Improving The Exhaust Performance Of Blow Moulding Die
A Blow Mould material is the most important factor to determine the manufacturing method. Aluminum is difficult to cast, only certain aluminum alloys can be cast.
Generally, the high silicon content of aluminum alloy is most suitable for casting, and high-strength aluminum alloy can not be cast, to use mechanical processing methods. Copper-beryllium alloy die has good performance. Most steel Blow Moulds are machined and zinc alloys are easy to cast.
If the cavity number is more, the cavity is complex or irregular, the cavity dimension tolerance is lower, the cavity volume is larger or the production batch is less, the casting method can be used to make the mould. The cost of casting dies is lower, but the durability and thermal conductivity are lower than that of machined moulds.
Some special casting methods can be used to manufacture high performance Blow Moulds, such as the pressure casting method can reduce the porosity of aluminum and copper-beryllium alloy, to ensure that the cavity has a high precision. The mechanical processing method of blow mould mould cavity is mainly milling, grinding and so on.
The manufacturing method of die cavity is cold extruding, hot extruding, EDM and welding. The cold extrusion method is suitable for small moulds, especially for the multi cavity mould, to ensure the consistency of each cavity.
For large volumes such as 3m. ) Die cavity can be manufactured by mechanical machining combined with welding method. It is necessary to use the method of profiling to manufacture the mould cavity when the blow mould products have high dimension precision. The shrinkage rate should be considered when designing the cavity size.
The shrinkage rate of the machined cavity includes the shrinkage rate of the blow mould products and the shrinkage rate after the die processing. For the casting cavity, the shrinkage rate of the die material casting process should also be considered. The final stage of the cavity fabrication is polishing, sandblasting or etching.
Etching, especially in the need to etch fine pattern patterns, to remove cutting, EDM, grinding or extrusion of the scale produced by processing and traces, to ensure a certain smoothness. Unless the production volume is large, the Blow Mould cavity generally does not need to be hardened treatment, also rarely coated metal (such as Chrome).
If the cavity should be hardened or chrome plated, it should be done after etching. Most of the steel or copper-beryllium alloy, such as the clamping block, the rod, the guide pillar and the guide sleeve, are machined and hardened.
When forming the same container, the amount of air to be discharged in the blow mould is much larger than that of the injection moulding mould. The air volume to be discharged in the injection Blow mould is equal to the amount of melt volume in the injection Blow Mould cavity.
And on the blow Blow Mould, to exclude the air volume is equal to the Blow Mould cavity volume minus the full die instant Parison has been blown up after the volume, the latter accounted for a large proportion, but there is still a certain air clip between the Parison and Blow Mould cavity, especially on the bucket, fuel tank, such as large volume blow products.
To blow the 120L large bucket For example, the cavity volume is about 145L, complete die-forming instant parison has been blown into a volume of about 90L, so that the final stage of blown up (about 2~38) to discharge about 55L air. In addition, compared with injection Blow Mould, the pressure in the Blow Mould die is very small (generally less than 1 NPa). Therefore, the blow Blow Mould exhaust performance requirements are higher (especially the cavity polishing Blow Mould).
If the air between the Blow Mould cavity and the parison is not discharged completely or as soon as possible, Parison can not be quickly blown, blown up after the good contact with the Blow Mould cavity (especially the edges and corners), will make the surface of the product rough, concave marks and other defects, the surface text, the pattern is not clear, affect the appearance of the product and external shape, Especially when Parison is extruded, streaks or melt rupture occurs.
The poor exhaust will also prolong the cooling time of the product and reduce its mechanical properties, resulting in uneven distribution of the wall thickness. To improve the exhaust performance of blow Blow Mould die.