What should you know when selecting gear oils?

Lubricant is required for gear reducers to work correctly and give the torque, efficiency, and efficiency that you want from your equipment. With so many various kinds of lubricants available, it's difficult to know which one is right for your purpose.

What Makes Lubricants Work?

To address this problem, we must first comprehend what lubricant do for gear removers. Gears and bearings face friction in all gear reducer applications. As a result, any lubricant's principal role is to reduce friction created by the sliding or rolling motion of gears and bearings. The correct lubricant will form an electrohydrodynamic layer that prevents the rotating/meshing components' faces from colliding.

Lubricants also keep operational parts cool. Gear reducers double the torque transmitted by prime movers, resulting in heat generation inside the gearbox. The quantity of heat produced is proportional to the box's efficiency, with higher efficiency boxes producing less heat and lower efficiency boxes producing more.

Lubricant also prevents corrosion between mating steel contacts and removes any particles that build during regular operation.

The kind of gearing, environment in which it operates, running speed, and operating temperature all influence which lubricant to use. When a force is applied, these circumstances cause the viscosity — the resistance to flow – to increase. Lubricants with lower viscosity flow more freely, whereas those with higher viscosity flow more slowly.

Viscosity

Finding the recommended viscosity grade in a component's maintenance manual is generally all that is required. Unfortunately, the manual is not always available, or the equipment is used in situations that are not consistent with the OEM's guidelines. As a result, it's critical to comprehend the approaches for viscosity selection as well as the components that influence the requirement.

A gear lubricant's viscosity is mainly selected to create a desirable film thickness between contact surface at a particular speed and load. Because most viscosity selection techniques make it impossible to estimate the load, the load is assumed, and speed becomes the deciding factor.

The ANSI/AGMA 9005-E02 standard, developed by the American National Standards Institute and the American Gear Manufacturers Association, is one of the most widely used techniques for assessing viscosity. Assumptions are made about the load, viscosity index, and pressure-viscosity coefficient of the lubricant in this procedure.

Worm gears and open gearing have their own charts. To apply this approach, you must first know the kind of gear set, gear shape, operating temperature, and slow speed gear speed. The needed viscosity grade may be read from the table using the unit's maximum expected operating temperature after computing the pitch-line velocity of the slowest gear in the unit.

Different types of gearing

Worm gear units with sliding engagement have greater tooth contact and hence have more friction. Because the increased friction generates more heat, a thicker (higher viscosity number) lubricant is recommended for this application. Helical gearing that uses rolling engagement, on the other hand, is more efficient and requires less viscous lubricants. It's worth noting that greater speeds (lower ratio units) generate more heat, therefore viscosity figures may need to be adjusted.

Operating circumstances and ambient temps will affect your choice of lubricant viscosity for any kind of gearing. Because oil's capacity to resist flow reduces as it heats, lubricants with greater viscosity values are required for higher working temperatures.

Choosing the Best Option

With their goods, all manufacturers provide operating instructions manuals. These companies have carried out laboratory testing to identify the best oil viscosity for your specific needs. Most helical gear units working in an industrial environment of 40°C (104°F) will work well with SAE10W for higher speeds (3000RPM) and SAE 40 for lower speeds. This range would be changed to SAE 10W to SAE 20W if the ambient temperature was cooler.

SAE140 (600W) worm reducers would be suitable for ambient temperatures of 40°C, but larger weights would be necessary for higher temperatures.

Using Inappropriate Lubricants

Your gear box might be damaged if you use lubricants with the wrong viscosity. Low SAE numbers hinder the electrohydrodynamic layer from properly forming and enable direct metal-to-metal contact between gears and bearings. Too-viscous lubricants form a thick coating, which may cause internal (sump) temperatures to rise, resulting in damage.

It's also crucial to avoid using motor oil in a gear reducer. Motor oils come in a variety of viscosities, such as SAE 10W40, and include additives that trap combustion byproducts. In a gear reducer, motor oil will foam, speeding up gear wear as entrained air insulates and breaks the oil coating, causing metal-on-metal contact that may cause a reducer to fail fast. Motor oils have different viscosity numbers than gear oils. The viscosity of SAE 40 motor oil and SAE 90 gear oil is the same. The additives in motor oil are to blame for these discrepancies.

Replacing Your Oil

In a gear reducer, oil is a wear component. As part of your routine maintenance, you should replace the oil in your gear reducer on a regular basis. Oil changes should be scheduled depending on the strains that your equipment faces due to running hours and environmental conditions.

For freshly installed devices, most manufacturers suggest changing the oil after one month, then every 2,500 running hours or 6 months, whichever comes first. For synthetic oils, this cycle may be prolonged, with some manufacturers claiming that, depending on circumstances, gear reducers may operate for up to 25,000 hours before requiring an oil change.

If your vehicle runs at higher ambient temperatures or in unclean or moist settings, you may wish to change your lubricant more regularly, since this might accelerate lubricant deterioration.

For all of your gear reducers, an oil testing program should be planned and implemented. These programs are meant to discover units that are at danger of failing before they fail and cause downtime.