US2937942A - Process for making metal strip from metal powder - Google Patents

Description

F. V. LENEL May 24, 1960 PROCESS FOR MAKING METAL STRIP FROM METAL POWDER Filed Jan. 23, 1957 INVENTOR /Z/7Z 1 [Awe-4 ATTORNEY Unite States I tier being processed. I

to animproved process for controlling the permeability andotherlimportant properties across the width of a metal strip formed by roll compacting a metal powder layer inxa continuous operation. The invention is especially" useful forIminimizing the variation in properties and characteristics normally obtained across the width ofr the metal strip whereby more efiicient utilization of the resulting product is-made possible in connection with its various 'applications. 1 1

1 It has been known for some time that metal powders maybecompacted by rolling to produce a so-called green compact in the form of strip which is then heat treated or---sintered and, if necessary, re-rolledto develop the desired final properties.

I whilerolling orthe powder in accordance with prior art proeeduresresults in the production of strip material which maybe generally useful-for some applications, a 'serioiisdis'advantage often resulting in 'the rejection of considerable amounts of the finished-product has been thevariation in properties across the width of the rolled stocki This variation of properties occurring across the width of the strip affecting, for example, the density,

7 porosity and particularly'thepermeability of the material is highly detrimentalfor many applications where more uniform properties are essential.

atent I The above disadvantages are overcome by this invention which provides for controlling the permeability and related properties of roll compacted metal strip by supplying the roll gap of a set of ordinary rolls witha continuous layer of loose metal powderof predetermined progressively increasing thickness laterally from the center of the loose metal powder layer. When the powder layer of modified cross-sectional thickness as'hereinafter described in detail is subjected to roll compacting in the usual manner, the provided increase, in thicknesstoward the lateral extremities enables the production of'strip'having permeability and other properties which may be controlled substantially as desired. It is readily apparent that strip of more uniform properties along its entire width may be obtained by compensating for the spreading tendency in this manner. I I

It is therefore a principal object of this invention to provide an improved process for controlling the permeability across the width'of metal strip formed by rolling metal powder in a continuous operation. I

Another object of this invention is to provide a proc- I ess for producing strip from metal powder of improved I The-permeability of metal strip which is a measure of the-amount of a-giverrfluid (including air) which can be passed through a unit area of strip of equivalent thickness under equivalent conditions of. pr'essureand time is a property of prime significance This particular property is especially important where roll c'ompacted'metal I strip is to find eventual application in the manufacture of bearings, filters and transpiration cooled aircraft componentssuch as turbine blades, combustion chambers and deicing' devices. r

I iBasically, the reason for theaforesaid-variation in permeability and other related properties in a metal strip formed by the rolling ofmetal powders between a set of conventional parallel rolls is the natural tendency of the powder to spread sideways or laterally under the roll pressure. Because' ofthis-spreading, all too frequently only a certain portion of the metal strip, such as the center portion thereof, as distinguished from the portions to either side of the'centen'can be utilized for the manufacture of'specific articles therefrom. This is due to the fact that the desired permeability on either side of the center diverges unacceptably far from the specified or average properties desired. Variations of 30% or more in permeabilityare not unusual between the center and terminal sections of strip in the absence of control measures.

-The use of-shaped rolls to provide a differential roll pressure across the width of the strip or, alternatively, roll pairs with cooperating recesses and projections to limit the spreading of the-powders have been previously suggested. These solutions are, however, cumbersome at best inasmuch as theyi'equire a manufacturer to maintain a large inventory ofexpensive rolls which must be exchanged for'anothersuch set of rolls with each and every change in the specifications of the strip to be made as well as upon changes in the kind or particle size of metal pow:

uniformity with respect to the permeability, density and porosity of the compacted product. I I

A further object of this invention is to. provide a process for minimizing the'variation of properties of metal tion, it will be understood that these advantages and ob- I I jects are also equally attained in terms of 'eitherdens'ity or porosity of the metal strip which are relatedproperties of permeability. The relationship of density, porosity andpermeability can be qualitatively understood in the sensethat permeability is the amountand'size'of inter! connected porosity, which in turn is a direct function of the particle'size of the powder and of the extent of compacting or densification of the metal particles comprising the strip.

The invention will be more clearly understood byreference to the accompanyingdrawing in which:

Fig. 1 schematically illustrates a side view of a general arrangement of apparatus incorporating a contoured gate suitable for practicing the invention, i U r Fig. 2 is a perspectiveview of the control gate in an adjustable mounting at the head of; an inclined feed trough, used for continuously'feeding a contoured layer of metal powder to the roll gap,

Fig. 3 is a side view of the control gate, and

Fig. 4 is a sectional view taken along the line 4-4 in Fig. 1 showing the metal powder layer in contoured form prior to compacting.

Referring now to the drawing, a supply of loose metal powder 10 is contained in a sloped bottom feed hopper 11 which is fitted withgate guides 12 in which a control gate 13 is slidably supported to permit vertical movement of. the gate in the guides thereby providing an outlet apere ture 14 for passage of the powder from the hopper 11 upon a feed trough 20. I Adjustment of aperture 14 may be made either manually or by mechanical means (not shown) associated with gate lifter 15. Indexing the vertical movement enables rapid and accuratepositioningiofthe control gate and any suitable lockingmeans' may be used for securing the adjustment once the desired position is determined.

' In the embodiment shown in Fig. 2, control gate 13*com-' prises a sheet ,metalplate having aflixed along its bottom;

oil edge a shaping or contouring metal blade 16 which is attached to the gate by strap 17 thereby permitting ready changing of the blade whenever required. The lower extremity of blade 16 designated at 18 which defines the shape of the outlet aperture and which effects the contour ing of the loose metal powder layer upon its passage therethrough is preferably bevelled across its entire width to a knife edge most clearly shown in Fig. 3. Best results are obtained when the bevelled edge is positioned outwardly as shown in Fig. 1.

Outlet aperture 14 opens into a feed trough 20 having sides 21 and a bottom 22 which is abutting and coextensive with the bottom 23, of the hopper 11. The width of the feed trough should correspond to the width of the aperture between the inner edges of the guides 12 in order to prevent disruption of the contoured metal powder layer once it is formed. A minimum distance of travel represented by the length of the trough is of importance for the same reason.

The feed trough 20,-which may be structurally supported in any suitable manner, conducts and deposits the contoured loose metal powder layer on the lower of the two cooperating rolls 24 whereupon the powder is drawn into the roll gap 25 by the friction between rolls and powder and is compacted to a so-called green strip 26 by the roll pressure.

A representative specimen of a layer of loose metal powder which has been passed through an arcuate shaped aperture in accordance with the present invention resulting in a controlled distribution of the powder is shown in section in Fig. 4 wherein the layer is characterized by a progressively increasing thickness from the center line 27 toward the extremities comprising the width of the strip. The difference in height from the center to the extremities of the strip corresponding to the contour of the control gate or more specifically the shaping blade is designated by the letter W in the figure.

Any metal powder suitable for the fabrication of metal strip by compacting may be used in practicing the present invention. Metal and alloy powders as, for example, copper, iron, brass, lead, bronze, stainless steel may be used. Such metal powders have been found to compact readily, particularly when in a fineness preferably below IOO-mesh sieve size. Where the properties of the strip are not too exacting as in the fabrication of some types of porous metallic filters, the strip may be made from powders of considerably larger particle sizes up to 30-mesh sieve size.

After compacting in the rolls, the green strip is normally sintered by heat to develop strength and finally the strip is usually re-rolled to meet any desired surface and thickness specifications. While the operations subsequent to compacting will quantitively modify the permeability, porosity, or density of the green strip, the initial control of these properties derived by virtue of the progressive thickening herein disclosed in conjunction with the production of the green strip is substantially preserved throughout the complete processing cycle. In other words, the usual processing steps subsequent to roll compacting of the loose metal powder do not adversely affect the control of permeability initially provided by the progressive thickening step herein disclosed.

Accordingly, where it is desired that strip have more uniform permeability and related properties laterally outwards from the center of the strip, the loose metal powder is passed under a shaped control gate, the lower extremity of which is in the shape of a depending arch or of arcuate configuration so that after passage of the loose metal powder thereunder the layer of powder produced will have a corresponding variable thickness which is progressively greater on both sides of the center of the powder layer.

Although the gradual and progressive increase in thickness from the center along the width of the strip formed by passage of the powder layer through the contoured 4 control gate is generally effective for reducing the usual variation in permeability and other properties, it is apparent that the degree of blade curvature defining the layer-forming aperture must be taken into consideration. Other factors determined by particular conditions of actual operation must also be considered including (a) the kind and particle size of the metal powder being used, .(b) the width and thickness of the strip to be produced, ('0) the initial compacting pressure and (d) the feed rate of powder to the rolls. Variation of one or more of these factors or conditions will alter the degree of contouring required which is conducive to optimum results.

By changing the distribution of the powder fed into the mill, the typical permeability distribution of high permeability at the edges and low permeability'in the center of the strip can be changed to more uniform permeability distribution. If desired, the relationship may actually be reversed to eifect a higher permeability at or near the center compared to the edges of the strip by increasing the flow of powder toward the edges to the extent required. Changing the gate opening has a pronounced effect on the average permeability of the strip irrespective of the contouring. It will thus be seen that the gate must be adjusted to the opening corresponding to the desired average permeability level. The contouring may then be utilized to control the distribution of permeability across the width of the strip in accordance therewith.

It has been found that the bottom curvature of the blade for effecting the desired distribution of powder may be varied depending upon conditions met in actual operation. In the production, for example, of strip of final thickness values ranging from .010 to .125 inch, a contoured gate which provides an opening which is about & to A inch wider at the edge than in the center may be advantageously employed. Dependent upon the width of the strip to be made and the permeability gradient desired, etc. it will be readily apparent that blade curva tures providing somewhat larger or smaller difierences in the height of the metal layer (h value) may be used. In general, quite satisfactory results have been obtained in practice with the use of curved gates providing an opening at the outer edge which is between 7 to inch larger than at the center of the gate.

The control of powder distribution indicated by the data in Table I was determined by attaching small chutes to the bottom of the feed trough or ramp. Each of these chutes was arranged to collect the powder from one quarter of the width of the trough. The distribution was determined for one setting of the control gate opening using (a) a straight edge gate, (b) a inch curved edge gate and (c) a inch curved edge gate.

TABLE I.-FLOW DISTRIBUTION AT EXIT END 1 Left outside, left center, right center, right outside.

i "It white headdress the data that the larger opening zittlfu: edges'of gates Hand III results'ina highertlow Percent OniOO mesh V .5 Through 100 mesh, on 140. mesh v..-.. 25.6 Throughv 140 mesh, on. 200. mesh 33.4 Through 200 mesh, on 3.25tmesh. -..22.5 Through 325 mesh 18.O

Stainless steelpowder was passed through a control gate equipped with a inch .curvedhlade providing a metal powder layer varying in thickness from the center to its width extremities. Y I

The gate opening was set t'o'an index reading .of 33 2 corresponding to a powder flow r'at'e' of approximately 3050 grams per minute. -Thepowderlayer was-rolled to form green-strip-from--which was cut a piece-8% inches long and 4 A incheswide which was subsequently sintered. The sintered piece had a thickness of .032 inch. Sectional distribution of permeabilityacross the-width of the sintered strip was determined by measuring the per- 'meability coeflicient of each of four sections in accordance with conventional permeability evaluation procedures. The four sections ran along 7% inches of the length of the strip and covered a width of inch each starting about a inch from the outside edge of the strip. The four sections together, therefore, covered 3% inches or about 77% of the entire width. The results are summarized below:

Green strip was prepared following the same procedure used in the preceding example with the exception that a inch curved edge was positioned in the control gate and the gate setting was decreased to 3 corresponding to a powder flow rate of approximately 2200 grams per minute. The green strip obtained upon rolling was sintered to yield strip of .034 inch uniform thickness. The permeability data obtained on strip sections corresponding to those in the previous example are listed below:

Percent Flow, Cu. Diff. in.

In./Sq. Perme- Perme- In./Sec. ability ability Position of Section under Coeflicient Coeflieient 50 p.s.i. in Sq. In Between Pagssflure XlO- Outsade Center Example 111 In another run varying from the preceding example I Percent l .Flow, Cu. Diff. in. In./Sq. Perme- Perme- In./See. ability ability Posltionoisection under Coeificient Coeiiicient;

50-p.s.i. inSq. Between Pressure XlO-" Outside ,Difi. and

Center Example IV For comparison purposes, strips were rolled usinga control gate having an uncontoured lower edge i.e. a straight edge blade. In a typical run thegreenstrip was formed by passing the material through the rolling .mill and the resultingproduct was sintered as in the preceding examples. A sintered. strip having a uniform thickness of .036 inch wasobtained. The measurement of permeability distribution, on quarter sections similarly ;cut, from the original strip yielded the following values:

Percent Flow, Cu. Difi. in. In./Sq. Perme- Perme- In./Sec. ability ability Position of Section under Coefficient Coeflicient 50 p.s.i. in Sq. In. Between Pressure X10 Outside Difi. and

Center g l as. 7 1. a 4. o 5

It will be seen from the foregoing examples that the permeability distribution across the width of the strip is markedly improved by virtue of the control of powder distribution provided by the use of a contoured control gate.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It will be readily apparent to those skilled in the art, for example that it is possible to roll a strip having a lateral gradient of permeability from one edge to the other by a suitable choice of the curvature of the blade. Then too, the control of powder distribution may be exercised by the use of control gates of a design other than the curved edge type herein described in detail. A serrated blade for the use of multiple chutes capable of supplying variable amounts of the powder in the amounts required to effect the desired powder distribution'may be incorporated in the process. It is also apparent that a moving belt arrangement could be used in lieu of the stationary structure shown which utilizes the gravity feeding principle. The arrangement and special relationship between the feed trough and the rolls may also be varied. By way of illustration, instead of rolling the powder in a rolling mill having rolls which are arranged vertically above each other as shown in Fig. 1, the rolling operation may be carried out in a mill having its rolls arranged horizontally side by side with the amounts of powder fed between the rolls being varied across the width of the strip.

It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. In the process for making strip from metal powder wherein a layer of loose metal powder is compacted between rolls to produce green strip, the step of forming the loose powder layer to provide a progressive increase in thickness fror'nthe center to the lateral extremities across the width thereof prior to feeding said layer to the rolls.

2. The process wherein strip is made from metal powder comprising the steps of contouring loose metal powder to provide a layer of progressively increasing thickness from the center across the width thereof, and thereafter roll compacting the layer of contoured loose metal powder in the absence of lateral support therefor to form green strip of modified permeability distribution characteristics compared to strip made by compacting loose metal powder of uniform thickness across its width.

3. The process of claim 2 wherein the progressively increasing thickness for a strip at least 4 inches in width is between 3& and A of an inch at the extremities thereof relative to the thickness at the center.

4. The process of claim 2 wherein the progressively increasing thickness for a strip at least 2 inches in width is from 1, to A of an inch at the extremities thereof relative to the thickness of the center portion.

5. The process wherein a strip is produced from metal powder comprising the steps of forming a continuous layer of loose metal powder having a concave upper surface whereby the distribution of said powder is progressively increased from the center across the width of said layer, compacting said concaved layer while the same is laterally unsupported with respect to its width dimension and thereafter sintering the green strip produced thereby.

6. The process of claim 5 wherein the progressive increase in the distribution of powder from the center to the extremities across the width of the layer is sufiicient to effect a substantially more uniform permeability across the width of the: processed strip by comparison with similarly processed strip excepting that a layer of uniform thickness across its width is used. 7. The process wherein a strip is produced from metal powder comprising contouring a layer of loose metal powder to provide a progressively increasing thickness from the center'of the metal powder layer to the width extremities thereof, and thereafter compacting the layer of loose metal powder in the absence of lateral confinement of the layer with respect to its width dimension.

References Cited in the file of this patent UNITED STATES PATENTS 476,706 Van Oostrum June 7, 1892 1,510,745 Montgomery Oct. 7, 1924 2,134,366 Hardy Oct. 25, 1938 2,332,746 Olt Oct. 26, 1943 2,350,971 Pecker et al June 6, 1944 2,746,741 Naeser May 22, 1956 2,771,637 Silvasy et a1 Nov. 27, 1956 2,851,354 Scanlan Sept. 9, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 937 942 May 24 1960 Fritz V Lenel It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 6, for "layer 10" read layer 19 =-3 column 6, line 54 for "blade for" read blade or Signed and sealed this 15th day of November 19606 S EAL) Attest:

KARL H. AXLINE Attesting Oflicer ROBERT C. WATSON Commissioner of Patents UNITED STATESPATENT OFFICE CERTIFICATE UF CGRRECTTN Paiens Noe 2 937 942 May 24 1960 Fritz Lenel It is herebfi certified that error appears in the-printed specification oi the above "numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 6 for "layer 10" read layer 19 eelumn 6 line 54 for "blade for" read blade or -=-a Signed and sealed this 15th day of November 1960,

(SEAL) Attest:

KARL He AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Claims (1)

1. IN THE PROCESS FOR MAKING STRIP FROM METAL POWDER WHEREIN A LAYER OF LOOSE METAL POWDER IS COMPACTED BETWEEN ROLLS TO PRODUCE GREEN STRIP, THE STEP OF FORMING THE LOOSE POWDER LAYER TO PROVIDE A PROGRESSIVE INCREASE IN THICKNESS FROM THE CENTER TO THE LATERAL EXTREMITIES ACROSS THE WIDTH THEREOF PRIOR TO FEEDING SAID LAYER TO THE ROLLS.

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