Category Archives: Plastic Injection Moulding

Make Your Plastic Injection Products Better

Most Chinese injection mould companies are clustered around Guangdong province and Zhejiang providence. But, how can we choose the most suitable injecton mould maker from so many companies and factories?
We can choose from the following aspects:
Have a correct mold flow analysis before the whole mold design is very necessary.

And second, you can start your design, which must be based on the customer’s actual requirements. A reasonable design will help a lot to the following workflow.
And also, a good precious mold tooling is the very key to the quality of plastic injection moulding products. Because if the injection moulds have some problems, and that will directly reflected on the plastic products.


The Blowing and Stretching Process

Stretch blow molding is a two-stage process similar to injection blow molding. Firstly, a test-tube like preform is made using plastic injection moulding or a similar process. The neck of the preforms is fully finished but the diameter and length of the body portion are much smaller than the final product. The preform then undergos a stretch-and-blow process.
A small piece of thermoplastic material is preformed to a test-tube shape and installed near the tip of the blow stem. The setup is placed in the closed chamber of a divided mold.
Compressed air is injected into the preform via the blow stem while the blow stem is pushing forward to stretch the preform further into the mold.
The blowing and stretching process continues. The blow stem stops near the far end of the mold.
Compressed air continues to blow in until the preform reaches the wall of the mold.
The plastic piece is removed from the mold after it cools and hardens.

The single most important product made by stretch blow molding is the 2-liter PET bottle for carbonated soft drinks introduced in 1978 and updated to one-piece bottle in early nineties. The PET bottles are virtually unbreakable, lightweight, transparent. They and have various barrier properties. The traditional glass containers cannot compete with PET bottles and are almost extinct from the field of carbonated soft drinks.

Regulation of Injection Process

The design purpose of injection process regulation is to make these negative influences ineffective, and thus to attain an even higher reproducibility of the parts.

The dicisive factor for all quality features that are concerned with dimension and weight is the internal pressure of the mould. Constant maintenance of this pressure curve in every cycle guarantees uniformity of the quality of injection moulded parts. If the mould internal pressure curve is maintained at a constant, all of the negative factors mentioned above are compensated.

During plastic injection moulding without injection process regulation, a specified pressure curve is established for injection and holding pressure, which can also be maintained with assurance with a regulated machine. However, the mould internal pressure curve that arises can only be assumed. Pressure losses through the runner manifold as well as the mould specific filling behavior cannot be identified.

With the application of injection process regulation, the mould internal pressure is first measured and compared with a nominal value. If there is a deviation, a hydraulic valve that applies pressure to the injection cylinder is actuated. It is thus possible to follow the nominal value precisely and independently of negative factors. The switch over from injection to holding pressure also occurs as a function of internal pressure. Thus, no pressure spikes can occur since the switch over takes place when a specified threshold value is reached.