Welding a chain link

"David Todtman" wrote: (clip) Do you think I need

^^^^^^^^^^^^^^^^^^^^^^ Nothing to worry about. The maximum tension in the chain will occur between your hands and the first pulley. The tension in the other strands will be (max tension)/(number of strands holding the load). If you can't rip the chain apart with your arms, it certainly won't break under load.

I don't know anything about the coating or your idea for removing it.

I'm going to give my two pennies from two angles. First as a certified welder and then as a certified rigger. You can weld and repair a chain, and have it hold for small loads. You can use a repaired chain safely if you don't exceed the limit of the repaired chain.

BUT, you won't know how good a weld you have, or what capacity the chain has unless you test it to failure. Why take the chance?

It can be done, but I wouldn't do it. No safety inspector would allow it. If it fails, results could be catastrophic. Chain isn't that expensive, and I've bought long pieces of big chain very very cheap. Be safe. Use good chain.

Just the way I would do it.

Steve

I'd hazard a guess that the gold finish is Cadmium plating. Would possibly sand off fairly easily.

Yes, I'd like a clarification too. You seem to be describing a continuous loop, which would usually not be the load-bearing hoisting chain. That you could weld without much concern about breakage. All it'll see is whatever force you put on it yourself.

The hoisting chain, on the other hand, is another story. Unless I had some way to test the weld, I wouldn't try it.

Chain hoists can be a little deceptive, having the hoisting chain attached to the hoist's frame and dropping a loop of it just to get higher lift.

If you're an experienced TIG welder, with full confidence in your ability, disregard the above. :)

You need to clarify the nature and strength of the loads and the strength of your chain.

If the chain appears to be golden in color, it is probably cadmium, and I would try to stay as far away from welding cadmium plated stuff.

If it was up to me, I would rather use a special link for connecting chains. There is quite a bit of choices for various chains.

i

I'm assuming that what you are working on is what I've always called a "chain fall" hoist? Double wheel on top, single on the hook end, one long continuous loop of chain? If so then you have to weld it. No type of a lap link, cold shut or other repair link will pass through the wheels.

Weld it. Hook it to a load heavier than you will ever lift with the welded link in the load bearing position. Pull. If your feet leave the floor before the link breaks it should be fine.

Your plan seems sound for your application. Test to perhaps 3 times your planned load if you want to play it extra safe.

For other lifting arrangements, it's relatively simple to check all your tackle for safety so long as you don't overdo it. Here's a handy item that's convenient and relatively affordable

some gauges with different scales (up to 5000psi) to add flexibility and accuracy with varying loads. Or you can build one from a surplus hydraulic cylinder, as I did recently to test to 20 tons - total cost for a new cylinder and a large-diameter gauge was about $100. You can do the (easy) math to convert the gauge reading to load on each lift, or do the math for a range of gauge readings and re-mark the gauge face. This place is a good source for parts example, you could test to about 5000lb for about $60 with these two items ?UID=2009011409122389&item=21-1637-BU&catname=hydraulic.Add a larger diameter gauge for reading from a distance, and hooks etc. if needed. Don't forget the common (or perhaps it should be uncommon :-) ) sense - tie off anything that might break and so on.

Wayne

The responses are very helpful.

The device is, in fact, a chain fall. That's why I need a continuous loop.

As far as to whether the lifting stress would apply to this chain: it will apply directly so if I weld a link it must be able to hold for the weight I lift.

Thank you for the simple advice to test the weld (and whole setup) with substantially more weight than what I intend to actually lift. I can do that easily. The heaviest weight I want to lift at this point is my cabinet saw which weighs about 550lbs. I can set up a pallet with 2 or 3 times that weight and do a test.

I tried the toilet bowl cleaner (acid based) on a sample of the chain link and found it takes the finish off (whatever the finish is). I'll do a test weld on this sample to see if I get any fuming but I would imagine from past experience I should be okay.

I also have a 3 ton ratchet hoist and could use that for heavier or danger-posing lifts.

Best, David

"David Todtman" wrote: The device is, in fact, a chain fall. That's why I need a continuous

^^^^^^^^^^^^^^^^^^^^^^ That was fairly clear from your first post, and from the fact that you have to use sepecial pitch chain. ^^^^^^^^^^^^^^^^^^^^^ As far as to whether the lifting stress would apply to this chain: it

^^^^^^^^^^^^^^^^^^^^ Here I think you are mistaken. In a chain fall, the chain runs through your hands, and then over and under some number of pulleys. The MAXIMUM tension in the chain will be what you supply with your hands. This figure is multipled by the number of strands running between pulleys to lift the load. Unless you can tear the weld apart with your hands, you will not break it.

Quoting from Bill Marrs, "Pull. If your feet leave the floor before the link breaks it should be fine."

Okay. Thanks. If I understand correctly what you guys are saying is that this is about the mechanical advantage provided by the pulleys and strands (and the different diameters of the two pulley races on the upper block).

So, one way to test the weld might be to take a short section of chain that includes the welded link and use that along with my 3 ton rachet hoist and lift, say 500 lbs. If that works, then I can assume the chain is good for 1000 lbs because the chain fall has two strands (between the upper and lower blocks). Yes?

Best, David

"David Todtman" wrote: Okay. Thanks. If I understand correctly what you guys are saying is that this is about the mechanical advantage provided by the pulleys and strands (and the different diameters of the two pulley races on the upper block).

So, one way to test the weld might be to take a short section of chain that includes the welded link and use that along with my 3 ton rachet hoist and lift, say 500 lbs. If that works, then I can assume the chain is good for 1000 lbs because the chain fall has two strands (between the upper and lower blocks). Yes? ^^^^^^^^^^^^^^^^^^^^^^ David, you're getting closer. The part about mechanical advantage is correct, except that the diameters of the pulleys does not come into it. You count the number of chains supporting the load--that is the mechanical advantage.

If you have two pulleys on the upper block, you must have *three* strands supporting the load (don't forget to count the one coming down and attaching to an eye on top of the lower pulley. If you intend to lift 500 lb, then, you will have to pull on the chain with 167 lb.

I suggest that even if you pound the link closed and don't weld it at all, you will not be able to pull it open with just your hands, arms and body weight (I'm not suggesting you actually do that.) What I am suggesting is that with the link welded even reasonably well, you are not going to break the chain.

Why not tack it together and run it through and remove the old section.

Or is this an end of a continuous loop chain. I have one both ways.

Might look into a link that is a chain link. They are sprung open with two hooks on one end and a loop on the other. Often used to link hooks.

Mart> Hi all,

Oh I get it! Yeah, three chains holding the wight; weight is distributed to the three chains.

I would not do that but this actually 'feels' right and thus bolsters the 3-chain concept.

Best, David

Martin, It is a continuous loop chain. (I have wanted a chain fall for a long time)

I thought about getting one of those 'add-in' links--what I think you are referring to. I am not sure such a link would go through the pulleys properly and besides you'd just have to bank it closed. I like the idea of welding one of the chain's original links.

Best, David

I just have to ask for clarification: there are two types of "chain hoists" The new style (which is all I can find in the catalogs)

an endless loop of lightweight chain that turns a gear drive in the hoist head to raise or lower a much heavier chain. You can weld links on this loop all day long, if your weld breaks the load stays put. The lift chain should not be welded by anyone except an expert.

There is an older style that I would call a "differential cha> >> Why not tack it together and run it through and remove the old section. >>

Leo, I think you are confused about what type of hoist is being talked about here.

I believe the person is talking about the type described by RoyJ as the "differential chain hoist".

With that type of system, there is only one chain, and it's in a continuous loop. But it doesn't work like a traditional block and tackle system like you are talking about. That's because the upper block has teeth on it which act as a gear system. The are two wheels at the top which are actually connected together as one large wheel (like the gears on a bike). One wheel is slightly larger than the other with one extra tooth. One loop from the top just falls to the ground, and you pull one side of it with your hands to make it work. The other loop holds the weight of the load with a single free turning pulley and hook at the bottom.

The loop you hold with your hand has one side of the chain going to the large pulley and one side going to the smaller pulley. Same thing for the weight bearing loop - so it all forms one large continuous loop.

The weight you hold with your hand is only a small fraction of the weight being lifted (not just 1/2 as it would be with a straight block and tackle with 2 lines holding the weight).

This is because the top pulleys have teeth on them and the weight from the load is pulling on opposite sides of the top pulley and off setting each other. But because one side is pulling on the large pulley and the other side is pulling on the small pulley, there is a small differential force making the pulley turn - and it's that small differential that you have to hold with your hand.

Each time you pull the chain enough to make the top wheel set turn one revolution, the weight bearing loop becomes shorter by one tooth length. I don't know what's typical on these hoists, but if the larger wheel has 10 teeth, and the smaller wheel has 9, then the load is raised by 1 tooth length when you pull 10 teeth worth of chain. So for that you would get a

10 to 1 mechanical advantage on the load - you would only have to hold only 1/10th of the load with your hands. But you have to pull 10 times the amount of chain through the hoist to make it lift a given distance.

Here's a drawing of one (item B in the picture):

"Curt Welch" wrote: Leo, I think you are confused about what type of hoist is being talked

^^^^^^^^^^^^^^^^^^^^^^ Curt, I realize that you are right. In that case, two strands of chain hold the load, and chain tension wuld be very much higher than your pull on the chain you are holding. Have it welded by an expert, or test it, as others have suggested. Sorry for the misdirection.

I just spent 30 minutes or so searching the internet and I can't find that old style chain hoist for sale anywhere. Looks like they don't make them anymore. I guess the more complex ones with the gear drive work better and don't cost that much more and have just replaced that old style. It was many many years ago I last saw one of those old style hoists in use.

Curt, Excellent description.

I am sure I can weld the link properly. I'll be surer once I test it with an excess load.

Best, David