Helical gears or spur gears?

Wednesday - 05/09/2018 14:44

Helical gears or spur gears?

Gears are a key component of motor and machinery actuators; they increase the output torque and control the direction of rotation or the speed.
Dolin has an extensive experience in the manufacturing of metal gears in many shapes and sizes: spur gears, globoid gears, planetary gears and helical gears; with pinion, bolt, or different types of tooth.
 
Among them, helical and spur gears are usually the most widespread across many industrial applications. Do you want to know their differences and features in-depth? This article can help you.
 
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Helical gears: advantages and drawbacks
 
Helical gears operate more smoothly and silently when compared to spur gears. This difference is due to the oblique manner in which their teeth interact in relation to the rotational axis. This axis may be parallel, or generally crossed at 90°. In case it is crossed, helical gears are applied together with a worm gear, even though on these cases, two bevel gears may alternatively be used.
 
When two of the teeth move, contact is gradual, beginning at one end of the tooth, and staying in contact with the gear, which rotates until full contact is achieved. The typical helix angle ranges from about 15 to 30 degrees. On the other hand, the thrust load varies in direct proportion to the magnitude of the tangent of the helix angle.
 
Finally, delving deeper into the available types, we can highlight:
 
Crossed-axis helical gears: They are the simplest within the helical gear category. They produce a screwing or wedging action as a result of a high degree of slide along the sides of the tooth.
 
Parallel-axis helical gears: They are composed of an infinite number of low-thickness, staggered spur gears. This will result in each tooth being skewed along the side as if it were a cylindrical helix. When contacting each other, they should have the same helical angle, but in opposite directions. As a result of the angle of the helix, there is an axial thrust in addition to the load.
 
Double helical, or “herringbone”: They are a right-side and left-side helix combination. The axial thrust absorbed by the bearings of the helical gears is a disadvantage.
 
 
Advantages of helical gears
 
The angled teeth work more gradually, allowing for smoother and more silent gear operation when compared to spur gears or toothed wheels.
 
Helical gears last longer and are ideal for high-load applications, since they have a higher amount of teeth in contact.
 
Load is at all times distributed among several axes, which produces less wear.
 
They can transfer motion and power both among parallel and straight-angle axes.
 
Drawbacks
 
One of the disadvantages of these gears is the thrust which results along the gear axis, which needs to be accommodated by using adequate thrust bearings. There is a greater degree of sliding friction between the teeth. This produces greater wear during operation, and the need for lubrication systems.
 
The helical gear efficiency is lower due to the contact between its teeth, which produces axial thrust and generates heat. A greater loss of energy reduces efficiency.
 
Higher manufacturing cost than spur gears.
 
Spur gears: advantages and drawbacks
 
Spur gears or toothed wheels are the most common type of gear, and are differentiated from others since their teeth are set up along parallel axes. They are used to achieve large gear ratios, slow speeds and medium speeds. Spur gears are very useful when motion needs to be transferred from one shaft to another one that is parallel and close.
 
Advantages of spur gears
 
They can be used to transfer a significant amount of power (up to approximately 50.000 Kw).
 
They are very reliable.
 
This pieces are the simplest ones to design and manufacture. An actuation project that involves spur gears can be deployed faster.
 
They provide a constant and stable gear ratio.
 
A spur gear tends to be more efficient when compared to a helical gear of the same size.
 
Since the tooth is parallel to its axis, no axial force is produced. Therefore, the gear shafts can easily be mounted with ball bearings.
 
Drawbacks
 
These are low-speed gears.
 
They cannot transfer power between non-parallel axes.
 
Spur gears generate too much noise when operated at high speeds.
 
The wheel’s teeth experience a great amount of stress.
 
They cannot be used for transferring energy over long distances.
 
They are not as resilient when compared to other types of gears.
 
As for their applications, it is common to use them in sectors where a slow motion is required and sound levels are not as important, as is the case of vending or the security system industry. They also see significant use when transferring motion within a planetary gear motor.
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