Advantages:
• When the number of castings is substantial, the additional cost of metallic patterns and other equipment is compensated by the high rate of production, and the overall cost per piece works out lower than in the case of hand moulding.
• It affords great saving in time, especially when a large number of similar castings in small sizes are required.
• A semi-skilled worker can do the machine job whereas hand moulding requires skilled craftsmanship.
• The castings obtained are more uniform in size and shape and more accurate than those obtained by hand moulding due to steadier lift of the pattern.
Types of Moulding machine:
1. Hand Operated molding machine
a. Pattern draw type
b. Pattern draw and Squeeze type
c. Pin Lift type machine
d. Roll Over type machine
2. Power operated Molding Machine
a. Squeeze machine
b. Jolt machine
c. Jolt squeeze machine
d. Jolt squeeze roll over pattern draw machine
e. Sand Slinger
Squeeze machine
A squeeze machine is very useful for shallow patterns. A squeezer (squeeze head) plate or presser board slides inside the flask to compress the sand above and around the pattern.
For squeezing action the squeeze piston may by forced upward, pushing the flask up against the squeezer or presser board the presser board being forced into the flask.
The sand is rammed harder at the back of the mould and softer on the pattern face. In other words sand has greatest density at the surface where pressure is applied to sand and sand density decreases progressively towards the pattern.
Moulding force (Mf) = P (π. d2/4)-W
Where, P – Pressure in squeeze cylinder
d – Piston diameter
W – Weight of flask pattern and sand