Auger Shaft Bushing?

[500cubes]

Hello,

I am new to designing auger conveyors. I've noticed that the CEMA Standards calls out for brass bushings on all of the shafts that are inserted into the screw's pipe. Question is, why and do i really need a bushing? why not just machine a solid stock of shaft to fit inside the pipe and then turn it down to the size required.

Im assuming the need of a brass bushing is so that you can use a single diameter shaft while the bushing makes up for the difference of the pipe ID and shaft OD? but, the solid shaft will still need to be surfaced for a bearing clearance and turned back down after the bearing if needed for the gear box (shaft mount drive). So really, you are not saving much in machining cost with a bushing.

my other assumption is that the brass bushing allows the shaft to be easily removed when needed replaced? couldn't you accomplish this with a single piece while using a looser tolertolerance between pipe ID and Shaft OD. Also, applying anti-sieze would help.

What's your guy's thoughts?

 

[SWComposites]

from wiki:

Noun
bushing (plural bushings)
(mechanical engineering) A type of bearing, a cylindrical lining designed to reduce friction and wear inside a hole, often used as a casing for a shaft, pin or hinge.

bushings also allow for replacement after wear, as opposed to having to trash the entire assembly.

YES, you need bushings. Why would you question an industry standard?

 

[Tmoose]

CEMA = Conveyor Equipment Manufacturers Association ?

Which standard(s) are you looking at?

 

[500cubes]

Not many follow industry standards for various reasons. Our fab. shop have repaired countless off auger shafts that do not have bushings. 90% of the reason why we repair the shaft is because the keyways have been damaged, shaft surface damage, bent shaft, or cracked shaft. Many with and without the bushings. Those that had the bushings, had the bushings undamaged or not worn.

So my thought is, they are some what not needed. Because it's not so much the bushings that need replaced 90% of the time, but the shaft it self.

For existing augers, if needed we replace the bushings. But for new augers, that is where i am questioning the need of bushings.

 

[500cubes]

Yes, that is the one.

 

[Tmoose]

Which specific CEMA standard(s) are you looking at?

 

[Jboggs]

You need brass or bronze bushings as bearing surfaces because dissimilar surfaces (not steel to steel) are required. Otherwise they will gaul up and bind, or wear very quickly.

 

[3DDave]

One reason that would appeal to me is non-sparking contact or otherwise reduce the ability to overheat and start a fire.

 

[lucky-guesser]

So my thought is, they are some what not needed. Because it's not so much the bushings that need replaced 90% of the time, but the shaft it self.

Maybe you never need to replace them BECAUSE they are brass, and do their job very well.

My first eng internship was working on screw conveyors. I remember adding the bushings to the models but I can't remember the material we used. I would suspect having the softer brass would help prevent wear. Working in place of what would be a very awkward bearing design.

 

[TugboatEng]

I seriously doubt the bushings are brass...