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.

Backpressure in Injection Molding

Injection Molding Machine: The backpressure counteracts against the backwards movement of the screw during plasticising.

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Screw Speed

This glossary of plastic industry is provided by PLEXPERT Canada Inc.

Clamping Force

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.

Clamp Force in Plastic Industry

Injection Molding Machine: The curve of the clamp force helps to choose the correct machine size.

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This glossary of plastic industry is provided by PLEXPERT Canada Inc.

Columnless Injection Molding Machine

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.

Columnless Injection Molding Machine in Plastic Industry

Injection molding machine: A movable platen of a columnless injection molding machine.

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Setting up

This glossary of plastic industry is provided by PLEXPERT Canada Inc.


When planning a production hall for plastics processing the footprint of every machine is very important.
Not only the space for the machine, but also the space for the necessary peripheral devices needs to be considered.
In addition to that the height of the machine is important in order to check if a hall crane can be used to mount/unmount molds.
The dimensions of the machine are available in a technical drawing or in a 3D-model.
The footprint is an important factor in the calculation of the part costs as well. The larger the footprint, the higher the part costs.

Footprint in Plastic Industry

Injection Molding Machine: Technical drawing of an injection molding machine to calculate its footprint.

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Connection Load

This glossary of plastic industry is provided by PLEXPERT Canada Inc.


In injection molding, the resin to be processed is fed via a hopper into the injection molding machine.
The shape of the hopper can be rounded or squared. The hopper leads into a cylindrical drain inlet connected to the screw cylinder.
The hopper can be moved in axial direction before a material change.
This way its content can be released before it is filled with another material.
The filling of the machine hopper is either be done manually or automatically via a central material supply.
Depending on the application, the hopper is often also equipped with dryers or mixers.

Hopper in Plastic Industry