Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/04—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the coating material
  • C23C4/06—Metallic material
  • C23C4/08—Metallic material containing only metal elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
  • B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
  • B05B7/16—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed
  • B05B7/20—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed by flame or combustion
  • B05B7/201—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed by flame or combustion downstream of the nozzle
  • B05B7/205—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed by flame or combustion downstream of the nozzle the material to be sprayed being originally a particulate material
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/129—Flame spraying

Definitions

• the present invention relates to a method of coating an object to be coated with a fusible coating material comprising the steps of: establishing a flame having a maximum flame speed and a flame direction which coincides with a flame axis and which is directed towards the object to be coated; - introduction of a quantity of the fusible coating material into said flame;
• the maximum flame speed and the distance between the object to be coated and the flame being chosen so that the fusible coating material is sprayed onto the object to be coated, and so that at least part of the amount of the fusible coating material is in the molten state upon impact on the object to be coated.
• Flame spray coating methods are known. In such methods a coating material is introduced as a wire into a flame, which melts the material, so that droplets of coating material are formed. These droplets are then entrained by the combustion gases of the flame and projected onto an object to be coated.
• the known flame spray coating methods have a yield of about 60%.
• the yield is defined by the ratio of the quantity of material which effectively adheres to the object to be coated to the quantity of material introduced into the flame. About 10% of the material is lost by evaporation. The rest of the material, therefore about 30% of it, does not adhere to the object to be coated, and accumulates in the form of residual powder.
• This degraded residual powder is difficult to recycle and has only a low economic value, in particular in the case of impure powders such as that of mixtures of different materials and / or alloys such as Zn-Al.
• the object of the present invention is to provide an economical flame coating process.
• the subject of the invention is a method of the aforementioned type, characterized in that the quantity of fusible coating material comprises powder made up of particles, and in that the flame has a temperature sufficiently low that the particles of the powder is not completely evaporated and high enough for the powder particles to be at least partially melted.
• the method according to the invention may include one or more of the following characteristics:
• the quantity of material consists of powder; the particles have a larger dimension of less than 1000 ⁇ m, preferably less than 800 ⁇ m and in particular less than 500 ⁇ m; - The particles have a smaller dimension greater than 20 ⁇ m, preferably greater than 40 ⁇ m, and in particular greater than 60 ⁇ m;
• the material is introduced into the flame in at least one direction of introduction, and the direction of introduction comprises a radial component relative to the flame axis; the direction of introduction is directed substantially radially with respect to the flame axis; the object to be coated extends along a longitudinal axis, and the direction of introduction has a component extending parallel to the longitudinal axis; and the direction of introduction extends substantially parallel to the longitudinal axis of the object to be coated;
• the material is introduced into the flame in at least two directions of introduction, and these two directions extend symmetrically on either side of a plane which comprises the flame axis and which extends perpendicularly to the longitudinal axis of the object to be coated;
• the powder comprises at least 50% by weight a metal or an alloy whose melting point is between 400 ° C and 500 ° C, preferably between 425 ° C and 475 ° C; -
• the powder consists of an alloy comprising at least 50% by weight of Zn, in particular at least 85% by weight of Zn, and preferably at least 95% by weight of Zn; the residual part of the alloy comprises aluminum, and in particular consists of aluminum; - the maximum flame speed is between
• - at least part of the powder is a waste powder;
• the waste powder comes from a spray coating process, and in particular from an arc-wire coating process using a wire or a bead of fusible coating material as starting material; said part of the powder is obtained by sieving an amount of raw waste powder;
• At least said part of the powder is subjected to a drying or deoxidation operation before introduction into the flame; and -
• the maximum flame temperature is between 2000 ° C and 3000 ° C, preferably between 2250 ° C and 2750 ° C, and in particular between 2400 ° C and 2600 ° C.
• the subject of the invention is also a coating device by means of a flame suitable for carrying out the method according to any one of the preceding claims, of the type comprising:
• a burner adapted to be connected to a source of combustible gas and adapted to establish a flame along a flame axis, means for introducing a fusible coating material into the flame, characterized in that the means of introduction meltable coating material are adapted to introduce the meltable coating material into the flame in powder form.
• the device according to the invention may include one or more of the following characteristics: - the introduction means comprise an injector suitable for introducing a powder mixture of coating material / conveying gas into the flame in a direction of introduction; the direction of introduction is directed substantially radially with respect to the flame axis; and
• the device further comprises a powder coating material / conveying gas mixer comprising a powder inlet, a conveying gas inlet, adapted to be connected to a source of conveying gas, and an outlet powder coating material / conveying gas mixture, the mixer is adapted to mix the powder with a flow of conveying gas, and the material powder mixture outlet of coating / conveying gas is connected to at least one injector.
• a powder coating material / conveying gas mixer comprising a powder inlet, a conveying gas inlet, adapted to be connected to a source of conveying gas, and an outlet powder coating material / conveying gas mixture
• the mixer is adapted to mix the powder with a flow of conveying gas
• the material powder mixture outlet of coating / conveying gas is connected to at least one injector.
• Figure 1 shows schematically an installation comprising coating devices 1 according to the invention
• Figure 2 is a schematic view of a coating device according to the invention
• FIG. 3 is a longitudinal sectional view of part of the coating device of Figure 2.
• Figure 4 is a front view of the part of the coating device of Figure 3.
• Figure 1 is shown a coating installation by means of a flame according to the invention, designated by the general reference 2.
• the installation comprises a device 4 for recovering raw powder, a main tank 6, three supply tanks 8A, 8B, 8C, and three flame coating devices 10A, 10B, 10C.
• the raw powder recovery device 4 is adapted to recover directly, that is to say without treatment, residual powders or waste produced during the implementation of known coating methods. Such methods use a wire or cord as the base material and produce powders of residual coating material, consisting of particles, the most large dimension is generally located between 0 ⁇ m and 2000 ⁇ m.
• Such powders generally comprise alloy particles based on a metal with a low melting point, situated between 400 ° C and 450 °, and preferably between 425 ° C and 475 ° C.
• the alloy is for example a Zn-based alloy, which comprises at least 50% by weight of Zn, but preferably more than 85% by weight of Zn, and in particular more than 95% by weight of Zn.
• the residual part of the alloy comprises, for example, aluminum and is preferably made of aluminum.
• the installation 2 further comprises first supply means 12 for coating material powder, adapted to supply the main tank 6.
• These first supply means 12 comprise a first conveyor 14A, the inlet of which is connected to an outlet of the recovery device 4 for raw powder and the outlet of which opens into the main reservoir 6.
• the installation 2 also comprises second supply means 14B for coating material powder, adapted to supply each of the supply tanks with coating material powder, from the main reservoir 6.
• these second supply means 14B consist of three conveyors 16A, 16B, 16C, each of which is connected to an outlet of the main tank and to an inlet of the supply tanks 8A, 8B, 8C.
• Third powder supply means 18 are adapted to convey powder from each of the supply tanks 8A, 8B, 8C to each of the coating devices 10A, 10B, 10C.
• these third supply means 18 consist of three screw conveyors 20A, 20B, 20C.
• a raw powder treatment device 22 is placed in the first conveyor 14A and separates the latter into an upstream part 24 and a downstream part 26.
• the raw powder treatment device 22 is formed by a sieving device 28.
• This sieving device 28 is suitable for separating the particles from the powder, the largest dimension and the smallest dimension of which lie within a predetermined range.
• This screening device 28 comprises two large screens 29A and fine screens 29B.
• the coarse sieve 29A is placed above the fine sieve 29B.
• the sieving device 28 further comprises an inlet 30 through which the raw powder coming from the recovery device 4 is introduced above the coarse sieve 29A by means of the upstream part 24.
• a first outlet 32 of the sieving device, disposed between the coarse sieve 29A and the fine sieve 29B is connected to the downstream part 26 of the first conveyor 14A.
• the screening device is provided with two other outlets 34, 36 respectively upstream of the coarse screen 29A and downstream of the fine screen 29B.
• outlets 34, 36 are provided for particles whose largest or smallest dimension is located above or below the above limits.
• the largest dimension of each of the particles is less than 1000 ⁇ m, preferably less than 800 ⁇ m, and in particular less than 500 ⁇ m.
• the powder consists of particles whose smallest dimension is greater than 20 ⁇ m, preferably greater than 40 ⁇ m and in particular greater than 60 ⁇ m.
• the coating device 10A will be described by way of example.
• the two other coating devices 10B, 10C are identical.
• Figure 2 is shown schematically the coating device 10A according to the invention and an object to be coated.
• the object to be coated is a pipe 40 of generally hollow cylindrical shape having a longitudinal and horizontal axis X-X.
• the pipe is for example made of metal and in particular cast iron.
• the pipe 40 is fixed on a support (not shown) and can be driven in rotation about its longitudinal axis X-X as well as in translation relative to the coating device 10 along this axis.
• the coating device 10 comprises a burner 42 which is shown in partial section in FIG. 2, as well as a device 46 for introducing the powder of coating material into a flame 44.
• the burner 42 is suitable for establishing the flame 44 along a horizontal flame direction F, which is defined by a flame axis YY and which is directed towards the pipe 40.
• the flame axis YY and the longitudinal axis XX define an angle different from 0 ° between them.
• These axes define a plane P-P, which extends perpendicular to the axis X-X and which coincides with the axis Y-Y (see Figure 4).
• the burner 42 is formed by a burner head 48 and means 50 for cooling and guiding the flame 44.
• the burner head 48 is provided with an oxidant gas inlet 52 connected to a source of oxidant gas 54, such as as oxygen, via an oxidizing gas line 56 and a first regulating valve 58 for flow and pressure.
• the burner head 48 is provided with a fuel gas inlet 60, connected to a source of fuel gas 62, such as natural gas, acetylene or propane, via a fuel gas line. 64 and a second pressure and flow adjustment valve 66.
• the burner head 48 and part of the device 46 for introducing the powder are shown on a larger scale in FIG. 3, the burner head 48 being shown in longitudinal section.
• the burner head 48 is generally of revolution around the axis YY.
• the mixer 68 forms the fuel gas inlet 60 and the oxidant gas inlet 52 of the burner 42.
• the mixer 68 and the fuel gas nozzle 70 comprise a fuel gas passage 76, coaxial with the axis YY and a plurality of oxidizing gas passages 78 distributed regularly around the combustible gas passage 76. These components are known per se.
• the combustible gas passage 76 of the mixer 68 has a diameter adapted to a large gas flow.
• the ratio of the diameters of the passages 76 and 78 is adapted to establish a mixture of stoichiometric gas, at high flow rate.
• the oxidizing gas nozzle support 74 is a part of revolution of axis Y-Y, which has a through bore 80 through which the cross section decreases from the rear end towards the front.
• the oxidizing gas nozzle support 74 comprises a threaded cylindrical base 82, to which a frustoconical external part 84 is connected.
• the means 50 for cooling and guiding the flame 44 comprise a cooling sleeve 86, in which the burner head 48 is arranged.
• the sleeve 86 includes a gas inlet end 88 and a flame outlet end 90.
• the sleeve 86 comprises, on the side of the inlet end 88, a tapped bore on stage 92, in a part from which the base 82 of the oxidizing gas nozzle support 74 is screwed, so that the frustoconical part 84 and the rest of the stage bore 92 form an annular cooling chamber 94 surrounding an axial part of the nozzle support 74.
• a radial bore 96 for cooling gas inlet is formed in the sleeve 86, bore 96 which opens into the cooling chamber 94, and which is connected to means 98 for supplying cooling air.
• these means 98 for supplying cooling air comprise a first air compressor 100 connected to a compressed air line 102 which opens into the cooling chamber 94 and into which a third valve is inserted. 104.
• the sleeve 86 further comprises bores 106 which extend axially from the cooling chamber 94 and which open onto a front surface of the sleeve 86, disposed on the side of the outlet end 90 and formed by an annular groove 108 open in the direction of the flame F in order to allow the flame to be confined without disturbing the initial flow.
• the sleeve 86 comprises eight bores 106.
• the burner 42 is also provided with a device 110 for igniting the flame (see FIG. 2).
• This priming device 110 comprises two priming electrodes 112 which terminate near the outlet end 90 of the sleeve 86.
• the priming electrodes 112 are connected by wires 114 to a source of electricity 116.
• a switch 118 is interposed in one of the wires 114, and makes it possible to control the electrodes 112.
• the device 46 for introducing the powder into the flame 44 comprises four injectors 120A, 120B, 120C, 120D of the known type (see FIG. 4) as well as a device 122 for supplying a powder / air mixture, to which the injectors 120A, 120B, 120C, 120D are connected.
• Each injector 120A, 120B, 120C, 120D essentially consists of a tube having a powder outlet 124, adapted to introduce powder of coating material into the flame 44 in a direction of introduction IA to ID.
• Each of the directions of introduction IA to ID is directed substantially radially to the flame axis Y-Y.
• the two directions of introduction IA and IB of the two injectors 120A, 120B are inclined at 45 ° downwards, while the direction of introduction IC and ID of the two injectors 120C, 120D extend substantially horizontally, parallel to the axis XX and are directed towards each other.
• the directions of introduction IA to ID therefore each have a component extending along the longitudinal axis X-X of the pipe 40.
• the directions of introduction IA, IB and IC, ID are arranged symmetrically with respect to the plane P-P.
• the powder particles projected towards the pipe 40 are distributed over an imaginary spot whose preferential direction extends along the axis X-X. Consequently, few particles are projected over or under the pipe 40.
• the device 122 for supplying a powder / air mixture comprises a powder / air mixing chamber 126 having an inlet hopper 128 for the powder of coating material and a compressed air inlet 130 which is connected to means compressed air supply, formed by a second compressor 132 and a fourth control valve 134.
• a metering device 140 in this case a vibration conveyor, is arranged above the inlet of the inlet hopper 128.
• the metering device 140 is adapted to be supplied with powdered coating material by the screw conveyor 20A.
• the installation according to the invention operates as follows.
• the cast iron pipe 40 is installed on the support (not shown) and is rotated around the axis X-X.
• valves 58, 66 are open.
• the pressure of the combustible gas is adjusted to approximately 3 bars in the case of propane as combustible gas.
• the pressure of the oxidant gas is adjusted to approximately 8 bar in the case of oxygen as the oxidant gas.
• the fuel gas flow is adjusted to obtain a power of up to 70 kW.
• As for the flow rate of the oxidizing gas it is adjusted to generate a stoichiometric flame.
• the power of 70k corresponds to a flow
• the first compressor 100 is started and the cooling chamber 94 is supplied with pressurized air, for example at a pressure of around 2 bars.
• the flame 44 is started by the starting device 110.
• the flame 44 which is established has a power between 30 kW and 70 kW.
• the maximum flame temperature 44 is between 2000 ° C and 3000 ° C, preferably between 2250 ° C and 2750 ° C, and in particular between 2400 ° C and 2600 ° C.
• the maximum speed of the gases of flame 44 is between 500 m / s and 2000 m / s, and preferably between 700 m / s and 900m / s.
• the mixture supply device 122 is started up and conveys an air / powder mixture to the injectors 120A, 120B, 120C, 120D.
• the powder flow rate of a single injector 120A, 120B, 120C, 120D is between 15 kg / h and 50 kg / h, and is preferably about 35 kg / h per injector.
• the powder flow rate of all the injectors is between 60 kg / h and 250 kg / h.
• the injectors 120A, 120B, 120C, 120D then introduce the air / powder mixture into the flame 44 according to the directions of introduction IA to ID.
• the speed of injection of the powder into the flame 44 is between 20 m / s and 50 m / s.
• the powder particles are then entrained by the flame 44 in the direction F thereof. They are completely melted by flame 44 and form droplets of molten coating material. Thanks to the fact that the dimensions of the particles are located within the aforementioned range, the particles are completely melted without however evaporating.
• the droplets leave the flame 44 in a sufficiently rapid manner to avoid their evaporation.
• the droplets are projected onto the pipe 40.
• the distance between the flame 44 and the pipe 40 is chosen so that the droplets are still in the liquid state when they meet the pipe.
• the droplets adhere to pipe 40 and solidify to form a coating.
• the latter is driven in translation along the axis X-X.
• the method according to the invention makes it possible to coat an object with a coating layer at a high mass flow rate of powder while using powder recovered from previous coating processes.
• the method according to the invention achieves a yield similar to that of flame coating methods using a wire-shaped coating material, namely of the order of 60%.
• the device according to the invention and the process parameters make it possible to use a powder consisting of an alloy with a low melting point (approximately 450 ° C.), such as Zn 85 Al ⁇ 5 , as a coating material.
• a powder consisting of an alloy with a low melting point (approximately 450 ° C.), such as Zn 85 Al ⁇ 5 , as a coating material.
• the powder consists of at least 50% of a metal or an alloy whose melting point is between 400 ° C and 500 ° C, preferably between 425 ° C and 475 ° C.
• the mixing chamber 126 can be connected to a source of conveying gas other than air, for example a source of an inert gas.
• the coating device can be provided with a number of injectors other than four, for example two injectors or six injectors.
• the powder treatment device may include a device for drying and / or deoxidizing the powder, in order to improve the flow ability of the latter and / or the quality of the coating.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Plasma & Fusion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Physics & Mathematics (AREA)
• Combustion & Propulsion (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Nozzles (AREA)
• Materials For Medical Uses (AREA)
• Vending Machines For Individual Products (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Insulated Conductors (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

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• 2003
  • 2003-04-23 FR FR0304986A patent/FR2854086B1/fr not_active Expired - Fee Related
• 2004
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  • 2004-04-16 US US10/553,597 patent/US20070026157A1/en not_active Abandoned
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  • 2004-04-16 RU RU2005136352/02A patent/RU2353704C2/ru not_active IP Right Cessation
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