×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Braking of a spinning disc

Braking of a spinning disc

Braking of a spinning disc

(OP)
Hi

Hopefully i have put this in the right forum, thinking the application i want is similar to braking an automotive vehicle or similar.

I have a vertical disc of 0.6m Ø weighing about 15 Kg. This has coil loaded onto it (via a ctr spindle) which is pulled off, thus rotating the disc. The coil weighs about 10Kg and the OD is 0.6m Ø. (Obviously this reduces as the coil is unwound but i only want to know the max. worst case value.) The speed of the 'puller' is max 30m/min.

I want to add a brake onto the shaft to stop the spinning disc, time to stop in say 1 sec (i.e emergency situation). How can i work out the torque of the disc to compare with the brake torque values to ensure i spec the right one? Obviously i will approach a supplier for their input, but i would like to try to work it out and understand the maths myself. I dont care about the fact the disc will speed up or the OD of the product will reduce as it is pulled as if the brake can stop in the worst case sceanrio, then all bases should be covered.

Any help is greatly appreciated,

Regards

Jim

RE: Braking of a spinning disc

You're a mechanical engineer and you can't calculate the energy in a spinning disk of known weight/size?

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Braking of a spinning disc

Geeze, I'm electrical and don't see how hard it is to do that.

If you know the inertia in lbs-ft and the speed in rpm then the torque in ft-lbs is calculated as

T = Inertia X Speed / (308 x decel time)

At least I think I got that right. I didn' spend to much time on it.

It should be simple to calculate the rotating speed given the circumference and the product take off speed. To calculate a rough inertial this sounds like a couple of cylinders, the disk and the product, so the forula for that is simple too.
 

RE: Braking of a spinning disc

ahhh. Well one should start from conservation of angular momentum to ensure understanding (for the OP). pipe (imo, just because someone signs up here doesn't mean they are an engineer, probably most are not) {I have read very informative posts only from a group of about 10-15 posters}
Although, I am a fan of the pokes. smile

peace
Fe

RE: Braking of a spinning disc

I have got a real engineering degree and a license to go with it but I get "poked" every now and again.  We are not infallible either.

That said, I see a lot of threads that ask questions so simplistic to anyone with real engineering knowledge or training that I take the position that if their understanding is at the level of their question, that level of understanding won't allow them to understand an answer that I would give, so I don't get involved.

A lot of good dedicated members got involved once in a thread where it turned out that the poster was a glass blowing artist who wanted to generate power and light the world with the waste heat from his glass furnace.  What he wasted was the time of a lot of good engineers who didn't pick up on his level of ignorance and spent a lot of valuable time trying to propose solutions to someone who ended up being incapable of understanding them.

So after I get this rant submitted I think I'll go back up and give Dan a star for his initial answer.

rmw

RE: Braking of a spinning disc

(OP)
Thanks eveyone for your replies, helpful and not.

Greg thank you though for at least showing me a route to the problem.

I have one question though, and so prepare to open myself to more abuse. You calculated the angular velocity (omega) presumably into rad/m ? I thought SI unit of this should be rad/s...i only seem to be able to get t=1.873Nm

Open to comments   

RE: Braking of a spinning disc

Quote (GregLocock):

Sorry, there's an error of 2 pi in there, should be 112 Nm

Quote (jimsmiff):

You calculated the angular velocity (omega) presumably into rad/m ? I thought SI unit of this should be rad/s...i only seem to be able to get t=1.873Nm
Ow ow ow, my head is really starting to hurt now...

Are you freakin' kidding me?!

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Braking of a spinning disc

oops, I misread 30 m/s not 30 m/min.

So yes IRstuff and I agree, not very much is the answer.

As a comparison, operating a  butterfly nut with your thumb and forefinger will generate about that much torque.

 

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

RE: Braking of a spinning disc

I have to put in a few  words in support of Smiffy - there is far too many outraged "You're wasting our incredibly valuable time" type of comments on this forum in general.  His original question was perfectly reasonable.    

RE: Braking of a spinning disc

Ah, that explains it, Greg.  

That's one of the beauties of using units in Mathcad; it tends to keep things straighter...winky smile

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Braking of a spinning disc

Fully agree with YvesLLewelyn.

Maybe that jimsmiff is not an engineer, i don't know and i don't care. I still have respect for his willingness to learn and improve on a personal level.

Why the whining? Replying is not manditory i believe.


 

RE: Braking of a spinning disc

Yves & 321go

I notice neither has really served this community all that much, but you feel you have the right to tell long serving very active members who contribute a lot that they should support the breaking of site rules.

The rules are for a reason. Those reasons should be obvious.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
http://eng-tips.com/market.cfm
for site rules
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources