|
Question
#189
Subject: We have a problem with the web shifting to one side.
We are facing a problem when we run PET30 liner through our dryer that the web shifts to the drive side.
Dryer is an airfloating dryer and has it's own tension zone and we do have a driven vacuum roll on a steering frame at the dryer exit. The vacuum-steering roll has traction and when this phenomenon happens, one sees the guide roll trying to correct this. Still, the web shifts to the other side and causes a web break.
The supplier suggested a 'non rotating air roll' on a pivot. What's your opinion about this? Will it work? Is this a dryer allignment and/or nozzle issue? We know that some rawmaterial rolls are more 'sensitive' to it, but roll hardness issues can't be found.
Answers (links jump to full text of answer below)
#198
Author: Ed Cohen, Edward D Cohen Consulting
Email: cohened@146aol.com
Subject: Tracking problems in a floater oven can be caused by...
Tracking problems in a floater can be caused by mechanical factors such as
uniformity of air supply; tension controls upsets, inadequate tension control
and roll steering systems, and roll alignment. The nature of the base can
also affect the tracking in particular the skew and planarity of the base. In
your situation you indicate, “ some raw materials are more sensitive to it”.
This suggests that differences in the skew of the various rolls of support
could be leading to the problem. When a support has some skew, it tends to
curve and move to one side of the dryer, instead of running straight. If it
is bad enough the guide rolls cannot correct for the skew and cannot keep it
running straight.
A simple way to check this out is when you see the web shifting. Reverse the
base in the unwind so that the sides of the base are reversed, when going
through dryer, If it is base the web drift to the other side, You can also
check out skew by laying a long section of base on flat floor and measuring
curvature. Comparison of a good support and drifting support should have
differences.
The air pressure uniformity of nozzles and spacing should also be measured to
insure they are uniform and in specifications. Variations in air pressure
across the nozzle might also be a source of the motion.
Back to top
|
#199
Author: David Roisum, Finishing Technologies, Inc.
Email:
Subject: If the web consistently shifts to the drive side, then something is 'crooked'.
If the web consistently shifts to the drive side, then something is 'crooked'. The candidates are: one side of web is baggy or cambered, dryer area is mechanically misaligned, dryer area 'pneumatically misaligned'. Most often it is the airflow that is not uniform and symmetrical.
Assuming that you are correct that the guide corrects by tipping in the appropriate direction and is in traction, the guide can still be handicapped or even disabled by the presence of a roller just upstream of the guide. It may be that the guide is working properly, but just is not up to the task above. Losing traction on the guide roll, as I interpret the suppliers recommendation for an air roll, would also disable the guide.
I would get a guide expert in to check out the guide. I would get a dryer expert in to balance the airflows.
Back to top
|
|
