7 types of pattern materials which are commonly used in casting are mentioned below.
- Plaster of Paris or gypsum cement
- Expanded polystyrene
- Aerated concrete
Let me give a short and simple information about each type of pattern material along with their advantages and disadvantages.
#1) Wood pattern
- The most common material used for pattern making is the wood. The reason behind this is that it fulfills all the necessary requirements of a good pattern.
- Wood is easily available at low cost and it is also light in weight.
- Deodar, teak, and sheesham wood are commonly used for wood patterns.
The advantages and disadvantages of wood pattern are mentioned below.
Advantages of wood pattern
- Wood is easily available in abundance and it is also available at low cost.
- It is very easy to give the desired shape to wood.
- Handling and transportation of wood patterns is easy as wood is light in weight.
- Wood patterns can get a good surface finish and ultimately the casting prepared will also be of good quality.
- Wood pattern can be preserved for a longer time by applying varnish on it.
Disadvantages of wood pattern
- As the wood is soft, it cannot handle more wear and tear for a longer run.
- Sometimes buckling and swelling are seen on wood patterns due to weather conditions.
- Wood patterns are generally prefered when the required number of castings are small. And the reason behind this is that the wood patterns have a shorter life and they cannot be used for a longer run.
#2) Metal pattern
- Metal patterns are generally used when the mass production of castings with good accuracy are required.
- The metal patterns are more durable than wood patterns as metal does not change its shape due to moist weather.
- For metal patterns, the most commonly used metals are cast iron, brass, white metal, aluminum, and alloys of aluminum.
- Metal pattern is made by casting process and in this process the wood pattern is used for preparing the mould cavity. This wood pattern is called the master pattern.
The advantages and disadvantages of metal pattern are mentioned below.
Advantages of metal pattern
- Metal patterns can withstand wear and tear for the longer run.
- Metal patterns can be used for mass production.
- Metal patterns do not show any changes in dimensions due to weather conditions.
Disadvantages of metal pattern
- Metal patterns are costly as compared to wood patterns, so they are not preferred for a small number of castings.
- Shaping the metal pattern is also costly as it requires tools and skilled labour.
- Handling and manipulation of metal patterns are difficult as it is very heavy.
- To get the proper finished surface on the pattern, proper machining is required to be done on the pattern which ultimately adds some extra cost for manufacturing the pattern.
#3) Plaster of Paris or Gypsum cement
- Plaster of Paris (aka POP) is very advantageous as a pattern material because it can take difficult shapes easily.
- Also the POP has a good compression strength of around 300 kg/cm2.
- Patterns of POP are used for casting which requires very accurate shapes and dimensions.
#4) Wax pattern
- Wax patterns are generally used for the investment casting process.
- Wax patterns are manufactured by pouring the molten wax into a metal mould or a split die. The wax is kept cool by circulating water around the die parts.
- After solidifying the wax, the outer die is separated and the final wax shaped pattern is taken out.
The advantages and disadvantages of wax pattern are mentioned below.
Advantages of wax pattern
- Wax patterns are used in centrifugal casting for preparing things like carburetors, jewellery, silver simithing, gold smithing such as rings, bracelets, etc.
- The wax pattern is simple and easy to use for creative works.
Disadvantages of wax pattern
- Wax pattern is generally used for small size castings, because large size castings require more amount of wax and handling of big wax patterns is also difficult.
- Temperature changes affect the shape of the wax pattern.
#5) Plastic pattern
- Plastic patterns are very important nowadays as they possess some specific properties like high strength, resistance to wear, light weight, good surface finish as well as less shrinkage.
- Thermosetting resins like phenolic resin and foam plastic are used as plastic pattern materials.
- For preparation of plastic patterns, the moulds are first made with POP.
- The molten resin is then poured into this mould, which finally gives the plastic pattern on solidification.
The advantages of plastic patterns are mentioned below.
Advantages of plastic pattern
- Plastic patterns are light in weight as compared to wood pattern and metal pattern.
- It also has good strength and durability as compared to wood patterns.
- It is resistant to wear and it does not have any effect of moisture.
- Plastic patterns show less shrinkage and they are also cheap to manufacture.
#6) Expanded polystyrene
- Expanded polystyrene are the patterns which are generally shaped by using hand tools, like saws, hot wires or sharp knives, etc.
The advantages and disadvantages of expanded polystyrene patterns are mentioned below.
Advantages of expanded polystyrene
- By using expanded polystyrene, the use of cores can be eliminated.
- Riser can be added to the pattern to provide the entry of the molten metal.
Disadvantages of expanded polystyrene
- The casting produced by this pattern gets a poor surface finishing.
#7) Aerated concrete
- Aerated concrete type patterns are made with the hand tools like old saws, files, drills, etc.
- This type of patterns are used for casting of sculptures.
- Proper care is required to handle the pattern otherwise the pattern may develop a crack.
- Skilled labor is required to properly set the riser gate with the pattern.