KR20220020254A - Coated wear-resistant metal substrate and manufacturing method thereof - Google Patents

Abstract

The use of tungsten, molybdenum, tungsten or molybdenum alloys to coat metal substrates using the single wire arc blasting method results in coatings characterized particularly by increased Vickers hardness (VH).

Description

Coated wear-resistant metal substrate and manufacturing method thereof

FIELD OF THE INVENTION The present invention relates to a coated metal substrate susceptible to wear, and a method for manufacturing the same. In particular, the present invention relates to a modified filling chamber for a pressure die casting machine.

The inner surface of the filling chamber of a pressure die casting machine is most susceptible to wear in the feed port area. Since, for example, a hot casting material, such as liquid aluminum, is fed mechanically through a feed port, the material always strikes the same location on the inner surface of the filling chamber below the feed port. After prolonged use of the filling chamber, leaching may occur in the area below the filling port, as a result of which the sliding movement of the pressure piston in the chamber is impeded and the pressure piston experiences greater wear and tear. Moreover, in the case of vacuum pressure die casting, it becomes more difficult to reliably create the required vacuum. For example, the German patent specification DE 42 29 338 C2 discloses a filling chamber consisting of a jacket element with a removable cylindrical insert. wherein the insert extends axially from the outer end of the filling chamber down the feed port, at the inner end of the insert, the peripheral surface is brought into contact with the inner wall of the filling chamber in a narrow annular region, while the outer end of the insert is in contact with the filling chamber Guided coaxially with respect to the filling chamber by a central ring that engages between the outer periphery and inner wall of the In this way, a filling chamber has already been created for a pressure die casting machine in which the main wear area is directly replaceable in the pressure die casting machine. However, a longer service life would be desirable for such inserts.

Furthermore, the German patent specification DE 102 05 246 B4 discloses a filling chamber for a pressure die-casting machine having a supply port for a liquid casting material, wherein cooling means are provided in the supply opening and in the filling chamber wall in the half-heat area. The cooling means comprises a disk which can be inserted into the filling chamber wall from the outside and is provided with at least one guide channel for the coolant. Among other things, this measure is intended to prolong the service life of the filling chamber insert.

European patent application EP 3 184 203 A1 likewise discloses a cylindrical inner surface serving as a sliding surface for the pressure piston, having a supply port for a liquid casting material and a removable cylindrical insert in which the pressure piston slides along the inner surface, the filling A filling chamber for a pressure die casting machine provided with a radial opening in the jacket filling connected to the supply port of the chamber is disclosed. wherein the inner surface of the removable insert is at least partially composed of molybdenum or a molybdenum alloy. The removable insert is made of a metal sheath (steel) and an inner bushing made of molybdenum or a molybdenum alloy (Mo/Mo-alloy).

In the cases mentioned - where a cylindrical insert is used to protect the feed port or filling chamber and can be replaced with a new insert when wear and tear occurs - in most cases of wear and tear of the sliding surface of the normally abutting pressure piston Relatively quick recovery is possible.

International patent application WO 00/10752 A1 relates to a casting tool for cast molded parts made of non-ferrous metals (eg made of Al or Mg). Here, the casting molds are made of a heavy metal alloy (eg tungsten alloy), or their contact surfaces facing the molded part are coated in a corresponding manner. For this purpose, heavy metal alloys are used in the form of sintered elements.

US patent application 2017/0266719 A1 discloses a die casting system and a corresponding casting method. Here, certain system components are provided with a coating that chemically reacts with the metal to be cast to a much lesser extent than the iron alloys used in the prior art (such as, for example, Al, Cu, Ti and alloys thereof).

However, it is still a goal to extend the replacement interval of the mentioned inserts, generally speaking, the service life of the pressure die casting machine or the most wear-prone parts, i.e. the filling chamber, in order to realize the casting process as efficiently as possible without major interruptions. am. In general, there is also an object to make the surface coatings on metal substrates susceptible to wear mechanically and chemically more stable and therefore more wear-resistant.

This object is achieved according to the invention in that the inner surface of the filling chamber or of the insert according to the invention for the filling chamber is wholly or partly coated with tungsten or a tungsten alloy. This also generally applies to metal substrates that are prone to wear.

It is known that the greatest wear and tear in the filling chamber occurs in the filling area. Thus, for example, in the case of aluminum pressure die casting, an aluminum alloy with a low iron content attacks the steel of the filling chamber or of the installed replaceable bushings, causing leaching, especially in this area. For this disadvantage, the inner surface of the filling chamber, which is usually made of steel, is preferably provided entirely, at least in the filling area, with tungsten or a tungsten alloy. The invention likewise comprises lining the inner surface of an insert for a filling chamber, preferably made with tungsten or a tungsten alloy from steel, which can in turn be carried out in whole or in part.

Accordingly, the present invention comprises a filling chamber for a pressure die casting machine in which the cylindrical inner surface serves as a sliding surface for the pressure piston and has a supply port for a liquid casting material such as aluminum, for example in the case of an aluminum pressure die casting machine. do. In a preferred embodiment, the filling chamber has an insert, preferably made of steel, provided with an opening in the circumferential surface connected to the feed port of the filling chamber. Here, the inner surface of the filling chamber or the inner surface of the aforementioned insert is provided or coated with molybdenum or a molybdenum alloy in whole or in part, preferably in the filling region. The insert is about one quarter long and about half the wall thickness of the filling chamber.

The use of tungsten or tungsten alloys for the aforementioned uses is likewise encompassed by the present invention.

In contrast to the insert described in European patent application EP 3 184 203 A1, the insert according to the invention is not a replaceable bushing in the form of a sleeve system arranged so that the molybdenum insert fits precisely into an outer sleeve made of steel, but rather generally The inner surface of the insert according to the invention made of steel is coated wholly or partially with tungsten or a tungsten alloy.

Except for the essential differences in terms of durability of the insert and the type of coating, the filling chamber according to the invention corresponds to the filling chamber of European patent application EP 3 184 203 A1. In this context, explicit reference is made to the filling chamber shown in FIG. 1 and its description, for example in paragraph [0029], which may therefore serve as a description of the filling chamber according to the present invention.

Tungsten or a tungsten alloy serves as a coating material for the inner surface of the filling chamber or insert according to the invention, whereby the inner surface of the filling chamber and the insert is preferably entirely coated. The alloys may be binary, ternary or quaternary alloys or alloys with additional (metal) components. Examples thereof are preferably WNiFe alloys comprising more than 50% by weight of tungsten (W) or WMoNiFe alloys in which the sum of tungsten and molybdenum is more than 50% by weight of the finished alloy.

A particularly suitable alloy comprises more than 50% by weight of tungsten. Particularly suitable forms for tungsten and tungsten alloys are wire and powder forms. Subsequent production uses basically powder metallurgy methods known to the person skilled in the art. Moreover, tungsten and corresponding tungsten alloys are available, inter alia, on the Internet from various manufacturers and metal suppliers.

The descriptions given above for preferred coating or coating materials also apply to the coating of metallic substrates in general.

In addition to the selection of suitable coating materials for producing chemically, thermally and mechanically stable coatings for filling chambers or metal substrates, it has been found that the coating method is equally important. In this context, the coefficients of linear thermal expansion of tungsten (α = 4.5 * 10 ^-6 1/K at 20 °C) and steel (α = 11 - 13 * 10 ^-6 1/K at 20 °C) are significantly different from each other, It should be borne in mind that this makes it quite difficult to apply thermally and/or mechanically stable tungsten to steel substrates.

The method of surface coating of thermal spray has proven particularly suitable for the purpose according to the invention. In an embodiment according to the invention, this method generally results in a very significant hardening of the infused layer of >800 HV Vickers hardness, whereas, for example, a tungsten alloy would otherwise only have a hardness of 280 HV to 400 HV. In addition to significant improvements in chemical/thermal and mechanical stability, surface coatings applied by thermal spray also exhibit good solvent resistance to liquid aluminum, making them desirable and particularly suitable for use in aluminum pressure die casting systems.

Thermal spraying methods include:

arc blast method

Wire flame spraying method (or using rod)

Powder flame spraying method

High-speed injection method / High-speed flame injection method (HVOF: high-speed oxygen fuel)

laser blast

Low temperature spray method

explosion spray

plasma spray

PTA (plasma transfer arc)

Through the choice of the spraying method as coating technology, hardness values of the coatings which are very advantageous for the application are achieved, these values are in turn decisive for achieving a significant increase in the service life of the filling chambers, inserts and metal substrates coated in this way .

All these methods can basically be used for the purpose of the present invention.

Thus, in addition to tungsten-based materials (fillers (spray fillers)), the present invention likewise relates to a coating method to which the materials are applied. The method of thermal spraying is a surface coating method. According to a standardized definition (DIN EN 657), the filler, the so-called blast filler, is melted inside or outside the blasting torch, then accelerated in a gas stream in the form of blasting particles and cast on the surface of the component to be coated. Here, the component surface does not melt (as opposed to the cladding) and is only subjected to slight thermal stress. When the sprayed particles strike the component surface, to some degree depending on the process and material, they are flattened, mainly due to mechanical clamping, adhesion, and layering as the sprayed coating is layered. . The quality characteristics of the sprayed coating are low porosity, good adhesion to components, the absence of cracks and a homogeneous microstructure. The coating properties achieved are substantially affected by the temperature and velocity of the sprayed particles at the time of striking the surface to be coated. The surface condition (purity, activation, temperature) likewise influences quality characteristics such as adhesive strength.

Electric arc (arc injection), plasma jet (plasma injection), fuel oxygen flame injection or fuel oxygen high-speed flame injection (conventional and high-speed flame injection), high-speed preheat gas (cold gas injection) and laser beam (laser beam injection) It acts as an energy carrier for melting the filler material. According to DIN standard EN 657, spraying methods are classified according to this criterion.

When a tungsten/tungsten alloy is used in wire form, the preferred method is wire arc spraying. Plasma spraying is particularly suitable for finely divided tungsten/tungsten alloys.

ftsbereich (Business Unit) Linde Gas, Unterschleissheim, Germany를 참조하라. The methods of thermal spraying described above are known in the art and therefore also known to those skilled in the art; For example, http://www.gts-ev.de/html_d/ts-info.htm or the information brochure LINSPRAY® - "Gase und Know-how beim thermischen Spritzen"("Gases and Know-how for Thermal Spraying" ), Linde AG, Gesch

See ftsbereich (Business Unit) Linde Gas, Unterschleissheim, Germany.

For the purposes of the present invention, it has been found that specific representative coating methods which are generally known in the prior art and which will be suitably modified to achieve the objects according to the invention lead to surprising results in terms of quality, wherein in particular the achievement of the applied coatings The hardness obtained is noted.

Basically, a method of thermal spraying and also a method of welding to coating materials are preferred according to the invention. Here, the thermal spray method provides a broad application spectrum of a number of materials to be applied.

In particular, among the thermal spraying methods, arc spraying is preferred according to the invention and is used in the so-called two-wire method and particularly preferably in the so-called single-wire method. A preferred coating material is tungsten or a tungsten alloy.

In the following, without limiting the subject matter of the invention in this process, a preferred coating or spraying method will be described in more detail by way of example with reference to FIG. 1 . Here, Fig. 1 schematically shows the jetting head of a single wire device. Here, the electrode 4 (tungsten electrode) is provided rotatably around the wire.

In the two-wire method shown in FIG. 1 , the arc is ignited between two wires, and in the single wire method, the arc is ignited between the tungsten electrode 1 and the spray wire 7 . Here, the emitted electrons, ie the arc, first pass through a shielding gas 2 , in this case argon or an argon-hydrogen mixture, then consisting of a shielding gas 2 and an atomizing gas 5 consisting of N ₂ or air A gas mixture is passed, whereby the gas is ionized into a plasma (4) and heated to about 15,000°C. The plasma 4 consists of a gas mixture consisting of an atomizing gas 3 [literally, (5)] together with a shielding gas 1 , ie argon or argon/hydrogen (Ar/ArH ₂ ). Exclusively the shielding gas 2 is kept flowing around the electrode 1 to shield it. In this process, the arc 4 melts the spray wire 7 before the atomizing gas 5 atomizes the molten droplets of the spray wire 7 at a very high pressure or at a very high velocity. The atomizing spray wire with atomizing gas and shielding gas is designated with the reference number (8). The atomizing gas stream need not flow annularly around the shielding gas 2 as in the case of plasma welding, but rather can flow through the nozzle. In this case, the atomizing gas nozzle 6 shown in FIG. 1 will be removed and replaced with a separate nozzle.

The spatial separation between the electrode 1 and the wire 7 allowing the electrode 1 to rotate around the wire 7 allows the use of inexpensive nitrogen gas instead of an inert gas. In this way, a hardness increase of up to about 600 HV can be achieved compared to about 300 HV for the starting material. It has been found that by using air as atomizing gas 5 a further and substantial hardness increase up to about 900 HV can be achieved. Preferably a current in the range of 60 A to 159 A is used for single wire jetting with a wire made of tungsten or a tungsten alloy.

The invention is interpreted in particular for a longer service life for filling chambers subjected to higher stresses and also to a correspondingly longer service life for pressure die casting systems, the invention relates to coated filling chambers or corresponding inserts, such a configuration methods for coating elements, correspondingly mounted pressure die casting systems and the use of tungsten or tungsten alloys to coat (in whole or in part) a filling chamber or filling chamber insert. These statements apply correspondingly with respect to metal substrates coated according to the invention.

In this context, it should be pointed out:

Tungsten/tungsten alloys are less brittle and less susceptible to oxidation than molybdenum (Mo) or molybdenum alloys. The thermal spray preferred according to the invention makes it possible to protect not only the insert but also the entire filling chamber.

Due to the spraying, the material hardens considerably, and as a result there is an improvement in the dissolution aspect caused by liquid melting, as well as an improvement in mechanical wear and tear at the same time. Thus, the hardness of tungsten or a typical tungsten alloy increases from, for example, 250-300 HV to more than 800 HV (eg 900 HV) for sprayed coatings (HV = Vickers hardness). This hardening is significant and does not occur if, for example, iron or nickel alloys are used otherwise. The thermal spray method also allows for very simple repair of worn inserts in the filling chamber. In this context, they do not need to be provided with an original coating.

Furthermore, the following embodiments and application forms which are likewise encompassed by the present invention have been found.

In addition to thermal spraying, welding a tungsten/tungsten alloy to the substrate to be protected also improves the thermal, chemical and mechanical properties of the (coated) surface. The hardness of the welded tungsten/tungsten alloy is likewise improved significantly compared to standard values, but generally does not reach values achievable by thermal spraying. Welding is performed with conventional welding processes such as TIG, MIG and MAG welding.

Thermal spraying or welding to the substrate surface as described for tungsten/tungsten alloys also achieves significant improvements in thermal, chemical and mechanical properties (hardness) in the case of molybdenum or molybdenum alloys. For this reason, thermal spraying of molybdenum or molybdenum alloys of the type described, for example, in European patent application EP 3 184 203 A1 (see paragraphs [0009] to [0012]) and expressly incorporated herein by reference for the purpose of disclosure, or The coating of the surface of a metal substrate by welding is likewise included in the invention for the purpose according to the invention.

Finally, the application according to the invention of a tungsten/tungsten alloy or molybdenum or molybdenum alloy is not limited to the coating of the inner surfaces of the filling chambers and filling chamber inserts of pressure die casting machines (where tungsten/tungsten alloys are preferred), For example, it relates to all areas prone to wear and tear during casting of aluminum, zinc and copper and their alloys. Accordingly, the use of the coating applied according to the invention encompasses all components claimed during the casting process and their use likewise includes, for example, forming tools for aluminum, copper and steel, camshafts, shunts, It covers all other wear and tear applications conceivable such as coatings for pistons and similar applications. As presented herein, these are examples of metal substrates that are susceptible to wear.

1 cathode (tungsten electrode)
2 Shielding gas argon or argon/hydrogen
3 shielding gas nozzle
4 arc (plasma composed of shielding gas Ar/ArH ₂ )
5 atomizing gas (N ₂ or air)
6 atomizing gas nozzle
7 jetting wire
8 atomizing injection wire (with atomizing gas and shielding gas)

Claims (15)

Use of tungsten, molybdenum, tungsten alloy or molybdenum alloy for coating a metal substrate susceptible to wear, wherein the coating is applied to the substrate surface by thermal spraying or welding. The use of tungsten or a tungsten alloy for coating a substrate surface by thermal spraying according to claim 1 . Use according to claim 1 or 2, characterized in that the metal substrate susceptible to wear refers to the inner surface of the filling chamber or filling chamber insert of a pressure die casting machine. Use according to any one of the preceding claims, characterized in that the tungsten alloy is an alloy comprising more than 50% by weight of tungsten. 5. Use according to any one of the preceding claims, characterized in that the tungsten alloy is a WNiFe alloy comprising more than 50% by weight of tungsten or a WMoNiFe alloy in which the sum of the tungsten and molybdenum portions is in an amount greater than 50% by weight. 4. TZM according to any one of the preceding claims, wherein the molybdenum alloy is composed of 0.5% by weight titanium, 0.08% by weight zirconium, 0.01% to 0.04% by weight carbon and the balance molybdenum making up 100% by weight. Use characterized in that it is molybdenum. Use according to any one of the preceding claims, characterized in that the metal substrate susceptible to wear comprises areas of the metal casting system susceptible to wear and also the surfaces of forming tools, pistons, camshafts or shunts. . A metal substrate whose surface is coated wholly or partially with tungsten, molybdenum, tungsten alloy or molybdenum alloy by thermal spraying or welding. 9. The metal substrate of claim 8, wherein the coated surface is an interior surface of a filling chamber or filling chamber insert of a pressure die casting machine. A pressure die casting machine having the filling chamber or filling chamber insert according to claim 8 . The pressure die casting machine according to claim 10, characterized in that it is an aluminum pressure die casting machine. A method for surface coating a metal substrate, characterized in that tungsten, molybdenum, or a tungsten alloy or molybdenum alloy is applied to the surface by arc spraying. 13. The method of claim 12, wherein the coating is applied by arc spraying. 14. The method of claim 13, wherein the arc spraying is a single wire method. 15. Process according to claim 13 or 14, characterized in that air is used as atomizing gas.

Images