In his 1725 book "Theatrum machinarum generale," Jacob Leupold, when explaining a plain bearing, writes, "To eliminate friction, the rough parts should be well lubricated with tree oil or grease." However, it was known long before that oil, grease, or other suitable lubricating substances, such as wood tar and even water, could reduce friction and thus the wear of surfaces moving relative to each other.
Despite technological advances in the development of new bearing materials, some of which require little or no maintenance, lubrication remains essential in many applications even today. As practical experience has shown, the lubricant applied to the friction point not only reduces friction, thereby minimizing wear and increasing efficiency, but it also prevents dirt from penetrating the friction point and/or transports wear particles away from it.
Despite technological advances in the development of new bearing materials, some of which are low-maintenance or maintenance-free, lubrication is still often necessary today. Therefore, in many areas of mechanical and automotive engineering, lubrication is essential for achieving a long service life and high efficiency.
As machines and systems become more powerful, the demands on their reliability increase. Today, systems are expected to operate "around the clock, 7 days a week." Average operating times of 17 shifts or more are now desirable. This means that machine availability must be at least 92-97%. With flexible manufacturing centers, values of 96% or more are achievable.
There is no longer any time available for manual lubrication of bearings. Furthermore, the bearings are no longer accessible without extensive disassembly of covers, etc. Only automated central lubrication systems with programmed control and monitoring can enable such productivity.
Of course, development in the field of central lubrication technology has also continued. These systems, their functions, and their components are described in detail in this book.
The systems differ in the method of lubricant distribution. The following systems are common today:
- Single-line or parallel system
- Progressive system (single-line system)
- Dual-line system
- Multi-line system
- Throttle system
- Oil mist system
- Oil+air system
Not every system is suitable for every lubricant. The areas of application depend on the lubricant – oil or grease. These systems can be used as consumable lubrication and partially as circulating lubrication.
In total-loss lubrication, also known as consumption lubrication, the lubricant is supplied to the friction point only once per lubrication cycle. The amount of lubricant per lubrication pulse is very small, typically ranging from a few mm³ to 2 cm³. The current trend is to supply less lubricant per lubrication pulse, but at shorter intervals. Collecting and reusing the lubricant is therefore not economical and in many cases not even possible, for example, with grease lubrication.
In circulating lubrication (oil only), larger quantities of lubricant are continuously pumped through the friction points because the oil is also intended to dissipate the frictional heat generated in the bearing. This oil is returned to the lubricant reservoir, either by gravity or by a pump. The returned oil is cleaned by appropriate filters and, if necessary, cooled, dehydrated, and degassed.