SE186885C1 - - Google Patents

Description

Inventors: GH Smith, RC Eschenbach and JF Pelton Priority Requested as of May 2, 1955 (USA) material with high melting point on foremal.

In recent times, it has been common to provide a form with a protective coating by spraying the form with a narrow and finely divided material, which adheres to a previously cleaned surface of the form. Surface spraying has been carried out by inserting the transverse material, usually in the form of a rod, into the layer of a gas burner for melting the material and the molten material was then ejected by means of a stream of air or an inert gas towards the surface to be coated. To date, such spraying with the greatest success has been carried out with metals with a low melting point, but even such coatings have not been satisfactory in many applications, as they are usually unobtrusive and often unevenly distributed. As such, they lack many of the most desirable properties of a good protective coating, e.g. hardness for obtaining high groove strength as well as impermeability for obtaining corrosion resistance.

The present invention seeks to remedy the above-mentioned malfunctions in connection with known spraying methods.

In general, the invention relates to a set for applying by flame spraying a surface coating to a mold, according to which a solid coating material is heated in a continuously burning combustion mixture of fuel fluid and an oxidizing agent and according to which the heated material is thrown into the finely divided form. shall be transferred, by means of a gas stream. According to the invention, the combustion mixture is combusted in the presence of the transverse material in a combustion zone formed by combustion of a mixture of separately supplied streams of fuel fluid and oxidizing agent, inside a non-displaced tube with substantially uniform bore, which Or arranged to accelerate the combustion products. high velocity, whereby entrained particles of the coating material are expelled from the tube with so much energy that they form an adherent coating as they are thrown against the form.

The invention also relates to a flame spray gun for expelling the kit, which gun Or is provided with an internal combustion chamber, arranged to receive a combustible mixture, an elongate discharge channel for acceleration of the combustion products to high speed and separate channels for the introduction of a fuel fluid and a fuel fluid. solid transfer material in said combustion chamber. The gun according to the invention can be characterized by a tube of substantially uniform bore, which at its closed side Or provided with an injection nozzle, arranged to impart to one of the gases entering in said combustible mixture together with said Coating material a direction of movement axially into said bore, wherein rum, corn surrounds namtida nozzle, stands in connection with supply means for the tivriga nananda input gases.

The spraying process is continuous and in the preferred embodiment of the invention comprises a suspension of finely divided solid material in a combustion mixture, which consists of a fuel and a combustion-maintaining substance in such proportions that an excessively volatile and charring atmosphere is avoided during combustion. The combustion-containing substance may be constituted by Iuft, but Or fOretradesvis acid, especially when Dupl. at 48 b: 12 2— - Covers are made of materials with a high melting point, with regard to the higher flame temperatures, which are generated when using oxygen. Coating material can be introduced into the combustion zone by being suspended either in the fuel or in the oxygen, but it can also be suspended in the combustion mixture before or even after the combustion has started. The high flame temperatures and the high linear velocity of the flame jet, which were essential for successful coating with the aid of a flame jet, are obtained by directing the mixture entraining the particles to a burner of the type in which the ignition of the mixture under pressure generates large volumes of flaming combustion gases. , which are released into the open through a restrictive channel, which facilitates acceleration of the gases to high speeds.

The high temperatures to which the particles can be heated by being entrained in the combustion mixture and in the flame jet, and the significant increase in temperature corresponding to the destruction of kinetic energy, make the particles reach the workpiece at high speed. melting point (or at least the constituent of such materials, as here Idgsta melting point) to a sufficient extent to ensure a solid mechanical connection with the surface of the body to be coated. The high speed at which these particles are imparted at these temperatures causes such a deformation of the particles as they trample against the form that they are welded together with other particles in the coating, forming a% It durable, substantially non-porous coating. In addition, in the case of the above-described otters, the thermal and kinetic energy of the coating particles is so great that the surface of the workpiece does not need to be heated to high temperatures as in hard or fill welding and the like. Accordingly, non-porous coatings with good maintenance can be produced according to the invention without causing any stone changes in the microstructure of the workpiece.

In the accompanying drawings, Fig. 1 is a longitudinal section through a preferred embodiment of a jet flame gun for practicing the mode of invention, and Fig. 2 is a partial section through a modified embodiment of the gun of Fig. 1.

The spray gun 10 Or shown in Fig. 1 is provided with a tubular burner 11, which represents the type preferred according to the invention. Such a tubular burner comprises a non-displaced channel from an inlet to an outlet, in which channel a fuel fluid mixture received through the inlet at one linden is ignited to pass through the channel and discharged at the other as a strain of hot, burning gases. for generating a layer with high heat transfer intensity, high speed and significant pressure.

In order to obtain satisfactory results, it is necessary to maintain such working conditions during combustion, that in the following equation K has a value between 75 and 750: K - "A.2P.2 Ao PoW in which equation Ai = cross-sectional area of the stream of combustible material at the inlet of the stream in the combustion chamber, expressed in Ao = cross-sectional area of the strip of combustible material at the discharge stall from the combustion rune, expressed in cm2 Pi = the pressure at the steel where the stream of fuel fluid is introduced into the combustion chamber, expressed in kg / cm

Po = the pressure at part stalle, where the stream of burning combustible material is discharged from the enclosed space, expressed in kg / cm2 abs.

W = weight of spent fuel fluid, expressed in kg / sec.

The burner 11 in the gun 10 is provided with a hollow cylindrical portion 12, which tapers at one end towards an integrally formed, elongated, central bore provided with a barrel 13 and a corn or open at the other end for receiving a fuel injector 14, coin Or provided with a central channel 15, which Egger axially in line with the barrel 13 axis. An outer center portion of the injector Or engages an internally threaded portion 16 on the portion 12, the injector being held in a predetermined axial position in the burner by means of a lock nut 17.

The injector 14 is provided with a ledge 18, through which a mixer section 19 of reduced diameter is formed, which is spaced apart from the portion 12 and which terminates in an outlet 20, which there is used towards the combustion channel 21 in the bore of the barrel 13. The mixer 19 is located at some distance from the conical duct wall of the portion 12, whereby an annular channel is formed for the flow of fluid from the annular space 22 around the mixer 19 into the barrel 13. A fuel supply line 24 is connected to the channel 15 through an opening located in the side wall. 23 and an oxygen supply line 25 Or connected to the chamber 22 through an opening 26 in the side wall. In order to ensure the retraction of the layer, which to an initial -Uncles outside the combustion channel 21, into it, the minimum diameter of the outlet 30 should not be significantly less than 0.51 mm. the coating material can be introduced into the burner in finely divided form as a suspension in the fuel or in the oxygen or in the combustion mixture. In the embodiment according to Fig. 1, finely divided material is transported by a carrier gas, e.g. vate, into a nipple 27, corn Or inscribed in the head of a central bore insert plug 28, which closes the rear end of the channel 15. Nipple protruding rear end Or arranged to be connected to a Ulla for everdrag material. In the frangible spirit of the nipple Or a forwardly directed hollow shaft 29 is fitted, which extends into the channel 15 at least to a stalk beyond the side wall opening 23 for fuel supply and which introduces bare gas and entrained coating material into the mixer 19.

Fuel and oxygen are introduced into the combustion duct under pressure, preferably at least 1 kg / cm 2. As the particulate fuel enters the combustion channel 21, it mixes intimately with the oxygen in the rear portion of the channel 21 and forms a stream of combustion mixture which begins to burn shortly after mixing, forming large volumes of flaming combustion gases which move forward at high speed through the non-combustion chamber. displaced space in the combustion channel and then the frail outlet 30 is discharged at the mouth of the barrel as a flame jet. The coating particles entrained with the combustion gases are ejected from the gun in a directional flame jet with high heat transfer intensity, high speed and significant pressure. In order to prevent excessive heating of the pipe 13 during operation, a sleeve 31 is arranged around and at a radial distance from the pipe, whereby a water jacket 32 is formed, through which cooling water can be caused to circulate Iran an inlet 33 to an outlet 34.

The coating material can be introduced directly into the combustion zone in the form of powder oil in rod form. The latter was located in Fig. 2, where an elongate rod 40 of solid coating material is inserted through an opening 41 at the rear end of the injector 14, which rod extends in the longitudinal direction through the injector and projects as much as the Iran mixer 19 into the rear of the combustion duct 21 that the front tip of the rod is in the combustion zone. The rod is driven directly forward with the aid of some suitable device, e.g. opposite rotating friction wheel 42 in engagement with opposite sides of the rod 40. The opening 41 is tightly closed by means of an o-ring 43.

A spray gun with a burner for internal combustion has the unique advantage that the trajectory of the particles throughout its length through the enclosed combustion and discharge space is not forced and that consequently the particles do not have any obstacles where they could settle and shrink. tap to the channel.

The atmospheric composition, the high powder speed and the high powder temperature required according to the method of invention can be obtained with the described spray guns by regulating the variable operating conditions and by raft dimensioning of certain parts of the gun.

The powder temperature is determined by a number of factors. The most important of these concerns are the nature of the reactants, the fuel-oxygen ratio, the residence time of the coating powder in the burning gases, the cooling losses in the burner, the distance between the burner and the workpiece and the powder speed. The fuel with high flame temperatures, e.g. acetylene, Oro onskvarda and, as far as possible, such oxygen-fuel conditions should be used, that maximum flame temperatures are reached. Such ratios may not be used in conjunction with many coating materials of shells, as indicated below, but are suitable for flame plating of ceramic materials.

The coating powder depends on both the powder speed and the flame temperature in terms of the thermal energy of the powder, while the kinetic energy of the particles is effectively converted into thermal energy, as the powder hits the workpiece. This is shown in the following table regarding the temperature increase at impact, whereby the calculations Oro challenge during the assumption of completely inelastic collision.

Temperature increase on impact Powder speed mjs oak Resulting theoretical temperature increase 213.4 71 ° C 304.8 160 C 442.0 360 ° C 609.6 693 ° C 914.4 1582 ° C The minimum temperature at which the powder becomes sufficiently plastic for formation of a good Over-coating, depends of course on the material used. In yule cases, however, minimum temperature means the lowest permissible coating temperature of the particle at the time of impact; the impact temperature will be the sum of the temperature equivalents of the thermal energy supplied by Fagan and the kinetic energy released by the impact of the powder on the formal. Thus, an otherwise satisfactory fuel, the flame temperature of which would be too low at low speed processes, can now be used successfully according to the method of invention due to the additional heat energy supplied to the Ore coating material at high speed dosing in accordance with the invention.

When using many coating materials, especially metals, metal compounds and metal alloys, it is important to maintain the burning gases in a non-oxidizing and non-charring state in order to obtain a coating of desired quality. The nature and oxygen-fuel ratio of the fuel affect the modulus of the atmosphere, which in turn determines the composition of the coating. For example, the carbon content of certain tungsten carbide powders initially states 4.5-5.0% by weight. At a volume ratio of 1.0 between oxygen and acetylene, the carbon content of the coating was found in the combustion analysis to be about 3.0%. At a ratio of 1.4 the carbon content was 2.0% and at a ratio of 2.0 it amounted to 1.5%. The coating quality varied with the carbon content of the coating, which was shown by variations in hardness, roughness and surface appearance. The effective oxidation potential, measured in this case by carbonization, in various combinations of fuel and oxygen was closely related to the amount of oxidizing fuel in the hot, burning gases. Wdderande anmen, .t. ex. carbon dioxide and water, can be defined as substances with oxidizing properties at operating temperatures within the framework of the present 4— description. It has been found that when applying, for example, a tungsten carbide coating, the fuel-oxygen ratio should be such that less than 67% by volume of oxidizing substances can be detected in the final reaction, ie. the ratio of the volume of the oxidizing agent to the total volume of products generated by the reaction must be less than 67%. It is especially important to limit the oxidation potential in the atmosphere when using coating materials, which are very prone to oxidation at high temperatures, e.g. metal and metal carbide, bond, nitride and silicide powders. It is clear that the composition of the law must be regulated in order for the desired coating temperatures and thus the coating properties to be obtained.

Different industries can be used. Acetylene, which has extremely high flame temperatures in fuel-oxygen conditions at which adverse flame compositions are obtained, has been found to be particularly suitable for use in flame plating. However, other industries which can meet the temperature and composition requirements are equally useful. Vale, methane and ethylene have, for example, been used successfully in the Ramplating Kit according to the invention.

The powder velocity in a spray gun of the type described above is largely proportional to the gas velocity. Since the supply pressure Or is the determining factor for gas velocity in the front room, the usable pressure becomes an important factor in the choice of an industry. The higher the usable supply pressure for a given industry Or, the higher the powder rate that can be reached. higher powder velocities are an effective means of supplying the powder with additional thermal energy. This Or a folide of the increased temperature rise upon the release of kinetic energy, as the powder states against the surface of the workpiece. Thus, the industries which allow higher feed pressures and higher powder velocities may have lower flame temperatures and yet be suitable for use in the practical application of the flame plating set according to the invention. the liard and porosity of the coated arc to a significant extent depending on the powder velocity. This is shown in the following table, obtained by spraying a tungsten carbide-cobalt alloy with the aid of a gun equipped with a burner according to Fig. 1: 10% 122-183 1000-1200 is 5% 183-244 1100-1600 less On 2% 396 457 Hardness determination • according to Knoop is described in Metall's handbook (1961) volume 1 page 22.

The advantages of high powder speed and high temperature, which are made possible by the present invention, appear whenever a non-porous, selective coating is to be produced. These advantages are not limited to a particular coating material, although the invention is of particular importance for coating with high melting point materials, but equally lam- pad for coating surfaces with any material among a large number of metals, alloys, metal compounds, plastics. , ceramic materials and minerals. The base surfaces, which can be pre-cleaned ph anything conveniently set, can also be best. of many different materials. The following table shows a number of typical examples of substances which have been plated with the set according to the invention. In general, the coatings were prepared using 16.9 ms / h. of oxygen and acetylene in a burner according to Fig. 1. Oxygen-acetylene ratios of 1.0-1.6 were used. When the bile copper powder was used, only 8.4 matt hours were used. of oxygen and acetylene. The covers were made in the form of buttons ph a flat workpiece.

Powder adhesion * Coated aluminum quite good cobalt good copper-good iron-good silicon (through 0.074 mm fairly good salt openings) silver-marked tungsten + 12% Cobra (through 0.043 mm sail openings) tungsten carbide + 8 ° A, good Co (-3 microns) tungsten carbide -I- 12% good Ni (-10 microns) tungsten carbide -1- 20% good Ag (-20 microns) chromium carbide + 15% excellent Ni (-10 microns) tungsten carbide 1- 8% quite good Co tungsten carbide + 8% good Co (through 0.043 mm saddle openings ) The adhesion assessments have the following inboard: Fairly good - examination of cross-sectional samples showed a crack at some stable between the coating and the substrate metal. std.l stal stal sthl stal stal stal stal copper copper stainless std.]. - 185 885 - Utrnarkt - the adhesion between the cover and the base metal was good with very few or no inclusions at the spruce surface.

Illustrative of the effectiveness of the inventive method is that it is possible to achieve a substantially non-porous coating on a rain-resistant, hard material with a high melting point, e.g. tungsten carbide material. Using a spray gun according to Fig. 1, a material composed of tungsten, carbon and cobalt with about 4% carbon and 9% cobalt in the form of a finely divided powder, capable of passing through 0.043 mm sall openings, was introduced into the gun burner in a quantity of 6.8 kg / h in vale sasom bararegas in an amount of 1.7 m3 / h. Acetylene and oxygen are fed to the burner at a pressure of 2.46 kg / cm2 and in a ratio of 1.4 m3 oxygen to 1 m3 acetylene and in a total amount of 16.9 ma / h. The workpiece, which consisted of a cylindrical piece of steel with a diameter of 1.27 cm and a length of 3.81 cm, was rotated at 150 rpm and advanced 3.2 mm per vary past the burner outlet at a distance of 10.2 cm. On this salt, the workpiece was coated to a radial thickness of 0.10 mm in about 5 seconds. The coated sample was ground and polished in a conventional manner to a very high smoothness and the surface hardness was measured to 1200 knots. The pistol used had a water-cooled cylindrical nozzle with an inside diameter of 7.1 mm and a length of 20.3 cm.

The continuous nature of the method of invention makes it possible to supply a steady stream of coating particles to a surface, while the particles are constantly standing. under the influence of substantially uniform forces. On this salt, a uniform, non-porous coating can be applied to a surface in a relatively short time.

In practice, the gun can be tilted horizontally or vertically and the workpiece can be moved in relation to the gun or the gun in relation to the workpiece. When transferring certain workpieces, e.g. cylindrical interpreters, the workpiece can be held and rotated in the chuck by a lathe, while the gun is moved in the longitudinal direction of the workpiece. In this way, a uniform layer is applied to the interpreter.

Claims (7)

Patent claim: 1. For application by flame spraying to a surface coating on a mold, in which a combustion mixture of fuel fluid and an oxidizing agent is continuously burned in a combustion chamber in connection with a discharge duct, where the combustion products are accelerated to high speed, a solid coating material is introduced into the fuel and the daryid formed very fast stream of combustion gases as well as the particles of the coating material directed towards the surface of the article, characterized in that the coating material is introduced into a combustion zone formed by combustion of a mixture of separately supplied streams of fuel fluid and fuel fluid. a non-displaced wire with substantially uniform bore, such combustion conditions being maintained that K has a value between 75 and 750 in the following equation: A-2P-2 K = "Ao PoW in which Ai = the cross-sectional area of the stream of combustible material yid the stable; for strOm while in-Rwanda in the combustion chamber, expressed in cm2 Ao = cross-sectional area ay the stream of combustible material at the discharge station from the combustion chamber, expressed in cm2 Pi = the pressure yid the steel, where the stream of fuel fluid is introduced into the combustion chamber, expressed in kg / cm2 abs. Po = pressure yid the stfihle, where the current ay burning combustible material is discharged from the enclosed space, expressed in kg / cm2 abs. W = weight ay Consumed industry fluid, expressed in kg / sec Salt according to claim 1, characterized in that fuel fluid is supplied under an Oyer pressure of at least 1 kg / cm 2 and that the oxidizing agent is supplied under substantially the same or higher pressure. Salt according to claim 1 or 2, characterized in that oxygen and acetylene are introduced into the tube in a ratio between 0.8: 1 and 1.9: 1 and that the polymerized composition of tungsten carbide, which is capable of passing through 0.043 mm sight openings, inserted in the combustion zone. A flame spray gun for use according to any one of the preceding claims, provided with an internal combustion chamber, arranged to receive a combustible mixture, an elongate discharge channel, for accelerating the combustion products to high speed and channels for introducing fuel fluid and a solid, an oxide coating material in said combustion chamber, characterized by a tube of substantially uniform drilling, which in its closed spirit is provided with an injection nozzle, arranged to impart to ay the gases contained in said combustible mixture together with said coating material a direction of rotation axially into the said combustion chamber. wherein the space surrounding said nozzle is in communication with supply means for the other said input gases. 5. Apparatus according to claim 4, characterized in that the bore Or of the injection nozzle is provided with a coaxial tube for dust-forming gas, which extends beyond a side-by-side inlet for a gas contained in the combustible gas mixture. 6. Apparatus according to claim 4, characterized in that the injection nozzle is provided partly with a rear cradle, in which there is a hall for gas-receiving a rod of coating material, and partly with an inwardly arranged inlet for a gas entering the combustible gas mixture. Cited publications: Patents (rein Sweden 62 758, 91 905; Norway 34 018; Germany 371 456, 811 899; USA 2 137 442, 2 317 173, 2 502 94 7.