Pulleys are load-bearing parts in metallurgical cranes. They can change the working tension inside flexible parts or change their speed and direction of movement due to different conditions of use.
So, pulley in metallurgical crane can both serve as a guide pulley, there can be used to form a pulley block.
The pulley of crane has two kinds, one kind is fixed pulley, it is equal arm lever actually, although do not save effort also is not laborious, but can change acting force direction, in many cases, change the direction of force can bring convenience to the job.
Another kind is movable pulley, it is the lever that dynamical arm is resistance arm 2 times, use movable pulley to be able to save half force, but expend a distance.
This is because when the metallurgical crane USES the movable pulley, the hook yard is hung by two pieces of rope, each piece of rope only bears half of the weight of the hook yard.
So although the use of movable pulley saves force, but the distance of power movement is greater than the distance of the hook yard, is the cost of distance.
If these two sliders are combined to form a pulley block, it both saves force and can change the direction of the force, because the pulley block with several pieces of rope hanging objects, lifting objects used by the force is a fraction of the total weight;
And the free end of the rope around the movable pulley is a section of the calculation, and around the fixed pulley is not calculated.
Metallurgical cranes use pulley block although saving force, but cost distance, the distance of power movement is greater than the distance of weight movement, the distance of power movement is greater than the distance of goods.
It seems that no form is the best of both worlds, according to the actual lifting situation to choose the appropriate pulley.