Plastic Poultry Cage Injection Mould

How to set the injection molding machine parameters?

Injection molding machine introduction technology: Polycarbonate injection molding is an engineering technology that involves transforming plastic into useful and original products. Important process conditions for polycarbonate injection molding are temperature, pressure, and corresponding individual time of action that affect plasticizing flow and cooling.

1. Injection moulding machine setting – temperature control

The temperature to be controlled during the molding process is barrel temperature, nozzle temperature, and mold temperature.

* Barrel temperature

The first two temperatures primarily affect plasticization and flow of plastic, while the latter temperature primarily affects the flow and cooling of plastic. Each plastic has a different flow temperature. Same plastic has a different flow and decomposition temperatures due to different sources or grades. This is due to the difference in average molecular weight and distribution. Plastics are injected in different types. Plasticizing process in the machine is also different, so the temperature of the selected cylinder is also different.

* Nozzle temperature

Nozzle temperature is usually slightly lower than the maximum temperature of the barrel. This is to prevent the “flowing phenomenon” of melt in a straight-through nozzle. Nozzle temperature should not be too low, otherwise, it will cause early condensation of melt to block nozzle, or affect the performance of product due to injection of early aggregate into the cavity.

* Mold temperature

Mold temperature has a great influence on the intrinsic properties and the apparent quality of the product. The temperature of the mold depends on the presence or absence of crystallinity of plastic, size, and structure of product, performance requirements, and other molding process conditions (melt temperature, injection speed, and injection pressure, molding cycle).

2. Injection moulding machine setting – pressure control

Pressure during the molding process includes plasticizing pressure and injection pressure and directly affects the plasticization of plastics and the quality of products.

* Plasticizing pressure: (back pressure) When using a screw-type injection machine, the pressure that the top melt of the screw receives when the screw rotates backward is called plasticizing pressure, also known as backpressure. This pressure can be adjusted by a relief valve in the hydraulic system. In injection, plasticizing pressure is constant with the rotation speed of the screw. When plasticizing pressure is increased, the temperature of the melt is increased, but plasticizing speed is reduced. In addition, increasing plasticizing pressure often makes the temperature of melt uniform, mixing of colorant uniform, and discharge of gas in the melt. In general operation, the determination of plasticizing pressure should be as low as possible to ensure the quality of the product. Specific value varies with the type of plastic used, but usually rarely exceeds 20 kg/cm 2 .

Injection pressure: In the current production, the injection pressure of almost all injection machines is based on the pressure exerted by the plunger or top of screw-on plastic (converted from oil pressure). Injection pressure plays a role in polycarbonate injection molding by overcoming flow resistance of plastic from barrel to cavity, giving melt filling rate and compacting melt.

3. Injection moulding machine setting – molding cycle

The time required to complete a molding process is called the molding cycle. It actually includes the following parts:

Molding cycle: The molding cycle directly affects labor productivity and equipment utilization. Therefore, in the production process, relevant time in the molding cycle should be shortened as much as possible under the premise of ensuring quality. Injection time and cooling time are of the utmost importance throughout the molding cycle and they have a decisive influence on the quality of the product. Filling time in injection time is directly inversely proportional to the filling rate, and filling time in production is generally about 3-5 seconds.

Holding time in injection time is the pressure time of plastic in the cavity, which accounts for a large proportion in the whole injection time, generally about 20-120 seconds (extra-thick parts can be as high as 5-10 minutes). Before melting of melt at the gate, the amount of dwell time has an effect on the dimensional accuracy of the product. If after, it has no effect. Holding time also has the best value, which is known to depend on material temperature, mold temperature, and size of main runners and gates. If dimensions and process conditions of main runners and gates are normal, it is usually the value of pressure at which the fluctuation range of product shrinkage is the smallest.

Cooling time is mainly determined by the thickness of the product, thermal properties and crystallization properties of plastic, and temperature of the mold. The endpoint of cooling time should be based on the principle of ensuring the product does not cause changes during demolding. Cooling time is generally between 30 and 120 seconds. It is not necessary to cool too long, which not only reduces production efficiency, but also causes difficulty in demolding complicated parts, and even mold release stress is generated when mold is released. Other times in the molding cycle are related to continuity and automation of the production process, as well as the degree of continuity and automation.