Oils offer a wider range of operating speeds than greases. Also, they are
easier to handle and are
more effective because of their liquid nature.
16.4 Grease
Grease is a combination of liquid and solids, in which the latter serve as a
reservoir for the liquid lubricant as well as imparting certain of their own
properties. Grease has the advantage of remaining in place and not spreading as
oils, and has a much lower evaporation rate. Also, it can provide a lubricant
film at heavy loads and at low speeds.
16.5 Solid Lubricants
In recent years a number of "dry fllm" lubricants have been developed. These
have the advantages of wide temperature range, no dispersion, and no
evaporation. Hence, they are well suited for space and other vacuum
applications; and they are easier to use in open gearing since they do not
contaminate as rapidly as oils and grease. However, most solid films alter
dimensions significantly - and some
drastically. The latter cannot be tolerated in quality gearing. Dry-film
lubricants represent a one-shot application of lubricant that must last the life
of the gears, despite a continual eroding and wearing away of the film from the
start of its use.
16.6 Typical Lubricants
The choice of lubricants is very wide. Military specifications govern most
types and classes of lubricants, to which many manufacturers’ products
qualify. Table 1.31 is a list of typical gear oils and grease lubricants and
their applications.
17.0 GEAR FABRICATION
The fabrication of a complete gear normally includes most or all of the
following operations:
1. Blank fabrication
2. Tooth generation
3. Refining of tooth shape (shaving, grinding, honing)
4. Heat treatment
5. Deburring and cleaning
6. Finish Coating
Although it is not necessary to apply all six operations to every gear, the
basic operations 1, 2, and determine the quality level of a gear.
Blank fabrication involves all the general and special features of the gear
body. Tooth generation involves only machine-cut or around gears, as in other
fabrication methods, the teeth and body are formed simultaneously. The refining operation (shaving, grinding, or honing) is a
special means of improving quality, particularly in high-volume production. Heat treatment is limited to
gears requiring surface hardness and/or strength. Deburring and cleaning is essential for all
gears irrespective of method of manufacture or quality. Finish coats are limited to
certain materials and environments requiring corrosion protection or improved
appearance.
Modern methods of producing gear teeth cover a wide variety: