24-10-2014, 09:31 AM
Abstracts: Plastic extrusion of tube, hose and pipe is a steady-state process for converting a thermoplastic raw material to a finished or near-finished annular product. The raw material is usually in the form of plastic pellets or powder. The conversion takes place by forming a homogeneous molten mass in the extruder and forcing it under pressure through an extrusion die orifice that defines the shape of the product's cross section. The formed material or extrudate is cooled and drawn away from the die exit at a controlled rate. The extrudate can then be wound on a spool, cut to a specified length, or directed into another in-line process. By contrast with injection molding or blow molding,which are cyclic processes, extrusion is a steady-state process. This steady-state characteristic produces some unique benefits and challenges as a manufacturing process. Extruded products are very long and continuous, and have a cross section that is usually constant with respect to the axis or direction of production. Injection-molded products are discrete items with varying cross sections in each axis. The fact that the extrusion of tube, hose and pipe is a steady-state process will be discussed in many areas of this article. The terminology used for describing tube, hose and pipe varies from industry to industry. For the use in this article, tube products are 1” in outer diameter or less, and are products that need to be flexible in their use. Examples of tubing include medical catheters or flexible pneumatic tubing. Hose products are generally 1” in outer diameter and greater, and are products that also are flexible in their use. Garden or irrigation hose are good examples of hose products. Pipe products are generally rigid in form when compared to tubing and hose, and can be any diameter in size. Pipe products can range from ¼” diameter water pipe made from CPVC, up to 60” diameter corrugated drainage pipe made from HDPE. These naming conventions are arbitrary and are used for convenience.