Abstract:
A method and device for forming slabs of dry ice is shown. A dry ice extruding machine has been modified with a die that has a slot for extruding a slab of dry ice therethrough. The slot is blocked until a puck is formed in an end of a forming chamber of the dry ice extruding machine. The block is then removed and dry ice extruded to a desired length and then broken to give a slab of dry ice. The last step is repeated over and over as the extruded portion reaches the desired length to give the number of slabs wanted.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates generally to the manufacture of dry ice and, more particularly, to a method and apparatus for producing slabs or blocks of dry ice.  
         [0003]     2. Background Information  
         [0004]     Solid state carbon dioxide (CO 2 ), known as dry ice, is used in many different applications. Dry ice is ideal for preserving food because it sublimates directly from its solid phase to its gaseous phase, leaving no odor, color, taste, or residue and causes no deleterious effects to the food. In cooling and preserving food, dry ice pellets may be placed directly onto the food to rapidly cool it below some specified temperature to prevent spoilage.  
         [0005]     Dry ice has traditionally been produced and distributed in blocks with each block weighing about 55 pounds. The blocks are cumbersome, expensive and require extra effort to crush or break apart to make the dry ice easy to use by reducing the block to reasonable size pieces. In recent years, dry ice has been produced in pellet form, which pellets are much easier to use.  
         [0006]     A dry ice pelletizer that is made by Tomco Equipment Co. is shown in U.S. Pat. No. 4,780,119, to Brooke, where liquid CO 2  is injected into a chamber known as an extrusion chamber and flashed at atmospheric pressure. In this flashing process, part of the liquid CO 2  changes phase to a solid known as “snow,” with the remaining part of the liquid CO 2  changing phase to gas. The gaseous CO 2  can exit the extrusion chamber through gas vents and the remaining snow may be compressed at the end of the extrusion chamber. The proportionate amount of the gaseous CO 2  versus the snow depends upon the pressure and temperature of the liquid CO 2  that is fed into the extrusion chamber and the surrounding pressure and temperature of the extrusion chamber. The lower the pressure and temperature, the greater the amount of snow produced in the flashing process.  
         [0007]     When liquid CO 2  is flashed under ideal conditions at atmospheric pressure, approximately 48% of the liquid CO 2  is changed to snow, while approximately 52% of the liquid CO 2  is changed to gas. Because the percentage of snow formation is directly proportional to the pressure inside the extrusion chamber, when flashing occurs, it is important that the pressure inside the extrusion chamber be kept as close to atmospheric pressure as possible.  
         [0008]     Once the snow is formed in the extrusion chamber, a piston is used to compact the snow in one end of the extrusion chamber against a die. In the traditional pelletizer, the snow will collect in the openings of the die and before long block the openings. While some small amount of snow may escape, it is not that significant. Thereafter, when the pistons move back and forth to compress the snow, the snow is compressed at the end against the die to form what is called a puck. As additional dry ice (i.e., snow) is compressed against the puck, the puck will extrude through the openings in the die.  
         [0009]     For some applications, the use of pelletized dry ice is not the ideal situation. For example, in some occasions, blocks or slabs of dry ice are much better than pellets of dry ice. However, the 55 pound blocks of dry ice are normally much larger than desired. Sometimes it is necessary to cut the blocks of dry ice into other shapes or sizes, such as shown in U.S. Pat. No. 5,189,939, to Allen. However, when the blocks of dry ice are cut, there is attendant waste in the cutting process.  
         [0010]     As an example of an industry that uses smaller blocks or slabs of dry ice, the airline industry uses thousands of pounds of dry ice per day to keep food cool in their serving carts. At the bottom of the serving cart is a tray located a block or slab of dry ice that is approximately 1″×5″×5″. In other words, the 55 pound block would have to be cut into small slabs of dry ice that can be put in the tray in the bottom of the serving cart for the airline industry. This small slab of dry ice will then sublimate directly from the solid to gaseous state leaving no odor and no deleterious effects while keeping the food cool. The airline industry uses large amounts of dry ice per day for this particular purpose.  
         [0011]     Slabs or blocks of dry ice could be used for many other purposes other than in the airline industry. Anytime there is a necessity to keep something cool for a period of time in which there is no residue to be dealt with during or after cooling, dry ice becomes an ideal candidate because it sublimates from solid to gaseous state, which gaseous state has no adverse effects.  
         [0012]     If smaller blocks or slabs of dry ice can be formed directly from liquid CO 2 , the losses attendant with cutting of large blocks of dry ice would not occur. The present invention is designed to solve this problem by providing for the extrusion of smaller blocks or slabs of dry ice that can be used in many different applications. None of the devices known by applicant allow for direct extrusion of blocks of dry ice, which blocks could be used by an end user, such as the airline industry.  
       SUMMARY OF THE INVENTION  
       [0013]     A conventional dry ice pelletizer is used, which consists of a cylinder in which liquid CO 2  is introduced through an injection port for flashing to form gaseous CO 2  and solid CO 2  therein. The gaseous CO 2  is vented and a piston is used to compress any solid CO 2  (snow) that forms in the chamber into a single mass of dry ice at one end of the cylinder, which mass of dry ice is known as a puck. For traditional pelletizers, the openings in the die quickly fill up with snow that blocks the openings. Then the snow is compressed against the die with each stroke of the piston. Ultimately, the piston pushes against the snow and puck with sufficient pressure to force the solidified CO 2  out the openings in the die as a continuous rod of dry ice. Periodically, the rod of dry ice is broken off into pellets.  
         [0014]     In the present invention, the die has been changed. In the die, there is a large slot with 1″×5″ being a typical size slot. If nothing is done to block the slot, the CO 2 , either in the gaseous state or as snow, will simply escape through the slot. To prevent that from occurring, a gate is moved over the slotted opening. The gate, once in place, prevents CO 2  either in the gaseous state or solid state of snow from escaping from the compression chamber. Now as a piston moves back and forth with the introduction of liquid CO 2 , the snow begins to compress against the die. Once a puck is formed against the die, then the gate can be removed. Thereafter, as the piston continues to reciprocate inside the cylinder with the introduction of liquid CO 2  that flashes to a combination of gaseous CO 2  and snow, the snow is compressed against the puck, and the puck is extruded through the die. If the slot in the die is approximately 1″×5″, the extruded dry ice will have a cross-sectional area of approximately 1″×5″.  
         [0015]     Immediately upon passing through the die, the 1″×5″ slab of dry ice has not set up into a good solid form. Therefore, an additional distance known as a forming chamber will be located adjacent to the die. The forming chamber may be a part of the die or a separate item attached thereto. Typically, the forming chamber would be approximately 2 inches thick.  
         [0016]     As the extrusion process continues and the 1″×5″ slab of dry ice is extruded, at some time the slab of dry ice will reach a desired length. A sensing device, such as a photocell, would be used to indicate the desired length of the slab has been reached. Assuming the desired length is 6 inches, once the extruded 1″×5″ cross-section of dry ice reaches 6 inches, the photocell will send a signal back indicating the desired length has been reached. That signal can then be used to activate a sizing cylinder that will move a sizing block that breaks off the extruded dry ice into slabs of approximately 1″×5″×6″ size. The sizing block can be controlled by any type of actuation device that has sufficient strength and speed, but in the present process, a pneumatic cylinder is probably ideal. Therefore, a pneumatic sizing cylinder would move a sizing block that would break off the extruded dry ice into desired lengths.  
         [0017]     Since liquid CO 2  is continuously being fed to the extrusion chamber for compression by the piston, snow continues to compress and the rectangular shaped cross-sectional area continues to be extruded. The next time the rectangular shaped extruded dry ice reaches the desired length, the process is repeated again. By repeatedly using this process, numerous blocks or slabs of dry ice of the desired dimensions are formed without the necessity for sawing or cutting.  
         [0018]     The gate only needs to be used during startup of the extrusion process. At that time, some force needs to hold the gate against the die. That force of holding the gate against the die may be provided by any of a number of different means, including a track that would force the gate against the outside of the die. On the other hand, the sizing block does not need the force to push it against the die because all the sizing block is doing is breaking off the extruded rectangular section of dry ice.  
         [0019]     It is an object of the present invention to provide a device for extruding blocks or slabs of dry ice.  
         [0020]     It is another object of the present invention to provide a dry ice extruder that can automatically extrude blocks or slabs of dry ice.  
         [0021]     It is yet another object of the present invention to modify a dry ice extruder to have a die that will extrude a rectangular shaped slab of dry ice, which slab may be broken upon reaching a predetermined length.  
         [0022]     It is another object of the present invention to provide a die with a slot therein for extruding a rectangular cross-section of dry ice, which slot is blocked during startup of the extruder to allow for the building of a puck of dry ice therein.  
         [0023]     It is still another object of the present invention to provide a dry ice extruder for extruding a slab of dry ice, which slab may be broken into predetermined lengths, the process being automated for blocking the slot in the die upon startup and thereafter to actuate a sizing device for breaking the extruded slab into predetermined lengths.  
         [0024]     These and other objects of the present invention are met when practicing the method or device as described hereinbelow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a perspective view of a Tomco type dry ice extruder which has been modified to extrude blocks or slabs of dry ice in accordance with the present invention.  
         [0026]      FIG. 2  is an exploded perspective view of the extrusion cylinder portion of the dry ice extruder, including the die, forming chamber, gate and sizing device.  
         [0027]      FIG. 3  is an elevated end view of the die on the dry ice extruder.  
         [0028]      FIG. 4  is an elevated partial cross-sectional view of  FIG. 3  showing the extrusion cylinder on the dry ice extruder showing the die, forming chamber, gate and sizing device.  
         [0029]      FIG. 5  is a simplified schematic diagram indicating hydraulic, pneumatic and liquid CO 2  supply systems for the dry ice extruder. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]      FIG. 1  shows a commercially available, widely used, dry ice extruder  10  that has been modified from a pelletizer to extrude blocks or slabs of dry ice. The dry ice extruder  10  is commercially available for purchase without the modifications from companies, such as Tomco Equipment Company. Initially hereinbelow, the items commercially available through Tomco or some other supplier will be described before describing the modifications that constitute the present invention. Because dry ice extruders are widely available in the marketplace, dry ice extruder  10  will only be described generally hereinbelow.  
         [0031]     Dry ice extruder  10  has a pair of side-by-side extrusion cylinders  12  that are operated by a pair of side-by-side hydraulic cylinders  14 . The hydraulic cylinders  14  are separated from the extrusion cylinders  12  by a spreader box  16 . Extrusion cylinders  12 , hydraulic cylinders  14 , and spreader box  16  are all mounted on frame  18 , as well as other components that will be described hereinbelow.  
         [0032]     To operate dry ice extruder  10 , liquid CO 2  is delivered to extrusion cylinders  12  through liquid CO 2  feed hoses  20  from a source of liquid CO 2  (not shown). Feed hoses  20  feed liquid CO 2  into extrusion cylinders  12  through injection connectors  22 . Inside of extrusion cylinders  12 , the liquid CO 2  is flashed so a portion thereof forms gaseous CO 2  and the remainder forms solid CO 2  in what is commonly called “snow.” The gaseous CO 2  is vented or removed from the extrusion cylinders  12  (see  FIG. 2 ) and the snow compacted or compressed by piston  24  (see  FIG. 2 ) as will subsequently be explained.  
         [0033]     To operate piston  24  inside of extrusion cylinders  12 , hydraulic cylinder  14  is connected via hydraulic hoses  26  through a pump (not shown) to a reservoir of hydraulic fluid  28 . A control box  30  controls the operation of the dry ice extruder  10  with motor controller  32  receiving commands from connection  34  to spreader box  16  and from control box  30 . Hydraulic hoses  26  are connected through fittings  36  to deliver hydraulic fluid to and from hydraulic cylinders  14 .  
         [0034]     Extrusion cylinders  12  are connected on one end of spreader box  16  through extrusion flange  38 , while hydraulic cylinders  14  are connected on the opposite end of spreader box  16  by hydraulics flange  40 .  
         [0035]     The parts described in the foregoing Description of the Preferred Embodiment are old and can be found in a Tomco extruder. The portions described hereinbelow are what is new and added by the present invention.  
         [0036]     Referring to  FIG. 2  now in combination with  FIG. 1 , extrusion cylinders  12  are held together by four prestressed rods  42  that connect from extrusion flange  38 , around extrusion cylinders  12 , through die holder  44 , die  46 , and forming chamber  48 , and extend there beyond. On one end, the prestressed rods  42  can end at the extension flange  38  of spreader box  16 , or they may extend therethrough to hold together hydraulic cylinders  14  and end with hydraulic flange  50  (see  FIG. 1 ).  
         [0037]     While it may not be immediately clear upon viewing  FIG. 1 , the dry ice extruder  10  is a dual system with two extrusion cylinders  12  and two hydraulic cylinders  14  being side by side. The operation of extrusion cylinders  12  alternates with piston  24  being retracted by piston rod  52  (see  FIG. 2 ) in the first extrusion cylinder  12  and extended in the second extrusion cylinder  12 . This operation is controlled by hydraulic cylinders  14 , alternately extending and retracting piston rods  52  connected to pistons  24  in the side-by-side extrusion cylinders  12 . This alternating type of compression and retraction provides balance to dry ice extruder  10 , so it will operate much smoother. Because extrusion cylinders  12  are identical, only one extrusion cylinder  12 , along with die holder  44 , die  46 , forming chamber  48 , and the controls associated therewith, will be explained in detail.  
         [0038]     Prestressed rods  42  extend through holes  54  of die holder  44  and notches  56  in die  46 . Nuts  58  thread onto the prestressed rods  42  to clamp the inner lip  60  of the die holder  44  around cylinder  62  of extrusion cylinders  12 . Forming chamber  48  can be made either integral with die  46  or may be bolted thereto by recessed bolt  68 . Die  46  is also held to die holder  44  by bolts  64  connecting into holes  66 . In the center of die  46  is an extruding slot  70 , through which dry ice may be extruded. The dry ice feeding through extruding slot  70  has not yet formed, so forming slot  72  in forming chamber  48  will give the dry ice sufficient time to form and harden prior to being exposed to atmosphere.  
         [0039]     In typical operation, liquid CO 2  from a suitable source would be injected into cylinder  62  of extrusion cylinder  12  through feed hoses  20  and injection connectors  22 . Inside of cylinder  62 , the liquid CO 2  will be flashed to atmospheric pressure thereby forming gaseous CO 2  and solid CO 2  in the form of snow. The gaseous CO 2  will be vented to either atmosphere or a gaseous CO 2  collection system through vent holes  74 . Pressure port  76  on cylinder  62  is used to monitor the pressure inside of cylinder  62  through either a pressure gauge  78  (see  FIG. 1 ) or by appropriate feedback to control box  30 . Depending upon the pressure inside of cylinder  62 , the amount of liquid CO 2  being injected or the repetition rate of piston  24  can be varied.  
         [0040]     To prevent the gaseous CO 2  and the solid CO 2  (snow) from escaping through extruding slot  70  and forming slot  72  to atmosphere, something must block slots  70  or  72 . In the present invention, a mounting plate  80  is bolted onto prestressed rods  42  by nuts  82 . (See  FIGS. 3 and 4  in combination with  FIGS. 1 and 2 .) Mounting plate  80  is located along the prestressed rods  42  so that gate  84  and sizing block  86  are flush with an outer surface  88  of the forming chamber  48 . Mounted on the mounting plate  80  is a sizing cylinder  90  for operating the sizing block  86 . Also mounted on mounting plate  80  is a gate cylinder  92  for operating gate  84 .  
         [0041]     On the ends of prestressed rods  42  is located an end plate  94  on which a photocell  96  is located. The photocell  96  may be adjusted inward or outward by adjusting slotted rod  98  and screw  100 .  
         [0042]     In actual operation, when someone starts the dry ice extruder  10 , liquid CO 2  comes in through feeder hoses  20  from a source of liquid CO 2  (not shown) into cylinder  62  of extrusion cylinders  12 . The liquid CO 2  is flashed to gaseous CO 2  and to solid CO 2  (snow) inside of cylinder  62 . The gaseous CO 2  is removed through vent holes  74 . At this time, the forming slot  72  of the forming chamber  48  should be blocked by gate  84 . Gate  84  may either be a manual operation of physically bolting a plate over forming slot  72  or may be an automatic gate  84  that is moved into place by gate cylinder  92 . Gate  84  should be pressed tightly against the outer surface  88  of the forming chamber  48  by any convenient means, such as tracks (not shown), that press gate  84  tightly over forming slot  72 .  
         [0043]     As liquid CO 2  is continually flashed inside cylinder  62  while piston  24  is operating therein via hydraulic cylinders  14 , the extrusion cylinder  12  will be cooled down. With the cooling of extrusion cylinder  12 , snow will begin to accumulate therein and be pushed against die  46  at the end of cylinder  62 . Further accumulation of snow (solidified CO 2 ) will further consolidate to form a puck at the die end of cylinder  62 . The puck once sufficiently solidified and formed, it is now time for extruding cylinder  12  to start extruding dry ice. Therefore, gate cylinder  92  retracts gate  84  to allow solid dry ice to be pushed through extruding slot  70  of die  46  and formed or hardened in forming slot  72  of forming chamber  48 . Thereafter, solidified dry ice in slab form is extruded out through extruding slot  70  and forming slot  72 . Extruding slot  70  has the normal amount of taper as is normally used for extruding dry ice. Typically there is an approximately 1° taper in both extruding slot  70  and forming slot  72 .  
         [0044]     As the slab of dry ice continues to be extruded through extruding slot  70  and formed in forming slot  72 , at some point the slab of extruded dry ice will reach a desired length. In the present invention, photocell  96 , which is mounted on end plate  94 , may be adjusted to determine that length. Assume photocell  96  is set to give a signal to control box  30  via connection  102  when the slab of extruded dry ice reaches a predetermined length. The signal being fed back to control box  30  via connection  102  from photocell  96  will actuate the sizing cylinder  90  that moves sizing block  86  against the dry ice to break off the slab of dry ice that has been extruded. Assuming photocell  96  is set for 6 inches, the extruded slab of dry ice will be approximately 6 inches long.  
         [0045]     While different types of actuating devices may be used to move gate  84  or sizing block  86 , in the preferred embodiment the sizing cylinder  90  and gate cylinder  92  are pneumatically operated. The pneumatic pressure may be provided by pneumatic pressure in the facility or can be from gaseous CO 2  that has been formed. Even a hydraulic cylinder can be used for gate cylinder  92 , but typically a hydraulic cylinder would be too slow for the sizing cylinder  90 . Sizing cylinder  90  must be fairly rapid in operation to break off the extruded slab of dry ice while the extrusion process continues. Electrical solenoids can be used in place of sizing cylinder  90  and gate cylinder  92 . Assuming pneumatic pressure is used in sizing cylinder  90  and gate cylinder  92 , the supply lines  104  (see  FIG. 1 ) are connected to a suitable source of pneumatic pressure (not shown).  
         [0046]     Referring now to  FIG. 5 , a schematic illustration as to the operation of the dry ice extruder  10  is illustrated in a schematic diagram. Where appropriate, like numbers will be utilized the same as numbers previously used hereinabove.  
         [0047]     Hydraulic fluid  28  is pumped by pump  106  through control valve  108  to extrusion cylinders  112  in an alternating manner. In other words, as piston  24  (not shown in  FIG. 5 ) is compressing in one extrusion cylinder  112 , the piston  24  is retracting in the other extrusion cylinder  112 . Control valve  108  acts as a double-pole, double-throw electrical switch except control valve  108  is controlling the direction of fluid flow rather than current. From control valve  108 , fluid is returned through return line  110  to the reservoir for hydraulic fluid  28 .  
         [0048]     On the other end of extrusion cylinder  112 , the liquid CO 2  is introduced through CO 2  lines  114  via control valve  116  from liquid CO 2  reservoir  118 . Inside of extrusion cylinder  112 , the liquid CO 2  is flashed to form gaseous CO 2  and solid CO 2  (snow). The gaseous CO 2  is vented through vents  120 , either to atmosphere or to a gaseous CO 2  collection system.  
         [0049]     On the end of the extrusion cylinder  112  is mounted a die  122 , followed by forming chamber  124 . Initially, when starting the operation, gate actuator  126  moves a gate (not shown) to block the extruding slot (not shown) through die  122  and forming chamber  124 . In this illustrative embodiment, gate actuator  126  is a pneumatic cylinder operated by gate valve  128 , which receives pressurized air from pressurized air source  130 . After the extrusion cylinder  112  has operated for a sufficient length of time to form a puck at the die end thereof, gate valve  128  operates gate actuator  126  to move the gate (not shown) from blocking the extrusion slot (not shown in  FIG. 5 , but previously explained in connection with  FIGS. 1-4 ). Thereafter, dry ice is extruded in slab form through die  122  and forming chamber  124 . However, once the dry ice reaches a predetermined length, the extruded slab of dry ice will be sensed by photocell  132 , which will send a signal to sizing valve  134 . Sizing valve  134 , which receives pneumatic pressure from pressurized air source  130 , will deliver pressurized air to sizing cylinder  136 . Sizing cylinder  136  will actuate sizing block  138 , which will be pressed against the extruded slab of dry ice causing the slab to break off at the face of forming chamber  124 . The actuation of sizing cylinder  136 , causing the movement of sizing block  138 , is fairly rapid because the extrusion process continues without interruption. In other words, sizing block  138  is moved downward to break the extruded slab of dry ice and retracted in a fairly rapid manner. The extrusion process continues uninterrupted until again photocell  132  senses the end of the extruded slab of dry ice to again operate the control valve  134  to actuate the sizing cylinder  136  and move sizing block  138 .  
         [0050]     In this manner, continual slabs of dry ice are extruded that will have a predetermined thickness, width and length. The length is controlled by adjustment of photocell  132 , with the width and thickness determined by the size of the slot in die  122  and forming chamber  124 .  
         [0051]     While in the preferred embodiment it is envisioned the extruded slabs of dry ice would be approximately 1″×5″×5″, different dimensions can be extruded with the equipment currently available on the market today. It is envisioned that current equipment could extrude slabs of dry ice as thick as 2 inches and as wide as 5 inches without significant modification. The length can be any length desired, but a 5 inch length is what is typically used in the airline industry. Depending upon how the slab or block of dry ice is to be used, the length of the slab or block can be changed very quickly. If other dimensions are desired to be changed, simply by changing the die, the other dimensions can also be changed.  
         [0052]     Initially, the gate that blocks the extruding slot, because it only needs to be used once at the beginning of the extrusion process, could be set up by any of a number of different means, including even the bolting of a blank plate on the end of the forming chamber and removing the blank plate once the puck has been formed.