We have defects in the gate area during the injection mold process. What causes this phenomenon? Is there a good way to solve it?

1. www.moldclamps.net info@moldclamps.net 0086-17322110281
DGMF Mold Clamps Co., Ltd
mingfeng425@gmail.com
Please browse our website or contact us for more articles, thank you.
How to solve the product defects in the gate area?
Written By Jasmine HL
We have defects in the gate area during the injection mold process. What causes this
phenomenon? Is there a good way to solve it?
Light line
Cause:
In the design of the point gate in the direction of the vertical part, a radiation system composed
of different color depths and glosses, which is centered on the gate, appears on the surface of the
part during injection molding, which is called a ray. There are roughly three manifestations,
namely dark lines with a dark background, dark lines with a dark background, and dark lines
around the gate which are dense and white.
Most of these defects occur in the injection of polystyrene and modified polystyrene mixtures,
and are related to the following factors: the two materials have differences in rheological
properties, coloring properties, etc. There are differences in heating conditions; burnt filaments
are generated due to thermal decomposition of plastics; interference of gaseous substances
when plastics enter the mold.
Solution:
①. When using mixed plastics, plastics must be mixed well, and the particle size of the plastics
must be the same and uniform.
②. Plastic and colorant should be mixed uniformly, if necessary, appropriate dispersant should be
added and mechanically mixed.
③. Plasticizing should be complete, and the plasticizing performance of the machine should be
good.
④. Reduce injection pressure and speed, shorten injection and dwell time, increase mold
temperature, increase nozzle temperature, and reduce forehearth temperature.
⑤. Prevent the melt and coking substances that increase viscosity due to the degradation of

2. www.moldclamps.net info@moldclamps.net 0086-17322110281
DGMF Mold Clamps Co., Ltd
mingfeng425@gmail.com
Please browse our website or contact us for more articles, thank you.
plastics. For example, pay attention to whether the screw and barrel are worn and there is a dead
angle, or the heating system is out of control. Improper processing operations cause long-term
heating and decomposition of plastics. This can be done by polishing the inner surface of the
screw and barrel front end.
⑥ Improve the gate design, such as enlarge the gate diameter, change the gate position, change
the gate to a rounded transition, try to locally heat the gate, and add a cold material well at the
end of the runner.
Coldspot
Cause:
Cold spots are mainly fog or bright streaks near the gate or curved scars from the gate that look
like earthworms sticking to them. They are caused by the plastic striker entering the cavity or due
to excessive pressure. Caused by cold material that is subsequently squeezed into the cavity;
Due to the cooling effect of the nozzle or runner, the forward material is cooled and solidified
before entering the cavity. When the injection is expanded through the narrow gate, the melt
fractures, and then it is subsequently heated by the subsequent heat. The molten material was
pushed and became cold spots.
Solution:
①. Cold material wells should be opened. It is also necessary to consider the form, size, and
position of the gate to prevent the cooling rate of the material from being disparate.
②. The center of the nozzle should be adjusted, and the matching size between the nozzle and
the mold feed should be designed to prevent material leakage or cold material being brought into
the cavity.
③. The mold exhaust degree is good. Gas interference can cause turbid markings at the gate.
④. Increase the mold temperature. Slow down the injection speed, increase the injection
pressure, reduce the holding pressure and injection time, and reduce the holding pressure.
⑤. Dry the plastic well. Use less lubricant to prevent powder from being contaminated.