CH670104A5 - - Google Patents

Description

DESCRIPTION In many operations, such as in the case of hydroelectric power stations, the maintenance and reconstruction of equipment damaged by cavitation, delivery and various efforts play an important technical and economic role. These works, guaranteeing the smooth running and optimal performance of the installations, are very often expensive and tedious. They consist, periodically, in spray coating with materials particularly resistant to wear, the stressed surfaces, or in reconstituting by welding the deteriorated parts in a material of the same kind as that of the substrate.

The spraying operations are generally carried out using a flame or non-transferred arc plasma. The deposits thus obtained have the advantage of being made at a relatively low temperature which does not affect the basic material and have a surface state making grinding superfluous. On the other hand, their adhesion is insufficient and they cannot help to resist the internal mechanical stresses to which the base metal is subjected (dangers of tearing). On the other hand, during a repair of the substrate, such a deposit must generally be removed.

In the case of reconstitution by arc welding in its various forms (E, TIG, MIG, MAG, UP, Plasma with transferred arc) of worn parts, the deposit obtained by fusion is metallic in nature and is integral with the metal basic. It meets both the requirements relating to surface stresses and internal constraints. The operation being carried out at high temperature with a high energy input, the workpiece is affected thermally and mechanically (deformation). Subsequent heat treatment is, in many cases, essential. The major drawback of reloading by arc welding is the grinding work necessary to guarantee the desired surface finish, a tedious and costly operation.

For the manufacture of carbon steel or low-alloy tubes having an internal coating of stainless steel (clad pipes), this internal coating is provided by welding. This has the disadvantage of causing a dilution of the carbon of the external envelope in the stainless steel coating and therefore of reducing its corrosion resistance properties.

In the two aforementioned examples, it can be seen that the current manufacturing or repairing methods are not entirely satisfactory.

To overcome the aforementioned drawbacks, the licensee has set itself the goal of carrying out a process for coating a support with a metallization layer which meets the following conditions:

1. The metallization layer must have a resistance to abrasion at least equal to that of the base material of the support.

2. The thickness of the metallization layer may vary at will in a continuous manner. The surface will be smooth enough so that shaping grinding is not necessary.

3. The coating will be perfectly homogeneous and will not exhibit porosity.

4. After metallization, no heat treatment will be necessary.

5. The temperature the part will reach during metallization will not change the metallurgical properties of the base material.

6. The process can be used again later without the already deposited layer having to be removed.

7. The process will guarantee the possibility of making repairs to the metallization layer as well as to the base material. The properties of the added layer will not be affected when the base material is held by possible annealing.

8. The metallization layer and its adhesion will have the properties necessary to withstand, without damage or fatigue, the flexions and vibrations of the workpiece.

9. The process will not require any special technical knowledge once the operational plan has been drawn up and will not present any danger to people and installations.

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10. The process can be mechanized or robotized.

11. The support must be able to be metallic or not such as stony material (concrete, ceramic), or synthetic.

The subject of the present invention is a process, and the products which result therefrom, tending to obviate the aforementioned drawbacks of the existing processes and making it possible to satisfy all the conditions listed above. This process is distinguished by the features set out in the claims.

Particular embodiments of the method according to the present invention are defined in the dependent claims.

The accompanying drawing illustrates schematically and by way of example the structure of parts obtained using this process.

Figure 1 illustrates in section the metallization layer deposited on the support and not yet fused.

FIG. 2 illustrates in section a part provided with a partially fused metallization layer.

FIG. 2 illustrates in section a part having been recharged for the first time by welding and then provided with a fused metallization layer.

Figure 4 illustrates Figure 3 in detail.

The present method of coating a metal support with a metallization layer comprises the following successive operations:

1. After a simple cleaning of the surface of the part to be coated, for example by sandblasting, a metallization material of laminated structure is projected onto the support, using an arc plasma under vacuum or under gas protection. mechanically hooks to the support.

2. Then at least partial melting of the metallization layer of the laminated structure is caused to give it, in its molten part, a crystalline structure.

The first phase of this coating process consists in projecting onto the surface of the support, which is a metal part, generally a piece from foundry, a metallization layer using a plasma torch operating with a non-transferred arc alone. or with arcs transferred and not transferred simultaneously, for example that used for VPS “Vacuum plasma spray coating” coatings. It is also possible to use a plasma torch at atmospheric pressure with gas protection. Protection by vacuum or by gas being used to avoid any oxidation of the material, metallic powder, constituting the material constituting the metallization layer.

By this spraying operation, the support is formed by a metallic layer of dense, layered structure, mechanically attached to the surface of the support. This mechanical attachment is good, sufficient in many applications, but is however insufficient for the metallization layer to participate in the mechanical strength of the finished part and to support the elastic deformations of the part and the mechanical stresses which it undergoes.

The material, powder or metallic wire, constituting this metallization layer can be of the same composition, or of the same shade, as the metal or the steel forming the support. This metallization layer may, however, have a composition other than that of the support, a compatible composition, that is to say allowing the formation by fusion of an alloy between the support and the metallization layer, or even in some cases a composition. incompatible with that of the support for cases where the mechanical attachment of this coating layer is sufficient. Under these conditions a non-metallic support can be envisaged, for example, a stony material (concrete, ceramic) or synthetic material.

By acting on the power of the electric arc column, the flow rate of the filler material and the speed of movement of the torch relative to the support, it is easy to adjust the thickness of the metallization layer deposited without however exceeding a temperature. maximum tolerated by the support in order to avoid any deformation thereof and the need for subsequent heat treatments.

It goes without saying that for obtaining very thick metallization layers this projection operation can be repeated several times in succession the successive layers of laminated structures clinging to each other.

The constitution of the metallization layer on the support is relatively rapid. Deposits of the order of ten kilos per hour are easily obtained.

The second phase of the process consists in fusing the final layer or successive metallization layers added to the support, which then gives it a crystalline structure allowing a compact deposit to be obtained with a smooth surface. This eliminates any grinding operation of the workpiece which is a huge time saver.

This melting of the metallization layer is carried out for example using a plasma torch with transferred arc, a TIG torch or a laser. By controlling the intensity of this arc, the speed of movement of this fusion torch relative to the support being the same as that of the deposition torch of the metallization layer, it is easily possible to determine the depth over which the layer of metallization is melted.

In this way it is possible, depending on whether the metallization layer is melted over its entire thickness or only over a part thereof, to obtain parts of different structures.

If the metallization layer is completely fused and its composition is identical, close to or simply compatible with the composition of the support, a part is obtained whose coating, formed by the metallization layer is fused with the support, which makes this part monolithic . In this case the coating participates in the deformations and the stresses undergone by the part in operation.

If the metallization layer is completely fused but its composition is incompatible with that of the support, a part is obtained in which the connection between the support and its coating, although mechanical, remains very intimate. There is no formation of an alloy between the support and the coating.

If the metallization layer is only fused over part of its thickness, a part is obtained, the outer part of the coating of which is fused and has a crystalline structure and therefore a smooth and compact surface, but the inner part of which, in contact with the support has a laminated structure which prevents any dilution of support elements in the coating and vice versa. Under these conditions, the composition of the metallization layer can be either compatible or not compatible with that of the support.

FIG. 1 illustrates with a magnification of 200 × a metal support 1 on which a metallization layer 2 of laminated structure has been sprayed. This metallization layer 2 has not yet been totally or partially fused to obtain a crystal structure.

FIG. 2 illustrates with a 25 × magnification a metallization layer 2 of which only a part 2a has been fused. We can clearly see the stratified structure 2 distinguished from the merged part 2a. Parts 2 and 2a are linked by a zone 3 of partial fusion. In this case, the metallization layer is made of stainless steel of the X5CrNi 134 type.

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FIG. 3 illustrates with a magnification of 25 × a support from the foundry which has been recharged by weld beads 4,4a, 4b by a conventional welding process, followed by grinding. We can clearly see the weld layers 4, 4a, 4b. This part thus recharged was provided with a coating according to the present process. The metallization layer 5 has here been fused over its entire thickness so that a crystalline bond 6 by fusion has taken place between the solder layers 4, 4a and this metallization layer 5 of entirely crystalline structure.

Finally, FIG. 4 illustrates with a magnification of 100 × a detail A of FIG. 3. It shows the limit between the crystal bond 6 and the fused metallization layer 5. We can clearly see that the final structure obtained is crystalline and that the piece is entirely monolithic.

In the case of FIGS. 3 and 4, the composition of the metallization layer must be compatible with that of the support, which is not necessary in the case of FIG. 1.

The part illustrated in Figure 3 was obtained as follows:

On a V5CrNil34 type stainless steel support recharged by welding, a VPS “plasma spray spray coating technology” was sprayed with a metallization layer with a thickness of approximately 5 mm, the same composition as the support.

This metallization layer was then fused by a transferred arc plasma with an average intensity of 200A, a pulse of a frequency of 10 Hz at an advance speed of 0.5 mm / s.

During the melting phase of the metallization layer, a bath width of approximately 22 mm was observed, a penetration of the order of 6 mm, a calm, smooth and very stable bath without projection.

It is interesting to note that the fact of fusing all or part of a metallization layer sprayed by arc plasma under vacuum or under gas protection goes against the opinion of all specialists in this type of coating. Indeed, the reaction of welding specialists is that a fusion of a metallization layer projected by plasma will inevitably cause a shrinkage of this layer due to insufficient compactness (laminated structure) and to the surface tension of the molten metal and that the surface thus obtained, would present large cavities incompatible with the desired goal.

This process can advantageously be used for the repair of machined turbine blades or any other machined or cast mechanical part. We can, using a metallization layer compatible with the support and fully fused, restore the mechanical part to its original characteristics.

Another application for which this process proves particularly useful is the manufacture of tubes provided with internal coating (clad pipes). In this application the tube is made of carbon steel or of low alloy and its coating in stainless steel, it is then important that the melting of the metallization layer is partial only to avoid any dilution of the carbon of the tube in the internal coating which would harm to its anticorrosive qualities. In such an application, the internal coating does not participate in the resistance of the tube and a purely mechanical attachment of the metallization layer to its support is sufficient.

In addition, this process is economically very advantageous because it allows faster execution than the provision of a coating by conventional welding processes and moreover it eliminates the ancillary work of machining and grinding of the affixed coating.

Finally, it should also be noted that this process can be very easily automated or robotic since it suffices to control the relative displacements between the support and the torches, in speed and path, as well as the intensity of the arcs of these torches and the flow filler material.

A particular advantage of this process is that it is able to control precisely the supply of energy to the support during its treatment while obtaining a coating of the desired quality.

In fact, in this process, the addition of material constituting the metallization layer is dissociated from the melting of this layer. The energy to be provided for the fusion of all or part of this metallization layer depends mainly on its thickness. Since this thickness is controllable at will, it follows that the energy supply necessary for the fusion is also controlled and maintained within the desired limit.

This process can also be used to deposit an electrically conductive metallic coating with a crystalline structure on a non-metallic support, for example ceramic.

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1 sheet of drawings

Claims (11)

670104 1. A method of coating a support with a metallization layer, characterized in that a metallization material is sprayed onto the support, using an arc plasma, under vacuum or under gaseous protection. creating a metallization layer of laminated structure mechanically attached to the support; then that at least part of this metallization layer of stratified structure is caused to merge to give it, in its molten part, a crystalline structure. 2. Method according to claim 1, characterized in that the support is non-metallic. 2 3. Method according to claim 1, characterized in that the support is metallic and that the composition of the metallization layer is substantially identical to that of this metallic support. 4. Method according to claim 1, characterized in that the support is metallic and that the composition of the metallization layer is different from that of this metallic support. 5. Method according to claim 3 or claim 4, characterized in that the composition of the metallization layer allows the formation, by fusion, of an alloy with the material constituting the metal support. 6. Method according to claim 2 or claim 4, characterized in that the composition of the metallization layer prohibits the formation, by fusion, of an alloy with the material constituting the support. 7. Method according to one of the preceding claims, characterized in that the metallization layer is fused over only part of its thickness, thus leaving in contact with the support an area with a laminated structure of this metallization layer. 8. Method according to one of the preceding claims, characterized in that the melting of at least part of the metallization layer with a laminated structure is carried out using a transferred arc plasma, welding with an inert gas arc using a non-consumable electrode (TIG) or a laser. 9. Method according to one of the preceding claims, characterized in that the arc plasma used for the projection of the metallization material on the support is an arc plasma operating with an arc not transferred alone or with arcs transferred and not transferred simultaneously . 10. Product obtained according to the method of claim 1, characterized in that it comprises a support partially covered at least with a metallization layer having a crystalline zone and a zone of laminated structure in contact with the support. 11. Product according to claim 10, obtained by the method of claim 5, characterized in that it comprises a support partially covered at least with a metallization layer of crystalline structure, this layer being fused with the material constituting the metal support.