PATTERN MATERIALS IN CASTING CLASS: BY POLAYYA CHINTADA

PATTERN MATERIALS IN CASTING CLASS: BY POLAYYA CHINTADA

1. P roduction Technology: Pattern Materials COURSE CODE: C211 REGULATION: R19 2 nd BTECH 2 nd SEM PREPARED BY : POLAYYA CHINTADA M.TECH,M.B.A,(PhD) ASSISTANT PROFESSOR LENDI INSTITUTE OF ENGINEERING AND TECHNOLOGY

2. 2 PRODUCTION TECHNOLOGY SYLLABUS UNIT 1: Introduction: Importance and selection of manufacturing processes. Casting Processes : Introduction to casting process, process steps; pattern: types, materials and allowance; Cores: Types of cores, core prints, principles and design of gating system; Solidification of casting: Concept, solidification of pure metal and alloy; Special casting processes: Shell casting, investment casting, die casting, centrifugal casting, casting defects and remedies. provide insight into Working principles of different metal casting processes and gating system COURSE OBJECTIVE: COURSE OUTCOMES: Explain different metal casting processes and gating systems. (L2) APPLICATIONS: Identify different patterns and their allowances (L3) 1 . Heavy Equipment : Construction, farming and mining 2. Defence : Vehicles, artillery, munitions, storage and supporting equipment 3. Hardware : Plumbing industry pipes, joints, valves and fitting Identify the various casting defects. (L3 )

3. PATTERN  Pattern is a mirror image or replica of the component that has to be manufactured by casting process.  It may be also defined as a model around which sand is packed to give rise to a cavity called mold cavity .  A pattern is required even if one object has to be cast.  The materials generally used for pattern are wood, metal or plastics.

4. Functions of a patterns A pattern prepares a mold cavity for the purpose of making a casting. A pattern may contain projections known as core prints if the casting requires a core and need to be made hollow. Runner, gates and risers (used for introducing and feeding molten metal to the mold cavity) may form a part of the pattern. A pattern may help in establishing locating points on the mold and therefore on the casting with a purpose to check the casting dimensions. Patterns establish the parting line and parting surfaces in the mold. A pattern may help position a core (in case a part of mold cavity is made with cores), before the molding sand is rammed. Patterns that are properly made and having finished and smooth surfaces, reduce casting defects. Properly constructed patterns minimize overall cost of the castings .

5. PATTERN MATERIALS Selection of pattern materials The following factors assist in selecting proper pattern material: The number of castings to be produced . Metal patterns are preferred when the production quantity is large. The desired dimensional accuracy and surface finish required for the castings. Nature of molding process i.e., sand casting, permanent mold casting, shell molding, investment casting etc. Method of molding i.e., hand or machine molding. Shape, complexity and size of the casting. Type of molding materials i.e., sand etc. The high probability of changing the casting and hence the pattern in near future .

6. PATTERN MATERIALS Patterns may be constructed out of the following materials. (a ) W ood (b) Metal (C) Plastic (d) Wax (e) Plaster (POP)

7. PATTERN MATERIALS :W OOD The most common materials for making patterns for sand casting is the wood The most common pattern are teak wood and mahogany Advantages Inexpensive. Easily available in large quantities. Easy to machine and to shape to different configurations and forms Easy to join to acquire complex and large pattern shapes Light in weight Easy to obtain good surface finish Wooden patterns can be preserved for quite long times with the help of suitable wood preservatives . Limitations Wooden patterns are susceptible to shrinkage and swelling. They possess poor wear resistance. They are abraded easily by sand action. They absorb moisture , consequently get deformed and change shape and size. They cannot withstand rough handling. They are weak as compared to metal patterns.

8. PATTERN MATERIALS :M E T ALS M e t al p a t t erns a r e emp l o y e d whe r e l a r g e num b er of castings have to be produced from the same patterns. Metal patterns are cast from wooden patterns. Th e d i f f e r e n t m e t als a n d all o y s u s ed f o r maki n g patterns are, Aluminium and Aluminium alloys Steel Cast Iron Brass White Metal

9. PATTERN MATERIALS : W AX A wax pattern is made in the exact shape of the item to be cast This pattern is coated with a refractory ceramic material. A wax pattern is made in the exact shape of the item to be cast Advantages Wax patterns provide very good surface finish They impart high accuracy to the castings. After being molded, the wax pattern is not taken out of the mold like other patterns; rather the mold is inverted and heated ; the molten wax comes out and/or is evaporated. Thus there is no chance of the mold cavity getting damaged while removing the pattern . Applications Wax patterns find applications in Investment casting process. Ex: Paraffin Wax, Bees Wax

10. PATTERN MATERIALS Different type of plastic used for pattern making, because they are light as wood durable as metal. Thermo-setting plastic such as Epoxy resins with suitable fillers are the one of the most common material for making plastic pattern. The plastic patterns are made by using molds made of plaster of Paris or clay molds. : PLA S TIC Advantages Durable Provides a smooth surface. Moisture resistant. A plastic pattern does not involve any appreciable change in its size or shape. Lightweight. Wear and corrosion resistant. Provides good surface finish. It possesses low solid shrinkage. Limitations Plastic patterns are fragile and thus light sections may need metal reinforcements. Plastic patterns may not work well when subject to conditions of severe shock as in machine moulding .

11. PATTERN MATERIALS The pattern is made of gypsum Plasters (also known as plaster of Paris). the plasters will expand during solidification. They have different expansion rate, setting time. Plaster mixture is poured into a mould made by sweep pattern or wooden master pattern ,in order to obtain plaster pattern : PLASTER Advantages can be easily worked by using wood working tools. Intricate shapes can be cast without any difficulty. It has high compressive strength (up to 285 kg/cm 2 ) Disadvantages Can be used for small castings only Applications: (I ) Small and intricate patterns, (ii) Core boxes.

12. Y ours : POLAYYA CHINTADA M.TECH,M.B.A,(PhD) ASSISTANT PROFESSOR