US2252714A - Process and apparatus for making metal powder - Google Patents

Description

` Aug. 19,'1941. E. J. HALL 2,252,714

PROCESS AND APP'AATUS FOR MAKING METAL POWDER Filed June 29, 1957 Sheets-Sheet l Ham/fr L. HALLbr/a/x BY Aug. 19, 1941. E, J, HALL V2,252,714 Y PRocEss AND APPARATUS FoR MAKING METAL POWDER Filed June 29, A937 2 sheets-sheetg 2 al 'ATTORNEY5 Patented ^Aug. 19, 1941 UNITED STAT Es PATENT o FFICE raooass AND APPARATUS Foa MAKIN METAL POWDER Everett J. H all, deceased, late of Elizabeth, N. J., by Harriet L. Hall, executrix, Elizabeth, N. J., assigner to Metals Disintegrating Company, Inc., Union Township, Union County, N. J., a corporation of New Jersey Application June 29, 1937, Serial No. 150,934 l (Cl. l-'12) `1e claims.

This invention relates to the production of copper powder by reducing oxides of copper and then breaking up the resultant friable mass of metallic copper. While not restricted thereto, the invention is particularly adapted to the production of copper powder for bronze bearings and other molded objects.

- In manufacturing bearings from copper powder, other materials (e. g. tin and/or graphite)` cooling of the batch furnace necessaryto reduce the temperature of the newly formed copper powder below the oxidation point. Furthermore, the batch procedure is limited as to the control of the reduction obtainable to produce y powder to meet different specifications, and to are often mixed with the copper. Large pro- 'ducers of bearings use automatic pressing ma-- chinery equipped with automatic filling devices. To insure uniform bearings and continuous performance of the pressing machinery, the bearing material must have requisite iiowability.

underthe molding pressure must be uniform. After the bearing has been molded, it is sintered or heat treated; and the` size of the bearing is Ad.-v `ditionally, the compressibility of the material changed by this manufacturing step. If the'20 `heat treated bearing is too short it must be l scrapped; if it is too long, it must be ground down,as the bearing material does not machine satisfactorily. Thus, the bearing material must produce a powder which uniformly meets a given specification. Among the general objects of the present invention are to provide a more eilicient and economical process for reducing copper oxides to form copper powder, to provide a process which can be adequately varied to produce powder to meet different specifications, to provide a proc- Y ess which can be adequately controlled to produce A,copper powder having uniform predetermined` characteristics, and to provide apparatus suitable for such improved processes.

Various specific and detailed objects of the iiivention will be apparent to those skilled inthe k art from the disclosure herein of the preferred be Vsuch that a uniform and predetermined change of size will take place when the bearing is sintered. Furthermorep the finished bearing l must have sufficient strength; and the bearing material must be such4 as will give the strength.

From the foregoing it will be seen that the bearing Imanufacturer requires a copper powder. which is exceedingly uniform as to the various physical characteristics that affect the manufacture of the bearing. And these physical characteristics must be correlated with the pressing.35

fdies, iilling machinery, other ingredients added by the bearing manufacturer, size and type of bearing to `be made, etc. T he result is that the manufacturer of the copper powder is `called upon to meet a wide range of powder specicafw tionssubmitted by bearing manufacturers; and, as` to each specification a uniform powder must be supplied.

VHeretofore copper powder has been made in batches. Trays containing thin layers of oxides of copper were placed in a chamber or furnace which was then closed and reducing gas passed therethrough. After the reduction had been effected the resultant copper` powder (and the batch chamber) had to be cooled sufficiently to 50 prevent the powder from being oxidized by contact of the air. l

This prior art batch procedure is inefficient and wasteful because (a) to get the desired dethe reducing gasmust be discharged before its reducingv constituents are substantially oxidized, (b)` the batch reducing furnace cannot be recharged immediately, but must be iirst cooled,-

and (c) there is a large net heat loss due-to the` .gree of completeness of reduction of thel oxidesf form of the invention.

In its preferred form the invention comprises i a process of continuously reducing oxides in a muil-le furnace, but the improvement is not merely that vordinarily obtained by changing from batch procedure to continuous procedure. In various other manufacturing lines batch processes have been quickly replaced by continuous processes, but that has not been the case with the manufacture' of copper powder by the reduction of copper oxides. oxide requires treatment of a powder with a gas;

and this does not readily lend itself to a continuous process, owing to the fact that a powder cannot be introduced or withdrawn through a gastight trap, as can be done with a liquid. On the other hand, it has been found, in accordance with the present invention, that there are chemical factors which can be so utilized in an appropriate continuous process as to overbalance the disadvantages inherent` in continuous treatment of a powder with a gas. These chemical factorsl will now be pointed out.

The rate of reduction of cupric and cuprous Y out at this time that continuous operation en-n ables the temperature to be controlled incre ad The reduction of copper 0f course, a hard cake is unde Furthermore, too high lreduction tem- Vapor in the gas.

f vantageously, as wellas permitting the material treated to be raised morequickly to proper reducing temperature, and subsequently -cooled morerapidly and Veconomically below the atmospheric oxidation point. i

,When a reducing 'gasfis used which contains both carbon monoxide and hydrogen, a number of reactions occur:

Thereductionof the oxides of copper is added, catalytically, by the presence of freecopper and is retarded, catalytically, by the presence of water At temperatures around 200 C., theinhibiting action of Water vapor is very pronounced. While such 'action decreases as the temperature rises, it is a factor to be reckoned =with at1400 C., and even at 450 to 550 C.

Accordingly, reactions 1) and (3) catalyze themselves,lwhile reactions (2) and (4) inhibit themselves. Reaction (5) takes place readily at 450.,to 550 C., particularly in the presence of a readily oxidized than CO and Hz, so that, if the reducing gas used has any considerable hydrocarbon content, a part of the gas may to advantage be recirculated toy give the residual hydrol to condense the water vapor formed and then recirculate. f

As in' the case of the batch process, it is ordinarily advisable to use a mixture of cuprous copper Ywill'ordinarily be present with the oxides catalyst so that while CO is present in the gas in any considerabley concentration, the `water vformed is largely eliminated. i

'I'hese facts, coupled withthe mass action laws, Amake it especially desirable to carry out the reduction countercurrent. The .fresh reducing gas with maximum content of C and Hz and a minimum content of H2O strikes the nearly re duced oxide when the tendency for the reversible reactions:

toproceed to the right is a maximum according to the mass action law in view of the fact that, at such time the ratios Cu': CuO and Cu CuzO are very high. The presence ofthe reduced copperalso aids in overcoming the normal tendency of the mass action law to retard further reduction.

Due to reaction mentioned above, the water vapor does not reach seriously high con' centrations until afterA the gas and powder have moved countercurrent a considerable distance and the ratio of Cu CuO or Cu CuzO has dropped to the point at which mass action law ceases to be an important factor, so far as the solid components ofthe reactions are concerned.

The heats of reaction are. such that when a reducing gas containing both CO and I -h are brought into contact with copperoxides at 450 to ,550 C., there is a strong tendency for the CO t\obe converted into CO2 before `appreciable amounts of-water vapor are formed. The heats of oxidation of copper, carbon monoxide and hydrogen are as follows:

Calories Cu+O 34,900 2 Cu+o 39,900 CO-|O v 67,960V 2 H--O 57,826

Consequently, if a gaslcontaining both carbon i monoxide and hydrogen is brought into counter,- current contact with copper oxides, the latter will pass iirst through a zone in which the hydrogen is the chief reducing agent and then through a,

and cupric oxides, the proportions usually ranging from 60 to 90% CuzO, with a complementary amount of lCuO, allowance being made for the free copper present withlthe oxides. Some free matically, by way of example, inthe accompany- I ing drawings, in which:

Fig. 1 is a longitudinal vertical section through the muiile furnace in which the reduction takes place; f

Fig. 2 is a Iside elevation of the cooling section of theapparatus;

Fig. 3 is a section on the line 3-3 of Fig. 1; Fig. 4 is -a detail view of the feed end of the muiile' furnace 'with water extracting apparatus connected thereto; y

Fig. 5 isa detail section on the line 5--5 of Fig. 2:

Fig. 6 is a'detail section Fig.' 2; and

Fig. 7 is a detail section on the line 'I-I of Fig. 6.

'I'he apparatus vcomprises two main parts, a

on the lines-6.61

4heating and reducing section (shown in Fig.'1) l and a cooling section (shown in Fig. 2).' Inthe ilrst section the mixed oxides are heated to around 450' to 550 C. in a reducing atmosphere to convert the oxides into metallic copper, and in is a fiat steel belt I0 passing over pulleys Il, II,

one of which is driven by any suitable means not shown. Preferably, the bearings of one pulley s' are movable and are biased to tension the belt.

The upper half of the belt "is wholly enclosed in a iiattened steel casing designated as a whole by I2, open at both ends and composed of a lplurality of sections which are bolted and welded together.

The tube I2 may be considered as having `four operating zones or sections I2a, I2b, I2c, and

I2d. The feed end I2a of this casing is provided with a hopper I3 for mixed oxides. vA vertically adjustable gate I4 regulates the thickness of the layer of oxides carried forward by the belt and also serves to some extent as a closure to prevent ,escape of reducing gas or entry of atmospheric air, according to the manner in which the ap ratus is operated. Some gas can and will pass in or out through the interstices of the powder on the belt, according to the relative pressure in and outside the casing.

After leaving the hopper the belt passes under a series of pivotally supported weighted bars I (see also Fig. 3 which serve to form furrows in the oxide layer for the dual purpose, first of aiding the reduction, and second of rendering thev friable mass of reduced copper more easily broken and pulverized.

Attached to the casing section I2a above-the bars l5 is a fiue IB for the discharge of spent reducing gases. The adjoining portion |2b of the casing forms the inner chamber of a muilie furnace. Surrounding `this section of the casing is at around 425 to 450 C., 450 t 500 C., 475 to 550 C., and 400 to 425 C., respectively. These ytemperatures are given more as a general guide for average operation and not 4as fixed ranges never to be departed from. Thus, where slow reduction is desired, the temperatures may be reduced, and vice versa.

Beyond the furnace section is the gas-introducing and gas-preheat'ing section |2c, to which is connected a pipe 24 for supplying thereto city or other suitable reducing gas. In addition to the pipe 24, other pipes, as 25 and 2G, may be used to supply further amounts of reducing gas direct to the furnace section 12b.

. Ordinary coal gas contains preponderating proportions of hydrogen and methane and only a small amount of carbon monoxide. Such gas is not as suitableas city gas composed inpart of water gas and hence having a high proportion of carbon monoxide. A gas of this type which has been found to give good results has the following approximate composition:

The gas-introducing section I2c is connected `to the cooling section |2d by a gate valve 29 comprising a vertically slidable gate (Fig. 6) which may be raised and lowered by turning the Vhand- `wheel 3| at the upper end of a threaded rod 32.

'I'he gate is set so Athat it just clears the layer of `reduced copper on the belt i0 and thereby acts been deoxidized by kburning oil in it or by passing it over red hot coke or the like. Such gas is often referred to as DX" gas. It may be slightly reducing, which is preferred for the present purpose. Alternatively, an actively reducing gas may be used, such as ordinary city gas. Also, a part or all of the spent reducing las passing up the ue I6 may'be supplied to the pipe 34, but it is rst preferably cooled below '70 C.

'I'he non-oxidizing gas ilows along the cooling section in the same direction as the belt moves therethrough and is drawn on through a flue adjacent the discharge end of the casing.

As the belt I0 passes over the pulley Il it contacts with one edge of a hopper 36 and the repassing it through a condenser to eliminate the.

greater part of the water vaportherein. An attachment for recirculating a part of the reducing gases after condensing out the majority of the water is shown in Fig. 4. A centrifugal blower 40 draws gas from the casing section I2a through pipe 4i and discharges it through condenser 42 and pipe 43 back to the gas inlet pipe 24. A valve-controlled by-pass 44 enables the amount of gas re-circulated to be regulated.'

Good results have been obtained with a muiile furnace section 35 feet long, a cooling section of i8 feet, and a belt speed of 5 to 20 feet per hour, depending on the rate of ow of the reducing gases, depth of oxide layer on the belt, temperature in the reducing zone, and other factors. An

as a constriction in the casing to prevent flow of v gas therealong at that point.

33,50 that by the time the reduced copper on the The cooling sec- `tion `is provided with one or more water jackets A't the e'nd of the cooling section I2d adjacent the gate valve is an inlet pipe 34 for some suitablenon-oxidizing gas, such as` air which has average speed under present commercial practice is 8 feet, per hour. Changing the rate of reduction has a marked influence on the properties of the finished product. Slow reduction gives lower density, liner particle size and lower ilow than rapid reduction.

In operating the apparatus reducing gas is introduced through the pipe 24, flows countercurrent to the direction of movement of the belt I0 through casing sections |2c and i2b and is discharged up the flue I6. As the spent gas Ainevitably contains small amounts of carbon monoxide, it is desirable to apply sumcient `suction to the tube IS/so that the gaseous pressure at .the bottom of the flue is slightly below atmospheric and sdrne air is drawn in under the gate I4. For the same reason, it is desirable to put slight suction on the flue 35 to prevent any non-oxidizing gas passing out into the room where the apparatus is located. To this end fiues I6 and 35.

may be connected to a chimney which is heated to produce a draft. In addition, or in the alternative, suction may be'produced by eductor jets ISa and 35a. Butterfly valves `Ilib and 35D provide furtherv control.

'I'he mixed oxides passing through the casing sections |2b and I2c are first heated to the temperature of reduction, then pass through a zone in which hydrogen isthe chief reducing agent, next through a zone in which carbon monoxide is the chief reducing agent and nally through a zone in-which the hot reduced copper preheats the reducing gases.

In compliance with the patent statutes, the best known forms of the invention have been disclosed, but it will be understood that the disclosure is illustrative and not limiting.

what reiaim is:

phere in the second section `of the casingpand 1. An apparatus for producing a friable mass of copper, comprising an endless moving belt, a tubular casingsurrounding the upper section of the belt, means for depositing a layerof copper oxides on the belt at the feed end of the casing, gas discharge fiues adjacent each end of the casing, a constriction near the -middle,

of the casingfor preventing the ow of gas along the casing at that point, means for introducing reducing Agas on the feed side of such constriction for countercurrent flow with respect, to the movement of oxides by the belt, means for introducing non-oxidizing gas on the discharge side of such restriction for flow in the same direction as the movement ofthe belt, and means for cooling the reduced copper on the-belt between such constriction and the discharge endofthe casing.

2. In the art of reducing copper oxides by causing a continuous ribbon-like stream of the comminuted oxides to travel horizontally and uninterruptedly through a furnace and thence, without change of form or direction, through ,a cooling chamber that is in communication with the furnace, the improvement which consists in supplying reducing gas to the furnace and causing it to make contact with the oxides` in` the furnace and to move horizontally counter-current to the direction of travel of the oxide stream; in applying to the furnace, at selected intermediate points along itsv length,`means for establishing within the furnace in connection with the reaction, heat inside the` furnace, different selected temperatures at such selected intermediate points, and controlling the temperature-` establishing means by means responsive `to `fluctuations in the temperatures, to compensate for such fluctuations, whereby those 'tempera-` tures are substantially maintained despite variations in reaction heat; in supplying non-oxidizing gas to the cooling chamber and causing it to travel in the same direction as the oxide stream;

- and in` substantially preventing thev movement of gas from the furnace into the cooling chamvber and from the cooling chamber into the furnace. i

3. The method of producing a-friable mass of metallic copper, comprising passing a continuous `horizontally moving stream of reducing gas over a continuous. longitudinally scored ribbon-like stream of heated copper oxides moving horizontally in the oppositeI direction, and thereafter causing the stream of copper to travel rwithin a stream of cool non-oxidizing gas moving in the direction oftravelof the copper stream, while -preserving the crossesectional dimensions: of the stream throughoutj its travels. i

4. An apparatus for producing a friable mass of copper, comprising an endless moving belt whose upper course is disposed and travelshori- -zontally, a tubular casing surrounding the upper course of the belt, means for supplying to the upper course of the belt, before it yenters the casing, a layer of copper oxides; a gas outlet V iiue at said end of the casing, means located be-` tween the iluefand the oxide supplying means Vfor regulating the thickness of the layer so deposited on the belt, means forautomatically maintaining different selected temperatures in different portions of the length of the casing ady jacent its feed end,` means for' cooling a section of the casing adjacent its discharge end, meansV for maintaining-a reducing atmosphere in` the first named section. of the casing, means for maintaining a. cooling and-non-oxidizing atmos` means to prevent mingling of the two atmospheres.

5. An apparatus for producing a friable massy of copper, comprising an endless movingr belt whose upper course is disposed and travels'horizontally, a tubularcasing surrounding the upper course of the belt and comprising a furnace section into which the upper course of thebelt first enters, and a communicating cooling section into which the belt Upasses as it leaves said furnace section, means for depositing a layer of copper oxides on the belt at the outer end of the furnace section, means for removing reduced copper from the belt at the outer end of the cooling section, a gas discharge ue at the outer end of the furnace section, a gate located between said iiueand the layer-depositing means, movable towards and from the belt to regulate the depth of the layer entering the furnace section, a` second gate located, at the junction between the furnace and cooling sections and adjustably fixed to `permit clearance of the oxide stream while offering an impediment to the movement of gas between the furnace and cooling sections, and means for introducing reducing gas into the inner end of the Vfurnace section and on the furnace side of said second named gate. Y i l,

6.An apparatus for producing a friabl'e mass of copper, comprising 'an `endless moving belt whose upper course is disposed and travels horizontally, a tubular casing surrounding the upper courseof the belt and comprising a furnace section into which the upper course of the belt first enters, and a communicating cooling section in 'to which the belt passes as it leaves said furnace' section, means for depositing a layer of copper oxides on the belt at the outerend of the furnace section, means for removing reduced copper from the belt at the outer end of the cooling section, a gas dischargeflue` at the outer end of the furnacel section, a gate located between said ue and the layer-depositing means, movable towards and from the belt to regulate the depth of the layer entering the furnace section, a second gate located at the junction between the furnace and cooling sections and adjustably xedto permit clearance of the oxide stream While offering an impediment to the movement of gas between the f furnace and cooling sections, means for introducing reducing gas into the inner end of the furnace section and on the furnace side of said second named gate, means forintroducing cooling gas into the inner end of` the cooling section and on the cooling section side of said second named gate, and a gas discharge flue at the outer end of the cooling section.

from the belt at the outer end of the cooling sec- A tion, a gas discharge flue at the outer end of the furnacesection, `a gate located between said ue and the layer-depositing means, movable towards and from the belt to regulate the depth of the layer entering the furnace section, a second gate located at the junction between the furnace and cooling sections and adjustably fixed to permit clearance of the oxide stream while offering an impediment to the movement of gas between the -furnace and cooling sections, and means for inaasam. l

, reaction heat, and thereafter causing the stream troducing reducing gas into the inner end of the i furnace section and on the furnace side of said second named gate. .x

8.,A reducing furnaceof the kind described,

comprising a horizontally disposed tubular casing section with an endless belt having its upper course moving horizontally through the casing section, means for depositing a layer of copper oxides on the upper course of the belt before it enters the casing section, a gate at the feed end of the'casing section permitting the layer so deposited to pass it, but obstructing the movement of gas outwardly from the casing section, means for introducing reducing gas at the other end of the casing section, a flue at the said feed end'of the casing section for causing movement of the gas counter-current to the travel of the belt, means for. heating ythe casing section located `at different intermediate points along its length, and' vmeans for cooling the casing section located at A different intermediate` points along its length, said heating and cooling means being thermostatically `controlled substantially as and for the purposes set forth.

9.` The method which comprises passing a continuous ribbon-like stream of comminuted copper oxides horizontally and slowly through a horizontally disposed furnace in an atmosphere of reducing gas, applying to the furnace at selected intermediate points along the length of the fury nace, means for establishing within thefurnace in connection with the reaction heat inside the furnace, dierent selected temperatures at such selected intermediate points, and controlling the temperature-establishing means by means responsive to fluctuations in the temperatures, to

compensate for suchuctuations, whereby those temperatures are substantially maintained despite variations in reaction heat.

10. The method which comprises passing a continuous ribbon-like stream ofcomminuted copperoxides horizontally and slowly through a horizontally disposed furnace in an atmosphere of reducing gas moving countercurrently to the oxide stream, applying to the furnace at. selected intermediate points along the length .of the furof copper to travel, without change of form or direction, within a stream of cool non-oxidizing gas moving in the direction of travel of the copper stream. g i' 12. Apparatus of the kind described comprising, a tubular horizontally disposed casing with an endless belt having its upper course moving horizontally in the casing, means for continuously supplying copper oxides to said belt the casing being divided into aiurnace section and a cooling section in communication with each other, the

nace, means for establishing within the furnace p intermediate points along the length of the furnace, means for establishing within the furnace in connection with the reaction heat inside the furnace.4 different selected temperatures4 `at such selected intermediate points, controlling the temperature-establishing means by means responsive to fluctuations inthe temperatures', to compensate fory such fluctuations, whereby those temperatures are substantially maintaineddespite variations in upper course of the belt entering the furnace section and emerging from the cooling section, means for introducing reducing gas at the junction of the two sections and positively causing it to move towards and discharge from the outer end of the furnace section, means for establishing `within the furnace section, at selected `intermediate points` along its length, different selected temperatures at such selected intermediate points,

means responsive to fluctuations in the temperatures to compensate'for such fluctuations and maintain the temperatures substantially constant, and means for introducing non-oxidizing gas at the Junction of the tworsections and positively causing it to move towards and discharge from the outer end of the cooling section.

13. The method which comprises passing a continuous ribbon-like stream l of comminuted `copper oxides horizontally .and slowly through a horizontally disposed furnace in an atmosphere or reducing gas moving countercurrently to the oxide stream, applying to the furnace, at selected intermediateI points along the length of the furnace, means for establishing withinthe furnace in connection with the reaction heat inside` the furnace, different selected temperatures within a range of about 425 C.-550 C. at' such selected intermediate points, and controlling the temperature-establishing. means by means, responsive to fluctuations in the temperatures, to compensate for such fluctuations, whereby those temperatures'are substantially maintained despite `variations in reaction heat; the depth of the copper stream, the speed of its travel, and the rateof flow of the gas being chosen each in view of the others, whereby eiective reduction of a maximum amount of material may be accomplished in a given time.

14. The method which comprises passing a continuous ribbon-like stream of comminuted copper oxides horizontally and slowly through a" horizontally disposed furnace in an atmosphere of reducing gas moving countercurrently to the oxide stream, applying to the furnace, at selected intermediate points'along the length of the lfurnace, means for establishing within the furnace in connection with the reaction heat inside` the furnace, different selected temperatures within a range of about 425 C.550 C. at such selectedintermediate points, controlling the temperatureestablishing means ,by means responsive to fluctuations in the temperatures, to compensate for such fluctuations, whereby those temperatures are substantially maintained despite variations in reaction heat; the depth of the copper stream, the

speed of its travel, and the rate of ow of -the gas being chosen each in view'of the others, whereby effective reduction of a Imaximum amount of material may be accomplishedy in a given time; and thereafter continuing to move the metal stream and subjecting it to the action of a stream of non-oxidizinggas moving in the direction of, travel of themetal stream.

15. A reducing furnace ofthe kind described comprising a horizontally disposed tubular casing with an endless belt having its upper course moving `horizontally through the casing, means for depositing a layer of copper oxides on the upper course of the belt before it enters thecasing,

means for introducing reducing gas at the other end of the casing and discharging such gas at the feed end of the casing, means for establishing temperature conditions inside the `furnace, and 10 means responsive to temperature fluctuations inside the furnace, controlling said temperature- 'establishing means to compensate for such flucl tuation's, whereby temperature conditions established inside theY furnace may be substantially 15- maintained despite variations in reaction heat. v

16. Ihe method which comprises passing a 'continuous ribbon-like stream of comminuted "6 i ci i 2,252,714

copper oxides khorizontally and slowly through a horizontally disposed furnace in an atmosphere of reducing gas, applying to the furnace at selected intermediate points along the length of. the furnace, heating and cooling means for establishing Within the furnace in connection with

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