JP4701309B2 - Exhaust valve spindle for internal combustion engine and method of manufacturing the same - Google Patents

Description

  The present invention relates to an exhaust valve spindle for an internal combustion engine, in particular a two-stroke crosshead engine. The exhaust valve spindle has a base portion of alloy steel and an outer surface that forms the surface of the valve spindle towards the combustion chamber. The outer surface is formed from a particulate starting material of a hot-corrosion-resistant alloy that is nickel-based, chromium-based or cobalt-based, and the particulate seed material is a coherent layer).

Reference 1 (US Pat. No. 6,173,702) describes a known exhaust valve spindle of this kind, in which a corrosion resistant outer surface is provided on the base part by powder metallurgy processing. In this case, the particulate material of the corrosion resistant alloy is molded on the foundation (mould;
In the mold) and integrated with the foundation by a HIP (Hot Isostatic Pressur) process. The mold is evacuated to remove as much air or gas as possible. The HIP process is performed in a room that can be heated and set under pressure. In order to make use of the chamber in an effective manner, the chamber is filled as much as possible with foundation parts or other parts, and these objects undergo the same HIP treatment in the room. When processing is initiated, the chamber is heated and pressurized to the HIP state, and such state is then maintained for the required period of time, typically at least 8 to 12 hours.

  During HIP processing, the pressure affects the particulate material with isostatic pressure (fully uniform pressure in all directions) and the volume of the particulate material is compressed on the base, so it decreases uniformly in all directions To do. In the resulting outer surface microstructure, the particles appear to remain in a spherical shape with a circular contour when viewed in a ground and polished sample from the finished valve spindle. 1 and 10 are photographs of such samples.

  The lower valve head surface has a large area and is therefore exposed to large thermal stresses, for example when the engine load is changed, especially when the engine is started or stopped. Thermal shock is greatest at the center of the surface. This is partly because the combustion gas has a maximum temperature near the center of the combustion chamber, partly while the valve is closed, the valve head is on the outer rim (here on the upper surface). This is because the seat area is cooled in the vicinity of the water-cooled stationary valve seat). The cold peripheral material prevents the thermal expansion of the hot central material, thus creating a large thermal stress. The slowly changing but large thermal stress caused by this thermal effect creates very high demands on the strength and quality of the outer surface.

US 6,173,702 (US patent specification) WO97 / 47862 (International pamphlet)

  Although the HIP process is known to provide a high quality microstructure on the outer surface and excellent tack, the HIP process consumes a very long time, and a long process time at elevated temperatures is also Undesirable metallurgical processes similar to the diffusion of components from one alloy to another can occur. The object of the present invention is to obtain a high strength of the outer surface and to obtain a microstructure with a tough structure on the outer surface, in particular in the vicinity of the transition zone to the base part.

  For this purpose, the exhaust valve spindle according to the invention is characterized in that the particles in the particulate material on the outer side forge the outer side and the base part, at least in the transition zone to the base part. The resulting shear strain is deformed into an oval or elongated shape and the forged outer surface has a density of at least 98.0%.

  The shear strain induced by forging causes displacement of the powder particles relative to other powder particles, and the particles rub against each other and penetrate the oxide film layer that may be present on the surface of the particles. Since particulate material is typically produced by atomization in oxygen-free gas, any oxide film layer is thin, but it is inevitable that the oxide being stored will form on the particles. Shear strain transforms particles into a non-spherical shape that may be characterized as an egg shape or an elongated shape. During forging, the particulate material is compressed into a dense layer, and the particles combine as an adhesive material that adheres to the adjacent layer. This adjacent layer is the base portion if the particulate material is located directly on the base portion. A density of at least 98.0% can also be expressed as a maximum of 2% porosity.

  The shear strain induced by forging causes the particulate material to flow at least in the radial direction, such radial direction being perpendicular to the axial direction of the exhaust valve spindle, and thus such radial direction is below the valve head. Parallel to the surface and parallel to the substantially flat transition zone between the outer face material and the base material. The radial motion within the material in the vicinity of the shear strain and the resulting transition zone ensures the occurrence of effective adhesion between the materials and is associated with a very effective method of mutual friction of the particles during deformation. Thus, the resulting microstructure has only a very small number of internal defect points within the microstructure. Thus, the joint bonding of materials within the transition zone can have a tough microstructure and completely eliminate the need for geometric locking between the outer surface and the base portion.

  In a preferred embodiment, the transition area between the outer surface and the base portion extends along at least one linear plane in a region extending from inside the rim region of the valve head to the central region of the valve head. In the rim region, the outer surface can have an enlarged portion, which extends upwardly and on the periphery so that the outer surface is itself a dish-like shape with upstanding walls on the periphery. Enclose the foundation part along. At some distance from the rim, the transition zone begins to extend toward the valve head along a straight plane, and this extension of the plane is free of sudden changes in the thickness or shape of the outer surface. Thus, it provides the advantage that there is no significant local change in the method of processing part particle material in the outer surface during forging. In the vicinity of the flat transition zone, the particulate material undergoes substantially the same treatment in the local region, and when one or more flat regions extend from the interior of the rim region to the central region, they are the majority of the valve head. Cover the area.

  The outer surface can be located directly on the foundation part. Alternatively, at least one buffer layer of the alloy is located between the base portion and the outer surface. When such a buffer layer is used, the alloy of the buffer layer is a third alloy having a composition different from that of the base part alloy steel and different from the high temperature corrosion resistance alloy of the outer surface. A difference in composition means that the analysis of the buffer layer alloy differs in the alloying component or in one or more amounts (wt%) of the alloying component. The buffer layer may be alloy steel with different amounts of carbon or other components such as different amounts of chromium, iron or nickel. Thus, the term composition can be considered as meaning an analysis of the alloy. The position of the buffer layer between the base portion of the alloy steel and the outer surface has the effect that the alloy steel is in direct contact only with the metal of the buffer layer and not with the corrosion resistant alloy of the outer layer (surface). The buffer layer acts to reduce or prevent the diffusion of alloying components from the outer surface to the base portion and from the base portion to the outer surface.

  Preferably, the buffer layer is selected from the group consisting of steel, austenitic steel, a nickel-based alloy and an alloy that is iron or nickel based apart from inevitable impurities. Such alloys are believed to be compatible with both the base steel and the outer alloy.

  In one embodiment, the base alloy steel is austenitic stainless steel. For many years it was allowed to make the entire valve spindle from the alloy NIMONIC 80A (registered trademark by Special Metals). However, special alloys similar to this are not as readily available as austenitic stainless steel, and stainless steel also has high strength, and its corrosion resistance exceeds that of stainless steel on the surface facing the combustion chamber. If it can be improved, it will generally work very well, especially in two-stroke crosshead engines. However, stainless steel has a somewhat higher carbon content. The buffer layer absorbs the diffused carbon, so the advantage of using stainless steel for most parts of the exhaust valve is impaired by the high demand for high temperature corrosion resistance and long-term flexibility of the finished exhaust valve. Absent.

  In a preferred embodiment, the buffer layer has a thickness of at least 2 mm. This thickness is even when the buffer layer is of an alloy that exhibits carbide forming ability (in which case the carbon diffusing into the layer is converted to carbide and thus does not cause an increase in carbon activation of the layer). Is sufficient to ensure that carbon cannot diffuse across the buffer layer.

  The invention also relates to a method of manufacturing an exhaust valve spindle for an internal combustion engine, in which the exhaust valve spindle forms a valve head having a base part of alloy steel and a surface of the valve spindle facing the combustion chamber. And an outer surface that is formed from a high temperature corrosion resistant alloy particulate seed material that is nickel-based, chromium-based, or cobalt-based.

  According to the present invention, the method is characterized in that the particulate material is heated to the forging temperature and forged while the particulate material of the high temperature corrosion resistance alloy is held in the enclosure at the base, whereby the particulate The material undergoes a shear strain that causes the particles to deform into an elongated or egg shape, and this forging compresses the particulate material to a density of at least 98.0% and bonds the outer surface to the base portion or to the buffer layer and the base portion. It is to be.

  Forging occurs very quickly compared to HIP processing, so the alloying components have only a short time for diffusion from one alloy to the adjacent alloy while the valve part is at an elevated forging temperature. . As described above, forging presses the particulate material together, and shear strain moves the particles in a direction parallel to the transition zone, causing the particles in the particulate material to rub together and fuse together. During transfer, rubbing and fusing, any oxide film initially present on the particles decomposes and brand new alloy material from any one grain's internal grain is from other internal grain's grain. It is in direct contact with a brand new alloy material, so that the grains can be effectively connected at the microstructure level.

  In one example, the particulate material within the enclosure is provided as a layer of substantially uniform thickness in a region extending from the interior of the rim region of the valve head to the central region of the valve head. When the layer of particulate material is of a substantially uniform thickness within the enclosure and a substantially uniform forging condition is applied, the resulting outer surface has a substantially uniform thickness. Thus, the transition area between the outer surface and the base portion extends in the radial direction of the valve head along that plane in a single straight plane.

  In another example, the particulate material in the enclosure includes a layer of increasing thickness in the region extending from the interior of the valve head rim region to the central region of the valve head toward the central longitudinal axis of the valve. Provided. Since the lower surface of the valve head is usually a flat surface, the lower surface of the base portion can be made with a recessed central region that allows for greater thickness of the outer surface. Thus, the transition area between the outer surface and the base portion can extend along several straight planes, or the transition area can have a slightly curved shape. The increased thickness of the outer surface in the central region of the lower surface of the valve head provides an exhaust valve with a longer life compared to the consumption of particulate material.

  The reason is that during use, the maximum temperature shock (effect) during operation and the maximum loss of material occur in the central region of the lower surface of the valve head. When using an exhaust valve spindle in an engine where material loss is expected to be greatest in the vicinity of the rim area or in other local areas, the outer surface instead increased in the direction of the rim area. It can have a thickness or an increased thickness in such local areas.

  A further method according to the invention is characterized in that a high temperature corrosion resistance alloy particulate material is sprayed at high temperature in an inert atmosphere to produce a pre-formed part, and the pre-formed part and the base part are forged. Heated to temperature and forged, whereby the particulate material undergoes shear strain that deforms the particles into an elongated or egg shape, the forging compresses the particulate material to a density of at least 98.0%, To bond to the base part or to the buffer layer and the base part.

  By this method, the particulate material is initially shaped as a preformed part with a sufficiently stable shape, allowing the particulate material to be located on the base portion as a single body. It is even possible to spray the particulate material directly onto the base part. If the particulate material does not have interconnect porosity, the use of an enclosure can be avoided. If an enclosure is used, the enclosure must be removed by machining after forging is complete. Although the particulate material in the pre-fabricated parts has an irregular shape prior to forging, forging produces the same effect as described in connection with the first-mentioned method. However, the resulting deformed particles have a completely irregular shape.

Whatever method is used, the outer surface material is preferably decompressed to a pressure lower than 1 × 10 ⁻⁴ bar before forging. The vacuum removes gas from the cavities in the particulate material to be forged, which facilitates compression of the material. The gas present in the outer surface material is typically oxygen-free, such as an inert gas, but in practice it is more advantageous to have as little gas as possible. As a result, the outer surface material is preferably depressurized to a pressure lower than 1 × 10 ⁻⁷ bar.

  If a third alloy buffer layer is to be used, this third alloy is different from the base alloy steel (first alloy), and the outer surface hot corrosion resistance alloy (second alloy) Have different compositions. The third alloy is preferably applied to the surface of the base part before the material of the outer surface is located on the surface of the base part. Alternatively, the third alloy can be applied to the outer surface material. However, the surface of the base part is usually regular and smooth so that the third alloy can be applied on it in a very well controlled manner (especially well controlled in terms of quantity and distribution of material in a uniform manner). Surface.

  It is possible to forge in two or more steps or steps to obtain a valve head with an outer surface. Following the forging process of joining the base part and the outer face, the joined base part and the outer face can be forged in at least one subsequent process to obtain the final shape. This is advantageous, for example, when the base part and the outer surface have a cylindrical shape when joined in a first forging process, and subsequently the head part of the valve is forged in a subsequent process. May be. In order to reduce diffusion across the transition zone, forging is preferably carried out in less than 10 minutes and the foundation with the outer surface is cooled immediately after forging.

  In a further development of the method, after completion of the forging, the valve shaft part is friction welded onto the foundation part. One advantage of this is that the amount of material that has to be heated to the forging temperature is much less than in the absence of the valve shaft portion. Another advantage is that instead of having a shaft portion that extends to the side facing away from the outer surface, the base portion is completely enclosed and supported in the mold on that side.

  The forged valve head or the completed valve with the valve head and shaft can optionally undergo a final heat treatment such as tempering or annealing. Heat treatment can cause diffusion of alloying components in the transition zone and can strengthen the metallurgical bond between the materials.

FIG. 5 is a photomicrograph of a ground and polished sample taken from a valve spindle when the outer surface is provided by conventional HIP processing. FIG. 2 is a cross-sectional view of an exhaust valve spindle in the form of an exhaust valve according to the present invention. It is a figure showing roughly forging of a valve head concerning the present invention. It is a figure showing roughly forging of a valve head concerning the present invention. It is a figure which shows the valve head and valve shaft which concern on this invention. FIG. 4 is a photomicrograph of a ground and polished sample taken from a valve spindle when the outer surface is provided in accordance with the present invention. FIG. 4 is a photomicrograph of a ground and polished sample taken from a valve spindle when the outer surface is provided in accordance with the present invention. It is a top view of a test sample. It is a side view of a test sample. FIG. 5 is a photomicrograph of a ground and polished sample taken from a valve spindle when the outer surface is provided by conventional HIP processing. FIG. 3 shows particulate material retained in an enclosure prior to forging according to the method of the present invention.

  1 and 10, the sample is removed from the HIP compacted particulate material, and the circular shape from the cut through the particles is shown. This indicates that the particle maintains its spherical shape during compacting. The spherical shape of the particles is a typical proof of HIP compression, which is the result of isostatic pressure applied during compression. Isostatic pressure causes the particulate material to shrink in such a way that the particles do not move around in the material during the process. This is a very orderly process in which the mutual position between the particles is maintained. In order to more clearly identify the conventional microstructure, three circles have been added to the photograph of FIG. 10 to outline three of the particles that appeared in the photograph.

  FIG. 2 schematically shows an exhaust valve spindle 1 for an exhaust valve for a two-stroke crosshead engine. The left half of the valve is shown from the outside, and the right half of the valve is shown as a cross section that visualizes an example of the position and extent of the outer surface 5. The valve spindle 1 has a valve shaft 2 shown only in its lower part in FIG. 2 and a valve head 3 with a base part 4 and an outer surface 5. The axial direction of the exhaust valve is indicated by an arrow A directed in the direction of a line C extending at the center of the shaft, and the arrow R indicates a radial direction perpendicular to the axial direction.

  The valve seat 6 on the upper surface of the valve head 3 is made of a high temperature corrosion resistant alloy suitable to prevent the formation of indentation marks on the seal surface of the seat. Such seat alloys are well known and are described in the applicant's international patent application WO 97/47862, incorporated herein by reference in connection with the seat alloys.

  The outer surface 5 on the valve head prevents the material from peeling from the exhaust valve and forms a high temperature corrosion resistant material that forms a surface 7 facing downwards towards the combustion chamber when the exhaust valve spindle is mounted in the engine. Of layers. The high temperature corrosion resistant material is formed from a particulate seed material of an alloy that is nickel based, chromium based or cobalt based. In operation, in the engine, the exhaust valve spindle is in a closed position such that the valve seat 6 abuts a stationary valve seat in an exhaust valve housing (not shown) at an appropriate time in the engine cycle, The spindle 1 moves downward and moves between an open position where the valve seat 6 is at a distance from the stationary valve seat. The exhaust valve spindle 1 together with the cylinder inner and cylinder cover (not shown) defines the combustion chamber of the internal combustion engine and is therefore exposed to the high temperature and invasive environment resulting from the combustion.

  The internal combustion engine that utilizes the exhaust valve spindle can be a four-stroke engine or a two-stroke crosshead engine. The two-stroke engine may be a MAN diesel such as MC or ME type, or a Wartsila such as RTA-RTA RTA type. Or it can be made by Mitsubishi. For such a two-stroke crosshead engine, the piston diameter can range from 250 mm to 1100 mm, and the valve head outer diameter can range from 120 mm to 600 mm, typically It can be at least 170 mm.

  From these dimensions, it is clear that the surface of the exhaust valve spindle facing the combustion chamber has a large area, which is large in the outer surface 5 and in the interface area between the outer surface and the foundation part, respectively. Causes thermal stress. In an embodiment of the invention, the outer face 5 is firmly connected to the base part 4 in a flat area extending from the center of the exhaust valve spindle towards the rim area 8 of the valve head.

  The exhaust valve spindle 1 can also be used in smaller engines, such as medium-speed or high-speed four-stroke engines, but the exhaust valve spindle is heavily loaded and favors continuous demand without failure. This is particularly applicable to a two-stroke engine which is a large engine.

  In one embodiment, the outer surface 5 is applied directly on the surface of the base portion 4. In another embodiment of the exhaust valve spindle from which the samples shown in the photographs of FIGS. 6 and 7 are taken, the buffer layer 9 is located between the base portion 4 and the outer surface 5. The buffer layer 9 can be a substantially pure nickel layer applied to the surface of the base part, apart from inevitable impurities. The nickel layer can be applied to the surface in different ways, such as provided as a particulate material placed on top of the base portion. The nickel layer can also be provided in a separate procedure prior to placing the outer surface particulate material on top of the buffer layer. In another such procedure, the base portion can be placed in the plating layer and nickel can be deposited by nickel electroplating, with a thickness in the range of 30 μm to 150 μm, preferably 30 μm to 70 μm. Forming a layer having. The electroplated layer has the advantage that it is a very dense layer of pure nickel. The electroplated layer has a metallurgical bond to the foundation.

  In another embodiment, the buffer layer is of an iron layer, apart from inevitable impurities. One advantage of making a pure or nearly pure iron or nickel buffer layer is that the buffer layer has no or very little carbide source. In this case, the formation of carbide in the buffer layer is suppressed, and the diffusion of carbon into the buffer layer increases the activity of carbon in the buffer layer, so that further diffusion of carbon into the layer is resistant. Receive. Only carbon has very little solubility in iron or nickel. As an example, the solubility of carbon in nickel at a temperature of 500 ° C. is less than 0.1 wt%, so that even if a small amount of carbon diffuses in the buffer layer, the buffer layer has 100% carbon activity. Thus substantially preventing further diffusion of carbon into the layer.

  As another example, the buffer layer 9 can be of steel or austenitic steel. The buffer layer can be a steel plate. As a more specific example, the base part 4 is of forged valve steel (SNCrW—Alloy 1 in Table 1), the outer surface 5 is of Alloy 671, and the steel plate is of Alloy W—Table 2. No. selected from alloys 1.4332. As another example, the buffer layer 9 can be provided as a particulate material of alloy UNS S31603 and the outer surface 5 can be of a particulate material of alloy 671. The base part 4 is forged steel. In this case, both the particulate material of the buffer layer and the particulate material of the outer surface are bonded to the adhesive material on the base part 4 during forging.

  As an alternative embodiment, the buffer layer can be of a nickel-based alloy. This type of alloy is particularly suitable for sufficient bonding with the outer surface alloy, alloy IN625 with 20-23% chromium, alloy INCOLOY 600 with 19-23% chromium or 10-25% chromium. Significantly less chromium than the outer surface, such as less than 25 wt% chromium content, such as alloy IN718 or alloy NIMONIC alloy 105 having about 15% chromium or alloy Rene220 having 10 to 25% chromium Can have a quantity. The buffer layer can also be of a higher nickel-rich alloy because higher amounts of nickel tend to prevent carbon diffusion.

  The particulate material can be made in several different ways well known in the art. For example, a particulate material can be sprayed with a liquid jet of a molten alloy of the desired composition into an inert atmosphere chamber (which causes the material to quench and solidify as particles with a very fine dendritic structure. ). The particulate material can also be referred to as a powder.

  Instead, the particulate material sprays a liquid jet of a molten alloy of the desired composition into an inert atmosphere chamber (in which case the spray of sprayed particles is directed to impinge on the solid part and deposit on it) ). The solid part can be cooled, and in this example, the particles create a preformed part that is separate from the solid part. Instead, the particles can be bonded to the solid part and the base part 4 can be used as it, so that the preformed part is glued directly to the base part.

  A suitable material for the base part 4 is stainless steel. Examples of such materials are shown in Table 1 below. W. -No. Is the German standard number for the alloy. The percentages shown are% by weight.

(Note: C is carbon, Si is silicon, Mn is manganese, Cr is chromium, Ni is nickel, W is tungsten, Mo is molybdenum, and N is nitrogen)
A suitable material for the optional buffer layer is steel as illustrated in Table 2 below. W. -No. Is the German standard number for the alloy. The percentages shown are% by weight.

(Note: C is carbon, Si is silicon, Mn is manganese, Cr is chromium, Ni is nickel, Nb is niobium, Mo is molybdenum)
Another suitable material for the buffer layer is 0.5-1.0% manganese, 16.5-18% chromium, 11.5-14% nickel, 2.5-3.0% Alloy UNS S31603 containing molybdenum, 0-0.1% nitrogen, 0-0.025% oxygen, 0-0.03% carbon and balance iron. If the buffer layer is of plate material, there is usually no requirement for nitrogen and oxygen content. However, when the buffer layer is a fine particle material, the nitrogen content is preferably at most 0.1%, and the oxygen content is preferably at most 0.03%.

  Suitable materials for the outer surface are well known in the exhaust valve industry, examples being Stellite 6, type 50% chromium and 50% nickel alloy, and 48-52% chromium, 1.4-1. .7% Niobium, up to 0.1% carbon, up to 0.16% titanium, up to 0.2% carbon + nitrogen, up to 0.5% silicon, up to 1.0% iron, up to 0 An alloy of type IN657 containing a balance of 3% magnesium and nickel.

  Another example is 40-51% chromium, 0-0.1% carbon, 1.0% or less silicon, 0-5.0% manganese, 1.0% or less molybdenum, 0.05% Up to 0.5% boron, 0 to 1.0% aluminum, 0 to 1.5% titanium, 0 to 0.2% zirconium, 0.5 to 3.0% niobium, up to 5. An alloy with a composition comprising a balance of 0% cobalt and iron agglomerates, up to 0.2% oxygen, up to 0.3% nitrogen and nickel. Other surface alloys suitable for use as exterior surfaces were published in 1990 by the Institute of Marine Engineers in London, “Diesel engine combustion chamber material for heavy fuel operation”. It is described in the article “Review of operating experience with current valve materials” in a book entitled “combustion chamber materials for heavy fuel operation”.

  Forging is prepared by placing the base part 4 of the valve head in the forging position and applying a buffer layer 9 (if any) to the surface of the base part. The particulate material of the outer surface 5 can be provided in several different ways. In one example shown in FIG. 11, the outer surface 5 is provided as a particulate material held in an enclosure 12 at a base portion 4, and the base portion with the enclosure and particulate material is cast as a preparation for forging. Placed in the part. The placement of the enclosure 12 and particulate material on the base portion can be done in several different ways. The enclosure 12 can be welded onto the base portion 4 and can comprise a pipe stud, which is used to fill the particulate material into the enclosure and then used to connect a vacuum device. And then closed before forging.

  Instead, the enclosure 12 is secured to the base portion 4 after the particulate material has been placed in the enclosure. This fixation can be done by using welding or, as another example, by vacuum brazing. As a further alternative, the enclosure is secured to the base portion and subsequently the particulate material is filled into the enclosure and finally brazing is performed. When using vacuum brazing, the enclosure can be cup-shaped and can have a rough thread inside, which threadedly engages with an external thread on the foundation. Solder on the screw part. Heating and fixing can then occur in a vacuum oven. In another example, the particulate material of the outer surface 5 is provided as a preformed part located on the base portion 4 as shown in FIG. The formation of such pre-formed parts will be described in more detail later.

  Prior to forging, the particulate material of the outer face 5 and possibly the base part 4 with the buffer layer 9 and the enclosure 12 are heated to a forging temperature, preferably in the temperature range of 950 ° C. to 1100 ° C. The heated part is introduced into a forging press having a lower mold part 10, an upper mold part 11 and a drive mechanism that can be driven mechanically or hydraulically. The operation of the forging press displaces one mold part towards the other mold part, and the material held in the mold part is mechanically deformed during this displacement. The force required to accomplish forging depends on the dimensions of the valve head. For a valve head with a diameter of about 490 mm, an effective forging operation can be performed with a forging press capable of supplying a compression force in the range of about 250 to 400 MN.

  For smaller diameter valve heads, the compression force utilized can be even smaller, such as 35 MN, for an exhaust valve with a 150 mm diameter valve head. The forging operation is preferably carried out within 10 minutes, more preferably within 3 minutes. During forging, the particulate material of the outer surface 5 is typically compressed such that the thickness of the outer surface is reduced to 30-70% of the initial thickness of the particulate material. If a dense preformed part is used, the density can be somewhat higher before forging, in this example the outer surface thickness is 30-95% of the initial thickness of the particulate material. Can be reduced. The particulate material reduces its thickness so that the resulting density of the outer surface is at least 98.0%. When compacted to this extent using forging, a particulate material of suitable density is obtained. Of course, it is more preferred to further compress the particulate material, for example, to a density of at least 99.0%, better still to a density of at least 99.5%, most preferably to a density of 100%.

  During forging, the particulate material undergoes shear strain, which moves the position of the particles and deforms the material. Strain is a geometric measure of deformation that represents the relative displacement between particles in a material. Shear strain causes the location of the particles to move and deforms the particles during particle interaction. Shear strain acts parallel to the surface affected by forging. Forging affects this surface 7 in the axial direction of the exhaust valve spindle which is perpendicular to the surface 7, so that shear strain acts parallel to this surface (in the radial direction of the exhaust valve spindle). During compression of the outer layer (surface), the shear strain causes the particles to displace radially and rubs the particles together, forcing the particles into a non-spherical shape such as a rectangular shape, egg shape or irregular shape. When forging is complete, the forged valve head is removed from the mold and air cooled or otherwise cooled.

  The amount of effective strain in the outer surface material is preferably at least 0.3. Effective strains are "Manufacturing engineering and technology" by Kalpakjian and Schmid in the 5th edition of Prentice Hall in 2006, or National Swedish technology in Stockholm, 1978. Calculations using traditional methods disclosed in basic textbooks such as “Formelsamgling I Hallfasthetslare” (pages 222-223) by Gert Hedner in publication 104 of the Royal Swedish Technical University Is done. More preferably, the effective strain is at least 0.4. This ensures a very effective and strong bond between the outer surface particles and the base or buffer layer material.

  The first method for manufacturing the exhaust valve spindle is as follows. The exhaust valve spindle has a valve head with a base part of alloy steel and an outer surface that forms the surface of the valve spindle towards the combustion chamber. The base part of the alloy steel is prepared, for example, by forging the material into a suitable shape. A particulate seed material for forming the outer surface is prepared. The material is of a high temperature corrosion resistant alloy. The particulate seed material is enclosed in an enclosure, and the interior of the enclosure has the shape of an outer surface. In other words, the enclosure is prepared to be removed after the valve head has been forged. While the high temperature corrosion resistance alloy particulate material is held in the enclosure by the base portion, the particulate material and the base portion are heated to the forging temperature and positioned within one of the mold parts, typically the lower mold part 10. Is done. The material is then forged, whereby the particulate material is subjected to a shear strain that causes the particles to deform into an elongated or egg shape. At the same time, the particulate material is compressed to a density of at least 98.0% and bonded to the base part or to the buffer layer and the base part.

  A second method of manufacturing the exhaust valve spindle is to hot spray a particulate material of a high temperature corrosion resistance alloy to make a preformed part. The pre-formed part can be formed directly on the base part during the spraying procedure, or the part can be formed separately, placed on the base part and heated to the forging temperature. The preformed part and foundation part and the optional buffer layer can then be forged as an exhaust valve part. During forging, the particulate material undergoes a shear strain that deforms the particles into an elongated or egg shape, and forging compresses the particulate material to a density of at least 98.0%, with the outer surface at the base portion or the buffer layer and the base portion. To join.

  High temperature spraying of the particulate material can be performed by supplying a spray dryer nozzle with a molten alloy and spraying the atomized particles onto the base part 4, in which case the particles are partially bonded. , Stay in a dense state. The base part with preformed parts applied with high temperature spray is heated to the forging temperature, placed in one mold part as described in the above description, and then forged to a dense state. The The particulate material prepared for the outer surface is preferably evacuated prior to forging to reduce the amount of oxygen present in the particles. In this way, the formation of an oxide film on the particles is hindered.

  In forging, the outer surface 5 is compressed to a smaller thickness, such as a thickness that is about 25% less than the initial thickness. At the same time, the density of the material in the outer surface decreases from about 65% to near 100%. The resulting density is preferably at least 98.0%.

  The valve head 3 manufactured by any of the methods described above is a valve head having an outer surface 5 at a surface directed towards the combustion chamber. If the base part 4 of the valve head 3 is formed integrally with the valve shaft 2, the valve head can have a valve shaft or alternatively if it is desired to be simpler, the valve head It can also be manufactured without the shaft 2. In the latter case, the valve shaft must be attached to the valve head after the manufacture of the valve head is complete. FIG. 5 shows the completed valve head and valve shaft 2. These two parts can be joined by friction welding in a known manner. In such friction welding, one part, typically the valve head, is held stationary, while the other part, such as the valve shaft, is first rotated and then abutted against the valve head. As a result, these two parts become a single exhaust valve spindle and are friction welded together.

  The resulting tough microstructure produces a strong bond of material in the transition zone. In accordance with the present invention, this binding can be tested. In order to test the strength against tearing of the material due to the shear load, a special specimen is prepared based on the sample cut from the exhaust valve. The test piece has a shape as shown in FIGS. The test piece has a width (w =) of 9.0 mm, a length (L =) of 40.0 mm, a distance between the centers of the pull holes (d =) of 25.4 mm, and a thickness of the base portion (t =) of 3.5 mm. And an outer surface thickness T. The thickness of the outer surface is measured and set to the thickness T. Then, a groove with a width of at least 2 mm is cut from either side through the entire material, and due to such mutual separation in the longitudinal direction, the resulting overlap due to the interconnection of the layers is the measured thickness of the outer face It becomes smaller than T.

  Eight examples were run and the results are shown in Table 3. It can clearly be seen that the shear strength obtained is at a high level. This level corresponds to the shear strength of the solid material. Thus, the bonds obtained according to the invention do not cause material weakening.

In a further embodiment, the high temperature corrosion resistant alloy particulate material is mixed with particles of isolating material similar to the ceramic material zirconia (ZrO ₂ ). The isolating material can have a greater concentration in the vicinity of the outer surface of the outer surface, and preferably there is no isolating material in the transition zone between the outer surface and the base portion. The outer side particulate material may comprise 5 to 60% by weight of isolating material, but preferably the amount of isolating material does not exceed 40% by weight of the outer side.

  Within the scope of the appended claims, the details of the above embodiments can be combined as other embodiments. Furthermore, the details of the above-described embodiments can be modified within the scope of the claims. For example, the valve seat 6 can be of the same alloy as the valve head, and the buffer layer 9 can be terminated at the valve seat 6 and sloped at the maximum diameter (in the area under the valve seat 6). Or it can have a vertical spread. Any of the above-described embodiments can undergo a final heat treatment such as tempering or annealing. For example, the heat treatment can have a duration in the range of 2 to 6 hours and can occur at a temperature in the range of 800 to 1050 ° C. Other temperatures are possible.

  The exhaust valve spindle is an important engine component and the information for identifying the specific exhaust valve spindle and possible manufacturing details can be stored in a tag embedded in the exhaust valve spindle. Preferably, the tag is of an RFID format that can be read and written remotely, and more preferably includes individual certification data that provides traceability. If desired, a particular spindle can be equipped with more than one tag. The tag can be positioned at a position in the exhaust valve spindle that is well shielded from heat and other tag hazard parameters.

1: exhaust valve spindle, 2: valve shaft, 3: valve head, 4: base part, 5: outer surface, 6: valve seat, 7: surface, 8: rim area, 9: buffer layer, 10: lower mold part 11: Upper mold part, 12: Enclosure.

Claims (15)

An exhaust valve spindle for an internal combustion engine ,
A valve head having a base portion of alloy steel and an outer surface formed from a particulate seed material of a high temperature corrosion resistance alloy that is nickel-based, chromium-based or cobalt-based, forming the surface of the exhaust valve spindle toward the combustion chamber; Have
The particulate seed material is bonded to an adhesive layer;
In the transition zone between the outer face and the base part, the particles in the particulate material on the outer face are deformed into an egg shape or an elongated shape by a shear strain generated by forging the outer face and the base part, and forged. An exhaust valve spindle, characterized in that the outer surface material has a density of at least 98.0%.   The transition area between the outer surface and the base portion extends along at least one linear plane in a region extending from the interior of the rim region of the valve head to the central region of the valve head. Exhaust valve spindle.   At least one buffer layer of the alloy is positioned between the base portion and the outer surface, the buffer layer alloy having a composition different from the alloy steel of the base portion and different from the high temperature corrosion resistance alloy of the outer surface. 3. The exhaust valve spindle according to claim 1, wherein the exhaust valve spindle is a third alloy.   4. The exhaust valve spindle of claim 3, wherein the buffer layer is selected from the group consisting of steel, austenitic steel, nickel-based alloy, and an alloy that is unavoidable of iron or nickel. .   The exhaust valve spindle according to any one of claims 1 to 4, wherein the alloy steel of the base portion is austenitic stainless steel.   6. The exhaust valve spindle according to claim 3, wherein the buffer layer has a thickness of at least 2 mm. A valve head having a base part of alloy steel and an outer surface formed from a particulate seed material of a high temperature corrosion resistance alloy that is nickel-based, chromium-based or cobalt-based, forming the surface of the exhaust valve spindle towards the combustion chamber A method of manufacturing an exhaust valve spindle for an internal combustion engine comprising:
While the particulate material of the high temperature corrosion resistance alloy is held in the enclosure at the base, the particulate material is heated to the forging temperature and forged, thereby causing the particulate material to deform the particles into an elongated or egg shape. A method of manufacturing an exhaust valve spindle, wherein the exhaust valve spindle is subjected to strain and the forging compresses the particulate material to a density of at least 98.0% and the outer surface is bonded to the base part or to the buffer layer and the base part. 8. The exhaust valve spindle of claim 7, wherein the particulate material within the enclosure is provided as a substantially uniform thickness layer in a region extending from the interior of the rim region of the valve head to the central region of the valve head. Production method. 8. In the region extending from the interior of the rim region of the valve head to the central region of the valve head, the particulate material within the enclosure is provided as a layer of increasing thickness toward the center of the valve. Manufacturing method of exhaust valve spindle. A valve head having a base part of alloy steel and an outer surface formed from a particulate seed material of a high temperature corrosion resistance alloy that is nickel-based, chromium-based or cobalt-based, forming the surface of the exhaust valve spindle towards the combustion chamber A method of manufacturing an exhaust valve spindle for an internal combustion engine comprising:
A high temperature corrosion resistance alloy particulate material is hot sprayed to create a preformed part, and the preformed part and foundation are heated to the forging temperature and forged, whereby the particulate material causes the particles to become elongated or Exhaust valve characterized by shear strain that deforms into an egg shape, forging compresses the particulate material to a density of at least 98.0% and bonds the outer surface to the base part or to the buffer layer and the base part Spindle manufacturing method. 11. The method of manufacturing an exhaust valve spindle according to claim 10, wherein the material of the outer surface is reduced to a pressure of 1 × 10 ⁻⁴ bar or less before the forging.   Before the outer surface material is located on the surface of the base portion, a third alloy having a different composition from the alloy steel of the base portion and different from the high temperature corrosion resistance alloy of the outer surface is formed on the surface of the base portion. 12. The method of manufacturing an exhaust valve spindle according to claim 7, wherein the exhaust valve spindle is applied.   13. The forging step of joining the base portion and outer surface, wherein the joined base portion and outer surface are forged in at least one subsequent step to obtain a final shape. Manufacturing method of any exhaust valve spindle. 14. The forging of joining the base part and the outer face is carried out within 10 minutes and the base part with the outer face is cooled immediately after forging to obtain the final shape. A method for manufacturing such an exhaust valve spindle. The method for manufacturing an exhaust valve spindle according to any one of claims 7 to 14, wherein the valve shaft portion is friction welded to the base portion after completion of the forging to obtain the final shape .