METHOD FOR MANUFACTURING A VALVE

Abstract

A method for manufacturing a valve may include welding two components to each other via a combined induction/friction welding process. One of the two components may be a valve head and the other of the two components may be a valve stem.

Claims

1. A method for manufacturing a valve comprising welding two components to each other via a combined induction/friction welding process, wherein one of the two components is a valve head and the other of the two components is a valve stem.

2. The method according to claim 1, wherein welding the two components to each other via the combined induction/friction welding process includes: arranging an induction heating system between opposing parallel surfaces of the two components; heating the opposing surfaces of the two components via the induction heating system to a first temperature above a recrystallisation point of the two components in a non-oxidising atmosphere; continually moving at least one component of the two components relative to the other component parallelly to the opposing surfaces of the two components; welding the opposing surfaces of the two components via bringing together the opposing surfaces of the two components with an axial force while the at least one component is continually moving such that at least approximately 90% of a welding energy is contributed via the induction heating system and an equalisation welding energy is contributed via conventional friction welding, and wherein a total length loss of the two components is less than 1.0 axial millimetre per millimetre of wall thickness of the two components.

3. The method according to claim 2, wherein heating the opposing surfaces of the two components includes heating the opposing surfaces of the two components to the first temperature in less than approximately 30 seconds.

4. The method according to claim 2, wherein welding the opposing surfaces of the two components includes i) welding the opposing surfaces of the two components together in approximately one second after heating the opposing surfaces of the two components, and ii) maintaining the axial force for approximately five seconds thereafter.

5. The method according to claim 4, further comprising rotating at least one of the two components, and wherein welding the opposing surfaces of the two components includes welding the opposing surfaces of the two components together in less than approximately four revolutions of the at least one rotating component after heating the opposing surfaces of the two components and maintaining the axial force until a temperature of the opposing surfaces of the two components is below the first temperature.

6. The method according to claim 2, wherein heating the opposing surfaces of the two components includes induction heating the opposing surfaces of the two components to the first temperature in less than approximately ten seconds.

7. The method according to claim 2, wherein heating the opposing surfaces of the two components includes heating the opposing surfaces of the two components via the induction heating system at a frequency of approximately 10 kiloHertz or more.

8. The method according to claim 2, further comprising passing a non-oxidising gas over the opposing surfaces of the two components while heating the opposing surfaces of the two components to the first temperature via the induction heating system.

9. The method according to claim 2, further comprising holding the opposing surfaces of the two components substantially in a vacuum.

10. The method according to claim 9, wherein heating the opposing surfaces of the two components includes heating the opposing surfaces of the two components to the first temperature while holding the opposing surfaces of the two components substantially in the vacuum via the induction heating system.

11. The method according to claim 2, further comprising pre-coating the opposing surfaces of the two components with less than 0.025 mm of a metallurgically compatible material while heating the opposing surfaces of the two components to the first temperature via the induction heating system.

12. The method according to claim 2, wherein continually moving the at least one component includes continually moving the at least one component in a rotary movement.

13. A valve comprising at least two metal components welded together via a combined induction/friction welding process, wherein one of the at least two components is structured as a valve stem and the other of the at least two components is structured as a valve head.

14. The method according to claim 2, wherein: heating the opposing surfaces of the two components includes heating the opposing surfaces of the two components to the first temperature in less than approximately 30 seconds; and welding the opposing surfaces of the two components includes: welding the opposing surfaces of the two components together in approximately one second after heating the opposing surfaces of the two components; and maintaining the axial force for approximately five seconds after welding the opposing surfaces of the two components.

15. The method according to claim 2, wherein the heating the opposing surfaces of the two components includes heating the opposing surfaces of the two components via the induction heating system at a frequency of approximately 3 kiloHertz or more.

16. The method according to claim 15, wherein the heating the opposing surfaces of the two components includes heating the opposing surfaces of the two components via the induction heating system at a frequency of approximately 25 kiloHertz or more.

17. The method according to claim 8, wherein passing a non-oxidising gas over the opposing surfaces of the two components includes passing a non-oxidising gas including nitrogen gas over the opposing surfaces of the two components.

18. The method according to claim 11, wherein pre-coating the opposing surfaces of the two components includes pre-coating the opposing surfaces of the two components with less than 0.025 mm of pure aluminum, wherein the two components have iron based compositions.

19. The method according to claim 12, wherein welding the opposing surfaces of the two components includes welding the opposing surfaces of the two components together in less than approximately four revolutions of the at least one rotating component after heating the opposing surfaces of the two components and maintaining the axial force until a temperature of the opposing surfaces of the two components is below the first temperature.

20. A method of manufacturing a valve comprising: arranging an induction heating system between opposing parallel surfaces of two components, wherein one of the components is a hollow valve head and the other of the two components is a hollow valve stem; producing approximately 90% or more of a welding energy via heating the opposing surfaces of the two components to a first temperature in a non-oxidising atmosphere with the induction heating system, the first temperature being higher than a recrystallisation point of the two components; producing an equalisation amount of the welding energy via continually, parallelly moving at least one component of the two components while applying an axial force to the two components such that the opposing surfaces of the two components abut each other; and welding the opposing surfaces of the two components together via the welding energy such that a total length loss of the two components is less than 1.0 axial millimetre per millimetre of wall thickness of the two components.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the schematic drawings,

[0028] FIG. 1A shows a partial longitudinal cross section through a valve that has been welded according to a conventional friction welding process,

[0029] FIG. 1B shows a partial lateral cross sectional view of a valve that has been welded according to the solid-state welding process of the invention,

[0030] FIG. 1C shows a partial longitudinal cross section of a second variant of a valve that has been welded according to the solid-state welding process of the invention,

[0031] FIG. 2A shows a longitudinal cross section of an area of the device for the solid-state welding process,

[0032] FIG. 2B shows a cross section along sectional plane B-B,

[0033] FIG. 3 shows a valve that has been welded with the method according to the invention.

DETAILED DESCRIPTION

[0034] FIG. 1A illustrates a welded valve 111, which in the case shown for example is in the form of a hollow valve but may also be a solid valve, and which has been manufactured according to conventional friction welding techniques, for example conventional flywheel welding. Valve 111 has a component 10 constructed as a valve head 10a and a component 11 constructed as a valve stem 11a, which are welded to each other by friction welding, by rotating one of the components 10, 11 relative to the other component 11, 10 while simultaneously pressing the two components together. In friction welding, the opposing surfaces heat up to the hot working temperature. The greatest problem with such friction welded joints is the excess flash material which forms on the insides and outsides of the welded joint and looks like a double torus.

[0035] Particularly in the case of hollow valves 111a, the internal flash detail F1 must be removed, or at least kept very small, which involves additional effort and/or can impair the notch effect and obstruct the flow of the coolant present in hollow valve 111a. Moreover, as described previously the large volume of flash results in a weaker welded joint due to concentrations of non-metal inclusions from the loss of length in the weld interface. The solid-state welding process according to the invention therefore not only reduces the loss of material and length during the welding cycle, it also improves structural integrity.

[0036] FIGS. 1B and 1C represent the characteristic profiles of welded joints that are produced in the method according to the invention.

[0037] FIG. 1C shows an induction coil 9 (see FIG. 2) of appropriate dimensions resulting in a fully bonded external flash F4. The total quantity of flash material, F4 and F5 can also be reduced. The flash volume and length loss were significantly reduced in both of the embodiments represented in FIGS. 1B and 1C, and the integrity of the welded joint was improved.

[0038] The combined induction/friction welding process according to the invention comprises the following steps: [0039] heating opposing, particularly parallel surfaces of the components 10,11 by means of an induction heating system 40 to a first temperature, which is in particular above the recrystallisation point of components 10,11 in a non-oxidising atmosphere by arranging the induction heating system 40 between the opposing surfaces or externally, [0040] continually moving at least one component 10,11 relative to the other component 11,10 parallel to the opposing surfaces, [0041] bringing together the opposing surfaces of the components 10, 11 to be joined with an axial force while at least one of the components 10,11 is still being moved in order to weld the opposing surfaces of the components 10,11 to each other, wherein a part of the welding energy, preferably at least about 90%, is contributed by the induction heating system 40 and the equalisation welding energy is contributed by conventional friction welding, and wherein a total length loss of components 10,11 is less than 1.0 axial millimetre per millimetre of the wall thickness of the components 10,11.

[0042] A particular advantage in the production method according to the invention is that only a fraction of the axial length is used, so that a much smaller volume of welded joint flash is generated. Unlike the previous friction welding process, the welding method according to the invention actually starts before the two components to be joined come into contact with one another. The induction heating phase, which supplies most of the necessary welding energy, runs synchronously with the acceleration of the rotating component 10, 11 and is completed a few tenths of a second before the two components 10, 11 come into contact. This is necessary to ensure that there is time to retract the induction coil 9 between the components 10, 11 and subsequently close the axial gap for contact.

[0043] In the example of joining two components 10, 11 which are designed with clean, smooth, straight cut parallel ends, the induction coil 9 may be arranged between the opposing longitudinal ends of the two components 10 and 11, which leaves a small gap 12 and 13 on either side. Normally, the induction coil 9 is a coil with a simple winding formed by a hollow, rectangular copper pipe to enable cooling water to circulate through it during the induction heating cycle. The induction coil 9 is connected to a high-frequency energy supply either via flexible energy supply cables or alternatively via rotating or sliding connections. The size of gap 12 and 13 is normally adjusted to the minimum possible value before the start of the physical contact and/or before the flashover between induction coil 9 and one of the components 10 and 11, either during the heating phase or during the withdrawal. If the two components 10 and 11 have the same diameter, wall thickness and metallurgy, induction coil 9 is arranged equidistantly between the opposing ends of components 10, 11. Alternatively, it is also conceivable to dispose the induction heating system externally. In applications in which one or more of these three parameters are different for the two components 10, 11 of valve 111, the heat supply to the two components 10, 11 is equalised by moving the induction coil 9 closer to the component 10 or 11 which requires the supply of extra heat. The primary objective of adjusting the gap is to ensure that both components 10, 11 reach their respective hot working temperatures at the same time. Gap 12, 13 may be determined and adjusted either before the start of the induction heating phase, or alternatively continuously throughout the induction heating by means of a contactless temperature sensor.

[0044] Gaps 12 and 13 serve two purposes. Firstly, they prevent physical contact between the induction coils 9 and one of the components 10 and 11, which would result in contamination of the component surface and an electrical short-circuit of the induction coil 9. They also provide a path of the flow of a shield gas 14 which prevents undesirable oxidation of the heated ends of components 10 and 11. Although nitrogen is preferred in many applications for the reason given previously, the shield gas may be nitrogen, carbon dioxide, argon or other non-oxidising gases or mixtures thereof, selected according to metallurgical requirements availability in the workshop. The gas is surrounded on the outside by a flexible curtain 15 which lies closely against the outer periphery of each component 10 and 11, so that gas 14 is forced to flow radially inwards, and thus continually displaces any oxygen away from the exposed components. It is also provided to allow the induction coil 9 to be withdrawn while the flexible curtain 15 is held in position.

[0045] The selection of a suitable shield gas 14 depends mainly on the metallurgy of components 10, 11 and the high temperature ionisation properties of gas 14. For most applications involving ferrous compounds and nickel-based alloys, nitrogen is sufficient. However, a different gas may be necessary for certain metallurgies, e.g., for titanium compounds. Although it is preferred to use a suitable shield gas 14, it should be recognised that the components 10, 11 can be protected from harmful gases by alternative and additional methods such as pre-coating. For this purpose, the opposing surfaces of the components 10, 11 may be pre-coated directly with protective barrier substance, for example a chloride-based flux or the like, which preferably excludes hydrogen.

[0046] Finally, FIG. 3 shows a valve 111, 111a which has been produced in the method according to the invention, with a component 10 embodied as valve head 10a and a component 11 embodied as valve stem 11a.

[0047] The method according to the invention (spinduction) may be used in particular to produce bimetallic valves with important advantages: One key advantage is the avoidance of the interior hollow-on-hollow friction weld bead which is left after the usual friction welding and inhibits sodium movement, and would thus impair the thermal management and cooling of hollow valve 111a. If the friction weld seam is eliminated or at least minimised, the coolant is able to flow without obstruction and function to transport heat away from valve head 10a and towards valve stem 11a. The method according to the invention also enables the friction weld seam 16 to be shifted towards valve head 10a, so that less of the usually higher alloyed material is used there (cost saving). A further advantage is the potentially shorter duration of material consumption, which also results in a smaller quantity consumed.