In double helical gear the helix angle is

SOLUTION

Explanation:

Helix angle:

• It is the angle between any helix and an axial line on its right, circular cylinder or cone.
• Helix angles are selected to obtain a minimum overlap ratio and to provide good load sharing.
• Helix angles vary from 5° to 45°.
• The helix angle for Single-helical gear falls between 12° and 20°, and for double-helical gears it falls between 20° and 45°.
• The thrust generated is also a function of the helix angle.
• An increase in the helix angle increases the thrust; thus, this increase is the main reason for the lower helix angles in single-helical gearing.

Double Helical Gear:

• A double helical gear is equivalent to a pair of helical gear secured together, one having a right-hand helix and the other has a left-hand helix. The teeth of the two rows are separated by a groove i.e. used for tool run out.
• In double helical gear the helix angle is 45°.
• Axial thrust occurs in the case of single helical gears eliminated in double helical gears. This is because the axial thrust of two rows of the teeth cancels each other.
• These gears can be run at high speeds with less noise and vibrations.

Helical Gear:

• They have curved teeth, each being helical in shape.
• Two mating gear have the same helix angle but have teeth of opposite hands.
• At the beginning of the engagement, contact occurs only at the point of the leading edge of the curved teeth. As the gear rotates, the contact extends along a diagonal line across the teeth. Thus load application is gradual, low impact stresses and reduction in noise.
• Helical gears have the disadvantages of having end thrust as there is a force component along the gear axis. The bearing and mounting must be able to withstand the thrust load.