05-12-2012, 02:55 PM
DESIGN OF SCREW JACK
DESIGN OF SCREW.docx (Size: 32.29 KB / Downloads: 34)
INTRODUCTION :
Power screw is a screw & nut system used to change angular or rotory motion in to linear motion & normally to transmit power.
The essential elements of power screw are a screw and a nut.
A power screw can be machine powered or manually operated.
In order to cause relative motion between two elements i.escrew and nut ,a torque is applied to one of these twoelements ,causing it to rotate and either itself or other elements in an axial direction.
Design of power screw
Question-
A screw jack is to lift to a load of 110KN through a height of 400mm.The elastic strength of screw material in tension and compression is 420MPa .The material for nut is phosphor bronze for which the elastic limit may be taken as 190MPa in tension, and 95MPa in shear.Handle is made up of plain carbon steel having yield strength in tension is 420MPa. The bearing pressure between the nut and the screw is not to be exceed 10N/mm2.Design the screw jack assuming factor of safty is 5,coefficint of friction between nut & screw and cup & collar is 0.18 & 0.20 respectivly.
CONCLUSION :
From the design of screw jack,calculated values of stresses are less than permissible stress value.