GB2041413A - Production of metal by extru- sion - Google Patents

Abstract

A method of producing ferrous metal elongate products from a metal ore comprises the steps of beneficiating the ore into a concentrate form, forming the concentrate into agglomerates, passing the agglomerated concentrate through a furnace in the presence of a reducing gas acting as the sole or primary reductant and extruding the reduced agglomerates to produce an elongate body of ferrous metal.

Description

SPECIFICATION Production of metal by extrusion This invention relates to the production of elongate ferrous metal bodies by extrusion from a metal ore starting material and it is an object of the present invention to provide a new or improved method of manufacturing such metal bodies.

In accordance with the invention there is provided a method of producing ferrous metal elongate products from a metal ore comprising the steps of beneficiating the ore into a concentrate form, forming the concentrate into agglomerates such as pellets or briquettes, passing the agglomerated concentrate through a furnace in the pesence of a reducing gas acting as the sole or primary reducatant and extruding the reduced agglomerates to produce an elongate body of ferrous metal.

The metal ore may be beneficiated into concentrate form by subjecting the ore to a series of grinding, magnetic or gravity separation and filtration stages.

Althernativeiy chemical (e.g. chloride) beneficiation may be utilised. Thus for example the ore may be subject to reaction with hydrogen and hydrogen chloride gas (at 700"C to 900 C) the resultant iron chloride being condensed from the product gases to produce a finely divided concentrated iron chloride.

Additions of alloying materials, either as elements, oxides or chlorides may be made at the appropriate stage in the method prior to extrusion.

A plurality of separate metal ores may be used in the method, blending occurring at a suitable stage.

The reduction of the concentrate àgglomer- ates may be carried out in a furnce in a continuous or batch mode of operation íri the pesence of hydrogen and/or carbon monoxide or any other suitable reducing gas or gases.

The reduced agglomerates may be fed direct to the extruder from the reducing furnace.

The agglomerates may be retained at substantially the temperature of the furnace, or in some cases, may be subject to necessary process temperature adjustment.

Alternatively, the reduced agglomerates may be cooled and stored after the reduction stage and subsequently subject to necessary process temperature adjustment before being fed to the extruder.

Extrusion may take place by any convenient and practicable means. Thus a ram extruder may be used, and semi-continuous production may be achieved by using a reciprocating ram extruder. Alternatively for example extrusion may be achieved in known manner by feeding the agglomerates into a passageway formed between a rotating wheel having a groove around its outer periphery and a shoe covering part of the length of the groove, a die orifice being provided at the outlet end of the passageway, and the wheei being rotated such as to compress the pellets towards the die orifice.

It is to be appreciated that with some extrusion arrangements the elongate body of ferrous metal produced may have, on extru sion, 100% density, i.e. full compaction or a density and compaction approaching this magnitude. With other extrusion arrange ments however the extruded body may have a compaction and density value of much lower magnitude and in such cases the extruded body of ferrous metal may subsequently be I subjected to mechanical working such as roll ing, forging or hot rolling so as, amongst other things, to increase its density and com paction.

It is possible by means of the invention to produce a composite elongate body of ferrous metal having segregated portions of different constitutions.

Thus by means of appropriate extrusion arrangements it is possible to extrude a com I posite body having segregated zones trans verse to its elongate axis. This can be achieved for example by means of an extru sion arrangement in which a can or shell of preformed ferrous material is supplied to an extrusion chamber which is then filled with the reduced agglomerates and then extruded as a composite body having a peripheral shell of different composition to the interior of the body. Such composite bodies can be of im ported value in providing, for example, rein forcing bars in a corrosive environment where the shell can be of a stainless steel composi tor.

Two examples of the invention will now be described in more detail with reference to the accompanying drawings wherein: Figures la and ib show a block diagram of one example including a series of mechanical and magnetic ore beneficiation stages; Figure 2 is a block diagram including a chemical beneficiation route; and Figure 3 is a diagrammatic elevation of an extruding arrangement for use with the meth ods.

Referring to Fig. 1 of the drawings, iron ore is conveyed from a dry store to a closed circuit primary grinding mill which may be of the type manufactured by the Alice Chalmers Corporation from which the ground ore is passed through successive low and high in tensity magnetic separators which may be of the type manufactured by Boxmag Rapid. The non-magnetic content is pumped out of the separators, whilst the magnetic content is then passed to a thickener which may be of the type manufacture by Dorr-Oliver. From the thickener the ore is passed through a filter which may be of the rotary disc type manufac tured by Dorr-Oliver and after drying the ore is then then subjected to a final closed circuit grind- ing operation.

At this stage the beneficiation of the ore is complete and is in a concentrate powder form having a Blaine size of 1300-2200. The gangue content of the ore is conveniently of less than 3%. The beneficiated ore is then passed to a pelletising unit which may be of the type manufactured by the Head Wrightson Group from which the pelletised ore is passed to a reduction furnace. The pellet size of the ore is conveniently less than 1 2 mm.

The reduction furnace may be of a shaft furnace or a travelling grate kiln or a static bed furnace and in the furnace the pelletised ore is subjected to the action of a reducing gas which conveniently and as illustrated is hydrogen.

Yet again the reduction furnace may comprise a fluidised bed high temperature reactor, the bed being provided by the agglomerates and the fluidising action by the reducing gas.

Conveniently the reduction furnace operates at a temperature within the range 500"C to 1 O00 C.

The reduced pellets may be removed from the reducing furnace in either a continuous or batch mode of operation dependent upon the type of furnace which is utilised.

Alternatively the reduced iron pellets may be manufactured by a chemical beneficiation route as shown in Fig. 2. Iron bearing material is fed into a chlorinator which typically may be a shaft reactor, or where the particle size is appropriate, a fluidised bed.

The ore is reacted at a temperature of 700-1000 C (depending on the ore) with a mixture of hydrogen chloride and hydrogen, preferably, although not essentially, in the ratio 2:1. Iron chloride is produced and is separated from the other product gases by cooling the gas stream to less than 550"C in a condenser and cooler. The finely divided iron chloride is separated from the gas steam in a cyclone.

Solid iron chloride is then compacted to provide pellets of an appropriate size, typically with the smallest dimension being less than 2.5 cm.

The iron chloride pellets are then passed to a reducation furnace. The reduction furnace may be a rotary kiln, travelling grate kiln or a static bed furnace. Within the furnace the pellets are reduced with hydrogen gas at a reaction temperature of 400"C to 900"C. The reduced pellets may be removed from the reducing furnace in either a continuous or batch mode of operation dependent upon the type of furnace which is used.

The reduced pellets from both of the above examples are fed through a reheating furnace and thence to an extruder as illustrated in Fig.

3 of the drawings.

In Fig. 3 there is shown a reheating furnace 1 having a reducing atmosphere in which the reduced pellets are heated or reheated to a temperature of the order of 750"C to 1 200 C. The heated pellets are ejected from the furnace 1 by means of a ram 2, and pass to a breach inlet 3 of an extruder 4.

The extruder 4 includes a ram 5 which compacts the pellets against a diaphragm (not shown) situated immediately behind an extrusion die 6. Upon the ram causing a predetermined pressure to be reached within the extruder, the diaphragm and compacted pellets are extruded and guided away by means of rolls 7.

The extrustion can be made semi-continuous by the reciprocating action of the ram 5.

A fresh intake of hot pellets can be compacted against the discard of the previous extrusion and extruded in turn, giving a cyclic operation.

It will be appreciated that by suitable choice of extruder and die configuration, the extruded ferrous product can be of any convenient cross-section, e.g. rod or tube or sections.

The pellets from the reducing furnace may be transported hot to the extruding arrangement under a protective atmosphere. Such atmosphere may be reducing and may comprise nitrogen with the addition of hydrogen at a concentration below the explosive limit, e.g. 5% by volume.

Conveniently the mass per unit volume of the pellets in the extruder may be optimised by utilising a mix of pellet sizes.

Claims (11)

1. A method of producing ferrous metal elongate products from a metal ore comprising the steps of beneficiating the ore into a concentrate form, forming the concentrate into agglomerates, passing the agglomerated concentrate through a furnace in the presence of a reducing gas acting as the sole or primary reductant and extruding the reduced agglomerates to produce and elongate body of ferrous metal.

2. A method according to Claim 1 wherein the ore is beneficiated by means of a series of grinding, magnetic or gravity separation and filtration stages.

3. A method according to Claim 1 wherein the oe is beneficiated by chemical means.

4. A method according to Claim 3 wherein the oe is beneficiated by subjecting it to reaction with hydrogen and hydrogen chloride gas, the resultant iron chloride being condensed from the product gases in a finely divided concentrate form.

5. A method according to any one of the preceding claims wherein the agglomerates into which the concentrate is formed are pellets.

6. A method according to any one of the preceding claims wherein additions of alloying materials are made prior to extrusion.

7. A method according to any one of the preceding claims wherein a plurality of separate ores are used.

8. A method according to any one of the preceding claims wherein the reduction of the concentrate agglomerates is carried out in a furnace in a continuous mode of operation in the presence of hydrogen and/or monoxide.

9. A method according to any one of claims 1 to 7 wherein the reduction of the concentrate agglomerates is carried out in a furnace in a batch mode of operation in the presence of hydrogen and/or carbon monoxide.

1 0. A method according to any one of the preceding claims wherein the reduced agglomerates are fed direct to the extruder from the reducing furnace at substantially the temperature of the furnace.

11. A method according to any one of the preceding claims wherein the reduced agglomerates are extruded in combination with material or different constitution so as to provide a composite extruded elongate body of ferrous metal.

1 2. A method according to any one of the preceding claims wherein the extruded elongate body of ferrous metal is subjected to mechanical working.

1 3. A method of producing ferrous metal elongate products substantially as hereinbefore described.