EP2494183A1

EP2494183A1 - A nozzle for a fuel valve in a diesel engine

Info

Publication number: EP2494183A1
Application number: EP10826127A
Authority: EP
Inventors: Harro Andreas Hoeg
Original assignee: MAN Energy Solutions Filial af MAN Energy Solutions SE; MAN Diesel and Turbo Filial af MAN Diesel and Turbo SE
Current assignee: MAN Energy Solutions Filial af MAN Energy Solutions SE
Priority date: 2009-10-30
Filing date: 2010-10-29
Publication date: 2012-09-05
Anticipated expiration: 2030-10-29
Also published as: CN102667135A; JP2012510024A; ES2661363T3; KR20120074327A; EP2494183A4; KR101388613B1; CN102667135B; EP2494183B1; WO2011050814A1; JP5328927B2

Abstract

A nozzle for a fuel valve (1) for an internal combustion engine, particularly a two-stroke crosshead engine, which nozzle for a fuel valve comprises a valve head (3) with a core portion (4) of an alloyed steel, and an outer facing (5) forming the surface of the nozzle towards a combustion chamber. The outer facing (5) has been formed from particulate starting material of a hot-corrosion-resistant alloy being nickel-based, chromium-based or cobalt based, where said particulate starting material has been united to a coherent layer. At least at the transition zone to the core portion (4) the particles in the particulate material of the outer facing (5) have been deformed into oval or elongate shapes by shear strain caused by forging the outer facing and the core portion, and that the forged outer facing (5) has a density of at least 98.0 %.

Description

A nozzle for a fuel valve in a diesel engine.

The present invention relates to a nozzle for a fuel valve for an internal combustion engine, particularly a two-stroke crosshead engine, which nozzle for a fuel valve comprises a core portion of an alloyed steel, and an outer facing forming the surface of the nozzle towards a combustion chamber, which outer facing has been formed from particulate starting material of a hot-corrosion-resistant alloy being nickel-based, chromium-based or cobalt-based, where said particulate starting material has been united to a coherent layer.

WO 2004/030850 describes a known nozzle for a fuel valve of this kind where the corrosion-resistant outer facing is provided onto the core portion by powder-metallurgy processing where particulate material of the corrosion-resistant alloy is placed in a mould on the core portion and unified with the latter in a HIP process (Hot Isostatic Pressure). The mould is evacuated in order to remove as much air or gas as possible. The HIP process is performed in a chamber that can be both heated and set under pressure. In order to utilize the chamber in an efficient manner it is filled with as many nozzles or other parts as possible, and these objects are all subjected to the same HIP treatment within the chamber. When the treatment is initiated the chamber is heated and pressurized to HIP conditions, and these conditions are then maintained for the required period, typically at least 8 to 12 hours.

During the HIP treatment the pressure influences the particulate material as isostatic pressure (completely even pressure in all directions), and the volume of the particulate material is reduced evenly in all directions as it is compacted onto the core portion. In the resulting mi- crostructure of the outer facing the particles are seen to remain shaped as spheres with circular outlines when viewed in a ground and polished sample taken out from the completed nozzle. In the drawings Figs. 1 and 10 are photographs from such samples.

The HIP process is known to provide a microstructure of high quality and fine coherency of the outer facing, but the HIP process is very time consuming, and the long process time at elevated temperature may also cause undesirable metallurgical processes, like diffusion of a component from the one alloy to the other alloy.

The present invention aims at obtaining high strength of the outer facing and at obtaining a microstructure in the outer facing with a strong structure, in particular near the transition zone to the core portion.

With a view to this the nozzle for a fuel valve according to the present invention is characterized in that at least at the transition zone to the core portion the particles in the particulate material of the outer facing have been deformed into oval or elongate shapes by strain caused by forging the outer facing and the core portion, and that the forged outer facing has a density of at least 98.0 %.

The strain induced by forging causes displacement of powder particles in relation to other powder particles so that the particles rub against each other and penetrate oxide film layers that may be present on the surface of the particles. The strain may in particular be shear strain. Any oxide film layer will be thin because the particulate material is typically manufactured by atomization in an oxygen-free gas, however during storage some oxides will unavoidably form on the particles. The strain deforms particles into non-spherical shapes that may be characte- rized as oval or elongate shapes. During the forging the particulate material is compressed into a dense layer, and the particles unite into a coherent material bonded to the adjacent layer, which is the core portion when the particulate material is located directly on the core portion.

The shear strain induced by the forging causes the particulate ma- terial to flow at least in directions along the transition zone between the material of the outer facing and the material of the core portion. The shear strain and the resulting movements within the material near the transition zone ensures creation of effective bonds between the materials and in conjunction with the extremely effective manner of rubbing particles against one another during the deformation, the resulting microstructure will have only a very low number of inner failure points within the microstructure. The binding together of the materials in the transition area thus has a strong microstructure and it is possible to completely dispense with geometrical locking between the outer facing and the core portion. The forging is applied as the subsequent step to assembling, evacuating and heating the enclosure encasing the particulate material and the core portion. It is considered important that there is no intermediate step, such as a HIP treatment, because such treat- ment is prolonged and may cause diffusion between the materials.

It is possible that the outer facing is located directly onto the core portion. As an alternative, at least one buffer layer of an alloy is located in between the core portion and the outer facing. When such a buffer layer is used, the alloy of the buffer layer is of a third alloy having a composition different from the alloyed steel of the core portion and different from the hot corrosion-resistant alloy of the outer facing. The difference in composition means that the analysis of the alloy of the buffer layer differs in alloying components or in the amounts (in percentage of weight) of one or more of the alloying components. The buffer layer may e.g. be an alloyed steel with a different amount of carbon or different amounts of other components, such as chromium, iron or nickel. The term composition is thus to be taken to mean the analysis of the alloys. The location of the buffer layer in between the core portion of alloyed steel and the outer facing has the effect that the alloyed steel is directly in contact with only the material of the buffer layer and not with the corrosion-resistant alloy of the outer layer. The buffer layer acts to reduce or to prevent diffusion of alloying components from the outer facing to the core portion, and vice versa.

Preferably, the buffer layer is selected from the group comprising steel, austenitic steel, a nickel-based alloy, and an alloy which, apart from unavoidable impurities, is of Fe or Ni. These alloys are considered compatible both with the steel of the core portion and with the alloy of the outer facing.

In an embodiment the alloyed steel of the core portion is an auste- nitic, stainless steel. The stainless steel has high strength and is considered all in all to perform very well, especially in two-stroke crosshead engines. The stainless steel, however, has a rather high content of carbon. The buffer layer absorbs diffused carbon, so that the advantages of utilizing stainless steel for the major part of the nozzle are not impaired by the high requirements for hot-corrosion resistance and for long-term ductility of the completed nozzle.

In a preferred embodiment the buffer layer has a thickness of at least 0.3 mm, such as at least 0.5 mm, and preferably at least 0.75 mm. The thickness hinders carbon diffusion across the buffer layer, even when the buffer layer is of an alloy exhibiting carbide formation abilities where the carbon diffusing into the layer can be converted into carbides and thus cannot cause an increase in the carbon-activity of the layer.

The present invention also relates to a method of manufacturing a nozzle for a fuel valve for an internal combustion engine, which nozzle for a fuel valve comprises a valve head with a core portion of an alloyed steel, and an outer facing forming the surface of the nozzle towards a combustion chamber, which outer facing is formed from particulate starting material of a hot-corrosion-resistant alloy being nickel-based, chromium-based or cobalt based.

According to the present invention the method is characterized in that, while the particulate material of the hot-corrosion-resistant alloy is held in an enclosure at the core portion the particulate material is forged, whereby the particulate material is subjected to strain that de- forms the particles into elongate or oval shapes, said forging compacting the particulate material to a density of at least 98.0% and uniting the outer facing with the core portion or with a buffer layer and the core portion.

The forging occurs very quickly in comparison to a HIP-treatment, and alloying components thus have only short time for diffusion from the one alloy to the adjacent alloy while the valve parts are at the elevated forging temperature. As described in the above, the forging presses the particulate material together and shear strain moves particles in directions parallel with the transition zone and makes the particles in the par- ticulate material rub against one another and merge. During the movement, rubbing and merging any oxide films initially present on the particles break up and clean alloy material from grains inside any one particle is brought into direct contact with clean alloy material from grains inside other particles, and the grains can thus effectively connect at the microstructure level.

In one example the particulate material in the enclosure is provided in a layer of substantially even thickness in an area extending along a cylindrical outer surface of the core portion. When the layer of particu- late material is of substantially even thickness in the enclosure and substantially even forging conditions are applied, the resulting outer facing will have a substantially even thickness.

A further method according to the present invention is characterized in that the particulate material of the hot-corrosion-resistant alloy is hot sprayed in an inactive atmosphere to build a pre-formed part, that the preformed part and the core portion are heated to forging temperature and forged whereby the particulate material is subjected to shear strain that deforms the particles into elongate or oval shapes, said forging compacting the particulate material to a density of at least 98.0% and uniting the outer facing with the core portion or with a buffer layer and the core portion.

With this method the particulate material is firstly shaped into a pre-formed part of sufficient stability of shape to allow the particulate material to be located on the core portion as a single body. It is even possible to spray the particulate material directly onto the core portion . In case the particulate material is without interconnected porosities it is possible to avoid using an enclosure. When an enclosure is used, it has to be machined off after completed forging. Although the particulate material in the pre-built part will have irregular shapes before the forging, the forging causes the effects as described in connection with the first- mentioned method, but the resulting deformed particles will have quite irregular shapes.

Whatever method is utilized it is preferred that prior to the forging, the material of the outer facing is evacuated to a pressure of less than 1 x 10^"4 bar. The evacuation removes gasses from voids within the particulate material to be forged, and this facilitates the compression of the material. Although gasses present in the material of the outer facing are typically oxygen-free, such as inert gasses, it is still an advantage to have as little gas present as practically possible. Consequently it is pre- ferred that the material of the outer facing is evacuated to a pressure of less than 1 x 10^"7 bar.

The particulate material of the hot-corrosion-resistant alloy held in the enclosure may be heated to a forging temperature prior to the forging.

In one forging method according to the present invention the particulate material of the hot-corrosion-resistant alloy held in the enclosure is introduced in a fluid-filled chamber, in which the forging is carried out by increasing the pressure in the fluid.

In another forging method according to the present invention the particulate material of the hot-corrosion-resistant alloy held in the enclosure is forged by being pressed through a tool reducing the outer diameter of the enclosure.

If a buffer layer of a third alloy is to be used, this third alloy has a composition different from the alloyed steel of the core portion (the first alloy) and different from the hot-corrosion-resistant alloy of the outer facing (the second alloy). The third alloy is preferably applied to the surface of the core portion before the material of the outer facing is located at said surface of the core portion. The third alloy can alterna- tively be applied to the material of the outer facing . The surface of the core portion is, however, normally a regular and smooth surface onto which the third alloy can be applied in very well controlled manner, in particular well controlled as to the amount and to the spreading out of the material in an even manner.

In order to reduce the diffusion across the transition zone the forging is preferably carried out in less than 10 minutes, and the core portion with the outer facing are cooled immediately after the forging.

The nozzle as forged, and/or the nozzle after machining into a completed nozzle, can optionally be subjected to a final heat treatment, such as tempering or annealing. The heat treatment may cause diffusion of alloying components at transition zones and can strengthen the metallurgical bonding between materials.

Examples of embodiments according to the present invention are in the following described in more detail with reference to the highly schematic drawings, on which

Fig. 1 is a photograph in a microscope of a ground and polished sample taken out from a nozzle where an outer facing has been provided by a prior art HIP treatment,

Fig. 2 illustrates a cross-sectional part view of a nozzle for a fuel valve in form of a nozzle according to the invention,

Fig. 3a, 3b are schematic illustrations of forging of a valve head according to the present invention,

Figs. 4 and 5 are schematic illustrations of units prepared for forg- ing of a valve head according to the present invention,

Figs. 6 and 7 are photographs in a microscope of a ground and polished sample taken out from a nozzle where an outer facing has been provided according to the present invention,

Figs. 8 and 9 are top view and side view, respectively, of a test sample,

Fig. 10 is a photograph in a microscope of a ground and polished sample taken out from a nozzle where an outer facing has been provided by a prior art HIP treatment, and

Fig. 11a, l ib are schematic illustrations of a further forging of a valve head according to the present invention.

In Fig. 1 and in Fig. 10 the sample has been taken from a HIP compacted particulate material and the circular shapes from cut through particles can be seen. This shows that the particles retain their spherical shape during the compacting. It is a typical sign of the HIP compacting that the particles are spherical, and this is a result of the isostatic pressure applied during compacting. The isostatic pressure makes the particulate material shrink in a manner where the particles are not moved around within the material during the process. It is a very orderly process where the mutual positions among particles are maintained. In order to more clearly discern the microstructure of the prior art three circles have been added to the photograph in Fig. 10 so as to outline three of the particles appearing in the photograph.

Fig. 2 illustrates in schematic form a nozzle 1 for a fuel valve for a two-stroke crosshead engine having more than one fuel valve on each cylinder, such as two or three fuel valves 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 an outer facing 10 of a corrosion-resistant first alloy and of a core portion 12 of a second alloy. The outer facing 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 outer facing 10 on the nozzle is a layer of hot-corrosion resistant material counteracting the burning off of material from the nozzle. The hot-corrosion resistant material is formed of particulate starting material of an alloy which is nickel-based, chromium-based or cobalt based.

The internal combustion engine utilizing the nozzle for fuel valves may be a four-stroke engine or a two-stroke crosshead engine. The two- stroke engine may be of the make MAN Diesel, such as of the type MC or ME, or may be of the make Wartsila, such as of the type RTA of RTA- flex, or may be of the make Mitsubishi. For such two-stroke crosshead engines the diameter of the piston may range from 250 to 1100 mm, and for each cylinder there is typically two or three fuel valves.

The nozzle 1 for a fuel valve can also be exploited in smaller engines, for example four-stroke engines of the medium or high-speed type, but the nozzle for a fuel valve is especially applicable in the two stroke crosshead engines, which are large engines where the loads are heavy and the requirement of continuous operation without failure is dominant.

In one embodiment the outer facing 10 is applied directly onto the surface of the core portion 12. In another embodiment of the nozzle for a fuel valve, the one from which the specimens photographed in Figs. 6 and 7 have been taken, a buffer layer 29 is located between core portion 12 and outer facing 10. The buffer layer 29 may apart from unavoidable impurities be a layer of substantially pure nickel applied to the surface of the core portion. The nickel layer can be applied to the surface in different manners, such as being provided as particulate material placed on the core portion. The nickel layer can also be provided in a separate procedure prior to placing the particulate material of the outer facing on top of the buffer layer. In such a separate procedure the core portion can be placed in a galvanic bath and the nickel be deposited by nickel electroplating forming a layer having a thickness in the range from 30 to 150 Mm, preferably 30 to 70 Mm . The electroplated layer has the advantage of being a very dense layer of pure nickel.

In another embodiment the buffer layer is, apart from unavoidable impurities, of Fe. One advantage of making the buffer layer of pure, or almost pure, iron or nickel is that the buffer layer has no or only very small amounts of carbide formants. When this is the case, the formation of carbides in the buffer layer is suppressed, and diffusion of carbon into the buffer layer increase the carbon-activity in the buffer layer and thus further diffusion of carbon into the layer will be resisted. Carbon only has very small solubility in iron and nickel. As an example, the solubility of carbon in nickel at a temperature of 500°C is less than 0.1 % by weight, so when even small amounts of carbon has diffused into the buffer layer, the buffer layer will obtain a carbon-activity of 100 % and thus virtually prevent further diffusion of carbon into the layer.

As another example the buffer layer 29 may be of steel or austenit- ic steel. The buffer layer may be a plate of steel. As a more specific example, core portion 12 is of forged tool steel (H13 tool steel in Table 1), the outer facing 10 is of Alloy 671, and the plate of steel is of the alloy W.-No. 1.4332 selected from the alloys of Table 2. As another example the buffer layer 29 can be provided as particulate material of alloy UNS S31603 and the outer facing 10 be of particulate material of Alloy 671. The core portion 12 is of forged steel. In this case, both the particulate material of the buffer layer and the particulate material of the outer facing are united into a coherent material on the core portion 12 during the forging.

As an alternative embodiment the buffer layer can be of a nickel based alloy. An alloy of this type is particularly suitable for binding well with the alloy of the outer facing, and it may have a content of chromium that is considerably lower than the outer facing, such as a chromium content of less than 25 % by weight, such as the alloy IN 625 having from 20 to 23 % chromium, the alloy INCOLOY 600 having from 19 to 23% chromium, or the alloy IN 718 having 10 to 25 % chromium, or the alloy NIMONIC Alloy 105 having about 15% chromium, or the alloy Rene 220 having from 10 to 25 % chromium. The buffer layer may also be of a more nickel-rich alloy as nickel in larger amounts has a tendency to prevent diffusion of carbon.

The particulate material may be manufactured in several different manners which are well-known in the art. The particulate materials may, for example, have been manufactured by atomization of a liquid jet of a melted alloy of the desired composition into a chamber with an inactive atmosphere, whereby the material is quenched and solidifies as particles with the very fine dendritic structure. The particulate material may also be called a powder.

The particulate material may alternatively be manufactured by atomization of a liquid jet of a melted alloy of the desired composition into a chamber with an inactive atmosphere, where the spray of atomized particles are directed so as to hit and deposit on a solid part. The solid part may be cooled and in this instance the particles build up a preformed part which is separate from the solid part. The particles may alternatively bind to the solid part, and a core portion 12 be used as such, so that the pre-formed part is bonded directly to the core portion.

Suitable materials for the core portion 12 comprise tool steels. Ex- amples of such materials are given in the following Table 1. The ASTM No. is the US standard designation for the alloy. Other materials for the core portion are the stainless steels presented in Table 1 with the W.- No., which is the German standard number for the alloy. The percentag- es stated are percentages by weight. The tool steels (ASTM) are preferred due to their high strength and in particular their high resistance to wear. For nozzles to be used in fuel injection systems for heavy fuel oil the high wear resistance provides the nozzle with a long life. For nozzles to be used in fuel systems for gas fuel the demand for wear resistance may be lower than when the fuel is heavy fuel oil.

Table 1

Suitable materials for the optional buffer layer comprise steels as exemplified in the following Table 2. The W.-No. is the German standard number for the alloy. The percentages stated are percentages by weight.

Table 2 W.-No. c Si Mn Cr Ni Other Balance

1.4370 0.08% 0.8% 7% 18% 8% - Fe

1.4316 0.03% 0.5% 1.5% 20.5% 10.5% Nb > 12 x C Fe

1.4551 0.04% 0.8% 1.8% 19.5% 10% - Fe

1.4430 0.025% 0.8% 1.8% 18.5% 12% 2.6% Mo Fe

1.4332 0.03% 0.5% 1% 24.5% 13% - Fe

- 0.08% 0.8% 1.8% 23.5% 13.5% - Fe

Another suitable material for the buffer layer is the alloy UNS S31603 comprising 0.5 - 1.0 % Mn, 16.5 - 18% Cr, 11.5 - 14% Ni, 2.5 - 3.0% Mo, 0 - 0.1% N, 0 - 0.025% O, 0 - 0.03 % C, and the balance Fe. When the buffer layer is of plate material then there are normally not any requirements to the contents of nitrogen and oxygen. However, when the buffer layer is of particulate material then it is preferred that the content of nitrogen is at the most 0.1% and preferred that the content of oxygen is at the most 0.03%.

Suitable materials for the outer facing are well known in the art of nozzles, and examples are Stellite 6, an alloy of the type 50% Cr and 50% Ni, an alloy of the type IN 657 comprising 48-52% Cr, 1.4-1.7% Nb, at the most 0.1% C, at the most 0.16% Ti, at the most 0.2% C+N, at the most 0.5% Si, at the most 1.0% Fe, at the most 0.3% Mg, and a balance of Ni. Another example is an alloy having the composition 40 to 51% Cr, from 0 to 0.1% C, less than 1.0% Si, from 0 to 5.0% Mn, less than 1.0% Mo, from 0.05% to less than 0.5% B, from 0 to 1.0% Al, from 0 to 1.5% Ti, from 0 to 0.2% Zr, from 0.5 to 3.0% Nb, an aggregate content of Co and Fe of maximum 5.0%, maximum 0.2% 0, maxi- mum 0.3% N, and the balance Ni. Other suitable facing alloys for use as the outer facing are given in the article "Review of operating experience with current valve materials", published in 1990 in the book "Diesel engine combustion chamber materials for heavy fuel operation" from The Institute of Marine Engineers, London.

The forging is prepared by placing the core portion 12 of the valve head at the forging location and applying the buffer layer 29, if any, to the surface of the core portion. The particulate material of the outer fac- ing 10 can be provided in several different manners. In one example illustrated in Fig. 4 the outer facing 10 is provided as particulate material held in an enclosure 15 at a core portion 12 while the core portion with enclosure and the particulate material is arranged in a die part as a preparation for the forging. The arrangement of the enclosure 15 and the particulate material on the core portion can be effected in several different manners. The enclosure may be welded with weld seams 20 around the core portion and be provided with a pipe stud 17, which is used for filling particulate material into the enclosure and then used to connect vacuum equipment and then removed or closed off prior to forging. Alternatively, the enclosure 15 may be fixed around the core portion 12 after the particulate material has been deposited within the enclosure. This fixing may be by use of welding, or as another example by vacuum brazing. As a further alternative the enclosure may be fixed around the core portion, and subsequently the particulate material is filled into the enclosure, and finally brazing is performed. When using vacuum brazing the enclosure 15 may be provided with a threading at the inside, which threading matches external treading on a base portion 18 of the core portion. The base portion 18 has a larger diameter than a cylindrical portion 19 of the core portion . Solder is provided on the threading. Then the heating and fixing may take place in a vacuum oven. In another example the particulate material of the outer facing 10 is provided as a pre-formed part that is located on the core portion 12.

In one example, prior to forging, the core portion 12 with the parti- culate material of the outer facing 10, and possibly the buffer layer 29 and the enclosure 15, are heated to forging temperature which preferably is in the range from a temperature of 950°C to 1100°C. The heated parts are introduced into a forging press having a lower die part 50 and an upper part 51 and a drive mechanism (not shown) which may be me- chanically driven or hydraulically driven. The drive of the forging press displaces the one die part towards the other die part, and the material held within the die part is mechanically deformed during this displacement.

The forging operation is preferably carried out within 2 minutes, and more preferably within 1 minute. During the forging the particulate material of the outer facing 10 is compacted, typically so that the thickness of the outer facing is reduced to from 30 to 70% of the initial thickness of the particulate material. If a dense pre-formed part is used the density can be rather high prior to the forging, and in this instance the thickness of the outer facing may be reduced to from 30 to 95% of the initial thickness of the particulate material. The particulate material is reduced in thickness so that the resulting density of the outer facing is at least 98.0%. When compacted to this degree by using forging, the parti- culate material has obtained a suitable density. It is of course more preferable to further compact the particulate material, such as to a density of at least 99.0% or even better to a density of at least 99.5%, and most preferable to compact it to 100% density.

During the forging the particulate material is subjected to shear strain that makes the particles shift position and deforms the material. Strain is a geometrical measure of deformation representing the relative displacement between particles in the material. The shear strain causes particles to shift place and it deforms particles when the particles 5 interact. Shear strain is acting parallel to the surface affected by the forging. The forging affects the outer surface of the outer facing, and the shear strain acts in parallel with this surface. During the compacting of the outer layer, the shear strain displaces particles in the radial direction and causes the particles to rub against each other and force the particles to be deformed into non-spherical shapes, such as oblong shapes, oval shapes or irregular shapes. When forging is completed the forged valve head is removed from the dies and air cooled or cooled in another manner.

It is preferred that the amount of effective strain in the material of the outer facing is at least 0.3. The effective strain is calculated in the traditional manner disclosed in basic textbooks, such as in "Manufacturing engineering and technology" by Kalpakjian and Schmid, 5th edition, Prentice Hall, year 2006, or in "Formelsamgling I Hallfasthetslare" by Gert Hedner, publication 104, Royal Swedish Technical University, Stockholm, year 1978 on pages 222-223. Even more preferably the ef- fective strain is at least 0.4. This ensures a very effective and strong bonding between the particles of the outer facing and the material of the core portion or the buffer layer.

A first method of manufacturing the nozzle for a fuel valve is de- scribed in the following. The nozzle for a fuel valve has a core portion of alloyed steel, and an outer facing forming the surface of the nozzle towards a combustion chamber. A particulate starting material for forming the outer facing is prepared. The material is of a hot-corrosion-resistant alloy. The particulate starting material is enclosed within an enclosure 15 the inside of which has substantially the shape of the outer surface the outer facing plus machining and forging tolerances. The enclosure 15 is in other words prepared for being removed after the valve head has been forged. While the particulate material of the hot-corrosion-resistant alloy is held in the enclosure at the core portion, the particulate material and the core portion are heated to forging temperature.

As illustrated in Fig. 3a the core portion 12 with the particulate material 10 and the enclosure 15 and mounted to upper die part 50. The upper die part then moves the parts down towards lower die part 51. The lower die part 51 has a bore with three sections, namely a lower section shaped as a cylindrical bore with a diameter corresponding to the outer diameter of the enclosure 15, when forged, a middle cylindrical section having a diameter slightly larger than the outer diameter of the enclosure 15 before forging, and an upper entry section. An annular surface 53 connects the middle cylindrical section with the lower section. Annular surface 53 is conical. The diameter of the enclosure 15 is reduced when the enclosure 15 is pressed down past the conical annular surface 53, because the conical surface 53 acts on enclosure 15 with forging forces causing a compaction of the particulate material to a density of at least 98.0 % and shear strain in the particulate material in the transition zone to the core portion 12 deform the particles into elongate shapes. In Fig. 3b the forging step has been completed by moving the upper die part 50 downwards until a shoulder at an upper portion of the core portion abuts a conical annular surface 54 at the transition between the upper entry section and the middle cylindrical section of the bore in the lower die part 51. After completion of the forging step the upper die part 50 is moved upwards and retracts the forged specimen from the lower die part 51.

An alternative forging method is illustrated in Figs. 11a and l ib. The upper die part 50 moves the core portion with particulate material and the enclosure 15 down into a lower die part 60 having an internal chamber filled with fluid at elevated temperature, such as molten glass or molten salt, and an annular conical guide surface 61 at the upper surface of the lower die part. The guide surface 61 centers the enclosure with respect to a cylindrical bore leading down into the internal chamber. Guide surface 61 also serves as abutment for a shoulder at an upper portion of the core portion and thus as a stop for the downward movement. When enclosure 15 has been fully introduced into the internal chamber, then the pressure in the chamber is increased, and the in- creased pressure causes forging of the enclosure 15 and the particulate material contained therein. During the forging the particulate material is subjected to shear strain that deforms the particles into elongate or oval shapes. At the same time the particulate material is compacted to a density of at least 98.0% and united to the core portion or to a buffer layer and the core portion.

A further method of manufacturing the nozzle for a fuel valve is to hot spray the particulate material of the hot-corrosion-resistant alloy to build a pre-formed part. The preformed part can be formed directly on the core portion during the spray procedure or it can be formed sepa- rately and be located on the core portion and be heated to forging temperature. Then the pre-formed part and the core portion, and optionally also the buffer layer, can be forged into a nozzle part. During forging the particulate material is subjected to shear strain that deforms the particles into elongate or oval shapes, said forging compacts the particulate material to a density of at least 98.0% and unites the outer facing with the core portion or with a buffer layer and the core portion.

The hot spraying of particulate material can occur by supplying a spray dryer nozzle with molten alloy and spraying the alloy as atomized particles onto a core portion 12 where the particles partly unite, but re- main in a non-dense condition. The core portion with the hot spray applied pre-formed part is heated to forging temperature, and placed in one of the dies as mentioned in the above description, and then forged to a dense condition.

It is preferred that the particulate material prepared for the outer facing is evacuated prior to the forging, in order to reduce the amount of oxygen present to the particles. In this manner the formation of oxide films on the particles is counteracted.

At the forging the outer facing 10 is compressed to smaller thick- ness, such as to about 25% less thickness in comparison to the initial thickness. At the same time the density of the material in the outer facing increases from about 65% to close to 100%. It is preferred that the resulting density is at least 98.0%

The nozzle produced by any of the above mentioned methods has an outer facing 10 at the surface directed towards the combustion chamber.

The strong microstructure obtained by the forging causes a strong bonding of the materials in the transition area. According to the present invention this bonding may be tested. In order to test the strength against tearing apart the materials in shear loading, a special test specimen is prepared on basis of a sample cut out of a nozzle. The test specimen is shaped as illustrated in Figs. 8 and 9. The test specimen has a width w = 9.0 mm, a length I = 40.0 mm, a distance d = 25.4 mm between centers of pulling holes, a thickness t = 3.5 mm of the core por- tion, and a thickness T of the outer facing. The thickness of the outer facing is measured and set at thickness T. Then a groove gl, g2 through the entire material is cut from either side in a width of at least 2 mm and with such a mutual separation in the length direction that the resulting overlap with a binding together of the layers is less than the measured thickness t of the outer facing.

Eight examples have been carried out, and the results are presented in Table 3. It is clearly seen that the shear strength obtained is at a high level. The level is corresponding to the shear strength of a solid material. The bonding obtained in accordance with the present invention thus causes no weakening of the material .

Table 3

In a further embodiment, the particulate material of the hot- corrosion resistant alloy is mixed with particles of isolating material, like the ceramic material Zirconia (Zr02) . The isolating material may have a higher concentration near the outer surface of the outer facing, and pre- ferably there is no isolating material in the transition zone between the outer facing and the core portion . The particulate material of the outer facing may include from 5 to 60% by weight of isolating material, but preferably the amount of isolating material does not exceed 40% by weight of the outer facing .

It is possible to combine details of the above-mentioned embodiments into other embodiments within the scope of the patent claims. It is furthermore possible within the scope of the patent claims to make variations in the details of the above-described embodiments.

Any of the above-mentioned embodiments can be subjected to a final heat treatment, such as tempering or annealing . The heat treatment may e.g. have a duration in the range from 2 to 6 hours and take place at a temperature in the range from 800 to 1050° C. Other temperatures are also possible.

The nozzle for a fuel valve is an important engine part, and information for documentation of the identity and possibly manufacturing details of the specific nozzle for a fuel valve may be stored in a tag embed- ded in the nozzle for a fuel valve. The tag is preferably of remotely write and readable RFID-type, preferably even containing individual authenticating data providing traceability. A specific spindle may be provided with more than one tag, if desirable. The tag may be located at a location within the nozzle for a fuel valve, where it is adequately shielded from heat and other tag-harming parameters.

Claims

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

1. A nozzle for a fuel valve for an internal combustion engine, particularly a two-stroke crosshead engine, which nozzle for a fuel valve comprises a valve head with a core portion of an alloyed steel, and an outer facing forming the surface of the nozzle towards a combustion chamber, which outer facing has been formed from particulate starting material of a hot-corrosion-resistant alloy being nickel-based, chromium-based or cobalt based, where said particulate starting material has been united to a coherent layer, ch a racte rized in that at least at the transition zone to the core portion the particles in the particulate material of the outer facing have been deformed into oval or elongate shapes by shear strain caused by forging the outer facing and the core portion, and that the forged outer facing has a density of at least 98.0 %.

2. A nozzle for a fuel valve according to claim 1, ch a racte r

- i z e d in at least one buffer layer of an alloy is located in between the core portion and the outer facing, that the alloy of the buffer layer is a third alloy having a composition different from the alloyed steel of the core portion and different from the hot-corrosion-resistant alloy of the outer facing.

3. A nozzle for a fuel valve according to claim 3, ch a racte r -i z e d in that the buffer layer is selected from the group comprising steel, austenitic steel, a nickel-based alloy, and an alloy which, apart from unavoidable impurities, is of Fe or Ni.

4. A nozzle for a fuel valve according to any one of claims 1 to

3, c h a ra cte rized in that the alloyed steel of the core portion is a tool steel.

5. A nozzle for a fuel valve according to any one of claims 2 to

4, c h a r a c t e r i z e d in that the buffer layer has a thickness of at least 0.5 mm.

6. A method of manufacturing a nozzle for a fuel valve for an internal combustion engine, which nozzle for a fuel valve comprises a core portion of an alloyed steel and an outer facing forming the surface of the nozzle towards a combustion chamber, which outer facing is formed from particulate starting material of a hot-corrosion-resistant alloy being nickel-based, chromium-based or cobalt-based, c h a ra cte- ri zed in that, while the particulate material of the hot-corrosion-resistant alloy is held in an enclosure at the core portion the particulate material is forged, whereby the particulate material is subjected to strain that deforms the particles into elongate or oval shapes, said forging compacting the particulate material to a density of at least 98.0% and uniting the outer facing with the core portion or with a buffer layer and the core portion.

7. A method of manufacturing a nozzle for a fuel valve according to claim 6, c h a racte rized in that prior to the forging the material of the outer facing is evacuated to a pressure of less than 1 x 10^"4 bar, preferably less than 1 x 10^"7 bar.

8. A method of manufacturing a nozzle for a fuel valve accord- ing to claim 6 or 7, c h a ra cte ri zed in that a third alloy having a composition different from the alloyed steel of the core portion and different from the hot-corrosion-resistant alloy of the outer facing is applied to the surface of the core portion before the material of the outer facing is located at said surface of the core portion.

9. A method of manufacturing a nozzle for a fuel valve according to any of claims 6 to 8, c h a ra cte r i z e d in that the forging is carried out in less than 1 minute, and that the core portion with the outer facing is cooled immediately after the forging.

10. A method of manufacturing a nozzle for a fuel valve accord- ing to any of claims 6 to 9, c h a ra cte ri zed in that the particulate material of the hot-corrosion-resistant alloy held in the enclosure is heated to a forging temperature prior to the forging.

11. A method of manufacturing a nozzle for a fuel valve according to any of claims 6 to 10, ch a racterized in that the particulate material of the hot-corrosion-resistant alloy held in the enclosure is introduced in a fluid-filled chamber, in which the forging is carried out by increasing the pressure in the fluid.

12. A method of manufacturing a nozzle for a fuel valve according to any of claims 6 to 10, ch a racterized in that the particulate material of the hot-corrosion-resistant alloy held in the enclosure is forged by being pressed through a tool reducing the outer diameter of the enclosure.