why scrape sleeve bearings?
why scrape sleeve bearings?
(OP)
As has been discussed before on this forum, typical practice for some folks after replacing a bearing is as follows:
Do a blue check or a dry roll check to estimate the contact pattern between the shaft and the babbit.
Scrape to get the desired contact pattern (> 80%).
What is the purpose of this procedure?
To my way of thinking, the cylindrical geometry of the sleeve should be a natural result of manufacture. The diameter of bearing should be a little larger than shaft to develop a wedge. The clearance can be checked separately by plastigage. Also important to note, the position where the shaft rests during blue check (bottom dead center) is much different than where it will sit while running.
So... I don't get what it is that we are trying to gain through this blue-check and scraping procedure.
Do a blue check or a dry roll check to estimate the contact pattern between the shaft and the babbit.
Scrape to get the desired contact pattern (> 80%).
What is the purpose of this procedure?
To my way of thinking, the cylindrical geometry of the sleeve should be a natural result of manufacture. The diameter of bearing should be a little larger than shaft to develop a wedge. The clearance can be checked separately by plastigage. Also important to note, the position where the shaft rests during blue check (bottom dead center) is much different than where it will sit while running.
So... I don't get what it is that we are trying to gain through this blue-check and scraping procedure.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.





RE: why scrape sleeve bearings?
Where we poured a split bearing it is fit by the millwrights or the company that poured the bearing by bluing and scraping. Bluing is used as plastigage can't give the whole picture.
RE: why scrape sleeve bearings?
With that said, it is usually preferable to buy a precisely machined bearing and mount it in a precisely machined housing. If the contact is not good enough, we will usually reposition the bearing housing to get better contact. With a motor, this may not be possible since you also have to maintain the rotor to stator concentricity (air gap). And my limited experience with motors is that they tend to be less precisely machined and less robust by construction. Scraping may be the only alternative that achieves the necessary contact area.
Johnny Pellin
RE: why scrape sleeve bearings?
RE: why scrape sleeve bearings?
I still have all my grandfather's and father's tools for bearing work. There are all manner of "spoons" for scraping and what I call ladles, also called spoons, for pouring bearings. There are also numerous burnishing tools, radius tools, and oil groove cutting tools.
I've gotten to use the smaller ones numerous times. These tools got a workout during WWII in the US Steel machine shop fitting bearings to shafts. My father ran the horizontal press that put bronze bearings on ship shafts and if there were no shafts in the shop they worked on bearings. The majority of the Liberty ship shafts came through this shop.
These tools are good conversation pieces.
RE: why scrape sleeve bearings?
I'm working for an outfit involved in many phases of power generation, especially coal burning.
Turning many tons of coal per hour into a precise, dry fine dust requires a pulverizer like this.
http://w
Down at the bottom is a gear box with a thrust bearing that must handle TONS of load from the crushing process.
Tilting pad thrust bearings are a popular design.
Despite careful manufacturing a blue check is often used at assembly to confirm each pad is sharing the load correctly. The penalty can be thrust bearing life measured in minutes.
RE: why scrape sleeve bearings?