posted January 19, 2003 10:03 AM               

As a general guide you want to balance the pumping capacity of the extruder with the melting capacity. The setpoint for the process in order to achieve this are not intuitive, and this is why simulators were created.

Simulators work great when they closely mimic the physical phenomenon inside the extruder. Fortunately in many cases they work well, as the most common behaviors are well know and studied. In some cases things happen inside an extruder which is different than the norm, and simulators have problems.

If you are interested in seeing what a simulator predicts about this situation I would be willing to give it a try. First we need to verify that we can simulate the present condition. Please provide as much of the operating conditions, equipment description, and material information as you can. Typically you will need the permission of top management in order to release this proprietary information. If you can, I think it would be interesting for forum members to see.

posted January 19, 2003 12:45 PM               

I don't understand- your topic asks about temperature changes with a change in extruder size, but then you say that you're using the same extruder with a new barrel and screw. Which is it?

If your new screw is capable of 27% more output, is that because your old screw was very worn, or is the new screw a higher output (deeper) design?

Other factors affect this too- I assume from your name that you are making strapping, presumably PP?

Can your downstream equipment handle a 27% higher output? Not only the line speed of the converting equipment, but the higher pressure in the die, screenchanger, etc.?

posted January 20, 2003 01:28 PM               

But if I had to guess, I would think that the new screw is going to be deeper to give you the higher rate. A deeper screw means less shear- less shear means less heat. Less heat *might* mean that you'll get unmelted material through the end of the screw. If this happens, then you'll have to bump up the extruder heats to compensate. If this doesn't happen and a cold melt has no other bad effects on your process, then you can take your 27% more material and be happy!

One other thing to watch is the melt pressure. If the melt is colder, your viscosity will increase, meaning you'll have higher pressures. If you were running quasi-high pressure before, it will really be high now! Not to mention that the higher rate alone will also give you higher pressures (takes more pressure to force more material out of the same die). If the higher pressures also cause no problems, then you are golden.