August 3, 2011
Words to Make You Stop & Think
By Patrick Lawrence
- What the…??
- What did it say again…??
- But I just did that…
- How in the world…??
- There’s no way…
- Sacre bleu!
We hear phrases like these in class and in the field. Chances are if you’ve been aligning equipment for a while, you have a feel for how the job should progress. When something goes wrong, you’ll see it in the numbers. Shim it up, take them out, push it over here, push it over there…. Statements like these should not go unchecked. Trust your gut feeling–it’s time to do some troubleshooting.
Here are a few things to look for if your alignments are not successful after two attempts.
Problems while taking data:
- Loose chain brackets
- Loose extension rod on chain/magnetic bracket
- Sensors mounted to something loose (hub loose on shaft? Mounted on coupling element cover instead of solid part of coupling?)
- Sensor brackets deflecting while turning (rubbing bearing housing, hitting a bolt, etc.)
- Background vibration (through piping, bases/foundations)
- Wrong dimensions entered
Problems with machines being aligned:
- Soft foot
- Loose hold down bolts on movable
- Loose hold down bolts on stationary
- Looseness in coupling
- Shaft deflection while turning
- Temperature changes
- Looseness/rubs in bearings
- Inadequate base (thin, cracked grout, etc.)
- Cupped washers
- Bolts/tapped threads not true
- Crowned/cupped bases affecting horizontal/vertical moves
I would consider looseness in coupling as backlash.
Backlash may affect the alignment job but not machine performance.The reason is if the machine turns in the correct direction the coupling elements always run on the driven tooth flanks in gear coupling. This is also valid for all coupling type as they always run on the driven side of elements. Then there is not the problem of looseness while machine is running.