Is the oil suitable for ball screw lubrication?

The Ball Screw can be lubricated with grease or oil. Grease is more commonly used for ball screw lubrication because it does not require complicated delivery methods and does not require frequent relubrication intervals. However, despite the simplicity of using grease, oil lubrication is a better choice for ball screw assemblies in many applications.

First, the oil provides cooling and minimizes heat accumulation in the ball screw assembly. Heat will cause the thermal expansion of the screw shaft, which will change the size of the thread and negatively affect the positioning accuracy. Therefore, in applications that require high speed and high precision, reducing heat is essential. If the oil is circulated through an external lubrication system, the cooling effect of the oil will be significant. The circulation system also allows debris to be filtered from the oil, thereby extending the life of the lubricating oil and reducing the wear of the screw components. The disadvantage is that the external circulation system increases the complexity and cost of the components.

When using oil for ball screw lubrication, it is important to use an appropriate amount of oil with a suitable viscosity. If the viscosity of the oil is too high, or there is too much oil, too much heat will be generated. On the other hand, if the viscosity of the oil is too low or the oil is insufficiently lubricated, the screw will experience additional friction and wear will accelerate. The appropriate oil viscosity depends on the average screw speed, diameter and operating temperature. If the applied load is very high-usually greater than 15% to 20% of the dynamic load capacity-manufacturers usually recommend oils with extreme pressure (EP) additives to provide additional wear protection.

Manufacturers usually provide a selection guide to help select the appropriate oil viscosity for ball screw lubrication based on the screw's operating temperature and average speed.
For oil lubrication, it is also important that the application conditions are sufficient to form an elastohydrodynamic (EHD) lubricating film. The film separates the Bearing ball from the raceway and prevents metal-to-metal contact.

Having the right viscosity and the right amount of oil will allow the ball screw to operate in the area of elastohydrodynamic friction.
There are three main conditions that determine whether to form a lubricating film: the viscosity of the lubricant, the speed of the screw, and the pressure between the ball and the raceway. Due to the influence of speed on EHD lubrication, low-speed applications usually require grease, which provides better protection under boundary lubrication (basically metal-to-metal contact) or mixed lubrication (metal-to-metal contact and mixed lubrication).