How Is HDPE Pipe Manufactured?
HDPE pipe is a type of plastic pipe that’s used to transfer fluids and gases or to replace ageing concrete or steel mains pipelines. HDPE pipe (which stands for high-density polyethylene pipe) is flexible, highly impermeable, and suitable for high pressure pipelines. Most commonly, HDPE pipe is used for water mains, gas mains, sewer mains, slurry transfer lines, rural irrigation, fire system supply lines, electrical conduits, communication conduits and drainage pipes.
HDPE pipe is made of food-grade polyethylene virgin material, which makes it safe for the transfer of drinking water. It is also resistant to many chemicals, which makes it a good choice for use in process plants or around corrosive environments without needing to use protective coatings (such as is required with steel pipes). Since HDPE pipe has a low thermal conductivity, it can maintain more uniform temperatures compared to metal pipes, which reduces the need for insulation to control condensation around the pipeline. Unlike metal piping systems that corrode over time, HDPE pipe does not rot, rust or corrode. With the use of HDPE pipe, water does not need to be treated to help slow the rust and pitting that is inevitable with metal pipes.
To manufacture HDPE pipe, HDPE resin is heated and squeezed through a mold in a process called extrusion. First, raw polyethylene material in the form of pellets is moved from a silo into a hopper dryer in order to remove any moisture. The raw material is then pulled out by a vacuum pump and moved into a device called the blender. Inside the blender, a barrel heater heats the raw material until it becomes molten (at about 356 degrees Fahrenheit), which makes the material soft enough to feed through a mold. The mold, called a die, shapes the molten material into its final cylindrical form.
Once exiting the die, the pipe quickly enters the cooling tank, which spray water onto the pipe’s exterior in order to reduce the temperature of the pipe. This is done in 10-degree increments; since polyethylene has a high specific heat capacity, the pipe must be cooled in stages to avoid its shape from deforming.
By the time the pipe is set onto the “haul-off tractor,” it has cooled and is solid enough to be pulled by the belts. At this stage, a laser printer prints the size, type, date, and manufacturer’s name on the side of the pipe, and the pipe is cut by a saw cutter into the appropriate length, or coiled on a coiler.
When working with striped pipe, a different type of mold is used. This mold has small channels into which the colored material is fed before it is pushed through the mold. With this process, the stripes are crafted as part of the pipe and will not separate from the main body or wash away.
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