A plastic extruder consists of three systems: the extrusion system, the drive system, and the heating and cooling system.
1. Extrusion system
The extrusion system includes the screw, barrel, hopper, head, and die. Plastic is plasticized into a uniform melt in the extrusion system. Under the pressure built up in this process, the screw pushes it continuously out through the head.
(1) Screw: The screw is the most important part of an extruder. It directly affects the extruder's application range and output. It is made of high-strength, corrosion-resistant alloy steel.
(2) Barrel: The barrel is a metal cylinder. It is usually made of heat-resistant, pressure-resistant, strong, wear-resistant, corrosion-resistant alloy steel, or a composite steel tube lined with alloy steel. The barrel works with the screw to crush, soften, melt, plasticize, vent, and compact the plastic. It also delivers the compound continuously and evenly to the forming system. The barrel length is generally 15 to 30 times its diameter. The goal is to heat and plasticize the plastic fully.
(3) Hopper: The bottom of the hopper has a cut-off device to adjust and stop material flow. The side has a sight hole and a calibrated metering device.
(4) Head and die: The head consists of an alloy steel inner sleeve and a carbon steel outer jacket. A forming die is installed inside the head. The head changes the rotating plastic melt into parallel linear movement. It guides the melt evenly and steadily into the die sleeve and gives the plastic the forming pressure it needs. The plastic is plasticized and compacted in the barrel. It passes through a porous filter plate, follows a flow channel through the neck of the head, and enters the forming die in the head. The mandrel and die sleeve fit together to form an annular gap that narrows along the path. This makes the plastic melt form a continuous, dense tubular covering around the core wire. To keep the plastic flow channel in the head reasonable and remove dead spots where plastic can collect, a splitter sleeve is often installed. A pressure equalizing ring is also used to reduce pressure fluctuation during extrusion. The head also has a die alignment and adjustment device. This makes it easier to adjust and align the concentricity of the mandrel and die sleeve.
According to the angle between the material flow direction of the head and the screw centerline, extruder heads are divided into angled heads (120° angle) and right-angle heads. The head housing is fixed to the machine body with bolts. The die in the head has a mandrel seat. It is fixed to the wire inlet port of the head with a nut. A mandrel is installed in front of the mandrel seat. The centers of the mandrel and mandrel seat have holes for the core wire to pass through. A pressure equalizing ring is installed at the front of the head to balance pressure. The extrusion covering section consists of a die sleeve seat and a die sleeve. The die sleeve position can be adjusted by bolts through a support. This adjusts the relative position of the die sleeve to the mandrel and helps control the uniformity of the covering thickness. Heating and temperature measuring devices are installed outside the head. We can machine precision parts such as screws, barrels, head inner sleeves, mandrels, and die sleeves from customer drawings.
2. Drive system
The drive system drives the screw. It supplies the torque and speed the screw needs during extrusion. It usually consists of a motor, reducer, and bearings. Hansheng Automation can also machine reducer housings, bearing seats, and drive shafts from customer drawings.
3. Heating and cooling device
Heating and cooling are necessary for the plastic extrusion process. There are two parts.
(1) The main machine of an extruder now usually uses electric heating. This includes resistance heating and induction heating. Heating elements are installed on the machine body, neck, and head. The heating device heats the plastic in the barrel from outside to raise its temperature to the temperature required by the process.
(2) The cooling device keeps the plastic within the required process temperature range. It removes excess heat generated by the shear friction of the rotating screw. This prevents the plastic from decomposing, scorching, or becoming hard to shape due to excessive temperature. Barrel cooling is divided into water cooling and air cooling. Air cooling is more suitable for small and medium extruders. Large extruders often use water cooling or a combination of both. Screw cooling mainly uses center water cooling. The purpose is to increase the solid conveying rate of the material, stabilize the output, and improve product quality. Cooling at the hopper has two purposes. First, it strengthens the conveying of solid material and prevents plastic pellets from becoming sticky and blocking the feed opening due to rising temperature. Second, it keeps the drive section working normally.
Beyond extruders, our precision custom machining capability is not limited to one industry. Hansheng Automation can machine non-standard metal parts for filling machinery, tobacco packaging machinery, medical devices, and food processing equipment from customer drawings. We also machine yacht components and RC car components. We focus on build-to-print custom machining and produce single pieces or small batches according to customer drawings. We do not sell complete machines.
