Brush seal

from Wikipedia, the free encyclopedia

A brush seal ( English brush seal is) a contacting seal , the core of which is a highly flexible sealing member. It consists of thousands of wires or fibers and adapts to the area to be sealed. Brush seals can take on dynamic and static sealing functions.

history

In the aftermath of the first and second oil crises in the 1970s, the development of new sealing concepts was pushed forward in aircraft engine construction in order to improve the efficiency of the engines. Because up to this point, so-called labyrinth seals were used almost exclusively to seal dynamic components against the gas flows in engines . However, these have a comparatively high leakage rate. MTU Aero Engines AG, headquartered in Munich , started its first attempts with brush seal components in military engine construction in 1983. The company successfully applied for a patent for the new technology in 1985.

The first brush seal was developed and tested by MTU Aero Engines AG in 1995 for the RB199 engine of the multi-purpose combat aircraft Tornado in order to increase its operational safety and performance. The previous labyrinth seals in the engine were replaced by specially adapted brush seals, which finally went into series production in 1999. In the same year, brush seals for industrial compressors and turbines, which had been tested since 1996, were also suitable for series production. In 2002, the testing of seals made of aramid fibers ( Kevlar ) began, which have been produced in series since 2006 and are characterized by a lower leak rate.

In the meantime, there has been a significant increase in brush seals in engines and industrial gas turbines. The flagship model here is the PW1100G-JM engine , in which four brush seals - two each in the compressor and the turbine - are installed. They contribute to a significant increase in efficiency in the Airbus A320neo .

technology

Structure and functionality

Structure of the MTU brush seal

Brush seals are an effective and simple sealing system. A sealing element can seal a differential pressure of up to 20 bar. Thousands of thin wires or fibers that are fixed with a core wire in a clamping tube form a very flexible seal that adapts almost perfectly to the area to be sealed. As a result, a gap to be sealed can largely be closed. Incoming gases are forced to flow through the approximately two millimeter thick wire package. The gas presses the wires against a support ring, thereby compressing the package. This reduces permeability to a minimum. Thanks to their elasticity, the wires or fibers can compensate for axial and radial rotor movements with almost no wear and tear and then return to their original position.

The patented brush seal from MTU Aero Engines AG consists of a sealing element and a housing. The sealing element consists of a core wire, a wire or fiber package and a clamping tube. The housing consists of a cover ring and a support ring. The cover ring protects the sealing element, in particular the front wires, from disruptive flow influences. The support ring stabilizes the wires in the axial direction when the wire package is applied under pressure. The actual sealing element, which represents the core of the brush seal, is located between the support and cover ring. The outer contour of the housing can be designed as required, so brush seals are largely independent of the external properties of the component to be sealed. This means that the seal can be individually adapted to a component.

material

The sealing elements of the brush seals can be made of metallic wires, e.g. B. Haynes 25, or fibers such as aramid ( Kevlar ) or ceramic fibers. When choosing the right materials, the most important factors are their temperature resistance and weight. Haynes 25 is an alloy of cobalt, nickel, chromium and tungsten. It withstands very high temperatures and oxidizing atmospheres of up to 980 degrees Celsius and is also resistant to sulfides. The wires have a diameter of 0.07 to 0.15 mm. Aramid fibers (Kevlar) seal even better than metallic wires and are used in thicknesses of 0.012 mm. Thanks to their high elasticity, they compensate for all movements of the rotor and then return to their original position and shape.

Future developments

As part of national and international research projects and collaborations with renowned universities, alternative types of construction as well as new wire materials and fibers are examined. The focus is on new sealing positions and applications, especially in the high temperature range. There are also attempts to manufacture the housing using additive processes. Components are melted directly from the powder bed using CAD design data using a laser.

Areas of application

Brush seals can be used flexibly and are therefore not only used in the aviation industry, but also in steam and industrial gas turbines, compressors and in general mechanical engineering. Brush seals are installed in the PW1100G-JM ( Airbus A320neo ), TP400-D6 ( Airbus A400M ) and EJ200 ( Eurofighter Typhoon ) engines, among others .

Sealing systems are in great demand in steam turbines because they can significantly increase efficiency - by up to two percent. The same applies to industrial gas turbines, and there is also great potential here for improving sealing systems.

In industrial compressors, the use of brush seals can drastically reduce leakage losses, which also greatly reduces the energy requirement under the same conditions. In addition, the reliability of the seal increases considerably compared to labyrinth seals, since less wear and tear as a result of grazing or erosion can be determined.

In mechanical engineering, the use of brush seals at all sealing points with high demands on sealing effect and reliability is conceivable. This often simplifies the sealing environment.

In addition to brush seals, which are used in industry, brush seals are also used in door, window and roller shutter construction. They are used for thermal insulation, avoid drafts and rattling noises from roller shutters and protect against the ingress of insects. Brush seals with polypropylene trim are used here.

Advantages over other sealing systems

In contrast to conventional labyrinth seals, there are hardly any losses: the greatest advantage of brush seals is therefore a reduction in leakage by up to 80 percent. In addition, the brush seals can be used to maintain an optimal gap, which also reduces wear on the seal and enables a long service life to be achieved. Due to the great ability to compensate for axial and radial expansion, robust behavior is guaranteed during operation. In the event of a radial movement of the rotor, the brushes are only pressed in briefly and then continue to function normally.

Brush seals require less space than other systems with the same sealing effect and therefore enable a much more compact and lighter design. With regard to the repair, it is a further advantage that brush seals are not only very easy to install, but are also easy to replace.

Brush seals are installed in engines in the aviation industry primarily because of their high efficiency. In comparison to labyrinth seals, cooling air losses in particular can be reduced by more than half. This enables a higher level of efficiency, lower fuel consumption and CO 2 emissions to be achieved.

literature

  • C. Rossow, K. Wolf, P. Horst (Hrsg.): Handbuch der Luftfahrzeugtechnik. Carl Hanser Verlag, Munich 2014.
  • S. Pröstler: Modeling and numerical calculation of shaft seals in brush design. Dissertation . Dr. Hut-Verlag, 2005, ISBN 3-89963-242-7 .

Individual evidence

  1. ^ C. Rossow, K. Wolf, P. Horst (eds.): Handbuch der Luftfahrzeugtechnik. Carl Hanser Verlag, Munich 2014
  2. ↑ Martin Deckner: Properties of combined labyrinth brush seals for turbo machines. Munich 2009, accessed online on May 21, 2015 at
  3. ↑ MTU Aero Engines AG: Top position in brush seals. ( online , accessed May 21, 2015)
  4. ↑ MTU Aero Engines AG: Top position in brush seals. ( online , accessed May 21, 2015)
  5. ↑ MTU Aero Engines AG: Brush seals - top-class sealing technology. MTU, Munich 2014. ( online , accessed May 21, 2015)
  6. ^ C. Rossow, K. Wolf, P. Horst (eds.): Handbuch der Luftfahrzeugtechnik. Carl Hanser Verlag, Munich 2014
  7. ↑ MTU Aero Engines AG: Brush seals - top-class sealing technology. MTU, Munich 2014. ( online , accessed May 21, 2015)
  8. ↑ Brush seals reduce consumption. In: Flugrevue. 10/2014, accessed on May 21, 2015.
  9. ↑ MTU Aero Engines AG: Brush seals - top-class sealing technology. MTU, Munich 2014. ( online , accessed May 21, 2015)
  10. ^ C. Rossow, K. Wolf, P. Horst (eds.): Handbuch der Luftfahrzeugtechnik. Carl Hanser Verlag, Munich 2014.
  11. ↑ MTU Aero Engines AG: Brush seals - top-class sealing technology. MTU, Munich 2014. ( online , accessed May 21, 2015)
  12. ↑ MTU Aero Engines AG: Brush seals - top-class sealing technology. MTU, Munich 2014.
  13. ^ C. Rossow, K. Wolf, P. Horst (eds.): Handbuch der Luftfahrzeugtechnik. Carl Hanser Verlag, Munich 2014
  14. ↑ MTU Aero Engines AG: Brush seals - top-class sealing technology. MTU, Munich 2014. ( online , accessed May 21, 2015)
  15. ↑ MTU Aero Engines AG: Brush seals - top-class sealing technology. MTU, Munich 2014. ( online , accessed May 21, 2015)
  16. ↑ Brush seals in all variants for every application. Retrieved October 5, 2018 (German).
  17. ↑ MTU Aero Engines AG: Brush seals - top-class sealing technology. MTU, Munich 2014. ( online , accessed May 21, 2015)
  18. ^ C. Rossow, K. Wolf, P. Horst (eds.): Handbuch der Luftfahrzeugtechnik. Carl Hanser Verlag, Munich 2014