EP2228462B1 - Method for applying a coating to a valve seat of a workpiece - Google Patents

Description

The invention relates to a method for applying a coating to a seat surface of a workpiece, in particular a seat in a nozzle body of an injection nozzle of a two-stroke large diesel engine, and a workpiece, in particular injection nozzle with a coated seat according to the preamble of the independent claim of the respective category.

It is well known that, for example, needle valves have a seat surface which is often provided deep in very long thin bores such that a nozzle needle of the valve, for example a nozzle needle in an injection valve for injecting fuel into the combustion chamber of an internal combustion engine, with the seat functionally cooperate. For example, in the case of injectors, the nozzle needle interacts functionally with the seat as a valve. When the nozzle needle lifts out of the valve seat, fuel can flow from a pressure chamber into a longitudinal bore adjoining the valve seat downstream and from there into the combustion chamber of the internal combustion engine via nozzle holes. If the nozzle needle moves back into the valve seat, so the fuel supply to the nozzle holes is interrupted and the injection of the fuel is terminated in the Berennraum.

Here are the specific work in question such as injectors, control valves for injection components, such as control valves for injection pumps, seats in lubricating oil holes in cylinder inserts of internal combustion engines, for example, in two-stroke large diesel engines, etc. often made special requirements regarding the usable material. For example, workpieces that are operated in an aggressive environment made of corrosion-resistant materials, so that the corresponding component is protected, among other things against high temperatures or chemical attack.

A prominent example of such a highly loaded component are injection nozzles for two-stroke large diesel engines, which are often operated, among other things, with highly aggressive heavy oil.

In large diesel engines, which are used, inter alia, as power units for ships or for power generation in stationary facilities, the fuel - typically, as mentioned above, a heavy oil or other diesel fuel - is introduced by means of fuel injection nozzles in the combustion chamber. These injectors normally include a nozzle head partially projecting into the combustion chamber, also referred to as a nebulizer. The nozzle head is a wear part, which is subject to a high thermal, mechanical and chemical load collective. Depending on the degree of stress, damage to the nozzle head may occur, for example material removal as a result of corrosion, erosion and / or abrasion, or even cracks that can lead to breakup.

The mechanical loads are also based on the high injection pressure, which can be over a thousand bar. Inside the nozzle head, material losses due to cavitation and / or erosion can occur. The thermal loads are based on the high temperatures in the Combustion chamber and the enormous temperature changes between the combustion temperature and the temperature of the freshly supplied purge air. Also in the interior of the nozzle head, through which the fuel is introduced, the intermittent injection leads to shock-like temperature changes. The chemical load of the nozzle head is mainly due to high temperature or hot corrosion. Hot corrosion, which is primarily caused by vanadium, sodium and sulfur contained in the fuel, promotes material degradation and erosion. In particular, the corrosion is the reason that a nozzle head can be unusable after a few thousand hours of operation and must be replaced.

As a material for the nozzle heads in large diesel engines therefore usually steels or alloys based on nickel or cobalt, such as Stellite 6 are used. With the cobalt-based alloy Stellite 6, it is now possible to achieve acceptable component service lives for nozzle heads in large diesel engines with regard to erosion, abrasion and cavitation (in particular in the bores of the nozzle head).

It has been shown that alloys with high chromium and nickel content, in which the chromium and nickel content is, for example, around 50% weight percent, but above all, alloys with a chromium content of more than 50% - weight percent, such as Cr / Ni 65/35 alloys, which are produced by means of a so-called HIP process, although have very good properties in relation to the above-mentioned problems with high-temperature or hot corrosion. Such materials with high chromium content and excellent chemical properties in terms of high-temperature and hot corrosion are already in the EP 1 353 061 disclosed and described in detail.

In the EP 2 000 550 the Applicant has already proposed an improved material which brings significant progress, in particular with regard to brittleness or ductility. In particular, because the development in engine construction, especially in the case of two-stroke large diesel engines can be expected that in future, still more powerful engines, especially the mechanical load requirements especially for highly loaded parts such as the nozzle heads or prechambers will continue to increase. That is, more and more new or modified materials will be needed, but at the same time, the excellent chemical properties of the above-described known materials with respect to high-temperature or hot corrosion must be maintained. In the EP 2 000 550 Therefore, a new material based on a CrNi alloy for producing a semifinished product as a starting material for the formation of a component of an internal combustion engine, in particular large diesel engine, proposed, wherein the material has a nitrogen content of less than 0.1% - weight percent.

Although in the EP 2 000 550 Proposed new material leads to significantly improved properties in terms of chemical and physical loads of the components produced from it, so it is associated with certain components, a compromise.

For example, good corrosion properties of certain materials are at the expense of hardness. For example, in the case of injectors for injecting fuel, the nozzle bodies themselves are well protected against chemically and physically aggressive environments. However, the seating surfaces with which, for example, the nozzle needles co-operate have insufficient hardness, which can cause the respective seating surfaces and / or the nozzle needles to wear prematurely, which can lead to leaks, fuel metering inaccuracies, and the like.

In order to avoid damage to the engine as a whole, increased by the premature wear of the injector fuel consumption or, for example, an increase in pollutants in the combustion gases, the injectors or at least their affected components must be replaced or maintained early, which is of course personnel and costly and if the wear damage is not detected in time In the case of ocean-going vessels, these damages can be a significant security risk.

In principle, these problems can be solved by providing the seating surfaces with a suitable coating so that the seating surface is given the required physical and / or chemical properties by the coating.

The international patent application WO2007148716 A1 discloses a method for coating the seating surface in a bore in which an electrode is guided into the bore and the electrode material is vaporized by electrical discharge and applied to the seating surface.

However, there are so far no satisfactory methods for the production or coating of seats available that must be provided deep down in long thin holes.

To illustrate the problem is based on the Fig. 2a will be briefly considered as an example of an injection nozzle for a two-stroke large diesel engine. For better distinction of the prior art of the present invention, the reference numerals to features of known workpieces are provided with an apostrophe, while the reference numerals to inventive features carry no apostrophe in the context of this application.

The known injection nozzle 31 'of Fig. 2a includes a nozzle body 300 'having a nozzle head 301' connected to the nozzle body 300 '. In the embodiment described here, the connection takes place by means of a holding sleeve 302 ', which tapers at its lower end to the longitudinal axis A' of the fuel injector 31 'out. The longitudinal axis A 'is at the same time also the longitudinal axis A' of the nozzle head 301 '. The retaining sleeve 302 'is by means of a union nut 303' and an elastic member 304 ', for example a snap ring, attached to the nozzle body 300'. The nozzle head 301 'is supported in the tapered portion of the retaining sleeve 302' from.

The nozzle head 301 'has a longitudinal bore 305' and in the region of its lower end at least one nozzle hole 306 ', typically z. B. five nozzle holes 306 ', from the longitudinal bore 305' go out and through which the fuel in the combustion chamber B 'can escape.

In the interior of the nozzle body 300 'is a pressure chamber 307' is provided, in which a feed line 308 'opens for the fuel. The pressure chamber 307 'is bounded in the axial direction by a valve seat 2'. Further, in the interior of the nozzle body 300 ', a nozzle needle 7' is arranged, which extends substantially in the direction of the longitudinal axis A 'and which cooperates with the valve seat 2'. In the in Fig. 2a shown closed position, the lower tip of the nozzle needle 7 'is pressed into the valve seat 2', so that the passage from the pressure chamber 307 'in the downstream adjoining longitudinal bore 305' is closed. The nozzle needle 7 'is spring-loaded in a conventional manner by means of a compression spring, not shown, and biased against the valve seat 2'. In the open position of the nozzle needle 7 ', this is lifted up out of the valve seat 2', so that between the lower end of the nozzle needle 7 'and the valve seat 2', a passage is open, through which the fuel from the pressure chamber 307 'in the longitudinal bore 305 'can get.

The volume between the valve seat 2 'and the nozzle holes 306' is commonly referred to as a blind hole.

The longitudinal bore 305 'is designed in the specific example described here as a substantially cylindrical bore which extends in the direction of the longitudinal axis A'. The diameter d 'of the longitudinal bore 305' defines a flow area, which means the available for the flow of the fuel cross-sectional area in the longitudinal bore 305 'is meant.

The nozzle needle 7 'is in the bore 4', which in Fig. 2a for reasons of space only partially shown, provided and has an inlet opening 5 ', through which the nozzle needle 7' in the bore 4 'can be inserted. The seat surface 2 'is provided from the inlet opening 5' at a distance L ', wherein the bore 4' itself has an inner diameter D ', which is slightly larger than an outer diameter of the nozzle needle 7', so that the nozzle needle 7 'safe and precisely in the bore 4 'is guided.

The distance L 'is typically large against the diameter D' of the bore 4 '. That is, when in the context of the present application of a long thin bore is mentioned, then it is meant a bore whose diameter is small compared to a typical or typical for the bore length.

In the example of an injection nozzle according to Fig. 2a For example, the distance L 'of the seat surface 2' from the entrance opening 5 'is in the range of L' = 30 mm, while the diameter D 'of the bore 4' is only D '= 2.5 mm, for example.

That is, in a long thin bore in the context of the present application, the diameter of the bore is e.g. about 10% of the relevant length of the bore, which of course also significantly different ratios of diameter to bore are possible, depending on which workpiece is concerned.

In the example described above by way of example, it is clear that it is basically difficult to machine the seat inside a long, thin bore. If the absolute dimensions are even e.g. ranging from only a few millimeters to a few 10 millimeters, as in the example of an injection nozzle discussed above, a coating of a seat deep inside in such a thin bore is not possible at all.

The object of the invention is therefore to propose a method for applying a coating to a seat surface of a workpiece, as well as a corresponding workpiece, so that the known from the prior art problems with the seat surfaces of the workpiece are avoided, and in particular higher service life and thus shorter maintenance intervals and ultimately a higher level of operational reliability is achieved.

It is thus provided in particular a method with which a workpiece, in particular a nozzle can be produced, which in a thin and long bore, ie in a relation to the diameter long bore, a coating on a seat surface. A further object of the invention is to provide a method with which a coating can be produced on a seating surface in a thin and long bore. In particular, a method is to be made available with which a seat in a thin and long bore of a workpiece can be retrofitted with a coating. Moreover, it is an object of the invention to provide a workpiece, in particular a nozzle body having a coated seat in a thin and long bore.

The objects of the invention solving this object are characterized by the features of the independent claim.

The dependent claims relate to particularly advantageous embodiments of the invention.

It is thus proposed a method for applying a coating to a seat surface of a workpiece, wherein the seat is provided within a bore in the workpiece at a predetermined distance from an inlet opening of the bore. According to the invention, a coating material is applied to the seat surface in a preceding process step, and in a further process step the coating is formed on the seat surface by means of an energy beam, by directing the energy beam through the bore onto the seat surface.

By the method of the present invention, it is possible for the first time to choose the material properties of a base material from which a workpiece, such as an injection nozzle for a two-stroke large diesel engine is made, completely independent of the material requirements are required to a reliably functioning seat deep inside a long thin bore in the workpiece.

This is achieved by providing the seat deep inside the long thin bore with a coating whose material can be freely selected according to the requirements of the seat surface.

Thus, for the workpiece itself, e.g. a Ni-based, Cr-based, Cu-based or Fe-based alloy material which is relatively soft but offers very good protection against hot gas corrosion or chemical attack. As a coating material for the seat then, for example, a significantly harder material can be selected, so that the seat against permanent mechanical stress better against premature wear, for example. is protected by material removal, cavitation, erosion, micro-welding or material fatigue, etc.

In another example, it is also possible that the coating of the seat surface is made of a softer material than the workpiece itself, for example, to achieve a better seal on the seat or other or to realize another desired material property on the seat For example, a material of a metal matrix with embedded particles whose hardness is equal to or higher than that of the metal matrix, are used.

Other properties can be optimized by the coating on the seat. For example, it is possible that the seat itself must be protected against other corrosive processes, such as e.g. an outer wall of the workpiece itself, which is exposed to another aggressive environment with harmful effects.

The skilled person immediately understands that the present invention is so flexible that by suitable choice of the material for the coating on the Seat and / or the fact that the coating process itself certain coating conditions are selected specifically, such as the energy density of the energy beam or the action of the energy beam during the coating process, virtually any desired property of the coating on the seat can be selectively adjusted.

The coating material is applied to an energy input by the energy beam, preferably in the form of a coating powder and / or in the form of a coating wire, or in the form of small pieces of a coating wire and / or in the form of a prefabricated coating body at least on a part of the seat.

In another embodiment of the invention, the coating material may also be applied to the seating surface simultaneously with energy input by the energy beam, i. It is a special case of the well-known order welding.

In particular for the production of a new workpiece, e.g. a new injection nozzle for a two-stroke large diesel engine, after the formation of the coating on the seat through the coating through a function hole can be introduced through which can be transported in the operating state, for example, fuel.

Particularly preferably, a laser beam is used as the energy beam, but also other energy beams such as an electron beam can be used advantageously in certain cases.

As mentioned several times, the seat is provided in a workpiece according to the invention in a long thin bore deep in the workpiece, wherein a smallest diameter of the bore in a region between the inlet opening and the seat maximum 50% of the distance, in particular not more than 25% of the distance, and the smallest diameter of the Bore preferably a maximum of 10% of the distance from the inlet opening amounts.

In this case, the workpiece is preferred, but not necessary, a nozzle body of a nozzle, in particular an injection nozzle of a two-stroke large diesel engine, or a safety valve or a control valve for a component of an injection system or a lubricating oil hole in a cylinder insert.

As a coating material is in principle any material in question, with which a desired property of the coating can be adjusted on the seat. For example, a cobalt-based alloy, and / or a chromium-based alloy and / or a nickel-based alloy and / or an iron-based alloy may be used as coating material.

The disclosure further relates to a workpiece in which a seat surface is provided within a bore at a predetermined distance from an entrance opening of the bore, wherein on the seat surface, a coating is formed, which made by means of a directed through the bore on the seat energy beam of a coating material is.

In particular, a function bore can be provided through the coating.

A smallest diameter of the bore is in a region between the inlet opening and the seat maximum 50% of the distance, in particular a maximum of 25% of the distance, and the smallest diameter of the bore may preferably not exceed 10% of the distance of the seat from the inlet opening amount.

For example, as the coating properties on the seating surface are virtually arbitrarily flexibly adjustable, a hardness of the coating other than a hardness of the workpiece and / or a corrosion resistance of the coating may be different from a corrosion resistance of the workpiece and / or any other property of the coating differ from the corresponding characteristic of the workpiece.

Fig. 1a - 1 c:

ein erfindungsgemässes Verfahren zur Herstellung einer Beschichtung auf einer Sitzfläche;

Fig. 2a - 2d:

ein erfindungsgemässes Verfahren zur Nachrüstung einer Einspritzdüse mit einer Sitzflächenbeschichtung;

Fig. 3a - 3d:

ein erfindungsgemässes Verfahren zur Herstellung einer Einspritzdüse mit einer Sitzflächenbeschichtung.

In the following the invention will be explained in more detail with reference to the schematic drawing. Show it:

Fig. 1a - 1c:

an inventive method for producing a coating on a seat surface;

2a-2d:

an inventive method for retrofitting an injection nozzle with a seat surface coating;

3a-3d:

an inventive method for producing an injection nozzle with a seat surface coating.

Based on Fig. 1a to 1c a first simple embodiment of a method for producing a coating 1 on a seat surface 2 in a long thin bore 4 of a workpiece 3 is exemplified. The workpiece 3 of Fig. 1 is a partially sectional control valve 3 of a component of an injection system for a two-stroke large diesel engine. The seat 2 is used in the assembled state of the control valve 3 for supporting a movable along the axis A valve needle, which is used only after application of the coating 1 to the valve seat 2 in the control valve 3. In the hole 4 according to Fig. 1a - 1c it is a thin long hole in the sense of registration. In the present case, the bore has a diameter of 3.5 mm and the Seat 2 is arranged from the inlet opening 5 at a distance L of about 25 mm deep in the bore. That is, the smallest diameter D of the bore, which is constant in the present case along the axis A, is only about 14% of the distance L of the seat 2 of the input port. 5

In a previous process step is according to Fig. 1a a coating powder 100, 101 applied to the seat 2 in such a predetermined amount that the coating 1 in the predetermined thickness and geometry on the seat surface 2 can be generated. In a further process step is according to Fig. 1b an energy beam 6, which in the present case is a very fine laser beam 6, which has a diameter which is smaller than the diameter D of the bore 4, generated by a laser 600 and directed through the bore 4 on the seat surface 2.
By the energy input by the laser beam 6, the coating powder 100 is heated, thereby wholly or partially melted or melted, so that finally on the seat 2, the coating 2 is formed, for example due to formation of a fusion metallurgical compound or adherence of the layer.

In Fig. 1c is to see the finished coating 1 on the seat 2, which may need to be reworked, if necessary, to ensure a secure fit of the valve needle, not shown on the coating 1.

Based on Fig. 2a to 2d will be explained schematically below, as with the aid of the invention, a per se known injector 31 'for a two-stroke large diesel engine with a coating 1 can be retrofitted.

In Fig. 2a is an injection nozzle 31 'known from the prior art partially and schematically shown in section. The Fig. 2a has already been described in detail above, so that with the description of the Fig. 2b is continued.

For applying a method according to the invention was according to Fig. 2b from the injection nozzle 31 ', first the nozzle needle 7' removed.

In Fig. 2c , which shows the area of interest around the seat 2 somewhat more clearly in detail, a prefabricated coating body 102 made of a coating material 100 was placed on the seat surface 2 through the bore 4. Since the injection nozzle 3, 31 is already a workpiece 3 according to the present invention at the latest, and no longer an injection nozzle 31 'known from the prior art, from now on all reference symbols without apostrophes are used, since the corresponding ones are used Features relate to an inventive injection nozzle 3, 31.

In Fig. 2d is the completion of the seat 1 just completed. The laser is about to shut down. The coating body 102 was heated by the laser beam 6 from the laser 600 in a predetermined heating process such that the coating body 102 was reliably connected to the seat surface 2 and thus forms a coating 1 according to the present invention on the seat surface 2. Thus, a known per se injection valve has been successfully retrofitted with a seat coating 1 according to the invention.

Based on Fig. 3a to 3d Finally, yet another embodiment of a method according to the invention will be explained schematically with which an injection nozzle 3, 31 of the present invention can be newly manufactured.

In Fig. 3a is a blank of a nozzle head 301 partially and schematically shown in section. The blank of the nozzle head 301 has a blind bore 4, at the lower end of which a seat 2 is provided at a distance L from an inlet opening 5 such that the seat surface 2 extends over the entire cross section of the blind hole 4. In the bore 4, a coating powder 100, 101 introduced, which covers the seat 2. The laser 600 has just been switched on and heated with the laser beam 6 through the bore 4 through the coating material 100, 101, whereby a coating 1 on the seat surface 2 is formed. In Fig. 3b the laser 600 has already been switched off because the coating 1 on the seat surface 2 is finished.

Thus, in the finished state, the injection nozzle 31 can fulfill its function, according to Fig. 3c by means of a suitable drill through the bore 4 through a longitudinal bore 305 in the form of a blind hole through the coating 1 and the seat 2 is introduced.

Finally, in the nozzle head 301 from the outside nor nozzle holes 306, as in Fig. 3d shown schematically, so that in the operating state fuel via the longitudinal bore 305 and the nozzle holes 306 can be injected in a conventional manner through the injector 301 into the combustion chamber of an internal combustion engine.

By a workpiece 3, for example in the form of a nozzle 31 so far unreachable service life can be realized, which is particularly important from an economic point of view of great importance.

The nozzle head is on the one hand thus, among other things, especially for future generations of large diesel engines, which are even more powerful and even higher demands on the load capacity of the nozzle heads. On the other hand, already in-service components according to the invention can be retrofitted.

Of course, the invention is not limited to special applications in large diesel engines, but the invention can be used successfully wherever long thin holes in the sense of present invention seating surfaces must be provided with coatings that have to fulfill certain functions.

Claims (6)

1. A method of applying a coating (1) to a seat surface (2) of a workpiece (3), wherein the seat surface (2) is provided within a bore (4) in the workpiece (3) at a predefined spacing (L) from an input opening (5) of the bore (4) and a smallest diameter (D) of the bore (4) amounts to at most 50% of the spacing (L) in a region between the input opening (5) and the seat surface (2), characterized in that a coating material (100, 101, 102) is applied to the seat surface (2) in a prior method step and the coating (1) is formed at the seat surface (2) in a further method step by means of a beam of energy (6), in that the beam of energy (6) is directed at the seat surface (2) through the bore (4), wherein a laser beam (6) or a beam of electrons (6) is used as a beam of energy (6).
2. A method in accordance with claim 1, wherein the smallest diameter (D) of the bore (4) amounts to at most 25% of the spacing (L) in a region between the input opening (5) and the seat surface (2), and the smallest diameter (D) of the bore (4) is preferably selected to be at most 10% of the spacing (L).
3. A method in accordance with claim 1 or claim 2, wherein the coating material (100) is applied to at least a part of the seat surface (2) in the form of a coating powder (101) and/or In the form of a coating wire (101) and/or In the form of a prefabricated coating body (102) prior to the Introduction of energy by means of the beam of energy (6).
4. A method in accordance with any one of the preceding claims, wherein a functional bore (7) is introduced through the coating (1) after the formation of the coating (1) at the seat surface (2).
5. A method in accordance with any one of the preceding claims, wherein the workpiece (3) Is a nozzle body of a nozzle (31) or is a safety valve or a control valve for a component of an injection apparatus or a lubrication oil bore In a cylinder insert.
6. A method In accordance with any one of the preceding claims, wherein the coating material (100, 101, 102) is a cobalt base alloy and/or a nickel base alloy and/or a chrome base alloy and/or an iron base alloy.

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