface of the teeth to minimize friction and
to prevent dry metal-to-metal contact. The lubricant should have the properties listed in
Table 20-3.
Table 20-3 The Properties that Lubricant Should Possess
20.2.1 Viscosity of Lubricant
The correct viscosity is the most important consideration in choosing a proper lubricant.
The viscosity grade of industrial lubricant is regulated in JIS K 2001. Table 20-4 expresses
ISO viscosity grade of industrial lubricants.
No.
Properties
Description
1
2
3
4
5
6
Correct and
Proper Viscosity
Antiscoring
Property
Oxidization and
Heat Stability
Water Antiaffinity
Property
Antifoam
Property
Anticorrosion
Property
Lubricant should maintain a proper viscosity to form a stable oil
film at the specified temperature and speed of operation.
Lubricant should have the property to prevent the scoring failure
of tooth surface while under high-pressure of load.
A good lubricant should not oxidize easily and must perform in
moist and high-temperature environment for long duration.
Moisture tends to condense due to temperature change, when the
gears are stopped. The lubricant should have the property of
isolating moisture and water from lubricant.
If the lubricant foams under agitation, it will not provide a good oil
film. Antifoam property is a vital requirement.
Lubrication should be neutral and stable to prevent corrosion from
rust that may mix into the oil.
