Broke off electric motor fan blade. Try to fix or replace?
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  1. #1
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    Default Broke off electric motor fan blade. Try to fix or replace?

    Wondering if someone with some electric motor experience could help me out. I made a huge mistake and broke half a blade off of this 7 blade fan on my electric motor. It is a 132S frame 7.5 HP motor. I believe the fan is fiberglass of some type. Would you trust jb weld to hold it back on at 1500 RPM? Would any replacement electric motor fan work as long as the shaft and bore are correctly sized? Is balancing an issue if I was to replace fan?

    Please Help. I really stepped in it. LOL

    img_5756.jpg

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    I notice you're located in Alaska so this may be bum info. Almost any reputable motor shop has a bin full of fans they've removed from junk motors as well as generic fans with a universal hole for different size shaft adapters which they would also have.

    Having said that...it's not verboten, depending on the service duty of the motor, to trim all the blades of the fan to fit the shape of the broken fin, thus making them all the same. This will work if the broken fin is still mostly intact. The fan will move slightly less cooling air but unless the motor is in a severe application it will make little difference.

    Stuart

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    I would put it into service as it is if that were mine, and only go back in if it seemed to cause any issues. If you are worried about balancing then trim the opposite blade to balance it out, and leave the rest intact. I wouldn't think that small blade will show much vibration in a used motor. (I could be wrong)

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    Or drill a hole in the broken blade and use a nut and bolt to approximate the lost piece weight.............Bob

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    If it is drawing under 4hp I would just run it as is until I could source a fan. Try JB weld or an equivalent but use the slow set version and in a temperature controlled environment say 70F so that it has time to react and cure. I have had good success with the JB plastic weld.

    On the other hand I had a TEFC motor run over 10 years without a fan just above a sand wash screen. Continuously sprayed, it was water cooled and was still running when I sold the business.

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    I'd have no hesitation in gluing that blade back on. I've done it before and it didn't seem to have any adverse affect.

    Just running it as is would probably also be fine, as others have said.
    Last edited by awander; 01-12-2020 at 04:20 PM. Reason: punctuation

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    Don't "glue" it on... If it comes off and jams the motor at startup, you will be in far worse shape. Maybe mechanically fasten it but I wouldn't. The mass of the fan is so low in comparison to the stator it will not affect balance materially. If it's a reputable brand, you can just order another fan as a spare part, and replace later. Heck, if you know someone with a 3d Printer, give them the old and they they can make you another.

    Not so sure about trimming the other blade to be the same... this type of fan needs fairly small clearance to the shroud to move air well. If you are really worried about cooling, take the fan off and mount a standard 4 inch computer fan on the end. As others have said, the need for the fan really depends on your load and duty cycle. If you are unsure what that is, measure your input current wrt the FLA rating on the name plate (it's not linear, but if you tell us what it is someone can help). Best way, put your hand on the motor and see how hot it gets in use.

    Also, just splitting hairs, is it really 1500 rpm? at 60hz, more like 1750.

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    When I read about this I regret not buying a plastic welding kit.

    If you like strange or weird motor noises then just put it back together.
    Some plastics will never hold together no matter what glue.
    I would come up with a few metal pins with tapped 2-56 holes going radially on each end. Each pin is half way in each piece, then fasten with 2-56 screws.

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    Just run it you will never know.
    Don


    Sent from my iPhone using Tapatalk Pro

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    Believe it or not there is an outfit that has motor fans for just about any configuration.Not at work now but I found them on Google.
    As others have said just trim the opposite blade the same wont make any difference or just cut them both flush with the base so you don't have to fiddle around trying to match them.

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    Ignore it and run the motor. It's not a precision matched aerodynamic design and it's so light that the motor won't notice the difference in balance.

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    Quote Originally Posted by D Nelson View Post
    Just run it you will never know. . .
    Quote Originally Posted by Mark Rand View Post
    Ignore it and run the motor. . .
    Agreed. Besides, you can't trim 'the' opposite blade on a 7-blade fan! And, trying to take half off the two opposite blades isn't worth the effort. Plastic motor fans get damaged all the time, and usually aren't noticed until teardown for some other reason.

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    I would just run it as is. But, if you wanted to fix the blade and give it some tensile strength, drill some small holes along each edge, then stitch it back together with some buss wire. Then cover it with hot glue.

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    How hard can it be to make a little sheet metal circle, cut some strips of metal and fold them to 90 degrees lengthwise and pop rivet them to the circle? You don't have to make a propeller. Something like a paddlewheel will work fine. Just smash the air and it will find its way out of the motor leaving lower pressure behind so a continuous air flow results.

    Or order the right replacement fan blade from Grainger.

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    Quote Originally Posted by metalmagpie View Post
    How hard can it be to make a little sheet metal circle, cut some strips of metal and fold them to 90 degrees lengthwise and pop rivet them to the circle?. . .
    A lot harder than just running it the way it is!

    Quote Originally Posted by metalmagpie View Post
    . . .Or order the right replacement fan blade from Grainger.
    Grainger charges 100-200% more than 'normal' for everything they offer.

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    Quote Originally Posted by Gordon Heaton View Post


    Grainger charges 100-200% more than 'normal' for everything they offer.
    and another 200% for shipping

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    If Grainger has it, buy it from Zoro. Same outfit, WAY better prices and free shipping for orders over $50

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    I was able to call around and find a used fan from a electric motor shop. He is going to slip it in the mail for me. It is a american motor sized fan but nothing my lathe and a boring bar can't fix to make bore fit my 38mm shaft. It was the OD and depth that is important. I considered trimming the opposite blades, but this replacement fan only cost me shipping and little time so that is what I'm gonna do.

    Thanks for help PM!

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    I did something like this with a 1-1/2 HP motor. The plastic fan broke and melted. I cut a disk.
    6" dia. from a sheet of 1/8" 6061 aluminum. Made a hub, screwed disk to the hub and added 1/2" x 1-1/2" angles. Needed 6 blades. Pop riveted the angles to the disk . Bored and tapped the hub for a set screw.
    Took about an hour. The fan was the easy part. Removing the motor was a PITA. Bottom nuts were inaccessible until the entire lathe was raised off the table.
    mike


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