In this article we will learn about properties of sand which are desirable in moulding process. A material which has high refectories
can be used as mold manufacturing. There are many metallic and non metallic
material used to mold manufacturing but sand is the mostly used non metallic
material for moulding. It has high refectories properties and has high chemical
stability at high temperature. It is easily available, cheap and can be shaped
easily. These are the basic properties of sand due to which it is used in moulding.
Sand Properties:
The basic and main sand properties for moulding are given
below.
Refectoriness:
It is the basic and most desirable properties of moulding material.
It is define as the property of a material to withstand with high temperature without
any crack or braking of mold, which can provide good casting. This property of sand
can be extending to some extent by mixing some adhesive. The poor refectories
give poor surface finish and poor casting. The degree of refectoriness depend
on the SiO2 contain and grain size of the sand. The higher the SiO2 contain give
higher refectoriness.
Permeability:
It is the property which allow to escape any gas, air and moisture
contain from the mold. It is also known as porosity of sand. This property is
desirable for making cast without any defect. All of these gases and air particles
generated during pouring and solidification of molten metal into the mold.
These particles should be removed from the mold before casting, otherwise it
will generate many defects in the casting product and decrease its strength. Permeability
is function of grain size, moisture and clay contain.
Cohesiveness:
Cohesiveness is the property due to which the sand particle
attracts each other within the mold. It is the property which increases the binding
capacity of moulding sand which make good mold.
Green strength:
It is known as the strength of sand mold mixed with water. The
sand mixed with water should have sufficient strength and toughness to handle the
mold. Green strength of sand is mostly depends on the adhesive and cohesive property
of sand. Adhesive is property by virtue of which the sand particles attract
other particles which makes strong bond between sand, clay and moisture particle.
It is desirable for strong mold. The cohesiveness of particle is desirable to
taking out the pattern from the mold without breaking it. The green strength is
depends the grain size, clay contain and moisture contain in the sand.
Dry strength:
When the molten metal gets contact with the mold, the moisture
of adjacent layer evaporates which makes it dry. So the dry strength of sand should
be sufficient enough so it can be withstand with molten metal.
Flow ability and plasticity
It is the ability of sand which allows it to flow like fluid
into the mold. This property of sand is required to make uniform mold. It allows
the sand particle to flow all over the mold during ramming process. It increases
with decreasing in green strength. It is also depends on the grain size, clay
and moisture content.
Adhesiveness:
It is the property of sand due to which sand particles
attract other particles. It is desirable for the making strong mold.
Collapsibility:
This property of sand is required to avoid cracks in casting
after solidification. After the molten metal get solidified into the mold, the
mold should be collapsible which allow free contraction of metal which avoid tearing
and cracking of casting product.
These all are desirable properties of sand which allow the sand
to use in moulding process. It you have any doubt about this article, ask by
commenting.