Moulding Machines:
Moulding
processes may be classified as hand moulding or machine moulding
according to whether the mould is prepared by hand tools or with the aid
of some moulding machine. Hand moulding is generally found to be
economical when the castings are required in a small number.
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 (Ï€. d2/4)-W
Where, P – Pressure in squeeze cylinder
d – Piston diameter
W – Weight of flask pattern and sand
Jolt-Squeeze machine
It
combines in single machine the operating principles of the jolt and
squeeze machines. Combination of jolting and squeezing produces
beneficial compaction effects on sand density and thus a more uniform
hardness throughout the mould is attained. A jolt-squeeze machine makes
use of match plate moulding.
Sand slinger
The
sand slinger consists of a base, a sand bin, a bucket elevator, a
swinging or movable arm, a belt conveyor and the sand impeller. Prepared
sand lying in the sand bin is picked up by the elevator buckets and is
dropped on to the belt conveyor which takes the same to the impeller
head.
Inside
the impeller head, rapidly rotating cup shaped blade picks up the sand
and throws it downward into the moulding box as a continuous stream of
sand with machine gun rapidity and great force.
The
sand is discharged into the moulding box at a rate of 300 to
2000kg/minute. This force is great enough to ram the mould
satisfactorily.
In moulding boxes, sand is filled
and rammed at the same time. The density of sand which is the result of
sand’s inertia is uniform throughout the mould.
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