©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!
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