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WPC extrusion machine: equipment, process, formula introduction

July 26,2023

With the country’s increased investment in environmental protection industry, infrastructure areas, environmental protection new materials are increasingly welcomed and received by the market. This article on the current domestic mainstream PP PE wood-plastic products production equipment, processes, formulations to do a simple comb, for your reference.


Now, the production of wood-plastic processing is mainly divided into one-step and two-step ways.
Wpc profile extrusion lineis PP / PE back to the resin, fiber (wood fiber, bamboo fiber, rice bran, etc.); inorganic materials (calcium powder, talc); additives (lubricants, dispersants, compatibilizers, coupling agents, color powder, weathering agents, mildew agents, etc.) in the high mixer required temperature into the cold mixing machine to cool down to 40-50 degrees through the flat double granulator granulation and then added to the conical double extruder extrusion products, this is the Two-step production. The mixed material is directly added to the cone extruder without pelletizing one-step production.

II.The choice of equipment, mold

1. Mixer
The traditional mixing equipment consists of hot and cold mixing. Hot mixing is the resin, fiber, inorganic materials, additives into the hot mixing pot through high-speed movement to raise the temperature of the additives melted and dispersed in the resin and fiber inorganic materials, the more evenly dispersed material production and product quality is more stable. Material dispersion is good or bad with its blade design and blade wear level. The size of domestic hot mixing pot commonly used 200L/300L/500L/800L. Cold mixing pot is the hot mixing of materials in the cold mixing pot through the low-speed operation of the motor and the circulation of water to take away the heat to reduce the temperature of the material. The material is mixed by cold mixing to the temperature we set for production and color stability, eliminating water vapor and reducing the decomposition of the material. The common size of cold mixing pot in China is 300L/600L/1000L/2000L.
At present, many customers according to the actual material situation, in the case of moisture does not exceed 5%, the use of ordinary mixers to mix raw materials, and then directly into the granulator, the use of granulator exhaust function to remove excess moisture; in the case of moisture higher than 5%, the use of hot mixer mixing, and then directly into the granulator, the use of mixing preheating to further pelletizing, is also a method of energy-saving production.
2. The choice of granulation equipment. Used for PP / PE wood shaping granules have cone double and flat double two kinds, cone double PP / PE wood plastic granules are not very good mainly because the fiber is difficult to disperse easy to agglomerate, so as to affect the use of the product such as: products with high water absorption, easy to mildew and so on. Flat double will not appear the phenomenon of fiber agglomeration, the domestic PP / PE wood pellets basically use flat double granulation. Jwell DAYUN Plastic Recycling Auxiliary Equipment Manufacturing Co., Ltd. production of pelletizing machine, pelletizing directly after crushing, the material into the extruder, saving time and energy.
3. The choice of extruder: domestic extruder whether one-step or two-step method is basically used cone double to extrude products. Because PP / PE wood-plastic fiber content is high on the equipment (screw, barrel) wear and tear is serious, coupled with fiber, additives, PP / PE back to the material after high temperature will produce free acid will also produce a certain degree of corrosion of the screw, barrel, so the quality of the screw barrel is very important. Currently, manufacturers of double alloy screw barrel, using segmented structure, the inner hole of the whole alloy sintering technology, can extend the service life of the screw barrel.
4. Mold with the same equipment, steel quality should be good wear resistance, long service life, mold design is good or bad on the quality of the product, molding, product compactness, production speed. Especially the solid thick products on the mold requirements are higher.

III.Selection of raw materials

1. PP / PE back to the choice of material, back to the best choice of melting finger is not too high back to the best in the 1.0 or less. The color is not too dark, the particle size is uniform, the particles have no holes or fewer holes. It is best to use a level of back to the material, some back to the material has been used several times, will reduce the mechanical properties.
2. Fiber selection mesh in the 50-80 mesh or so, and ash, moisture content is lower than the best fibers (ash, moisture are less than 5%) color consistency and uniformity.
3. The choice of additives. To do a good job of PP / PE wood-plastic additives selection is very important, it is related to the stability of production, speed, product quality (product molding, mechanical properties, mechanical properties, water absorption, the product in the use of the process of whether or not there is precipitation of additives, etc.) and product life.

IV.Choice of process

Domestic production of PP/PE wood-plastic is basically a two-step method of production, the advantage is stable production and product quality.
1. The production process of raw materials:
Wood fiber is a more absorbent material in general water content of about 15% or even higher, inorganic filler also reaches 5% or so, and the water content of the high and low is to affect the stability of the production of plastics, especially wood-plastic production and the quality of the product of the natural enemy, such as affecting the foaming multiplier, the product of the water absorption rate, the product of the deformation of the products, products of the weather resistance and other physical properties.
Therefore, it is better to control the moisture within 1%. Control the reasonable moisture of the fiber and filler —– added to the high mixer —– mixed to 100 degrees —– add the appropriate amount of coupling agent —- mixed to 110-115 degrees —- turn off the motor does not move open the mixer lid for 2-3 minutes —– add PVC, stabilizers —– mixed to 80 degrees —– with lubricants and other additives —– 100 degrees plus processing aids, foaming agents ——120-125 unloading powder —– powder unloading after the motor stops and then open the lid for 2-3 minutes before mixing the next handful of material (it is best to mix five handfuls of material to clean up the mixer once) —– powder in the mixing tank to make it to 40 degrees can be pelletized or added to the twin-screw production (the mixing tank must have a cycle of water cooling). In the mixing is must pay attention to observe the temperature and time such as general cold pot mixing a handful of material in about 20-25 minutes, hot pot in about 12-15 minutes (temperature setting of about 125 degrees), if there is a difference of 3 minutes or longer, it may be the temperature sensing line problem or temperature control is not allowed, or the mixing machine bullhorn knife wear serious. This will affect the stability of the foam multiplier, color. Pelletizing often need to pay attention to the temperature control temperature is accurate, whether the fan is running normally, the size of the current, particle size, surface, length, whether the sticky material, whether the material is stable, can not break the material occurs.

2. Extrusion process: the main attention to the following aspects
a. the extruder temperature setting of each section, the key is the compression section, measuring section, mold. The accuracy of the temperature control, such as temperature control is not allowed to affect the foam rate and color. Foaming is mainly the compression section and metering section temperature setting, molding is mainly the mold temperature.
b. the normal operation of the fan of each section.
c. the size and stability of the host current. If the host current fluctuation is big, it means the sliding agent. Processing aids. Fiber and PVC components of the dispersion is not very uniform.
d. the host must maintain the same speed, because the speed of the speed will affect the foam multiplier and color.
e. the dryer temperature is generally set at 60-80 degrees between, and often kept in the barrel volume of about 80%, which is conducive to the production and color stability to improve the apparent quality of products.
f. different colors, different machines, the length of time the pellets are stored in the production of different temperature settings. And wood-plastic foaming by the external environment and other factors such as foaming multiplier has a greater impact so the operator should know the appearance of different product abnormalities when the appropriate adjustments to the industry.

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