©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

Power Screws

Lecture-3(b)

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

COURSE OUTCOMES

CO# CO Description POs Addressed

CO1 Design the basic mechanical components in

engineering systems. PO1, PO2, PO3, PO4

CO2 Develop engineering models of the

components / systems. PO1, PO2, PO3, PO4

CO3 Apply materials selection in the design of

mechanical systems, e.g. for DFM and DFA. PO1, PO2, PO3, PO4

CO4 Apply Failure Modes and Effects Analysis

(FMEA) on mechanical system design. PO1, PO2, PO3, PO4

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

1.1 Recap!

1.2 Example #1

1.3 Example #2

1.4 Summary

CONTENT

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

Application of Power Screws

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

• Square and Acme threads are used in power screws when power is

to be transmitted.

• The torque for raising the load

• The torque required to lower the load

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

• When a positive torque is obtained, the screw is said to be self-

locking.

or

mfd l

• The efficiency of power screw is

• For Acme or other threads

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

• Collar torque

• Total torque to raise a load

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

Example #1

Solution:

A power screw is 25 mm in diameter and has a thread pitch of 5 mm.

(a) Find the thread depth, the thread width, the mean and root diameters,

and the lead, provided square threads are used.

(b) Repeat part (a) for Acme thread.

(c) Calculate linear velocity of the nut if the screw rotates at 100 rev/sec.

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

Example #2

FIGURE 1

A square-threaded power screw has a major diameter of 32 mm and a pitch of 4

mm with double threads, and it is to be used in an application similar to that in

FIGURE 1. The given data include f = fc = 0.08, dc = 40 mm, and F = 6.4 kN per

screw.

(a) Find the thread depth, thread width, pitch diameter, minor diameter, and lead.

(b) Find the torque required to raise and lower the load.

(c) Find the efficiency during lifting the load.

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

Total torque:

Lead:

l = number of thread X pitch

When a positive torque is obtained, the screw is said to be self-

locking.

or

mfd l

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

8.1, 8.4, 8.9 & 8.10

Tutorial Problems

©2015 Mechanical Engineering Design, MCB3083 Universiti Teknologi PETRONAS

Thank You!