WO1997049525A1

WO1997049525A1 - An abrasive blasting apparatus

Info

Publication number: WO1997049525A1
Application number: PCT/GB1997/001733
Authority: WO
Inventors: Steven Charles Liversedge
Original assignee: Wizard Technology Limited; Dyer, Alison, Margaret
Priority date: 1996-06-27
Filing date: 1997-06-27
Publication date: 1997-12-31
Also published as: AU3269897A

Abstract

An abrasive blasting apparatus comprises a hopper (12) for an abrasive medium such as sodium bicarbonate. The hopper vents to atmosphere and has a lowermost abrasive media outlet (22). A control valve assembly (24) communicates with the outlet, and includes an ambient air inlet port (36), a suction outlet port (54) and an adjustable three-way valve member (24) for allowing selective communication between the inlet and outlet ports. A spray gun assembly (58) is connected to the suction outlet port (54) via a suction hose (52). The three-way valve member is arranged simultaneously to adjust the sizes of both the media inlet and the ambient inlet ports whilst communicating with the suction outlet port, thereby controlling the flow of abrasive media and air through the suction outlet port. The spray gun assembly (58) includes a housing having a venturi chamber (86) into which the suction outlet hose (52) is connected. The venturi chamber is in turn coupled to a high pressure air hose (44) which creates a venturi effect so as to propel the media from an outlet nozzle (92) via the suction outlet hose.

Description

AN ABRASIVE BLASTING APPARATUS

BACKGROUND TO THE INVENTION

THIS invention relates to an abrasive blasting apparatus for cleaning surfaces.

Abrasive blasting as a cleaning and surface preparation technique has been used for many years. Two basic categories of equipment are utilised, namely pressurised and non-pressurised systems. In both types of equipment, abrasive media is fed into a pressurised stream of air or water. In a pressurised system, the entire system is pressurised, including the media container, whilst in a non-pressurised system, the media container is open to ambient air.

In recent years, there has been a move away from silica sand as an abrasive due to health and environmental concerns, and a concomitant increase in the use of alternative materials such as glass beads, plastic particles, process slags, steel shot and mineral sands. Specialised abrasives such as sodium bicarbonate and plastic and glass beads are relatively expensive, with the result that it is critical to control and optimise consumption rates.

In the case of pressurised systems, which are normally utilised for high productivity applications, various metering valves have been developed such as the "Thompson valve" made by Schmidt Manufacturing of Houston, Texas, USA. Valves of this type are pressurised with the entire system, and have a media outlet orifice which can be adjusted according to the quantity of media flow required.

Relatively little development has taken place in the control of media consumption from non-pressurised systems. Typically, the vacuum force created by a venturi action dictates the amount of abrasive media that is consumed. In US patent 5,366,560 to Rubey et al, an abrasive blasting apparatus and method is disclosed in which abrasive particles such as sodium carbonate particles are deposited in a hopper having a lowermost discharge passage. An orifice ring is inserted in the discharge passage, the ring having a bore diameter selected for the particle size of the sodium bicarbonate. A horizontal pipe is located beneath the orifice ring in a T-connection. A blasting nozzle having a venturi configuration bore is connected via a hose to the pipe. Pressurised water is supplied through the venturi configuration bore, as a result of which a suction force is applied on the pipe so as to suck the sodium bicarbonate particles in the pipe in a continuous flow stream through the hose and into the pressurised water stream issuing from the nozzle. The atmospheric air flow into the other end of the pipe is adjusted so as to limit the volume of particles flowing through the hose to less than 25% of the flow area of the hose. This is achieved by means of a conventional adjustable flow valve located upstream of the T-connector.

There are a number of limitations with the above apparatus.

1. The suction or vacuum force drops in the T-piece due to the increase in surface area, as a result of which the ambient air inlet has to be partially closed to create a suitable suction force through the vertical section of the media outlet.

2. Media flow rate is restricted by the orifice size selected at the media outlet as well as by the size of particles being used. Once a particular orifice ring has been selected, the only accessible variable control is the ambient inlet air valve which in reality has a minimal affect on flow rate adjustment due to the fact that the vacuum force in the vertical abrasive media outlet as well as in the horizontal ambient air inlet pipe must be controllable so as to effectively adjust flow rate. Opening or closing of the ambient air inlet only partially achieves this.

3. A variety of different orifice sizes are required if the end user is using different abrasives or particle sizes within the system. Adjustment of the orifice ring can only take place by the cumbersome process of emptying the vessel of abrasive, replacing the orifice ring with one of a different size and re¬ filling the vessel.

4. When using moisture sensitive abrasive media, the media outlet is still susceptible to clogging if the media is contaminated with water. Clearing of a blockage requires the vessel to be emptied or the bore valve to be closed, thereby increasing the vacuum force through the outlet. This requires the operator to stop blasting.

5. Different compressors and high pressure water units having varying pressures and flow rates will create entirely different vacuum forces via the venturi chamber in the suction hose. Due to the limited stepwise-type control of media flow by replaceable orifice rings, the system disclosed in the above US patent is unable to cope adequately or sufficiently with the broad spectrum of vacuum forces. SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided an abrasive blasting apparatus comprising an abrasive media container venting to atmosphere and having an abrasive media outlet; a control valve assembly including a valve body defining a media inlet port communicating with the media outlet, an ambient air inlet port and a suction outlet port, and an adjustable three-way valve member for allowing selective communication between the inlet and outlet ports; and a spray gun assembly communicating with the suction outlet port, the three-way valve member being arranged simultaneously to adjust the sizes both of the media inlet and the ambient air inlet ports whilst communicating with the suction outlet port so as to control the flow of abrasive media and air through the suction outlet port.

Preferably, the control valve assembly includes an axial displacement valve, with the valve body having a passage defined therein which communicates with the media inlet port, the ambient air inlet port and the suction outlet port, the three-way valve member being arranged to travel axially within the passage, and being movable between a closed position, in which there is no communication between the media inlet port, the ambient air inlet port and the suction outlet port, an open position, in which there is full communication between the aforementioned ports, and a series of intermediate positions, in which the sizes of the ambient air inlet port and the media inlet port are simultaneously increased or decreased, whilst being in communication with the suction outlet port.

Conveniently, the three-way valve member includes a foremost round cylindrical valve head, a threaded portion located rearwardly of the head and being arranged to threadingly engage with a complementally threaded portion in the passage, sealing means located between the threaded portion and the valve head for preventing the ingress of abrasive media into the threaded and complementally threaded portions, and a shaft extending from the threaded portion, the shaft terminating in a handle for rotating the entire valve member so as to effect axial adjustment thereof.

Typically, the air inlet port is arranged to open just prior to the media inlet port, so that a vacuum is created prior to entry of the media into the suction outlet port.

In an alternative form of the invention, the valve member is a rotary displacement valve movable between a first position, in which the ambient air inlet port is blocked and the media inlet port communicates with the suction outlet port, a second position in which the media inlet port is blocked and the ambient air inlet port communicates with the suction outlet port, and a series of intermediate positions in which both the media inlet port and the ambient air inlet port communicate with the suction outlet port, with the valve member being arranged progressively to increase the size of media inlet port as the size of the ambient air port is being decreased, and vice versa.

Typically, the size of the vacuum outlet port is progressively decreased with a decrease in size of the ambient air port, in inverse proportion to the flow rate of the abrasive media.

Advantageously, the spray gun assembly communicates with the suction outlet port via a suction outlet pipe, the spray gun assembly including a housing defining a venturi chamber into which the suction outlet pipe is connected and an outlet nozzle, the venturi chamber being arranged to receive a stream of fluid from a compressed a high pressure fluid source via a compressed fluid line for creating the venturi effect so as to propel the media from the outlet nozzle via the suction outlet pipe.

In one form of the invention, the abrasive blasting apparatus may incorporate an in-line moisture separator in the compressed air line for removing moisture from compressed air before the compressed air is fed to the venturi chamber, thereby reducing clogging of the abrasive media.

Conveniently, at least an inner portion of the venturi chamber housing is formed predominantly from a heat- or temperature-stable material, the surface temperature of which does not tend to drop below the dew point of incoming compressed air, thereby avoiding or at least reducing the formation of media-clogging condensate in the venturi chamber which tends to clog hydrophilic media such as sodium bicarbonate.

Advantageously, at least the inner portion of the venturi chamber housing is in the form of a removable venturi chamber insert.

Preferably, the removable venturi chamber insert is interchangeable with at least one other insert which is formed from a wear-resistant material such as tungsten carbide for use with relatively hard abrasive media such as aluminium oxide or mineral sands.

Conveniently, the spray gun assembly includes an airjet insert upstream of the venturi chamber and a nozzle insert downstream of the venturi chamber. with the inserts being interchangeable with inserts having different internal diameters so as to cater for different compressor sizes and/or abrasive types.

Typically, the heat or temperature stable material is a suitable hard plastics material chosen from the group including nylons, polycarbonates and Teflon®.

The spray gun assembly may incorporate a deadman control lever which is arranged to shut off the compressed fluid line at a point remote from the spray gun assembly.

Conveniently, the spray gun assembly includes a water line venting onto an external flared opening of the outlet nozzle of the spray gun assembly, whereby pressurized or unpressurized water flowing through the opening is entrained by the pressurised stream of air and abrasive particles for dust suppression and cleaning purposes.

Typically, the abrasive blasting apparatus includes remote ambient air valve means communicating with the ambient air inlet port for further controlling the size of the ambient air inlet.

The invention extends to an abrasive blasting apparatus comprising an abrasive media container venting to atmosphere and having an abrasive media outlet; a control valve assembly including a valve body defining a media inlet port communicating with the media outlet, an ambient air inlet port and a suction outlet port, and an adjustable three-way valve member for allowing selective communication between the inlet and outlet ports: and a spray gun assembly communicating with the suction outlet port via a suction outlet pipe, the spray gun assembly including a housing defining a venturi chamber into which the suction outlet pipe is connected and an outlet nozzle, the venturi chamber being arranged to receive a stream of fluid from a compressed a high pressure fluid source via a compressed fluid line for creating the venturi effect so as to propel the media from the outlet nozzle via the suction outlet pipe.

According to a still further aspect of the invention there is provided an abrasive blasting apparatus of the type described which includes a plurality of control valve assemblies communicating with at least one abrasive media container, an array of spray gun assemblies communicating with the suction outlet ports of the control valve assemblies, and at least one high pressure fluid source having fluid lines communicating with each of the spray gun assemblies.

Preferably, central control means are provided for automatically controlling the operation of the array of spray gun assemblies.

By the term "spray gun assembly" is meant any manually or automatically controllable outlet nozzle assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a partly schematic side view of a first embodiment of a blasting apparatus of the invention;

Figure 2 shows a more detailed cross section on the line 2-2 of Figure Figure 3 shows a cross-sectional front view of a first type of three-way valve assembly forming part of the abrasive blasting apparatus;

Figure 4 shows an exploded side view of the valve assembly of Figure J ;

Figure 5 shows a cross-sectional side view of a first embodiment of a spray gun forming part of the abrasive blasting apparatus of the invention;

Figure 6 shows a partly cross-sectional exploded side view of a second embodiment of a valve assembly of the invention;

Figure 7 shows a partly cross-sectional assembled side view of the valve assembly of Figure 6;

Figure 8 shows a cross-sectional end-on view on the line 8-8 of Figure

Figure 9 shows a partly schematic side view of a second embodiment of a blasting apparatus of the invention incorporating a moisture separator;

Figure 10 shows a cross-sectional side view on the line 10-10 of Figure 9; Figure 11 shows a partly cross-sectional side view of a second embodiment of a spray gun of the invention;

Figure 11 A shows an exploded detail of a nozzle assembly of the spray gun of Figure 1 1 ;

Figure 12 shows a right side view of a third embodiment of an abrasive blasting apparatus of the invention;

Figure 13 shows a left side view of the abrasive blasting apparatus of Figure 12;

Figure 14 shows a rear view of the abrasive blasting apparatus of Figures 12 and 13;

Figure 15 shows an underplan view of the blasting apparatus of Figures 12 to 14 illustrating the pipe layout; and

Figure 16 shows a schematic view of a fourth multi-nozzle automated embodiment of a blasting apparatus of the invention.

DESCRIPTION OF EMBODIMENTS

Referring first to Figure 1, an abrasive blasting apparatus 10 includes a cylindrical abrasive media container or hopper 12 which is designed to contain an abrasive medium such as sodium bicarbonate. The container 12, which is non-pressurised, has a lid 14 formed with a handle 16 and fixed to the body of the container by means of latches 18. The container 12 typically has a capacity ranging from 2kg to 200kg of media, and is formed with a conical base 20 which has a central lowermost outlet 22 communicating with a valve assembly 24. The container 12 is supported on a skirt 26 which serves as a stabilising stand. The valve assembly 24 is controlled by means of a valve handle 28 which extends from the skirt 26 and which is connected to the valve assembly 24 via an adjustment arm 30. A compressed air inlet port 32 for accommodating a compressed air hose and a water inlet port 34 for accommodating a water hose are formed in the skirt. Similarly, an ambient air port 36 is provided for accommodating an ambient air hose.

Referring now to Figure 2, an abrasive medium such as sodium bicarbonate 38 is shown in the base of the container or hopper 12. It can clearly be seen how the sodium bicarbonate is fed through the media outlet 22 into a corresponding media inlet 40 forming part of the three-way valve assembly 24. A compressed air hose 44 extends from the compressed air inlet port 32 which is formed with an attachment for a source of compressed air. Similarly, a water hose 46 extends from the water inlet port 34, which incorporates an attachment for fitting an external water hose. The compressed air hose 44 and the water hose 46 extend through the void beneath the skirt 26 and out through corresponding apertures in the skirt 26. from where they lead to a spray gun 58 which will be described in more detail further on in the specification. An ambient air hose 48 extends via the ambient air opening 36 in the skirt to an ambient air inlet port 50 formed in the three-way valve assembly 24. A vacuum or suction hose 52 is coupied to a suction or vacuum outlet port 54 in the three-way valve assembly 24. The opposite ends of the various hoses 44, 46, 48 and 52 are connected to a spray gun 58 which is illustrated in more detail in Figure 5. Referring now to Figures 3 and 4, more detailed cross-sectional side and exploded views of the three-way valve assembly 24 are shown. The valve assembly includes a valve housing 60 within which the ambient air port 50, the media inlet port 40 and the suction outlet port 54 are defined. The three- way valve includes a cylindrical valve body 62 with a rectangular passage 64 extending diametrically through the body 62. The body forms a relatively snug fit within a complemental cylindrical chamber formed in the valve housing, and is held captive within the chamber by means of a sealing plate 66. The adjustment arm 30 extends through an aperture 68 in the sealing plate, and insertion pins 70 extend from the valve housing 60 so as to mount the sealing plate 66 in position.

In its Figure 3 position, the passage 64 is aligned so that both the media inlet port 40 and the ambient air inlet port 50 communicate with the suction outlet port 54. It can clearly be seen how the valve body is rotatable into a first position indicated in broken outline at 65A in which the ambient air inlet port 50 is blocked off and the media inlet port 40 communicates with the suction outlet port 54. If the valve body is now rotated clockwise to a second position indicated in chain outline at 65B, the media inlet port 40 will be completely blocked off and the ambient air inlet port 50 will communicate directly with the suction outlet port 54. In a third position indicated at 65 C, the suction outlet port 54 is blocked off completely.

Referring now to Figure 5, the spray gun 58 is shown in more detail. The compressed air hose 44 is connected to a passageway 70 extending through the handle 72 of the spray gun. A trigger 74 of the spray gun acts on a piston 76 via a trigger pin 78. The piston 76 is biased by means of a compression spring 80 into a closed position in which there is no communication between the compressed air passage 70 and a compressed air passage 70A extending through the barrel of the spray gun. The flow of compressed air through the passage 70A is controlled by squeezing on the trigger 74 so as to vary the degree of communication between the passages 70 and 70A via the port 82. The passage 70A communicates in turn with a venturi or vacuum chamber 86, with a tubular insert 88 extending into the chamber so as to channel the flow of compressed air through the chamber and to enhance the venturi effect. The suction hose 52 is clamped to a branch spigot 89 so that it communicates with the venturi chamber 86. The chamber 86 in turn communicates with an outlet passage 90 defined by an outlet nozzle 92. The outlet nozzle 92 is formed with a flared opening 94, and a pair of water outlet apertures 96 are provided adjacent one another approximately mid-way along the opening 94. The apertures 96 communicate with the water hose 46 via a passageway 98 formed in the outlet nozzle 92, an inlet control valve 100 being formed in the passageway 98 to control the flow of water through the outlet.

The ambient air hose 48 is connected to a blind chamber 102 extending into the handle of the spray gun. The ambient air hose 48 has a threaded end 104 and an opening 106 adjacent the threaded end. A knurled internally threaded sleeve 108 is arranged to be screwed up and down along the threaded end so as to vary the size of the opening 106.

The operation of the abrasive blasting apparatus will now be described in more detail with reference to the drawings. Referring still to Figure 5, the flow of compressed air through the venturi chamber 86 will cause a vacuum or suction in the suction hose 52. With the valve passage 64 in the intermediate position illustrated in Figure 3, the vacuum at the suction inlet 54 will cause a mixture of sodium bicarbonate or another abrasive media and air to be sucked through the suction hose and out via the flared opening 94 in the nozzle 92 of the spray gun. By rotating the valve body 62 clockwise, the size of the media inlet 40 is progressively decreased and the size of the air inlet 50 is progressively increased. At the same time, the size of the vacuum or suction outlet port 54 is increased slightly. Anti-clockwise rotation of the valve has the opposite effect. The accompanying table illustrates the inter-relationship of the three orifices and how rotation of the passage will vary the orifice sizes. It must be appreciated that the table serves merely as an indication of expected flow rates. Actual flow rates will be dependent on the media type and size as well as the vacuum force. It should be noted that there is a direct relationship between media orifice and ambient air orifice size. Closure of the media orifice has a double effect on flow rate due both to orifice size reduction and to increasing the ambient air orifice size.

The knurled nut or collar 108 provides a secondary control mechanism of the ambient air intake. The operator of the apparatus can select a media inlet orifice size that will give a flow rate less than the desired flow rate. By adjusting the secondary ambient air intake control, the ambient air intake into the passage 64 is reduced, thereby creating a high vacuum force at the media inlet and thus increasing the flow rate of media through the media orifice. By fine tuning the ambient air intake, the media flow rate can be accurately set and adjusted. As the secondary air intake 106 is mounted on the spray gun, remote fine tuning of the flow rate is facilitated, together with the clearing of clogs, by completely shutting off the air intake 106, which will in turn create a 100% vacuum force at the media inlet. This facility is particularly advantageous when the operator is working away from the container, as only momentary interruption occurs.

As the mixture of air and abrasive is propelled out of the nozzle 92, water is fed onto the flared nozzle opening via the two apertures 96. It has surprisingly been found that even if the two streams of water are fed as a non-pressurised trickle out of the opening, the fact that the air stream is travelling at a much higher velocity than the water creates an upward draught of surrounding air, thereby drawing the water stream into the compressed air stream. This allows the water to be used for specific abrasives as a dust suppressant. As the water jets are externally introduced into the air stream, no clogging is encountered within the spray gun. When using abrasives such as sodium bicarbonate, there is a need after cleaning to wash or rinse away any residue. This is simply achieved by closing the media inlet 40 and using the compressed air with water to rinse or wash away the residue. When soft, water soluble abrasive media are used, the cleaning and abrasive nature of these media are not compromised, which could occur in the case of atomised water being injected into the air stream. The water control valve 100 allows the operator to switch the water on and off at will. This is particularly useful when initially setting media flow rate, or if water is not required during the cleaning operation. As the water is not supplied under pressure, a small diameter light weight hose may be used, thereby reducing overall weight and increasing the manoeuvrability of the spray gun.

Referring now to Figures 6 to 8, a second embodiment of a three-way valve 1 10 is shown. The three-way valve 1 10 includes a valve body 1 1 1 defining a media outlet port 112 which communicates with a slot-shaped media inlet port 1 13 formed in a valve body 1 14. The valve body 114 is formed with a slot-shaped air inlet port 1 15 which is positioned just beneath the media inlet port 113 at right angles to it. The valve body is essentially tubular in form, and has a restricted central passageway 116 with which the inlets 113 and 115 communicate, and a vacuum outlet port 117 onto which the suction hose 52 is coupled.

A screw-in valve member 1 18 is formed with an elongate shaft 120 which terminates in a knurled handle 122 extending from the skirt of the abrasive blasting apparatus in a manner similar to the handle 28 and shaft 30 illustrated in Figure 1. The screw-in valve 118 includes a threaded portion 124 which screws into a complementally threaded portion 126 at an opening of the passageway opposite the outlet port 116. A round cylindrical valve head 128 locates snugly within the restricted passageway 1 14 in the manner illustrated in Figure 8. An O-ring 130 provides a rotary seal between the media inlet 108. the threaded portion 124 of the screw-in valve 1 18 and the complementally threaded portion 126, thereby preventing the ingress of abrasive media into the threaded portions.

Clockwise rotation of the handle 122 will cause the valve head 128 to move in the direction of arrow 132, and anti-clockwise rotation of the handle 122 will cause the screw-in valve to move in the opposite direction. This has the effect of gradually and simultaneously opening and closing the media inlet 108 and the air inlet 112 and controlling the extent of communication of these inlets with the vacuum outlet port 116. It can clearly be seen from Figure 6 that the air inlet port 112 extends a distance "d" further than the media inlet port 108. As a result, a vacuum is created before the media is allowed to enter the vacuum port 116.

Naturally, the relative shapes and sizes of the ports 108 and 112 can be adjusted so as to control the relative ratios of air and media. By changing the profile of the ports to a profile which is wedge-shaped, for example, the relative ratios of the port sizes can also be varied as the ports are simultaneously opened or shut by rotation of the screw-in valve. The advantage of the embodiment illustrated in Figures 6 to 8 is that the operating portion of the screw-in valve constituted by the threads 124 and 126 does not tend to get clogged with abrasive media owing to the pressure of the O-ring 130. In addition, the threads allow the sizes of the ports to be adjusted extremely finely. The fine adjustment facility allows the intake 106 in the spray gun to be eliminated completely. The surface areas of the inlets can vary from 4mm² to 200mm², depending on the overall size of the abrasive blasting apparatus and the size of the media particles to be used. In addition, the abrasive blasting apparatus has the capacity to operate in conjunction with a range of compressors delivering from lOcfm^"1 to lOOOcfm^'1 (0.005mV to 0.5m³s^"') of air at pressures ranging from 300kPa to lOOOkPa. In the particular embodiment described, the ambient air inlet port is rectangular and has a width of 2.5mm and a length of 12mm. the media inlet and outlet ports 112 and 1 13 are similarly rectangular, having a width of 5mm and a length of 1 Omm. The diameter of the restricted central passageway 116 is 5mm, increasing to 8mm at the vacuum outlet port 117. The result distance "d" is 2mm, the length difference between the ambient air inlet port 115 and the media inlet port 1 13.

The valve body 1 14 is in the form of an insert which can be interchanged with other value body inserts having differently sized ports to cater for different media types and compressor sizes.

Turning now to Figures 9 and 10, the media hopper 12 may include a moisture separator 136. The moisture separator 126 is formed with a spigot 138 for connection to a compressed air source. The compressed air is fed via a tangential inlet 138 A into a vortex chamber 140 which is fitted with a stainless steel screen or mesh 141 for breaking up the air stream, for cooling it and for encouraging a separation of moisture from the air. The air follows a spiral path in the direction of arrows 142 through an outer annular chamber 144 defined by an intermediate tube 146 which terminates in a flared skirt 148 which is arranged to trap moisture and allow it to drip down into a sump portion 150 of the separator. The air then travels upwards through an opening defined between the flared skirt 148 and an internal tube 152 in the direction of arrows 154, and then migrates downwards through the central internal tube 152 in the direction of arrows 156 through an outlet 158 which is coupled to the compressed air hose 44. Water and other condensed liquid gathers in the sump portion and drains through a drain outlet 160.

The moisture separator 136 is particularly effective in humid conditions where most abrasive media tend to clog unless provided with a suitable anti- caking agent. Further, in most environments, heated air from the compressor is saturated with water vapour which tends to condense in the cold venturi chamber. The moisture separator dries the air from the compressor, which then passes into the spray gun 58 and creates a venturi suction in the manner previously described.

In an alternative form of the invention, the abrasive blasting apparatus operates off a pressurized water unit rather than an air compressor delivering water at from 10 to 1001/min at pressures ranging from 10 to 150MPa.

Referring now to Figures 1 1 and 11 A, a second embodiment of a spray gun 162 is shown, which is intended for heavier duty industrial applications than the spray gun 58 illustrated in Figure 5, where increased production rates and greater cleaning and stripping power is required. The spray gun 162 has a gun barrel 164 formed from bent aluminium tubing. The upstream end 166 of the barrel 164 is arranged to be fitted to a compressed air hose which is coupled to a compressor having a capacity of 65 to 250 cfm^'1 (0.0325 to O.πSmY¹). A nozzle assembly 168 is coupled to the downstream end of the barrel 164, and a barrel grip 180 is provided just upstream of the nozzle assembly 168. A handle 169 to which a deadman control assembly 170 is fitted is located towards the upstream end of the barrel. The deadman control assembly includes a control lever 172, which, is spring biased into a downward position by means of a spring 173 in which it effectively shuts off the compressed air supply on release of the lever 172. An air valve control pipe 174 leads through the deadman control assembly 170 to a normally closed air valve 176 (refer to Figure 14). Closure of the air valve control pipe 174 on release of the lever 172 causes the air valve 176 to revert to its normally closed position, thereby cutting off the compressed air supply closer to source. An advantage of this feature is that the air supply hose is not pressurized when the abrasive blasting apparatus is not operational.

The nozzle assembly 168 includes a venturi housing 182 injection moulded from a suitable hard plastics material, and reinforced with a tubular steel jacket 183. A tubular airjet insert 184 is fitted within the venturi housing 182 and is formed from a hard wear-resistant material such as tungsten carbide. A bush 186 is optionally fitted within the venturi housing adjacent an opening 187 to which the abrasive and air hose 52 is fitted, depending on the type of abrasive being used. A nozzle 188 bears up against the insert 186, and is held in position by means of a nozzle holder or shroud 190. A water shroud 192 is coupled to the front end of the nozzle shroud 190. A water hose 46 is fitted to a passageway 194 defined in the water shroud. The passageway 194 communicates with a ring-shaped manifold chamber 196 from which three equi-spaced small diameter outlets 198 extend and mouth into the flared nozzle opening 200. Water ejected through the openings 198 is entrained in the air and media jet the manner described earlier on in the specification. The water hose 42 and the abrasive and air hose 52 are provided with respective manual control valves 201 and 201 A.

In this particular embodiment, the only main metallic components are the hard wearing components, namely the tungsten carbide airjet insert 184 and the steel or brass nozzle 188. The airjet insert 184 is interchangeable with a number of different airjets varying in internal diameter size from 4mm to 15mm so as to suit usage with different compressor sizes. Similarly, the nozzle 188 is interchangeable with different sized nozzles. The internal diameter size range of the nozzles varies from 8mm to 30mm, with the result that a nozzle having an internal diameter x is designed to be used in conjunction with an airjet of internal diameter x/2. The interchangeable nozzles are designed for use with both soft and hard abrasives, and are matched so as to produce a suitable vacuum for abrasive flow, as well as an appropriate blast pattern.

Both the venturi housing 182 and the nozzle shroud 190 are formed from a hard plastics material such as nylon. As was described previously, a major downfall with previous systems is the cooling effect created by the compressed air as it travels through the venturi vacuum chamber. This tends to cool the heat sensitive material (such as steel, aluminium, copper or brass) from which the vacuum chamber housing is conventionally formed. The hot moisture-laden air travelling from the compressor thus condenses on the walls of the chamber. This condensation constitutes a major restriction in the use of soft, water-soluble media such as sodium bicarbonate, which is dampened by the condensate, thereby causing blockages in the chamber As the gun housing 182 and the nozzle shroud 190 are formed from a temperature stable material such as nylon, the surface temperature of these materials does not tend to fall below the dew point of the air entering via the compressed air hose 44 and the air and media hose 52.

One disadvantage of temperature stable materials of the type described above is that they are softer and more susceptible to wear when hard abrasives such as aluminium oxide and mineral sands are used. For this reason, a vacuum chamber insert in the form of the insert 186 has been designed which is made of a wear-resistant material such as tungsten carbide. The aforementioned harder abrasives are generally not as hydrophilic as sodium bicarbonate, as a result of which the condensate on the walls of the chamber has relatively little effect on these abrasives. Consequently, the tungsten carbide insert 186 is fitted so as to provide a chamber having metallic walls, without the resultant condensate on the walls of the insert not having an undue effect on the abrasive. The tungsten carbide bush or insert 186 is thus only used for harder hydrophobic abrasives, and is removed when softer hydrophilic abrasives such as sodium carbonate are used.

As an alternative, a hard plastics insert may be provided to replace the tungsten carbide insert. As a further alternative, the entire body defining the venturi chamber may be formed from a hard metal, with the inner walls of the body being adapted to receive a hard plastics insert of Teflon®, polycarbonate or nylon for softer hydrophilic media.

In Figure 12, a right side view of a mobile abrasive blasting apparatus 210, which is designed for use with the spray gun 162, is shown in an upright operative position in which the rear wheelset 212 in conjunction with a front foot 214 hold the main hopper section 216 of the apparatus in a vertical position. An outlet bayonet hose coupler 218 is provided for connecting the compressed air hose 44 to the spray gun.

Referring now to Figures 13 to 15, the compressed hose from a compressor is similarly fitted to the blasting apparatus via a similar inlet bayonet hose coupler 220. A compressed air pipe line 222 extends between the aforementioned inlet and outlet hose couplers 220 and 218. Pressure - 2.

between the inlet and outlet of the compressed air pipe line 222 is monitored by means of an inlet pressure gauge 226 and an outlet pressure gauge 228 which are fitted to respective inlet and outlet pressure take-offs 230 and 232. Inlet and outlet pressure is controlled by means of a pressure regulator 234 having a manually operated control knob 236 which may be used to adjust the inlet and outlet pressures to a desired value on the basis of the readings on the gauges 226 and 228.

The pipework illustrated in Figure 15 also includes a water pipe 46 A having inlets and outlet couplings 46B and 46C for respective connection to a water source and the water hose 46. It is also clear from Figure 15 how pipe connectors 174A and 174B connect the separate lengths of the valve control pipe 174 from a high pressure take-off 174C to a high pressure intake 174D venting into the normally closed air valve 176, which is held open via pressurized air from the take-off 174C via the intake 174D. An air and media outlet pipe 52A extends from the three-way valve 102 and terminates in a hose coupler 52B for connecting the air and media hose 52. A manually operable vent control valve 240 is used as an additional control for venting compressed air. That portion of the valve control pipe 74 leading from the deadman control lever to the take-off 174 A may be disconnected from the take-off 174 and used to clear blockages that may arise in the air and media outlet pipe 52A.

The abrasive blasting apparatus of the invention may be incorporated into a blasting cabinet for enabling closed, dust free blasting and the recycling of media. In addition, the blasting apparatus may be used in incorporation with the blast recovery system in which a vacuum recovery head is attached to the spray gun nozzle for recovery of spent abrasives. With suitable modifications, including multiple three-way valves 102, a number of spray guns may operate off a single compressor.

Referring now to Figure 16, a fourth multi-nozzle automated embodiment of an abrasive blasting apparatus 242 is shown. The abrasive blasting apparatus 242 comprises a single large hopper 244 which is typically capable of accommodating from 2 to 10 tons of sodium bicarbonate. The base of the hopper is fitted with four three-way valves 110.1, 110.2, 110.3 and 110.4 of the type illustrated in Figure 7. Four air and media hoses 52.1, 52.2, 52.3 and 52.4 extend from the respective valves 1 10.1 to 1 10.4 and are coupled to nozzle assemblies 168.1 to 168.4 of the type illustrated in Figures 1 1 and 1 1 A. A large compressor (not indicated) feeds the compressed air line 246, which extends via a normally closed air valve 248, a pressure regulator valve 250 and a four-manifold outlet 252 from which four separate high pressure air outlet pipes 254.1, 254.2, 254.3 and 254.4. extend into the respective nozzles 168.1 to 168.4 via respective control valves 256.1 to 256.4. A water control line 258 similar to the water line 46 leads to water shrouds 192 at the outlets of the nozzle assemblies 168.1 to 168.4.

The operation of the entire blasting apparatus is automated via a central computer-based control unit 260 which is typically housed in a central control room. The inlet and outlet gauge 226 and 228 may be located at the control room, together with a level sensing gauge operated via a level sensing line 262 for sensing the level of sodium bicarbonate in the hopper 244. The three-way valves 110.1 to 1 10.4 may be automatically adjusted by means of one or more stepper motors 264 operated via a control line 266 from the central control unit 260. A sensing line 268 may also extend from each three-way valve 1 10.1 to 110.4 for sensing the position of each valve. Output control lines 270 and 272 lead respectively to the normally closed air valve 248 and the pressure regulator valve 250 for operating these valves in response to the readings on the inlet and outlet gauges 226 and 228. Output control lines in the form of pneumatic or hydraulic lines 274 also lead from the control unit to the individual shut-off valves 256.1 to 256.4.

The nozzle assemblies 168.1 to 168.4 are positioned in an array that will enable them to clean a particular blast surface 276. In one typical application, the blast surface is constituted by the underside of a rail wagon, in which case a linear array of ten or more nozzle assemblies may be used, with the railway wagons passing over the nozzle array at a predetermined set speed in order to enable thorough cleaning of the undersides of the wagons to take place. The configuration of the nozzle arrays is unlimited. For example, an inwardly facing circular or semi-circular nozzle array may be used in the cleaning of aeroplane fuselages. In certain applications, individual nozzles may be movable and may be arranged to follow predetermined cleaning patterns, depending on the configuration of the particular surface requiring cleaning.

The abrasive blasting apparatus of the invention can easily be adjusted to suit different types and sizes of abrasive media. Further, the abrasive blasting apparatus is designed to be adjustable so as to be used with a broad range of compressors with various operating pressures and volumes of compressed air outputs. These will create varying vacuum forces in the venturi chamber, with the previously mentioned three-way and secondary valves being used to readily adapt the abrasive blasting apparatus to cater for the various different input conditions.

Claims

An abrasive blasting apparatus comprising an abrasive media container venting to atmosphere and having an abrasive media outlet; a control valve assembly including a valve body defining a media inlet port communicating with the media outlet, an ambient air inlet port and a suction outlet port, and an adjustable three-way valve member for allowing selective communication between the inlet and outlet ports; and a spray gun assembly communicating with the suction outlet port, the three-way valve member being arranged simultaneously to adjust the sizes both of the media inlet and the ambient air inlet ports whilst communicating with the suction outlet port so as to control the flow of abrasive media and air through the suction outlet port.

An abrasive blasting apparatus according to claim 1 in which the control valve assembly includes an axial displacement valve, with the valve body having a passage defined therein which communicates with the media inlet port, the ambient air inlet port and the suction outlet port, the three-way valve member being arranged to travel axially within the passage, and being movable between a closed position, in which there is no communication between the media inlet port, the ambient air inlet port and the suction outlet port, an open position, in which there is full communication between the aforementioned ports, and a series of intermediate positions, in which the sizes of the ambient air inlet port and the media inlet port are simultaneously increased or decreased, whilst being in communication with the suction outlet port.

3. An abrasive blasting apparatus according to claim 2 in which the three-way valve member includes a foremost round cylindrical valve head, a threaded portion located rearwardly of the head and being arranged to threadingly engage with a complementally threaded portion in the passage, sealing means located between the threaded portion and the valve head for preventing the ingress of abrasive media into the threaded and complementally threaded portions, and a shaft extending from the threaded portion, the shaft terminating in a handle for rotating the entire valve member so as to effect axial adjustment thereof.

4. An abrasive blasting apparatus according to either one of claims 2 or 3 in which the air inlet port is arranged to open just prior to the media inlet port, so that a vacuum is created prior to entry of the media into the suction outlet port.

5. An abrasive blasting apparatus according to claim 1 in which the valve member is a rotary displacement valve movable between a first position, in which the ambient air inlet port is blocked and the media inlet port communicates with the suction outlet port, a second position in which the media inlet port is blocked and the ambient air inlet port communicates with the suction outlet port, and a series of intermediate positions in which both the media inlet port and the ambient air inlet port communicate with the suction outlet port, with the valve member being arranged progressively to increase the size of media inlet port as the size of the ambient air port is being decreased, and vice versa.

6. An abrasive blasting apparatus according to claim 5 in which the size of the vacuum outlet port is progressively decreased with a decrease in size of the ambient air port, in inverse proportion to the flow rate of the abrasive media.

7. An abrasive blasting apparatus according to any one of the preceding claims in which the spray gun assembly communicates with the suction outlet port via a suction outlet pipe, the spray gun assembly including a housing defining a venturi chamber into which the suction outlet pipe is connected and an outlet nozzle, the venturi chamber being arranged to receive a stream of fluid from a compressed a high pressure fluid source via a compressed fluid line for creating the venturi effect so as to propel the media from the outlet nozzle via the suction outlet pipe.

8. An abrasive blasting apparatus according to claim 7 which incorporates an in-line moisture separator in the compressed air line for removing moisture from compressed air before the compressed air is fed to the venturi chamber, thereby reducing clogging of the abrasive media.

9. An abrasive blasting apparatus according to either one of claims 7 or 8 in which at least an inner portion of the venturi chamber housing is formed predominantly from a heat- or temperature-stable material, the surface temperature of which does not tend to drop below the dew point of incoming compressed air, thereby avoiding or at least reducing the formation of media-clogging condensate in the venturi chamber which tends to clog hydrophilic media such as sodium bicarbonate.

10. An abrasive blasting apparatus according to claim 9 in which at least the inner portion of the venturi chamber housing is in the form of a removable venturi chamber insert.

11. An abrasive blasting apparatus according to claim 10 in which the removable venturi chamber insert is interchangeable with at least one other insert which is formed from a wear-resistant material such as tungsten carbide for use with relatively hard abrasive media such as aluminium oxide or mineral sands.

12. An abrasive blasting apparatus according to any one of the preceding claims 7 to 1 1 in which the spray gun assembly includes an airjet insert upstream of the venturi chamber and a nozzle insert downstream of the venturi chamber, with the inserts being interchangeable with inserts having different internal diameters so as to cater for different compressor sizes and/or abrasive types.

13. An abrasive blasting apparatus according to claim 9 in which the heat or temperature stable material is a suitable hard plastics material chosen from the group including nylons, polycarbonates and Teflon®.

14. An abrasive blasting apparatus according to any one of the preceding claims 7 to 13 in which the spray gun assembly incorporates a deadman control lever which is arranged to shut off the compressed fluid line at a point remote from the spray gun assembly.

15. An abrasive blasting apparatus according to any one of the preceding claims 7 to 14 in which the spray gun assembly includes a water line venting onto an external flared opening of the outlet nozzle of the spray gun assembly, whereby pressurized or unpressurized water flowing through the opening is entrained by the pressurised stream of air and abrasive particles for dust suppression and cleaning purposes.

16. An abrasive blasting apparatus according to any one of the preceding claims which includes remote ambient air valve means communicating with the ambient air inlet port for further controlling the size of the ambient air inlet.

17. An abrasive blasting apparatus comprising an abrasive media container venting to atmosphere and having an abrasive media outlet; a control valve assembly including a valve body defining a media inlet port communicating with the media outlet, an ambient air inlet port and a suction outlet port, and an adjustable three-way valve member for allowing selective communication between the inlet and outlet ports; and a spray gun assembly communicating with the suction outlet port via a suction outlet pipe, the spray gun assembly including a housing defining a venturi chamber into which the suction outlet pipe is connected and an outlet nozzle, the venturi chamber being arranged to receive a stream of fluid from a compressed a high pressure fluid source via a compressed fluid line for creating the venturi effect so as to propel the media from the outlet nozzle via the suction outlet pipe.

18. An abrasive blasting apparatus according to any one of the preceding claims 7 to 17 which includes a plurality of control valve assemblies communicating with at least one abrasive media container, an array of spray gun assemblies communicating with the suction outlet ports of the control valve assemblies, and at least one high pressure fluid source having fluid lines communicating with each of the spray gun assemblies.

19. An abrasive blasting apparatus according to claim 18 in which central control means are provided for automatically controlling the operation of the array of spray gun assemblies.