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Full text of "Modern Mechanical Engineering Vol-I"

ESSENTIAL  MACHINES  AND  APPLIANCES

165

fixed (fig. 71), in which case only the top face is used. In a relatively
small group, top and bottom faces of fixed tables are used, by pressing
boxes of sand simultaneously against pattern parts mounted on each face,
these being worked hydraulically (fig. 72). Using a turn-over table, the
sand is rammed (fig. 73) or pressed (figs. 69 and 70) over the pattern portion
on the upper face. After being turned over, with the box, the latter is with-
drawn downwards, and the other portion of the pattern, on the opposite face,
being brought upwards (fig. 74), is rammed. The closed mould is seen in
fig. 75. The majority of machines of small and medium dimensions have

Fig. 70.—Hand-moulding Machine with Turn-over Table
A, Turn-over Table.   B, Plates to secure patterns.   C, Sand frame.   D, Presser head.
tables of this kind. The large machines must generally have fixed tables.
In these, the mould is lifted off its pattern with rods or " stools ", or with
power. In some designs the table is rocked over to permit of the lifting of
the pattern out of the mould, or, in a very large number of cases, the pattern
is withdrawn downwards through a stripping plate (figs. 71, 76, 77, 78),
this being necessary in all those patterns which have deep perpendicular
sides, and desirable even when depths exceed 3 or 4 in., being beyond the
limit at which delivery can be assisted by rapping.
After plating, the two important details in the moulding operations are
ramming and delivery. Mechanical aids are provided for these in most
machines, but not in all. The cost of hand-ramming increases with the
dimensions of the mould, and with the intricacy of its details, so that several
hours may be occupied thus in moulds measuring several feet across. Here