Coated wear-prone metal substrate and method of manufacturing same

Abstract

To extend the life of abrasive metal substrates. The surface of an abradable metal substrate is coated by arc spraying with tungsten, molybdenum, a tungsten alloy, or a molybdenum alloy.

Description

Technical Field

[0001] The present invention relates to a coated easily wearable metal substrate and a method for manufacturing the same. In particular, the present invention relates to an improved filling chamber for a pressure (die) casting machine (or die-casting machine: Druckgiessmaschiene).

Background Art

[0002] The inner surface (inner circumferential surface) of the filling chamber of a pressure die casting machine is most worn in the region of the supply port. For example, when a hot casting material such as liquid aluminum passes through the supply port and is mechanically injected, the casting material always appears (collides) at the same position below the supply port on the inner surface of the filling chamber. After using the filling chamber for a longer time, leaching (Auswaschungen) may occur in the region below the supply port, which can inhibit the sliding of the pressure piston in the chamber and expose the pressure piston to greater wear. In the case of vacuum pressure casting, it is further more difficult to reliably generate the required vacuum. Therefore, a filling chamber composed of a jacket element having a separable cylindrical insert member is known from DE 42 29 338 C2. In this case, the insert member extends axially from the outer end of the filling chamber to the inside of the supply port, and its inner end abuts against the inner wall of the filling chamber with its outer circumferential surface in a narrow ring-shaped region. On the other hand, its outer end is coaxially guided with respect to the filling chamber by a centering ring fitted between its outer circumference and the inner wall of the filling chamber. Thereby, a filling chamber for a pressure die casting machine, in which its main wear region can be directly replaced in a pressure die casting machine, is already formed. However, it would be desirable for the life of this type of insert member to be longer.

[0003] Furthermore, DE 102 05 246 B4 provides a filling chamber for a pressure die casting machine having a supply port for liquid casting material, in which case a cooling device is provided in the region of the filling chamber wall facing the supply port. The cooling device is fitted into the filling chamber wall from the outside and is formed from a disc having at least one guide channel for the coolant. This measure is intended, in particular, to extend the lifespan of the filling chamber insert member.

[0004] EP 3 184 203 A1 similarly describes a filling chamber for a pressure die casting machine. The cylindrical inner surface of the filling chamber serves as a sliding surface for the pressurizing piston, and the filling chamber has a supply port for the liquid casting material and a removable cylindrical insert member, the pressurizing piston sliding along the inner surface of the insert member, the insert member having radial openings for jacketed filler (Mantelfuellung) that are in communication with the supply port of the filling chamber. In this case, the inner surface of the removable insert member is formed at least partially from molybdenum or a molybdenum alloy. The removable insert member is formed from a metal sleeve (steel) and an inner bush made of molybdenum or a molybdenum alloy (Mo / Mo alloy).

[0005] In the above case, where a cylindrical insert member is used to protect the supply port or filling chamber and can be replaced with a new insert member when wear occurs, relatively rapid removal is possible if wear on the sliding surface for the pressurizing piston occurs very frequently.

[0006] WO 00 / 10752 A1 relates to casting tools for casting molded members made of non-ferrous metals (e.g., Al or Mg). In this case, the casting mold is made of a heavy metal alloy (e.g., W alloy) or its contact side with the molded member is appropriately coated. For this purpose, the heavy metal alloy is used in the form of a sintered element.

[0007] US 2017 / 0266719 A1 describes a pressure die casting machine and a corresponding casting method. In this case, a given apparatus part(s) is coated with a coating that has far less chemical reactivity with the metal to be used for casting (such as Al, Cu, Ti and their alloys) than iron alloys used in the prior art. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] DE 42 29 338 C2 [Patent Document 2] DE 102 05 246 B4 [Patent Document 3] EP 3 184 203 A1 [Patent Document 4] WO 00 / 10752 A1 [Patent Document 5] US 2017 / 0266719 A1 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, in order to construct the casting process as efficiently as possible and with less interruption, the challenge remains of extending the replacement interval (the period between replacements) for the above-mentioned insert components, or more generally, the lifespan of pressure die casting machines or their most wearable parts, i.e., the filling chamber. Furthermore, there is generally the challenge of making surface coatings, especially on easily wearable metal substrates, more mechanically and chemically stable and thereby more wear-resistant. [Means for solving the problem]

[0010] [Modes for carrying out the invention]

[0011]

[0012] The above problems are solved, in accordance with the present invention, by coating the inner surface (inner circumferential surface) of the filling chamber or the inner surface (inner circumferential surface) of the insert member for the filling chamber according to the present invention with tungsten or a tungsten alloy, either completely or partially. This also generally applies to easily wearable metal substrates.

[0013] It is known that the greatest wear in a filling chamber occurs in its injection area. For example, during aluminum pressure casting, low-iron (low-iron content) Al alloys attack the steel of the filling chamber or incorporated replaceable bushings, causing leaching (Auswaschungen) particularly in this area. To eliminate these drawbacks, in filling chambers that are normally made of steel, the inner surface is preferably fully lined with tungsten or a tungsten alloy, at least in its injection area. The present invention also includes lining (processing) the inner surface of an insert member for a filling chamber, preferably made of steel, with tungsten or a tungsten alloy, which is also fully or partially feasible in this case.

[0014] The present invention therefore includes a filling chamber for a pressure (mold) casting machine (or die-casting machine), wherein its cylindrical inner surface serves as a sliding surface for a pressurizing piston, and the chamber has a supply port for a liquid casting material, such as aluminum in the case of an aluminum pressure casting machine. In a preferred embodiment, the filling chamber has an insert member, preferably made of steel, having an opening on its outer circumferential surface (jacket surface) that connects to (communicates with) the supply port of the filling chamber. In this case, the inner surface of the filling chamber or the inner surface of the insert member is entirely or partially, preferably in the injection area, coated with tungsten or a tungsten alloy. The insert member has a length of approximately 1 / 4 the length of the filling chamber and a wall thickness of approximately half the wall thickness of the filling chamber.

[0015] The use of tungsten or a tungsten alloy for the above application (application) is also included in the present invention.

[0016] Unlike the insert members described in EP 3 184 203 A1, the insert members according to the present invention are not replaceable bushings in the form of a sleeve system in which the molybdenum insert member is precisely fitted into a steel outer sleeve, but rather the inner surface of the insert member according to the present invention, which is generally made of steel, is coated completely or partially with tungsten or a tungsten alloy.

[0017] Except for this difference and the type of coating, which are important for the durability of the insert member, the insert member according to the present invention corresponds to that described in EP 3 184 203 A1. To that extent, Figure 1 and its description in paragraph

[0029] , for example, of the filling chamber described in the said publication are explicitly referenced and may also serve as a description of the filling chamber according to the present invention.

[0018] As a coating material for the inner surface of the filling chamber or insert member according to the present invention, it is preferable that the inner surface of the filling chamber and insert member be completely coated, and tungsten or a tungsten alloy is used. The alloy may be a binary, ternary, or quaternary alloy or an alloy containing further (metallic) components. Examples of this alloy are preferably WNiFe alloys containing more than 50% by mass of tungsten (W) or WMoNiFe alloys in which the sum of W and Mo is more than 50% by mass of the finished alloy.

[0019] Particularly suitable alloys contain more than 50% by mass of tungsten. Particularly suitable forms for tungsten and tungsten alloys are wire and powder. Manufacturing is carried out by powder metallurgy, which is known in principle to those skilled in the art. Furthermore, tungsten and corresponding tungsten alloys are available from various manufacturers and metal trading companies, especially via the internet.

[0020] The above embodiments regarding preferred coating materials or coating substances generally apply to the coating of metal substrates as well.

[0021] In addition to the selection of a suitable coating material for generating a chemically, thermally and mechanically stable coating on a filling chamber or a metal substrate, it has been found (by the present invention) that the coating method is also extremely important. In this regard, since the linear thermal expansion coefficient α is very different between tungsten (α = 4.5 × 10 -6 (1 / K) at 20°C) and steel (α = 11 - 13 × 10 -6 (1 / K) at 20°C), it should be noted that it is extremely difficult to apply (allocate) a thermally / mechanically stable tungsten film to a steel substrate.

[0022] The surface coating method of thermal spraying (spraying) has been found (by the present invention) to be particularly suitable for the purposes of the present invention. In one embodiment of the present invention, this method typically results in a significantly large hardening of the layer formed by spraying with a Vickers hardness > 800HV, while, for example, tungsten alloys otherwise have a hardness of only 280 - 400HV. In addition to a remarkable improvement in chemical / thermal and mechanical stability, the surface coating (coating) applied by thermal spraying (spraying) also has the characteristic of special melting resistance to, for example, liquid (molten) aluminum, and is therefore preferably and particularly suitable for use in an aluminum die casting machine.

[0023] The thermal spraying method (spraying method) includes the following methods: Arc spraying method Wire flame spraying method (or rod type) Powder flame spraying method High velocity spraying method / high velocity flame spraying method (HVOF: high velocity oxy fuel) Laser spraying (method) Cold spraying method Detonation (explosion) spraying (method) Plasma spraying (method) PTA (plasma transferred arc)

[0024] The selection of thermal spraying as a coating technology achieves a highly advantageous hardness for use, which is crucial for a drastic increase (extension) in the lifespan of the thus coated filling chambers, insert components, and metal substrates.

[0025] All of these methods are, in principle, usable for the purposes of the present invention.

[0026] The present invention therefore relates not only to tungsten-based materials (additional (adhesion) materials (thermal spray materials)) but also to coating methods for applying (spraying) materials. The thermal spray method is a surface coating method. According to the standard definition (DIN EN 657), the addition material, i.e., the so-called thermal spray material, begins to melt, progresses or completes melting inside or outside the thermal spray torch, is accelerated in the form of thermal spray powder in the gas flow, and impacts the surface of the member to be coated. At this time, the member surface is not melted (unlike build-up welding) but is thermally loaded only to a small extent. The thermal spray particles flatten more or less strongly upon impact with the member surface, depending on the method and material, and maintain their adhesion mainly by mechanical bonding, thereby constructing a thermal spray layer in a layered manner. The qualitative characteristics of the thermal spray layer are low porosity, good bonding to the member, crack-free, and a uniform microstructure. The resulting layer (coating) properties are essentially influenced by the temperature and velocity of the sprayed particles at the point of impact with the coated surface. Surface conditions (cleanliness, activity, temperature) also affect qualitative properties such as adhesion strength.

[0027] As energy carriers for the progression or completion of the melting of the material to be sprayed (adhered), electric arcs (arc spraying), plasma streams (or jets) (plasma spraying), fuel-oxygen-flame or fuel-oxygen-high-velocity flame (traditional and high-velocity flame spraying), preheated high-velocity gas (cold gas spraying), and laser beams (laser (beam) spraying) are used. According to the DIN standard EN657, spraying methods are classified according to these criteria.

[0028] When W or W alloy (W / W alloy) is used as a wire, the preferred method is wire arc spraying. For powdered W / W alloys, plasma spraying is particularly suitable.

[0029] The above method of thermal spraying is known in the prior art and is therefore known to those skilled in the art; see, for example, http: / / www.gts-ev.de / html_d / ts-info.htm or the information catalog LINSPRAY® “Gase und Know-how beim thermischen Spritzen”, Linde AG, Geschaeftsbereich Linde Gas, Unterschleissheim (Germany).

[0030] For the purposes of the present invention, a particular representative (example) of a coating method known in principle in the prior art, appropriately modified for solving the problems of the present invention, has been found to yield remarkable results with respect to the coating (film) applied, with respect to quality and, in this case, particularly, to the hardness achieved.

[0031] Basically, the thermal spraying method is also preferred in accordance with the present invention for methods of overlay welding of coating materials. In this case, the thermal spraying method offers a wide range of applications for a very diverse range of applicable materials.

[0032] Among the various thermal spraying methods, arc spraying, which can be used in the so-called two-wire or, more preferably, a single-wire method, is preferred in accordance with the present invention. The preferred coating material is tungsten or a tungsten alloy.

[0033] Preferred coating or thermal spraying methods are described in detail below with reference to Figure 1, but this does not limit the scope of the present invention. [Brief explanation of the drawing]

[0034] [Figure 1] [Examples]

[0035] Figure 1 shows a schematic diagram of a spray head in an example of a single-wire spray device. Electrode 1 (tungsten electrode) is rotatably mounted around the wire.

[0036] In the case of a double-wire system, the arc is generated between the two wires, and in the case of a single-wire spray as shown in Figure 1, it is generated between the tungsten electrode 1 and the spray wire 7. In this case, the emitted electrons (multiple) i.e., the arc first pass through the shielding gas 2, in this case argon or an argon-hydrogen mixture, and then pass through a mixed gas consisting of the shielding gas 2 and an atomizing (precipitating) gas (Zerstaeubergas) consisting of N2 or air. At that time, the gas is ionized to generate plasma 4, which is heated to approximately 15,000°C. Plasma 4 is composed of a mixed gas of shielding gas 1 i.e., argon or argon / hydrogen (Ar / ArH2) and atomizing gas 5. Electrode 1 is protected as shielding gas 2 continuously flows around it. The arc 4 melts the spray wire 7, and then the atomizing gas 5, which has an extremely high pressure or extremely high velocity, atomizes (precipitates) the molten droplets (multiple) on the spray wire 7. The atomized spray wire containing the atomizing gas and shielding gas is denoted by reference numeral 8 in the drawing. The atomizing gas flow does not need to flow in a ring around the shielding gas 2, as in plasma welding, but can be introduced through, for example, multiple nozzles. In this case, the atomizing gas nozzle 6 shown in Figure 1 would be unnecessary and could be replaced by multiple individual nozzles.

[0037] By spatially separating electrode 1 and wire 7, electrode 1 can still rotate around wire 7, but a more favorable nitrogen gas can be used instead of a noble gas. Thus, an increase in hardness to approximately 600 HV is already achieved compared to the starting material which has approximately 300 HV. It has been found (by this invention) that by using air as the atomizing gas 5, a further substantial increase in hardness to approximately 900 HV can be achieved. For the single-wire spray method using wires made of W or W alloy, it is preferable to use a current in the range of 60 to 159 A.

[0038] The present invention, in particular, provides a longer lifespan for heavily loaded filling chambers and, therefore, a longer lifespan for the corresponding pressure casting machine, and includes the use of tungsten or tungsten alloys for coating (fully or partially) the coated filling chamber or filling chamber insert member, a method for coating these components, a suitably configured pressure casting machine, and the filling chamber or filling chamber insert member. These descriptions generally apply to metal substrates coated according to the present invention, in accordance with their respective meanings.

[0039] In relation to this, the following can be pointed out:

[0040] W / W alloys are less brittle and less susceptible to oxidation compared to molybdenum (Mo) or molybdenum alloys. The preferred thermal spraying method according to the present invention not only protects the insert members but also protects the entire filling chamber.

[0041] The material hardens significantly when sprayed, achieving not only improvements in dissolution (or leaching) by the liquid molten material, but also improvements in mechanical wear. Thus, the hardness of tungsten or a typical tungsten alloy increases from, for example, 250-300 / 400 HV to over 800 HV (e.g., 900 HV) for a single sprayed layer (HV is Vickers hardness). Such hardening (increase in hardness) does not occur in conventionally used iron alloys or nickel alloys, for example. This method using thermal spraying also allows for the simple repair of worn insert members in filling chambers. In this case, it is not necessary that these members were originally coated.

[0042] Furthermore, the following embodiments and usage patterns have been discovered, and these are also included in the present invention.

[0043] In addition to heat spraying, welding or overlay welding of W / W alloy to the substrate to be protected also results in improvements to the thermal, chemical, and mechanical properties of its (coated) surface. The hardness of overlay-welded W / W alloy is similarly significantly improved compared to the standard value, but generally does not reach the values ​​achievable by heat spraying alone. Overlay welding is performed using conventional welding methods such as WIG welding, MIG welding, and MAG welding.

[0044] Thermal spraying or build-up welding of a substrate surface—as described for W / W alloys—results in a significant improvement in the thermal, chemical, and mechanical properties (hardness) of molybdenum or molybdenum alloys. Accordingly, coating of a metal substrate surface by thermal spraying or build-up welding of Mo / Mo alloys is also included in the present invention for the purposes of this invention, as described, for example, in EP 3 184 203 B1 (see paragraphs

[0009] to

[0012] ), which is incorporated herein by reference for disclosure purposes.

[0045] Finally, the application of W / W alloy or Mo / Mo alloy according to the present invention is still preferred for W / W alloy, but is not limited to coating the inner surface of the filling chamber and filling chamber insert members of a pressure (die-casting) machine, but relates to all wear-prone areas in the casting of aluminum, zinc, copper and corresponding alloys, for example. Accordingly, the use of coatings applied according to the present invention includes all parts subjected to load during the casting process, and its use includes all conceivable further wear countermeasures, such as coatings for forming tools, camshafts, shunts (Weichen), pistons and comparable application areas for aluminum, copper and steel. These are examples of wear-prone metal substrates in the sense of the present invention.

[0046] [Explanation of Symbols]

[0047] 1. Cathode (tungsten electrode) 2. Shielding gas (argon / argon-hydrogen) 3. Shielding gas nozzle 4. Arc (Plasma consisting of shielding gas Ar / ArH2) 5. Atomizing (fine-forming) gas (N2 or air) 6. Gas nozzle for atomizing gas 7. Spray (thermal spray) wire 8. Sprayed (including atomizing gas and shielding gas) spray wire

Claims

1. 1. A method for coating a surface of a metal substrate, comprising: applying tungsten or a molybdenum-free tungsten alloy to the surface of the metal substrate by arc spraying; the arc spraying is a single wire method; The metal substrate is the inner surface of a filling chamber or a filling chamber insert of a pressure casting machine, or the surface of a molding tool, a piston, a camshaft, or a switch. A method characterized by:

2. 10. The method of claim 1, Air is used as the atomizing gas A method characterized by:

3. 3. The method according to claim 1 or 2, The method is characterized in that the tungsten alloy is an alloy containing more than 50% by mass of tungsten.

4. The method according to any one of claims 1 to 3, The tungsten alloy is a WNiFe alloy containing more than 50% by mass of tungsten. A method characterized by:

5. A method for manufacturing a pressure casting machine, the pressure casting machine having a fill chamber or a fill chamber insert; the surface of the filling chamber or the filling chamber insert is completely or partially coated by arc spraying using a tungsten or molybdenum-free tungsten alloy as the spray material; The arc spraying is a single wire method. A manufacturing method characterized by:

6. The manufacturing method according to claim 5, Air is used as the atomizing gas A manufacturing method characterized by:

7. 7. The method according to claim 5 or 6, The manufacturing method is characterized in that the tungsten alloy is an alloy containing more than 50 mass% of tungsten.

8. In the manufacturing method according to any one of claims 5 to 7, The tungsten alloy is a WNiFe alloy containing more than 50% by mass of tungsten. A manufacturing method characterized by:

9. The manufacturing method according to claim 5, The pressure casting machine is an aluminum pressure casting machine. A manufacturing method characterized by:

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