Why Proper Lubrication And Cooling Are Important For Helical Gears

Why Proper Lubrication And Cooling Are Important For Helical Gears

Date: April 5, 2018

The main purpose of helical gears is to reduce the speed of equipment and for use in fan drive service. It is critical for your entire gearbox to have proper lubrication and cooling in order for it to run efficiently. If proper lubrication has been provided, then the gears turn against one another smoothly.

The meshing of the gears creates contact and stress simultaneously, which can cause many issues over time. As gear oil is used to lubricate the mating gear teeth, scuffing, wear, and more severe damage to the gear tooth surface can be prevented. Oil viscosity increases with pressure, making the lubrication thicker, which separates the mating gear tooth despite all of the stress on the gears. Lubrication oil can be used to cool down the surface as well, preventing high temperatures and overheating.

Surface distress

The surfaces on gear teeth are often not perfectly smooth because they are full of small abrasions and machine-made marks. Some will call this surface roughness. If the oil film is thick enough, these imperfections will develop near the mating gear teeth and rarely come in contact with one another.

The elastohydrodynamic lubrication (EHL) theory says that gears usually fall into one of three sections. The first two sections involve some contact with the mating gear teeth, but most helical gears fall into the third category. Gears in the third category develop an oil film and asperities on the tooth surface, but they also rarely come into contact with one another.


Scuffing is when damage occurs to the gear tooth surface because of welding and tearing of the area on the side of the mating gear. Usually, the damage is characterized by radial scratch lines. This issue typically happens when lubrication thickness is inadequate, allowing composite roughness of other components to cause metal-to-metal contact.

Initially, scuffing occurs when friction is created through a combination of high velocity and contact stress. You can tell this is happening if markings are found near the top or bottom of the tooth surface. The cause of this issue can be a change in temperature, which causes friction during gearbox operation. If the gears have not had enough time for the lubrication to set in, the teeth may end up rubbing together.

Wear and tear

Wear and tear can be defined as the removal or displacement of metal from the gear tooth surface. Any damage done by scuffing is usually not considered “wear” of the equipment. This issue often reduces the thickness and shape of a tooth. Wear can be a direct result of a mechanical, chemical, and electrical reaction. Gears that are regularly lubricated will show less wear and tear because they will only have marks from normal machine use.


Micropitting is a common problem that occurs when the lubrication layer is not thick enough. It typically happens in an area where multiple functions are occurring at the same time, which makes it difficult to recognize the issue is happening. Micropitting reduces the accuracy of the gears, with sudden vibrations and noises coming from the affected area. One theory on why micropitting takes place is that asperities form on the gear tooth surface, causing stress on the components. If untreated, micropitting could cause surface cracks.

This problem can happen in any location on the gear tooth surface, but most of the time, it will develop in areas that have a high velocity rate. Lubrication can play a key role in preventing micropitting from occurring in high temperature locations.


Macropitting is another surface fatigue problem that occurs because of asperities and metal-to-metal contact between the meshing teeth. However, helical gears can develop a smooth surface area with proper lubrication. This helps prevent any chance of metal-to-metal contact, and macropitting, from occurring.

Temperature issues

Another reason to properly lubricate your gearbox is that doing so can cool down the gear tooth surface. Overheating can quickly become a major issue, especially if an air/oil mixture becomes trapped in the gear mesh where carbon deposits form on the surface. This can overload the gears and ultimately cause failure.

If you need high-quality industrial gearbox inspection, repair, or maintenance, contact the experts at Amarillo Gear Service in Amarillo, Texas today. We are a division of Amarillo Gear Company, which has been in continuous operation since 1917. Call us at (806) 622-1273 or Contact Us via email for more information about our Amarillo Gear™ and Marley™ gearbox repair services. We will be glad to tell you more about the Regions We Service and the quality workmanship we can bring to the repair or Renewal of your drive.

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