Whether it is a one-hundred-yard-long tube or a thousand crazy straws, plastic extrusion is frequently used in today's plastics industry because it is readily available and easy to operate. The plastic extrusion machine with water ring process involves melting the plastic material, pressing it into a mold, forming it into a continuous profile, and then cutting it into a certain length. For applications that require a constant cross-section of the final product, this process is a good choice. Low cost and high productivity make it a popular manufacturing choice for pipes, plastic films, weather strips, wire insulation and tapes, just to name a few common plastic extrusion products. We will find more about pvc extruder and plastic extrusion in this article.
The following knowledge points are listed below:
l The plastic materials that used in the pvc extruder
l The process basics of the pvc extruder
Before starting the plastic extrusion process, appropriate machinery and materials must be obtained, especially a plastic extruder. This equipment is a fairly simple machine that facilitates the extrusion process from beginning to end. The main components of the pvc extruder include hopper, barrel, screw drive and screw drive motor.
The second most important component is the thermoplastic raw material used for extrusion. Most extrusion operations rely on resin plastic (small solid beads) to achieve simple loading and fast melting time. Commonly used plastic materials in the extruder process include high impact polystyrene (HIPS), PVC, polyethylene, polypropylene and ABS.
The last part required for plastic extrusion is the mold. The mold is used as a plastic mold in plastic high speed extruding machine, and the mold allows the molten plastic to flow uniformly. Molds usually have to be customized and may require additional lead times before starting the manufacturing process.
The plastic extrusion process starts by putting the raw resin into the hopper of the pvc extruder. If the resin lacks additives required for special applications (such as UV inhibitors, antioxidants or colorants), add them to the hopper. After the resin is in place, it is usually gravity fed into the extruder barrel through the feed port of the hopper. There is a long, rotating screw inside the barrel, which pushes the resin in the barrel toward the direction of the mold.
When the resin moves in the barrel, it is exposed to extremely high temperatures until it starts to melt. Depending on the type of thermoplastic, the temperature of the barrel ranges from 400 to 530 degrees Fahrenheit. Most pvc extruders have a barrel, and the heat from the charging end to the feed tube is gradually increased in order to gradually melt and minimize the possibility of plastic degradation.
Once the molten plastic reaches the end of the barrel, it is forced through a screen and into the feed tube leading to the mold. Due to the high pressure in the barrel, the screen is reinforced by a crushing plate to remove possible contaminants in the molten plastic. The porosity of the screen, the number of screens and other factors can be controlled until uniform melting occurs due to proper back pressure.
Once in the feed tube, the molten plastic is fed into the mold cavity, where it cools and hardens. In order to speed up the cooling process, the newly formed plastic uses a sealed water bath. In the case of plastic film extrusion, cooling rolls replace the water bath.
When manufacturing plastic bottle extruded machine products, maintaining the correct temperature level and melting rate of the resin is an important consideration. The optimal temperature maximizes the uniform fluidity of the plastic and minimizes the possibility of stress and warpage in the final product. Variables such as pressure and friction accumulate in the extruder barrel, meaning that the temperature will not remain constant. The heater must be monitored, lowered, raised, or turned off as needed to maintain constant heat in the cooling fan of the extruder, and the cast heater jacket also helps to maintain the proper extrusion temperature.
Since heating rate, feed rate and other overall extrusion factors directly depend on the only moving part in the plastic extruder, the screw must carefully consider the size and design of this part. The calculation of screw diameter and length is based on melting rate, resin size, raw plastic type, and pressure required to maintain uniformity. For the application of composite materials in the extruder barrel, a twin-screw design can be used to achieve full mixing.
Many applications require specialized extrusion processes to obtain sufficient results or speed up the production process. Common special extrusion processes include:
(1) Blown film extrusion: used to make plastic film products, such as grocery bags and food storage bags. In this process, the mold is characterized by an upright, cylindrical design, which pulls the molten plastic upwards during molding and cooling.
(2) Co-extrusion: Extruding several layers of materials at the same time. Two or more pvc extruders feed different types of plastic into one pvc extruder head.
(3) Outer sheath: Extrusion is used to cover items on a protective plastic coating. The outer sheath of wires and cables is the most common application of outer sheath.
(4) Pipe extrusion: similar to traditional extrusion, but the mold includes internal pins or mandrels to facilitate the production of hollow plastic materials.
That's all about the twin screw pvc extruder.
