26 Jan 2024

The Dynamic Overpacking System, developed by Cannon Afros R&D, solves the common issue of shrinkage in some plastics during the cooling and polymerization phases. Discover it at JEC World 2024.

During polymerization and the cooling phase, all plastics display a certain degree of thermal and chemical shrinkage that often causes defects in the finished product which cannot always be hidden or removed.

To solve this problem, Cannon Afros R&D developed the Dynamic Overpacking System, a hydraulic actuated cylinder which allows a double-sequence injection of the chemical into the mold. Thanks to this second injection, defects caused by shrinkage can be avoided.

Let’s have a detailed look at how the Dynamic Overpacking System works.

A common issue

Thermal and chemical shrinkage of plastic during polymerization and cooling time depends on the material type and the temperature difference between the mold and environment. This usually leads to a lack of material on the product’s surface, resulting in superficial and aesthetic defects, distortions and porosities. In some cases, the defects can be covered with paint, but in others they are more difficult to conceal.

This is particularly true for complex aesthetic parts or composite surfaces and, in some cases, for structural components, whose mechanical resistance may be compromised.

The solution

To solve this issue and reduce the possibility of flawed surfaces – thus wasting materials – we developed an innovative double-sequence injection using a Dynamic Overpacking System placed near the injection port.

Once most of the formulation has been injected into the mold, the hydraulic cylinder moves back, creating a buffer volume which starts receiving part of the remaining liquid at the same time as this fills the mold.

After injection has ended, when shrinkage of the polymerizing resin begins, a sensor detects the pressure variation and the Dynamic Overpacking System’s piston, which performs a constant-pressure injection, moves into action.

Dynamic Overpacking System
Cannon Dynamic Overpacking System with Mixing Heads and closed mould
Cannon Dynamic Overpacking System (left) is placed near the injection port where mixing head (right) is placed
Cannon Dynamic Overpacking System during formulation injection
Once most of the desired formulation has been injected into the mould, the Dynamic Overpacking System moves back and fills up with liquid
Cannon Dynamic Overpacking System filling with formulation
After the end of the injection and the closing of the mixing head, the shrinkage of the polymerising resin appears as noticeable

The contained mixed resin is progressively transferred to the mold – at a pressure ranging between few bars up to over 200, depending on the technology involved, clamping force available or presence of fragile inserts – filling the gaps created by the shrinkage. At the operator’s convenience, it is possible to leave a minimal quantity of formulation inside the self-cleaning accumulation cylinder, creating a small solid sprue that is removed with the molded part.

Cannon Dynamic Overpacking System keep the pressure stable during plastic shrinkage in closed mould
A sensor is able to detect the pressure variation and the Dynamic Overpacking System is put into action, controlling the injection pressure
Cannon Dynamic Overpacking System refilling the mould after plastic shrinkage
The mixed resin contained in it is progressively transferred to the mould
Cannon Dynamic Overpacking System can create a solid sprue
It is possible to leave a minimal quantity of formulation in the self-cleaning accumulation cylinder, creating a small solid sprue that is removed with the moulded part

To avoid polymerization of the formulation in the buffer cylinder during post-injection, we added dual-temperature control, ensuring that the refilling blend’s reactivity is slowed down while inside the Dynamic Overpacking System.

Want to know more about our Dynamic Overpacking System?

Contact our experts using the form below

    Name

    Surname

    Company

    Email

    Your message

    I have read the Privacy Policy and accept the terms and conditions, in accordance with the data protection statement.