Helical gears are a type of cylindrical gears with slanted teeth. The teeth are set at an angle rather than parallel to the axis of rotation. Since the gear teeth are curved, the angling allows it to take the shape of a helix. This enables the teeth to mesh gradually from point contact to line contact as the engagement progresses. Many tend to lump helical gears and spur gear together but they are in fact quite different. One notable difference is that helical gears make less noise, especially at high speed. Also, the teeth of helical gears are always in mesh, meaning there is less load on each individual tooth. This translates to a smoother workflow from one tooth to the next so that wear can be minimized.
Helically gears are typically utilized for heavy load operations. Applications in which helical gears would be preferred are often quiet and require smooth and efficient workflow. To elaborate, helical gears are mainly used in fertilizer, printing, and earthmoving industries. Other industries in which helical gears are used also include textile, steel, rolling mills, section rolling mills, plastic, food, conveyors, elevators, blowers, compressors, oil, and cutters industries.
As mentioned above, helical gears are sometimes confused with spur gears. So it is important that we address the differences in this article. Spur gears are the most simple and common form of gears. They are designed with straight teeth parallel to the axis of the gear. And because of the simple design, spur gears are the easiest and most economical to manufacture. In contrast, spur gears are not exactly known to be quiet and smooth gears, they however are highly efficient and can produce substantial power. Although spur gears run well at slow to moderate speeds, they do tend to make louder noise at higher speeds due to vibration.
On the contrary, the teeth of helical gears are set on an angle to the gear axis. And the key difference lies in the quieter operation because of how the teeth engage. Compared with spur gears, helical gears also provide greater strength and carrying capacity of load. Moreover, helical gears are able to transmit power between either parallel or non-parallel shafts, whereas spur gears can only transfer power between parallel shafts. What also needs to be addressed is the axial force pertaining to the selection of bearing. Bearings of a gear need to withstand both radial and axial forces, so helical gears are typically equipped with larger (also more expensive) bearings than spur gears.
Although not as easy to design and manufacture, helical gears do offer quite a handful of benefits. As we have already touched base previously, the gradual engagement of helical gears allows force to be spread continuously throughout the teeth as the gears rotate, thereby reducing noise and vibration, as well as ensuring smooth operation.
Also, helical gears can be used to transfer power and motion between the two parallel shafts as well as between the non-parallel shafts, making them one of the most prevalent gears for heavy load applications. Lastly, wear and tear are less likely to occur with helical gears during operations as opposed to spur gears operation. During helical gears operation, load is distributed uniformly among several teeth at any time, resulting in less wear and tear.
Being a relatively more intricate gear type, helical gears do suffer from certain drawbacks. During the gradual meshing, axial thrust load on gear will be created, and gearbox designers will have to select bearings that can support the relative forces. Furthermore, the sliding movement between the meshing gear teeth tends to generate more heat compared to spur gear applications. Therefore, helical gear applications generally require high-quality lubrication.
In terms of efficiency, mating spur gears of similar size tend to be superior to that of helical gears. Power loss in the event of helical gear train operation is also more prone to occur as opposed to spur gear train operation. In summary of everything mentioned above, extra manufacturing cost and maintenance cost will be likely to incur.
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