Hydrostatic plain bearings carry loads where heavy machinery must run precisely and without wear: in rolling mills, presses, rotary tables, and generators. Their lubricating film is not built up by the rotation of the shaft but by an external pressure supply that actively forces the lubricant between the bearing surfaces. Providing that supply is the job of KAMAT high-pressure technology: plunger pumps and valve systems that deliver oil pressures of 1,500 bar for Morgoil bearings in rolling mills and hydrostatic relief up to 3,500 bar, continuously and with low pulsation.
What Is a Hydrostatic Plain Bearing?
A hydrostatic plain bearing is a plain bearing in which the load-carrying lubricating film is built up by an external pressure supply. A high-pressure pump actively feeds the lubricant, usually oil, in some applications water or HFA emulsion, into bearing pockets between the sliding surfaces. From there it flows off across the bearing gap and completely separates the bearing shell from the shaft.
This is the difference from the hydrodynamic plain bearing, which only builds up its film through the rotation of the shaft itself: the hydrostatic bearing carries load even at standstill and at the lowest speeds, from the first revolution and without start-up wear.
How Does Force-Fed Lubrication Work?
In force-fed lubrication, a high-pressure pump delivers the lubricant at a defined pressure and constant flow rate into the bearing pockets. The pocket pressure adjusts to the load: if the load on the shaft rises, the pocket pressure rises with it and the film is maintained. Restrictors or control valves upstream of each pocket distribute the flow so that the bearing carries the load stably even when it is unevenly distributed.
Characteristics of Hydrostatic Lubrication
- The lubricating film is fully developed at all times, independent of speed and relative movement of the sliding surfaces.
- There is practically no solid-to-solid contact; the bearing runs almost wear-free, with very low friction, high stiffness, and high load-carrying capacity.
- The load-carrying capacity is determined by pump pressure and pocket geometry, not by rotational speed.
- The supply must run continuously: if the pressure fails, the bearing loses its load-carrying capacity.
Where Hydrostatic Plain Bearings Are Used
Morgoil Bearings in Rolling Mills
The most demanding application is the Morgoil bearing, the oil-film bearing of the roll necks in rolling stands. In an environment of heat, scale, and roll coolant, the pressure supply has to provide oil pressures of 1,500 bar for a wafer-thin oil film that reliably prevents metal contact between roll neck and bearing. This calls for valve technology that only a few pump manufacturers can supply; KAMAT has many years of experience in this segment.
Further Applications
Hydrostatic plain bearings and hydrostatic relief also work in slow-running heavy-load systems: in rotary tables of large machine tools, in generator and turbine bearings, in press lines, and in the roll adjustment systems of steel mills. In rolling mill hydraulics, hydrostatic relief of plain bearings extends up to 3,500 bar.
Requirements for the Pressure Supply
The pressure supply is the bearing’s life insurance. It has to meet four conditions at the same time:
- Constant pressure and flow over thousands of operating hours, because any interruption means solid contact and bearing damage.
- Low-pulsation operation, so that the lubricating film of just a few micrometres does not collapse under pressure peaks.
- Precise valve technology that holds the pressure per bearing pocket and follows load changes.
- Resistance to harsh environments: heat, scale, and coolant in the rolling mill, continuous duty without planned downtime.
KAMAT High-Pressure Technology for Hydrostatic Plain Bearings
KAMAT supplies the complete pressure supply from a single source: high-pressure pumps in triplex and quintuplex design from the modular system, matched valve technology, and monitoring. The full programme extends to 4,000 bar, 3,000 kW, and 10,000 l/min; from it, units with precisely controlled pressure and flow are configured for bearing lubrication. Integrated gears with pressurised oil lubrication and stainless steel wetted parts make the pumps robust for continuous duty in the rolling mill. Developed and manufactured in Witten, Germany, since 1974.
Why High-Pressure Technology From KAMAT?
- Morgoil experience: Oil pressures of 1,500 bar in the harsh rolling mill environment, with valve technology only a few manufacturers master.
- One modular system: Pumps for bearing lubrication, descaling, and roll adjustment from the same series, with a shared spare parts stock.
- Continuous duty: Designed for uninterrupted supply without planned downtime; seal changes without dismantling the pump head.
- Media flexibility: Oil, water, or HFA emulsion as lubricant.
- Made in Germany: Family-owned company in Witten since 1974.
For the design of a bearing lubrication system, KAMAT specifies the right pump and valve configuration based on bearing type, pocket pressure, and flow rate.
Frequently Asked Questions About Hydrostatic Force-Fed Lubrication
A high-pressure pump feeds lubricant into bearing pockets at a defined pressure. The lubricant flows across the bearing gap, completely separating the shaft and bearing surfaces. The pocket pressure automatically adjusts to the applied load and maintains the lubricating film even under peak loads.
Hydrodynamic bearings generate the lubricating film only through shaft rotation and therefore cannot support loads at standstill or low speed. Hydrostatic bearings receive their lubricating film from an external high-pressure pump and support loads from the very first revolution without start-up wear.
The load-carrying capacity of hydrostatic bearings is created entirely by externally supplied pressure. If the pressure supply fails, metal-to-metal contact occurs, leading to bearing damage. Reliable, low-pulsation high-pressure pumps are therefore essential.
Hydrostatic plain bearings are used wherever heavy loads require precise guidance, including Morgoil bearings in rolling mills, large machine tools, generators, turbines, press lines, and roll adjustment systems in steel production.
Required pressure depends on the application. Morgoil bearings typically operate at around 1,500 bar, while hydrostatic bearing relief systems in rolling mills can require up to 3,500 bar. The KAMAT product range covers applications up to 4,000 bar.
KAMAT supplies complete pressure supply systems including triplex and quintuplex plunger pumps, application-specific valve technology for each bearing pocket, and monitoring systems. All solutions are configured from the modular product system and designed for continuous operation in harsh industrial environments.
