WO2004030850A1

WO2004030850A1 - Method of manufacturing a nozzle for a fuel valve in a diesel engine, and a nozzle

Info

Publication number: WO2004030850A1
Application number: PCT/DK2003/000658
Authority: WO
Inventors: Harro Andreas Hoeg
Original assignee: Man B & W Diesel A/S
Priority date: 2002-10-07
Filing date: 2003-10-03
Publication date: 2004-04-15
Also published as: EP1549449A1; NO337143B1; JP4529159B2; EP1549449B1; ES2318153T3; RU2005114359A; DE60325077D1; ATE416056T1; JP5680859B2; RU2313422C2; JP2006502334A; KR20050051634A; KR101073494B1; CN100579690C; NO20052218L; CN1691995A; JP2010144251A; AU2003269842A1

Abstract

In a mould (13) a corrosion-resistant first alloy (10) is arranged at least in an outer area which is to constitute the outer surface of a nozzle around the nozzle bores (4). A second alloy (11) is used in another area of the nozzle. The materials in the mould are treated by isostatic pressing into a consolidated material. The boundary area between the two alloys (10, 11) is free of cracks.

Description

Method of manufacturing a nozzle for a fuel valve in a diesel engine, and a nozzle.

The present invention relates to a method of manufacturing a nozzle for a fuel valve in a diesel engine, particularly a two-stroke crosshead engine, a first material of a corrosion-resistant first alloy being arranged in a mould at least in an outer area which is to constitute the outer surface of the nozzle around the nozzle bores.

Such a method is known from WO 95/24286, which describes that after filling with the first material, which constitutes the entire nozzle, the mould is subjected to a HIP treatment, resulting in a nozzle with extremely good properties as concerns nozzle strength and corrosion resistance. Moreover, a very accurate geometry around the nozzle bores is obtained, resulting in good atomization of the fuel. In this HIP treatment (HIP: Hot Isostatic Pressing), a fine-grained powder is consolidated into an entire nozzle blank at high pressure and a high temperature, and the nozzle blank produced retains an isotropic, extremely fine-grained alloy structure.

EP 0 982 493 Al describes a fuel valve with a nozzle extending far up into the valve housing past the primary valve seat and onwards past the slider guide. These parts of the fuel valve are made of steel to give the valve seat, etc., the requisite hardness. The lowermost part of the nozzle is provided with a corrosion-protective coating by means of laser welding, plasma welding or thermal powder spraying, whereby fully or partially melted material bonds to the steel . The material in the bonding area has properties that may cause the corrosion-resistant alloy to flake off either in connection with hardening or after a certain period of operation. In operation, the nozzle is exposed to strong thermal, cyclical loads causing a risk of degradation of the adhesion of the corrosion-resistant alloy.

It is an object, of the present invention to manufacture a nozzle with long life. In view of this, the first-mentioned method of manufacturing a nozzle according to the invention is characterized in that a second material of a second alloy is also arranged in the mould in an inner area, and that the materials so arranged are treated by isostatic pressing into a consolidated (unified) nozzle blank free of microcracks in the boundary area between the first alloy and the second alloy.

Despite the fact that the use of a second alloy in the nozzle results in a change in the structure of the nozzle and that a change of material or structure normally affects longevity negatively, the nozzle longevity is improved. Presumably the ^' improved longevity is obtained because the boundary area between the two alloys is free of microcracks. Consolidation (unification) of the different materials by means of isostatic pressing produces a diffusion-conditioned consolidation without any boundary area proper of the kind known from application of a melted material on a solid material. Even though a nozzle of the kind known from EP 0 982 493 Al is heat-treated into a more uniform hardness before use, microcracks will occur in a melting-based mixing area which is thin and very hard immediately upon application, and in the heat-affected zone of the steel. The diffusion-conditioned consolidation according to the invention does not form any melting- based mixing area with a pertaining heat-affected zone. The avoidance of the microcracks in the transition between the two different materials removes a very substantial source of initiation of fatigue failures in the nozzle, which results in a considerable improvement in the longevity of the nozzle. The diffusion-conditioned consolidation also results in an extremely low risk of bonding errors between the two different materials.

Preferably, in order to obtain a further improvement of the longevity, the second material of the second alloy has a higher fatigue strength than the corrosion-resistant first alloy in the finished nozzle. Fatigue strength is of importance to nozzle longevity because, in addition to the conventional thermally based loads on the nozzle, a considerable increase in the fatigue loads is expected to occur as a consequence of the use of higher injection pressures and faster pressure variations than applied so far in order to obtain more accurate control of the injection of the fuel in the diesel engine and thus better combustion of the fuel and reduced formation of polluting compounds.

At least when the corrosion-resistant alloy contains more than 0.6% Al , an oxygen-restricting diffusion barrier is preferably used between the first material and the second material before the isostatic pressing. The oxygen-restricting diffusion barrier counteracts diffusion of oxygen released from the second one of the alloys into the first one of the alloys and reaction with alloy components or undesired Al impurities. Oxygen may, for example, exist in a dissolved state in the second alloy or may be released at dissolution of oxides in the second alloy during heating of the materials. Even very small quantities of oxygen of merely a few ppm might lead to precipitation of aluminium oxides and/or other undesired precipitations in the boundary area between the two alloys with resulting deterioration of the overall fatigue strength of the nozzle. The diffusion barrier restricts or prevents the harmful diffusion of oxygen so that the nozzle maintains a high fatigue strength. Obviously, the diffusion barrier may also be used in cases where the alloy contains less than or exactly 0.6% Al . A positive effect of a barrier may, for example, be obtained at alloys of an Al content in the interval 0.1 to 0.5% Al . The barrier may also be used if the alloys in fact used present a risk of metallurgical processes resulting in other undesired precipitations, such as precipitation of intermetals, carbides or oxides other than aluminium oxides . The diffusion barrier has a restricting effect on the transport of other alloy components than oxygen from one to the other material. Particularly the small elements such as C and boron may diffuse from an alloy with a high content of the element in its free form into an alloy with a low content of the element. The use of a diffusion barrier provides greater freedom to choose the components of one alloy independently of the components of the other alloy. Limiting the carbon content in the second material may, for example, in relation to hardening of the nozzle to a high hardness, provide the advantage that the second material has a lower tendency to formation of hardening cracks in the areas of the nozzle with a complex geometry, such as around the nozzle bores. Such diffusion barrier may, for example, be of nickel, copper, or a nickel alloy, as both nickel and copper are suitable for forming a dense and stable coating in connection with the corrosion-resistant alloys which are suitable for use as nozzle materials. Alternatives may be a cobalt coating, a cobalt alloy or a chromium coating.

The manufacture of the nozzle may suitably be simplified by placing the diffusion barrier on the inner surface of a prefabricated member of the first material or on the outer surface of a prefabricated member of the second material . The prefabricated member may then act as the carrier of the diffusion barrier until all the material is placed in the mould and the isostatic pressing is carried out and consolidates the . materials . At the same time, the use of a prefabricated member enables the mould to be quickly and easily filled before the pressing as the member is either stacked together with another prefabricated member or used as a holder for particulate material which is filled around or into the member in the mould. In the latter case the prefabricated member is preferably made of the first material and is filled with particulate starting material of the second alloy. In terms of manufacturing, this provides an advantageous possibility of rapid filling of the mould. At the same time, the second material is manufactured by powder metallurgy, whereby it obtains the isotropic structure resulting in particularly fine fatigue properties.

When a prefabricated member of the first alloy is used, it is preferably cast or manufactured by powder metallurgy into a bowl-shaped or tubular wall which forms part of a mould used in the isostatic pressing. The use of such a prefabricated component as the mould simplifies or obviates subsequent removal of the mould from the blank manufactured, as the prefabricated component is part of the finished blank.

In another embodiment of the method according to the present invention, a pre-shaped core member of the second material is placed in a mould in which powder of the first alloy is arranged before the isostatic pressing is carried out. Because at least part of the second material is pre-shaped, the core member can be used to control the placing of the powder of the first alloy. The powder can be arranged directly adjacent to the core member without any risk of mixing powders from the first and the second alloys. The pre-shaped core member also facilitates arranging of the particulate material exactly at the desired places.

The pre-shaped member of the first material and/or the pre-shaped member of the second material may, for example, be manufactured from particulate material, such as by means of a CIP treatment, a HIP treatment, possibly followed by working or extrusion, or by means of sintering with subsequent pressing so that the member has the advantageous isotropic structure. It is also possible to use a member of cast or wrought material, the properties of which are improved by the isostatic pressing.

The isostatic pressing is suitably a HIP treatment, resulting in consolidation of the materials by diffusion without any actual grain growth, which makes it possible to maintain a finegrained structure resulting from the fact that one or more of the materials is/are of a fine-grained starting material consolidated into a cohesive material without melting. The isostatic pressing may also be a CIP treatment at which the pressurization takes place at a considerably lower temperature than at the HIP treatment. In another aspect, the present invention furthermore relates to a nozzle for a fuel valve in a diesel engine, particularly a two-stroke cross-head engine, having a central, longitudinal channel communicating with a number of nozzle bores opening out on the outer surface of the nozzle, the nozzle being made of a corrosion-resistant first alloy at least in an outer area around the nozzle bores and being made of a second alloy in an area differing from the said outer area. In view of improving the longevity of the nozzle, as also mentioned in connection with the description of the above method according to the first aspect of the invention, the nozzle is characterized in that the material in the boundary area between the first alloy and the second alloy has a structure free of microcracks . Concerning effects and advantages obtained by the nozzle according to the invention, please see the description above in connection with the description of the method according to the first aspect of the invention. In a preferred embodiment, the second alloy has a higher fatigue strength than the corrosion-resistant first alloy, which contributes further to achievement of long life as mentioned above.

In one embodiment an oxygen-restricting diffusion barrier is provided in the nozzle between the first alloy and the second alloy. The diffusion barrier makes it possible to determine the analysis of the corrosion-resistant first alloy on the basis of the desired properties and manufacturing conditions for this alloy without having to take into consideration whether components of this alloy might interact negatively with components of the second alloy. Similarly, the analysis of the second alloy can be determined without having to take into account the components of the first alloy.

The second alloy may be made by powder metallurgy, which results in improved properties compared with a material manufactures solely by melting into the desired member. In a preferred embodiment the first alloy is a nickel-based alloy, and the second alloy is an iron- based alloy. The iron-based alloy used in the inside of the nozzle provides high strength in the area of the nozzle having a complex geometry because a number of nozzle bores are located within a small area and are cut into a central, longitudinal channel at different angles. The nickel-based alloys are sensitive to carbide formation and therefore only have a limited C content, for example of up to 0.6% by weight. Conventional iron-based alloys with high fatigue strengths usually have high C contents of up to several per cent by weight. If necessary, the iron- based alloy may be selected so that it has less free carbon at the operating temperature of the nozzle than the nickel-based alloy. The carbide-forming alloy components in the iron-based alloy may, for example, be selected so that the dissolution temperature of the carbides is well above the operating temperature of the nozzle and also above the HIP temperature when the nozzle is manufactured by a HIP process. Release of free carbon by dissolution of carbides is thus avoided. Moreover, strong carbide formers may be selected as alloy components, which helps to catch and bind any free carbon. The nozzle is suitably designed as a separate unit located in the fuel valve in continuation of a spindle guide containing the primary valve seat of the fuel valve. With this design, the nozzle is not or only to a minimum extent influenced by the rather large stresses occurring at the primary valve seat. At nozzle replacement, the replacement is also limited to a smaller part mainly consisting of the piece of the fuel valve that projects into the combustion chamber. In a further embodiment, the second alloy constitutes more than 70% of the aggregate mass of the nozzle, which may also be a cost advantage, in addition to an advantage of strength, if the second alloy is less expensive than the first alloy. The invention will now be described in more detail below with reference to the highly schematic drawing, in which Fig. 1 is a longitudinal sectional view through a nozzle mounted in the lower end of a fuel valve, and

Figs. 2 to 7 show sections through various powder- filled moulds for use in HIP treatment of the nozzle. Fig. 1 shows a nozzle, generally designated 1, of a fuel valve in an internal combustion engine, which may be a four-stroke engine, but is preferably a two- stroke crosshead engine with more than one fuel valve on each cylinder. The latter engine typically makes strict demands on the longevity of the nozzle, among other reasons because the engines are often operated on heavy fuel oil, which may even contain sulphur.

The nozzle projects out through a central hole at the end of a valve housing 2, the annular surface 3 of which may be pressed against a corresponding abutment surface in a cylinder liner or in a cylinder cover indicated by a dashed line so that the tip of the nozzle with nozzle bores 4 projects into^' the combustion chamber A and can inject fuel when the fuel valve is open. The fuel valve has a valve slider 5 with a valve needle 6 and a valve seat 7 located, in the valve design shown, in the lower end of a slider guide 8. The slider guide is pressed down against an upwardly facing surface on the nozzle 1. The nozzle has a central, longitudinal channel 9, from which the nozzle bores 4 lead out to the outer surface of the nozzle. The nozzle is built up of a first material- of a corrosion-resistant first alloy 10 and of a second material of a second alloy 11. The first alloy constitutes at least the outermost area of the nozzle in the area around the nozzle holes and may extend upwards and constitute the outer surface of the nozzle over the whole part of the nozzle that projects from the valve housing 2. The first material of the corrosion-resistant first alloy may be made from particulate starting material or it may be made, for example, by casting. Examples of applicable alloys for use as the first alloy are nickel-based alloys which may, for example, by ^' weight% and apart from . generally occurring impurities, comprise from 15 to 30% Cr, from 0.02 to 0.55% C and optionally one or more of the following components: from 0 to 15% W, from 0 to 8% Al, from 0 to 5% Ti, from 0 to 20 % Co, from 0 to 2% Hf, from 0 to 5% Nb and/or Ta, from 0 to 35% Mo, from 0 to 10% Si, from 0 to 1.5% Y and from 0 to 20% Fe . The alloy may contain unavoidable impurities, and the remainder is nickel. A typical example of such an alloy has the following analysis: 23% Cr, 7% W, 5.6% Al, 1% Si, 0.5% C and 0.4% Y. This HIP-treated alloy has a fatigue strength σ_A of approximately ± 450 MPa. The nickel-based alloys may also be of the type which, by weight% and apart from generally occurring impurities, comprises from 35 to 60% Cr, from 0.02 to 0.55% C and optionally one or more of the following components: from 0 to less than 1.0% Si, from 0 to 5.0% Mn, from 0 to 5.0% Mo and/or W, from 0 to less than 0.5% B, from 0 to 8.0% Al, from 0 to 1.5% Ti, from 0 to 0.2% Zr, from 0 to 3.0% Nb, from 0 to a maximum of 2% Hf, from 0 to 1% N, from 0 to a maximum of 1.5% Y, and an aggregate content of Co and Fe of a maximum of 5.0%. The alloy may contain unavoidable impurities, and the remainder is Ni . This material has a high fatigue strength and extremely high resistance to both hot corrosion and erosion influences from the fuel. Other examples of alloys for use as the corrosion- resistant first alloy material are stated in Table 1.

The thermal expansion coefficient is stated above as the average linear thermal expansion coefficient for heating from 20°C to 500°C, that is, it is relevant for 500°C. Preferably, the first alloy has largely the same thermal expansion coefficient as the second alloy. Alternatively, the first alloy may suitably have a higher thermal expansion coefficient than the second alloy so that compression stresses occur in the central area of the nozzle in connection with the cooling from the HIP temperature to 20°C.

It is also possible to use cobalt-based alloys, such as Celsit 50-P, but in the HIP-treated condition they can only obtain fatigue strengths σ_A of around ± 150 MPa, for which reason they are not preferred materials.

As alloy materials for the second alloy, iron- based alloys are preferred, such as the tool steel AISI H13 with the analysis 0.4% C, 1.0% Si, 0.4% Mn, 5.2% Cr, 1% V, 1.3% Mo and the remainder Fe, or the tool steel AISI H19 with the analysis 0.45% C, 0.4% Si, 0.4% Mn, 4.5% Co, 4.5% Cr, 0.5% Mo, 2% V, 4.5% W and the remainder Fe, or the tool steels CPM1V and CPM3V from Crucible Research, U.S.A., CPM1V containing 0.5% C, 4.5% Cr, 1% V, 2.75% Mo, 2% W, 0.4% Si, 0.5% Mn and the remainder Fe, and CPM3V containing 0.8% C, 7.5% Cr, 2.5% V, 1.3% Mo, 0.9% Si, 0.4% Mn and the remainder Fe .

Tool steels can be manufactured by powder metallurgy as a fine-grained, isotropic powder with an extremely fine structure so that the formation of carbide networks is avoided despite high proportions of added alloy components. By pressure-atomizing melted alloy into a cold atmosphere, the carbides become extremely small and uniformly dispersed.

Other examples of alloy materials for the second alloy are mentioned in Table 2, in which the thermal expansion coefficients are stated in the same way as in Table 1. Table 2:

For a particular tool steel, the fatigue strength is adjustable by means of the heat treatment given to tne nozzle blank. After the isostatic pressing of the nozzle blank the external and internal geometry of the nozzle blank is finished. This typically means that the longitudinal central channel and the nozzle bores are machined into the blank, and the outer surface of the blank can also be turned or ground to its finished shape. When the geometrical machining is finished, the nozzle blank may be subjected to a heat treatment in which the second alloy is hardened to a suitable hardness. The hardening may, for example, be carried out at a temperature in the interval from 1000°C to 1100°C with a soaking time of from 10 to 40 min. Then a final heat treatment is carried out in the form of one or more tempering treatments, and. the tempering is of importance to the resulting fatigue strength of the finished nozzle. The tempering may, for example, be carried out with a soaking time of two hours at a temperature in the interval from 450°C to 600°C. Preferably, double or triple tempering with two or three periods of two hours is used. The tool steels mentioned may have fatigue strengths σ_A of around ± 500-900 MPa in the finished nozzle. Preferably the fatigue strength σ_A is at least + 750 MPa. At the same time the tool steels have advantageously high wear resistance and hardness.

For both the first and the second alloy, the powder used suitably has a size in the interval from 0 to 1000 μm.

Examples will now be given to show how the nozzle blank can be treated with isostatic pressing.

Fig. 2 shows a pre-shaped core member 12, which is inserted in a mould 13, built up from a bottom panel

14, a side wall 15, a cover 16 and a filling nozzle 17. The core member is made of the second alloy and has been made in advance from powder sintered together and cold-pressed to a so-called green blank. The core member may aiso be made by high-speed powder pressing or by a CIP or HIP process. The core member may also be made by conventional methods for tool steel or may be an ESR (Electro Slag Refined) recasting. The core member has a head section 18 with a substantially larger diameter than a body section 19 projecting upwards into the mould 13. The body section extends over an area which lies around the central channel 9 in the finished nozzle. The body section may end at a distance from the nozzle bores, or as shown in Fig. 1 it may extend further into the nozzle so that it encloses the entire central channel. In the latter case the nozzle bores pass through the second alloy in the area around the central channel and through the first alloy in the outermost area of the nozzle. The side wall 15 fits down around the head section

18 and narrows upwards into a smaller diameter. Around the body section the side wall is at a distance largely corresponding to the desired thickness of the corrosion-resistant first alloy. The circular bottom panel 14 is welded along its entire circumference to the lower rim of the side wall 15. Similarly, the cover 16 is welded to the upper rim of the side wall, and the filling nozzle is welded to the upper surface of the cover. The fine-grained powder of the first alloy 10 is filled through the filling nozzle 17 down into the cavity around the core member 12 , and the mould with powder is vibrated, post-filling with more powder is carried out, if necessary, the mould is evacuated and closed in a pressure-tight manner in the filling nozzle.

Then the mould is placed in a furnace, and the furnace chamber is pumped up with an inactive gas, such as argon, to a pressure of approximately 200 bar, and heated to a temperature in the interval from 1000 to 1300°C, typically 1150°C. Concurrently with the heating the pressure in the furnace chamber rises to approximately 900 to 1100 bar. Temperature and pressure are maintained for a period of from 4 to 8 hours, and during this period the materials inside the mould are consolidated into a dense, pore-free body.

After cooling the mould is removed from the HIP- treated blank. The mould used may, for example, be made of steel or of glass. In the latter case the welds mentioned above consist in melting heating of the glass.

The nozzle blank, which is annealed, is then machined to its finished shape, for example by turning and boring, whereupon the blank can be stress relieved, hardened and tempered. As a consequence of the HIP treatment at high temperature, the heat treatments of the nozzle can be carried out without substantial grain growth in the material, provided that the heat treatments take place at a lower temperature than the HIP temperature. This is an advantage, as larger grains result in a lower fatigue strength.

The life of the nozzle according to the invention is long, among other reasons because there are no microcracks in the transitional area between the two materials. A microcrack is a crack in a single crystal grain or a crack extending through several crystal grains. Microcracks may typically have an extent in the interval from 0.05 mm to 0.5 mm. Any cracks of sizes less than 0.05 mm may be disregarded. When microcracks occur in a nozzle, there will be many cracks in the nozzle. The reason is that cracking caused by the heat-affected zones mentioned above or by bonding errors affect a large area and not just a few grains. The presence of microcracks may • thus be. established by examination of a few stress-exposed boundary areas between the two alloys in the nozzle. If the most exposed areas are free of microcracks, the entire nozzle may be considered free of microcracks in the boundary area.

For the sake of simplicity, the following description of other examples utilizes the same reference numerals as are used above for details having the same function.

Fig. 3 shows a design of the mould 13 which is suitable for the manufacture of many nozzle blanks in the same mould. The side wall 15 is here circularly cylindrical with an internal diameter corresponding to the outer diameter of the head section 18. The thickness of the first alloy is controlled by placing a circularly cylindrical filler pipe 21 around the body section before filling the pipe with the powder. By making the side wall 15 longer than shown in the

Figure, a first core member 12 and an associated diffusion barrier 24 and a filler pipe 21 may be placed inside the side wall before mounting of the cover 16, whereupon powder is filled into the filler pipe to its upper edge. Then the next core member with pipe 21, barrier 24 and powder can be placed on top of the first one, and so forth until the side wall 15 is filled up, whereupon the entire mould is closed off by mounting of the cover 16. Then the HIP treatment is carried out as mentioned above.

The diffusion barrier 24 is located at the outer surface of the body section 19 and at the upwardly facing side of the head section 18. The barrier may be a coating, for example applied to the pre-shaped core member by means of electrolytic deposition or by means of other surface application methods, such as plating. The barrier may, for example, be made of nickel, copper, cobalt or nickel-phosphorus . Alternatively, the coating may be applied by spraying or by placing a thin foil of the desired material, typically a pure metal, such as nickel, cobalt or copper, around the body section 19. The barrier suitably has a thickness in the interval from 5 to 400 μm, preferably from 10 to 100 μm.

Fig. 4 shows another design in which the side wall 15 is circularly cylindrical and is welded at its lower rim onto the shoulder of the head section 18. This design makes the mould less expensive. In connection with the final machining of the nozzle after the HIP treatment, the weld with the associated heat-affected zone is removed by turning. The pre- shaped core member may, for example, be made by a preceding HIP treatment or a CIP treatment (Cold Isostatic Pressing) , but then no welds can be made on the material .

Fig. 5 shows a design in which a circularly cylindrical tubular wall 22 of the first alloy is placed around the body section 19. The internal diameter of the pipe is slightly larger than the outer diameter of the body section so that the diffusion barrier 24 is not damaged at assembly. The wall 22 may be manufactured by powder metallurgy, but may also be manufactured as a common pipe, preferably a seamless pipe. After powder of the first alloy 10 has been filled inside the wall, the HIP treatment is carried out as described above with the exception that the wall 22 remains on the core member and is part of the nozzle blank.

Fig. 6 shows a further design in which the wall 22 of the first alloy is bowl-shaped and provided with the diffusion barrier 24. After the mounting of the cover 16, the mould is filled with powder of the second alloy, and the HIP treatment is carried out as described above with the exception that the wall 22 remains on the HIP-manufactured internal part of the nozzle blank.

It is also possible that both the corrosion- resistant first alloy in the form of the wall 22 and the second alloy 11 and the diffusion barrier 24 are manufactured as two prefabricated members with the barrier located on either one or the other member, and that the members are inserted into each other as shown in Fig. 6, whereupon the cover 16 is mounted, the mould is evacuated and closed, whereupon the HIP treatment is carried out as described above. In this case the HIP treatment does not involve an actual consolidation of particulate material as the members are already prefabricated as mentioned above, but the HIP treatment causes the members to consolidate into a cohesive blank by diffusion bonding at the interfaces .

Fig. 7 shows a further embodiment in which the mould is divided inside by a panel partition 23 extending at the interface between the first and the second alloy. The panel partition 23 may be made of the first alloy or of the second alloy. It is also possible that the panel partition 23 is the oxygen- restricting diffusion barrier made of a third material. Since the panel partition is relatively thick, components from the second alloy cannot diffuse into the first alloy.

The bottom panel is also provided with a filling nozzle 17 for filling powder. First one powder is filled through the associated filling nozzle, whereupon air is evacuated and the nozzle is closed. Then the mould is turned upside down and the second powder is filled through the second nozzle, whereupon the air is evacuated from the second chamber. Then the HIP treatment is carried out as described above.

The nozzle may have other designs than the one shown in Fig. 1. It is possible to let the valve slider carry a second closing member which closes the nozzle bores 4 off down in the fuel channel 9. The secondary closing member may advantageously be made of tool steel, as it slides along the inner surface of the longitudinal channel, which may also be made of tool steel. This is a utilization of the fact that two tool steels run well along each other. It is also possible to place the primary valve seat down in the nozzle, resulting in a minimum volume in the fuel channel below the valve seat. It is moreover possible that the nozzle bores are directed not only to one side of the nozzle, but instead to both one and the other side or dispersed along the whole circumference of the nozzle. The pre-shaped core member of the second alloy and/or the bowl- or pipe-shaped wall of the first alloy may be manufactured in advance from material not based on particulate starting material, such as cast or wrought material . It is possible to control the temperature during the HIP treatment so that the second material is hardened and/or tempered or annealed during the HIP treatment or in direct connection therewith, thus obviating a step in a subsequent heat treatment. Details of the various embodiments and examples may be combined into new embodiments. It is also possible to mix the powder of the first alloy or the second alloy from a number of powder sizes, and powders of a number of different metallic alloys may also be used, which may be of the types mentioned above. It is furthermore possible to admix ceramic powder to obtain an insulating effect. The ceramic powder may, for example, be placed in a layer at a short distance from the tip of the nozzle. Then the ceramic powder is covered by powder of the first corrosion-resistant alloy. Graduated mixes of the various powders may also be used. Moreover it is possible, in connection with the filling of the mould before the HIP treatment, to place a screen of ceramic material in the powder of the first alloy, for example in the powder lying above the body section 19 in Fig. 2. Powder of the first alloy is placed on top of the screen so that the outermost of the nozzle is made of corrosion-resistant material .

Claims

P A T E N T C L A I M S

1. A method of manufacturing a nozzle for a fuel valve in a diesel engine, particularly a two-stroke crosshead engine, a first material of a corrosion- resistant first alloy being arranged in a mould ^' at least in an outer area which is to constitute the outer surface of the nozzle around the nozzle bores, c h a r a c t e r i z e d in that a second material of a second alloy is also arranged in the mould in an inner area, and that the materials so arranged are treated by isostatic pressing into a consolidated nozzle blank free of microcracks in the boundary area between the first alloy and the second alloy.

2. A method according to claim 1, c h a r a c t e r i z e d in that the second material of the second alloy has a higher fatigue strength than the corrosion-resistant first alloy in the finished nozzle .

3. A method according to claim 1 or 2 , c h a r a c t e r i z e d in that at least when the corrosion-resistant alloy contains more than 0.6% Al, an oxygen-restricting diffusion barrier is used between the first material and the second material before the isostatic pressing.

4. A method according to claim 3, c h a r a c t e r i z e d in that the diffusion barrier is of nickel, copper, or a nickel alloy.

5. A method according to claim 3 or 4, c h a r - a c t e r i z e d in that the diffusion barrier is placed on the inner surface of a prefabricated member of the first material or on the outer surface of a prefabricated member of the second material .

6. A method according to any one of claims 1 to 5, c h a r a c t e r i z e d in that a prefabricated member of the first material is filled with particulate starting material of the second alloy, preferably by means of high-speed powder pressing.

7. A method according to claim 6, c h a r a c t e r i z e d in that the prefabricated member of the first alloy is cast or manufactured by powder metallurgy into a bowl-shaped or tubular wall which ^•forms part of the mould used in the isostatic pressing.

8. A method according to any one of claims 1 to 5, c h a r a c t e r i z e d in that a pre-shaped core member of the second material is placed in a mould in which particulate starting material of the first alloy is arranged before the isostatic pressing is carried out .

9. A method according to any one of claims 6 to 8, c h a r a c t e r i z e d in that the pre-shaped member of the first material and/or the pre-shaped member of the second material is/are manufactured from particulate starting material, for example by means of high-speed powder pressing, a CIP treatment, a HIP treatment, possibly followed by working or extrusion, or by means of sintering with subsequent pressing.

10. A method according to any one of claims 1 to 9, c h a r a c t e r i z e d in that the isostatic pressing is a HIP treatment.

11. A nozzle for a fuel valve in a diesel engine, particularly a two-stroke cross-head engine, having a central, longitudinal channel communicating with a number of nozzle bores opening out on the outer surface of the nozzle, the nozzle being made of a corrosion-resistant first alloy at least in an outer area around the nozzle bores and being made of a second alloy in an area differing from the said outer area, c h a r a c t e r i z e d in that the material in the boundary area between the first alloy and the second alloy has a structure free of microcracks .

12. A nozzle according to claim 11, c h a r a c t e r i z e d in that the second alloy has a higher fatigue strength than the corrosion-resistant first alloy.

13. A nozzle according to claim 11 or 12, c h a r a c t e r i z e d in that an oxygen- restricting diffusion barrier is provided in the nozzle between the first alloy and the second alloy.

14. A nozzle according to any one of claims 11 to 13, c h a r a c t e r i z e d in that the second alloy is made by powder metallurgy.

15. A nozzle according to any one of claims 11 to

14, c h a r a c t e r i z e d in that the first alloy is a nickel-based alloy, and the second alloy is an iron-based alloy.

16. A nozzle according to any one of claims 11 to

15, c h a r a c t e r i z e d in that the nozzle is a separate unit located in the fuel valve in continuation of a spindle guide containing the primary valve seat of the fuel valve.

17. A nozzle according to claim 16, c h a r a c t e r i z e d in that the second alloy constitutes more than 70% of the aggregate mass of the nozzle.

18. A nozzle according to any one of claims 11 to

17, c h a r a c t e r i z e d in that the fatigue strength σ_A of the second alloy is at least ± 750 MPa.

19. A nozzle according to any one of claims 11 to

18, c h a r a c t e r i z e d in that insulating ceramic material covered by the first alloy is provided in the nozzle.