Brush seal

p0001The invention relates to a brush seal, comprising an elongated configuration applied to a support ring bristles.

p0002To in rotating turbomachinery, such as in steam turbines, to be able to seal two different pressure chambers, sealing elements of different types are used. are known non-contact seals such as labyrinth seals, which are used between rotors and stationary parts. Also contact sealing elements are known, which, however, during the contact yield due to the use of flexible materials.

p0003It is known to use so-called brush seal elements, which can be assigned to the category of contact with sealing elements. In the brush seals a package of bristles is used for sealing between spaces of different pressure. Brush seals are compared to a low pressure area used for sealing a high pressure area, as is required in the rotor-stator assemblies frequently. The bristles of the brush seal thereby extend substantially radially in an annular gap between the shaft (rotor) and housing (stator) and dense these off to inhibit the flow of fluids in an axial direction along the shaft.

p0004Brush seals here are particularly tolerant to an undershooting of the radial clearance between the rotating component and the stationary component. The bristles of the brush pass by at a falling below of the radial clearance and a rubbing of the seal on the rotating shaft, and there is a slackening of the bristles and to wear on the bristles when the contact between the bristles and the rotating component longer tIME. In addition, a brush is well suited to record a pressure difference. To overcome greater pressure differences are brush seals - as well as labyrinth seals - used.

p0005The brush seal itself can take various forms. The<patcit id="pcit0001" dnum="DE3907614A"><text>DE-OS 39 07 614</text></patcit> and the <patcit id="pcit0002" dnum="DE29600193U1"><text>DE 296 00 193 U1</text></patcit> describe for example, brush seals, whose bristles encircle a core ring such that it substantially protrude unilaterally radially therefrom. The core ring and arranged to these bristles are in turn surrounded by a clamping ring which prevents loose filaments of the core ring.

p0006The <patcit id="pcit0003" dnum="DE69627674T2"><text>DE 696 27 674 T2</text></patcit> describes a brush seal whose bristles are arranged between two mutually opposite support rings, wherein the bristles by means of welding or by means of another one of ordinary skilled in the art known mechanisms between the support rings are held.

p0007In operation, the package of bristles is pressed against a back support ring when pressure is applied. Brush seals have the advantage that the bristles are pressed due to the prevailing operational flow in and around the bristle pack to the shaft. This so-called cold column are closed. This effect is known as blow down. However, the movement of the bristles in a radial direction is hindered due to the compression in the axial direction. Leakage currents between the brush and the shaft are thus higher with increasing pressure, as when a pressure-loaded brush seal is released again (hysteresis effect). Ascending and descending pressure developments in so-called transient operation of a flow machine available. Therefore, the hindrance of the free mobility of the bristles in a radial direction by the pressing against the support ring during a transient operation is disadvantageous.

p0008Desirable would be a brush seal that even with increasing pressure shows an improved sealing effect and a unique function of the mass flow of the applied pressure difference without hysteresis.

p0009It is therefore an object of the invention to present a brush seal whose sealing effect is improved with increasing pressure.

p0010This object is achieved by a brush seal comprising an elongated configuration applied to a support ring bristles, wherein between the bristles and the support ring a reibarmes material is provided.

p0011With increasing pressure, the bristles are pressed against the support ring. Thus, the friction between the bristles and the support ring is large, since the frictional force is dependent in the radial direction of the normal force. The greater the normal force, the greater the frictional force. The free movement of the bristles in a radial direction is influenced by the normal force and the coefficient of friction of the bristles and the support ring. If the pressure rises further, prevents the frictional force between the bristles and the support ring a further radial movement of the bristles. The result is that a leakage flow rate is comparatively high.

p0012Another effect occurs when the pressure is lower. Because in this case the frictional force between the bristles and the support ring becomes smaller. This makes it possible to perform a radial movement of the bristles, since the normal force on the support ring becomes smaller. Through the inventive use of a low-friction material between the bristles and the support ring, the friction forces are significantly reduced. This means that with increasing pressure the bristles have better free radial mobility, since the frictional force between the bristles and the support ring is lower. This results in that the leakage currents are similar in ascending with the leakage currents in order of decreasing pressure.

p0013This gives the advantage that the efficiency of the entire fluid machine is increased by increasing the predictability of a unique density behavior is improved and by the ability of the brush to adapt to changing operating conditions and the rotor movement is improved.

p0014Advantageous further developments are described in the subclaims.

p0015Thus, it is advantageous if the coefficient of friction of the low friction material is lower than the coefficient of friction of the bristles and / or the support ring. In order to achieve the advantageous effect of the brush seal of the invention, it is necessary that the low friction material has a lower coefficient of friction than the coefficient of friction of the bristles. Almost the same effect is achieved if, instead of the bristles of the support ring has the low friction material with the lower coefficient of friction. Likewise, it is advantageous if both the bristles and the support ring is formed with the low-friction material. Through these measures, the production costs can calculate better because alternatives are offered, such as the advantage of the invention can be achieved.

p0016In an advantageous development of the overall backup ring from the low friction material is made substantially. Thereby, it is possible to achieve low manufacturing costs, since the processing time is comparatively short, if the entire support ring is made of a single material.

p0017Add a further advantageous embodiment of the low friction material is formed as a layer. This achieves the advantage that the cost of manufacture of the brush seal are comparatively low.

p0018Advantageously, the low friction material is a Teflon.

p0019In advantageous developments can be used as material reibarmes a ceramic or graphite-containing material.

p0020Hereinafter, various embodiments of the invention with reference to the accompanying drawing will be described in more detail. Show it:<dl id="dl0001"><dt>1 shows</dt><dd>a cross-section view of a brush seal according to the prior art,</dd><dt>FIG 2</dt><dd>an alternative embodiment of a brush seal according to the prior art,</dd><dt>FIG 3</dt><dd>a detail of a brush seal according to the invention,</dd><dt>FIG 4</dt><dd>Representation of the leakage flow during different pressure conditions in a part of the prior art brush seal,</dd><dt>FIG 5</dt><dd>Representation of the leakage flow during different pressure conditions in a brush seal according to the invention.</dd></dl>

p0021In Figure 1, a brush seal 1 is shown, which is currently used according to the prior art. The brush seal 1 comprises an elongated configuration bristles 2, which rest on a supporting ring 3rd The bristles 2 are fixedly supported on a component of a turbomachine. The component 4 may be a casing of a steam turbine. Various measures are known to mount the bristles and the support ring to the component 4th Thus it is known to clamp such as the one brush seal in a groove in the component 4, einzustemmen or to weld.

p0022The brush seal 1 is used for sealing a high pressure area 6 and a low-pressure region. 7 The brush seal 1 seals mainly from a gap 11 between the component 4 and a second component eighth The second component 8 can be for example a shaft (rotor). Between the tip 9 of the bristles 2 and the opposite surface 10 of the second component 8, a gap 11 is formed as a rule. The lower the gap 11 is formed, the smaller a leakage flow 12 is formed.

p0023In FIG 2, an alternative embodiment of a brush seal 1 is shown according to the prior art. The difference of the brush seal 1 shown in FIG 2 to the brush seal 1 shown in Figure 1 is that the support ring is designed bent in the radial direction thirteenth This curved version of the support ring 5 is formed a clearance 14 between the support ring 5 and the bristles 2. By bending a contact surface 15 of the support ring 5 on the bristles 2 decreased.

p0024With increasing pressure in the high pressure area 6 is a normal force Fn of the bristles 2 enlarged to the support ring 3. This movement of the bristles 2 in the direction 13 is inhibited because the friction between the bristles and the support ring 3 is increased due to an increased friction. This leads to that the gap 11 is not delayed or reduced because of the blow-down effect as above.

p0025However, once the pressure in the high-pressure region 6 decreases again, the normal force Fn decreases to the support ring 3, which means that the friction between the bristle seal 1 and the support ring 3 subside. A movement of the bristles 2 in the radial direction 13 is therefore given. This results in that the radial gap 11 may decrease. This has the effect that the leakage flow 12 is lower.

p0026In FIG 4 of this so-called hysteresis effect is illustrated by a curve. On the y-axis of the leakage flow 12 (m) for a part of the prior art brush seal (1) is shown. On the x-axis of the pressure difference between the high pressure area 6 and the low pressure region is shown 7 (Dp). The curve 16 represents the mass flow with increasing pressure is. Whereas, the curve 17 the mass flow in the descending pressure represents. From this graph it can be seen that the leakage current at the ascending pressure (curve 16) is higher than the leakage flow from descending pressure (curve 17).

p0027In FIG 5, the course of the leakage current is 12 (m) for a brush seal according to the invention (1). It is apparent that no hysteresis effect appears more and 16 and 17 coincide, the curves to a common curve.

p0028In FIG 3 a part of a brush seal 1 is shown. 2 between the bristles and the support ring 3, a reibarmes material 19 is provided. The low friction material 19 may be arranged over the whole length of the bristles of the second It is also possible, the low-friction material applied 19 only a portion of the 20th The low friction material 19 should have a coefficient of friction which is lower than the coefficient of friction of the bristles 2 and / or of the support ring 3 is formed between the low friction material 19 and the bristles of an abutment surface eighteenth

p0029In alternative embodiments the low friction material 19 may be applied to the bristles on the support ring 2 instead of the third

p0030In a further alternative embodiment 3 may be formed of the low friction material 19 even the entire support ring.

p0031It is also conceivable to simply form the low friction material 19 as a layer.

p0032As reibarmes material 19, for example, Teflon (tetrafluoroethylene), a ceramic or graphite-containing material can be used. It can be used equally well as non-ferrous metals and other soft metals.