Holding Pressure Setting


(1) The Significance of Pressure Holding/Pack
After the mold cavity is filled, holding pressure is applied to compensate for resin shrinkage caused by cooling. Appropriate holding pressure and holding time will be maintained to push the mold screw, to continue injecting molten resin into the cavity. Holding pressure has a great influence on product shrinkage rate.

(2) Confirmation of Holding Pressure/Time
The level of holding/pack pressure influences the shrinkage rate in plastic injection molding process. Holding pressure can be increased to make the product bigger, thus helpful for shrinkage compensation.

On the contrary, product dimensions will be reduced, leading to shrinkage. However, if the holding pressure is too high, mechanical force and residue stress will be caused, leading to product deformations.

Usually, an appropriate holding/pack pressure is 70 – 80% of the max. injection pressure.

Holding Time: The holding time is correlated to cavity thickness, because a thicker product takes a longer time to cool down. Resin needs to be continuously filled during that period of time, or product shrinkage will occur. However, the molten resin cannot enter the cavity after the gate is solidified. After all, holding time is equal to the solidification time of the gate, so the gate should be appropriately designed based on product thickness. Gate solidification time is dependent on gate thickness and length.
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Wypraski wytwarzano z zastosowaniem ciśnienia docisku, a także bez niego.
The parts were molded either with or without holding pressure.

Rys. 3. Masa wyprasek z HDPE: litej i z dodatkiem różnych poroforów, wytworzonych: – z zastosowaniem ciśnienia docisku, – bez ciśnienia docisku
Fig. 3. Mass of molded parts (from solid HDPE and HDPE with addition of various blowing agents) produced: – with holding pressure, – without holding pressure


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ciśnienie docisku
Mariusz Kuklinski

https://www.proz.com/kudoz/english-to-polish/manufacturing/4...