What is Plastic Extrusion?

What is Plastic Extrusion?

One of the core areas within our business is Injection Moulding, however we offer many other varied products and services. One such service that we provide is Plastic Extrusion.  And we are often asked, ‘What is Plastic Extrusion?’


Plastic extrusion is the continuous process of producing a core by forcing molten plastic granules through a die. The granules are fed from a mounted hopper into the barrel of the extruder and then heated and mixed. The melted granules are pressed into the die (which gives the molten plastic its shape) and then drawn through the extrusion tool and passed through a series of forming gates where the extruded core is cooled with water jets to set the final product.


Plastic Extrusion in more detail:


In the extrusion of plastics, the raw material compound is normally in the form of small beads that are gravity fed from a top-mounted hopper into the barrel of the extruder. Additives such as colourants and UV inhibitors are often used and can be mixed into the resin prior to arriving at the hopper. The extrusion process is similar to plastic injection moulding although it differs in that it is usually a continuous process.


The raw material enters through the feed and into the screw. The rotating screw forces the plastic beads into the heated barrel allowing the plastic beads to melt gradually as they are pushed through the barrel, lowering the risk of overheating which may cause degradation in the polymer.


Extra heat is added by the intense pressure and friction taking place inside the barrel. In fact, if an extrusion line is running certain materials fast enough, the heaters can be shut off and the melt temperature maintained by pressure and friction alone inside the barrel. In most extruders, cooling fans are present to keep the temperature below a set value if too much heat is generated.


At the front of the barrel, the molten plastic leaves the screw and travels through a screen pack to remove any contaminants in the melt. The screens are reinforced by a breaker plate since the pressure at this point can exceed 5,000 psi. The screen pack/breaker plate assembly also serves to create back pressure in the barrel. Back pressure is required for uniform melting and proper mixing of the polymer. How much pressure is generated can be altered by varying screen pack composition. This breaker plate and screen pack combination also eliminates the “rotational memory” of the molten plastic and creates instead, “longitudinal memory”.


After passing through the breaker plate molten plastic enters the die. The die is what gives the final product its profile and must be designed so that the molten plastic flows evenly from a cylindrical profile, to form the product’s profile shape. Uneven flow at this stage can produce a product with unwanted residual stresses at certain points in the profile which can cause warping upon cooling. A wide variety of shapes can be created, restricted to continuous profiles.


The product is then cooled. This is achieved by pulling the extrudate through a water bath. Plastics are very good thermal insulators and are therefore difficult to cool quickly. In a tube or pipe extrusion line, a sealed water bath is acted upon by a carefully controlled vacuum to keep the newly formed and still molten tube or pipe from collapsing.


Nordell Plastic Extrusions Cores & Tubes


Nordell have been manufacturing Plastic Extruded Cores & Tubes for almost 40 years and benefit from 24-hour production which is linked to our ERP system through real-time monitoring.


We produce a wide range of Cores, Tubes and Profiles up to 125mm diameter in a varied range of materials including HDPE, PP, ABS, HIPPS, Noryl, ASA, Polycarbonate, PCABS, PVC and more. Our full suite of modular tooling provides tube options in small batches across the entire size range both in our UK and China facilities.


Cores and Tubes can be cut and customised to requirements which eliminates the tooling costs to manufacture bespoke sizes. If you need just a few meters or a few kilometres, Nordell can offer you a solution. Let us know the diameter and quantity you require and we will be happy to quote from our standard core sizes or if you require a dedicated size and format we will be happy to prepare a tooling and parts quote.


Over 50% of our core and tube manufacture is exported to Europe and China. Our extruded cores and used in a broad array of markets including medical, pharmaceutical, commercial and food processing markets.


Nordell provide secondary processes alongside the plastic extrusion manufacture including online and offline cutting, offline notching and demand replenishment requirements.


If you have a question about Extrusion, or have a project you would like to discuss with us, then get in touch with us at enquiries@nordell.co.uk and we would be delighted to discuss this with you.


Posted 2 years ago By Nordell HQ
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