Classification of Moulding Machines

Classification of Moulding
Machines

The large variety of molding machines that are
available in different designs which can be classified
as squeezer machine,
jolt machine, jolt-squeezer machine, slinging machines,
pattern draw machines
and roll over machines. These varietiesย of machines are discussed as under.

ย Squeezer
machineย 

These machines may be hand
operated or power operated. The pattern is placed over
the machine table, followed by the molding box. In hand-operated
machines, the platen is
lifted by
hand operated mechanism. In power machines, it is lifted by the air pressure on
a
piston in the cylinder in the same wayย  as
in jolt machine. The table is raised
gradually.
The sandย in the molding box is
squeezed between plate and the upward rising table thus enabling a uniform
pressing
of sand in the molding
box. The main advantage of power operated
machines in comparison hand operated machines
is that more pressure can be applied
in power operated.

ย Jolt machineย 

This machine is also known as
jar machine which comprises of air operated piston
and cylinder. The air
is allowed to enter from the bottom side of the cylinder and acts on
the bottom face of the piston to raise it
up. The platen or table of the machine is attached at
the top of the piston which carries the pattern and molding box
with sand filled in it. The
upward movement
of piston raises the table to a certain height and the air below the piston is
suddenly released, resulting in uniform packing of sand around the pattern in
the molding box.
This process
is repeated several
times rapidly. This operation
is known as jolting technique.

ย Jolt-squeezer
machine

It uses the principle of both
jolt and squeezer machines in which complete mould is prepared. The cope, match
plate and drag are assembled on the machine table in a reverse position, that
is, the drag on the top and the cope below. Initially the drag is filled with
sand followed by ramming by the jolting action of the
table. After leveling off the sand on the upper surface, the
assembly is turned upside down and placed over a bottom board placed on
the table. Next, the cope is filled up with
sand and is rammed by squeezing between the overhead plate and the machine
table. The overhead plate is then swung aside and sand on the
top leveled off, cope is next removed and the drag is vibrated by air vibrator. This is followed by removal of
match plate and closing of two halves of the mold for pouring the molten
metal. This machine is used to overcome the
drawbacks of both squeeze and jolt principles of ramming molding sand.

Slinging machines

These machines are also known as
sand slingers and are used for filling and uniform ramming
of molding sand in molds.
In the slinging operations, the consolidation and ramming
are obtained by impact of sand which falls at a very high velocity on pattern.
These machines are generally preferred for quick preparation of large sand
moulds. These machines can also be used in combination with other devices such
as, roll over machines and pattern draw machines
for reducing manual
operations to minimum.
These machines can be stationary and portable types.
Stationary machines are used for mass production in bigger foundries whereas portable type machines are mounted on wheels and travel
in the foundry shop on a well planned fixed path. A typical sand slinger
consists of a
heavy base, a bin or
hopper to carry sand, a bucket elevator to which are attached a number of
buckets and a swinging arm
whichย carries a belt conveyor and the sand impeller
head.
Well prepared sand is filed in
a
bin through the bottom of which it
is fed to the elevator buckets. These buckets discharge
the molding sand to the belt conveyor which conveys the same to
the impeller head. This head can be moved at any location on the mold by
swinging the arm. The head revolves at a very high speed and, in doing so,
throws stream of molding sand into the molding box at a high
velocity. This process is known as slinging. The force of sand ejection and
striking into
the molding box compel
the sand gets
packed in the box
flask
uniformly. This way the satisfactory
ramming is automatically get competed on the mold. It is a very useful
machine in large foundries.

Pattern draw machines

These machines enable easy withdrawal of patterns from the molds. They
can be of the kind of stripping plate
type and pin lift or push off type. Stripping plate type of pattern draw
machines consists of a stationary platen or table on which is mounted a
stripping plate which carries a hole in it. The size and shape of this hole is
such that it fits accurately around the pattern.
The pattern is secured to a pattern plate and the latter to the supporting ram.
The pattern is drawn through the
stripping plate either by raising the stripping plate and the mould up and keeping the pattern
stationary or by keeping the stripping plate and mould stationary and moving
the pattern supporting ram downwards along with the pattern and pattern plate. A suitable mechanism can be incorporated in the machine
for these movements.

Roll-over machine

This machine comprises of a rigid frame carrying two vertical supports
on its two sides having bearing supports
of trunnions on which the roll-over frame of the machine is mounted.
The pattern is mounted on a plate which is secured to the roll-over frame. The
platen of the machine can be moved up
and down. For preparation of the mould, the roll-over frame is clamped in
position with the pattern facing upward. Molding box is placed over the pattern
plate and clamped properly. Molding sand is then filled in
it and rammed by hand and the extra
molding sand is struck off and molding board placed over the box and clamped to
it. After that the roll-over frame is
unclamped and rolled over through 180ยฐ to suspend the box below the frame. The platen is then lifted up to butt against
the suspending box. The box is unclamped from the pattern plate to rest over
the platen which is brought down leaving the
pattern attached to the plate. The prepared mold is now lowered. The frame
is then again rolled over to the original position for ramming another flask.
Other mechanisms are always incorporated
to enable the above rolling over and platen motion. Some roll-over machines may
carry a pneumatic mechanism for
rolling over. There are others
mechanism also which incorporate a
jolting table for ramming the sand and an air operated rocking arm to
facilitate rolling over. Some machines incorporate a mechanically or
pneumatically operated squeezing mechanism for
sand ramming in addition to the air operated rolling over mechanism. All such machines are frequently referred to
as combination machines to carry out the molding tasks automatically.

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