Disassembly of a centrifugal fan

[BroadReach]

Does anyone have any tips on how to disassemble a centrifugal fan?

It is a double inlet type with an external rotor motor, i.e. the central shaft is stationary and the rotor / impellor assembly rotates.

The impellor / rotor assembly comes out easily enough by removing one of the end support spiders.

What I wluld like to do is disassemble the impellor / rotor assembly to look at the bearings.

The image is of a similar design to the one I have.

Any ideas?

 

[telectrix]

remove all screws. pull it to bits. reassemble in reverse order and if you only have 5 or less screws left over, job's a good 'un.

 

[Spoon]

Take pics of each stage, just in case you forget there bits go.

 

[Guitarist]

To be perfectly honest, only you, with the fan in your hands, will be able to see how it needs to come apart. There is always the chance that it's pressed or riveted and not meant to have its bearings replaced.

 

[Engineer54]

What are you going to do if the bearing are found to be shot, (which would have been evident before any disassembly)?? Do you have the equipment to pull the bearings and drift the new bearings back onto the shaft?? These day's, it more cost effective to give the assembly to a workshop and have to job done professionally, than to start faffing around trying to do it yourself...

 

[vaughant]

What are you going to do if the bearing are found to be shot, (which would have been evident before any disassembly)?? Do you have the equipment to pull the bearings and drift the new bearings back onto the shaft?? These day's, it more cost effective to give the assembly to a workshop and have to job done professionally, than to start faffing around trying to do it yourself...

have to agree with that,extremely unlikely it will be more cost effective to repair than replace.
if its just cos you don't want to bin it and have a spare then have a play about,it's gonna be different for every motor so no real advice other than to google image the part number and see if there's an assembly diagram for it.

remember if its Ex equipment your not meant to fiddle about with it.

 

[stranded]

Take pics of each stage, just in case you forget there bits go.

Defo do that. Sometimes screws vary slightly for different bits, so set the screws with the bit you remove if you know what i mean. As guitarist says,though, might not be meant to come apart...

 

[stranded]

What are you going to do if the bearing are found to be shot, (which would have been evident before any disassembly)?? Do you have the equipment to pull the bearings and drift the new bearings back onto the shaft?? These day's, it more cost effective to give the assembly to a workshop and have to job done professionally, than to start faffing around trying to do it yourself...

have to agree with that,extremely unlikely it will be more cost effective to repair than replace.
if its just cos you don't want to bin it and have a spare then have a play about,it's gonna be different for every motor so no real advice other than to google image the part number and see if there's an assembly diagram for it.

remember if its Ex equipment your not meant to fiddle about with it.

Most things are built "disposable " nowadays anyway " ah sure it's broke. buy a new one. Stuffs not built like years ago, even electronics, cheap chineese crap now.

 

[chrish_1977]

remove all screws. pull it to bits. reassemble in reverse order and if you only have 5 or less screws left over, job's a good 'un.

Or I also like to call it weight saving too

 

[Marvo]

I can tell you that the Ziehl, EBM and Systemair fans with external rotor motors aren't designed to come apart. With the older generation I made a special tool for splitting them and also a checking fixture for reassembly with a press but the new ones are a lost cause. If anything fails the whole fan goes in the scrap bin.

 

[Silly Sausage]

Remember, we're men, we like taking things apart!




Then trying to work out how to put them back together...

 

[stranded]

Remember, we're men, we like taking things apart!




Then trying to work out how to put them back together...

Done that far too many times, cant help mself though...

 

[Silly Sausage]

Done that far too many times, cant help mself though...

I've got three pinball machines in several 1000s of bits at the moment.
Must deal with it, worth about £6000 when they're all done!

 

[vaughant]

Yeah if there's nothing better to do then have a go at stripping it out but if its important and not working get a new one first!!!!

 

[telectrix]

and if you fit it and it seizes and catches fire, who's in the dock? BIN IT.

 

[BroadReach]

Thanks for all the tips and comments.

I take on board what some have said about economics / viability of repair but in this instance it is not the intention.

Just looking to investigate bearing failures in a unit.

Got the thing apart in the end, not too dificult, but defo not designed to be stripped and re-assembled as many have suggested.

One bearing dry, signs of residue inside and a distorted ball carrier. Looks like the grease has separated and caused the failure. The other was on its way with dry gritty grease.

I will check the windings resistance against a spare unit tomorrow and see if I can work out cause and effect.

Looks to me like a mechanical issue but we will see.

 

[Marvo]

If the lubricant has dried out then it was probably running hot. The load on the motor is generally predictable because it's a fixed bladeset and centrif fans (especially backward curved) aren't prone to overloading. Assuming there was nothing jammed in it and assuming the capacitor hasn't failed my next question would be was the fan on some kind of speed controller?

 

[BroadReach]

Hi Marvo,

Speed controller yes. Voltage controlled using a torroidal transformer (wound as an auto transformer I think) and 5 relays to switch the voltage.

The fan motor is suitable for this arangement according to the manufacturers.

Overheating is what I thought too, just need to work out how.

 

[Marvo]

Overheating is far more likely if it was run on a voltage speed controller. The external rotor motors get away with murder because most of the heat in any motor is developed in the rotor and with these motors the rotor is directly in the airstream. However if they're installed in a system that might reduce that airflow (fire dampers, modulated diffusers etc) then things go south very quickly with runaway heat and usually the windings are the first victims.

If the motor runs hot but there's no thermal runaway then over a longer period it's usually the bearing lubricant that suffers. Once the lubricant starts breaking down the bearings run hotter causing further lubricant breakdown....more heat...less lube until catastrophic mechanical damage to the bearing rollers and races.

I would double and triple check the suitability of the fan for voltage 5-step speed control. Some models of fans were suitable with the older generation motors but not with the newer motors. This causes confusion because the fan model number stayed the same but the motor was actually different.

Rule of thumb, avoid voltage speed controllers like the plague. They're bulky, large form factor, expensive, inefficient and they cause hot running of motors. Stick to variable frequency drives.

 

[Engineer54]

What sort of system was this fan a part of??

 

[PEG]

I've got three pinball machines in several 1000s of bits at the moment.
Must deal with it, worth about £6000 when they're all done!

IF your customer is a deaf,dumb and blind kid,i think i know some of his songs....