Piston ring having a particle-containing wear protection layer, method for manufacturing the same, and use

Abstract

There is provided a piston ring for an internal combustion engine, the piston ring having a surface and a wear protective layer of iron or an iron alloy formed on the surface, the wear protective layer having cracks, the cracks having an average density of 10 to 160 cracks per mm of the wear protective layer, and 0.2 to 15 wt % of carbon particles, based on the total weight of the wear protective layer, and 0.2 to 15 wt % of solid particles that are not carbon particles, based on the total weight of the wear protective layer, incorporated in the iron or iron alloy. Further, there is provided a method for manufacturing the piston ring.

Description

[Technical Field]

[0001] The present invention relates to a piston ring made of iron or an iron alloy, wherein solid particles are embedded in the iron or iron alloy. The present invention also relates to a method for manufacturing a piston ring and to the use of a piston ring in an internal combustion engine. [Background technology]

[0002] Piston rings for internal combustion engines are exposed to high friction and high temperatures, and therefore must have a surface with high wear resistance and excellent sliding properties. For this purpose, a wear-resistant protective layer, such as an electrolytic hard chromium layer, is usually applied to the outer surface (running surface) of the piston ring. In addition to high wear resistance, the wear protective layer must have the highest possible dimensional stability; that is, even if the shape of the piston ring changes during engine operation, it is desirable that the wear protective layer be as durable as possible and not break.

[0003] Wear resistance can be improved by incorporating solid particles into a hard chromium layer. German Patent Application Publication No. 3531410 and European Patent Application Publication No. 0217126 describe an electroplated hard chromium layer in which solid particles are embedded in cracks.

[0004] However, one of the drawbacks of known hard chromium solid particle layers is that they require an electrolyte containing hexavalent chromium to produce, and hexavalent chromium is highly toxic. The process of producing hard chromium layers using hexavalent chromium will likely be prohibited within a few years. Therefore, to protect the environment and humans and animals, piston rings with a chromium-free wear protection layer are preferable.

[0005] Wear protection layers for iron piston rings embedded with solid particles are known from German Patent Invention No. 19508419. However, the hardness and wear resistance of these wear protection layers are no longer sufficient to meet the high thermal and mechanical requirements of piston rings in modern internal combustion engines. [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, an object of the present invention is to overcome the aforementioned drawbacks of the prior art and to provide a piston ring having a wear protection layer that does not contain chromium and has high wear resistance, hardness, and dimensional stability. Furthermore, an object of the present invention is to provide a method for manufacturing such a wear protection layer. [Means for solving the problem]

[0007] According to the present invention, this objective is achieved by a piston ring for an internal combustion engine having a surface on which a wear protection layer of iron or an iron alloy is formed, wherein the wear protection layer has cracks, the cracks have an average density of 10 to 160 per millimeter of the wear protection layer, and 0.2 to 15% by weight of carbon particles and 0.2 to 15% by weight of non-carbon solid particles based on the total weight of the wear protection layer are embedded in the iron or the iron alloy.

[0008] This objective is further, (a) an amount of iron(II) compound equivalent to 100-500 g / l of FeCl2, and an optional further metal salt, A step in which a piston ring is placed in an aqueous electrolyte containing carbon particles and solid particles other than carbon particles, wherein the pH of the aqueous electrolyte is 0 or less. (b) Abrasion protection layer of iron or iron alloy with a load capacity of 10-80 A / dm 2 Steps include galvanic deposition on the piston ring at the cathode current density, (c) The step of drying the piston ring together with the wear protection layer, (d) A step in which the mixture is heated to 300-700°C. This is achieved by a piston ring manufacturing method that includes [a specific component / method].

[0009] This objective is further achieved by the piston ring obtained by the above method and by the use of the piston ring according to the present invention in an internal combustion engine.

[0010] Surprisingly, in the background of the present invention, it was discovered that the wear protection layer of the piston ring according to the present invention has high hardness, high dimensional stability, and at the same time high wear resistance.

[0011] The crack density of 10 to 160 cracks per millimeter of the wear protection layer ensures high dimensional stability of the wear protection layer, which is achieved, in particular, by the low pH value of the electrolyte. The heat treatment mainly increases the hardness of the wear protection layer. Although this description does not limit the present invention, it is presumed that the carbon particles are partially converted into Fe-C compounds (iron-carbon compounds), which is one of the reasons for the above-mentioned advantageous properties of the wear protection layer, particularly the increased hardness. On the other hand, the solid particles that are not carbon particles remain in the wear protection layer, and although this description does not limit the present invention, it is presumed that these solid particles that are not carbon particles are the main cause of the layer's high wear resistance. In this way, the combination of higher hardness and good wear resistance of the wear protection layer according to the present invention is achieved.

[0012] Preferably, a piston ring having a surface and including an iron or iron alloy wear protection layer applied to the surface, wherein the wear protection layer has cracks, the cracks having an average density of 10 to 160 per mm of the wear protection layer, and based on the total weight of the wear protection layer, 0.2 to 15% by weight of carbon particles and 0.2 to 15% by weight of non-carbon solid particles are incorporated into the iron or iron alloy, and the carbon particles are partially or completely converted into an Fe-C compound. This means that the wear protection layer contains an Fe-C compound. This conversion is preferably carried out by heating the wear protection layer to 300 to 700°C.

[0013] In a preferred embodiment, the abrasion protection layer comprises 0.01 to 25% by weight of an iron-carbon compound, more preferably 0.05 to 10% by weight of an iron-carbon compound, and particularly 0.1 to 5% by weight of an iron-carbon compound, based on the total weight of the abrasion protection layer. The iron-carbon compound is generated from the carbon particles and the surrounding iron when heated to 300 to 700°C.

[0014] The heat treatment temperature of 300-700°C is particularly high compared to the temperature to which the piston rings are exposed when used in an internal combustion engine. This is because the temperature of the wear protection layer is always below 250°C. Therefore, the heat treatment of the piston rings or the wear protection layer before use in the engine is necessary to at least partially convert the carbon particles and improve the properties of the piston rings.

[0015] The temperature in the heat treatment of the piston ring or the wear protection layer is 300 to 700°C, preferably 320 to 650°C, more preferably 340 to 600°C, even more preferably 350 to 550°C, and particularly preferably 380 to 540°C. These temperatures allow for a particularly advantageous combination of increased hardness and high wear resistance of the wear protection layer. The heat treatment is preferably carried out for 15 minutes or more, more preferably 30 minutes or more, and even more preferably 1 to 4 hours.

[0016] Preferably, the carbon particles are made of diamond and / or graphite, and diamond particles are more preferred.

[0017] To achieve high wear resistance, hard material particles are preferably used as solid particles that are not carbon particles. For the purposes of the present invention, hard material particles are understood to be particles of a material having a Mohs hardness of 8 or more. Among these, hard material particles having a Mohs hardness of 9 or more are preferred, and particularly those having a Mohs hardness of 9.2 to 10 are preferred. The Mohs hardness is measured according to the Mohs hardness test known in the prior art. Preferred hard material particles are those composed of tungsten carbide, chromium carbide, aluminum oxide, silicon carbide, silicon nitride, boron carbide and / or cubic boron nitride. Most preferred is cubic boron nitride (body-centered cubic boron nitride).

[0018] By adding solid lubricating particles, the sliding characteristics of the wear protection layer can be further advantageously improved. Examples of solid lubricating particles are hexagonal boron nitride or polymer particles.

[0019] The ratio of the carbon particles and the ratio of the solid particles that are not carbon particles are, independently of each other, based on the total weight of the wear protection layer, 0.2 to 15% by weight, preferably 0.5 to 12% by weight, more preferably 1 to 10% by weight, and most preferably 2 to 8% by weight.

[0020] The average particle size (grain size) of the carbon particles and the solid particles that are not carbon particles is 0.02 to 5 μm, preferably 0.05 to 3 μm, particularly preferably 0.1 to 1 μm, and particularly 0.2 to 0.8 μm. The average particle size (d 50 ) is measured by laser diffraction using a dry disperser (device: Malvern (registered trademark) Mastersizer equipped with a sirocco dispersion unit). The average particle size (d 50 ) is a value such that 50% by volume of the particle sizes are smaller than the specified value and 50% by volume of the particle sizes are larger than the specified value.

[0021] Not only the average particle size, but it is more preferable that all particles are within a predetermined particle size range. Therefore, the particle sizes of the carbon particles and the solid particles that are not carbon particles are, independently of each other, preferably 0.02 to 5 μm, more preferably 0.05 to 3 μm, still more preferably 0.1 to 1 μm, particularly 0.2 to 0.8 μm.

[0022] The wear protection layer is made of iron or an iron alloy. The iron alloy preferably consists of 85% by weight or more of iron based on the total weight of the iron alloy, more preferably 95% by weight or more of iron, particularly 98 to 99.8% by weight of iron. The alloy components of the iron alloy are typical alloy elements of iron, preferably any one of Cr, Ni, Mo, Mn, V, W, Al and / or Nb.

[0023] The Vickers hardness of the wear protection layer according to the present invention is preferably 500 to 750 HV0.1, more preferably 550 to 700 HV0.1, and most preferably 600 to 700 HV0.1. The Vickers hardness is measured according to a method known in the prior art for measuring the Vickers hardness.

[0024] The piston ring having cracks in the wear protection layer exhibits improved dimensional stability as compared with the wear protection layer without cracks. Although the present invention is not limited by this explanation, the improvement in dimensional stability is because the stress in the layer is reduced or dispersed by the cracks, and as a result, the layer is not easily broken, that is, it is assumed that the material dropout is avoided. The avoidance of material dropout as a result of improved dimensional stability also leads to a significant reduction in wear.

[0025] When a piston ring wears on the surface facing the cylinder (the running surface of the piston ring), adhesive wear and abrasive wear are distinguished. Adhesive wear is the movement of material from the running surface (liner) of the cylinder to the piston ring, and vice versa; the movement of material basically occurs from the liner to the ring. Abrasive wear, on the other hand, involves friction between the running surfaces. Adhesive wear in the wear protection layer according to the present invention is improved, in particular, by the distribution of solid particles in the matrix, and on the other hand, by a reduction in breakout as a result of improved dimensional stability, while abrasive wear is improved, in particular, by the formation of a lubricating film. Preferably, engine oil accumulates in the open cracks formed on the surface that are not filled with material, and residues from the oil accumulate in the form of solid combustion residues, which also act as lubricants. Both of these improve the sliding properties of the surface of the wear protection layer and also provide significant advantages in cases where lubrication is too low, as can occur in an engine.

[0026] The process according to the present invention, which uses a low pH value of 0 or less, results in a wear-resistant protective layer with particularly high wear resistance and dimensional stability because the cracks and particles are distributed very uniformly within the layer.

[0027] Therefore, it is preferable that the particles are distributed throughout the entire wear protection layer, that is, unlike, for example, a hard chrome layer in which the particles are exclusively located in the cracks, they are not limited to the cracks. Such a uniform distribution means that there are no large areas in which the particles are absent or present in very small amounts, thereby uniformly improving the wear resistance of the layer. Furthermore, because the particles are particularly strongly bonded within the metal, they do not easily detach from the surface during operation, as is the case with, for example, a hard chrome layer in which the particles are only present in the cracks. Overall, this results in high wear resistance.

[0028] In order to form a wear-protective layer on a piston ring according to the present invention, the piston ring to be coated is placed in an electrolyte containing iron ions, optionally metal ions of metals other than iron, carbon particles, and solid particles other than carbon particles, and cathode-connected. A direct current or pulsating direct current, for example, a pulsating direct current with a frequency of 10 kHz, is applied to the piston ring, and thus an iron layer or iron alloy layer is galvanically deposited.

[0029] In the present invention, "electrolyte" or "aqueous electrolyte" means an aqueous solution in which electrical conductivity is generated by the electrolytic dissociation of the components of the electrolyte into ions. In addition to the components mentioned and other additives present, the electrolyte contains water as a residue.

[0030] In the method according to the present invention, the solid particles are preferably kept suspended in the electrolyte. This can be achieved, for example, by intensive stirring and / or by using a surface-active substance. Preferably, the electrolyte contains one or more surface-active compounds. These may be ionic, nonionic, and amphoteric surface-active (boundary layer-active) compounds. A preferred surface-active compound is a polyfluorosulfonate. Preferably, the surface-active compound does not contain PFOS.

[0031] In the deposition step (step b of the process), cracks are formed in the wear protection layer, which is made of iron or an iron alloy. These cracks are generally interconnected, at least partially, and can therefore be called a crack network. In a preferred embodiment of the present invention, the solid particles do not substantially deposit within the cracks in the process according to the present invention, even if they are sized to fit into the cracks. This is particularly due to the fact that the pH value of the electrolyte is 0 or less.

[0032] As described above, in preferred embodiments of the present invention, the carbon particles and / or non-carbon solid particles are not primarily located within the cracks. Rather, the carbon particles and / or non-carbon solid particles are substantially embedded in the matrix of the wear protection layer. For the purposes of the present invention, the term matrix refers to the entire metal wear protection layer excluding the cracks, i.e., the entire material of the wear protection layer that does not exist in the form of cracks and is not solid particles. This improves the wear behavior because the solid particles contribute significantly to the wear resistance, and there are no large areas where the particles are absent or present in very small quantities. Furthermore, because the particles are particularly strongly bonded in the matrix, they do not easily detach from the surface during operation.

[0033] In a preferred embodiment of the present invention, the ratio of the carbon particles and / or non-carbon solid particles disposed within the cracks to the total number of particles in the wear protection layer according to the present invention is 0.5% or less in each case, more preferably 0.1% or less in each case, even more preferably 0.05% or less in each case, and most preferably 0.02% or less in each case.

[0034] In a more preferred embodiment of the present invention, the ratio of the total number of carbon particles and non-carbon solid particles disposed within the cracks to the total number of particles in the wear protection layer according to the present invention is 0.5% or less, more preferably 0.1% or less, even more preferably 0.05% or less, and most preferably 0.02% or less.

[0035] The ratio of the particles within the crack to the total number of particles is measured by microscopic images of cross-sectional polishing or running surface polishing. For this purpose, particles are counted over an area of ​​at least 10 μm × 10 μm, and the ratio of the particles within the crack is measured. This area is selected according to the size and distribution of the particles, so that a sufficient number of particles, preferably at least 200 particles, are visible in that area. The preparation of the microscopic specimens is described in detail below.

[0036] In a more preferred embodiment of the present invention, surprisingly, the crack is substantially not filled with iron or iron alloy, i.e., substantially empty. This has the advantage that, because the crack is open, engine oil can fill the surface during the operation of the piston ring, and thus function as a lubricating film. Furthermore, combustion residue of the engine oil can accumulate in this open crack, which also improves the sliding properties. In this way, a particularly effective sliding film (tribofilm) is formed.

[0037] When heated to 300-700°C according to step (d) of the method according to the present invention, an iron oxide layer is formed on the surface of the crack. This is because the crack contains air, and the oxygen in the air oxidizes the iron surface of the crack. Therefore, preferably the surface of the crack has an iron oxide layer.

[0038] In a preferred embodiment of the present invention, based on the total volume of the crack, 3 volume% or less of the crack is filled with iron or an iron alloy. More preferably, based on the total volume of the crack, 2 volume% or less of the crack is filled with iron or an iron alloy, and even more preferably, based on the total volume of the crack, 1 volume% of the crack is filled with iron. The volume percentage of the crack filled with iron or an iron alloy can be measured using the color tone of a microscopic image during cross-sectional polishing or running surface polishing. This is because the metal in the dark-colored crack appears brighter, and the areas of the wear protection layer without cracks also appear brighter. Measuring the percentage of the area after several polishing cycles, preferably 2 to 3 polishing cycles, corresponds to the volume percentage.

[0039] The pH value of the electrolyte in the process according to the present invention is 0 or less. In the background of the present invention, it has been found that this low pH value makes it possible to form an advantageous crack structure, achieve a relatively low crack density, and at the same time prevent particles from being embedded in the cracks of the layer. As a result, the particle distribution within the layer is very uniform.

[0040] In particular, the crack structure ensures stress relaxation within the layer, and therefore ensures the high dimensional stability of the wear protection layer according to the present invention. As described above, the uniform particle distribution improves wear behavior because the solid particles contribute significantly to the wear resistance, and there are no large areas where particles are absent or present in very small quantities. Furthermore, the particles are not mainly present in the cracks but are located within the so-called matrix, and they are particularly strongly bonded to the matrix, so the particles do not easily detach from the surface during operation.

[0041] The pH value of the electrolyte is preferably -0.1 or less, more preferably -0.5 to -0.1. In a preferred embodiment of the present invention, the pH value is thus negative, i.e., H3O + The concentration is less than 1 mol / l. It is preferable to use a strong acid to adjust the pH of the electrolyte, and hydrochloric acid is preferred.

[0042] In a preferred embodiment of the method according to the present invention, after the deposition step (b), the direction of the current is reversed in a further step (b1). In this step (b1), also called the polarity reversal step, crack formation is interrupted. Furthermore, provided that the polarity reversal step is carried out for a certain period of time, the cracks are expanded in the polarity reversal step. Interrupting the crack formation by reversing the polarity is particularly advantageous, as a result new cracks are formed when the direction of the current is reversed again and a further wear protection layer is deposited. As a result, incorporating the polarity reversal step into the manufacturing process of the wear protection layer shortens the cracks in the layer. In contrast to long cracks, these short cracks better disperse the mechanical energy during deformation and improve the dimensional stability of the wear protection layer.

[0043] Therefore, the preferred method is, (b1) After step (b), the direction of the current is reversed and the anode current density is 1 to 30 A / dm 2 and This includes an additional step in which the direction of the current is reversed again and step (b) above is performed again.

[0044] In the polarity reversal step (b1), the direction of the current is reversed, preferably for at least 0.1 seconds, more preferably for at least 1 second, even more preferably for at least 10 seconds, most preferably for at least 30 seconds, and particularly for 30 to 180 seconds. The current density in the polarity reversal step is preferably 1 to 30 A / dm 2 (Amperes / square decimeter), more preferably 2-20 A / dm 2 Particularly preferred is 3-10 A / dm 2 That is the case.

[0045] In a preferred embodiment of the process according to the invention, the direction of the current is reversed at least 5 times, particularly at least 10 times, and most preferably 10 to 30 times. In this way, several individual wear protection layers are deposited on top of each other, and new cracks are formed in each of them. The plurality of layers form a complete wear protection layer.

[0046] Preferably, the electrolytic solution contains an iron(II) compound in an amount corresponding to 150 to 450 g / l of iron(II) chloride, particularly 200 to 400 g / l of iron(II) chloride. The electrolytic solution further preferably contains less iron(III) compound than corresponding to 30 g / l of iron(III) chloride, particularly less iron(III) compound than corresponding to 10 g / l of iron(III) chloride. More preferably, the electrolytic solution contains less than 50 g / l of iron(III) salt, particularly less than 30 g / l of iron(III) salt.

[0047] In a preferred embodiment of the invention, the electrolytic solution contains a metal salt other than iron salt in an amount of 20 g / l, more preferably less than 10 g / l, and most preferably less than 5 g / l of a metal salt other than iron salt. In a preferred embodiment, the iron(II) compound in the electrolytic solution is FeCl2.

[0048] Preferred electrolytes are 150 to 500 g / l of FeCl2·4H2O, particularly 200 to 45 g / l of FeCl2·4H2O, 1 to 40 g / l of carbon particles and each of the solid particles that are not carbon particles, and particularly preferably, one or more surface active compounds having a pH value of 0 or less, preferably -0.1 or less.

[0049] The current density in the deposition step (b) is 10 to 80 A / dm 2 , preferably 20 to 70 A / dm 2 , and most preferably 30 to 50 A / dm 2 is.

[0050] The temperature of the electrolyte in the process according to the present invention is preferably 50°C or lower, more preferably 15 to 45°C, and most preferably 20 to 40°C.

[0051] The electrolyte also contains conventional electrolytic additives and catalysts that support the deposition of the iron layer. These can be present in the electrolyte in normal amounts.

[0052] The deposition period is selected according to the desired thickness of the wear protection layer, and the higher the current density and the longer the deposition is performed, the thicker the layer becomes. The deposition is preferably performed for 5 to 240 minutes, particularly for 10 to 120 minutes. The polarity reversal step is advantageously performed for 0.1 to 600 seconds, particularly for 5 to 200 seconds.

[0053] The wear protection layer according to the present invention can be composed of a plurality of layers that are successively formed by repeating the deposition step (b) and the polarity reversal step (b1). As a plurality of layers are formed and particles are deposited, cracks are not always formed in the same place, so a more uniform distribution of cracks can be achieved over the entire thickness of the coating. The number of repetitions of steps (b) and (b1) is preferably 1 to 100 times, particularly 2 to 50 times, and more preferably 5 to 30 times.

[0054] The thickness of the abrasion protection layer is preferably 10 to 600 μm, more preferably 20 to 400 μm, particularly preferably 30 to 200 μm, and most preferably 40 to 150 μm. The layer thickness is measured by measuring the height of the layer by cross-sectional polishing. If the surface is uneven, the layer thickness is measured at at least 5 points, preferably 6 to 10 points, and the arithmetic mean is calculated. This is the layer thickness of the abrasion protection layer, and is also called the average layer thickness.

[0055] In the process according to the present invention, the amount of solid particles (carbon particles and non-carbon solid particles) contained in the electrolyte can vary over a wide range. It has been found to be advantageous for the electrolyte to independently contain 0.1 to 200 g / l each of carbon particles and non-carbon solid particles. Particularly preferred is 0.5 to 50 g / l, most preferably 2 to 30 g / l, based on the total amount of the electrolyte.

[0056] Depending on the density of the solid particles, the volume fraction of the solid particles relative to the total volume of the wear protection layer may vary over a slightly wider range than the weight fraction.

[0057] The average width of the cracks in the wear protection layer is preferably 0.02 to 2 μm, more preferably 0.05 to 1.5 μm, even more preferably 0.1 to 1 μm, and most preferably 0.1 to 0.8 μm.

[0058] The crack width is measured by measuring the width of at least 10 randomly selected cracks approximately perpendicular to the direction of crack propagation and calculating the arithmetic mean of these at least 10 measured crack widths. Microscopic images of surface polishing (running surface polishing) or cross-sectional polishing can be taken for measurement, and cross-sectional polishing is preferably used, as will be described in more detail below. Basically, for example, in the case of running surface polishing, the surface is polished with sandpaper and then observed with a microscope image to measure the crack width. The cracks differ in color from the rest of the wear protection layer, and the cracks have a darker color.

[0059] Furthermore, the surface area ratio of cracks on the surface of the wear-protective layer can be measured using running surface polishing. To measure the surface area of ​​the cracks, an area of ​​at least 40 μm × 40 μm is taken and the ratio of dark coloration, i.e., the ratio of cracks on the surface to the total area, is measured. This is done by randomly selecting three squares of at least 40 μm × 40 μm and calculating the arithmetic mean of the three measured values. The value obtained in this way is taken as the surface area ratio of cracks on the surface of the wear-protective layer. In all cases, the surface area ratio of cracks on the surface of the wear-protective layer according to the present invention is preferably 0.5 to 10%, more preferably 1 to 8%, relative to the entire surface of the wear-protective layer.

[0060] The average crack density of the wear protection layer according to the present invention is 10 to 160 cracks / mm (millimeters). Preferably, it is 20 to 140 cracks / mm, more preferably 30 to 120 cracks / mm, and most preferably 35 to 110 cracks / mm. To measure the average crack density, at least two cutting lines, each at least 1 mm long, are placed in different directions on a microscope image of the surface polishing (running surface polishing), the crack density (the number of cracks intersecting the lines) is measured by counting, and an arithmetic mean is formed from these at least two counts.

[0061] In a preferred embodiment of the present invention, the polarity reversal step (b1) following the deposition of the wear protection layer can slightly widen the cracks on the surface again. This increases the surface area of ​​the cracks on the surface, thereby allowing the cracks to absorb more lubricant, particularly engine oil, and thus enabling better sliding properties to be achieved immediately after the start of use of the wear protection layer according to the present invention. This improves the settling behavior of the wear protection layer.

[0062] The depth of the cracks in the wear protection layer according to the present invention can also be measured. Similar to the measurement of the crack width, a micrograph is prepared. For the depth of the cracks, the layer (including a substrate which may be coated) is cut perpendicular to the surface of the wear protection layer, and then the surface is polished with sandpaper in the same manner as in the production of a surface polish to produce a cross-sectional polish. The depth of the cracks can be measured from the intensity of the color of the cracks by observing the cross-sectional polish produced in this way under a microscope and measuring the extension in the direction perpendicular to the surface of the wear protection layer. The arithmetic mean is measured from at least 10 cracks. The average crack depth of the wear protection layer according to the present invention obtained in this way is preferably 1 to 40 μm, particularly preferably 3 to 30 μm, more preferably 5 to 20 μm, and most preferably 7 to 15 μm.

[0063] The piston ring is preferably a piston ring having a base, the base having an inner circumferential surface, a first flank surface, a second flank surface, and a running surface as its surfaces. The wear protection layer according to the present invention is formed on at least one of the surfaces, particularly the running surface. The base can be made of a common material used for piston rings, preferably the base is made of cast iron or steel, for example, chromium steel. Below or above the wear protection layer according to the present invention, there may be further layers, for example, an adhesive layer between the base and the wear protection layer, and / or a running layer above the wear protection layer, thereby further improving the break-in behavior.

[0064] The present invention also relates to a piston ring obtained by the method according to the present invention.

[0065] Preferably, it is a piston ring for an internal combustion engine, (a) A piston ring having a surface and comprising a wear protection layer of iron or iron alloy applied to the surface, wherein the wear protection layer has cracks, the cracks have an average density of 10 to 160 per 1 mm of the wear protection layer, and the iron or iron alloy incorporates 0.2 to 15% by weight of carbon particles and 0.2 to 15% by weight of solid particles other than carbon particles, based on the total weight of the wear protection layer, and (b) Heat the piston ring to 300-700°C. It can be obtained through [this method].

[0066] The present invention also relates to the use of the piston ring according to the present invention in an internal combustion engine. For this purpose, the piston ring according to the present invention is inserted into the piston of the internal combustion engine in a manner known to those skilled in the art.

[0067] The features described above, and the features described below, can be used not only in the combinations shown, but also in other combinations or in individual positions, without exceeding the scope of the present invention. [Brief explanation of the drawing]

[0068] [Figure 1] Figure 1 is a micrograph of the polished surface of the wear protection layer according to the present invention. The cracks can be seen on the surface. [Modes for carrying out the invention]

[0069] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0070] Examples : Production of an iron layer according to the present invention containing diamond particles and cubic boron nitride particles

[0071] An aqueous iron electrolyte with the following composition is provided. 300g / l FeCl2·4H2O 5 g / l polyfluorosulfonate 15 g / l, diamond particles with a diameter of 0.2-0.7 μm 15 g / l, cubic boron nitride with a diameter of 0.2-0.7 μm pH value = -0.2 (adjusted with hydrochloric acid)

[0072] In this iron electrolyte, 15 g / l of crystalline diamond particles with a particle size of 0.2 to 0.7 μm and 15 g / l of cubic boron nitride particles with a particle size of 0.2 to 0.7 μm are dispersed while stirring at 30°C. The chromium steel piston ring is pre-treated by pickling with hydrochloric acid and degreasing, forming a nickel layer approximately 2 μm thick. The piston ring is placed in the electrolyte and first switched to the cathode in the first step, at 40 A / dm 2 The iron layer is deposited for 5 minutes at a current density of 4A / dm². In the second step, the polarity is reversed, and the current density is 4A / dm². 2 The piston ring is then switched to the anode for 45 seconds. This cycle, consisting of 5 minutes of cathode chromium plating and 45 seconds of anode etching, is repeated a total of 10 times to form an iron-diamond particle layer approximately 60 μm thick. The coated piston ring is then heated at a temperature of 400°C for 1 hour.

[0073] To create a microscopic image of the aforementioned surface, the running surface of the piston ring is polished, and to create a microscopic image of the cross-section of the aforementioned layer, the cross-section of the piston ring is polished. To create the aforementioned running surface, the surface of the piston ring is polished with SiC wet abrasive paper, increasing the amount of abrasive particles (220 to 4000 particles), and then polished with a 1 μm diamond suspension until the sample is not scratched and the contour is sharp.

[0074] To perform cross-sectional polishing, the piston ring is cut perpendicular to the running surface, and the cut surface is polished with SiC wet polishing paper in the same manner as the running surface polishing.

[0075] Subsequently, microscopic images of the polished running surface and the polished cross-section are taken.

[0076] The crack density was 50 cracks / mm².

[0077] Comparative Example 1 Manufacturing of an iron layer containing diamond particles without cracks within the layer.

[0078] To produce a crack-free iron layer, deposition was carried out using a conventional iron sulfate electrolyte (pH=1.4) according to Example 1 of German Patent Invention No. 19508419. This electrolyte also contained a conventional wetting agent and diamond particles in the range of 0.2 to 0.7 μm in diameter.

[0079] As a result of the cross-sectional polishing and the running surface polishing, no cracks were observed in the layer according to this comparative example.

[0080] The layers on the piston rings according to the examples and comparative examples were subjected to wear tests and dimensional stability measurements.

[0081] A rig test was conducted to measure wear, in which the piston ring was run on a cylinder using engine oil at a stroke equivalent to a normal engine stroke for 23 hours. After that, the amount of wear on the running surface of the piston ring and the running surface of the cylinder was measured.

[0082] The amount of wear on the ring was 9 μm in the above example and 19 μm in Comparative Example 1. The amount of wear on the liner was 7.5 μm in the example and 16.5 μm in Comparative Example 1. Thus, in the example, both the amount of wear on the ring, i.e., the amount of wear on the wear protection layer according to the present invention, and the amount of wear on the mating surface, i.e., the running surface (liner) of the cylinder, are significantly reduced compared to Comparative Example 1.

[0083] To measure dimensional stability, the piston ring was clamped by machine and bent in both directions relative to its original shape until it broke. As a result, the wear protection layer according to the present invention in the above embodiment was found to have significantly higher dimensional stability than Comparative Example 1. This clearly demonstrates the advantages of the wear protection layer according to the present invention in terms of improved dimensional stability and reduced wear.

[0084] Comparative Example 2 Manufacturing of an iron layer containing diamond particles within a crack layer.

[0085] An aqueous iron electrolyte with the following composition is provided. 300g / l FeCl2·4H2O 5 g / l polyfluorosulfonate 15 g / l, diamond particles with a diameter of 0.2-0.7 μm pH value = -0.2

[0086] Crystalline diamond particles with a particle size of 0.2-0.7 μm and a concentration of 15 g / l are dispersed in an iron electrolyte at 30°C while stirring. The chromium steel piston ring is pre-treated by pickling with hydrochloric acid, degreasing, and forming a nickel layer approximately 2 μm thick. The piston ring is placed in the electrolyte and first switched to the cathode in the first step, at 40 A / dm 2 At this current density, the iron layer is deposited for 5 minutes. In the second stage, the polarity is reversed, and 4A / dm 2 The piston ring is switched to the anode for 45 seconds at the specified current density. This cycle, i.e., 5 minutes of cathode chromium plating followed by 45 seconds of anode etching, is repeated a total of 10 times to form an iron-diamond particle layer approximately 60 μm thick. The coated piston ring is then heated at a temperature of 400°C for 1 hour.

[0087] To create a microscopic image of the surface, the running surface of the piston ring was polished as described above, and to create a microscopic image of the cross-section of the layer, the cross-section of the piston ring was polished. Subsequently, microscopic images of the running surface polishing and cross-sectional polishing were created. From the cross-sectional polishing and running surface polishing, it can be seen that cracks have occurred in the layer according to this comparative example. The crack density was 80 cracks / mm.

[0088] The layer on the piston ring according to Comparative Example 2 was also subjected to a wear test. To measure the wear, the rig test described above was performed, in which the piston ring was run on a cylinder as a mating surface using engine oil, at a stroke equivalent to a normal engine stroke for 23 hours. After that, the amount of wear on the running surface of the piston ring and the running surface of the cylinder was measured.

[0089] The wear amount of the ring in Comparative Example 2 was 19.3 μm. The wear amount of the liner in Comparative Example 2 was 8.5 μm.

[0090] Overall, it was shown that in the embodiment of the present invention, both the amount of wear of the ring, i.e., the amount of wear of the wear protection layer, and the amount of wear of the mating surface, i.e., the running surface (liner) of the cylinder, are improved compared to both Comparative Examples 1 and 2.

Claims

1. A piston ring for an internal combustion engine, having a surface and comprising a wear protection layer of iron or an iron alloy formed on the surface, wherein the wear protection layer has cracks, the cracks having an average density of 10 to 160 per mm of the wear protection layer, and the iron or iron alloy is embedded with 0.2 to 15% by weight of carbon particles and 0.2 to 15% by weight of non-carbon solid particles based on the total weight of the wear protection layer. The solid particles other than carbon particles consist of tungsten carbide, chromium carbide, aluminum oxide, silicon carbide, silicon nitride, boron carbide and / or cubic boron nitride. A piston ring for an internal combustion engine, wherein the carbon particles may be partially or completely converted into an iron-carbon compound.

2. The piston ring according to claim 1, characterized in that the ratio of the carbon particles and / or non-carbon solid particles placed in the cracks to the total number of particles in the wear protection layer is 0.1% or less at each location.

3. The piston ring according to claim 1, characterized in that the ratio of the total number of carbon particles and non-carbon solid particles arranged in the cracks to the total number of particles in the wear protection layer according to the present invention is 0.05% or less.

4. The piston ring according to claim 1, characterized in that the carbon particles are partially converted into an iron-carbon compound.

5. The piston ring according to claim 1, characterized in that the average density of the cracks is 30 to 120 per 1 mm of the wear protection layer.

6. The piston ring according to claim 1, characterized in that the average width of the cracks is 0.05 to 1.5 μm.

7. The piston ring according to claim 1, characterized in that the carbon particles consist of diamond and / or graphite.

8. The piston ring according to claim 1, characterized in that the solid particles, which are not carbon particles, are made of cubic boron nitride.

9. The piston ring according to claim 1, characterized in that the iron alloy contains 90% by weight or more of iron based on the total weight of the iron alloy.

10. (a) 100-500 g / l of FeCl ２ An amount equivalent to an iron(II) compound, and an optional further metal salt, A piston ring is placed in an aqueous electrolyte containing carbon particles and solid particles other than carbon particles, wherein the pH of the aqueous electrolyte is 0 or less. (b) Abrasion protection layer of iron or iron alloy with a load capacity of 10 to 80 A / dm ２ Steps include galvanic deposition on the piston ring at the cathode current density, (c) The step of drying the piston ring together with the wear protection layer, (d) A step in which the temperature is heated to 300-700°C. A method for manufacturing a piston ring according to any one of claims 1 to 9, including the following:

11. The manufacturing method according to claim 10, characterized in that the pH value of the aqueous electrolyte is -0.1 or less.

12. After step (b), the direction of the current is reversed, and the anode current density is 1 to 30 A / dm ２ and The direction of the current is reversed again, and step (b) is performed again. The manufacturing method according to claim 10, characterized in that it

Images