EP2371994B1 - Method for depositing a stainless steel coating on a copper substrate - Google Patents

Description

The present invention relates to a method for producing a thin coating of stainless steel on a copper matrix using a heated carrier gas to convey unmelted stainless steel particles.

In the food field, it is customary to achieve a cooling of certain foodstuffs by heat exchange, that is to say by putting the food to be cooled in contact with metal plates acting as heat exchangers.

Stainless steel is a metal recommended for food but with poor thermal conductivity. On the other hand, copper has good thermal conductivity but its direct contact with food is not recommended.

From there, it has been proposed to use copper plates coated with a thin layer, that is to say a thin surface coating of stainless steel. Indeed, such an association has the advantages of copper and steel but without the disadvantages.

However, making stainless steel coatings on copper is not easy. Indeed, it is necessary not only to obtain a good bonding of the stainless steel on the copper but also to avoid the formation of porosities and any possible deformation of the matrix.

The problem is to be able to achieve a coating of a thin layer of stainless steel on a copper matrix which leads to a good attachment of the stainless steel on the copper without causing a significant proportion of porosities and / or deformations of the matrix.

FR 2520265 teaches the deposition of a stainless steel coating on a substrate. GB 2394479 describes the deposition of a copper layer on a stainless steel substrate.

The solution is a process for producing a stainless steel coating on at least a portion of the surface of a copper matrix, characterized in that unmelted or partially melted stainless steel particles are projected onto the matrix in copper to be coated using a carrier gas heated to a temperature between 50 and 800 ° C, said carrier gas being nitrogen or helium.

• le gaz vecteur est chauffé à une température d'au moins 70°C.
• le gaz vecteur est chauffé à une température d'au plus 700°C.
• les particules d'acier inoxydable sont non fondues.
• les particules d'acier inoxydable ont une taille moyenne comprise entre 5 et 50 µm.
• les particules d'acier inoxydable sont formées d'acier inoxydable austénitique.
• le revêtement est formé d'une ou plusieurs couches d'acier inoxydable.
• le revêtement a une épaisseur inférieure à 1000 µm, de préférence inférieure ou égale à 500 µm, de préférence inférieure ou égale à 200 µm, typiquement inférieure ou égale à 100 µm environ.
• le revêtement a une épaisseur supérieure à 1 µm, de préférence supérieure ou égale à 10 µm, de préférence supérieure ou égale à 25 µm.
• la matrice en cuivre est portée par ou formée d'une pièce de forme tubulaire ou une plaque.
• la matrice est une plaque de cuivre.
• la matrice est un tube en cuivre.
• le gaz est distribué à une vitesse entre 300 et 1600 m/sec, de préférence d'au moins 400 m/sec.
• le mélange gaz vecteur/poudre est distribué au moyen d'une tuyère de Laval, c'est-à-dire avec passage interne convergent/divergent.
• le chauffage du gaz est opéré au moyen d'un pistolet de projection comprenant des moyens de chauffage du gaz permettant de leur conférer la température souhaitée, de préférence les moyens de chauffage comprennent au moins une résistance électrique apte à et conçue pour réchauffer un gaz par contact direct ou indirect.

Depending on the case, the method of the invention may include one or more of the following features:

• the carrier gas is heated to a temperature of at least 70 ° C.
• the carrier gas is heated to a temperature of at most 700 ° C.
• the stainless steel particles are unmelted.
• the stainless steel particles have an average size of between 5 and 50 μm.
• the stainless steel particles are made of austenitic stainless steel.
• the coating is formed of one or more layers of stainless steel.
• the coating has a thickness less than 1000 microns, preferably less than or equal to 500 microns, preferably less than or equal to 200 microns, typically less than or equal to about 100 microns.
• the coating has a thickness greater than 1 μm, preferably greater than or equal to 10 μm, preferably greater than or equal to 25 μm.
• the copper matrix is carried by or formed of a tubular piece or a plate.
• the matrix is a copper plate.
• the matrix is a copper tube.
• the gas is distributed at a speed between 300 and 1600 m / sec, preferably at least 400 m / sec.
• the carrier gas / powder mixture is distributed by means of a Laval nozzle, that is to say with convergent / divergent internal passage.
• the gas is heated by means of a spray gun comprising means for heating the gas to give them the desired temperature, preferably the heating means comprise at least one electrical resistance adapted to and designed to heat a gas by direct or indirect contact.

Example

In order to show the efficiency of the process of the invention, the deposition of a layer 7 of the order of 100 μm of austenitic stainless steel type 304 on the outer surface 8 of a copper tube 10 ( matrix) of 1 cm thick by a thermal spraying method according to the invention, as illustrated in FIG. Figure 2 .

More specifically, fine solid (unmelted) stainless steel particles are accelerated in a heated gas stream, particularly nitrogen (N ₂ ) or helium (He) at a temperature less than 700 ° C, for example 350 ° C.

According to the invention, the carrier gas is therefore not sufficiently heated to allow the projected stainless steel to melt since it has a melting point of about 1450 ° C. to 1538 ° C. depending on the Cr and Ni it contains.

The heating of the particles and their projection are done by means of a heat spray gun 1, as illustrated in FIG. Figure 1 fed, on the one hand, with carrier gas 2, for example nitrogen from a storage tank or bottles of gas and, on the other hand, with powder 3 from a powder reserve .

The spray gun 1 is provided with gas heating means 4 to give them the desired temperature, for example an electrical resistance 4 of 17 kW which heats the gas by direct or indirect contact. The heated gas and the powder are mixed in a mixing chamber 5 located in the gun 1, before being expelled by a jet nozzle 6, for example a Laval nozzle with converge / divergent, and to go impact the copper matrix of the tube 10 to form the layer 7 (or the successive layers) of desired coating.

The injection of fine particles (approximate size between 5 and 50 μm) into the supersonic gas jet (i.e.> 360 m / sec) accelerates them sufficiently to allow their adhesion to the copper support matrix. The impact of the particles on the matrix actually causes plastic deformation of the particles thus releasing sufficient energy to obtain a good adhesion of the stainless steel particles on the support matrix.

The nozzle / die distance is chosen empirically so as to obtain a homogeneous coating over the entire surface covered, typically the nozzle is at a distance between 30 mm and 60 mm of the matrix to be coated.

It should be noted that, in general, the matrix may be prepared, in particular sandblasting, prior to the projection of the stainless steel particles, so as to clean it (degreasing) and to promote the attachment of the projected particles.

With the method of the invention, it is possible to make one (or more) layer (successive) of stainless steel on the copper matrix.

The coating obtained has good adhesion to the matrix, is of good quality and almost devoid of porosity and the substrate (matrix) has not undergone any deformation or modification of its characteristics because of the low temperatures used. The projected stainless steel powder has also retained its characteristics.

In addition, the stainless steel coating could then undergo, without breaking, a machining to give it a smooth surface appearance.

Claims (10)

1. Method for producing a stainless steel coating on at least part of the surface of a copper matrix, characterised in that particles of stainless steel which are non-molten or partially molten are sprayed onto the copper matrix to be coated using a carrier gas heated to a temperature of between 50 and 800 °C, said carrier gas being nitrogen or helium.
2. Method according to claim 1, characterised in that the carrier gas is heated to a temperature of at least 70 °C and/or the carrier gas is heated to a temperature of at most 700 °C.
3. Method according to any of the preceding claims, characterised in that the gas is heated by means of a spray gun comprising means for heating the gas.
4. Method according to any of the preceding claims, characterised in that the particles of stainless steel are non-molten.
5. Method according to any of the preceding claims, characterised in that the particles of stainless steel have an average size of between 5 and 50 µm.
6. Method according to any of the preceding claims, characterised in that the coating is formed of one or more layers of stainless steel.
7. Method according to any of the preceding claims, characterised in that the coating has a thickness of between 1 and 1000 µm, preferably between 10 and 500 µm.
8. Method according to any of the preceding claims, characterised in that the copper matrix is carried by or constitutes a tubular part or a plate.
9. Method according to any of the preceding claims, characterised in that the gas is distributed at a speed between 300 and 1600 m/sec, preferably of at least 400 m/sec.
10. Method according to any of the preceding claims, characterised in that the carrier gas / powder mixture is distributed by means of a Laval nozzle.

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