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Thread: Must double shielded bearings installed in a motor have their outer shields removed?

  1. #1
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    Confused Must double shielded bearings installed in a motor have their outer shields removed?

    This is an on-going discussion/argument between me (the grey-haired one...) and everyone else in my dept. I have been taught, and 40+ years of field experience has proven to me, that motors that come with shielded bearings in which the outer shields have not been removed at the factory will soon start making noise and eventually fail. And in my experience, that's how most of the motors fitted with shielded bearings come: both shields installed, with zerk fittings, and when you go to grease them the grease obviously goes nowhere because the outer shields are still in place. And the only way to verify what you have is to remove one end bell, which is what I do in all new installs. Any thoughts...?

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  3. #2
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    I agree with you if the bearing is going to be greased. If the bearing is going to be treated as permanently lubricated then leave the seals in.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

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  5. #3
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    There are open, shielded and sealed bearings.
    Sealed are meant to stay that way. Shielded may be lubed without removing the shields or shields may be removed. In any case they should be vented or allowed to drain after lubing and DO NOT over grease.

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  7. #4
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    Greasing bearings is for sure not a “bigger the gob, better the job” type ordeal. I agree if it’s sealed leave it alone and if it’s shielded and going to be treated as a serviceable bearing will depend on the course of action to take. If the gray haired one has years of good luck doing it a particular way, keep doing it whatever way that is.

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  9. #5
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    If it's only shielded it will take grease.if it's sealed it will not.
    It is rare, but I have occasionally seen shielded sealed bearings. But those were for severe service applications when I was still millwrighting.
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

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  11. #6
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    Quote Originally Posted by Restaurant mech View Post
    If it's only shielded it will take grease.if it's sealed it will not.
    It is rare, but I have occasionally seen shielded sealed bearings. But those were for severe service applications when I was still millwrighting.
    Millwright to restaurant tech? Near complete switch.

    Used to say to be a millwright you needed to know a little bit of everything and not a whole lot about anything.

    I went from millwright to industrial chiller service.

  12. #7
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    I have long forgotten where I read it, but evidently the Navy removed the grease fittings on many pieces of equipment because the "often and excessive" lubrication mentality was causing more failures than it was preventing. Modern lubricants are far superior and last a very long time without any service, and in many cases the grease used is very specific and contaminating it with a different type of grease will actually cause it to fail.

    Slightly related story - I put 330K miles on a 2002 VW TDI and in that time I changed a few wheel bearings. Fronts usually lasted about 130K and from what I recall, each failure came shortly after a winter carwash visit. The inner bearing seal would wear just enough to allow the warm bearing to suck in the cold water (bearings are mostly filled with air), and then the internals would rust and get noisy. The outer half of the bearing would still absolutely look like new - clean grease, shiny balls and almost zero wear on the races. Water and dirt are the enemy of rolling element bearings.

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  14. #8
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    For the electric motor application keep the manufacturer seal in place.

    1-if over lubricated it can fail the motor electric windings.

    2-If motor is VFD rated the bearings are designed for the application and they prevent shaft housing arching and current stray In rotor.

    3- IF VFD rated and lubricated design. If you use conductive cheap grease. The motor will eventually fail. If the motor Is designed to be lubricated, there is high dialect grease for this. Prevents metal bearings from arching as well.

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  16. #9
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    i usually try to match the bearings i take out. if the bearing coming out is open, i remove the shield(s) from the new bearing to match. there are little slits in the shield that are meant to let grease through but I'm skeptical of how well they actually work. if i take the old bearing out and its all dry and nasty inside then the new bearings are going in without the shield. i assume you can order them without shields but we keep a stock of a bunch of sizes and they always have the shields. they're so easy to remove that i get the impression they're meant to be able to be removed if needed.

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  18. #10
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    Quote Originally Posted by causa View Post
    For the electric motor application keep the manufacturer seal in place.

    1-if over lubricated it can fail the motor electric windings.

    2-If motor is VFD rated the bearings are designed for the application and they prevent shaft housing arching and current stray In rotor.

    3- IF VFD rated and lubricated design. If you use conductive cheap grease. The motor will eventually fail. If the motor Is designed to be lubricated, there is high dialect grease for this. Prevents metal bearings from arching as well.
    Most vfd rated motors do not have special bearings. The ones that do typically have a ceramic race that prevents arcing.

  19. #11
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    Quote Originally Posted by ehsx View Post
    Millwright to restaurant tech? Near complete switch.

    Used to say to be a millwright you needed to know a little bit of everything and not a whole lot about anything.

    I went from millwright to industrial chiller service.
    Actually many different careers. Heavy duty mechanic, welder, butcher, millwright, low voltage electrician and refrigeration/ hvac.
    Really, it's all the same trade in the end. It's just physics .
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

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  21. #12
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    Quote Originally Posted by Restaurant mech View Post
    Really, it's all the same trade in the end. It's just physics .
    So true. Today I'm plumbing up a couple of liquid line service valves they're just feeding a bathtub instead of a txv.
    "Is this before or after you fired the parts cannon at it?" - senior tech
    I'm tired of these mediocre "semi flammable" refrigerants. If we're going to do it let's do it right.
    Unless we change direction we are likely to end up where we are going.

  22. #13
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    Most motors: is a very general term.

    Plasma-sprayed aluminum oxide/ coated with resin.

    Bearing grade silicon nitride.

    Design is depending on cost. If your referring to the 25hp and lower maybe. Depending on duty cycle and application.

    I have seen 10 hp Ex T4 motors is class 1 division 2 with bearing grade silicon nitride. The cheap condenser fan motors in a CGAM, your probably correct- (but sell parts do we not).

    For all reading this: this study is good to further your advancement in the trades.

    Any motor >404T will have a combination of mitigation to protect the bearings. Some internal some external. Or a combination. The end bell most likely to find the special bearing in most cases.

    This is off topic but apprentices will read this.

    Don’t take my word for it. research the subject for your selves. The harmonic frequency that damages a circuit and the induced currents resulting from this. It will help with diagnosis of motor problems and VFD diagnostic.

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