Lube-Tips - How to choose the correct gear oil

Davor helps customer to choose the correct gear oil visosisty for optimum gear box performance. In order to sleect the best lubricant for a gear set, the following criteria must be addressed:

Base Oil Type

Properties	Mineral oil	Synthetic	Polyglycol	Ester
Viscosity-Temperature behaviour	normal	good	very good	good
Ageing Resistance	normal	good	very good	good
Low-Temperature Characteristics	poor	very good	good	good
Wear Protection	normal	good	very good	good
Friction Coefficient	normal	good	very good	very good
Neutrality towards sealing materials and paints	very good	very good	poor	poor

Viscosity-Temperature Relationship
A flat VT- curve permits the use of one and the same viscosity of an oil at low and high temperatures.
Viscosity

It is important to understand the methods for viscosity selection and the factors that affect the requirement.

 

The viscosity for a gear lubricant is primarily chosen to provide a desired film thickness between interacting surfaces at a given speed and load. Because it is difficult to determine the load for most viscosity selection methods, the load is assumed and the determining factor becomes speed. In general, the most common viscosity available in the market is gear oil ISO VG 220. 

The chart below is applicable to spur, helical and beveled enclosed gear sets. Other charts exist for worm gears and open gearing. To use this method, the type of gear set, gear geometry, operating temperature and the speed of the slow speed gear must be determined.

Additive
EP gear oils contain special additives called extreme pressure that enhance their film strength or load-carrying ability. The most common EP additives are sulfur phosphorous, which are chemically active compounds that alter the chemistry of machine surfaces to prevent adhesive wear under boundary lubrication conditions.

 

In less severe applications, antiwear additives may also be used to provide wear protection under boundary lubrication conditions.