hi all have a basic question about chain strength that I'm unsure about. Ok so from what I can understand about rope and pulleys (without being to scientific) if a rope is run around a pulley, it will effectively double the capacity or halve the load on each strand. A quick qoogle search suggests that the single strand is under friction/compression etc so doesn't take the full load. Probably not doing a very good job of explaining but I'm sure you'll know what I'm trying to say lol. Ok so here is my scenario, was having a few beers with my mates the other day and we were finishing up a silage pit. One bogged his grader and the other walked the digger over and I hook the chain up. Single chain hook each end, I run the chain through the drawbar on the grader and hook both ends on a loop on the digger bucket. My mates makes the comment why did I bother to double the chain there is only one link around the drawbar pin. You guys can see what I'm asking, I'm not sure he is correct?
A chain is only as strong as its weakest link. A pulley in a cable system doubles the load pulled due to multiplication or ratio.
Yeah agree, I understand that but that's not sorta what I'm asking. Say I have a ton hanging from a single strand of rope from a sky hook that strand will see the whole ton, if I put a pulley on the hook and run the rope around it and have both ends tied to the ton weight I have halved the load on each strand or effectively doubled the lifting capacity of the "link" between the hook and the weight/load. That's my understanding of it anyway, not necessarily correct. I'm wondering if that theory applies to my above example. Ie If it takes 5 ton to pull out the grader and I use a chain that brakes at 5 ton and I doubled the chain will I then have a 10 ton limit or still 5? I know each leg will only see 2.5 ton each this way but will it still break at the drawbar pin at 5t
I have broke a lot of chains over the years pulling equipment out. It is way stronger to double it like you did. I have gone around, made a loop 3 or 4 times if i have to.
And the safe load limit is half the breaking strain.
If you double the chain, Isn't each of the two sections taking half the strain? I'd guess that if the non-end portion of the chain is not doubled at the source of the strain, that it is now bearing more than half of the strain, perhaps all the strain, but if it is wrapped one time around the connection of the strain source, then ir has no more strain than does either of the two chain segments. Fire away...please tell me where I'm wrong in my thinking.
That’s what I was thinking TD, if you reeved it around the pin it would effectively become a two legged sling with almost twice the capacity....maybe. Slightly off topic, I remember pulling scrub with a bloke using his D7G, our 150hp Fiat Allis and a well worn 2'' chain. When the chain broke midway through the day he produced a length of 5/16 load chain. Half a dozen loops of this through both links of the big chain, secured with a half hitch and a bit of number 8 wire and we were able to keep pulling for the rest the afternoon.
This is not a simple question in theory but the answer is simple. that's why chain baskets ( as long as the radius doesn't kink the chain) is twice as strong as a straight chain.
Of course it would have twice the capacity of the single strand of chain. Unless the pin was so small that it kinked a link. The one link that was perpendicular to the chain stretched between the grader and bucket was only getting the force of each chain, even though they were both pulling on it. No different than if it were run behind the pin and hitched over to the frame of the grader, same force.
It might help to visualize the single link at the pin getting half the load at each end. If it's not half the load, the link moves until the load is equalized. Then visualize a single link in the single chain. Each end of the link is getting the full load.
Sooo, isn't like that saying that that single link is getting twice the load of every other link? But then isn't that single link in the middle getting the full load from both sides? (BTW, not a silly question, at least in my mind. I've wondered about it myself, and the opinions above don't quite have me convinced, which is why I'm questioning.)
Doesn't matter the medium. Put two ropes pulling a thousand pounds is the same as two chains pulling a thousand pounds. The chain is just more subject to damage on individual links. Another though is bolt two plate of metal together. One bolt can hold them together with 50,000 pounds of force. Two bolts will hold them together with 100,000 pounds of force all things be equaled out.
It's hard to apply a wire rope & pulley scenario to a chain being doubled up as the angles and point load on a single link will be the weak point. In theory yes it's double, in application not so much. Depending on how it's hooked the weak point could be the hook itself, the pinch point of whatever link is against, drawbar in this case, hook pins (I've seen a lot of bolts in place of clevis) etc. I don't think you're getting a true double of strength but it's certainly 50% more. No different than angles in rigging. Too sharp and you suffer a significant loss in capacity. How's that for muddy water? Haha
Every link in that chain on both sides is getting the full load from the links on both sides of it (unless the ends at the bucket are looped also) It's getting the same load as every other link.
No physics lecture here. but I do know the chain never breaks in the middle when doubled up around a pin or clevis. If the link around the pin gets more strain shouldn't it always break there? I don't ever recall making 2 10ft chains out of a 20ft. LOL
I think someone should volunteer to set up a test, maybe with some light chain, or even rope, and put us all out of our misery.
Let's forget the practical bits about edge loading or kinking, or twisting. examine each link's load. If the force on each end of the link is not equal, the chain is moving. If the chain is not moving between the load and pulling point, then there can't be more than half the load on each link. Balance is the key thought. Each link has balanced force on it. With one strand, the full load is on each link. With two strands, the force is half since there are two strands. Every wrap halves the force/load on each strand. Thanks for making me think about this...
I would imagine the d\d rule applys
Here's the full page
I do not fully understand all of Tradesman's post. However the folks I worked around lifting with cables had large diameter blocks or baskets compared to the size of the cable. Some of them had multiple wraps or pulley grooves and said each wrap halved the load. Never understood how the end of the cable or chain did not carry just as much load. From experience the chain deal you are talking about is of no advantage and the single link will break. Cable is superior to chain in pulling equipment out and those ropes like the extreme bubba are almost unbelievable. Do not remember who made the larger ones. You can always just get a bigger chain.
I try my best not to overthink what works .
The support of the pulley or the actual attachment point carries the entire load. Not the cable/ chain. Why do you think they have sheave blocks on cranes if the weight is the same on every strand? Wouldn't they just run one cable? Of course not that would be silly if you can use a lighter , more flexible and cheaper line to do the work. What you do give up is lifting speed because you have a mechanical advantage , every loop means more rope had to be pulled to lift the load.
Well here I was thinking there would be a simple answer lol.
Ok so here is something I just thought of. If a single length of chain had a 5 ton load on it each individual link would be experiencing a force of 5 ton pulling on each end of it. If I double it up each individual link is only experiencing 2.5 pulling on each end, therefore shouldn't the "middle" link at the drawbar pin only experience 2.5 on each end of it as well?
yes, your friend is wrong. The only qualifier is if the angle is so sharp that the chain is pulled sideways, that will reduce the strength to something less than twice the strength of a single chain perfectly hooked
You probably need to reduce the lifting capacity by the weight of the chain. Just a thought.
If ya don't double up & drop a block in the 750 Holmes will pop the cable ....... I like my chain & cable ..... Don't hurt to double them up when in doubt .....
What a good physics question... and since I'm a physicist.... I'm tempted to make drawings and wave my hands some, but I don't think that's necessary and I'm lazy. Most all of the posts above are right, to some extent. The problem is that a chain around a drawbar pin is very different from a cable around a pulley. The chain, under load, won't slide around the pin to redistribute an unbalanced load like a cable around a pulley will. In my experience, the chain, under load, will lock on the pin--usually with one link flat against the pin (of course, this all depends on chain size and pin diameter!). As long as both ends of the chain are under a load, the chain will remain locked and the load on the two runs can become very unbalanced--to the point that one side starts to go slack. As soon as slack is available, the chain will unlock and skip a link or more till the slack is taken up and the load rebalances a little (not all the way, though). It's difficult to put numbers on the scenario without knowing all of the dimensions and details--but I wouldn't count on more than a 25% increase in strength. Next time your friend asks why you hooked it up that way--just say "it was easier"!
Similar situation, sort of, to: I have a 15 ton single sheave quick reeve load block, and 2 sheaves in my boom tip, so I can rig a 3 part line. That makes me good for 22,500 lbs. But I can also use a 5 ton single sheave snatch block to rig to the boom tip (from it's designated pick point) for the final line, making it a 4 part line setup. The way I see it, even though I may be picking 26,000 lbs. from the 15 ton load block hook, that 5 ton snatch block is only seeing 6500 lbs. I've only done this twice, as it's rare for me to pick something that weight. Other wise I'd have a 2 sheave load block.
Here's what I know. When you look at the tag on a lifting chain a basket has double the capacity of a single leg. Seen chains looped through a shackle a thousand times. As long as your not wrapped around something sharp or a hard angle you double your capacity. The reason you see cables ran through sheeves when in a basket is to keep from kinking the cable. Or if the load is gonna shift as you come up.