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1. What is HDPE?
2. What does the cell classification of HDPE mean?
3. Why does HDPE Conduit have a memory?
4. What is regrind?

HDPE is the abbreviation for the preferred and most commonly used material to make fiber optic innerduct, High Density Polyethylene. HDPE is flexible in all weather and never gets brittle making the ideal choice for duct and innerduct products.
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The cell classification is a method of identifying and specifying the raw material properties of HDPE Conduit and Innerduct. It is a series of six numbers and one letter which describe the properties of the resin per ASTM D3350. The numbers, in order, represent the density, melt index, flexural modulus, tensile strength, slow crack growth, hydrostatic design basis, and the letter represents whether the material is black or colored.
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Actually, if HDPE conduit is laid along a trench on a warm or hot day, the conduit will eventually relax. Initially, the conduit will have a memory from winding on the real because the molecules align themselves during the manufacturing process of reeling, or "bending" the pipe. You can envision, one side of the pipe will be in tension, while the opposite is in compression. The molecules align themselves, relax and "remember" their position. Once un-reeled, they want to relax back into the original straight positions they were during the extrusion process.
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As defined by ASTM D5033, regrind is "product... that has been reclaimed by shredding and granulating for in-house use." Most manufacturers have pipe cut from production for our quality control testing. Additionally, as much as manufacturers strive to make perfect pipe, they have unanticipated shut downs (thunderstorms cut off the power occasionally) or just plain make mistakes. Manufacturers are allowed to grind this pipe, and use it in new pipe production. Typically, regrind is used in combination with virgin resin anywhere from a 10 - 40% ratio. The combined virgin/regrind pipe is tested to make sure the properties meet the specifications. ASTM, UL, and NEMA all allow use of regrind resin in their specifications.
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