Cranes : The Trolley (Pt. 1 of 2)

The trolley is the part to which the load is attached to, the trolley also allows for the load to traverse the length or at least a prescribed part of the boom. The load doesn’t have to attach directly to the trolley, the trolley can by means of bolt holes can accommodate a motorized winch, if not a block and tackle can be affixed to the trolley for easier lifting.

The trolley is not one continuous part, it a several component parts bolted together, the 2 parts on either side are the trolley plates. These plates sandwich the components within. The lowest part of the trolley is the load bracket, this is where either a hook or other motorized or mechanized lifting device. This bracket is affixed between the two plates.

The trolley overall sits on the edge of the I-beam by means of rollers. These rollers are non-metal polyurethane in nature (PUR). The are free to rotate on the beam edges and thus can traverse the beam edge. However on one end we have said rollers simply on shafts, on the other end the rollers are on keyed shafts with gears. The 2 geared shafts ultimately meshes with a smaller centre gear that is also on a keyed shaft. Now this shaft extends outward, with a sprocket on the other out most end.

Now on this “sprocketed” end a long chain can be attached and allowed to hang, thus despite the height of the trolley an operator can rotate the sprocket by, manipulating the chain, thus turning the shaft and centre gear thus turning the rollers, moving the trolley along the beam.

The trolley represents one of the smallest but mure intricate parts especially when we consider the geometry. The tight geometry of the trolley could lead to stress concentrations that could mean that the stresses exceed the yield strength of the choosen material Armstrong 240.

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