The injection molding process can be
roughly divided into the following six stages
Clamping, glue, pressure maintaining and
cooling, mould and products.
The above process again and again, can
batch periodically to produce products. Thermosetting plastic and rubber
molding including the same process, but a thermoplastic material barrel
temperature is low, the injection pressure is higher, the mould is heated,
finished material injection in the mold of the subject to curing or curing
process, and then strike off membrane.
The trend of the current processing
technology is developing towards the direction of the high and new technology,
these technologies include: micro injection molding, high filling compound
injection, water injection, mixed with a variety of special injection molding
process, foam injection molding, mold technology, simulation technology, etc.
The temperature control
Injection molding equipment and mold
1．nitrogen-treated
barrel temperature, injection molding process, the need to control the
temperature of the cylinder temperature, nozzle temperature and mould
temperature, etc. The first two main influence plastic plasticizing temperature
and flow, and then a temperature is mainly influence plastic flow and cooling.
Each kind of plastic flow with different temperature, the same kind of plastic,
due to different sources or brand, the flow temperature and decomposition temperature
is little different, this is due to the different average molecular weight and
molecular weight distribution, plastic in different type of injection machine
of plasticizing process is also different, so choose the cylinder temperature
is not the same.
2. The nozzle temperature, nozzle
temperature is usually slightly lower than expected tube maximum temperature,
this is to prevent the molten material in straight through the nozzle may be
"salivate phenomenon". Nozzle temperature also cannot too low, otherwise
will cause early setting of melting and the nozzle clogging, or due to early
coagulation material into the cavity affect the performance of the products.
3．Pictures of mold
temperature, mold temperature inner performance and apparent impact on the
quality of products. Mold temperature is determined by the size of the plastic,
of crystalline products and structure, performance requirements, and other
process conditions (melt temperature, injection speed and injection pressure,
molding cycle, etc.).
Pressure control
In the process of injection molding
pressure including plasticizing and injection pressure, and directly affects
the quality of plasticizing and plastic products.
1．plasticizing
pressure: (back pressure) adopts screw injection machine, screw at the top of
the molten material in the screw rotating back pressure is called the
plasticizing, which is also called back pressure. The size of the pressure can
be found on the overflow valve to adjust the hydraulic system. In injection, the
size of the plasticizing pressure is depending upon the design of the screw,
the product quality requirements, and the type of plastic and needs to change,
if the situation and the screw rotation speed is constant, increase
plasticizing pressure will strengthen shearing action, which will raise the
temperature of the melt, but will reduce the plasticizing efficiency, increase
the current and leakage flow, increase the driving power.
In addition, increase plasticizing pressure
often can make the melt temperature uniformity, color mixing and discharge gas
in the melt. general
Injection molding in the operation of the
pressure curve, the plasticizing pressure shall be on the premise of guarantee
the products quality is lower, the better, the specific values are vary with
the varieties of the plastic, but usually rarely more than 20 kg/cm2.
2. Injection pressure: in the current
production, almost all the injection pressure of injection machine are in
piston or screw at the top of the plastic
On the pressure (by oil pressure
conversion) shall prevail. Injection pressure in injection molding, the role of
is, to overcome the flow resistance of plastic flowing from cylinder cavity,
given the rate of molten material molding and compaction of molten material.
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