Only the best synthetic gear oil can cope with abnormal loads on these giant worm gears!

A gear box failure can be very costly, both in repair costs and downtime, that’s why most company’s use only the best synthetic gear oil. But how do you decide on the best synthetic gear oil?

Traditional theory often advocates that polyalkylene glycols (PAGs) perform better in worm gears than other lubricants due to their high lubricity. But is this true; and what benefits do they really offer over polyalphaolefin (PAO) worm gear lubricants or mineral oils
properly additized for worm gears?

Why would a PAG lubricant be the best synthetic gear oil for a worm drive?

There are a few reasons why a properly formulated PAG might perform better in specific circumstances than an equally correctly formulated mineral oil in a sliding contact zone.

Gear oils based on glycol stocks are highly polar. This extra surface affinity provides low frictional coefficients without the use of additives. This is often referred to as "lubricity."

Once fortified with the correctly formulated additive package, glycol lubricants can provide exceptional load-bearing performance (because of their film strength).

Glycols also often have a superior pressure-viscosity coefficient. This means that the relationship between the load placed on the oil film (pressure) at the dynamic load zone and the thickness of the oil film (viscosity) at that load, when all other factors (material, temperature, geometry, speed, load) are constant, is often better than other synthetic gear oils.

The pressure-viscosity coefficient equates to a mathematically estimated lubricant film thickness under a given set of conditions (often referred to elastohydrodynamic regime, or also known as an EHL or EHD regime).

The actual unit of measure (mm2/N) is less useful than the percentage improvement when selecting synthetic gear oil over the mineral oil at a given temperature.

An example of why PAO may be considered the best synthetic gear oil for worm drives.

At a temperature of less than 80 degrees C, mineral oil provides thicker films than a PAO lubricant, and at a temperature of less than 57 degrees C, mineral oil offers thicker films than a PAG lubricant. In the temperature range of 70 to 90 degrees C, there is only a 5-percent difference between the EHL film thickness of mineral and PAO lubricants.

In this same temperature range, a PAG lubricant gives thicker films ranging from 16 percent to 37 percent thicker than mineral gear oil.

Obviously, thicker EHL film formation contributes to reduced risk of wear and better long-term reliability.

It is worth noting that the performance of a lubricant in any given application depends on a number of factors, including performance expectations, machine application, machine design and operating environment.



While a PAG might provide superior overall performance in certain cases compared to mineral oil or PAO, there are other cases where a non-PAG lubricant in a worm gear application may be viewed as the best synthetic gear oil for the application.

At Habot Synthetic Lubricants we can recommend the best synthetic gear oil for your application, chosen from our high quality range. So contact us for all your requirements.