Solidified Gas Pellets And Apparatus For Manufacturing

Abstract

Carbon dioxide pellets of a high density formed in a manner to break easily into minute pieces yet not agglomerate during shipment, together with a head member for a pellet machine to form pellets of this kind.

Parent Case Text

This application is a division of application Ser. No. 660,790 filed Aug. 15, 1967 and now abandoned.

Description

This invention relates in general to pellet machines and to pellets produced by pellet machines of the reciprocating plunger type. More particularly, this invention is concerned with pellet machines for manufacturing frangible pellets from liquefied gas and to the pellets so formed.

The customary practice of furnishing finely shaved or crushed solid carbon dioxide presents problems to the user because of its tendency to cake. The prior art as described in U.S. Pat. Nos. 1,919,698; 2,200,577 and 3,077,081 illustrates carbon dioxide pellets in the form of rods which are cut or otherwise severed into smaller pellets. In copending application Ser. No. 500,426 rods of carbon dioxide formed with random transverse fracture lines which can be broken into pellets are described. However, carbon dioxide pellets manufactured by prior methods do not have the desired configuration and density to make them separate or shatter into small pieces for better heat transfer purposes when they are, for example, ground into food or other materials during a grinding stage and yet be capable of non-agglomeration during shipment thus affording free flow at time of use. It has now been discovered in operating the apparatus therein disclosed in U.S. Pat. No. 3,576,112, application for which was copending herewith filed Oct. 21, 1965 with a specially designed head or die that a novel configuration of a carbon dioxide pellet which promotes breaking up of the pellet into minute pieces could be produced.

It is accordingly an object of the present invention to provide a novel rod-like pellet formed from a liquefied gas. Another object of this invention is to provide an apparatus for producing laminar type pellets of a unique configuration. Still another object of this invention is to provide a novel carbon dioxide pellet having a high density and ability to break into minute pieces. It is yet another object to provide an apparatus for producing the unique carbon dioxide pellets at a rapid rate.

These, and other objects of this invention, will be readily appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawing wherein:

FIG. 1 is a vertical sectional view of a pellet machine for making the novel pellets of this invention.

FIG. 2 is a view in horizontal section taken along line 2--2 of FIG. 1.

FIG. 3 is a view in vertical section taken along line 3--3 of FIG. 2.

FIG. 4 is a fragmentary view of the head member of the pellet machine shown in FIG. 1 illustrating pellets being ejected therefrom.

FIG. 5 is a view in vertical section of an alternative head member for a pellet machine such as shown in FIG. 1 for making the present novel pellets.

FIG. 6 is a perspective view of the novel pellet of this invention.

FIG. 7 is a view in horizontal section taken along line 7--7 of FIG. 6.

FIG. 8 is a view in vertical section taken along line 8--8 of FIG. 6.

Briefly stated the novel carbon dioxide pellets are formed in a pellet machine having a reciprocating piston wherein liquid carbon dioxide is sprayed into a chamber, expanded into snow and then compressed and extruded through openings in a head member which is counterbored from each side of the head to present either: (a) a converging-diverging wall surface or (b) an annular straight wall contiguous with a diverging wall. The pellets produced in such a head member are formed with a solid core and have integral, uniformly spaced, radiating projections extending from the core formed with oblique lines of fracture substantially completely around the core. The relatively uniformly spaced projections are somewhat concavo-convex with the convex side in the direction of flow as it is extruded from the pellet machine. The core of the pellets forms about 10 to 25 percent of the cross-sectional area through the concavo-convex radiating projections and the pellets have a specific density in the range of 60 pounds per cubic foot to about 95 pounds per cubic foot.

Referring now to the drawings there is shown an apparatus generally indicated at 10 for making pellets, for example pellets 32 of solid carbon dioxide. The apparatus 10 in its overall operation is generally similar to that described in the previously referred to copending patent application Ser. No. 500,426 filed Oct. 21, 1965. Any suitable drive mechanism can be used such as the one illustrated in the copending patent application having the usual crank shaft and a connecting rod attached to a guide 16 which is mounted for reciprocation in a bore 18 in block 19. As guide 16 is reciprocated in bore 18, ram 17 rigidly bolted to the upper surface of guide 16 by bolt 15 is in turn reciprocated.

A cylindrical member or casing 20 is secured to block 19 by a tubular flanged connector 21. The cylindrical member 20 receives a porous separator or filter 22 which is preferably composed of sintered stainless steel or reinforced sintered bronze and is supported in the enlarged upper portion 23 of casing 20 by a porous filter support 24. Clearance is provided between ram 17 and the inner surface of separator 22.

A plug 28 of solid carbon dioxide snow is partly formed in bore 27 of casing 20 and partly in bore 29 of head 30. The head 30 has a plurality of small bores or openings 31 of the converging-diverging type which communicate with the bore 29.

A conduit 33 communicates with a standard insulated carbon dioxide storage tank 36 and a valve assembly 34 of the electrical type. A cooling coil, compressor, pressure regulator, and liquid and vapor separator for supplying carbon dioxide liquid through conduit 33 are standard and are described in U.S. Pat. No. 3,576,112, application for which was copending herewith.

The stroke of the ram 17 extends from the upper position shown in broken lines at the lower end of plug 28 to the lower end of bore 27 as shown in solid lines. The upper end of the ram 17 has a recess 54 which terminates in a sharp peripheral edge 55. A bearing 56 is disposed between a washer 57, on internal shoulder 59 and an upper shoulder 58 formed along bore 27. The bearing 56 is preferably composed of polytetrafluoroethylene known commercually as "Teflon." A seal ring 60 is disposed between the adjacent surfaces of casing 20 and connector 21. Encircling ram 17 is a U-cup seal 61 composed, for example, of leather into which a ring 62 fits. A compression spring 63 acts against an internal shoulder 64 of the connector 21 and against the ring 62. The seal 61 is urged against the upper portion 65 of T-shaped connector 66 which is secured to block 19 by bolts 67 and nuts 68.

Referring to the head member 30 as particularly shown in FIGS. 2, 3 and 4 it will be seen that a plurality of double frusto-conical passages 31 are arranged in a circular pattern with one such passage disposed centrally of the circular pattern. Each passage 31 is formed with a converging wall portion 70 which communicates with the compression side of head portion 30 and with its widest dimension proximate to the compression side. In direct extension from each converging wall portion 70 is a diverging wall section 71, the converging and diverging wall sections 70 and 71, respectively, being joined at their narrowest dimensions with the diverging wall section 71 of greatest divergence proximate to the discharge side of head 30.

FIG. 5 illustrates an alternative embodiment of a head member 80 wherein a plurality of passages 81 are formed each having a straight wall portion 82 proximate to the compression side of head member 80 and a frusto-conical section having a diverging wall portion 83 with its narrowest dimension in communication with straight wall section 82 and disposed with the wall portion 83 of greatest divergence proximate to the discharge side of head member 80.

The novel rod-like pellet generally 32 is particularly illustrated in FIGS. 6-8 and comprises a generally overall cylindrical configuration with a substantially solid cylindrical core portion 90 and radiating projections 92 integral with said core and spaced substantially uniformly along the core. The spaced projections 92 are formed in a generally concavo-convex configuration with the circumferential ends being substantially flat, thus providing together with the core a generally circular cross-section. The density of rod-like pellet 32 is in the range of about 45-95 pounds per cubic foot when the solidified gas is carbon dioxide. The core member 90 comprises about 10-25 percent of the cross-sectional area of the rod-like pellet member.

In operation, a suitable drive mechanism will continuously reciprocate ram 17 by means of guide 16, the drive mechanism and valve mechanism 34 being in synchronism so that liquid carbon dioxide from conduit 33 is flashed into chamber 27 when the head of ram 17 passes on its downward stroke the entrance of conduit 35 into chamber 27 and ceases the flashing of liquid carbon dioxide when the head of ram 17 begins its upward stroke. The operation of the valve 34 and the drive mechanism is substantially the same as that disclosed in copending application Ser. No. 500,426. The snow accumulates in the chamber designated by the letter "C" and carbon dioxide vapor or gas can pass from the chamber through porous filter 22 into outlet conduit 39 and subsequently to a storage chamber for reuse. When the ram 17 moves upwardly, the snow in chamber "C" is moved toward head 30 and is progressively compressed. Some of the solid carbon dioxide which constitutes the plug 28 is forced through the openings or bores 31, some of the solid carbon dioxide remaining in the bores and newly compressed snow constituting the plug 28 as the stroke cycle of ram 17 is repeated. It is apparent that with each stroke of the ram 17 toward the head 30 some solid carbon dioxide is forced through the openings 31 and rod-like pellets 32 are intermittantly made. Although not definitely known, it is postulated that with each stroke cycle of ram 17 one radiating projection 92 and an adjacent core section are formed.

The formation of the novel rod-like pellets 32 is effected by extrusion through either a straight wall section 82 followed by a diverging wall 83 or a converging wall 70 with subsequent passage through a diverging wall 71 although the use of the converging wall 70 to effect initial stresses is preferred as it produces more clearly defined radial projections 92. It is theorized that as the compacted carbon dioxide snow passes beyond the narrowest dimension of the diverging wall section a release of pressure occurs and thus the formation of the spaces between the circumferentially extending projections 92 around core 90 and the novel configuration of pellet 32. However, this release of pressure must not be too rapid lest the pellet will break or be ejected in piecemeal fashion. Under normal operating conditions with ram 17 in its retracting stroke an internal pressure of 45 p.s.i.g. remains. For this reason it will be noted that diverging wall sections 71 and 83 have only a slight taper not exceeding an included angle of 15.degree.. This preferred range provides expansion with simultaneous retention or frictional drag between the edges 93 of projections 92 and the surface of diverging walls 71 and 83. This frictional drag effects the convex and concave sides of projections 92 and in effect pre-weakens pellet 32 so that upon application of force on pellet 32 breaks will occur across core 90 between the projections 92 forming wafer-like objects which in turn then break into small pieces.

A head member which is approximately one-half inch in thickness is preferred with a converging wall countersunk at an angle of 30.degree. for an included angle of 60.degree. to a depth of approximately three-sixteenths of an inch. The outside diameter of opening 70 is five-eights inch and the narrowest diameter is three-eights of an inch. The diverging wall 71 contiguous therewith completing the passage 31 through head 30 is countersunk at a taper of 1.degree. 30 minutes for an included angle of 3.degree. and a depth of five-sixteenths of an inch. While converging wall 70 has a preferred angle of 30.degree. any angle of taper between 45.degree. and 30.degree. works well.

Pellets formed by pellet machine 10 can be formed with varying diameters and lengths, although it has been found that pellets having diameters of one-fourth to three-eights of an inch are preferred. When employing head members 31 and 81, pellets will attain a length in a range about equal to their diameter or twice their diameter before self-severance occurs.

Although the invention has been described as being practiced with carbon dioxide to make solid carbon dioxide pellets, it will be understood that any liquefied gas which will flash to both a solid and vapor below its triple point can be formed into pellets such as 32 when employing the head members 30 and 81 in a piston or ram type pellet machine.

The pellet 32 is unique in that it has a very high density and yet possesses laminations or uniform pre-weakened fracture lines which makes the pellet highly frangible into minute pieces upon forced contact with any solid object. The density of pellet 32 provides for a free flowing pellet which, although severed into suitable lengths will not agglomerate. Thus, a novel rod-like pellet member formed from a liquefied gas is provided which can be rapidly formed and readily shipped without the pellets agglomerating. Moreover, in use, the pellets can be shattered into minute particles thus affording greater heat transfer efficiency than any herebefore known carbon dioxide pellet.

Others may practice the invention in any of the numerous ways which will be suggested by this disclosure to those skilled in the art by employing one or more of the novel features disclosed or equivalents thereof. All such practice of the invention is intended to be within the scope of the appended claims.

Claims

We claim:

1. The method of forming pellets of solid carbon dioxide comprising the steps of providing a quantity of carbon dioxide snow in a compression cylinder having an extrusion head, compacting the snow into a plug against said head, maintaining said plug against said head while extruding successive portions of said plug through a passage in said head, said passage having a length to diameter ratio of about 1:1 and a frusto-conical section with an included angle not exceeding 15.degree. and its larger diameter at its discharge end.

2. The method of claim 1 wherein successive portions of the solid carbon dioxide plug are first passed through a straight wall section of said passage.

3. The method of claim 1 wherein successive portions of the solid carbon dioxide are first passed through a converging wall section of said passage.

4. The method of claim 3 wherein said passage has a length to diameter ratio of about 1:1.

5. An apparatus for making rod-like carbon dioxide pellets, comprising a closed chamber, means for flashing liquefied carbon dioxide into said chamber to form carbon dioxide snow, an extrusion head at one end of said chamber, said head having a compression side and a discharge side and at least one passage having a length about equal to its diameter and a frusto-conical section with an included angle not exceeding 15.degree. communicating with said sides of said head, said passage having its widest dimension proximate to said discharge side of said head, a ram reciprocable in said chamber toward and away from said head, the end of said ram at the end of its compression stroke terminating short of said compression side a distance sufficient to provide a plug of compacted snow across said passage.

6. The apparatus as defined in claim 5 wherein each said passage is about one-half inch long and further includes a converging wall portion with the widest dimension in direct communication with the compression side of said head, the diameter of said passage being from three-eights to five-eights of an inch.

7. The apparatus as defined in claim 5 wherein each said passage further includes an annular straight wall section in direct communication with the compression side of said head at one end and said conical section at the other end.

8. The apparatus as defined in claim 6 wherein said converging wall and said conical section are contiguous in said head at their narrowest dimensions.

9. The apparatus as defined in claim 8 wherein a plurality of said passages are disposed in a circular manner in said head with an additional passage disposed in the center of said circular arrangement.

10. The apparatus as defined in claim 6 wherein said conical section has a narrower taper than said converging wall.