The castle nut consists of the usual hexagonal nut but with an additional of upper cylindrical part. This cylindrical portion has six slots located at the centre of each face of the hexagonal part. Due to these slots, castle nut is sometimes called a slotted nut. A split pin is passed through diametrically opposite slot in the castle nut and a hole in the bolt. This ensures positive locking unless the pin gets sheared. The split pin consists of a wire of semicircular cross-section. It is bent over in such a way that its flat sides are in contact. The split pin has a looped head on one side. The two ends at the other side can be separated and bent back over the cylindrical portion of the castle nut. A castle nut is extensively used for joints that are subjected to vibrations. They are popular in automobile industry. (V.B. Bhandari, Design of Machine Elements, Tata Mc-Graw Hill Edu., 2010, Third Edition, p.226 )
Rivet
A rivet consists of cylindrical shank with a head at one end. This head is formed on the shank by an upsetting process in a machine called an automatic header. The rivet is inserted in the holes of the parts being assembled and the head is firmly held against the back up bar. In the riveting process, the protruding end of the shank is upset by hammer blows to form closing head. In rivet terminology the closing head is called the point. The head, shank and point are three main parts of rivet. (V.B. Bhandari, Design of Machine Elements, Tata Mc-Graw Hill Edu., 2010, Third Edition, p.298-299 )
Washer
A washer is a hardware component often used with threaded fasteners to ensure thickness of the mechanical joint; in its simplest form, it is a flat thin ring of sheet metal. Washers serve various functions. They (1) distribute stresses that might otherwise be concentrated at the bolt or screw head and nut, (2) provide support for large clearance holes in the assembled parts, (3) increase spring tension, (4) protect part surfaces, (5) seal the joint, and (6) resist inadvertent unfastening. (Mikell P. Groover, Fundamentals of Modern Manufacturing, John Wiley & Sons Inc., Third Edition, p.766-767)
Surface-Mount Technology
Surface mount technology (SMT) uses an assembly method in which component leads are soldered to lands on the surface of the board rather than into holes running through the board. By eliminating the need for leads inserted into through holes in the board, several advantages accrue: smaller components can be made , with leads closer together; packing densities can be increased; component can be mounted on both sides on the board; smaller PCBs can be used for the same electronic system; drilling of the many through holes during board fabrication is eleminated- via holes to interconnect layers are still required; and undesirable electrical effects are reduced, such as spurious capacitances and inductances. Typical areas on the board surfaces taken by SMT components range between 20% and 60% compared to through-hole components. (Mikell P. Groover, Fundamentals of Modern Manufacturing, John Wiley & Sons Inc., Third Edition, p.845-846)
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