Conveying Polystyrene/Dylite beads

[JCovey]

We've got an application where polystyrene beads are added to a mixing vessel that is charged with other dry ingredients. The current method involves measuring the beads by volume and pouring them into the top of the mixer. Quite messy since the mixer is under a positive pressure. Ideally, I would like to pneumatically convey them, but I hear that static electricity precludes this as a conveying option.

Has anybody had experience moving polystyrene and if so, what pointers may you have for me?

Many thanks,
John C

 

[YoungTurk]

Have you considered using a screw type conveyor? I know that this is the standard system used for supplying plastic beads to extrusion lines, and that you can get metering conveyors which work by built in calibrated scales wich control the screw rate. You might be able to modify the system such that the positive pressure is maintained all the way back to the bead storage area and eliminate your "messy" problem, or it may be simpler to just add a pressure release where the beads are fed in.

 

[patprimmer]

I have seen polystyrene beads handled by pneumatic means without static problems, but the system was well earthed.

These were injection moulding granules, not expandable polystyrene beads. EPS might be more of a problem due to the volatile nature of the medium for expansion.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[stanier]

I designed systems to convey polystyrene granules to injection moulding machines many years ago. Vacuum conveying proved better that positive pressure. The units That I used were a Brauer airmover from the UK. This device had a Coanda profile . Compressed air passed over the circular profile and caused a low pressure area . This was connnected to a hose that sucked the beads through to the machine. Air was switch on and off with a solenoid valve. A timer kept the air on and was accurate enought for measuring the shot.

Brauer were last in Milton Keynes in the UK but did export. I was a design engineer for them back in the 1970's.

http://www.brauer.co.uk/airmovers/stainless.html

 

[JCovey]

All,
Thank you for the responses. We have recently ordered a Line Vac from Exair. It appears to be very similar to the units that brauer manufactures. It's good to hear that it has been successfully used elsewhere.

Stanier, other than solid grounding, did you use any static elimination devices in the convey line?

We've considered a volumetric screw feeder as you mentioned, Turk, but this will be our backup plan if pneumatic conveying proves to be impossible.

Again, Thanks,
JCovey

 

[stanier]

I honestly cant recall what grounding was employed as it was thirty years ago. If it is a concern then perhaps a convuleted ss pipe could be used. Similar to what is used for truck exhausts. Being metal it could be grounded.

If you were to use a flexible PVC hose it would be of benefit to run a copper conductor up the bottom of the hose. How long it would last is a question.

The main point was the use of vacuum rather than pressure to kove the beads. I have used Airmovers as pressure device for wheat and other seeds but plastic beads wouldnt move.