Manufacturing companies employ extrusion moulding to make products with a consistent cross-section. Common items found in a home made by this process include PVC pipe, rain gutters and even straws. The process works by pressing melted plastic through a die - a tool that provides the correct shape. While the extrusion moulding process offers advantages to manufacturers, it has disadvantages as well.
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Advantage -- Low Cost
Extrusion moulding has a low cost relative to other moulding processes.This stems, in part, from the efficiency of the process. Most extrusion moulding uses thermoplastics, which can repeatedly undergo melting and hardening. Leftover materials, normally discarded as waste in other processes, can be reused. This lowers raw material and disposal costs. Barring mechanical failure or planned downtime, plastic extrusion machines operate continuously. This reduces the chances of inventory shortage and allows for 24 hours-a-day manufacturing.
Advantage - Flexibility
Extrusion moulding provides considerable flexibility in manufacturing products with a consistent cross-section. To picture a consistent cross-section, imagine cutting straight through a block of cheese in several places. No matter which pieces you pick up, they all maintain the rectangular block shape. So long as the cross-section remains the same, extrusion moulding can produce complex shapes, such as decorative trims. With minor alteration to the process, manufacturers use extrusion moulding for plastic sheets. Variation on the extrusion process also allow for the manufacturing of products that mix plastic attributes, such as hard and soft surfaces.
Advantage -- Post-Extrusion Alterations
The plastic remains hot when it leaves the extruder, which allows for post-extrusion manipulation. Manufacturers take advantage of this and use a variety of rollers, dies and shoes to alter the shape of the extruded plastic to fit their needs.
Disadvantage -- Size Variances
When the hot plastic exits the extruder, it frequently expands. The expansion of the plastic at this stage of the process is called die swell. Predicting the exact degree of expansion remains problematic as it arises from different factors in the process. Due to unpredictable expansion, manufacturers must often accept significant levels of deviation from the product dimensions or tolerance. While methods exist to limit this issue, the tolerance problem largely disqualifies extrusion moulding as a method for precision parts manufacturing.
Disadvantage -- Product Limitations
The nature of the extrusion moulding process places limits on the kinds of products it can manufacture. For example, plastic soda bottles narrow at one end to accommodate a cap, which normal extrusion moulding cannot achieve. Alternatives, such as extrusion blow moulding do provide an option for these types of products, but require investment in a different type of extrusion equipment.
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