posted July 13, 2003 02:02 PM               

i am doing a project on an extrusion machine..the problem is that..it is running at a constant speed of 52rpm but its pressure is varying erractically...
please if u have a solution mail me.

posted July 13, 2003 03:59 PM               

• Extruder L/D, screw dia,screw channel depths, screw layout,etc
  
• Material being processed (grade, MFR etc)
  
• Process parameters (settings and actual readings)
  
• Actual process (pipe/blown film/sheet etc)
  

Steve H

posted July 14, 2003 04:07 AM               

here are some details i have found out abt the Extrusion machine..
Extruder L/D = 35:1
screw dia = 120mm
material processed = Polyethylene HDPE
Process Parameters = geosynthetic material
like pozidarin.

For more information on these products please visit http://www.abg-geosynthetics.com/

posted July 14, 2003 06:31 AM               

What temps are you setting your barrel zones at?
Whats happening with the screw motor amps?
What grade of HDPE,Maker etc
What melt temp are you getting, is it varying?

In your first post, you state that the screw RPM is 52, have you confirmed that this is correct with a Tachometer? Tom's question about the nature of the pressure variation also needs an answer.

Is the variation in pressure accompanied by a variation in the gauge of your product?

posted July 14, 2003 07:45 AM               

Are you running any fluff or regrind?

Is that a grooved-feed extruder?

posted July 15, 2003 10:31 AM               

i am sorry for the delay in replying.
it was nice to hear from many of you.
thanks for that.
well i have got some details as some of you had asked for..
to start with STEVE's :
temp at the end of the barrel is 230 C
( i shall put up the zone temp and amps of the screw in a day or two)
the HDPE is bought from Exxon Mobil Chemicals.

NOW ON TO BOB:-
ya the feeding i think is good enough as we use suction pumps to feed this.and also an electronic equipment monitors the amount that needs to go in at a time.
No we are not rumming this machine on any kinda flux or regrind.

NOW ZABIELSKI:-
YES u'r right this pressure transducer is at the very end of the extrusion tip.

u can have a look at a latest version of the one we are using here on the following link...but this one is much similar in design to this. http://www.unionextrusion.it
Click Range
Click Extruders for Plastic.

Thanks Bye

posted July 15, 2003 10:51 AM               

I feeling left out.

You can see inside the extruder, but some of the measurements can help you diagnose the patient.

How much the pressure varies, and the period and duration of the pressure variations might lead us to a cause and cure.

The same applies to the amperage reading on the drive.

posted July 15, 2003 11:17 AM               

i am sorry ..but i don't know how i missed u'r point.
well to be frank enough i could'nt understand u'r question firstly, but now ya i have got it.
the pressure is supposed to be around 150 bar, but is not constant. it is varying sometimes between 100-160 whereas sometimes it is luring aroung 135-140...
this change is ona regular basic..in the morning we get huge variations whereas in the night shift we are near stability.
i take reading noting the variation in
1 minute.

posted July 15, 2003 07:27 PM               

Early in the morning sounds to me like a cold extrusion system that has not come to equilibrium. By the days end, all is in stable running conditions.

posted July 15, 2003 08:00 PM               

Keep the information coming At this point, I tend to agree with the Zmaster- if the pressure spikes are coinciding with the screw flight passing over the tip of the pressure transducer. If this is the case, you won't see much of a variation in the gauge of your film.

The larger variations that are occuring just after start up are probably accompanied by gauge variations. How long do they carry on for?

If your company purchased this extruder new, you could try asking the manufacturer for information on the screw ( Compression ratio, lenghts of feed zone, etc)

posted July 15, 2003 09:05 PM               

My understanding is that the pressure change period is one minute, while others are feeling it is once per second. Which is correct?

Is the extruder vented?

What is the output rate?

What is the drive kW and what is the motor load?

What is the screw type? Conventional, barrier, grooved feed, mixing head?

All this information will help in diagnosis.

Tom C