Lubrication is actually the formation of a thin film of oil under pressure between two contact surfaces. The thickness of the oil film is related to the pressure and working viscosity.
In other words, if a perfect oil film is formed during movement, the surfaces of the two gears should not be in direct contact.
In involute gears, if the processing and installation of the gear meet the design values, the meshing point should roll on the gear surface without slipping.
At this time, the source of friction is actually the movement resistance caused by the viscosity of the lubricating oil.
If the conditions are not perfect, the gear pair may not only roll along the surface of the gear, but also slide relatively due to gear machining and installation errors. Even if the contact stress of the oil film under pressure is supported, friction will be generated inside the oil film under pressure.
Let's imagine. Both sides of an object move in opposite directions with gears. The strength of the oil film under pressure is insufficient, the oil film under pressure is broken, and the metal surfaces of the two gears are in direct contact, and cold welding may occur.
In addition, the above-mentioned viscosity is an operating viscosity. The working temperature is different, the viscosity of the grease is different.
