EP0872563B1 - Method and device for heat treating - Google Patents

Description

The present invention relates in particular to a device and method for heat treatment of a material and, more particularly, to a device and a surface coating process by applying a thermal spray method with cooling.

In the context of the invention, by treatment thermal means any technique for treating a substrate-material using cooling at least part of said substrate material, in particular: surface coating, quenching, nitriding, case hardening, plasma spraying, flame cutting, laser cutting, HVOF projection (for High Velocity Oxy Fuel in English), flame projection .... These different heat treatment techniques are known and widely used in the field industrial.

For example, to produce coatings on materials, a spray jet consisting of hot carrier gas and particles of coated or softened coating material is directed onto the surface of the material to be treated or material-substrate, which surface is cooled before and / or after treatment with a jet of coolant, such as liquid argon or carbon dioxide (CO ₂ ).

So plasma projection is widely used to make coatings on any type of material, such as composite materials, for example resins or plastics, which must be coated with layers thin ceramic or metallic layers.

This technique is also used to make protective coatings in the mechanical field, for example for aeronautics or automotive, or in that of energy.

The thermal spraying technique involves very high temperatures and calorific values important. Indeed, the projection jet composed, in general, hot carrier gas and particles of coating material must be at a temperature high enough to soften or melt said particles of filler coating material and on the other hand, to obtain a heat treatment effective surface material or workpiece undergo the coating.

Said material to be coated or substrate material therefore undergoes considerable heating on the one hand, due to the amount of heat supplied directly by hot gases, and secondly, by coating particles at least partially melted which, when they come into contact with the substrate material, transfer to the latter an amount of significant heat in a very short time. Classically, the substrate material undergoes a warming of several hundreds of degrees and a thermal equilibrium is established, on the one hand, by heat exchange with the atmosphere ambient and, on the other hand, by diffusion of heat to across said substrate material and the layer of coating.

It has been observed that membership, i.e. the attachment of the coating layer to the substrate material, is favored with temperature. In others terms, the higher the temperature, the more anchoring mechanical and chemical reactions taking place between the coating layer and the substrate material evolve in a favorable sense and entail, in fact, a more effective overheating.

This can be explained in particular by better wettability of molten coating particles and therefore better spreading or crushing thereof on the substrate material.

However, it is also necessary to consider the microscopic properties not only of the layer coating, but also of the substrate material.

Indeed, during the successive stacking of multiple layers of coating or layering it internal tensions appear in said coating, which are all the more important as the thermal conductivity of the coating material deposited is small or that the thickness of the material deposited at each passage is important.

Such a phenomenon was notably observed during the projection of ceramic type particles, where we have noticed the appearance of cracks, even in in some cases delamination of the coating, due to too great a temperature difference between, on the one hand, the substrate material and the coating layer, and, on the other part, even within the ceramic coating layer.

Similarly, during cooling, if the difference in coefficient of thermal expansion (α) between the substrate material and the coating material becomes too large, residual constraints appear at the interface between the substrate material and the material of coating, which constraints are at the origin of decohesion or delamination phenomena.

This has been observed, in particular, during the projection of ceramic-type material onto metals, such as aluminum, where it has been observed that the ceramic layer (α = 8.10 ^-6 K ^-1 ) cannot adhere to a part. aluminum (α = 22.10 ^-6 K ^-1 ) if the temperature of the support exceeds a few hundred degrees.

From there, it follows that the thickness of the coating does not may in some cases exceed a few tenths of millimeter, which greatly limits applications industrial possibilities.

In fact, when the coating layer is intended to play the role of thermal barrier, that is to say thermal insulation, it must, in some case, have a thickness well beyond the millimeter what which is therefore not feasible.

We therefore understand that the properties of the substrate material to be coated also come into line of consideration, in particular, the coefficient thermal expansion and thermal conductivity, which reflects the material's ability to evacuate calories.

In order to overcome the above problems, it is of use to couple the heat treatment operation of the material, such as the deposition of a coating layer, at a cooling the substrate material beforehand and / or after the treatment of it, that is to say, for example, when projected onto the surface of it of said jet comprising the hot carrier gas and the coating material particles at least partially melted.

The implementation of additional cooling allows, in addition, to apply the projection technique thermal coating of so-called substrate materials "sensitive", on which the temperature can have a harmful influence, such as organic materials or composites, paper or wood, or low metals melting point, such as aluminum or copper.

In other words, one of the goals of cooling additional is to allow, by quenching, an evacuation efficient in calories and, in any case, faster that by letting the part to be treated cool down by itself, apart from the hot gas jet.

On the other hand, additional cooling allows establishing a much temperature gradient lower between the coating layer and the substrate material, which greatly improves the holding of the coating.

Furthermore, the implementation of cooling effective also significantly reduces the projection time and therefore costs, given that no need to leave time for the pieces processed to cool by themselves; it was possible, in some cases, to divide the projection time by one factor 10.

There are currently several techniques for cooling using fluids cooling of different types depending on the efficiency of the desired cooling, which is, as we we saw it above, function of intrinsic properties of the material-substrate / coating layer pair.

However, in all cases, ensure that the cooling air jet disturbs as little as possible the hot jet, that is to say the mixture comprising one or more hot gases and, in general, particles in fusion or softened, in order to avoid a cooling of it, oxidation of the particles of molten coating, contamination of the layer coating ...

However, as we saw earlier, the temperature of the substrate material is a parameter critical since if its temperature exceeds one some value, we can see a degradation irreversible of said substrate material.

So when you want to get a minor cooling, i.e. leading to maintaining the part to be treated at a temperature included in the range of 150 ° C to about 600 ° C, and that is, from more, easy to implement and inexpensive, we can use as air coolant compressed.

Conversely, compressed air is not suitable if one wants good cooling efficiency.

An alternative then consists in using as cooling fluid, a refrigerating fluid, such as argon or carbon dioxide (CO ₂ ).

Indeed, the liquid argon used as a cooling helps maintain the temperature of the substrate material and / or the coating layer at a temperature generally between 0 and 150 ° C, this temperature essentially dependent on pressure liquid argon and the argon gas flow rate used, which ensure atomization of the flow of liquid argon into fine droplets of varying diameter. Such a cooling efficiency allows layer deposition thick coating, for example of the order 3 mm.

However, the use of liquid argon as coolant causes an increase in production costs and installation of equipment more expensive. From there, use at scale industrial argon, as a cooling, is generally limited to treatment high value added parts.

Besides argon, it is also possible to use carbon dioxide as a coolant.

The use of CO ₂ is very advantageous because, on the one hand, it makes it possible to obtain similar performances with argon, since the temperature of the material-substrate can be maintained at values of the order room temperature and, on the other hand, its cost is significantly lower than that of argon. Such CO ₂ cooling can therefore be applied to the heat treatment of all kinds of parts, whatever their added value. By way of example, mention may be made of the deposition of a coating layer of silica, titanium dioxide or molybdenum, with a thickness of 1 to 1.5 mm, on a steel part or also the deposition of a layer of '' about 3 mm of zirconia to act as a thermal barrier on an aluminum alloy part.

In addition, CO ₂ cooling is also well suited for obtaining thin coating deposits on substrate materials with a high expansion coefficient, such as aluminum alloys. By soaking in a cryogenic liquid, it is then possible to separate the coating from the support material.

Similarly, during the implementation of a heat treatment process by HVOF spraying, CO ₂ cooling allows, in particular, the deposition of a coating layer of tungsten carbide / cobalt on a support material, avoiding the formation of carbide harmful for the desired properties, namely in particular the resistance to wear.

This CO ₂ cooling also allows the chromium / nickel layer to be deposited on aluminum parts, which cannot be achieved using compressed air, since the difference in expansion coefficient between the layer of chrome / nickel coating and the aluminum part requires keeping the temperature below 80 ° C.

In addition, the use of CO ₂ cooling makes it possible to avoid strong oxidation of the copper, when the latter is used as a coating material to produce a thick coating layer, i.e. '' order of 2 mm.

In some cases it is also possible to use nitrogen as coolant liquid.

Many methods and devices for processing surface by thermal spraying have already been described in the prior art and we can cite by way of example the documents: EP-A-0124432, US-A-3,744,262, FR-A-2,347,111, EP-A-0546359 or Research Disclosure, January 1997, p.30 N ° 39329.

Thus, document EP-A-546359 describes a device heat treatment comprising projection means delivering at least one jet containing at least one carrier gas hot, and cooling means comprising a nozzle delivering coolant, i.e. dioxide carbon, the nozzle being provided with an expansion nozzle forming a sleeve around a part of the nozzle, in which nozzle an expansion of the cooling.

Furthermore, document EP-A-124432 describes a heat treatment device comprising means for cooling comprising a nozzle delivering a fluid cooling, the nozzle being provided with a nozzle head forming a sleeve around part of the nozzle. The architecture of the nozzle is relatively complex since it includes a first internal passage for supply a coolant and a second internal passage to convey a carrier gas, the first and second passages ending in the free space located between the nozzle and the nozzle head, so as to obtain a mixture of said coolant and carrier gas in said free space.

These different processes or devices are very similar to each other. Schematically, a refrigerant, usually carbon dioxide liquid, is brought to distribution means delivering said fluid, in general, one or more nozzles, within which, liquid carbon dioxide expands and gives rise to a mixture two-phase consisting of carbon dioxide and snow carbonic.

In order to obtain a laminar jet, the nozzle usually in the form of a geometry tube well determined: size, shape ...

Sometimes, instead of using carbon dioxide to liquid state it has been described to use dioxide carbon in gaseous state only. However, this requires on the one hand, the implementation of pressure high, that is to say at least 45 bars and, on the other hand, to have a heating system allowing maintain the storage temperature of carbon, preferably above 30 ° C. In that case, expansion of carbon dioxide gas to a gas mixture and dry ice is carried through a nozzle whose end at least is flattened.

• le jet réfrigérant sortant des buses entre en contact intime avec le matériau-substrat;
• le débit et la forme du jet réfrigérant soient stables et réguliers dans le temps afin d'éviter les pulsations, c'est-à-dire une distribution par à-coups, dont l'une des causes est la condensation de la vapeur d'eau atmosphérique sur les buses;
• la perturbation occasionnée par le jet de fluide réfrigérant sur le jet constitué essentiellement de gaz chaud et, selon le cas, de particules en fusion soit minimale;
• les différents débits soient adaptés en fonction de la position des buses délivrant le fluide réfrigérant par rapport à celle des buses ou torches de projection thermique;
• la forme plutôt aplatie ou plutôt cylindrique de la buse délivrant le fluide réfrigérant soit adaptée au cas d'espèce.

If the implementation of cooling by means of a coolant, such as CO ₂ , in a heat treatment process has a number of advantages, it should nevertheless be ensured that:

• the cooling jet leaving the nozzles comes into intimate contact with the substrate material;
• the flow rate and the shape of the cooling jet are stable and regular over time in order to avoid pulsations, that is to say a distribution in spurts, one of the causes of which is the condensation of the vapor of atmospheric water on the nozzles;
• the disturbance caused by the cooling fluid jet on the jet consisting essentially of hot gas and, as the case may be, of molten particles is minimal;
• the different flow rates are adapted as a function of the position of the nozzles delivering the coolant relative to that of the nozzles or thermal spray torches;
• the rather flattened or rather cylindrical shape of the nozzle delivering the refrigerant is adapted to the present case.

However, there are still a number of problems arising in this area and having to date, not been resolved.

Of these, the most important is that of the condensation of water vapor in the air atmospheric operating on the nozzle (s) distributing the coolant and causing icing of these.

This icing of the nozzles is very harmful because it generally causes the formation of a plug which makes the jet of coolant, such as CO ₂ , unstable and turbulent, which results, on the one hand, in improper cooling and ineffective of the substrate material and / or of the coating layer and, on the other hand, can cause a harmful disturbance of the thermal spray jet.

Currently, the ice formed by condensation of the water vapor from the atmosphere is removed, so very basic, for example by approaching the covered nozzle frost from an external heat source, which involves a shutdown of the production chain and leads therefore a waste of time and productivity, therefore a unacceptable increase in production costs.

The aim of the present invention is therefore to solve this problem of icing of the nozzles delivering a cooling fluid, such as CO ₂ , and therefore, by the same token, of improving the existing heat treatment devices and methods, by avoiding condensation. ambient humidity at the outlet, that is to say at the distribution end, of the nozzle where the refrigerant expands into a gas / solid mixture, causing cooling of the nozzle, favorable to said condensation of ambient humidity.

The present invention therefore relates to a device heat treatment according to claim 1.

More particularly, the invention relates to a device according to claim 2.

• ledit manchon est fixé par une extrémité proximale auxdits moyens de distribution et, de préférence, en amont de la buse,
• ledit manchon comporte une extrémité distale libre et, de préférence, présentant un rétrécissement,
• ledit manchon comporte une extrémité distale obturée partiellement par un moyen d'obturation,
• la buse de distribution comporte une extrémité de section circulaire ou ovale, ou de section aplatie.

Depending on the case, the device may also include one or more of the following characteristics:

• said sleeve is fixed by a proximal end to said distribution means and, preferably, upstream of the nozzle,
• said sleeve has a free distal end and, preferably, having a narrowing,
• said sleeve has a distal end partially closed by a closure means,
• the dispensing nozzle has one end of circular or oval section, or of flattened section.

The present invention also relates to a method heat treatment, in which a material using a device according to the invention, preferably the heat treatment is a coating of surface, i.e. the application of one or more layers of one or more coating materials on at minus part of the surface of a substrate material or of a room.

The invention further relates to a method of heat treatment of a material according to claim 6.

• le jet chaud de projection comporte, en outre, des particules d'un matériau en fusion au moins partielle ou ramollies, c'est-à-dire sous une forme "pâteuse", et, de préférence, d'un matériau choisi dans le groupe formé par les métaux, les alliages de métaux, les céramiques, les plastiques ou polymères, la silice et les oxydes métalliques,
• le fluide réfrigérant est choisi parmi l'azote, le dioxyde de carbone, l'argon et les mélanges les comprenant,
• le balayage est effectué au moyen d'au moins un gaz sec et, de préférence, un gaz choisi dans le groupe formé par l'air sec, l'azote, l'hélium, l'argon et les mélanges les contenant. De manière générale, conviennent également les gaz ou mélanges gazeux permettant de modifier la mouillabilité des particules en fusion ou du refroidissement vis-à-vis du matériau-substrat,
• l'atmosphère gazeuse de protection est, dans le manchon, à une pression supérieure, à 0,9.10⁵ Pa, de préférence, supérieure ou égale à 10⁵ Pa, avantageusement comprise dans la gamme 1,1.10⁵ Pa à 3.10⁵ Pa, avantageusement encore dans la gamme 1,1.10⁵ Pa à 2.10⁵ Pa,
• le débit du flux gazeux de protection est fonction de la géométrie, en particulier du diamètre, de la buse. Ainsi, pour une buse de 0,5 mm à 30 mm de diamètre, le débit du flux de protection est compris, de préférence, dans la gamme 5 l/min à 30 l/min et pour une buse de 1 mm à 10 mm de diamètre, dans la gamme 8 l/min à 25 l/min.

Depending on the case, the method may also include one or more of the following characteristics:

• the hot spray jet further comprises particles of an at least partial or softened molten material, that is to say in a "pasty" form, and preferably of a material chosen from the group formed by metals, metal alloys, ceramics, plastics or polymers, silica and metal oxides,
• the refrigerant is chosen from nitrogen, carbon dioxide, argon and mixtures comprising them,
• the scanning is carried out by means of at least one dry gas and, preferably, a gas chosen from the group formed by dry air, nitrogen, helium, argon and the mixtures containing them. In general, gases or gas mixtures are also suitable for modifying the wettability of the molten particles or of the cooling with respect to the substrate material,
• the protective gas atmosphere is, in the sleeve, at a pressure greater than 0.9 × 10 ⁵ Pa, preferably greater than or equal to 10 ⁵ Pa, advantageously included in the range 1.1 × 10 ⁵ Pa to 3.10 ⁵ Pa, advantageously still in the range 1.1.10 ⁵ Pa to 2.10 ⁵ Pa,
• the flow rate of the protective gas flow is a function of the geometry, in particular of the diameter, of the nozzle. Thus, for a nozzle from 0.5 mm to 30 mm in diameter, the flow rate of the protective flux is preferably included in the range 5 l / min to 30 l / min and for a nozzle from 1 mm to 10 mm in diameter, in the range 8 l / min to 25 l / min.

Preferably, the method according to the invention is a surface coating process.

The device or method according to the invention can be used in a manufacturing process of a part made of a material chosen by metals, metal alloys, polymers or plastics, organic and mineral materials, for example a room combustion chamber or medical prosthesis.

As is apparent from the above, the Applicant surprisingly highlighted that it was possible to eliminate atmospheric humidity residual around the nozzle outlet, and therefore the condensation of said moisture in contact with said nozzle, protecting the part of the nozzle where this condensation by the implementation of a protection gas, whose flow and pressure are suitable for avoid ambient air from coming into contact with said cold part of the nozzle.

Although in this case, the gas protection either consisting of nitrogen or dry air, any gas or mixture gas with a dew point low enough to not not cause icing is likely to be used as such.

The present invention can be applied in all fields where cooling by means of a refrigerant, such as CO ₂ , is necessary.

• la figure 1 représente, de façon schématique, une vue en coupe longitudinale d'un premier mode de réalisation d'un dispositif selon l'invention;
• la figure 2 représente, de façon schématique, une vue en coupe longitudinale d'un deuxième mode de réalisation d'un dispositif selon l'invention;
• la figure 3 représente une vue de dessus du dispositif représenté sur la figure 2;
• et la figure 4 est analogue à la figure 3 à l'exception du fait que le dispositif représenté est cette fois muni d'une buse à section sensiblement circulaire.

The invention will now be described in more detail, using embodiments given by way of illustration, but in no way limiting, with reference to the appended figures, where:

• Figure 1 shows, schematically, a longitudinal sectional view of a first embodiment of a device according to the invention;
• Figure 2 shows, schematically, a longitudinal sectional view of a second embodiment of a device according to the invention;
• Figure 3 shows a top view of the device shown in Figure 2;
• and Figure 4 is similar to Figure 3 except that the device shown is this time provided with a nozzle of substantially circular section.

The cooling nozzles usable in a heat treatment process and shown on the Figures 1 to 4 are commonly accessible nozzles in trade that can be obtained from companies specialized in the marketing of this type of products, such as the companies AGEFKO or SPRAYING SYSTEM.

In FIG. 1, there is shown a nozzle 3 for distributing carbon dioxide (liquid CO ₂ ) conveyed from a place of storage in liquid CO ₂ , not shown, to said nozzle 3 by means, in particular, of a pipe. or hollow tube 1, in the direction shown by arrow F.

The nozzle 3 has a part 4 or downstream end whose section is of substantially cylindrical shape or oval and a part 4 'or upstream end connected to the downstream end 1 'of the pipe 1 by through connection means 2, for example by screwing.

In order to avoid icing of the nozzle 3 by deposition of the ambient humidity on this nozzle 3 where the expansion of the liquid CO _{2 takes place} , a part of revolution 5 having substantially the shape of a sleeve is arranged around said nozzle 3; this sleeve 5 has been partially shown in Figure 1 (longitudinal section).

More specifically, this sleeve 5, formed of one or several pieces, is fixed by its proximal end 5a by fixing means 7 on the body of the tube 1 to near its end 1 'and upstream thereof.

Preferably, the fixing means 7 allow also to provide a seal, preventing a harmful entry of atmospheric air at the connection of the proximal end 5a to the tube 1.

The other end of the sleeve 5 or distal end 5b is free and comprises a part or part 12 advancing towards the end 4 of the nozzle 3 and making it possible to sheath the shielding gas around said end 4 of the nozzle 3, which prevents ambient humidity from settling there and cause icing.

The part 12 can be an attached and fixed part on the end 5b, for example by screwing, or make integral with the end 5b, that is to say that the end 5b and the part 12 are in one piece.

The sleeve 5 therefore forms a sort of corolla protective covering the nozzle 3, and makes it possible to maintain the latter under a gaseous protective atmosphere.

In this sleeve 5 are arranged one or more perforations or orifices 18 making it possible to introduce a dry shielding gas, such as nitrogen or air dry, inside the sleeve 5, so as to create a gas sweep and / or a protective gas atmosphere in the vicinity 15 of the nozzle 3 or of the nozzle part 3 located inside 15 of the protective sleeve 5.

Here, three orifices 18 have been arranged on the sleeve 5 so as to be equidistant from each other other; however this number of perforations 18 and this arrangement of said perforations on the sleeve 5 are not in no way limiting.

The dry protective gas is brought from a place of storage or production, by means of routing 6, such as pipes, to the orifices 18, of kind of crossing said orifices 18 in the direction indicated by arrow F '.

Preferably, connection means 17 allow fixing said pipe 6 to the sleeve 5 in look of the perforations 18; sealing means 16, like an O-ring, seal this connection by preventing parasitic air inlets atmospheric charged with humidity at the level of said connection.

Figure 2 is similar to Figure 1 and from there the common parts, identical or similar, will not not detailed below.

However, Figure 2 has two differences with Figure 1, namely, on the one hand, that the nozzle 3 has a downstream end 4 of flat section or flattened, whereas in the case of FIG. 1, the downstream end 4 or outlet orifice of the nozzle 3 was of substantially circular section.

On the other hand, the part 12 of FIG. 1 has been replaced by a flat 12 'piece or 12' plate, within which is an orifice 13 (see Figure 3 and Figure 4), in which is housed the downstream end 4 of the nozzle 3. Such a plate 12 ' constitutes a mechanical barrier making it possible to limit the atmospheric air inlets inside 15 of the sleeve 5. However, care must be taken to keep minus a passage 14a, 14b, 14c and 14d intended to allow creating a sweeping gas flow around the end 4 of the nozzle 3 and / or to evacuate the excess gas dry protection contained inside 15 of the sleeve 5.

Indeed, the gas sweeping carried out using dry gas, for example nitrogen or dry air, on the end 4 of the nozzle 3 creates a flow of gas which is evacuated by the orifice (s) 14a, 14b, 14c and 14d without disturbing the distribution of coolant, such as CO ₂ , by the nozzle 3 and prevents atmospheric air from entering inside 15 of the sleeve 5 and of being deposited on part 4 of nozzle 3, causing icing there.

The plate 12 'is, in this case, held on the end 5b of the sleeve 5 by holding means 12 "by screwing.

Figure 3 shows a schematic top view from the downstream end 4 of the nozzle 3 shown in the Figure 2. More specifically, we see the sleeve 5 surrounding the nozzle 3 whose downstream end 4 is shaped flattened. The plate 12 'is fixed by the means of holding 12 "at the sleeve 5 and / or at the end 4 of the nozzle 3 and has a perforation 13, in which is inserted said end 4 of the nozzle 3. The gas dry protection contained inside the sleeve 5 is evacuated through the orifices 14a, 14b, 14c and 14d while preventing thus the atmospheric air to penetrate inside said sleeve 5.

It goes without saying that the arrangement, in particular the part 12, shown in Figure 1 is not limited to substantially circular section nozzles and that it can also be suitable for nozzles with a flat section, such as that shown in Figure 2. Similarly, the arrangement constituted by the plate 12 'of Figure 2 is not limited to flat section nozzles, but can be adapted to circular section nozzles, such as that shown in FIG. 1, with an adaptation to the range of one skilled in the art. Besides, this is clear in FIG. 4, which is in all respects analogous to the Figure 3, except that the nozzle shown this time, not a flat section, but a substantially circular section 4, such as that of the nozzle 3 shown in FIG. 1.

The two types of nozzles, namely nozzles having one end of circular shape and those at the end flattened, make it possible to obtain liquid jets refrigerant of different shapes and are therefore used for different applications.

In order to verify the effectiveness of the the invention for both embodiments shown respectively in Figures 1 and 2, experimental tests have been carried out and are documented in the examples below.

Example 1

A heat treatment device provided with a round jet cooling nozzle (circular end) and delivering a CO ₂ type coolant was used.

The nozzle is equipped at its downstream end with a protective sleeve into which gas is introduced protection, so to create a sweep on the part downstream of the carbon dioxide spray nozzle.

In this example, the shielding gas used is industrial compressed air, which is previously filtered mainly to remove moisture, but also the fat from compression.

During the operating time of the nozzle, i.e. for 5 to 10 minutes, a sweep of said nozzle is carried out by means of compressed dry air and filtered.

This device gives complete satisfaction at the start, that is, for the first 5-10 minutes no icing of the downstream end of the nozzle is observed. However, after this time, a slight condensation on the downstream end of the nozzle appears from by saturation in humidity of the filter used for purify the compressed air serving as a protective gas.

In other words, slight condensation, or icing, observed is due not to the device of the present invention but to the inability of the filter put in works to fully fulfill its role.

Example 2

This example 2 is completely analogous to the example 1, except that in this case the gas protection used is not dry compressed air, but nitrogen gas, which is, on the one hand, easier to handle and, on the other hand, does not require filtering.

Nitrogen of two different qualities was used, namely N45 nitrogen and standard nitrogen N25. N45 nitrogen has maximum water and oxygen of the order of 5 ppm (part per million in volume) while standard N25 nitrogen has a content maximum water of the order of 40 ppm and its content oxygen is variable.

In this example 2, during the implementation of the installation, no icing is observed on the CO ₂ distribution nozzle.

From there, standard nitrogen N25 or nitrogen N45 can be used effectively to form a gas protection against icing of the nozzles distributing a refrigerant, such as CO2, used in processes heat treatment.

Furthermore, this example 2 confirms that the slight condensation appeared on the nozzle in example 1 is good the result of saturation of the filter with humidity.

In examples 1 and 2 above, the shielding gas is delivered at a flow rate of the order of 15 l / min and at a pressure of approximately 1.2 × 10 ⁵ Pa.

Claims (10)

1. Heat-treatment device which includes cooling means (1, 2, 3, 4, 4') comprising:

   delivery means (3, 4, 4') which deliver at least one coolant, the said delivery means (3, 4, 4') being one or more delivery nozzles (3), and

   shielding means (5, 5a, 5b, 12, 12') including a sleeve (5) which surrounds, at least partially, one or more delivery nozzles, the shielding means (5, 5a, 5b, 12, 12') being connected to means (6, 16, 17) for supplying at least one gaseous shielding stream, so as to maintain a gaseous shielding atmosphere around at least part of the said delivery means (3, 4, 4'), the said sleeve (5) having at least one orifice (18) via which the gaseous shielding stream conveyed by the said supply means (6, 16, 17) is introduced, the said device being characterized in that the orifice (18) is located in the wall of the said sleeve (5).
2. Device which includes:

   spraying means which deliver at least one jet containing at least one hot carrier gas, and

   cooling means (1, 2, 3, 4, 4') comprising delivery means (3, 4, 4') which deliver at least one coolant, the delivery means (3, 4, 4') being one or more delivery nozzles (3), and

   shielding means (5, 5a, 5b, 12, 12') connected to means (6, 16, 17) for supplying at least one gaseous shielding stream, the said shielding means (5, 5a, 5b, 12, 12') including a sleeve (5) which surrounds, at least partially, one or more delivery nozzles (3), so as to maintain a gaseous shielding atmosphere around at least part of the said delivery means (3, 4, 4'), the said sleeve (5) having an orifice (18) via which the gaseous shielding stream conveyed by the said supply means (6, 16, 17) is introduced, the said device being characterized in that the orifice (18) is located in the wall of the said sleeve (5).
3. Device according to either of Claims 1 and 2, characterized in that the said sleeve (5) is fastened at a proximal end (5a) to the said delivery means (3, 4, 4'), preferably upstream of the nozzle (3).
4. Device according to one of Claims 1 to 3, characterized in that the said sleeve (5) has a free distal end (5b), preferably having a restriction (12).
5. Device according to one of Claims 1 to 4, characterized in that the said sleeve (5) has a distal end (5b) partially closed off by a closing-off means (12, 12').
6. Process for the heat treatment of a material, in which:

   at least part of the surface of the said material is sprayed from at least one jet containing at least one hot carrier gas;

   at least part of the said material is cooled by means of at least one delivery nozzle which delivers a coolant, the said delivery nozzle being at least partially surrounded by shielding means including a sleeve, which sleeve has at least one orifice located in the wall of the said sleeve, and

   at least part of the delivery nozzle is maintained under a gaseous shielding atmosphere by means of at least one shielding gas by flushing the said nozzle with the said gaseous shielding stream, the said gaseous shielding stream being introduced into the said sleeve via the said at least one orifice located in the wall of the said sleeve, so as to create the said flushing on the inside of the said shielding sleeve by the shielding gas.
7. Process according to Claim 6, characterized in that the spray jet furthermore includes particles of an at least partially molten material, or softened particles, and, preferably, of a material selected from the group formed by metals, metal alloys, ceramics, plastics, silica and metal oxides.
8. Process according to either of Claims 6 and 7, characterized in that the flushing is performed by means of at least one dry gas, preferably a gas selected from the group formed by dry air, nitrogen, helium, argon and mixtures thereof.
9. Process for coating a surface, using a device according to one of Claims 1 to 5 or a process according to one of Claims 6 to 8.
10. Use of the device according to one of Claims 1 to 5 in a process for the heat treatment of a component made of a material selected from metals, metal alloys, polymers, organic materials and inorganic materials.

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