Machinery's Handbook, 31st Edition
Plastic Tube 2775 because LDPE has poor environmental crack resistance, which can be accentuated when solvents are present. HDPE is similar to LDPE in terms of material compatibility. It is fairly opaque, and is more dense and rigid than LDPE. Polypropylene has high impact resistance combined with good stiffness and excellent chemical resistance. PP is often mixed with polyethylene or rubber to improve its impact and low temperature properties. PP is more heat resistant than PE, with an operating range up to 60°C. Nylons can be used at elevated temperatures. They cost more than PE and PP, but exhibit superior abrasion resistance and stiffness. Types 11 and 12 are more flexible than type 6, and have better chemical resistance to acids and bases. Silicone tubing is suitable for elevated temperatures and can be sterilized using heat. It is extremely soft and flexible, and is non-toxic. There are different ways to cure silicone tubing, so material properties may vary. Polyurethane tubing is flexible and can be relatively transparent. This type of tubing has good abrasion resistance and tensile strength. It is flexible at low temperatures and holds its properties over time. There are two types of polyurethane: esters and ethers. Esters have good chemical and oil resistance. Ethers have good water compatibility and are suit- able for outdoor applications. Both can be made FDA compliant. Fluoropolymers are chemically inert and often chosen for harsh applications or high purity applications. They are also suitable for high temperatures in the 300–500 °F (148–260 °C) range. Rigidity varies with composition, but they are generally stiff but bendable. FEP is flexible and transparent. PEEK is fairly rigid but bendable, has excellent mechanical stability and chemical com patibility, and can be used to 100 °C. It is often used where stainless steel tubing has mate rial compatibility issues. PEX tubing is of the same material and properties as PEX piping, discussed in the sec- tion Plastic Pipe starting on page 2767. It comes in a variety of colors, or a natural hazy clear state. There are many more materials than those listed. In addition, there are many brand- name and proprietary formulations. Sizes: Most plastic tubing is sized according to OD, ID, and wall thickness. A wide vari ety of sizes are available for each material. PEX tubing is sized according to the Copper Tube Size standard for outer diameter. Standard PEX dimensions are given in Table 20. Table 20. Standard PEX Dimensions Nominal PEX Size inch Outside Diameter inch Inside Diameter inch Wall Thickness, inch 3 ⁄ 8 0.500 0.350 0.070 1 ⁄ 2 0.625 0.475 0.070 5 ⁄ 8 0.750 0.574 0.083 3 ⁄ 4 0.875 0.677 0.097 1 1.125 0.863 0.125 All dimensions are in inches. Pressure Ratings: Care must be taken when using plastic tubing because pressure ratings are generally much lower than with metal tubing. In addition, if vacuum is to be used in the system, the tubing must be vacuum rated to ensure that it does not collapse. Pressure rating will depend on material, diameter, and wall thickness. Consult the manufacturer’s pressure rating when specifying plastic tubing.
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online