Shaft Brake Centering: Bushing or Bearing???

[mrpi]

We currently manufacture a system that uses a shaft-brake to fix the rotation of a gear-box drive train.

The output of the gear-box is a hollow keyed shaft. I have designed a 25mm shaft to be made from 17-4 H1150 to pass through the hollow shaft. One end of the 25mm shaft is the output, the other end is attached to an over-hung shaft brake.

I have attached a screenshot of a section view of the brake/25mm shaft setup. NOT shown is the hollow-shaft of the gearbox. ALSO I just noticed that the bore on the BRAKE STATOR is not-quite to scale (28mm instead of 35mm shown).

The process of assembly is as follows:

1. Bolt the BRAKE STATOR to the BRAKE MOUNT PLATE from the back side.

2. Use and alignment jig to center the 28mm bore on the BRAKE STATOR to the 25mm hollow-shaft. The BRAKE MOUNT PLATE is allowed to float radially while the jig is inserted, only then the BRAKE MOUNT PLATE is then bolted down against a flange.

3. Bolt the BRAKE ROTOR to the 25mm shaft and insert it into the hollow-shaft. (rotor and shaft shown as a single piece for clarity).

HOWEVER, the shaft brake is a crown-gear design and concentricity is critical to reach full torque holding capacity. We have been having problems related to concentricity of the brake assembly, which I believe is due to difficulty in using the jig tool.

Due to the nature of the flange, it is not possible to provide an alignment pilot boss to center the brake (thereby eliminating the centering jig tool).

What I proposed is to press a plain bearing (BUSHING)into the bore in the BRAKE STATOR which will provide "automatic" centering during assembly. I believe it will also provide additional protection against shock and vibe which could potentially jar the BRAKE MOUNT PLATE out of alignment.

My question is what material is suitable for the plain bearing?? Speed of the shaft is low, ~200 rpm and duty cycle is extremely low as well. There would be very low load on the plain bearing as the BRAKE MOUNT PLATE would fix the brake radially.

I was looking at the INA Permaglide or Garlock DU bushings as they are both available in sizes that would be direct fits for this application.

The 25mm shaft is lathe turned to f6 tolerance, and the surface finish appears quite good (to my untrained eye).

There just isnt enough room to fit a needle bearing in there that I have found (28mm OD with 25mm ID).

Suggestions or ideas are appreciated!

Thanks.



Beat to fit, paint to match.

 

[MintJulep]

How does the brake stator engage the rotor?

 

[mrpi]

There is a mating crown gear on the BRAKE STATOR that is sprung against the ROTOR. It is shown "disengaged".

Beat to fit, paint to match.

 

[MintJulep]

In general terms, when you find that you need to control the tolerances or alignment tighter and tighter just to get something to work right your design is fundamentally flawed.

You need some radial compliance designed into the system.

Something like a spring-centered Oldham coupling. Either at the shaft to rotor connection, or in place of your rigid mounting plate.

 

[mrpi]

The shaft-brake is not self-centering. Concentricity must be maintained by the mounting arrangement.



Beat to fit, paint to match.