FIELD OF THE INVENTION

The present invention relates to an apparatus for abrasive cleaning wherein an abrasive media from a storage vessel is entrained into a fast flowing gaseous stream, which carries the abrasive along a hose or conduit to an outlet nozzle, whereby the abrasive media can be applied to a surface entrained in said fast flowing gaseous stream via said outlet nozzle.

BACKGROUND OF THE INVENTION

At present, a variety of different types of equipment are available for abrasive cleaning for a wide variety of industrial applications including wall and stone cleaning, tank and container cleaning, ship or oil rig maintenance, or other industrial applications where a finishing process may be required such as in the forging or casting of metal objects, or simple surface preparation for further processing, for example, painting.

In the abrasive blast cleaning industry a wide variety of abrasive media may be used for sand or shot blasting including a variety of different grades of sand or grit, steel shot, glass beads or many of a wide variety of other available abrasive materials. Moreover, blasting may take place in a "wet" and a "dry" manner. In the case of "wet" blasting, an abrasive media is mixed with water and this mixture is sprayed under pressure. In the case of "dry" blasting, the blasting medium is conducted to the spray nozzle in dry condition and sprayed there under pressure, the pressure typically being obtained through a feed of compressed air.

In existing types of portable blast cleaning machines, the abrasive media is stored under pressure in a storage hopper from which the abrasive under pressure may be introduced into a fast flowing high pressure airstream, which carries the abrasive along a suitable "blast" hose, which is terminated in a delivery nozzle. The storage hopper has to be pressurised to avoid the high pressure airstream from flowing back into the hopper and to deliver the abrasive media into the airstream by differential pressure.

The need for a pressurised storage hopper for the abrasive media requires complex pressure regulation equipment and makes refilling and inspection of the storage hopper difficult. Furthermore, the passage of the abrasive media entrained in the high pressure airstream through the blast hose leads to rapid wear of the blast hose and frequent replacement as well as safety concerns for the operator. An example of such known portable blast cleaning machines can be seen in WO 2018/055012.

It is an object of the present invention to provide an apparatus for abrasive blasting and cleaning which overcomes the abovementioned disadvantages of the prior art.

SUMMARY OF THE INVENTION

According to the present invention there is provided an apparatus for abrasive cleaning comprising an abrasive media storage vessel for storing a supply of abrasive media at ambient pressure, said storage vessel having an outlet supplying abrasive media into a first gas stream at a first gas pressure in a first flow passage, said first flow passage supplying a mixture of gas and abrasive media to an outlet nozzle, a main gas stream communicating with the outlet nozzle via a second flow passage at a second gas pressure, said second gas pressure being higher than the first gas pressure, whereby the mixture of gas and abrasive media from the first flow passage is entrained into the main gas stream from the second flow passage in or downstream of the outlet nozzle.

In a preferred embodiment the mixture of gas and abrasive media from the first flow passage is entrained into the main gas stream from the second flow passage within the outlet nozzle.

A first venturi may be provided in said first flow passage adjacent an outlet of the storage vessel whereby abrasive media from the storage vessel is entrained into said first gas stream. Abrasive media from said storage vessel may pass into a throat of the first venturi under gravity. A control valve may be provided for controlling the flow of abrasive media from the storage vessel into the throat of the first venturi.

The mixture of gas and abrasive media from the first flow passage may be entrained into the main gas stream from the second flow passage in a second venturi located in or upstream of the outlet nozzle.

The first and main gas streams may be supplied from a common source of compressed gas, pressure regulating means being provided for controlling the first and second gas pressures. The first and main gas streams may comprise air streams from a common source of compressed air.

The apparatus may further comprise means for selectively adding water into said main gas flow to selectively provide dry or wet blasting. Water may be selectively added to said main gas flow in said outlet nozzle from a water supply via one or more water injection ports provided in said outlet nozzle. The supply of water to said one or more water injection ports may be controlled by a water control valve. The or each of said one or more water injection ports may be associated with a non return valve.

Preferably the storage vessel includes a flow control valve in an outlet at a lower end of the storage vessel for controlling the passage of abrasive media into the first flow passage. Said flow control valve may comprise a normally open pinch valve.

The outlet nozzle may be provided with one or more gas vents for venting excess pressure from the first gas stream as it enters the main gas stream. Said one or more gas vents may communicate with an outlet passage of the outlet nozzle downstream of said one or more gas vents.

BRIEF DESCRIPTION OF THE DRAWINGS

An apparatus for abrasive cleaning in accordance with embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a front view of an abrasive cleaning apparatus in accordance with an embodiment of the present invention;

Figure 2 is a sectional view on line A-A of Figure 1 ;

Figure 3 is a detailed sectional view of the abrasive media eductor of the apparatus of Figure 1 ;

Figure 4 is a sectional view of an outlet nozzle of the apparatus of Figure 1 ;

Figure 5 is a sectional view of an outlet nozzle in accordance with an alternative embodiment of the present invention; and

Figure 6 is a perspective sectional view of the outlet nozzle of Figure 5.

DETAILED DESCRIPTION OF THE DRAWINGS

In a first embodiment of the present invention, as illustrated in the drawings, the present invention provides an apparatus for abrasive cleaning that utilizes an unpressurized abrasive storage hopper 2 mounted on a wheel frame 4. An abrasive media eductor 6 is mounted below the hopper 2 communicating with an abrasive media outlet at a lower end of the storage hopper 2 and adapted to mix abrasive media gravity fed from the storage hopper 2 into a relatively low pressure first flow of air in a first air flow passageway 8.

A venturi induction outlet nozzle 10, such as that shown in either Figure 4 or Figure 5, is adapted to mix said first flow of air and the abrasive media entrained therein with a main flow of air supplied by a main air flow passageway 12 at a second and much higher pressure than the first flow of air, such that the abrasive media can be projected at a surface from said outlet nozzle 10 in the combined first and main flows of air for cleaning, profiling or surface preparation. As shown in Figures 4 to 6, the main and first air flow passageways 8,12 converge within the outlet nozzle 10 through converging and diverging flow paths, causing the first flow of air, carrying the abrasive media, to be entrained and mixed into the main flow of air. Therefore the mixing of the abrasive media and the high pressure flow of air required to achieve the desired blasting effect only takes place in the outlet nozzle 10, reducing wear of the apparatus and allowing the abrasive media storage hopper to be unpressurised.

The apparatus may be adapted to operate dry when required through blast selection toggle switches 14 located on a main control panel 16, or wet as required similarly, wherein water can be added to the air flow in or upstream of the outlet nozzle 10. When wet blasting is selected the control panel 16 may activate a water pump to inject water under pressure into the outlet nozzle.

When wet blasting, water may be injected directly into the outlet nozzle 10 via one or more water injection ports 20 in the outlet nozzle 10, to ensure a slurry mix is created prior to exiting the outlet nozzle 10. Injecting water at the outlet nozzle 10 may eliminate blockages occurring when mixing air, water and abrasive as the three elements are kept separate until exiting the outlet nozzle 10.

The feed of abrasive media from the storage hopper 2 into the eductor 6 may be controlled by a control valve 18, such as a pinch valve. The control valve 18 may be controlled in a timed sequence, preferably controlled via a pneumatic timer module located in the control panel 16. This abrasive media feed timing may be adjustable at the control panel from 0 to 60 seconds, ideally 5 seconds but not limited to.

When dry blasting, post wet blasting, the apparatus may be adapted to purge the main air flow passage with air for an adjustable time of up to 60 seconds, ideally pre-set at 5 seconds - but not limited to, with dry air only, primarily to remove any moisture that may remain in the main blasting hose. Dry abrasive is then reintroduced to the blast stream when the timer module feeds air to the storage hopper control valve (for example pinch valve 18), opening the valve 18 again to reintroduce dry abrasive particles to the induction air stream, of which dry blasting is then activated without significant moisture in the lines allowing the apparatus to revert back to dry media expulsion and thus dry blast mode.

When wet blasting, water injection may be monitored via a water pressure sensor, for example using a normally closed pneumatic valve. This valve may be adapted to open, for example via a stainless steel compression spring loaded plunger, only when sufficient water injection pressure is present from the water pump, ideally more than 5 bar pressure - but not limited to.

If insufficient water injection pressure is present, the system will shut down the flow of abrasive media by ceasing air supply to the pinch valve 18, ceasing the supply of abrasive whilst in wet blast mode, primarily for safety in spark controlled environments to prevent the machine effectively defaulting to dry blasting mode if the water pump were to fail for example. If this happens the user can then recheck/reconnect water supply connection at the control panel 16, to continue wet blasting, or select dry blasting to continue without water present. An air powered water pump may be used to pressurise the water outlet from either an unpressurized or pressurized water source directly to the outlet nozzle 10 water injection port 20.

A non-return valve 22 (see Figure 5) may be located at the water injection port 20, with a cranking or opening pressure of ideally 5 bar, rated up to 16 bar - but not limited to. This may ensure that water is only injected when the wet-blast mode is selected and the“Deadman handle” is activated to activate the water pump thus enabling water injection.

The main benefit and inventive element of the apparatus is that the apparatus does not use a pressure vessel to store the abrasive media or deliver through differential pressure within a pressure vessel as in an ordinary pressure sand blast pot. Instead an unpressurized storage hopper 2 is used that the user can fill with all types of blasting media, and see the fill level visually and also monitor abrasive usage whilst in use, eliminating the need for pressure equipment directives and regulations required for manufacturing pressure vessel equipment, and eliminating routine vessel inspection and maintenance. Traditionally a pressure vessel is used on the principals of differential pressure to force abrasive into the blasting stream to overcome back pressure within the main blasting line, whereas with the apparatus of the present invention, abrasive is induced or sucked into the educator 6 in a relatively low pressure air flow and then introduced into a high pressure air flow at a secondary induction point within the outlet nozzle 10. Having a separate main air flow via the outlet nozzle 10 in conjunction with the lower operating pressure eductor 6 creates a push-pull method of abrasive induction into the air/blast stream by venturi effect causing suction of abrasive particles from the storage hopper 2.

An air pressure feed to the converging inlet of the eductor 6 is ideally set at 2 bar, but not limited to this pressure. Abrasive is induced by forced induction from the eductor 6 in combination with the higher velocity air passing through the outlet nozzle 10, then entering the abrasive induction feed located on the outlet nozzle. This method of abrasive pickup and delivery prevents the stored abrasive from being mixed with stationary compressed air within a typical pressure blast pot storage vessel, which ordinarily can cause blockages due to moisture from compressed air input.

Full pressure and flow are obtained with the use of the main large bore full flow main flow passageway or blasting tube, which carries unsuppressed full pressure and full flow air directly to the converging nozzle inlet within the outlet nozzle 10, wherein the main air flow is mixed with the first air flow carrying the abrasive media.

The educator 6 draws abrasive media directly from the storage hopper 2 via suction whilst wet or dry blasting. Abrasive media is induced into the first flow of air in the first flow passageway via negative static pressure and venturi effect. The delivery of abrasive media may be controlled by a pressure regulator on the main control panel 16, which directly controls the opening of the pinch valve 18. This enables the use of an unpressurized storage vessel 2 to hold stored abrasive media, which in turn enables the use of very fine abrasives without issues of moisture build-up mixing with stored abrasive, because the main flow of compressed air flows directly through the main flow passageway, bypassing the abrasive media storage vessel 2. Activating compressed air through the system may be operated through a “Deadman switch” located at the outlet nozzle 10, which may be connected to the main pneumatic circuit and ultimately a large bore pneumatic solenoid valve which may open and close air through the system on activating the“Deadman switch”. Likewise, this apparatus may be deactivated at any time by activing the a stop control located on the control panel 16.

A back pressure sensor may be provided to prevent backpressure surges from the first flow passageway downstream of the educator should it become blocked or become kinked to prevent abrasive being sprayed up into the hopper. A back pressure air tube may be provided, preferably fitted with a suitably sized abrasive mesh screen, to prevent abrasive particles entering the back pressure sensor. This sensor may be either pneumatic 2/3 type in actuation, normally closed or normally open, or pneumatic or electric limit switch may be used as an alternative means of sensing back pressure to halt the system should it be present.

Water feed monitoring:

The water monitoring systems may consist of a brass plunger valve with an inlet and outlet port, coupled to a pneumatic plunger valve, which is opened and activated when water injection to the pump outlet has pressure of ideally more than 5 bar present, but not limited to this pressure, whilst the water pump is pumping water in wet blast mode. The circuit may be connected to the airline controls of the abrasive media storage hopper 2 pinch valve 18, so that if water should cease to be present in wet-blast mode, abrasive media flow will immediately cease also, preventing the system running dry unintentionally. This is a safety feature for wet blasting in spark controlled environments; water injection rate of flow can be adjusted by adjusting the water dose valve located on the main control panel 16.

Storage Hopper:

The storage hopper 2 may be manufactured from either metal or plastic. The storage hopper is an unpressurized vessel and may include a built-in sieve and lid. The lower end of the storage hopper 2 may include a 60-degree cone angle to ensure smooth flow of abrasive to the educator 6. The hopper 2 is maintenance free and corrosion resistant. Larger or smaller volumes of hopper can be used with the same working principles with no limit to capacity.

Outlet Nozzle

The outlet nozzle 10 may be manufactured from any suitable non-ferrous material, and may have a tungsten carbide liner within the diverging nozzle part thereof to protect against abrasive wear. The diverging nozzle part creates venturi suction when in use to draw abrasive media into the main flow of air. Air feed pressure to the outlet nozzle may adjustable from 5 to 100psi ideally but not limited to these pressures. The outlet nozzle 10 may utilise interchangeable nozzle inlet 24 and outlet parts 26 with varying sizes. The outlet part 26 of the nozzle 10 can be interchanged to vary the output patterns effectively with different air input pressures and flow rates. An air vent 28 may be provided in the walls of the outlet nozzle 10 to relieve excess pressure build up through via angled hole at an opposing direction to the direction of abrasive media delivery induction point. Such air vent 28 may be provided to relieve excess air pressure existing from the abrasive eductor line feed. Such excess pressure may be relieved via such air vent 28 and preferably reintroduced at a downstream point of the outlet nozzle with the purpose of preventing back pressure at the eductor 6.

Eductor

The eductor 6 (see Figure 3) may be located below the abrasive media storage hopper 2, communicating with the hopper 2 via the pinch valve 18. The pinch valve may be adapted to induce abrasive media and conveys it directly to the eductor 6 by mains air pressure fed by a small bore solenoid. Air pressure supplied to the eductor as the first flow of air is ideally set at around 2 bar at a flow rate of around 4.3 litres per second (9 cubic feet per minute), but not limited to this pressure or flow rate. The eductor 6 conveys abrasive media via a“pull” method, forced by air through an abrasive flow tube via a push method and then again induced directly at the inductor nozzle (see Figure 3) via induction or venturi effect via a pull method. This provides a very reliable method of abrasive media pickup and delivery for abrasive blasting. As illustrated in Figure 3, the a portion of the main air flow passage 12 is mounted below the educator 6. A port 30 may be provided in the main air flow passage 12 which may be used for a pressure sensor or to inject water.

The eductor 6 may be manufactured from cast and machined aluminium or stainless steel with ceramic or tungsten carbide wear liners internally to protect against abrasive wear of internal surfaces from abrasive particles conveyed under air pressure.

Storage Hopper Pinch Valve:

The pinch valve may be manufactured from stainless steel and/or aluminium, featuring a normally closed inner rubber sleeve, the pinch valve is only opened when activing blasting modes, and the opening force and thus the flow of abrasive can be adjusted by adjusting the abrasive dose valve located on the machines main control panel, the abrasive pinch valve controls the rate of abrasive flow into the venture induction valve by adjusting the size of the open from 0-25mm but not limited to these sizes, larger or smaller orifice sizes are optional. The abrasive flow may be adjusted via an air pressure regulator, which either opens the rubber sleeve for increased flow, or closes for decreased flow of abrasive. The pinch valve 18 is normally closed, meaning when not in use the flow of abrasive media is ceased. When air is fed to the pinch valve, for example activated by the Deadman handle, the valve 18 then opens if the blasting mode selected is dry-blast or wet-blast.

The invention is not limited to the embodiments described herein but can be amended or modified without departing from the scope of the present invention as defined by the appended claims.