JP2005519190A - Thermal spraying of machine parts - Google Patents

Abstract

The present invention discloses a machine part surface (22) that is at least partially coated with a coating material by a thermal spray process. The coating material is exposed to heat treatment at an elevated temperature and for a time effective for the coating material to diffuse at least partially into the underlying surface, thereby creating a neck between the coating material and the underlying surface. Form. Furthermore, by applying a coating material layer (24) and subjecting each coating material layer to sequential heat treatment, a plurality of layers (24) of the same coating material are provided on the surface of the machine part (22), thereby The coating material forms a neck (23) at least at the point of contact between the particles (21) and the layer in the coating. Also disclosed is a method for producing such a coating on a machine part surface.

Description

  The present invention relates to a machine part, preferably an engine machine part, coated with a coating material by a thermal spraying process and subjected to heat treatment of the coating material at a high temperature. The present invention also discloses a method of applying a coating to a machine part.

  The machine parts must meet certain requirements, especially with respect to, for example, strength, corrosion resistance, wear resistance, ductility and material resilience.

  Today, machine parts are generally manufactured from cast-iron blanks, which substantially meet the requirements imposed on materials in terms of strength and resilience, but beyond a predetermined range. When heated, wear problems arise. A large number of machine parts suffer from wear caused by, for example, internal friction between sliding surfaces in an engine device. In particular, in a large marine diesel engine, the frictional force can be large. In addition to friction, high temperature environments can reduce the strength of the material and can cause significant wear on mechanical parts made of cast iron that have poor scuffing resistance required at high temperatures. Thus, cast iron engine parts often have a wear-resistant or running-in layer on the surface most exposed to wear.

  However, it is difficult to achieve a sufficiently strong bond between the blank material and the wear-resistant layer material, which causes problems. This is because the material of the wear-resistant layer may be worn out and peeled off from the blank material. When this happens, the material on the surface of the blank material is subject to wear in the contact area of adjacent machine parts, thus significantly reducing the life of the machine parts.

  Another problem is that the coating gradually wears away even when the bonding between the surfaces is relatively strong. Wear on mechanical parts proceeds slowly as long as the wear-resistant layer is intact, but proceeds rapidly when the wear-resistant layer is worn away. As a result, if possible, it may be difficult to determine an appropriate time to replace the machine part.

  Thermal spraying is convenient to use, for example, to apply a coating to an iron blank. In general, one problem that arises when using thermal spray to apply a coating is that the resulting coating contains a fraction of loose particles. These loose particles increase the risk of “three-body-abration” between the sliding surfaces of the two machine parts. Three-body wear often causes the above-described gradual wear process.

  During operation, some areas of the machine parts, particularly the engine parts, are exposed to high temperatures, significant temperature differences, and very corrosive environments. Therefore, in order to withstand the effects of these stress-inducing causes, the coating of the machine part must exhibit considerable ductility and thermal stability in addition to the wear resistance described above. In this specification, ductility means the maximum degree of strain of a material until cracking starts. Thermal shock and large temperature differences during manufacturing as well as during operation have similar effects on machine parts during the heat treatment process. This will be described in detail below.

  Various methods are known for post-heating or sintering the coating, and these have been implemented to achieve a strong bond between the coating and the support. U.S. Pat.No. 5,268,045 describes an example of such a conventional coating method in which a surface treatment is applied by chemically cleaning the part to be coated and coating the metal by thermal spraying. After that, the metal is diffused into the surface of the component by post-processing at a high temperature.

  During such a process, the coating reaches its melting temperature, and the support under the coating is also affected, creating a risk of stress being induced in the support. Furthermore, in such a process, a hard coating with low ductility is obtained.

  This is a challenge when coating a support and often a curved blank. When the coating applied to the blank is heated, the blank is also heated, causing the machine part blank to expand. After the heat treatment, when the machine part cools, the part regains its original shape, so that the newly bonded coating is forced to follow the machine part blank. If the coating is applied to, for example, a curved surface, the coating is subject to tensile stress during cooling and can crack or delaminate. This is thought to lead to a shortened operating life of the machine parts.

  Other issues related to the prior art are described in more detail in the literature. Therefore, it is desirable to find a way to achieve a ductile wear resistant coating on a machine part with a strong bond. It is also an object of the present invention to find a way to minimize the induced stresses and to coat the machine parts while reducing the risk of free particles and actual cracking in the coating. At present, there is no known method for applying a coating to a machine part that solves the above-mentioned problems.

  It is an object of the present invention to provide a method for applying a coating specifically intended for mechanical parts, which meets the requirements for wear resistance, resilience, corrosion resistance, hardness, thermal stability and ductility.

  Another object is to provide a coated machine part which overcomes the above-mentioned problems found in the prior art. Other features and advantages of the present invention will become apparent from the following description of the invention.

The present invention is a method for applying a coating material to at least a part of the surface of a machine part, comprising the following steps:
Applying the coating material by a thermal spraying process;
Heat treating the coating material at an elevated temperature and for a time effective for the coating material to diffuse at least partially into the surface of the support structure; and
In order to cover a plurality of layers of the same coating material on the surface of the machine part, a further coating material layer is applied, and each coating material layer is sequentially heat-treated (here, at least between the particles of the coating by the heat treatment). A neck is formed at the contact point);
Providing the method.

  In accordance with the method of the present invention, a strong bond between the coating material and the machine part surface as well as a strong bond within the coating is formed. By controlling the heating temperature to which the coating material is exposed when applying the coating material to the machine part, the coating material forms a neck (microwelds) at the point of contact between the coating and the particles on the machine part surface, This provides a strong bond between the particles. Depending on the material of the coating and the machine part, contact point necks are formed by exposing the material to a heating temperature below or close to the melting point of the coating material. Coating materials for machine parts typically include a matrix material and a reinforcement. Without limitation, the coating material applied to the machine part is preferably in the range of 60-80% of the melting temperature of the coating reinforcement. Thus, the matrix material is exposed to heat close to its melting temperature for a short period of time appropriate to cause the material to form the neck. The method of the present invention provides a coating having open pores between the particles of the coating. Furthermore, according to the method of the present invention, the object of reducing free particles in the coating of machine parts is achieved.

  Preferably, the thermal spraying device and the heat treatment device are connected to the machine part, and the coating material is applied to the machine part and the heat treatment is simultaneously performed while moving relative to the machine part.

  By controlling the movement, the heat exposure time can be controlled as desired.

  Induction heating is preferably used to achieve the desired high temperature heat treatment of the machine parts. Heat treatment by induction heating is considered effective and cost effective, but other methods known to those skilled in the art may be used. One such method is a laser.

  Another advantage of the method of the present invention is that the resulting coating of machine parts has a uniformly distributed porosity. Preferably, the resulting coating of machine parts has a porosity of 1-15% by volume. Therefore, the coating material having such a porosity can absorb strain and defects caused by stress induced during use.

  The use of open micropores as a lubricant buffer provides a lubrication effect on machine parts during use, thus reducing friction and wear. However, closed micropores are not very useful for machine parts if this is desired because they cannot easily accept externally supplied lubricant.

  Further, each of the coating material layers typically has a thickness of 0.005 to 0.40 mm. Preferably, one layer thickness according to the method of the present invention is about 0.01 mm. In order to form the desired neck at the point of contact between the particles of the coating layer during thermal exposure, the thickness of one coating layer according to the method of the present invention is preferably in the range of 0.005 to 0.10 mm.

  In a preferred method of the invention, the coating material is of the pulverulent type at the time of supply to the thermal spraying process. Alternatively, the coating material is in a wire-like form when supplied to the thermal spray process to achieve an efficient and controlled manufacturing process.

  In a particularly preferred method according to the invention, the method according to the invention is applied to a machine part comprising a curved surface, with the coating material being applied to at least some areas of the curved surface. In the case of such a machine part, as described above, the problem of stress induced when the conventional coating method is used on a machine part having a curved shape is a particularly difficult problem in the background art. Especially suitable. In order to further minimize the induced stress, the machine part is preheated prior to applying the coating material.

  According to the present invention, the coating material is applied by a thermal spraying process, at a high temperature and for a time effective for the coating material to diffuse at least partially into the underlying surface of the support structure. In order to be exposed to heat treatment and to provide multiple layers of the same coating material on the surface of the machine part, further coating material layers are applied and each coating material layer is sequentially heat treated, and the coating material is The machine part having a neck at least at the point of contact between the particles in the coating.

  According to a preferred embodiment of the machine part coating of the present invention, a strong bond within the coating is achieved along with a strong bond between the coating material and the machine part surface. By controlling the heat to which the coating material is exposed when applied to machine parts, the coating material forms a neck (microweld) at the point of contact between the particles in the coating, thereby increasing the strength of the particles. Bond is obtained. Depending on the material chosen for the coating and machine parts, a contact point neck is formed by exposing the material to a heating temperature below the melting point of the material.

  Although it is not limited, it is preferable that the high temperature heat treatment of the coating material applied to the machine part is performed within a range of 60 to 80% of the melting temperature of the reinforcing material used for coating. The method of the present invention provides a material that forms open micropores between the particles of the coating. The coating material is preferably selected from at least one of the following groups of materials: metals, alloys, carbides, silicates, ceramics, oxides, cermets, and mixtures thereof.

According to the present invention, a preferred coating material comprises a metal compound selected from the group consisting of Cr ₃ C ₂ , Cr ₂ O ₃ , CuAl and Al ₂ O ₃ . These compounds and alloys have proven to be well suited for the production of high quality mechanical part coatings with excellent wear resistance and sliding performance. The coating according to a preferred embodiment comprises a mixture partly in the form of a metal and partly in the form of a reinforcement. According to a preferred embodiment of the present invention, the coating material is cermet. Cermets are a group of coating materials that combine ceramics and metals or alloys. A commonly used example is chromium carbide (ceramic component) in a nickel / chromium matrix. Those skilled in the art will be able to use other ceramic compounds, alloys and cermets (not described herein) to provide coatings on machine parts according to the present invention.

  Furthermore, according to the present invention, there is provided a machine part in which each of the coating material layers typically has a thickness of 0.005 to 0.10 mm. Preferably, that one layer thickness of the mechanical component of the present invention is about 0.01 mm. In order to form the desired neck at the point of contact between the particles of the coating layer during manufacture, the thickness of one coating layer according to the method of the present invention is preferably in the range of 0.005 to 0.10 mm. The total thickness of the coating varies depending on the size and type of machine part. For mechanical parts used in marine diesel engines, the total coating thickness can be up to about 5 mm.

  The presently preferred embodiments of the invention will now be described in further detail with reference to the accompanying drawings.

  The presently preferred method according to the present invention will be described together with the preferred embodiments of the mechanical parts of the present invention with reference to the accompanying drawings.

  Referring to FIG. 1, a machine part 1 is arranged for applying a coating. The coating production assembly apparatus further includes a thermal spraying device 3 and a heat treatment device 5. Although not limited thereto, a protective cover (not shown) is preferably provided to cover surrounding elements and protect them from thermal spraying, for example. Furthermore, an inductor forms a heat treatment device 5. The inductor 5 can be attached in a number of ways depending on the size of the machine part 1. In this embodiment, one or more inductors 5 are shown. The cleaned machine part 1 is arranged for processing in a coating apparatus. The machine part is preferably a cast iron blank. According to a preferred embodiment of the invention, the coating material 4 is applied to the desired part of the machine part 1 by thermal spraying. For the thermal spraying device 3, it is preferable to use, for example, plasma, arc, HVOF, or flame spraying methods that are known to those skilled in the art.

  During thermal spraying, the machine part 1 moves continuously with respect to the thermal spraying device 3 and the heat treatment device 5 (or vice versa), and the coating material can be immediately subjected to heat treatment at a high temperature. According to a preferred method, the surface speed of the machine part to be coated is about 20 m / min for the thermal spraying apparatus applying the coating material as well as for the heat treatment apparatus.

  The coating according to a preferred embodiment comprises a mixture in part in metal form, part in reinforcement form. The coating material is preferably heated in a short time to 60-80% of the melting temperature of the reinforcement in the coating.

  Each cycle of applying the coating material 4 and heating the coating material 4 forms a new coating layer 24 on the surface of the machine component, as shown in FIG. In FIG. 2, only three layers 24 are shown to explain the principle, but usually more than ten layers, preferably more than fifty layers, are applied. Of course, the number of layers 24 varies depending on the thickness of the layers 24, for example. According to a preferred embodiment of the present invention, the thickness of each coating layer 24 is typically 0.01 mm. The total thickness of the applied coating 24a of the machine part 1 is about 0.8 mm, but can be up to about 5 mm. However, these figures are only given as an example to illustrate the concept of the properties to be used, and those skilled in the art will be able to understand the layer 24 according to the specific requirements of the machine part 1 to be coated. It will be appreciated that properties such as thickness, surface velocity during coating manufacture, and the number of layers 24 can be adjusted.

Furthermore, according to the present invention, the coating material 4 includes, for example, a metal compound selected from the group consisting of Cr ₂ O ₃ and Al ₂ O ₃ . These compounds and alloys have proven to provide high quality machine part coatings. According to a preferred embodiment of the present invention, the coating material is cermet. Cermets are a group of coating materials that combine at least one ceramic and at least one metal or alloy. A commonly used example is chromium carbide (ceramic component) in a nickel / chromium matrix. One skilled in the art would be able to use other ceramic compounds, alloys and cermets (not described in detail herein) to coat the mechanical parts of the present invention.

  According to a preferred embodiment of the machine part 1 of the present invention, a strong bond within the coating is achieved along with a strong bond between the coating material 4 and the machine part surface 22. By controlling the heat to which the coating material is exposed when applied to the machine part 1, the coating material 4 forms a neck (microweld) at the point of contact between the coating and the particle on the machine part surface, thereby A strong bond between these particles can be obtained. Although it does not necessarily limit, it is suitable to perform the high temperature heat processing of the coating material apply | coated to a machine component within the range of 60-80% of the melting temperature of a reinforcement material at least among coating materials.

  This is shown in more detail in FIG. 3, which shows an enlarged schematic view of the bonds between the particles 21 in one layer 24. The method of the present invention provides a coating of mechanical parts comprising micropores opened between the particles 21 of the coating. Depending on the coating and the material of the machine part 1, a contact point neck 23 is formed by exposing the material to heat below the melting temperature of the material. The contact point neck 23 further increases the strength of the coating. Thus, the step of exposing the coating to an elevated temperature results in a significantly stronger bond compared to the mechanical bond that is usually done by spraying alone.

  FIG. 4 shows the effect of applying excess heat to the coating layer or the entire coating of the support. This may be beneficial for other applications, but not for the type of machine part coating. When excessive heat is applied during coating of the support, the coating material melts. This is approximately the same size as FIG. 4 so that it can be compared with the size of the coated part shown in FIG. In the coating shown in FIG. 4, a significant decrease in the porosity is recognized, the porosity is not uniformly distributed, and it can be seen that the micropores are closed.

  Closed micropores generally cannot provide any lubrication effect. Furthermore, the ductility obtained by the above coatings having a small number and non-uniformly distributed micropores is generally not sufficient for use in coating machine parts. In such coatings, the bond will be strong, but as noted above, other features are not tailored to meet the conditions used for machine parts. During the heat treatment according to the invention, it has been found that a strong bond coating with excellent ductility and wear resistance can be achieved because the necks form within and between the multilayer coatings.

  In addition, if excessive heat is used to apply the coating, there is a risk that other properties of the machine part may be adversely affected. Thus, the present invention provides a method for achieving a coating on a machine part with limited damage to the machine part blank, with excellent bonding to the part, open micropores and sufficient porosity.

  The coating of the present invention is suitably applied to the sliding surfaces of mechanical parts that are subject to wear. Preferably, the coating can be used on the sliding surfaces of pumps, hydraulic pumps, and fire pumps. The coatings of the present invention are particularly suitable for coating mechanical parts used in internal combustion engines, and most preferably marine diesel engines.

  According to a preferred embodiment of the invention, the coating is applied to at least a part of the sliding surface of the cylinder liner. The cylinder liner may be coated entirely or on a desired portion with a predetermined pattern. An example of such a coating pattern is the helical shape on the inner surface of the cylinder liner.

  According to another preferred embodiment of the invention, the mechanical part is a piston, a piston rod or a piston skirt. It is considered particularly suitable to coat the annular groove of the piston using the coating of the present invention. According to still another embodiment of the present invention, the coating of the present invention is applied to a part or the whole of the predetermined portion of the inner sliding surface of the stuffing box ring.

  Other embodiments for applying the coating of the present invention are at least suitable portions of the camshaft and / or crankshaft and the sliding surface of the camshaft cam.

  Furthermore, it is considered beneficial to apply the coating of the present invention to the sliding surface of the shaft packing. According to the embodiment of the present invention, the coating material of the present invention is applied to the sliding surface of the fuel pump. According to yet another embodiment of the present invention, the heat and wear portions of the inlet and / or outlet valves can be coated, such valves being used in large two-cycle diesel engines. preferable.

  Although the invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made to the invention without departing from the spirit and scope of the invention. Let's go. Thus, it will be appreciated that the compositions of the present invention can be applied to machine parts using various methods such as plasma, HVOF, and arc spraying, or other related methods. Of course, the apparatus and method for applying a coating to the machine part 1 and heating the coating can be adjusted to the existing requirements and is not limited by the method described above, which is given as an example only. . Thus, another possible option for applying the coating is to use a laser device.

FIG. 2 is a schematic diagram illustrating a gathering apparatus for using a method of applying a coating material to a machine part according to the present invention. FIG. 2 is a schematic diagram illustrating a portion of a mechanical component including a coating of the present invention. FIG. 3 is an enlarged schematic view of a part of FIG. 2 according to the present invention. It is the schematic which shows an example of the coating obtained using another conventional method.

Claims (25)

A method of applying a coating material to at least a part of a surface (22) of a machine part (1), preferably an engine operating part, comprising the following steps:
Applying the coating material by a thermal spraying process;
Heat treating the coating material at an elevated temperature and for a time effective for the coating material to diffuse at least partially into the surface of the support structure; and
In order to cover a plurality of layers (24) of the same coating material on the surface (22) of the machine part, a further coating material layer (24) is applied and each coating material layer (24) is heat-treated in order (here And at least a neck (23) is formed at the contact point between the particles (21) of the coating by the heat treatment);
Said method comprising: The method according to claim 1, wherein a high temperature heat treatment temperature of the coating material of the mechanical part is within a range of 60 to 80% of a melting temperature of the coating material. The thermal spraying device (3) and the heat treatment device (5) are connected to the machine part (1) and move relatively, and at the same time, apply the coating material (4) to the machine part (1) and perform heat treatment. The method according to claim 1. The method according to claim 1, wherein the heat treatment of the mechanical part is performed by induction heating. The method according to claim 1, wherein the resulting coating of machine parts comprises a uniformly distributed porosity. The method according to claim 1, wherein the resulting coating of machine parts has a porosity of 1 to 15% by volume. 7. A method according to any one of the preceding claims, wherein at least 10% of the micropores of the resulting machine part coating are open micropores (23). The method according to any one of the preceding claims, wherein each of the coating material layers (24) typically has a thickness of 0.005 to 0.4 mm. The method according to claim 1, wherein the coating material is of a fine powder type when supplied to the thermal spraying process. The method according to claim 1, wherein the coating material is in a wire-like form when supplied to the thermal spraying process. The method according to claim 1, wherein the coating material comprises at least one of the following materials: metals, alloys, carbides, silicates, ceramics, cermets, and mixtures thereof. The method according to claim 1, wherein the coating material includes a metal compound selected from the group consisting of Cr ₃ C ₂ , Cr ₂ O ₃ , CuAl, and Al ₂ O ₃ . 13. A method according to any one of the preceding claims, wherein the machine part (1) is preheated before applying the coating material. 14. A method according to any one of the preceding claims, wherein the mechanical part (1) has a curved surface and the coating material is applied to at least some areas of the curved surface. Heat treatment of the coating material (1) coated with the coating material by a thermal spraying process at a high temperature and for a time effective for the coating material to diffuse at least partially into the surface of the support structure In order to provide multiple layers (24) of the same coating material on the machine component surface (22), a further coating material layer (24) is applied and each coating material layer is sequentially heat-treated. The machine part (1), wherein the coating material forms a neck (23) at least at the point of contact between the particles in the coating. The machine part (1) according to claim 15, wherein the high temperature heat treatment temperature of the coating material of the machine part is in the range of 60-80% of the melting temperature of the coating material. The machine part (1) according to any one of claims 15 to 16, wherein the heat treatment of the machine part (1) is performed by induction heating. The machine part (1) according to any one of claims 15 to 17, wherein the coating of the machine part has a uniformly distributed porosity. The machine part (1) according to any one of claims 15 to 18, wherein the coating of the machine part has a porosity of 1 to 15% by volume. The machine part (1) according to any one of claims 15 to 19, wherein at least 10% of the micropores of the resulting machine part coating are open micropores (23). 21. Mechanical component (1) according to any one of claims 15 to 20, wherein each of the coating material layers (24) typically has a thickness of 0.005 to 0.4 mm. The machine part (1) according to any one of claims 15 to 21, wherein the coating material comprises at least one of metals, alloys, carbides, silicates, ceramics, cermets, oxides and mixtures thereof. . Wherein the coating material comprises _{Cr 3 C 2, Cr 2 O} 3, CuAl and Al ₂ O _3, as well as metal compounds selected from the group consisting of mixtures according to any one of claims 15 to 22 Machine parts (1). The machine part (1) according to any one of claims 15 to 23, wherein the coating material is cermet. The machine part (1) according to any one of claims 15 to 24, wherein a coating material is applied to at least a part of the curved surface of the machine part (1).

Images