GEAR NUMENCLATURE & DEFECTS OF GEARS

Spur Gears are the very common gears for many gear boxes. As the helical gears are the development of the Spur gears, learning spur gears can help almost any type of gears. The design parameters for the gears depending upon the torque which is to be transmitted at a certain required speed. The area of contact will dictate the load capacity of the gears. For designing and application of these gears one should able to know the numnclature of the gears. I have given the details in the below picture.

For measuring the tooth thichness there always some mistakes people used to do. Here in the below picture I have given the method and the various tooth thicknesses acording to the gear modules in the below picture.

DEFECTS OF THE GEARS:

1. Wear is the major defects on the gears. The wear may be for one tooth or few or all the teeth.
2. One or few teeth broken or twisted.
3. Burrs on the bore or the key way.
4. Burrs on the internal splines of the gear bore or the tooth surface.
5. Crack or damage on the rim or the bore of the gear wheel.

LIMITS OF WEAR FOR DISCARDING:

Limits of wear for discarding is one of the important thing which many engineers will try to search here and there for the details. Hence I have given here for easy referrence.

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:

Perfect Meshing gears is one of the prerequisites for an healthy transmission of the power.
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.

The defects due to mis alignment which found during blue matching is shown in the below picture.

..... Suggestions are invited in the posts.