In a recent blog in these pages we weighed the case for plastic versus metal gears. In similar mode, we take a look at the case for helical and spur gears.
An article in Gear Solutions by our KHK USA colleague, Brian Dengel, praises (pardon the continued religious analogy) the introduction of a helix angle to enhance the performance in many applications compared to spur gears.
So what benefits can replacing spur gear pairs to a helical gear pairing deliver in terms of performance?
The article, linked here, gives the detail, but in short, a reduction in noise can be achieved as a helical design maintains constant rather than the intermittent contact characteristic of a spur gear pairing.
In addition, it can also result in an increase in torque carrying capacity. The article also describes the two types of helical gears and the issues you will need to address when making the transition.
By way of balance… An article in wheelzine.com compares and contrasts the pros and cons of each type of gear – obviously the choice is really governed by application…
HELICAL GEARS
Pros…
- In helical gears, as opposed to spur gears, the teeth engage a little at a time, instead of the entire face of each tooth at once. This allows for a silent operation.
- Along with the transmission of power between parallel shafts, though at the cost of efficiency, these also allow power transmission between non-parallel shafts.
- Since the teeth are diagonally positioned, they are larger in size as compared to the teeth in spur gears. Thus, for the same gear size, helical gears can handle more load comparatively.
- Due their unique design, at any given time the load is distributed along several teeth which are in contact with each other. This significantly reduces wear and tear, and further increases the load-bearing capacity as well as the operating lifespan of these gears.
Cons…
- In helical gear trains, there is a sliding-type contact between two gears. This causes an unwanted thrust in the axial direction, and also leads to the generation of more heat due to sliding friction. Both of these result in the loss of the transmitted power, lowering the efficiency.
- For addressing the unwanted axial thrust, special thrust bearings need to be used. Additionally, for reducing the sliding friction, additives need to be added to the lubricants. As such, a helical gear train design is more complicated, and the operating cost too is more
SPUR GEARS
Pros…
- Spur gears provide a constant velocity ratio.
- The teeth are made to be parallel to the gear axis (axis of rotation). Hence, these gears do not cause a thrust in the axial direction, and therefore can be easily mounted with the help of ball bearings.
- These gears are easiest and cheapest to design and manufacture, and are highly reliable.
- They are capable of transmitting significantly large amounts of power.
- Compared to helical gears, spur gears are more efficient in transmitting power.
Cons…
- During operation, the entire face of each tooth meshes with the respective tooth of the other gear all at once, leading to the generation of noise. As the operation speed increases, the amount of noise too increases. Hence, spur gears are best suited for low-speed applications.
- During operation, the teeth have to bear a large amount of stress.
- Spur gears cannot be used for power transmission between non-parallel shafts.
- These gears can only transmit power up to a small distance.