The valve plug assembled by brazing process

Abstract

A valve plug assembly includes a plug base having a first end configured for attachment to a valve stem, a second end having a forward-facing base seat surface and a shaft portion projecting outwardly from the base seat surface along a longitudinal axis. A plug tip has a rearward-facing tip seat surface and a cavity having an opening defined in the tip seat surface. The cavity is configured to receive the shaft portion of the plug base therein, such that the base seat surface and the tip seat surface extend adjacent to each other. Filler metal is disposed between the base seat surface and the tip seat surface during a brazing process to secure the plug tip to the plug base.

Description

Technical Field

[0001] The present invention relates generally to control valves and, more particularly, to a valve plug having a tip mounted on the plug using a brazing process. Background Art

[0002] In many control valve applications, particularly those involving severe service conditions, the internal components of the control valve may be subject to three-phase flow, such as flashing, cavitation, and particles, all of which may cause severe erosion and / or vibration. Therefore, such valves are often provided with a valve plug having a corrosion-resistant plug tip, which may be a ceramic material such as carbide, tungsten carbide, or other suitable material.

[0003] When such valve components are structurally designed, the plug top can be attached to the plug base using a shrink fit process, in which the relevant components are heated, fitted, and then cooled. An example of this construction is shown in FIG2 . This shrink fit process may introduce tensile stress into the plug top, which can have a negative impact on the plug top, particularly when the plug top is formed of a brittle material. For smaller plug tops, the shrink fit process may also cause corner fractures to occur in the top. Alternatively, a brazing process can be used to attach the plug top to the plug base. In either process, it is possible that stress risers may be formed at the junction between the plug top and the base below. This stress concentration can and sometimes does promote premature failure of the plug top by promoting the formation and / or propagation of cracks in the plug top. Nevertheless, brazing processes can generally provide the most robust bonding method between tungsten carbide top and metal plug base.

[0004] In order to avoid introducing stress into the plug tip during the brazing process, it has been proposed to mechanically couple the plug tip to the plug base. However, for smaller valves and valve plugs, it may be difficult to form and manipulate the mechanical joint components. Summary of the Invention

[0005] According to a first exemplary aspect, a valve plug assembly for a control valve is disclosed, the control valve having a valve stem, a flow channel, and a valve seat disposed in the flow channel. The valve plug assembly includes a plug base defining a longitudinal axis and having a first end and a second end. The first end of the plug base is arranged to be attached to the valve stem of the control valve. The second end of the plug base has a base seat surface facing forward and an axis portion protruding outward from the base seat surface along the longitudinal axis. The valve plug assembly also includes a plug top, the plug top having a rearward-facing top seat surface and a cavity having an opening defined in the top seat surface, wherein the cavity is arranged to receive the axis portion of the plug base therein so that the base seat surface and the top seat surface extend adjacent to each other. Filler metal is disposed between the base seat surface and the top seat surface during a brazing process to secure the plug top to the plug base.

[0006] According to a second exemplary aspect, a method of forming a valve plug assembly for a control valve is disclosed, the control valve having a valve stem, a flow passage, and a valve seat disposed in the flow passage. The method includes providing a plug base defining a longitudinal axis and having a first end and a second end; arranging the first end of the plug base for attachment to the valve stem of the control valve; and providing the second end of the plug base, the second end of the plug base having a forward-facing base seat surface and a shaft portion projecting outwardly from the base seat surface along the longitudinal axis. The method includes providing a plug tip having a rearward-facing tip seat surface and a cavity having an opening defined in the tip seat surface; and arranging the plug tip so that the cavity receives the shaft portion of the plug base therein, such that the base seat surface and the tip seat surface extend adjacent to each other. The method also includes placing a filler metal between the base seat surface and the tip seat surface in a brazing process to secure the plug tip to the plug base.

[0007] Further according to the aforementioned first and / or second aspects, the valve plug assembly and / or method may further include any one or more of the following preferred manners.

[0008] According to a preferred embodiment, the plug top may include an annular rear portion, a frustoconical middle portion and a front convex portion. According to a further preferred embodiment, the cavity may extend within the annular rear portion and the frustoconical middle portion.

[0009] According to another preferred embodiment, the cavity may be designed to have a size that provides a gap in front of the shaft portion when the shaft portion is completely received in the cavity.

[0010] According to another preferred embodiment, the base seat surface and the top seat surface may be perpendicular to the longitudinal axis. According to a further preferred embodiment, the base seat surface and the top seat surface may provide all brazing surfaces for brazing process between the plug base and the plug top.

[0011] According to another preferred embodiment, the shaft portion may be cylindrical, and the cavity may have a complementary cylindrical side wall.

[0012] According to another preferred embodiment, the shaft portion can be centrally arranged on the plug base and the cavity can be centrally arranged in the plug top end, and the plug top end is arranged so that the cavity receives the shaft portion of the plug base therein, so that the plug top end is centered relative to the longitudinal axis.

[0013] According to another preferred embodiment, the plug tip may include carbide or tungsten carbide.

[0014] According to another preferred embodiment, the plug tip may be selected from ceramic materials.

[0015] According to another preferred embodiment, the diameter of the top end of the plug is about 60 mm or less.

[0016] According to another preferred embodiment, the diameter of the shaft portion and the diameter of the remaining portion of the plug base have a ratio of about 1:4. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above needs are at least partially met by providing the embodiments described in the following detailed description, particularly when studied in conjunction with the accompanying drawings, in which:

[0018] Figure 1 is a cross-sectional view of a control valve having a plug assembly assembled according to the teachings of the first disclosed example of the present invention.

[0019] FIG2 is an enlarged partial cross-sectional view of a conventional valve plug showing details of a conventional shrink-fit design.

[0020] FIG3 is a partial cross-sectional enlarged view of a conventional valve plug, showing details of a conventional brazing process design.

[0021] Figure 4 is an enlarged cross-sectional view of a valve plug assembled according to the teachings of an exemplary aspect of the present disclosure.

[0022] Figure 5 is a cross-sectional view of a compression load test configuration showing a conventional tungsten carbide tipped valve plug assembled by a brazing process and a Figure 4 The valve plug shown in the figure is assembled with a tungsten carbide tip.

[0023] Figure 6 It means from Figure 5 The cross-sectional view of the stress diagram showing the results of the compression load test is shown in FIG.

[0024] Figure 7 is a cross-sectional view of a first bending load test configuration showing a conventional tungsten carbide tipped valve plug assembled by a brazing process and a Figure 4 The valve plug shown in the figure is assembled with a tungsten carbide tip.

[0025] Figure 8 It shows the Figure 7 The results of the first bending load test are shown in the cross-sectional view of the stress diagram.

[0026] Figure 9 is a perspective view of a second bending load test configuration showing a conventional tungsten carbide tipped valve plug assembled by a brazing process and a Figure 4 The valve plug shown in the figure is assembled with a tungsten carbide tip.

[0027] Figure 10 It shows the Figure 9 The results of the second bending load test are shown in the cross-sectional view of the stress diagram.

[0028] Those skilled in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the size and / or relative positioning of some elements in the drawings may be exaggerated relative to other elements to help improve understanding of the various embodiments of the present invention. In addition, common but well-known elements that are useful or necessary in commercially feasible embodiments are generally not depicted to facilitate less obstructive observation of these various embodiments. It will be further understood that certain actions and / or steps can be described or depicted in a specific order of occurrence, and those skilled in the art will appreciate that this specificity about the order is not actually required. It will also be understood that, unless different specific meanings are set forth herein, the terms and expressions used herein have the common technical meanings given to these terms and expressions by those skilled in the art as set forth above. DETAILED DESCRIPTION

[0029] Although the following text sets forth a detailed description of one or more exemplary embodiments of the present invention, it should be understood that the legal scope of the present invention is defined by the text of the claims set forth at the end of this patent. Therefore, the following detailed description is to be construed as exemplary only and does not describe every possible embodiment of the present invention, as describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments may be implemented using current technology or technology developed after the filing date of this patent. It is contemplated that such alternative embodiments will still fall within the scope of the claims defining the present invention.

[0030] Referring now to the accompanying drawings, Figure 1 A valve plug assembly 10 is shown assembled in accordance with the teachings of an exemplary embodiment of the present invention for use with a control valve 12 having a valve stem 14, a flow passage 16, and a valve seat 18. As will be readily appreciated by those skilled in the art, the control valve 12 includes an inlet 15 and an outlet 17 connected by the flow passage 16. The valve plug assembly 10 is coupled to the valve stem 14 and is moved by any suitable actuator (not shown) between an open position, in which the valve plug assembly 10 is spaced from the valve seat 18, thereby permitting flow through the control valve 12, and a closed position, in which the valve plug assembly 10 is seated against the valve seat 18, thereby preventing flow through the control valve 12.

[0031] Now refer to Figure 4 , the plug assembly 10 includes a plug base 20 that defines a longitudinal axis L and has a first end 22 and a second end 24. The first end 22 of the plug base 20 is arranged for attachment to the valve stem 14 ( Figure 1 ). The second end 24 of the plug base 20 includes a shaft or plug portion 26 of cylindrical configuration having a smaller diameter than the remainder of the plug base 20. An annular base seat surface 28 extends radially around the shaft portion 26. The shaft portion 26 is preferably centrally located so that the seat surface 28 has a uniform radial thickness extending therearound. The diameter of the shaft portion 26 can be between about 10 percent and about 75 percent of the diameter of the plug base 20, preferably between about 15 percent and 50 percent of the diameter of the plug base 20, more preferably between about 20 percent and 30 percent of the diameter of the plug base 20, and more preferably about 25 percent of the diameter of the plug base 20.

[0032] The plug tip 50 for the valve plug assembly 10 includes a body 52 having a rearward-facing tip seating surface 54 that extends around an opening 56 into a hollow interior or cavity 58 extending along the longitudinal axis L. The cavity 58 preferably has a depth at least as long as the length of the shaft portion 26 of the plug base 20. Furthermore, in some approaches, the depth of the cavity 58 can be sized such that when the shaft portion 26 is fully received therein, there is a gap with the seating surfaces 28, 54 abutting one another. In preferred approaches, the seating surfaces 28, 54 are generally perpendicular to the longitudinal axis L. Furthermore, a sidewall 60 extending around the cavity 58 preferably has a cross-section that is substantially complementary to the cross-section of the shaft portion 26, such as a substantially cylindrical sidewall 60 extending around the cylindrical shaft portion 26. With this configuration, the plug tip 50 advantageously uses less material due to the hollow interior 58 while protecting the plug assembly 10 in areas where it is needed. Furthermore, the plug base 20 and its shaft portion 26 may be made of a relatively soft material compared to the plug tip 50 , and with this configuration, the shaft portion 34 may absorb impact energy from the plug tip 50 .

[0033] The body 52 of the plug tip 50 includes an annular rear portion 62, a frustoconical middle portion 64, and a convex front portion 66. Thus, the cavity 58 extends within the rear portion 62 and the middle portion 64, wherein the front portion 66 has a solid cross-section. The front portion 66 can have a circular cylindrical structure, as shown. In a preferred form, the annular rear portion 62 has a diameter that is approximately equal to the diameter of the plug base 20, so that the cylindrical side surface 68 of the plug tip 50 is approximately aligned with the cylindrical side surface 70 of the plug base 20. Alternatively, the diameter of the annular rear portion 62 can be within 0 to about 20 mm of the diameter of the plug base 20. As shown in FIG. Figure 1 As shown in FIG, the inclined surface 72 of the frustoconical middle portion 64 of the plug tip 50 is configured to engage the valve seat 18 when in the closed configuration, wherein the front portion 66 protrudes toward the valve outlet 17. By a preferred method, the plug tip 50 can be a tungsten carbide or carbide tip, which can be formed by a sintering process. By another preferred method, the plug tip 50 can be selected from a ceramic material.

[0034] like Figure 4, the seat surfaces 28, 54 provide brazing surfaces during the brazing process and define a joint area 74 for bonding the plug tip 50 to the plug base 20. During the brazing process, which can be performed, for example, in an induction furnace, the plug tip 50 is bonded to the plug base 20 by melting a filler metal 76 and flowing it into the joint area 74. The filler metal 76 has a lower melting point than the metals of the plug base 20 and plug tip 50, so that the metals of the plug base 20 and plug tip 50 do not melt during the process. In some examples, the filler metal 76 can be silver or copper, depending on the intended application. Advantageously, the seat surfaces 28, 54 provide flat, horizontal surfaces of sufficient size for a successful brazing process, while also avoiding or minimizing vertical surface brazing, which could introduce adverse stresses into the plug tip 50. In contrast, as shown in FIG3 , conventional brazing processes for plug tips include relatively small horizontal and vertical brazing surfaces along the plug portion of the valve tip.

[0035] In order to Figure 4 The performance of the plug assembly 10 constructed as shown in FIG and described herein was compared with the performance of a conventional plug assembly constructed as shown in FIG3 , and finite element analysis (FEA) simulations were performed on each sample. Figure 5-10 Each load test is described in turn.

[0036] like Figure 5 As shown in FIG, the first load mode applies a vertical downward compressive force on the top surface of each valve plug structure, simulating a valve closed state, and provides a fixed support on the bottom surface of each valve plug structure, simulating a valve seat ring.

[0037] like Figure 6 As shown in the stress diagram in , in a conventional plug assembly, there is a high stress area that extends across the entire plug area and has a high risk of corner shear or tensile stress in the corner of the plug between the brazing surfaces. The corner shear / tensile stress in this area may cause cracks through the relatively brittle tungsten carbide tip. In contrast, the high stress area of the plug assembly 10 of the present disclosure is arranged along the horizontal brazing surface, which is compressive stress. In addition, due to the hollow interior 56, the stress area does not extend across the entire cross-section of the plug tip 50. Therefore, the construction of the plug assembly 10 described herein avoids the shear / tensile stress on the bonding area between the tip and the support structure of the plug base as in conventional assemblies.

[0038] like Figure 7 As shown in , the second load mode fixes the top surface of each valve plug configuration and applies a first horizontal bending force to the plug tip. Figure 9 As shown in FIG, the third load mode fixes the upper portion of each valve plug base and applies a second horizontal bending force to the valve plug base. Figure 7A plug tip of the same construction as shown in FIG.

[0039] as from Figure 8 and Figure 10 As shown in the stress graph of the bending test of FIG, there is no shear / tensile stress around the junction between the plug top and the plug base in the plug assembly 10 described herein. In addition, the plug assembly 10 also eliminates the corner stress of the traditional plug assembly.

[0040] These tests demonstrate that the plug assembly 10 provided herein does not have stress distribution throughout its structure. Therefore, if failure occurs, the plug tip 50 will tend to avoid breaking into pieces. This is advantageous because the plug tip could affect the operation of the entire process system.

[0041] When the structural design is completed, the valve plug assembly assembled according to the exemplary teachings outlined herein can provide one or more technical advantages that cannot be achieved by prior art teachings. The valve plug assembly is particularly suitable for abrasive and corrosive environments, such as coal chemical degassing processes.

[0042] When compared to prior art structures and assemblies, the plug tip described herein provides a more secure connection to the plug base using a brazing process while also resulting in reduced fracture failures around the connection surface, even accounting for thermal stresses introduced during the brazing process.

[0043] When compared to prior art structures and assemblies, the plug tip can further reduce the amount of material required and the associated costs compared to conventional plug tips of similar dimensions. More specifically, the plug tip has an inverted configuration of the inner cavity. Due to the inverted configuration, the plug tip also has a generally uniform thickness, thereby avoiding uneven shrinkage that may be caused by the sintering process.

[0044] When compared to prior art structures and assemblies, one or more aspects of the present invention hinder the development of deleterious and difficult to control internal stresses resulting from previous constructions, such as may be found during shrink-fitting.

[0045] When compared to prior art structures and assemblies, one or more aspects of the present invention result in an assembly that provides improved performance and life over a wider temperature range, which provides advantages over prior art brazed assembly structures and methods. This is particularly true for smaller valve plug sizes, such as those having a diameter of approximately 60 mm or less, due to the difficulty in providing a mechanical bond between relatively small components.

[0046] It will be appreciated that the brazed structures and methods described herein may be used in other components or areas subject to corrosion, where protection from abrasive and / or corrosive conditions may help extend the useful life of, for example, valve seats, cages, and the like.

[0047] While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes can be made in the methods and apparatus disclosed herein without departing from the scope of the invention.

Claims

1. A valve plug assembly for a control valve, the control valve having a valve stem, a flow passage, and a valve seat disposed in the flow passage, the valve plug assembly comprising: a plug base defining a longitudinal axis and having a first end and a second end; The first end of the plug base is arranged for attachment to a valve stem of the control valve; the second end portion of the plug base having a forwardly facing base seating surface and a shaft portion projecting outwardly from the base seating surface along the longitudinal axis; a plug tip having a rearwardly facing tip seating surface and a cavity having an opening defined in the tip seating surface, the cavity being arranged to receive the shaft portion of the plug base therein such that the base seating surface and the tip seating surface extend adjacent one another; as well as a filler metal disposed between the base seating surface and the tip seating surface during a brazing process to secure the plug tip to the plug base, wherein The base seating surface and the top end seating surface provide flat, horizontal surfaces of sufficient size to avoid or minimize vertical surface brazing.

2. The valve plug assembly according to claim 1, wherein The plug top includes an annular rear portion, a frustoconical middle portion and a front convex portion.

3. The valve plug assembly according to claim 2, wherein: The cavity extends within the annular rear portion and the frustoconical middle portion.

4. The valve plug assembly according to claim 1, wherein: The cavity is sized to have clearance in front of the shaft portion when the shaft portion is fully received in the cavity.

5. The valve plug assembly according to claim 1, wherein: The base seating surface and the top end seating surface are perpendicular to the longitudinal axis.

6. The valve plug assembly according to claim 5, wherein: The base seating surface and the tip seating surface provide all of the brazing surfaces between the plug base and the plug tip for the brazing process.

7. The valve plug assembly according to claim 1, wherein: The shaft portion is cylindrical and the cavity has complementary cylindrical sidewalls.

8. The valve plug assembly according to claim 1, wherein: The shaft portion is centrally disposed on the plug base, and the cavity is centrally disposed within the plug tip.

9. The valve plug assembly according to claim 1, wherein: The plug tip comprises carbide or tungsten carbide.

10. The valve plug assembly according to claim 1, wherein The plug tip is selected from ceramic materials.

11. The valve plug assembly according to claim 1, wherein: The diameter of the plug tip is about 60 mm or less.

12. The valve plug assembly according to claim 1, wherein The diameter of the shaft portion and the diameter of the remainder of the plug base have a ratio of approximately 1:

4.

13. A method of forming a valve plug assembly for a control valve having a valve stem, a flow passage, and a valve seat disposed in the flow passage, the method comprising: providing a plug base defining a longitudinal axis and having a first end and a second end; arranging a first end portion of the plug base for attachment to a valve stem of the control valve; providing a second end portion of the plug base, the second end portion of the plug base having a forwardly facing base seat surface and a shaft portion projecting outwardly from the base seat surface along the longitudinal axis; providing a plug tip having a rearwardly facing tip seating surface and a cavity having an opening defined in the tip seating surface; arranging the plug tip such that the cavity receives the shaft portion of the plug base therein such that the base seating surface and the tip seating surface extend adjacent one another; as well as Filler metal is disposed between the base seating surface and the tip seating surface in a brazing process to secure the plug tip to the plug base, wherein The base seating surface and the top end seating surface provide flat, horizontal surfaces of sufficient size to avoid or minimize vertical surface brazing.

14. The method according to claim 13, wherein Providing the plug tip includes providing a plug tip including an annular rear portion, a frustoconical middle portion, and a front convex portion.

15. The method according to claim 14, wherein Providing the plug tip includes providing a plug tip wherein the cavity extends within the annular rear portion and the frustoconical mid-portion.

16. The method according to claim 13, wherein: Providing the plug tip includes providing the plug tip wherein the cavity is sized to have a clearance in front of the shaft portion with the shaft portion fully received in the cavity.

17. The method according to claim 13, wherein: Providing the plug base includes providing a plug base having the base seating surface extending perpendicular to the longitudinal axis, and providing the plug tip includes providing a plug tip having the tip seating surface extending perpendicular to the longitudinal axis.

18. The method according to claim 17, wherein Disposing the filler metal between the base seating surface and the top end seating surface includes limiting brazing surfaces for a brazing process to the base seating surface and the top end seating surface.

19. The method according to claim 13, wherein Providing the plug base includes providing a cylindrical shaft portion projecting outwardly from the base seating surface along the longitudinal axis; and providing the plug top end includes providing a cavity having a cylindrical sidewall complementary to the cylindrical shaft portion.

20. The method according to claim 13, wherein Arranging the plug tip so that the cavity receives the shaft portion of the plug base therein includes centering the plug tip relative to the longitudinal axis.

21. The method of claim 13, further comprising forming the plug tip from carbide or tungsten carbide.

22. The method of claim 13, further comprising selecting the plug tip from a ceramic material.

23. The method according to claim 13, wherein Providing the plug tip includes providing a plug tip having a diameter of about 60 mm or less.

24. The method according to claim 13, wherein Providing the second end of the plug base includes providing the second end of the plug base having a shaft portion having a diameter having a ratio of approximately 1:4 to a diameter of a remainder of the plug base.

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