Bulk Moulding
Compounds for the Automotive
Industry
As BMC processing technology has evolved
now to produce parts of good consistency
it is expected that the market for this
material will grow fast in the coming
years for demanding applications like
automobiles.
Overview
It is a well known fact that use of plastics
in the automotive industry has been
increasing globally and some cars are
said to have about 100kg of plastics per
vehicle. Thermoplastics comprise of the
major portion of the plastics used in cars
and therefore draw more attention from
the moulding industry and others associated
with plastics. Thermosets like
sheet moulding compounds and bulk
moulding compounds, however, have
properties not available in reasonably
priced thermoplastics and are therefore
important for parts having high engineering
requirements.
The purpose of this article is to provide
basic information on Bulk Moulding
Compounds and their use in the automotive
industry to make injection
moulded parts.
Bulk Moulding Compounds
What are Bulk Moulding Compounds
Bulk Moulding Compounds (BMC) are
polyester based thermoset plastics. Also
called Dough Moulding Compounds
(DMC), these comprise of polyester
resin, mineral fillers, glass fibers, additives
and peroxide catalysts.
Characteristics of Bulk Moulding
Compounds
The heat and pressure during the moulding
process result in decomposition of
catalyst. This leads to cross-linking of
the molecules of resin making a network.
This cross linking results in a rigid
structure in which the molecules are
held by chemical bonds. These bonds
are the reason why Bulk Moulding
Compounds maintain their high properties
at high temperatures under load
for long periods.
On the other hand thermoplastic
compounds even with high reinforcing
fibers percentage (e.g., glass) have molecules
held together by electrostatic
forces. When exposed to heat and espe-
Automotive
Industry
Bulk Moulding
Compounds for the
Pablo Bai
Wah Hong Industrial Corporation
Taiwan
As BMC processing technology has evolved
now to produce parts of good consistency
it is expected that the market for this
material will grow fast in the coming
years for demanding applications like
automobiles.
THE ECONOMIC TIMES POLYMERS l FEBRUARY - MARCH 2006 25
cially under load, these molecules slide
over each other resulting in creep and
deterioration of other properties. Filled
thermoplastic compounds retain only a
small percentage of their properties at
high temperatures (close to their HDTHeat
Deflection Temperature) unlike
Bulk Moulding Compounds, which retain
high percentage of their properties
at their HDT.
....contd.
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