Page 290 - Cam Design Handbook

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278 CAM DESIGN HANDBOOK

TABLE 9.7 Greases

Recommended
Type Specification temp. range, °F General composition
High-speed, ball MIL-G-38220 -40 to +400 Thickening agent and
and roller bearing fluorocarbon
Synthetic, extreme MIL-G-23827 -100 to +250Thickening agent, low-
pressure temperature synthetic oils,
or mixtures EP additive
Synthetic, molybdenum MIL-G-21164 -100 to +250Similar to MIL-G-23827 plus
disulfide MoS 2
General purpose, wide MIL-G-81322 -65 to +350Thickening agent and
temp. range synthetic hydrocarbon
Oscillating, bearing MIL-G-25537 -65 to +160Thickening agent and mineral
oil
Gasoline- and oil- MIL-G-6032 +32 to +200 Thickening agent, vegetable oils
resistant, plug valve glycerols and/or polyesters
Fuel- and oil-resistant MIL-G-27617 -30 to +400 Thickening agent and
fluorocarbon or
fluorosilicone
Ball and roller bearing: MIL-G-25013 -100 to +450Thickening agent and silicone
Extreme high fluid
temperature

cams and followers dictate whether a grease lubricant can be utilized. Grease lubricants
are listed in Table 9.7.
Liquid Lubrication Systems. At low to moderate speeds, when the use of grease lubri-
cation is not suitable, other methods of supplying lubricant to the bearing can be used.
These include hand lubrication with open-cam follower systems, splash or bath lubrica-
tion, and wick, oil-ring, or oil-air mist lubrication. Felt wicks can be used to transport oil
by capillary action from a nearby reservoir. Oil rings, which are driven by frictional contact
with the rotating shaft, run partially immersed in an oil reservoir and feed oil mechani-
cally to the shaft, which is adjacent to the bearing. The cam may be partially immersed in
an oil reservoir to splash-lubricate itself. All of these methods require very modest ambient
temperatures and thermal conditions as well as speed conditions.
The most commonly used lubricant is mineral oil both in liquid and grease form
(Table 9.8). As a liquid, mineral oil usually has an antiwear or extreme pressure (EP)
additive, an antifoam agent, and an oxidation inhibitor. Grease does not require an
antifoam agent.
Oil-air mist lubrication supplies atomized oil in an airstream to the bearing, where a
reclassifier increases the droplet size, allowing it to condense on the bearing surfaces. Feed
rates are low and a portion of the oil flow escapes with the feed air to the atmosphere.
Friction losses and heat generation with mist lubrication are low, but ambient tempera-
tures and cooling requirements must be moderate because oil-air mist systems provide
minimal cooling.
9.5.3.2 Extreme-Pressure Lubricants. Extreme-pressure (EP) lubricants can signifi-
cantly increase the load-carrying capacity of cams. The extreme-pressure additives in the
lubricating fluid form a film on the surfaces by a chemical reaction, adsorption, and/or
chemisorption. These boundary films can be less than 1m in to several microinches thick