Understanding Rubber and Plastic Extrusion

September 23, 2015
Understanding Rubber and Plastic Extrusion

Extrusion technology is a profile-driven process that works on a cross-sectional track. The fabrication process is immensely popular in industry as a means of producing long components that can serve in the home or in industrial applications. For example, common rubber and plastic extrusion examples are seen everyday in the plumbing industry. Long PVC pipes carrying waste and water have been formed in these extrusion facilities by special machinery. Even a tiny bendable plastic straw uses this technique, a process referred to as profile extrusion. As briefly touched upon earlier, this type of work is reserved for parts that are formed with a continuous cross-sectional area, so pipes, hoses and tubing are fabricated in these profile extruders.

Uniformity is always a strong point in an engineering process, but rubber and plastic extrusion techniques need a little more versatility in order to satisfy the countless applications for the polymer production technology. Blown film extrusion is the next entry in this fabrication family. Blown film extrusion uses lengths of thin plastic to make plastic bags and sheets of polymer-derived products that can be used to wrap food or package fragile items. The material fabrication process, in this case, uses a vertically-mounted die and an annular opening. The molten plastic is pumped through the opening and shaped into a sack-like bladder by a central column pitted with openings. The openings release air, blowing the film into a bubble, which cools to form the film. Nip rollers and a slitter station process the collapsed bladder into sheets and bags.

The horizontal handling of a rubber and plastic extrusion cycle is a more common sight than the alternative blown film example, although both techniques are kept busy by client demands for countless extruded products. A rubber insulated electrical cable, for instance, is formed by the profile technique using special rotating screws and a top-mounted hopper filled to capacity with an elastomer that exhibits electrical resistance characteristics. The melted source material is liquefied further by screw action in a cavity, exiting the die to fall into a cooling trough of water. A cutting station and rollers slice the extruded parts to size and convey them forward to the next processing point.

It would do the technique a disservice to focus on round profiles, the pipes and tubes that are used in every conceivable piece of machinery. Angled components with uniform areas are produced on these machines, as are irregularly shaped hoses. Finally, imagine open-ended products, lengths of opaque plastic used, perhaps, as shades for fluorescent lighting fixtures. Friction, pressure and cavity deformation can extrude any number of these uniformly fabricated parts at speed, shearing each one to length at the end of the production line.