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The principle of plastic materials
1. Plastic materials most can be recycled, but due to turn plastic nozzle (material) than general material to brittle, so it can only new hybrid materials (raw materials) used together, the largest proportion of no more than 25% is appropriate, should be based on customer requirements standard principle. Various types of plastic materials due to the different melting point required, by injection pressure, production must not be confused.
. due to plastic products and color matching, so the plastic raw materials can be divided into: pumping aggregates, toner material, material, and recently appeared with liquid in the plastic raw materials, coloring. Smoke grain feedstock is have pigment mixed into raw materials, every grain of plastic materials are colored, so the formation of product has stable color uniform. Toner and color kind material is put to use in color or toner mixing raw materials, low cost, and do not store a large number of non-ferrous materials. But the color is unstable and difficult in production control unity.
Important principles editor
Mechanics
1 Mechanical Principles
The basic mechanism of extrusion is very simple - a screw in the barrel and the plastic to move forward. The screw is actually a slope or a ramp, wrapped around the center layer. The aim is to increase pressure to overcome the greater resistance. A extruding machines, there are three kinds of resistance to overcome: friction between solid particles (feed) on the cylinder wall friction and screw rotating the first few laps (area) between them; melt adhesion on the cylinder wall; melt is pushed forward the internal logistics resistance.
Most of the single - screw is right-handed, such as screw and bolt used in wood and machine. If from the back, they are the reverse rotation, because they have to do their best to turn the barrel. In a number of twin screw extruder, the two screw in the two cylinder reverse rotation and cross each other, so one must be right, the other must be left to the. In another bite twin screw, the two screw is rotated in the same direction so that it must have the same orientation. However, no matter what kind of situation has to absorb the thrust of the thrust bearing, Newton's principle is still applicable.
2 heat principle
The extruded plastic is hot plastic - they melt and melt again when they are heated. Where does the heat of melting plastic come from? Into the preheating and the cylinder / die heater may and in the start is very important, however, input energy of motor - motor to overcome viscous melt resistance when the screw is rotated generation in the cylinder frictional heat -- is the heat source of the most important of all plastic, small, low-speed screw, plastic with high melt temperature and extrusion coating applications except.
For all other operations, it is important to realize that the tube heater is not the primary heat source in the operation, so the effect on the extrusion is smaller than we expect (see article eleventh principle). The cylinder temperature may still be important because it affects the velocity of solid material in the teeth or in the feed. Die head and die temperature should normally be the melt temperature or close to this temperature, unless they are used for a specific purpose such as glazing, fluid distribution or pressure control.
3 reduction principle
In most of the extruder, the screw speed is changed by adjusting the motor speed. The motor rotates at full speed of about 1750rpm, but this is too fast for an extruder screw. If the rotation of such a rapid speed, it will produce too much friction heat and plastic retention time is too short to prepare a uniform, very good mixing of the melt. The typical deceleration rate is between 10:1 and 20:1. In the first stage, the gear can be used as a pulley block, but the second stage is also used by the gear and the screw is positioned at the last big gear center.
Sometimes the reduction rate is associated with a task that is incorrect - there is too much energy to use - and there may be a pulley block between the motor and the first deceleration phase of the maximum speed. This will either increase the screw speed to more than the previous limit or lower the maximum speed to allow the system to run at a maximum speed. This will increase access to energy, reduce the number of amps and avoid motor problems. In the two case, the output may increase depending on the material and the cooling needs of the material.
raw material
4 incoming coolant
Extrusion is the energy of the motor, and sometimes the heater, which is transferred to the cold plastic to convert it from the solid to the melt. The surface temperature of the cylinder and the screw in the feed zone is lower than that of the feed inlet. The surface of the screw rod is also cooled and cooled by the plastic feed particles (and air) from the wall of the cylinder. If the screw stops abruptly, the feed is stopped, and the screw surface becomes hotter in the feed zone because the heat is moved back from the hotter front end. This may lead to the adhesion or bridging of the particles at the root.
5 in the feeding area, stick to the barrel and slide onto the screw.
In order to make a single screw extruder, the volume of the solid particles in the feed zone of a single screw extruder reaches the maximum, the particles should stick on the cylinder and slide onto the screw. If the particles stick to the root of the screw, nothing can be put into the
PVC plastic raw materials
PVC plastic raw materials
They pull down; the volume of the channel and the inlet of the solid are reduced. Another reason for poor adhesion at the root is that the plastic may be hot in this place and produce gels and similar particles of pollution, or with the change of the output speed intermittent adhesion and interruption.
Most plastics are naturally sliding at the base as they enter the cold, and the friction is not as hot as the roots. Some materials are more likely to adhere to a high degree of plastic PVC, a non crystalline PET, and some of the final use of the adhesive properties of the polyolefin.