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machine design problem

I have the following problem. Please can anybody help me on how to solve it? A load of mass 2 tonne is raised by a single start square-threat screw. The load bears on a collar and doesn't not revolve with the screw. The screw pitch is 12 mm and the outside diameter of the thread is 56 mm. The effeciency of the jack of this load is 15 percent. The torque to overcome friction at the bearing collar is estimated to be 120 N-M. Find the torque to overcome thread friction and the coefficient of friction for t the screw thread. waiting to hear from you. ~Youssouf.

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Youssouf
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Here's one simple way to work this (presumably a school problem)

Find the work to raise 2 tonne load 12 mm (100% efficiency) times 100/15 gives actual work

Using a nominal 1 meter lever, 1 rev = 2 pi r (actually a little more) at the handle. So 2 pi r times X = actual work. X is force at the handle. Subtract 120 N to get force to overcome the thread friction. This conveniently provides torque using the 1 meter arm. Finally draw a triangle, with a vertical force due weight , a diagonal force (that you have found) due thread friction and you're almost there....

Brian W

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Brian Whatcott

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