Fabric guiding - basic rules, guidelines and setup procedures
Oct 30, 2018
Guiding of all types of fabrics follows similar basic rules, guidelines, and setup procedures. Here are some of the most important ones…
Normal entry principle
An ingoing fabric will tend to align itself at 90 degrees to the downstream guide roll. For low wrap angles, this means the fabric will steer toward the side it contacts first. For high wrap angles, such as stretch rolls, the fabric will steer toward the slack side.
Only the guide roll misalignment should be controlled. All other fabric rolls are aligned square to the machine and should not affect guiding. If the auto guide roll end is working hard to steer a fabric, other rolls may be affecting guiding and should be aligned square to the machine and leveled.
Some mills have found that cocking the stretch roll a little is required to run a straight trade line. In this case, tighten the side where the trade line is running ahead. This increases the length the fabric has to travel on that end, allowing the trade line to straighten out.
Rules
- Proper wrap angle of the guide roll is normally between 20-30 degrees.
- Adequate incoming to outgoing sheet run lengths, with the ingoing/outgoing length ratio approximately 1:1 to 2:1. Only the ingoing fabric sees the effect of the guide roll misalignment and moves accordingly. The downstream roller locks in the effect of the guide roll.
- Total in to out length around the guide roll should be greater than the fabric width, especially for stiff dryer fabrics.
Setup procedures
- After a new fabric has been installed, stretch the fabric to remove sags, but not too tight.
- Make sure the guide paddle is not caught on top of the fabric, and is set close to the proper position to center the fabric on the machine.
- Crawl the fabric under low tension to remove any wrinkles and straighten the trade line. Applying too much tension before the fabric has a chance to straighten out can permanently wrinkle the fabric.
- Tighten the fabric to manufacturing supplier recommended settings.
- Monitor the auto guide roll position (paddle controlled end). Adjust the manual guide end to get the auto guide end centered. Don't worry if the fabric is not exactly where you want it for now (unless the fabric is running off the rolls).
- Once the fabric auto guide end is running in the center of its stroke, now adjust the guide paddle to wherever you want to run the fabric in the machine.
- Increase the fabric speed, and monitor the guiding of the fabric. Adjust the manual guide end to keep the auto guide end centered.
- Adjust the height of the paddle arm if the fabric is oscillating too quickly or slowly. The closer the paddle is to the fabric, the greater the response rate will be to changes in fabric position and vice versa.
For more information on getting the most out of your fabrics with assistance on fabric guiding, stretching, care and handling, contact your Valmet representative.