Introduction to Basic Manufacturing Processes and ... - always yours

206 Introduction to Basic Manufacturing Processes and Workshop Technology
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.
11.4.2.5 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.
11.4.2.6 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 180° 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.
11.5 QUESTIONS
1. How do you classify the different tools and equipment used in foundries?
2. Name the different tools used in hand molding stating their use.
3. Sketch and describe the different types of molding boxes you know.
4. What are ladles and crucibles? How do they differ from each other?