US3613166A - Compaction of particulate matter - Google Patents

Abstract

AN APPARATUS AND METHOD FOR COMPRESSING PARTICULATE MATERIAL USING AT LEAST ONE DIE IN A MOLD WHEREIN AT LEAST ONE ACTUATOR IS EMPLOYED FOR FORCING THE DIE TOWARD AND AWAY FROM THE MOLD AND AT LEAST ONE SERVO VALVE IS EMPLOYED FOR CONTROLLING THE ACTUATOR SO AS TO APPLY THE DIE BOTH STATIC AND DYNAMIC FORCES.

Description

Oct. 19, 1971 w WALLACE ET AL 3,613,166

COMPACTION OF PARTICULATE MATTER Filed June 26, 1969 INVENTORS RICHARD W. WALLACE STANLEY R. PAVLICA mu M/MM ATTORNEY United States Patent 3,613,166 COMPACTION 0F PARTICULATE MATTER Richard W. Wallace, Pittsburgh, and Stanley R. Pavlica, Irwin, Pa., assignors to Dresser Industries, Inc., Dallas,

Tex.

Filed June 26, 1969, Ser. No. 836,810 Int. Cl. A22b /08 US. Cl. 18-16.5 3 Claims ABSTRACT OF THE DISCLOSURE An apparatus and method for compressing particulate material using at least one die in a mold wherein at least one actuator is employed for forcing the die toward and away from the mold and at least one servo valve is employed for controlling the actuator so as to apply to the die both static and dynamic forces.

BACKGROUND OF THE INVENTION Heretofore there have been two primary approaches for improving procedures for the preparation of unitary articles from a plurality of particles. One approach has been through the chemistry and/or mineralogy of the particles while the other approach has been through increased densification of the unitary article.

In the densification approach, larger and larger static forces have been used to achieve a greater density of packing of the particles in the final article through sheer brute force.

Compaction progresses from an initial particle accomrnodation stage through an elastic and/or plastic deformation of the particles stage to a final stage where further compaction is achieved only by fracturing the particles. Even with extremely large static forces, the individual particles strongly resist plastic and/or fracture compaction so that there is a limit on the density of packing of particles by static force alone.

Although static forces are very useful in compacting particles, the use of massive force alone to push the particles into a position of closest approach with one another and therefore greatest densification is not the best approach.

SUMMARY OF THE INVENTION According to this invention greater densification is achieved with lower static compaction forces by restructuring the particle mass into a position of closest approach for the particles by superimposing on the static force of compaction a cyclical force of compaction. In this manner high densities in the final unitary product are obtained without the necessity of very large static forces. This results in a great savings in the size of the compaction apparatus employed and therefore in the cost of building, operating, and maintaining such apparatus.

Accordingly, this invention relates to apparatus for compressing particulate material in a mold cavity with at least one die using at least one actuator means for forcing at least one die toward and away from the cavity and at least one servo valve means operably connected to each actuator to cause the actuator to apply to the die both a static force toward the cavity and a cyclical reciprocating, dynamic) force toward and away from the cavity.

Also according to this invention there is provided a method for compacting particulate material by imposing at least one static compressive force on said material and superimposing on said static force at least one additional force 'which is cyclically applied with and against said static force in the range of from about 0.2 to about 7000 cycles per second.

This invention is useful in the preparation of any unitary body from any solid or solid-like particulate material. For example, this invention is useful in the preparation of refractory shapes such as bricks from any known refractory material. This invention is also applicable to the formation of metallic parts from metal or metallic particles by general principles well known in the field of powder metallurgy.

Accordingly, it is an object of this invention to provide new and improved compaction apparatus. It is another object to provide a new and improved compaction method. It is another object to provide a new and improved method and apparatus for increasing the attainable density of a product formed from particulate material without also requiring increased high static compaction forces. It is another object to provide a new and improved method and apparatus for restructuring a mass of particles into positions of closest approach for the particles in relation to each other while compacting the composite of particles into a unitary product.

Other aspects, objects, and advantages of the invention will be apparent to those skilled in the art from the disclosure and the appended claims.

DETAIL-ED DESCRIPTION OF THE INVENTION The drawing shows a system employing one embodiment of this invention.

More specifically, the drawing shows a base 1 fixedly holding upright, spaced-apart support members 2. Members 2 carry horizontal support member 3 which in turn carries an upper hydraulic cylinder 4. Upper piston 5 of cylinder 4 is connected to upper crosshead 6 which is slidable on supports 2.

Base 1 carries a lower hydraulic cylinder 7 which contains lower piston 8. Piston 8 supports lower crosshead 9 which is also slidably carried on supports 2.

Mold 10 is supported by mold crosshead 11 which can also be slidably carried on supports 2.

Thus, crossheads 6 and 9 are vertically movable by means of the pistons 5 and 8 attached thereto while crosshead 11 can be vertically movable but by manual or other means not shown.

Mold 10 has a vertical passage therethrough which defines mold cavity 12.

Crosshead 9 has a lower die 13 attached thereto.

Crosshead 6 has an actuator means 14 attached thereto which actuator carries upper die 15.

Attached to actuator 14 are servo valve means 16 and 17.

As shown in the drawing, dies 13 and 15 are aligned with mold cavity 12 so that the dies can be moved into and out from that cavity by operation of pistons 5 and 8.

Actuator 14 comprises a body 20 having a first, lower piston chamber 21 therein which opens directly into an upper, second piston chamber 22 which is of smaller, cross-sectional area taken in a horizontal plane than the cross-sectional area of first chamber 21. Body 20 has an opening 23 in the lowest side thereof adjacent mold 10 which is of a horizontal cross-sectional area less than the horizontal cross-sectional area of first chamber 21.

Opening 23 allows a lower, first piston 25 to pass therethrough in a dynamically sealing engagement. Piston 25 extends into the interior of chamber 21 and extends downwardly outside of body 20 to carry die 15 fixedly attached thereto.

Piston 25 carries an annular flange 26 on a portion thereof (a top portion thereof being shown in the drawing) in the interior of chamber 21. Flange 26 extends out to the interior walls 27 for dynamic sealing therewith thereby dividing chamber 21 into upper and lower subchambers 28 and 29, respectively.

First piston 25 carries second piston 30 which mates with second chamber 22 in a dynamically sealing relation.

Conduit 31 in body 20 openly connects sub-chamber 28 with servo valve 16 while conduits 32 and 33 in body 20 openly connect second chamber 22 and lower cham ber 29, respectively, with servo valve 17.

Servo valves 16 and 17 can be any convention, high response servo valve which can be electrically actuated and which hydraulically operates by way of conduits 31 through 33 the pistons in the actuator. Such servo valves are commercially available and are well known in the art. For example, two applicable servo valves are fully and completely disclosed in Fluid Power International, volume 29, No. 334, January 1964, pages 6-9, the disclosure of which is incorporated herein by reference. A particularly suitable servo valve is a conventional valve which employs an electromagnetic (electrodynamic) driver for receiving the electrical signal and which also uses a pilot stage containing a pilot spool and a power stage containing a power spool. In such a device an electric signal to the electrodynamic driver moves the vertically aligned pilot spool to allow oil under pressure to one of the two ends of the power spool thereby shifting the power spool and allowing oil under pressure to leave the power stage and enter one of the chambers 22, 28, and 29 of actuator 14 and apply a force to one of pistons 30 or 25 in a direction either toward or away from mold cavity 12. The electric signals to the servo valve can be varied and reversed to cause the pilot and power spools to oscillate back and forth thereby causing pressurized oil to be admitted to the actuator in a cyclic fashion to cause reciprocation of piston 25 and, therefore, reciprocation of die 15.

In operation, crosshead 9 is raised by piston 8 until die 13 extends partially into cavity 12. A group of particles are charged into cavity 12 and come to rest on die 13.

Crosshead 6 is then lowered by piston until die 15 extends into the interior of cavity 12 just contacting the upper level of the particle composite resting in the cavity.

An electric signal such as from a conventional oscillator is applied to servo valve 16 by way of electrical conductor 35 which causes oil or other non-compressible liquid to pass from a pressurized source represented by arrow 36 through conduit 31 into upper chamber 28 thereby forcing piston 25 downwardly against the particle composite in the cavity and thereby applying a static force to that composite. Liquid is removed from the actuator and servo valve to its source by way of a line represented by arrow 36' when the process is completed.

An electrical signal is also supplied to servo valve 17 by way of electrical conductor 37 to admit pressurized liquid from its source, represented by arrow 38, through servo valve 17 and conduit 32 into chamber 22. This superimposes an additional force on piston 30 which is transmitted through piston 25 to die 15 and finally to the particle composite in cavity 12. By reversal of the signal in conductor 37, the flow of pressurized liquid through servo valve 17 is switched from conduit 32 to conduit 33 thereby employing through chamber 29 an upward force on piston 25 and causing a reduction in the downward force on piston 25 and die 15 thereby partially relieving the compacting pressure on the particle composite in cavity 12. By rapidly reversing the electric signals in conduit 37 the pressurized liquid and the low pressure return line, represented by arrow 38', are cyclically switched from chamber 22 to chamber 29 and back thereby causing a reciprocating or dynamic force to be applied through piston 25 and die 15 onto the particle composite in cavity 12. This reciprocating force is superimposed on the static force that is maintained by servo valve 16.

The static pressure applied to the particle composite can be any pressure up to 40,000, preferably about 7,000, pounds per square inch of die surface in contact with the particle composite. The reciprocating force controlled by 4 servo valve 17 can apply any additional pressure acting towards or away from cavity 12 up to 2,000, preferably 1,000, pounds per square inch of die area in contact with the particle composite. The cycling of the reciprocating force can vary from about 0.2 to about 7,000 cycles per second.

The static and cycling forces can be applied to the particle composite in any sequence. For example, the static force can be applied to the composite first followed by the cycling force or the cycling force can be applied first followed by the static force, or both forces can be applied at substantially the same time. The common element of this application of forces is that a static force with a superimposed cycling force are both applied to the particle composite over a finite period of time. The cycling force restructures the particles in the composite to positions of closest approach to adjacent particles and, therefore, acts as a mechanical lubricant, while the static force continually urges the particles together during the restructuring process.

As a further example in the operation of the apparatus of the drawing, assume a static force equivalent to 7,000 p.s.i. is applied through servo valve 16 on the particle composite in cavity 12. Thereafter, a cycling force equivalent to 1,000 p.s.i. is employed through servo valve 17. When the cycling force is applied through conduit 32 in chamber 22 it provides an additional 1,000 p.s.i. pressure to the 7,000 p.s.i. static pressure thereby providing a composite downward force equivalent to 8,000 p.s.i. When the cycling force is switched from conduit 32 to conduit 33, this force acts upwardly on flange 26 thereby reducing the total force acting downwardly to a magnitude equivalent to 6,000 p.s.i. Thus, in this example, at least 6,000 p.s.i. is always applied to the particle composite while a cycling force is imposed on this static force thereby raising the force equivalent acting on the composite from the static 6,000 p.s.i. up to 8,000 p.s.i. and back down to 6,000 p.s.i.

This procedure gives a final, compacted, unitary article of very great density without requiring the use of very high static forces. Densities of refractory articles such as refractory bricks can be achieved by this apparatus and process which are greater than that which can be achieved with only static forces and presently existing apparatus for applying such static forces. Existing apparatus such as conventional brick presses can be modi fied in a manner similar to that shown in the drawing to practice this invention.

It should be understood that the hydraulic cylinders 4 and 7 serve the function of positioning and that this function could be accomplished by other means, also that more than one actuator can be employed in a single press and that one or more servo valves (depending on the nature of the valve) can be employed with each actuator. For example, an actuator with one or more servo valves can be interposed between crosshead 9 and die 13 in the same manner shown for crosshead 6 and die 15 in the drawing. In this manner both dies 13 and 15 will carry the static force with the superimposed cyclic force. In the operation of this apparatus the cyclic forces can be applied to dies 15 and 13 in phase or up to out of phase as desired by merely controlling the electrical signals to the various servo valves. Similarly, more than one actuator can be employed between a given die and its supporting crosshead.

It should also be noted that the static force and/or the dynamic force or forces imposed on a given die can be varied during the compaction process. For example, light static loads can be applied at the initial compaction stage which, as noted above, is mostly taken up by accommodation of the particles in relation to adjacent particles. The static load can then be increased at the final stage of compaction where particle fracturing is necessary for further densification. Similarly, while varying the static force from one stage in the compaction procedure to the next, the cyclic force and/ or its frequency can be varied from one stage of the compaction procedure to the next. For example, the frequency of the compaction force in the initial stage of accommodation and secondary stage of elastic and/or plastic deformation of the particles can be low, e.g., 100 cycles per second, and then increased to, for example, 2,000 cycles per second during the final stage when compaction is achieved primarily by fracturing of the particles under the increased static force. Other variations and combinations of the static and cycling forces as well as other process parameters such as frequency are obvious to those skilled in the art and therefore will not be discussed in detail.

In the process of this invention a particulate material is compacted in a molding zone with at least one die, at least one of the dies having imposed thereon a static compressive force which is transmitted to the particulate material and a superimposed additional force which is cyclically applied in the range from about 0.2 to about 7,000 cycles per second. The static force is a finite force up to about 40,000 pounds per square inch of die area while the cyclic force is a finite force up to about 2,000 pounds per square inch of die area, both die areas being as defined above.

The process of this invention is applicable to any particulate material such as fireclay, alumina, mullite, corundum, magnesite, chrome ore, silica, zircon, zirconia, carbon, kaolin, and the like; subdivided metals normally used in powder metallurgy processes such as aluminum, beryllium and its alloys, copper, brass, bronze, iron, lead, magnesium, titanium, zinc, zirconium and its alloys, and the like. This invention is applicable to other subdivided materials such as ground glass, comminuted plastic, woodchips, carbon black, rubber particles, shreaded paper, and the like. Mixtures of two or more of the above materials can be employed if desired.

EXAMPLE In the apparatus of the drawing, magnesite brick mix consisting of a gradation of sizes ranging from 100 percent through 4 mesh to 25 percent through 325 mesh screen (Tyler) is charged into cavity 12 and die 15 moved downwardly just into contact with the upper surface of the magnesite particles in the cavity. A hydraulic pressure of 700 p.s.i. is applied through conduit 31 in chamber 28 which produces a static force of 125,000 pounds at die 15. Die 15 has an area in contact with the magnesite particles of 20 square inches and therefore a static force of 6,250 pounds per square inch is applied to the magnesite particles.

Hydraulic pressure of 3,000 pounds per square inch is cyclically applied through conduits 32 and 33 thereby resulting in a cyclic force of or 15,000 pounds (750 p.s.i.) at die 15. The cyclic force is applied at a frequency of 2,000 cycles per second using a hydraulic flow through servo valve 17 of about 3 gallons per minute.

After about 3 seconds the static and cyclic forces are terminated, die 15 removed from cavity 12 and die 13 raised further by piston 8 to raise the compacted magnesite brick from the interior of cavity 12 to the upper surface of mold for removal from the apparatus.

Reasonable variations and modifications are possible Within the scope of this disclosure without departing from the spirit and scope of this invention.

The embodiments of the invention in which an ex clusive property or privilege is claimed are defined as follows:

1. In apparatus for compressing particulate material in a molding cavity having an upper die and a lower die which enter the cavity opposing one another, thereby defining upper and lower cavity surfaces, the improvement comprising:

at least one actuator means operably connected to at least one die for forcing said die toward and away from. said cavity,

each actuator means having operatively connected thereto two servo valve means, to cause said actuator means to apply to a die both a static force toward said cavity and a reciprocatnig force toward and away from said cavity, and

means for controlling said servo valve means.

2. The apparatus according to claim 1 wherein said actuator means comprises a body having a first piston chamber therein and a second piston chamber opening directly into said first chamber, said body having an opening into said first chamber to allow a piston to pass through said opening into said first chamber, said opening being a smaller cross-sectional area than said first chamber, a first piston means extending through said opening into said first chamber, said first piston being of substantially the same cross-sectional area as said opening and having an annular flange on a portion thereof in the interior of said first chamber, said flange extending out to the interior walls of said first chamber thereby dividing said first chamber into two sub-chambers, second piston means carried by said first piston means and extending into said second chamber, conduit means in said body openly communicating with said second chamber and each of said sub-chambers in said first chambers, said conduit means being openly connected to said servo valve means.

3. The apparatus according to claim 2 wherein said servo valve means is an electrically actuated means which hydraulically operates said actuator means.

References Cited UNITED STATES PATENTS 2,549,642 4/1951 Seelig 2541 I X 2,569,226 9/1951 Carter 2541 I UX 2,747,231 5/1956 Reinhardt l816 R UX 3,129,463 4/1964 Gill, Jr. et al. 25-41 I X 3,423,794 1/1969 Wilson l816.5

OTHER REFERENCES American Ceramic Society Journal, Vibratory Compacting of Metal and Ceramic Powders," by William C. Bell et al., vol. 38, No. 11, November 1955, pp. 396-404.

WILLIAM s. LAWSON, Primary Examiner U.S. Cl. X.R.

Iii-DIG 28

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