Introduction to nine key elements in the process of plastic extruding

Today, in order to color printing packaging plastics extrusion laminating film manufacturers, if you want to try to save the production cost, improve product quality and effectively and give full play to the performance of the plastic extrusion equipment, must grasp the key elements of the extrusion process.

Key words: save the cost of production Improve the quality of products Master the key elements

Each plastic products production and processing enterprises, especially given priority to with color printing plastic extrusion composite packaging film production of plastic factory, every senior technical management personnel, must want to know your business very well products to raw material properties, processing technology, the performance of the extrusion equipment, product quality control, productivity, lower production costs and some other related factors, however, in the many factors, one thing is most important. Namely; Nine important element of extrusion production process. This is every composite extrusion plastic manufacturers, technical management personnel at all levels must firmly. For this, we groped through years of research, finally in the extrusion production technology have some shallow knowledge, the topic, for your reference.

First, fully understand the design requirements of extruder screw

Each extrusion laminating film manufacturers, in the use of their own extrusion machine, first to fully understand the important of screw all related to the number. We know extruder screw design is very important, even to buy a new screw, also want to be sure that the purchase of extruder screw design, whether to conform to the shape you want, function, material, and can speed the required screw. Such as, need to buy a used for the extrusion of PE screw extrusion film, you should know that it's material, heat treatment, and screw the screw thread and must complete some functions, for example, continuous adding resin, uniform melt resin, stable injection liquid homogeneous mixed resin and working cycle, such as amount of material, material bolus geometry, back pressure and screw geometry. There must be a set of screw function used in the display of data and parameters. Because, in today's world, computer simulation technology is easy and should be used for simulating all the screw, and unless you can get is suitable for the actual situation of the related data of the same material.

Because each screw wear is related to the design of the screw, a screw was wear is not necessarily a bad screw, sometimes wear even good for cylinder mixture, or when the pressure peak is beneficial to increase production, it is good to determine the position of the wear and tear, and the reason. But the actual need of wear is in trouble, that for a given input interface, is likely to mean that need higher melt temperature.

At the same time, we must grasp the development situation of the screw design, because the current by extrusion production factory is one of the most popular general screw, the manufacturers in the production of several kinds of raw materials for each, can be universal. But must grasp, understand the general screw compression screw is a kind of thread, a feeding section, a compression section and a metering section, respectively accounted for 50% of the total length of screw thread, 25% and 25%. Screw thread spacing is equal to its diameter, the screw threads of the tooth width is equal to 1/10 of its diameter. The taper machining of the compression section is gradually open, can produce compression ratio 2:1 to 3; 1, the calculation method is to use the charging period divided by the measurement of screw thread depth depth. Length of screw thread, and the screw diameter than the diameter L/D ratio is now ~ 24:1.

This kind of narrative without charging depth and the depth of measurement, it were not for the depth, compression ratio is meaningless. From different extruder manufacturers provide the screw feeding depth range between 6 mm and 10 mm screw is easy to see that the screw is 60 mm, raging, L/D, GP (general screw). These influence depth value material filling and conveying, the number of existing plastic screw cavity, material throughput, shear rate and the overall quality of the melt. Regardless of the screw of the exact depth, length, thread tooth width, by a screw or brought in the effective value for industry. The key is the general screw extruder used, and two elastic features set a direction for its future application. Features a is under the condition of without destroying the polymer performance, the function of the screw design, according to a variety of cycle and quantity of materials handling all kinds of resin, characteristics of the two is the general screw design manufacturing is the cheapest screw design.

The basic principle of extrusion plastic - each screw rotation of the cylinder and the plastic to push forward. Screw is actually a inclined plane or slope, wrapped around the center layer. Its purpose is to increase the pressure, in order to overcome the resistance of the larger, because, for each of the extruder, with resistance will need to overcome. Solid particles of wall friction laps before the screw rotation, the friction between them, the screw is not axial movement, while it may turn to rapid rotation around the circumference of a circle, but the axial force of the screw will be balanced. The single screw extruder are right hand thread, it has reverse rotation, when seen from behind because they try to spin out the back cylinder, which can exert a feeding tube of plastic melt in the big thrust forward, at the same time, also for an object to a same direction thrust, this power is ultimately fell behind the inlet of the thrust bearing.

Second, the operation stability

For various plastic manufacturers of conventional extruder, usually use will exist the following problems: 1, the improper control of technical conditions, and the motor load fluctuation will cause the fluctuation of extrusion temperature and pressure, affect the quality of extrusion products. 2, with the increase of extrusion pressure, flow quantity and leakage flow rate will increase, make the whole extrusion flow rate drops, screw drive material at the same time, the consumed power is big, the shear stress of the material is big, and energy consumption will be increased. 3, during the polymer blending modification, in order to make the extrudate with the distribution of temperature and pressure, inevitable requirement to increase the length of the metering section, but this will increase the screw processing difficulty and cost, and make the material stay time, go against processing of thermal sensitive material. How to solve this problem, we through our company imported equipment of large extruder structure were analyzed, and the best using a high temperature melt gear pump, the purpose of the gear pump, main is to make the polymer melt plasticization and metering separate, independent of sending the melt to the nose. This pump is actually a kind of is a transfer device, the outlet pressure is not affected by inlet pressure change, volume efficiency and energy efficiency is very high. It can meet the operational stability of the equipment, thus improving the quality of products requirements, and can meet the high efficiency, low energy consumption.

Extrusion machine is equipped with the melt pump at the same time, it is the biggest characteristic is that a steady extrusion pressure, can increase production, reduce wear and tear, increase the flexibility of production line and lower melt temperature, reduce the energy consumption. As a conditional plastic extrusion products manufacturers in the extrusion machine of this enterprise, can consider appropriately.

Three, heating elements

As we know, plastic extrusion plastic is heat, it melt when heated, and again when cooling solidification. Heat melt plastics, mainly feed preheating and cylinder/mould heater. But the motor also can input energy --, can overcome the resistance of the viscous melt, the friction generated in the cylinder body heat when the screw is the most important of all plastic heat source. For all other operations, should know machine barrel heater. The chief source of heat in the operation, after the barrel temperature remains perhaps the most important, because it affects the tooth or the solid material in the material conveying speed, die and mould temperature should be often melt temperature or close to the temperature. Therefore, we should bear in mind that during extrusion plastic, thermoplastics and its heating time is proportional to the amount of thermal degradation. Generally in plastics extrusion molding, in order to improve the quality of extrusion products, and should try to prevent melt thermal degradation, which should avoid melt in the die head for a long time.

Fourth, feed zone elements

Is known to all, each input feed extruder than feeding area of the cylinder and the screw surface temperature is low, feeding area of the cylinder surface, however, are almost always on plastic melting range, it is through contact with the feed grain cooling, heat from hot front-end backward heat transfer and controlled heating and maintain, or even the end by the viscous friction heat, keep and do not need cylinder heat input, the need to open the heater. The feed tube, especially the general groove dedicated to low pressure polyethylene, in order to make a single screw extruder barrel smooth feeding the thrift particles reach maximum throughput, plastic pellet should be on cylinder and slide to the screw. If these material in the root of the screw, nothing to put it down, the channel volume and will reduce the amount of solid entry. Most plastic naturally slide in the root, therefore, when they entered the is cold, and the friction force is not the root of heating to and compared.in the same heat, for example, high plasticization of PVC and some want to eventually use of polyolefin copolymer adhesive properties.

For the machine barrel, plastic adhesive in the cylinder body, so that it be removed and the screw thread to push forward. At this time between particles and wall should have a high friction coefficient, and friction coefficient to return to come over after the barrel temperature strongly influenced. If the material does not attach to, just on the rotation and not push forward, that is the reason why smooth feeding is not good.

The surface friction is not the only factor affecting the feed. Many particles always do not contact with the cylinder body or the root of the screw, so the friction inside the barrel must have a chain and mechanical and viscosity. Some of the grooved in the barrel, of course, is another story. The rest of the groove in the feed zone with barrel is thermal insulation, and depth of water cooling. Threaded push particles into the slot, and in a considerable distance to form a high pressure, which adds to the same output low amount of bite allow the screw rotation speed, so as to reduce friction heat generated by the front end, the melt temperature is lower. This may mean that accelerated cooling limit flow of film production line of flow. Therefore, in the cylinder slot is particularly suitable for PE.

Five, the screw elements at the ends of the pressure

The pressure at the ends of the screw is very important in the extrusion, the downstream pressure reflects the screw all the objects of resistance, filter and adapter duct, and the mold itself. It not only relies on the geometry of these components, also depends on the temperature in the system, which in turn affect the resin viscosity and movement speed. Although it does not rely on the screw design, except that it affects the temperature viscosity and throughput. Security elements, for each of the extruder temperature measurement is very important, if it is too high, die and mold may burst damage to the operators and the extruder. But the pressure within the barrel on mixing is good, especially in the screw measuring degrees. But too much stress will mean motor output energy, thus causing resin melt temperature is too high, but can provide pressure limit.

Six, when the plastic melting body stay within the die

All out of plastic, they melt in extrusion in arriving at the nose, the residence time in the nose is plastic is an important factor in the design of the die. In the process of extrusion, plastic material flow time should be controlled within the relaxation time and thermal stability of time, time is too short, the die swell is bigger, extrusion products will have a larger residual stress, if time is too long, the material will produce thermal degradation because of the heat impact on the quality of extrusion plastic products.

Seven, main motor and extrusion machine cylinder connected relations

All of the extruder, its main motor is the antithesis of the barrel body, barrel machine and main motor is opposite. Why the barrel control effect, and isn't always expected, especially temperature measurement zone. If the barrel body heat, the makings are compared.in the material viscosity decreases, the main motor in the more smooth barrel runtime needs less energy. Motor current down at this moment, on the contrary, if the cylinder cooling, material are compared.in the melt viscosity increases, the motor must turn more power, the current also increases.

At this moment, through the feeding tube to remove some of the main motor to heat. Usually material barrel adjuster does produce effect to melt, this is what we expected. Anywhere but the effects are not large area variables, the best way is by measuring the melt temperature to really understand the occurrence of all kinds of situation, in order to better take countermeasures.