SEAL TESTING APPARATUS

Abstract: A mechanical seal testing mechanism having a rotary shaft assembly (16) about which a series of seal assemblies are arranged for simulated testing. The eccentricity of the shaft assembly may be varied while the tester is operating by a fluidically responsive control mechanism (92) such that varying simulated conditions may be imparted to the seal assemblies being tested.

Description: This invention relates to a mechanism for testing mechanical seal assemblies under various, simulated operation conditions and especially to an apparatus for testing seal assemblies under various shaft misalignment conditions. A typical centrifugal pump includes a motor driven shaft which penetrates the pump housing DE-A-2 130 474. The shaft is sealed to the housing by a mechanical seal assembly and is supported by either a hydrostatic or other suitable bearing means. During pump operation, the unbalanced radial load at the pump impeller, an inherent characteristic of centrifugal pumps, causes the shaft to shift and/or bend. The shaft may also be displaced in the vertical direction (axial) during operation due to shaft end thrust (pressure loading) and thermal expansion. The magnitude and rate of shaft displacement and/or bending are dependent upon system operating conditions, such as operating temperature, pressure, and pump flow rate. Maximum radial displacement or offset of the shaft occurs close to the position of the seal elements of the seal assembly and affects the performance thereof. It is well understood that mechanical seal assemblies for use in nuclear and/or toxic fluid assemblies must meet higher standards of durability and "forgiveness" than mechanical seal assemblies used in less exotic applications. It is, therefore, desirable to test a seal assembly for a nuclear reactor pump under simulated conditions rather than in an actual application. In this manner, the manufacturer can readily determine whether the seal assembly is durable for its intended use. The document "Soviet Invention Illustrated Journal" week C50, January 28, 1981, Dervent Publications Ltd. discloses a seal testing apparatus comprising a generally cylindrical, hollow main shaft and means to support and rotate said main shaft. In this seal testing apparatus the means to support and rotate the main shaft includes a stationary head which is adjustable in an axial direction and furthermore is pivotal about an axis aligned with the contact plane of the mechanical seal to be tested. This allows to simulate working conditions including non-alignment and end play. However, the prior art seal testing apparatus does not allow to simulate orbital movements of the main shaft. The primary object of the present invention is the provision of a seal testing apparatus in which a seal assembly may be subjected to simulated changes in shaft position and orbits, to permit an analysis of whether the seal is durable for its intended use. To this end, a seal testing apparatus comprising a generally cylindrical, hollow main shaft and means to support and rotate said main shaft, according to the present invention, is characterized by: a stub shaft connecting said main shaft and said means to support and rotate said main shaft; said stub shaft having a first portion eccentric with respect to a second portion; means rotatably supporting said first portion and generally cylindrical means rotatably supporting said second portion, said means rotatably supporting said second portion being connected to said main shaft and having a bore in which said second portion is located, said bore being eccentric to said main shaft; a control piston received in said main shaft for axial movement only with respect to said main shaft; said control piston having internal helical teeth; a control gear in said control piston having external helical teeth meshing with said internal helical teeth; means for moving said control piston axially in said main shaft and thereby causing said control gear to rotate the said main shaft relative to said stub shaft and said means rotatably supporting said second portion thereof thus changing the eccentric relationship between the main shaft and the stub shaft. Amongst its many features, the testing apparatus of this invention simulates field operating conditions and comprises a unique and specially engineered shaft assembly having a series of seal assemblies arranged thereon. The specially engineered shaft allows the test operator to vary the operative rotary path of the shaft assembly. That is, the shaft assembly may be controlled to rotate or turn with little or no eccentricity or, alternatively, can be made to eccentrically rotate in an orbit to simulate the radial displacement or offset of a pump shaft caused by an unbalanced radial load as discussed above. In this manner, and in a test environment, the operator can analyze the seal assembly reaction to such simulated conditions. The shaft assembly is rotatably supported in a stationary frame of the seal testing apparatus. The unique shaft assembly comprises an extended hollow shaft having a bearing or support assembly provided at the free ends thereof and a control mechanism for affecting the rotary path of the shaft. Each bearing or support assembly includes an apertured support member secured to the free end of the shaft and a stub shaft assembly rotatably mounted to said frame. Each stub shaft has a first shaft portion which is received in a support bearing of the frame assembly and a second shaft portion which is eccentrically arranged with respect to the first shaft portion. The eccentric shaft portion of each stub shaft assembly is accommodated in the aperture or bore provided in the support member. The aperture or bore in the support member is eccentrically arranged relative to the longitudinal axis of the extended shaft. One or both of the stub shaft assemblies may be connected to a motor for operably driving the shaft assembly. An operator influenced control mechanism is further provided for controlling the magnitude of shaft displacement. Intermediate the ends of the shaft assembly, an equal series of seal assemblies with their rotating parts to be tested are mounted to the outside diameter of the main shaft. In addition to controlling the operative effect or rotary path of the shaft assembly, the control mechanism operably couples the extended hollow shaft to the rotatably driven stub shaft assembly. To effect these ends, the control mechanism includes at least one annular piston which is carried within an enclosed space on said shaft and is constrained to move between an initial or minimum position and an extended or maximum position. A first spline connection is provided between the piston and the extended shaft while a second spline connection is established between the piston and a control gear fixed to the driven stub shaft. As the control piston is axially moved, it entails relative angular displacement of the eccentric bore in the support member relative to the eccentric portion of the associated stub shaft. As the control piston causes the above mentioned relative rotation, the operative or total eccentricity of the extended shaft with respect to the stub shaft varies from zero to a maximum value equal to the vector sum of the eccentricity of the support member and the stub shafts. Hereinafter the invention is described by way of example with reference to the following drawings : FIGURE 1 is a side elevational view of a mechanical seal testing apparatus in which the shaft assembly of the present invention is used; FIGURE 2 is a longitudinal cross-sectional view taken along line 2-2 of FIGURE 1; FIGURE 3 is a cross-sectional view of the apparatus of FIGURE 1 taken along line 3-3 of FIGURE 1; FIGURE 4 is a view, partly in cross-section, of the shaft assembly of this invention; FIGURE 5 is an enlarged view, partly in cross-section, of a portion of the shaft assembly of FIGURE 4; and FIGURE 6 is a cross-sectional view taken along line 6-6 of FIGURE 5. Referring now to the drawings, wherein line reference numerals indicate like parts throughout the several views, the present invention is schematically illustrated in combination with a mechanical seal testing apparatus 10. It will be appreciated, however, that the apparatus of the present invention has a wide suitable application in imparting orbital motion to a rotary shaft. The testing apparatus 10 includes a support frame 12, a test cylinder 14 within the frame 12 and through which the shaft assembly 16 of this invention passes, a motor 18 for rotating the shaft assembly and a swivel 20. In the illustrated embodiment, the swivel 20 is connected to one end of the shaft assembly 16 and to a source 22 of pressurized hydraulic fluid. An operator actuated control valve 24 is arranged between the source of fluid 22 and the swivel 20. The test cylinder 14 is supported by ball bushings 26 shown in FIGURE 2, supported on spaced horizontal trunnions 28. A mechanism 30 allows the test cylinder 14 to be tilted to test the schematically illustrated mechanical seal assemblies 32 and 34, disposed within the cylinder 14, under varying conditions. While the supporting trunnions, ball bushings, and tilting mechanism permit various simulated conditions to be imparted to the tested seals, they are not part of the invention to be described herein and are illustrated and referred to for describing the environment in which the present invention finds utility. The rotary shaft assembly 16 of this invention is particularly illustrated in FIGURES 4, 5 an 6 of the drawings. The shaft assembly 16 includes an extended shaft 38 having a pair of shaft support assemblies 47 and 49 disposed at opposite ends thereof for mounting the shaft assembly to the frame assembly of the apparatus. The extended shaft 38 has a longitudinal axis 39 and is provided with an outside or exterior cylindrical surface 40 and an internal or axial bore 42 extending the length thereof. As best illustrated in FIGURES 4 and 5, the internal bore 42 opens to an enlarged cylindrical and axially arranged cavity or chamber 44 provided at one end of the shaft 38. In the illustrated embodiment, at least a portion of the cavity 44 is provided with internal gear teeth 46. As was mentioned above, a primary object of this invention is the provision of a tester assembly which may subject mechanical seals to simulated changes in shaft positions and/or orbits. To this end, the shaft support assemblies 47 and 49 combine with a new and unique control mechanism 92 in order that the orbital or rotary path of the shaft 38 may be varied at the will of the operator to subject the seal assemblies 32 and 34 (FIGURE 2) mounted about the shaft 38 to simulated field conditions. As will be described in detail hereinafter, each of the shaft support assemblies includes a variable eccentric mechanism which, in combination with the control mechanism 92, imparts the desired degree or magnitude of orbital motion to the shaft 38. The control mechanism 92 is effective to adjust the operative effect of the variable eccentric mechanisms whereby achieving the functional equivalent of having to continually replace a multitude of fixed throw eccentrics normally used for imparting various orbital motions to a shaft. For purposes of this description, suffice it to say, the operative radius or eccentricity of the variable eccentric mechanism is that which, in a device utilizing fixed throw eccentrics, would normally be effective to impart the observed magnitude of eccentric rotary or orbital movement to the shaft 38. Furthermore, while the shaft 38 is turning, the control mechanism 92 is capable of effecting a smooth and rapid change in the operative effect said variable eccentric mechanism will have regarding the orbital path traversed by the rotating shaft 38. Thus, unnecessary interruptions in testing the seal assemblies under various shaft misalignment conditions are eliminated. Each of the shaft support assemblies 47 and 49 includes a bearing carrier, a stub shaft, and means for rotatably supporting each shaft supporting assembly relative to the frame. Specifically, the upper shaft support assembly 47 includes a generally cylindrical carrier 48 which is affixed to one end of the shaft 38. The other and lower bearing support 49 is also provided with a generally cylindrical carrier 50 which is affixed to the opposite end of the shaft 38. To reduce unbalanced forces, the outside diameters of the carriers 48 and 50 are machined to be concentric with the cylindrical outer surface of the shaft 38. Each of the carriers 48 and 50, is provided with a bore 52 and 54, respectively, which is eccentrically arranged relative to the longitudinal axis 39 of the shaft 38. In the preferred embodiment, the eccentricities of the bores 52 and 54 relative to the longitudinal axis of the shaft are substantially similar. It will be appreciated, however, that the eccentricities of the bores relative to the longitudinal axis of the shaft may be different if a different result is desired. As mentioned, each shaft support assembly further includes a stub shaft. In the illustrated embodiment, the first or upper stub shaft 56 is driven by the motor 18 (FIGURE 1). The stub shaft 56 is rotatably supported in spaced bearings 58, 60 carried in the eccentric bore 52 of the bearing carrier 48. The stub shaft 56 is divided into first, second and third shaft sections 62, 64, and 74, respectively. The first shat section or portion 62 of the stub shaft 56 is accommodated for rotation within the carier 48 and is eccentrically arranged relative to the second shaft portion 64. The second portion 64 is rotatably supported in a shaft assembly thrust bearing 66 housed in a vertical height adjustment mechanism 68 (FIGURES 1 and 2) which is supported by the support frame 12 of the apparatus. The third section 74 is a depending coaxial extension of shaft portion 64 and extends into the bore 42 of the shaft 38 for reasons hereinafter described. A second and lower stub shaft 70 is provided as part of the other shaft support assembly 49. Like stub shaft 56, this second stub shaft 70 is provided with first, second, and third shaft sections or portions 86, 84, and 76, respectively. The first and second stub shafts 56 and 70 may be operably connected such that shaft eccentricity will be adjusted equally end to end. To connect the stub shafts, the extended portions 76 and 74 of the stub shafts 56 and 70 are pinned or otherwise connected as at 72. The lower stub shaft 70 is rotatably mounted in spaced bearings 78 and 80 carried in the eccentric aperture 54 of the lower bearing carrier 50 and is rotatably supported by the bearing portion 86 which is received in a radial bearing 82 fixed to the support framework 12 (FIGURE 2) of the apparatus. The shaft portion 84 of the lower stub shaft 70, arranged between bearings 78 and 80, is formed eccentric to the other portions 76 and 86 of the stub shaft 70. Moreover, the lower stub shaft is provided with a bore 88 which axially extends therethrough. The bore 88 permits the cavity 44 in the main shaft 38 to be in fluidic communication with the swivel 20 (FIGURE 2) which, in the preferred embodiment, is fixed to the lower end of the shaft 38. In the preferred embodiment, the eccentricity of the stub shaft portions 62 and 84 are substantially similar. It will be appreciated, however, that the eccentricity of these elements can be different if a different effect is desired. Moreover, the magnitude of the eccentricity of the stub shaft portions 62 and 64 is substantially equal to that of the bores 52 and 54 relative to the longitudinal axis 39 of the extended shaft 38. As mentioned above, the orbital path of travel of the shaft assembly 16 is controlled by a mechanism 92, now to be described. The control mechanism serves a dual purpose: first, it controls the orbital path of the rotating shaft assembly; and, second, it operably couples the extended shaft 38 to the driven stub shaft. In the presently preferred embodiment, the control mechanism 92 includes an annular fluidically responsive piston 94 which axially moves in the channel 44 between an initial position and an extended position. A fist spline connection is established between an outer grooved or toothed surface 96 provided on the piston 94 and a complimentary toothed surface 46 provided in the chamber 44. As best illustrated in FIGURE 6, a second spline connection is established between an inner grooved or toothed surface 98 of the piston and the outer toothed surface 100 of control gear 102. The control gear 102 is affixed or keyed to the extended section 74 of the stub shaft 56. In order for the shaft assembly to function in the manner hereinafter described, at least one of the above mentioned spline connections is required to be helicoidal. The interior of the piston 94 is provided with helical gear teeth 98 which engage and mesh with the exterior helical gear teeth 100 of the control gear 102. Because the shaft support assemblies 47 and 49 are interconnected, a common control mechanism, such as 92, imparts equal degrees of eccentircity to both ends of the shaft assembly 16. The provision of two separate control mechanisms for allowing separate control of each shaft support assembly, however, is within the intended scope of this invention. If two control mechanisms were provided, the operative eccentricity of each end of the shaft 38 could be regulated independently. Moreover, using direct mechanical rather than hydraulic force, for controlling the disposition of the control mechanism is within the spirit of the present invention. As best illustrated in FIGURE 2, two seal cartridges with the same set of mechanical seals, such as previously identified seals 32 and 34, are tested at one time. The seals are preferably placed back-to-back in the seal tester to avoid producing high axial thrusts. Each seal assembly is assembled about the outside diameter of the shaft assembly 16 and is retained by a clamp 104 or 106 bolted to the end of the test cylinder 14. An exemplary operative sequence of the present invention will now be described. The stub shaft connected to motor 18, through the control gear 102, rotatably drives the extended shaft 38 about its longitudinal axis. When the control piston 94 is disposed in its initial position, the shaft assembly 16 will be rotated about an axis which is coincident with the longitudinal axis 39 of shaft 38 such that a minimum circumferential rotary path of travel for the extended shaft 38 is achieved or effected. On the other hand, when the control piston 94 is disposed in its extended position, the shaft assembly 16 will move in an eccentric or orbital path having a maximum circumferential rotary path of travel for the extended shaft 38. Absent axial movment of piston 94, the eccentric relationship between the eccentric elements comprising the shaft support assemblies 47 and 49 remains the same for all rotational speeds of the shaft assembly 16. Axial movement, however, of the piston 94 effects a modification of the eccentric relationship between such elements and thereby modifies the operative effect the shaft support assemblies have on the rotational path of shaft 38. Axial movement of the piston is effected by the operator adjusting the pressure in cavity 44. As the piston 94 is forcibly moved under hydraulic pressure, introduced to the chamber 44 through the swivel 20 and interconnecting passageway 88, the piston 94 cannot rotate with respect to the shaft 38 because of the spline connection therebetween. Since the piston 94 cannot rotate with respect to the shaft, the helical control gear 102 must rotate if the piston 94 is to move. Rotation of the helical control gear will likewise affect rotation of the stub shaft with its eccentric crank portion and, thus, cause a modification or change in the eccentric reltionship between eccentric crank portions 62 and 84 of stub shafts 56 and 70, respectively, and the eccentric bores 52 and 54 of the bearing carriers 48 and 50 mounted on the extended shaft 38. Such a change in the mounting structure for the shaft has an effect on the orbital path of the shaft assembly. When hydraulic forces are removed from the piston, for whatever reason, the frictional torque characteristics of the seal assemblies cause the control mechanism 92 to return to its initial position whereat the shaft assembly turns concentrically about the longitudinal axis 39 of the shaft 38. That is, frictional torque applied to the outside diameter 40 of the shaft 38 is converted to an axial force on the piston by the inclined helical teeth on the control gear 102. When hydraulic forces are removed from the piston, this axial force is sufficient to forcibly return the piston to its initial position. As a skilled artisan will appreciate, the total eccentricity of the shaft 38 with respect to the stub shaft 56, 70 is the vector sum of the stub shafts' eccentricity and the carrier's eccentricity. As the eccentric relationship between the stub shafts' eccentric portions 62, 84 and the eccentric bores 52, 54 changes, the vector sum changes, causing the total eccentricity of the shaft 38 relative to the stub shaft 56, 72 to vary from zero to a maximum value over the total axial travel of the piston 94. Thus, there has been provided a seal testing apparatus which fully satisfies the objects, aims and advantages set forth above. While the invention has been described in connection with a specific embodiment thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the appended claims.

Claims: A seal testing apparatus comprising a generally cylindrical, hollow main shaft (16) and means to support and rotate (12, 18) said main shaft; characterized by: a stub shaft (56) connecting said main shaft and said means to support and rotate said main shaft; said stub shaft having a first portion (64) eccentric with respect to a second portion (62); means (66) rotatably supporting said first (64) portion and generally cylindrical means (48) rotatably supporting said second portion (62), said means (48) rotatably supporting said second portion (62) being connected to said main shaft (16) and having a bore (52) in which said second portion (62) is located, said bore being eccentric to said main shaft; a control piston (94) received in said main shaft (16) for axial movement only with respect to said main shaft; said control piston having internal helical teeth (98); a control gear (102) in said control piston (94) having external helical teeth (100) meshing with said internal helical teeth (98) and means (22, 24) for moving said control piston (94) axially in said main shaft (16) and thereby causing said control gear (102) to rotate the said main shaft (16) relative to said stub shaft (56) and said means (48) rotatably supporting said second portion (62) thereof thus changing the eccentric relationship between the main shaft (16) and the stub shaft (56). A testing apparatus as claimed in claim 1, in which said main shaft (16) has a bore (44) with axially extending internal teeth (46) and said control piston (102) has external and axially extending teeth (96) meshing with said internal teeth. A testing apparatus as claimed in claim 1 or in claim 2, in which said means for moving said control piston (102) comprises a source of hydraulic fluid (22) and means (24) to control the flow of hydraulic fluid to said control piston. A testing apparatus as claimed in any of claims 1 to 3, in which said control gear (102) is connected to said stub shaft (56). A testing apparatus as claimed in any of claims 1 to 4, further comprising a second stub shaft (70) connected to said first-named stub shaft (56), said second stub shaft having at least a portion (76) received in said hollow main shaft. A testing apparatus as claimed in claim 5, in which said control piston (102) is received in an enlarged part of said hollow main shaft (16) which defines a piston cavity (44) and further comprising a passageway (88) in said second stub shaft (70) communicating at one end with said piston cavity (44) and at the other end with a source of hydraulic fluid (22), and means (24) for controlling the flow of hydraulic fluid to said piston cavity (44). A testing apparatus as claimed in claim 5 or claim 6, in which said second stub shaft (70) has a first portion (86) eccentric with respect to a second portion (84), and further comprising means (80) rotatably supporting said second stub shaft first portion (86) and generally cylindrical means (50) rotatably supporting the second portion (84) of said second stub shaft (70), said last-named (50) being connected to said main shaft (16) and having a bore (54) in which said second portion (84) of said stub shaft (70) is located, said last-named bore (54) being eccentric to said second stub shaft. A seal testing apparatus as claimed in claim 7, wherein said main shaft (16) is mounted for movement in a rotary path and has one more seal assemblies (32, 34) affixed about the outside diameter thereof, said generally cylindrical means comprise shaft bearing carriers (48, 50) provided at opposite ends of said main shaft (16); and said stub shafts (56, 70) are supported by a frame (12) of the testing apparatus. The seal testing apparatus according to claim 8, wherein the axial movement of said control piston (94) is controlled by fluid pressure. The seal testing apparatus according to claim 8 or 9 wherein said stub shafts (56, 70) are operably connected to each other such that axial sliding movement of said control piston (94) equally effects the eccentric relationship between the eccentric bore (52, 54) of said bearing carrier (48, 50) and the eccentric portion (62, 84) of said stub shaft (56, 70) simultaneously at both ends of said main shaft (16). The seal testing apparatus according to any of claims 8 to 10, wherein frictional torque characteristics are imparted to said main shaft (16) by said seal assemblies (32, 34) in a manner effecting the disposition of said control piston (94). The seal testing apparatus of any of claims 8 to 11, wherein said shaft bearing carriers (48, 50) each include a cylindrical body whose outside diameter is concentric with the outside diameter of said main shaft (16) but whose bore (52, 54) is arranged eccentric thereto. The seal testing apparatus of claim 10, wherein said control piston (94) is axially shiftable between initial and extended positions, the initial position of said control piston (94) operably effecting a minimum circumferential rotary path for said main shaft (16) with the extended position of said control piston (16) operably effecting a maximum circumferential rotary path for said main shaft (16).

Inventors: SMITH, MARTIN LESLIE
Applicants: BW/IP INTERNATIONAL, INC.
Application year: 1986
Main classification: G01M13
IPC codes: G01M3, G01M13, F16C3