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Filed under: Rollers, Traction --- Tim Walker @ 09:14 AM

Here's a Top 10 reasons to align your rollers.

#1 keeping the web on centerline.

The parallel entry rule makes the web want to track parallel to the directing a roller is spinning (which is perpendicular to its axis of rotation). Parallel rollers, with good traction, keep a web tracking parallel to the machine's centerline.

#2 Reduce wrinkles

Roller misalignment is a big cause of wrinkles, especially in thin webs. Wrinkle causes are additive. So if you have misalignment, it may not create a wrinkle by itself, but it will lower your threshold to wrinkling from cause X.

#3 Reduce breaks

Misaligned rollers create web path variations between lanes of the web, shifting the tension from average across the width to high on one or both sides. The reason I advise running web handling tension at 10-20% of bad tension (the load to break or yield the web) is to provide a safety factor against misalignment-induced tension variations.

More...

Continue reading"Why Align Your Rollers?"

Filed under: General Business Topics --- Tim Walker @ 08:51 AM

Several times a year, I get involved as the "middle man" between buyers and sellers of converting equipment. I'm usually brought in to help develop a specification for a new process or product.
I used the analogy the other day that I'm a race car driver. I know what I want in a car and how to describe it, but I wouldn’t plan on building one myself. Similarly, many mechanics and design engineers building race cars would not say they are great race car drivers. So if the race car driver is asked to help in buying a new car that makes sense. At least a little bit, but if the buyer doesn't need a race car, just a family car or a go-cart for the kids, the race car driver better have a experience at all levels. OK, this analogy can only take you so far.
Writing the specification is the easy part. Recommending a converting line builder would be easy, but the converting world has as many levels as four-wheeled vehicles, ranging from go-carts, to NASCAR, to Hot Wheels toy cars, to space shuttle transports, and beyond. It's impossible to know everything.
Who do you send your Request for Quote (RFQ) to? If you send it out generously, you reduce the odds greatly of any one supplier getting the job. It costs a supplier time and money to reply to your RFQ. By including a supplier in your RFQ process, you automatically increase their overhead. But if you don't do enough fishing, you might not get the best supplier.
I've had a few conversations with suppliers on this issue...

Continue reading"Etiquette in the Request for Quote Process"

Filed under: Tensioning, Web Mechanics --- Tim Walker @ 02:46 PM

Draw control has always been a favorite topic of mine. Why? Because it is widely used in converting equipment, it is so simple to design, but the web's reaction to draw is somehow counter-intuitive.

I was recently working on a multi-station printing press. Presses are commonly run in draw control to keep the printing cylinder in registration. If you had each print station changing speed in closed loop tension control, you would hit your mark on average, but be off registration in both directions.

The tension in a press is based on draw control. The tension into the first press station is controlled by a constant tension infeed section (I hope it is). The tension between all subsequent stations is the baseline web strain modified up or down by the draw (relative speed) of each station to the first station. As a widely used rule of thumb, the series of print stations should be set at equal speed or a slight increase in speed from station to station. These guidelines imply that shifting to a lower speed (a.k.a. negative draw) would be a bad thing. Is it?

Continue reading"Don't be afraid of negative draw"

Filed under: Tensioning, Web Mechanics --- Tim Walker @ 10:34 AM

I've been at a couple of client operations lately that have winding tension control in either open-loop torque control or dancer feedback to torque control using motors in low speed processes (low speed is < 300 fpm, semi-low speed is motor rpm is >2x core or roller fpm).

The main problem with torque control is "what torque gets to the web"? Sure, you can get a good torque proportional to amps out of the motor, but to deliver this to the web and create tension, you usually have to go through a gearbox and other sources of torque losses before you get to the web. I've learned (though I'm open to being taught by new technology, etc.) that better closed-loop tension control is found by using your tranducer or dancer roller to trim motor speed.

Continue reading"Is Motor Torque Control EVER The Best Choice?"