Focus on Alignment: Eliminating human error in shaft alignment
By Ted Pater
Today's laser alignment systems can perform many alignment tasks, from the classic shaft alignment to more difficult jobs such as universal joint drives, cooling tower drives with the wall between the...
Today’s laser alignment systems can perform many alignment tasks, from the classic shaft alignment to more difficult jobs such as universal joint drives, cooling tower drives with the wall between the equipment (no line of sight), extruder barrels (bore-to-shaft alignment), hydro vertical shafts (plumbness), bearing pockets, steam turbine diaphragms, spindle alignment or reciprocating compressors, crosshead-to-cylinder alignment, and more.
Effective laser alignment solutions include optic systems that have come a long way since the introduction of the first industrial laser system in 1985 by Prftechnik AG in Germany. Today, the measuring principle still remains the same–a very precise laser detector measures a beam movement during the measurement. A computing unit calculates misalignment and all the necessary corrective moves.
The computerized system eliminates human errors in reading, recording and interpreting measurements. The alignment results can be stored in the memory of the hand-held computer, printed out providing a hardcopy, and also transferred to a PC for alignment trending.
Here is how it works. The laser beam movement from the emitter mounted on one shaft is recorded on the receiver mounted on the other shaft. The shafts can be coupled or uncoupled during the measurement. If one shaft cannot be rotated, a special magnetic sliding bracket can be used.
The heart of the measuring system is a high-precision laser detector consisting of two detectors and an electronic inclinometer as a part of the five-axis detector. A double detector allows measuring shaft angularity the same way as Sherlock Holmes was able to determine a bullet path looking at a double pane window.
The receiver is connected by cable or infrared link to a portable, hand-held computing device. After entering a couple of machine dimensions and rotating the shafts, the alignment results are calculated and displayed. The correction moves can be watched live on the screen. If there is a bolt bound problem, the computer can calculate the moves on the stationary machine. A train alignment can be checked and analyzed for the best moves through a simulation on the screen, before actually moving or shimming the machine feet.
The correction moves are continued until alignment is within the tolerance, which is indicated by happy face images on the screen. The tolerance table is based on the coupling type and RPM. The spacer couplings and jackshafts are more forgiving for misalignment than short ones.
System features include:
Alignment of coupled or uncoupled shafts of any length, including universal joints.
Shafts need to be rotated only a quarter turn from any position, in any direction.
Machine train alignment with multiple couplings.
Thermal growth calculation with built-in calculator.
Alignment simulation for “what if” scenario when some machine correction moves are not possible (i.e. bolt bound).
Cordless measurement (without the cable attached to the computer).
Time-saving machine templates with the real machine names can be created to match the plant database, including identifications, dimensions, tolerances, targets, etc. These are similar to the templates used in a word processing program.
Print graphic reports directly from the instrument.
Fully compatible with dial indicator readings. Laser alignment data can be converted into dial indicator format or vice-versa.
Record alignment job progress with user-defined labels such as “as found,” “piping attached,” “as left,” etc.
Soft foot analysis.
A soft foot condition occurs when the machine feet are not making contact with a machine base. The machine behaves differently each time it is aligned. This causes a lot of frustration during the alignment procedure, since the machine is still misaligned following all the precision adjustments. In addition, the additional stress can distort a machine housing when it is bolted down or when piping is attached.
There are four types of soft foot:
Parallel soft foot–when a machine foot is parallel to the machine base.
Angular soft foot–when a machine foot is at an angle with the machine base.
Squishy foot–when a surface is corroded or damaged. A feeler gauge cannot be inserted under the foot, however some shaft movement can be measured when a bolt is loosened.
Soft foot from external forces such as piping.
Each type of soft foot requires different corrections. A laser system can determine and measure the soft foot very precisely. One system available even has a special program called the Soft Foot Wizard, which can determine parallel or angular soft foot conditions.
Laser measurement and computer processing have changed forever the age-old mechanical procedures for performing shaft alignment. The cost savings in reduced machine downtime, added to the cost benefits of increased machine uptime, more than justify the acquisition of a laser shaft alignment system.
Ted Pater is the technical manager for Hyatt Industries Limited of Vancouver, B.C., a distributor of Prftechnik laser alignment systems. He can be reached at (604) 736-7301 or by e-mail at email@example.com.