Alignment

Alignment is important to avoid compounding problems.

Alignment must take into account all three dimensions and operating conditions.  Operating conditions include start up, shut down, thermal expansion, gravity, and all other forces.  Equipment moves.  Equipment that is started and stopped frequently is much more likely to experience misalignment.

Institute a program to frequently check for alignment.  The best programs are non-invasive, such as vibration analysis or thermal imaging.  Indications of misalignment that are further down the P-F curve include noise, as well as material degradation.  If you look closely at the photo on the left, you can see some dust to the right of the hub.  This is actually metal that has been worn off.  The shiny portions of the hub indicate that the material is from the hub itself.  The position of the dust on top of the plate is further indication that the material is from the hub and indicates the direction the hub is turning.

Improper equipment operation, intermittent speeds, missed operations, etc are indications of misalignment.  If equipment remains in misaligned or unbalanced condition, it starts to cannibalize itself, like the photo above.  This reduces the useful life of equipment and can even require parts to be swapped out in order to even perform an alignment/realignment.

Misalignment also can increase energy usage.  Although this has been documented at low rates (1-3%), it still affects the overall cost of the operation.

Gravity is thought to effect mostly large, heavy equipment.  Think of the massive shafts that remain spinning to avoid sag.   However gravity can affect smaller equipment if the tolerances are too loose, or if the installation is not in accordance with the engineered properties of the equipment.  Belt drives on the bottom of a piece of equipment, must be engineer for these forces. You cannot turn a normally horizontal belt drive on its side and expect it to perform optimally.  Similarly, I have seen gear drives where the motor is directly above the driving gear.  This puts any unsupported weight of the motor directly on the gear.  When operating, this force is likely negligible.  But starting and stopping the system causes jerk which may loosen supports.  The extra weight can force a misalignment much more easily than a gear that does not have a motor hanging over it.

Even deeper than the drive train, the bearings themselves must be able to handle the forces.  Ball bearings, tapered bearings, needle bearings, babbitt bearings all have their places.  Proper selection of these is key to good alignment.

There are many excellent tools out there to help perform alignments quickly and accurately.  These will even compensate for thermal growth.  However understanding the importance of alignment and the consequences of misalignment make using any tool much better.  Just as in math, don’t learn to add and subtract on a calculator, until you can perform it without one.  Don’t use a tool for alignment until you have performed one the old fashioned way – with dial indicators or even string.  The fundamental understanding from using these simple tools, makes using the advanced tools easier.  The tools don’t perform the alignment.  They give you information to perform the alignment.  People are still making the final decisions, and often the actual adjustments.

Does anyone have an alignment sheet that they find particularly useful?

 

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