Abstract
This paper presents a large amount of experimental and theoretical analysis and the related result concerning high pressure rotating unions. Rotating unions for high pressure are often found in tool machines and in mobile hydraulic machines. In this applications oil pressure between 5 and 30 MPa have to be sealed. Those pressures are mostly dynamic and have to be sealed on rotating or swivelling shafts with low turning speeds (below 1 m/s).
High pressure rotary shaft seals (so called rotor seals) are small radial acting seals that were used for this task. Troubles occur as those seals generate high friction forces or show high break away behaviour at the beginning of the shaft movement. Thermal problems and excessive wear leads to failures often caused by co-rotation of the seal ring with the shaft. The seals do not exceed their designated lifetime and the high friction forces disturb the function massively.
Literature to this topic is quite rare. Plenty of patents are concerned with reduction of the friction forces. They partly show an incomplete knowledge about the way rotor seals operate. Just two independent scientific investigations are concerned with radial shaft seals under such a high pressure.
Based on the seal rings available on the market and their materials the properties of rotor seals have been determined. Material tests allowed to figure out the properties concerning friction, wear and extrusion resistance of different seal ring materials. Test with varied conditions at low pressure showed by analyzing with statistic methods that the shape of the seal ring has a major impact on friction.
Seal rings have been tested on break away friction by varying the time before movement and the pressure at beginning of the shaft movement and seal ring material. Experiments with seal under pressure from both sides in combination with finite element analyses deposited the basis for a detailed model of the sealing mechanism of high pressure radial seals with a flat sealing face. Thereby the oil pressure in the sealing contact must be considered. That pressure has been experimentally identified.
The wear of the seals has been identified by long term tests with two different test programs that represented applications with interrupted and non interrupted shaft movement and intermitted pressure load. Failure pattern has been analyzed and described. The most common failure pattern could be dedicated to co-rotation of the seal ring with the shaft. Theoretical and experimental work showed causes and highlighted critical working conditions.
By using FEA, thermal loads in rotating unions have been simulated. Out of this, influences by the design have been quantified. Based on many calculations, a mathematical model was build up that allows an estimation of the temperature in the sealing contact between shaft and seal ring.
Out of the findings a very small prototype seal was developed that realizes many design guidelines that have been figured out within this work. The most important ones are together with the major findings written down in a separate chapter to use for the designer or development engineers. All the given advice is secured by experiments and a well-founded basis for the design of a high pressure radial sealing with the expected properties.
For the first time the user has information in hand that allows to figure out critical points of a design. The user is able to influence properties in a specific way and avoid failures or identify the cause of them to find pertinent solutions.
Users
Please
log in to take part in the discussion (add own reviews or comments).
