Anıl UZAL, 030070012, 8th Week

Cam Mechanisms: (01.04.2011 ; 01:10)

A simple cam mechanism consists of three basic parts, a cam, a follower, and a frame. A cam is an irregularly shaped machine member which serves as a driving link by rotating with a constant velocity and imparting motion through direct contact to a driven link, the follower, which in turn moves in a desired motion. A cam (K_A) is adjacent to a follower (K_Af) and a frame (K_F) with a cam joint (J_A) and a revolute joint (J_R), respectively. A follower, which is adjacent to the frame with a revolute joint or a prismatic joint (J_P), is usually driven to move with varying speeds in a noncontinuous and irregular motion.

(Hong-Sen Yan, Reconstruction Designs of Lost Ancient Chinese Machinery, page 65)

Brittleness: (01.04.2011 ; 01:37)

Brittleness is the property which renders substances easily broken, or separated into irregular fragments. This property belongs chiefly to hard bodies.

It does not appear that brittleness is entirely opposed to elasticity, since in many substances, both these properties are united. Glass is the standard, or type of brittleness, and yet a ball, or fine threads of this substance are highly elastic, as may be seen by the bounding of the one, and the springing of the other. Brittleness often results from the treatment to which substances are submitted. Iron, steel, brass, and copper, become brittle when heated and suddenly cooled, but if cooled slowly, they are not easily broken.

(Comstock J.L., A System of natural Philosophy: in Which The Principles of Mechanics, Hydrostatics, Hydraulics, Pneumatics, Acoustics, Optics, Astronomy, Electricity and Magnetism, page 22-23)

Wire Drawing: (01.04.2011 ; 02:30)

Drawing wire is a method similar to extrusion. Copper wire often starts as coils of thick wires produced by hot rolling, with successive coils welded together to maintain continuous production. Copper wire is then fed through an insulate line. Each insulate line performs several different functions, such as additional wire drawing, annealing (softening), and applying insulation.

The first step in the pulling process is to reduce the size of the copper wire by drawing it again, which uses diamond dies and reduces the wire to another size based on American Wire Gauge (AWG) codes (discussed in section 5.3, “Labeling and Certifying Cable”).

After being drawn, wire is very brittle and can be easily fractured if flexed. Finished copper wire has to be flexible to be useable, so the wire is annealed by passing a large electrical current through the wire for a fraction of a second. This raises the wire’s temperature briefly to 1000F. Wire is annealed in water to prevent oxidation, and also to cool and clean the wire before applying insulation. Wire that is not properly annealed tends to be brittle and break easily.

The wire is then passed through an extruder, where a thin coating of plastic containing high-density pellets of the insulating material is applied. As the wires are pushed through the extruder, the insulation pellets heat until they melt onto the wire.

(R. Shimonski, R.T. Steiner, S.M. Sheedy, Network Cabling Illuminated, page 124-125)

Alligatoring: (01.04.2011 ; 03:18)

Term describing the appearance of a film that is cracked into large segments resembling the hide of the alligator. When alligatoring is fine and incomplete, it is usually called checking.

Alligatoring may be caused by one coat being applied over another before the bottom coat is thoroughly hard and dry and/or having the material skinning over so that the lower portion of the film is still soft and elastic, or by less elastic material being applied over a more elastic undercoating. When these conditions are present and the finished article is exposed to actinic rays or changes in temperature and moisture content, expansion or contraction of the film cracks the hard outer crust while the softer core gives without breaking.

With excessively heavy coats of rather dilute materials, this cracking of the outer crust can take place without temperature change by the shrinking action of the bottom portion – much like clay mud is cracked under the summer sun.

Other causes of alligatoring include the too rapid evaporation of solvents or thinners and excessive air being forced into the film during spraying.

(National Research Council (U.S.). Building Research Institute. Conferences, New Joint Sealants: Criteria, Design, and Material, page 175)