CORE AND CORE BOX
A core is a preformed baked sand or
green sand aggregate inserted in a mold to shape
the interior part of a casting which
cannot be shaped by the pattern.
A core box is a wood or metal
structure, the cavity of which has the shape of the desired core which is made
therein.A core box, like a pattern ismade by the pattern maker.Cores run from
extremely simple to extremely complicated.
A core could be a simple round
cylinder form needed to core a hole through a hub of a wheel or it could be a
very complicatedcore used to core out the water coolingchannels in a cast iron
engine block along with the inside of the cylinders.
Dry sand cores are for the most part
made ofsharp, clay-free, dry silica sand mixed with a binder and baked until
cured;the binder cements the sand together.
When the metal is poured the core
holds together long enough for the metal to solidify, then the binder is finely
cooked, from the heat of the casting, until its bonding power is lost or burned
out.
If the core mix is correct for the
job, it can be readily removed from the castings interior bysimply pouring it
out as burnt core sand.
This characteristic of a core mix is
called its collapsibility.
The size and pouring temperature of
acasting determines how well and how long the core will stay together.
Dry sand core with support wire.
The gases generated within the core
during pouring must be vented to the outside of the mold preventing gas
porosity and a defect known as a core blow.
Also, a core must have sufficient
hot strength to be handled and used properly.
The hot strength refers to its
strength while being heated by the casting operation.
Because of the shape and size of
some coresthey must be further strengthened withrods and wires.
A long span core for a length of
cast iron pipe would require rodding to prevent the core from sagging or
bending upward when the mold is poured because of the liquid metal exerting a
strong pressure during pouring.
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