Gears are one of the most important components in the industrial world – they literally keep machines turning. So, knowing how to properly maintain these components is absolutely critical for any industrial operator.
This two-part tip series will discuss the different types of gears, how they function, and how to keep them running in tip-top shape over the long haul.
Key gear types
There are many different types of gears, and each of them functions slightly differently. Let’s take a look.
Spur gears: These are the simplest of the gears. They have teeth that are parallel to the axis of the gear. They are typically slow speed and carry low loads due to limited surface area, and they are subject to vibration as their speed increases due to support bearing float. You will find these gears in cars (rack and pinion steering devices), heavy mobile equipment (sun or planetary gears), cement mills (mill girth gears), paper mills (roll connecting gears), and in many more applications.
Helical gears: These are similar to spur gears in that the teeth are parallel, but they are set at an angle to the axis of the gear to provide more surface area on the tooth. It also enables the gear to withstand higher loading when compared to a spur gear. These gears can travel at increased speeds, but they produce thrust as a result of the helix angle. While they can travel faster than a spur gear, they also require thrust bearings on the shaft ends to limit axial movement. These gears are used in most industrial gear boxes.
Double helical gears: These are really two helical gears pressed up against each other. The helixes are parallel to the axis, but they oppose each other, producing zero net thrust. Double helical gears typically support twice the load of single helical gears and can go even faster due to the zero sum thrust. These are also found in many industrial gear boxes.
Herringbone gears: These are similar to double helical gears, except they are joined in the middle or apex. They are often called herringbone gears because the pattern is similar to the spine of a fish. Loading and speed are similar to double helical gears and they produce zero thrust. These are used in most industrial gears and marine reducers.
Straight bevel gears or bevel gears: This is a different design of gear in that the teeth are perpendicular to the gear axis and the axis of the driven and driving gears intersect. The gear transmits motion through a 90-degree direction change while allowing for large speed reductions. The gear will accommodate low to moderate loading. Often found in industrial gear boxes as a single set or in combination with helical, double helical and or herringbone gears.
Spiral bevel gears: Like straight bevel gears, the teeth of the gear are perpendicular to the axis of the gear. The gear axes of both gears intersect. The spiral design provides additional surface area for increased loading and smoother operation at increased speeds, again providing a direction change and large reduction ratios. Often found in industrial gear boxes as a single set or in combination with helical, double helical and or herringbone gears.
Hypoid gears: Right angle gearing where the pinion is offset to the ring gear, allowing for high input shaft speed, low output shaft speeds and a motion direction change. Teeth are typically curved to carry heavy and often variable loads. Shafts axes cross but do not intersect. They operate at multiple speeds and provides a 90-degree motion direction change. These gears are often found in automotive and commercial vehicle differential gearing, but they are occasionally found in industrial gearing where there are space constraints.
Worm gears: The axis of these gears are at right angles to each other, but the teeth are in-line. Their axes cross but do not intersect. The gear provides a large speed reduction, with extremely low output speeds possible and enough torque to move large loads. There are worm gear variations called single and double throated, which refers to the depth of mesh. More mesh depth means greater loading. Applications are mostly industrial and include conveyor drives.
I hope that this post was a helpful summary of key gear types and how they work. Our next post in this two-part series will focus on gear motions and lubrication best practices. In the meantime, if you have any questions or comments, leave a note below.
I will consider these materials that you mention to me in case of any Customer I requested a lubricant, consider it apart from the other factors, temperature, load and speed, operation or the machine, which recommends the Manufacturer.
iron, chrome, carbon, steel alloys.
Thank you for the answer to this doubt of the materials in the Manufacturing of the Gears, in addition to considering in the selection of the appropriate Oil, I wish I took this issue in the second part, mark.perkins greetings
Thanks for this sir.
The selection of material will depend on the application. Most industrial gearboxes with any of the gear types above, with the exception of worm gears, use some type of steel. The specific steel type is selected to match the application, load, required heat treatment, etc.
Worm gears typically use a steel worm and bronze gear. Again, applications determines the specific steel or bronze grade.
Any of these gears could be plastic as well (with lower load ratings of course).
I'd bet that Rick discusses selection of lubricant to match gear material and application requirements in Part 2.
Dear Rick, my question is, what are the main materials used to manufacture these gears?