PC board processing secondary processing forming process
PC sheets processing should strictly control the moisture content of polycarbonate below 0.02% to prevent the mechanical strength of the molded product from being reduced or the appearance of bubbles, silver streaks and other abnormal appearances. In order to prevent abnormalities caused by moisture, the polycarbonate should be dried by a hot air dryer for more than 3-5 hours before processing, and the temperature should be set to 120℃, or the moisture can be treated by a de-temperature dryer, but the dehumidified air is in the funnel. There should be a dew point of 30°C at the entrance. 1 Moisture control PC plastics will hydrolyze and break bonds, reduce molecular weight, and reduce physical strength even when they encounter very low moisture. So before the molding process. Extrusion molding In order to meet the needs of various extrusion molding processes, polycarbonate has different melt index specifications. Usually the melt index is between 5-25g/lOmin, which can be applied to extrusion molding. However, the best processing conditions are quite different due to the type of extruder, the shape of the molded product, and the specifications of polycarbonate, and should be adjusted according to the actual situation. 3 Key points of extruder selection 1. The clamping pressure is 0.47-0.78t per square centimeter or 3-5t per square inch by the projected area of u200bu200bthe waste product. Generally, the weight of the waste product is about 40%-60% of the capacity of the extruder. For ** If the capacity of the machine is expressed in polystyrene, it is usually necessary to reduce it by 10%. The length of the screw screw should be 15 diameters at least, and its L/D should be 201** and the compression ratio should be (1.5:1-301) The stop valve at the front end of the screw should adopt a sliding ring type, and the resin flowable clearance should be minimal. There is 3.2mm 4. The nozzle tip opening should have a diameter of 4.5mm at least.) If the waste mass is 5.5kg or more, the nozzle diameter should be 9.50mm or more.
processing In addition, the tip opening needs to be 0.5-10mm less than the gate diameter and the shorter the segment, the better, about 5mm. 4 Key points of molding conditions ①Melting temperature and mold temperature **Molding temperature setting is related to many factors, such as extruder size, screw configuration, mold and molded product design, and molding cycle time. Generally speaking, in order to gradually melt the plastic, set a lower temperature in the rear section/feeding zone of the material pipe, and set a higher temperature in the front section of the material pipe. However, if the screw design is improper or the L/D value is too small, the reverse temperature setting is also possible. In terms of mold temperature, the warm mold can provide a better appearance, the residual stress will be smaller, and it is easier to fill thin or long molded products. To a lower temperature can shorten the molding cycle. ② The rotation speed of the screw is generally recommended to be 40-70r/min, but it needs to be adjusted by the design of the machine and screw. ③Extrusion pressure In order to fill the mold as quickly as possible, the larger the extrusion pressure, the better, generally about 850-1400kg/cm2, and it can be 2400kg/cm2lkg/cm2u003d0.098MPa ④The back pressure is generally set as low as possible, but for demand The feed is uniform, it is recommended to use 3-14kg/cm2. ⑤Extrusion speed The shooting speed has a lot to do with the gate design. When using direct gate or edge gate, the application is slower in order to prevent sun and wave flow marks. The rate of fire. In addition, if the thickness of the finished product is above 5mm, in order to prevent bubbles or dents, slow injection will help.
processing Generally speaking, the firing rate principle is that the thinner is fast, and the thicker is slow. Switch from extrusion to holding pressure, and the holding pressure should be as low as possible to avoid residual stress in the molded product. The residual stress can be removed or reduced by annealing; the condition is that the barrel is cleaned at 120-130℃ at the molding temperature of polycarbonate, and the cleaning material (polystyrene) is added for continuous injection 20-30 times. Move the machine back and continue to empty the cleaning material until the injected cleaning material starts to expand and foam. Reset the barrel temperature to 200-230°C. Continue to spray the cleaning material until the melting temperature of the cleaning material reaches 260°C and the surface looks clean and transparent.
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