Page 338 - The Tribology Handbook

Gear and roller chain lubrication

Pitch line speed, ft/min Pitch line speed, ft/min
10 50 100 500 1000 2500 5000 10 000 10 50 100 500 10002000 5000 10 000
0 1000 1000
0 0
a0 0 % 500 d
m- 500
U i3 li- i3
"0 m, E
e
0 m "0 0)
v CO m
+ d =:
d
100 P) 100 m
0 's
i K? i 8
x 50 50
8 .-
c
P
.- 8
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> .-
101 ' I I i I I I' I lJ 5.
0.1 0.25 0.5 1.0 2.5 5 10 25 50 lo 0.1 0.25 0.5 1.0 2.5 5 10 25 50
Pitch line speed, m/s Pitch line speed, m/s
Figure 9. I Selection of oil for industrial enclosed Figure 9.2 Selection of oil for industrial enclosed
gear units worm gears
Figure 9.1 is a general guide only. It is based on the Suitable lubricants for worm gears are plain mineral oils
criterion: Sc HV/(Vp + 100) of a viscosity indicated in Figure 9.2. It is also common
practice, but usually unnecessary, to use fatty additive or
where Sc = Surface stress factor leaded oils. Such oils may be useful for heavily-loaded,
Load/inch line of contact
- slow-running gears but must not be used above
-
Relative radius of curvature 80°C( 170°F) running temperature as rapid oxidation may
and HV = Vickers hardness for the softer member of the occur, resulting in acidic products which will attack the
gear pair bronze wheel and copper or brass bearing-cages.
Worm gears do not usually exceed a pitch line velocity
Vp = Pitch line velocity, ft/min of 2000 ft/min, but if they do, spray lubrication is essential.
The chart applies to gears operating in an ambient tem- The sprayed oil must span the face width of the worm.
perature between 10°C and 25°C. Below 10°C use one grade
lower. Above 25°C use one grade higher. Special oils are Quantity Speed m/s 10 15 20 25
required for very low and very high temperatures and the
manufacturer should be consulted.
m3/sec
With shock loads, or highly-loaded low-speed gears, or 75x10dxC* Pressure kN/m2 100 170 270 340
gears with a variable speed/load duty cycle, EP oils may
be used. Mild EPs such as lead naphthanate should not be C* = centre distance in metres.
used above 80"C( 170°F) running temperature. Full hypoid
EP oils may attack non ferrous metals. Best EP for normal
industrial purposes is low percentage of good quality Quantity Speedftlmin 2000 3000 4000 5000
sulphur/phosphorus or other carefully inhibited additive.
Q= C/4 gpm Pressure lbf/in2 15 25 40 50

Spray lubrication Where C = centre distance, inches.
Recent developments in heavily loaded worm gear lubrica-
Quantity Speedmjsec 10 25 50 100 150 tion include synthetic fluids which:
(a) have a wider operating temperature range
85 x 10 -' x kW Pressure
m3/sec kN/m2 10 100 140 180 210 (b) reduce tooth friction losses
(6) have a higher viscosity index and thus maintain an oil
film at higher temperatures than mineral oils
(d) have a greatly enhanced thermal and oxidation
Quantity Speedftlmin 2500 5000 10000 20000 30000 stability, hence the life is longer
0.0085~ hp Pressure 1o 15 2o 25 3o Even mcire recent developments include the formulation
BPm Ibf/in2 of certain soft synthetic greases which are used in 'lubri-
cated-for-life' worm units. Synthetic lubricants must not
be mixed with other lubricants.

c9.1