Lecture - 2 Design of a Helical-Bevel Gear...
-
Upload
truongkien -
Category
Documents
-
view
231 -
download
4
Transcript of Lecture - 2 Design of a Helical-Bevel Gear...
Lecture - 2Design of a Helical-Bevel Gear Boxg
Part-II
(March 20 2017)(March 20, 2017)
Design of Helical & Bevel Gearsand Layout of Gear Box
1
Design of an Industrial General Purpose Reduction Gear Unit :
Data: The TWO- stage (1st stage Bevel and
Tasks (contd….) :Data: The TWO stage (1 stage Bevel and 2nd. Stage helical) reduction gear box has the following specifications.
(20 to 22 different problems). Z1
Z3 Z4
GROUP POWER(kW)
INPUT RPM
OUTPUTRPM
DUTY OVERHAULTIME LUBRICATIONSub
GroupDescription
IA, B, C, D,
12 1500 170 A,E,I,M,Q, U
Precision, Intermittent,
No shock2 years
Forced
II 10 1800 200 B,F,J,N,R General, Oil Sump
Z2
E, F,G,H Continuous,Medium shock
IIII, J, K, L
09 1450 125 C,G,K,O,S, V
General, Intermittent,Heavy Shock
Oil Sump
IVM,N,O,P
07 1200 125 D,H,L,P,T Precision, Continuous,
Medium Shock
Forced
V 05 1500 140
Assembled plan view(Not of the same one as below)
t i h ld d
VQ,R,S,T
05 1500 140
VIU, V
06 950 100 Horizontal input and vertical output (Forced Lubrication)
1st. stage ratio should not exceed 3.In general non co-axial horizontal input and output (except otherwise mentioned).
2
Gear Tooth Terminology
3
Gear Tooth Terminology (Contd.)
[N t W ki l b diff t f t d d
Pressure Angle ( ) : Also known as ‘angle of obliquity’, is the inclination of the“line of action” of the contact force between a pair of meshing teeth withrespect to a line drawn tangent to pitch circles at pitch point.
[Note- Working pressure angle may be different from standardpressure angle].
Direction of ‘line of action’ depends on driver & driven gears and their directions of rotation.
4
Gear Tooth Terminology (Contd.)
Base Circle: It is an auxiliarycircle used in involute gearingcircle used in involute gearingto generate tooth profiles.
Line of actions a commontangent, which passes throughth it h i t b th b
[Note: For a particular generated
the pitch point, both basecircles.
involute gear the base circleremains fixed and can beconsidered as reference. ]
Pinion & Gear: In a pair of gears in mesh smaller oneis called ‘Pinion’ and the bigger one is called ‘Gear’is called Pinion and the bigger one is called Gearirrespective of any of them is driver or driven.
5
Gear Tooth Terminology (Contd.)
Module (m) : Pitch circle diameter / Number of teeth.
It is standardized and expressed in mm.
[Note: In case of helical teeth ‘normal module’ (i em[Note: In case of helical teeth normal module (i.e.,
module in normal direction is standard one].
It is followed in Metric and SI unit system.
nm
Standard Module: 1, (1.25), 1.5, 2, 2.5, 3, 3.5, 4, 4.55 6 7 8 10 12 15 17 20 255 6 7 8 10 12 15 17 20 25
Diametral Pitch (DP) : Average number of teeth
per unit length (inch) of pitch circle diameter.
To compare with module system 1”/DP i.e., 25.4/DP gives
l l t t d d d la value close to a standard module.
Standard 1, 2, 3, 4, ………………….. 25 6
Involute Toothed Gear : Fundamental Relations :
Pitch diameter
Referring to straight tooth spur Gear:
mZrd pp 2Pitch diameter
mZrp pc /2Circular pitch (arc)
p
Base circle radius
cospb rr
7
Involute Toothed Gear : Fundamental Relations (Contd.):
Referring to straight tooth spur Gear:
Tip or Addendum circle radius
maZr
( ‘-‘ for internal toothed gear)
mar fa
2
Root or Dedendum circle radius
mdZr fd
2
( ‘+’ for internal toothed gear)
8
Involute Toothed Gear : Fundamental Relations (Contd.): Recapitulation :Referring to straight tooth spur Gear:
Tooth thickness ( ) and space ( )
at standard pitch circle of
tt
st
at standard pitch circle of
uncorrected (standard) gear
they are equal (arc). ttst
tt st
c= p / 2 = πm / 2
9
Minimum Number of Teeth in a Gear, Interference and Undercut
2sin
2 fc
aZ
10
Gear DesignGear Design
Straight Tooth Spur Gear
11
Strength of gear teeth-Lewis St e gt o gea teet e sequation
12
Strength of gear teeth-Lewis St e gt o gea teet e sequation
Stress at root
22
66bthF
btM t
Stress at root
btbt
Where, b is the width of gear.
Ymht
6
2
Y is called the Lewis form factor
13
Strength of gear teeth-Lewis St e gt o gea teet e sequation
Y Lewis form factorY Lewis form factor
Y = 0.484 - 3.28 / ZFormative number of teeth.Z
bYmFt o at e u be o teetZ
bYSF
Introducing Allowable Strength And velocity factor
bYmcSF vot
14
Gear DesignGear Design
Helical Tooth Spur Gear
15
Design of Helical Gear
Pitch Diameter of Helical Gear
3cos
ZZFormative number of teeth is expressed as:Zcos
16
Design of Helical Gear
Design of first stage gear set:
Module on the basis of bending strength:Module on the basis of bending strength:
The Lewiss Formula for module calculation.
2Tcosβm =n3 d
m = S ψYZc cv wc c
17
Design of Helical Gear
Centre Distance of Mating Helical Gear Pair
cosnpcp
p
pZpZD
cosngcg
g
pZpZD
2/)( gp DDA gpn ZZmA
2gp gpcos2
18
Gear DesignGear Design
Straight Tooth Bevel Gear
19
Bevel Gear Nomenclature & Terminology :
20Straight Tooth Bevel Gear.
Different Type of Bevel Gears:
Straight Bevel
Spiral Bevel
21
Hypoid Bevel
Herringbone BevelWorm & Worm Wheel
Straight Bevel Gear Design:
Module (m, in meter) can be estimated as:b
b2
2Tm
For straight tooth bevel gear:
mean r
2
3 (1 )bevel
do
v w
m S ZYc c
mean r
Mean PCD (Straight Bevel)
2 mean r Z m 2 bevelmean r Z m
90o
Other relations.
90p g
sin / sin /p g p gZ Z And,
22Straight Tooth Bevel Gear.
p g p g
Design of a Bevel- Helical Two Stage Gear Box:
IMPORTANT:
Complete the Gear Design Partand
fDraw the layout of gears on 27 March, 2017
Z1
Z2
Z3 Z4
IMPORTANT:Al S b it f h d k t h f
Assembled plan view
Also Submit a freehand sketch of plan view (one copy per group).
23of 2-stage (Bevel-Helical) gear box.(Top cover open)
(Not of the same one as below)