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Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large or produce large axial force It is always desired to reduce number of screws
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Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Dec 19, 2015

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Page 1: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Fasteners, Powers Screws, Connections

Helical thread screw was an important invention.

Power Screw, transmit angular motion to liner motion

Transmit large or produce large axial force

It is always desired to reduce number of screws

Page 2: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Definition of important Terminologies

Major diameter d, Minor diameter dr Mean dia or pitch diameter dp

Lead l, distance the nut moves for one turn rotation

Page 3: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Single and Double threaded screws

Double threaded screws are stronger and moves faster

Page 4: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Screw Designations

• United National Standard UNS

• International Standard Organization

Roots and crest can be either flat or round

Pitch diameter produce same width in the thread and space,

Page 5: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Coarse thread Designated by UNC

• Fine Thread UNF, is more resistance to loosening, because of its small helix angle.

• They are used when Vibration is present• Class of screw, defines its fit, Class 1 fits have

widest tolerances, Class 2 is the most commonly used

• Class three for very precision application• Example:1in-12 UNRF-2A-LH, A for Ext. Thread

and B for Internal, R root radius• Metric M10x1.5 10 diameter mm major

diameter,1.5 pitch

Page 6: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Some important Data for UNC, UNF and M threads

• Lets Look at the Table 8-1 on Page 398

Page 7: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Square and Acme Threads are used for the power screw

Preferred pitch for Acme Thread

d, in 1/4 5/16 3/8 1/2 5/8 3/4 7/8 1 1 1/4

p,in 1/16 1/14 1/12 1/10 1/8 1/6 1/6 1/5 1/5

Page 8: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Mechanics of Power Screws

Page 9: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Used in design to change the angular motion to linear motion, Could you recall recent failure of power screw leading to significant causalities

Page 10: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

What is the relationship between the applied torque on power screw

and lifting force F

Page 11: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Torque for single flat thread

)sec

sec(

2

fld

fdlFdT

m

mmR

)(2

)(2

fld

lfdFdT

fld

fdlFdT

m

mmL

m

mmR

If the thread as an angle α, the torque will be

Wedging action, it increases friction

Page 12: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Stresses in the power Screw

pnd

F

A

V

pnd

F

pnd

Fd

T

tr

trb

tmB

3

2

3

6

2/

163

Shear stress in the base of the screw

Bearing stress

Bending stress at the root of the screw

Shear stress in the thread

nt number of engaged thread

Page 13: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Loading to the fasteners and their Failure considerations

Page 14: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Bolts are used to clamp two or more parts

It causes pre tension in the bolt Grip length is the total thickness of parts and washers

l

ld

l t

Page 15: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

t2

ldh

L’ effective grip= h+t2 if t2<d

=h=d/2 for t2 d

lt=L’- ld

Page 16: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Failure of bolted or riveted joints

Page 17: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Type of Joints• Lap Joint (single Joint) But Joint

Page 18: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Example 1

Page 19: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Example 2

Page 20: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Example 2

Page 21: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Example 3

Page 22: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Weld

Page 23: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.
Page 24: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.

Weld under Bending

Page 25: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.
Page 26: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.
Page 27: Fasteners, Powers Screws, Connections Helical thread screw was an important invention. Power Screw, transmit angular motion to liner motion Transmit large.