Introduction to Basic Manufacturing Processes and ... - always yours

180 Introduction to Basic Manufacturing Processes and Workshop Technology
5 Properly constructed patterns minimize overall cost of the casting.
6 Pattern may help in establishing locating pins on the mould and therefore on the
casting with a purpose to check the casting dimensions.
7 Properly made pattern having finished and smooth surface reduce casting defects.
Patterns are generally made in pattern making shop. Proper construction of pattern and
its material may reduce overal1 cost of the castings.
10.2 COMMON PATTERN MATERIALS
The common materials used for making patterns are wood, metal, plastic, plaster, wax or
mercury. The some important pattern materials are discussed as under.
1. Wood
Wood is the most popular and commonly used material for pattern making. It is cheap, easily
available in abundance, repairable and easily fabricated in various forms using resin and
glues. It is very light and can produce highly smooth surface. Wood can preserve its surface
by application of a shellac coating for longer life of the pattern. But, in spite of its above
qualities, it is susceptible to shrinkage and warpage and its life is short because of the reasons
that it is highly affected by moisture of the molding sand. After some use it warps and wears
out quickly as it is having less resistance to sand abrasion. It can not withstand rough handily
and is weak in comparison to metal. In the light of above qualities, wooden patterns are
preferred only when the numbers of castings to be produced are less. The main varieties of
woods used in pattern-making are shisham, kail, deodar, teak and mahogany.
Shisham
It is dark brown in color having golden and dark brown stripes. It is very hard to work
and blunts the cutting tool very soon during cutting. It is very strong and durable. Besides
making pattern, it is also used for making good variety of furniture, tool handles, beds,
cabinets, bridge piles, plywood etc.
Kail
It has too many knots. It is available in Himalayas and yields a close grained, moderately
hard and durable wood. It can be very well painted. Besides making pattern, it is also utilized
for making wooden doors, packing case, cheap furniture etc.
Deodar
It is white in color when soft but when hard, its color turns toward light yellow. It is
strong and durable. It gives fragrance when smelled. It has some quantity of oil and therefore
it is not easily attacked by insects. It is available in Himalayas at a height from 1500 to 3000
meters. It is used for making pattern, manufacturing of doors, furniture, patterns, railway
sleepers etc. It is a soft wood having a close grain structure unlikely to warp. It is easily
workable and its cost is also low. It is preferred for making pattern for production of small
size castings in small quantities.
Teak Wood
It is hard, very costly and available in golden yellow or dark brown color. Special stripes
on it add to its beauty. In India, it is found in M.P. It is very strong and durable and has wide
applications. It can maintain good polish. Besides making pattern, it is used for making good