CH329742A - Method for forming a coating layer on a surface of a workpiece, and apparatus for carrying out this method - Google Patents

Description

       

  Method for forming a coating layer on a surface of a part, and apparatus for carrying out this method The present patent relates to a method for forming a coating layer on a surface of a part, which is characterized by that one ignites an explosive charge formed at least for its major part, in volume, of gas, and capable of detonating, in a long barrel directed towards the surface to be coated of said part, so as to produce a wave of detonation which is made to act on particles introduced into the space traversed by the detonation wave propagating towards said surface, so that said particles are projected onto this surface and form the coating layer there.

      The patent also relates to an apparatus for carrying out this process, which is characterized in that it comprises a barrel, means for bringing into the barrel a mixture of a fluid fuel and a gas. oxidizer as well as said particles, and a device for igniting this mixture in the barrel. The drawing shows, by way of example, an embodiment and variants of the apparatus according to the invention, for the implementation of embodiments, also given by way of example, of the method according to 'invention. Fig. 1 shows, in part schematically, this embodiment.

      Fig. 2 represents a first variant. Fig. 3 shows, also partially schematically, a second variant. Fig. 4 is a side elevation, also partly schematic, of a third variant; and fig. 5 is a photomicrograph at 300 times magnification of a coating layer, made of a material containing tungsten carbide and cobalt, deposited on a steel part by means of one embodiment of the method according to 1. 'invention. Like reference numbers denote corresponding parts in the various figures.

      In the apparatus shown in fig. <B> 1, </B> a combustible gas, for example acetylene, is fed through a pipe 10, and an oxidizing gas, for example air or oxygen or a mixture of air and oxygen through a pipe 11, in a mixing chamber 12 in which the two gases form a detonating gas charge which arrives through a short communication pipe 13 in a chamber of ignition 14, comprising a spark igniter 15, which is included in a barrel 16. The spark from the spark plug 15 ignites the charge forming a de-toning wave which propagates in the barrel 16 and comes out through its open end.

   The spark from the spark plug 15 is produced by an ignition coil 17, a battery 18 and a cam breaker 19. The frequency of the sparks is adjustable, a variable speed motor 20 rotating the cam of the breaker 19.



  Particles of solid matter are entrained in suspension in the oxidizing gas arriving through the pipe 11, or else in the fuel gas. The particles are heated and accelerated by the detonation waves and are projected at high speed through the open end of the barrel 16.



  In the variant of FIG. 2, the particles are introduced into the inlet pipe 11 of the oxidizing gas, coming from a tank see 21 at a flow rate regulated by a valve 22. A pressure equalization pipe 23 starts from a point located in upstream of the place 24 for the introduction of the powder particles and ends in the space located above the powder in the tank 21. To achieve an in-time mixture of the fuel gas with the oxidizing gas, the first gas in the mixing chamber 12 from two opposite sides through pipes 10 and 10a. The formation of the detonation waves is promoted by giving the small ignition chamber 14a a conical shape.



  In the variant of FIG. 3, the introduction into the mixing chamber of gases, for example oxygen and acetylene, is controlled by valves 25 controlled in the usual way by a motor 26 and a cam 27 to obtain the frequency which is required. desire to open and close the valves. A T-fitting 28 between the ignition chamber 14 and the open end of the barrel 16 has an inlet pipe which serves to introduce particles of the powder. Coats were also applied by introducing the powder between the open end of the barrel and the part.

      The variant of FIG. 4 is similar to that of FIG. 3, except that an inert gas such as nitrogen is introduced into the barrel through a pipe 29, via a valve 31, so as to purge the mixing chamber and thus protect the valves. The valve 31 is controlled by a second cam 32 mounted on a camshaft 33 driven by an automatic timer 26 and constructed and disposed with respect to the cam 27 and with respect to a cam 34 for adjusting the ignition so as to carry out the succession of the following timed operations 1. Cam 27 simultaneously opens valves 35 and 37 so as to admit the combustible gas and the oxidizing gas into the mixing chamber (with or without powder particles). 2.

   Cam 27 allows valves 35 and 37 to close. 3. As soon as the valves 35 and 37 are closed, the cam 32 opens the valve 31 which supplies the inert nitrogen gas to the mixing chamber. The gaseous nitrogen passes over the valves 35 and 37 so as to dilute any leaks through these valves liable to cause a flashback under the effect of the detonation of the mixture.



  4. As soon as the nitrogen valve 31 opens, and while it remains open, the cam 34 closes the primary circuit of the ignition coil 17 and, as a result, ignites the spark in the spark plug d. ignition 15.



  5. Once the detonation has been produced, the nitrogen passing through the open valve 31 enters the barrel to expel the hot products of combustion therefrom and forms a protective zone between them and the next charge of the combustible mixture.



  6. The cam 32 then allows the nitrogen valve 31 to close and the cycle is ready to begin again by reopening the valves 35 and 37 to form the next fuel mixture. The barrel 16 must have a sufficient length. If the barrel is too short, the gas mixture, when ignited, does not form a detonation wave. Satisfactory results have been obtained with a tube of 25 mm internal diameter and a length of between 38 cm and 3 m. The best results have been obtained with guns with an internal diameter of 25 mm and a length between 1 and 2 m. With a 13 mm inner diameter tube, the length may be 20 cm with some gas mixtures, but a length of 3 m is generally better.



  The air cooling of the barrel 16 is generally satisfactory. If, in certain particular cases of use of the device, for example when using almost continuously mixtures of oxygen and acetylene, it is found that the barrel becomes too hot, it can be cooled by water circulation.



  The devices of fig. 1 and 2 operate without valves in the gas pipes. Oxidizing gas and combustible gas must enter these devices at the same pressure to reduce the risk of backfire. An ordinary fire screen can be inserted in the fuel inlet pipe, to increase safety.



  In addition to gaseous fuels, liquid fuels such as gasoline or solid fuels, such as pulverized coal, suspended in the form of dust in an oxidizing gas can be used. The most suitable gaseous fuels are acetylene, hydrogen, propane, butane, pentane and ethylene.



  The temperature of the .ob detonation wave held with the devices described is high and reaches 2800 ° C. for certain mixtures. But one can operate so that a large part of the heat is dissipated before the particles meet the part and, consequently, the application of a layer on the part only gives a small rise in temperature of. this piece. In this case, therefore, there is no deformation of the part by heat. It would, moreover, be easy to render harmless any heating of the part by interrupting operations from time to time to allow the part to cool, or by directing on it a current of a cooling fluid, for example a current of 'air.

   You can also cool the room on the outside by spraying it with a liquid in the form of rain or fog, just as you can cool it inside with water if it is hollow. In a particular embodiment, it is possible to apply and fix particles and materials such as tungsten carbide, on the surface of a part with a substantially different coefficient of thermal expansion, such as steel, in cooling the room as described above.



  The gas flow can be adjusted so as to fill the barrel exactly with the mixture during the time that elapses between ignitions. The flow may however be less.



  The frequency of detonations is a factor on which the efficient operation of the devices described depends. When it comes to forming a thin deposit over a small area, a single detonation may suffice. Thus, by operating with the aid of any one of the apparatuses shown, a single detonation has formed a coating layer of 12,

  5 microns thick on a steel surface with a diameter of 25 mm using an acetylene-air gas mixture of 7-13% acetylene and particles of a material composed of tungsten carbide and 9% cobalt, the particles having less than 50 microns. Several detonations per second are usually required to apply thicker coats or to cover larger areas quickly.

   For example, to form coating layers consisting of tungsten carbide and cobalt on various tools and parts, with a barrel with a diameter of 25 mm and a length of about 1.5 m by means of A detonating mixture of oxygen and acetylene, very satisfactory results have been obtained with a detonation frequency of about 4 per second, although satisfactory results have also been obtained with a frequency of 7.8. To obtain an aluminum coating layer by means of an explosive mixture of air and acetylene, a frequency of 40 per second can be used, although satisfactory results have also been obtained with a frequency of up to 70 .

   When the frequency exceeds 7.8 with a mixture of oxygen and acetylene, and 70 with a mixture of air and acetylene, the gun tends to overheat and flashbacks and continuous combustion occur. tendency to occur.



  The flow rate of the powder particles introduced in the devices described is not of a particularly critical value, except that it exerts an influence on the economic conditions of the operation, that is to say on the cost price. and the speed of the formation of a given layer. A flow rate of 4.5 kg of powder per hour appears to be the most suitable for the formation of a layer of good quality, of maximum hardness, with. a flow rate of 5.1 ms / h of acetylene, oxygen and nitrogen (used to drive the powder and to protect the valves) in an apparatus such as that of FIG. 4, fitted with a 25 mm internal diameter barrel with a detonation frequency of 4.3 per second.

   Flow rates not exceeding 0.25 kg of powder per hour or up to 11 kg per hour have, for example, given satisfactory results with tungsten carbide particles smaller than 44 microns.



  A large number of metals, alloys, metal compounds, plastics, ceramics and minerals can be employed for the formation of coating layers by means of the apparatus described. The visible parts of a covering can be made of metal, glass, wood, fabric, paper, or plastic, for example. The surface to which the layer is to be applied may be at a small distance from the end of the barrel, for example between 13 mm and 25 cm. For example, a part to be covered with a layer of tungsten carbide coating is generally disposed at a distance of about 7.5 cm from the end of the barrel.

      The devices described have made it possible, for example, to apply to a smooth glass surface layers of satisfactory quality of aluminum, copper, brass, tin, lead, zinc and magnesium. By means of the methods described, copper and zinc layers have been successfully applied to aluminum, aluminum and nickel layers to carbon, aluminum to an aperture stainless steel wire mesh. 0.25 mm mesh, aluminum on paper, aluminum, copper, magnesium, nickel and tin on wood, aluminum on methacrylate, tin, aluminum, molybdenum, copper, tungsten , because tungsten bide, austenic stainless steel, chromium, cobalt alloy, chromium and tungsten,

   alloy of nickel and molybdenum, boron carbide, and porcelain sintered on steel, and tungsten carbide on refractory bricks. The apparatus described also makes it possible to operate with particles of various materials. For example, a friction plate can be made by using a mixture of particles of a metal such as aluminum and particles of a hard substance such as alumina, and forming therewith a layer coating on a steel support, this layer comprising particles of alumina in a mass of aluminum. A coating layer can be formed on the steel by using a mixture of particles of iron, chromium and nickel to make it resistant to corrosion and wear.

   It may sometimes be advantageous to add to the particles intended to form the coating layer particles of a non-metallic flux to improve the adhesion of the layer.



  In general, particles of low melting point substances, below 700 C, such as tin, lead, zinc, aluminum and magnesium, can be larger, for example up to 150 microns , and those of substances with a higher melting point, above 1000 C, such as chromium, tungsten and tungsten carbide, give the best results when their size is less than about 50 microns, forming layers adherent, teeth. But these size limits are not critical, for example excellent results have been obtained with a copper powder in particles of 12 to 32 microns, to coat the aluminum,

      similarly, a coating layer has been successfully applied to a metal part using particles of a material consisting of tungsten carbide and cobalt up to 74 microns in size.



  Using aluminum particles smaller than 44 microns in size, a minute and a half was formed on a pickled steel surface at a distance of about 5 cm from the open end of a 25 mm barrel. mm in diameter and at a detonation frequency of a mixture of air and 101% acetylene of about 30 cycles per second, a layer 0.43 mm thick and a diameter of 3.5 cm. This layer is appreciably waterproof.



  By means of the methods described, a layer of copper or other metal can be formed which readily welds to substances such as glass, porcelain, wood, plastics, or aluminum, which does not weld or weld only with difficulty, and it is easy to then weld the substances thus covered to form a joint.



  A foil tape was covered with a layer of aluminum, slowly advancing the tape in front of the muzzle to prevent it from charring. In both cases, the explosive charge was a mixture of air and acetylene.



  In one embodiment of the process, it is possible to use particles of a product containing tungsten carbide, of dimensions less than 50 microns, generally between 10 and 40 microns, the product containing, in addition to the tungsten. ,

          about 9% cobalt and 4% carbon. These particles are made to arrive at a flow rate of approximately 4.5 to 6.75 kg / h in an apparatus such as that of FIG. 4, having a barrel of approximately 1.5 m in length and 0.25 mm in internal diameter.

   Acetylene and oxygen are introduced in proportions of about 1 volume of the first to 1 to 2 volumes of the second, with an average flow rate of about 10.2 m 3 / h of the mixture. The average nitrogen flow rate is approximately 5.1 m3 / h. The ignition frequency is about 4 / sec. A stripped surface of iron or of mild or hard steel, for example tool steel, preferably granite, for example, with a sandblast, or covered with a thin layer of a metal such as copper, nickel or cobalt, to a thickness of 6 to 12 microns, for example, at a distance of about 7.5 cm from the open end of the barrel.

   In this way, a dense, adherent layer of a product containing tungsten carbide with a thickness of 0.5 mm can be obtained at a speed of about 6.5 cm 2 / min. Thinner or much thicker layers can be applied by varying the duration of application.



  Fig. 5 shows, by way of example, with a magnification of 300 times, the appearance of a <I> WC </I> layer of a material composed of tungsten carbon and 91% cobalt, deposited by the method described on a steel support S. The sample shown was polished, then it was subjected to an anodic attack with chromic acid, followed by an attack with potassium permanganate.



  The resulting layer has a fine-grained, dense, lamellar structure, consisting of mixed layers of tungsten carbide <I> WC, </I> cobalt-tungsten complex carbide and a small amount of carbide. of secondary tungsten W2C. The layer is formed of the thin overlapping threads, with a diameter much greater than their thickness.



  The apparent specific gravity of the tungsten carbide layer of the example shown is about the same as that of the cast solid product, i.e. 14.5 g / cm 3. The porosity is less than 1%. The adhesion of the layer to the substrate is excellent, as evidenced by the fact that it is possible to grind the substance of the layer to and through the interface without the layer flaking off. at the edges. If the base surface consists of a thin sheet, it can be bent without the layer flaking off, although it probably creaks.

   The hardness on the Vickers scale is at least 1100. The surface of the layer is smooth and matt and can be given a good polish by normal grinding and polishing operations.



  The properties of this layer make it likely to form the surfaces of parts such as stamping and minting core rods, burnishing pins, tolerance gauges, crushing jaws, washers and plates. lining shafts, electrical contacts, reamers, saw teeth, knife blades, textile thread guides, valve seats and heads and bearing surfaces. To manufacture certain electrical contacts by means of the methods described, it may be advantageous to use particles of a metal of high conductivity such as silver.


    

Claims (1)

CLAIM I Method for forming a coating layer on a surface of a part, characterized in that at least one explosive charge formed at least for its major part, by volume, of gas, is ignited and capable of detonate, in a long gun directed towards the surface to be coated with said part, so as to produce therein a detonation wave which is made to act on particles introduced into the space traversed by the detonation wave propagating towards said surface, so that said particles are projected onto this surface and form the coating layer there. SUB-CLAIMS 1. Process according to Claim I, characterized in that one operates by igniting successive charges in order to produce a series of successive detonation waves projecting particles onto said surface. 2. Method according to claim I and sub-claim 1, characterized in that the barrel is purged with an inert gas between the successive detonations. 3. Method according to claim I and sub-claim 1, characterized in that the introduction of new charges is carried out by continuously causing a mixture of fluid fuel and oxidizing gas to arrive in the barrel, between the successive detonations. 4. Process according to claim I and sub-claim 1, characterized in that the flow rate of a fluid fuel and of an oxidizing gas is regulated so as to fill the barrel with their mixture during the time which elapses between ignitions. 5. Method according to claim I, charac terized in that the explosive charge is formed of a combustible gas and an oxidizing gas. 6. Process according to claim I and sub-claim 5, characterized in that the feed consists of a mixture of acetylene and air, containing from 7 to 13% by volume of acetylene. 7. Method according to claim I and sub-claim 1, characterized in that the frequency of the detonations is at least 4 per second. 8. Process according to claim I and sub-claim 1, characterized in that the particles are suspended in one of the constituents of a mixture of fluid fuel and oxidizing gas, are introduced into a mixing chamber, and then are then in trails in the barrel, in suspension in this mixture. 9. The method of claim I and sub-claim 1, characterized in that the particles are introduced into the gun at a point located downstream from the point where the detonation begins. 10. The method of claim I, characterized in that the particles are particles of a material having a melting point below 7000 C and have a size of up to 150 microns. 11. A method according to claim I, characterized in that the particles are particles of a material with a melting point above 10,000 C and have a size of less than 50 microns. 12. The method of claim 1, characterized in that the particles are particles of a hard material, resistant to wear, melting point above 1000 C. 13. The method of claim I and Sub-claim 12, characterized in that the particles are particles of a material consisting at least for its major part by weight of tungsten carbide. 14. The method of claim I and sub-claim 13, characterized in that the particle size is less than 50 microns. CLAIM II Apparatus for carrying out the process according to claim 1, characterized in that it comprises a barrel, means for bringing into the barrel a mixture of a fluid fuel and an oxidizing gas as well as said particles, and a device for igniting this mixture in the barrel. SUB-CLAIMS 15. Apparatus according to claim II, characterized in that the barrel comprises an ignition chamber provided with an ignition candle, a supply device causing this candle to produce successive separate sparks. 16. Apparatus according to claim 11, characterized in that the barrel communicates at one end with a mixing chamber communicating with channels supplying the fluid fuel and the oxidizing gas separately. 17. Apparatus according to claim II and sub-claim 16, characterized in that at least one of the channels supplying the fluid fuel and the oxidizing gas respectively comprises a mechanically actuated valve. 18. Apparatus according to claim II and sub-claims 15, 16 and "17, characterized in that it comprises a channel which arrives a stream of particles between the ignition chamber and the open end of the barrel. . 19. Apparatus according to claim II and sub-claims 16 and 17, characterized in that the mixing chamber communicates with an inlet channel for an inert gas via a separate valve controlled by a mechanic: i - @ also controlling a fluid fuel valve and an oxidizing gas valve. 20. Apparatus according to claim II and sub-claims 16, 17 and 19, characterized in that the valve for the inert gas is disposed relative to the barrel upstream of the other valves. 21. Apparatus according to claim II and sub-claims 16, 17 and 19, characterized in that it comprises an automatic timer which first opens and then closes the inlet valve for the fluid fuel and the gas valve. oxidizer, thus charging the barrel with a detonating mixture, which opens secondly the inlet valve of the inert gas, which thus begins to arrive, which, thirdly, activates a spark plug thereby triggering a detonation, and which, fourthly, after a time allowing the inert gas to purge the barrel of the gaseous products of combustion, closes the inert gas valve. CLAIM III Part having a surface provided with a coating layer, obtained by the process according to claim I, characterized in that the coating layer is formed of numerous thin lamellae overlapping each other and strongly adhering to this surface, these strips being made of a material other than that of the part.