Download - CHAPTER 3 - Keys and Pins
-
7/28/2019 CHAPTER 3 - Keys and Pins
1/30
CHAPTER 3:
DESIGN OF MECANICAL JOINT
-
7/28/2019 CHAPTER 3 - Keys and Pins
2/30
DefinitionAMechanical joint is a part of a machine which is
used to connect another mechanical part ormechanism
2 types of mechanical joint:-
Temporary
Permanent
-
7/28/2019 CHAPTER 3 - Keys and Pins
3/30
Topic to be covered Key and pin joint
bolt and nut joint
Welding joint
-
7/28/2019 CHAPTER 3 - Keys and Pins
4/30
Keys and Pins Keys and pins are used on shafts to secure rotating
elements, such as gears, pulleys or other wheels
Keys are used to enable the transmission of torquefrom the shaft to the shaft-supported element
Pins are used for axial positioning and for the transferof torque or thrust or both
-
7/28/2019 CHAPTER 3 - Keys and Pins
5/30
a. Square keyb. Round key
c. Round pind. Round pin
e. Taper pinf. Split tabular spring pin
Keys and Pins
-
7/28/2019 CHAPTER 3 - Keys and Pins
6/30
Split tabular spring pin
-
7/28/2019 CHAPTER 3 - Keys and Pins
7/30
keys Stock key material is typically made from low carbon
cold-rolled steel, and is manufactured such that itsdimensions never exceed the nominal dimension.
This allows standard cutter sizes to be used for thekeyseats.
-
7/28/2019 CHAPTER 3 - Keys and Pins
8/30
Keys Square and rectangular keys are commonly used for shaft size up to
6.5inch
Advantages of square and rectangular key
1. Cost effective
2. Easy to replace damaged component
3. Easy to installation
-
7/28/2019 CHAPTER 3 - Keys and Pins
9/30
Function
The shaft and rotating machine element must have a keyway, also known asa keyseat, which is a slot or pocket for the key to fit in. The whole system iscalled a keyed joint
-
7/28/2019 CHAPTER 3 - Keys and Pins
10/30
Keyways Key ways can be milled horizontallyorvertically
-
7/28/2019 CHAPTER 3 - Keys and Pins
11/30
Classification of keys Saddle keys
Hollow saddle key
Flat saddle key
Sunk keys Taper sunk keys
Parallel sunk keys
Feather keys
Woodruff key (adjustable keys)
Round keys Parallel pin
Taper pin
-
7/28/2019 CHAPTER 3 - Keys and Pins
12/30
Sunk keys Sunk keys are sunk in the shaft and the hub. These keys are
suitable for heavy duty since they rely on positive drive
-
7/28/2019 CHAPTER 3 - Keys and Pins
13/30
Tapered sunk key
-
7/28/2019 CHAPTER 3 - Keys and Pins
14/30
Tapered sunk key
-
7/28/2019 CHAPTER 3 - Keys and Pins
15/30
Tapered sunk key The gib-head keyis tapered so that, when firmly
driven, it acts to prevent relative axial motion
This also gives the advantage that the hub positioncan be adjusted for the best axial location.
The head makes removal possible without access tothe other end
-
7/28/2019 CHAPTER 3 - Keys and Pins
16/30
Taper sunk keys The key is sunk in the shaft to a depth of half its
nominal thickness when measured at the side. Rectangular cross-section
let D = diameter of the shaft
width of the key W = D/4
nominal thickness T = (2/3)W = (1/6)D
Square cross-section:T = W
-
7/28/2019 CHAPTER 3 - Keys and Pins
17/30
Taper sunk keys
-
7/28/2019 CHAPTER 3 - Keys and Pins
18/30
Parallel sunk key It is uniform in width and thickness throughout. It is thus taper less and is used where the pulley or other mating
piece is required to slide along the shaft.
It may be rectangular or square cross-section and their endsmay be squared or rounded
-
7/28/2019 CHAPTER 3 - Keys and Pins
19/30
Parallel sunk keyThe keyway in a shaft for a parallel key
A sprocket with an internal parallel keyway
Cross-section of a parallel keyed joint
-
7/28/2019 CHAPTER 3 - Keys and Pins
20/30
Feather keys
It is a key attached to one member of a pair It is a particular kind of parallel key that permits axial
moment
A feather key is secured either to the shaft or to the hub,the key being a sliding fit in the keyway of the machineelement on which it moves.
Double
Headed Key
Peg Key
-
7/28/2019 CHAPTER 3 - Keys and Pins
21/30
Woodruff keys
-
7/28/2019 CHAPTER 3 - Keys and Pins
22/30
Woodruff keys It is an adjustable sunk key in the form of a semi-circular disc of uniform thickness.
The key fits into a semi-circular keyway in the shaftand the top of the key fits into a plain rectangular keyway in the hub of the wheel.
Since the key and the key seat bear the same radius , ithas the advantage of adjusting itself to any taper of theslot of the hub or boss of wheel
Used in feed gear box of lathe, other machine toolsand in automobiles
-
7/28/2019 CHAPTER 3 - Keys and Pins
23/30
Woodruff keys
-
7/28/2019 CHAPTER 3 - Keys and Pins
24/30
Hollow saddle keyThis key has curved underside so that it can be placed on the curvedsurface of the shaft. The keyway is cut in the mating piece (hub) only
-
7/28/2019 CHAPTER 3 - Keys and Pins
25/30
Hollow saddle keySaddle key are taper keys and are sunk into the hubonly
Taper prevents axial movement along the shaft
Saddle key is suitable for lightduty, since they rely on a frictiondrive alone and are liable to slip on
the shaft under load
-
7/28/2019 CHAPTER 3 - Keys and Pins
26/30
Flat saddle key
holding force is comparative large
than the hollow saddle key
Flat surface on the
shaft
Let D = diameter of the shaftWidth of the key, W = D/4Nominal thickness at largeend , T = W/3 = D/12Length of the key , L = D to1.5DTaper on the top surface =
1:100
-
7/28/2019 CHAPTER 3 - Keys and Pins
27/30
Sunk taper key
-
7/28/2019 CHAPTER 3 - Keys and Pins
28/30
Round key or Pin Key:
l h f d h b
-
7/28/2019 CHAPTER 3 - Keys and Pins
29/30
Spline shaft and hub
A spline shaft is used when the hub is
required to slide along the shaft.These shafts are used mostly forsliding gear application as inautomotive gear box and propellershaft of aircraft.
A spline shaft in which are cutequiangular longitudinal groove, themetal between these groove formingsplines or feathers of uniform depth.
By this means the power transmittedis equally divided amongst thenumber of keys giving great strengthand security against total failure thanby using a single key.
-
7/28/2019 CHAPTER 3 - Keys and Pins
30/30
Serrated shafts A spine shaft - disadvantage of
reduced strength A serrated shaft gives
maximum strength for a givenweight of material.
number of correspondinggrooves are cut in the shaft andmating piece, the two beingtightly pressed, one over theother
the bottom of the serrationsand the crests of the teeth areflat.
these are used in aircraftassemblies