Silly question maybe

[Neily]

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?

 

[Tenwheeler]

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.

 

[Neily]

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

 

[farmerlund]

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.

 

[Tones]

And the safe load limit is half the breaking strain.

 

[Tarhe Driver]

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.

 

[Queenslander]

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.

 

[redneckracin]

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.

 

[Delmer]

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.

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.

 

[hosspuller]

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.

 

[digger242j]

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.

Sooo, isn't like that saying that that single link is getting twice the load of every other link?

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.

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.)

 

[John C.]

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.

 

[Junkyard]

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

 

[Delmer]

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?

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.

 

[farmerlund]

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

 

[Queenslander]

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.

 

[hosspuller]

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...

 

[Tradesman]

I would imagine the d\d rule applys

 

[Tradesman]

Here's the full page

 

[Tenwheeler]

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.