PROJECT ON…

ISPAT

People are the most important and expensive resources in the industry. The difference between gain and loss in an industry depends upon the skill of its employees and the extent to which such skill can be effectively applied.People are able to change, grow and develop, while other industrial resources are concrete. Growth and development is best achieved through training. The employee must be trained, tested and be declared competent before he/she can accept the responsibility of his/her post

GEAR TRANSMISSION

• Gearing is a very vital form of transmission of mechanical power.

• Universally adopted for almost all machine mechanisms.

• Type of Gear Transmissions:

1. Spur Gear,

2. Helical Gear,

3. Herring bone Gear,

4. Bevel Gear,

5. Rack and pinion,

6. Worm and worm wheel.

SPUR GEAR Spur Gears in any

transmission system are employed for changing the speed and the torque and are fixed on shafts either rigidly or with sliding traverse.

HELICAL GEAR

Helical Gears can be used for transmitting motion between parallel shafts as between perpendicular shafts. Helical gears used for transmission at an angle are called SPIRAL GEARS.

Advantages of Helical Gears:

•Noiseless motion even at higher speeds.

•Smooth transmission of small gears with fewer teeth, at large transmission ratio ( up to 15:1)

These gears must be rigidly installed on the shaft. These gears result in an axial force in one direction depending upon the direction of rotation and are used for transmitting small power.

HERRING-BONE GEAR

HERRING-BONE Gears are pairs of Helical Gears. These gears are used for large power transmission.

Advantages of Herring-bone Gears in addition to Helical Gears:

•No Axial Force. It is balanced axially in both direction of rotation.

•Large power transmission can be done at impact loads having frequent starts (inching).

These gears also must be rigidly installed on the shaft.

BEVEL GEAR

Bevel Gear transmission is employed for transmitting motion from one direction to the other at any angle. In general 90° transmission is used mostly.

WORM & WORM WHEEL

Worm and worm wheel gives a large single stage speed reduction in perpendicular direction. Such transmission gives lower efficiency of transmission due to increased frictional losses. For a noiseless motion, worm 1 is usually made of medium carbon / alloy steel and the worm wheel 2 of bronze (or in some cast iron).

RACK & PINION

The rotary motion of pinion 1 (small gear) is transformed into linear motion of the rack 2. For transmitting large power worm & worm rack transmission is employed.

SPUR GEAR NUMENCLATURE

SPUR GEAR NUMENCLATURENomenclature Symb

olFormulae

ModuleDiametral PitchPitchNumber of teethPitch Circle DiameterTooth heightAddendumDedendumRoot circle diameterOutside diameterDistance between the axis of the two mating gears t 1 & t2Pressure angle

mD.P.

PtDhh’h”D1Do

Aα

m=p/Π = D/tt/D = Π/p = 1/mP= Π.m = 3.14mt = D/mD = t.mh = 2.2 mh’ = mh” = 1.2 mD1 = Do – 4.4mDo = m (t+2)

A = (t1 + t2) m/220˚(usually) or 14½°

Tooth Thickness Measurement

Tooth Thickness = Sx

Tooth Depth = Hxsx

Hx

Module (m) 1 1.5 2 2.5 3 3.5 4 5 6 7 8 9 10

Hx= 0.7485 m

0.75 1.12 1.5 1.87 2.24 2.62 2.99 3.74

4.49 5.24 5.98

6.73 7.48

Sx = 1.387 m 1.39 2.08 2.77 3.47 4.16 4.85 5.56 6.94

8.32 9.71 11.1

12.48

13.87

DEFECTS OF THE GEARS

• Wear of one, few or all the teeth.• One or few teeth broken or twisted.• Burrs on the bore or the key way.• Burrs on the internal splines of the gear

bore or the tooth surface.• Crack or damage on the rim or the bore

of the gear wheel.

LIMITS OF WEAR FOR DISCARDING

OPEN GEAR TRANSMISSION and the surface speed up to 2 meter / second – The tooth thickness (Sx) reduces due to wear by (0.5m) mm, where m is the module, or about 33% of the original tooth thickness.

CLOSED GEAR TRANSMISSION (GEAR BOXES) for surface speeds over 2 meter / sec. – the tooth thickness (Sx) reduces due to wear by (0.3m) mm or about 20% of the original tooth thickness.

MESHING OF GEARS

The spur and helical gears must be assembled in such a way that the axes of the meshing gears are parallel and the distance between their axes is correctly established.

The correct meshing of the spur and helical gears is decided by applying blue paste on the teeth of the driving gear, giving it several rotations and seeing to the blue marks on the teeth faces of the meshing driven gear.

(a) Correct meshing covering 70 – 80% tooth surface contact.

(b) Axis not parallel. (c) Axis not parallel and distance between them is too small.

(d) Axis not parallel and distance between them is excess.

(e) Axis are parallel and distance between them is excess.

(f) Axis are parallel and distance between them is too small.

LUBRICATION• Proper Lubrication with timely addition / replacement

plays vital role in maintaining the gear boxes with efficiency and increasing its working life.

• Oil level should be checked in all the gear boxes oil indicators / dip sticks.

• Oil level should be in between the minimum and maximum limits of the dip stick (or indicator).

• Testing of the lubricating oils used to be carried out periodically. The following tests are to be done…

1. Dirt contamination2. Moisture3. Volatile materials (Benzene, kerosene, spirit

etc,)4. Viscosity5. Acidity6. Alkalinity due to soda (Na2 Co3) etc.,