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.
January 26, 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.
Cannon Dynamic Overpacking System (left) is placed near the injection port where mixing head (right) is placed
Once most of the desired formulation has been injected into the mold, the Dynamic Overpacking System moves back and fills up with liquid
After the injection ends and the mixing head closes, the shrinkage of the polymerizing resin is noticeable
A sensor detects the pressure variation and the Dynamic Overpacking System goes into action, controlling the injection pressure
The mixed resin contained in it is progressively transferred to the mould
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 molded 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.
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