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Anonymous Poster

How Much Weight A Chain Block Can Lift

06/23/2010 10:16 AM

May be a silly question.

I am thinking how much weight can a 3 ton chain block can lift. Is it possible to lift 3 ton by manual chain block?

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#1

Re: How Much Weight A Chain Block Can Lift

06/23/2010 10:49 AM

should be under rated to avoid liability issues

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#2

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:24 AM

Not a bad question.

It may, or may not be possible, for a given person to lift 3 tons. The chain block will not be damaged by such a load (and there is an additional safety factor built in) but the person pulling might not be able to pull hard enough.

You can check the overall ratio (if you can't find it easily) by pulling out 100 inches feet of chain, and measuring how far the hook moves. Suppose the load moves 5 inches. Then the ratio is 20:1. To lift a 6000# load would then require 300 lbs pull (ignoring friction). You'd need a 300 pound person who can climb a rope without using his feet... unlikely. But manual chain lifts have very high ratios -- so it depends on the lift ratio and the person doing the lifting.

Of course the overhead attachment point must be rated for the load too.

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#3
In reply to #2

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:33 AM

Of course the overhead attachment point must be rated for the load too.

Good point!!!

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Anonymous Poster
#6
In reply to #2

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:40 AM

Can you please simplify your answer

We know the average force a person can exerts in pulling the chain is 120 N so can this person lift the 3 ton load? how to solve this using statics?

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#7
In reply to #6

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:43 AM

Can't get much more simple than moronicbumbles explanation

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#9
In reply to #6

Re: How Much Weight A Chain Block Can Lift

06/23/2010 12:44 PM

"Can you please simplify your answer"?

Yes.

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Anonymous Poster
#27
In reply to #6

Re: How Much Weight A Chain Block Can Lift

06/24/2010 11:05 AM

How'bout doing your homework yourself?

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#4

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:37 AM

Why would the manufacture rate it at 3 tons if it couldn't lift it.

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#5
In reply to #4

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:39 AM

IT can, but YOU might not have enough weight or strength to pull it

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#10
In reply to #5

Re: How Much Weight A Chain Block Can Lift

06/23/2010 12:47 PM

You are right but what would be the use of building one that the average man did not have the strength to use. The person should not have to place a lot of his body weight onto the chain to get the load to lift. In that position he has no control of himself or the load.

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#8

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:50 AM

Has been some discussion about pull force here.

Is this what you are using?

The type with the looped chain? This one requires 84 lbf @ 6,000 lbs.

I doubt a manufacturer would offer a mechanism that most people could not use.

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Anonymous Poster
#11
In reply to #8

Re: How Much Weight A Chain Block Can Lift

06/23/2010 1:12 PM

can some one tell what is the average mechanical advantage a 3 ton chain block have or it depends on the manufacturer?

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#13
In reply to #11

Re: How Much Weight A Chain Block Can Lift

06/23/2010 1:21 PM

Well, let's see...

I will ask the question posed in #8 differently: What Type of Chain Block?

If the type shown in #8, that particular model from that manufacturer is, well, listed right there under the picture.

How are your studies coming along? Are a lot of your friends in school as well?

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#17
In reply to #11

Re: How Much Weight A Chain Block Can Lift

06/24/2010 12:39 AM

The mechanical advantage is simply the ratio of output force/input force. Thus if 84 lb of force can lift a 6000 lb weight, the mechanical advantage is 6000/84=71.4. Another posted illustration indicated 92 lb force required to lift 6000 lb of weight. That unit would have a mechanical advantage of 6000/92=65.2. Note that these two sets of values are force values, which presumably take friction into account. If the units get rusty or are not properly lubricated, the effort required will increase, and the mechanical advantage will drop to a lower value

One of the early posts mentioned input distance and output distance. A rough theoretical value for the mechanical advantage can be calculated as the ratio of input distance/output distance. If you have to move the input chain 150 inches to lift the weight 2 inches, then you have a theoretical mechanical advantage of 150/2=75. Since chain hoists do have considerable friction, the actual mechanical advantage will be significantly lower. How much lower depends mostly on the condition and lubrication of the hoist.

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#29
In reply to #17

Re: How Much Weight A Chain Block Can Lift

06/24/2010 3:45 PM

GA, dk. You've got the most straightforward answer I've seen so far.

Manual hoists are designed to require a force of 75-100 lb (333-444 N) on the control chain to lift the design capacity of the hoist. With the input force fixed, different hoist capacities will produce different mechanical advantage ratios.

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#12

Re: How Much Weight A Chain Block Can Lift

06/23/2010 1:20 PM

Of course it's possible for a 3 ton chain block to lift 3 tons. That is what it's rated for. It is also possible to misuse a 3 ton chain block in trying to lift 3 tons so that untrained people or only equipment get crushed. While rigging is certainly not as complicated as some engineering disciplines discussed here, it should not be taken lightly. (No pun intended ) A 3 ton mass raised to a height of 1 meter is about 26,700 Joules of potential energy. This much energy can do considerable damage.

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#14

Re: How Much Weight A Chain Block Can Lift

06/23/2010 5:57 PM

This one will lift 3T 15 feet with a 92lb pull: There are others here

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#15

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:25 PM

From the various replies and the responses for rating, I doubt, many of us have not used the chain block personally.

(Regarding rating: few have rated Farmatt's post as off topic. It is not off topic. As Farmatt says, the support to the block ... may be a pipe tripod, must be suitable to support 3T load)

Now about the chain block:

If the chain block has 3T specified capacity, it will lift 3T load.

When capacity specified is 3 T, that means the ratios of pulleys are so selected that a normal person can lift 3T. No problem of human capacity or extra force requirements. Only thing, because of the pulley ratios, the speed of lifting the load will be proportionately slow.

No need to underrate it for liability, as sufficient safety margin / design safety factor is already considered.

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#20
In reply to #15

Re: How Much Weight A Chain Block Can Lift

06/24/2010 4:39 AM

You remember a quote by Newton (Yes, same Newton who discovered the laws of gravity) "Give a long enough and strong enough lever and a (place for)fulcrum, I will lift the earth"

So even the force of common man can lift a earth, provided proper mechanism and sufficient tiem is available.

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#22
In reply to #20

Re: How Much Weight A Chain Block Can Lift

06/24/2010 7:46 AM

Actually Archimedes is attributed to that quote. But your point is the same.

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#33
In reply to #20

Re: How Much Weight A Chain Block Can Lift

06/25/2010 7:32 PM

It was Archimedes, not Newton.

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#34
In reply to #20

Re: How Much Weight A Chain Block Can Lift

06/27/2010 11:54 PM

Good quote but it was not by Newton.

This quote is from Archimedes

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#35
In reply to #34

Re: How Much Weight A Chain Block Can Lift

07/05/2010 11:20 PM

Thanks all for correcting me.

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#16

Re: How Much Weight A Chain Block Can Lift

06/23/2010 11:36 PM

Guest, (jeeze why not sign up a be a real person?),, yeah it's a silly question. If it's a three ton block, it's rated to safely lift a three ton load, probably with a safety factor of 4. Further it will be geared so that a normal human male can, by himself lift said load.

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Anonymous Poster
#24
In reply to #16

Re: How Much Weight A Chain Block Can Lift

06/24/2010 7:54 AM

Further it will be geared so that a normal human male can, by himself lift said load.

And if you are not then try hanging weights on the lift side of the pull chain. With enough additional weight for leverage you can pull the chain with two fingers. The big draw back is all of the additional weight hanging from the lifting point and you having to move them up the chain as they reach the floor.

Of course you could develop an overunity wheel to allow it to move on its own. Just replace the lift chain with your magic device. You will need to design in a brake to stop you overunity device before the load is pulled into the rafters.

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#25
In reply to #24

Re: How Much Weight A Chain Block Can Lift

06/24/2010 8:05 AM

Sorry, I forgot to login.

I take full blame for recommending the overunity device as a lifting aid. The joke seemed appropriate due to the nature of the question.

The Mechanic-

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#30
In reply to #25

Re: How Much Weight A Chain Block Can Lift

06/25/2010 2:33 AM

Um - I think I must have an over-unity hoist.

It doesn't have that chain loop and the only energy I exert is depressing the small disk in the yellow box.

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#28
In reply to #16

Re: How Much Weight A Chain Block Can Lift

06/24/2010 11:25 AM

probably a highschool student doing homework.

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#18

Re: How Much Weight A Chain Block Can Lift

06/24/2010 1:22 AM

As many others have answered, of course it can - that is is what is made for. If excessive force is required to operate it - I would say anything more than about 25-30kg is excessive - there is something wrong with it, you are not meant to use your whole weight to make it work. There are 10 & 20T manual chain blocks which allow one person to lift these weight so long as they have enough time - the ratio is so high you actually need a team to take it in turns but it works.

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#19

Re: How Much Weight A Chain Block Can Lift

06/24/2010 4:27 AM

The maximum weight anything can lift is that stated on its test certificate filed in the General Register. The tests will have been carried out by an insurance company's Engineer/Surveyor with a view to assessing it for indemnity insurance cover.

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#21

Re: How Much Weight A Chain Block Can Lift

06/24/2010 7:42 AM

If a chain block could lift weight.

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#23
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Re: How Much Weight A Chain Block Can Lift

06/24/2010 7:48 AM

But what if the woodchuck was named Archimedes?

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#26

Re: How Much Weight A Chain Block Can Lift

06/24/2010 9:16 AM

As far as figuring it out using "statics", go back and open up your Static & Strength of Materials textbook and study how pullys work....same principle as your lifting hoist.....

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#31

Re: How Much Weight A Chain Block Can Lift

06/25/2010 3:10 AM

You can easily lift 3 Ton if Chain Pulley block is in good condition.In India we subject Chain Pulley Blocks to 50% overload which means we test at 4.5 Ton. But you are not supposed to lift beyond 3 Ton. Also we design Chain Pulley Blocks with Factor of Safety of 5 as Indian Standard:3832. Which means break load of C.P.Block is 15 Ton.This is just for your information. I have worked for C.P.Block mfr for 33 years.

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#32

Re: How Much Weight A Chain Block Can Lift

06/25/2010 3:53 AM

Yes! But check what you hang the chain block from. I have seen a 1.5 Ton block hanging from under a verandah off the middle of a 3 inch x 2 inch timber bearer 10 ft long, simply supported at each end. Boards were nailed to the top side of the bearer. Safety factor? Luckily, it was only for lifting a 4 cylinder car (auto) engine.

The chain is geared, using a worm and gear, or a set of spur gears. The mechanical advantage is such that one man can pull the endless chain, and up she lifts.

The fact that the block doesn't let itself down automatically tells you that the efficiency of the gearing is less than 50 percent (I had this as an exam question once, can't remember how I worked it out). Just in case though, there is usually a way of locking the chain after lifting. This is called a belt-and-braces arrangement.

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#36

Re: How Much Weight A Chain Block Can Lift

09/19/2010 2:58 PM

Are you refering to a "chain block" or a "chain hoist"?

Chain block usually refers to pulleys ie. blocks connected by chains in such manner that by pulling on the chain you achieve a mechanical advantage. These are not common at the current time. Most of this type unit now uses rope as the connecting medium and is for relatively light loads. An example of this would be the pulley and rope device that hunters use to lift game (deer and larger) up inorder to gut them.

A chain hoist usually refers to the lifting device which has a hoist chain which the user manipulates to raise and lower the load and also a load chain which the load is hung from and is raised and lowered. These are often used to lift engines out of cars.

Manual chain hoists are usually manufactured with a ratio which enables one person to lift the total rated load of the hoist. Don't remember specifically but it is usually around 50-70 lbs pull to raise the capacity of the hoist.

Hoists are usually not limited by the "manufacturers load capacity' in their total user capacity. Depending on the construction of the hoist they can sometimes be used above the rating. In doing so you have to exert more than the rated pull on the hoist chain to acheive this. For example, a 2-ton hoist with a 80:1 ratio would require a pull of 50 lbs., using it for 4 tons would require a pull of at least 100 lbs. (probably more due to increased load on the gearing).

The best way to determine the load capacity is to contact the manufacturer (or look it up on the web) and ask them.

3 tons for a chain block would be alot of equipment since you would have to achieve about a 100:1 ratio with blocks and chain. Thats many blocks and a long piece of chain.

There is also a device which functions as a differential pulley system but that is too long to explain here.

Good Luck, Old Salt

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