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Floor Deck Roll Forming Machine Basic Mechanism

Jun 09, 2017

Floor Deck Roll Forming Machine Basic mechanism

Structure principle

For the basic mechanism of the extrusion process, simply a screw is rotated in the cylinder and the plastic is pushed forward. The screw structure is a bevel or ramp wound on the center layer, the purpose is to increase the pressure in order to overcome the larger resistance. For the extruder, there are three kinds of resistance to work to overcome: First, the friction, it contains solid particles (feed) on the cylinder wall friction and the screw rotation before a few laps (feed area) between them Mutual friction between the two; the second is the adhesion of the melt in the cylinder wall; Third, the melt is pushed forward when the internallogisticsresistance.

According to Newton's theorem, if an object is in a certain direction at rest, then the object in this direction is in balance with the balance of force. For the circumferential movement of the screw, it is no axial movement, that is to say the axial force on the screw in equilibrium. So if the screw to the plastic melt to exert a large forward thrust, then it also to another object to exert a similar size but the direction of the back thrust. It is clear that the thrust it exerts is on the thrust bearing behind the inlet.

Most single screws are right-handed threads, and if they are in the reverse direction, they are rotated backwards by rotating motion. In some twin-screw extruders, the two screws in the two barrels in the reverse rotation and cross each other, it must be a right, a left, for the bite double screw, the two screws are the same The direction of rotation, and therefore must have the same orientation. However, no matter what the situation has to withstand the backward force of the thrust bearing, still conform to Newton theorem.

2. Temperature principle

The extrudable plastic is a thermoplastic which melts upon heating and solidifies again upon cooling. So in the extrusion process requires heat, to ensure that the plastic can reach the melting temperature. So where does the heat of molten plastic come from? First, the load is preheated and the cylinder / mold heater may work and is very important at start-up. In addition, the motor enters the energy, that is, the resistance of the motor to overcome the friction of the viscous melt. When the screw is rotated, All plastic is the most important heat source, of course small system, low speed screw, high melt temperature plastic and extrusion coating applications except.

In operation, it is important to realize that the cylinder heater is not a major heat source and that it may be less effective than the one we expected. The rear cylinder temperature is more important because it affects the rate at which the solids are fed in the feed or in the feed. In general, the die and mold temperature should reach the desired temperature of the melt or close to this temperature, for some specific purpose (eg glazing, fluid distribution or pressure control).

3. The principle of deceleration

In most extruders, the change in screw speed is achieved by adjusting the motor speed, which drives the motor at a full speed of about 1750 rpm, which is too fast for an extruder screw. If such a fast speed of rotation, it will produce too much friction heat, it will be because the plastic retention time is too short and can not prepare a uniform, very good mixing of the melt. The typical reduction ratio should be between 10: 1 and 20: 1, the first stage can be either a gear or a pulley block, but the second stage is preferably a gear and the screw is positioned at the center of the last large gear.

For some slow-running machines (such as twin screws for UPVC), there may be three deceleration phases, with maximum speeds as low as 30 rpm or less (60: 1). On the other hand, some very long twin screws for agitation can run at 600 rpm or faster, thus requiring a very low deceleration rate and more deep cooling. The following are the same as the "

If the deceleration rate and work with a mistake, there will be too much energy to be wasted. It may be necessary to add a pulley block between the motor and the first deceleration phase that changes the maximum speed, either increasing the screw speed even beyond the previous limit or reducing the maximum speed. This increases the available energy, reduces the current value and avoids the motor fault. In both cases, the output may increase due to the material and its cooling needs.

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