Abstract:
A seal is disposed between a rotating part and a stationary part. At least one of the parts is provided with projections which protrude into the seal gap. The seal gap ( 5 ) extends approximately radially so that both parts are provided with projections which extend in an axial direction, which are located concentrically in relation to the axis of rotation of the rotating parts and which engage with each other. Said projections are configured in the form of rows of blade-like elements. This effectively seals approximately radially extending seal gaps.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a dynamic seal between a rotating part and a stationary part where at least one of the parts is provided with projections which protrude into the seal gap. 
     In particular in the instance of vacuum pumps there frequently exists the requirement of having to seal shafts which penetrate a separating wall between two chambers at different pressures. Commonly, labyrinth seals are employed to this end, as is also known from U.S. Pat. No. 3,399,827, for example. 
     In the instances of seals for gaps extending approximately radially it is known (c.f. U.S. Pat. No. 5,165,872, gap seal  43  in FIG. 5) to employ purge gases (nitrogen, argon or alike) to protect, for example, a bearing/motor chamber against the ingress of detrimental gases. The purge gas is admitted into the bearing/motor chamber and passes through the seal for the gap into the pump chamber so that it is ensured that gases can not pass from the pump chamber into the motor chamber. 
     SUMMARY OF THE INVENTION 
     It is the task of the present invention to create an effective dynamic seal for gaps extending approximately radially between a rotating and a stationary component. This task is solved through the characterizing features of the patent claims. 
     Through the employment of projections designed by way of engaging rows of blades, not only can the desired sealing effect be improved; moreover, there exists the possibility of assigning to the seal pumping properties beneficial to the application in each instance. If, for example, a chamber is to be protected against the ingress of gases, the rows of blades, respectively the angle of incidence for the blades forming the rows of blades, may be so selected that the seal provides a pumping action in a direction opposed to the direction of the flow of the detrimental gases. 
     Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention. 
     FIGS. 1 and 2 are sectional views through an embodiment of the seal in accordance with the present invention; 
     FIGS. 3 and 4 are section al views through a double flow embodiment; 
     FIGS. 5 and 6 are embodiments where the rotors are cantilevered; 
     FIGS. 7 to  9  are embodiments of vacuum pumps equipped with a rotor system having bearings at both face sides. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 depict a seal  1  in accordance with the present invention with stationary rows of rotor blades  2  and rotating rows of rotor blades  3 , the longitudinal axes of which extend in parallel to the rotational axis  4  of the rotating component. They are arranged in concentric rows about the rotational axis  4  and extend into the gap  5  which is to be sealed. The chambers which are to be mutually sealed off against each other and which are separated by the sealing gap  5  are generally designated as  8  and  9 . The rows of the rotor blades  2  and the rows of stator blades  3  are arranged in alternating fashion. In the area of the gap  5  which is to be sealed they engage and have if a pumping action is desired in a manner basically known changing angles of incidence in the direction of the flow. From FIG. 2 it is apparent that the blades  2 ,  3  are components of the neighboring rotating resp. stationary components  6  and  7  respectively, between which there is located the gap  5  which is to be sealed. 
     Depicted in FIGS. 3 and 4 is a double flow embodiment of a seal  1  in accordance with the present invention. An inner group of rows of blades pumps the gases radially towards the inside (arrow  11 ), an outer group of rows of blades from inside to outside (arrow  12 ). Thus an equally effective separation of the chambers  8  and  9  which are to be sealed is achieved. This arrangement offers the benefit that in the chamber which is to be protected (e.g.  8 ) the vapor pressures of components in said chamber will not drop to inadmissibly low levels. In addition, this separation may be supported by the admission of inert gas between the two groups. The inert gas supply is effected through the stationary component  6 . An inlet bore is depicted (also several may be provided) and designated as  14 . 
     Depicted in FIG. 5 is the way in which the present invention is applied in a blower  20 . It consists of a drive section  21  in which the drive motor, not depicted, is accommodated, and the gas pumping section  22 . The drive motor drives a shaft  23  which is guided as gas-tight as possible (labyrinth seal  24 ) through the flange  25  of the drive&#39;s housing. Affixed to the unoccupied end of the shaft  23  is blower wheel  26 . To support the labyrinth seal  24 , a seal  1  in accordance with the present invention has been implemented in the gap  5  between the bottom side of blower wheel  26  and the flange  25 . The flange  25  carries the rows of stator blades  2 , the blower&#39;s wheel  26  carries rotating rows of blades  3  arranged concentrically about the shaft  23  and which engage in the area of gap  5 . If the seal  1  shall have the effect of preventing the entry of gases pumped by blower wheel  26  into the motor chamber, then it is expedient to design the seal in such a manner that it exhibits a pumping action directed radially towards the outside. 
     Depicted in FIG. 6 is a partial section through a turbomolecular pump  31 , the base section of which is designated as  32 . In the base section  32  with the drive motor  33 , the shaft  34  is supported by bearing  35 . The shaft  34  carries the rotor  36  with its rotor blades  37 , which are located together with the stator blades  38  in the pump chamber  39 . In order to effectively separate this pump chamber  39  from the motor and bearing chamber  41 , a sealing system  1  designed in accordance with the present invention is provided. It comprises stator blades  2  arranged on two levels carried by a ring-shaped component  42 , said component being L-shaped in its sectional view and encompassing the shaft  34 . The rotor  36  is equipped with a recess  43  matching the contour of the ring-shaped component  42 . The rotor blades  3  related to the stator blades  2  are affixed to the rotor  36 . If in an embodiment of this kind a reliable separation of the chambers  39  and  41  is to be achieved for example, then it is expedient to design seal  1  in such a manner that the inner (upper) group of rows of blades  2 ,  3  has a pumping action directed towards the motor chamber  41  and the outer (lower) group of rows of blades  2 ,  3  has a pumping action directed towards the pump chamber  39 . By admitting and inert gas between the two groups of rows of blades, the separating effect can even be improved. Both the ingress of hydrocarbons from the motor and bearing chamber  41  into the pump chamber  39 , and also the ingress of detrimental (for example, corrosive or toxic) gases from the pump chamber  39  into the motor chamber  41  can be reliably avoided. The benefit also mentioned in connection with FIGS. 3 and 4 exists. 
     Depicted in FIG. 7 is the application of a seal in accordance with the present invention in an axially compressing friction pump  51  according to the state-of-the-art. The friction pump  51  consists of a turbomolecular pumping stage  52  arranged on the suction side and a molecular pumping stage  53  arranged on the delivery side which may be designed as a Holweck pump (as depicted) or as a Gaede, Siegbahn, Englander or side channel pump. The seal  1  and the friction pump  51  are located in a joint housing  55  approximately cylindrical in shape with a side inlet  56 . A shaft  59  supported by bearings (bearings  57 ,  58 ) at both face sides carries the rotating components in each instance (rotor disk  6  of the seal  1 , rotor  61  of the turbomolecular pumping stage  52 , cylinder  62  of the Holweck pumping stage  53 ). The side inlet  56  of the pump  51  opens between the seal  1  and the axially compressing pumping stages  52 ,  53 . The outlet  64  of the pump  51  is located on the delivery side of the molecular pumping stage  53 . 
     The special feature of the solution in accordance with FIG. 7 is, that the drive motor  68  is located on the high vacuum side of the axially pumping pump  51  (and not, as is common, on the delivery side of the Holweck pumping stage  53 ). In that the seal  1  is located between the inlet  56  and the drive motor  68 , a relatively high pressure (for example 1×10 −2  mbar) can be maintained in motor chamber  41 . The usage of high vacuum capable materials in motor chamber  41  is not required. 
     The embodiment in accordance with FIG. 8 differs from that in accordance with FIG. 7 in that the seal  1  has a pumping action directed radially from the outside to the inside. Moreover, a bypass  67  is connected to the motor chamber  41  said bypass being linked to the suction side of the molecular pumping stage  62 . In line with the entered arrows  69 , the gases pumped by the seal  1  enter through the motor chamber  41  into the bypass  67  and from there into molecular pumping stage  53 . In this way, maintaining of a forevacuum pressure in the motor chamber  41  is ensured. Moreover, the seal  1  supports the pumping capacity of the turbomolecular pumping stage  52  without significantly increasing the total length of the pump  51 . 
     Depicted in FIG. 9 is an embodiment of a pump  51  for deployment in multi-chamber systems, two chamber systems in this instance. Such systems are, for example, analytical instruments having several chambers which need to be evacuated down to different pressures. Thus the distance from the intake ports is given, often resulting in state-of-the-art systems in the necessity for relatively long cantilevered rotor systems requiring involved bearing arrangements. 
     The embodiment in accordance with FIG. 9 has two side inlets  56 ,  56 ′. These are separated from each other by at least one seal  1 . The seal  1  is so designed that it has a pumping action from outside to inside. The inlet  56  “sees” the inlet area of the axially pumping friction pump  51  as well as the periphery of the seal  1  pumping from outside to inside. The outlet of the radially pumping seal  1  opens into the inlet area of a second turbomolecular pumping stage  52 ′ to which the second inlet  56 ′ is connected. The seal  1  effects a lower pressure at inlet  56  compared to that at inlet  56 ′. The drive motor  68  is located on the delivery side of the turbomolecular pumping stage  52 ′. This delivery side is linked via the bypass  67  to the suction side of the molecular pumping stage  53 . 
     The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.