Abstract: The apparatus comprises a storage vessel (19) for abrasive particles, a source of pressurised carrier fluid and a first conduit (11) to convey at least a major proportion of the incoming carrier fluid to a nozzle (16). A second conduit (9) connects the source of carrier fluid to an inlet of the storage vessel (19) and a third conduit (18) connects its outlet to the nozzle (16). A switching device (6) is selectively operable either to allow a minor proportion of incoming carrier fluid to flow through the second conduit (9) to the storage vessel (19), or to direct all of the carrier fluid through the first conduit (11). When a minor proportion of carrier fluid is directed through the second conduit (9), abrasive particles in carrier fluid are discharged from storage vessel (19) into the third conduit (18). When all of the carrier fluid is directed through the first conduit (11), fluid from the second conduit is entrained, thereby reversing fluid flow in the second (9) and third (18) conduits.

Abstract: An apparatus for dispensing a pressurized stream of gas having particles suspended therein, is described. A double acting pinch valve suitable for use in the apparatus is also described. The apparatus finds particular utility in the dental industry.

Abstract: An improved hand piece apparatus for use with abrasive cleaning devices uses a control switch that can be controlled manually by an operator to controllably regulate the amount a mixture of a pressurized air with abrasive particles at the nozzle head inlet port of the nozzle head assembly.

Abstract: A nozzle assembly for a hand piece in an air abrasion system for delivering an abrasive laden air stream to a surface, the nozzle assembly having a connecting member having a channel and being removably mountable to said hand piece, an arcuate conduit member having a channel, the conduit member secured to the connecting member and a nozzle member formed with the channel, the nozzle member mounted within the channel of the conduit member, the nozzle member defined by a tapered channel portion in fluid communication with the channel of the conduit member and a cylindrically-shaped channel portion in communication with said tapered channel portion for directing the abrasive laden air stream in a substantially cylindrically-shaped cross section to the surface to be abraded.

Abstract: A workpiece includes a surface adjoining an aperture. The aperture is filled with a plug to provide a step adjoining the surface. A stream of pliant shot in a carrier fluid is discharged at a shallow angle of incidence against the plug and directed toward the step for selective abrasion thereof.

Abstract: A removable nozzle head for a miniature sandblaster used for medical or industrial applications is disclosed comprising a nozzle, a handpiece nozzle adapter, a nozzle locking ring where the nozzle and nozzle handpiece adapter each have corresponding first and second bore in fluid communication to allow delivery of independent supplies of a gas and an abrasive laden stream to a mixing chamber in the nozzle for delivery through a orifice tube to a surface to be abraded, cleaned or modified.

Abstract: An improved structure of a sand blast gun includes a body, a guide tube accommodated in the body in a longitudinal direction, and a stop valve disposed in a radial direction. The stop valve has two guide posts. A shaft having a sleeve fitted on the outside straddles over upper portions of the guide posts. The guide posts are respectively fitted with pressure springs and inserted into holes of the body. An urging top end is firstly fixed on a center of a securing plate that is screwably mounted at the bottom side of the guide posts such that the urging top end extends into a radial round hole of the body to urge against a catgut tube to close the passage. When a trigger of the sand blast gun is pulled, it pushes the shaft and the guide posts to cause the pressure spring to retract to thereby cause the securing plate on the bottom of the guide posts and the urging top end to displace outwardly.

Abstract: The present invention relates to a device and a method for abrasive blasting, in particular for the sand-blasting of relatively small workpieces, for example in the hobby sector (model building). The device comprises a chamber (2), which is closed in an essentially airtight manner on all sides and has at least one, and preferably a plurality of, closable openings (3), it being possible to evacuate the chamber. A blasting pipe unit (5), which can be introduced into the chamber via one of the openings and which has an inlet (12) for the blasting agent, an inlet (13) for air and an outlet opening (14) for the blasting agent, is connected to a blasting-agent container (8) via a feed line (7). Both the method and the device operate using subatmospheric pressure, so that it is possible, for example, to use a commercially available vacuum cleaner for evacuating the chamber.

Abstract: A particle blasting nozzle has a nozzle body having an outlet opening and a suction connection with an acceleration tube extending at least partly within the nozzle body. The front end of the acceleration tube is arranged in the region of the outlet opening and its rear end has a further suction connection.

Abstract: Disclosed is an improved apparatus for delivery of pressurized particulate matter against a surface or target to abrade, etch, erase, cut, penetrate, smooth, clean, polish and/or harden the surface or target. The most important use to which the present invention is adapted is use by dentists and oral hygienists to very effectively clean teeth, employing a particulate matter such as aluminum oxide, while at the same time having no effect on soft tissue such as the gums. This is accomplished using a prefilled, sealed, and disposable fluidizing chamber and cannula assembly that avoids contamination and which has already been approved by the FDA for dental use. Included is a fluidizing chamber having a discharge end of an inlet tube that is disposed below or overlaps the intake end of the cannula such that the discharge of the inlet tube blows the particulate matter into the fluid above the intake end of the cannula, thereby suspending it therein, without clogging.

Abstract: This invention is a method and apparatus for an air abrasive unit such as those used in the dental field. This method and apparatus utilizes an internal vibrator motor with vibration transmitters which transmit the vibration throughout the abrasive jar. The abrasive pickup assembly uses pressure differentials to suck up abrasive through a screen which controls the flow rate and particle size of the abrasive flowing through the system. The system can utilize a photo-optical detection system to detect the abrasive level. Alternatively, a pressure/pulse detection system may be used to measure abrasive level. Dilution of the air/abrasive mixture and "air only" modes are possible with the present system. Depressurization and mere reductions of pressure can also be accommodated. The invention also includes a system for easily modifying the content of an air abrasive stream exiting the mixing chamber.

Abstract: A device for removing material from biological organisms by directing an abrasive fluid stream onto a surface of a biological organism. The device operates on a standard household pressure source and includes a converging-diverging nozzle that produces a super-sonic abrasive-laden air stream having a temperature that is harmless to the biological organism. The device operates at such a temperature without the use of external elements, such as additional heaters or coolers. The internal contour of the nozzle bore is variable and determines conditions, such as, for example, velocity, temperature and shape of the particle-laden air stream.

Abstract: An emergency control system for selectively activating and deactivating an apparatus. The system includes a fiber optic transmitter for emitting radiation and a fiber optic receiver for receiving and measuring a wavelength and an intensity of the radiation. A manually-operated fiber optic switch is placed in optical communication with the fiber optic transmitter and the fiber optic receiver. In operation, the switch is selectively actuated, thereby selectively opening and closing a fiber optic circuit defined by the transmitter, receiver, and the switch. The system further includes a relay controller in communication with the fiber optic receiver, such that the relay controller is actuated when the fiber optic receiver receives a predetermined wavelength and intensity of radiation from the transmitter. When the relay controller is actuated, it allows a signal to pass through the relay to a point of use.

Abstract: A method is provided for cleaning an electronic circuit board having first and second opposing surfaces. The method includes directing a stream of carbon dioxide particles against the first surface. Steam is sprayed toward the first and second surfaces such that condensation of the steam caused by cooling from the CO.sub.2 particles forms a thin film of water on the first surface for conducting electrostatic charge away from the first surface. The CO.sub.2 particles substantially remove residue present on the first surface, thereby cleaning the circuit board.

Abstract: A blast nozzle assembly for wet blasting is provided comprising a blast nozzle for accelerating a blast stream of abrasive particles in compressed air toward a targeted surface and in combination therewith, a water atomizer means which is releasibly secured to the exterior of the blast nozzle. The water atomizer means is formed of two parts, a manifold body which includes a water supply means and an outlet assembly which includes a mixing chamber for receiving the blast stream leaving the blast nozzle, a plurality of spaced water nozzles for directing a stream of water into the mixing chamber and an outlet for directing the mixture of blast stream and water to the targeted surface.

Abstract: An improved cutting head for a water jet cutting assembly utilizing water or other liquid medium at ultra high pressure, with the cutting head including an assembly with an elongated body having a central bore along its axis and including a delivery nozzle at the distal end of the assembly. Alignment of the components is maintained by incorporating a process of manufacture which utilizes the formation of a single bore extending through the body so as to both form and maintain axial alignment of the components. The arrangement is further characterized by having mating surfaces which are free of gaskets or other packing material, thereby establishing, maintaining, and preserving proper axial alignment of components.

Abstract: A disposable apparatus for propelling particulate matter against a surface of a target material includes, a mixing chamber having a chamber wall and a gas receiving port in the chamber wall in fluid communication with the compressed gas source and having a mixture discharge port in the chamber wall, a gas delivery conduit extending from the gas receiving port into the chamber, a mixture discharge conduit extending from the mixture discharge port into the chamber, and a quantity of particulate matter inside the chamber.

Abstract: An improved mixing tube for use in a high-pressure abrasive fluid jet system is shown and described. In a preferred embodiment, the mixing tube is provided by forming a first piece and a second piece, each piece having a length that is substantially equal to the length of the mixing tube. A longitudinal groove is provided in each piece, the longitudinal groove extending from a first end to a second end of each piece. The first and second pieces are coupled together, such that the first and second longitudinal grooves meet to form a bore that extends longitudinally through the length of the mixing tube. Although the first and second pieces may be joined in a variety of ways, in a preferred embodiment, the two pieces are joined by shrink fitting a metal sheath around the outer surface of each piece. The first and second pieces are made of a hard ceramic material, and the longitudinal grooves are formed by grinding the pieces to remove material along their length.

Abstract: A method and apparatus for an air abrasive unit such as those used in the dental field. This method and apparatus utilizes an internal vibrator motor with vibration transmitters which transmit the vibrations throughout the abrasive jar. The abrasive pickup assembly uses pressure differentials to suck up abrasive through a screen which controls the flow rate and particle size of the abrasive flowing through the system. This system can utilize a photo optical detection system to detect the abrasive level. Alternatively, a pressure/pulse detection system may be used to measure abrasive level. Dilution of the air/abrasive mixture and "air only" modes are possible with the present system. Depressurization and mere reductions of pressure can also be accommodated.

Abstract: A shot peening method and apparatus enables low intensity peening at a velocity which is equal to or less than the minimum velocity required to assure conveyance of the media through the transport hose in pneumatic systems or the minimum velocity necessary to project a coherent shot stream in the case of wheel systems.

Abstract: An improved system for generating an abrasive fluid jet is shown and described. In a preferred embodiment, abrasive is fed from a bulk hopper into an air isolator having a baffle that limits the flow of air and abrasive through the air isolator, thereby venting air from the abrasive. An on/off device having a rod coupled to a stopper is provided within the air isolator, the rod being selectively raised and lowered in a vertical direction. A discharge orifice is provided in a bottom surface of the air isolator, the stopper covering the discharge orifice when the rod is in a lowered position, thereby preventing the discharge of abrasive from the air isolator.A metering disk is provided adjacent the discharge orifice, an orifice in the metering disk being aligned with the discharge orifice, such that abrasive exiting the air isolator flows through the metering disk.

Abstract: CO.sub.2 jet spray cleaning apparatus that monitors CO.sub.2 snow plume characteristics. The present invention is a CO.sub.2 jet spray cleaning system that comprises a holding tank for containing liquid CO.sub.2, a spray nozzle coupled to the holding tank, a valve coupled between the holding tank and the spray nozzle, and a temperature sensor coupled to the nozzle for sensing the temperature of a plume of CO.sub.2 that is sprayed by the nozzle and for providing a signal indicative thereof. The system may also comprise a display coupled to the temperature sensor for displaying the temperature of the plume of CO.sub.2 to an operator, or an alarm coupled to the temperature sensor for alerting an operator that the temperature of the plume of CO.sub.2 has risen to a predetermined level. Either the displayed signal or the alert signal indicates that the quality of the plume has diminished and that the liquid CO.sub.2 in the holding tank should be replenished. The present CO.sub.2 jet spray cleaning system and CO.

Abstract: A pressurized feeder vessel feeds powdered material into a stream of propellant gas. The feeder vessel includes a funnel-shaped hopper that is resiliently suspended by an elastic member inside the vessel. A vibrator such as an electric motor with an eccentric weight on its shaft vibrates the bottom end of the hopper. The vibration forces of the vibrator are preferably transferred to the hopper via a flexible diaphragm. The hopper is thus subjected to primary vibration forces and torques from below, and secondary, reaction vibration forces and torques from above. This induces the powder in the hopper to fluidize thoroughly and to circulate. In particular, it circulates over and past an inlet orifice, through which powder exits the hopper and enters the propellant stream. Powder circulation thus also prevents clogging of the inlet orifice and leads to more even flow rates. The invention is particularly well suited for delivering abrasive powder to a hand-held dental tool for abrasive treatment of teeth.

Abstract: A device for use with artistic sandblasting. The device is a hand-held gun which receives an air/abrasive mixture via a flexible tube which enters the gun through a rear end of the gun. The tube extends through the gun's rear end, between a pinch point and a curved end of an adjustable, spring biased pivotal lever provided internally in the barrel of the gun and attaches to a nozzle removably provided at the front end of the gun. When the trigger is not depressed, the curved end of the lever is biased toward the pinch point, thus squeezing the tube and cutting off flow of the air/abrasive mixture through the gun. The air/abrasive mixture flows through the gun via the tube and out the nozzle when a trigger which is attached to the curved end of the pivotal lever is depressed toward a handle provided on the rear end of the gun and thereby moves the curved end of the lever away from the pinch point, allowing the tube to resume its original unsqueezed configuration.

Abstract: A device for mixing compressed air and abrasive and providing the air/abrasive mixture to a delivery gun for use in artistic abrasive blasting. The device is provided with a vessel having an upper chamber for holding abrasive. Compressed air is supplied to a head space located in the upper chamber above the abrasive. An air delivery line extends from the head space to a mixing chamber located below the upper chamber in order to supply compressed air thereto. An adjustable mixing valve admits abrasive from the upper chamber into the mixing chamber where the abrasive is mixed with the compressed air before it exits the mixing chamber on its way to the delivery gun.

Abstract: In a method of and apparatus for accelerating and pressurizing a fluidized stream of particulate material, e.g. for blast cleaning by ice particles, the stream flows through a constriction in a flow passage. A flow of blast medium is discharged from a blast nozzle at supersonic speed into the fluidized stream so as to form within the fluidized stream a flow front which is impenetrable by the fluidized stream and which co-operates with the constriction to form an effective nozzle for accelerating the fluidized stream. Grounding is provided controlling electrostatic charges for either better work effect or neutralization in unwanted or hazardous conditions, and safety pressure relief, blast intensity control, articulation and changement of final nozzles for effective operation are also provided.

Abstract: In performing micro-cleaning and micro-blasting, a dry micro-cleaning abrasive powder is sprayed having a very small grain size. This enables high cleaning speeds to be reconciled with exceptionally fine blasting in order to remove dirty stains and encrusted deposits from valuable, delicate, or fragile medium as is the case when having to blast off pollutants and pollution that become stuck to the surfaces of monuments and buildings. Jets of compressed air charged with fine abrasive particles having grain sizes of less than 200 micrometers can also be sprayed towards the surface. The jets are emitted from nozzles at high speeds so that they sweep the surface with at least ten jets, each of which has a cross section lying in the range of 400 micrometers to 4 millimeters, so that very low kinetic energy is imparted to the surface.

Abstract: An abrasive blast cabinet includes a housing defining a blast chamber, a blast nozzle disposed in the blast chamber and connected to a source of an abrasive blast media for directing a flow of the blast media against a surface of an article to be cleaned, an elongated chute supported in the interior of the housing and having a first open end in fluid communication with a gas supply, a rotatable second open end in the vicinity of a work place for the article and an opening placed adjacent a window in the housing so that an operator located outside the blast chamber can direct his or her line of sight through the window and second rotatable open end and observe the article in the work place.

Abstract: Disclosed is a method and apparatus for the blast cleaning of the surface of an object using solid carbon dioxide pellets as the abrasive projected by a gaseous carbon dioxide propellent. The method and apparatus of this invention subjects a portion of a quantity of liquified carbon dioxide contained within a storage vessel to adiabatic expansion to provide a solid phase carbon dioxide and then compressing or extruding the solid phase carbon dioxide to form a plurality of pellets. Another portion of the liquified carbon dioxide is vaporized to provide a volume of gaseous carbon dioxide at above atmospheric pressure which is then used as a carrier and propellent to project the carbon dioxide pellets against the surface of the object to be cleaned. This invention eliminates the need to use a separate compressed air or nitrogen propellent system for a blast cleaning operation.

Abstract: A radial grip remote control for the operation of abrasive blast machines. The handle of the grip is permanently attached to a linear bearing. The bearing utilizes the abrasive blast hose as a journal, and may be rotated manually by adjusting the radial position of the handle. The inside diameter of the bearing is adjustable. The adjustment is intended to allow the bearing to rotate freely about its journal (hose), and to cause seizure of the bearing to this journal when the hose is pressurized. The steel handle acts as a protective housing for a positive shut-off type valve which is internally installed. The remote control is designed to be ergonomically accommodating and to increase the safety of abrasive blasting operations. The base of the handle comprises a female connecting socket for adaptation to automated or remotely operated abrasive blast systems.

Abstract: A symmetrically balanced, integrated, portable, refillable, serviceable, adjustable, self contained tool, suitable for single hand operation, for ejecting a stream of particulate, powdered, or liquid material toward a target combining a supply reservoir containing the materials, a portable propellant container adapted to the supply reservoir, carrying compressed propellant liquid, a propellant release valve delivering propellant from the container via a constricted air jet orifice to a angular mixing chamber positioned above the uppermost level of materials the materials supply reservoir, a delivery conduit connecting the lower portion of the supply materials reservoir chamber to the angular mixing chamber through an adjustment valve, delivering a stream of materials aspirated from the materials supply reservoir by the negative atmospheric pressure deferential created by a Venturi effect to the angular mixing chamber, driving the compressed gas and materials through the connected nozzle containing a cylindric

Abstract: To reduce dust and improve the productivity of wet blasting, a blast nozzle and a method of using same are provided for directing a stream of abrasive particles entrained in compressed air to a targeted surface and for injecting a pressurized water stream into the stream of abrasive particles at a point downstream of the orifice of the blast nozzle and in the expansion portion of the nozzle. At the injection point, the velocity of the entrained abrasive particles is substantially equivalent to the velocity of the injected water stream.

Abstract: A particle blast cleaning apparatus for use with sublimable blast media, a source of compressed gas, and a discharge nozzle. The apparatus includes a mixing device for mixing the sublimable media with compressed gas, which mixing device includes a lower section having an outlet port formed therein and an upper section positioned over the lower section and having two sublimable media inlet ports and a compressed gas inlet port. A transfer member is mounted between the lower section and the upper section for reciprocal movement and has at least two transfer chambers for transporting sublimable media.

Abstract: A blast nozzle for directing a stream of abrasive particles against a surface to remove surface contaminants therefrom further includes multiple water atomization nozzles which are spaced externally on the blast nozzle and which direct a stream of atomized water droplets which surround the abrasive particle stream directed to the surface so as to suppress dust formation.

Abstract: A blast nozzle for directing a stream of abrasive particles against a surface to remove surface contaminants therefrom further includes an externally attached atomized water nozzle which directs a stream of atomized water particles to the surface to suppress dust formation. Blast nozzles of preferred dimensions to improve productivity of blast cleaning with a sodium bicarbonate blast media are also disclosed.

Abstract: A small parts abrasion cleaning basket having a tubular neck portion and a tubular main body housing. The bottom end of the neck portion has an outlet port that is in communication with the top end of the main body housing. A wire screen having a concave top surface has its outer edges secured to the inner wall surface of the main body housing. The area between the top edge of the main body housing and the top surface of the wire screen forms an abrasion chamber for cleaning small parts preparatory to painting, coating, etc. The small parts abrasion cleaning basket would be used inside an abrasive blast cleaning cabinet where it would be held by a person's hand inserted into rubber or plastic gloves within the cabinet.

Abstract: A system and method for cleaning or removing coatings, such as paint, from a surface with a stream of particles. A carbon dioxide (CO.sub.2) pelletizer forms carbon dioxide pellets, which are delivered by a delivery system against a surface to be cleaned. The delivery system includes a hopper for containing the pellets and a high pressure air supply. A feeder introduces the pellets from the hopper into the high pressure air. The combined high pressure air and pellets are directed along a delivery hose to a nozzle, which directs the air and pellets against a surface to be cleaned. Temperature sensors are provided to monitor the temperature of the pressurized air at various points in the delivery system. Signals from the temperature sensor are provided in a feedback control manner to a control valve. The control valve controls the introduction of liquid nitrogen (N.sub.2) into the air stream at a mixing chamber in the delivery system.

Abstract: A process for removing paint by high pressure waterjet blasting of painted surfaces wherein the waterjet comprises a ferrofluid or other liquid containing tiny magnetic particles suspended therein. The particles may be in colloidal suspension or be suspended by agitation and are preferably polymer coated. The liquid-magnetic particle mixture lends itself to electromagnetic process control, run-off maintenance and waste processing capabilities. Thereby, the process can employ process control and waste remediation options.

Abstract: In a machining device for machining precision, in particular dental, workpieces in a machining chamber surrounded by a housing, having an inspection window with two gripping holes arranged to the two sides of the inspection window, the machining chamber is preferably connected or connectable to a suction device and arranged in the machining chamber is at least one blasting nozzle for blasting and/or a demolding tool for demolding and/or an air nozzle for blowing off the workpiece.

Abstract: A blast nozzle for accelerating a stream of abrasive particles to a surface for the cleaning thereof has a nozzle body formed of a non-electrically conductive material and is provided with an encapsulating coat to prevent breakage of the nozzle body. To prevent the accumulation of static electric charge during the blast cleaning operation, the exterior surface of the blast nozzle core is covered with an electrically conductive layer disposed between the nozzle body and the encapsulating coat, the nozzle further including an electrically conductive grounding pathway contacting the electrically conductive layer and passing through the encapsulating coat so that the electrically conductive layer can be bonded to ground to provide a pathway for removing the accumulated static charge and prevent periodic sparking.

Abstract: A frame member is capable of connection to a lifting cable moving the frame relative to a surface to be cleaned. The carriage is supported on the frame member and is adjustable on tracks between sides of the frame members. A hose support is pivotally mounted on the frame member on a lateral axis and has an operator's handle for moving the carriage and pivoting the hose support. The hose support includes a clamp for multiple hoses for large area treatment. One or more of the hoses may be individually removed for operation independent of the multiple hose support. An auxiliary clamp for the hoses is provided to free up movement of the carriage. The operator's handle for the carriage has switches thereon for operation of the multiple hoses, at least one of the switches being removable for controlling operation of a single hose that has been removed from the carriage.

Abstract: A particle blast cleaning apparatus for use with sublimable blast media, a source of compressed gas, and a discharge nozzle. The apparatus includes a mixing device for mixing the sublimable media with compressed gas, which mixing device includes a lower section having an outlet port formed therein and an upper section positioned over the lower section and having two sublimable media inlet ports and a compressed gas inlet port. A transfer member is mounted between the lower section and the upper section for reciprocal movement and has at least two transfer chambers for transporting sublimable media. A control mechanism is provided for controlling the flow of compressed gas to the compressed gas inlet port such that compressed gas is only provided to the compressed gas inlet port when at least one of the transfer chambers is in fluid communication with the compressed gas inlet port.

Abstract: A nozzle expels liquid CO.sub.2 through an orifice for converting the liquid into CO.sub.2 snow. The nozzle is contained within an elongated cavity within a body which in turn is coupled to an exhaust nozzle for directing the CO.sub.2 snow toward a workpiece. A mixing device is provided for receiving and mixing pressurized air at ambient temperature with liquid nitrogen for precooling the air and then directing the resulting mixture of gases into the cavity and toward the nozzle. In this manner, the precooled shop air will enhance the efficiency of the conversion of the liquid CO.sub.2 into CO.sub.2 snow particles.

Abstract: A system for abrasively cleaning surfaces such as by sandblasting and including a vacuum arrangement for recovering the material abrasively removed from the surface as well as the abrasive material is provided with a control circuit operable to actuate an alarm and/or deactivate the abrasive cleaning operation by sensing a drop in the vacuum pressure at the blast head which is indicative of an inappropriate positioning of the blast head and thus discharge of the abrasively removed material and abrasive material to the surrounding environment.

Abstract: A blast nozzle is provided for cleaning a surface with a blast media which is softer and more friable than sand such as sodium bicarbonate and which comprises an inlet section which contains a passageway which converges substantially along only one .[.planar axis.]. .Iadd.direction .Iaddend.to a rectangular venturi orifice and a fan-shaped outlet section which contains a passageway which diverges along substantially only one .[.planar axis.]. .Iadd.direction .Iaddend.perpendicular to the .[.planar axis.]. .Iadd.direction .Iaddend.of convergence of the converging passageway, the inlet passageway being .[.greater.]. .Iadd.longer .Iaddend.than twice the diameter of the inlet of the nozzle so as to provide streamlined flow and reduce turbulent flow of the friable blast media in the blast nozzle. The passageways in the blast nozzle are formed by opposed modular structures which are releasably secured to the nozzle and can be changed to change the length and angle of convergence and expansion ratio of the nozzle.