I'm a chemist functioning as a Process/Materials engineer and have a problem that is well beyond my mechanical engineering skill set. We have a continuous production process where stranded aluminum or copper conductor is insulated. The conductor naturally twists over sheaves and a twisting motion is imposed during one section. I need to design a method to connect two ends of the conductor with a device that can handle the torsional load imposed in the process and be equal to or less than the diameter of the conductor. I don't know how to calculate the load imposed by the process or determine what load the device can handle. I know the conductor will rotate 8 times over 600 ft. worst case assuming it is fixed at each end. It isn't totally fixed at each end but if I can design as if it is I have a safety factor built in. Can the problem be simplified for example if the device is fixed relative to the longitudinal axis of each end of the conductor, does the device simply have to be the same or stronger than any section of the conductor? Sean
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designing for torsional load 2
- Thread starter Shylanel
- Start date
So you want something that is smaller than the diameter of the cable that prevents the cable twisting, but presumably allows the cable to still pass axially?
That sounds impossible.
Consider also that if you take a cable that wants to twist, and restrain both ends while whatever causes the twisting is still going on in between you will wind up with a pretzel.
That sounds impossible.
Consider also that if you take a cable that wants to twist, and restrain both ends while whatever causes the twisting is still going on in between you will wind up with a pretzel.
I get the impression that this is similar to the hollow plastic pieces used to connect the ends of glow sticks to turn them into necklaces or bracelets. But you want to prevent any thickness increase. Not sure of a tip, but maybe that can help explain to others.
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- #4
I obviously didn't explain it well. Miles and miles of this is made all over the world everyday though there isn't an off the shelf solution. Every place does it a little differently and most allow the connection to twist. This creates more scrap. I'm trying to find a better solution.
Imagine the cable moving continuously into fixed point A (capstan) through fixed point B (capstan). At a point close to B a twisting motion is applied to the cable. The fixed points don't allow the cable to twist but do pull the cable through so only a fixed amount of twist is applied to any point in the cable (in reality there is some twist allowed through the fixed points). What I need is something the same or smaller in diameter that connects two pieces of cable end to end and will twist with the cable but not more than the cable (fixed radially) and not break under the torsional load. Make sense?
Imagine the cable moving continuously into fixed point A (capstan) through fixed point B (capstan). At a point close to B a twisting motion is applied to the cable. The fixed points don't allow the cable to twist but do pull the cable through so only a fixed amount of twist is applied to any point in the cable (in reality there is some twist allowed through the fixed points). What I need is something the same or smaller in diameter that connects two pieces of cable end to end and will twist with the cable but not more than the cable (fixed radially) and not break under the torsional load. Make sense?
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- #6
Technically I'm splicing the conductors of two cables together. I can splice two of the same size easy enough. I need to splice 2 different size cables together. That's where the challenge comes in because you have a different size "splice" for each cable and something in between to connect them.
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A critical first step in solving engineering problems is defining the problem to be solved.
Read back through this post. With each of your posts we get a new, not previously disclosed requirement.
Take some time to read some of the threads here to get a better feel for what makes the different between a well asked question and a poorly asked question.
Read back through this post. With each of your posts we get a new, not previously disclosed requirement.
Take some time to read some of the threads here to get a better feel for what makes the different between a well asked question and a poorly asked question.
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- #14
You are correct. The first step to solving engineering problems is defining the problem. The first step in this case is to understand what forces will be imposed on the solution so the design will work. My original question remains how to calculate the load on the device or if it can be simplified to saying it just has to be stronger than the conductor. If it can be simplified I then need to understand how to relate the normally referenced tensile yield strength to the torsional or shear yield strength of whatever design is made. I did not start out asking for a design solution. If I had, the post would have been much different defining the various requirements of the design.
So, how do I calculate the torsional load on the system and how can I relate that load back to standard referenced materials properties so a design solution can be found? Once this is established I will be happy to share the overall problem and ask for potential design solutions. I have been looking for off the shelf solutions to this of and on for about 5 years now. If there is an off the shelf solution I will be surprised but extremely grateful and ecstatic.
So, how do I calculate the torsional load on the system and how can I relate that load back to standard referenced materials properties so a design solution can be found? Once this is established I will be happy to share the overall problem and ask for potential design solutions. I have been looking for off the shelf solutions to this of and on for about 5 years now. If there is an off the shelf solution I will be surprised but extremely grateful and ecstatic.
"Can the problem be simplified for example if the device is fixed relative to the longitudinal axis of each end of the conductor, does the device simply have to be the same or stronger than any section of the conductor?"
Answer: Yes.
"So, how do I calculate the torsional load on the system and how can I relate that load back to standard referenced materials properties so a design solution can be found?"
Answer: Start off with a university course in statics, then dynamics. Follow this up with a materials course. You may want to include calculus. When you have the background, you will be able to calculate the torsional load on the system.
Answer: Yes.
"So, how do I calculate the torsional load on the system and how can I relate that load back to standard referenced materials properties so a design solution can be found?"
Answer: Start off with a university course in statics, then dynamics. Follow this up with a materials course. You may want to include calculus. When you have the background, you will be able to calculate the torsional load on the system.
- Thread starter
- #16
Wow Dave, thanks for your help. I have the calculus and know materials better than most. Already shared that I'm not a mechanical engineer. Perhaps you could walk me through the calculation anyway. I'm pretty sure I can keep up. Who knows you may have a chemistry or materials question I can help with some day.
You presently don't know enough to ask the question. It's like complaining your car is making a funny noise and asking how to fix it.
If you'd had a materials class or paid attention to it, you would already know "how to relate the normally referenced tensile yield strength to the torsional or shear yield strength" for materials.
If you'd had a materials class or paid attention to it, you would already know "how to relate the normally referenced tensile yield strength to the torsional or shear yield strength" for materials.
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- #18
Why don't you ask me for the information needed for the calculation? You might find I do actually have the answers or can get them. If you have no desire to help and only want to spew insults why do you even hang out in a forum like this or do you just like to sit on a pedestal thinking all other humans are too inferior to bother with your brilliance and this is the only way to make sure everyone knows? If you don't want to help, keep your pompous arrogance to yourself. I don't need the aggravation.
For the record, I know the rough and dirty estimation is the shear yield is 50% of the tensile yield. I was looking for something a little more exact or data that says 50% is worst case.
For the record, I know the rough and dirty estimation is the shear yield is 50% of the tensile yield. I was looking for something a little more exact or data that says 50% is worst case.
I suspect that the torque v. torsional twist relation of a stranded cable is non-trivial, and depending on lay possibly non-linear and directional.
So I'd suggest a test of some reasonable length of cable. Obtain torque v. twist.
From there, I suspect you could get away with using equations for solid shafts. Knowing torque, angle of twist and length you can calculate the polar modulus of inertia of the "equivalent solid shaft".
Then design your connector with an equal or greater polar moment of inertia.
So I'd suggest a test of some reasonable length of cable. Obtain torque v. twist.
From there, I suspect you could get away with using equations for solid shafts. Knowing torque, angle of twist and length you can calculate the polar modulus of inertia of the "equivalent solid shaft".
Then design your connector with an equal or greater polar moment of inertia.
Shylanel:
A capstan to me means three wraps of the rope or cable around the capstan so it can be used to pull the load or lift the sail. And, I’ll bet that’s not what you mean, so start there, and explain. What you see as a capstan, we can’t even imagine, and we can’t see it from here. What applies and how is it applied, on both the cable pulling tension and the torsion/twisting action, that’s 2. Is this a cable pulling operation from floor to floor, that’s 3. What kind of cable is this, fiber optic, computer cable, how’s it made, is it a twisted/layed up cable which twists a bit by the nature of its construction, when you pull it over the capstan, that’s 6, 7, 8 and 9? There aren’t many simple answers to complex problems. And, if you think this is a simple problem with all the variable you have already laid out, and the limitations you have put on it; that just shows that you don’t understand your own problem very well, and sure aren’t describing it very well. You can weld some of these, but they have to be taken apart when they reach the upper fl., that just doesn’t wash. Can you lose or gain wire length in the separation? The connector must be smaller than the wire dia., that’s a tall order and a dream. Are some wires in the cable splices and others not, that’s 10? I’d wrap the cable in electrician’s tape, and unwrap it at the upper fl. Would something like the old Chinese finger lock/puzzle work? There are cable pullers like that on the market. We don’t even know what size the cable and individual wires are, or what size duct you are fishing this through.
MintJ. is right on the money above. So many of the questions we get here are so pie-in-sky that the OP’er. can’t begin to describe them sufficiently to illicit some meaningful discussion. We are all guessing, wasting our time, and getting nowhere; and if by chance someone guesses crazy enough to find a solution, they get a shout-out. You’ve got several smart people posting on this thread, and your just not getting through to them, and that’s not for their lack of effort. These problems, on this forum, are a real pain in the arss, because we have to ask so many questions before we tease another important fact out of you, and you didn’t even know it was important. You haven’t described what it is or how it works well enough so we can ask some meaningful questions, we’re all just fishin in the dark. These discussions would be so much more productive if we could see some properly proportioned sketches, with dimensions, loads, etc. and some photos of the system, so we knew what you where dealing with, what your idea of a capstan was. If we could be standing together looking at the problem, this give-n-take or exchange of ideas would flow much better. And, if the OP’er. gives out important info. in drib-n-drabs it just frustrates the hell out of a bunch of smart people trying to be helpful.
Shylanel.... this is not specifically directed only at you, it just happened to finally get posted on your thread. I am not trying to pile on here. This seems to be all too common an occurrence on these fora, the issue of ill defined questions or problems. You haven’t presented a simple problem, and you certainly have not presented it well. Again, WE CAN’T SEE IT FROM HERE.
Good Luck
A capstan to me means three wraps of the rope or cable around the capstan so it can be used to pull the load or lift the sail. And, I’ll bet that’s not what you mean, so start there, and explain. What you see as a capstan, we can’t even imagine, and we can’t see it from here. What applies and how is it applied, on both the cable pulling tension and the torsion/twisting action, that’s 2. Is this a cable pulling operation from floor to floor, that’s 3. What kind of cable is this, fiber optic, computer cable, how’s it made, is it a twisted/layed up cable which twists a bit by the nature of its construction, when you pull it over the capstan, that’s 6, 7, 8 and 9? There aren’t many simple answers to complex problems. And, if you think this is a simple problem with all the variable you have already laid out, and the limitations you have put on it; that just shows that you don’t understand your own problem very well, and sure aren’t describing it very well. You can weld some of these, but they have to be taken apart when they reach the upper fl., that just doesn’t wash. Can you lose or gain wire length in the separation? The connector must be smaller than the wire dia., that’s a tall order and a dream. Are some wires in the cable splices and others not, that’s 10? I’d wrap the cable in electrician’s tape, and unwrap it at the upper fl. Would something like the old Chinese finger lock/puzzle work? There are cable pullers like that on the market. We don’t even know what size the cable and individual wires are, or what size duct you are fishing this through.
MintJ. is right on the money above. So many of the questions we get here are so pie-in-sky that the OP’er. can’t begin to describe them sufficiently to illicit some meaningful discussion. We are all guessing, wasting our time, and getting nowhere; and if by chance someone guesses crazy enough to find a solution, they get a shout-out. You’ve got several smart people posting on this thread, and your just not getting through to them, and that’s not for their lack of effort. These problems, on this forum, are a real pain in the arss, because we have to ask so many questions before we tease another important fact out of you, and you didn’t even know it was important. You haven’t described what it is or how it works well enough so we can ask some meaningful questions, we’re all just fishin in the dark. These discussions would be so much more productive if we could see some properly proportioned sketches, with dimensions, loads, etc. and some photos of the system, so we knew what you where dealing with, what your idea of a capstan was. If we could be standing together looking at the problem, this give-n-take or exchange of ideas would flow much better. And, if the OP’er. gives out important info. in drib-n-drabs it just frustrates the hell out of a bunch of smart people trying to be helpful.
Shylanel.... this is not specifically directed only at you, it just happened to finally get posted on your thread. I am not trying to pile on here. This seems to be all too common an occurrence on these fora, the issue of ill defined questions or problems. You haven’t presented a simple problem, and you certainly have not presented it well. Again, WE CAN’T SEE IT FROM HERE.
Good Luck
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