Pattern


Pattern is a principle tool during casting process.


A pattern may be defined as a replica or facsimile model of the desired casting which, when packed or embedded in a suitable moulding material, produces a cavity called mould. . This cavity, when filled with molten metal, produces the desired casting after solidification of the poured metal.


The ways in which a pattern differs from an actual component are,

1. It carries an additional allowance to compensate for metal shrinkage.


2. It carries additional allowances over those portions which are to be machined or finished ather wise.


3. It carries the necessary draft to enable its easy removal from the sand mass.


4. It carries additional projections, called core prints, to produce seats for cores.




Difference between Pattern and Casting


1. Pattern is slightly larger in size than casting because pattern is given shrinkage allowance and machining allowance


2. Pattern is slightly tapered because it is given draft allowance of 1 for external and 3 for internal surfaces.


3. Pattern is provided with care prints to support the core to make holes in the casting.


4. Pattern may be made in two or three pieces whereas casting is a single piece. 


5. Pattern may not have all slots and holes of casting because they are machined afterwards.