posted April 26, 2002 01:22 AM               

quote:

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Originally posted by sibabrata:
In a 30:1L/D 150 mm pipe extrusion system
there is drop in output if attempted higher
linespeed(1mpm) associated with increase in melt temperature and drop in melt pressure

howevere not all brands creating this problem
what could be the reason(s)/solution

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HDPE with HLMI=2.5(av), SRPM=35, Temp 180-220
Melt temp-200degC, Melt pressure-300bar

posted April 26, 2002 04:06 PM               

Too much extra heat in the feed section will
cut down the Coefficent of Friction between
barrel wall and material- this results in less material being pushed along by the screw, resulting in less output.

If you want to run a higher screw speed, you could try a reversed barrel profile-
much hotter in the feed section, and then
tapering down to the temps you normally set at your screenchanger etc. For example B1=230, B2=215, B3=210 and so on.

You'll have to experiment to get the right settings for your machine/material, but you
should get 10-15% more output and a reduction in melt temp of 2-5C. Screw motor current will go down.

Have you looked at a grooved feed section, if more output is a big issue.

posted May 03, 2002 05:24 AM               

pl note also following

screw speed is very low 35rpm
line speed is only 0.8mpm
reverse profile does not help much

as material from different souces does not give this sudden drop, could it be due to material properties rather than processing problem

how to see the effect of co-efficient of friction of material wrt screw/barrel, can be modified to have better material forward movement ?

Thanks once again

Sibabrata

posted May 03, 2002 05:35 PM               

At the desired RPM, change the screw temperature and fix the first barrel zone temperature, and visa-versa. Record the setting temperature used where you get the highest extruder amps in each case. Then set the barrel and screw to those temperatures.

If that does not work, then you need a more radical change. Try a low friction fluoropolymer screw coating in the feed. Provided by SPR (US 800-868-4777).

If in the unlikely case that does not work, a friction study and screw design can also be provided by SPR. SPR's feed designs have proven to be very effective on difficult to feed materials.

posted May 03, 2002 07:34 PM               

If you have noticed a drop in output from the
latest batch, then posibily your supplier has sent you a fractional melt HDPE rather than your normal 2.5MI.

If the difference in output has always been present, then you may need to compare resins
on the basis of curves produced from a capillary rheometer- which will give a better idea of how a one grade of a material will process compared to another at real extrusion shear rates.

As Tom has said- if your screw is bored and tapped for screw cooling, experimenting will
barrel/screw temps may improve output.
What you should see, if you plot output against barrel temp in the feed zone, is a
bell shaped curve. The feed zone temp at the top of the curve is the optimum setting.

Have you pulled the screw lately and cleaned it- What you want in the feed zone is the pellets slipping on the screw and sticking to the barrel wall.

posted May 07, 2002 07:22 PM               

quote:

---

Originally posted by sibabrata:
In a 30:1L/D 150 mm pipe extrusion system
there is drop in output if attempted higher
linespeed(1mpm) associated with increase in melt temperature and drop in melt pressure

howevere not all brands creating this problem
what could be the reason(s)/solution

---

The problem could be comming from your material. Your material can shear thin with increase in your rpm which can lower the viscosity of the melt. Melt temperature rises due to viscous dissipiation. So you should lower your temperature near discharge zone. You should try reverse temperature profile. You need to check also screw design.
Have you check your screw and barrel for wear. Too much clearance between screw and barrel can create a situation where melt can experience high shear between flight and barrel. You can email me your current screw design.

posted May 10, 2002 12:59 AM               

will be trying now systematically reverse temperature profile, effect of temperature of feed zone on output with also considering reducing cooling at feed zone. as mentioned a particular brand giving problem blend options tried to find dissociate material problem with screw problem.

will post results as and when trial is over

Thanks & Regards

posted May 31, 2002 06:14 PM               

When was the last equipment califbration?

quote:

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Originally posted by sibabrata:
thanks all for many suggestions

will be trying now systematically reverse temperature profile, effect of temperature of feed zone on output with also considering reducing cooling at feed zone. as mentioned a particular brand giving problem blend options tried to find dissociate material problem with screw problem.

will post results as and when trial is over

Thanks & Regards

Sibabrata

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