High-quality transparent plastic injection molding Service by Special injection molding machines
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Because transparent plastic injection moulding has high light transmittance, so it pays a high requirement to plastic product quality, any hole, marking, whitening is not allowed.
Therefore, raw material preparation, equipment and tooling requirements, injection moulding processes and products of the material handling all should be carried out strictly.
1, Raw Plastic Material
Any impurity in plastic will affect the transparent of the plastic products. so during storage, transportation, and feeding, the material must be sealed, keeping the material clean.
In particular, raw materials containing water, heating will cause deterioration of raw materials, so they must be dried, we can use drying copper during injection. Another point is, during the drying, the air we use should be filtered, to avoid polluting raw material.
The drying process as shown below
Transparent plastic of the drying process:
Materials /Process drying temperature (℃) Drying time (h) material thickness (mm) Remarks
PMMA 70～80 2～4 30～40
PC 120～130 >6 <30 dried by hot wind
PET 140～180 3～4 dry feeding equipment is optimal
2, The cleaning of barrel, screw and spare parts.
before or after using a machine, we should clean every part with PE, PS and other washing agents, makes it clean. When the temporary shutdown, to prevent the material at high temperatures to stay a long time, causing solution drop, and barrel dryer should lower the temperature, such as PC, PMMA, PS other barrel temperature should be reduced to below 160 ℃.
3, Issues should be noted in the mold design (including product design)
Uneven cooling will cause bad plastic molding and produce surface defects and deterioration, so when design mould, we should note the following points:
a) Wall thickness should be uniform, the stripping gradient should be large enough.
b) Gate. runner should be wide enough, chunky enough, and gate location should be set according to the contraction process, if necessary, add cold slug well.
c) Part of the transition should be gradual. smooth transition, to prevent any sharp corners. PC products, in particular, must not have gaps.
d) Mold surface should be smooth, the roughness is low (preferably less than 0.8);
e) Air vent. sufficient tank will ensure to discharge the gas in melt and air.
f) In addition to PET, wall thickness should not be too thin, generally not less than 1 mm.
4, Issue should be noted in the injection moulding process (including injection machine requirement)
To decrease internal stress and surface quality defect, we should pay attention to the following aspects in the injection molding process:
a) use special screw: injection mould with separate temperature control nozzle
b) use high injection humidity
c) injection pressure: generally, we use high injection pressure, to overcome the shortcomings of high melt viscosity. but high pressure may cause internal stress, it makes stripping and deformation difficultly.
d) injection speed: the injection speed should be low, fast and slow multi-stage injection is the best.
e) holding time and the molding time: under the condition that mould filled fully, holding time and the molding time should short as possible, to minimize the melt residence time in the barrel.
f) Screw speed and back pressure: if quality to meet the premise of plastics, screw speed, and back pressure should be as low as possible and prevent the possible solutions down.
g) mold temperature: cooling system have a great impact on the quality of the product, so the mold temperature must precisely control the process, if possible, higher mold temperature should be good.
5, Other problems:
To ensure the surface quality, we should never use the release agent, because of any release agent will be displayed on the part surface.
In addition to PET, products need post-processing, to eliminate internal stress, PMMA should be in the 70-80t 4-hour hot air circulation drying. PC should use clean air or glycerin.
Liquid paraffin and other heat to 110-135 ℃, the time determined by product, the highest time need more than 10 hours. Meanwhile, in order to obtain good mechanical properties, PET needs a two-way stretch process.
Below are some transparent plastic injection molding we have made before