5. Fill in the gaps.

use, torque, allow, distinguished, assembled, prevent.

The main function of a key is to trans­mit ____ between a shaft and a machine part ____ on it. In most cases keys ____ relative mo­tion, both rotary and axial. In some constructions keys ____ an axial motion, between

the shaft and the hub. According to various characteristics, keys can be

____ as straight and tapered, rectangular, etc., and accor­ding to their

____ , for light duty and for heavy duty

6. Discuss the machine details using participles as well as the connective and introductory words.

1. The distinctive features of a key. 2. Kinds of a key. 3. Keys application.

Text 4

1. Find in the text the information about the mechanisms mentioned. Study the text deeper for the details, classiffications, and arrangement.

Cams and Other Mechanisms

The cam is an especially important ele­ment of a machine ─ simple and

practical, allowing an in­finite variety of output motions. In the simplest cam system there are a fixed link, the frame; a driving link, which is generally the cam; and an output link called the follower. (See Figure ). The cam-follower system is the distinctive feature of valve trains in gasoline and Diesel engines, all types of printing machinery, textile machinery, pumps, and machine tools.

Three kinds of cams are the disk, cylindrical, and three-dimensional. An alternate classification based on the type of output motion include constant-velocity, uniform-acceleration-deceleration, sim­ple harmonic, cycloidal, or polynomial cams.

Geneva wheel (Fig. 20) consists of a driver wheel and a driven wheel. The driver rotates at a constant speed. It contains a pin, which enters a slot on the driven wheel and thus turns it. After the pin leaves the slot, the driven wheel stays

still until the pin enters the next slot. Thus the constantly rotating driver pro­duces intermittent rotation in the driven wheel.

Fig. 19. Geneva wheel with two cams, follower (top) and fixed link

(bottom).

Geneva wheel is often used on machine tools for indexing the rotation

of a shaft ─ that is, to rotate the shaft a certain amount and then stop for a certain length of time before the next rotation.

Ratchets are vital parts of mechanical devices ranging from automobile parking brake, jacks to typewriters.

Fig. 20. Driven wheel. Fig. 21. Rolamite.

A rolamite (Fig. 21) consists of two cylindrical rollers suspended in an S-shaped, flexible band. In the arrangement shown (a), if the rollers roll in the

direction of the arrows, they will both move to the right (b). The ends of the band

are fastened to the two guide rails. Rolamites are used princi­pally in mechanical and electromechanical com­ponents.