BELT TENSIONING METHODS, Chain drive introduction, Power transmitted by chain, Polygon effect in chain

Prepared By…
KAMAL AKHTAR F.(120450119156)
MECHANICAL-5C MACHINE DESIGN - 1
S.V.M.I.T.-BHARUCH

Topic’s….
 BELT TENSIONING METHODS
 Chain drive introduction
 Power transmitted by chain
 Polygon effect in chain

BELT TENSIONING
METHODS
 In order to transmit the power, the belt must be
provided with the sufficient initial tension.
 In addition to the other parameters, the power
transmitting capacity of the belt drive also depends
upon the initial tension.
 When a new belt is mounted on pulleys under tension;
it loses its initial tension due to elongation during its
service.
 Hence, it is necessary to make a provision to adjust
the belt tension from time to time.
 When the belts are hinged, as in case of flat belts, a
small length of belt can be cut to remove the slack .
However, this is not possible with endless belts.

Manual adjustment
 In this method, as shown in the fig. the motor
can slide in the guidways provided in the base
plate.
 The position of motor, and hence the initial
tensing can be adjusted manually with the help
of the screw and nut arrangement.
 Once the desired tension is achieved, then the
bolts are tightened to fix the motor to the base
plate.

 There are the weight of the motor is used to
maintain the belts tension.
 The motor is bolted to the base plate which is
mounted on the pivoted support.
 The belt tension is due to product of the weight W
of the motor and the moment arm ‘e’.
 By shifting the motor along the pivoted support,
the moments arm ‘e’ can be adjusted so that the
belt tension can be adjusted according to the
power recruitments. This arrangement is popularly
known as ROCKWOOD BELT DRIVE.

풆 =
(푭풕ퟏ× 풂) + (푭풕ퟐ× 풃)
푾

 There are idler pulley is held against the belts
by is own weight and the adjustable weight.
 By changing the position of the adjustable
weight, the required belts tension can be
achieved.
 In addition to adjusting the belt tension, the
idler pulley arranging also increases the arc of
contact.
 Hence, this method’s advantage is as in drives
with short center distance and having a high
speed ratios.

What is chain Drive?
 Chain drive is a way of transmitting
mechanical power from one place to another.

Construction
 Chain drives consists of endless chain i.e rigid
links hinged together by pin joints running
around two sprocket (toothed) wheels.

ADVANTAGES.
 Chain drives do not slip
 Is a positive drive..so can be used in
application where constant speed
ratio is required.
 Can be used for short as well as
long centre distances

 Transmits large power over long
distance
 Compact compared to belt drives
 Chains requires no tension on
slack side, so bearing loads are
reduced
 Less expensive than gear drives.

 Can operate at higher
temperatures than belts
 No. of shafts can be driven by single
driving shaft using chain drive
 Has high transmission efficiency as
much as 98%.

LIMITATIONS
 High production cost of chains.
 Due to polygon effect,it is not suitable
where precise motion is required.
 Operates with noise.

 Require proper maintenance.
 Periodic lubrications & slack
adjustment are required.

Applications
 Used for speed ratios upto 10:1
,velocities upto 25m/s & power
ratings upto 150kw.
 Used in bicycles,motor
cycles,rolling mills,conveyors etc.

Power Transmitting Chains
 These chains are used for transmission of
power, when the distance between the centers
of shafts is short. These chains have provision
for efficient lubrication.
 The power transmitting chains are of the
following three types….
Block chain
Bush roller chain
Inverted tooth or silent chain.

Block chain
 A block chain, as shown in Fig11.31. is also known as
bush chain. This type of chain was used in the early
stages of development in the power transmission.
 It produces noise when approaching or leaving the teeth
of the sprocket because of rubbing between the teeth
and the links.
 Such type of chains are used to some extent as
conveyor chain at small speed.

Bush roller chain
 A bush roller chain, as shown in Fig. 11.32, consists of outer plates or pin link plates,
inner plates or roller link plates, pins, bushes and rollers.
 A pin passes through the bush which is secured in the holes of the roller between the
two sides of the chain.
 The rollers are free to rotate on the bush which protect the sprocket wheel teeth
against wear.
 A bush roller chain is extremely strong and simple in construction.
 It gives good service under severe conditions. There is a little noise with this chain
which is due to impact of the rollers on the sprocket wheel teeth.
 This chain may be used where there is a little lubrication.
 The rollers then fit unequally into the cavities of the wheel.
 The result is that the total load falls on one teeth or on a few teeth.

Inverted tooth or silent chain.
 An inverted tooth or silent chain is shown in Fig. 11.33. It is designed to
eliminate the evil effects caused by stretching and to produce noiseless
running.
 When the chain stretches and the pitch of the chain increases, the links ride
on the teeth of the sprocket wheel at a slightly increased radius.
 This automatically corrects the small change in the pitch.
 There is no relative sliding between the teeth of the inverted tooth chain
and the sprocket wheel teeth.
 When properly lubricated, this chain gives durable service and runs very
smoothly and quietly.

퐷 =
푝
sin(180
푧 )
 훾 =
360
푧

BELT TENSIONING METHODS, Chain drive introduction, Power transmitted by chain, Polygon effect in chain

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BELT TENSIONING METHODS, Chain drive introduction, Power transmitted by chain, Polygon effect in chain