Blow molding machine and method for cooling a dynamic seal

Abstract

Blow molding machine for the production of a plastic container (23), comprising a treatment station (20) with a compressed air supply (21) for the expanding forming of plastic preforms (22) into the plastic container (23) in a hollow mold (24), wherein the treatment station (20) is arranged on a rotating rotary unit (27) which has a rotary feedthrough with a sealing arrangement comprising a housing (9) and a shaft (8) arranged in the housing (9) and a dynamic seal for sealing a component rotating about an axis of rotation (10) against a stationary component comprising a first sealing ring (1) and a second sealing ring (2), each of which slides against an opposing sealing surface (3) at a relative rotational speed and encloses a leakage chamber (4) between them, in which a plurality of leakage bores (5.1, 5.2) opens, comprising, wherein the components are formed by the shaft (8) and the housing (9), the sealing surface (3) is formed by an outer surface of the shaft (8) and the sealing rings (1, 2) are held in the housing (9), and a leakage channel (11) extending around the axis of rotation (10) is provided in a surface of the housing (9) opposite the shaft (8) and / or the outer surface of the shaft (8), which forms at least part of the leakage chamber (4) and in which the leakage bores (5.1, 5.2) open; wherein the shaft (8) rotates about the axis of rotation (10) and the housing (9) is stationary, or wherein the housing (9) rotates about the axis of rotation (10) and the shaft is stationary, with at least one medium-carrying channel (13) connected to the compressed air supply (21), which extends in a sealed manner into the housing (9) and the shaft (8), with at least one medium supply (14) and / or one medium discharge (15) on the housing (9), which is connected to the medium-carrying channel (13) via an interface (16) between the shaft (8) and the housing (9), wherein the interface (16) is sealed on one or both sides in the direction of the axis of rotation (10) with the dynamic seal, wherein a compressed air supply (6) is connected to at least one first leakage bore (5.1) and at least one second leakage bore (5.2) has a compressed air outlet (7) trains.

Description

The present invention relates to a blow molding machine according to the preamble of claim 1 and a method for cooling a dynamic seal in a blow molding machine according to claim 8. It is generally known that in a dynamic seal used to seal a rotating component against a stationary component, or to seal two components rotating at relative speeds around a rotational axis, a leakage chamber with multiple leakage holes is provided between two sealing rings. This ensures that a pressure chamber on one side adjacent to the dynamic seal is reliably sealed against the other side, because any medium that unintentionally flows over the first sealing ring, thus forming a leak, is discharged through the leakage holes and therefore cannot reach the other side of the second sealing ring. A particularly reliable seal can thus be achieved with such a dynamic seal. The sealing rings of dynamic seals of this type each bear against an opposing sealing surface. Due to a relative rotational speed between the sealing ring and the sealing surface, sliding friction occurs, leading to heat input into the seal. In many applications, however, the heat generated during operation of the dynamic seal can be sufficiently dissipated from the seal by the illustrated leakage flow or simply by the flow of a medium within a space sealed off from its surroundings by the seal. DE 37 42 079 C2 describes the sealing of a propeller shaft with a shaft seal whose leakage channel is connected to a compressed air supply. A drain channel is opened periodically at predetermined time intervals to allow the leakage fluid to drain from the leakage chamber. DE 10 2017 106 495 A1 discloses a cooling unit for a barrier medium of a cleaning device for the inner wall cleaning of a container. US 2005 / 0093246 A1 discloses a shaft seal supplied with a lubricant. EP 2 960 201 A1 discloses a rotary distributor for distributing flowable media. US 2012 / 0070529 A1 discloses a blow molding machine with two mold halves, each containing a mold cavity, joined together on a shaft and rotatably mounted thereon. Cooling channels are provided in the walls of the mold halves, which are supplied with coolant via axial bores in the shaft. Sealing rings seal the shaft against the mold halves at the bearings and between the cooling channels. DE 10 2007 062 470 A1 discloses a further device for distributing media. DE 94 08 594 U1 discloses a shut-off valve. DE 10 2015 011 978 A1 discloses a rotary feedthrough for the passage of a flowable medium, in which a compressed air supply is connected to leakage bores. DE 199 13 821 A1 discloses a shaft seal for sealing between a shaft and a machine housing. According to a particular application of the present invention, conditions can occur during the operation of the dynamic seal in which the medium flow or leakage flow is temporarily reduced, but the heat input into the seal through sliding friction is maintained, which can lead to an impermissible temperature increase in the dynamic seal. For example, if a dynamic seal is used to seal a medium supply or discharge in a rotary union, and the medium supply and / or discharge is temporarily interrupted, the heat from the seal can no longer be dissipated via the medium supply or discharge. Even maintaining a comparatively reduced medium supply or discharge can lead to impermissible heating of the dynamic seal, which is why a minimum flow rate through the medium supply and discharge must be maintained. In applications where a leakage flow is deliberately set via the seal, a reduced pressure in the medium supply and / or medium discharge can lead to a reduced leakage flow via the dynamic seal with reduced heat dissipation. The application area of ​​the present invention, in which a medium flow in a medium supply and / or medium discharge can be temporarily interrupted, is described in EP 2 987 618 B1. The application area relates to a mold filling machine and the forming and filling of containers with such a mold filling machine. DE 20 2016 101 447 U1 describes an embodiment of a rotary feedthrough with leakage bores, wherein the rotary feedthrough is free of sealant, so that no temperature is introduced into the seal by frictional forces on a sealing ring. An embodiment of a generic dynamic seal is further described in DE 25 15 568 A1, wherein a leakage chamber with a leakage bore is provided between two sealing rings. DE 10 2014 216 562 A1 discloses a further mold-filling machine and method for molding and filling containers in which the invention can be applied accordingly. The present invention is based on the objective of improving a blow molding machine with a dynamic seal comprising a first and a second sealing ring enclosing a leakage chamber with leakage bores between them, and in which frictional heat can be generated, in such a way that sufficient heat dissipation in every operating state of the dynamic seal is possible with low energy expenditure, cost-effectively and safely. The problem according to the invention is solved by a blow molding machine with a dynamic seal having the features of claim 1 and a method for cooling the dynamic seal in a blow molding machine according to claim 8. The dependent claims describe particularly advantageous embodiments of the invention. The blow molding machine according to the invention for the production of a plastic container comprises a treatment station with a compressed air supply for the expanding forming of plastic preforms into the plastic container in a hollow mold, wherein the treatment station is arranged on a rotary runner. The rotary joint comprises a rotary feedthrough with a sealing arrangement with a housing and a shaft arranged in the housing and a dynamic seal for sealing a component rotating about an axis of rotation against a stationary component with at least one first sealing ring and at least one second sealing ring, each of which slide against an opposing sealing surface at a relative rotational speed and enclose a leakage chamber between them, into which a plurality of leakage bores open. The components are formed by the shaft and the housing, the sealing surface is formed by an outer surface of the shaft, and the sealing rings are held in the housing. A leakage channel extending around the axis of rotation is provided on a surface of the housing opposite the shaft and / or on the outer surface of the shaft, forming at least part of the leakage chamber and into which the leakage bores open. The shaft rotates around the axis of rotation and the housing is stationary, or the housing rotates around the axis of rotation and the shaft is stationary. The rotary feedthrough comprises at least one medium-carrying channel connected to the compressed air supply, which extends in a sealed manner within the housing and the shaft, and at least one medium inlet and / or outlet on the housing, which is connected to the medium-carrying channel via an interface between the shaft and the housing, wherein the interface is sealed on one or both sides in the direction of the axis of rotation by the dynamic seal. According to the invention, a compressed air supply is connected to at least one leakage bore, and at least one other leakage bore forms a compressed air outlet. For the purposes of this invention, the at least one leakage bore to which a compressed air supply is connected is referred to as the first leakage bore. Several such first leakage bores can also be provided, to which at least one common or several compressed air supplies are connected. The at least one leakage bore that forms a compressed air outlet is referred to for the purposes of this invention as the second leakage bore. Several corresponding second leakage bores, each forming a compressed air outlet, can also be provided. According to a preferred embodiment of the invention, in addition to the at least one first leakage bore and in addition to the at least one second leakage bore, one or more further leakage bores are provided through which, as is conventional, a leakage current can be discharged. Preferably, the first and second leakage bores are arranged offset from each other around the axis of rotation and at a distance from each other, particularly preferably at least substantially diametrically opposed to each other. This allows cooling with compressed air over the entire circumference or nearly the entire circumference of the dynamic seal. According to a particularly advantageous embodiment of the dynamic seal, which ensures a particularly reliable sealing effect, the sealing rings are elastically pressurized such that they are pressed elastically against the sealing surface. They thus bear against the sealing surface under elastic pressure. Such elastic pressure can be generated by the material of the sealing rings themselves, but preferably by a spring element that presses the respective sealing ring, which can then be elastic or inelastic, against the sealing surface. The spring element can comprise one or more mechanical compression springs, or preferably an elastic ring, for example an elastomer ring, which, together with the sealing ring, is housed, for example, in a casing. The sealing surface of the dynamic seal opposite the first and / or second sealing ring, in particular the surface of the shaft, can have a low-friction and / or wear-resistant coating, especially at least in the area where the sealing rings bear against it, and particularly exclusively in the sections where the sealing rings are positioned. For example, a coating of chromium oxide or a coating of tungsten carbide is suitable. The tungsten carbide can preferably be embedded in another, comparatively softer material or alloy within the coating. If the coating, and especially the material of the sealing rings in contact with the coating, has low thermal conductivity, there is a risk of detrimental heating of the sealing rings and / or the spring elements. If the sealing rings and / or the spring elements harden as a result, wear at the sealing points increases because component displacements at the sealing point can no longer be dampened as effectively. A coating made of or containing Stellite is therefore particularly advantageous. Stellites are cobalt-chromium-based hard alloys that are particularly heat-stable and exhibit high hardness. This makes the sealing points particularly wear-resistant to corrosion and abrasion, while simultaneously dissipating heat effectively. Stellite, especially apart from unavoidable impurities, preferably has the following composition, each given in wt.%: Cr20-32.5% Mo0-12%, preferably >0 to 12% W0-19%, preferably >0 to 19% CO0.1-3.4% Fe 0.5-20%, preferably 0.5-3% Ni1-22%, preferably 1-3% Si1-2% Mn0-1.9%, preferably >0-1.9% or 1.9% CoRest In particular, the sealing rings are made of plastic, for example polytetrafluoroethylene (PTFE), or at least have such a coating on their sealing surface. In the compressed air supply of a dynamic seal according to the invention, a vortex tube is preferably provided, with which the compressed air introduced into the first leakage bore can be cooled. Such a vortex tube, also called a vortex tube (VT) or Ranque-Hilsch vortex tube (RHVT), has a compressed air connection and a vortex chamber, wherein opposing hot and cold air streams are generated in the vortex chamber and the cold air stream can be directed to the first leakage bore via a cold air outlet. Additionally or alternatively, another air cooler can also be used to cool the compressed air supplied to the seal. Preferably, a distributor is provided in the direction of flow of the cold air stream behind such a vortex chamber if several first leakage bores in a dynamic seal are to be supplied with a correspondingly cooled compressed air stream, or if several dynamic seals are each to be supplied with a correspondingly cooled compressed air stream via at least one first leakage bore. According to one embodiment of the invention, at least one first leakage bore can be permanently supplied with compressed air. Preferably, however, at least one first leakage bore is only supplied with compressed air temporarily, in particular depending on a temperature detected in or in the area of ​​the dynamic seal and / or depending on a quantity on which the temperature input into the dynamic seal and / or the heat dissipation from the dynamic seal depends. For example, compressed air is only introduced into the leakage chamber via at least one initial leakage bore if there is no leakage flow or a leakage flow that is comparatively reduced compared to normal operation in the sealing arrangement and / or if a flow through a space sealed with the seal is comparatively reduced or fails compared to nominal operation. In particular, a bearing, especially a rolling bearing, is arranged on the side of the at least one dynamic seal (each) facing away from the medium supply and / or medium discharge, with which the shaft is supported in the housing or the housing is supported on the shaft. The dynamic seal reliably prevents the ingress of medium from the medium supply and / or medium discharge into the bearing and thus, for example, the discharge of grease or oil in a grease- or oil-lubricated bearing. Conventionally, in such blow molding or mold filling machines, when they are switched to standby mode so that no compressed air is supplied to the mold via the compressed air supply, air is released via an idle or bypass valve in such a way that a certain airflow is maintained through the medium supply and / or medium discharge of the rotary union. This results in the necessary cooling of the at least one dynamic seal at an interface between the housing and the shaft. However, a disadvantage of this method is the high non-productive compressed air consumption. According to the invention, by introducing compressed air through at least one first leakage bore through the leakage chamber in the dynamic seal(s) and out of the second leakage bore(s), the necessary cooling can be maintained with a comparatively much smaller compressed air flow.In particular, more than 50% of the previous compressed air flow can be saved, which is significant in terms of the associated energy savings. An inventive method for cooling a dynamic seal or a sealing arrangement involves supplying compressed air to the leakage chamber via at least one first leakage bore and discharging the compressed air introduced into the leakage chamber via at least one second leakage bore from the leakage chamber. Compressed air is only introduced into the leakage chamber via the at least one first leakage bore if no medium, or a reduced medium flow compared to nominal operation, flows into or out of the at least one medium-carrying channel via the interface sealed by the corresponding dynamic seal, because the cooling effect of the medium flow is then eliminated or reduced, and / or because a leakage flow in the dynamic seal is reduced. The invention will below be described by way of example using an embodiment and the figures. Figure 1 shows a rotary feedthrough according to the invention; Figure 2 shows a dynamic seal according to the invention, as provided several times in the rotary feedthrough of Figure 1; Figure 3 shows an embodiment of a sealing arrangement according to the invention; Figure 4 shows a schematic representation of a blow molding machine according to the invention. Figure 1 shows a rotary feedthrough with multiple medium inlets 14, 14' and medium outlets 15, 15'. The medium inlet 14 and the medium outlet 15 are connected to each other by the medium-carrying channel 13, which is designed as an annular channel around the shaft 8. The medium inlet 14' and the medium outlet 15' are also connected to each other by an annular channel 13'. However, the invention is not limited to this. The annular channels 13, 13' are bounded by hollow tubes mounted on the shaft 8 and arranged concentrically to the axis of rotation 10. The outer annular channel 13 is also bounded by the shaft 8. The housing 9 is mounted on the stationary shaft 8, rotating about the axis of rotation 10. In principle, the housing 9 could also be stationary, with the shaft 8 rotating about the axis of rotation 10. In the illustrated embodiment, a further channel is designed as a central channel in the shaft 8 along the axis of rotation 10, which could, for example, be used as a cable duct or could connect another, unspecified medium supply and discharge system. The shaft 8 is supported against the housing 9 by bearings 17, each designed as a rolling bearing. The radially extending channel for the medium discharge 15 is connected between the two bearings 17 and opens into an interface 16 between the shaft 8 and the housing 9. The interface 16 is sealed on both sides in the direction of the axis of rotation 10 with a dynamic seal according to the invention, as shown in enlarged view in Fig. 2. Each dynamic seal has at least one first leakage bore 5.1 and at least one second leakage bore 5.2. A compressed air supply 6 is connected to the first leakage bores 5.1, and the second leakage bores 5.2 each form a compressed air outlet 7. The radially extending channel for medium discharge 15' also opens into an interface 16 between the shaft 8 and the housing 9. This interface 16 is also sealed on both sides in the direction of the axis of rotation 10 with a dynamic seal according to the invention, as shown in enlarged view in Fig. 2. Each dynamic seal has at least one first leakage bore 5.1 and at least one second leakage bore 5.2. A compressed air supply 6 is connected to the first leakage bores 5.1, and the second leakage bores 5.2 each form a compressed air outlet 7. In the illustrated embodiment, but not necessarily, compressed air is passed through the medium supply 14, the channel 13 and the medium outlet 15, and in particular also through the medium supply 14', the channel 13' and the medium outlet 15', and can therefore be used as a compressed air supply 6. For example, compressed air at different pressures can be supplied to the medium outlets 15, 15' via these two mutually sealed channel arrangements. Specifically, a compressed air line 18 branches off from the medium discharge 15, which, for example, has a comparatively higher pressure than the medium discharge 15', and is connected to the first leakage bores 5.1 between the two bearings 17. In the illustrated embodiment, the leakage bores 5.1 are also supplied with compressed air from this compressed air supply 6, which is fed by the medium discharge 15, by dynamic seals that enclose the radial channel of the medium discharge 15'. However, they could also be supplied with compressed air by their own compressed air supply 6, for example, from the medium discharge 15'. A control valve 19 is provided in the compressed air line 18, with which the airflow flowing into the leakage bores 5.1 can be controlled or regulated. Optionally, as indicated, a pressure regulator and / or pressure sensor and / or temperature sensor are also provided in the compressed air line 18. In order to cool the compressed air diverted from the medium discharge 15 before it is introduced into the leakage bores 5.1, in order to achieve better heat dissipation from the dynamic seals, a vortex tube 12 is arranged in the compressed air line 18, which in a vortex chamber 12.1 separates the supplied airflow into a cold airflow and a counter-rotating hot airflow, with the cold airflow being directed to the first leakage bores 5.1. In normal operation of the rotary feedthrough shown in Fig. 1, the dynamic seals on both sides of the medium outlet 15 and the medium outlet 15' are cooled by the medium flows passing through the medium inlets 14, 14', the channels 13, 13', and the medium outlets 15, 15'. In particular, a leakage flow also escapes from the medium outlet 15 and the medium outlet 15' via the dynamic seals and their leakage bores 5.1, 5.2, which generates a certain cooling effect. However, this is not essential if, for example, a complete seal or a seal as complete as possible is desired. If, during standby operation, the medium flow through one or both medium inlets 14, 14', channels 13, 13' and medium outlets 15, 15' is reduced, this medium flow, and in particular a correspondingly reduced leakage flow, carries away less heat from the dynamic seals. To still generate sufficient cooling, cooling compressed air is now passed through the dynamic seals via the compressed air supply 6, specifically into the dynamic seals through the first leakage bores 5.1 and out of the dynamic seals through the second, diametrically opposite leakage bores 5.2.In this case, a particularly small compressed air flow can be sufficient for cooling because it passes directly into the dynamic seals, and it is not necessary to maintain a comparatively large medium flow through the medium inlets 14, 14' and the medium outlets 15, 15', which was conventionally discharged unused into the environment, especially via a bypass valve. Figure 2 shows a dynamic seal in detail, such as the one that can be provided on each side of the medium outlet(s) 15 and / or 15' in the rotary feedthrough shown in Figure 1. In principle, one or both medium inlets 14, 14' can also be sealed with corresponding dynamic seals. The dynamic seal has a first sealing ring 1 and a second sealing ring 2. The first sealing ring 1 is, for example, arranged directly next to the medium outlet 15 and / or medium outlet 15', and the second sealing ring 2 is located on the side of the first sealing ring 1 facing away from the medium outlet 15 and / or medium outlet 15'. The first sealing ring 1 and the second sealing ring 2 enclose a leakage chamber 4 in the axial direction, i.e., in the direction of the axis of rotation 10, advantageously in the form of a leakage channel 11 completely enclosing the axis of rotation 10. The first leakage bore 5.1 and the second leakage bore 5.2 open into the leakage chamber 4 or the leakage channel 11, respectively. The first sealing ring 1 and the second sealing ring 2 bear elastically against the sealing surface 3, which is formed by the radially outer surface of the shaft 8. Advantageously, a coating is provided on the sealing surface 3 in the area of ​​sealing rings 1 and 2, which is optimized with regard to heat resistance, heat dissipation and / or wear reduction. The coating comprises, for example, stellite, tungsten carbide and / or chromium oxide, or consists thereof. In the illustrated embodiment, the elastic pressure bearing of the sealing rings 1, 2 is achieved with elastically deformable O-rings 25, which, in their elastically deformed state, are inserted together with the sealing rings 1, 2 in grooves in the housing 9. However, other embodiments are also possible, for example with at least partially elastic sealing rings 1, 2. The sealing rings 1, 2 are, for example, made of PTFE or coated with PTFE. Because a compressed air supply 6 is connected to the first leakage bore 5.1 and the diametrically opposite second leakage bore 5.2 forms a compressed air outlet 7, heat input caused by friction on the sealing surface 3 in the area of ​​both sealing rings 1, 2 can be reliably controlled by heat dissipation via the compressed air passed through. In an embodiment where, unlike that shown in Fig. 1, no medium flow passes through the medium outlet 15 and / or medium outlet 15' during operation with the shaft 8 or housing 9 rotating, an external compressed air supply 6 can also be connected to the first leakage bores 5.1 to cool the dynamic seals. Naturally, such an embodiment is also possible when a medium flow passes through the medium outlet 15, 15'. Figure 3 shows an exemplary sealing arrangement according to the invention. Compressed air is supplied as a cooling medium through the dynamic seal between the shaft 8 and the housing 9 via the compressed air supply 6, which in turn comprises a vortex tube 12 and a downstream distributor block 26, from which cooled compressed air is distributed to the individual first leakage bores 5.1. The warm air separated in the vortex tube 12 is, for example, released to the environment. Figure 4 schematically illustrates a preferred application example of the invention. Figure 4 shows a blow molding machine for forming plastic containers 23, for example, but not necessarily, in the form of a mold filling machine for forming and filling plastic containers 23 as disclosed generically in EP 2 987 618 B1. The plastic containers 23 are produced by expanding the plastic preforms 22. Each preform 22 is formed in a separate processing station 20. The blow molding machine includes a rotary unit 27, which carries the processing stations 20 and rotates around the axis 10. The rotary unit 27 includes a rotary feedthrough, such as the one shown in Fig. 1, to supply compressed air and, optionally, a filling product to the processing stations 20. The compressed air is supplied to the processing stations 20, for example, in two different, sequentially connected pressure stages, via the medium inlets 14, 14', the channels 13, 13', and the medium outlets 15, 15' shown in Fig. 1. However, other designs of the rotary feedthrough are also possible. Each of the treatment stations 20 comprises a mold 24 in which the plastic containers 23 are formed and, if necessary, the filling product is poured into the formed plastic containers 23. The molds 24 are opened to insert the plastic preforms 22 and closed for demolding and filling. The plastic preforms 22 are heated in an oven 28, for example, by means of infrared or microwave radiation, and transported to the respective treatment station 20 by means of an infeed star wheel 29. After demolding and filling, the plastic containers 23 are removed from the molds 24 by means of an outfeed star wheel 30 in the outfeed area of ​​the blow molding machine. The compressed air supply 21 to the treatment stations 20, which is supplied with compressed air via the rotary union in or for the rotary unit 27, is shown schematically only in Fig. 4. The corresponding compressed air supply 21 is connected to a medium discharge of a rotary union according to the invention, in particular in the form shown in Fig. 2. Reference symbol list 1 Sealing ring 2 Sealing ring 3 Sealing surface 4 Leakage chamber 5.1 First leakage bore 5.2 Second leakage bore 6 Compressed air supply 7 Compressed air outlet 8 Shaft 9 Housing 10 Shaft of rotation 11 Leakage channel 12 Vortex tube 12.1 Vortex chamber 13 Channel 14 Medium supply 15 Medium discharge 16 Interface 17 Bearing 18 Compressed air line 19 Control valve 20 Treatment station 21 Compressed air supply 22 Plastic preform 23 Plastic container 24 Hollow form 25 O-ring 26 Distributor block 27 Rotary runner 28 Oven 29 Inlet star wheel 30 Outlet star wheel

Claims

Blow molding machine for the production of a plastic container (23), comprising a treatment station (20) with a compressed air supply (21) for the expanding forming of plastic preforms (22) into the plastic container (23) in a hollow mold (24), wherein the treatment station (20) is arranged on a rotating rotary unit (27) which has a rotary feedthrough with a sealing arrangement comprising a housing (9) and a shaft (8) arranged in the housing (9) and a dynamic seal for sealing a component rotating about an axis of rotation (10) against a stationary component comprising a first sealing ring (1) and a second sealing ring (2), each of which slides against an opposing sealing surface (3) at a relative rotational speed and encloses a leakage chamber (4) between them, in which a plurality of leakage bores (5.1, 5.2) opens, comprising, wherein the components are formed by the shaft (8) and the housing (9), the sealing surface (3) is formed by an outer surface of the shaft (8) and the sealing rings (1, 2) are held in the housing (9), and a leakage channel (11) extending around the axis of rotation (10) is provided in a surface of the housing (9) opposite the shaft (8) and / or the outer surface of the shaft (8), which forms at least part of the leakage chamber (4) and in which the leakage bores (5.1, 5.2) open; wherein the shaft (8) rotates about the axis of rotation (10) and the housing (9) is stationary, or wherein the housing (9) rotates about the axis of rotation (10) and the shaft is stationary, with at least one medium-carrying channel (13) connected to the compressed air supply (21), which extends in a sealed manner into the housing (9) and the shaft (8), with at least one medium supply (14) and / or one medium discharge (15) on the housing (9), which is connected to the medium-carrying channel (13) via an interface (16) between the shaft (8) and the housing (9), wherein the interface (16) is sealed on one or both sides in the direction of the axis of rotation (10) with the dynamic seal, wherein a compressed air supply (6) is connected to at least one first leakage bore (5.1) and at least one second leakage bore (5.2) has a compressed air outlet (7) trains. Blow molding machine according to claim 1, characterized in that the first leakage bore (5.1) and the second leakage bore (5.2) are arranged offset from each other about the axis of rotation (10), in particular at least substantially diametrically opposite each other. Blow molding machine according to one of claims 1 or 2, characterized in that the sealing rings (1, 2) are elastically pressurized against the sealing surface (3). Blow molding machine according to one of claims 1 to 3, characterized in that an air cooler, in particular in the form of a vortex tube (12), is provided in the compressed air supply (6) for cooling compressed air introduced into the first leakage bore (5.1). Blow molding machine according to one of claims 1 to 4, characterized in that the sealing surface (3) opposite the first sealing ring (1) and / or second sealing ring (2) is coated with chromium oxide or tungsten carbide or comprises chromium oxide or tungsten carbide. Blow molding machine according to one of claims 1 to 4, characterized in that the sealing surface (3) opposite the first sealing ring (1) and / or second sealing ring (2) is coated with or comprises Stellite. Blow molding machine according to one of claims 1 to 6, characterized in that a bearing (17), in particular a rolling bearing, is arranged on the side of the dynamic seal facing away from the medium supply (14) and / or medium discharge (15), with which the shaft (8) is supported in the housing (9) or the housing (9) is supported on the shaft (8). Method for cooling a dynamic seal in a blow molding machine according to one of claims 1 to 7, characterized in that compressed air is introduced into the leakage chamber (4) via the at least one first leakage bore (5.1) and discharged from it via the at least one second leakage bore (5.2), wherein compressed air is introduced into the leakage chamber (4) via the at least one first leakage bore (5.1) only if no medium or a medium flow reduced compared to nominal operation flows out of or into the at least one medium-carrying channel (13) via the interface (16) which is sealed with the corresponding dynamic seal.

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