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The Main Components of China Plastic Injection Molding

China Plastic Injection Molding: The 5 Main Components.

China plastic injection molding contributes to the Chinese plastic market and works to supply global plastic markets with first-rate plastic products. No matter what plastic part a plastic molding machine is manufacturing, the plastic molding process comprises a few essential components.

Understanding the Process

In China Plastic injection molding process, an injection molding machine (IMM) melts solid granular plastic in a heated barrel. A screw-type plunger then pushes the molten plastic through a nozzle and into the mold cavity, where the molten plastic takes the shape of the mold. After filling the mold, the injection molding machine allows the plastic to cool in the mold.

After the plastic has cooled, solidified, and taken the desired shape, ejector pins present on the mold's core side push the part out of the mold, and the mold closes back for the next shot.

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The point from the injection of molten plastic to the solidified plastic part's ejection makes up one cycle of the process.

This process has been in use for many years for the mass production of plastic parts. However, it has been highly automated and integrates technology with conventional plastic molding practices to produce superior quality plastic products.

china plastic injection molding

Defining the Basic Steps of China Plastic Injection Molding

China plastic injection molding and all plastic molding processes, in general, comprise of four fundamental steps. However, if we look into the details, many smaller processes are going on, like shrinkage and melting. But the four primary stages of the molding process include all the minor sub-processes of the injection molding process.

The four fundamental stages of injection molding are:

1.      Injection/Filling Stage

Every individual cycle in the china plastic injection molding process commences in the injection/filling step. In this step, the hydraulic pump-driven screw-type plunger moves forward and pushes the molten plastic through the barrel's nozzle and into the mold cavity. The screw shot size is adjusted such that it fills 95% of the mold cavity in this stage.

2.      Packing/Holding Stage

In this stage, hydraulic back pressure pushes the screw-type plunger further, and it injects more molten material into the cavity. The machine pushes more material into the cavity to pressurize the molten plastic and make it occupy and fit into the mold perfectly.

Moreover, plastic (and all solids) shrink on cooling. Therefore, the plunger injects additional material to make up for any voids or sink marks that may appear due to shrinkage. Exerting appropriate holding pressure in this stage is crucial.

3.      Cooling Stage

After the pack/hold stage comes to the cooling stage. As the screw-type plunger recovers and prepares for the next shot, the previous shot's molten plastic cools and solidifies inside the cavity. Water is the most-used coolant that circulates in the water lines, which snake around the mold cavity.

4.      Ejection Stage

The ejection stage begins after the plastic part cools down to a temperature at which it has become a firm, sturdy solid.

In this stage, the core side of the mold retracts and opens the mold. As the core side moves back, the ejector plate moves forward, bringing ejector pins with it. These ejector pins push the material that sticks to the core during the process out. The core plates move back and close the mold, thus completing one cycle of the process.

The Main Components of China Plastic Injection Molding

Five basic systems constitute the process of China plastic injection molding. These mechanisms work in conjunction and curate high-quality plastic part(s) in every cycle with consistency and efficiency. We have tried to brief each of these components below to help you understand the complex process of plastic molding.

·         Hydraulic Mechanism

Plastic molding involves a lot of pressure, a lot of push and force. And China plastic injection molding's hydraulic mechanism supplies all of this pressure, push, and force. This hydraulic mechanism is responsible for pushing and rotating the screw-type plunger and for driving the clamp mechanism.

The hydraulic system utilizes a motor-driven hydraulic pump and appropriate hydraulic liquid (mostly oil) and a complex circuit of pipes and tubes to supply pressure. The process uses this pressure to push the screw-type plunger forward to inject molten plastic through the barrel's nozzle. This hydraulic system also supplies power to rotate the screw at the right RPM.

china plastic injection molding

Moreover, the hydraulic injection molding machine system also supplies pressure that drives the clamp mechanism. This system is required and is capable of providing enough pressure to keep the molds clamped shut during the filling stage.

·         Injection Mechanism

The injection mechanism is responsible for taking the granular feed and injecting it in molten form in the mold. Every China plastic injection molding machine comprises a barrel that carries a screw-type plunger.

The entire length of the screw is divided into three zones. These zones are; the feed zone, transition zone, and metering zone. Plastic, as raw material, is fed into the barrel by a hopper.

The first zone is the feed zone and covers 50% of the screw length. The feed zone takes the feed and transfers it to the transition zone. The second is the transition zone, covering 25% of the screw length and it uniformly melts plastic grains to form molten plastic. The third zone is the metering zone. This zone, covering the remaining 25% of the screw, pushes the molten plastic through the nozzle into the mold.

A band-heater provides heat to the barrel and melts plastic, allowing the hydraulic pressure driven injection mechanism to inject molten plastic into the mold.

·         Molding Mechanism

All the china plastic injection molding process components are of utmost significance; however, leading all other essential components might be the molding mechanism. Taking the molding mechanism out of the plastic molding process would be equivalent to taking the chicken patty out of your chicken burger.

The molding mechanism is responsible for molding the molten plastic into customer-defined shape and specification. Even though the molding mechanism cannot create the perfect part single-handedly, it does an essential job of giving the part its required shape and size.

A mold consists of two sides. A cavity side or plate-A is immovable and has the cavity, sprue, runners, and mold gates. This plate is right next to the barrel. The molten plastic that the plunger injects enters the mold cavity from this side.

The other side of the mold is the core side. The core side contains the core to which the plastic part sticks. This side moves and is thus responsible for opening and closing the mold.

·         Clamping Mechanism

Clamping mechanism in China plastic injection molding process has the critical job of keeping both sides of the molds 'clamped' together tightly during the filling, packing, and cooling stages.

During the filling and packing stage, the mold has to bear an excessive amount of linear pressure. If the mold's core side is not held tightly against the cavity side, the pressure from the screw plunger during the filling and packing stage can push open the molds.

Opening of mold in the middle of any stage can cause the molten plastic to seep out of the mold and lead to defects in the plastic part.

Therefore, the clamping mechanism by utilizing pressure that the hydraulic mechanism provides plays a vital role in ensuring defect-free parts.

·         Control Mechanism

All efficient plastic molding processes are very tightly-controlled processes. Thus, China plastic injection molding process utilizes many sensors and transducers that detect temperature, pressure, screw speed, viscosity, and many other parameters and transmit it over to the controller. The controller may then take necessary action to adjust any parameters that have deviated from their set point.

china plastic injection molding


China plastic injection molding is a process encompassing many components. Each component or system of this process has its significance. Taking any one of these mechanisms out of the process would translate into rendering the entire process inefficient and, might I say, useless.

Each of the five necessary components of the plastic molding process works in synchrony and produces premium plastic products with unprecedented efficiency and prodigious uniformity.

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