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Solvent bonding differs from adhesive bonding, because the solvent does not become a permanent addition to the joined substrate. [4] Solvent bonding differs from other plastic welding processes in that heating energy is generated by the chemical reaction between the solvent and thermoplastic, and cooling occurs during evaporation of the solvent.
HDPE is known for its high strength-to-density ratio. [4] The density of HDPE ranges from 930 to 970 kg/m 3. [5] Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength (38 MPa versus 21 MPa) than LDPE. [6]
HDPE pipe is a type of flexible plastic pipe used to transfer fluids and gases. It is often employed for replacing aging concrete or steel main pipelines . Constructed from the thermoplastic HDPE (high-density polyethylene ), it has low permeability and robust molecular bonding, making it suitable for high-pressure pipelines .
Polyethylene was first synthesized by the German chemist Hans von Pechmann, who prepared it by accident in 1898 while investigating diazomethane. [12] [a] [13] [b] When his colleagues Eugen Bamberger and Friedrich Tschirner characterized the white, waxy substance that he had created, they recognized that it contained long −CH 2 − chains and termed it polymethylene.
As joint gap increases, the joint strength increases to a point, then begins to decline fairly sharply. At larger gaps sufficient pressure cannot build during the fusion time, and the joint strength is low. [12] The effect of joint gap on strength is why the scraping of the pipes before welding is a critical step.
Ultra-high-molecular-weight polyethylene (UHMWPE, UHMW) is a subset of the thermoplastic polyethylene.Also known as high-modulus polyethylene (HMPE), it has extremely long chains, with a molecular mass usually between 3.5 and 7.5 million amu. [1]
The joint is then heated, typically by using a propane or MAPP gas torch, although electrically heated soldering tools are sometimes used. Once the fitting and pipe have reached sufficient temperature, solder is applied to the heated joint, and the molten solder is drawn into the joint by capillary action as the flux vaporizes. "Sweating" is a ...
The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin. The glue is sticky when hot, and solidifies in a few seconds to one minute. Hot-melt adhesives can also be applied by dipping or spraying, and are popular with hobbyists and crafters both for affixing and as an inexpensive alternative to resin casting.