WO2011054113A1

WO2011054113A1 - Methods and apparatuses for preparing spheroidal powders

Info

Publication number: WO2011054113A1
Application number: PCT/CA2010/001814
Authority: WO
Inventors: Michel Drouet
Original assignee: Ap&C Advanced Powders & Coatings Inc.
Priority date: 2009-11-05
Filing date: 2010-11-05
Publication date: 2011-05-12

Abstract

A method for producing a spheroidal powder substantially free of contaminants by plasma atomization comprising preheating a material in the form of a wire or rod to a temperature below the melting point of the material prior to melting and atomization of the material. The method improves the productivity of the spheroidal powder. The apparatus comprises a heating means for preheating the material, a melting and atomization means including electric arc and plasma gas jet or hot gas jet, and a separating means for minimizing the contact between the atomized powder and contaminants generated in the process.

Description

METHODS AND APPARATUSES FOR PREPARING SPHEROIDAL

POWDERS

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to the field of production of spheroidal powders such as metal (or alloy) spheroidal powders or ceramic spheroidal powders. More particularly, it relates to methods and apparatuses for preparing metal, alloy and ceramic powders by means of an atomization process.

BACKGROUND OF THE DISCLOSURE

[0002] Various solutions have been proposed so far concerning methods and apparatuses for preparing metal powders via a plasma atomization process. However, several problems have been encountered with those proposed solutions. For example, some of the proposed methods and apparatuses do not permit to obtain spheroidal powders, which are substantially free of satellites. Satellites are known to be very fine particles such as metal dust particles that are produced during atomization of the metals and which agglomerate to the desired spheroidal metal powders. These satellites considerably affect some of the characteristics of the desired metal powders such as fluidity of the powders.

[0003] Moreover certain proposed solutions still involve high productions costs and low production rates.

SUMMARY OF THE DISCLOSURE

[0004] According to one aspect, there is provided a method for preparing a spheroidal powder comprising: feeding an apparatus effective for atomizing a material chosen from metals, alloys and ceramics, the apparatus being fed with the material that is preheated by an electrical current; submitting an end portion of the material to a heat source and to at least one electric arc generated between the end portion and at least one electrode, so as to melt the material contained into the end portion;

atomizing the material contained into the end portion with atomization means; and

cooling the atomized material in order to cause spheroidization of the atomized material and obtain the spheroidal powder.

[0005] According to another aspect, there is provided a method for preparing a spheroidal powder comprising:

feeding an atomization zone of an apparatus effective for atomizing a material chosen from metals, alloys and ceramics with a wire or rod preheated by an electrical current, the wire or rod comprising the material;

submitting an end portion of the wire or rod disposed in the atomization zone to a heat source and to at least one electric arc generated between the end portion of the wire or rod and at least one electrode disposed adjacently thereof, so as to melt the material contained into the end portion;

[0006] According to another aspect, there is provided a method for preparing a spheroidal powder comprising:

continuously feeding at least one plasma jet of at least one plasma torch with a preheated material chosen from metals, alloys and ceramics so as to cause atomization of the material, the material being preheated in such a manner that, for a given portion of the material, its temperature increases as it approaches from the at least one plasma jet and prior to contact the at least one plasma jet or its atomization zone, the temperature of the portion is below the melting point of the material in order to substantially minimize contamination of the material with at least contaminant generated when the method is carried out; and

[0007] According to another aspect there is provided a method for preparing a spheroidal powder comprising: contacting a material chosen from metals, alloys and ceramics with at least one plasma jet of at least one plasma torch adapted to atomize the material,

cooling the atomized material in order to cause spheroidization of the atomized material and obtain the spheroidal powder, wherein the material comprises a plurality of portions disposed one after the other, each of the portions being submitted to the at least one plasma jet one after the other, when a given portion is substantially completely atomized, the subsequent portion is then submitted to the at least one plasma jet, and wherein each of the portions, prior to contact the at least one plasma jet or its atomization zone, is preheated at a temperature below the melting point of the material.

[0008] According to another aspect there is provided in a continuous method for producing a spheroidal powder comprising atomizing a material by means of at least one plasma torch, the improvement wherein the material is heated at a temperature below the melting point of the material before contacting the plasma jet of the at least one plasma torch or its atomization zone. [0009] According to another aspect there is provided in a continuous method for producing a spheroidal powder comprising atomizing a material by means of at least two plasma torches, the improvement wherein the material is heated in such a manner that melting of the material is reached at an apex generated by the jets of the at least two torches whereat there is substantially no contact between the material and other particles generated during the process.

[0010] According to another aspect, there is provided an apparatus for producing a spheroidal powder comprising:

an electric power supply for preheating a material chosen from metals and alloys by means of an electric current;

a heat source for heating the material and at least one electrode adapted to generate at least one electric arc with the material to thereby heat the material, the combination of heat provided by the electric power supply, the heat source and the at least one electric arc being effective to melt the material;

a feeder for feeding said apparatus with said material;

atomization means effective for atomizing the molten material; a chamber adapted for receiving and cooling droplets of the atomized material; and

optionally separating means for substantially preventing other particles generated during the preparation of the spheroidal powder or other materials from contacting the material before, during, and after atomization of the material.

[0011] According to another aspect there is provided an apparatus for producing a spheroidal powder comprising:

at least one plasma torch adapted to produce a plasma jet sufficient so as to cause atomization of the material;

a feeder for continuously providing the plasma torch with the material; a chamber adapted for receiving and cooling the droplets of the atomized material; and

separating means for substantially preventing other particles generated during the preparation of the spheroidal powder or other materials from contacting the material before, during, and after atomization of the material.

[0012] It was observed that by using the methods, devices and apparatuses of the present disclosure, it was possible to obtain a powder of higher quality i.e. more uniform, less satellites. For example, it was possible to obtain a powder which is substantially free of satellites. Moreover, it was observed that by using the methods, devices and apparatuses of the present disclosure, it was possible to increase the production rate of powder and thereby to obtain a lower production cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Further features and advantages will become more readily apparent from the following description of various embodiments as illustrated by way of examples in the appended drawings wherein:

[0014] Fig. 1 is a schematic representation of an apparatus for preparing a spheroidal powder according to one example;

[0015] Fig. 2 is a Scanning Electron Miscroscope (SEM) image of a sample of titanium powder (0-45 μιτι) produced with the apparatus of Fig. 1 ;

[0016] Fig. 3 is a schematic representation of an example of apparatus for preparing a spheroidal powder as found in the prior art;

[0017] Fig. 4 is a SEM image of a sample of titanium powder (0-45 pm) produced by an apparatus as shown in Fig. 3; and [0018] Fig. 5 is a schematic representation of a device which permits to heat and melt a conductive material according to another example, this device can be used as a component of an apparatus for preparing a spheroidal powder as represented in Fig. 1.

DETAILED DESCRIPTION OF VARIOUS EXAMPLES

[0019] The following examples represent in a non-limitative manner, various embodiments of the present disclosure.

[0020] The expression "atomization zone" as used herein, when referring to a method, device or an apparatus for preparing a spheroidal powder, refers to a zone in which the material is atomized into droplets of the material. The person skilled in the art will understand that the dimensions of the atomization zone will vary according to various parameters such as temperature of the atomizing means, velocity of the atomizing means, power of the atomizing means, temperature of the material before entering in the atomization zone, nature of the material, dimensions of the material, electrical resistivity of the material etc.

[0021] For example, an atomization zone of the apparatus can be fed with the material.

[0022] For example, the material can be comprised within a wire or rod.

[0023] For example, an end portion of the wire or rod disposed in the atomization zone can be submitted to the heat source and the at least one electrode.

[0024] For example, the at least one electrode can be disposed adjacently to the atomization zone. For example, the at least one electrode can be disposed inside the atomization zone. [0025] For example, the material can comprise at least one metal chosen from titanium, molybdenum, silver, copper, niobium, tantalum, tungsten, rhenium, osmium, iridium, hafnium, vanadium, chromium zirconium, and mixtures thereof. The material can thus be a metal or an alloy. For example, the material can comprise a metal chosen from titanium, molybdenum and silver. For example, the material can comprise titanium.

[0026] For example, the material can be a titanium alloy. For example the material can be an alloy chosen from nitinol and inconel.

[0027] For example, the material can be an alloy comprising at least two metals chosen from titanium, molybdenum, silver, copper, niobium, tantalum, tungsten, rhenium, osmium, iridium, hafnium, vanadium, chromium, zirconium, and mixtures thereof. For example, the material can be an alloy comprising at least two metals chosen from titanium, molybdenum and silver. For example, the material can be an alloy chosen from nitinol and inconel.

[0028] For example, the material can be a metal chosen from titanium, molybdenum, silver, copper, niobium, tantalum, tungsten, rhenium, osmium, iridium, hafnium, vanadium, chromium and zirconium. For example, the material can be titanium, molybdenum or silver. For example, the material can be titanium.

[0029] For example, the material can be a ceramic chosen from boron nitride, silicon nitride, silicon dioxide, aluminum oxide zirconium oxide, and mixtures thereof.

[0030] For example, the heat source can comprise at least one, at least two or at least three plasma jet(s) or a hot gas jet(s). For example, the temperature of the plasma jet(s) can be about 350°C to about 5000°C. [0031] For example, the atomization means can comprise at least one, at least two or at least three fluid jet(s). For example, the fluid can be a hot gas. For example, the temperature of the gas can be about 350°C to about 1200°C.

[0032] For example, the atomization means can comprise at least one, at least two or at least three plasma jet(s).

[0033] For example, the atomization means and the heat source can be the same or different.

[0034] For example, the atomization means and the heat source can be the same and can be at least two or at least three plasma jets. The end portion can contact the at least two plasma jets and the at least two jets can converge into an apex and the end portion can be contacting the at least two jets at the apex.

[0035] For example, there can be at least two electrodes or at least three electrodes.

[0036] For example, at least two electric arcs can be generated between the end portion and at least two electrodes, one electric arc being generated between the end portion and each of the electrodes.

[0037] For example, at least three electric arcs can be generated between the end portion and at least three electrodes, one electric arc being generated between the end portion and each of the electrodes.

[0038] For example, portions of the wire or rod, before contacting the atomization zone, can be progressively preheated from room temperature to a temperature below the melting point of the material. [0039] The wire or rod and the at least one electrode can be connected to a DC electric power supply in such a manner that the wire or rod can act as a cathode and the at least one electrode can act as an anode. Alternatively, the wire or rod and the at least one electrode can be connected to a DC electric power supply in such a manner that the wire or rod can act as an anode and the at least one electrode can act as a cathode.

[0040] For example, preheating the wire or rod can be carried out while feeding the atomization zone.

[0041] The wire or rod can be preheated in such a manner that, for a given portion of the wire or rod, its temperature increases as it approaches from the atomization zone.

[0042] For a given portion of the wire or rod during the preheating, the temperature of the wire or rod can be maintained below the melting point of the material in order to substantially minimize contamination of the material with at least one contaminant generated during preparation of the powder.

[0043] For example, the material can be preheated in such a manner that when the end portion of the wire or rod enters in the atomization zone, its temperature increases and reaches the melting point of the material and then, atomization of the end portion occurs, thereby substantially minimizing contacts between the molten material and the at least one contaminant generated during preparation of the powder.

[0044] For example, the atomized material can be in the form of fine droplets of the material.

[0045] For example, a shielding gas can be injected in order to substantially prevent the droplets from being contaminated by at least one contaminant. [0046] The methods and apparatuses of the present disclosure can further comprise substantially preventing at least one contaminant from contacting the molten material, atomized particles or the obtained spheroidal powder. For example, the methods and apparatuses can comprise continuously sucking or vacuuming at least one contaminant generated so as to substantially minimize contamination of the desired spheroidal powder with at least one contaminant. For example, at least one contaminant can be sucked by means of a vacuum generated by the action of the at least one plasma jet and/or by means of a pump.

[0047] The methods and apparatuses of the present disclosure can further comprise cooling a gas recovered by means of the vacuum.

[0048] The methods and apparatuses of the present disclosure can further comprise filtering the gas recovered by means of the vacuum.

[0049] For example, the gas can be recycled and reused as a shielding gas.

[0050] For example, the at least one contaminant can comprise dust particles generated during the method.

[0051] For example, the spheroidal powder can be a spherical powder.

[0052] For examples, the methods and apparatuses of the present disclosure can be continuous or semi-continuous.

[0053] For example, in a continuous method for producing a spheroidal powder comprising atomizing a material by means of at least one plasma jet, the improvement can comprise that the material is heated at a temperature below the melting point of the material before contacting an atomization zone of the plasma jet.

[0054] For example, in a continuous method for producing a spheroidal powder comprising atomizing a material by means of at least two plasma torches, the improvement can comprise that the material is heated in such a manner that melting of the material is reached at an apex generated by the jets of the at least two torches whereat there is substantially no contact between the material and other particles generated during the method.

[0055] In the methods and apparatuses of the present disclosure, the material can be preheated in such a manner that when a portion of the material enters in the atomization zone of the at least one plasma jet, the temperature of the material reaches the melting point of the material and then, atomization of the portion occurs, thereby substantially minimizing contacts between the molten material and the at least one contaminant generated during the process. For example, the material can contact at least two plasma jets generated by at least two plasma torches, the at least two jets converging into an apex and the material can be contacting the at least two jets at the apex. According to another example, the material can contact at least three plasma jets generated by at least three plasma torches, the at least three plasma jets converging into an apex and the material can be contacting the at least three jets at the apex.

[0056] According to an embodiment, each of the given portions of the material, before contacting the at least one plasma jet, can be progressively preheated, from room temperature to a temperature below the melting point of the material. For example, the material can be preheated by means of an electrical current. The material can be in the form of a wire or a rod.

[0057] According to another embodiment, the atomized material can be in the form of fine droplets of the material. A shielding gas can be injected in order to substantially prevent the droplets from being contaminated by the at least one contaminant.

[0058] For example, the methods and the apparatus of the present disclosure can further comprise substantially preventing the at least one contaminant from contacting the molten material, the atomized particles or the obtained spheroidal powder. The methods and apparatus can also further comprise continuously sucking the at least one contaminant generated during the process so as to substantially minimize contamination of the desired spheroidal powder with the at least one contaminant. The at least one contaminant can be sucked by means of a vacuum generated by the action of the at least one plasma jet and/or by means of a pump. The methods and aspparatus can also further comprise cooling a gas recovered by means of the vacuum and/or filtering the gas recovered by means of the vacuum. The gas can be recycled and reused as a shielding gas.

[0059] In the methods and apparatus of the present disclosure, the at least one contaminant can comprise dust particles generated during the methods or during use of the apparatus. The spheroidal powders can be spherical powders. For example, the spheroidal powders can be at least substantially free of satellites. The portion of material which enters in the atomization zone of the at least one plasma jet is an end portion of the material.

[0060] The apparatus can comprise at least two plasma torches or at least three plasma torches. The separating means can comprise a separator including an aperture, the separator defining at least a portion of a reaction chamber whereat the material atomized by the at least one plasma torch, and a cooling chamber whereat the atomized material is cooled so as to obtain the desired spheroidal powder. The aperture can define a passage between the chambers. The separating means can further comprise means for injecting a shielding gas through the aperture from the reaction chamber to the cooling chamber so as to substantially prevent the other particles or materials from entering into the reaction chamber. The separating means can also further comprise vacuum means for collecting the other particles or materials present in the cooling chamber. For example, the vacuum means can comprise at least two collecting orifices for receiving the other particles or materials. The vacuum means can also comprise a cooler adapted for cooling gases recovered from the cooling chamber and/or a filter adapted for filtering gases recovered from the cooling chamber. The other particles or materials can be dust particles generated during preparation of the powder.

[0061] For example, the methods and apparatuses of the present disclosure can comprise the separating means.

[0062] For example, when using the methods and apparatuses of the present disclosure, portions of a wire or rod comprising the material, before contacting an atomization zone disposed adjacently to the heat source and the at least one electrode, can be progressively preheated, from room temperature to a temperature below the melting point of the material.

[0063] For example, when using the methods and apparatuses of the present disclosure, a wire or rod comprising the material and the at least one electrode can be connected to a DC electric power supply in such a manner that the wire or rod acts as a cathode and the at least one electrode acts as an anode.

[0064] For example, when using the methods and apparatuses of the present disclosure, a wire or rod comprising the material and the at least one electrode can be connected to a DC electric power supply in such a manner that the wire or rod acts as a anode and the at least one electrode acts as an cathode. [0065] For example, the separating means can comprise a separator including an aperture, the separator defining at least a portion of a reaction chamber whereat the material is atomized, and a cooling chamber whereat the atomized material is cooled so as to obtain the desired spheroidal powder, the aperture defining a passage between the chambers.

[0066] For example, the separating means can further comprise means for injecting a shielding gas through the aperture from the reaction chamber to the cooling chamber so as to substantially prevent the other particles or materials from entering into the reaction chamber.

[0067] For example, the separating means can further comprise vacuum means for collecting other particles or materials present in the cooling chamber.

[0068] For example, the vacuum means can comprise at least two collecting orifices for receiving the other materials.

[0069] For example, the vacuum means can comprise a cooler adapted for cooling gases recovered from the cooling chamber.

[0070] For example, the vacuum means can comprise a filter adapted for filtering gases recovered from the cooling chamber.

[0071] In the methods and apparatuses of the present disclosure, the other particles or materials can be dust particles generated during manufacture of the powder.

[0072] In the methods and apparatuses of the present disclosure, the apparatus used for preparing a spheroidal powder can be a plasma atomization apparatus such as an apparatus comprising at least one plasma jet. [0073] Fig. 3 illustrates a plasma atomization apparatus 10 used for an apparatus for preparing a spheroidal powder 18, as known in the prior art, for making powder from a rod or wire 11 , heated, melted and atomized by the plasma jets 12a and 12b of plasma torches 13a and 13b. The atomization produces fines droplets of molten metal 14 which solidify as they travel downwardly to the bottom of the atomization chamber 15 so as to form the powder 18. The high velocity plasma jets induce a reverse gas flow 16, which carries very fine dust particles 17. These dust particles collide and remain stuck on the surface of the just atomized and still hot droplets 14; this is well illustrated by the image of Fig. 4 which shows numerous large particles (about 30 to 50 prn) with satellites of about 5 μπι on their surface.

[0074] Fig. 1 illustrates a plasma atomization apparatus 20 used for preparing a spheroidal powder 18a substantially without satellites (or substantially free of satellites) such as shown on micrograph presented in Fig. 2. The expression "substantially free of satellites", as used in the present disclosure when referring to a powder, refers to a powder that contains a quantity of satellites that is similar or less to the quantity of satellites present in Fig. 2. For example, the expression "substantially free of satellites refers to a powder that contains a quantity of satellites that is similar to the quantity of satellites present in Fig. 2. The apparatus 20 comprises two chambers 21 and 22 connected by an aperture 23 through which a shielding gas, represented by arrows 24a and 24b, is injected to shield the just atomized and still hot droplets 14a from the upwards flowing dust. In chamber 21 , there are two plasma torches 25a and 25b used to heat, melt and atomize the rod or wire 26. Chamber 22 is provided with orifices 40 through which the dust laded gas (comprising dust particles 17a) is sucked to be treated in a device 27, which can be a cooler and/or a filter, before reintroduction in chamber 21 to be used for shielding the powder stream as discussed above. Additional cold shielding gas may be introduced through port 28. The acceleration of the shielding gas is made possible by the sucking action of the plasma jets 28a and 28b through the orifice 23. The injection of the gas through orifice 23 can be further accelerated by a pump (not shown) installed in pipe 29. The cold shielding gas is used not only to shield the hot just atomized droplets 14a against the dust laded gas but also contributes to the rapid cooling of the droplets 14a that eventually provide the powder 18a.

[0075] Fig. 5 illustrates a device 130, which can be used in a plasma atomization apparatus as shown in Fig. 1 instead of the plasma torches assembly shown in Fig. 1. The device 130 allows for an independently and simultaneously heat and even melt a rod or wire 131 prior to atomization of the latter by a plasma jet 135. In this device 130, the rod or wire 131 is driven downwardly by a feeder (such as a set of wheels 132) which is also fed by an electrical current from a power supply 33 into the rod 131. In the device 130, the current flows from the power supply 133, through the set of wheels 32 down the rod 131 , into a plasma jet 135 produced by a plasma torch 136, through at least one electrode 138 (for example a water cooled electrode) and back to the power supply 133. The electrode 138 can be considered as an auxiliary electrode. A single electrode can be present, at least one, at least two or at least three electrodes can alternatively be present. In Fig. 5 only one electrode is shown for illustrative purposes. For example, the electrodes can be of various shapes such as cylindrical, disc shape, ring shape etc.

[0076] An electric arc 140 is formed between the rod or wire 131 and the electrode 138. When there are several electrodes, there will be several electric arcs. For example, when there are two electrodes, a first arc will be generated between the rod or wire and the first electrode and a second arc will be generated between the rod or wire and the second electrode. For example, when there is a plurality of electrodes, there will be one electric arc formed between the rod or wire and each of the arcs. [0077] The device 130 is shown with a single plasma jet for illustration purposes but this device can also be provided with at least one, at least two, or at least three plasma jets.

[0078] The rod or wire 131 is preheated by the electric current. The heating occurs over the length of the rod or wire 131. As the rod or wire 131 travels down, its temperature increases by Joule heating. The temperature reached by the rod or wire 131 before getting into the atomization zone (in the present case in the plasma jet 135) depends upon various parameters such as the rod or wire traveling speed, the nature of the material, the electrical current, etc. The values of these parameters may be adjusted in order to have melting of the rod as it enters the atomization zone.

[0079] The rod or wire 131 is also heated by the heat transferred from the plasma jet 135 produced by the plasma torch as well as by the electric arc 140 generated between the end portion of the wire or rod 131 and the electrode 138 (see Fig. 5). The combination of the electric current heating (preheating), heating source heating (plasma jet in the present example) and electric arc is effective for melting the material contained in the rod or wire 131. Such a preheating is done in such a manner that the melting point of the material in rod or wire 131 is reached only in the atomization zone. In the atomizing zone, the atomizing means (plasma jet in the present example) is effective to atomize the material and produce the droplets that will eventually be cooled down to obtain the desired powder.

[0080] The power supply 133 which supplies the current to the rod 131 is different than the power supply 137 which energizes the plasma torch 136. Such a configuration allows for independent adjustments of both the rod or wire 131 temperature and the power in the plasma jet 135 to maximize the powder rate of production and obtain the desired characteristics for the powder. In another embodiment, the power source supplying the rod or wire 131 and the plasma torch 136 can be the same. [0081] The electric current used for both the electrical arc heating and the preheating (wheels 132) (Joule heating) flows into the wire or rod 131 itself from the power supply 133 (which can be a DC or AC power supply) and back through the end portion of the wire or rod 131 and the electrode 138 connected to the other terminal of the power supply 133. It has been found that the atomization performance and the powder produced can depend upon the fact that the wire or rod 131 is connected to the positive or the negative polarity of the power supply i.e. the wire or rod is acting as an anode or a cathode (and vice versa for the electrode 138). The person skilled in the art would understand that various parameters can have to be adjusted in order to optimize the atomization process.

[0082] When using a device such as device 130 of Fig. 5, the feed rate of the wire or rod 131 can vary according to certain parameters. For example, the feed rate can depend upon:

(i) the characteristics of the wire or rod material such as dimensions (cross section), nature of the material, density, electrical resistivity of the material, heat capacity and latent heat of fusion; and

(ii) the operating parameters: atomizing means power (for example torch power and temperature) and gas flow, plasma jet velocity, heating current and the length of wire or rod subjected to that current flow.

[0083] This is illustrated by the following example which gives the operating conditions (when using the device 130) allowing a feed rate of 30 mm per second:

Wire material : Titanium

Wire diameter : 3.125 mm

Wire current : 100 amperes

Heated length : 500 mm

Torch power : 3 x 25 kW

Pressure : 1 atm [0084] By contrast, the feed rate allowed without preheating (i.e. with wire current = 0) was only 8 mm per second. It can thus be seen that such a technology permits to considerably increase the production (3.75 times higher (30 mm per second / 8 mm per second).

[0085] The following table illustrates the effect of the type of material used (nature of the material) on the feed rate (wire size, wire current, heated length and torch power being the same):

[0086] The person skilled in the art would understand that, based on the results previously shown concerning various metals and alloys, various ceramics could also be used as material. The person skilled in the art would understand that by using, for example, an AC electrical current having a high frequency, it would be possible to use the technology shown in Fig. 5 and described above. In such a case, the aim would be to render the ceramic conductive by using such a type of AC electrical having a high frequency.

[0087] In other words, Fig. 5 shows a method and device that can be used for simultaneously passing an electric current through a piece of a conductive material (for example a piece of metal) while melting a portion of the piece, for example an end portion of the piece. The person skilled in the art would understand that such a method and device can be used for heating up to a temperature just below the melting temperature of any type of metals or conductive materials in various applications. For example, such a method and device can be used in the metallurgic industry or in any applications in which it is desirable to simultaneously heat and even melt if required a piece of metal or of conductive material. The person skilled in the art would also understand that such a method and device can be used for heating up to the welding or forging temperature of any type of metals or conductive materials in various applications.

[0088] It has to be noted that even if in Figs. 1 and 5 the rod or wire is shown as downwardly displaced, the methods, devices and apparatuses of the present disclosure also encompass wire or rod displaced in any other directions. For example, the wire or rod can also be upwardly displaced, horizontally displaced, or displaced at a particular angle. In such alternative configurations, the other component would be displaced accordingly. The wire or rod used in the methods, devices and apparatuses of the present disclosure can be of various shapes. It can be for example, of cylindrical shape or a parallelepiped shape.

[0089] It can be said that the methods, apparatuses and devices shown in Figs. 1 and 5 are considerably different from certain prior art atomization systems which atomize liquid metal poured from a crucible where contamination of the molten metal by the crucible is likely to occur.

[0090] There is also provided, in a method for simultaneously heating a conductive material and melting a portion thereof, the improvement of using a plasma torch for simultaneously melting the portion with a plasma jet thereof and conducting an electrical current through the plasma jet. For example, the plasma jet conducts electrical current between the conductive material and a power supply.

[0091] Such methods, apparatuses, and devices that can simultaneously heat and melt a conductive material offer several advantages over the prior art methods and apparatuses such like those which imply several steps involving molten metal. In particular, since the methods, apparatuses, and devices described in the present disclosure can, for example, maintain the temperature of the material below its melting point until the material reaches the atomization zone or region of the plasma jet(s). They allow a considerable economy of energy. In fact, by avoiding to involve a molten material over long periods of time or through several steps, thermal losses are considerably avoided. Moreover, the methods, apparatuses, and devices described in the present disclosure permit to avoid situations in which considerable amounts of energy are stocked as molten metal. When a shut down occurs and large amounts of molten material are involved, a lost of the energy invested to obtain such a molten material is often lost. Also, this feature presents a considerable safety advantage over the situation encountered when having a large molten bath of material as it is the case very often for example in the metal industry. The fact of minimizing the use of molten material by maintaining the material below its melting point until it reaches the atomization zone of the plasma jet permits to considerably reduce oxidation reaction and other side reactions that can occur with the material at high temperatures.

[0092] Finally, as previously discussed, it was shown that the production rate is considerably increased and the costs are considerably lowered when using the methods, devices and apparatuses of the present disclosure. The fact of providing a preheating and having heat from three different sources (electrical heating (Joule effect), electric arc and atomizing means) provided very interesting results : higher production rate and lower production costs.

[0093] While a description was made with particular reference to the illustrated embodiments, it will be understood that numerous modifications thereto will appear to those skilled in the art. Accordingly, the above description and accompanying drawings should be taken as specific examples and not in a limiting sense.

Claims

WHAT IS CLAIMED IS:

1. A method for preparing a spheroidal powder comprising: feeding an apparatus effective for atomizing a material chosen from metals and alloys, said apparatus being fed with said material that is preheated by an electrical current;

submitting an end portion of said material to a heat source and to at least one electric arc generated between said end portion and at least one electrode, so as to melt said material contained into said end portion;

atomizing said material contained into said end portion with atomization means; and

cooling said atomized material in order to cause spheroidization of said atomized material and obtain said spheroidal powder.

2. The method of claim 1 , wherein an atomization zone of said apparatus is fed with said material.

3. The method of claim 2, wherein said material is comprised within a wire or rod.

4. The method of claim 3, wherein an end portion of said wire or rod disposed in said atomization zone is submitted to said heat source and said at least one electrode.

5. The method of any one of claims 2 to 4, wherein said at least one electrode is disposed adjacently to said atomization zone.

6. The method of any one of claims 2 to 4, wherein said at least one electrode is disposed inside said atomization zone.

7. A method for preparing a spheroidal powder comprising: feeding an atomization zone of an apparatus effective for atomizing a material chosen from metals and alloys, with a wire or rod preheated by an electrical current, said wire or rod comprising said material;

submitting an end portion of said wire or rod disposed in said atomization zone to a heat source and to at least one electric arc generated between said end portion of said wire or rod and at least one electrode disposed adjacently thereof, so as to melt said material contained into said end portion;

8. The method of any one of claims 3, 4 and 7, wherein portions of said wire or rod, before contacting said atomization zone, are progressively preheated from room temperature to a temperature below the melting point of said material.

9. The method of any one of claims 3, 4, 7 and 8, wherein said wire or rod and said at least one electrode are connected to a DC electric power supply in such a manner that said wire or rod acts as a cathode and said at least one electrode acts as an anode.

10. The method of any one of claims 3, 4, 7 and 8, wherein said wire or rod and said at least one electrode are connected to a DC electric power supply in such a manner that said wire or rod acts as an anode and said at least one electrode acts as a cathode.

11. The method of any one of claims 3 to 10, wherein said method comprises preheating said wire or rod while feeding said atomization zone.

12. The method of any one of claims 3 to 11 , wherein said wire or rod is preheated in such a manner that, for a given portion of the wire or rod, its temperature increases as it approaches from said atomization zone.

13. The method of any one of claims 3 to 12, wherein, for a given portion of said wire or rod during said preheating, the temperature of said wire or rod is maintained below the melting point of said material in order to substantially minimize contamination of said material with at least one contaminant generated during preparation of said powder.

14. The method of claim 13, wherein said material is preheated in such a manner that when said end portion of said wire or rod enters in the atomization zone, its temperature increases and it reaches the melting point of the material and then, atomization of said end portion occurs, thereby substantially minimizing contacts between said molten material and said at least one contaminant generated during preparation of said powder.

15. The method of claim 14, wherein said atomized material is in the form of fine droplets of said material, and wherein a shielding gas is injected in order to substantially prevent said droplets from being contaminated by said at least one contaminant.

16. The method of claim 15, further comprising substantially preventing said at least one contaminant from contacting said molten material, atomized particles or said obtained spheroidal powder.

17. The method of claim 16, comprising continuously sucking said at least one contaminant generated so as to substantially minimize contamination of said desired spheroidal powder with said at least one contaminant.

18. The method of claim 17, wherein said at least one contaminant is sucked by means of a vacuum generated by the action of said at least one plasma jet and/or by means of a pump.

19. The method of claim 18, further comprising cooling a gas recovered by means of said vacuum.

20. The method of claim 19, further comprising filtering said gas recovered by means of said vacuum.

21. The method of claim 19 or 20, wherein said gas is recycled and reused as a shielding gas.

22. The method of claim 19 or 20, wherein said at least one contaminant comprises dust particles generated during said method.

23. The method of any one of claims 1 to 22, wherein said heat source comprises at least one plasma jet or a hot gas jet.

24. The method of any one of claims 1 to 22, wherein said heat source comprises at least one plasma jet.

25. The method of any one of claims 1 to 24, wherein said atomization means comprises at least one fluid jet.

26. The method of claim 25, wherein said fluid is a hot gas.

27. The method of any one of claims 1 to 24, wherein said atomization means comprises at least one plasma jet.

28. The method of any one of claims 1 to 24, wherein said atomization means and said heat source are the same.

29. The method of any one of claims 1 to 24, wherein said heat source comprises three plasma jets.

30. The method of any one of claims 1 to 24, wherein said atomization means comprises three plasma jets.

31. The method of any one of claims 1 to 30, wherein at least two electric arcs are generated between said end portion and at least two electrodes, one electric arc being generated between said end portion and each of said electrodes.

32. The method of any one of claims 1 to 30, wherein at least three electric arcs are generated between said end portion and at least three electrodes, one electric arc being generated between said end portion and each of said electrodes.

33. The method of any one of claims 1 to 22, wherein said atomization means and said heat source are the same and are at least two plasma jets, said end portion contacts said at least two plasma jets, said at least two jets converging into an apex and said end portion is contacting said at least two jets at said apex.

34. The method of any one of claims 1 to 22, wherein said atomization means and said heat source are the same and are at least three plasma jets, said end portion contacts at least three plasma jets, said at least three jets converging into an apex and said end portion is contacting said at least three jets at said apex.

35. In a continuous method for producing a spheroidal powder comprising atomizing a material by means of at least one plasma jet, the improvement wherein said material is heated at a temperature below the melting point of said material before contacting an atomization zone of said at least one plasma jet.

36. In a continuous method for producing a spheroidal powder comprising atomizing a material by means of at least two plasma jets, the improvement wherein said material is heated in such a manner that melting of said material is reached at an apex generated by said at least two plasma jets whereat there is substantially no contact between said material and other particles generated during said method.

37. The method of any one of claims 1 to 36, wherein said spheroidal powder is a spherical powder.

38. The method of any one of claims 1 to 37, wherein said material comprises at least one metal chosen from titanium, molybdenum, silver, copper, niobium, tantalum, tungsten, rhenium, osmium, iridium, hafnium, vanadium, chromium, zirconium, and mixtures thereof.

39. The method of any one of claims 1 to 37, wherein said material comprises a metal chosen from titanium, molybdenum and silver.

40. The method of any one of claims 1 to 37, wherein said material comprises titanium.

41. The method of any one of claims 1 to 37, wherein said material is a metal chosen from titanium, molybdenum, silver, copper, niobium, tantalum, tungsten, rhenium, osmium, iridium, hafnium, vanadium, chromium and zirconium.

42. The method of any one of claims 1 to 37, wherein said material is a metal chosen from titanium, molybdenum and silver.

43. The method of any one of claims 1 to 37, wherein said material is titanium.

44. The method of any one of claims 38 to 40, wherein said material is an alloy.

45. The method of any one of claims 1 to 37, wherein said material is a titanium alloy.

46. The method of any one of claims 1 to 37, wherein said material is an alloy chosen from nitinol and inconel.

47. An apparatus for producing a spheroidal powder comprising:

a heat source for heating said material and at least one electrode adapted to generate at least one electric arc with said material to thereby heat said material, the combination of heat provided by said electric power supply, said heat source and said at least one electric arc being effective to melt said material;

a feeder for feeding said apparatus with said material;

atomization means effective for atomizing said molten material; a chamber adapted for receiving and cooling droplets of said atomized material; and

optionally separating means for substantially preventing other particles generated during the preparation of said spheroidal powder or other materials from contacting said material before, during, and after atomization of said material.

48. The apparatus of claim 47, wherein said apparatus comprises said separating means.

49. The apparatus of claim 47 or 48, wherein said heat source comprises at least one plasma jet or hot gas jet.

50. The apparatus of claim 47 or 48, wherein said heat source comprises at least one plasma jet.

51. The apparatus of any one of claims 47 to 50, wherein said atomization means comprises at least one fluid jet.

52. The apparatus of claim 51 , wherein said fluid is a hot gas.

53. The apparatus of any one of claims 47 to 50, wherein said atomization means comprises at least one plasma jet.

54. The apparatus of any one of claims 47 to 50, wherein said atomization means and said heat source are the same.

55. The apparatus of claim 50 or 54, wherein said heat source comprises three plasma jets.

56. The apparatus of claim 53 or 55, wherein said atomization means comprises three plasma jets.

57. The apparatus of claim 47, wherein said atomization means and said heat source are the same and are at least two plasma jets.

58. The apparatus of claim 47, wherein said atomization means and said heat source are the same and are at least three plasma jets.

59. The apparatus of any one of claims 47 to 58, wherein at least two electric arcs are generated between said end portion and at least two electrodes, one electric arc being generated between said end portion and each of said electrodes.

60. The apparatus of any one of claims 47 to 58, wherein at least three electric arcs are generated between said end portion and at least three electrodes, one electric arc being generated between said end portion and each of said electrodes.

61. The apparatus of any one of claims 47 to 60, wherein when said apparatus is in use, portions of a wire or rod comprising said material, before contacting an atomization zone disposed adjacently to said heat source and said at least one electrode, are progressively preheated, from room temperature to a temperature below the melting point of said material.

62. The apparatus of any one of claims 47 to 60, wherein when said apparatus is in use, a wire or rod comprising said material and said electrode are connected to said electric power supply in such a manner that said wire or rod acts as a cathode and said electrode acts as an anode, said electric power supply being a DC electric power supply.

63. The apparatus of any one of claims 47 to 60, wherein when said apparatus is in use, a wire or rod comprising said material and said at least one electrode are connected to said electric power supply in such a manner that said wire or rod acts as a anode and said at least one electrode acts as an cathode, said electric power supply being a DC electric power supply.

64. The apparatus of any one of claims 47 to 63, wherein said separating means comprises a separator including an aperture, said separator defining at least a portion of a reaction chamber whereat said material is atomized, and a cooling chamber whereat said atomized material is cooled so as to obtain said desired spheroidal powder, said aperture defining a passage between said chambers.

65. The apparatus of claim 64, wherein said separating means further comprises means for injecting a shielding gas through said aperture from said reaction chamber to said cooling chamber so as to substantially prevent said other particles or materials from entering into said reaction chamber.

66. The apparatus of claim 64 or 65, wherein said separating means further comprises vacuum means for collecting other particles or materials present in said cooling chamber.

67. The apparatus of claim 66, wherein said vacuum means comprises at least two collecting orifices for receiving said other materials.

68. The apparatus of claim 66 or 67, wherein said vacuum means comprises a cooler adapted for cooling gases recovered from said cooling chamber.

69. The apparatus of claim 66, 67 or 68, wherein said vacuum means comprises a filter adapted for filtering gases recovered from said cooling chamber.

70. The apparatus of any one of claims 66 to 69, wherein said other particles or materials are dust particles generated during manufacture of said powder.