One’s teeth of a helical gear are set at an angle (relative to axis of the gear) and take the form of a helix. This allows the teeth to mesh gradually, starting as point get in touch with and developing into range get in touch with as engagement progresses. Probably 
the most noticeable benefits of helical gears over spur gears is helical gear china usually less noise, especially at moderate- to high-speeds. Also, with helical gears, multiple tooth are often in mesh, which means much less load on every individual tooth. This outcomes in a smoother changeover of forces in one tooth to another, so that vibrations, shock loads, and wear are reduced.
But the inclined angle of one’s teeth also causes sliding get in touch with between the teeth, which creates axial forces and heat, decreasing efficiency. These axial forces enjoy a significant role in bearing selection for helical gears. As the bearings have to withstand both radial and axial forces, helical gears need thrust or roller bearings, which are usually larger (and more costly) compared to 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 speed and smoother motion, the helix angle is typically limited by 45 degrees because of the production of axial forces.