Sealing arrangement for a rotating shaft

A sealing arrangement for a rotating shaft, which is in particular designed as a drive shaft of a pump, has a stationary seal holder in which a first and a second slide ring seal are supported. The slide ring seals each have a co-rotating rotary seal part and a stationary seal part. A sealing space is formed between the slide ring seals and the seal holder to which sealing fluid can be supplied via a feed line. In order to enable good rotor dynamics of the shaft with the seal arrangement, a bearing is arranged between the first and the second slide ring seals by means of which the shaft can be supported with respect to the seal holder.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Application No. 12170163.5 filed on May 31, 2012, the disclosure of which is incorporated by reference herein.

The invention relates to a sealing arrangement for a rotating shaft.

DE 199 28 141 A1 describes a sealing arrangement for a rotating shaft. The sealing arrangement can in particular be used for a drive shaft of a pump, wherein the sealing arrangement is in this case fixedly connected to a housing of the pump and the drive shaft projects out of the housing. The sealing arrangement has a stationary seal holder which has a cut-out through which the shaft can project. A first and a second slide ring seal are supported in the seal holder, with the slide ring seals each having a co-rotating rotary sealing part and a stationary sealing part. A sealing space is formed between the slide ring seals and the seal holder and sealing fluid can be supplied to said sealing space via a supply line. The slide ring seals are arranged so that the shaft can project through both slide ring seals and through the cut-out of the seal holder. Such slide ring seal combinations are usually marketed as ready-to-fit units which can be checked for leak-tightness before installation and which prevent assembly errors.

Such seal arrangements are usually used with rotating shafts which project out of a housing, for example out of a pump housing. The sealing arrangement serves to seal the housing in the region in which the shaft projects through the housing. Depending on the conditions of use, it is in this respect mainly a question of preventing an entry of fluid or particles from the environment into the housing or an exit of the fluid contained in the housing.

Rotating shafts, however, not only have to be sealed, but also supported. Solutions are known in which the support is arranged within the housing. This has the result that a part of the shaft, the so-called overhang, projecting out of the housing is comparatively long. This can result in unfavorable rotor dynamics, that is in vibration problems at the shaft. Solutions are moreover known in which the support of the shaft is arranged behind the seal arrangement viewed from the housing. This makes a separate support housing necessary to receive and seal the bearing. Since the bearings used usually also have to be lubricated, a separate lubricant supply of the bearing is also necessary in this case. On the arrangement of the bearing within a pump housing, the lubrication can also take place by the fluid to be conveyed. This can, however, also result in problems if the fluid to be conveyed contains particles which can damage the bearing, that is the fluid to be conveyed has abrasive properties.

In view of this, it is the object of the invention to propose a sealing arrangement for a rotating shaft which enables good rotor dynamics of the shaft with a simple design of the seal arrangement. The object is satisfied by a sealing arrangement such as the exemplary sealing arrangement described herein.

In accordance with the invention, a bearing is arranged between the first slide ring seal and the second slide ring seal by means of which the shaft can be supported with respect to the seal holder. The overhang of the rotating shaft is thus comparatively short, which allows good rotor dynamics of the shaft. At the same time, the bearing is arranged in the sealing space bounded and shielded by the seal holder and by the slide ring seals so that no separate housing for the bearing is necessary.

In an embodiment of the invention, a co-rotating rotary sealing part and a stationary seal part of the slide ring seals are arranged next to the bearing. The slide ring seals are thus arranged in a so-called tandem arrangement. The sealing fluid which is supplied to the sealing space is in this case called a so-called “quench fluid” or “quench medium”. The pressure of the sealing fluid is in this case equal to or smaller than the pressure to be blocked in the housing. If a leak occurs at the slide ring seal arranged closer to the pressure to be blocked, the exiting fluid is taken up by the sealing fluid and can neutralized. In addition, the leak can be recognized by analysis or monitoring of the sealing fluid. A secure operation of the sealing arrangement is thus made possible.

In an embodiment of the invention, both co-rotating rotary sealing parts of the slide ring seals are arranged next to the bearing. The slide ring seals are thus arranged in a so-called “back-to-back” arrangement. The sealing fluid which is supplied to the sealing space is in this case called a so-called “barrier fluid”. The pressure of the sealing fluid is in this case larger than the pressure to be blocked in the housing. If a leak occurs at the slide ring seal arranged closer to the pressure to be blocked, the sealing fluid flows into the housing due to the higher pressure in the sealing space and it is in every case prevented that fluid can exit the housing. A leak at one of the two slide ring seals can be recognized by monitoring the pressure of the sealing fluid. An indication for this is a pressure drop of the sealing fluid. A particularly secure operation of the sealing arrangement is thus made possible.

In an embodiment of the invention, the bearing is designed as a slide bearing. The bearing can, for example, be manufactured from a bronze alloy, from an aluminum alloy or from a steel composite material. The running surfaces can additionally be coated, with a white metal layer being possible, for example. It is also possible that the sliding bearing can be made up of two parts, namely the stationary part and the rotating part, with both parts each being composed of a plurality of layers which are connected, for example, soldered, to one another. The two inner layers form the respective slide layers which slide on one another on rotation of the shaft. The use of slide bearings allows a simple and inexpensive design of the sealing arrangement. Slide bearings additionally require less construction space and are low-maintenance.

In an embodiment of the invention, the sealing fluid is used for lubricating the bearing. The bearing is therefore arranged within the sealing space such that it comes into contact with the sealing fluid and in particular the sealing fluid can arrive at the points of the bearing to be lubricated. The bearing can have special bores for this purpose via which the sealing fluid can be conducted to the relevant points of the bearing. The sealing fluid can be so-to-say freely selected. A sealing fluid can therefore be selected, for example a light petroleum product, with which an effective lubrication of the bearing is possible. In addition, the sealing fluid usually does not contain any contaminants so that the bearing does not have to be made robust with respect to contaminants. It is therefore not necessary for the bearing to be made up of particularly high-quality materials, which allows the use of an inexpensive bearing.

In an embodiment of the invention, the sealing arrangement also has, in addition to a supply line for the sealing fluid, a lead-off line via which sealing fluid can be led off from the sealing space. A circuit can thus be set up for the sealing fluid. In particular a sealing fluid pump is arranged in the circuit which conducts the sealing fluid to and from the sealing space. The circuit can contain a filter for filtering the sealing fluid and/or a cooler for cooling the sealing fluid. A sealing fluid reservoir can also be connected to the circuit and the sealing fluid pump can convey sealing fluid from it as required and introduce it into the circuit. An effective cooling of the bearing and also of the side ring seals can thus be ensured so that a secure operation of the sealing arrangement is made possible.

In an embodiment of the invention, the seal holder is designed in multiple parts. The seal holder can be composed of two, three or more parts which are connected to one another. Seals, in particular in the form of O rings, can be arranged between the individual parts. The multipart design of the sealing container allows a simple and thus inexpensive assembly of the sealing arrangement.

In an embodiment of the invention, guide elements are arranged in the sealing space for influencing a flow of the sealing fluid. The sealing fluid can thus be conducted directly to points at which it is needed particularly urgently. A particularly effective use of the sealing fluid is thus made possible.

The guide element in particular has a first guide element part and a second guide element part, with the first guide element part being stationary and the second guide element part rotating with the shaft. The two guide element parts are then arranged so that the sealing fluid flows between the guide element parts. The guide element can in particular be designed so that a pump effect arises on a rotation of the second guide element part so that the sealing fluid is pumped through by the guide element. An effective distribution of the sealing fluid in the sealing space can thus be made possible and a particularly effective influencing of the flow of the sealing fluid is possible.

The sealing arrangement in accordance with the invention can in particular advantageously be used with a pump. It is in particular arranged at a drive shaft of the pump via which the pump is driven, for example, by an electric motor.

In accordance withFIG. 1, a shaft10, which is designed as a drive shaft of a pump, has a connector coupling12for an electric motor, not shown, at a shaft end11and the shaft10and thus the pump can be driven by it. The pump is represented by a detail of a pump housing13from which the shaft10projects through a circular shaft passage14. The pump housing13has a circular cut-out15around the shaft passage14. The pump serves for the conveying of a working fluid, for example water or oil, which is present at a working pressure in the pump housing13. To prevent the working fluid from exiting the pump housing13via the shaft passage14, a sealing arrangement16is arranged around the shaft10. A part of the seal arrangement16is received by the cut-out15of the pump housing13.

The sealing arrangement16has a seal holder17which is arranged about the shaft10and projects into the cut-out15of the pump housing13. It has a cut-out28through which the shaft10projects. The seal container17is screwed to the pump housing13via screws, not shown, and is thus stationary. It has a predominantly cylindrical base shape.

The sealing holder17has a first disk-shaped holder18which is oriented in the direction of the shaft10and which is arranged within the cut-out15of the pump housing13. A first stationary sealing part19of a first slide ring seal20is fastened and thus supported at the first holder18. The first stationary sealing part19has a first sealing surface21to a first co-rotating rotary sealing part22of the first slide ring seal20. The first co-rotating rotary sealing part22is rotationally fixedly connected to the shaft10.

The seal holder17moreover has a second disk-shaped holder23which is oriented in the direction of the shaft10, which is arranged outside the cut-out15of the pump housing13and forms a closure of the seal holder17in the direction of the shaft end11. A second stationary sealing part24of a second slide ring seal25is fastened and thus supported at the second holder23. The second stationary sealing part24has a second sealing surface26to a second co-rotating rotary sealing part27of the second slide ring seal25. The second co-rotating rotary sealing part27is rotationally fixedly connected to the shaft10.

The two slide ring seals20,25thus seal the pump housing13against an exit of the working fluid contained in the pump housing13via the shaft passage14. They are arranged so that the shaft10can project through both slide ring seals20,25and through the cut-out28of the holding part17.

A sealing space29is formed between the first slide ring seal20and the second slide ring seal25and is divided by a third disk-shaped holder30into an outer sealing space31and an inner sealing space32. An outer ring33of a slide bearing34is fastened to the third holder30. An associated inner ring35of the slide bearing34is rotationally fixedly connected to the shaft10so that the shaft10is supported by means of the slide bearing34with respect to the seal holder17.

The first slide ring seal20is arranged so that the first stationary sealing part19is arranged next to the slide bearing34. The first rotary sealing part22is thus arranged toward the pump housing13. The second slide ring seal25is arranged so that the second sealing part27is arranged next to the slide bearing34. The second sealing part24is thus arranged toward the shaft end11. The slide ring seals20,25are thus arranged in a so-called tandem arrangement.

The seal holder17has a supply line36which leads from the outside to the outer sealing space31. Sealing fluid is supplied via the supply line36to the outer sealing space31and thus to the sealing space29. The sealing fluid is made as a light petroleum product and is known as a so-called “quench fluid”. The pressure of the sealing fluid is equal to or smaller than the pressure of the working fluid to be blocked in the pump housing13. The sealing fluid moves via a passage line37in the third holder30from the outer sealing space31to the inner sealing space32. The sealing fluid is led off outwardly from the inner sealing space32and thus from the sealing space29via a lead-off line38in the seal holder17.

A sealing fluid pump39which conveys sealing fluid to the supply line36is provided outside the sealing arrangement16. The sealing fluid pump29sucks in sealing fluid via the lead-off line38from the inner sealing space32. The sealing fluid pump39can additionally also suck in sealing fluid from a sealing fluid reservoir40. The sealing fluid is cooled and purified in a cooling and purifying device41before the entry into the sealing fluid pump39.

In the event that a leak should occur at the first sealing surface21of the first slide ring seal20, the working fluid exiting the pump housing13mixes with the sealing fluid and is led off together with it via the lead-off line38.

In addition, the sealing fluid also serves to lubricate and cool the sliding surfaces21,26of the slide ring seals20,25. A further important function of the sealing fluid is the lubrication and cooling of the slide bearing34which is flowed around by sealing fluid. Additional bores can be provided in the slide bearing34and/or in the third holder30via which sealing fluid can be conducted directly to particularly strained points of the slide bearing34.

Two slide ring seals can also be arranged in a so-called back-to-back arrangement in addition to the tandem arrangement shown inFIG. 1. Such an arrangement is implemented in a second embodiment of a sealing arrangement for a rotating shaft which is shown inFIG. 2. The sealing arrangement in accordance withFIG. 2is of a very similar structure to the sealing arrangement16in accordance withFIG. 1so that only the differences of the two sealing arrangements will be looked at.

The sealing arrangement116in accordance withFIG. 2likewise has a first slide ring seal120and a second slide ring seal125. However, unlike the sealing arrangement16ofFIG. 1, the first slide ring seal120is arranged so that a first rotary sealing part122is arranged beside a slide bearing134. A first stationary sealing part119is thus arranged toward a pump housing113. The second slide ring seal125, like the first slide ring seal25inFIG. 1, is arranged so that a second rotary sealing part127is arranged next to the slide bearing134. A second stationary sealing part124is thus arranged toward a shaft end111of a shaft110. The slide ring seals120,125are thus arranged in the above-named back-to-back arrangement.

A supplied sealing fluid is likewise designed as a light petroleum product and is in this case known as a so-called “barrier fluid”. The pressure of the sealing fluid is greater than the pressure of the working fluid to be blocked in the pump housing113.

A sealing arrangement216for a rotating shaft210with an integrated bearing234is shown in a detailed representation inFIG. 3. The structure of the sealing arrangement216in principle corresponds to the structure of the sealing arrangement116ofFIG. 2. In the description of the sealing arrangement216predominantly smaller differences or additional details with respect to the sealing arrangement116ofFIG. 2will therefore be looked at.

A sealing holder217of the sealing arrangement216is of a three-part design. A first sealing holder part217aserves for holding a first slide ring seal220whose first stationary sealing part219is pressed by a first spring250toward a first rotary sealing part222. The first seal holder part217ais in this respect arranged next to a shaft passage214of a first pump housing213.

A first seal holder part217ais adjoined by a second seal holder part217bto which an outer ring233of the slide bearing234is fastened. The outer ring233is in this respect made up of three layers.

The second seal holder part217bis adjoined by a third seal holder part217cfor holding a second slide ring seal225whose second stationary sealing part224is pressed by a second spring251toward a second rotary sealing part227.

The seal holder parts217a,217band217care sealed with respect to one another by seals in the form of O rings not further designated.

A guide element252for influencing a flow of the sealing fluid is arranged in an outer sealing space231. The guide element252is made in two parts. A first, stationary guide element part253is fixedly connected to the second seal holder part217b. A second, rotating guide element part254is fixedly connected to the second rotary sealing part227of the second slide ring seal225. The outer contour of the second rotating guide element part254is in this respect designed so that sealing fluid is conveyed by its rotation from the outer sealing space231into a middle sealing space255which is arranged between the outer sealing space231and an inner sealing space232.

The middle sealing space255and the inner sealing space232are connected by one or more passage lines. The passage lines are not located in the plane shown inFIG. 3so that they cannot be seen inFIG. 3.