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tomcd3

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Reply with quote  #46 
A nice addition to the well made NSK reference and a decent substitute for the removed presentation (though you will have to register at skf.com). Competition tends to breed improvements.

http://www.skf.com/group/knowledge-centre/subscriptions/displayfactbox.html?itemid=tcm:68-297619

The 106-page publication is a comprehensive handbook that contains valuable insight about bearing damage; showing what the damage looks like and the possible causes. Chapters include: Inspection and troubleshooting, path patterns, failure mode classifications, damage and actions.

tomcd3

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Reply with quote  #47 
Yes Danny the entire base of a flat bottomed pillow block must be well supported to prevent flexing of the hsg and subsequent pinching of the internal bearing.

First rules of pillow block applications:

1.  surface roughness of foundation Ra < or = 12,5 µm (.0005")

2.  flatness (planicity) measured diagonally on housing foundation should be < or = ISO IT7 tolerance grade (approx. .0023" for a 15" diagonally long housing)

3.  if necessary, any shim / spacer should support the entire housing base (see pic)

Attached Images
jpeg hsg shim.jpg (20.41 KB, 1 views)

MarkL

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Reply with quote  #48 
Thanks, Tom, I have that book already and its a great reference material.
Interesting on the pillow blocks I have had a few applications with Pillow blocks recently SAF units where the mounting arrangement was less than desirable.

tomcd3

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Reply with quote  #49 
I've found over 25yrs that only 1 in 5 foundations is even close to being IT7 flat.
Danny Harvey

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Reply with quote  #50 
Tom,

Thanks.  I'm assuming that the same logic applies to bearings that are not foot-supported in the center.  The entire foot print must be shimmed. Correct?


dnk

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Reply with quote  #51 

First rules of pillow block applications:

1.  surface roughness of foundation Ra < or = 12,5 µm (.0005")

2.  flatness (planicity) measured diagonally on housing foundation should be < or = ISO IT7 tolerance grade (approx. .0023" for a 15" diagonally long housing)

3.  if necessary, any shim / spacer should support the entire housing base (see pic)


These are very good rules to follow. I have worked on several very old kilns and furnaces. Bases have been overheated and warped. Management doesn't want to spend money for new pedestals.
You need to get both bearings and shaft on same plane. There are times you have to half shim to achive this. This is not ideal, but best you can do.



tomcd3

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Reply with quote  #52 
Step shimming is better than nothing when it comes to fixing an unflat surface. Once had to step shim a .020 concavity under a hsg that limited brg life to 6months due to 3point pinching in the SRB. Step shimming got them to 4+yrs.
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