band brake steel material suggestions

[mod231]

General question- what classes / alloys would be good candidates for a band brake application-(the band itself)? This is a very preliminary concept for a design at this point, application would be static and room temperature. Anectdotal applications or experience are welcomed, also feel free to shotgun. I found nothing specific in the ASM handbook and little in online searches, just need some ideas as a jumping off point for further research.

Regards.

 

[tbuelna]

mod231,

Can you provide a better description of the brake construction, and possibly the operating conditions (stresses/temperatures/load cycles/environment) you anticipate for the band brake components. This will make it easier to provide recommendations for the band and drum materials. You mentioned the application is static and RT, but does this truly mean the brake will never be required to absorb power when slowing/stopping a rotating shaft, or experience friction heating from slipping in an overload condition?

There are also both internal and external band brakes. Is your example the common external type, where there is a friction lining bonded to the ID of a flexible band wrapped around the outside of a steel or iron drum? Or is it like the internal type used for parking brake applications on cars/trucks with rear disc brakes?

Regards,
Terry

 

[mod231]

Tbuelna,

The conceptual device is going to be an external style brake unscrewing two components, the bottom component has a keyway to prevent rotation, while the top component is machined smooth and the customer is unwilling to machine any mechanical interlock features into it. The smooth surface of the component essentially leaves me with clamping or band brake options, which I am investigating. The smooth component will have an o.d. of 7", and based on testing of a similar component that did have interlock features, we have determined the maximum torque capacity of the clutch should be 8,000 lb-ft. (this is conservative). The band brake will not have to absorb any significant power as this is going to be a machine manned by an operator who will simply stop it if slippage should occur. Use will be maybe once or twice a week.

I have done some quick calculations based on band brake formulas from Shigley's, and the P1-P2 net tension will need to be about 27,500lbs due to the small diameter and high torque requirement. The band can be no wider than 2".

Frankly I am not sure about picking a preliminary cross section for the band because I have not researched how to calculate the stresses properly for this yet (whether it is going to be simple tension or thick enough to be considered a curved beam in bending, etc.). This is where the material question came in.

Regards.

 

[EdStainless]

Start with some high strength steel banding. If you assume that you can get 100ksi strength, 30,000lb load, 2" wide; I think that come out about 0.166" thick (double check, that is in my head).
Sounds too thick for that diameter.
Since this is a locking mechanism you may be able to look at other friction enhancing ideas. Maybe a composate band with a traction surface on it? Let you use lower tension.

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Plymouth Tube

 

[mod231]

Thank you both for the input.

Regards

 

[tbuelna]

As EdStainless noted, your 2" wide band would need to be fairly thick even assuming a generous material working stress limit of 100ksi. For an industrial machinery application where operator safety could be a concern, you might consider a slightly more conservative material stress limit. A 150ksi wrought stainless steel band material with a 3.0SF gets you to 50ksi, so your band would end up around 9/32" thick (using a simple P/A).

It would be possible to manufacture the thick steel band with a conformal inner profile to match the drum OD in a free state. But due to the high bending stiffness of the thick band, it would likely not produce a uniform radial pressure on the drum OD surface when tension force is applied to the band ends.

8,000ft-lb of braking force from a 7" diameter x 2" wide friction surface is a pretty tall order. As EdStainless suggested, you might take a look at other types of friction brakes. Ones that provide a balanced clamping force, or ones that utilize self-energizing mechanisms.

Good luck to you.
Terry

 

[EdStainless]

If I were going to make this ban out of steel I might use a PH stainless grade.
You could form it while annealed and then age it. Maybe even then re-form it to get the shape closer and re-age.
That way the aging will give you stress relief.
17-4PH aged at 1025F will have a 155kis min UTS and decent elongation.
After forming age at 1025, then cool and do any re-forming (and maybe lightly machine) needed and re-age at 1000. This will not reduce the strength.

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Plymouth Tube

 

[mod231]

Thanks for the information and material ideas. I did end up contacting a band brake manufacturer just to get additional info, and of course they agreed it is a difficult application. They indicated that stopping the friction material from shearing off would be a challenge given the relatively low amount of area. They did mention that an external style drum brake could be an option, which I hadn't considered. I am keeping the band, external drum, and heavy wall (possibly fastener tightened) clamp all in mind at this point. The 17-4 PH sounds like a good material for the band or clamp options.

Thanks again.