Patent Application
20240278324
The present subject matter relates to advanced materials and, more particularly, to the production of metal powders for diverse applications, such as additive manufacturing for the aerospace and medical industries.
Plasma atomization typically uses a wire as a feedstock, and a source of plasma (a.k.a. plasma torch) as atomizing agent to simultaneously melt and break-up the particles. Using a wire provides the stability required so that the narrow plasma jets are aiming properly at the wire, since the plasma jets have to melt the wire and atomize it in a single step. As best known, this technology currently produces the finest, most spherical and densest powders on the market. In other words, the yield of powders produced in the 0-106 micron range is very high, sphericity is near perfect, and gas entrapment is minimized.
However, this technology has the main disadvantage of having a relatively low production rate in comparison to water and gas atomization due to the fact that plasma atomization is a very energetically inefficient process. Reported production rates for plasma atomization are between 0.6 and 13 kg/h for Ti-6Al-4V. However, it is realistic to assume that operating around the upper bound will lead to a coarser particle size distribution. For example, U.S. Pat. No. 5,707,419, which is entitled “Method of Production of Metal and Ceramic Powders by Plasma Atomization” and issued in the names of Tsantrizos et al. on Jan. 13, 1998, reports a feed rate of 14.7 g/min or 0.882 kg/h for titanium, while U.S. Patent Application Publication No. 2017/0326649-A1, which is entitled “Process and Apparatus for Producing Powder Particles by Atomization of a Feed Material in the Form of an Elongated Member” and which was published on Nov. 16, 2017 with Boulos et al. as inventors, has reported a feed rate of 1.7 kg/h for stainless steel.
All three current plasma atomization technologies use either a single centrally fed torch [see reference 4], or three torches aiming at one wire at the center [see references 1, 2 and 3]. In the case of the three torches technology, heat transferred from the plasma plumes to the wire is very low, and in the order of magnitude of 0.4%. The low heat transfer efficiency implies the need for a large amount of plasma gas to maintain a certain metal feed rate, and this imposes a lower limit to the gas-to-metal ratio, a standard process efficiency metric in atomization. Also, using three torches means that many electrodes erode over time, which can be a source of contamination and increase the operating costs. In the case of the centrally fed torch, an inductively coupled plasma torch is used, for which the power supplies are difficult to obtain on the market.
Wire arc spray is a mature and reliable technology that is used in the field of thermal spray to apply coating onto surfaces. It essentially consists of passing a high current through one or two wires and having an electrical arc between the two wires, or between the single wire and an electrode. Quality wire arc systems can run with near 100% duty cycle at very high throughput (˜20 to 50 kg/h). Moreover, this technology is highly energy efficient, since the arc contacts directly the wire. However, the purpose of this technology is to produce coatings and not to produce powders. Since this technology uses a cold gas to atomize the spray, it produces very irregular and angular shapes, which Is not desirable for most applications.
It would therefore be desirable to provide an apparatus and method for producing metallic powders from one or two wires at a significant production rate while maintaining the quality provided by plasma atomization, namely fine, spherical and fully dense powders.
It would thus be desirable to provide a novel apparatus and method for producing metallic powders at significant rates from one or two wires.
The embodiments described herein provide in one aspect a plasma atomization process comprising:
Also, the embodiment described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and a wire adapted to be fed in the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc Is adapted to be formed between the wire, which acts as a cathode, and an electrode.
Furthermore, the embodiments described herein provide in another aspect a plasma atomization process comprising:
Furthermore, the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and a wire adapted to be fed in the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode.
Furthermore, the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and at least one wire adapted to be fed in the apparatus, the plasma torch being adapted to atomize the molten wire into particles, and a cooling chamber adapted to solidify the particles into powders, and wherein the wire is adapted to serve as a cathode in the plasma torch.
Furthermore, the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and at least a pair of wires adapted to be fed in the apparatus, the plasma torch being adapted to atomize the molten wires into particles, wherein one of the wires is adapted to serve as an anode, whereas the other wire is adapted to serve as a cathode.
Furthermore, the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and a wire adapted to be fed in the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode.
Furthermore, the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and at least one wire adapted to be fed in the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein the apparatus is adapted to be cooled by a gas thereby heating up the gas, with the so heated gas being adapted to be used as the plasma gas.
Furthermore, the embodiments described herein provide in another aspect a plasma atomization process comprising:
Furthermore, the embodiments described herein provide in another aspect a plasma atomization process comprising:
For a better understanding of the embodiments described herein and to show more clearly how they may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, which show at least one exemplary embodiment and in which:
The present approach disclosed herein provides methods and apparatuses for producing metallic powders, by combining features of the above-described plasma atomization and wire arc spray technologies, including by using some of the concepts of the wire arc spray technology and adapting it to make it suitable for the production of high purity spherical powders. More specifically, the gas jet is replaced by a source of plasma and the molten wire is atomized into a cooling chamber as seen in atomization processes.
One key consideration is powder quality. Wire arc was not developed for high quality powder production and must therefore be adapted and tuned towards powder quality. The current disclosure includes a control strategy that improves stability of the melting process, which will be described in more details further below.
A source of plasma (such as one or multiple plasma torches or an electrical arc), delivers a plasma stream that can be accelerated to supersonic velocity prior or after hitting the molten stream with high momentum.
In the current embodiments, the supersonic plasma jet source is produced via an arc plasma torch because it is widely available. However, many other ways could be used for achieving the same supersonic plasma jet. For example, any thermal plasma sources, such as inductively-coupled and microwave plasma sources, could be used as well.
The details of the main embodiment will now be described.
The benefits of using this embodiment over known technology (Ref. 2) are presented in Table 1. It shows a clear advantage in favor of using the current subject matter as opposed to the technology of Ref. 2.
The recommended operating conditions of the main embodiment are disclosed in Table 2 for two materials, namely Ti64 grade 23 and Zirconium.
The performance of two products generated via the main embodiment are disclosed in Table 3, the two products being TA-015-EK-01 and ZH-006-FQ-01, which correspond to Ti64 20-63 μm and Zr 20-120 μm, respectively.
A ceramic tip 510 provides the electrical Insulation of a water-cooled contactor 514 from the body of the reactor through a gas sheath nozzle 513 and of the torch's supersonic nozzle 505. The intense heat emitted by the plasma torch 501 and the transferred arc requires the contactors to be water cooled while the contact tip Itself is a replaceable consumable. As such, water enters at 503 the contactor's manifold 515 at the rear and is directed towards the tip where it is returned upwards again and out through exit 504. Electrical power is provided to the transferred arc system via the manifolds through a lug mount 511.
In the current embodiments, the wires 502 (
To ensure stability of the wire arc system for atomization, the system needs to control 2 out of 3 parameters, namely voltage, current and feed speed. These three parameters need to reach a steady state in equilibrium to be considered in continuous operation. In steady state, the distance between the wire, the length of the arc and the power become constant. To reach this steady state, several configurations can be employed, such as:
Fixed wire speed, current/voltage-controlled hybrid power supply was found to be most suitable for the present application.
Using a Servo motor, it is possible to have very precise and constant feed speeds.
Using two power supplies in parallel, one in voltage-controlled mode and another one in current-controlled mode, is the key to achieve a stable configuration. Since the two power supplies are in parallel, the voltage-controlled one will force the same voltage to both power supplies to be fixed. This removes another variable. To add another layer of stability, the other power supply is set to current control mode, with a relatively high current setting (around ⅔ of the total current required), which helps to create a current baseline.
The only variable in the process is a portion of the total current, which needs to fluctuate to allow the other parameters to remain constant (degree of freedom). Therefore, the voltage-controlled power supply provides an additional current that is variable to complement what is missing to the current already provided by the current-controlled power supply to melt the proper amount of metal, so the system remains in steady state.
For example, assuming 20 kW are required to melt a certain metal at a certain feed speed, and assuming that this feed speed remains constant, if the voltage was fixed at 30 V by the voltage-controlled power supply, a total of 667 A must be supplied by the power supplies. If the current-controlled power supply is set at 400 A, the voltage-controlled one would fluctuate around 267 A with little ripples. This remaining fluctuation is required to keep the system in steady state by compensating against all other sources of variability of the process, such as wire diameter variation, argon flow rate fluctuation, arc length variability, arc restrike pattern, mechanical vibration of the wire, wire feed speed micro-fluctuations, etc.
Such stable operation, as shown in
Although the current control herein presented is mentioned and tested specifically for the main embodiment, the same control strategy would apply to other embodiments presented as well.
In the second example shown in
In the third example shown in
The embodiments described herein provide in one aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and one or two wires adapted to be fed in the apparatus, the plasma torch being adapted to atomize the molten wire into particles, and a cooling chamber adapted to solidify the particles into powders, and wherein the wire is adapted to serve as a cathode in the plasma torch.
Also, the embodiment described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and a pair of wires adapted to be fed in the apparatus, the plasma torch being adapted to atomize the molten wires into particles, wherein one of the wires is adapted to serve as an anode, whereas the other wire Is adapted to serve as a cathode.
Moreover, an embodiment includes an electrical control strategy that allows for the smooth and stable operation of the said embodiment.
Furthermore, the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and a wire adapted to be fed into the apparatus, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode of the torch.
Finally, the embodiments described herein provide in another aspect an apparatus for producing metallic powders from wire feedstock, comprising a plasma torch and at least one wire adapted to be centrally fed inside the plasma torch, the plasma torch being adapted to atomize the molten wire into particles, wherein an arc is adapted to be formed between the wire, which acts as a cathode, and an electrode within the torch.
While the above description provides examples of the embodiments, it will be appreciated that some features and/or functions of the described embodiments are susceptible to modification without departing from the spirit and principles of operation of the described embodiments. Accordingly, what has been described above has been intended to be illustrative of the embodiments and non-limiting, and it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the embodiments as defined in the claims appended hereto.
This Application claims priority on U.S. Provisional Application No. 62/681,623, now pending, filed on Jun. 6, 2018, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62681623 | Jun 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16972949 | Dec 2020 | US |
| Child | 18372685 | US |
