Power transmission

Part 2

Helical gear

• The teeth cut on the periphery are of helical screw form

• A helical teeth is inclined at an angle to the axis

BEVEL GEAR

• Used to connect between 2 non parallel shaft with intersecting axes.

HERRIGBONE GEAR

• A herringbone gear, a specific type of double helical gear.

• It is a side to side (not face to face) combination of two helical gears.

Worm gear• Worm gears are used for power transmission

between non intersecting shafts that are right angle to each other.

• It consists of a worm (threaded screw) and a toothed wheel.

Gear terminology

• Pitch cylinder– Imaginary cylinders which by rolling together transmit the

same motion as the pair of gears.• Pitch circle– It is the circle with radius equal to the radius of the pitch

cylinder.

• Circular pitch (Pc)– It is the distance measured along the circumference of

pitch circle from one tooth to the corresponding point on the adjacent tooth.

``Where d is the diameter of the pitch circle and T is the no. of teeth on gear

• Tooth thickness– It is the width of the tooth measured along the pitch circle

• Module (m)– It is the ratio of pitch circle diameter in millimeter to the number

of teeth.

• Addentum – It is the radial distance between pitch circle and addentum circle.

• Dedentum– It is the radial distance between pitch circle and dedendum circle

• Clearance – It is the radial difference between the addendum and dedentum

of of a tooth

FOR MESHING OF GEARS

• Velocity of the gears should be equal.

V= r ω

• Circular pitch of the gears should be same.

ROPE DRIVE• Ropes are used when considerable power is to be

transmitted over long distances.• Ropes are placed in grooves provided in the pulley.• The groove angle varies from 40 to 60 degree, but

is generally 45degree• Wire ropes are made up of wires, which are

twisted together to form a strand.• A no. of strands twisted together to form a rope.• Ropes are designated by specifying the no. of

strands and no. of wires on it. Eg: 6*19

Rope materials

• Wrought iron, cast steel, aluminium alloys, copper bronze and stainless steel.

• Ropes are generally galvanized to protect them against corrosion

Belt drive equations