EP1616041B1 - Flame covering method and corresponding device - Google Patents

Abstract

Coating of an object (40) with a fusible coating material consists of establishing a flame (44) directed towards the object to be coated and introducing a quantity of the fusible coating material into the flame. The flame has a temperature sufficiently elevated to at least partially melt the coating material. The flame speed is chosen such that the molten coating material is projected onto the object to be coated and at least a part of the coating material is in a molten state during its impact with the object. An independent claim is also included for a device for the flame coating of an object by this means.

Description

The present invention relates to a method of coating an object to be coated according to the preamble of claim 1.

It applies in particular to processes for coating cast iron pipes with a zinc or Zn-Al alloy layer.

Flame spray coating methods are known. In such processes 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 on 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 amount of material that actually adheres to the object to be coated to the amount of material introduced into the flame. About 10% of the material is lost by evaporation. The rest of the material, so about 30% of it, does not adhere to the object to be coated, and accumulates as a residual powder.

This degraded residual powder is difficult to recycle and has little economic value, especially in the case of impure powders such as mixtures of different materials and / or alloys such as Zn-Al.

The object of the present invention is to propose a method of flame coating which is economical.

For this purpose the subject of the invention is a process according to claim 1.

According to other embodiments, the method according to the invention may comprise one or more of the features of the method claims dependent on claim 1.

The invention further relates to a coating device by means of a flame adapted for carrying out the method according to any one of the preceding claims, of the type comprising the characteristics of the independent device claim.

According to other embodiments, the device according to the invention may comprise one or more of the features of the device-dependent claims.

By means of the parameters indicated above, such as the gas velocity, the flame temperature and the injection point, a satisfactory operation of the device and a uniform coating are obtained.

• la Figure 1 représente de façon schématique une installation comprenant des dispositifs de revêtement selon l'invention;
• la Figure 2 est une vue schématique d'un dispositif de revêtement selon l'invention;
• la Figure 3 est une vue en coupe longitudinale d'une partie du dispositif de revêtement de la Figure 2; et
• la Figure 4 est une vue de face de la partie du dispositif de revêtement de la Figure 3.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which:

• the Figure 1 schematically represents an installation comprising coating devices according to the invention;
• the Figure 2 is a schematic view of a coating device according to the invention;
• the Figure 3 is a longitudinal sectional view of a part of the coating device of the Figure 2 ; and
• the Figure 4 is a front view of the part of the coating device of the Figure 3 .

On the 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 raw powder recovery device 4, a main reservoir 6, three feed 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 processes. Such processes use a wire or cord as a base material and produce powders of residual coating material, consisting of particles the most large dimension is usually between 0 μm and 2000 μm.

Such powders generally comprise low melting point metal alloy particles, located 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 portion of the alloy comprises aluminum and is preferably made of aluminum.

The installation 2 further comprises first feed means 12 in powder coating material, adapted to feed the main tank 6.

These first feed means 12 comprise a first conveyor 14A whose inlet is connected to an outlet of the raw powder recovery device 4 and whose outlet opens into the main tank 6.

The installation 2 further comprises second powder coating material feed means 14B, adapted to supply each of the coating material powder feed tanks, from the main tank 6.

In this case, 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. As it happens, these third feed means 18 consist of three screw conveyors 20A, 20B, 20C.

A raw powder treatment device 22 is disposed in the first conveyor 14A and separates the latter into an upstream portion 24 and a downstream portion 26.

The raw powder treatment device 22 is formed of a sieving device 28. This sieving device 28 is adapted to separate the particles from the powder, the largest dimension and the smallest dimension are located in a predetermined range. This sieving device 28 comprises two large screens 29A and 29B end. The large sieve 29A is disposed 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 over the thick sieve 29A by means of the upstream portion 24. A first outlet 32 of the sieving device, disposed between the large screen 29A and the fine screen 29B is connected to the downstream portion 26 of the first conveyor 14A. The sieving device is provided with two other outlets 34, 36 respectively upstream of the large screen 29A and downstream of the fine screen 29B. These outlets 34, 36 are provided for particles of which the largest or the smallest dimension is located above or below the aforementioned limits.

In this case, the largest dimension of each of the particles is less than 1000 μm, preferably less than 800 μm, and in particular less than 500 μm. In addition, at the first outlet 32 of the sieving device 28, the powder consists of particles whose smallest dimension is greater than 20 μm, preferably greater than 40 μm and in particular greater than 60 μm.

In what follows the coating device 10A will be described by way of example. The other two coating devices 10B, 10C are identical.

On the Figure 2 is schematically represented 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 cylindrical hollow shape having a longitudinal and horizontal axis X-X. The pipe is for example metal and in particular cast iron. The pipe 40 is fixed on a support (not shown) and can be rotated about its longitudinal axis X-X and 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 on the Figure 2 , as well as a device 46 for introducing the coating material powder into a flame 44.

The burner 42 is adapted to establish the flame 44 in a horizontal direction of flame 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 a angle different from 0 ° between them. These axes define a plane PP, which extends perpendicular to the axis XX and which coincides with the axis YY (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 oxidizing gas inlet 52 connected to a source of oxidizing gas 54, such as oxygen, via a combustion gas pipe 56 and a first gas valve. flow and pressure setting 58.

The burner head 48 is provided with a fuel gas inlet 60, connected to a fuel gas source 62, such as natural gas, acetylene or propane, via a fuel gas pipe. 64 and a second control valve 66 for pressure and flow.

The burner head 48 and a part of the device 46 for introducing the powder are represented on a larger scale on the Figure 3 , the burner head 48 being shown in longitudinal section.

The burner head 48 is generally of revolution about the Y-axis. It comprises, arranged successively one behind the other, and in the direction of flame F, a mixer 68, a fuel gas nozzle 70, and an oxidizing gas nozzle 72. The combustion gas nozzle 72 is maintained by a nozzle holder 74. The mixer 68 forms the fuel gas inlet 60 and the combustion 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 YY axis and a plurality of combustion gas passages 78 distributed regularly around the fuel gas passage 76. These components are known per se.

The fuel 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 a high rate.

The oxidizing gas nozzle holder 74 is a Y-Y axis revolution member, which has a stepped through bore 80 whose cross-section decreases from the rear end to the front. The oxidizing gas nozzle holder 74 comprises a threaded cylindrical base 82, to which a frustoconical outer portion 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 stepped threaded bore 92, in a part of which is screwed the base 82 of the oxidizing gas nozzle holder 74, so that the frustoconical portion 84 and the remainder of the stepped bore 92 form an annular cooling chamber 94 surrounding an axial portion of the nozzle holder 74.

A radial bore 96 of 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.

As illustrated on the Figure 2 these cooling air supply means 98 comprise a first air compressor 100 connected to a compressed air pipe 102 which opens into the cooling chamber 94 and into which is inserted a third control valve 104.

The sleeve 86 further comprises bores 106 which extend axially from the cooling chamber 94 and open onto a front surface of the sleeve 86, disposed on the outlet end side 90 and formed by an annular groove 108 open in the direction of the flame F to allow a confinement of the flame without disturbance of the initial flow.

As shown on the Figure 4 the sleeve 86 comprises eight bores 106.

The burner 42 is further provided with a device 110 for igniting the flame (see FIG. Figure 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 an electricity source 116. 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. Figure 4 ) and a supply device 122 of 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 the coating material powder into the flame 44 in an insertion direction IA to ID. Each of the introduction directions 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 introduction directions IC and ID of the two injectors 120C, 120D extend substantially horizontally, parallel to the XX axis 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 introduction directions IA, IB and IC, ID are arranged symmetrically with respect to the plane P-P.

With this arrangement, the particles of the powder projected towards the pipe 40 are distributed on an imaginary spot whose preferential direction extends along the axis X-X. As a result, few particles are projected over or under the pipe 40.

A symmetrical position with respect to a horizontal axis would give the same result in the case where the pipe 40 is arranged in such a way that its axis X-X extends vertically.

The supply device 122 of a powder / air mixture comprises a powder / air mixing chamber 126 having an inlet hopper 128 for the coating material powder 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 disposed above the inlet of the inlet hopper 128.

The metering device 140 is adapted to be supplied with powder coating material by the screw conveyor 20A.

The installation according to the invention operates as follows.

First, the cast iron pipe 40 is installed on the support (not shown) and is rotated about the X-X axis.

Then the valves 58, 66 are open. The pressure of the fuel gas is set at about 3 bar in the case of propane as a fuel gas. The pressure of the oxidizing gas is set at about 8 bar in the case of oxygen as the oxidizing gas.

en gaz naturel.The fuel gas flow rate is set to achieve a power of up to 70 kW. As for the flow of the oxidizing gas, it is set to generate a stoichiometric flame. The power of 70kW corresponds to a flow of about $7\frac{{\mathit{nm}}^3}{h}$

in natural gas.

The first compressor 100 is started and the cooling chamber 94 is supplied with pressurized air, for example at a pressure of about 2 bar.

Then, the flame 44 is initiated by the priming device 110. The flame 44 which is established has a power between 30 kW and 70 kW.

The maximum temperature of the flame 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 the flame 44 is between 500 m / s and 2000 m / s, and preferably between 700 m / s and 900 m / s.

Then the supply device of the mixture 122 is started 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 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 in the directions of introduction IA to ID. The injection speed of the powder in the flame 44 is between 20 m / s and 50 m / s.

The powder particles are then driven by the flame 44 in the direction F thereof. They are melted completely by the flame 44 and form droplets of molten coating material. Because the particle sizes are within the above range, the particles are melted completely without evaporating. The droplets exit the flame 44 in a sufficiently rapid manner to prevent 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 the pipe 40 and solidify to form a coating.

In order to coat the outer surface along the length of the pipe 40, 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 flow rate in mass of powder while using powder recovered from previous coating processes. In addition, the process according to the invention achieves a yield similar to that of flame coating processes using a wire-like coating material, namely of the order of 60%.

The device according to the invention as well as the process parameters make it possible to use a powder consisting of a low melting point alloy (about 450 ° C.), such as Zn ₈₅ Al ₁₅ , as a coating material.

In general, the powder consists of at least 50% of a metal or alloy whose melting point is between 400 ° C. and 500 ° C., preferably between 425 ° C. and 475 ° C. ° C.

Alternatively, the mixing chamber 126 may be connected to a source of gas other than air, for example a source of an inert gas.

In another variant, the coating device may be provided with a number of injectors other than four, for example two injectors or six injectors.

Furthermore, the powder treatment device may comprise a device for drying and / or deoxidation of the powder, in order to improve the flowability of the latter and / or the quality of the coating.

Claims (19)

1. A process for coating an object (40) requiring coating using a fusible coating material comprising the stages of:

   - establishing a flame (44), having a maximum flame speed and flame direction (F) which coincide with a flame axis (Y-Y), which is directed towards the object (4) requiring coating,

   - adding a quantity of fusible coating material into the said flame (44),

   - selecting the maximum flame speed and the distance between the object (40) requiring coating and the flame (44) so that the fusible coating material is projected onto the object (40) requiring coating in such a way that at least part of the quantity of fusible coating material is in the fused state when it impacts against the object (40) requiring coating,

   - the quantity of usable coating material comprising powder made up of particles,

   - the flame (44) having a temperature sufficiently low for the powder particles not to be wholly evaporated and sufficiently high for the powder particles to be at least partly fused,

   characterised in that at least a portion of the powder is a waste powder originating from a spray coating process, in which the powder comprises 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, and in that the remainder of the alloy includes aluminium, and in particular comprises aluminium.
2. A coating process according to claim 1, characterised in that the quantity of material is in powder form.
3. A coating process according to claim 1 or 2, characterised in that the particles have a largest dimension of less than 1000 µm, preferably less than 800 µm and in particular less than 500 µm.
4. A coating process according to any one of claims 1 to 3, characterised in that the particles have a smallest dimension of more than 20 µm, preferably more than 40 µm, and in particular more than 60 µm.
5. A coating process according to any one of claims 1 to 4, characterised in that the material is added to the flame (44) in at least one direction of addition (IA to ID) and in that the direction of addition (IA to ID) comprises a radial component in relation to the flame axis (Y-Y).
6. A coating process according to claim 5, characterised in that the direction of addition (IA to ID) is directed substantially radially with respect to the flame axis (Y-Y).
7. A coating process according to claim 5 or 6, characterised in that the object (40) requiring coating extends along a longitudinal axis (X-X) and in that the direction in which a component is added (IA to ID) extends parallel to the longitudinal axis (X-X).
8. A coating process according to claim 7, characterised in that the direction of addition (IC, ID) is substantially parallel to the longitudinal axis (X-X) of the object (40) requiring coating.
9. A coating process according to claim 7 or 8, characterised in that the material is added into the flame (44) in at least two directions of addition (IA, IB; IC, ID) and in that these two directions are symmetrical on either side of a plane (P-P) which includes the flame axis (Y-Y) and is perpendicular to the longitudinal axis (X-X) of the object requiring coating.
10. A coating process according to any one of the preceding claims, characterised in that the powder is added to the flame through at least one injector (120A, 120B, 120C, 120D) and in that the flow of powder injected into the flame is between 60 kg/h and 250 kg/h.
11. A coating process according to any one of the preceding claims, characterised in that the maximum flame speed is between 500 m/s and 2000 m/s, and preferably lies between 700 m/s and 900 m/s.
12. A coating process according to any one of the preceding claims, characterised in that the waste powder originates from an arc-wire coating process using a wire or bead of fusible coating material as the starting material.
13. A coating process according to any one of the preceding claims, characterised in that the said portion of the powder is obtained by screening a quantity of unprocessed waste powder.
14. A coating process according to claim 13, characterised in that at least the said portion of powder is subjected to an operation of drying or deoxidation before addition to the flame (44).
15. A coating process according to any one of the preceding claims, characterised in that the maximum temperature of the flame is between 2000°C and 3000°C, preferably between 2250°C and 2750°C, and in particular between 2400°C and 2600°C.
16. A flame coating device designed to implement the process according to any one of the preceding claims, of the type comprising:

    - a burner (42) designed to be connected to a source of combustible gas (62) and designed to produce a flame (44) along a flame axis (Y-Y),

    - means (46) for adding a fusible coating material to the flame,

    - characterised in that

    the device comprises a feed container (8A, 8B, 8C) containing at least in part a waste powder originating from a spray coating process and feed means (18) for the means (46) for addition from the feed container (8A, 8B, 8C), in that the means (46) for addition of the fusible coating material are designed to add the fusible coating material to the flame (44) in powder form, and in that the powder comprises 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, and in that the remainder of the alloy includes aluminium, and in particular comprises aluminium.
17. A device according to claim 16, characterised in that the means (46) of addition comprise an injector (120A, 120B, 120C, 120D) designed to add a powder mixture of coating material/delivery gas to the flame (44) in a direction of addition (IA, IB, IC, ID).
18. A device according to claim 17, characterised in that the direction of addition (IA, IB, IC, ID) is substantially radial with respect to the flame axis (Y-Y).
19. A device according to either of claims 17 or 18, characterised in that it also comprises a mixer (120) for coating material/delivery gas comprising a powder inlet (128), a delivery gas inlet (130) designed to be connected to a source of delivery gas (132) and an outlet for the coating material powder/delivery gas mixture, in that the mixer (120) is designed to mix the powder with a flow of delivery gas, and in that the output of the mixture of coating material powder/delivery gas is connected to at least one injector (120A, 120B, 120C, 120D).

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