MACHINERY LUBRICATION- INDIA SEPTEMBER-OCTOBER 2019 | Page 29

MLI
TYPES OF WORM DRIVE EFFECTS ADVANTAGE OF A SYNTHETIC GEAR OIL OVER A
MINERAL OIL
Reduction of total losses 30% or more
Improved efficiency 15% or more
Reduction of operating temperature 20˚C or more
have provided a better understanding
of common worm drive failure modes
and offered clues for optimizing the
solutions. Lubricants are no exception
to these enhancements for worm drives.
Generally speaking, a high-quality
worm drive lubricant will have low
friction, high oxidation resistance, good
anti-wear protection and high viscosity
index.
Figure 6. Advantages of synthetic gear oil over mineral oil
Also, because of the sliding nature of
the worm drive, metals with a low
coefficient of friction are generally used.
The worm wheel typically contains
yellow metals, while the worm is usually
made of steel. This results in more
favorable wear characteristics, better
loading ability and less heat generation
not found in other metal combinations.
Yellow metals like bronze that are used
on the worm wheel can present unique
lubrication challenges when selecting a
compatible additive package. With this
metallurgical combination, it is also
expected that the worm wheel act
sacrificially in comparison to the worm
due to the relative effort and costs in
worm drive rebuilds.
The Right Base Oil
While using lubricants formulated with
mineral oil is quite common within
worm drives, employing synthetic base
l
co
1500
Worm drive designs have one major
drawback: the relative motion between
the mating teeth of the two elements is
almost entirely sliding. This poses a
significant challenge because the
lubricant is continually scraped aside.
The sliding friction losses result in
elevated temperatures and inadequate
hydrodynamic pressure development.
Consequently, wear debris generation
can increase. In many cases, the higher
temperatures will be the limiting factor
on the worm drive before the loading
limitations are reached. The load
distribution of enveloping gear designs
can lessen this problem, but the
challenge still persists.
Gearing designs and materials have
been modernized through the years to
achieve better load-carrying capability,
higher torque conversions and improved
longevity.
Sophisticated
testing
platforms and computerized methods
ly
lyg
Po
1000
il
Mineral O
500
50
100
150
200
250
300
350
Viscosity @40°C
1.6
Lubrication Challenges
Lubrication Solutions
1.4
1.2
l
i
l O
ra
ne
Mi
1.0
ISO
220
400
ISO
150
ISO
220
ol
lyc
yg
Pol
450
0.8
0.6
40
• • Low noise and vibration results from
minimal moving components in
worm drives in comparison to
alternative gear designs.
80
100
120
Torque T, (daNm)
60
110
140
160
100
90
80
l
Oi
eral
Min
ol
glyc
Poly
70
60
50
400
600
800
1000
1200
Torque T, (daNm)
1400
Figure 7. Polyalkylene glycol vs. mineral oil
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