ISO 19349:2019 pdf free.Plain bearings with liquid lubrication一Lubricant supply arrangements and monitoring.
4 Lubrication arrangements
4.1 Self-contained bearings
The low-pressure lubrication of self-contained bearings is ensured by an internal oil reservoir and a supply mechanism, driven by the main shaft rotation. Typical self-contained bearing lubrication supply mechanisms include ring lubrication and viscosity pump lubrication. The lubrication does not require external energy or equipment. The lubricant does not leave the bearing internal reservoir.
4.2 Circulated lubrication (forced lubrication)
4.2.1 General
The oil supply of forced-lubricated bearings consists of a closed circulation system. The oil supply in these cases is provided by pumping the lubricant through the bearings. In the supply system, the oil is pumped out of the reservoir, filtered, cooled and controlled at the desired flow rate or pressure before being fed to the machine bearings. For this purpose, a complete oil supply system consists of a reservoir,pumping, filtering, cooling and controlling units. After lubricating the bearings, the oil returns to the reservoir. Some lube oil units are operated independently of the machine being supplied. Others have the main lube oil pump being driven by the shaft of the machine.
4.2.2 Oil feed and oil return
To minimize the possibility of vibrations or thermally induced tensile or compressive stresses occurring in the bearing housing, flexible compensators or connections shall be provided in the oil supply and drain piping systems if applicable.
For electrically insulated plain bearings, it is necessary to consider whether oil supply and drain pipes connected to the bearing also need insulating to prevent short circuit of the bearing insulation.
To restrict the pressure losses in the piping system to an economically justifiable amount, the oil mean flow velocity should not exceed 2 m/s in the supply lines according to experience.
The design of the return fluid flow path from the bearing to the oil reservoir shall be determined by the technical requirements of the bearing housing and the design requirements of the overall system installation.
When the return flow is driven by gravity, oil return lines shall have a slope of at least 5 %. According to ISO 10438-1, oil drains shall be sized to run no more than half full when flowing at normal drain operating temperature at maximum flow conditions and shall be arranged to ensure good drainage (recognizing the possibility of foaming conditions). Junctions and changes in the direction of pipes shall be designed so as not to impair lubricant flow. Sharp bends and down or up loops shall be avoided. Junctions in return pipes shall be located in the direction of flow. In order to prevent foaming, vertical slopes exceeding I m in length shall be avoided. No devices significantly impeding the flow in the return line, such as filters, etc. shall be installed.
Where more than one device (bearings, and possibly other consumers) is to be supplied with lubrication oil, the design of the oil supply and circulation system should mitigate against the potential harmful interactions in the return lines and oil reservoir caused by differential air pressure conditions.
4.2.3 Oil reservoirs
The basic design requirements for oil reservoirs are given by ISO 4413 in conjunction with ISO 10438-1. Based on experience and with respect to air release and oil aging, the capacity of oil reservoirs should be approximately eight times the quantity delivered per minute. The factor eight may be reduced to three depending on the ratio of exposed surface area to volume in the oil reservoir, lubricant properties (air release additives), operating conditions, duty cycle and oil change interval. Small oil reservoirs in particular should have an internal weir or baffle plate between return and suction pipe to settle the returning oil and to permit entrained air in the oil to escape.
Oil reservoirs shall be suitably vented to allow entrained air to escape. In the — recommended — case of return pipes discharging below the reservoir oil level, vent holes shall be provided above the oil level so that the air in the reservoir is able to communicate with the air in the bearing housing via the partly filled return pipe. Oil reservoirs shall be equipped with an oil level indicator.ISO 19349 pdf download.