Jul 17, 2019
During plasticising in injection molding process, the melt is pushed forward by the rotating screw.
The pressure that is build up in front of the screw (P1) is responsible for her backward movement.
Backpressure (P2) is needed to withstand this backwards movement of the screw for a certain time.
This is to ensure a better mixing of color and additive, better melt uniformity, and controlling shot volume.
In the process shear heat is applied to the melt as well.
A recommended range of backpressure for most plastic materials range from 20 bar to 200 bar.
PVC on the other side uses backpressures of up to 400 bar.
Injection Molding Machine: The backpressure counteracts against the backwards movement of the screw during plasticising.
Related topics:
Screw Speed
This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Jan 17, 2019
The machine is pressing the mold halves against each other to counteract the pressure of the melt in injection and packing phase.
The needed force for this is called clamp force.
Most injection molding machines contain this value in their name.
The unit might be displayed in kN or t.
If the clamping force is too low, the mold halves will be pushed away from each other by the melt and flash appears.
The injection molding simulation helps to determine the necessary clamp force in advance to choose a machine with the correct size.
The clamp force can be estimated by multiplying the projected surface with the cavity pressure.
Injection Molding Machine: The curve of the
clamp force helps to choose the correct machine size.
Related topics:
This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Feb 15, 2019
The clamping unit of an injection molding machine is typically guided on columns. However, columnless injection molding machines are also available on the market. The clamping force is applied over a C- or H-shaped frame. The big advantage of the columnless design is the very good accessibility for mold installation and handling. In comparison to the column-guided clamping unit, the entire surface of the platens can be used to mount the mold.
Feb 13, 2025
The process in which plastic granulate is melted in the plasticizing unit and prepared in the required amount for the next injection cycle is called dosing.
During this process, the screw conveys the material forward while it melts through friction and external heating. The screw moves back axially, forming a defined melt cushion. A non-return valve prevents the material from flowing back into the rear section of the screw. The dosing amount is precisely controlled to ensure consistent cavity filling and reproducible part quality. Factors such as temperature, screw speed, and back pressure influence the dosing process and, consequently, the melt quality. Accurate dosing is crucial for the efficiency and quality of the injection molding process.
Injection molding machine: Schematic representation of the
dosing process
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.
Feb 20, 2025
The front section of the plasticizing unit on an injection molding machine, where plastic granulate is fed into the screw, is called feeding zone.
In this zone, the material begins its journey along the screw flights and is transported forwards by their rotary motion. The main function of the feed zone is to evenly intake the granulate and ensure a continuous material flow. An optimized feed zone prevents air entrapment and ensures uniform melt preparation. The temperature in this area is usually lower than in the subsequent zones, as the material is not yet fully plasticized. Factors such as screw geometry, granulate size, and moisture content influence the efficiency of the feed zone. A well-functioning feed zone is essential for stable processing and high part quality.
