When aligning rolls, be they paper mill, printing presses or film lines, the most difficult alignment is the horizontal parallelism. The vertical parallelism or levelness can easily be check using a machinist level or with Hamar's new EL-905 or EL-905 Electronic Bubble Level.

Choosing a Reference

Conventional methods of roll alignment usually use floor benchmarks (monuments) at the side of the machine as references (See "Choosing A Reference Point"). The L-742 or L-732 offers the versatility of using these benchmarks or of picking up a reference roll, such as a cooch roll on paper mills.

However, we strongly believe that using a reference roll provides the most accurate reference and results in better alignments. Benchmarks are usually set in a thin concrete floor, are rarely covered, and are routinely run over and nicked. More importantly, they move with the slab of concrete and rarely hold their position relative to the mill itself. Most floors in a typical plant have multiple slabs and are usually cracked throughout, creating instability of the monuments. Unless checked every time they are used, the use of the benchmark probably will result in significant alignment errors.

Horizontal Roll Parallelism

Here's how the process works for picking up a reference roll: (keep in mind that the L-742 or L-732 is like having 2 walls, both perpendicular to each other, 100 feet (30.5 M) in radius and very flat).

First, the laser is placed on an instrument stand near the reference roll at the side of the machine and leveled using its 1 or 2-arc-second level vials. Then, the vertical laser plane is made approximately parallel to the reference roll using visual aids.

Second, one target is placed horizontally on the reference roll at the closest point to laser, adjusted until it detects the laser and zeroed. It is then moved to the far end of the roll. A second target is placed on the same point on the roll that is closest to the laser (see "buck-in" graphic) and zeroed out. Since both targets were zeroed at the same point on the roll, they become the reference points for the roll.

Then the vertical laser plane is "bucked in" or adjusted until the same reading appears on the 2 reference targets. The laser plane is now parallel to the reference roll.

Third, since the laser is placed outside the machine and the second vertical laser plane is perpendicular to the first, the second laser plane, in effect, becomes the offset centerline of the mill. This offset centerline has a range of 100 feet (30.5 meters) on either side of the laser. To measure other rolls for parallelism, the offset centerline must be temporarily established by placing 2 reference targets, horizontally, either on floor fixtures or on the side frame of the mill. The reference targets are zeroed, thus becoming the offset reference line and are not touched during the remainder of the alignment.

Fourth, to check the parallelism of an individual roll, the laser and stand are moved along the offset centerline until the desired roll or section of rolls is reached. The laser should be positioned to allow about 4-5" of horizontal space between the laser plane and the roll to be measured. The instrument is then leveled.

Fifth, the yaw adjustment on the laser base is used to make the second vertical laser plane parallel to the offset centerline, using the temporary reference targets as guides. When the same reading appears on both reference targets, the laser is parallel to the centerline. This task has been greatly simplified by "A-B" Feature of the R-1309 Cassiopeia Readout and the A-1519 Single-Axis Wireless Targets. The feature subtracts one reference target reading from the other and displays the difference in a graphical format. Simply adjust the laser until the difference is zero and the laser is bucked in!

Finally, a target is placed horizontally on the roll closest to the laser and zeroed. The target is then moved to the far end of the roll and the deviation from parallel is measured. Since the readings are live, the roll can then be adjusted until both near and far target positions read zero, which would mean the roll is aligned and parallel to the reference roll.

Since the laser generates a plane, rolls at any elevation in that section that are within 2 feet (610 mm) horizontally of the laser plane can be measured for parallelism without changing the setup of the laser.

Leveling Rolls

For checking level on applications with multiple rolls in the same horizontal plane, the L-743 or L-733 must be used since they have a horizontal laser plane in addition to the 2 vertical planes of the L-742 or L-732. The laser is leveled and a target is placed on one end of the roll and zeroed. The target is then moved to the other end of the roll and the deviation from level is measured. If both readings are zero, then the roll is level. If not, it can be adjusted using the target as an electronic indictor.

For checking level of rolls at many different elevations, our A-700 Electronic Level can be used. It has a swiveling readout, v-block base, 1 arc second accuracy and a strapping system to prevent it from falling off the roll.

Checking Drive Shaft Alignment

To check the drive shaft alignment, the L-742 or L-732 is placed either at the end of the drive shaft or in the middle, depending on the how long it is. The horizontal plane is made parallel to the top of the closest drive shaft using vertically mounted targets and the vertical scan plane is made parallel to the side of the same shaft.

Each shaft is checked for parallelism to the reference shaft and aligned accordingly. To check a shaft for parallelism/colinearity, a target is moved from the reference shaft without re-zeroing, and two measurements are made, one at either end of the shaft. The difference between the two readings is the angle of the shaft relative to the reference shaft and the average is how far off center it is from the reference shaft. Up to 200 feet of drive shafts can be checked with one setup.
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