- January 01, 2008, By Jay Tannan, Pruftechnik Service Inc.
Roll alignment is a requirement for every converting process that produces some sort of web, film, or coating. When a machine is first installed, each roller should be measured to be tram (horizontal) and level (vertical) with the machine. Components and parts of a machine can shift outside the original specified tolerances over time. Many converting processes run at extremely high speeds, to 5,000 fpm, making roll alignment even more crucial. Any misalignment can lead to a variety of different operating issues. Tracking, tension, and coating problems are just a few of the many issues that can lead to unplanned downtime.
There are several methods available for checking roller parallelism. The most common measurement is by optical means, otherwise known as theodolites. For theodolites, line of sight is required and the measurement can take place only on one plane at a time. Since many parts of machinery are not accessible due to encased or hard-to-reach rolls, traditional optical means cannot carry out an entire measurement. Due to such limitations, a complete survey of roller alignment has been difficult to achieve and very time-consuming for customers.
Inertial Roll Alignment Technology
A new technology designated PARALIGN has been developed for measuring roller parallelism simultaneously in the tram and level position. This system uses inertial technology to achieve a roll alignment survey of an entire process. It uses three ring laser gyroscopes to measure a roll's relative position in space regardless of line-of-sight issues or subjective readings. The software is capable of producing a complete graphical and numerical assessment of an entire machine in a fraction of the time it normally would take for an optical team.
The unit is approximately the size of a loaf of bread and weighs about 20 lbs. It is a completely self-contained system that has no mechanical moving parts inside.
Figure 1 shows the approximate location of the three ring laser gyroscopes in the system. The three positions are called roll, pitch, and yaw and are arranged perpendicular to each other.
Each gyroscope is capable of detecting even the smallest of spatial movements. Figure 2 represents the anatomy of a ring laser gyroscope in which two HeNe lasers are emitted in opposite directions between three mirrors.
As the unit is swept across the surface of a roll for a minimum of 20 deg, indicated in Figure 3, one laser is lengthened as the other is shortened in each of the gyroscopes. From the change in length, an angular offset is calculated instantaneously to determine the roll's relative position in space.
The protocol shows the offsets of all the rolls in comparison to a reference roll as displayed in Figure 4. The green side represents the operator side while the red shows the drive side of a roll.
The reference roll chosen in Image 1 is Roll ‘A.’ The remaining rolls shown have vertical and horizontal offsets in which adjustments would need to be made at the bearing in order for them to be parallel with the reference roll.
The flexibility of the software allows the customer to switch the reference roll as desired. As an example, Image 2 displays Roll ‘C’ as the new reference roll and has all the other roll's vertical and horizontal values re-calculated.
Depending on the industry and machine specifications, the allowable tolerance for the parallelism of each roll normally would be between 0.002 in. and 0.030 in.
Roll Misalignment Issues
There are several possible web handling issues that can be derived from the sample protocol shown in Figure 4.
First, there might be a slight waviness or slack created between the rolls. Based on any two rolls having opposite offsets in the vertical and/or horizontal direction, the web might be slacked on one of the sides. (Image 1 Example — Rolls ‘E’ [V:-0.096, H:0.122] and ‘F’ [V:0.013, H:-0.074] have opposite offsets in both the vertical and horizontal direction, indicating the film might be slacked on the operator side.)
Second, there might be a wrinkling problem that can occur when moving through a series of rolls with opposite offsets. (Image 1 Example — Going from Roll ‘E’ […, H:0.122] to ‘F’[…, H:-0.074] to ‘G’ […, H:0.040] may have wrinkling issues because the horizontal values are changing oppositely each time.)
Finally, rolls that can be nipped and are used to apply a layer of coating onto a substrate, as shown in Figure 5, can have misalignment problems that lead to uneven coating thickness. This is because there might be an irregular nip pressure across the surface of the roll.
One thing to note is that the roll alignment unit can measure rolls in the nipped and un-nipped positions. The nipped position is the ideal way in which to measure the rolls since this is the running position.
In a set of applicator rolls, one roll is fixed and one is nipped. By setting the fixed roll as the reference roll, the vertical and horizontal offsets can be analyzed for the roll that nips. (Example — The nipped roll in Figure 5 is showing that the operator side is vertically higher by 0.222 in.) This might be why the coating is not spreading uniformly.
All of these issues could potentially lead to unplanned downtime and additional costs.
Since the roll alignment unit was introduced for industrial use, a variety of industries have been able to take advantage of the technology. Vacumet Corp. Plastics Div. in Austell, GA, used this service to check the roll alignment of its vacuum metallizer. Vacumet provides vacuum-metallized holographic paper and metallized film for many consumer brands.
At Vacumet, a vacuum metallizer was checked primarily for preventative maintenance. Since metallizers run at speeds to 3,300 fpm, alignment is crucial to ensure they can produce output that meets all quality specifications.
Figure 6 shows the rolls inside the vacuum metallizing chamber, in the open and non-running position, while Figure 7 shows the metallizer in the closed and running position. It is evident the rolls can be measured in the open position by either traditional optical means or by the new roll alignment technology. However, the rolls can be measured in the closed position only with the new technology since there is no line of sight that can be obtained.
Two engineers from Pruftechnik Service measured the rolls in both the open (Figure 6) and closed (Figure 7) positions. It was determined there were noticeable differences in the roll alignment between the two positions. Ideally, rolls should be measured in the closed position as this is the running position.
Figure 8 shows the final Pruftechnik protocol for the vacuum metallizing chamber in the closed and running position. The illustration depicts all of the unwind and rewind rollers inside a vacuum metallizing chamber. The drum roll, where the film is processed, was chosen as the master reference roll.
The approach by Vacumet was to correct all of the rolls within a 0.015-in. tolerance. This was accomplished by using dial gauges and indicators to adjust the rolls at the bearing on either the drive side or the operator side, whichever was more accessible. The running position of the vacuum metallizer, which had never been studied before, was completely validated in a short period of time.
Steven Ward, process engineer of Vacumet Corp., says, “In order to provide our customers with the optimum quality end product, we wanted to ensure that our metallizers were aligned using the best technology available. We are also very conscious of regular preventative maintenance procedures that provide us with proactive rather than reactive actions for our equipment. This equates to smooth running machines, quality product, and happy customers.
“Pruftechnik Service provided us with state-of-the-art new technology that was able to properly align our machine's rollers, even with the metallizer fully closed. We have noticed an improved operation of our machine with prolonged life on our rollers and quicker startups.”
Inertial roll alignment technology is an effective way to measure roller parallelism and make necessary corrections in a short period of time. This is done regardless of line of sight and subjective human interpretation.
Best of all, Pruftechnik can validate the running position most of the time. Results are easy to understand, and the software allows the customer to analyze different arrangements of the machine.
Jay Tannan is a sales and service engineer with Pruftechnik Service Inc., Blackwood, NJ. He holds a B.S. in chemical engineering from the Univ. of Wisconsin-Madison. Tannon was a presenter at the 2007 AIMCAL Fall Technical Conference, where he received the John Matteucci Technical Excellence Award for his presentation, “Measuring Roll Parallelism in a Vacuum Metallizing Chamber Using Inertial Alignment Equipment,” upon which this technical report is based. Contact him at 856-401-3095 X204 or at firstname.lastname@example.org.
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