外文翻译--齿轮和齿轮传动
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1、兰州交通大学毕业设计(论文) 1 Gears and gear drive Gears are the most durable and rugged of all mechanical drives. They can transmit high power at efficiencies up to 98% and with long service lives. For this reason, gears rather than belts or chains are found in automotive transmissions and most heavy-duty machi
2、ne drives. On the other hand, gears are more expensive than other drives, especially if they are machined and not made from power metal or plastic. Gear cost increases sharply with demands for high precision and accuracy. So it is important to establish tolerance requirements appropriate for the app
3、lication. Gears that transmit heavy loads or than operate at high speeds are not particularly expensive, but gears that must do both are costly. Silent gears also are expensive. Instrument and computer gears tend to be costly because speed or displacement ratios must be exact. At the other extreme,
4、gears operating at low speed in exposed locations are normally termed no critical and are made to minimum quality standards. For tooth forms, size, and quality, industrial practice is to follow standards set up by the American Gear Manufactures Association (AGMA). Tooth form Standards published by A
5、GMA establish gear proportions and tooth profiles. Tooth geometry is determined primarily by pitch, depth, and pressure angle. Pitch: Standards pitches are usually whole numbers when measured as diametral pitch P. Coarse-pitch gearing has teeth larger than 20 diametral pitch usually 0.5 to 19.99. Fi
6、ne-pitch gearing usually has teeth of diametral pitch 20 to 200. Depth: Standardized in terms of pitch. Standard full-depth have working depth of 2/p. If the teeth have equal addenda(as in standard interchangeable gears) the addendum is 1/p. Stub teeth have a working depth usually 20% less than full
7、-depth teeth. Full-depth teeth have a larger contract ratio than stub teeth. Gears with small numbers of teeth may have undercut so than they do not interfere with one another during engagement. Undercutting reduce active profile and weakens the tooth. Mating gears with long and short addendum have
8、larger load-carrying capacity than standard gears. The addendum of the smaller gear (pinion) is increased while that of larger 兰州交通大学毕业设计(论文) 2 gear is decreased, leaving the whole depth the same. This form is know as recess-action gearing. Pressure Angle: Standard angles are 020 and 025 . Earlier s
9、tandards include a 14- 02/1 pressure angle that is still used. Pressure angle affects the force that tends to separate mating gears. High pressure angle decreases the contact ratio (ratio of the number of teeth in contact) but provides a tooth of higher capacity and allows gears to have fewer teeth
10、without undercutting. Backlash: Shortest distances between the non-contacting surfaces of adjacent teeth . Gears are commonly specified according to AGMA Class Number, which is a code denoting important quality characteristics. Quality number denote tooth-element tolerances. The higher the number, t
11、he closer the tolerance. Number 8 to 16 apply to fine-pitch gearing. Gears are heat-treated by case-hardening, through-hardening, nitriding, or precipitation hardening. In general, harder gears are stronger and last longer than soft ones. Thus, hardening is a device that cuts the weight and size of
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