Conclusion

Depending on operating conditions, different regimes may exist in lubricated systems. To avoid wear, it is essential that an intermediate film completely separates the surfaces. So, when designing mechanisms, the engineer looks for conditions that enable a surface contact to operate in the hydrodynamic range and a hertzian contact to operate in the elastohydrodynamic range. If speeds and loads do not allow it, it is possible, in the case of surface contacts, to ensure separation of the surfaces by a hydrostatic or hybrid system which guarantees operation without risk of damage. In some cases, it may not be possible to avoid direct interaction between the contact surfaces; in such cases, anti-wear and extreme pressure additives can prevent rapid destruction of the surfaces, at the expense of moderate wear on the mechanism.

The tribology of dry contact is very complex...