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What's The Difference of Injection Blow Molding Machine & Injection Molding Machine
- Mar 08, 2018 -

What's The Difference of Injection Blow Molding Machine & Injection Molding Machine

1. The process is not the same, injection blow molding is injection + blowing, injection molding is the injection + pressure, rolling plastic is squeezed + pressure; Blow to do must have that pull out of the pipe left the head, injection molding must have the gate section, the rolling plastic does not cut must have burrs.


2. In general, injection molding is a solid core, blow molding and rotational molding are empty cores. The surface of the injection molded parts is shiny, and the blow moulding and the rolling surface are not smooth. Blow molding and roll molding is more at least blow the air inlet. This is a general comparison. I don't know if you understand!!!


3. Plastic shrinkage rate and its influencing factors

The characteristic of thermoplastic is to swell after heating, shrink after cooling, and of course the volume will shrink after pressure. In the process of injection molding, the first injection of molten plastic into the mold cavity, after the completion of the melt cooling solidification, from the mold to remove the plastic when the contraction, which is called forming shrinkage. Plastic parts from the mold out to stabilize this period of time, the size will still be small changes, a change is to continue to shrink, this contraction is known as contraction. Another variation is the swelling of some hygroscopic plastics due to moisture absorption. For example, nylon 610 water content is 3%, the size increase is 2%, glass fiber reinforced nylon 66 water content of 40% when the size increase is 0.3%. But the main effect is forming contraction.

At present, a variety of plastic shrinkage (forming shrinkage and after shrinkage) method, generally recommended the German national standard DIN16901 provisions. That is to 23℃±0.1℃ the mold cavity size and after the formation of 24 hours, at a temperature of 23 ℃, relative humidity for the 50±5% conditions of the corresponding plastic parts measured the difference calculated.

Shrinkage S is represented by the following expression: s={(d-m)/d}x100% (1)

of which: s-shrinkage, D-die size, M-Plastic parts size.

If the mold cavity is calculated according to the size of the known plastic parts and the shrinkage rate of the material (1+s) in the mold design in order to simplify the calculation, the general use of the d=m/mold size:

D=m+ms (2)

If more precise calculations are required, the following are applied: D=M+MS+MS2 (3)

However, in determining the shrinkage rate, because the actual shrinkage is affected by a number of factors can only use the approximate value, so the use of formula (2) to calculate the size of the cavity also basically meet the requirements. When the mold is manufactured, the cavity is machined according to the deviation, and the core is machined on the deviation, and the appropriate trimming can be made when necessary.

The main reason why it is difficult to determine the shrinkage rate accurately is that the shrinkage rate of various plastics is not a fixed value, but a range. Because the shrinkage rate of the same materials produced by different factories is not the same, even a factory produces different batches of the same material shrinkage rate is not the same. Therefore, the factory can only provide users with the production of plastic shrinkage range. Secondly, the actual shrinkage rate in the forming process is also affected by the shape of the plastic parts, mold structure and forming conditions.