Speed, Time and Rate - The Keys to Set the Injection Rate of an Injection Molding Machine

You cannot have the cake and eat it too. The same goes for the setting of injection rate of an injection molding machine. An appropriate foothold should be determined between production quantity and production quality when marginal benefits are considered.

Here are some tips on how to set the injection rate of an injection molding machine

Injection Rate in Injection Molding

The basic principle to set the injection rate is to increase or reduce it according to the section size formed by the flow of plastic in the mold cavity, and to follow the sequence of slow to fast to slow and as fast as possible (to identify any appearance defects). 

Quality assurance goes first
Generally, under the premise of not causing side effects, high-speed mold filling should be performed as far as possible to ensure the welding strength and appearance quality of plastic pieces, with lower pressure to reduce their internal stress and improve their strength. 

To avoid shrinkage defects
High-pressure slow feeding can make the flow rate stable, the shear rate lower, and the size of plastic pieces unvaried, so as to avoid shrinkage defects. Such "pressure" refers to the injection pressure set in the system, and such "rate" refers to the injection rate set in the system.  

Tips on inactive ingredients
For nonpolar plastics without active atomic groups (e.g., PP), an increase in shear stress causes a decrease in the viscosity of the melt, which benefits injection, as the injection rate can be used to control and adjust the viscosity of the material as a third means other than temperature and pressure. 

Relationship between injection speed, injection time and injection rate
Injection speed refers to the speed at which the screw or plunger moves during injection. As it goes faster, it takes a shorter time to complete one injection stoke, and allows greater yield. 

Injection time refers to the shortest time used by the screw or plunger to complete the longest injection stroke, or the shortest time needed for the complete injection of the material with injection capacity and volume. 

Injection rate refers to the volume flow rate that can be achieved per unit time at the time of injection, such as the ratio of injection capacity and injection time. 

To sum up the setting of injection rate of an injection molding machine, the set ideal injection molding rate should allow the most evenly molten plastic to be injected to the mold in the shortest time and solidified in a uniform state under the condition that the appearance quality of the plastic and the structure of mold remain unchanged. 

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