There are two methods of manufacturing plastic tubing -these are extrusion and pultrusion. The main difference between the two is the way how the molten plastic moves through the die. In the extrusion method, the molten plastic is pushed through the die. On the other hand, in the pultrusion method, the molten plastic is pulled through.
There are a series of steps to the extrusion process. The main ingredient is a polymer resin referred to as flakes, powders, granules, nurdles, or pellets. These materials are fed into a hopper mounted on the extruder's barrel. The resin goes down the hopper feed throat into the barrel that has a screw. This crew will then move the resin toward the die. During the downward movement in the barrel, which is pushed along by the screw, the resin is slowly heated to a melting temperature. The extrusion uses automation integrated equipment to control the temperature, speed, force, tension, and time of the process. Modern extrusion is monitored by computerized equipment and IoT devices to ensure the finished product's quality matches the engineered profile.
Pultrusion method, similar to extrusion, uses a continuous feed process used to produce a tubing profile. Compared to extrusion, pultrusion pulls the reinforced fibers that have been wetted in a thermoplastic resin through the mold. Polymerization happens as the fibers integrate through the mold. This fabricating process is a low maintenance and efficient method for producing plastic tubing.
Designing for Plastic Tubing
With the wide variety of materials and applications for plastic tubing, producing tubing to fit a specific application requires a close examination of the qualities necessary. Since plastic is such a resilient material, it is easy to decide to use it as a component. The difficulty arises when deciding what will be the necessary features.
The first determination for choosing a material will be based on their mechanical properties and tensile strength. Tensile strength is the stress capacity of the plastic before breaking. The tensile strength of plastic can be rated between 12,400 psi up to over 20,000 psi.
Diameters and Wall Thickness
Plastic tubings are nominally measured by the inside diameter (ID) and outside diameter (OD), which can vary between 0.125" to 4". The wall thickness is the measurement between the ID and OD. Wall thickness is a means for determining the strength of the tubing.
The flexibility of plastic tubing varies with the material used. The most flexible among the materials are PVC and polyurethane.
Many types of fittings for plastic tubing include compression, barbed, push to connect, quick turn, flanged, threaded, and socket. These types of fittings are made to suit any specified application.
The color choices for manufacturing plastic tubing are endless, which also include translucent and transparent.
Plastic tubing can be made to any length, determined by the requirements of the application. These lengths may range from 12 inches up to hundreds of feet.
Plastic tubings are an economical choice because of their potential strength, given the low cost. One of the most significant advantages of plastic tubing over metal tubings is the cost. Producing a half dozen stainless steel tubes has an equivalent value of making hundreds of flexible plastic tubes.
The durability and strength of plastic will be directly affected by the wall thickness and the blend of raw materials. The strength of plastic tubing is defined by the amount of stress it will endure before breaking.
The main feature of most plastics is their corrosion resistance. The type of polymer used determines the degree of corrosion resistance -some of the types of corrosion-resistant plastics are polyolefins and PVC. Polyolefins are a variation of polyethylene and polypropylene. These plastic come in various densities and molecular structures for ease of design.
Anti Microbial Properties
For food-grade applications, plastic tubing can be manufactured with antimicrobial properties included in the pellets. These plastic tubings are perfect for food storage, coolers, water tubes, and medical tubing. These types of additives help prevent contamination and maintain sanitation.