Posts: 2
From:Malawi
Registered: Jul 2005

posted July 26, 2005 01:41 PM               

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I wanted to get your opinion on a dilema we have in our management team. Can a counter rotating twin screw extruder designed for profile extrusion be used to produce pipes ?

I look forward to your favourable response,

Kind regards,

Bilal

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Posts: 560
From:Brodheadsville, PA USA
Registered: Jun 2001

posted July 26, 2005 02:49 PM               

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Why not? A pipe is just a round profile.

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Best Regards,

Tom Cunningham

Extrusion Technical Services

www.ExtrusionTechnicalServices.com

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Posts: 98
From:Silver City, NM, USA
Registered: Jun 2001

posted July 26, 2005 03:03 PM               

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Bilal,

Echoing Tom, yes of course your counter-rotating twin screw now doing profiles can certainly be used for pipe! Not knowing your screw design configuration, I would suggest you contact the extruder manufacturer and ask if they have a better recommendation for a pipe screw than you now have. Twin screw extrusion of pipes generally favors deep-cut flights--wider in the feed zone, to acheive maximum output rates at flood-feeding conditions.

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Posts: 4
From:Blantyre, Malawi
Registered: Jul 2005

posted July 26, 2005 04:12 PM            

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Hi 2beeps / Tom,
Thanks for the clarifications, I am still not satisfying the critics in my group.

Barring any changes to the extruder would we obtain a higher maximum rated output (kg/hr) when producing pipes with the OEM profile screws design ?

I have tried contacting the manufacturer (Cincinnati Austria) regarding advice on the screws - but not very forthcoming.

Regards,

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Posts: 560
From:Brodheadsville, PA USA
Registered: Jun 2001

posted July 26, 2005 04:51 PM               

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Pipes tend to have thicker walls than profiles. This has some implications; Die backpressure will be lower and the pipe will be more tolerant of poorly mixed or melted (fused) material. That is the type of melt that will be developed by higher capacity screws. Those screw should also consume less motor power per pound. So that same extruder should be able to put out more material making pipe if the screws are changed.

Skip can speak to the differences in formulation and how that will change things.

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Best Regards,

Tom Cunningham

Extrusion Technical Services

www.ExtrusionTechnicalServices.com

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Posts: 4
From:Blantyre, Malawi
Registered: Jul 2005

posted July 27, 2005 01:52 AM            

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Thank you for the response Tom,

My next question may be silly but here goes:

We are currently experimenting the use of one pack stabiler sourced from Baelocher Germany (SMS 50348R) and have found reduced torque. Our production manager is interested in increasing the Calcium Carbonate filler content - will we have to adjust our formulation to account for this ?
I have pointed out that the filler content and formulation for conical screws is critical for minimsing wear whilst acheiving maximum output, and can not be changed just "willy nilly".

Also, we are looking to produce mPVC pipes, but have failed to get a stable formula for this product. Can you refer us to anybody who can assist ?

Kind regards

Bilal

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Posts: 98
From:Silver City, NM, USA
Registered: Jun 2001

posted July 27, 2005 10:49 AM               

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You can add more CaCO3----how much depends on the product you wish to make. I'd suggest choosing a small particle (1-2 micron)stearate coated filler to minimize screw/barrel wear & abrasion in the twin screw extruder--especially when flood feeding at max. RPM for maximum output rates--the desired mode of operation.
If you are extruding pressure-rated pipe for potable water, do not exceed 5phr filler! For non pressure,sewer,irrigation,DWV you can go up to 20-30 phr.
A slight increase in your one-pack stabilizer/lubricant may be needed for added lubricity requirements at the higher filler levels.

As to m-PVC pipes (I assume you mean Mass-Polymerized PVC?).The main difference between m-PVC and s-PVC is a higher powder bulk density for the m-PVC, which means the dryblend compound entering the extruder will have a higher bulk density. Which in turn means a higher weight/screw flight--and at a given screw RPM,more compaction and faster fusion---and higher amps.
You could increase slightly the one pack for added lubricity,&/OR decrease material entering the feed zone (starve) slightly,
but not too much as to hurt productivity.
Basically the same formulation should work for both resin types---with the operating differences noted above.

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Posts: 4
From:Blantyre, Malawi
Registered: Jul 2005

posted July 28, 2005 11:39 AM            

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Thanx for the advice regarding mPVC.

Have you any particular views with regards to Baelocher one pack lead stabiliers ? Unfortunately we have had no experience with tin (Sn) stabilisers, your comments on merits would be much appreciated.

Kind regards,

Bilal

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