What is Pattern?
A pattern is a replica of the object to be cast that is used in casting to prepare the cavity into which the molten material will be poured during the casting process. Sand casting patterns can be made of wood, metal, plastics, or other materials. Patterns are built to exact construction standards to last for a reasonable amount of time, depending on the quality grade of the pattern being built, and to provide dimensionally acceptable casting consistently.
Typically, wood, metal, or plastics are used to create different types of patterns. Wax and Plaster of Paris are used only in limited circumstances. Investment casting is a casting technique that makes use of wax patterns. Plaster of Paris is commonly used to create master dies and moulds.
Types of Pattern in Casting
As previously stated, casting objects are heavily reliant on types of patterns in casting. Patterns are classified as follows based on the shape and size of the casting and the method of making the cavity.
- Single piece pattern
- Two-piece pattern
- Multi-piece pattern
- Match plate pattern
- Gate pattern
- Sweep pattern
- Skeleton pattern
- Loose piece pattern
- Cope and drag
- Shell pattern
- Follow board pattern
- Segmental pattern
Single Piece Pattern
The single-piece pattern is a type of pattern also known as the solid pattern. It is the most affordable casting pattern. It is ideal for simple processes and small-scale production, and large casting manufacturers prefer it because this type of casting pattern requires only simple shapes and flat surfaces, such as simple rectangular blocks. A single flat surface separates planes. It is used to make steam engine stuffing boxes.
The two-piece pattern, also known as the split-piece pattern, is a popular casting pattern for intricate casting. Parting planes with flat or irregular surfaces are used in this pattern, and the exact position of the plane is determined by the shape of the casting. The split-piece pattern consists of two pieces. One of the parts is made of drag, while the other is made of cope. Dowel pins are always used in the cope part. The two halves of the split piece pattern can be aligned using dowel pins.
A multi-piece pattern is a good solution for difficult-to-make complex designs. This type of pattern consists of three or more patterns that aid in mould making.
As an example, consider the three-piece pattern. The pattern is divided into the top, bottom, and middle sections. The top part is called the cope, the bottom part is called drag, and the middle part is called the check box.
Match Plate Pattern
This type of pattern is made in two halves and is mounted on opposite sides of a match plate, which is made of wood or metal. The plate also holds the gates and runners. In machine moulding, this type of pattern is used. It is widely used in manufacturing and typically has a high yield, precise casting, and a high cost. And this type of casting pattern is commonly used in metal casting, such as aluminium.
Multi cavity moulds are used in the mass production of casings. The figure shows that such moulds are created by connecting some patterns and gates and providing a common runner for the molten metal. These types of patterns are made of metals, and metallic pieces are attached to the pattern to form gates and runners.
The sweep type of pattern shapes the cavity by rotating a wooden board along one edge. This type of casting pattern creates a cavity in the vertical direction, and the base of it is attached with sand. It also creates casting in a very short time, and it has three parts: spindle, base, and sweep, which is also known as a wooden board.
Skeleton patterns are large in size, and they are a good choice for castings with simple size and shape. This type of casting pattern is costly and unadaptable. It is not the most cost-effective option, but it is very effective at removing extra sand. This type of pattern is widely used in pit or floor welding industries.
Loose piece pattern
This type of pattern can assist manufacturers in removing one piece of the solid pattern that is above or below the mould's parting plane. Because this pattern necessitates additional skilled labour, it is an expensive casting pattern in castings.
Cope and Drag
The cope and drag parts of the mould are prepared separately in this case. This occurs when the entire mould is too heavy for one operator to handle. The pattern is divided into two halves that are mounted on separate plates. The figure displays an example of a standard match plate pattern.
The shell type of pattern is an excellent choice for creating hollow-shaped structures. It splits down the middle and dowels the resulting halves.
Follow Board Pattern
When solid or split patterns become difficult, a follow board is made with a contour corresponding to the exact shape of one-half of the pattern.
This type of pattern is commonly used for circular castings such as wheel rims, gear blanks, and so on. Such patterns are sections of a pattern that are moved to form each section of the mould to form a complete mould. A central pivot guides the movement of the segmental pattern.
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