PART- III: Advanced Agricultural Machinery Design - CHAIN DRIVES.pptx

Adama, Ethiopia
Biniam Zewdie G/Kidan *
•Haramaya Institute of University
P.O.Box:138; Dire Dawa, Ethiopia
•Mobile: +251910408218/+25191582832
•E-mail: nzg2001nzg@gmail.com/zewdienico@gmail.com

CHAIN DRIVES
A chain is a power transmission element made as a
series of pin-connected links. The design provides for
flexibility while enabling the chain to transmit large
tensile forces.

CHAIN DRIVES
• Today chain drives play an important part in many
agricultural machines such as hay balers, corn
pickers, combines, cotton pickers, and beet
harvesters.
• Another benefit is that chain drives are capable of
transmitting a large amount of power at slower
speeds.
• However, chain drives require better shaft
alignment and more maintenance than V-belt

• The maximum permissible speed decreases
as the pitch is increased.
• Multiple-width chains of short pitch can be
used for extremely compact drives at high
speeds.
• Roller chains are precision-built and under
favorable conditions may have efficiencies
as high as 98% to 99%.
Chain Drives Cont.…

• Sprockets may be driven from either the
inside or the outside of a roller chain.
• Although oil-bath lubrication is recommended
for high-speed drives, this system often is
not practical on agricultural machines.
• Standard-pitch roller chain is several times as
expensive as steel detachable-link chain.
• Double-pitch chains are suitable for slow and
moderate speed drives

• Method of Lubrication: The American
Chain Association recommends three
different types of lubrication depending on
the speed of operation and the power being
transmitted.
Type A. Manual or drip lubrication: oil is applied
copiously with a brush or a spout can, at least once
every 8 hours of operation.
Type B. Bath or disc lubrication: The chain cover
provides a sump of oil into which the chain dips
continuously.
Type C. Oil stream lubrication: An oil pump delivers a
continuous stream of oil on the lower part of the chain.

• Recommended
Lubricant for Chain
Drives

Design Consideration Of Chain
Roller Chain Construction
• Roller chains are assembled using link
plates, pins and rollers and connecting
them in an endless chain using a
connecting link.

Design Consideration Of Chain Cont.…
Roller Chain Components

Cont.…
• Chain sections are made up from two
separate assemblies called the Roller
Link and the Pin Link.
• Note: Smaller pitch chains (1/4 and less)
do not have rollers.
Chain Size (Pitch)
• Chains are sized according to their pitch. The
center-to-center distances of the link pins determine
pitch.

• The pitch of chain drive components is specified by a 2
digit number.
• The first digit specifies the center –to center distance of
the chain link pins in 1/8ths of an inch, the second
number specifies the chain style.
• #25 chain means:
Cont.…
• Chain pitch = 2 x 1/8 or ¼” pitch
• Chain style =5 = roller less
chain.
Roller Chain Pitch

Roller Links and Pin Links
• Chains are made up using two types of link
assemblies; Roller links (Inside links) and pin links
(outside links).
• Roller links and pin links are assembled in a
continuous loop using a connecting link.
Roller Links and Pin
Links
Cont.…

Pin Links
Cont.…

Designing Chain Drives
• Chain Pitch is determined by the forces torque
and RPM acting on the shafts and sprockets.
• Larger pitch chain and sprockets are needed
to handle higher torques and higher RPM.
Drive Ratios
• Drive ratios greater than 10:1 should not be
used.
• In order to achieve higher ratios it is good
practice to create multiple drives using two
drives in series.
Design of Chain Cont.…

• The sprocket pitch diameter is an imaginary
circle through which the chain pin centers
move around the sprocket.
• The pitch diameter is the fundamental design
geometry that determines the size shape and
form of the sprocket teeth dimensions.
Cont.…

• Pitch of chain. It is the distance between the hinge
center of a link and the corresponding hinge center of the
adjacent link.
• Pitch circle diameter of chain sprocket. It is the
diameter of the circle on which the hinge centers of the
chain lie, when the chain is wrapped round a sprocket.

Chain Length Calculation
• Chain length is a function of the number of teeth of the
drive and driven sprockets as well as the center-to-
center distance.
• Chain length is customarily expressed in (even numbers)
of pitch units since chains can only be shortened or
lengthened by multiples of their pitch units.
• If an odd number of pitches is required then a special
link called an offset link is used.
The chain length for a given drive is
determined by:
• The number of teeth in the drive sprocket
• The number of teeth in the driven sprocket
• The pitch diameter (PD) of the drive sprocket
• The pitch diameter (PD) of the driven sprocket

Calculate the pitch circle
radius for the drive sprocket
• Calculate the pitch circle radius
for the driven sprocket.

3. Calculate the length of side DF
a. Line AF is parallel to line BE and
perpendicular to AB and DE
b. Line BE is tangent to circles K and M
c. Line DF = DE-AB
4. Calculate angle a.
a. Triangle AFD is a right triangle
b. Use the math. find the sine of angle a.

5. Calculate the length of the chain between
the pitch circle tangent points, BE.
BE = AF = AD cosine a
6. Find the pitch lengths of chain wrapped
around each of the sprockets.
Note: Each tooth on the sprocket represents a
pitch unit. Therefore, if we calculate the arc lengths of
chain wrapped around the sprocket in terms of teeth,
we will have the arc lengths in pitch units and it will be
unnecessary to convert inches to pitch units.

Design Parts Cont.…Procedure
• Half the chain wrapped around the large
sprocket is represented by arc ME.
Measured in pitch units (teeth) we find;
• Half the chain wrapped around the small
sprocket is computed in a similar way,
except, the arc length of angle a is
subtracted from the 90 degree arc KG.

7. Using the information from the 6 preceding
steps, we can find the chain length (In pitch
units) for these 2 sprockets.
• Calculating Center Distance From a
Known Chain Length.

8. Factor of Safety for Chain Drives
The factor of safety for chain drives is defined as the
ratio of the breaking strength (WB ) of the chain to the
total load on the driving side of the chain ( W ).
Mathematically,
• Factor of safety = Breaking strength(WB)/load(W)
The breaking strength of the chain may be obtained
by the following empirical relations, i.e.
WB = 106p2 (in newton's) for roller chains
= 106p (in newton's) per mm width of chain for
silent chains.

9. The Total Load (or Total Tension): on the
driving side of the chain is the sum of the
tangential driving force (FT), centrifugal tension
in the chain (FC) and the tension in the chain
due to sagging (FS).
W = FT + FC + FS
10. Tangential driving force acting on the
chain,
11. Centrifugal tension in the
chain,

12. Tension in the chain due to
sagging
Where,
• m = Mass of the chain in kg per meter length,
• x = Centre distance in meters, and
• k = Constant which takes into account the
arrangement of chain drive
• = 2 to 6, when the center line of the chain is
inclined to the horizontal at an angle less than 40º
• = 1 to 1.5, when the center line of the chain is
inclined to the horizontal at an angle greater than
40º.

13. Power Transmitted by Chains
The power transmitted by the chain on the basis of
breaking load is given by
where
WB = Breaking load in newton's,
v = Velocity of chain in m/s
n = Factor of safety, and
KS = Service factor = K1.K2.K3

• The power transmitted by the chain on the basis
of bearing stress is given by
where b = Allowable bearing stress in MPa or
N/mm2,
A = Projected bearing area in mm2,
v = Velocity of chain in m/s, and
KS = Service factor

14. linear velocity
d = Pitch circle diameter of the
smaller or driving sprocket in
meter
N = constant speed of r.p.m.

Minimum Center Distance
• The arc of the chain engagement on the smallest sprocket
should not be less than 120 degrees.
• For drive ratios greater than 3:1, the center distance of the
sprockets should be equal to or greater than the difference of
the 2 sprocket diameters.
• This will ensure 120 degrees of chain wrap around the smaller
sprocket.
Maximum Center Distances
• The American Chain Association suggests that center
distances between sprockets should not exceed 80 Pitch
Units ( For unsupported chain drives).
• Excessively long center distances create catenary tensions
that act to increase chain wear and result in unnecessary
chain vibration.
• Consider supporting the chain on guides or rollers where long

Outside Sprocket Diameters (OD)
• In order to accurately calculate the
clearances for a given chain and sprocket
drive, it is necessary to determine the outside
diameters of the sprockets.
• This dimension can be approximated using
the following formula: Do = D + 0.8 d1
• where d1 = Diameter of the chain roller.

Advantage Disadvantage
9. No slippage between chain and sprocket teeth.
10. Long operating life expectancy because flexure and friction contact
occur between hardened bearing surfaces separated by an oil film.
11. Operates in hostile environments such as high temperatures, high
moisture or oily areas, dusty, dirty, and corrosive atmospheres, etc.
12. Long shelf life because metal chain ordinarily doesn’t deteriorate with
age and is unaffected by sun, reasonable ranges of heat, moisture, and oil.
13. Certain types can be replaced without disturbing other components
mounted on the same shafts as sprockets.

6. Noise is usually higher than with belts or gears, but silent
chain drives are relatively quiet.
7. Chain flexibility is limited to a single plane whereas some
belt drives are not.
8. Usually limited to somewhat lower-speed applications
compared to belts or gears.

Gears & Gear Trains……
Discussion Map
o Gears are toothed, cylindrical wheels used for
transmitting motion and power from one rotating
shaft to another.
o Most gear drives cause a change in the speed of
the output gear relative to the input gear.
o Some of the most common types of gears are spur
gears, helical gears, bevel gears, and worm/worm
gear sets.

• Gears are toothed members which transmit
power/motion between two shafts by meshing
without any slip. Hence, gear drives are also
called positive drives.
• In any pair of gears, the smaller one is called
pinion and the larger one is called gear
immaterial of which is driving the other.
• When pinion is the driver, it results in step down
drive in which the output speed decreases and
the torque increases.

• On the other hand, when the gear is the
driver, it results in step up drive in which the
output speed increases and the torque
decreases.

• The fundamental law of gearing states that the
angular velocity ratio between the gears of a
gear set must remain constant throughout the
mesh.
• The law of gearing states that the common
normal at the point of contact between a pair
of teeth must always pass through the pitch
point. Pitch point is the common point of
contact between two pitch circles of the gears
Law of Gearing

• Spur gears have teeth that are straight and
arranged parallel to the axis of the shaft that carries
the gear.
• The curved shapes of the faces of the spur gear teeth
have a special geometry called an involute curve.
• This shape makes it possible for two gears to operate
together with smooth, positive transmission of power.
• The teeth of helical gears are arranged so that they
lie at an angle with respect to the axis of the shaft.
• The angle, called the helix angle, can be virtually any
angle. Typical helix angles range from approximately
10° to 30°, but angles up to 45° are practical.

Details of two meshing spur gears showing
several important geometric features

• The helical teeth operate more smoothly than
equivalent spur gear teeth, and stresses are lower.
Therefore, a smaller helical gear can be designed for
a given power transmitting capacity as compared with
spur gears.
• One disadvantage of helical gears is that an axial
force, called a thrust force, is generated in addition to
the driving force that acts tangent to the basic
cylinder on which the teeth are arranged.
• The designer must consider the thrust force when

Cycle of engagement of gear teeth

Figure : Identities of the three primary planes for helical gears

Pitches for Helical
Gears
To obtain a clear picture of the geometry of helical
gears, you must understand the following five
different pitches.
➭ Transverse Circular Pitch pt = πD/N =
π/Pd
➭ Normal Circular Pitch pn = pt
cosψ
➭ Axial Pitch px = pt/tanψ = π(Pd/tanψ) = πm >
tanψ
➭ Diametral Pitch Pd =
N/D
➭ Normal Diametral Pitch Pnd =
Pd/cosψ

Figure : Identities of the three primary planes and associated
angles shown on a helical rack

Figure shows details of spur gear teeth with the many terms
used to denote specific parts of the teeth and their relationship
with the pitch diameter.

Terminology and spur gear
formula
• Number of Teeth, (N): It is essential that there are an integer number of
teeth in any gear. This seminar uses the symbol N for the number of
teeth, with NP for the pinion and NG for the gear.
• Pitch: The pitch of a gear is the arc distance from a point on a tooth at
the pitch circle to the corresponding point on the next adjacent tooth,
measured along the pitch circle.
• Pitch Circle and Pitch Diameter. When two gears are in mesh, they
behave as if two smooth rollers are rolling on each other without
slipping.
➭ Circular Pitch p = πD/N
➭ Diametral Pitch Pd = NP/DP =
NG/DG

Pitch radii: RP = DP/2 and RG = DG/2
• Center distance: C = RP + RG = DP/2 + DG/2
➭ C = (DP + DG)/2
• Diametral pitch system:
➭ Center Distance in terms of NG, NP, and Pd
• DP = NP/Pd and DG = NG/Pd
• C = (DP + DG)/2 = (NP/Pd + NG/Pd)/2 ➭C = (NP + NG)/2Pd
➭ Center Distance in terms of NG, NP, and m
DP = mNP and DG = mNG
• C = (DP + DG)/2 = (mNP + mNG)/2 ➭ C = m (NP + NG)/2
Pressure Angle: The pressure angle is the angle
between the tangent to the pitch circles and the line
drawn normal (perpendicular) to the surface of the gear

Two spur gears in mesh showing the pressure angle,
line of action, base circles, pitch diameters, and other
➭ Base Circle Diameter Db = D cosϕ

• Standard values of the pressure angle are established by
gear manufacturers, and the pressure angles of two gears
in mesh must be the same. Current standard pressure
angles are14
1
2
°
, 20°, and 25° as illustrated in Figure.
• Actually, the 14
1
2
°
tooth form is considered obsolete.
Although it is still available, it should be avoided for new
designs. The 20° tooth form is the most readily available at
this time.
• Figure : Illustration of how the shape of gear teeth
change as the pressure angle, (phi), changes

Where,
• ϕ = Pressure angle, RoP = Outside radius of the pinion = DoP/2 =
(NP + 2)/ (2Pd)
• RbP = Radius of the base circle for the pinion = DbP/2 = (DP/2) cosϕ
= (NP/2Pd) cosϕ
• RoG = Outside radius of the gear = DoG/2 = (NG + 2)/ (2Pd)
• RbG = Radius of the base circle for the gear = DbG/2 = (DG/2) cosϕ
= (NG/2Pd) cosϕ
• C = Center distance = (NP + NG)/ (2Pd)
• p = Circular pitch = (πDp/Np) = π/Pd
The contact ratio is defined as the ratio of the length of
the line-of-action to the base pitch for the gear.

TABLE : Formulas for Use When
Implementing Gear Pair Contact
Ratio Calculation in U.S. and SI
Systems in Terms of Diametral
Pitch and Module

• Bevel gears are used to transfer motion
between nonparallel shafts, usually at 90° to
one another.
• The four primary styles of bevel gears are
straight bevel, spiral bevel, zero spiral bevel,
and hypoid.
Bevel Gear
Geometry

• Bevel gears have teeth that are arranged as
elements on the surface of a cone.
• The teeth of straight bevel gears appear to be similar
to spur gear teeth, but they are tapered, being wider
at the outside and narrower at the top of the cone.
• Bevel gears typically operate on shafts that are 90° to
each other. Indeed, this is often the reason for
specifying bevel gears in a drive system.
• Specially designed bevel gears can operate on shafts
that are at some angle other than 90°.

• When bevel gears are made with teeth that form a helix angle
similar to that in helical gears, they are called spiral bevel
gears.
• The major difference between hypoid gears and the others just
described is that the centerline of the pinion for a set of hypoid
gears is offset either above or below the centerline of the gear.

Worm and Worm-Gearing
• Worm-gearing is used to transmit motion and power
between non-intersecting shafts, usually at 90° to
each other. The drive consists of a worm on the
high-speed shaft which has the general appearance
of a power screw thread: a cylindrical, helical thread.

• A worm and its mating worm gear operate on shafts
that are at 90° to each other. They typically
accomplish a rather large speed reduction ratio
compared with other types of gears.
• The worm is the driver, and the worm gear is the
driven gear. The teeth on the worm appear similar
to screw threads, and, indeed, they are often called
threads rather than teeth.

• The teeth of the worm gear can be straight like spur
gear teeth, or they can be helical. Often the shape of
the tip of the worm gear teeth is enlarged to partially
wrap around the threads of the worm to improve the
power transmission capacity of the set.
• One disadvantage of the worm/worm gear drive is
that it has a somewhat lower mechanical efficiency
than most other kinds of gears because there is
extensive rubbing contact between the surfaces of
the worm threads and the sides of the worm gear
teeth.

GENERAL GUIDELINES FOR WORM AND
WORMGEAR DIMENSIONS
• Typical Tooth Dimensions Table shows typical
values used for the dimensions of worm threads and
gear teeth.

Table: Summary and Evaluation of Gear
Types

Gear Train
• A gear train is combination of gears that is used for
transmitting motion from one shaft to another.
• There are several types of gear trains. In some cases, the
axes of rotation of the gears are fixed in space. In one case,
gears revolve about axes which are not fixed in space.
• Simple Gear Train In this gear train, there are series of
gears which are capable of receiving and transmitting
motion from one gear to another.
• They may mesh externally or internally. Each gear rotates
about separate axis fixed to the frame. Figure shows two
gears in external meshing and internal meshing.

Let N1, N2 be speed in rpm for
gears 1 and 2. The velocity of P,
𝑉
𝑝 =
2𝜋𝑁1𝑑1
60
=
2𝜋𝑁2𝑑2
60
𝑁1
𝑁2
=
𝑑2
𝑑1
=
𝑡2
𝑡1
t1, t2, t3, . . . be number of teeth of
respective gears 1, 2, 3, . . .

SUMMARY
• The power transmission devices are belt drive, chain drive
and gear drive. The belt drive is used when distance
between the shaft axes is large and there is no effect of slip
on power transmission. Chain drive is used for intermediate
distance.
• Gear drive is used for short centre distance. The gear drive
and chain drive are positive drives but they are
comparatively costlier than belt drive.
• Similarly, belt drive should satisfy law of belting otherwise it
will slip to the side and drive cannot be performed. When belt
drive transmits power, one side will become tight side and
other side will become loose side.

RECOMMENDATION
• Gear, Belt and chain drives can be used for transmission of
mechanical power between two rotating shafts. Belt drives are often
cheaper than the equivalent gears and useful for transmitting power
between shafts that are widely separated or nonparallel drives.
Chain drives are usually more compact than the equivalent belt
drive and can be used in oily environments where the equivalent
belt would be prone to slipping. There is a wide range of belt and
chain drives and this seminar has served to reviews the technology
and the selection and specification of wedge and flat belt and roller
chain drives. The technology is constantly developing with new
materials and surface treatments, improvements in understanding
of kinematics, and wears and associated modeling procedures. As
recommendation; Belts and chain drives thus represent an
innovation opportunity area, particularly for new applications,
extended life, and improved reliability, as well as miniaturization.

99
END!!
10qvm 4u
Attentions!!

PART- III: Advanced Agricultural Machinery Design - CHAIN DRIVES.pptx

Recommandé

Recommandé

Contenu connexe

Similaire à PART- III: Advanced Agricultural Machinery Design - CHAIN DRIVES.pptx

Similaire à PART- III: Advanced Agricultural Machinery Design - CHAIN DRIVES.pptx (20)

Plus de Haramaya Institute of Technology, & Adama Science and Technology University, Eth

Plus de Haramaya Institute of Technology, & Adama Science and Technology University, Eth (7)

Dernier

Dernier (20)

PART- III: Advanced Agricultural Machinery Design - CHAIN DRIVES.pptx