How much plastic can you inject in one mould

Precious Plastic Machine Development
#1

Hi,

What would be the maximum amount of molted plastic you could push into a mould with the injection machine, without the quality of the product deteriorating? Could you fill up a mould in multiple pushes, allowing for products that need more plastic? I am thinking about products that are 10x10x10cm (not solid, for example a lampshade). Of course there’s also the compression machine, but I wonder if it’s more efficient (time needed, energy consumption) compared to injection when using one mould. Of course you could put multiple moulds in the compression oven, but that will cost more. Is there also some kind of maximum weight you can screw underneath the injection machine (mould+plastic)?

Cheers, Erik

#2

As far as I could remember, ~30mm inner diameter (ID) pipe is used for injection. Suppose you have just 30cm length for the column, the pipe has a capacity of 850cm^3.

For your lampshade, calculate the volume using the formula (8) in http://mathworld.wolfram.com/ConicalFrustum.html. I used volume of (R1,R2,h)=(10,8,10) subtracted from the volume of (9.4,7.4,10) [=3mm shell thinkness]. Then the volume is 2555-2227=328cm^3.

So its ok to inject the volume. For weight, the screw thread is likely to be DN28/DN35, they are strong. Total weight of all plastic that can be holded in the column is merely 850 * density = 1.19kg for PET (probably the heaviest you will recycle)