Task 13. Match the first part of a sentence (1-5) with the second one (a-e).
1) Hypoid gears are offset and in effect, are spiral …
2) The visualization of hypoid gears is based on an …
3) The staggered axes result in meshing conditions that are …
4) With spiral gears, great differences in sliding motion arise over various portions of …
5) Surface pressures are thus reduced so that there is less …
a) … imaginary flat gear which is a substitute for the theoretically correct helical surface.
b) … beneficial to the strength and running properties of the gear teeth.
c) … the tooth surface, creating vibration and noise.
d) … gears whose axes do not intersect but are staggered by an amount decided by the application.
e) … wear and quieter operation.
Task 14. Match the words from column A with column B to make up word combinations and translate them into Ukrainian:
Task 15. Write a short report (80-100 words) about the process shown in the picture below.
Task 16. Watch the video file “Planetary Gear System”. Write a short report (100-120 words) on how it works.
UNIT 3. GEARED SYSTEMS AND MECHANISMS (Part 2)
Task 1. What is the role of mechanisms in the modern world and what do you know from its history? Have you ever tried to mend your bicycle? What mechanical parts of it can you name?
Task 2. Study the following words. Make sure you know the meaning and translation of them.
a gear, to mesh, teeth, translation motion, rotation, angle, torque, transmission, ratio, pulley, pitch, magnitude, rack, wheel, slip, verify, shape, injection, resistant.
Task 3. Read the text and translate all unfamiliar words.
Gears and Gearing
A gear or more correctly a "gear wheel" is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, magnitude, and direction of a power source. The most common situation is for a gear to mesh with another gear, however a gear can also mesh a non-rotating toothed part, called a rack, thereby producing translation instead of rotation.
The gears in a transmission are analogous to the wheels in a pulley. An advantage of gears is that the teeth of a gear prevent slipping. When two gears of unequal number of teeth are combined a mechanical advantage is produced, with both the rotational speeds and the torques of the two gears differing in a simple relationship.
In transmissions which offer multiple gear ratios, such as bicycles and cars, the term gear, as in first gear, refers to a gear ratio rather than an actual physical gear. The term is used to describe similar devices even when gear ratio is continuous rather than discrete, or when the device does not actually contain any gears, as in a continuously variable transmission.
An external gear is one with the teeth formed on the outer surface of a cylinder or cone. Conversely, an internal gear is one with the teeth formed on the inner surface of a cylinder or cone. For bevel gears, an internal gear is one with the pitch angle exceeding 90 degrees. Internal gears do not cause direction reversal.
Numerous nonferrous alloys, cast irons, powder-metallurgy and plastics are used in the manufacture of gears. However steels are most commonly used because of their high strength to weight ratio and low cost. Plastic is commonly used where cost or weight is a concern. A properly designed plastic gear can replace steel in many cases because it has many desirable properties, including dirt tolerance, low speed meshing, and the ability to "skip" quite well. Manufacturers have employed plastic gears to make consumer items affordable in items like copy machines, optical storage devices, VCRs, cheap dynamos, consumer audio equipment, servo motors, and printers.
Gears are most commonly produced via hobbing, but they are also shaped, broached, cast, and in the case of plastic gears, injection molded. For metal gears the teeth are usually heat treated to make them hard and more wear resistant while leaving the core soft and tough. For large gears that are prone to warp a quench press is used. Gear geometry can be inspected and verified using various methods such as industrial CT scanning, coordinate-measuring machines, white light scanner or laser scanning. Particularly useful for plastic gears, industrial CT scanning can inspect internal geometry and imperfections such as porosity.
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