Injection molding process

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.