Question

6. Consider a power screw used in an application to lift a load. In the following, select a standard power screw, and determine: the torque to raise and lower the load, and the efficiency of the power screw. Use a friction factor of 0.15. (15 marks) a) Select an Acme screw thread ( 14.5°) to lift a load of 15,000 Ib, limiting the tensile strength to 8,000 psi b) Select a metric trapezoidal screw thread (= 15°) to lift a load of 44 kN, limiting the tensile strength to 55.0 MPa. e) Which power screw is more efficient?

Answer 1

Given data friction factoy= o.15=tano Cay For ACTma tthread d14.5 W= 15,000 eb tensilestreanth 8;000 Rsi Face raquisad to lift the load -W(4Sec+ tana) -ASecd tana (o ISsE4s 1- o.ISSeci4.5°xo IS IS000(0.155 to'Isu683.9Lb An Sooo 0.IS 1 o ISS xO L Force Requird to lower he load F (usec-tana) 1 +usecd tand 15000(0.155--o-1S) aO15Sxo IS = 73.29 Lb Ans Efficiency tana i-ASec tana Sec d t tand oIS (015Sec 14.s ko 15) O.15 Seci4 So o.1S O.IS (1 155x0 1S) O.ISS to.1S O.4804 OR 48.04%, Ane For mutsic tapezo idal (b) 4150, W u4 kN,tensilo Streng th5SMA Forte Requiud to Lift thaload w (LSecd +tana uSec tand 44(0.15 Seels+o15 o.15 Sec Iso LS 13.7KN Ans
y
Force Required to lowe the load w(usecd tana) +usec tand uy lo.15 Seci501S) 21S kNAny o1SSecisxos tana (-u Secd tana) usecd tano o15 (1-0.158eciggxoIS) -O.2 Efficiency n O IS Sec ls IS 48.04% ) Both pouer screw is equal efficient.