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Chapter 11Keys and Couplings

ENTC 463

Mechanical Design Applications II

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Keys and Couplings

Keys

Machine elements placed at the interfacebetween a shaft and the hub of a gear,sprocket, or sheave to transmit torque

Couplings

Machine elements used to connect two shafts

to transmit power

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Keys

Types of Keys

Parallel keys Square keys

Rectangular keys

Tapered Keys and Gib Head Keys

Pin Keys

Woodruff Keys

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Parallel Keys

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Taper, Gib Head, and Pin Keys

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Woodruff Keys

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Parallel Keys

Parallel to the axis of shaft

Square keys Preferred size: 3/32 to 1

Rectangular keys Preferred size: 1 and up

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Parallel Keys

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Materials for Keys

AISI 1020 Cold Drawn

AISI 1040, AISI 1045 Heat treated steel

Consider fatigue, shock/impact loading(elongation > 10% needed)

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Forces and Stresses on Keys

Failure due to shear (shear stress)

Failure due to compression (bearing stress)

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Failure Due to Shear

DWS

TNL

N

S

DWL

T

A

F

WLA

D

TF

y

y

4

5.02

area)(shear

2

>

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Failure Due to Compression

( )( )

DHSTNL

N

S

DLH

T

LHD

T

A

F

LHA

y

y

c

c

4

4

22

2

>

Fore square key, W = HFor rectangular key, W > H, calculate L based on compression

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Key Example

Design a key for a shaft (D = 1.0) rotating

at 350 rpm and transmitting 4.0 hp

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ENTC 463

HW#11 Key, Spline, and Coupling

Due 4/1/2008 Chapter 11 1, 3, 5 (for the application in

problem 3)

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Next Thursday4/3/2008

Meet @ Thompson 009B

ENTC 463

Mechanical Design Applications II

Allen to Hagan 2:20 to 3:00 PMHigginbotham to Winniford 3:00 to 3:35 PM

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Splines

Splines

Concept: multipleparallel keys

SAE specifications: 4,

6, 10, 16 splines

Torque capacity rating

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Straight Splines

SAE Standard

Torque capacity is based on the limit of 1000psi bearing stress

???

splinesofnumber:

222

1000

L

N

hdDNT

+=

T is per inch spline length

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Straight Splines

( )( )

( )( )

( )

LdDdD

N

T

dDDD

LhD

T

Splines

LHD

T

A

F

Keys

aa

a

+=

+=

=

==

24

)2(diameteraverage:

22

:

22

:

+

=

==

241000

"0.1and1000Since

dDdDNT

Lpsi

(11-10)

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Straight Splines

+=24

1000dDdD

NT

LdDdD

NST

S

LdDdD

N

T

y

y

+