The production process of raw material plastic sheets for vacuum forming process has a certain complexity. Not all plastic sheets will be suitable for the thermal forming process. Generally, the extrusion plate can be used for vacuum forming process, therefore I will do a simple description of the extrusion process of plastic sheet, this is just like the research I provide for discussion in this article, it is based on the simple description of our plastic sheet production line. If there are errors that exist, warmly welcome our readers to correct them.
Raw Material:
We first purchased the raw materials from the raw material supplier. The raw materials are granular in the bag, as shown in the figure below. The main examples of this article are ABS materials, but no matter what material we use, ABS, HIPS, HDPE, or others, the original materials are extrusion granular.
Material tube and spiral pole-
The material tube and spiral pole are the main part of the extrusion machine. The tube is a cylindrical container with a spiral pole. The friction and shear force produced by the spiral pole/screw pole during the rotation process melted the raw materials granular and then transmitted them to the head part through the barrel channel. The internal environment of the tube is determined by the high-speed rotation of high temperature, high pressure, and internal transmission of the tube. Therefore, the extrusion machine, the tube, and the spiral pole can be worn during operation, which reduces the performance of the extrusion machine. The wear situation is mainly divided into three categories, namely adhesion, rubbing wear, and corrosion wear. The adhesion wear is due to the contact between the spiral pole thread and the tube wall. The rubbing wear is caused by the addition of solid particles, inorganic fillers, or some solid additives of the raw material. Although this wear is sometimes caused by the particles of the tube and the spiral pole surface, most of them are caused by the fine gap between the particles being sandwiched between the thread and the tube wall……corrosion wear is caused by chemical reactions caused by the moisture and thermal decomposition of polymer melting substances during the processing. Most ingredients of the extrusion machine are made of steel or synthetic metals treated with nitride. Nitride treatment technology is a technology that enhances metal abrasion resistance. Synthetic metal tube refers to their internal use of alloys to enhance their abrasion and corrosion resistance, and the outside is made of the structure. Compared with nitride, dual metal tube is durable. At present, the materials used in the dual metal tube are carbonized composite, chromium-modified-boron iron, and nickel alloys.
Most of the spiral poles are slightly worse than the ingredients, which are generally carbon alloy steel, and the wear-resistant screw is made of other materials as a whole, or the surface modification of the steel screw or a layer of resistance to the screw surface is attached to the surface of the spiral pole substance. The most serious part of the extrusion machine is the outside of the board of the spiral pole. To protect the outside of the plate to protect the screw, it is usually welded with a layer of hardening alloy on its surface for reducing costs.
when the temperature of the tube is generally divided into 7 areas to control the processing ABS material sheet, the temperature of each area is controlled between 195 and 230 ℃; when the HIPS board is processed, the temperature in each area is controlled between 180 and 220 ℃. In order to ensure that ABS/HIPS raw materials can be plasticized in the tube, the temperature of each area must be adjusted according to the plasticization of the original material.
ABS/HIPS raw materials have a very important impact on the ABS/HIPS extruded sheets during the extrusion process. The temperature of the barrel is too low, which can easily cause ABS/HIPS raw materials to be plasticized in the tube, so it is in this way are raw materials in the extrusion sheet; the temperature of the tube is too high, which can easily lead to excessive heat and aging in the tube in the tube, resulting in a decline in the mechanical properties of ABS/HIPS extruded sheet. The ending of the inner linery is cracking during use. It is worth noting that during the long-term operation of the spiral pole, the raw materials accumulated at the dead corner of the screw pyramid trough due to long-term heating, and carbonizes are formed. Affects the surface and internal quality of the plastic sheet.
Diversion board and filter
The diversion and the filter are set in the transition area between the oral mold and the screw head. Its role is to change the material flow from a spiral movement to a straight line motion, prevent the inspiring particles from entering the oral mold, and filter the carbide and other impurities. In addition, the diversion plate and filter can also improve the melt pressure and make the extruded plates dense. When the material is passed through the hole, it can be further plasticized to achieve the purpose of controlling plasticized quality. There are many forms of diversion plates. The ABS/HIPS extrusion machine uses a flat-type diversion plate. The principle of the distribution of the hole eye distribution on the shunting plate is to make the material flow velocity evenly. The diameter of the hole eyes is generally 3 ~ 7mm, and the total area of the hole eye is about 30% to 50%of the total area ofthe shifting sheet. The thickness of the diversion is determined according to the size of the extrusion machine and the pressure of the shunting sheet. Its experience data is about 20%of the inner diameter of the tube. The diversion plate is generally made of stainless steel. The tunnel should be smooth and have no dead ends. In order to facilitate the cleanup of materials, the tunnel feed end should be poured out of the diagonal angle. The distance between the diversion plate from the screw end should not be too large, otherwise, it is easy to cause material storage and accelerate the decomposition of plastic; if the distance is too small, the material flow is unstable, affecting the quality of the extruded plate, generally controlled at about 0.1d (D is the diameter of the screw). Almost all material manufacturers add a different proportion of regeneration returns during the extrusion process of ABS/HIPS sheet, so the importance of melting filtering in the extrusion out of ABS/HIPS raw materials is increasingly valued, because even a small amount of impurities will have a great impact on the appearance and performance of the extrusion material sheet, so the use of filters will have an important role in the quality of the extrusion material sheet. The filter is generally made of iron mesh or stainless steel mesh composed of densely prepared and then placed on the filter switch with a filter with a multi-layer different meson. The combination of frequently used mesh combinations is 40 mesh+80 mesh and +100 mesh+40 mesh. The filter switch is divided into two types: round-trip and continuous. The round-trip type is the same right of the same right or more filters. One of them is used in the melting resin. replace. Continuous filter exchanges are continuously invested in new filters. They go out to block filters at the same speed. According to changes in the impurities in the resin, the movement speed of the filter is automatically adjusted.
Three rollers set the machine
When the melt came out of the machine, the temperature was high. Immediately entered the three-roller machine, and the three-roller machine pressed the light and gradually cooled. The three-roller machine consists of three rollers with a diameter of 200 ~ 400mm, and the steam (water or oil) inner steam (water or oil) in the roller is controlled. When installing the three-roller light machine, the coaxial axis can be installed as much as possible, and the depression does not exceed 0.025mm. The three-roller machine can also play a certain traction role, and adjust the line speed of each point of the board to ensure the straightness of the board. At the same time, the roller speed of the three rolls should be matched with the speed of the screw to ensure that the plate is stretched evenly. When the ABS/HIPS board is extrusion out, the temperature of the three rollers generally controls the following temperature range: upper roller: 40 ~ 80 ° C; upper roller: 40 ~ 70 ° C; lower roller: 40 ~ 60 ° C. The distance between the three-roller light machine and the head of the machine should be as close as possible, generally, 50 ~ 100mm, and the distance is too large. Material texture has a special roller over this part, you need to customize a certain roller and just put the corresponding roller on the machine, after heating the plastic pellets to form the sheet, then after the roller printing can form the texture. Then you may wonder, what if I want to customize a new, different texture from the one described above? This is certainly possible, as long as the quantity of the product order is large enough, then a new roller can be made to print a new texture. If the number of products is not very large, we do not recommend making a new pattern because the cost will be quite high.
Traction devise and cutting device
The traction device is generally the lower roller is an active roller, and the upper roller is a passive roller. To increase friction, the upper roller is often a rubber roller. The diameter of the roller is generally 150mm. Its role is to pull the board evenly to the shear device to prevent the three rollers from accumulating and flatter the plastic sheet. It must be noted that the roller speed of the traction device is kept consistent with the line speed of the three-roller light machine roller. Prevent the plates from being excessively stretched and wrinkled on the surface of the pocket. The cutting of ABS/HIPS boards includes cutting edges and tailoring. During the extrusion of the plastic sheet, both sides are often uneven and not neat, so a part must be cut off. Generally, the cutting knife is used to cut the edge. The main part of the tailoring device is usually composed of cutting beds and counting recorders. The size of the cutting bed has a great impact on the quality of the simple sheet shear. Because the gap is too large, it is easy to cause the edge of the shear (especially the HIPS material sheet) to cut the residual “deburring” affects the subsequent processing of the sheet
With the continuous development of science and technology, the manufacturing of the extrusion machine is improving in the direction of satisfactory product quality and production efficiency. To improve the efficiency of torque transmission to improve the production efficiency of the extrusion machine, but during the extrusion process of the ABS/HIPS/HDPE material sheet, how to accurately control the temperature, pressure and other engineering variables during the extrusion process to maximize the reduction of the maximum reduction unqualified quality and obtaining high -quality ABS/HIPS material sheet are the goals we are seeking for.
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