Plastic Extrusions

At Cellular Mouldings we commonly uses plastic chips or pellets for our plastic extrusion. It is very common to add in colour to molten plastics during the extrusion application series.

The Process

The raw plastic materials, these are the pellets or chips, are treated and formed by melting.

The polymer resin is heated up until it becomes molten and liquid. In order for this to happen, a combination of heating and shear heating elements are needed from the extrusion screw which pushes the resin througha die. Each die can be a different shape, so when the resin is forced through, it is formed to the specific desired shape. Heating the polymer to the point it becomes molten as it goes through the die enables it to be extruded more easily. As it is pulled through the die it will eventually cool down and then become solidified. A caterpillar haul-off machine is used to provide tension while pulling extruded strands so they are ready to be cut to length. By having a consistent pull, we avoid having any distortions, poor quality and improves the in-out of tolerance in the production. This is where the skill is.

The extrusions screw will play a key driving force configuration. This force is entirely dependent on the application and the complexity of the die and product required.

Commonly, there are five possible zones in a thermoplastic screw.
Since the terminologies in the industry are not standardised there are some zones which are referred to by different names.

Certain screws have three zones which are the following:

- Feed zone

- Melting zone

- Metering zone

The feed zone basically feeds the resin into the extruder. Usually on the feed zone the channel depth is consistant throughout. The melting zone is where the most of the melting of the polymer happens, and in this section the channel depth gets smaller over the progression to better heat the polymer using shear heating. The metering zone is making sure the last of the particles are melted and mixed into temperature and composition. Similar to the feed zone, the channel depth is constant throughout to maintain an even heating process to ensure the polymer is equally heated as it is extruded.

Additionally, there is also a second stage for a vented screw. There is a de-compression zone which is around two thirds down the screw. The channels get deeper allowing the relief of pressure so that any trapped gases can come out of the vacuum and produce a smoother, higher quality finish. Lastly, there is the second phase metering zone. Similar to the metering zone mentioned earlier, the channels remain at a constant depth, re-pressurising the melt in order for it to go through the screen’s resistance as well as the die.

Each zone is equipped in the barrel wall for temperature control. For each zone, temperature is extremely important in terms of the characteristics and the quality and is the main contribution of how the final extrusion comes out.

Some of the most commonly extruded materials are:

- Polyethylene (PE)

- Polypropylene, acetal, acrylic, nylon (polyamides)

- Polystyrene, polyvinyl chloride (PVC)

- Acrylonitrile butadiene styrene (ABS)

- Polycarbonate

Our services

Here at Cellular Mouldings we specialise and provide good quality Plastic Extrusions bespoke to your specific requirements. If you would like to discuss further about a project, please get in touch with us through our contact page.