PATTERN :
During the casting method pattern is that the primary tool . It’s the copy of the object to be created by the casting method with some modifications.
The main modifications are the addition of pattern allowances and also the provision of core prints.
If the casting is to be hollow further patterns referred as cores.
FUNCTION OF PATTERN :
A pattern prepares a mould cavity for the aim of making a casting.
A pattern could contain projections called as core prints if the casting needs a core and want to be made hollow.
Runner, gates, and risers used for feeding molten metal within the mold cavity could form a part of the pattern.
Patterns properly made and having finished and smooth surfaces reduce casting defects.
A properly constructed pattern minimizes the overall cost of the castings.
TYPES OF PATTERN :
SINGLE PIECE PATTERN (OR) SOLID PATTERN
This is the simplest type of pattern exactly like the desired casting.
For making a mould the pattern is accommodated either in cope or drag. This is often used for manufacturing a large castings.
Example - stuffing box of steam engine.
SPLIT PATTERN (OR) COPE & DRAG PATTERN
These patterns are split on the parting plane to facilitate the extraction of the pattern out of the mould before the pouring operation.
The two part of the pattern are joined at the side of the assistance of dowel pins. For a more complex casting, the pattern could also be split in more than two parts.
MATCH PLATE PATTERN
This type of pattern is used for a large number of castings. A match plate pattern having the cope and drags parts mounted on opposite sides of a plate referred to as match plate that conforms to the contour of the parting surface.
The gates and runners are also mounted on the match plate so hand work is required.
Example - piston rings of I.C. engines.
LOOSE PIECE PATTERN
When a one piece solid pattern has projections or back drafts that lie above or below the parting plane it’s not possible to with draw it from the mould.
With such patterns the projections are made with the assistance of loose pieces.
A loose piece is attached to the main body of the pattern by a pin. While moulding the sand was rammed properly then the loose piece was removed.
GATED PATTERN
A gated pattern is a one or more loose patterns having gates and runners.
Used for producing small castings due to higher cost these patterns.
SWEEP PATTERN
A sweep may be a section or board of proper contour that’s rotated about one edge to shape mould cavities having shapes of rotational symmetry.
This type of pattern is used when a casting of large size is to be produced in a short time.
SKELTON PATTERN
Skeleton patterns are used for large castings having simple geometrical shapes. Rather like sweep patterns these are simple wooden frames that outline the shape of the part to be cast.
This type of pattern is also used in pit or floor molding process.
SEGMENTAL PATTERN
It is perform similar to sweep pattern in the sense that both employ a part of the pattern rather than a complete pattern for getting the required shape of the mould.
The segmental pattern is in the form of a segment and is used for making moulding parts having circular shapes.
To create the mould, it’s rotated about the post in the same way as in sweep pattern however it is not revolve continuously.
Example - Big gears and wheel rims.
SHELL PATTERN
It is a hollow pattern. The outer shape is used as mould the core is placed inside the pattern hence it is named as block pattern.
This pattern is made of two half similar to split pattern but only for curved path joined by dowel pin. Example: curved drainage fitting.
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