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Frequently Asked Questions
Yes. Rolls should be parallel to ensure that the product being created is uniform and of good quality. Parallelism of rolls is even more important when machines are running at very high speeds and when the rolls are very close to each other.
How has parallelism traditionally been measured? Traditionally, parallelism has been measured by optical means, using a theodolite and measurement telescopes. This is a time consuming method that depends on many factors including line of sight, dependence on an external "centerline" that is separate from the actual machine, and optical readings. PARALIGN uses three ring laser gyroscopes that can detect inertial movement. No line of sight is required. This helps us achieve very reproducible results. How does a ring laser gyroscope work? Two lasers travel in opposite directions on a triangular route. When the gyroscope is rotated on its axis, one of the lasers’ rotational paths is shortened while the other beams’ path is lengthened. The difference in time between the two laser beams is its angular change. PARALIGN consists of three ring laser gyroscopes, enabling is to take measurements in three-dimensional space. (Roll, Pitch, and Yaw).
How can PARALIGN be parallel on the roll without V-Blocks? Before measurement, PARALIGN is calibrated relatively parallel to the rolls in the machine. The PARALIGN software has a filter that ensures that PARALIGN stays within range. It also has an audible validation clicking sound which is heard when in range and only values in that range are used in its calculations. These algorithms allow us to achieve the most reliable results without additional mechanical support. Why must PARALIGN re-calibrate every 20-30 minutes? Due to the fact that the rolls position is measured in space, the PARALIGN must factor in the constant rotation of the Earth. Can I move the roll with PARALIGN on it? There is no need. A graphical report is generated that specifies direction on how to move rolls. Re-measurement after movement can be done in a matter of minutes. It is beneficial to have the PARALIGN service team measures the location of each roll, and then decide which rolls the millwrights should move. Where on the roll can PARALIGN take a measurement? The PARALIGN can be placed anywhere on the rolls’ surface as long as we have access to 20 degrees (minimum) for the patented Sweep measurement. This includes top, bottom, or sides. 'Sweep' measurement: To record the measured values PARALIGN simply slides a short distance along the surface while the roll is stationary.
How many rolls can be measured in one day? Depending on where each roll is located and the accessibility available, in an 8 hour day, 40 or more rolls can typically be measured in a paper mill, and 60 or more rolls in other applications are typical. We offer PARALIGN Service for roll alignment as a service to our clients. PRUFTECHNIK does not sell PARALIGN at this time. Why does your service not also move the rolls? In most cases it makes more sense for a mill to make corrections while the PARALIGN service team continues taking measurements. The graphical report shows the customer the entire map of their machine and allows them to decide which rolls are the best choices to move. Why are there two service engineers? There are always two engineers at a site. One Engineer is used to measure on the surface of the roll, while the other holds the computer to view and validate all data received. What can be used as a reference for parallelism? The term ‘reference’ refers to any roll that is repeatedly used as a fixed point. Readings can be plotted out using any roll as a reference point. This reference point can be changed later with no effort. Does accuracy depend on the location of the roll? The accuracy of PARALIGN does not depend on the location of the roll. The roll can be 10 feet high, behind a wall, or in another building. Line-of-sight or distance do not matter either. What is the smallest roll that can be measured? The smallest roll can be 43cm (17 inches) in length and 8mm (0.315 inches) in diameter. Can PARALIGN determine crowned or bowed rolls? If the crowned or bowed condition of the roll is known, rolls of that type can be measured using the Sweep method in three positions (operator, center, and machine/drive) on the surface of the roll. Can the PARALIGN determine level of a roll? PARALIGN can determine the level and square (horizontal and vertical offsets) between any rolls; it cannot determine absolute elevation in the machine. What is the calibration plate? The calibration plate is the reference point that is used to re-calibrate every 20-30 minutes for the rotation of the earth. This plate is set relatively parallel to the rolls in the plant at the beginning of each measurement job. The "reference roll" does not have to be a roll. Ideally, a calibration plate is attached close to the machine and used by the PARALIGN as a reference. Or PARALIGN is "zeroed" on the reference roll before beginning measurement, i.e. the laser gyroscopes are adjusted for the earth's rotation.
When can we see the report for the measured machine? The graphical report can be presented as soon as a set of measurements are performed. Usually we present different stages of intermediate reports throughout a day. Why does PARALIGN not use a centerline? PARALIGN measures relative parallelism between rolls and does not require an external reference such as a centerline. This way any errors because of a faulty centerline (ground settling, bad plugs) are avoided. What if I want to change the reference roll? With the click of a button the reference roll can be changed. More than one reference roll can be given at the customers’ request. What if my reference roll is not suitable? Since the reference roll can be changed very quickly and easily, a more suitable roll can be chosen at any time. There is no such thing as a ‘right’ or ‘wrong’ reference roll. Do you need optics to set-up your measurements? The use of optics is not needed to set-up our measurements. We do not need to use the centerline or have any line-of-sight in order to find the parallelism between rolls.
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