Commercial Fan Unit

paul_79

we get these from a local vfd install company for about a $ 125 they are brass and have a carbon type brush with a spring assembly that keeps the brush against the shaft as it wears down . we have had some on for 4 years and they have hardly worn at all . we have made a little bracket that holds the assembly and its grounded simple to install . I will try and get you a name and part number for this brush kit. go to emcsolutions.com and get the service number and ask for t.c. or bruce

Darrell

help me please

I spent way too long beating a bearing off of a 1-3/16 shaft ther other day. Broke my puller, and my knuckles...had a blood letting. Discovered under the five year old bearing alot of tracking and corrosion. This unit is a large, (48"), wheel that is 6 feet wide and runs quite fast...I can't read my rpm note. An engineer is telling me that the tracking and scoring is static discharge going to ground through the bearing and shaft and that my bearing was actually welded to to shaft. Another engineer is telling me the sidewise pressure of the large motor and 80 inch belts and the 18" shaft between the driven bearing and the pulley is putting enough strain on the bearing it created a "peizo-electric discharge" going to ground through my gearing and shaft.

The original shaft and bearing lasted 20years.

Can anybody give me some real insight here? The building sup is furious that a five year old bearing needed changing and that it took so long to do so. The bearing did not spin on the shaft...I temp it regularly and changed it when the temp started to climb.

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paul_79

bearing

was this air handler on a vfd drive

paul_79

bearing

was this air handler on a vfd drive

bob_46

Brg.

Darrell, what did the rest of the bearing look like, was it fried? I can't see how it could be a piezoelectric effect as there is no crystal to squeeze. I have found the easiest way to remove a bearing race welded to a shaft is with a 4" grinder and a thin wheel. Cut the race, maybe in two places, almost all the way to the shaft and give it a whack with a cold chisel. It will fall off and sometimes you can save the shaft.

Darrell

No, the fan turns at a fixed rate, with variable vanes on the ends that regualte the amount of air allowed to flow through the wheel.

The bearing did not fail. I regularly temped it with an infrared gun and when the temp started to rise on the chart I made plans to change it out before it failed because re-shafing this unit was a royal pain five years ago. I s'pose I'm kinda paranoid about bearing failure. The trailing bearing is running about 20 degrees over ambient. The driven end bearing ran about 35 degrees over ambient for nearly five years and then started to gradually climb...when I changed it this last week it was running about 75 degrees over ambient.

The air stream is clean and dry.

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paul_79

i have had trouble with bearings failing on blower motors with older vfd drives on the units we have( about 50 air handlers 20hp and the bearing races get pitted from transient voltages from the drives. newer drives have eliminated this problem .But for the blower bearings you may be getting something of the same problem. we have been putting on a brush kit on the motor shaft to take care of the problems. since we have been putting on the brush kits after we put in new bearings we have not had any bearing problems. we sometimes replaced bearing on the same motor every 6 months before this fix

paul_79

maybe you could use this on the blower shaft

Darrell

What are these brush kits? The engineers talk about usng grounding bearings and I've ordered a set...but I want to know what the problem is so I know I'm fixing it. Plus, it makes me sound a little more intelligent...and that helps.

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mtfallsmikey

Hey Paul!

Can you explain this phenomenon? I have honestly never heard of this before. I have 12 100 ton Trane self-contained's in my buildings, one with bad motor bearing, another with a fan bearing starting to get noisy...and is this problem common?

paul_79

vfd

it is a problem that surfaced when people begin to use vfd variable frequency drives on air handler motors pumps ect. if you google vfd and bearing problems you can read the the engineering papers and some of the fixes. we have had this problem at our facilities for years because we have older misubishi drives on our air handlers (15 years now ) our crew was changing bearings on motors on AH way to often so we took the bearings down to a motor shop and they pulled it apart and it had the classic vfd pitting or tracking on the race. they had just read an article in a trade magazine and a grouding brush kit is the way we went. i hear from the vfd installers the new drives don't cause these problems .i dont know if the blower shaft pitting on the blower bearing is the same but it sounds as though his engineer thinks it is the same type of transient voltage caused by maybe static off of the belts dry air ect. on the turnig guide vane set up

Darrell

When I put the grounding bearings on I'll get some pictures and re-up this thread.

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mtfallsmikey

Great!

I brought this up at our quarterly engineer's meeting yesterday...mostly blank stares!

Darrell

Well, you're no help! But, I appreciate the effort.

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