Passivation of stainless steels
is a necessity for good practice and military equipment standards.
Even for non-military applications, this is advisable to preclude discolorations
from free iron particles and minimization of galvanic interaction with other
parts.
Bronze gears could be chromate coated after cutting or cadium plated in the
blank state, followed by chromating after tooth generation. Table 1.30
summarizes features of the various coatings.
16.0 LUBRICATION
Lubrication serves several purposes, but its basic and most
important function is to protect the sliding and rolling tooth surfaces from
seizing, wear, and other phenomena associated with surface failure by film
separation. This is particularly pertinent to power gearing. In addition,
lubrication aids all gearing in that it reduces friction and protects against
corrosion.
16.1 Lubrication of Power Gear.
Power gear trains require sealed housings with a lubricant
bath. Depending on the magnitude of the transmitted power and speed, it may be
necessary to use a circulating system with lubricant cooling. Lubricant can be
supplied as a liquid bath or fine spray. Lubrication of small, low-power gear
trains can be accomplished with a grease pack in some cases. Many consumer
home products are so lubricated.
16.2 Lubrication of instrument Gear.
Because of their much smaller size and capacity, generally
lower speeds, and small or negligible power transmission, instrument gear
lubrication is very different from that of power gears. Often, the lubricants
main purpose is to reduce friction.
Instrument gears that are relatively highly loaded and
working near full capacity require equally good lubrication systems as power
gears. The difference is that, in these extremely low powers, the heat
dissipation is not a problem, therefore the unit can be packed and sealed
without concern for lubricant circulation, filtering, etc.
The lightly loaded gear trains can be of the open variety,
in which a thin lubricant film is brushed on the teeth during assembly and
reapplied only as maintenance and usage dictate. In such applications, it is
important that gear speeds are not so great that the lubricant is flung away
by centrifugal force. Also, the lubricant should have a minimum
"Spreading" rating. For this reason, greases are often favored.
Open housing gear trains are subject to contamination and
it is advisable to guard against excessive exposure. Instruments, the outer
enclosures of which must often be removed far maintenance of other items,
should be.worked on in clean and controlled environments. Where prolonged or
uncontrollable exposure occurs, temporary or permanent inner dust covers for
the gear train are recommended. This is particularly advisable in hybrid
electronic instrument boxes in which the danger of solder splatter and other
debris is high.
16.3 Oil Lubricants
Oils are the most common lubricants and come in
various-types. The compounding of oils provides combinations and generation of
various properties. The most basic lubricant is petroleum to which animal,
vegitable and synthetic oils and additives are combined to yield specific
properties.
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