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PATTERNS

SUBJECT: Machining Process – 2

Index

What does patterns mean?

Types of Patterns

Sweep Patterns

Sweep Patterns (Images)

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What does Patterns mean?

In the method of casting, patterns is to duplicate an object which has to be casted. This is used to prepare a cavity into which molten material will be poured during the casting process.

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Types Of Patterns

1. Sweep pattern

2. Split piece pattern

3. Loose piece pattern

4. Single piece pattern

5. Skeleton pattern

6. Shell pattern

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Sweep Patterns

1. A sweep pattern is just a form made on a wooden board which sweeps the shape of the casting into the sand all around the circumference. The sweep pattern rotates about the post

2. Once the mould is ready, sweep pattern and the post can be removed

3. Sweep pattern avoids the necessity of making a full, large circular and costly 3D pattern

4. Making sweep patterns save a lot of time and labour as compared to making a full pattern

5. A sweep pattern is preferred for producing large casting of circular sections and symmetrical shapes

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Process of Sweep Pattern

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Split piece pattern

•Pattern with complex shaped cannot be made due to the inherent difficulties related to molding operations

•The upper and the lower parts of the split piece patterns are accommodated in the cope and drag portions of the mold respectively.

•Parting line of the pattern forms the parting line of the mould. Dowel pins are used for keeping the alignment between the two parts of the pattern.

•Examples: Hallow cylinder Taps and water stop cocks etc.,

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Loose piece pattern

In this pattern basically one once embedded in molding then cannot be withdrawn.

Such patterns are usually made with one or more loose pieces for facilitating from the molding box and are known as loose piece patterns.

Loose parts or pieces remain attached with the main body of the pattern, with the help of dowel pins. The main body of the pattern is drawn first from the molding box and thereafter as soon as the loose parts are removed, the result is the mold cavity.

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Single piece pattern

Single piece (solid) pattern: Made from one piece and does not contain loose pieces or joints. Inexpensive. Used for large size simple castings. Pattern is accommodated either in the cope or in the drag. Examples: Bodies of regular shapes. stufflingbox of steam engine.

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Skeleton pattern

Skeleton pattern: A skeleton pattern is the skeleton of a desired shape which may be S-bend pipe or a chute or something else. The skeleton frame is mounted on a metal base The skeleton is made from wooden strips, and is thus a wooden work. The skeleton pattern is filled with sand and is rammed. A strickle (board) assists in giving the desired shape to the sand and removes extra sand. Skeleton patterns are employed for producing a few large castings. A skeleton pattern is very economical, because it involves less material costs.

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Shell molding

However, in shell mold casting, the mold is a thin-walled shell created from applying a sand-resin mixture around a pattern..

Shell mold casting allows the use of both ferrous and non-ferrous metals, most commonly using cast iron, carbon steel, alloy steel, stainless steel, aluminum alloys, and copper alloys. Typical parts are small-to-medium in size and require high accuracy, such as gear housings, cylinder heads, connecting rods, and lever arms.

The shell mold casting process consists of the following steps:

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Thankyou

By:

Pradip Darji Jay Desai

130510119031 130510119032

Mechanical (A) Mechanical (A)

Kuntal Deshpande Vinit Gadhoya

130510119034 130510119035Mechanical (A) Mechanical (A)

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