Claims:1. A method for producing a high density reduced iron powder, comprising steps of:
rolling a reduced iron cake by a roller with 50% -80% cake thickness reduction to form a rolled iron cake;
heat treating rolled iron cake in reducing or non-oxidizing atmosphere of thermo chemical furnace at 800 0C to 1050 0C for a duration 60 minutes to 120 minutes, to form a heat-treated iron cake; and
comminuting the heat-treated iron cake by a comminution unit below 45-micron particle size.

2. The method as claimed in the claim 1, wherein precursor to reduced iron cake is spray roasted iron oxide with composition (all in wt%)
Fe(total)- 69.10-69.70, FeO-0.30-1, CaO-0.012-0.1, SiO2-0.08-0.17, S-0.009-0.019, MgO-0.03-0.08, MnO-0.1-0.27, Al2O3-0.16-0.25, C-0.025-0.15.

3. The method as claimed in the claim 1, wherein the reduced iron cake is obtained by reduction of iron oxide in a thermo chemical furnace under hydrogen rich gaseous atmosphere for a duration 60 minutes to 240 minutes.

4. The method as claimed in the claim 3, wherein the thermo chemical furnace is Fixed bed or industrial furnace.

5. The method as claimed in the claim 4, wherein the industrial furnace is pusher type or belt type.

6. The method as claimed in the claims 1 and 3, wherein the reduced iron cake is obtained by reduction at temperatures 600 0C to 10000C.

7. A method as mentioned in the claim 1, wherein reducing or non-oxidizing atmosphere is one or combination(s) of N2 gas, cracked ammonia, pure hydrogen and hydrogen from cracked methane.

8. A method as mentioned in the claim 1, wherein the roller is an opposite rotating rollers with vertical feeding system.

9. A method as mentioned in the claim 1, wherein the comminution unit is either or combination(s) of impact, shear, attrition, compression forces.

10. A high density reduced iron powder, comprising
irregular morphology,
mean particle size (D50) 10-21 microns,
purity Fe(T) wt.% 97-99 %, and
apparent density 1.4-1.62 g/cc. , Description:TECHNICAL FIELD
The present invention relates to the field of Powder metallurgy. More specifically it relates to producing dense reduced iron powder.
BACKGROUND OF THE DISCLOSURE

Iron particles in the powdered form with size range of 5-200 µm are termed as iron powders. Iron Powder production technique involves chemical method (Reduction, Decomposition), physical method (Atomization, electrolytic) and mechanical method (Comminution). In the present scenario few processes like atomization (air, gas and water), reduction (Solid/Gas), carbonyl, and electrolytic synthesis are commonly used for production. These processes are economically viable and well accepted for bulk production.

Iron Powders are used in different applications such as mechanical components for automobiles (Gears, valve guides and connection rods etc), soft magnetic composites, welding rods, chemical catalysts, water purification etc. Each application requires specific Purity, size and shape of iron powder. Iron powder used in automobile application are relatively coarser as compare to powder used for metal powder injection application this in turn decide the production method.

Water atomization technique produced powder of irregular shape and apparent density in the range of 2.5 to 3g/cc with mean particle size 75 to 150 micron. Carbonyl route produces powder of spherical morphology, apparent density (AD) of 2.5 to 3.5g/cc and mean particle size of 2 to 5 microns. Flaky morphology with apparent density 2 to 2.9g/cc powder obtained in electrolytic route.

Iron Powder produced through reduction route using spray roasted iron oxide which is an oxide form of iron possess relatively low apparent density in the range of 0.8 to 1 g/cc with powder mean particle size 45-75 micron. This low apparent density iron powder is used in producing low density parts such as oil bearing. Low Apparent density limit the usages of Iron powder produced through reduction route. Reduction of iron oxide to iron powder is done using reducing agents like coal (solid) or hydrogen (gaseous) or carbon monoxide (gaseous) or mixture of the same. Powder produce through reduction routes are of irregular shape and this powder particle can be pulverized is smaller fine particles in the range of 5-10 micron. This particle size range suites the application such metal injection molding. However, lower apparent of the reduces powder limit the usage.

Thus, it is evident that production of reduced iron powders with high apparent density is important to diversify its usage in metal injection molding and other related applications. However, this is challenging due to the irregular shape and high internal porosity in the powder particles.

Prior art on production of reduced iron powders of various morphologies from iron oxide exists, but production of high apparent density powders from irregular iron oxide is explored by very limited number of inventors. In a patent US20130263698A1, researchers proposed a method of producing high density iron powder in which, iron oxide powder is heated over 700 oC in a reducing atmosphere followed by crushing and spheroidizing. This spheroidized powder again annealed at temperature range of 500-800 oC followed by crushing and spheroidizing. In the instant work, iron oxide after reduction is grinded and spheroidized that involve processing cost.

In another work, US2902357, iron oxide is firstly reduced, and agglomerated reduced particles are mechanically grinded to lower sizes. In the next step this powder particles are rolled into the form of frangible sheet. This rolled sheet is ground in a second grinding step to produce final high-density powders.

In US2902357 work rolled powder sheet is grinded to produce the final product. In the process of rolling and grinding a lot of work hardening effect will take place that will make powder particles very hard and in turn it will hamper the compressibility of powder.

The present disclosure is directed to overcome one or more limitations stated above or any other limitations associated with the conventional mechanisms.

OBJECTIVE OF THE DISCLOSURE

An object of the invention is to produce a high density reduced iron powder.

Another object of the invention is to identify a method for producing a high density reduced iron powder.

SUMMARY OF THE DISCLOSURE

One or more shortcomings of the prior art are overcome by a method as claimed and additional advantages are provided through the method as claimed in the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

The present invention provides a method for producing a high density reduced iron powder, comprising steps of:
rolling a reduced iron cake by a roller with 50% -80% cake thickness reduction to form a rolled iron cake;
heat treating rolled iron cake in reducing or non-oxidizing atmosphere of thermo chemical furnace at 800 0C to 1050 0C for a duration 60 minutes to 120 minutes, to form a heat-treated iron cake; and
comminuting the heat-treated cake by a comminution unit below 45-micron particle size
The provision of rolling a reduced iron cake helps in squeezing the internal porosity, with heat treatment enhancing the self-diffusion of iron particle. The further communition helps in achieving the dense reduced iron powder.

In a preferred embodiment, precursor to reduced iron cake is spray roasted iron oxide with composition (all in wt%) Fe(total)- 69.10-69.70, FeO-0.30-1, CaO-0.012-0.1, SiO2-0.08-0.17, S-0.009-0.019, MgO-0.03-0.08, MnO-0.1-0.27, Al2O3-0.16-0.25, C-0.025-0.15.

In a preferred embodiment, the reduced iron cake is obtained by reduction of iron oxide in a thermo chemical furnace under hydrogen rich gaseous atmosphere for a duration 60 minutes to 240 minutes.

In a preferred embodiment, the thermo chemical furnace is Fixed bed or industrial furnace with the industrial furnace being pusher type or belt type.

In a preferred embodiment, the reduced iron cake is obtained by reduction at temperatures 600 0C to 10000C.
In a preferred embodiment, reducing or non-oxidizing atmosphere is one or combination(s) of N2 gas, cracked ammonia, pure hydrogen and hydrogen from cracked methane.

In a preferred embodiment, the roller is an opposite rotating rollers with vertical feeding system.

In a preferred embodiment, the comminution unit is either or combination(s) of impact, shear, attrition, compression forces.

In another embodiment, the present invention describes a high density reduced iron powder, comprising
irregular morphology,
mean particle size (D50) 10-21 microns,
purity Fe(T)% 97-99 wt%, and
apparent density 1.4-1.62 g/cc.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiments when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

FIG. 1 illustrates a flowsheet of a method for producing a high density reduced iron powder in accordance with an embodiment of the invention.

FIG. 2 shows a scanning electron microscopy (SEM) image of the high density reduced iron powder in accordance with an exemplary embodiment of the invention.

FIG. 3 shows a scanning electron microscopy (SEM) image of the high density reduced iron powder in accordance with another exemplary embodiment of the invention.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the system and method illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that, the conception and specific embodiments disclosed may be readily utilized as a basis for modifying other methods, mechanisms, systems, assemblies, devices, and processes for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that, such equivalent constructions do not depart from the scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristics of the disclosure, to its system, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

The terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusions, such that a mechanism, an assembly, or a device that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.

Reference will now be made to the exemplary embodiments of the disclosure, as illustrated in the accompanying drawings. Wherever possible, same numerals will be used to refer to the same or like parts. The following paragraphs describe the present disclosure with reference to Figs. 1 to 3.

As used herein, the phrases ‘irregular iron oxide’ or ‘iron oxide’ or ‘raw material’ refer to iron oxide particles comprising either or combination of natural or synthetic hematite and magnetite with irregular morphology and an average particle diameter between 1 µm and 200 µm with an apparent density of not more than 1 g/cc.

As used herein, the phrase ‘hydrogen rich gaseous’ refers to the gas comprising either or combination of pure hydrogen, cracked methane, purified coke oven gas, cracked ammonia and other hydrogen containing gases.

In accordance with an embodiment of the disclosure, FIG. 1 illustrates a flowsheet a method (100) with Steps 104-112 for producing a high density reduced iron powder.
At Step (104), a reduced iron cake is rolled by a roller with 50% -80% cake thickness reduction to form a rolled iron cake. The instant step helps in squeezing the internal porosity of iron particles that in turn densify the particles. The reduced iron cake thickness ranges from 3cm to 4cm.
At Step (108), the rolled iron cake is heat treated in reducing or non-oxidizing atmosphere of thermo chemical furnace at 8000C to 10500C for duration of 60 minutes to 120 minutes to form a heat-treated cake. This step helps in enhancing the self-diffusion of iron particle, that leads to further densify the iron particle.
The reducing or non-oxidizing atmosphere is one or combination(s) of N2 gas, cracked ammonia, pure hydrogen and hydrogen from cracked methane.
The reduced iron cake in an embodiment is obtained by reduction of iron oxide in a thermo chemical furnace at temperatures 600 0C to 10000C under hydrogen rich gaseous atmosphere for a duration 60 minutes to 240 minutes.

In an embodiment of the present disclosure, the raw material or precursor used for making reduced iron cake is spray roasted iron oxide which is obtained from spray roasting process during acid regeneration process of spent pickle liquor. The spray roasted iron oxide powder comprises the composition as mentioned in Table 1
Table 1
Composition (wt %) Fe(total) FeO CaO SiO2 S MgO MnO Al2O3 C
Spray Roasted Iron Oxide 69.10-69.70 0.30-1 0.012-0.1 0.08-0.17 0.009-0.019 0.03-0.08 0.1-0.27 0.16-0.25 0.025-0.15
Small wt% of elements such as Cr, Ti, Cu and P are also present to make up the final composition to 100 wt%.
The iron oxide refers to particles com¬prising either or combination(s) of natural or synthetic hematite and magnetite with irregular morphology and an average particle diameter between 1 µm and 200 µm with an apparent density of not more than 1 g/cc.
In an embodiment, the thermo chemical furnace is Fixed bed or industrial furnace, with the industrial furnace being pusher type or belt type.
The rolling of the reduced iron cake is done with opposite rotating rollers with vertical feeding system.
In an embodiment, the reducing or non-oxidizing atmosphere is one or combination(s) of cracked ammonia, pure hydrogen and hydrogen from cracked methane.
At Step (112), the heat-treated iron cake is comminuted below 45-micron particle size by a comminution unit. The comminution is either or in combination(s) of impact, shear, attrition, compression forces. The apparent density maintained is more than 1.4g/cc
The obtained high density reduced iron powder has the following properties of
irregular morphology,
mean particle size (D50) 10-21 microns,
purity (Fe(T)% 97-99 wt%,
apparent density not less than 1.4-1.62 g/cc.

Experimental Analysis 1:
High density powders are synthesized by the method comprising following steps
- Thermo chemical reduction of iron oxide (chemical composition shown in table-1) at temperature of 800 0C under cracked ammonia gaseous atmosphere for a duration of 240 minutes to obtain reduced iron powder cake.
- Rolling of reduced iron cake in opposite rotating roller to reduce the cake thickness by 55%.
- Heat treatment of rolled cake in N2 atmosphere at temperatures of 850 0C for a duration of 60 minutes followed by communition in combination of impact, shear and attrition forces to obtain the powder size below 45-micron.
Obtained High density reduced iron powder possess, Fe (T) 98.1 %, AD- 1.42g/cc, mean particle size D50 – 17 microns and irregular morphology.

Experimental Analysis 2:
High density powders are synthesized by the method comprising following steps
- Thermo chemical reduction of iron oxide (mentioned in Table-1) at temperature of 800 0C under cracked ammonia gaseous atmosphere for a duration of 240 minutes to obtain reduced iron powder cake.
- Rolling of reduced iron cake in opposite rotating roller to reduce the cake thickness by 60%.
- Heat treatment of rolled cake in N2 atmosphere at temperatures of 900 0C for a duration of 60 minutes followed by communition in combination of impact, shear and attrition forces to obtain the powder size below 45-micron.
Obtained High density reduced iron powder possess, Fe (T) 97.6 %, AD- 1.46g/cc, mean particle size D50 – 21 microns and irregular morphology.

Experimental Analysis 3:
High density powders are synthesized by the method comprising following steps
- Thermo chemical reduction of iron oxide (mentioned in Table-1) at temperature of 900 0C under cracked ammonia gaseous atmosphere for a duration of 240 minutes to obtain reduced iron powder cake.
- Rolling of reduced iron cake in opposite rotating roller to reduce the cake thickness by 50%.
- Heat treatment of rolled cake in N2 atmosphere at temperatures of 950 0C for a duration of 120 minutes followed by communition in combination of impact, shear and attrition forces to obtain the powder size below 45-micron.
Obtained High density reduced iron powder possess, Fe (T) 97.4 %, AD- 1.62g/cc, mean particle size D50 – 18 microns and irregular morphology.
Scanning electron microscopy image of high density reduced iron powder is shown in FIG. 2.

Experimental Analysis 4:
High density powders are synthesized by the method comprising following steps
- Thermo chemical reduction of iron oxide (mentioned in Table-1) at temperature of 900 0C under cracked ammonia gaseous atmosphere for a duration of 240 minutes to obtain reduced iron powder cake.
- Rolling of reduced iron cake in opposite rotating roller to reduce the cake thickness by 50%.
- Heat treatment of rolled cake in N2 atmosphere at temperatures of 1000 0C for a duration of 120 minutes followed by communition in combination of impact, shear and attrition forces to obtain the powder size below 45-micron.

Obtained High density reduced iron powder possess, Fe (T) 97.6 %, AD- 1.58g/cc, mean particle size D50 – 17 microns and irregular morphology.

Experimental Analysis 5:
High density powders are synthesized by the method comprising following steps
- Thermo chemical reduction of iron oxide (mentioned in Table-1) at temperature of 900 0C under cracked ammonia gaseous atmosphere for a duration of 240 minutes to obtain reduced iron powder cake.
- Rolling of reduced iron cake in opposite rotating roller to reduce the cake thickness by 60%.
- Heat treatment of rolled cake in N2 atmosphere at temperatures of 1050 0C for a duration of 60 minutes followed by communition in combination of impact, shear and attrition forces to obtain the powder size below 45-micron.

Obtained High density reduced iron powder possess, Fe (T) 97.6 %, AD- 1.44g/cc, mean particle size D50 – 16 microns and irregular morphology

Experimental Analysis 6:
High density powders are synthesized by the method comprising following steps
- Thermo chemical reduction of iron oxide (mentioned in Table-1) at temperature of 900 0C under cracked ammonia gaseous atmosphere for a duration of 240 minutes to obtain reduced iron powder cake.
- Rolling of reduced iron cake in opposite rotating roller to reduce the cake thickness by 60%.
- Heat treatment of rolled cake in N2 atmosphere at temperatures of 1050 0C for a duration of 120 minutes followed by communition in combination of impact, shear and attrition forces to obtain the powder size below 45-micron.

Obtained High density reduced iron powder possess, Fe (T) 97.6 %, AD- 1.51g/cc, mean particle size D50 – 16 microns and irregular morphology.
Scanning electron microscopy image of high density reduced iron powder is shown in FIG. 3.

In this disclosure method to produce high density iron powder from reduced cake is successfully demonstrated. Said high density iron powder is useful in application areas such as Diamond cutting tolls, metal injection molding and other similar high-density product.

Equivalents:
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.