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 AFST (F Estrada) Industrial Co., Ltd > News |
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| Transparent plastic injection molding plastic injection molding knowledge --- Introduction |
| Published Time:2019-01-16 14:35:37 |
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In the plastic injection molding, the transparent plastic processing for knowledge description and requirements
The company has more than ten years experience in injection molding, injection molding machine size from 60 grams to 1200 grams, the quality system, from mold making to injection molding, painting, screen printing, assembly, full-service, products related to auto parts, electronic communications, audio, home appliances, daily necessities, stationery, municipal facilities, poultry husbandry and health and other fields.
Transparent plastic due to the high transmission rate, an inevitable requirement demanding surface quality of plastic products, can not have any markings, pores, whitening. Fog halo, black spots, discoloration, poor gloss and other defects, so in the injection molding process on raw materials, equipment. Mold, and even product design, have very strict attention and even made a special request. Second, because of clear plastic, mostly high melting point, poor mobility, so as to ensure the surface quality of products, often in the machine high temperature, injection pressure, injection speed and other parameters to make minor adjustments to make when both full of plastic injection mold, not will produce distortion products caused by internal stress and cracking.
Therefore, from raw material preparation, equipment and tooling requirements, injection molding processes and products of the material handling aspects of the operation should be carried out strictly.
(A) the preparation of raw materials and dry as any point in the plastic contains impurities, may affect the product's transparency, and storage and transportation. Feeding process, must pay attention to sealing to ensure the material clean. In particular, raw materials containing water, heating will cause deterioration of raw materials, they must be dry, and in the injection, the feeding must use the drying hopper. Also note that the drying process, the input should preferably be filtered air, dehumidification, to ensure no contamination of raw materials.
Transparent plastic of the drying process:
Materials Technology drying temperature () Drying time (h) material thickness (mm) Remarks
pmma 70 ~ 80 2 ~ 4 30 ~ 40
pc 120 ~ 130> 6 <30 with hot air circulation drying
pet 140 ~ 180 3 ~ 4 better than using a continuous drying feeder
(B) of the barrel, screw and cleaning accessories
To prevent pollution and raw materials and accessories for depression in the screw there is old material or impurities, in particular, poor thermal stability of the resins exist, so before use, are applied after the shutdown clean screw the pieces of cleaning agent, it may not stick with impurities, when there is no screw cleaning agent, the available pe, ps and other resin cleaning screw. When the temporary shutdown, to prevent raw materials at high temperatures to stay a long time, causing solution drop, and barrel dryer should lower the temperature, such as pc, pmma other barrel temperature should be reduced to below 160 . (Hopper temperature for the pc should be reduced to below 100 )
(C) in the mold design should pay attention to the issues (including product design)
To prevent back flow of poor, uneven cooling caused by plastic molding or negative, resulting in surface defects and deterioration in general in the mold design, should note the following points.
a) wall thickness should be uniform, stripping slope be large enough;
b) part of the transition should be gradual. Smooth transition, to prevent any sharp corners. Have sharp edges, especially pc product must not have gaps;
c) gate. Flow as large, chunky, and should be set according to location of the gate during the cooling contraction, when necessary, add cold slug well;
d) the mold surface should be smooth, the roughness is low (preferably less than 0.8);
e) vent. Tank must be sufficient, and when the exhaust gas in the air and melt;
f) In addition to pet, the walls should be no thin, generally not less than lmm.
(D) injection molding process should pay attention to the issues (including the requirements of injection molding machine)
In order to reduce the quality of internal stress and surface defects in injection molding process should pay attention to the following aspects.
a) should use special screw, with separate temperature control of injection molding machine nozzle;
b) plastic resin injection temperature did not decompose in the premise, to use the higher injection humidity;
c) injection pressure: generally higher melt viscosity in order to overcome the shortcomings, but the pressure is too high will produce stripping difficulties caused by internal stress and deformation;
d) Injection speed: the case of filling in the meeting, the general should be low, preferably using slow fast and slow multi-stage injection;
e) holding time and the molding cycle: to meet the product filling, no depression, the case of the bubble; should be as short as possible to minimize the melt residence time in the barrel;
f) screw speed and backpressure: in meeting the premise of quality plastics, should be as low as possible and prevent the possible reduction solutions;
g) Mold temperature: cool products, good or bad, a great impact on the quality, so the die temperature must be able to precisely control the process, if possible, higher mold temperature should be good.
(E) Other issues
In order to prevent the deterioration of surface quality on general release agent injection with as little as possible; when material shall not go back more than 20%.
For the addition to pet, the products should be post-processed to eliminate stress, pmma should be 70-80t hot air circulation drying 4 hours; pc should be clean air, glycerol. Liquid paraffin and other heating 110-135 , the time determined by product, the highest for 10 hours. The pet must be biaxially oriented processes in order to obtain good mechanical properties.
Manufacturing company with over ten years experience in injection molding, injection molding machine size from 60 grams to 1200 grams, the quality system, from mold making to injection molding, painting, screen printing, assembly, full-service, products related to auto parts , electronic communications, audio, home appliances, daily necessities, stationery, municipal facilities, poultry husbandry and health and other fields.
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