Abstract: The invention relates to a process for jet grinding inorganic pigments comprising the steps of compacting the inorganic pigments on a roller compactor at a predetermined linear force, and jet grinding the compacted inorganic pigments.

Abstract: A method of preparing particles of a drug substance or diagnostic imaging agent which comprises grinding the drug substance or imaging agent in the presence of grinding media comprising a polymeric resin. The method provides particles exhibiting reduced contamination.

Abstract: A method for producing a milled powder including imparting an electrostatic charge to the starting powder and milling the electrostatically charged starting powder is provided.

Abstract: A free-flowing powder of coated particles is produced by means of a spray dying plant using a hot drying gas or a spray cooling plant using cold drying gas. A coating composition in liquid form is supplied to the atomizing means of the plant, and the liquid coating composition is atomized into a flow of liquid droplets, which are allowed to collide with particles of a carrier material dispersed in a transport gas. The direction and rate of flow of the transport gas are adapted to prevent contact between the drying gas and the droplets, so that the liquid coating composition, before any substantial drying thereof, will form a continuous liquid coating layer on the particles. The thus applied continuous coating layer on the particles is then allowed to at least partially dry by contact with the drying gas before withdrawal of the coated particles from the spray-drying chamber of the plant to a moving bed in the form of loose agglomerates.

Abstract: A gas stream classifier includes: a gas stream classifying means for classifying feed powder into at least a coarse powder fraction and a fine powder fraction by an inertia force acting on particles and a centrifugal force acting on a curved gas stream due to Coanda effect in a classifying chamber, and a feed supply pipe opening into the classifying chamber for supplying the feed powder into the classifying chamber. The efficiency of the classifier is improved by providing the feed supply pipe with a mixing zone for mixing an upper stream and a lower stream of the feed powder and an accompanying gas stream, respectively flowing through within the feed supply pipe. The classifier is particularly suitably used for producing a toner for developing electrostatic images having a sharp particle size distribution from toner particles having a weight-average particle size of at most 10 .mu.m, especially at most 8 .mu.m.

Abstract: A foundry sand is regenerated in an upright chamber to which air is admitted at the junction between a peripheral wall and between while an abrating rotor is in a horizontal plane close to the bottom to establish a vertical line with columns of fluidized sand outwardly of the orbit of the rotor.

Abstract: A pneumatic pulverizer comprises an acceleration pipe for transporting powders under acceleration by a high pressure gas, a pulverization chamber, a collision member for pulverizing the powders ejected from the acceleration pipe by a force of collision, the collision member being provided against the outlet of the acceleration pipe, a raw material powder supply inlet provided on the acceleration pipe, and a secondary air inlet provided between the raw material powder supply inlet and the outlet of the acceleration pipe.

Abstract: This invention provides a co-micronized bicarbonate salt composition which is a blend of ingredients having a particle size between about 0.01-1.0 micron. The composition is produced by mill co-micronization of a crystalline bicarbonate ingredient and a crystalline inorganic compound ingredient having a Mohs hardness value between about 3-7. A co-micronized blend such as sodium bicarbonate and zinc oxide is free-flowing and essentially free of agglomerated particles.

Abstract: Method and device for fluidized jet mill grinding wherein a nozzle construction is provided in which the momentum of the jet issuing from the nozzle is varied between areas of high momentum and areas of low momentum immediately after leaving the nozzle. A drop in pressure from the periphery to the core area of the jet develops so that flow channels are formed at right angles to the flow direction of the jet. Particles of the material to be comminuted are thereby drawn into the center of the jet where they are accelerated to the impact velocity necessary for their comminution during the course of the jet travel.

Abstract: An improved method of milling a particulate material in a jet mill is described. The material is fed from a holding vessel to be entrained by a gas, the holding vessel having an ullage which is maintained at a pressure of at least 0.05 MPa but less than the pressure at which gas is introduced to the jet mill. The method is particularly usefully employed in an impact jet mill in which the entrained particles impinge upon a surface, are reflected into another jet and passed into a cylindrical separation chamber. The method enables such an impact mill to be operated under more energy-efficient conditions.

Abstract: Adherent silicon spheres (10) are broken apart into separate spheres by entraining them in a high velocity gas stream (12) which is directed at a surface (20). When the adherent spheres (10) impact on the surface (20) they break apart. The gas (12) and the separated spheres (10) are directed away from the surface (20) along divergent paths and the spheres (10) are collected for use.

Abstract: Prior pulverizing apparatus which use rotating blades to pulverize the material require air as a pulverizing medium. The present invention uses a rotor structure which can operate in a vacuum if necessary.

Abstract: A pneumatic pulverizer includes an accelerating tube for conveying and accelerating a material to be pulverlized by a high-pressure gas and a pulverizing chamber for finely pulverizing the material to be pulverized. The pulverizing chamber is provided with a colliding member having a colliding surface provided in opposed relation to an outlet of the accelerating tube. The colliding surface of the colliding member has a protruding central portion, and an outer peripheral colliding surface provided around the protruding central portion for secondarily pulverizing the material primarily pulverized by the protruding central portion. The pulverizing chamber has a side wall for performing tertiary pulverization on the material secondarily pulverized by the outer peripheral colliding surface.

Abstract: A supersonic jet crusher of a collisional type has an injecting nozzle for injecting a jet stream into a crushing chamber; a jet stream path for supplying a crushing material into the jet stream; a collisional plate disposed in a position opposite to the injecting nozzle; a detachable jig disposed in said crushing chamber; and a secondary collisional plate detachably arranged in the detachable jig such that the crushing material collides with the collisional plate and further collides with the secondary collisional plate. Another supersonic jet crusher of a collisional type has an injecting nozzle for injecting a jet stream into a crushing chamber; a supplying port for supplying a crushing material into the jet stream; and a collisional member opposed to the injecting nozzle and having a crushing face on which the crushing material directly collides against to finely crush the crushing material.

Abstract: An improved glass crushing apparatus for a reverse bottle vending, crushing and sorting machine having an opentop, rotatable receptacle mounted at the top of the bin for catching the bottle to be smashed in the bin. After receipt of the bottle, the receptacle is rotated by a stepping motor controlled by the microprocessor and the bottle is dropped onto and smashed by a rotating impeller which contacts and throws the bottle against a reinforced, sharp corner of the bin. The crushed glass or glass cullet is then collected in a predesignated collection bin.

Abstract: A jet pulverizing method is described for preparing silicon seed particles from silicon feed particles without contamination. The method comprises accelerating silicon feed particles by fluid jet energy and colliding them with each other within a pulverizing chamber to fracture or split them into small particles which are recovered for use as seed particles. The method is characterized by the technique that silicon particles fluidized within the pulverizing chamber are formed into a dilute-phase fluidized bed with low particle density. Thus, the generation of fine powders may be suppressed and additional sieving to separate larger particles is not required.

Abstract: A process for impact crushing of rock and ore lumps, in which a rock lump is subjected to a primary impact force P.sub.1, and then the plurality of resultant smaller pieces are subjected to a secondary impact force P.sub.2. The application of the impact forces P.sub.1 and P.sub.2 is synchronized in time. The velocity vector V.sub.1 of the lump subjected to the primary impact force P.sub.1 and the vector of the secondary impact force P.sub.2 lie on a line running through the center of the lump mass. The invention also covers an apparatus for performing the above process, which comprises a housing accommodating a primary crushing rotor and a secondary crushing rotor, and also means for synchronizing the rotation of the secondary crushing rotor and the primary crushing rotor, coupled kinematically to said rotors. The secondary crushing rotor has two hammers, and its mass increases along the longitudinal axis of symmetry in a direction away from the axis of rotation.

Abstract: A pneumatic pulverizer comprises an acceleration pipe for transporting powders under acceleration by a high pressure gas, a pulverization chamber, a collision member for pulverizing the powders ejected from the acceleration pipe by a force of collision, the collision member being provided against the outlet of the acceleration pipe, a raw material powder supply inlet provided on the acceleration pipe, and a secondary air inlet provided between the raw material powder supply inlet and the outlet of the acceleration pipe.

Abstract: The method permits recovery of spent foundry sand for reuse by eliminating, by combustion, the organic and carbon substances with which the spent sand is impregnated; spent sand, after grinding to a uniform grain size, is placed into a cylindrical container (2) inclined with respect to the vertical and rotated slowly (4-6 revolutions per minute); then, a stream of oxygen is blown into the base of the container through a distributor (5) which uniformly distributes it into the spent sand mass (20), and local combustion is initiated on the surface of the sand mass, at the top of container, by a burner (31); finally the burner is extinguished whilst the delivery of the oxygen stream is maintained and the combustion proceeds and feeds itself by the effect of a progressive descent of the flame front (30) towards the base of the container until complete destruction of the organic and carbon substances contained in the sand has taken place.

Abstract: A comminuting device for breaking-up charge bodies of frangible material to free their value content and to reduce it to a desired size employs an upright enclosure into which charge bodies are fed so as to minimize in-air flow and to provide a steady stream of the bodies into the upper end of a centrally positioned downflow feed duct from which a series of horizontally, radially outwardly extending and vertically spaced-apart discs of a rotating assembly are suspended to define a central chamber selection passageway that is open at its upper end to the lower end of the duct, and at its bottom end through a grating to a motor drive compartment into which a fluid is introduced under positive pressure.

Abstract: A process for reducing the particle size of particulate crystalline energetic material such as HMX or RDX by slurrying the particulate energetic particles in an inert liquid wherein the liquid coats the surfaces of the particles and introducing the slurried energetic particles at a predetermined pressure into a Microfluidizer.RTM. high-pressure grinding chamber wherein high-pressure interparticle collision reduces the mean particle size of the energetic particles, thereby reducing the sensitivity of the energetic material.

Abstract: A micromilling device includes a milling chamber, at least one nozzle for injecting a stream of solid particles to be milled into the chamber in a predetermined path, and impact elements positioned in the path for impacting the stream of solid particles.

Abstract: A milling method for pulverizing agricultural products, minerals, etc. comprises the steps of whirling a grain material within a pulverizing chamber; and pulverizing the material by utilizing the friction due to a difference in moving speed between material particles which is generated as the material is whirled. A milling device comprises: a body frame; first and second rotary blades arranged opposite to each other within the body frame and defining, together with the inner walls of the body frame, a pulverizing chamber; a material feeding inlet formed on the body frame on the side of the first rotary blade and communicating with the pulverizing chamber; and a collection outlet provided axially in alignment with the second rotary blade and communicating with the pulverizing chamber. The collection outlet communicates with an associated suction device.

Abstract: An improved comminuter/dehydrator apparatus and method includes a body having an inverted, coaxially shaped cavity with an open truncated lower end and an open upper end connected to a cylindrically shaped chamber. A sleeve, which extends through the chamber and into the cavity, is adjustable axially by a pair of jacks. A damper is adjustable relative to the sleeve to control air escaping from the cavity into the ambient atmosphere. A manifold with a velocity-enhancing venturi mechanism directs air from a blower tangentially into the chamber to create cochleated and resonating, oscillatory cyclonic air-flow activity. A portion of the air from the blower to the chamber is diverted through a feeder containing the material being comminuted and dehydrated. The comminuted and dehydrated material is gravitationally discharged through the cavity lower end. The body has a removable nozzle tip to extend the operational characteristics of the apparatus.

Abstract: The apparatus and its process utilization enables a higher throughput of ore bodies being comminuted, provides a closer or more accurate selection of size of particles or particulates produced, has a low noise level in its operation, and uses its rotor impeller to facilitate the charging-in of ore bodies to be processed, the breaking-up of such bodies, and the delivery of such bodies in the form of sized particles or particulates is introduced by suction peripherally into one of the compartments of a motor-drive impeller and axially into all of the compartments, ore bodies are introduced into all of the compartments and are thrown under centrifugal force from one of the compartments against an anvil. Broken-up bodies of a desired size are fluidized and moved upwardly out of the apparatus while those of a rejected size are returned to the impeller for reprocessing with additional ore bodies being newly introduced therein.

Abstract: A process for the selective reclamation treatment of used foundry sands wherein separation of parts of the binding materials from the basic granular material is effected by mechanical means and, thereafter, the sand grains are accelerated to produce an abrasive action of the individual sand grains with one another. The treated grains are then separated into large and small grains and further treatment is effected on the small grains.

Abstract: A method is shown for removing minute traces of thermally fused foundry bonding clays from foundry sands reclaimed by a thermal sand reclaimer. The sand grains are passed to a dual fluid bed sand cooler-scrubber having sparge tubes for fluidizing air distribution, finned water cooling tubes and baffle plates for directing sand travel across the tube banks. The fluidized bed extends under a series of dry scrubber cells where the sand grains are hurled through blast tubes toward target plates by blast nozzles. Air current created within the interior of the device creates a controlled negative atmosphere which carries off unwanted traces of oxides and clays, as well as unwanted fine sand grains. The sand grains which are suitable for reuse are captured and deflected into a discharge section of the fluid bed where they flow over a weir by gravity and are discharged for re-use.

Abstract: A method and apparatus for fine grinding materials normally difficult to grind at ambient temperature, e.g. plastic and elastomeric materials in a fluid classification type impact mill utilizing liquid cryogen to pre-cool the material to be ground, to cool the material and the mill during grinding and to recycle vaporized cryogen from the mill back into the mill as the medium for conveying material to be ground into the mill.

Abstract: A rotating mill for comminuting a product, such as a food product, is disclosed in which the shape and orientation of the impeller blades, as well as the increased peripheral speed of the impeller, produce a finely comminuted product that was heretofore only capable with a multi-stage production process. The impeller rotates within an annular array of knives and the product is fed into the center area of the impeller. Centrifugal force urges the product across the rotating impeller, and into contact with the impeller blades and the knife array. The impeller has a generally circular impeller body that is rotatable about a generally centrally located rotational axis and a plurality of impeller blades attached to the impeller body. Each of the impeller blades has a product directing surface that extends parallel to an axis extending in a generally chordal direction across the impeller body and a product impact surface.

Abstract: The particle size of a particulate energetic material such as HMX or RDX is reduced by introducing the energetic material as a water-containing slurry at less than 40 percent solids into a high velocity fluid stream in a fluid energy mill and controlling the fluid temperature, fluid velocity, and energetic material feed rate to achieve a particle size of about 10 microns or less.

Abstract: A method and apparatus for communicating feed stock in the form of shreds or the like to form a low density particulate product. The shredded feed stock is fed to a material handling rotor that functions as a centrifugal blower. The apparatus includes a housing that defines a cylindrical rotor chamber formed about a horizontal axis and a volute-shaped internal passage having at least one convolution formed around the rotor chamber. Located within the housing is a cylindrical screen with perforations that open into the rotor chamber. The centrifugal blower rotor is mounted in the rotor chamber and has a plurality of radial vanes with rakers attached to the outer ends closely spaced from the inner surface of the screen so that they continuously wipe pass the perforations to prevent clogging or blinding.

Abstract: A process for preparing an X-ray phosphor comprising the steps of:(a) mixing a predetermined ratio of phosphor precursors;(b) grinding the mixture in a fluid grinding mill to obtain particles of a predetermined size;(c) firing the mixture; and(d) recovering the phosphor.

Abstract: A method and a equipment for processing of particularly finely divided material. The material is fed by means of a mechanical feeder device (2) and a pressurized equalization tank (4) into a fluidization chamber (5). A fluidized gas-solids suspension received is accelerated through acceleration nozzles (20) into a grinding chamber of a counter-jet grinder (19) so as to grind the solid particles. The ground gas-solids suspension is passed through connecting pipe (7) into a centrifugal classifier (8). A fine fraction is removed as a gas suspension through an opening (9). Additional air of low pressure is passed into the connecting pipe (7) and the coarse fraction is removed from the centrifugal classifier through a removal opening (10) in the peripheral face of the classifier into a pocket (12) outside said peripheral face, whereby the coarse fraction in the pocket (12) is removed batchwise by means of a closing device (13).

Abstract: A fluidized bed jet mill has a grinding chamber with a peripheral wall, a base, and a central axis. An impact target is mounted within the grinding chamber and centered on the chamber's central axis. Multiple sources of high velocity gas are mounted in the peripheral wall of the grinding chamber, are arrayed symmetrically about the central axis, and are oriented to direct high velocity gas along an axis intersecting the center of the impact target. In another embodiment, a fluidized bed jet mill has a grinding chamber with a peripheral wall, a base, and a central axis. Multiple sources of high velocity gas are mounted in the peripheral wall of the grinding chamber, are arrayed symmetrically about the central axis, and are oriented to direct high velocity gas along an axis intersecting the central axis of the grinding chamber.

Abstract: The compound grinding apparatus comprises a roller mill and rollers, installed in one body and fixed in such a way that they can be rotated relative their own axes of symmetry which are above a slewing table with a rotation drive and a rotating air separator fixed above the roller mill and made in the form of a screened rotor installed inside an impingement ring and equipped with a controlled rotation drive, the unique feature of which is that with the aim of specific power consumption reduction for required grinding degree, capacity increase and improvement of grinding quality it is equipped with a jet grinder with the material circulation units and feed pipelines which end in nozzles elements connected with a pressure source, the jet grinder being mounted between the roller mill and the air separator inside the same body.

Abstract: A toner for developing an electrostatic latent image is produced by classifying a pulverized feed material in a first classifying means into coarse powder and fine powder; pulverizing the coarse powder and feeding back the pulverized product to the first classifying means; introducing the fine powder to a second classifying means having a multi-division classification zone divided into at least three sections, where it is classified into a coarse powder portion, a median powder portion, and a fine powder portion; and feeding back the coarse powder to said pulverizing means or first classifying means. The median powder has a volume average particle diameter of from 4 .mu.m to 10 .mu.m and a coefficient of variation of number distribution, represented by A, satisfying the following condition: 20.ltoreq.A.ltoreq.45, and the weights B, C, F, G and M are controlled to satisfy the expressions: 0.3 .ltoreq.weight B/weight C.ltoreq.0.8, 0.2.ltoreq.weight G/weight C.ltoreq.0.7 and 0.8.ltoreq.

Abstract: An apparatus for disintegrating a fiber agglomerate has a feed tank for receiving and holding a batch of a fiber agglomerate. A turbulence chamber is connected to the feed tank for receiving a subquantity of the batch of fiber agglomerate and disintegrating the fiber agglomerate into separate fibers with air turbulence. A screening chamber is connected to the turbulence chamber for receiving the subquantity of the batch of fiber agglomerate and screening out separate fibers from shot particles and remaining fibers. The residual fibers and shot particles are fed back to the feed tank for reprocessing to obtain the maximum output of cleaned, separated fibers.

Abstract: A method of performing granulating, coating, drying of a powdry or granular material having a relatively minute particle diameter and an apparatus therefor. A nozzle for supplying the powdery or granular material and a nozzle for supplying a coating liquid are parallelly provided at adjacent positions where air streams dispersed from the both nozzles are not in contact with each other and directed to the interior of a processing cylinder. The two nozzles are connected to compressed air sources independently of each other. Drying air-stream blow-in openings are provided on the way from collision of the powdery or granular material and the coating material to catching thereof. Drying air streams are supplied from a direction tangent to the processing cylinder having a circular section.

Abstract: A pulverizer capable of effectively eliminating the production of a back pressure during the pulverization of a material on the pulverization surface of a collision member, to thereby accomplish the pulverization with a high efficiency. A collision member arranged in a pulverization chamber opposite to an injection nozzle is formed with a pulverization surface including a central conical surface section formed so as to project from the collision member in the direction opposite to the direction of injection of a jet and have a conical angle of no less than 30 degrees and an annular surface section formed contiguous to the central conical surface section to surround it and perpendicular to the direction of the jet.

Abstract: This invention relates to a method for pulverizing gelatin and to products in which pulverized gelatin is used. The present invention relates to a method for pulverizing hydrophilic and water-soluble dry gelatin with relatively high jelly strength using as a medium hydrophilic organic solvent dimethylformamide or organic solvent admixed with dimethylformamide in an atmosphere where moisture is shut out. It further relates to paints containing synthetic resin solutions in dimethylformamide or the organic solvent admixed with dimethylformamide which contains gelatin particles pulverized into 30 microns or smaller in size by the invention method. It provides paint layers, coating layers, films and finished cloths that are formed by using said paints and synthetic resin solutions. By eluting gelatin particles with hot water, paint layers, coating layers, film and finished cloths with excellent moisture permeability can be obtained.

Abstract: A granulating and coating method using the drying air streams to effectuate granulating, coating and drying and apparatus therefore wherein:a nozzle for supplying an article to be coated and another nozzle for supplying a coating material are provided at such positions that the article to be coated and the coating material collide with each other before the article to be coated and the coating material are dispersed by the drying air streams.

Abstract: A method for forming a pigment containing film on a work-piece includes the steps of circulating coating liquid containing pigment through a circulation path, and pulverizing the pigment to disperse the pigment in the coating liquid during the circulating step. The method further includes the steps of dipping a work-piece in the coating liquid during the circulating step, and raising the work-piece from the coating liquid. An apparatus for forming a pigment containing film on a work-piece includes a coating tank, having an inflow portion and an overflow portion, for holding coating liquid containing pigment, and a circulation path having one end connected to the inflow portion of the coating tank and the other end connected to the overflow portion of the coating tank, for circulating the coating liquid. In the circulation path, a pulverizing device is arranged for pulverizing the pigment to disperse the pigment in the coating liquid and to cause the coating liquid to flow in the circulation path.

Abstract: A method for the production of a metallic powder molding material is disclosed which comprises a step of imparting mechanical energy due to at least one of such physical actions as vibration, pulverization, attrition, rolling, shocks, agitation, and mixing a metallic particles in a vessel whose interior is held under vacuumized atmosphere or an atmosphere of inert gas thereby enabling the metallic particles to contact each other and acquire improvement in surface quality and a step of hot molding the metallic particles thereby producing a molding material.

Abstract: The improved deagglomerator and method of deagglomeration of the invention provides deagglomeration and/or attrition of particles within a cloud utilizing rapid particle acceleration and turbulent flow and sufficient resident time to assure deagglomeriation or attrition, and addition of a minimum of additional energy and in a manner to control bulk flow to minimize adverse effects on subsequent processes, and allowance for cloud diffusion as desired.

Abstract: A separator for classifying powder with air current, comprises a powder feed pipe and a classifying chamber, provided in said separator; a guide chamber provided at the upper part of said classifying chamber to communicate with said powder feed pipe; a plurality of introducing louvers provided between said guide chamber and said classifying chamber, at which the powder is flowed in from said guide chamber to said classifying chamber through the openings between said introducing louvers together with carrying air; an inclined classifying plate raised at its central part, provided at the bottom of said classifying chamber; classifying louvers provided along the side wall of said classifying chamber, through the openings of which the air is flowed to produce a whirling stream by which said powder fed into said classifying chamber together with carrying air is centrifugally separated into fine powder and coarse powder; a discharge opening provide at the central part of said classifying plate and from which the cl

Abstract: A system for separating contaminants from the plastic flake obtained by granulating synthetic plastic containers and products, which have contaminants bonded thereto, has a cryogenic housing for receiving the flake and a transport mechanism incorporated with the housing for moving the flake in a flow stream through the housing. The flake is mixed with a cryogenic medium at a subzero temperature and an impeller receives the frozen flake in a flow stream. An impact wall is provided outboard of the impeller and the impeller is rapidly revolved to radially separate the flakes and hurl the flakes individually at the impact wall with sufficient force to break the bond between the flakes and contaminant.

Abstract: Hazardous substances are separated from used foundry sand by means of a triple fluid bed thermal reactor, second stage sand cooler and third stage pneumatic attrition scrubber. Temperatures in each of the reactor's beds are precisely controlled, depending upon the nature of the sand being treated, so that hazardous substances can be separated and disposed of, rather than fixing the substances onto the sand grains in insoluble form.

Abstract: Fluidized-bed counter-jet mills are gas-jet mills with which extremely fine milling results can be produced with very little wear and tear. An improvement in the milling results can be achieved by cooling the gas jets with a refrigerant, but the improvement that can be achieved is not substantial and the consumption of refrigerant is very high. In order to lower the consumption of refrigerant while considerably improving the fineness of the milled material, the coarse material which is separated by the grader of the mill is cooled by the refrigerant within the fluidized-bed counter-jet mill and fed back into the milling chamber. Liquid nitrogen is the preferred refrigerant with which the sump of the mill is cooled.

Abstract: A process for explosive comminution of cellular material in which the material is subjected to compressed gas in a pressure chamber and then discharged from the pressure chamber with explosive pressure release in small portions against the grinding means of a mill.

Abstract: A method and apparatus for fiberizing feed stock in the form of shreds or the like to form a low density cellulosic product. The shredded feed stock is fed to a material handling rotor that functions as a centrifugal blower. The apparatus includes a housing that defines a cylindrical rotor chamber formed about a horizontal axis and a volute-shaped internal passage having at least one convolution formed around the rotor chamber. Located within the housing is a cylindrical screen with perforations that open into the rotor chamber. The centrifugal blower rotor is mounted in the rotor chamber and has a plurality of radial vanes with rakes attached to the outer ends closely spaced from the inner surface of the screen so that they continuously wipe pass the perforations to prevent clogging or blinding.