US3121631A - Method of and apparatus for forming metal strips - Google Patents

Description

Feb. 18, 1964 G. J. sowls'rocK 3,121,631

METHOD OF AND APPARATQS FOR FORMING METAL STRIPS Filed Sept. 11, 1961 44%, C094 w T T awE-ys United States Patent 3,121,631 METHOD ()F AND APPARATUS FOR FORMING METAL STRIPS Gregory J. Comstock, Essex, Conn.,. assiguor to Ehe Comstoelr Company, Hi ganum, Colin a corporation of Connecticut Filed Sept. 11, 1961, Ser. No. 137,219 6 Qlaims. (Cl. 75-214) This invention relates to the art of either high density or porous metal sheet or web formation and contemplates the provision of an improved metal product, and to a novel method of, and an apparatus for, fabricating the same. More particularly defined the invention is concerned with the art of powder metallurgy and provides an improved method of, and apparatus for, converting a metal or alloy powder, or a mixture of metal or alloy powders with or without nonmetallic powders into a solid metallic product having the desired dimensions and having uniform physical characteristics throughout. Advantageously the improved method and apparatus may be employed in the continuous fabrication of strips or webs of powdered metal which strips may be subsequently fashioned into commercially useful strips or sheets by other procedures, as by rolling, heat treating, etc.

It has heretofore been proposed that elongated metal shapes may be formed from metal powders by feeding dry metal powders from a bin or the like into and through the pass between closely spaced parallel oppositely rotating rolls so as to form the metal powder into strips, such strips of powdered metal then being sintered, rolled and then annealed to produce the finished product.

It has been found, however, that strips of powdered metal which are formed in the manner described are generally nonuniform in texture and character, having certain areas in which the metal is more closely or densely compacted than it is in other areas, thus promoting or bringing about nonuniformity in the finished product. It has been suggested that, by adding suitable lubricating agents to the dry powdered metal this difliculty may to some extent be overcome, but it has been generally found that, even in those processes in which lubricant is employed, the strip of powdered metal is not in best condition for subsequent working or use because of nonuniformity of distribution of the powder of which the strip is composed. It has also been found that when a mixture of powdered metal and a lubricant is placed in a mold and compressed certain portions of the resulting article will unavoidably have been compacted to a greater extent than other portions.

We have discovered that such undesirable variations of density in articles formed from a metal or alloy powder, or mixtures of metal powders, may be avoided by utilizing a liquid of such character or consistency that it will support individual particles of metal powder introduced into the liquid equidistantly from each other, or uniformly dispersed throughout the bath, and thereafter casting, extruding, flowing or otherwise delivering the metal carry liquid, or slip in such manner as to form a strip or sheet upon a carrier or support. The sheet or strip of metal powder carrying liquid thus deposited is of uniform character throughout and, after drying, and preferably after the dried strip has been remoistened, may be further processed with most satisfactory results. The liquid employed as a suspending medium for the powder supports the powder in such manner as to form with it a colloidal suspension.

The improved method contemplates the initial formation of a bath comprising metal powder suspended in a liquid vehicle such as an aqueous suspension of sodium or ammonium alignate or of liquid methanol or other 3,121,631 Patented Feb. 18, 1964 alcohol plus an organic thickening agent. After casting or extruding the powder carrying liquid upon a supporting member, the liquid is removed by a suitable absorptioner drying procedure. As [the deliquifying proceeds the binding material which forms an essential element of the slip or bath remains within the powdered constituent and first turns into a jelly and thereafter, when the deliquifying has been completed, into a relatively hard igluedike substance which forms, with the powdered metal, a moderately strong but brittle sheet or casting. While this may be sintered and thereafter further processed if care is used, we prefer to gently spray the strip or casting with a liquid of the type initially employed to form the bath, this spraying having the effect of softening and toughening the article and making it flexible or somewhat rubbery. When so treated it may be handled without danger of breaking and thus may be conducted intact to a sintering furnace. In the fabrication of sheets or strips, which may be relatively wide and thin, it is highly desirable to so remoisten the article after casting and drying. Instead of weakening the deliquified sheet or casting as might be expected, remoistening toughens these products, thereby removing a difficulty previously encountered with serious consequences.

In the accompanying drawing a simple form of apparatus for carrying out the novel process is rather diagrammatically illustrated. In the drawing, a receptacle for the reception and retention of a bath of the colloidal suspension of metal powder is indicated at 10, and the bath at S. The slip or slurry is formed by depositing a calculated quantity of metal powder in an aqueous suspension of one of the previously mentioned dispersing agents, i.e. sodium or ammonium alginate, or other alkaline alginate, or any other suitable dispersing agent having the property of evenly distributing the suspended pulverulent material. The quantities of metal powder, water and dispersing agent are proportioned so that the resulting slip or slurry has a thick, heavy creamlike consistency.

A drum 13 is disposed directly above the slip containing pan or vessel from which the powder suspension (liquid vehicle plus suspending and dispersing agents) is directly deposited upon the surface of this drum as it rotates in the liquid suspension in the direction of arrow A at a carefully regulated speed.- The drum 13 may be formed of plaster of Paris or other suitable liquid absorbent or porous or foraminous material having myriads or macroscopic openings therethrough.

The level of the upper surface of the bath S in the receptacle 10 is maintained at a desired elevation, and the desired consistency of the slip ensured by a suitable means such as that shown, thus means including a supply tank T having a delivery conduit C controlled by a valve V and a return conduit K the inlet end of which, indicated at K, is so positioned that the level of the bath is at the desired point, a pump P being provided for effecting the return of suspension entering the return conduit to the supply tank T. The volume of suspension entering the receptacle it) exceeds the volume removed by the action of the drum 13 so that a constant level of bath is maintained and the desired gentle agitation of the suspension obtained.

Preferably means which is not illustrated but is of known type is employed to create a vacuum within the interior of the drum for the purpose of expediting the withdrawal of moisture from the strip R as the drum rotates. As the moisture in strip R is removed, the dispersing agent being in suspension rather than solution, remains intermingled with the metal particles in the strip, first asstuning a jelly-like consistency and then rapidly turning into a dry adhesive substance. It thus serves as a binder and functions to consolidate the metal powder into a coherent mass. When the strip R is completely dry it is quite brittle and may be readily broken. To render it flexible it is gently sprayed with liquid of the type utilized in the formation of the original bath S, by means of any suitable spraying device, diagrammatically indicated at 14, causes the dry rigid strip to become readily flexible, having a consistency similar to that of wet tissue paper, only stronger.

The strip R then leaves the drum 13 and passes onto a heat resisting conveyor belt 15 mounted upon rolls 16 and 17. The belt 15 supports the strip R and causes it to move slowly through a furnace 18 where it is sintered into a coherent mass. Upon leaving the sintering furnace is, the strip R is mechanically strong and of uniform but low density. The sintc-red strip R may then be passed between pressure rolls l9 and 20 where thickness reduction and densification take place. The densified strip R then preferably passes onto a second heat resistant conveyor belt 21 which is mounted on rolls 22. and 23. The conveyor belt 21 then advances the densified strip R through a second furnace 24- in which the densified strip is annealed. Upon issuing from the furnace 24, the strip R is a finished metal strip of uniform density and thickness. It will be understood that the sintering and annealing mechanisms are of conventional character.

Following are several specific examples by means of which a slip or slurry may be made which is suitable for practicing the present invention:

Example 1.To 500 cc. of distilled water add 12 /2 grams of sodium alginate in the form of a dry granular powder. The Water and sodium alginate are mixed with the aid of a Brookfield counter-rotating mixer, or its equivalent, for about minutes or until all of the sodium alginate has been converted to a colloidal suspension. 3990 grams of minus 325 mesh No. 316 stainless steel powder (spherical particle preferred) are slowly added and thoroughly blended into the vehicle fluid. The resulting suspension of stainless steel powder will have a sufiicientl'y high viscosity to render it suitable for casting in the process described heretofore.

Exam le 2.To 1200 cc. of distilled water add 6.4 grams of ammonium alginate in the form of a dry granular powder. Gently stir the mixture of water and ammonium alginate until all of the ammonium alginate has been converted to a colloidal suspension. Slowly add 786 grams of minus 200- mesh attrited beryllium powder and blend thoroughly into the vehicle fluid. When the blending is completed, the prepared slip is ready for continuous casting on a porous plaster drum or its equivalent in the manner of the present invention.

Example 3.To a mixture of powders consisting of 85% stain-less steel particles and 15% aluminum oxide particles add distilled water and sodium alginate. The proportion of water added being of the total by volume and the proportion of sodium alginate being 2.5% of the total by weight. Again the resulting slip will have a high viscosity suitable for casting or extruding.

As an alternative drying means or to assist in drying the strip R upon the drum 13, a second drum 26 may be provided this being so disposed that its surface will lightly contact the surface of the advancing strip R. The drum 26 is provided with a surface of felt or other absorbent material for extraction of moisture from the strip R. The drum 26 may also seive as a molding drum, by providing its surface with suitable forming means. A vacuum may be established in the interior of the drum to accelerate the moisture extraction from the strip R.

It should be noted that, while in'the foregoing description reference has been made only to alkaline alginates, as they are suitable for suspending and dispersing stainless steel, beryllium and many other metals and alloys in powdered form, many other suspending and dispersing agents may be similarly employed. For example, Carbopol, a B. F. Goodrich proprietary synthetic large molecule ring compound, which thickens alcohol and other liquid by solution, may be utilized to permit pseudoplastic suspension of the metal powder. In the case of compounds of this character, however, it has been found necessary to employ a different type of drying drum. In this case, the drum surface is not porous plaster of Paris, but an impervious metal surface and the vehicle is removed by evaporation. This can be accomplished by gentle heating which drives oil the volatile vehicle leaving behind the metal; the particles of which are held together by the dryin and finally dried Carbopol which acts in a manner similar to that of the alginates in producing strong transient adhesive action. Again, similarly to the alginate which is filterable and therefore remains in the metal strip when it is dewatered by the porous plaster drum, these suspending media first turned into a jelly-like substance and then, on subsequent drying, into strong adhesives.

While the present invention has been discussed primarily as a method of producing continuous webs, strips or sheets of solid metal, it will be obvious that the method is susceptible of use in the production of products other than solid metal webs or strips. For example, it is also possible to use the method of the present invention for the production of continuous strips or sheets of porous character and of materials suitable for filtering purposes. The porosity of the strip can be controlled by regulation of the amount of mechanical deformation which takes place during the rolling operation after the strip has been sintercd.

It is to be understood that the aforedescribed materials, apparatus and techniques are susceptible, in utilizing the invention, considerable variation without departure from the invention.

What is claimed is:

1. The method of producing a continuous metal strip which includes the steps of forming a thin flowable bath comprised of metal powder and a colloidal suspension, said suspension comprising a liquid carrier and an organic pulverulent compound which is characteristically insoluble in said liquid carrier, separable therefrom by filtration and, when thus separated, adapted to serve as a binder, the metal powder being substantially uniformly dispersed throughout said suspension, withdrawing a portion of the bath thus formed and depositing the same upon a support to form a strip of desired thickness, removing the liquid content of said strip while leaving with the metal the organic binding compound, consolidating the strip into a coherent mass from which the organic material has been substantially removed by the application of heat, and subsequently densifying the strip by a rolling operation.

2. The method set forth in claim 1 in which the deposited strip is, prior to being heated, maintained in moist condition by the application thereto of a quantity of said colloidal suspension.

3. The method set forth in claim 1 in which the powder introduced into the bath comprises a mixture of powdered metal and a metal oxide.

4. The method of producing a continuous metal strip which comprises the steps of mixing metal powder with a thickened liquid comprising a solvent and a solublc organic compound characterized by its ability to thicken the solvent and remain with the metal powder when the solvent is evaporated, said organic compound being further characterized by an ability, upon evaporation of the solvent, to first assume a jelly-like consistency and to thereafter become a relatively hard glue-like substance which forms with the metal powder a moderately strong but brittle strip, withdrawing a portion of the bath thus formed to create a strip of desired thickness, evaporating the liquid content of said strip while leaving with the metal the deliquefied organic compound, consolidating the strip by heat into a coherent mass from which the organic material has been substantiall removed, and densifying the l y l ct g t to a, rolling operation.

References Cited in the file of this patent UNITED STATES PATENTS 2,903,787 Brennan Sept. 15, 1959 6 Wagner Mar. 15, 1960 Mouwen Apr. 11, 196-1 Szymaszek Apr. -11, 1961 Thien-Chi et al. Sept. 26, 1961 Moutaud Apr. 23, 196 3 FOREIGN PATENTS Great Britain Oct. 2, 1957

Claims (2)

1. THE METHOD OF PRODUCING A CONTINUOUS METAL STRIP WHICH INCLUDES THE STEPS OF FORMING A THIN FLOWABLE BATH COMPRISED OF METAL POWDER AND A COLLOIDAL SUSPENSION, SAID SUSPENSION COMPRISING A LIQUID CARRIER AND AN ORGANIC PULVERULENT COMPOUND WHICH IS CHARACTERISTICALLY INSOLUBLE IN SAID LIQUID CARRIER, SEPARABLE THEREFROM BY FILTRATION AND, WHEN THUS SEPARATED, ADAPTED TO SERVE AS A BINDER, THE METAL POWDER BEING SUBSTANTIALLY UNIFORMLY DISPERSED THROUGHOUT SAID SUSPENSION, WITH DRAWING A PORTION OF THE BATH THUS FORMED AND DEPOSITING THE SAME UPON A SUPPORT TO FORM A STRIP OF DESIRED THICKNESS, REMOVING THE LIQUID CONTENT OF SAID STRIP WHILE LEAVING WITH THE METAL THE ORGANIC BINDING COMPOUND, CONSOLIDATING THE STRIP INTO A COHERENT MASS FROM WHICH THE ORGANIC MATERIAL HAS BEEN SUBSTANTILLY REMOVED BY THE APPLICATION OF HEAT, AND SUBSEQUENTLY DENSIFYING THE STRIP BY A ROLLING OPERATION.

4. THE METHOD OF PRODUCING A CONTINUOUS METAL STRIP WHICH COMPRISES THE STEPS OF MIXING METAL POWDER WITH A THICKENED LIQUID COMPRISING A SOLVENT AND A SOLUBLE ORGANIC COMPOUND CHARACTERIZED BY ITS ABILITY TO THICKEN THE SOLVENT AND REMAIN WITH THE METAL POWDER WHEN THE SOLVENT IS EVAPORATED, SAID ORGANIC COMPOUND BEING FURTHER CHARACTERIZED BY AN ABILITY, UPON EVAPORATION OF THE SOLVENT, TO FIRST ASSUME A JELLY-LIKE CONSISTENCY AND TO THEREAFTER BECOME A RELATIVELY HARD GLUE-LIKE SUBSTANCE WHICH FORMS WITH THE METAL POWDER A MODERATELY STRONG BUT BRITTLE STRIP, WITHDRAWING A PORTION OF THE BATH THUS FORMED TO CREATE A STRIP OF DESIRED THICKNESS, EVAPORATING THE LIQUID CONTENT OF SAID STRIP WHILE LEAVING WITH THE METAL THE DELIQUEFIED ORGANIC COMPOUND, CONSOLIDATING THE STRIP BY HEAT INTO A COHERENT MASS FROM WHICH THE ORGANIC MATERIAL HAS BEEN SUBSTANTIALLY REMOVED, AND DENSIFYING THE STRIP BY SUBJECTING IT TO A ROLLING OPERATION.

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