US3122434A

US3122434A - Continuous process of producing strips and sheets of ferrous metal directly from metal powder

Info

Publication number: US3122434A
Application number: US33703A
Authority: US
Inventors: William A Reed; Irving P Whitehouse
Original assignee: Republic Steel Corp
Current assignee: Republic Steel Corp
Priority date: 1960-06-03
Filing date: 1960-06-03
Publication date: 1964-02-25
Anticipated expiration: 1981-02-25

Description

Feb. 25, 1964 w. A. REED ETAL 3,122,434

CONTINUOUS PROCESS OF PRODUCING STRIPS AND SHEETS 0F FERROUS METAL DIRECTLY FROM METAL POWDER Filed June 3, 1960 2 Sheets-Sheet 1 xEVAc.

INVENTORS WILL/14M 4. R550 By new/v6 WHUZ'WOZ/J'E 1M4. umdiagd' ATTOGI/EV Feb. 25, 1964 w. A. REED ETAL 3,122,434

CONTINUOUS PROCESS OF PRODUCING STRIPS AND SHEETS OF FERROUS METAL DIRECTLY FROM METAL POWDER 2 Sheets-Sheet 2 Filed June 5, 1960 INVENTORS W/ZZ/AM A @550 BY MV/A/ P WH/IZ HOVSE United States Patent Ofifice 3,122,434 Patented Feb. 25, 1964 CONTINUOUS PROCESS OF PRODUCING STRIPS AND SHEETS F FERROUS METAL DIRECTLY FRQM METAL PGWDER William A. Reed, West Richfield, and Irving P. Whitehouse, South Euclid, Ohio, assign'ors to Republic teel Corporation, Cleveland, Ohio, a corporation of New Jerse y Filed June 3, 1960, Ser. No. 33,703

15 Claims. (Cl. 75-214) The present invention relates to a continuous process for making flattened, elongate metallic bodies as strips, sheets and the like, and more particularly for making such bodies from iron and iron alloys in the form of flowable particles, such for example as powdered metal, wherein the particles may be of a size similar to that used in the powder metallurgy industry.

There have been a number of proposals in the past tending to teach the reduction of a metal compound, such as an iron oxide or an iron ore concentrate, followed by the semi-fabrication into a sheet-like form of such reduced metal material by compacting and subsequent sintering operations. Some of these proposals applicable to metals other than iron and alloys thereof have even included direct rolling of powder into sheets or strips. These suggestions have made no impression on the commercial art as far as is known, at least that art having to do with iron and ferrous metals generally.

The iron and steel industry particularly has utilized conventional means for making flattened, elongate metallic bodies, as strips or sheets of metal, including the wellknown blast furnace reduction of the ore, the processing of the cast iron composition material produced by the blast furnace by further conventional steel making processes, such as the open hearth process, and then followed by fabrication, successively into billets, slabs and sheet or strip. The general object of the present invention, therefore, is to provide a practicable and commercially operable process for the making of strips or sheets of ferrous metal by the direct rolling of powdered metal and to teach the essentials of such a process.

Summarizing the present invention, it comprises a process including the supplying by gravity of ferrous metal such as iron, steel or conventional alloy steels in composition, and in the form of fiowable particles of the type usable in powder metallurgy, through a downwardly extending opening of a supply hopper to a pair of rolls, which are arranged side by side with their axes substantially horizontal. At least one, and preferably both, of these rolls is positively driven and serves to compact the loose flowable particles of the ferrous metal supplied thereto into the form of a flattened body which will be sub stantially self-sustaining. In so doing, it is necessary that the compacting be suflicient so as to form the material into a body which has at least about 45% of the theoretical maximum density of the metal being used. It is also necessary that each of the compacting rolls shall have a diameter which is at least about 100 times the thickness of the body to be formed from the metal powder by rolling between these rolls. This preliminary rolling or compacting may be done either hot or cold, (i.e. at room temperature) and is normally done with rolls which are unheated, except to the extent that they may become heated by contact with the metal supplied to and through these rolls. The rolls are spaced apart to provide a space therebetween of predetermined thickness, which is a measure of the thickness of the strip emerging from the rolls.

It is also a feature of the present invention that the first roll pair, when using rolls of the relative dimensions with respect to the thickness of the strip being formed as aforesaid and when using ferrous metal powders, will tend to form the strip in part by a sort of extrusion operation in that in any given time period, the length of the metal body leaving the first pair of rolls will be greater than the number of revolutions of the rolls of the first pair 1n the same period multiplied by the circumference of these rolls (it being assumed that the rolls of the first pair are both of the same diameter).

The body or strip emerging from the first roll pair or first roll pass, as it may be called, is then conducted into a heating zone, in which the temperature of the material is brought to a point such that the metal in question will be in the plastic range. For ferrous metals, such as iron or alloys of iron including alloys simulating steel to which the present invention pertains, it is found that this plastic range of temperature is the range of about 1800 F. to about 240G F. The flattened body is then passed from the heating zone into a second pair of rolls or roll pass, as it may be called, in which the material of the body is further compressed and the particles permanently bonded together, so as to bring the body to a condition of substantially full density, which condition will be explained more in detail hereinafter.

Inasmuch as the first and second roll passes and the travel of the flattened body through the heating zone intermediate these roll passes are all continuous, and as the two pairs of rolls are at fixed positions along the path of the strip, it is necessary that the relative speeds of these rolls be properly coordinated so as to maintain a substantially constant length of metal strip therebetween. For this purpose, one possible solution is to provide means responsive to the deflection of a portion of the strip intermediate the two pairs of rolls from a theoretical or predetermined path for controlling the relative speeds of the two roll pairs. Practically, it is usually sufiicient to run the first pair of rolls at some predetermined speed and then merely control the speed of the second roll pair; although a reverse action could be resorted to if desired; or a relative control of the speeds of the two roll pairs could be effected.

Means are also necessary for protecting the metal being fabricated from chemical reaction with gases with which this metal may come into contact at one time or another during the fabrication operation. With iron and iron alloys, for example, this chemical combination is usually restricted tooxidation, so that the means in question are merely some means effective to prevent contact between the metal and oxidizing gases, such as the oxygen of the air, at all times when the metal is heated suificiently so that such oxidation might otherwise occur. This object may be attained by enclosing portions of the path of the metal body where it may be heated to temperatures at which it is sensitive to oxidizing gases, and then passing through this enclosed space some relatively inert or nonoxidizing gas or gaseous mixture, whether or not that mixture be positively reducing in character.

Other detailed objects and advantages of the present invention will become apparent from a careful consideration of the following detailed specification and the appended claims, all when taken in connection with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic illustration of apparatus embodying the present invention in which the course of the metal particles and the elongate body formed therefrom is substatntially vertical; and

FIG. 2 is a similar view of another embodiment of the invention in which the metal passing through the first roll pass moves substantially vertically downwardly and in passing through the intermediate heating step and the second roll pass moves substantially horizontally.

The first element of the invention to be considered is the character of the material which must be supplied to the process and upon which the process can operate. This material is a ferrious metal, consisting essentially of iron or alloys of iron, such as those simulating alloy to be used in the process and the outside air.

steels in composition, or some mixture of these materials, all of which material is in the form of flowable particles such as would be usable in powder metallurgy.

The method of fabrication or preparation of the metal particles supplied to the present invention is not a part of this invention per se. It is contemplated, for exarnple, that in the case of iron, an iron ore, such as magnetite, may be finely comminuted and then separated from the gangue naturally occurring therewith by magnetic separation. Following this, it is contemplated that the resulting concentrate of iron oxide may be suitably reduced to a metallic state at temperatures below the melting points of materials present. In the event that the reduced material is in the form of more or less spongy masses, it is contemplated that such masses may be comminuted or reduced in particle size by any suitable means, so that the largest particles present will be of a size not greater than about half the thickness desired for the flattened body following the first roll pass as hereinabove generally outlined and as hereinafter set forth in detail. In most instances, however, it is contemplated that the starting material for the present process will be in the form of a relatively fine powder of the one or more metals as the case may be, wherein the particle size of the metal powder is approximately that now in use in the commercial powder metallurgy industry, which will be very much smaller than 50% of the desired thickness for the metal strip following the first roll pass as hereinafter set forth and as illustrated by examples which are included herein.

It has been stated that the metal powder usable in the present process must be flowable. By this is meant that the powder will ordinarily flow by gravity through the orifices provided. It is conceivable, however, that in some instances and in the case of some metals or combinations thereof as aforesaid, the metal powder used and otherwise usable may tend to stick in or bridge over an orifice, so as not to flow easily therethrough. Under these circumstances, it is contemplated that conventional vibrating means may be used to keep the metal powder in a sufficiently agitated state, so that it may flow by gravity. Any material which can be handled in this or some similar manner is to be considered flowable as this term is used in the present specification and claims.

It is further recognized that as powdered metals are progressively heated, there comes a point at which they will tend to agglomerate or sinter together. When this occurs, the metal powder becomes progressively less fiowable as herein defined. In the case of iron powder, the flowable characteristic starts to diminish at about 1400 F.

Referring now to the accompanying drawings, there is shown in each embodiment of the invention a supply hopper 10. The hopper may be supplied with the metal particles from an upper hopper or supply chamber '11 which, as shown in FIG. 1, is connected to the hopper 10 by a duct 12 including upper and lower valves 13 and 14 (FIG. 1) defining an intermediate lock portion 15. When provision is made as later described with respect to the form of the invention shown in FIG. 1, for conducting a number of the steps of the process in a substantially evacuated chamber, then the lock chamber 15 may be provided with a suitable vacuum pipe connection 16 under control of a valve 17. Other equivalent means may be provided as desired for preventing contact at this stage of the operation between the metal particles This is important if the metal is maintained hot between the reduction-preparation thereof on the one hand and the fabrication according to the present process on the other,

whereby the latent heat in the metal from the reduction is retained for assisting in the fabrication thereof. Under such circumstances, many metals including iron would react very rapidly with the atmospheric oxygen if they were exposed to the air at this stage and while hot.

The form of the invention of FIG. 2 employs a star valve 18 between the

hoppers

10 and 11, which may be sufiicient for certain types of operation, particularly for example, when the metal being supplied is cold (i.e., substantially room temperature) or at such a temperature that the manner of handling it is not critical. Inasmuch, however, as these valves and their uses are well known in the art, they are not further described in detail here.

The first process step particularly embodying the present invention is a first roll pass, which is effected by supplying the metal particles from a downwardly directed opening of the supply hopper 10 to the space between a pair of rolls 19 and 2t). These rolls are arranged substantially side by side and have substantially parallel horizontal axes. They are both preferably arranged to be driven by means (not shown) in a manner which will be understood by those skilled in the art of metal rolling. It is contemplated, however, that but one of these rolls need be driven positively, the other being in effect an idler, such an arrangement having been proved by actual tests to be fully operative. The

rolls

19 and 20 preferably have substantially smooth surfaces, in that no particular provision is made for serrated or pitted surfaces on the outside of the rolls, even though they may not in some instances have polished surfaces. As a possible alternative at this point, it is contemplated that for some purposes and for some types of metal powder, it may be desirable to roughen the surface of one or both the

rolls

19 and 26 to provide greater friction. The rolls are of such a diameter and have such spacing between their adjacent portions that the width of the space between the rolls is coordinated with the desired thickness for the flattened body emerging therefrom, as shown at 21. It has been found that there is a reasonably critical relationship between the diameter of the rolls and the thickness of the strip or sheet which may be formed by rolling ferrous metal powder therebetween. This relationship or ratio is such that the rolls should be at least about times as great in diameter as the thickness of the metal strip to be formed by rolling metal powder between these rolls. This will further be illustrated in an example hereinafter given. It is also found that there is a reasonably determinable amount of spring back following the rolling, which is a function of the particular metal powder being handled, so that the width of the space between the rolls is almost always less than the unconfined thickness of the flattened body emerging from these rolls. However, while it is possible to measure the space between the rolls when idle or empty, this is not practically possible under normal working load, for even if the rolls were rigidly mounted, there is some elastic deformation thereof. Thus, the only values which can be determined practically are the space between the rolls when empty and the thickness of the strip after it has emerged from the rolls. The downwardly extending opening of the supply hopper 10 which is generally indicated at 22 is elongated in a direction parallel to the axes of the

rolls

19 and 29, so as to have a length which will be commensurate with the width of the flattened body to be made. This length may be the same as the axial extent of the rolls themselves or may be somewhat less. In any event, the desired dimensions of the body to be made must be taken into account and in some instances provision should also be made for somewhat irregular edge portions of the body, which may be cut off following the completion of the fabrication thereof to leave a substantially perfect center section. It is contemplated that some provisions may be made for forming a flattened body in a manner which will not involve the forming of irregular edge portions which must later be discarded. Such special provisions are, however, no necessary part of the present invention and are not included in this disclosure but are described in detail and claimed in Patent No. 2,933,305, issued April 19, 1960.

The amount of pressure which must be exerted on the metal particles to compact them so as to produce a flattened body which will be substantially self-sustaining during subsequent operations is, of course, a variable depending upon the chemical and physical character of the material supplied to the process, as well as upon the dimentions of the body being formed with respect to the particular size range distribution of the material supplied to the process. It is found, however, that in order to obtain satisfactory flattened bodies from the first roll pass and particularly to provide such a body which may be handled in a practicable manner as hereinafter set forth, the metallic material supplied thereto must be compacted sufficiently so as to have a bulk density which is at least about 45% of the theoretical maximum density of the metal of which the strip is composed. With pure iron, for instance, the theoretical maximum density is about 7.86 grams./ cc. As hereinafter set out in examples which follow, the first roll pass may provide a sufficient compression to convert the metal to a state which is up to about 90% of theoretical density.

While the compression of the powder as aforesaid is primarily a function of the pressure effective thereon, it will be understood that the pressure effective between a pair of rolls is difficult to ascertain in practice. It has been found that the practical way of controlling the pressure effective on material of this kind is to control the spacing between the rolls for any given pair of rolls which may be done within the ratio limitations given above between roll diameter and strip thickness.

An unusual phenomenon has been recognized, which is apparently a function of operating Within the limitations of the present invention and is characteristic thereof when ferrous metal powders are rolled into strips or sheets by rolls having the roll diameter to strip thickness ratio of at least about 100:1, as herein specified. This phenomenon may be termed an extrusion phenomenon, in that in any given period of time, the length of strip formed in the first roll pass is greater than the number of revolutions of the rolls during this given period of time (assuming both rolls to be of the same diameter), multiplied by the roll circumference. This phenomenon can be particularly noted and proven by having one roll so formed or arranged as to make a mark at a particular place in the strip being formed each time it rotates. The distance along the sheet or strip between adjacent marks will then be found to exceed the roll circumference, as hereinafter set forth in an example of the invention.

As the temperature at which the material is supplied to the first roll pass is increased, the densification effected with a given pressure in the first roll pass increases. Thus, for example, it is easier to obtain a given density in a rolled body with a metal powder at a relatively higher temperature than at a relatively lower temperature, both within the temperature range at which this operation is possible. This is reflected in practice in lower power requirements for driving the rolls as the =temperature of the metal powder supplied to the rolls is increased and with a given roll spacing.

The body 21 is next passed to a heating zone 23. This zone may be disposed in vertical alignment with the path of the body through the first roll pass as shown in FIG. 1 or it may be disposed in a horizontal portion of the path of the body as shown in FIG. 2. In either case, heat may be supplied to the material of the body in any suitable manner, with particular concern being had to the other ambient conditions. Thus, as shown in FIG. 1, the operations from a point in advance of the first roll pass to a point beyond the second roll pass are enclosed within an evacuated chamber 24. Under these circumstances the heating means should be such as not to interfere with the maintenance of the desired vacuum in this chamber. For this purpose then the heat may be supplied as generally indicated in FIG. 1 by an electrical coil 25 energized by a high frequency current from a suitable source, so that the heat is generated by induction in the body 21 to be heated. Alternatively, other heating means, not embodying the generation of products of combustion, may also be used, such as heated mufiies means wherein products of 6 combustion are kept from passing into the evacuated chamber 24. In FIG. 2, for example, the heat may be supplied by electric heating elements 26 disposed in heat radiating relationship to the path of the body which is shown at 27 in this figure. Further, a possible arrange ment is contemplated in which the heating zone is provided in a substantially enclosed space through which a neutral gas is passed, as in FIG. 2 as hereinafter set out.

The purpose of the heating step is to render the metal further compaotible in a second roll pass to a condition of substantially full density. Thus, it is essential that the metal be brought to such a temperature that it will be in a plastic range as generally set forth hereinabove.

In addition, it is necessary that the metal particles shall coalesce or bond together into a continuous body, comparable in its physical characteristics with strips or sheets made in a conventional manner. It is a present theory that this action takes place to a major extent during the second roll pass and that it is effected by what might be termed diifusion of the metal, so that the interparticle boundaries are finally greatly diminished in extent or wholly absent. It is a further theory, which is presently believed to be correct, but is not relied upon directly in support of the patentability of the present invention, that in the case of alloys, such as stainless steel, an oxide envelope on the particles must be ruptured during this bonding or coalescence action. Thus the term plastic as herein used is intended to mean somewhat more than merely malleable and is intended to embrace a condition in which molecular diffusion, to the extent necessary for coalescence or bonding, is reasonably possible.

While it is believed that this bonding takes place to a major extent during the second roll pass and after the metal has been heated, this is not intended to preclude some bonding or coalescence action taking place during the first roll pass, particularly if the metal is heated during this first pass, which is contemplated as one of the possibilities according to the present invention.

The plastic range for ferrous metal is from about G F. to about 2400 F. (preferred about 2100 F.) and is required to be at least this high in order that the metal be raised to a temperature in the range in which it is deformable under pressure, i.e., in which it will not crack when worked mechanically. The temperature range to which a metal is heated should always be less than the melting point of the particular metal being worked which is, of course, a function of the composition of the metal.

It is not the normal function of this heating step to fuse any metal present; although it is possible that in case of some alloys, some low melting metallic constituent may be present, usually in a minor percentage amount, and the heating be to a temperature as high or higher than the melting point of such a relatively low melting constituent. In any event, the purpose is not to melt the metal as a whole, but rather to raise the metal to a plastic temperature range, such that it may be further compacted and coalesced or bonded as aforesaid by a mechanical means such as a second pair of rolls.

It has been stated that the body or strip emerging from the first roll pass is substantially self-sustaining. This is so as long as the metal is relatively cool and also is so, irrespective of the temperature, as long as it is moving in a substantially vertical path as shown, for example, in FIG. 1. On the other hand, when such a strip is diverted from a vertical to a horizontal path as in the form of the invention shown in FIG. 2, and when the metal is then heated, it is usually necessary to provide some support therefor at relatively frequent intervals. This may be done, for example, as shown in FIG. 2, wherein the metal body 27 passing through the heating zone 23 is shown supported upon a plurality of spaced rollers 41. These rollers may, if desired, be provided with suitable surface coatings, so as to prevent any damage to the metal body passing thereover by adherence or otherwise.

The metallic body 21 passes from the heating zone to a second pair of rolls or second roll pass, which may be arranged vertically beneath the other portions of the path of the body as in FIG. 1 or be horizontally disposed as in FIG. 2. As shown in these figures, the second roll pass includes rolls 2% and 29. These rolls may be generally similar to the first pair of

rolls

19 and 29, except that they do not have to be as large in diameter and the spacing therebetween is always somewhat less than the spacing between the rolls 1) and 21), so asto effect a further compression and bonding of the metallic material of the body 21, this time usually and preferably to a condition of substantially full density.

It has been said above that the second roll pass reduced the metal to a condition of substantially full density. It is recognized that there is in practice a difference between the theoretical maximum density of a given metallic composition and the full density thereof which is practically attainable, in that it is found that at substantially full density, whether this condition be attained by the working of material starting with a finely divided form of such material, as in the present case, or whether it be attained in metallic material prepared by melting and working processes, the condition of theoretical 100% or maximum density is seldom actually fully attained. This is due to the fact that there usually are minute voids in almost any metal, as well as some impurities, such as metallic oxides,which exist in admixture with most, if not all, commercially produced metals (particularly ferrous metals in powder form suitable for powder metallurgy). In addition to this, some foreign materials may be actually dissolved in the metal, which results in reducing the overall density thereof to a certain extent. When the starting material is a material in fiowable particle form, such as powdered metal, the practical limit of mechanical workingoperations, with or without heat, is usually a condition of about 93% to 98% of theoretical maximum density. Under these circumstances, such voids as may exist in the metal are discontinuous and have little or no effect upon the physical properties of the resulting metal pieces, whether those pieces be in the form of sheets, strips or other shapes. Thus, the second roll pass is in fact intended to produce an actual density in the range of about 93% to about 98% of the theoretical maximum density for the metal composition in question, which is to be considered substantially full density from a practical point of view. For many commercial purposes, this density, or sometimes even lower densities, may be adequate to fulfill all the practical requirements.

Inasmuch as the entire process as hereinabove generally outlined takes placeby simultaneous Workings on different portions of a single integral body or strip (once the particles have been converted into such a body by the first roll pass), it is necessary that the speeds of the two pairs of rolls be coordinated with one another, so as to prevent undue and damaging strains on the material of the body or strip, particularly during its passage between the two sets or pairs of rolls. in order to control the roll speeds, resort may be had, for example, to expedients which have been developed by the prior art and which include electrical systems responsive to the strip deflecting from a predetermined path at some point between the positions of the two pairs of rolls. This subject matter has been developed to a practical and workable extent and is embodied, for example, in the disclosures of the following United States patents:

Beaumont--l,749,060 Stephenson-2,147,467 Heinz2,3 89,047 Ayers2,4-22,65 1 Fegely-2,547,20'l

In some instances a portion of the strip in moving from the first roll pass to the second roll pass is deflected, for example, as shown in FIG. 1 at 30, by a roller or other contact means 31 which is urged to the right as shown in FIG. 1 by a suitable light spring or other equivalent means and in connection with which suitable means (not shown) may be provided, subject to the attained position of the means 3 1, for controlling the relative driving speed for the second pair of

rolls

28, 29 with respect to the speed of the first pair of

rolls

19, 20. As a practical matter, either pair of rolls maybe driven at any desired speed and the automatic control used to govern the speed of the other pair of rolls. Alternatively, the relative speeds of the two pairs of rolls may be controlled in response to this or some other type of automatic control means.

In the form of the invention shown in FIG. 2, the path of the elongate body 21 from the first pair of rolls 19', 20 through which this body proceeds in a vertical downward direction is changed to a horizontal path in which the body 21 moves through the heating zone 23 and thence through the second pair of

rolls

28, 29. Incident to the change in the course of this path, and in this embodiment of the invention, on the side of the heating zone toward the first pairs of

rolls

19, 29 as distinguished from the side of the heating zone toward the second pair of rolls (as in FIG. 1), there is provided a means sensitive to a deflection of the body 21 from a predetermined or normal path at a point or zone 32.. In this instance, if the loop of the body 21 extends downwardly (or to the left as seen in FIG. 2) an excessive amount at 32 due to the

rolls

28, 29 not taking up on the elongate body quite at the rate at which it is supplied to the point or zone 32 from the first pair of rolls 19, 2%, then the loop or part-loop of the body 21 will interfere with the path of a beam of light between a light source 53 and a light-sensitive means 34, so as to control the operation of a suitable roll drive speed control system (not shown). In some instances, as shown in the patents hereinabove referred to, there may be two or more light sources and two or more light-sensitive means subject to the position of a loop of the elongate body defleeting from a theoretical or predetermined path, an arrangement being provided so that the loop will be adjusted by adjustment of the relative roll speeds to be in a predetermined position with respect to the sensing means. The use of this or other known means in controlling the speeds or relative speeds of one or both the pairs of rolls forms in general a part of the present invention, although the detailed means for carrying this out may be selected from the prior art, examples of such prior art disclosures being hereinabove referred to. These examples are intended as illustrative, however, and not as limiting.

It is recognized as generally hereinabove set forth that some metals, at least while hot, are subject to chemical combination with gases with which they may be brought into contact, particularly until the metals have been compacted and bonded to substantially full density as herein defined. Similar subject matter is disclosed, for example, as a process for eliminating pyrophorism, which might otherwise occur, in the patent to Graham et al., No. 2,875,035, issued February 24, 1959. It has been found that when iron is produced by certain known prior art processes, and is in the form of fine powder, it may be pyrophoric, even after cooling under non-oxidizing conditions and when subsequently exposed to the atmosphere.

It is known that many metals, when hot and in a porous physical state, will react chemically with atmospheric oxygen and some with other gases. It is necessary, therefore, to protect hot metals in relatively porous, finely divided and/ or spongy form from contact with atmospheric oxygen and other oxidizing gases.

There has been described in connection with the form of the invention of FIG. 1 a means by which the metal may be introduced into the supply hopper 10 under sub stantially evacuated conditions and then the entire process up to and including the compacting of the strip through the second roll pass be enclosed within an evacuated casing, as shown at 24 (FIG. 1). In the FIG. 2 form of the invention, it may be assumed that the metal is being handled under conditions in which the first roll pass takes place with the metal at substantially room temperature, which may be done when the metal is not initially pyrophoric in character. Under these circumstances, it may be adequate to leave the first pair of

rolls

19, 20 unshielded and open to the atmosphere and to have a part of the path of the elongate body 21, i.e., from this roll pass to the heating zone 23, also open to the atmosphere. However, once the metal is heated in the heating zone, it is quite vulnerable to chemical reaction on contact with certain gases, as atmospheric oxygen. Under these cir cumstances, it may be desirable and be sufficient to enclose the heating zone and the second roll pass in a casing 35 with a minimum size entrance opening 36 for the metal body 21 to move thereinto and with the casing closely approaching the

rolls

28 and 29 at 37 and 38, respectively. If then the casing 35 is completely flooded with an inert gas, the heated metal will be protected during the critical period and until it is compacted to an extent such that it is no longer substantially reactive chemically. This inert gas may be supplied to the interior of the casing 35 through a duct 39 and some may pass out through the spaces at 36, 37 and/or 38. The remainder of the inert gas may pass from the casing to a suitable disposal point through a duct or passage 40 or be recirculated as desired. When operating with iron or iron alloys in accordance with the present invention, some relatively cheap gas such as producer gas, blast furnace gas or other available nonoxidizing gases may be used as the inert gas supplied through the passage 39 as aforesaid and will serve to prevent undesired oxidation of the heated body during the time it is sufficiently porous so that it would be damaged by contact with atmospheric oxygen. Once the body 21 has been further compacted and bonded or coalesced as aforesaid in the second roll pass i.e., between

rolls

28, 29, so as to be at substantially full density, it is no longer vulnerable to reaction with any ambient gases and may be handled in the same way in which metal bodies are handled in standard commercial rolling mills.

The process of the present invention will be further understood by a consideration of the following examples:

EXAMPLE I This example is given to show one preferred embodiment of the invention and also some data as to the working of the process using ferrous alloys.

In a first test there was used an iron powder made in accordance with the teachings of the Crowley Patent No. 2,744,002, granted May 1, 1956. This powder had an apparent or bulk density of 2.31 grams/cc. It was supplied to the first roll pass unmixed with any other mate rial and at about room temperature. The rolls of the first pass were 24 inch diameter rolls and had an axial dimension at the rolling surface of about 2 inches. The spacing between the rolls (empty measurement) was 0.118 inch. The strip emerging from the first roll pass was about 0.15 inch in thickness and had a density equal to about 80% of the theoretical density (bulk density equalled 6.31 grams/cc). This strip was then heated by radiant heat in a furnace having a wall temperature of about 2800 F. and until the strip itself had a temperature of about 2100 F., the heating taking place in about onehalf minute actual heating time. The speed of travel of the strip emerging from the first roll pass and travelling through the heating furnace was about 50 feet per minute. The rolls used as the second rolls were 4 inch diameter rolls, but were backed up by other rolls as a l-high mill. These second rolls had rolling surfaces 2 inches wide (axia1 dimension). The spacing between the rolls of the second roll pass was about 0.10 inch (empty measurement) and the product emerging from the second roll pass had a thickness of 0.11 inch, equivalent to a reduction in thickness in the second roll pass of about 26%. The final density of the body emerging from the second roll pass was 7.34 grams/cc, which is equivalent to 93.4% of theoretical density.

During the heating of the iron strip as aforesaid, it was maintained in an atmosphere of hydrogen to prevent oxidation thereof; this atmosphere enveloping it not only in the zone in which it was heated, but also through the second roll pass and during a subsequent cooling thereof.

There is further set out in Table 1 which follows, certain data as to the reduction in thickness of strips of various iron alloy materials in the second roll pass only. The several materials which are referred to in Table 1 were all rolled in the second roll pass at 2000 F. in an enclosed space which was maintained under a quite high vacuum-5 microns in each instance. The table shows the percent of theoretical full density which was attained as a (result of this second roll pass effective on different material composition, it being understood that in each instance the first roll pass was carried out as hereinabove set out. I

Table 1 This example is given to illustrate the effect of temperature and of roll setting on the vdensification effective in the first roll pass.

Rolling has been effected on iron powder, for example, at various temperatures from about room temperature up to 1440 F. -At this last temperature, no satisfactory results could be obtained because the powder tended to agglomerate and the particles thereof to adhere together prior to the rolling per se. On the other hand, operations were successfully conducted with the iron powder at about 1200 F. It is a general conclusion based upon this work that the temperature range for practical operation with iron powder is up to about 1400 F.

It is further found that as tfihe temperature of the iron powder is increased, progressively denser bodies are formed as a result of the first roll pass only, other conditions [remaining essentially the same as far as possible. For instance, at 980 F, bodies having a density of about 55% of theoretical density were made using 12" diameter rolls; while at 1200 F. (other conditions being essentially the same), densities of about 78% of theoretical density were obtained.

Density can also be varied as aforesaid with different roll settings as set forth, for example, in Table 2 which follows:

Table 2 Roll Spac- Thickness ing (inches) of Strips Density (measured Produced (grams/cc.)

empty) (inches) This example is presented to illustrate the densification efieoted in the second roll pass and particularly the manner in which different variables affect this densification.

Considering first the question of the temperature at which the elongate body is supplied to the second roll pass and the eliect of this temperature, there is illustrated in Table 3 which follows certain results of rolling strips of iron at temperatures between 1800 F. and 2400 In each instance the density given in the table may be compared with a theoretically 100% density of 7.86

From the above it will be seen that as might be expeoted, it is easier to obtain higher densities with the metal hotter than with the metal cooler, other conditions being substantially constant. This example further illustrates the variations in temperature resulting from the heating step of the process and also the attainment of certain percentages of theoretical density in the final product.

In connection with the tests made at different temperatures as set forth in Table 3 above, it was found that the higher the temperature at which the second roll pass was efiected, the greater was the ductility and resistance to cracking of the stnips thus formed when bent at a substan-tial angle. This tends to confirm the theories previously set out that the second roll pass eflfects not only a further compacting of the metal particles, but also effects a bonding or coalescence between the particles themselves into an integral metallic body.

As in the first roll pass, densities may also be varied within quite wide limits for a given temperature by controlling the roll spacing. This roll spacing is demon strated in the data which follows as percent reduction in thickness rather than as roll spacing in inches and finished thickness in inches. In each instance in the data which follows in Table 4, iron was formed into a ribbon or strip as in Example I and was heated between the two roll passes to 2100 F. The final rolling, as a final step of the process, was then conducted with the variations set out in Table 4 which follows:

of diiferent tests, which are not necessarily in a sequential series, so that each test result must be considered to some extent by itself. It is noted that in some instances the percent reduction in thickness is relatively high and in others is relatively low, compensating in many instances for substantial variations in the density of the strip or ribbon as received from the first roll pass. Thus, it will be seen that the product of the first roll pass may be carried forward to a condition of substantially increased and substantially full density for a wide variety of physical characteristics after the first roll pass only and by suitable adjustments of some of the controllable variables eifective on the second roll pass, including the temperature of the body supplied to this pass, the roll diameter, the roll spacing, and possibly other factors which will suggest themselves to those skilled in the art of metal rolling.

The elongate metal body emerging from the second roll pass may be treated in the same way as a strip, sheet or the like formed by conventional fabrication procedures and rolled to the dimensions as attained in the second roll pass according to this disclosure. This product has similar properties to those correspondingly shaped of metal bodies fabricated in a conventional manner and having the same composition. This product may thus be used as such, if it is the desired thickness, or it may be further fabricated by conventional rolling and/or other fabrication practices in ways which will be familiar to those skilled in the art of metal forming and fabrication and which per se form no necessary part of the present invention.

EXAMPLE IV This example illustrates the so-called extrusion eifect of operating in accordance with the present invention. In the tests set out in this example, iron powder was rolled through the first pass in a so-called 12-inch powder mill, consisting of a pair of rolls having exact rolling diameters of 11.835 inches and circumferences of 37.338 inches. One of the rolls was arranged to make a mark on the rolled strip on each revolution thereof.

In a first test, when the powder was rolled to a thickness of 0.087 inch and to a density of 5.85 gr./cc., the roll marks on the strip were 37.60 inches apart. In a second test, with the same equipment, but with the rolls set to give a dificrent thickness and density strip, the strip formed was 0.111 inch thick and had a density of 4. 83 gr./cc., with the roll marks 37.69 inches apart. From this it is seen that with relatively lower densities, the amount of extrusion or increase in length of the strip with respect to the roll circumference is greater; while increased densities cause the resulting strip to be more nearly the same as the roll circumference for each revolution of the rolls. 011 the other hand, it is noted that in both instances, a greater length of strip is rolled for each revolution of the rolls than the circumference of the rolls per se.

EXAMPLE V This example is given to illustrate the rolling of powder to provide a substantial minimum of strip density, while at the same time illustrating a very low, if not the minimum, rolling speed. In this test, iron powder was rolled hot, specifically at about 1050 F. The powder prior to rolling had an apparent or bulk density of 1.45 gr./cc. The strip resulting from the rolling in a first roll pass had a density of 3.52 gr./-cc., which is about 45% of maximum density for iron. The strip thickness resulting from the rolling was 0.133 inch and the rolling speed was 25 feet per minute. The powder was rolled on 24 inch rolls giving a so-called bite angle of 720.

EXAMPLE VI The purpose of this example is to illustrate a first roll pass for rolling iron powder resulting in a strip of minimum thickness for 24 inch diameter rolls. In this instance iron powder was rolled at a speed of 65 feet per minute and the resulting strip thickness was 0.073 inch. The iron powder prior to rolling had a bulk or apparent density of 2.30 gr./cc. and the rolled strip had a density of 5.54 gr./cc.

EXAMPLE VII This example is given to illustrate a high, if not the maximum rolling speed, using 24 inch rolls and iron powder. In this instance, the rolling speed, as measured by the length of strip produced from the first roll pass, was about 136 feet per minute. The strip thickness produced at this speed and with the powder supplied to the rolls at 13 about room tempenature (approximating 25 C.) was 0.090 inch. The iron powder used had a bulk or apparent density of 1:6 8 gr./=cc.; while the resulting strip had a density of 6.13 gr/cc. This example also illustrates a relatively high compaction of iron powder with respect to that in other examples.

EXAMPLE VIII This example is 'given to illustrate a minimum compression ratio in the first set of rolls and a maximum strip thickness using 24 inch rolls. The thickness of the strip produced from iron powder in the first roll pass in this example was 0.217 inch with an average strip density of 4.75 gr./ cc. The bite angle as this term is convention- 'ally used was 731 and the roll speed was about 100 feet per minute. The iron powder as supplied to the rolls had an apparent or bulk density of 2.50 gr/cc. It will be noted that in this example, the roll diameter is only about 110 times the strip thickness. Based upon this example, and allowing a reasonable margin to which this ratio is believed entitled, it is concluded that the roll diameter should be at least about 100 times the thickness of the strip to be rolled in the first roll pass.

While there is herein shown and described certain apparatus for carrying out the present process, and as the process itself has been described in considerable detail, further variations will occur to those skilled in the art from the foregoing disclosure. We do not wish to be limited, therefore, except by the scope of the appended claims, which are to be construed validly as broadly as the state of the prior art permits.

What is claimed is:

1. The process of making flattened, elongate metallic bodies as strips and sheets, comprising the steps of continuously supplying ferrous metal in the form of flowable particles and by gravity through a downwardly extending opening of a supply hopper to a pair of substantially horizontal axis and substantially smooth surfaced rolls, in which the rolls are substantially side by side and are spaced apart by a predetermined amount, said opening having a length commensurate with the width of the metallic bodies to be made, and the size of said particles being such as to be usable in the forming of parts by powder metallurgy processes, and in which each of said rolls has a diameter which is at least about 100 times the thickness of the body to be produced as a result of rolling in said rolls; positively and continuously driving at least one of said rolls and thereby compacting the flowable particles to the form of an elongate metallic body having a length in a predetermined time period which is greater than the number of revolutions of either of said rolls in the same time period multiplied by the circumference thereof, said elongate body being rolled to a thickness such that the density thereof will be at least about 45 percent of the theoretical maximum density of the metal of which said body is composed and will be substantially self-sustaining; continuously passing said body from said rolls through a heating zone and therein heating said body to a temperature such that the metal thereof is in a plastic range; continuously passing the heated metallic body from said heating zone to a second pair of rolls, positively and continuously driving the rolls of said second pair and controlling the spacing therebetween, so as further to compress the metal of said body to a condition of increased density, coordinating the relative driving speed of the rolls of said second pair of respect to the driving speed of the rolls of the first pair so as to maintain a substantially constant length of metal strip therebetween thereby preventing damaging strains on the material of said metal strip; and substantially preventing contact between the metal of said body and the metal particles from which it is formed with any gases which could combine chemically therewith during substantially all the time this metal is sensitive to chemical combination with any such gases,

14 so as to prevent substantial changes in the chemical state of said metal during all the time aforesaid.

2. The process in accordance with claim 1, in which said ferrous metal in the form of flowable particles is predominantly iron and also contains steel-alloying constituents in the proportions in which said constituents exist in commercial alloy steels.

3. The process in accordance with claim 1, in which said metal in the form of flowable particles is supplied to the first named pair of rolls substantially at room temperature.

4. The process in accordance with claim 1, in which said ferrous metal in the form of flowable particles is predominantly iron and also contains steel-alloying constituents in the proportions in which said constituents exist in commercial alloy steels, said metal being in the form of powdered metal and having a particle size such as to be usable in the forming of metallic parts by powder metallurgy processes, and in which said metal as supplied to the first named pair of rolls is at a temperature in the range of about 800 F. to about 1400 F.

5. The process in accordance with claim 1, in which said metal in the form of flowable particles is compacted in the first roll pass to a strip having an average density of about 45% to about of the theoretical maximum density for the metal being rolled; and after heating, said strip is rolled in the second roll pass to a density of about 93% to about 98% of said theoretical maximum density.

6. The process in accordance with claim 1, in which the first named pair of rolls are arranged so that said body, in the form of a strip issuing therefrom, moves vertically downwardly, and in which the course of the strip is changed from vertical to horizontal intermediate the first and second roll pass as aforesaid, the strip passing through the second named pair of rolls in a substantially horizontal direction.

7. The process in accordance with claim 1, in which the first named pair of rolls are arranged so that said body, in the form of a strip issuing therefrom, moves vertically downwardly, and in which the course of the strip is changed from vertical to horizontal and thereafter passes in succession through said heating zone and the second named pair of rolls.

8. The process in accordance with claim 1, in which said body after emerging from the first named pair of rolls, passes thence in succession through said heating zone, a zone in which the deflection of said body from a predetermined path is sensed for coordinating said relative driving speeds of the two pairs of rolls, and the second named pair of rolls.

9. The process in accordance with claim 1, in which said body, after emerging from the first named pair of rolls, passes in succession through a zone in which the deflection of said body from a predetermined path is sensed for coordinating said relative driving speeds of the two pairs of rolls, a heating zone, and the second named pair of rolls.

10. The process in accordance with claim 1, in which said body, after emerging from the first named pair of rolls, passes in succession through a zone in which the course of said body is changed from substantially vertical to substantially horizontal and in which the deflection of said body from a predetermined curved path is sensed for coordinating said relative driving speeds of the two pairs of rolls, a heating zone, and the second named pair of rolls.

11. The process in accordance with claim 1, in which said ferrous metal in the form of flowable particles is selected from the group consisting of iron and alloys of iron in which the alloying ingredients present are in the proportions in which such ingredients exist in commercial alloy steels, and in which said body is heated in said heating zone to a temperature in the range of about 1800 F. to about 2400" F.

12. A continuous process for making a flattened, elongated body from powdered ferrous metal, which body is comparable in physical characteristics to a body made by conventional fabrication, which process consists essentially of:

continuously supplying by gravity flow, to a first pair of rolls, a stream of flowable particles of ferrous metal, which metal is selected from the group consisting of iron and alloys of iron, which alloys are predominantly iron and also contain steel alloying constituents in proportions in which said alloying constituents exist in commercial alloy steel, said particles being of a size such as to be usable in the forming of parts by powder metallurgy processes but not greater in size than about half the thickness desired for the flattened body produced by passage of said particles through said first rolls; said first pair of rolls being of substantially horizontal axis and being substantially smooth-surfaced; said first rolls being positioned substantially side by side and being spaced apart a predetermined amount, said first rolls having a length commensurate with the width of said flattened body, at least one roll of said first pair of rolls being positively and continuously driven whereby said stream of particles flowing into said first pair of rolls is compacted into a substantially self-sustaining, flattened, elongated body having an apparent density of at least about 45% of the theoretical maximum density of the metal from which said particles are formed but said body having an apparent density less than the substantially full density of said metal; passing said body produced by said first pair of rolls to a heating zone and therein heating said body to a temperature such that the metal thereof is in a plastic range; passing said heated body to a second pair of rolls having a substantially smooth surface, said second pair of rolls being positioned substantially side by side and being spaced apart a predetermined controlled amount so as to further compress said body to a condition of substantially full density; substantially preventing contact between the metal of said body and the metal particles from which it is formed withany gases which could combine chemically therewith during substantially all the time this 16 metal is sensitive to chemical combination with any such gases, so as to prevent substantial changes in the chemical state of said metal during all the time aforesaid; the flattened, elongated body produced by said first pair of rolls has a length in a predetermined time period, which length is greater than the number of revolutions of either of said first pair of rolls in the same time period multiplied by the circumference thereof; and said first pair of rolls and said second pair of rolls being coordinated as to their relative speed so as to maintain a substantially constant length of elongated body between them, whereby damaging strains are prevented from being imparted to the flattened, elongated body produced by said second pair of rolls. 13. The process of claim 12 wherein said metal is iron and said metal is supplied to said first pair of rolls at a temperature between about room temperature and about 1400 F.

14. The process of claim 12 wherein said flattened, elongated body produced by said second pair of rolls has a density of about 9398% of the theoretical maximum density and the flattened, elongated body produced by said first pair of rolls has an apparent density of about 45 to about of the theoretical maximum density.

15. The process of claim 12 wherein means are provided to sense the deflection of the flattened, elongated body from a predetermined path between said first pair and said second pair of rolls and in response to said deflection coordinate the relative speeds of said two pairs of rolls to return said body to the predetermined path.

ReferencesCited in the file of this patent UNITED STATES PATENTS

Claims

1. THE PROCESS OF MAKING FLATTENED, ELONGATE METALLIC BODIES AS STRIPS AND SHEETS, COMPRISING THE STEPS OF CONTINUOUSLY SUPPLYING FERROUS METAL IN THE FORM OF FLOWABLE PARTICLES AND BY GRAVITY THROUGH A DOWNWARDLY EXTENDING OPENING OF A SUPPLY HOPPER TO A PAIR OF SUBSTANTIALLY HORIZONTAL AXIS AND SUBSTANTIALLY SMOOTH SURFACED ROLLS, IN WHICH THE ROLLS ARE SUBSTANTIALLY SIDE BY SIDE AND ARE SPACED APART BY A PREDETERMINED AMOUNT, SAID OPENING HAVING A LENGTH COMMENSURATE WITH THE WIDTH OF THE METALLIC BODIES TO BE MADE, AND THE SIZE OF SAID PARTICLES BEING SUCH AS TO BE USABLE IN THE FORMING OF PARTS BY POWDER METALLURGY PROCESSES, AND IN WHICH EACH OF SAID ROLLS HAS A DIAMETER WHICH IS AT LEAST ABOUT 100 TIMES THE THICKNESS OF THE BODY TO BE PRODUCED AS A RESULT OF ROLLING IN SAID ROLLS; POSITIVELY AND CONTINUOUSLY DRIVING AT LEAST ONE OF SAID ROLLS AND THEREBY COMPACTING THE FLOWABLE PARTICLES TO THE FORM OF AN ELONGATED METALLIC BODY HAVING A LENGTH IN A PREDETERMINED TIME PERIOD WHICH IS GREATER THAN THE NUMBER OF REVOLUTIONS OF EITHER OF SAID ROLLS IN THE SAME TIME PERIOD MULTIPLIED BY THE CIRCUMFERENCE THEREOF, SAID ELONGATE BODY ROLLED TO A THICKNESS SUCH THAT THE DENSITY THEREOF WILL BE AT LEAST ABOUT 45 PERCENT OF THE THEORETICAL MAXIMUM DENSITY OF THE METAL OF WHICH SAID BODY IS COMPOSED AND WILL BE SUBSTANTIALLY SELF-SUSTAINING; CONTINUOUSLY PASSING SAID BODY FROM SAID ROLLS THROUGH A HEATING ZONE AND THEREIN HEATING SAID BODY TO A TEMPERATURE SUCH THAT THE METAL THEREOF IS IN A PLASTIC RANGE; CONTINOUSLY PASSING THE HEATED METALLIC BODY FROM SAID HEATING ZONE TO A SECOND PAIR OF ROLLS, POSITIVELY AND CONTINUOUSLY DRIVING THE ROLLS OF SAID SECOND PAIR AND CONTROLLING THE SPACING THEREBETWEEN, SO AS FURTHER TO COMPRESS THE METAL OF SAID BODY TO A CONDITION OF INCREASED DENSITY, COORDINATING THE RELATIVE DRIVING SPPED OF THE ROLLS OF SAID SECOND PAIR OF RESPECT TO THE DRIVING SPEED OF THE ROLLS OF THE FIRST PAIR SO AS TO MAINTAIN A SUBSTANTIALLY CONSTANT LENGTH OF METAL STRIP THEREBETWEEN THEREBY PREVENTING DAMAGING STRAINS ON THE MATERIAL OF SAID METAL STRIP; AND SUBSTANTIALLY PREVENTING CONTACT BETWEEN THE METAL OF SAID BODY AND THE METAL PARTICLES FROM WHICH IT IS FORMED WITH ANY GASES WHICH COULD COMBINE CHEMICALLY THEREWITH DURING SUBSTANTIALLY ALL THE TIME THIS METAL IS SENSITIVE TO CHEMICAL COMBINATION WITH ANY SUCH GASES, SO AS TO PREVENT SUBSTANTIAL CHANGES IN THE CHEMICAL STATE OF SAID METAL DURING ALL THE TIME AFORESAID.