Tension on Lifting Chain


A movable bin and its contents have a mass of 300kg.Determine the shortest chain sling ACB which may be used to lift the loaded bin if the tension in the chain is not to exceed 6250N. DIAGRAM:ACB-TRIANGLE WITH AC AND CB SAME LENGTH(TENSION WIRE)PULLING A BIN. SQUARE BIN WITH LENGTH 1.2M AND HEIGHT 0.7M.


A 300kg load in normal earth gravity weighs about 2940N. Assuming that the load is carried equally by each chain segment, which implies essentially no friction of the chain over the lifting hook, probably as risky assumption, each segment must provide a vertical lift of 2940/2N or 1470N.

In order for a tension in a chain segment to be no more than 6250N, the angle must be greater than or equal to that angle whose sine is 1470/6250. I calculate that limiting angle to be 13.79 degrees.

Half the width of the box (0.6m) divided by the length (x) of the minimum half chain will be the cosine of 13.79 degrees. So x=0.6/cos(13.79). I make x out to be 0.618 meters so the whole minimum chain length will be 1.236 meters if the chain ends are attached at the top edge of opposite sides of the box. If the chain is to wrap clear under the box you must add the 1.2+.7+.7 to the length. Of course if you want the lifting rig to actually lift the box you will need some reserve capacity to provide for an upward acceleration.

I am fairly confident my approach is right but I must caution you to always check my arithmetic.

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