Selecting Injection Molding Screws

otherwise quality and/or productivity rates will suffer. The injection unit must be capable of generating enough injection pressure (with some in reserve) to maintain consistent fill times and as a consequence, maintain the quality.
Serious thought should be given to using a heat-treated screw and barrel as these will provide longer life than non heat-treated parts. This is especially important when the material contains some level of reinforcement as this is much more abrasive and will wear out the screw and barrel sooner than material without reinforcement.
Once the screw and barrel start to wear, part quality will start to suffer and it will only be a matter of time before a replacement will be needed. This is a large cost, not just because of the cost of the replacement screw but for the loss in production.
The tip is a non-return valve at the front of the screw which allows the melt to pass through during the plasticizing stage but stops the melt from back flowing into the screw during the injection stage.
There are 2 basic designs the ball check valve and the sliding ring check valve. The ring check valve is generally preferred because it allows an easier path for the melt to pass through compared to a b

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