Methods and Apparatuses for Defrosting and Clearing Internal Components of a Blasting Apparatus

This application claims priority to U.S. Provisional Patent Application Ser. No. 63/652,259, filed May 28, 2024, entitled “METHODS AND APPARATUSES FOR DEFROSTING AND CLEARING INTERNAL COMPONENTS OF A BLASTING APPARATUS,” the disclosure of which is incorporated by reference herein.

The present invention relates to methods and apparatuses which entrain blast media particles in a flow and is particularly directed to methods and apparatuses for defrosting internal components of such a blasting apparatus and clearing ice or debris therefrom.

Carbon dioxide systems, including apparatuses for creating solid carbon dioxide particles, for entraining particles in a transport gas and for directing entrained particles toward objects are well known, as are the various component parts associated therewith, such as nozzles, are shown in U.S. Pat. Nos. 4,744,181, 4,843,770, 5,018,667, 5,050,805, 5,071,289, 5,188,151, 5,249,426, 5,288,028, 5,301,509, 5,473,903, 5,520,572, 6,024,304, 6,042,458, 6,346,035, 6,524,172, 6,695,679, 6,695,685, 6,726,549, 6,739,529, 6,824,450, 7,112,120, 7,950,984, 8,187,057, 8,277,288, 8,869,551, 9,095,956, 9,592,586, and 9,931,639, all of which are incorporated herein in their entirety by reference.

Additionally, U.S. patent application Ser. No. 11/853,194, filed Sep. 11, 2007, for Particle Blast System With Synchronized Feeder and Particle Generator; U.S. Patent Provisional Application Ser. No. 61/589,551 filed Jan. 23, 2012, for Method And Apparatus For Sizing Carbon Dioxide Particles; U.S. Patent Provisional Application Ser. No. 61/592,313 filed Jan. 30, 2012, for Method And Apparatus For Dispensing Carbon Dioxide Particles; U.S. patent application Ser. No. 13/475,454, filed May 18, 2012, for Method And Apparatus For Forming Carbon Dioxide Pellets; U.S. patent application Ser. No. 14/062,118 filed Oct. 24, 2013 for Apparatus Including At Least An Impeller Or Diverter And For Dispensing Carbon Dioxide Particles And Method Of Use; U.S. patent application Ser. No. 14/516,125, filed Oct. 16, 2014, for Method And Apparatus For Forming Solid Carbon Dioxide; U.S. Pat. No. 10,315,862 issued Jun. 11, 2019, for Particle Feeder; U.S. patent application Ser. No. 14/849,819, filed Sep. 10, 2015, for Apparatus And Method For High Flow Particle Blasting Without Particle Storage; U.S. Pat. No. 11,607,774, issued Mar. 21, 2023, for Blast Media Comminutor; and U.S. patent application Ser. No. 15/961,321, filed Apr. 24, 2018, For Particle Blast Apparatus, which disclose various apparatuses and methods that involve blast media, including solid carbon dioxide particles, are all incorporated herein in their entirety by reference.

U.S. Pat. No. 5,520,572 illustrates a particle blast apparatus that includes a particle generator that produces small particles by shaving them from a carbon dioxide block and entrains the carbon dioxide granules in a transport gas flow without storage of the granules. U.S. Pat. No. 5,520,572, 6,824,450 and US Patent Publication No. 2009-0093196 disclose particle blast apparatuses that include a particle generator that produces small particles by shaving them from a carbon dioxide block, a particle feeder which receives the particles from the particle generator and entrains them which are then delivered to a particle feeder which causes the particles to be entrained in a moving flow of transport gas. The entrained flow of particles flows through a delivery hose to a blast nozzle for an ultimate use, such as being directed against a workpiece or other target.

For some blasting applications, it may be desirable to have a range of small particles, such as in the size range of 3 mm diameter to 0.3 mm diameter. U.S. Pat. No. 11,607,774) discloses a comminutor which reduces the size of particles of frangible blast media from each particle's respective initial size to a second size which is small than a desired maximum size.

While operating a particle blast apparatus with cryogenic material, such as carbon dioxide particles (commonly referred to as “dry ice”), the temperature of the internal components of the particle blast apparatus can be lowered to levels that result in the formation of water condensation and immediate freezing of that condensation on those components during operation and/or once the particle blast apparatus is left idle. By way of example only, in such scenarios, the internal components may reach temperatures of about minus 78 degrees Celsius and ice can form on various components, including, but not limited to, the metering element, comminutor, and feeding rotordescribed herein. The operation time required to result in such temperature drops and subsequent ice formation varies depending on various operating parameters, including, but not limited to, the size of the particles being created by the particle blast apparatus and the level of humidity in the transport gas being used in the particle blast apparatus. Generally, as the size of particles created by the particle blast apparatus decreases, then the amount of operating time before ice begins to form on the internal components will also decrease, and, as the level of humidity in the transport gas increases, the amount of operating time before ice begins to form on the internal components will decrease. For example, in some instances, ice may begin forming on the internal components of the particle blast apparatus after about ten minutes of operation, while in other instances, with other operating parameters, it may take about sixty minutes or longer of operation before ice begins to form on the internal components of the particle blast apparatus. The presence of ice on these components, such as rotors, can prevent the rotors from being able to rotate and lock up the motors (also referred to as drives) connected to the rotors. In addition, during operation, ice can build up in and obstruct the internal pathway of the particle blast apparatus, thereby preventing blast media from flowing through the particle blast apparatus. The presence of ice on the internal components of the particle blast apparatus can result not only in the particle blast apparatus becoming inoperable, but the internal components can also be damaged.

In the following description, like reference characters designate like or corresponding parts throughout the several views. Also, in the following description, it is to be understood that terms such as front, back, inside, outside, and the like are words of convenience and are not to be construed as limiting terms. Terminology used in this patent is not meant to be limiting insofar as devices described herein, or portions thereof, may be attached or utilized in other orientations. Referring in more detail to the drawings, one or more embodiments constructed according to the teachings of the present innovation are described.

It should be appreciated that any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference.

Although this patent refers specifically to carbon dioxide, the invention is not limited to carbon dioxide but rather may be utilized with any suitable frangible material as well as any suitable cryogenic material or other type of particle such as water ice pellets or abrasive media. References herein to carbon dioxide, at least when describing embodiments which serve to explain the principles of the present innovation are not necessarily limited to carbon dioxide but are to be read to include any suitable frangible or cryogenic material.

Referring to, there is shown a representation of a particle blast apparatus, generally indicated at, which includes cart, delivery hose, hand control, and discharge nozzle. Internal to cartis a blast media delivery assembly (not shown in) which includes a hopper and a feeder assembly disposed to receive particles from the hopper and to entrain particles into a flow of transport gas. Particle blast apparatusis connectible to a source of transport gas, which may be delivered in the embodiment depicted by hosewhich delivers a flow of air at a suitable pressure, such as, but not limited to, 70-80 PSIG. Particle blast apparatusis also connectible to a source of defrost gas, which may be delivered in the embodiment depicted by hosewhich delivers a flow of gas at a suitable pressure, such as, but not limited to, about 70-80 PSIG. Hoseand hoseare each depicted as a flexible hose, but any suitable structure may be used to convey the transport gas and defrost gas. In some embodiments, at least a portion of hoseand hosemay comprise a single hose, while in other embodiments hoseand hosemay be separate hoses. Hosemay be connected to particle blast apparatusvia defrost valveand defrost port(described below) in order to allow defrost gas to be selectively introduced into the interior of particle blast apparatus. In some embodiments, the defrost gas has a pressure of about 80 PSIG when it reaches defrost portfrom defrost valve. After passing through defrost port, in some embodiments, the pressure of the defrost gas may vary from almost zero PSIG to about 80 PSIG depending on if the interior portion of particle blast apparatuswhere the defrost gas is introduced (e.g., roller cavity(described below)) is air tight (i.e., completely sealed) or if there are gaps present that allow the defrost gas to escape to atmosphere. The pressure of defrost gas in the interior of particle blast apparatusis greater the closer the interior of particle bast apparatusis to being completely sealed. In some embodiments, the transport gas and the defrost gas may be supplied by the same source, although this is not necessarily required. In some embodiments, the defrost gas may comprise air. Preferably, the temperature of the defrost gas is greater than or equal to about minus 78 degrees Celsius, and more preferably the temperature of the defrost gas is greater than or equal to about zero degrees Celsius. If the temperature of the defrost gas is greater than or equal to about minus 78 degrees Celsius but less than zero degrees Celsius, then that defrost gas will help sublimate ice that is formed of carbon dioxide particles. If the temperature of the defrost gas is greater than or equal to about zero degrees Celsius, then that defrost gas will help melt both ice that is formed of carbon dioxide particles and ice that is formed of water (commonly referred to as “water ice.”)

Blast media, such as, but not limited to, carbon dioxide particles, indicated at, may be deposited into the hopper through topof the hopper. The carbon dioxide particles may be of any suitable size, such as, but not limited to, a diameter of 3 mm and a length of about 3 mm. The feeder assembly entrains the particles into the transport gas, which thereafter flow at a subsonic speed through the internal flow passageway defined by delivery hose. Delivery hoseis depicted as a flexible hose, but any suitable structure may be used to convey the particles entrained in the transport gas. Hand controlallows the operator to control the operation of particle blast apparatusand the flow of entrained particles. Downstream of control, the entrained particles flow into entranceof discharge nozzle. The particles flow from exitof discharge nozzleand may be directed in the desired direction and/or at a desired target, such as a work piece (not shown).

Discharge nozzlemay be of any suitable configuration, for example, discharge nozzlemay be a supersonic nozzle, a subsonic nozzle, or any other suitable structure configured to advance or deliver the blast media to the desired point of use.

Controlmay be omitted and the operation of the system controlled through controls on cartor other suitable location. For example, the discharge nozzlemay be mounted to a robotic arm and control of the nozzle orientation and flow accomplished through controls located remote to cart.

Referring to, there is shown hopper(shown in dashed lines for clarity) and feeder assemblyof particle blast apparatus. Hoppermay include a device (not shown) for imparting energy to hopperto aid in the flow of particles therethrough. Hopperis a source of blast media, such as cryogenic particles, for example, but not limited to, carbon dioxide particles. Hopper exitis aligned with guide, at hopper seal. Any suitable source of blast media may be used, such as without limitation, a pelletizer.

Feeder assemblyis configured to transport blast media from a source of blast media into a flow of transport gas, with the blast media particles being entrained in the transport gas as the flow leaves feeder assemblyand enters delivery hose. In the embodiment depicted, feeder assemblyincludes metering portion, comminutorand feeding portion. Feeder assemblymay also be referred to as coreand metering portionand comminutormay be referred to collectively as particle control system (PCS). As discussed below, comminutormay be omitted from feeder assemblymetering portionmay be omitted from feeder assembly, and feeding portionmay be of any construction which entrains particles into the transport gas whether a single hose, multiple hose and/or venturi type system. The pressure and flow of transport gas delivered to feeding portionis controlled by pressure regulator assembly. In embodiments that include metering portionbut omit comminutor, metering portionmay discharge directly to feeding portion. In embodiments that omit metering portionbut include comminutor, comminutormay receive particles directly from a source of blast media such as hopper. In embodiments that omit metering portionand comminutor, feeding portionmay receive particles directly from a source of blast media, such as hopper.

Feeder assemblyincludes a plurality of motors to drive its different portions. These motors may be of any suitable configuration, such as pneumatic motors and electric motors, including, but not limited to, DC motors and VFD. Metering portionincludes drive, which, in the embodiment depicted, provides rotary power. In the embodiment depicted, comminutorincludes three drives,andwhich provide rotary power. In the embodiment depicted, feeding portionincludes drivewhich provides rotary power through right angle driveAny suitable quantity, configuration and orientation of drives, with or without the presence of right angle drives, may be used. For example, fewer motors may be used with appropriate mechanisms to transmit power to the components at the appropriate speeds (such as chains, belts, gears, etc.). As can be seen in, with the drives and right angle drive removed, locating pins may be used to locate the drives.

Feeder assemblymay include one or more actuators, each having at least one extendable member (not illustrated), disposed to be selectively extended into the particle flow from hopperto feeder assemblyat guide, capable of mechanically breaking up clumps of particles, as such is described in U.S. Pat. No. 6,524,172.

As can be seen in, feeder assemblyincludes a defrost portconfigured to allow defrost gas to be introduced into feeder assembly. In the illustrated embodiment, defrost portis located on support(described in more detail below).

Referring also to, metering portionincludes guideand metering element. Metering elementis configured to receive blast media, such as cryogenic particles, from a source of blast media, such as hopper, at first regionand to discharge blast media at second region. Metering elementincludes outer peripheral surfaces. Guidemay be made of any suitable material, such as aluminum, stainless steel, or plastic. Guideis configured to guide blast media from hopperto first region. Guidemay have any configuration suitable to guide blast media from hopperto first region, such as, without limitation, converging walls. Metering elementis configured to control the flow rate of blast media for particle blast apparatus. The rate may be expressed using any nomenclature, such as mass (or weight) or volume per unit time, such as pounds per minute. Metering elementmay be configured in any way suitable to control the blast media flow rate. In the embodiment depicted, metering elementis configured as a rotor-a structure which is rotatable about an axis, such as axisIn the embodiment depicted, metering elementis supported by shaftwith a key/keyway arrangement preventing rotation between metering elementand shaftDriveis coupled to shaftand may be controlled to rotate shaftabout axisthereby rotating metering elementabout axisMetering elementwill also be referred to herein as rotor, metering rotoror even doser, it being understood that references to metering elementas a rotor or a doser shall not be interpreted in a manner which limits metering element to the rotor structure illustrated. As a non-limiting example, metering elementmay be a reciprocating structure. Metering rotor, as depicted, includes a plurality of cavities, which are also referred to herein as pockets. Pocketsmay be of any size, shape, number or configuration. In the embodiment depicted, pocketsopen radially outwardly and extend between the ends of metering rotor, as described below. Rotation of metering rotorcyclically disposes each pocketat a first position adjacent first regionto receive particles and a second position adjacent second regionto discharge particles.

Comminutorincludes rollerwhich is rotatable about an axis, such as axisand rollerwhich is rotatable about an axis, such as axisIn the embodiment depicted, rolleris supported by shaftwith a key/keyway arrangement preventing rotation between rollerand shaftDriveis coupled to shaftand may be controlled to rotate shaftabout axisthereby rotating rollerabout axisIn the embodiment depicted, rolleris supported by shaftwith a key/keyway arrangement preventing rotation between rollerand shaftDriveis coupled to shaftand may be controlled to rotate shaftabout axisthereby rotating rollerabout axisRollers,may be made of any suitable material, such as aluminum.

Rollersandhave respective peripheral surfacesGapis defined between each respective peripheral surfaceConverging regionis defined upstream of gapby gapand rollers,. (Downstream is the direction of flow of blast media through feeder assembly, and upstream is the opposite direction.) Converging regionis disposed to receive blast media from second regionwhich has been discharged by metering element. Diverging regionis defined downstream of gapby gapand rollers,.

Comminutoris configured to receive blast media, which comprises a plurality of particles, such as carbon dioxide particles, from metering elementand to selectively reduce the size of the particles from the particles' respective initial sizes to a second size which is smaller than a predetermined size. In the embodiment depicted, comminutorreceives blast media from metering portion/metering element. In an alternative embodiment, metering portion/metering elementmay be omitted and comminutormay receive blast media from any structure, including directly from a source of blast media, including, but not limited to, hopper. As is known, rollers,are rotated to move peripheral surfacesin the downstream direction at gap, the terminus of converging region. As blast media particles travel in the downstream direction through gap, the sizes of particles which are initially larger than the width of gapbetween peripheral surfaceswill be reduced to a second size based on the gap size.

The size of gapmay be varied between a minimum gap and a maximum gap. The maximum gap and minimum gap may be any suitable size. The maximum gap may be large enough that none of the particles traveling through gapundergo a size change. The minimum gap may be small enough that all of the particles traveling through gapundergo a size change. Depending on the maximum gap size, there may be a gap size, which is less than the maximum gap size, at which comminution of particles first begins. At gap sizes at which less than all of the particles traveling through gapare comminuted, comminutorreduces the size of a plurality of the plurality of particles. In some embodiments, the minimum gap is configured to comminute particles to a very fine size, such as 0.012 inches, which may be referred to in the industry as microparticles, with the minimum gap being as small as 0.006 inches in some embodiments. In some embodiments, the maximum gap is configured to not comminute any particles, with the maximum gap being 0.7 inches. Any suitable minimum and maximum gap may be used.

Feeding portionmay be of any design which is configured to receive blast media particles and introduce the particles into the flow of transport gas, entraining them in the flow. In the embodiment depicted, feeding portionincludes feeding rotor, guidedisposed between gapand feeding rotor, and lower seal. Feeding rotoris rotatable about an axis, such as axisIn the embodiment depicted, shaft(see) is integral with feeding rotor, and may be of unitary construction. Alternately, shaftmay be a separate shaft which carries feeding rotorso that feeding rotordoes not rotate with respect to shaftFeeding rotormay be made of any suitable material, such as stainless steel.

As illustrated, driveis coupled to shaftthrough right angle driveand may be controlled to rotate shaftand, concomitantly, feeding rotorabout axis

Feeding rotorcomprises peripheral surface(see), also referred to herein as circumferential surfacewhich has a plurality of pocketsdisposed therein. Each pockethas a respective circumferential width. Guidedefines cavity. Guideis configured to receive particles from comminutorand guide the particles through cavityinto pocketsas feeding rotoris rotated about axisAs mentioned above, in some embodiments, comminutormay be omitted from feeder assemblywith guidereceiving particles directly from metering element. In addition, in some embodiments, metering elementand comminutormay be omitted from feeder assemblywith guidereceiving particles directly from a source of blast media, such as hopper. Guideincludes wiping edgeadjacent peripheral surfaceand extending longitudinally, generally parallel to axis. Feeding rotorrotates in the direction indicated by the arrow such that wiping edgedefines a nip line for feeding rotorand functions, with the rotation of feeding rotor, to force particles into pockets. During operation of the particle blast apparatus, ice can form in pocketson feeding rotor. As a result, the particles may not be effectively evacuated from pockets, which can result in a build up of ice and particles within roller cavity, thereby inhibiting the rotation of rollers,, blocking the flow of particles within feeder assembly, and negatively impacting the overall performance of particle blast apparatus.

Lower sealseals against peripheral surfaceLower sealmay be of any suitable configuration.

Feeding portiondefines transport gas flow pathindicated by flow linesandthrough which transport gas flows during operation of particle blast apparatus. Transport gas flow pathis connectable to a source of transport gas, either directly or through pressure regulator assembly(described below), with the appropriate fittings external to feeding portion. Transport gas flow pathmay be defined by any suitable structure and configured in any suitable way which allows the entrainment of particles discharged from pocketsinto the transport gas. In the embodiment depicted, lower sealand pistondefine at least a portion of transport gas flow path, with part of flow pathbeing through pockets, as described in U.S. Pat. No. 11,607,774.

Rotation of feeding rotorintroduces particles into the flow of transport gas, entraining them in the flow. The entrained flow (particles and transport gas) flows through delivery hoseand out discharge nozzle. Thus, there is a particle flow path extending between the source of blast media to the discharge nozzle, which, in the embodiment depicted, extends through metering portion, comminutorand feeding portion.

Referring to, there is shown an enlarged fragmentary cross-sectional view of metering rotorand guide. Guideincludes wiping edgedisposed adjacent outer peripheral surfacesof metering rotor. Outer peripheral surfacestravel past wiping edgeas metering rotoris rotated. Wiping edgeis configured to wipe across openingof each pocketas metering rotoris rotated. Wiping edgeis disposed at wiping angle a relative to a tangent to metering rotor, with an arcuate section transitioning from the sloped sides of guideto wiping edgeIn the embodiment depicted, this arcuate transition section has a radius of 0.29 inches, although any suitable radius or transition shape may be used. As used herein, wiping angle is the angle formed between the wiping edge and a tangent to metering rotor as illustrated in. Wiping angle a is configured to not result in a nip line between wiping edgeand outer peripheral surfacesas metering rotoris rotated in the direction indicated. If a nip line is present at this location, particles could be forced and/or crushed into pockets, which for carbon dioxide particles, results in the particles tending not to fall out of the pocket at discharge. In the embodiment depicted, wiping angle a is greater than 90°.

illustrates the overhang of entrancerelative to metering rotor, the overhang of housingrelative to roller, and that roller(and correspondingly roller) is wider than metering rotor. As shown, surfaceof entranceaxially overhangs first endof metering rotorand surfaceof entranceaxially overhangs second endThe upper portions of both endsare disposed in recesses, defined by surfacesin housingsrespectively. With this construction, particles traveling through guideare blocked from reaching endsSimilarly, surfaces′ and′ overhang the ends of roller(and concomitantly the ends of roller, not seen in). The upper portions of both ends of rollers,are disposed in recesses. As can be seen in, roller(and concomitantly roller) is wider than metering rotor. This construction avoids ledges where ice could build up.

Referring to, an exploded perspective view of feeding portionis depicted. In addition to the above description, in the embodiment depicted, feeding portionincludes housingand base. Base includes centrally disposed raised portion. Similar to the structure described in U.S. Pat. No. 10,315,862, an internal cavity of pistonsealingly engages raised portion, forming a chamber which is in fluid communication with the transport gas. Springis disposed to urge piston upwardly, with pilotengaging pistonas seen in. In the embodiment depicted, lower sealis secured to pistonby fastenerswith appropriate seals.

Housingincludes boreswhich receive bearingsBearingsrotatably support feeding rotor. Bearingis retained in boreby retainerwhich is secured to housing. Bearingis retained in boreby support, which is secured to housing by fasteners. Right angle drivemay be attached to support. Housingmay be made of any suitable material, such as aluminum.

Inletand outlet(see) of transport gas flow pathare formed in housingas shown. Fittings,sealing engage housingat inletand outlet, respectively, with retainerssecuring them thereto.

Referring to, there are illustrated exploded perspective views of metering portionand comminutor. In the depicted embodiment, housinghouses metering rotorand rollers,. Shaftmay be rotationally supported by bearingsHousingmay be made of any suitable material, such as aluminum, and of any suitable configuration. In the embodiment depicted, housingcomprises eight parts. As illustrated, housingsandcarry roller, while housingsandcarry roller. Housingsandcarry metering rotor. Housingalso includes skirtsandIn the illustrated embodiment, skirtcomprises a substantially solid panel that is attached to an outer surface of housingand skirtcomprises a substantially solid panel that is attached to an outer surface of housingSkirtsmay be made of any suitable material, including, but not limited to, polycarbonate plastic, such as Lexan™. As shown, each skirtincludes an openingwith an axis that aligns with the axis of shaftto allow shaftto pass through the respective skirtAs shown, openingsare circular. In the illustrated embodiment, each skirtalso includes an elongated openingconfigured to engage with a projection on each respective housingSkirtsmay help prevent contaminants from entering the interior of housing. In addition, when defrost gas is introduced into feeder assembly, the skirtsmay also help direct defrost gas around the internal components of comminutor, such as rollers,, and generally keep the defrost gas from easily escaping through openings in housing. An embodiment of skirtis shown in.

Housingsdefine roller cavity, which includes converging region, gap, diverging regionand the area between peripheral surfacesof rollers,and the interior surfaces of housingsAs can be seen in, defrost portis in fluid communication with roller cavityvia defrost port outlet. Accordingly, defrost gas can be introduced into roller cavityvia defrost port. The defrost gas that is introduced into roller cavitymay escape roller cavitythrough small gaps between adjacent parts that define roller cavity. Some of these gaps may be present even when the defrost gas is not being introduced into roller cavity, while other gaps may be created by the force resulting from the defrost gas such that those gaps are only present when the defrost gas is introduced into roller cavityand is being forced out of the gaps. By way of example only, defrost gas may escape roller cavitythrough gaps between each skirtand the respective portion of shaft(and its associated couplings) passing through the openingin each skirtAdditional gaps may be present or created by defrost gas between the face of skirtand the adjacent portions of housingand between the face of skirtand the adjacent portions of housing

Housingsandare moveable relative to housingsandso as to vary the width of gap. Housingsandhave corresponding supportsandSupportsrotatably support shaftsandand supportsrotatably support shaftSupportsandmay be made of any suitable material, such as aluminum. Housingsand supportsare depicted as not being moveable relative to feeding portionand hopper.

Referring also to, feeder assemblyincludes gap adjustment mechanismwhich is connected to supportsto move and dispose supports(along with housings) at and between a plurality of positions, including a first position at which gapis at its minimum and a second position at which gapis at its maximum. Gap adjustment mechanismcomprises shaftwhich is rotatable about an axis, such as axisand external teeth or threadsdisposed extending longitudinally as illustrated. Driveis coupled to shaftand may be controlled to rotate shaft. Gap adjustment mechanismcomprises memberwith internal teeth or threadsdisposed about axiswhich are shaped complementarily with external teeth or threadsengaging therewith. Rotation of shaftcauses relative longitudinal motion between shaftand member.

Memberis secured to plateby a plurality of fasteners. Plateis secured to supportby fastenerand to supportby fastener

Shaftincludes flangewhich is captured between supportand retainer, allowing rotational motion about axiswith little or no axial motion. A plurality of rodssecure supportto supportswith no movement therebetween. Rodssupport plateso that it can move axially along rods. Plateincludes a plurality of guideswhich are disposed in complementarily shaped boresSince plateis secured to supportsby fastenersthere is no relative movement between guidesand supportsGuidesare sized to allow rodsto slide axially therein.

Supportsinclude guidesrespectively which are disposed in complementarily shaped bores (not seen) in supportsThese bores are sized to allow guidesto slide axially therein. Guidessupport and guide supports,at and between the first and second positions of their travel. Rodsextend through guidesboresand guidesbeing fastened to supportssuch that supportis supported and does not move relative to supports

Rotation of shaftmoves platealong axisand concomitantly moves supportshousingsand rollerrelative to supportshousingsand roller, thereby varying the width of gap. In the illustrated embodiment, when supportshousingsand rollerare in the first position (i.e., when gapis at its minimum), then defrost port outletis at least partially obstructed by housingDefrost port outletmay still be capable of introducing defrost gas into roller cavitywhen it is partially obstructed by housingDefrost port outletbecomes more exposed (i.e., less obstructed) as supportshousingsand rollermove toward the second position (i.e., when gapis at its maximum). In some embodiments, defrost port outletis completely exposed, thereby allowing defrost gas to freely flow into roller cavitywithout any obstructions, when supportshousingsand rollerreach the second position, while in other embodiments, defrost port outletis completely exposed as supportshousingsand rollertransition toward, but prior to reaching, the second position.

Rollersandmay comprise a plurality of rollers. As seen in, rollermay comprise sub-rollers A and B non-rotatably carried by shaftand rollermay comprise sub-rollers C and D non-rotatably carried by shaftEach individual sub-roller A, B, C, D has a respective peripheral surface A′, B′, C′ and D′.

Rollers,, regardless whether comprised of single rollers or a plurality of rollers, may include a plurality of borestherethrough. If rollers,comprise a plurality of rollers, boreswithin each roller may be aligned axially. Boresreduce the overall mass of rollers,. Such reduced mass reduces the time required for a temperature change in rollers,, such as a reduction in the time required for any ice built up on rollers,during operation to melt during periods that particle blast apparatusis not being operated. In another embodiment, air or other gas may be directed to flow through boresto promote a faster temperature change.

For additional clarity,provides a cross-sectional perspective view of feeder assembly.

Referring to, supports(not visible in) are disposed at the second position at which gapis at its maximum. Rolleris spaced apart from rollerat a maximum distance. Regardless of the position of rollerand the concomitant size of gap, rollerremains in the same position. Rollerdefines first edgeof gap, which also remains in the same position regardless of the position of roller.

First edgeis always disposed at a location disposed intermediate axisand wiping edgeWiping edgedefines a boundary of wiping regionGenerally wiping regionextends about the width of one pocketwhen the leading edge of such pocketis disposed at wiping edgeWiping regionis in alignment with first edgeWhen supportsare disposed at the first location at which the size of gapis at a minimum, the entire gap is aligned with wiping regionsuch that the comminuted particles may fall or be directed into pocketsproximal wiping edge

is similar to, depicting gapat a size in between the maximum gap and minimum gap. Feeder assemblyis configured such that gap adjustment mechanismmay move and dispose supportsat and between a plurality of positions intermediate the first and second positions such that gapmay be set at a plurality of sizes intermediate the maximum gap and the minimum gap. In the depicted embodiment, the configuration of gap adjustment mechanismessentially allows the size to be set at the maximum, minimum and any size intermediate thereof.

Peripheral surfacesmay be of any suitable configuration. In the embodiment depicted, peripheral surfaceshave a surface texture, which may be of any configuration. It is noted that for clarity, surface texture has been omitted from the figures except in.illustrate rollers,having a surface texture comprising a plurality of raised ridges.illustrates rollers,comprised of sub-rollers A, B, C and D, viewed from the top into converging region. Each peripheral surface A′, B′, C′, D′ comprises a plurality of raised ridgesdisposed at an angle relative to either edge. The angle may be any suitable angle, such as° relative to the axial direction. In the embodiment depicted, the angles of each peripheral surface A′, B′, C′, D′ ridge are the same, although any suitable combination of angles may be used.