Web Works
- What are the drawbacks to draw control?
David Roisum, Ph.D., Consulting Technical Editor, 07/01/2008
Speed or draw control is quite simple for electrical engineers. They merely need to make a motor turn at a target speed to an accuracy of a few parts per thousand. Maintenance is simply a matter of knowing roller diameters accurately to 4 or 5 digits. Speed control is exceptionally complex for everyone else, including those ranging from operators to process-control people. More - What is draw control?
David Roisum, Ph.D., Consulting Technical Editor, 06/01/2008
Draw control should be called what it actually is: Speed control. The word draw is ambiguous. It could mean the intentional and permanent elongation of material, which is a web-forming concern. Alternatively, it could be an alias for speed control. In speed control, we make adjacent motors go an ever-so-slightly different speed. More - What do you mean by web machine quality?
David Roisum, Ph.D., Consulting Technical Editor, 05/01/2008
We have lots of ways to define web quality. But how do we judge the machine's quality? Here, we can seldom use any conventional web or uptime measurements. For example, let's say that you have side-by-side machines with drastic differences in runnability. It could be due to a different product mix or raw material, neither of which is the machine's fault. More - What do you mean by process and product quality?
David Roisum, Ph.D., Consulting Technical Editor, 04/01/2008
Everyone has an idea about what constitutes process quality. It's often defined as the absence of negatives. However, if the machine crashes, the cause may be related to man (operator), machine, material, method or some combination. So who or what is at fault (i.e., lacking in some key quality)? Leaving the operator out for the moment, the problem is almost always machine and material. More - When do I need to align my machine?
David Roisum, Ph.D., Consulting Technical Editor, 03/01/2008
Roller alignment costs money. It takes a couple of technicians something like an hour to move a typical roller into alignment. This is not a large cost if the machine is already down because it is being installed or rebuilt, or it is not fully utilized. Thus, there is absolutely no excuse not to align to precision ingoing standards in those situations. More - How closely do I need to align my machine?
David Roisum, Ph.D., Consulting Technical Editor, 02/01/2008
A decade ago in this column I tried to answer this complicated question and did not do a very good job. I can now answer this question definitively: It depends. More - Can you apply DFM to winding?
David Roisum, Ph.D., Consulting Technical Editor, 01/01/2008
Of course you can. However, you really have to think outside the box so that the winder is considered a vital step in manufacturing instead of an after-thought. DFM (or Design For Manufacturability) recognizes the futility of making a product that the end-user really likes if manufacturing costs prohibit profitability. More - How can I wind material with bad gauge profile?
David Roisum, Ph.D. Consulting Technical Editor, 12/01/2007
You really only have a few options: Wind very short rolls (a few dozen wraps ought to be okay), send the ugly raw material back to the supplier, or wind soft and live with the remaining gauge-related defects. Our greatest fear in winding is being asked to wind a material with a profile problem. The word “profile” means variation of ____ across the width, where ___ could be thickne... More - What is the best taper tension that I should run on my winder?
David Roisum, Ph.D., Consulting Technical Editor, 11/01/2007
I wish taper tension had never been invented. It was invented solely as a convenience to the electrical people decades ago when cams and proportional controls were about all there was available. There are far better ways to do things now. Taper tension has two settings that must be selected by an operator: starting tension and percent (%) taper. More - What is the best instrument for measuring wound-roll quality?
David Roisum, Ph.D., Consulting Technical Editor, 10/01/2007
Your eyes. Seriously. If you look at the 100+ defects in the encyclopedic Roll and Web Defect Terminology, you will see a picture for every single defect. However, not a single measurement is given anywhere in this must-have reference. If you consider the customary practice in the industry, visual culling is the norm, and roll quality measurements are not. More - How do I calibrate dancers?
David Roisum, Ph.D., Consulting Technical Editor, 09/01/2007
There are even more reasons to calibrate dancers than load cells. Just like load cells, dancers are a tension indicator, and the native units are not proper tension units. In the case of load cells, the native units might be 4-20 mA or 0-5 V, which have to be converted to lb/in. In the case of dancers, the native units are cylinder-pressure units, which also must be converted to proper tension ... More - How do I calibrate load cells?
David Roisum, Ph.D.Consulting Technical Editor, 08/01/2007
Calibration is required of all sensors simply because none can be trusted. Consider the ubiquitous scale for weighing produce or the flow meter on gasoline pumps. Regular calibration with documentation is required by law even though these sensors are simple and seemingly bulletproof. One of the tenets of ISO is to calibrate important gauges. More - What should I expect of pneumatic trim-removal systems?
David Roisum, Ph.D.Consulting Technical Editor, 07/01/2007
Pneumatic trim-removal systems are something like industrial-sized vacuum cleaners. Even so, there are many things that can go wrong. The first component—the inlet or trim chute— has had the least attention and is often the most troublesome. Here is where there is some true economic disparity. More - How can I take away trim?
David Roisum, Ph.D.Consulting Technical Editor, 06/01/2007
Nearly every web manufacturer and most web converters have to cut and remove trim at one time or another. Unfortunately, you can have as much trouble with this small piece of waste as the entire rest of the web. There are three vital tasks for smooth trim takeaway: cutting, pulling and removing. First we must cut the trim, which is often the same as cutting intermediate positions. More - What is your favorite troubleshooting method?
David Roisum, Ph.D., Consulting Technical Editor, 05/01/2007
I have written a book about, teach and regularly practice a variety of troubleshooting methods. Thus, I may be considered as much of a problem-solving expert as a web-handling one. I value troubleshooting skills even more than web literacy. Consider this: Even if you have read and understood every word ever written on web handling, you may still have difficulty solving many web-handling problems. More - What is your favorite management program?
David Roisum, Ph.D., Consulting Technical Editor, 04/01/2007
It has been two decades since I was a manager, so my credentials are a bit dated. Nonetheless, I have been in about 1,000 plants and have seen much. Programs come and go, like fads. Many a plant worker rolls his eyes when he hears about the next “improvement” coming from above. Zero defects, quality is king, the customer is always right, lean, 5s and Six Sigma are just a few of the ... More - What is the most important web-handling sensor?
David Roisum, Ph.D., Consulting Technical Editor, 03/01/2007
Without a doubt, the most important web sensor is your eye. How many sensors do we have to even detect wrinkling, which may be the most devastating defect in our industry? Only one, the eye. Of 1,000 web machines, how many are equipped to measure bagginess, which is epidemic in most plants? I doubt there would even be one. More - What can I do about wrinkling?
David Roisum, Ph.D.Consulting Technical Editor, 02/01/2007
A: The first thing you need to know is where the wrinkles form, not why. In most cases rejectable wrinkles form on a roller, even if the cause is upstream. This is no more difficult that just paying close attention. Two caveats: first, there may be a couple of rollers that initiate trouble, so each source must be identified. More - Is it hard to speed up a line?
David Roisum, Ph.D.Consulting Technical Editor, 01/01/2007
There are two speed “limits”—real and perceived. Most of the real limits are drive related. Maximum motor RPM or horsepower ratings are the most common. Most other limits exist only in the mind. Has Dr. Roisum gone off his rocker? What about dryer limits? Dryer “limits” are common on many coating, printing and other converting lines. More - Why does my web shift at roll change?
David Roisum, Ph.D.Consulting Technical Editor, 920/725-7671, drroisum@aol.com, www.roisum.com, 12/01/2006
It is so common that you might expect that the web will shift sideways at a roll change. However ordinary, it is no more desirable than the common cold. Whether this is a mere nuisance—or fatal—depends on the health of the raw material, the converting machine and the product being made. It is important to understand that an outcome, such as a sideways shift of the web, can be a res... More - Next »
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