FR2574148A1 - ROTATING JOINT HAVING A VARIABLE STEP HYDRODYNAMIC ACTION NET - Google Patents

Abstract

AN ANNULAR PTFE SEALING ELEMENT 10 FOR A ROTARY SEAL HAS HYDRODYNAMIC STRUCTURAL ELEMENTS 15 WHICH ARE MORE DISTANT IN A REGION 20 ADJACENT TO THE SEALING EDGE 16 THAN IN A REGION 22 REMOTE FROM THIS SEALING EDGE.

Description

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  Rotating joint fitted with a hydrodynamically active thread

not variable.

  The present invention relates to improvements to seals having a ring-shaped sealing member.

  whose main constituent is polytetrafluoro-

ethylene, hereinafter referred to as PTFE.

  Such seals are relatively well known; the outer regions of the annular sealing element are fixed between casing elements or bonded to a single rubber-coated shoemaking element, while the internal edge cooperates with the surface of a shaft passing through the seal, this which deforms the initially planar element giving it a curved shape or

trumpet.

  It is an object of the present invention to provide on the surface of the sealing element which is in contact

  with the tree an improved structure which improves the water

dynamic cheity.

  In or for a rotary joint, the present invention provides an annular sealing element made of PTFE, the internal edge of which has a structure having regions

  circumferential in which the struc-

  turels are parallel to one another being inclined with respect to the internal edge, the spacing of these structural elements at the level of the internal edge being greater

  at their spacing away from this internal edge.

  Preferably, the structural elements are notches in the surface of the PTFE, which open to form grooves when the sealing element deforms on the shaft. Structural elements can include one or more

  helical notches, ribs or grooves.

  There is preferably a first region adjacent to the internal edge in which the spacing is constant, a second region, remote from the internal edge, in which the spacing is constant, but less than the spacing in the first region, and a third region, between

  the first region and the second, in which the

  ment varies from that of the first region to

that of the second region.

  The invention will be better understood on reading the

  following detailed description, given by way of example only, of a preferred embodiment, in conjunction with the attached drawing, in which: the single figure is a half cross-section through a sealing element according to the invention, mounted sure

a tree.

  The drawing shows a PTFE sealing element

  where it is in contact with a tree 11.

  The element 10 initially has the shape of a ring in the plane 12 and its outside diameter (not shown) is fixed in the plane 12 between elements of a metal case or glued to a single case element covered with rubber. However, when mounted on a tree

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  11, the sealing element is deformed in the shape of a trom-

  pette with the inside diameter 14 of the stretched ring

along the tree 11.

  On the surface of the element 10 are provided hydrodynamic structural elements 15 which improve the dynamic sealing of the element 10 on the shaft. Numerous configurations of such structural elements, namely ribs or grooves, which can be used in the present invention have been proposed, but the preferred structure consists of helical notches. These notches are cut in the PTFE element during its manufacture while the face thus notched is

  plane. No material is removed during this notching.

  However, when the element 10 is deformed by its mounting

  on the shaft 11, the notches open to form effective

  grooves which provide a hydro-

  dynamic. In the illustrated embodiment, there are four

  helical notches, but, as their number is determin-

  undermined by the diameter of the joint and the desired angle between the notch and the internal or sealing edge 16, it is understood that any number of helical notches can be provided, including only one. What is important in the present invention is that, when one moves axially along the shaft from the sealing edge 16, one can meet, in at least certain circumferential regions of the joint, a succession of substantially structural elements parallel inclined on the internal edge 16. For example, in the case of a single propeller, the structural elements encountered would be

  the successive turns of the propeller.

  We can see in the drawing that, as we move away from the sealing edge 16, the pitch of the propeller,

  or more precisely the spacing of the notches

  cessive, is initially constant in region 20 and becomes progressively smaller in a transition region 21 to become constant in the region

  22, but less than the spacing in region 20.

  This variation in the spacing of the successive structural elements ensures maximum hydrodynamic pumping near the sealing edge and the maintenance of a film of lubricant at the point of maximum stress in the transition region 21 and it prevents clogging of the cuts in region 22 by dust and dirt, because the greater number of cuts in this region means that each cut is less open

  widely and has less pumping action.

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Claims (5)

Claims.   1. Annular sealing element made of PTFE (10), in or for a rotary joint, characterized in that its internal edge (14) has a structure having regions   circumferential in which the structural elements   rels (15) are parallel to each other being inclined relative to the internal edge, the spacing of these structural elements at the internal edge being greater   at their spacing away from this internal edge.   2. Sealing element according to claim 1, character-   in that the structural elements are notches (15) in the surface of the PTFE which open to form grooves when the sealing element (10) deforms on a tree (11).   3. Sealing element according to claim 2, character-   laughed at in that the structural elements are notches helical.   4. Sealing element according to claim 1, character-   laughed at in that the structural elements are ribs or grooves.   5. Sealing element according to any one of the res-   previous indications, characterized in that there is a first region (20) adjacent to the internal edge in which the spacing is constant, a second region (22), distant from the internal edge, in which the spacing is constant, but less than the spacing in the first region, and a third region (21), between the first region and the second, in which the spacing varies from that of the first region to that of the second region.