01-09-2014, 12:47 PM
HISTORY OF METAL CASTING • 3000 B.C earliest castings include the 11 cm high bronze dancing girl found at Mohan-jodoro. • 2000 B.C Iron pillars, Hooks, nails, Bowls and daggers or earlier have been found in Delhi, Roper, Nasik and other places. • 500 A.D Cast crucible steel was first produced in India but the process was lost until 1750 when Benjamin Huntsman reinvents it in England. Advantage of castings • Intricate shapes can be made. • Flexibility of size and weight. • Simple and inexpensive tools. • Any material can be cast (ferrous or non ferrous). • Wastage of raw materials is less. • Only alternative for certain materials. Limitations • Labour intensive process. • Dimensional accuracy. • Surface finish.
PATTERN Function of pattern • It prepares the mold cavity. • It enables creation of core prints. • It makes provision for runner, gates and risers. • Pattern property made and having smooth surfaces reduce casting defects. • A property constructed pattern minimizes the overall cost of the castings. Pattern material Some materials used for making patterns are:- Wood Metals and alloys Plaster of peris Plastic and rubbers Wax and Resins Each material has its own advantages, limitations and field of application. Ideal characteristics of pattern material: • Easily worked, shaped and joined. • Light in weight. • Strong hard and durable. • Resistance to wear and abrasion. • Resistance to carrion and chemical reactions. • Dimensionally stable and unaffected by variations in temperature and humidity. • Available at low cost. Pattern allowance The selection of correct allowances greatly helps to reduce costs and avoid rejections • Shrinkage or contraction allowance • Draft or taper allowance • Machining or finish allowance • Distortion or camber allowance • Rapping allowance
PATTERN Function of pattern • It prepares the mold cavity. • It enables creation of core prints. • It makes provision for runner, gates and risers. • Pattern property made and having smooth surfaces reduce casting defects. • A property constructed pattern minimizes the overall cost of the castings. Pattern material Some materials used for making patterns are:- Wood Metals and alloys Plaster of peris Plastic and rubbers Wax and Resins Each material has its own advantages, limitations and field of application. Ideal characteristics of pattern material: • Easily worked, shaped and joined. • Light in weight. • Strong hard and durable. • Resistance to wear and abrasion. • Resistance to carrion and chemical reactions. • Dimensionally stable and unaffected by variations in temperature and humidity. • Available at low cost. Pattern allowance The selection of correct allowances greatly helps to reduce costs and avoid rejections • Shrinkage or contraction allowance • Draft or taper allowance • Machining or finish allowance • Distortion or camber allowance • Rapping allowance