The parallelism of rollers in a coil coating production line is critical to the quality of the product. While coil coating lines are running at faster speeds and becoming more complex to meet demand, rollers are still typically aligned using the time consuming optical means. However, a relatively new PARALIGN inertial roll alignment system offers a faster approach to roll alignment. While this system is typically used alone, it can also integrate readings taken by other techniques.
A case study of the utilization of this new system to compliment an optics team in a coil coating line has been examined.
Inertial Roll Alignment System
PRUFTECHNIK AG has developed a new approach for measuring roller parallelism that uses inertial technology to perform a roll alignment survey. The Paralign is a portable, self-contained device which houses three high precision ring laser gyroscopes that can measure the roll, pitch and yaw of the device. This is the same technology used by air and spacecraft for navigation.
In the ring laser gyroscope, two laser beams travel in opposing directions on a triangular path. When the gyroscope is rotated on its axis, one of the laser beams' path is lengthened while the other beams' path is shortened. The PARALIGN then measures the difference in time between the two laser beams and uses the information to determine the device's angular displacements.
During the PARALIGN service the device is placed on a roll and swept 20° across its face. The system takes the angular displacements and computes the vertical and horizontal operations of the rolls.
This information is immediately sent to a computer running the PARALIGN software, which contains a drawing of all the rolls on the line to be measured. Offsets are instantly displayed on the drawing. Offsets can be displayed in reference to any roll on the line. Typically, it takes about 30 seconds to measure a roll. Due to the advanced software used, the skill of the PARALIGN user does not affect the accuracy of the readings, as poor readings are filtered out.
Inertial Versus Optical
Optical measurements depend on the establishment of monuments and maintain a line of sight with the theodolites, the monuments and the rolls. If a theodolite is moved or bumped, the entire alignment process will need to be restarted. Unlike optics, PARALIGN does not require a line of sight. As long as the roll is accessible, has a somewhat smooth face, and 20° sweep can be performed, the roll can be measured. Therefore the service is far more versatile and less intrusive to other activities that may be performed during an outage.
Other measurements also become less accurate as they measure rolls farther away from the reference toll. The system can accurately measure rolls independent of their location. A roll located 100 yards away and three stories up from the reference roll will be measured with the same precision as a roll five feet away.
While the system is the fastest method to measure the parallelism of rollers, it does have limitations. It can only compare offsets to another roll on the line. Therefore, it cannot determine the level of the rolls with respect to the Earth surface, nor can it determine the rolls orientation with respect to the centerline of the machine. However, an optics team can make these measurements. Therefore, it is possible to use an optic team to align the reference roll to both level and the centerline of the machine. The system can then be used to measure that roll and the rest of the line. This approach will give you the advantages of optical methods and the speed and precision of a PARALIGN service.
PARALIGN service in a Coil Coating Line
Earlier this year, we performed a Paralign service for an Amerimax Building Products coil coating line in the company's Helena, AR. facility. The project called for all aligning all rolls on the horizontal plane to one of the coating drums in the line's "wet" section. In addition to having the rolls aligned with respect to each other, Amerimax also wanted the have the line leveled to the Earth's surface.
On the first day, our engineers measured 130 rolls. The next day, the optics team leveled a roll true to the Earth's surface to be used as the reference of the vertical plane. Engineers then measured this roll with PARALIGN. The fact that the references for each dimension came from a different roll was not an issue. The system software allowed us to insert a Master roll that has the desired alignment in both dimensions. That roll was then set as reference roll by which the other rolls' offset would be calculated.
One of the most problematic sections of the line was the washing tanks. There were six rolls in the bottom of the tanks which were enclosed and would have been difficult to measure with optics. Our engineers were able to access these rolls via hatches at the base of the tanks. It was found that one roll was significantly misaligned and all were adjusted to be aligned with the master roll.
Rolls located at the top of these tanks, several stories above the ground would also have been difficult to measure with optics. However, we were able to measure all rolls within 20 minutes. After readings were taken, all necessary adjustments were made to correct offsets and Amerimax officials were completely satisfied with the results.
Published in: Coilworld (October 2013)