Highly thermally conductive valve seat ring

Abstract

The invention relates to a valve seat ring, produced by powder metallurgy, with a carrier layer and a function layer. The problem addressed by the invention is that of creating a valve seat ring of the aforementioned type with considerably higher thermal conductivity. To solve this problem, the invention provides a valve seat ring of the aforementioned type, such that the carrier material of the carrier layer has a thermal conductivity greater than 55 W / m*K with a total copper content of >25 to 40% by weight.

Description

[0001] The invention relates to a method for the powder metallurgical production of a valve seat ring, comprising a support layer and a functional layer.

[0002] Valve seat rings of the type mentioned are known, for example, from Japanese patent application JP 6145720 A. This application describes a copper-infiltrated multilayer valve seat ring with cobalt and molybdenum content for internal combustion engines.

[0003] US 4,485,147 discloses a powder metallurgy process for producing a copper-infiltrated iron-based sintered material that does not require a separate copper infiltration step. The process specifically includes producing two powder mixtures, one of which has a predetermined composition with an infiltration material powder containing copper powder or copper alloy powder as the main component, and the other of which has a predetermined composition without the infiltration material powder.

[0004] In principle, the previously known valve seat rings have the advantage of exhibiting excellent strength. This is primarily due to the use of two different material layers. The base material, in particular, possesses outstanding strength properties.

[0005] However, the previously known valve seat rings of the aforementioned type have the disadvantage that they no longer meet the increasing demands of internal combustion engines due to their poor thermal conductivity. The thermal conductivity of conventional substrate materials is typically below 45 W / m*K.

[0006] The object of the invention is to provide a method for manufacturing a valve seat ring of the aforementioned type that exhibits significantly higher thermal conductivity. Furthermore, the valve seat ring should meet the usual requirements for tightness, dimensional accuracy, and strength.

[0007] To solve this problem, the invention proposes a method according to claim 1. The total copper content of the valve seat rings produced according to the inventive method preferably consists of an iron-copper alloy, added copper powder, and infiltrated copper.

[0008] All percentages below are weighted %.

[0009] The valve seat ring produced according to the invention is characterized by its high thermal conductivity combined with high strength, making it suitable for use in modern internal combustion engines. This results in the following advantages: faster heat transfer in the cylinder head, reduction of valve temperature, reduction of knocking tendency in the internal combustion engine due to lowered valve temperatures, more uniform temperature distribution in the valve seat ring, reduced deformation of the valve seat rings due to inhomogeneous temperature distributions, reduced leaks in the combustion chamber due to less deformation of the valve seat rings.

[0010] A preferred embodiment provides that the substrate material has a thermal conductivity greater than 65 W / m*K. This variant is particularly suitable for use in turbocharged engines. In a gasoline engine, the combustion temperature is higher than in a diesel engine. Conversely, in a diesel engine, the ignition temperature is approximately 200 to 300°C higher than in a gasoline engine. In any case, it is necessary to dissipate the high temperature quickly to prevent damage to the engine block.

[0011] A particularly preferred embodiment of the valve seat ring manufactured according to the invention provides that the support material has a thermal conductivity greater than 70 W / m*K. This embodiment is particularly required in high-performance engines, such as those in sports cars or motorsport, where the engines are operating at their maximum performance capacity. Increased thermal conductivity then increases the engine's service life.

[0012] Preferably, the substrate material is an iron-copper alloy. In this combination, the high strength of iron and the good thermal conductivity of copper result in particularly positive properties of the substrate material in application.

[0013] The powder-metallurgically produced valve seat ring exhibits particularly good properties when the copper content of the iron-copper alloy exceeds 5 wt.%, especially at 10 wt.%. In this alloy configuration, the advantages of iron and copper are particularly well utilized. The maximum solubility of copper in austenite is 8.5 wt.% at 1094°C. However, the copper can be incorporated into the iron-copper alloy either as an alloying element or by diffusion bonding. With diffusion-bonded copper, proportions significantly exceeding 8.5 wt.% are achievable. According to the invention, an iron-copper alloy also includes iron with diffusion-bonded copper.

[0014] An advantageous embodiment of the valve seat ring produced according to the invention provides that the carrier material is a mixture of the iron-copper alloy and copper powder. Here, the copper bonds the iron components and forms a cohesive matrix. The increased copper content allows for particularly good heat conduction through the material. This ensures the longevity of the machine elements involved in the area of ​​the valve seat ring. A particularly good combination of thermal conductivity and strength can be achieved when the proportion of copper powder is between 8 and 12 wt.%, especially at 10 wt.%. The matrix formed by the copper offers particularly good thermal conductivity without significantly impairing the load-bearing function of the iron.Due to the ever-increasing performance and associated operating temperatures of engines, an increase in the thermal conductivity of valve seat rings is associated with a beneficial extension of their service life.

[0015] A particularly preferred embodiment of a valve seat ring manufactured according to the invention provides that the support material and / or the functional material additionally contain copper, which is supplied by infiltration. The infiltration serves to fill the pores of the green compact. This occurs during the sintering process. The liquid copper is drawn into the pores by capillary action. While pores in sintered products typically have a heat-insulating effect, the thermal conductivity is significantly increased compared to the base material, in this case, the support and functional material. This results in optimal utilization of the workpiece volume for optimizing thermal conductivity.

[0016] Powder metallurgy-produced valve seat rings with infiltrated copper contents of approximately 20 wt.% are known per se. However, it has been found that the thermal conductivity of the valve seat ring produced according to the invention is particularly favorable when the copper content of the carrier material is >25 wt.%, especially between 25 and 40 wt.%, without compromising the strength properties of the iron. Iron generally has higher strength than copper, but copper has higher thermal conductivity. In the aforementioned alloy composition for the carrier material, both advantages of these metals can be combined without their disadvantages. Such high copper contents of the carrier material are achieved when, in addition to copper infiltration, an iron-copper alloy powder is used for the carrier material, to which copper powder is added.

[0017] The total copper content of the valve seat rings produced according to the invention is preferably >28 to 40 wt.%.

[0018] The following table shows a particularly advantageous composition of the carrier material: 0,5 until 1,5 % by weight C 0,1 until 0,5 % by weight Mn 0,1 until 0,5 % by weight S >25 until 40 % by weight Cu (total) rest Fe.

[0019] In a preferred embodiment, the alloy composition of the functional material consists of: 0,5 until 1,2 % by weight C 6,0 until 12,0 % by weight Co 1,0 until 3,5 % by weight Mon 0,5 until 3,0 % by weight Ni 1,5 until 5,0 % by weight Cr 0,1 until 1,0 % by weight Mn 0,1 until 1,0 % by weight S 8,0 until 22,0 % by weight Cu (infiltrated) rest % by weight Fe.

[0020] This is a conventional functional material. Since the alloying elements are expensive materials, every effort is made to optimize or minimize the proportion of the functional layer in the entire valve seat ring. Because valve seat rings are mass-produced, this results in a significant cost reduction due to the reduced proportion of these expensive materials.

[0021] An alternative embodiment of the functional layer consists of the following functional material: 0,5 until 1,5 % by weight C 5,0 until 12,0 % by weight Mon 1,5 until 4,5 % by weight W 0,2 until 2,0 % by weight V 2,2 until 2,8 % by weight Cr 0,1 until 1,0 % by weight Mn 0,1 until 0,5 % by weight S 12,0 until 24,0 % by weight Cu (infiltrated) rest % by weight Fe.

[0022] The choice of materials for the functional layer depends on the requirements of the valve seat ring. If the required properties are met by the functional material, the more cost-effective option should be chosen.

[0023] In the valve seat ring manufactured according to the invention, the functional and support layers exhibit different properties. While the functional layer of the valve seat ring is designed specifically with regard to thermal stress, the support layer possesses the necessary strength and improved thermal conductivity. For this purpose, the support material consists of an iron-copper alloy powder.

[0024] The carrier layer consists of an iron-copper alloy powder. The iron provides strength, and the copper improves the thermal conductivity of the carrier layer. The powder is then pressed into a semi-finished product. The surface inclination towards the inner edge of the valve seat ring semi-finished product can be adjusted to meet specific requirements. According to the invention, the angle of inclination to the horizontal plane is between 20° and 40°. This allows for precise control over the thickness of the functional layer at specific points. The adjustable tapered profile of the carrier layer minimizes the proportion and therefore the cost of the functional layer. This semi-finished product is coated with a powdered functional material and then pressed into a green compact. This green compact comes into contact with copper during the sintering process.Due to the pores of the pressed green compact, the liquid copper penetrates the workpiece via capillary action. This form of copper enrichment significantly increases the thermal conductivity of the workpiece, while maintaining the load-bearing function of the substrate and functional layers.

[0025] A preferred embodiment of the process involves combining the iron-copper alloy powder of the substrate layer with copper powder, where the proportion of copper powder in the total alloy exceeds 15 wt.%. Surprisingly, it has been found that this approach does not result in the loss of the load-bearing properties of the iron, while the thermal conductivity steadily increases due to the copper. The copper powder bonds the iron-copper particles together, and the relatively low proportion of copper (up to 15 wt.%) means that it has no unacceptable impact on the material's strength.

[0026] A particularly preferred embodiment of the method provides that the iron-copper alloy powder is combined with graphite, wherein the proportion of graphite in the total alloy is between 0.5 and 1.5 wt.%. The lubricating effect of the graphite prevents galling of the surface of the support layer and thus increases the service life of the valve seat ring.

[0027] A helpful embodiment of the method involves compressing the carrier layer to a density of 6.5 to 7.5 g / cm³ into a semi-finished product using a pressure of 450 to 700 MPa. These parameters have proven unexpectedly beneficial with regard to copper infiltration, as the pore size corresponds to an ideal size for the necessary capillary action. The copper to be infiltrated is guided into the workpiece via these pore channels. Excessively high pressures and densities prevent the copper from penetrating the workpiece, while excessively low pressures and densities fail to achieve the necessary strength values ​​for the valve seat ring. According to the invention, the pressure is reduced compared to conventional pressures, which also reduces the density of the green compacts. The lower density results in more pores, which are then filled by the copper infiltration.This leads to a higher copper uptake via infiltration than previously usual.

[0028] Special and complex properties of the valve seat ring can be achieved by layering and compacting the green compact in multiple layers. This offers two key advantages. Firstly, a cost-effective material can be used in less stressed areas of the valve seat ring. Secondly, the properties can be tailored to specific requirements at different locations by adjusting the alloy composition and layer thickness.

[0029] The sintering process takes place at a temperature higher than the melting point of copper. This enables copper infiltration, whereby the molten copper penetrates the workpiece through the opened pores via capillary action during the sintering process.

[0030] The copper can be added to the green compact as a ring for infiltration.

[0031] The invention will be explained in more detail below with reference to the drawings. The drawings show: Figure 1: Sectional view of the valve seat ring; Figure 2: Microstructure of the old support layer; Figure 3: Microstructure of the new support layer; Figure 4: Diagram of the thermal conductivity of the entire valve seat ring according to the prior art and according to the teaching of the invention; Figure 5: Diagram of the thermal conductivity of the support layer according to the prior art and according to the teaching of the invention.

[0032] In Figure 1A cross-sectional view of a valve seat ring 1 produced according to the invention is shown. The support layer 2 forms the bulk of the valve seat ring 1. The functional layer 3 is located in the upper region of the valve seat ring 1 and essentially forms the bearing surface for the valves. The slope between the support layer 2 and the functional layer 3 is clearly visible; this slope runs as parallel as possible to the bearing surface for the valves along the valve seat ring. A diffusion layer 4 forms at the contact point between the support layer 2 and the functional layer 3. The diffusion layer 4 forms particularly during the sintering of the previously compressed green compact.

[0033] In the Figures 2 and 3 The structural images of the support layer 2 of the valve seat ring 1 are shown. Figure 2 The structure of a conventional support layer 2 according to the state of the art is shown. In contrast, the following shows Figure 3A microstructure image of the support layer 2 of a valve seat ring 1 according to the invention. The microstructure image of the support layer 2 clearly shows... Figure 3 a significantly higher copper content. The copper content is in the Figures 2 and 3 The light areas indicate the proportion of iron or iron-copper.

[0034] The Figures 4 and 5 Diagrams are shown regarding the thermal conductivity of the valve seat rings 1 and the support layer 2. A comparison is made between the old (state of the art; SdT) and the new (teaching of the invention; LdE) manufacturing method for the valve seat rings 1. The thermal conductivity was measured using the laser flash method at RWTH Aachen University.

[0035] The Figure 4Figure 1 shows a diagram of the thermal conductivity of finished valve seat rings 1. Variant 1 has a different composition of the functional layer 3 compared to variant 2. The functional layer 3 is assumed to be known according to the prior art. The composition of the support layer differs according to the prior art and according to the invention. It is clearly evident that the thermal conductivity of variants 1 and 2 according to the invention is significantly higher than the thermal conductivity of variants 1 and 2 according to the prior art.

[0036] The Figure 5Figure 1 shows a diagram of the thermal conductivity of support layers 2 for two different variants of functional layers 3 of valve seat rings 1. It shows that the thermal conductivity of the conventional support layer 2 according to the prior art decreases with increasing temperature from 48 W / m*K. In contrast, the average thermal conductivity of the support layer 2 for both variants according to the invention remains slightly above 70 W / m*K. At a temperature of 500 °C, the thermal conductivity of variants 1 and 2 according to the invention (approximately 70 W / m*K) is 46 wt.% higher than the thermal conductivity of variants 1 and 2 according to the prior art (approximately 38 W / m*K).

[0037] The invention is further explained by the following example: Example:

[0038] The substrate layer is pressed from a carrier material at 550 MPa to form a semi-finished product. The carrier material consists of a combination of copper powder and iron-copper alloy powder. The substrate layer has the shape of a ring with a steep inward slope. This semi-finished product is then coated with a functional material in powder form and pressed into a green compact, thus creating the functional layer. This green compact is sintered at 1100 °C, during which copper wire is added. This copper melts and is drawn into the green compact undergoing the sintering process via capillary action.The finished valve seat ring has an alloy composition in the support layer of 1.2 wt% C, 0.3 wt% Mn, 0.2 wt% S and 35 wt% Cu and in the functional layer an alloy composition of 1.1 wt% C, 9.7 wt% Co, 1.4 wt% Mo, 2.5 wt% Ni, 3.0 wt% Cr, 0.5 wt% Mn, 0.5 wt% S and 19.0 wt% Cu, whereby the copper content is a combination of the iron-copper alloy, the copper powder and the copper infiltration.

[0039] The manufactured valve seat ring has high strength, while also offering good thermal conductivity and lubricity.

Claims

1. A method for the powder-metallurgical production of a valve seat ring, comprising a carrier layer (2) made of a carrier material and a functional layer (3) made of a functional material, wherein the carrier material of the carrier layer (2) has a total copper content of > 25 to 40 wt.%, so that a thermal conductivity greater than 55 W / m*K can be achieved, comprising the following steps: producing a carrier layer (2) with a carrier material made of an iron-copper alloy powder, wherein the copper proportion of the iron-copper alloy is above 5 wt.%; optionally pressing the powder of the carrier layer (2) into a semi-finished product; producing a functional layer from a customary powdery functional material; pressing the powder into a green compact; sintering the green compact in contact with copper.

2. The method according to claim 1, characterized in that the iron-copper alloy powder of the carrier layer (2) is combined with copper powder, wherein the proportion of the copper powder in the carrier layer is 5 wt.% to 15 wt.%.

3. The method according to claim 1 or 2, characterized in that the iron-copper alloy powder is combined with graphite, wherein the proportion of the graphite in the carrier layer is between 0.5 and 1.5 wt.%.

4. The method according to any one of claims 1 to 3, characterized in that the carrier layer (2) is compressed by means of a pressing pressure of 450 to 700 MPa to a density of 6.5 to 7.5 g / cm3 into a semi-finished product.

5. The method according to any one of claims 1 to 4, characterized in that the green compact is layered and compacted in multiple layers.

6. The method according to any one of claims 1 to 5, characterized in that the copper to be infiltrated is supplied as a ring.

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