US3162708A

US3162708A - Method for compacting metal powder

Info

Publication number: US3162708A
Application number: US118732A
Authority: US
Inventors: John A H Lund; Silins Vilnis
Original assignee: Sherritt Gordon Mines Ltd
Current assignee: Viridian Inc Canada
Priority date: 1961-06-21
Filing date: 1961-06-21
Publication date: 1964-12-22
Anticipated expiration: 1981-12-22

Description

Dec. 22, 1964 J. H. LUND ETAL 3,162,708

METHOD FOR COMPACTING METAL POWDER Filed June 21. 1961 20 i i I I l I l I l I g Inventors J. A. H. LUND V/LN/S S/LINS Attorney United States Patent 3,162,703 METHOD FOR (IQMPACTENG METAL PGiiEJER .lolin A. H. Land, Vancouver, British Columbia, and Viinis Silins, Edmonton, Alberta, Canada, assignors to Sherritt Gordon Mines Limited, Toronto, Untario, Canada, a company of Canada Filed June 21, 1961, Ser. No. 113,732 2 Claims. (Ci. 264-4111) This invention relates to the utilization of an improved roll construction for roll compacting metal powders into metal rods, sheets, strips, wire and the like.

Metal powder is compacted initially into a green shape, such as in the form of sheet or strips, by feeding it, usually at a predetermined, uniform rate, into the roll gap of a pair of oppositely positioned, horizontally disposed, pressure rolls. The rolls are spaced to produce a self-supporting, partially densifled green shape of desired thickness.

There is a problem in rolling metal powder by this method if the metal powder, during compaction, is not confined along the outside edges of the rolls in that metal powder tends to flow or leak from the edges of the rolls with the result that the longitudinal edges of the strip are not compacted to the same density, coherence and thickness as is the centre portion. Thus, compacted shapes formed without some provision for confining the powder metal within the roll gap must be trimmed along the edges, thus necessitating an additional step in the overall process and resulting in the production of an appreciable percentage of waste material in addition to non-uniformity in the physical characteristics of the product across its width.

Devices are known and used for confining the powder metal within the roll gap and thus preventing flow or leakage from the ends of the rolls. For example, flanges or discs of greater diameter than the roll on which they are mounted have been provided at the ends of one of the rolls, or a flange has been provided at one end of one roll and at the other end of the other roll. These flanges are pressed tightly against the opposing faces of the rolls and serve to confine the metal powder within the roll gap but they tend to create a further problem. The compacted shape tends to become wedged between the flanges and is diflicult to discharge from the rolls. Attempts to overcome this wedging effect by drawing the compacted shape from the rolls results in distortion and breaking of the sheet or strip.

We have found that the problems of confining the metal powder to the roll gap and preventing leakage of metal powder from the ends of the rolls and of discharging the compacted shape from the rolls without damage either to the physical characteristics of the shape or to the longitudinal edges can be overcome by mounting a flange, of greater diameter than the roll, at each end of one of the rolls or at one end of one roll and at the opposite end of the other roll, but spaced a short distance from each opposing end of the roll so that there are relatively narrow spaces between the ends of the rolls and the opposing flanges.

In the operation of the roll compacting unit, in one modification of the invention, some of the powder fed to the roll gap flows into and fills the space defined between the inner face of the flanges and the ends of the roll to which they are attached to the level of the surface of the roll and provides, in effect, an extension of the roll surface to the flanges. The longitudinal edges of the strip or sheet passing through the roll gap rest on these narrow layers of metal particles which, in effect, provide an opposing surface which is relatively soft and yielding as compared to the hard, unyielding surice faces of the rolls. Also, since a space of equal width is defined between the inner face of that portion of the flange which overlaps the unflanged roll and the opposing end of this roll, the outer longitudinal edge of the strip is subjected to smaller compacting forces than the rest of the strip. The result is that the strip has an edge which, though quite regular, has a relatively friable border which crumbles readily thus allowing easy exit of the compacted strip from between the flanges. In an alternative modification of the invention, the yielding or slightly resilient effect can be provided along the longitudinal edges of the strip or sheet by filling the spaces between the opposing ends of the rolls carrying the flanges and the inner face of the flanges to the level of the flange carrying roll or rolls with a resilient or yielding material such as rubber. The combined effect of the layer of metal particles or the resilient material at the ends of the rolls and the open ended space between the outer ends of the unflanged rolls and the inner faces of the flanges is that the longitudinal edges of the strip or sheet are not compacted to the same degree of density or coherency as is the main body of the shape and constitute lines of weakness which permit, in effect, the main body of the shape to be torn evenly along the lines of weakness at the marginal edges as it is discharged from the rolls. Thus, the shape leaving the rolls is of substantially uniform thickness, density, and coherency between its longitudinal edges and requires only superficial trimming along its edges during subsequent conventional hot and/or cold working procedures.

An understanding of the utilization of the improved metal powder compacting rolls of this invention can be obtained from the following description, reference being made to the accompanying drawings in which:

FIGURE 1 is a perspective view of a pair of metal powder compacting rolls which incorporate an embodiment of powder metal confining flanges of this invention;

FIGURE 2 is a top plan view;

FIGURE 3 is an end elevation; and

FlGURE 4 is a front elevation of a modification of the invention in which a flange is mounted on a roll shaft of one of the rolls and the other flange is mounted on the roll shaft at the other end of the other roll.

Like reference characters refer to like parts throughout the description and drawing.

Referring to the modification of the invention illustrated in FIGURES l to 3, a flange is provided at each end of one of the rolls. It will be understood that one of the flanges can be mounted on the roll shaft of one of the rolls and the other flange can be mounted on the roll shaft at-the opposite end of the other roll as illustrated in FIGURE 4.

Referring to FIGURES l to 3 of the drawing, the

numerals

22 and 23 indicate rolls of a conventional type used for compacting metal particles. In the modificaticn illustrated, they are plain, or unproflled rolls, adapted to compact the metal particles into sheet or strip of a desired width. The rolls are mounted on shafts 25-25a which are driven according to conventional practice, such as by an electric motor through a train of speed reducing gears. The rolls are formed of conventional material such as steel and, conventionally, are adjustably mounted to apply a pressure on the particulate material fed into the roll gap or the space 27 between the rolls, with provision to increase or reduce the roll gap to increase or reduce the thickness of the compacted sheet or strip. Using smooth, hard, ground steel rolls six inches in diameten'metal strip from 0.02 to 0.04 inch in thickness was obtained with pressures estimated at up to about tons per square inch.

Methods and apparatus are known and are in use 3 for feeding metal powder to the roll gap at a relatively uniform rate and do not form part of this invention.

The numerals -21 indicate discs or flanges, as illustrated in FIGURES l to 3, one of which is mounted on each end of roll shaft adjacent to but spaced a short, predetermined distance from the opposing end of the roll 22 leaving spaces 2442411 between the opposing faces of the flanges 21-2ti and the ends of the

rolls

22, 23.

The flanges or discs 20-21 are formed of steel or other rigid material capable of withstanding the lateral force of the metal particles applied against their faces in the operation of the rolls. The radius of the flanges is greater than the radius of the rolls, at least to the extent of the width of the roll gap during operation, for example, from about 0.5 to about 1 inch greater, depending on roll radius and on the width of the roll gap.

The flanges can be adjustably secured to the roll shaft 25 by any conventional means which will hold them securely in their predetermined positions relative to the opposing faces of the ends of the rolls. In the modification illustrated in FiGURES 1 to 3, the flanges are formed with outwardly extending hub portions 3944041 which are drilled to receive set screws SL315; by means of which the flanges are rigidly secured in their predetermined positions.

The flanges are adjusted on the roll shaft to leave gaps or spaces 2424a of predetermined width between the opposing faces of the flanges and the ends of the

rolls

22, 23. The width of the spaces depends on the size and the flow characteristics of the metal particles being compacted. If the gap is too wide relative to the particle size of the metal powder being compacted, powder will pass between the ends of the working faces of the unflanged roll (23 in FIGURES 1-3) and the inner face of the

flanges

20, 21 too rapidly and very low or no compaction pressures at all are developed along the edge zone. If, on the other hand, the

gaps

24, 24a are too narrow, powder particles may jam in the space between the end of unflanged roll 23 and the inner face of the

flanges

20, 21. This may impede the smooth operation of the equipment or result in extremely high compaction forces at the edge zones with the result that the compacted strip emerging from the mill jams between the flanges. We have found that the distance between the opposing faces of the ends of the rolls and the flanges should be at least about 0.001 inch and very satisfactory results have been obtained within the range of from about 0.001 to 0.05 inch when roll compacting, relatively free flowing metal particles of from submicron to about 150 microns in size. As the flanges 20-21 are adjustable on the shaft, the spaces can be readily determined from which the best results are obtained in compacting a particular metal powder and the flanges secured to the shaft accordingly in non-yielding relation.

FIGURE 4 illustrates a modification of the invention in which a flange is mounted on a roll shaft adjacent to but spaced a short distance from a roll 42. The other flange 43 is mounted on the other roll shaft 44a adjacent to but spaced a short distance from the other roll 44. The flanges 40-43 are mounted on the

shafts

45 and 44a in the manner described above. Provision can be made to remove the particles trapped in the spaces 24-24a during the rotation of the rolls after the discharge of the compacted strip or sheet, such as by a high pressure air blast, as indicated by the numeral 35, FIGURE 2, or by a stationary tool, not shown, which dislodges the particles trapped in the space. Thus, the beds of particles in the spaces are continuously replaced and they do not become compacted to the extent that they expose hard, unyielding surfaces to the layer of particles along the marginal edges of the layer of particles in the roll gap.

In the modification of the invention illustrated in FIG- URE 4, a resilient material 41, such as a strip of rubber, is inserted in each of the spaces 50-50a. between the opposing faces of the ends of the rolls and the flanges. The resilient material fills the spaces to the level of the roll surface and, possibly, a little higher. The layer of metal or metal coated particles which rests on these resilient surfaces is not compacted to the same extent as is the main body of the shape and thus form lines of Weakness along which the main body of the shape is separated as it is discharged from the roll gap. This modification has the advantage that no particles enter the spaces and it is not necessary to clean them during the rotation of the rolls after the discharge of the compacted strip or sheet from the roll gap.

The improved metal powder compacting rolls of this invention have been found to have important advantages. The flanges serve to confine the powder in the roll gap which, in effect, extends between the opposing faces of the flanges. However, the roll surfaces are hard and unyielding while the surfaces of the beds of particles trapped in the spaces 2424a are yielding. Thus, the strip or sheet formed in the gap which extends the length of the rolls is strongly coherent and is of substantially uniform thickness and density while the portion which extends between the ends of the rolls and the flanges is substantially less dense and coherent. Thus, in discharging the strip or sheet from the rolls, it tears easily along the lines of weakness at its less dense and less coherent edges. As a result, there is no damage to the main body of the strip or sheet in discharging it from the rolls and only a very minor amount is lost in the edge trimming operation. Particles which collect in the spaces between the opposing faces of ends of the rolls and the flanges can be dislodged during the rotation of the rolls or they can be prevented from entering the spaces by filling them with a resilient material such as rubber. A further important advantage is that it has been found in the operation of the rolls that they tend to move laterally slightly relative to each other, as indicated by the arrows, FIGURE 4. This causes binding of the ends of one of the rolls and the opposing face of one of the flanges, depending on the direction of movement, when the flanges are fixed tightly against the end of the rolls, with resultant wear on the face of the roll. This binding effect can be reduced, if not completely overcome, by mounting the flanges in the manner illustrated in FIGURES 13 and it can be overcome completely by determining the normal direction of the lateral movement by operation of the rolls and then mounting the flanges, one on each of the roll shafts, as illustrated in FIGURE 4, so that each roll can move laterally without binding at either end against an opposing face of a flange.

It will be understood, of course, that modifications can be made in the embodiments of the invention described and illustrated herein without departing from the scope of the invention defined by the appended claims.

What we claim as new and desire to protect by Letters Patent of the United States is:

1. The method of compacting metal powder into elongated strips which comprises feeding finely divided metal particles to a roll gap defined between two rotatable rolls of a roll compacting unit, confining the metal powder at the ends of the roll gap by means of circular flanges adjustably mounted on a roll shaft at each end of the rolls adjacent to but in spaced relation to the opposing faces of the rolls leaving spaces therebetween, compacting the longitudinal edges of the strip on yielding surfaces at the ends of the rolls formed of particles forced into said spaces and thereby forming lines of weakness between the main body of said strip and the longitudinal edges thereof, and discharging the compacted strip from the roll gap.

2. The method of compacting metal powder into elongated strips which comprises feeding finely divided metal particles to a roll gap defined between two rotatable rolls of a roll compacting unit, confining the metal powder at the ends of the roll gap by means of circular flanges adjustably mounted on a roll shaft at each end of the rolls adjacent to but spaced between 0.001 inch and 0.05 inch from the opposing faces of the ends of the rolls leaving spaces therebetween, compacting the longitudinal edges of the strip on yielding surfaces at the ends of the rolls formed of metal particles forced into said spaces and thereby forming lines of Weakness between the main body of said strip and the longitudinal edges thereof, and discharging the compacted strip from the roll gap.

Hilgerd Oct. 24, 1876 Hohne et al Apr. 26, 1887 6 Sims Feb. 18, 1890 Ncvegold Oct. 6, 1891 Longanesi Dec. 30, 1924 McConouglley Aug. 23, 1932 Smith Aug. 27, 1935 Blume Feb. 4, 1936 Johnson Apr. 2, 1946 Fe-ther Apr. 10, 1951 Cofek Nov. 5, 1957 Heck Sept. 22, 1959 Melville et al. Apr. 19, 1960 Dasher Nov. 28, 1961 Leib et a1. Apr. 2, 1963 FOREIGN PATENTS v Italy Of 1926

Claims

1. THE METHOD OF COMPACTING METAL POWDER INTO ELONGATED STRIPS WHICH COMPRISES FEEDING FINELY DIVIDED METAL PARTICLES TO A ROLL GAP DEFINED BETWEEN TWO ROTATABLE ROLLS OF A ROLL COMPACTING UNIT, CONFINING THE METAL POWDER AT THE ENDS OF THE ROLL GAP BY MEANS OF CIRCULAR FLANGES ADJUSTABLY MOUNTED ON A ROLL SHAFT AT EACH END OF THE ROLLS ADJACENT TO BUT IN SPACED RELATION TO THE OPPOSING