subject: Plastic extruders commonly convert granular resin feeds into sheets [print this page] Plastic extruders commonly convert granular resin feeds into sheets
Plastic extruders commonly convert granular resin feeds into sheets, films and shapes such as pipes. Normally plastic pipe is produced by extruding molten plastic through a pipe shaping die orifice of an extruder. As used herein a pipe shaping die orifice is an elongated annular opening formed between an internal mandrel and a surrounding bushing which is spaced apart from the internal mandrel.
Since the viscosity of the molten plastic is temperature dependent, temperature measurement is an important operational guide to extruder operation. Temperature control schemes generally divide the extruder barrel into temperature control zones, with a temperature control loop including a controller, temperature sensor, heater and an over temperature alarm for each zone. Band-type electrical resistance heaters of two piece construction to facilitate removal are generally employed for directly heating the barrel.
Extruders require large heater ratings to decrease heating time. After plastic extrusion lines have begun, however, heat is internally generated from friction, and at high production speeds the internal temperature, if uncontrolled, rises above the accepted maximum. Once the plastic has entered into metering section of the barrel, it is ready to be extruded into a die. The die is attached to the barrel and it represents the final shape or profile that the plastic is intended to take. The plastic is forced into the die. As the plastic moves forward into the die, it will be separated by a mandrel, which is centered in the extrusion channel.
Pressurized air is forced though the mandrel structure as a means of keeping the plastic from collapsing as it moves through the die. As the plastic leaves the die, it will enter into a vacuum environment. Inside the vacuum, there are sizing rings meant to keep the plastic in the desired shape. The vacuum environment also will be filled with water as a means of cooling the Plastic extrusion machine . After the extruded plastic has passed through the water-filled vacuum environment it can be cut or spooled as appropriate.
