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June 23, 2005
Can a Web Guide Create Wrinkles?
Mike Flanagan wrote in asking this great question.
The short answer is YES.
Here's Mike's question in whole "Are there not some dynamics involved in guiding that can create wrinkles downstream from guides that are improperly installed? Seems to me I have seen wrinkles show up on some steering guide applications that have to do with overly short entry spans. Is that the case?"
Many wrinkles are created by grossly uneven tensions across the web. Usually this is caused by misalignment, but any thing that overly bends or twists the web can do it. How can a guide do this?
1. A guide may be over steering. If a guide is poorly tuned or the geometry is off (like a edge sensor too far downstream) the lateral oscillation of the web at the guides output can be worse than the error it was meant to correct.
2. If spans are set short and corrections are large, the severe bending or twisting may be too much for the web. This can happen when two sequential guides fight each other or the web lines has a dominate pull to one side. If an unwind guide sensor is misplaced and guides the web to one side, the next correctly set guide will pull the web back, but if the correction is extreme, the result may be a wrinkle. A smart positioning of an upstream guide can reduce the work of a downstream guide and eliminate the problem. Usually guides don't talk to each other, but this is a case where teamwork among web guides can solve a problem.
3. Get the geometry right (cont'd)
For all guides, don't cramp them in too much.
For steering guides, since they bend the web, which is much more severe and likely to cause wrinkles than twisting, make sure to only use steering guides when you have a long span.
For displacement guides, longer displacement and twisting spans will reduce wrinkle problems.
For sidelay, especially unwind, there are some limitations to the lateral correction rate. If a roll is overly telescoped and you unwind too fast, a guide actuator may not be fast enough or have enough range of motion to correct the input error. One a slitter, operators know to slow down when they see dramatic shifts.
There are many good guidelines to setting up web guides. Following these solve most problems. Wrinkles from web guides usually mean your try to apply the guide outside of know best practices.
Posted by Tim Walker at June 23, 2005 11:44 AM
Comments
Most (99%) of the wrinkles at a web guide occur when a steering roll type guide is used and the span prior to the guide is too small. The optimum entry span can by calculated considering such variables as web width, correction required, elasticity of the web etc. When in doubt use a displacement type guide.
Posted by: Don Ross at June 23, 2005 04:44 PM
I agree with Don's comment that steering type guides in short spans are a wrinkle waiting to happen. Steering guides should be thought of as "long span correctors". They are excellent as the first roller at the end of an air floatation oven. But if you don't have a long span, don't use a steering guide.
Posted by: tjwalker at June 28, 2005 07:38 PM
A agree with Don's and Tim's comments. But, I would like to add that if you are not sure about what is causing your wrinkles, "Don't Not Guess", have a Web Handling Special or Engineer come in and survey your particular cituation. Wrinkles are caused by the process, not by the material. Think about it in terms of your material has the right-of-way, all guides, rollers, ovens, and coaters must yeild to that mateial right-of-way. You are only allow to do so much to any given material.
Posted by: John Sanders at July 9, 2005 06:34 PM
Be sure your steering roll is aligned to the machine in its neutral position. If it is mounted in a horizontal plane, check the level with a roll level. Shoot for 0.001"/ft. Might also want to keep track of skew vs. steering problems. Some webs are hopeless.
Posted by: Jack Ryan at July 11, 2005 10:23 AM
Nice blog site! I'm new to converting world.
Posted by: Jerry Shea at September 2, 2005 11:42 AM
Given a long (3xWidth) entry span, what's the min/max distance a steering guide should be from the downstream process into which you are trying to control the lateral web position?
If the closest you can get is further away than the maximum best-practice distance, what are the options for improving steering control?
Posted by: T Higgins at October 28, 2005 07:15 AM
