Oversized extruder????

[NZBen]

I want to trial a prototype extrusion from polyprop, I'm only semi familiar with the extrusion process and have never officially operated a machine. I'm currently building up a die and I have managed to pick up a hardly used extruder from a university for a song.

However I'm starting to be concerned that the extruder might be too big for my application and was wanting some thoughts The extruder is quite old, not really sure on specifics of it, I'd guess the screw is about one meter long, it only has two heat zones on the screw, however when it was used it had three other heat zones on the die area giving five zones - these three are going to be scrapped and I'll only have a third heat zone on the die. The machine has a 7.5kW (10hp) motor driving it.

From that I'm assuming it's capacity is around 25kg/hr based on hp specs from other machines I've seen. The parts of my die I've made so far look very petite when stuck on the end of the extruder and I'm assuming I'll only want a flow of around 500g/hr. Is this going to cause me a problem with plastic working, stagnant time etc? I should be able to slow the screw enough as I picked up a pretty flash VSD for a song also, can run down to 1Hz if I put a cooling fan on the motor.

Thanks for any heads up/advice in advance

 

[patprimmer]

25 kg/hour is a fairly slow rate of extrusion, even for a small profile.

1 metre long is a very short screw.

Screw profile and temperature control in the barrel and the head and the die itself and the haul off are all important.

Regards
Pat
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[NZBen]

I realize that a 10hp is a very small extruder by industrial standards, however the profile I'm wanting to extrude is really tiny. I'm only estimating that 25kg an hour is the throughput, but may be off by several factors. So I was wondering if running a machine at several times (around 50 times) lower than it's capacity causes any problems with the finish/quality of the extruded form. I was thinking about running the first heat stage of the extruder quite cool say 130C to limit the time the PP stays at elevated temperature, but have been thinking that may over torque the screw?

 

[patprimmer]

A lot depends on the screw profile. If you have a high compression high shear screw you will have problems, but if you have a gentle screw profile and a motor/transmission that can run relatively high torque at low speed you should be OK, but no one can really say.

Regards
Pat
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