DE1089614B - Method and device for flame spraying - Google Patents

Description

GERMAN

The present invention relates to the application of improved surface coatings Objects of all kinds by means of a flame spray gun, which is particularly advantageous for applying Surface coatings made of materials with a high melting point is suitable.

It is known to provide an object with a protective coating by the object with a molten and atomized material is sprayed onto a pre-cleaned surface attached to the object. The coating material, usually in the form of a rod, was inserted into the The flame of a gas burner was introduced to melt it, and the melted one was then melted. material against the surface to be coated with the aid of a stream of air or a stream of inert Blown gas. However, some success has been achieved using metals with a low melting point These coatings are not sufficient for many applications because they are often porous and often distributed unevenly are. In many cases they lack the very desirable properties of a good protective coating, such as hardness, as well as good wear resistance and corrosion resistance.

The present invention aims to meet the various to eliminate the above-mentioned disadvantages of the known spraying process.

The invention relates to a flame spraying process as well as a flame spray gun with one connected to the internal combustion chamber Discharge channel, wherein a mixture consisting of a fuel gas, an oxidizing agent and a solid coating material and optionally a carrier gas, with the help of an injector nozzle into the combustion chamber or discharge channel arrives.

The new flame spray gun is characterized in that the injector nozzle with one of essentially even bore existing. Discharge channel connected and the bore of the injector nozzle is expanded coaxially backwards and behind the laterally arranged inlet channel for the Fuel gas extends.

Further features of the invention emerge from the representations of exemplary embodiments. It shows

1 shows a longitudinal section through a preferred embodiment of the flame spray gun,

FIG. 2 shows a partial section through a modified form of the pistol shown in FIG. 1.

The flame spray gun 10 illustrated in FIG. 1 is provided with a burner 11, with an enlarged section 12 which merges into a channel that is not narrowed from the inlet to the outlet. The combustible mixture introduced into the sewer is then ent-method and device
for flame spraying

Applicant:

Union Carbide Corporation,
Ne ^ York, NY (V. St. A.)

Representative: Dipl.-Ing. H. Görtz, patent attorney,
Frankfurt / M., Schneckenhofstr. 27

Claimed priority:
V. St. v. America May 2, 1955

George Harvey Smith, Kenmore, N.Y.,

Richard Corey Eschenbach, Lafayette,

and John Franklin Pelton, Indianapolis, Ind.

(V. St. A.),
have been named as inventors

ignites, passed through and then discharged at the other end as a stream of hot combustion gases, whereby a flame jet is generated which has a high degree of heat transfer, a high speed and has compressive force.

In order to achieve satisfactory results, it is essential that, in order to produce a surface coating on an object using a flame spray gun according to the present invention, conditions are maintained whereby a value K is maintained on the order of between 75 and 750, the value K being determined as follows will:

A ₀ P ₀ W

Here, A _{1 means} the cross-sectional area of the gas-powder mixture in cm ² when entering the discharge channel, A ₀ the cross-sectional area of the gas-powder mixture in cm ² when exiting the discharge channel, P ₁ the absolute pressure in kg / cm ² of the gas-powder mixture when entering the

009 608/198

charge channel, P _{0 is} the absolute pressure in kg / cm ^{2 of} the gas-powder mixture when it exits the discharge channel and W is the weight of the combustible gas mixture supplied in kg / sec.

In detail, the pistol 10 has a torch 11 with a hollow cylindrical portion 12, the at one end in the direction of an elongated central drilled hole made in one piece with it Tube 13 is tapered, while it is open at its other end for receiving a fuel injector 14 which has a central passage 15 aligned axially with the axis of the pipe 13. A threaded central portion of the injector engages a threaded portion 16 of portion 12, while the injector 14 is held in the burner in a predetermined axial position by means of a lock nut 17 will.

The injector 14 is stepped at 18 to provide a mixer 19 of reduced diameter, which is disposed radially inwardly of part 12 and terminates in an outlet 20 which extends into the through the bore of the pipe 13 formed combustion channel 21 leads. The mixer 19 is spatially a little different End wall of part 12 disposed away to an annular passage for the gas flow from the annular space or chamber 22 around the mixer 19 in the pipe 13. One Fuel supply line 24 is connected to the passage 15 via a lateral opening 23, while an oxygen supply line 25 communicates with the chamber 22 via a lateral opening 26. To prevent the flame, which is initially ignited outside the duct, from flashing back into duct 21, the minimum diameter of the outlet 30 should be substantially no less than 0.5 mm.

The coating material can be in the burner in finely divided form in the fuel, in the oxygen or be introduced in the combustion mixture. In the embodiment illustrated in FIG. 1 the finely ground material from a carrier gas, e.g. B. hydrogen, introduced into a nipple 27, the is screwed with threads in the head of a centrally open receptacle 28, which is the rear end of the passage channel 15 closes. The rear protruding end of the nipple can be connected to the supply source of the coating material. In its front end is one extending forward hollow shaft 29 fitted into the passage 15 at least beyond the lateral Fuel supply opening 23 protrudes and carrier gas and the coating material carried along to the Mixer 19 supplies.

Fuel and oxygen are fed to the channel under pressure, preferably at least 1 kg / cm ² overpressure. As soon as the fuel carrying the particles enters the combustion duct 21, it mixes intimately with the oxygen in the rear of the duct 21 to form a stream of combustible mixture which, soon after mixing, begins to burn and generate large amounts of combustion gases, which flow forward at high speed through the non-tapered narrow space of the channel and then come out of the outlet 30 at the mouth of the tube 13 as a jet of flame. The coating particles carried along by the combustion gases are then ejected from the pistol in a straight-ahead jet of flame which has a high degree of heat transfer, a high speed and an extensive compressive force. To prevent excessive heating of the tube 13 during operation, a sleeve 31 is disposed around the tube radially outwardly to form a cooling jacket 32 through which cooling water can circulate via inlet 33 and outlet 34.

The coating material can also be fed directly into the combustion zone in powder form or in the form of a Rod are introduced. The latter is illustrated in Fig. 2, where a rod 40 consists of a solid Coating material is introduced through an opening 41 at the rear end of the injector 14, into Extends longitudinally through this and from the mixer 19 far enough forward into the rear part of the channel 21 protrudes so that its front tip lies in the combustion zone. the Rod is inevitably moved by suitable drive means, e.g. B. by rotating friction rollers 42. which grasp the rod 40. A ring 43 is used

ao for sealing the opening 41.

It can be seen that a spray gun with such an internal burner has the advantage that the way the particles are not hindered while flowing through the combustion chamber and consequently the particles do not encounter any obstacles that could cause clogging.

The required gas composition, the high powder velocity and the high powder temperature can with the described spray guns by correct control of the operating conditions and by Proportioning of certain parts of the pistol can be achieved.

There are several factors that control powder temperature. The most important are the properties the reactant, the fuel-oxygen ratio, the residence time of the coating powder in the combustion gases, the torch cooling losses, the distance between the torch and the workpiece and the powder speed. Fuels with high flame temperatures, such as acetylene, are suitable and where permissible, only use oxygen-fuel ratios that reflect maximum flame temperatures can be used. Such ratios can, however, with many coating materials, from the in the following reasons, are not used, but they are for coating with ceramic Materials suitable.

The thermal energy of the coating powder is dependent on both powder speed and depends on the flame temperature, since the kinetic energy of the particles after hitting the Workpiece is converted into thermal energy. This can be seen from the table below, which shows the temperature rise shows after impact, the calculations being based on the assumption completely inelastic Collisions are based.

Temperature rise after impact

Powder speed Received theoretical
Temperature rise 213.4 m / sec
304.8 m / sec
442.0 m / sec
609.6 m / sec
914.4 m / sec 71 ° C
160 ° C
360 ° C -
693 ° C
1582 ° C

The minimum temperature at which the powder becomes plastic enough to be a good coating

will, however, depend on the material used. In any case, however, means Minimum temperature the lowest allowable coating temperature of the particle at the time of impact. the Impact temperature is the sum of the temperature equivalents the heat energy given off by the flame and the kinetic energy released on impact Energy of the powder. In this way, an otherwise satisfactory fuel can also be used has too low a flame temperature for low speed processes, now after the present process is successful because of the additional heat energy that is transferred to the coating material upon impact at the high velocities according to the present invention can be used.

With many coating materials, especially with metals, metallic alloys and compounds, it is important to consider the composition of the combustion gases among non-oxidizing and not To maintain decarburizing conditions in order to obtain a coating of the desired quality. The kind of the fuel and the oxygen-fuel ratio influence the oxidation potential of the atmosphere, which in turn affects the composition of the coating. For example, that is Carbon content of certain tungsten carbide powders 4.5 to 5.0 percent by weight. At an oxygen to acetylene volume ratio of 1.0, the carbon content in the coating was found to be approximately 3.0% by combustion analysis. At a When the ratio was 1.4, the carbon content was 2.0%, and when the ratio was 2.0, it was 1.3%. the Coating quality changed with the carbon content of the coating, which was due to fluctuations in the Hardness, brittleness and surface appearance was detectable. The effective oxidation potential various combinations of fuel and oxygen, in this case by carbon removal measured, is closely related to the amount of oxidizing agents in the hot combustion gases. As such oxidizing agents, e.g. B. carbon dioxide and water, can be related With this method, substances are defined that are oxidative at the operating temperatures 4-5 have shafts. It has been found that when a tungsten carbide coating is applied, the Fuel-oxygen ratio z. B. should be such that less than 67 volume percent oxidant found in the reaction being carried out, d. i.e., the ratio of the volume of the oxidizing agents to the total volume of the reaction products must be less than 67%. It is especially important that Oxidation potential of the atmosphere when using coating materials that are exposed to high temperatures are easily oxidized, as with powders made of metals, metal carbides, metal borides, metal nitrides and silicides. It is understandable that the scheme the composition of the flame is important to achieve proper coating quality.

Different fuels can be used. It has been found that acetylene is specific to Flame spraying is suitable because there are particularly high flame temperatures with advantageous fuel-oxygen ratios having. However, other fuels are temperature and compositional requirements also meet, also suitable .. For example, hydrogen, methane and ethylene are has been used successfully in the flame spraying process of this invention.

The powder velocity in a spray gun of the type described is approximately the gas velocity proportional. Since the supply pressure is the most important factor in gas velocity, the Pressure can be crucial when choosing a fuel. The higher the supply pressure, the at A specific fuel can be used, the higher the achievable powder speed. Higher powder speeds also increase the thermal energy of the powder. This follows from the increased temperature rise when the kinetic energy is released when the powder hits the Workpiece surface. This means that fuels with lower flame temperatures can still be used if they allow higher feed pressures and higher powder speeds.

The hardness and porosity of the coating depend to a considerable extent on the speed of the powder away. This is shown in the table below, which occurs when spraying a tungsten carbide-cobalt alloy with a pistol according to Fig. 1 resulted in:

Partial service speed

122 to 183 m / sec
183 to 244 m / sec
396 to 457 m / sec

Hardness of the coating

Knoop
Pyramid number

800 to 1000
1000 to 1200
1100 to 1600

porosity

up to 10%

approximately 5%

less than 2%

The advantages of a high powder velocity and a high temperature are particularly evident when a non-porous, well-binding coating is desired. These benefits are not limited to any particular coating material; although the invention is particularly suitable for coating with materials having a high melting point. it is also useful for coating surfaces with any of the wide range of metals, alloys, metallic compounds, plastics, ceramics, and minerals. The surfaces, which can be pre-cleaned in any way, can also consist of a wide variety of materials. The following table shows several illustrative examples of fabrics that have been coated using this process. The coatings were made by using 16.9 m ^{3 of} oxygen and acetylene per hour in a burner according to FIG. The oxygen-acetylene ratio was 1.0 to 1.6. In the case of copper powder, only 8.4 m ^{3 of} oxygen and acetylene were used per hour. The coating samples were produced on a flat workpiece.

An example of the importance of the invention is the ability to apply a substantially non-porous coating of wear-resistant hard material having a high melting point, such as tungsten carbide alloys. When using a spray gun according to FIG. 1, a tungsten-carbon-cobalt alloy with approximately 4% carbon and 9% cobalt was in the form of a finely divided powder which penetrates through a mesh size of 0.043 mm, in a hydrogen carrier gas of 1, 7 m ³ / h is fed into the torch of the gun at a speed of 6.8 kg / h. Acetylene and oxygen at a pressure of 2.46 kg / cm ² were fed to the burner in a ratio of 1.4 m ^{3 of} oxygen to 1 m ^{3 of} acetylene at a combined rate of 16.9 m ³ / h. The workpiece, a cylindrical piece of steel 1.27 cm in diameter and 3.81 cm in length,

powder Upper pull workpiece detention aluminum capability*) stole cobalt acceptable stole copper Well stole iron Well stole nickel Well stole silicon Well stole (through 0.074mm acceptable Mesh size) silver stole the end Tungsten + 12% CO drawn stole (through 0.043mm Well Mesh size) Tungsten carbide + 8% CO stole (-3 microns) Well Tungsten carbide + 12% Ni stole (-10 microns) Well Tungsten carbide + 20% oAg stole (-20 microns) Well Chromium carbide + 15% Ni stole (-10 microns) the end Tungsten carbide + 8% CO drawn copper Tungsten carbide + 8% CO acceptable Rustproof (through 0.043mm Well stole Mesh size)

*) The classification of the adhesion was carried out as follows:

Acceptable:

Examination of the cross-sectioned samples revealed a tear at some points between the coating and the base metal.

Good:

Black inclusions were observed on the interface between the base metal and the coating cross-sectioned samples, although the adhesion otherwise appeared to be tight.

Excellent:

The bond of the coating to the base metal is good, with very little or no inclusions on the Parting surface.

be moved. In addition, when coating certain workpieces, such. B. with caliber mandrels, the Workpiece to be held and rotated in a lathe while the gun is along the length of the Workpiece is moved. In this way, an even layer can be applied to the caliber mandrel will.

Claims (5)

Patent claims: ίο 1. Flame spray gun to make a Surface coating on an object with one connected to the internal combustion chamber Discharge channel, whereby a mixture consisting of a fuel gas, an oxidizing agent and a solid coating material and optionally a carrier gas with the aid of a Injector nozzle enters the combustion chamber or discharge channel, characterized in that the injector nozzle with one of essentially ao evenly bore existing discharge channel is connected and the bore of the injector nozzle is expanded coaxially backwards and is located behind the laterally arranged inlet channel for the fuel gas extends. 2. Flame spray gun according to claim 1, characterized in that the injector nozzle for the gas-tight Feeding of wire-shaped coating material on its rear side with a coaxial one Has bore provided wall. 3. Method of making a surface coating on an object using a flame spray gun according to claims 1 and 2, characterized in that the combustion conditions be guided in such a way that according to the equation 35 40 was rotated at 150 min and 3.2 mm per revolution at the burner outlet with a distance of Moved past 10.2 cm. In this way, the workpiece was obtained with a radial thickness of 0.10 mm in coated for about 5 seconds. The coated coupon was applied to a very smooth polish sanded and polished, the hardness of the surface was measured with 1200 Knoop. The gun used had a water-cooled cylindrical nozzle with an inside diameter of 7.1 cm with a length of 20.3 cm. The continuous operation of the process according to the invention enables a steady flow of coating particles to be applied to a surface, the particles always imparting uniform forces will. In this way, a uniform, non-porous coating can be applied to a surface in a relatively short time getting produced. In practice, the gun can be held either in a horizontal or vertical position and the workpiece to be coated can be A ₀ P ₀ W with respect to the gun or the gun with respect to the workpiece for K results in a value between 75 and 750, where A _{1 is} the cross-sectional area of the gas-powder mixture in cm ² when entering the discharge channel, A _{0 is} the cross-sectional area of the gas-powder mixture in cm ² when exiting the discharge channel, P _% is the absolute pressure in kg / cm ^{2 of} the gas-powder mixture when entering the discharge channel, P _{0 is} the absolute pressure in kg / cm ^{2 of} the gas-powder mixture when it exits the discharge channel and W is the weight of the combustible gas mixture supplied in kg / sec means. 4. The method according to claim 3, characterized in that the fuel gas is ^{supplied under a pressure of at least 1 kg / cm 2} above atmospheric pressure and the oxidizing agent under the same or a higher pressure. 5. Process according to Claims 3 and 4, characterized in that the combustion zone is oxygen and acetylene in a ratio between 0.8: 1 and 1.9: 1 and powdered tungsten carbide of a particle size of less than 0.043 mm mesh size can be fed. Considered publications:
German Patent No. 808 794;
French patent specification No. 903 239. 1 sheet of drawings © O09 608/198 9.60