EXTRUSION ARRANGEMENT FOR CRYOGENIC CLEANING APPARATUS

Abstract: Apparatus for forming relatively small, high density pellets of a sublimeable material in a cryogenic cleaning apparatus in which carbon dioxide liquid is injected under pressure into a cylinder (14). The apparatus includes a die assembly support (12) mounted at one end of the cylinder (14) in which is positioned a piston (6). Carbon dioxide crystals form in the cylinder (14) and are compressed by the piston (6) to form a dry ice block (5) which is forced under high piston pressure against an extrusion die (1). Small dry ice particles are extruded through holes (4) in the die (1). The die (1) and a breaker plate (2) are mounted to the support (12) by a backing plate (3). Axes of holes (18) found in the breaker plate (3) are non-parallel to axes of the holes (4). Relatively small, high density carbon dioxide pellets with ragged edges suitable for use in a cryogenic cleaning apparatus are thus produced in contrast to known equipment where lower density pellets of a size similar to small ice cubes are used.

Description: BACKGROUND EXTRU S I O N ARRANGEMENT FOR CRYOGENIC CLEANING APPARATUS Field of the Invention This invention relates to the design of dies for the ex¬ trusion of small, high-density, solid, carbon-dioxide or "dry ice" pellets of desired size and length. Description of the Prior Art The production of solid carbon-dioxide or "dry ice" by injection of liquid carbon-dioxide under pressure into a cylin¬ der, collecting the small crystals thus formed and then com¬ pressing the crystals to form solid carbon dioxide is a process well known to those familiar with the art. A further step of extruding the solid material thru a die to form pellets is also well known. In equipment presently available, such pellets are generally of the size of ordinary small ice cubes, and the pel¬ lets are of only medium density in relation to the highest pos¬ sible density of the solid carbon-dioxide. The normal use of such pellets is to provide temporary refrigeration of food¬ stuffs or similar products during transportation. The present invention pertains to an economincal design of a die for producing small, high density, sharp edged pellets of solid carbon dioxide for use in a blast cleaning process where¬ in the pellets are impacted at high velocity against a surface from which it is desired to remove unwanted material or con¬ tamination. The extrusion of the solid carbon dioxide or "dry ice" requires very high pressure, but because of the multipli¬ city of holes required in the die and very high pressure, it is difficult to make the die plate sufficiently strong without excessive fabrication costs. SUMMARY OF THE INVENTION This invention provides a more economical means of fabri¬ cating the parts, provides a convenient method of changing the die to produce different size pellets, and because of the novel configuration of the holes in the dies, provides an effective means of producing the small, high density pellets required for the blast cleaning process. Therefore the objects of this invention are: To provide an economical means of fabricating the dies for extruding the dry ice pellets. To provide the high strength supporting structure for the extrusion dies by economical fabrication methods. To provide a means of readily changing the die size with¬ out necessity of handling excessively heavy parts or the use of large cumbersome tools. To provide a means of forming carbon dioxide pellets of suitable size and density from a solid cake of carbon dioxide or "dry ice". To accomplish the extrusion process with no moving parts, thus eliminating the need for lubrication of active mechanisms in the cryogenic temperature range. To control the production of the pellets such that they are of the desired length and incorporate broken and irregular ends to further enhance the abrasive properties of the pellets. To extrude the solid dry ice through a pattern of holes contoured such that they compress the solid dry ice smoothly to prevent erratic fracturing and breaking of the pellets while in storage in a hopper or in transit to the blasting nozzle. To passively break the pellets by incorporating a breaker plate comprised of holes that register with the holes at the exit of the extrusion die but are set at an angle, thus break¬ ing the pellets to the desired length. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the invention will become apparent with reference to the following specification and to the drawings, wherein: FIGURE 1 is a fragmentary, side elevation view in section of a die made in accordance with an embodiment of this inven¬ tion; FIGURE 2 is a view taken along lines 2-2 of Figure 1; and, FIGURE 3 is an enlarged, fragmentary view in section of extrusion and fragmenting holes of the die of Figure 1. DETAILED DESCRIPTION Referring now to the drawings, a die assembly is shown having an extrusion die 1 and a breaker plate 2. The extrusion die and breaker plate are mounted by backing plate 3 to a die assembly support 12. Screws 16 secure the die, breaker plate and support plate to the support body 12. In operation, solid carbon dioxide cake 5, produced as mentioned previously, is positioned in a cylinder 14 and is compressed by a piston 6 and is thus extruded through holes 4 in the extrusion die 1. As the small cylinders of "dry ice" are forced through the holes, 4, they come in contact with the side of angular holes 18 in the breaker plate 2 and, being very brittle, are broken to the de¬ sired length, leaving rough sharp ends which provide better cutting edges when impinged against a surface to be cleaned. The pellets thus produced are propelled through large holes 7 in the backing plate 3 and thence into a storage hopper. The size and character of a pellet produced depends on the relationship of the size of hole 4 in the extrusion die 1, the angle which the hole 18 forms relative to the holes 4, the pri¬ mary taper 8 and the secondary taper 9, the length of the cyl- indical section 10 of the hole 4 and the velocity of the piston 6. The commercial advantages of this invention lie in both the method of producing the pellets and in the methods of fab¬ rication of the extrusion die. If the pellets are made by crushing or grinding large blocks of "dry ice" a large percen¬ tage of the material goes to very fine particles which are not useful in the blast cleaning process for which these pellets are intended. The result is an uneconomical loss of material. The other advantage comes from the design of the die assembly. Very high pressures are required by the extrusion process. Be¬ cause of the multiplicity of holes in the extrusion die, it is greatly weakened. The necessary strength can be obtained by making the die plate very thick. The requirement to drill a large number of small and very deep holes, accurately located, results in high fabrication costs. This invention overcomes these costs by incorporating a backing plate to provide the necessary strength and is economically fabricated because of the large easily drilled holes. While a particular embodiment of the invention has been described, it will be apparent to those skilled in the art that variations may be made thereto without departing from the spir¬ it of the invention and the scope of the appended claims.

Claims: What is claimed is: 1. In a cryogenic cleaning apparatus wherein pellets of material which sublime from the solid to the vapor state are projected at a body to be cleaned for abrasively cleaning the body, an improved arrangement for producing the pellets com¬ prising: (a) a cylinder for receiving a sublimeable material from which the pellets are to be created; (b) an extrusion die positioned at one end of said cylinder; (c) a piston positioned in said cylinder for forcing the sublimeable material against said extrusion die and causing the said material to be extruded through said holes in said die; and, (d) a backing plate having a plurality of relatively larger holes for mounting said extrusion die in position at one end of said cylinder. 2. The extrusion die arrangement of Claim 1 including a breaker plate positioned intermediate said extrusion die and said backing plate. 3. The extrusion device of Claim 2 wherein said extrusion holes have an axis thereof, said breaker plate includes a plur¬ ality of holes having an axis thereof, and the axes of said extrusion holes and breaker plate holes are non-parallel.

Inventors: MOORE DAVID E, MOORE, DAVID, E.
Applicants: CRYOBLAST INC, CRYOBLAST INC.
Application year: 1985
Main classification: B24C3
IPC codes: B24C1, C01B31, F25J1