US2134366A - Production of metal sheets - Google Patents

Description

Oct. 25, 1938. c, HARDY 2,134,366

PRODUCTION OF METAL SHEETS Filed Sept. 3, 1956 50 0 0027 k ess/hy 90/15 I Jqo) 0/6 INVENTOR (7707/65 f/a/ay BY Patented Oct. 25, 1938 1 UNITED STATES PATENT OFFICE 2,134,366 I PRODUCTION or METAL SHEETS Application September 3, 1936, Serial No. 99,241

1 Claim.

This invention relates to a method of producing lengthy metal shapes of substantially uniform cross-section. More particularly, the invention relates to the production of lengthy metal shapes from metal powders, and has for its principal object the provision of a method of utilizing metal powders in the continuous production of metal sheets, wire, rods, tubes, and the like.

In carrying out the invention, metal powders are continuously passed through an opening having substantially the cross-section of the metal shape which it is desired to produce. As the metal powder passes through the opening, it is subjected to sufiicient pressure to cause the particles of metal powder to cohere. The resulting coherent product is suitably treated, for example by subjecting it to an appropriate heattreatment operation, to obtain a finished metal product having desired physical properties.

The method of the invention may be employed in the production of metal shapes of a single metal, such as sheets, wire, rods, tubes or angles of substantially pure metals such as copper and nickel. Further, the method of invention may be employed in the production of shapes composed of alloys, such as sheets, rods, and the like of copper-cadmium alloy, magnetic alloys such as alloys of iron cobalt and nickel, and other alloys. The invention may be employed, for instance, in preparing rods or sheets of alloys, such as copper-lead alloys, which are diflicult to prepare by ordinary methods.

If it is desired to prepare a lengthy shape of v a single metal, such as copper, substantially pure powder of the chosen metal is employed as the metal powder. If a. shape composed of an alloy is to be produced, then a mixture of powders of the two or more metals entering into the alloy, substantially in the proportion in which the respective metals appear in the alloy, is prepared and this mixture is employed as the-metal powder. It is, of course, possible also to employ powders of the alloy itself.

In forming metal sheets in accordance with the invention, the chosen metal powder or mixture of metal powders is passed between rolls spaced apart a distance corresponding to the thickness of the sheet to be produced. Shapes such as wire, rods, tubes and angles are produced from metal powders or mixtures of metal powders by introducing thepowder into a suitable extrusion press having a die formed therein and forcing the powder through the die. In both cases the pressure exerted on the powder is sufficiently high to cause the particles of powder to cohere. The coherent product resulting from this operation is then heat-treated to obtain a finished product having desired physical properties.

Virtually any metal-rolling roll may be employed in preparing metal sheets in accordance with the invention. The rolls themselves should be well polished and should be 'kept clean and dry to prevent sticking of the powder to them, for if the powder partly sticks to the rolls it will not be possible to obtain uniform sheets.

Although it is possible, under favorable conditions, to roll coherent sheets direct from metal powder by simply introducing metal powder between revolving rolls, best results are obtained by introducing a carrier sheet between the rolls, spreading the metal powder on the carrier sheet, and passing the carrier sheet with its load of metal powder between the rolls, as shown in the single figure. The carrier sheet may be of any suitable metal, but steel is preferred. The carrier sheet should be. smooth (advantageously it is polished on the surface on which the powder is spread) and free from irregularities. It should be sufficiently hard to resist deformation as it passes through the rolls, and flexible enough so that it may be used in the form of an endless sheet or belt. A sheet of a good grade of tempered steel possesses all of these qualifications and is sufhciently inexpensive to be available commercially.

In preparing metal sheets, the rolls themselves exert the pressure necessary to cause the particles of metal powder to cohere. Owing to the v relatively high pressure that must be applied to the powder, there is a tendency for it to spread out, particularly near the edges of the rolls, as it passes through them. This results in a ragged, non-uniform edge on the sheet, and this edge must be trimmed to secure a uniform sheet. If such trimming must be resorted to, scrap losses are relatively high. It is advantageous, therefore, to take precautions to minimize the formation of ragged edges. To this end the edges of the carrier sheet may be turned over, or a band may be secured to its side edges,vto limit the extent to which the powderspreads. The same result may be attained by forming the rolls so that their end portions, outside the actual rolling zone, are of slightly greater diameter than the central portion of the roll which actively employed in rolling the powder.

,The rolls employed in preparing coherent sheets from metal'powder maybe heated or not,

, volved and upon the properties desired in the fln-' as is preferred. Whether or not heated rolls are employed will depend on the nature of the particular metal powder being used and the nature of the sheet which it is desired to produce.

The coherent product of the rolling operation is suitably treated to obtain a finished product having desired physical properties. Ibis treatment generally takes the form of a heat-treating operation to cause the particles of metal powder to sinter together and to produce a sheet of substantial homogeneity. In preparing alloys, the heat-treating operation may also serve to impart to the alloy those properties customarily secured by ordinary alloy heat-treatment.

; The coherent sheet from the rolls may be fed directly to a heat-treating furnace and be passed therethrough at substantially the rate at which the coherent sheet emerges from the rolls. Where possible, it is usually advantageous to separate the coherent sheet from the carrier sheet before passing the former through the heat-treating furnace, for frequent passage of the carrier sheet through the furnace might very well render it unsatisfactory for its principal duty of carrying the metal powder through the rolls and sup! porting the coherent product of the rolls for a short distance after it emerges from the rolls. If the character of the coherent sheet is such that it requires support in the heat-treating furnace,

) however, the carrier sheet may be so employed. .In such cases the carrier sheet may be passed all the way through the furnace before the rolled product is separated from it, or it may be passed only a part of the distance through the furnace 5 and be separated from the partially heat-treated coherent sheet at a point beyond which its service as a carrier is no longer required. The carrier sheet may then be taken out through a suitable opening in the floor of the furnace and be refturned to the rolls, after being cooled ii such is necessary, to receive a fresh load of metal powder. As an alternative to passing the carrier sheet from the rolls through the heat-treating furnace, two carrier sheets may be employed. One, such 5 as described above, serves to carry the metal powder through the rolls and to carry the coherent rolled sheet for a short distance beyond the rolls. The coherent sheet from the rolls is then transferred to the second carrier sheet, which supports it during its passage through the heattreating furnace, or for such a distance through the furnace as is necessary. The drive mechanism for the two carrier sheets should be synchronized so that the two sheets travel at the same rate of speed, thus to avoid buckling or otherwise distorting the coherent sheet from the rolls while it is still in a relatively fragile state.

The particular nature of the heat treatment operation will depend upon the particular metal inished sheet. Thus, in preparing sheets of copper, the heat-treatment may involve heating the coherent product from the rolls at a temperature of about 70W C. to 800 C. in an atmosphere of hyi5 drogen. Other specific heat-treatment operations may be carried out when other metals or alloys are employed, or if particular physical properties in the finished sheet are sought.

The above-described method of preparing sheets from metal powders is adapted to be carried out as a continuous process. The metal powder may be fed continuously to the rolls and the coherent sheet produced thereby may be passed continuously through the heat-treating 75 furnace. In this manner very long sheets or ribbons may be produced. The fact that the invention contemplates a continuous process, however, is not understood as indicating that the invention is not applicable to semi-continuous or intermitter it operation. The rolling operation may be interrupted periodically so that sheets of a desired length may be produced. The invention may also be carried out in such manner that the rolling operation only is continuous or semi-continuous, the heat-treatment operation being conducted intermittently Thus, the coherent sheet from the rolls, in cases where it is suiiiciently strong and pliable, may be rolled up as it emerges from the rolls and the rolls of coherent sheet may be heat-treated in bulk at a later time. If the coherent sheet from the rolls is not able to resist rolling or bending, it may be cut to suitable lengths as it emerges from the rolls and the several lengths may be stored fiat, on a suitable carrier if necessary, until it is desired to heat-treat them.

In producing metal or metal alloy wire, rods, tubes, angles, and the like in accordance with the invention, the chosen metal powder or mixture of metal powder is introduced into a suitable extrusion press. The press comprises a die having an opening therein of substantially the crosssection of the shape to be produced. Behind the die is a cylinder adapted to receive charges at metal powder, and suitable means are provided for introducing the powder into the cylinder. A piston operates in the cylinder and serves to force metal powder in the cylinder through the opening in the die. The means operating the piston are powerful enough so that as the piston forces the metal powder through the die, it exerts sufficient pressure to cause the particles of metal powder to cohere.

The means whereby the cylinder of the press is charged with metal powder advantageousky is such that substantially continuous, lengthy metal shapes may be prepared. Thus, the charging means may be such that after the piston has forced a charge of powder through the die, and has returned to its original position, a fresh charge of powder is introduced into the cylinder. In this manner, although the piston operates intermittently, shapes of almost any length may be,

produced, regardless of the capacity of the cylinder. Such charging means may, of course, be operated either manually or automatically.

As in the case of rolling sheets from metal powder, an extrusion press in which coherent shapes are made from metal powder may be operated hot or cold, as the nature of the powder employed or in? properties desired in the finished shape die- With some powders, such as copper, the shapes extruded from the press are sufllciently strong so that they may be handled without the aid of supporting members. Shapes extruded from other powders do not possess suilicient mechanical" strength prior to heat-treatment to be handled without the aid of supports. When,deal ing with such powders, supporting or carrier members may be arranged close to the discharge side of the die in the extrusion press, these members being adapted to lend the support necessary to prevent distortion of the extruded product prior to heat-treatment. A considerable variety of supporting devices are available. For example, a simple, flat table will prove satisfactory in many cases. In dealing with particularly fragile extruded shapes, an endless belt, preferably of metal, may be employed. Such a of relatively short lengths permits the use of a belt advantageously is operated at the same rate as that at which the product of the press is extruded therefrom, thereby to minimize the application of stresses to the extruded shape. In some cases, the supporting device may be in the form of a row of rollers along which the product from the press travels as it is extruded. Where the need for support is not great and there is little danger of stressing or distorting the extruded shape, non-rotating bars may take the place of the rollers.

The coherent product of the press is converted to a finished shape by suitable heat-treatment. The particular nature of the heat-treatment operation will depend upon the metal of which the shape is composed and on the physical properties which it is desired to impart to the finished shape. The furnace in which the heattreatment is carried out advantageously is an ranged with respect to the press so that the coherent product of the press may be passed directly to and through the furnace. By so arranging the furnace, the production of wire, rods, tubes, angles and the like may be made continuous. This is particularly advantageous in producing wire in accordance with the invention, because it generally is desired to produce wire in rather long lengths.

Instead of thus continuously making extruded shapes. the method of the invention contemplates cutting the product of the extrusion press into suitable lengths and heat-treating the relatively short lengths thus obtained in groups. This mode of procedure is of advantage in the production of metal shapes such as rods, angles and various special shapes, because such shapes ordinarily arenot wanted in very long lengths and treatment heat-treatment furnace of simpler construction and more convenient dimensions than furnaces employed in a strictly continuous operation.

Considerable variation may be had in the physical properties imparted to metal shapes produced in accordance with the invention. For example, by conducting the heat-treatment to insure vir- C tually complete fusion together of the particles of powder in the coherent shape. dense and homogeneous metal structures may be obtained. On the other hand, by carrying out the heat-treating operation so that the powder particles are simply sintered into a uniform mass, porous structures may be produced. This feature of the invention renders it of considerable value in preparing self-lubricating bearings. Such bearings may be produced by extruding a tube substan tially or the diameter and wall thickness of the bearing, and heat-treating the resulting tube to obtain a porous structure in which oil or other lubricant may be incorporated by mown means. The tube is then cut into lengths corresponding to the width of the bearings which it is desired to produce.

I claim:

A method of producing metal sheets which comprises feeding metal powders onto a rotating endless smooth metal surface, passing the surface carrying the powders through rolls, exerting pressure on the powder between the rolls to cause the powder particlesto cohere into a sheet, andpasslng the surface carrying the sheet through a heating zone to cause further consolidation of the sheet. the rotating endless metal surface being subsequently cooled and returned for additional feed of metal powders.

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