EP0904171B1 - Drying of atomized metal powder - Google Patents

Drying of atomized metal powder Download PDF

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Publication number
EP0904171B1
EP0904171B1 EP97921034A EP97921034A EP0904171B1 EP 0904171 B1 EP0904171 B1 EP 0904171B1 EP 97921034 A EP97921034 A EP 97921034A EP 97921034 A EP97921034 A EP 97921034A EP 0904171 B1 EP0904171 B1 EP 0904171B1
Authority
EP
European Patent Office
Prior art keywords
liquid
container
pump
powder
protective gas
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP97921034A
Other languages
German (de)
French (fr)
Other versions
EP0904171A1 (en
Inventor
Rutger Larsson
Erik Axmin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rutger Larson Konsult AB
Original Assignee
Rutger Larson Konsult AB
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Filing date
Publication date
Application filed by Rutger Larson Konsult AB filed Critical Rutger Larson Konsult AB
Publication of EP0904171A1 publication Critical patent/EP0904171A1/en
Application granted granted Critical
Publication of EP0904171B1 publication Critical patent/EP0904171B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
    • F26B21/06—Controlling, e.g. regulating, parameters of gas supply
    • F26B21/08—Humidity
    • F26B21/086—Humidity by condensing the moisture in the drying medium, which may be recycled, e.g. using a heat pump cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B21/00—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
    • F26B21/14—Arrangements or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects using gases or vapours other than air or steam, e.g. inert gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B5/00—Drying solid materials or objects by processes not involving the application of heat
    • F26B5/04—Drying solid materials or objects by processes not involving the application of heat by evaporation or sublimation of moisture under reduced pressure, e.g. in a vacuum

Definitions

  • the invention relates to a process for drying and possibly cooling atomized metal powder which is moist from a liquid used during the atomizing process, and which is surrounded by an atmosphere typical of manufacturing processes for metal powder, e.g. a substantially inert atmosphere, and equipment for performing the process.
  • a stream of molten metal is atomized with the aid of an atomizing agent.
  • the atomizing agent may be in gaseous or liquid form and may comprise a liquid hydrocarbon such as paraffin, fuel oil class 1, water or the like, for instance, in an environment substantially free from oxygen.
  • the powder formed falls down into a pool of coolant which may consist of the atomizing agent.
  • the powder is tapped to a transport container and the powder, usuall with increased temperature, e.g. 60-90°C, is then dried in a separate drying operation which constitutes an important part of the manufacturing process for many types of metal powder, particularly iron/steel powder having low oxygen content.
  • the powder is kept in a protective atmosphere (i.e. the typical atmosphere mentioned above or substantially inert atmosphere) until the risk has been substantially eliminated of the powder being adversely affected by the surrounding atmosphere.
  • a protective atmosphere i.e. the typical atmosphere mentioned above or substantially inert atmosphere
  • the moist powder is kept in an oxygen-free atmosphere of nitrogen, where the nitrogen may be of particularly oxygen-free quality in order to prevent oxidation.
  • the atomizing liquid is first allowed to run off the powder mass which is then tumbled by heated inert gas which is allowed to circulate through the tumbling powder mass so that the atomizing agent is vaporized and the vapour accompanying the inert gas is condensed and separated from the gas before the latter is recirculated.
  • the conventional technology has been found to require extensive and consequently expensive drying equipment, as well as entailing relatively high energy consumption.
  • the dried powder also has a high temperature which means that it must be cooled before it can be exposed to the surrounding atmosphere, and such powder cooling is expensive since it requires a cooling arrangement and since the thermal energy is cooled off.
  • An object of the invention is to provide a drying method that can be performed in a relatively simple apparatus and with relatively low energy consumption, preferably so that the dried powder immediately acquires a relatively low temperature and can preferably be immediately subjected to subsequent treatment, such as screening using conventional screening means.
  • the moist metal powder is contained in a container on a screening member disposed transversely in the container, that a vacuum is applied to the lower side of the screening member in order to draw off some of the liquid atomizing medium, that after the liquid has been drawn off, inert gas such as nitrogen gas, is circulated through the container in order to absorb residual moisture in the form of vapour from the powder mass, and that the vapour is removed from the gas forced through the container prior to recirculation in the container.
  • inert gas such as nitrogen gas
  • the liquid moistening the powder can be drawn off by means of a liquid jet pump (ejector pump).
  • ejector pump Such an ejector pump can also be used to subsequently withdraw vapour and gas from the container and to circulate the inert gas.
  • the ejector pump comprises a circulation circuit for the liquid driving the pump.
  • the driving liquid may consist entirely or partly of the atomizing medium used for manufacture of the powder.
  • the vapour sucked out by the pump is condensed in the liquid driving the ejector pump.
  • the liquid-circulation circuit of the ejector pump may also contain a heat exchanger allowing the circulating liquid to be heated or cooled.
  • the circulation circuit may also include a holding tank.
  • an upper gas space can be established in conventional manner, so that inert gas is permitted to separate from the liquid of the circulation circuit in the holding tank, and rises to the upper part of the holding tank so that inert gas can be conveyed for recirculation to the powder container.
  • the inert gas pipe may contain a heat exchanger to enable heating or cooling of the inert gas before it is reintroduced into the powder container.
  • a negative pressure is preferably established in the container in order to accelerate vaporization of the atomizing medium, whereby the temperature of the powder mass can also be reduced to a desired level.
  • the liquid can first be withdrawn from the container with the aid of a suitable liquid suction pump, such as a membrane pump. After which an ejector pump can be used as described above.
  • a suitable liquid suction pump such as a membrane pump.
  • a relatively "dense" cake may be formed on the screening member and according to one embodiment of the invention the cake is broken up in order to facilitate a flow of inert gas through the powder mass, thus facilitating drying of the powder.
  • An important feature of the invention is that the outflow, particularly the outflow of vapour from the container, is combined with the flow of driving liquid in an ejector pump so that the vapour leaving is condensed in the flow of driving liquid, while the inert gas can easily be separated for recirculation.
  • the drying process is initiated with suction of liquid atomizing medium from the powder mass, the residual moisture in the powder mass will be low and the energy required for the final drying process is reduced and thus also the heat of the powder itself (possibly in combination with a negative pressure) can provide the vaporization energy necessary for final drying. After final drying, therefore, the temperature of the powder is sufficiently low to enable additional cooling to be partly or entirely eliminated, which would otherwise be needed to prevent subsequent oxidation of the powder if exposed to the surrounding atmosphere.
  • Figure 1 shows a wet container 1 with a screening plate 2 disposed transversely in the container and carrying a metal powder mass 3.
  • a stirrer 4 is also shown schematically to break up the powder bed 3 if necessary.
  • the container has upper inlets 10, 14 and a lower outlet 12 with closing valves 11, 15 and 13, respectively.
  • the container 1 can be connected to a powder-atomizing plant and receives wet powder produced there via the inlet 14.
  • the closed container 1 can then be connected into a gas-circulation circuit 20, with valves 21, 22, as shown in the drawing.
  • the gas-circulation circuit 20 contains an inert gas such as nitrogen with a low content of oxygen and other damaging compounds.
  • the circuit 20 is supplied with inert gas from the gas source 23 as needed.
  • the circuit 20 includes a holding tank 25 for liquid atomizing medium, and a suction pump 30.
  • the suction pump e.g. an ejector pump, first withdraws liquid atomizing medium from the powder mass 3 and conveys this liquid to the holding tank 25.
  • the particle filter not shown, separates out any particles that may have accompanied the liquid.
  • the holding tank 25 has an upper space 26 which thus contains inert gas.
  • the tank 25 naturally also contains a mass 27 of liquid atomizing medium and this liquid mass 27 can be kept at a constant level by means known per se.
  • the liquid atomizing medium is circulated from the tank 25 via a pump 60 and a cooler 61 to the ejector pump 30, causing this to produce a negative pressure in the outlet side of the container 1.
  • the quantity of liquid in the powder can be reduced to an optimally low proportion by means of suction and the residual moisture departs in the form of vapour, to the gas flow circulating in the circuit 20 with the aid of the pump 30.
  • the vapour accompanying the gas flow is condensed in the cooled atomizing liquid circulating through the circulation circuit 70.
  • the partial pressure in the lower side of the container 1 facilitates vaporization of the remaining liquid in the powder mass 3, as well as lowering the temperature of the powder mass 3.
  • a heater 80 may be connected in the gas-circulation circuit 20 upstream of the container 1, if the powder itself is not sufficiently hot to vaporize the remaining moisture at the prevailing pressure.
  • the drawing shows an ejector pump 30 both for removal of liquid and circulation of gas.
  • a liquid suction pump e.g. a membrane pump
  • the ejector pump 30 may be replaced by another type of pump for circulating the gas.
  • gas-circulation circuit and the liquid-circulation circuit have a common section so that vapour accompanying the gas flow is condensed in the liquid, preferably cooled, and that the gas circuit and liquid circuit are preferably joined via an ejector pump.

Description

The invention relates to a process for drying and possibly cooling atomized metal powder which is moist from a liquid used during the atomizing process, and which is surrounded by an atmosphere typical of manufacturing processes for metal powder, e.g. a substantially inert atmosphere, and equipment for performing the process.
When manufacturing metal powder, e.g. steel powder with the lowest possible oxygen content and possibly with a selected relatively high carbon content, a stream of molten metal is atomized with the aid of an atomizing agent. The atomizing agent may be in gaseous or liquid form and may comprise a liquid hydrocarbon such as paraffin, fuel oil class 1, water or the like, for instance, in an environment substantially free from oxygen. The powder formed falls down into a pool of coolant which may consist of the atomizing agent. The powder is tapped to a transport container and the powder, usuall with increased temperature, e.g. 60-90°C, is then dried in a separate drying operation which constitutes an important part of the manufacturing process for many types of metal powder, particularly iron/steel powder having low oxygen content.
The powder is kept in a protective atmosphere (i.e. the typical atmosphere mentioned above or substantially inert atmosphere) until the risk has been substantially eliminated of the powder being adversely affected by the surrounding atmosphere.
According to conventional drying technology the moist powder is kept in an oxygen-free atmosphere of nitrogen, where the nitrogen may be of particularly oxygen-free quality in order to prevent oxidation.
According to the known technology, the atomizing liquid is first allowed to run off the powder mass which is then tumbled by heated inert gas which is allowed to circulate through the tumbling powder mass so that the atomizing agent is vaporized and the vapour accompanying the inert gas is condensed and separated from the gas before the latter is recirculated.
However, the conventional technology has been found to require extensive and consequently expensive drying equipment, as well as entailing relatively high energy consumption. The dried powder also has a high temperature which means that it must be cooled before it can be exposed to the surrounding atmosphere, and such powder cooling is expensive since it requires a cooling arrangement and since the thermal energy is cooled off.
The reason the powder now has to be cooled is a desire to avoid subsequent oxidation of the powder when it is emptied from the drying equipment, and also that the screening cloths of conventional screening means are attached by material which melts at low temperature, e.g. 60°C.
An object of the invention is to provide a drying method that can be performed in a relatively simple apparatus and with relatively low energy consumption, preferably so that the dried powder immediately acquires a relatively low temperature and can preferably be immediately subjected to subsequent treatment, such as screening using conventional screening means.
The object of the invention is achieved with the technology defined in the appended independent claims. Embodiments of the invention are defined in the appended dependent claims.
Additional objects and advantages of the invention are revealed in the following or will be obvious to one skilled in the art upon a study of the following description of one embodiment of the drying equipment.
Central features of the process according to the invention are thus that the moist metal powder is contained in a container on a screening member disposed transversely in the container, that a vacuum is applied to the lower side of the screening member in order to draw off some of the liquid atomizing medium, that after the liquid has been drawn off, inert gas such as nitrogen gas, is circulated through the container in order to absorb residual moisture in the form of vapour from the powder mass, and that the vapour is removed from the gas forced through the container prior to recirculation in the container.
The liquid moistening the powder can be drawn off by means of a liquid jet pump (ejector pump). Such an ejector pump can also be used to subsequently withdraw vapour and gas from the container and to circulate the inert gas. The ejector pump comprises a circulation circuit for the liquid driving the pump. The driving liquid may consist entirely or partly of the atomizing medium used for manufacture of the powder. The vapour sucked out by the pump is condensed in the liquid driving the ejector pump. The liquid-circulation circuit of the ejector pump may also contain a heat exchanger allowing the circulating liquid to be heated or cooled. The circulation circuit may also include a holding tank. In such a holding tank an upper gas space can be established in conventional manner, so that inert gas is permitted to separate from the liquid of the circulation circuit in the holding tank, and rises to the upper part of the holding tank so that inert gas can be conveyed for recirculation to the powder container. The inert gas pipe may contain a heat exchanger to enable heating or cooling of the inert gas before it is reintroduced into the powder container. A negative pressure is preferably established in the container in order to accelerate vaporization of the atomizing medium, whereby the temperature of the powder mass can also be reduced to a desired level.
If desired the liquid can first be withdrawn from the container with the aid of a suitable liquid suction pump, such as a membrane pump. After which an ejector pump can be used as described above.
With certain particle size gradients of the atomized powder a relatively "dense" cake may be formed on the screening member and according to one embodiment of the invention the cake is broken up in order to facilitate a flow of inert gas through the powder mass, thus facilitating drying of the powder.
An important feature of the invention is that the outflow, particularly the outflow of vapour from the container, is combined with the flow of driving liquid in an ejector pump so that the vapour leaving is condensed in the flow of driving liquid, while the inert gas can easily be separated for recirculation.
Since the drying process is initiated with suction of liquid atomizing medium from the powder mass, the residual moisture in the powder mass will be low and the energy required for the final drying process is reduced and thus also the heat of the powder itself (possibly in combination with a negative pressure) can provide the vaporization energy necessary for final drying. After final drying, therefore, the temperature of the powder is sufficiently low to enable additional cooling to be partly or entirely eliminated, which would otherwise be needed to prevent subsequent oxidation of the powder if exposed to the surrounding atmosphere.
Additional objectives and advantages of the invention are revealed in the following or will be understood from a study of the following description of one embodiment of a drying apparatus.
Figure 1 shows a wet container 1 with a screening plate 2 disposed transversely in the container and carrying a metal powder mass 3. A stirrer 4 is also shown schematically to break up the powder bed 3 if necessary. The container has upper inlets 10, 14 and a lower outlet 12 with closing valves 11, 15 and 13, respectively. The container 1 can be connected to a powder-atomizing plant and receives wet powder produced there via the inlet 14. The closed container 1 can then be connected into a gas-circulation circuit 20, with valves 21, 22, as shown in the drawing. The gas-circulation circuit 20 contains an inert gas such as nitrogen with a low content of oxygen and other damaging compounds. The circuit 20 is supplied with inert gas from the gas source 23 as needed. The circuit 20 includes a holding tank 25 for liquid atomizing medium, and a suction pump 30. The suction pump, e.g. an ejector pump, first withdraws liquid atomizing medium from the powder mass 3 and conveys this liquid to the holding tank 25. The particle filter, not shown, separates out any particles that may have accompanied the liquid. The holding tank 25 has an upper space 26 which thus contains inert gas. The tank 25 naturally also contains a mass 27 of liquid atomizing medium and this liquid mass 27 can be kept at a constant level by means known per se. The liquid atomizing medium is circulated from the tank 25 via a pump 60 and a cooler 61 to the ejector pump 30, causing this to produce a negative pressure in the outlet side of the container 1. The quantity of liquid in the powder can be reduced to an optimally low proportion by means of suction and the residual moisture departs in the form of vapour, to the gas flow circulating in the circuit 20 with the aid of the pump 30. The vapour accompanying the gas flow is condensed in the cooled atomizing liquid circulating through the circulation circuit 70. The partial pressure in the lower side of the container 1 facilitates vaporization of the remaining liquid in the powder mass 3, as well as lowering the temperature of the powder mass 3.
If desired, however, a heater 80 may be connected in the gas-circulation circuit 20 upstream of the container 1, if the powder itself is not sufficiently hot to vaporize the remaining moisture at the prevailing pressure.
The drawing shows an ejector pump 30 both for removal of liquid and circulation of gas. However, it should be evident that a liquid suction pump, e.g. a membrane pump, can be connected at least temporarily in parallel with the ejector pump 30, for instance, to provide optimal liquid suction conditions. Furthermore, the ejector pump 30 may be replaced by another type of pump for circulating the gas.
An important feature of the embodiment shown is that the gas-circulation circuit and the liquid-circulation circuit have a common section so that vapour accompanying the gas flow is condensed in the liquid, preferably cooled, and that the gas circuit and liquid circuit are preferably joined via an ejector pump.

Claims (9)

  1. A process for drying atomized metal powder contained in a protective atmosphere and moist from a liquid used during the atomizing process, where the moist metal powder (3) is contained in a container (1), and in that vapour is separated from the protective gas circulating through the container prior to a recirculation in the container,
    characterized in that the metal powder (3) is contained on a screening member (2) disposed transversely in the container, in that a vacuum is applied to the lower side of the screening member (2) in order to draw off some of the liquid, in that after the liquid has been drawn off, protective gas is circulated through the container in order to absorb vaporized liquid from the powder mass.
  2. A process as claimed in claim 1, characterized in that the liquid is drawn off by means of a suction pump such as a membrane pump.
  3. A process as claimed in claim 1 or claim 2,
    characterized in that a liquid jet pump (30) is connected to the lower part of the container (1) in order to establish negative pressure below the screening member (2), and in that the liquid pump is driven by a circulating liquid flow, the vapour condensing in the circulating liquid flow of the ejector pump, said flow consisting partly or entirely of the liquid with which the powder was moistened.
  4. A process as claimed in claim 3, characterized in that the liquid-circulation circuit of the pump (30) includes a holding tank (25) which is kept only partially filled with liquid in order to permit separation of the protective gas accompanying the circulation liquid, said gas being withdrawn from the holding tank and circulated to the container.
  5. A process as claimed in any of claims 1-4,
    characterized in that the flow of protective gas is heated (80) before being returned to the powder container (1).
  6. A process as claimed in any of claims 1-5,
    characterized in that the cake of moist powder mass (3) formed on the screening member (2) at withdrawal of the liquid is broken up (4) in order to facilitate circulation of the protective gas through the powder mass.
  7. Equipment for drying atomized metal powder contained in a protective atmosphere in a container (1) and moist from a liquid used during the atomizing process, characterized in that the moist metal powder (3) in the container (1) rests on a screening member (2) disposed transversely in the container, in that said equipment includes a pump member (30) to draw liquid from the powder mass (3), and in that the pump member is arranged to circulate protective gas through the container (1) to take with it vapour stripped from the powder mass, and in that condensors (25, 26, 27) are arranged to condense the vapour accompanying the protective gas so that the protective gas is substantially freed from the vapour before being recirculated to the container (1).
  8. Equipment as claimed in claim 7, characterized in that the pump member comprises a circulation circuit (70) for a liquid, in that the upper and lower parts of the container (1) are connected to a circulation circuit (20) for the protective gas, in that both circuits (20, 70) join each other at the pump member, which is in the form of a liquid jet pump (30), so that the vapour accompanying the protective gas is condensed in the liquid-circulation circuit (70) of the pump member.
  9. Equipment as claimed in claim 8, characterized in that the liquid in the liquid-circulation circuit of the liquid jet pump consists entirely or partly of the liquid with which the powder was moistened.
EP97921034A 1996-04-18 1997-04-18 Drying of atomized metal powder Expired - Lifetime EP0904171B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
SE9601481 1996-04-18
SE9601481A SE509031C2 (en) 1996-04-18 1996-04-18 Drying of atomized metal powder
PCT/SE1997/000655 WO1997038812A1 (en) 1996-04-18 1997-04-18 Drying of atomized metal powder

Publications (2)

Publication Number Publication Date
EP0904171A1 EP0904171A1 (en) 1999-03-31
EP0904171B1 true EP0904171B1 (en) 2001-07-18

Family

ID=20402253

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97921034A Expired - Lifetime EP0904171B1 (en) 1996-04-18 1997-04-18 Drying of atomized metal powder

Country Status (6)

Country Link
EP (1) EP0904171B1 (en)
AU (1) AU2718697A (en)
CA (1) CA2251752C (en)
DE (1) DE69705715T2 (en)
SE (1) SE509031C2 (en)
WO (1) WO1997038812A1 (en)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1171762B1 (en) * 1999-04-17 2005-02-02 Limited Genevac Evaporation of liquids and recirculation of purified gas
US20150260454A1 (en) * 2014-03-12 2015-09-17 Ut-Battelle Llc Adsorbed water removal from titanium powders via water activation
KR102240416B1 (en) 2016-08-24 2021-04-15 5엔 플러스 아이엔씨. Low melting point metal or alloy powder atomization manufacturing process
JP2021514028A (en) 2018-02-15 2021-06-03 ５エヌ プラス インコーポレイテッド Melting point metal or alloy powder atomizing manufacturing process
CN111300655A (en) * 2020-02-24 2020-06-19 中国水利水电第五工程局有限公司 Method for accelerating dehydration of sand material in double-pressure circulating sand silo
CN113913797A (en) * 2021-09-17 2022-01-11 金华职业技术学院 Method for drying and protecting chemical plating powder

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ZA785312B (en) * 1977-09-22 1979-08-29 Davy Loewy Ltd Production of metal powder
CA2038449C (en) * 1990-03-20 1999-03-16 Naotsugu Isshiki Method of and apparatus for producing metal powder

Also Published As

Publication number Publication date
SE509031C2 (en) 1998-11-30
DE69705715D1 (en) 2001-08-23
SE9601481L (en) 1997-10-19
CA2251752A1 (en) 1997-10-23
EP0904171A1 (en) 1999-03-31
CA2251752C (en) 2005-08-02
WO1997038812A1 (en) 1997-10-23
AU2718697A (en) 1997-11-07
DE69705715T2 (en) 2002-06-13
SE9601481D0 (en) 1996-04-18

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