There are two types
of injection features: the thermoplastic type
and thermosetting plastic type. Thermoplastic
type material can be recycled and reusable, while
the runner or material waste for thermosetting
plastic type cannot. Usually, the material is
thermoplastic type if the product material is
plastic; the material is thermosetting type if
the product is Bakelite and melamine.
The difference between Bakelite machine and normal
injection machine is that normal injection machine
uses heater band method to heat, while the Bakelite
(thermosetting) injection machine uses mold temperature
controller to heat. That is, the thermosetting
injection machine first heats the material up
to reach 60 to 90°C inside barrel so the material
flows. Then, it injects the material to the mold,
which the mold needs to be heated up to reach
160 to 190°C in order to melt the material and
form. Therefore, the thermosetting injection machine
uses mold temperature controller to heat. In few
cases, it uses heater band to heat the mold that
causes extremely high temperature on the mold,
a clamping unit must be equipped with the insulating
plate to prevent harm from the mold base to operators.
During the injecting operation, the injecting
action must be all the way to the end and must
not store any waste material in order to prevent
material becomes hard and solid and blocks the
next cycle. The barrel temperature must be controlled
accurately and steady to ensure product quality
and stability. One must completely clean up all
remaining material in the barrel before calling
it a day to prevent material forms inside the
barrel, which might damage or even break the entire
barrel and screw.
When designing the mold, it must have a good
air vent system. If the mold does not have an
air vent system, then the machine mechanism design
must include an air vent function. Even if the
two stage ejector knock out action is available
for the mold design, the air vent function should
still be included for the machine mechanism design
so the product and runner can be easily separated
after mold opens.
All Bakelite products have flashing, which requires
an extra process to modify it. Sand blow or rotation
tumbler are two primary methods to modify the
flashing. There are also several different types
for sand blow method, but in short, small size
products are suitable for rotation type sand blow,
while large size products are suitable for conveyer
type sand blow that prevents the damage to the
object angle.
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