The plastic extrusion of pipes, hoses and tubes is a stationary process for converting a thermoplastic raw material into a finished or almost finished ring-shaped product. The raw material is usually in the form of plastic pellets or powder. The conversion takes place in that a homogeneous melt is formed in the extruder and this is pressed under pressure through an extrusion nozzle opening that defines the shape of the product cross-section. The formed material or extrudate is cooled and withdrawn from the nozzle outlet at a controlled rate. The extrudate can then be wound onto a spool, cut to a specific length or fed to another inline process.
In contrast to injection molding or blow molding, which are circular processes, extrusion is a stationary process. This steady state property introduces some unique advantages and challenges as a manufacturing process. Extruded products are very long and continuous and usually have a constant cross-section in relation to the production axis or direction. Injection molded products are discrete items with different cross-sections in each axis. The fact that the extrusion of pipes, hoses and tubes is a stationary process is discussed in many places in this article. The terminology used to describe pipes, hoses, and tubes varies from industry to industry.
The main components of a hose, hose or pipe extrusion system are often divided into components that are upstream of the extruder, the extruder itself and those that are downstream of the extruder. Upstream components include resin handling equipment for conveying the raw materials to the extruder and resin conditioning equipment that preheats the resin or controls the moisture content of the resin before it enters the extruder feed port. The downstream components include a melt resin filter or screen changer, the extrusion nozzle unit, the quench or vacuum classifying container, any product measuring instruments, the speed controller of the extrusion line in the form of a belt or pinch roller set and finally a product separating device or winding device. There are additional extrusion processes that take the extruded product straight to another in-line process for adding reinforcement braid or adding other coatings or layers of resin.
Extrusion techniques can be used to process most thermoplastics and some thermosets. The most commonly extruded resins for pipes, hoses and pipe products include high and low density polyethylene, polypropylene, polyurethane, polystyrene, fluoropolymers, PTFE, polyester, and flexible and rigid PVC. One characteristic that often distinguishes extruded resins from injection molded resins is the melt viscosity of the plastic at normal processing temperatures. Extruded plastics often have a higher melt viscosity which allows the extrudate to maintain the shape imparted to it by the die while the extrudate is in the quenching stages. Combinations of different resins can be used to obtain specific physical, biological or chemical properties. Many additives can be used during the extrusion process to improve the processing properties of the polymer or to change the product properties. Such additives include lubricants, thermal stabilizers, antioxidants, radiation protection agents, and dyes.
The parameters that are important for extrusion processing are similar to those of injection molding processes. Resin temperature, resin pressure, resin moisture content, screw speed and screw motor amperage are normally controlled or monitored to provide a homogeneous melt at a controlled volumetric rate. The quench temperature and the rate at which the extrudate is drawn are controlled or monitored to provide a controlled product size. Dimensional measurements of the extrudate can be made using a variety of measurement methods during manufacture. In contrast to injection molding, extrusion allows the size of the end product to be varied without having to change the tool. Usual manufacturing tolerances or process consistency in extrusion are kept within 1% of the nominal measured value. Since these manufacturing processes involve steady-state conditions, any action that can stabilize any parameter or condition is beneficial to the process.
Company Name: SuKo Polymer Machine Tech Co., Ltd.
E-mail: Send e-mail
Address:No. 5 Lvshu Street, Xuejia, Xinbei District
Condition: Jiangsu, 213000