HK1076648B - Method for providing a component of a large machine with a protective coating - Google Patents

Description

Method for providing a protective layer for a large machine component

Technical Field

The invention relates to a method for providing a large machine component, in particular a piston head or an exhaust valve disk of a two-stroke large diesel engine, with a protective layer which is applied to the surface by means of build-up welding.

Background

In the execution of the method of the type described above, a very severe thermal load is generated on the component to be provided with the protective layer as a result of the welding process. There is therefore a risk of exceeding the permissible temperature of the component material. Starting from the protective layer of a large machine component of the type described above, this risk is particularly great when the protective layer has a relatively large mass.

When machining a protective layer by build-up welding, it is therefore necessary to interrupt the welding process several times in order to cool the component. This is time consuming and uneconomical. Furthermore, the interruption of the welding process due to the intermediate cooling can also have an adverse effect on the achievable strength of the protective layer. Especially nickel-based alloys are particularly sensitive to this. Furthermore, the interruption of the welding process causes a certain deformation, which requires repeated reworking several times.

Disclosure of Invention

The object of the present invention is therefore to improve a process of the above-mentioned type in such a way that an economical and reliable process can be achieved in simple and economical manner.

According to the invention, this object is achieved in that the large machine component to be provided with the protective layer is cooled during the build-up welding process, wherein the cooling is effected in such a way that, at least after a certain start-up time, the heat input as a result of the welding process is substantially equal to the heat dissipated by the cooling medium.

These measures ensure that the protective layer or each of the protective layers can be welded without interruption. Thus, a time-saving and economical process can be achieved. However, the temperature of the component to be coated can be kept below a critical value, so that the substrate bearing the protective layer is not damaged. The possible thermal distortion is also minimized due to the lower temperature of the substrate during welding. Permanent deformation of the substrate due to thermal deformation and internal stresses due to permanent deformation are thus avoided to the greatest possible extent, which ensures a high stability of the entire component. The cooling of the large machine components to be coated, which is effected during the welding process, is expediently carried out in such a way that the heat input by the build-up process is substantially equal to the heat dissipated by the cooling medium, and that an equilibrium state is established after a defined start-up time. It is thus ensured that, even in the case of relatively long durations of the welding process beyond the start time, i.e. in the case of very large components, no noticeable temperature increase can occur from a certain temperature. The above-mentioned disadvantages and difficulties are accordingly completely overcome by the measures according to the invention.

According to a further development of the invention, advantageous further developments of the above-mentioned measures and suitable embodiments are provided.

It is desirable to use water as the cooling medium. Such media are relatively economical to use and can therefore be used in a continuous process, thus eliminating the recycling and disposal costs.

Advantageously, the cooling medium may be sprayed onto the surface. This also results in a good distribution of the cooling medium in the case of irregular component geometries.

Another expedient can be to arrange the component to be coated in such a way that it is provided with a protective layer from above and is cooled from below in order to weld the protective layer. This allows the cooling medium to be automatically discharged downward.

In a further development of the above measure, the cooling medium is injected into a space enclosed by a surrounding wall. This ensures that the cooling medium can be kept out of contact with the welded material.

Further advantageous configurations and suitable further embodiments of the above-described measures are specified below by way of example illustration with the aid of the drawings.

Drawings

The figures show:

FIG. 1 is a schematic view of a first example of application of an exhaust valve according to a large two-stroke diesel engine, and

fig. 2 is a schematic view of a second application example of a piston head according to a two-stroke large diesel engine.

Detailed Description

The main field of application of the invention is to provide components of large machines, such as large two-stroke diesel engines, with a protective layer produced by bead welding, wherein the protective layer to be applied has a considerable mass of at least 10kg, as is usually the case for protective layers of exhaust valves or piston heads of large two-stroke diesel engines.

Fig. 1 shows an exhaust valve 1 of a two-stroke large diesel engine. This may be, for example, a venting valve suitable for an 80cm opening. The exhaust valve is provided with a protective layer 4, for example made of a nickel alloy, on the bottom 2 of its valve disk 3, which in operation faces the combustion chamber, and which is applied by a welding device 5 in a build-up welding process. The welding device 5 may be a gas shielded welding device (GMAW) or an electroslag welding device (ESW).

The welding device 5 is equipped with a clamping device 6, in which the exhaust valve 1 is clamped with its shank. The welding device 5 is located above the clamping device 6. The exhaust valve 1 is clamped in the clamping device 6 in such a way that in operation the bottom surface 2 of the valve disk 3, which is directed downwards, is directed upwards. The welding device 5 and the venting valve 1 are moved relative to each other in such a way that the entire surface of the base surface 2 can be provided with a protective layer 4.

In the example shown, the clamping device 6 can be rotated about a vertical axis a as indicated by the arrow. During the corresponding operation of the clamping device 6, the exhaust valve fixed in the clamping device 6 is also correspondingly rotated about its vertical axis. The welding device 5 is moved back and forth transversely to the axis a as indicated by the directional arrow. The entire surface of the bottom surface 2 of the valve disk 3 can be coated for the rotating outlet valve 1 by the reciprocating movement of the welding device 5. Of course, other movement mechanisms are also possible, for example, by the fixedly arranged outlet valve 1 and the welding device 5 moving in a spiral manner.

The mutual movement between the welding device 5 and the outlet valve 1 is effected in such a way that the protective layer 4 is welded in the desired layer thickness. The coating rate is 11kg/h in the example shown. The corresponding build-up welding process lasts about 1h with a total mass of 11kg of the entire protective layer 4. However, in order to prevent excessive heating of the vent valve during the weld overlay process, this vent valve is cooled during the weld overlay process. The cooling is expediently effected in such a way that, after a certain start-up time, the heat transferred from the build-up process to the exhaust valve 1 is completely or largely removed by the cooling medium used.

During the start-up time, i.e. during the initial phase of the weld deposit process, the heat transferred from the weld deposit process to the large machine component being machined, in this case the exhaust valve 1, is generally also greater than the heat removed by the cooling medium, so that a certain heating of the large machine component being machined occurs during the start-up time. However, the heat transfer is also improved with increasing temperature in such a way that, after a certain time, the above-described equilibrium between the input and output heat and thus the elimination of heating of the large machine components results. It is desirable to design the cooling such that the above-mentioned equilibrium state is reached at an optimum process temperature. This temperature is 200 ℃ in the case shown. The cooling is then effected in such a way that the large machine component is no longer heated further from the temperature of 200 ℃ during the welding process.

In the example shown, a cooling medium is applied to the surface 7 of the valve disk 3 which is directed downwards, i.e. the surface opposite the surface to be provided with the protective layer 4, during the welding process in order to achieve the desired cooling. It is expedient to use water as cooling medium, which is sprayed onto the surface 7 to be cooled. For this purpose, a ring pipe 8 is provided, which surrounds the neck of the exhaust valve 1 and is arranged concentrically to the axis a, and which, in the region facing the surface 7 to be cooled, is provided with nozzles 9 which are directed at the surface 7 and which can be formed simply as openings. The loop 8 is connected via a supply line 10 to a source of cooling medium, here for example a water network. The nozzles 9 are arranged such that the surface 7 to be cooled is uniformly supplied with the cooling medium. A collar 8 surrounding the valve neck at a distance can be fixedly arranged.

In order to prevent the cooling medium or a possibly occurring cooling medium vapor from coming into contact with the protective layer 4 during the welding process, a flange-shaped protective collar 11 projecting downward is arranged on the circumference of the valve disk 3. The protective ring can be a simple circumferential sheet metal housing. The protective ring 11 delimits, together with the valve disk 3, a circumferentially closed space 12 which is open only in the downward direction and into which the cooling medium can be injected without the cooling medium entering the surface region to be provided with the protective layer 4. The cooling medium can be conveniently discharged through an opening in the space 12 directed downwards. It is of course also conceivable to close the space 12 downwards and to provide it with a bottom discharge drain. The discharged cooling medium can be conveniently conveyed to a drainage system. The above-mentioned closed space 12 can also advantageously be connected to a suction device for sucking out steam. In this case, the pressure equalization is usually achieved by the existing non-tightness, so that additional air supply can be dispensed with.

The method procedure of the example shown in fig. 2 corresponds substantially to the example shown in fig. 1. The same reference numerals are therefore used for the same components in the following description of fig. 2.

In the example shown in fig. 2, the piston head 13 of a two-stroke large diesel engine piston is provided with a protective layer 4 on the surface 14 of its piston bottom 15, which protective layer is applied by a welding device 5 in a build-up welding process. The piston head 13 is fixed to a rotary table 17 by the lower end face of its skirt 16. This rotary table may be provided with suitable clamping means. The welding device 5 is located above a rotary table 17, which can be moved to and fro.

The underside of the piston bottom 15, on which the protective layer 4 is to be arranged, is provided with a cooling medium during the welding process. For this purpose, a ring pipe 8 is provided, which is arranged concentrically to the piston axis and is equipped with nozzles 9 and is connected via a supply pipe 10 to a cooling medium source, here likewise expediently to a cooling water source in the form of a water pipe network.

In the piston head 13 of the type shown here, a circumferential space 12a delimited circumferentially by the surrounding wall in the form of a piston skirt 16 or a bearing flange 18 and upwards here through the piston bottom 15, i.e. the component to be coated, is automatically obtained on account of the piston skirt 16 connected to the piston bottom 15 or the bearing flange 18 arranged concentrically thereto, into which space the cooling medium can be injected without entering the region of the surface 14. The grommet 8 is in the example shown located inside the space surrounded circumferentially by the support flange 18. The rotary table 17 is suitably provided with an opening 19 for the passage of the supply pipe 10. In the example shown, the openings 19 simultaneously serve as drainage openings for the coolant. A suction pipe for sucking out steam from the space 12a is also conceivable.

The piston head 13 is provided here in the circumferential region of the piston base 15 with a circumferential cooling channel 10, which communicates with inlet and outlet lines, not shown. A cooling medium can also be applied to the cooling channel 20 in order to achieve an additional cooling effect. In this case, a rotary through-hole is required for the rotary table 17, which is associated with the supply and discharge lines. For a stationary table, a rotary through-hole may be dispensed with, which may simplify loading of the channel 20.

Although some preferred embodiments of the present invention have been described in detail above, it should not be limited thereto. The method according to the invention can of course also be used for other associated large machine components, such as cylinder liners or cylinder heads of large two-stroke diesel engines.

Claims (14)

1. A method for providing a large machine component with a protective layer (4) which is applied to the associated surface (2 or 14) by means of build-up welding and has a mass of at least 10kg, characterized in that the large machine component to be provided with the protective layer (4) is cooled during the build-up welding process, wherein the cooling is effected in such a way that, in the initial phase of the build-up welding process, the amount of heat transferred from the build-up welding process to the large machine component is greater than the amount of heat removed by the cooling medium, and after this start-up time, the amount of heat input by the build-up welding process is substantially equal to the amount of heat removed by the cooling medium.

2. The method according to claim 1, characterized in that water is used as cooling medium.

3. A method according to any of the preceding claims, characterized in that the large machine component is subjected to a cooling medium during the build-up welding process on the surface opposite the surface (2 or 14) to be provided with the protective layer (4).

4. Method according to claim 1, characterized in that for welding the protective layer (4) the large machine component is arranged so that it is cooled from below with the protective layer (4) arranged from above.

5. The method of claim 1, wherein the cooling medium is sprayed onto the surface.

6. A method according to claim 5, characterized in that the cooling medium is sprayed onto the surface through at least one loop (8) provided with nozzles (9) connected to a source of cooling medium.

7. A method according to claim 5, characterized in that the cooling medium is injected into a space (12 or 12a) enclosed by a surrounding wall (11 or 16, 18).

8. A method according to claim 7, characterized in that for a piston head (13) the cooling medium is injected into the space (12a) delimited by the piston skirt (16) or a support flange (18) concentric therewith.

9. Method according to claim 7, characterized in that for a venting valve (1), a circumferential housing (11) is arranged on the circumference of the valve disk (13) in order to form a circumferentially closed space (12) to which a cooling medium can be applied.

10. The method according to any one of claims 7-9, wherein the cooling medium is discharged downwards.

11. Method according to any of claims 7-9, characterized in that the space (12 or 12a) is subjected to suction.

12. A method according to claim 1 or 2, characterized in that for a large machine component, which has an internal cooling system consisting of at least one cooling channel (20) arranged in the region of the wall to be provided with the protective layer (4), this cooling system is supplied with a cooling medium during the build-up welding process.

13. A method according to claim 1 or 2, characterized in that the large machine component is rotated during the build-up welding.

14. A method according to claim 1 or 2, wherein the large machine component is the piston head or exhaust valve disc of a two-stroke large diesel engine.