The extrusion process is one that predates plastic itself but it’s one that has become synonymous with plastic applications today. To get the perfect extruded part, plastic manufacturers use several techniques, machines and methods.

To help extruders save money, yield higher quality products, and use equipment more efficiently, industry expert Allan L. Griff put together 10 important principles to keep in mind. We take a brief look at these principles in this three-part post.

The feed acts as the coolant

The entering feed is cooler than the barrel and screw surfaces in the feed zone. The barrel surface in the feed zone, however, is almost always above the melting range of the plastic. It is cooled by contact with the entering particles, but is kept hot by the conduction of heat backward from the hot front end, as well as by controlled barrel heating. Even when the front end is kept hot by viscous friction and no barrel heat input is needed, the rear heaters may need to be on.

Stick to the barrel and slip on the screw, in the feed zone

For maximum solids conveying in the feed zone of a smooth-barrel, single-screw extruder, the particles should stick to the barrel and slip on the screw. If the particles stick on the screw root there is nothing to pull them off; channel volume and the infeed of solids are then reduced. Sticking to the root is also undesirable because the plastic may cook there and produce gels and similar contaminant particles, or stick and break loose intermittently with corresponding changes in the output rate.

Material is the greatest expense

In some cases, material costs represent as much as 80 percent of the total manufacturing cost. This principle naturally leads to two further conclusions: Processors should reuse as much trim and scrap as possible in ways that replace virgin material, and keep very close thickness tolerances as anything greater than the aim thickness is wasted and anything less risks product failure.

Don’t miss part three of our post where we look at four more principles of extrusion.

Plastic & Chemical Trading together with our international partners deliver world class extrusion solutions to South Africa. If you’re in the market for a plastic manufacturing solution that can stand the test of time, contact Plastic and Chemical trading today.

Source: Allan L. Griff

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