Pattern Materials:Types, Uses, Advantages, Disadvantages

Today we are going to discuss pattern materials in which you will learn types of pattern materials as well as their advantages, disadvantages, uses, etc.

As we know that patterns are used in the casting process to make a mould cavity.

In which the pattern is prepared by giving a particular pattern allowances, but at the same time it is very important to select the pattern material, which we will know in detail further.

Shrink rules are used to avoid pattern allowances when making patterns.

So without wasting time let's get started.

Selection of Pattern Material

The following factors aid in the selection of the appropriate pattern material: 

1. The number of castings to be produced.  
2. Quantity of production.
3. Dimension accuracy and surface finish.
4. Nature of molding process like sand casting, permanent mold casting, shell molding, investment casting, etc.  
5. Method of moldings like a hand or machine moulding.  
6. Complexity and size of the casting.  

Casting Process

Types of Pattern Materials

The common materials from which patterns are made are the following:

• Wood
• Metal
• Plaster
• Plastic
• Wax

Wood

Wood patterns are used where the number of castings to be produced is small and the size of the pattern is large.

Commonly used woods for making patterns are teak, deodar, mahogany, pine, etc.

Advantages of Wood Materials

It is a common material for making patterns as it has the following advantages. 

1. It is cheap and available in abundance.  
2. It can be easily shaped into various forms and intricate designs.  
3. Due to its lightness in weight, it is easy to change it.  
4. A good surface can be easily achieved only by planning and sawing.  
5. It can be preserved for a long time by applying appropriate preservatives like shellac varnish.

Disadvantages of Wood Materials

1. It wears out quickly due to its low resistance to abrasion of sand that is why a wooden pattern cannot be used continuously for a long time.  
2. It is susceptible to moisture, due to which it may crack or split.  
3. Its life, due to the above reasons, is shorter than that of other pattern materials.  
4. It is used in cases when a small number of castings are required.

Metal

A metal pattern is used where only the number of castings is large and near dimensional accuracy is desired.

Commonly used metal patterns are aluminum or its alloy, brass, white metal, steel, etc.

Advantages of Metal

Metals are used with the following advantages.  

1. The life of the metal pattern is much longer than that of the wood pattern and largely eliminates the natural damage of wood. 
2. Do not absorb moisture.  
3. More stronger.  
4. Get longer life.  
5. Precise and smooth surface finish.  
6. Good machinability.

Disadvantages of Metal

1. They are expensive as compared to wood, so it is used less, where less number of castings have to be done, it is not used.
2. It requires machining to obtain different shapes and finer surfaces and again it takes a separate cost.  
3. Most of these are very heavy patterns and in the case of large castings, the weight of the pattern always becomes a problem in its manipulation.  
4. It has a tendency to rust in large numbers.

Plaster

Plaster can be made from plaster of Paris or gypsum cement.  

To obtain the plaster pattern, the plaster mix is ​​poured into a mold made by a sweet pattern or master pattern of the wood.

Advantages of Plaster 

Plaster of Paris or gypsum cement is used advantageously as a patterned material because:

1. It can be easily cast into complex shapes and worked easily.  
2. Its expansion can be easily controlled, and it has very high compressive strength. 
3. A distinctive feature of this cement is that unlike the action of the metal, it expands upon solidification. 
4. If a cement of the proper coefficient of expansion is selected, the effect of shrinkage of the casting can be automatically neutralized.
5. It can be worked easily using wood working tools.

Disadvantages of Plaster

1. Can only be used for small castings.

Plastic

The plastic used as a patterned material is thermosetting resins, epoxy, PVC, polyurethane foam, etc.

Advantages of Plastic Material

Plastic is gradually adapting to the pattern material due to its distinctive features: 

1. Light in weight.  
2. High strength.  
3. High resistance to wear.  
4. High resistance to corrosion due to moisture.  
5. Fine surface.  
6. Low solid shrinkage.  
7. Reasonable cost. 

Disadvantages of Plastic Material

1. These are fragile.  
2. These may not work well when subjected to severe shock conditions like machine molding.

Wax

Wax patterns are used exclusively in investment casting.  

For this, a die or metal mold is made in two parts in which hot wax is poured.  

The die is kept cool by spreading water around it.  

When the wax cools, the parts of the die are separated and the wax pattern is drawn.

Advantages of Wax

1. Provide a very good surface finish.  
2. Provide high accuracy for costs.  
3. After being molded, the wax pattern is not pulled out of the mold like other patterns rather the mold is inverted and heated by which it comes out or evaporated. Thus, there is no chance of the mold cavity being damaged while removing the pattern.

Disadvantages of Wax

1. Equipment and process costs are high.
2. This process requires a high level of skill.

In this post, we’ve discussed types of pattern materials as well as their uses, advantages, and disadvantages.

I hope you like this post.

FAQ for Pattern Materials

What is the most common material used for patterns?

Wood is the most common material which is used for patterns.

What are the properties of pattern material?

The properties of pattern material should be:

1. It should be easily worked and formed in existing shape.
2. Always pattern materials weight should be light.
3. It should be strong and hard.
4. It has capable to resist wear and abrasion.
5. It has the capability to resist corrosion as well as any type of chemical reaction.
6. It should be unaffected by variation in temperature as well as humidity.
7. It should be dimensionally stable as well as available at a low price.

Which is the most commonly used metal for patterns?

Aluminum is the most commonly used metal for patterns.

What materials are used for making the pattern for investment casting and why?

For making the pattern in the investment casting process wax materials are used because in wax pattern materials there is no chance of the mold cavity being damaged while removing the pattern.

Can Aluminium be used for making patterns?

Yes, Aluminium is the most common metal which is used for making patterns.

Which of the following is the best material for making patterns?

Aluminum is the best material for making a pattern because it's lightweight and easy to cast in any shape, it is also available at an affordable price.

Which one of the following pattern materials are affected by moisture?

Wood is the only pattern material that is affected by moisture.

For good dimensional tolerances and smooth surface which of the following is used as pattern material?

Metal is used for good dimensional tolerances and smooth surface as a patterns material.