What are the conditions for PET plastic from preform to molding

Information summary

Every handicraft is produced with accurate data and various conditions. When pet plastic is injection molded, it will also undergo various debugging experiments to reduce unnecessary defective products.

, PET’s hygroscopicity is slightly larger than PBT, and pellets are more sensitive to water at high temperatures. When the water content exceeds the standard, hydrolysis will occur during molding and processing, which will greatly reduce the quality. Therefore, before molding, it must be Dry the raw materials. , The crystallinity of PET is smaller than that of PBT, and it decreases with the increase of relative molecular weight, so the molding cycle is longer, and it cannot be quickly molded like PBT. The molding shrinkage rate of PBT is relatively large, generally about .%, and glass fiber reinforced PET is .%~.%. The shrinkage rate of plastic parts obtained at high mold temperature is large, while the shrinkage rate of low mold temperature plastic parts is small. , PET products often have a certain amount of internal stress, so post-processing is usually required after molding. , The recycled material added during PET molding should be fully dry and not thermally degraded, and the added amount should not exceed %. , The rheology of PET in the molten state is non-Newtonian, and temperature has little effect on the melt viscosity. The pressure can be adjusted to increase the shear stress or shear rate. , PET has an obvious melting point, and the processing temperature range is narrow, ~ ℃, when it exceeds ℃, thermal degradation will occur.

、 The holding time of PET molding should not be too long, otherwise it will increase the internal stress, generally ~s. 、Because the PET melt solidifies faster, high-speed injection should be used to prevent the melt from filling the mold cavity as soon as possible . , PET, like PBT, is very sensitive to sharp corners and gaps. These places are prone to stress concentration, which greatly reduces the load-bearing capacity, and is prone to breakage when subjected to force or impact. Therefore, arc transitions should be adopted as far as possible for these places. , The flow channel of the PET mold should reduce the pressure drop of the melt as much as possible, avoid the use of higher melt temperature, the flow channel should be short and thick, the ratio of the surface area to the cross-sectional area should be small, and the circular flow channel should be used. , Under the premise of avoiding melt jetting, the PET gate should be opened at the thickest part of the plastic part to avoid the shortcomings of large flow resistance and fast cooling, and to ensure that it fills the mold cavity. , The opening position of the PET gate is best to face the cavity wall or the thick core, so that the flow direction can be changed, the flow rate can be reduced, so that the melt can evenly fill the cavity and avoid surface defects. , PET is pseudo-plastic when melted.

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