Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/16—Sealings between relatively-moving surfaces
  • F16J15/34—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member
  • F16J15/3404—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member and characterised by parts or details relating to lubrication, cooling or venting of the seal
  • F16J15/3408—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member and characterised by parts or details relating to lubrication, cooling or venting of the seal at least one ring having an uneven slipping surface
  • F16J15/3412—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member and characterised by parts or details relating to lubrication, cooling or venting of the seal at least one ring having an uneven slipping surface with cavities
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/16—Sealings between relatively-moving surfaces
  • F16J15/34—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member
  • F16J15/3464—Mounting of the seal
  • F16J15/3468—Means for controlling the deformations of the contacting faces
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/44—Free-space packings
  • F16J15/447—Labyrinth packings
  • F16J15/4472—Labyrinth packings with axial path

Definitions

• the present invention relates to lubricating film type gas seals for rotating equipment.
• gas seals have commonly utilized stationary and rotating rings of simple ring type geometry which maintain a lubricating film (gap) between their respective sealing faces by means of hydrodynamic fluid forces.
• hydrodynamic and hydrostatic as used herein are meant to convey their conventional meanings (as discussed, for example, at page 661 of Principles and Design of Mechanical Face Seals, Lebeck, A., 1991; ISBN 0-471-51533-7).
• the stationary sealing ring (stator) is generally disposed in the sealing housing and the rotating sealing ring (mating ring) is generally disposed on and fixed to the shaft.
• Geometric symmetry of the mating ring and application of pressure balancing techniques about the mating ring ensures the mating ring sealing face remains perpendicular to the axis of the shaft and parallel to the stationary sealing face throughout all operating conditions.
• Prior theoretical art shows that a slightly converging gap (converging coning angle) between the adjacent sealing faces is a fundamental requirement for stable seal operation.
• a slightly diverging gap between seal faces causes hydrostatic and hydrodynamic fluid instability and destruction of the sealing faces due to touchdown and rubbing.
• a diverging gap is defined as where the axial distance between sealing face surfaces is smallest at the high pressure diameter.
• a non-distorting mating ring as well as a stationary ring (stator) with momentary or transient self alignment features based on generating interfacial hydrodynamic pressures in excess of pressures sealed.
• Mating ring symmetry shown by Sedy is believed to result in the sealing face remaining essentially perpendicular to the axis of the shaft when the ring is subjected to centrifugal force due to rotation.
• a non-symmetrical mating rotor would cause the sealing face to tilt in a diverging or converging manner as speed is varied, resulting in changing stable and/or unstable operating characteristics throughout the seals operating range.
• the two o-rings shown by Sedy at the rear face and inside diameter of the mating ring provide a flexible mount to presumably enhance mating ring dynamic stability as well as seal the process fluid. Mating ring distortion is further prevented by a pressure balancing feature provided by the o-ring shown at the rear face of the mating ring. Although the function of this o-ring is not described by Sedy, its purpose is presumably to preclude the loss of fluid through the rear of the seal.
• the present invention provides:
• a dry gas seal having a rotor and a stator, wherein said dry gas seal is operable with a machine having a rotating shaft
• the improvement comprising: a) a flexible rotor which:
• the mating rotor is an integral piece which consolidates the following components of the seal in U.S. patent 4212475: mating ring, drive sleeve with radially extending flange, spacer sleeve, multiple drive pins and o-ring at the inner diameter of the mating ring.
• the present seal allows the removal of the pressure balance o-ring (which is located behind the mating ring of prior seals). This is a significant improvement as it eliminates seal failure due to explosive decompression of the o-ring.
• Another significant benefit of the seal of this invention is that it allows the elimination of drive pins and drive pin holes in the mating ring. This prevents stress induced mating ring failure due to the stress concentration caused by these pins and holes. Manufacturing cost is also reduced by the reduction of the number of components.
• Figure 1 shows a cross-section of a gas seal according to the invention.
• Figure 2 shows a cross-section of seal of this invention with multiple radial and annular sealing surfaces located on the mating rotor at different radial locations.
• Figure 3 shows a cross-section of seal of specific embodiment of the invention in which multiple radial and annular sealing surfaces are located on the mating rotor in a back to back configuration.
• Figure 4 shows a schematic describing mating rotor and stator angular deformation and resulting coning angle.
• Figure 5 shows hydrostatic pressure profiles across seal face with various coning angle configurations.
• SUBSTITUTE SHEET Figure 6A shows a cross section of a mating rotor according to this invention for example I.
• Figure 6B shows cross sections of mating rotors with varying flexibility for examples II to IV.
• Figure 6C shows cross sections of mating rotors with varying flexibility for examples V to v ⁇
• a preferred embodiment of the invention is depicted in Figure 1.
• a rotating shaft 4 extends through compressor housing 1.
• the seal of this invention seals high pressure process fluid in chamber 15 from leaking to lower pressure chamber 16 (e.g. atmosphere).
• the mating rotor 2 is fixed to the shaft 4 with retaining nut 5 and rotation is prevented by drive pin 17.
• O-ring 12 prevents leakage between shaft 4 and mating rotor 2.
• Stator housing 6 is located in compressor housing 1 by retaining device 18. Process fluid is sealed between the respective housings by o-ring 9.
• Stator 3 is located in stator housing and prevented from rotating by anti- rotation device 11.
• stator sealing face 14 is forced to axially contact radially extending mating rotor sealing face 13 by compression of a plurality of helical springs 7 mounted in stator housing spring recess 19 and retaining disk recess 20.
• Retaining disk 8 is axially forced against stator and locates sealing o-ring 10.
• Shallow, preferably spiral, grooves 21 are located on the mating rotor. As will be appreciated, the grooves may be alternatively located on the stator.
• grooves can be designed according to well known principles and hence may vary in shape, size and depth depending on application.
• the mating rotor is preferably manufactured from a ductile ferrous or non-ferrous material and preferably possesses a minimum Modulus of Elasticity of approximately 10,000,000 pounds per inch squared.
• a suitable material for the stator would be carbon graphite but other materials that possess a low coefficient of friction and preferably possess a minimum Modulus of Elasticity of approximately 1,800,000 pounds per inch squared may also be utilized.
• the mating rotor can be mechanically deformed by shrink fitting a circumferential ring 24 to the mating rotor. This allows the mating rotor seal face to tilt in a preferred direction to enhance seal performance.
• a deformable slot (e.g. a circumferential groove) 29 can be introduced to the mating rotor to adjust (tune) mating rotor flexibility if required to ensure seal face deflection remains within limits.
• Circumferential rings 25 and 28 can be shrink fitted to the stator to deform the stator and /or enhance the performance of the stator.
• the mating rotor 2 may also possess one or more annular cylindrical sealing surfaces 22 which mate to an opposite sealing surface 23.
• the cylindrical sealing surface may be smooth or possess a labyrinth or other complex geometry to mate with an opposing cylindrical sealing surface.
• a dry gas seal may be further configured such that the mating rotor has a first radially extending sealing face 13a and a second radially extending sealing face 13b, wherein the second radially extending sealing face is located at a greater radial distance from the axis of rotation of said rotating shaft in comparison to first radially extending sealing face.
• SUBSTITUTE SHEET at the seal face may be different for each seal face as shown in Figure 2.
• a dry gas seal with this configuration is useful for applying an axial load to the shaft.
• a dry gas seal may be configured such that the flexible mating rotor has a first radially extending sealing face 13a and a second radially extending sealing face 13b, wherein the first radially extending sealing face, 13a, is located at a different axial position, 13b, with respect to the length of the rotating shaft in comparison to the axial position of the second radially extending sealing face 13b.
• This configuration adds redundancy to the seal and may improve reliability and safety.
• both sealing faces 13 and 14 are flat to within 10 helium light bands (116 micro inches); and substantially parallel; and are essentially perpendicular to the shaft axis within 0.002 inches when not subjected to pressure or rotation.
• the mating rotor sealing face can deflect from an initial flat plane surface (perpendicular to the axis of the shaft) to a tilting, conical surface.
• the mating rotor seal face 13 may deflect up to approximately 0.400 degrees in the converging direction and up to approximately 0.200 degrees in the diverging direction due to pressure imbalance and rotational forces.
• Mating rotor seal face tilt (coning) is described by angle, ⁇
• stator seal face tilt (coning) is described by angle, ⁇ , in Figure 4.
• each angle is measured from a reference plane which extends radially from said shaft at a perpendicular angle to the axis of rotation of said shaft;
• the sign of the angle is a function of the convention that is used.
• a different convention may describe the same physical result in a different manner (for example, if the rotor is moved from the left hand side to the right hand side of the plane, then a 'positive' angle is defined according to the convention otherwise set out in a) to c) above would become 'negative').
• the gap between the mating rotor and stator seal faces is deemed to be converging if the gap is smallest at the low pressure diameter of the seal.
• the coning angle, ⁇ is equal to the stator seal face tilt, a, minus mating rotor seal face tilt, ⁇ .
• a converging gap is a positive coning angle , ⁇ , while a diverging gap is a negative coning angle , ⁇ .
• Figure 5 shows a hydrostatic seal pressure profile variation and following action of the stator for typical seal configurations.
• SUBSTITUTE SHEET stator to lift off and form a converging gap and generate enough hydrodynamic stiffness to prevent the stator seal face from contacting the rotating mating rotor seal face.
• E Modulus of Elasticity
• I Moment of Inertia
• pressure profile and coning angle is dependent on groove type utilized.
• a non- pumping groove e.g. a rectangular, bi-directional groove
• a pumping groove e.g. uni-directional spiral grooves
• Hydrodynamic effects must also be considered in matching stator and mating rotor properties and flexibility in order to optimize seal coning angle ( ⁇ ) and performance.
• a similar seal to that depicted in Figure 1 was fabricated and tested.
• the mating rotor used in this seal is depicted in Figure 6a.
• the seal had a mating rotor seal face outside diameter of approximately 5.8 inches and a seal face inside diameter of approximately 4.3 inches.
• the minimum thickness of the radially extending sealing face i.e. the thickness of the mating rotor seal face
• Tj The minimum thickness of the radially extending sealing face
• Tj was approximately 1.21 inches thick and the annulus was approximately 0.32 inches thick.
• the total length of the annular element (i.e. annulus lengih), L was approximately 1.6 inches.
• the mating rotor material was stainless steel.
• Shallow spiral grooves were introduced into the mating rotor seal face to provide a hydrodynamic fluid flow component.
• the stator had similar inside and outside dimensions and was approximately 0.380 inches thick.
• the stator material was carbon graphite.
• the stator used in each of these examples was the same as the stator used in Example I.
• the mating rotor of Examples ⁇ to IV were modified by machining away pieces of the mating rotor of Example I (i.e. the mating rotor became progressively smaller and more flexible as pieces were machined away).
• the mating rotor of examples V to VH were also modified by machining away pieces from another mating rotor similar to the one used in Example I.
• the interior lines shown in Figure 6B which enclose the numerals ⁇ to IV indicate the pieces of the mating rotor which were successively machined away for examples II to IV respectively.
• the interior lines shown in Figure 6C indicate the pieces of the mating rotor which were successively machined away for examples V to VII. (Note: one rotor was used for examples I to IV and a different rotor was used for examples V to VII. Both rotors started with the same geometry as the rotor for example I.)

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Sealing Using Fluids, Sealing Without Contact, And Removal Of Oil (AREA)
• Sealing Devices (AREA)

Applications Claiming Priority (4)

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• 1993
  • 1993-07-09 CA CA002100230A patent/CA2100230C/en not_active Expired - Lifetime
• 1994
  • 1994-07-07 AU AU72247/94A patent/AU675154B2/en not_active Ceased
  • 1994-07-07 WO PCT/CA1994/000382 patent/WO1995002137A1/en not_active Ceased
  • 1994-07-07 EP EP94921560A patent/EP0664860A1/de not_active Withdrawn

Non-Patent Citations (1)

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