Compression ratios

Does anynone know what are the typical compression ratio (feed channel / metering channel depth) and screw length (L/D) ranges for PVC, PE and halogen free/flame retardant materials (e.g. filled EVA)? For which of the above materials are double-flight screws beneficial?

Can anyone suggest further reading/information sources on screw design and applications?

Hello There,

Please go here and purchase the following WAI book:
www.wirenet.org/waistore/productdetail.cfm?productid=172

This should get you almost everything you are asking about. As far as filled EVA is concerned, I suggest you discuss this with your material compounder.

As far as true double flight screws are concerned (Not Barr or barrier screws), our only experience was with very accurate tubing that was made into balloon sausages and applied hot over the inner conductor of intermediate frequency coaxial cable. This was a very small extruder (1") and the output was very accurate and repeatable on LD PE. All other extruders for manufacturing wire and cable products were single screw.

Kindest regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates

hi,
L/D Compression Ratio

pvc 24-26 1.7 - 2.0 if it is plasticized pvc
hffr 20-25 max 1.2
xlpe 24-25 3.0-3.5
pe 24-26 2.5-3.0

Thank you vettecoupe, I'll take a look at the WAI book you suggest.

Serdar1970, thank you also for your answer.