I'm going back to the hot fan syndrome again.

We just installed a new overhung 8-blade fan and new housing. Fan blade weighs in a 480 pounds. Started it up in Feb. We had a two week shut-down on this unit, and this past Friday it came back up. Operations wrote it up as vibrating badly. Yesterday I went down and balanced it. Had 1.75 amplitude on the reference run, wow! Ended up adding 12.0 oz of weight split on two blades. Terrible...Shook all the oil out of it and everything.

I'm still trying to figure out a way we can run these until they cool, and have suggested this to our supervisor. Got to be this shaft sag we've been talking about...I've mentioned installed a vent valve after the fan, to vent to the atmosphere, just like we do our blowers when we bring them up. Must be a way to solve this problem!

Take Care

Rod,

Good timing I am getting ready to tackle my customers again next week.
One of the ones we were having trouble with we found the outlet (under the floor where it attaches to a dryer) all corroded and ate up. There was 1 bolt out of 8 left in it. The problem is you can't get to or see this area without taking a lot of insulation and crap off. Finally convinced management that we had to look in there. It has behaved much better, but IT STILL runs higher hot than when we balance it cold. We balance it down to 0.08 to 0.1 mills at 2900 RPM. IT will run 1.0 - 1.6 mills at 2900 when hot. It is better than 8 mills which is what it was before fixing the base.

Next week I am going to inspect the bottom end of one other that we have had the same problem with.
I'll let you know what we find.

Dave

Good luck there Dave...!

The thing that really gets my goat is that it's a new fan assembly, but it has a reconditioned carbon steel wheel on it. I didn't like that to begin with, but it's what we had available here. Not even 1/4 thick. More like 3/16 down to 1/8"....Thin stuff. My final trim run was .14 not too bad consdering it was running 1.7 ips....I found out immediately after finishing that job that the fan would be down again for 2 to 3 more days...I suspect I will have to redo the job...You think??

Later

Rod, have you checked the runnout on the shaft, outboard of the fan-end bearing next to the housing. You could then extrapolate out to the end of the wheel to guesstimate the shaft centerline offset at the wheel. Had a hot fan recently on a lime kiln that I found running 20 mils at 700 rpm. The TIR was 0.007 about 4" from the bearing. I extrapolated that to about 0.040" at the wheel.... that would do it, I think. Took about 10 lbs. of weight to balance this.

Rod, I was wondering if the fan is constructed with a cone in the center or with hollow blades? I have had several cases with water and or sand blast sand inside the wheel that would cause the fan to have to be rebalanced after downtime of the fan. Remedy was to burn weep holes in the fan tips or the cone and balance after that. Operations sand blast or water wash fans to clean to clean them and if there are any hair line cracks it will get inside. Regards!

No, everything is solid standard carbon steel.