The teeth of a helical gear are set at an angle (in accordance with axis of the gear) and take the shape of a helix. This allows one’s teeth to mesh gradually, starting as point get in touch with and developing into series contact as engagement progresses. Probably the most noticeable benefits of helical gears over spur gears is less noise, especially at moderate- to high-speeds. Also, with helical gears, multiple teeth are usually in mesh, which means much less load on each individual tooth. This outcomes in a smoother transition of forces in one tooth to another, to ensure that vibrations, shock loads, and wear are reduced.
However the inclined angle of the teeth also causes sliding contact between your teeth, which generates axial forces and heat, decreasing performance. These axial forces play a significant role in helical gear china bearing selection for helical gears. As 
the bearings have to endure both radial and axial forces, helical gears require thrust or roller bearings, which are usually larger (and more costly) than the simple bearings used in combination with spur gears. The axial forces vary in proportion to the magnitude of the tangent of the helix angle. Although bigger helix angles offer higher acceleration and smoother movement, the helix angle is typically limited to 45 degrees due to the creation of axial forces.