Abstract:
An apparatus for creating ice pellets having a rotationally mounted drum, a cryogenic component for cooling the outer surface of the drum, a fluid droplet applicator for transferring droplets to the outer surface of the drum, and a particle removal blade for removing solidified particles from the drum surface. Methods are also disclosed for creating ice pellets including transferring fluid droplets to a rotating drum having an outer surface sufficiently cold to cause solidification of the droplets during a period of drum rotation. Upon solidification, the particles are removed and made available for subsequent use. Such subsequent use includes disposing the apparatus in a pressurized vessel, collecting the pellets, and feeding the same, under pressure, to the ambient environment.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of solidified fluid surface treatment and more particularly to methods and apparatus for creating ice pellets for use in ice blasting applications, and methods and apparatus for ice blasting. 
     2. Description of the Prior Art 
     Prior art apparatus for creating particulate ice for use in ice blasting applications has traditionally relied upon coating a rotating drum with a thin layer of water or other working fluid, permitting the water to solidify, and fracturing off the solid water to form the desired ice particles. An example of this conventional technology can be found in U.S. Pat. No. 5,913,711. 
     As noted in the referenced patent, common problems associated with conventional technology relate to non-uniform particle size, conduit blockages, clump formation, etc. A significant reason for these problems relates to the means by which the particles are formed, namely, by fracturing thin sheets of ice. This process results in particles having a predominantly rectilinear geometry. These forms of ice are more susceptible to delivery problems than are pellets. One need only to look to nature to see that ice crystals and flakes have a significant tendency to clump, while pellets or other pseudo-spherical formations such as hail does not. Moreover, the aerodynamic properties of flakes are inferior to those of pellets. Consequently, the velocity of fractured ice is much more difficult to maintain after it has left a conduit. 
     Heretofore, there has been no convenient and low cost means for creating ice pellets for use in blasting or other similar applications. 
     SUMMARY OF THE INVENTION 
     The present invention concerns methods and apparatus for creating and using solidified fluid particles, particularly for treating various surfaces, commonly referred to as ice blasting. While the term “ice” is used herein throughout, that term is intended to encompass all forms of solidified fluids resulting from a phase change from fluid to solid. The term “working fluid” then represents the fluid that undergoes the phase change from fluid to solid. In addition, the term “bubble” is synonymous with a water column or fountain. 
     Apparatus in accordance with the invention comprise a frame to which a curved surface such as a drum is rotationally mounted wherein the drum comprises an outer peripheral surface. A cryogenic component is employed for causing the outer peripheral surface to reach a temperature (T s ) sufficient to cause a working fluid in contact therewith to solidify over a period of time. The cryogenic component may be ducted to the internal portions of the drum or directed to the outer peripheral surface. 
     Also mounted or linked to the frame is a fluid droplet applicator, which is in fluid communication with a source of the working fluid wherein the applicator defines a plurality of orifices through which the working fluid may be expelled and wherein the orifices are in close proximity to the outer peripheral surface of the drum. To facilitate removal of the solid particles, a particle removal member comprising a blade for example, is positioned adjacent to the outer peripheral surface of the drum. 
     Methods in accordance with the invention comprise establishing a temperature (T s ) on an outer peripheral surface of a rotatable curved surface such as a drum where (T s ) is sufficient to cause a working fluid to reach a solid phase in an ambient environment. The drum is further rotated either prior to or during the application of a plurality of fluid droplets to the outer peripheral surface of the drum. Upon contacting the outer peripheral surface of the drum, the droplets are permitted to substantially solidify into solid phase particles, where after the particles are removed. 
     One of many advantages the invention has over the prior art is the ability to create dense yet relatively smooth particles or pellets from a fluid. These attributes beneficially enhance the abrasive and sustained velocity characteristics of a blasting applicator using the resultant particles. Thus, particles produced according to the invention can be siphon fed or pressure fed in blasting equipment. Heretofore, the irregular and rectilinear shape of ice particles produced according to the prior art have made it very difficult to engage in high velocity blasting of target surfaces and use of the same in pressure feed blasting equipment. Thus, a system for blasting a target surface comprises the previously described apparatus and an enclosure wholly surrounding the apparatus, a container for receiving removed particles, and an outlet conduit in fluid communication with the container and an external portion of the container wherein the enclosure is selectively pressurized, thereby causing migration of any particles in the container to the external portion of the enclosure via the conduit. From there, conventional blasting equipment can be employed. Naturally, siphon feed systems can be employed as will be appreciated by those skilled in the art. 
     A preferred embodiment of the apparatus includes a conventional cryogenic fluid generating system wherein the fluid is introduced into an inner chamber defined by the drum and circulated therein. Conduction causes heat to migrate from the outer peripheral surface of the drum into the circulating fluid, thereby causing the surface temperature (T s ) to drop approximately to the temperature (T f ) of the cryogenic fluid. The target temperatures (T s ) and (T 
     f) depend upon the type of working fluid being applied to the surface of the drum. When fresh water is being used as the working fluid, (T s ) is approximately −28° C. and (T f ) is approximately −37° C. 
     The preferred embodiment utilizes internal cooling of the drum to achieve surface cooling thereof. Alternatively, the outer peripheral surface temperature (T s ) of the drum can be modified externally. Thus, a cryogenic gas or fluid can be applied directly to the surface (such as by directed exposure or immersion), or thermocouples integrated with the drum can be used to achieve the desired level of surface cooling. 
     While a preferred embodiment has the outer peripheral surface being smooth, modifications of the surface are considered within the scope of the invention. Thus, the nature of the formed pellets or particles can be modified by altering the physical characteristics of the surface. 
     Another feature of the preferred embodiment is the use a foramenous tube that functions as the fluid droplet applicator. This tube, preferably oriented adjacent to and congruent with the drum axis, delivers the working fluid to the drum. Because the mode of droplet application is preferably by means of bubbling, any suitable fluid conduit having a plurality of orifices positioned proximate to the drum surface will meet the requirements of the invention. Thus, the droplet applicator can be in accordance with the preferred embodiment, or may have discrete fluid sub-conduits extending from a common manifold. Moreover, the location of the applicator is preferably at the lowest portion of the drum to enhance the geometric properties of the particles to be formed. However, the location of the applicator is not limited to the preferred location. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the apparatus with the cryogenic component not being shown for clarity; 
     FIG. 2 is a front elevation view of the apparatus illustrating the location of the fluid droplet applicator and the particle removal member for removing formed particles; 
     FIG. 3 is a bottom plan view showing the relative location of the applicator and particle removal member; 
     FIG. 4 is a partial cross section of various ridges and grooves that may be formed in the outer surface of the drum to modify the nature of particles produced; 
     FIG. 5 is a detailed perspective view of the fluid droplet applicator illustrating a groove and plurality of orifices defined thereby; 
     FIG. 6 is a schematic representation of fluid droplet application and particle removal into a hopper during operation of a preferred embodiment; 
     FIG. 7 is a detailed view of the representation of FIG. 6 illustrating the formation and expulsion of fluid droplets and adherence thereof on a rotating drum; 
     FIG. 8 is a partial cross sectional plan view of the apparatus illustrating the location of cryogenic fluid delivery and recovery within the drum and the structure for supporting the drum; and 
     FIG. 9 is a schematic diagram of the cryogenic component. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following discussion is presented to enable a person skilled in the art to make and use the invention. Various modifications to the preferred embodiments will be readily apparent to those skilled in the art, and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention as defined by the appended claims. Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 
     Turning then to the several figures wherein like numerals indicate like parts and more particularly to FIGS. 1-3, icemaker  10  comprises several assemblies, namely, frame assembly  20 , drum assembly  30 , cryogenic system  40  (shown schematically in FIG.  9 ), drive assembly  50 , droplet generator  60 , particle removal assembly  70 , and hopper  90  (shown for clarity in FIG.  6 ). The principle of operation is to deposit droplets of water or other working fluid on drum outer surface  36 , permit the droplets to substantially solidify, and remove the same for use in ice blasting or other applications. 
     Frame assembly  20 , which is constructed of steel or other appropriately supportive material, comprises support surface  22 , vertical support members  24   a  and  24   b , and suitable bearings. Drum assembly  30 , which is supported by vertical supports  24   a  and  24   b  by way of internal bearings (shown in FIG.  8 ), comprises evaporator drum  32 , previously mentioned drum peripheral or outer surface  36 , and shafts  38   a  and  38   b.    
     Evaporator drum  32 , which is manufactured by Weber Eistechnik GmbH of Germany, receives compressed refrigerant and permits the same to expand within the drum, thereby causing cooling of outer surface  36 . FIG. 8 best illustrates the fluid paths related to drum  32 . As shown, refrigerant is delivered to the inner volume of drum  32  and distributed along the inner surface of outer surface  36  via spiral channel  34 , which is formed in an ultra high molecular weight plastic. Conduction removes heat from drum outer surface  36  and returns it to cryogenic system  40 . Thus, channel  34  connects fluid conduits  46   a  and  46   b.    
     In the present embodiment, drum outer surface  36  is smooth. However, additional surface contours can be employed as is best shown in FIG.  4 . Each surface contour results in different particle formation characteristics, and is selected based upon design considerations. Any surface treatment can be radially constant, longitudinally constant, or can be intersecting with other surface features, such as cross-hatching. 
     To provide sufficient cooling of drum outer surface  36 , cryogenic system  40  is employed, which is shown schematically in FIG.  9 . System  40  is a conventional refrigerant system comprising compressor  42 , radiator  44 , fluid conduits  46   a  and  46   b , and rotatable fluid coupling  48 . Other components such as controls, expansion valves, safety valves, recovery reservoirs, and the like are shown but not labeled for simplicity with the knowledge that those persons skilled in the art are familiar with conventional cryogenic systems. 
     Cryogenic fluid is introduced into drum  32  via conduit  46   a  and distributed therein as previously described. Cryogenic fluid is returned from drum  32  via conduit  46   b  for recovery and recompression. Alternatively, drum  32  can be exposed to a chilled ambient environment such that drum surface cooling can be accomplished externally. Such an exposure can be indirect, e.g., as described below with respect to a system embodiment, or can be direct, e.g., exhausting cooled gas directly on outer surface  36 . 
     Rotatable fluid coupling  48 , which is also manufactured by Weber Eistechnik GmbH of Germany, serves to both facilitate fluid delivery and return, as well as provide support for rotational movement of drum  32 . The features of this coupling are best shown in FIG.  8 . 
     To impart rotational movement of drum  32 , drive assembly  50  is employed. Drive assembly  50  comprises motor  52  having drive pulley member  54  attached thereto. Belt  56  links pulley member  54  to pulley member  58 , which is attached to or forms part of coupling  48  as is best shown in FIG. 2. A servo control (not shown) modulates rotation of motor  52  to vary the drum rotation, and therefore the speed in which ice particles are formed. It should be noted that optimal speed is a function of drum surface temperature (T s ), ambient conditions surrounding drum  32 , working fluid temperature, and working fluid delivery rates. 
     Turning then to FIGS. 5-7, the details of droplet generator  60  are shown. In the present embodiment, tube  62  is used as droplet generator  60  and is fixed to horizontal support member  74 , which also provides a means for supporting particle removal assembly  70 . Tube  62  is in fluid communication with a source of working fluid, such as common fresh water, via supply tube  68 . Tube  62  also defines a plurality of orifices  64  formed in groove  66 . In the present embodiment, tube  62  has an internal diameter of 33.5 mm and each orifice has a diameter of approximately 0.8 mm. Tube  62  is preferably mounted approximately 2.0 mm from drum outer surface  36 . 
     As a principle of operation is to create fluid columns or bubbles (as opposed to gas bubbles contained by the fluid), tube  62  is preferably specially constructed to enhance this operational objective. Referring specifically to FIGS. 6 and 7, it can be seen that groove  66  is formed in tube  62 . Groove  66  functions to support the lower portion of a bubble, thereby increasing the height and stability of the bubble. Alternatives to groove  66  include forming dimples about each orifice, extension mini-conduits, or forming other structure to enable desirable bubble formation. In addition to modulating fluid flow through tube  62 , the characteristics of deposited droplets can be modified by support member  74  adjusters. These adjusters (not shown) permit a user to alter the relative distance between drum outer surface  36  and tube  62 . In most circumstances, such adjustments are only periodically carried out. 
     Also affixed to horizontal support member  74  is particle removal assembly  70  having blade  72  as a major component thereof. Blade  72  is positioned directly adjacent to drum outer surface  36  so as to contact each solid particle passing by it. The interaction between approaching particles deposited on drum outer surface  36  and blade  72  causes each particle to dislodge and collect in hopper  90 , as is exemplified in FIG.  6 . 
     Method of Operation: 
     Ice maker  10  functions in a manner quite different from the prior art icemakers. Initial operation of icemaker  10  requires that the cryogenic fluid be cooled to a desired temperature (T f ) and introduced into drum  32  for distribution and evaporation therein. Rotation of drum  32  is also commenced at this time to facilitate distribution of the cryogenic fluid/vapor and homogeneous cooling of outer surface  36  through conduction. The selection of the cryogenic fluid temperature (T f ) and drum rotation is based upon considerations such as ambient temperature, working fluid temperature, and working fluid flow rates. In the present embodiment, the cryogenic fluid temperature (T f ) is −37° C. and the drum rotation is 4.0 revolutions per minute. Once the desired conditions have been reached, formation of ice particles can commence. 
     As intimated above, droplets are formed on drum outer surface  36 , which in turn solidify to form particles or nuggets having substantially curvilinear geometries rather than rectilinear forms as is common with sheet ice formations. Thus, it is advantageous to initially deposit the droplets at the bottom portion of drum  32  so that when initially adhered, gravity will maintain a pseudo-spherical droplet form. It is important for optimal results that the droplet geometry be substantially maintained after adhesion to drum outer surface  36 ; if a droplet deforms (primarily a dribble effect) during drum rotation, the benefits of the invention are reduced. If deformation occurs, a decrease in cryogenic fluid temperature or flow volume, or drum rotation should be tried. 
     As noted previously, the size of particle formation is determined by several factors, including temperature of the working fluid (T f ) and drum outer surface temperature (T s ), working fluid pressure and droplet generator orifice size, and drum outer surface texture. Depending upon design considerations, one, some or all of these variables can be modified to produce the desired particles. 
     Once particle formation has begun, complete or substantial solidification occurs during rotation of drum  32 . Upon a particle encountering particle removal blade  72 , it is “chipped” off where after gravity causes such particle to fall into hopper  90 . 
     A systems approach then utilizes the particles deposited in hopper  90  and distributes these particles to an end use device such as a blasting nozzle. The means for distribution is preferable pneumatic; either pressure or suction can be employed. The pellets can be applied via the nozzle without modification, or the pellets can be mechanically altered (such as by impact) prior to ejection from the nozzle. If the pellets are mechanically altered, the resultant particle will have varying degrees of rectilinear shapes, which beneficially increases the abrasive characteristics of the pellets. Moreover, because the pellets are delivered to the nozzle in a substantially curvilinear form, common problems such as feed blockages are avoided. Thus, a user will receive the creation and feed benefits associated with smooth pellets and the abrasive benefits of angular pellets upon impact. 
     In a preferred systems embodiment, icemaker  10  and hopper  90  reside in a sealable pressurized vessel (alternatively, the hopper is integrated into the vessel design). Hopper  90  is coupled to a feed line that exits the vessel. When the feed line is opened, pressurized gas such as air in the vessel pushes particles from the hopper to the end of the feed line. A benefit of using this form of particle distribution is that the ambient environment surrounding icemaker  10  can be controlled, such as to lower the environment temperature to increase particle production and minimize particle melting prior to distribution. Moreover, higher delivery rates can be achieved by using a pressure delivery scheme as opposed to a suction delivery scheme. Notwithstanding the foregoing, any icemaker can be disposed in such a vessel and the benefits associated therewith will still be appreciated.