Molded products have excellent
electrical properties (especially anti-leakage properties), mechanical
properties, heat resistance, fire resistance, chemical corrosion resistance and
dimensional stability, and can be adjusted according to the needs of each
component type and dosage to obtain products with special performance
requirements. The main performance is as follows：
1.Electrical property
Molded plastics are widely used in high voltage
electrical applications due to their arc resistance, acer performance, flame
resistance, dimensional stability, moulding and low cost. The ability of arc
suppression is mainly due to the presence of inert inorganic fillers such as
hydrated alumina, silica and ceramic. Add a small amount of polyethylene powder
(5% by weight) and use nylon fiber to improve arc resistance. In order to
obtain better arc resistance, the resin and glass fiber content should be
reduced to the minimum, however, such results reduce the mechanical properties.
2. Mechanical property
The mechanical properties of molding
materials vary with the types and proportions of reinforced fibers and resin
substrates used. In DMC, when the fiber length exceeds 6.35mm, the modification
of product properties is very small.
Most SMC products are made from short-cut
felt, and there is no published data on the effect of fiber length changes. Although
the length of the general fiber is 50mm, this length is not necessarily
suitable for all applications.
Increasing the content of reinforcing
materials can improve the mechanical properties, but too much fiber content
will bring inconvenience to molding. For example, when the fiber content in DMC
exceeds 20%, it has little influence on its mechanical properties.
3. Heat resistance or fire
resistance
Heat resistance refers to the ability
of products to withstand thermal decomposition for long periods of time below
the flammable temperature. "Short-term thermal strength" or
"thermal strength" is related to the thermal deformation temperature
of the resin. Although some fillers can improve the heat resistance of
products, the heat resistance and thermal strength mainly depend on the
properties of the resin. Flammability is a measure of apparent combustion,
divided into "non-ignition", "self-extinguishing" and
"flame-retardant" according to the ability and speed with which a
material is able to extinguish easily or when the ignition source is removed. Polyester
resins achieve flame resistance by adding halogen and phosphorous compounds and
by using alumina hydrate as the main filler in the components.
Phenolic resins are inherently
fire-resistant. Halogen compounds and phosphorous compounds, as well as HET
anhydride used as hardener, can make epoxy resins flame resistant.
4.Dimensional stability
General molding materials have good
dimensional stability, water absorption rate: small, thermal expansion
coefficient and aluminum is very similar, when continuous exposure to high
temperature, size is almost no change.
5. Corrosion resistance
The chemical resistance or corrosion
resistance of molding material mainly depends on the selected resin matrix. The
suitable resin and filler can be used to prepare the moulded material which can
meet the requirement of resisting special bristle dew
DMC can be made of acid-resistant and
alkali-resistant ligulates and acid-resistant epoxy resins. The choice of a
resin for SMC is currently limited because the resin must also have a chemical
structure that thickens easily. In common fillers, clay and silica have better
corrosion resistance and other properties.
6.Contractility
The shrinkage of moulded material is
very low after release, the typical maximum shrinkage rate is 0.004, and the
shrinkage rate of many moulded materials is close to 0.001, which is mainly due
to the small thermal shrinkage of glass fiber and inorganic filler. However,
the combination of low-shrinkage, high-strength fibers with the resin systems
commonly used for rapid curing and high thermal shrinkage results in greater
stress on the resin matrix between the fibers. The collateral effects of this
stress cause surface ripples, cracks, warping, and internal voids. These
defects can be reduced by the use of organic fiber reinforced materials
compatible with resin shrinkage or by the use of short or filamentous glass
fibers.
