GB2112680A - Wet blast cleaning unit - Google Patents

Abstract

A wet blast cleaning unit of the kind in which a regulated volume of a liquid 14 or a mixture of liquid 14 and an inhibitor 16, is introduced into a pressure gas/abrasive line 20 at a point remote from the nozzle to permit adequate mixing prior to ejection. The liquid and mixture have separate supplies having flow control means 72, 75 to adjust the relative proportions supplied to a pump 52 connected by a line 82 to the pressure gas/abrasive line 20. A cleaning device for the operator's helmet, which device is supplied with liquid from the liquid circuit of the unit under control of the operator, is also described. <IMAGE>

Description

SPECIFICATION Wet blast cleaning unit This invention relates to improvements in wet blast cleaning, a technique which is now recommended in place of dry sand blasting and the so-called "wet process for cleaning land, sea and underwater installations.

The technique involves generating a pressurised stream of gas, usually air, entraining abrasive particles, normally sand, and introducing into this stream, at a pressure greater than the gas pressure (which would normally be in the region of 100-120 psi), a regulated volume of water. The admixture of gas under pressure, abrasive and water is directed at high velocity against the surface to be cleaned. By virtue of the presence of relatively small quantities of water (typically 0.4 to 1.5 gallons/minute) the disposal and/or supply of large volumes of waste water, or steam which is a problem associated with the "wet process" is avoided. Also, the water serves to damp down removed dust and dirt so creating an improved working environment for the operator, as compared with conventional (dry) sand blasting.In addition to the above advantages it has been found that the water also makes a significant contribution to the cleaning effect.

Various wet blast cleaning systems have been developed but none give adequate flexibility and control of the cleaning process and it is this problem that the present invention aims to mitigate.

Once cleaned by wet blasting, a surface tends to corrode rapidly by exposure to the water in the blast and to the elements. This is particularly significant in the case of offshore installations. To overcome this an inhibitor such as a solution of a polyphosphate may be mixed with the water for introduction into the gas stream and, in known, wet blast cleaning units two storage or header tanks are provided, one for water and the other for the water/inhibitor mixture. Either tank may be connected to the pump as required.

In accordance with a first aspect of this invention we propose a wet blast cleaning unit of the kind in which a regulated volume of a liquid or a mixture of the liquid and one or more liquid additives, in particular water or a mixture of water and an inhibitor, is introduced into a pressure gas/abrasive line, comprising a pump which is connected to a separate supply for each of the said liquids, flow control means being provided for adjusting the relative proportions of the two liquids supplied to the pump.

A flow control means may be fitted in both the liquid (water) and the liquid additive (inhi bitor) lines but this is not essential. Indeed in the perferred embodiment described below only the liquid additive line includes a flow control valve, a second flow control valve being fitted on the outlet side of the pump.

To facilitate accurate setting of the flow rate of the water/inhibitor mixture a visible flow meter may be fitted in each of the supply lines.

It is important to establish a substantially constant flow of liquid and, to this end we also propose, in accordance with a second aspect of this invention, a wet blast cleaning unit of the kind referred to, in which the liquid under pressure is delivered to the pressure gas/abrasive line by a double acting air operated pump preferably having a surge accumulator in communication with the inlet thereto.

Where visible flow meters are connected in the water and ibhibitor lines this has the added advantage of stabilising the readings so enabling more accurate setting and control of the water and inhibitor flow rates.

In known wet blast cleaning units, the liquid (water/inhibitor) is injected into the air stream in one of two places, either immediately downstream of the point at which abrasive is injected or at the nozzle. We have found neither to be satisfactory. In the former case this is because it is difficult to clear the hose of wet abrasive and, since the hose may be up to 100 m. long, this makes the hose extremely heavy and difficult to handle especially when the operator is located high above the control unit. In the latter case, there is insufficient mixing of the liquid and air/abrasive streams.

We now propose in accordance with a further aspect of this invention, a blast cleaning unit of the kind referred to, in which the liquid or a mixture of liquids is introduced into the pressure gas/abrasive stream via a hose coupling widely spaced from the nozzle up to a maximum distance so as to ensure adequate mixing, and consistent with the available gas pressure being sufficient to clear wet abrasive from the length of hose between the coupling and the nozzle.

The force of the blast generated by wet blast cleaning units is such that serious injury could be inflicted or extensive damage to property caused in the event of an accident and to this end we propose in accordance with a still further aspect of the invention a wet blast cleaning unit of the kind referred to and comprising safety control means in the pressure gas circuit responsive to an activator valve located at or near the nozzle on the end of the gas/abrasive line and biased toward a normally closed position. With such an ar rangement, the operator is required to hold the actuator in the closed position in order to override the safety control which, in a preferred embodiment, is adapted to inhibit means for injecting abrasive into the pressure gas line and to cut off motive pressure to the liquid injecting pump.

Also, at the nozzle, a regulating valve may be provided for adjusting the gas (air) flow to the nozzle and the quantity of abrasive injected therein.

Other features and advantages of the present invention will be apparent from the following description, by way of example, of a preferred embodiment of wet blast cleaning unit, a diagram of which is shown in Fig. 1 of the accompanying drawings. Fig. 2 shows an operator's helmet having a cleaning device connected to the wet blast cleaning unit shown in Fig. 1.

The wet blast unit shown in Fig. 1 is housed within a frame and incorporates a selfsealing blast pot or hopper 10 for storing and dispensing sand, a storage tank 1 2 which is divided into two separate tanks 14 and 16; one (14) for water and the other (16) for a liquid inhibitor, this latter having suspended therein an air driven agitator 18. The frame also incorporates a reel (not shown) from the blasting hose 20 and a control unit having a control panel 22. The unit is operated by compressed air which may be supplied by a separate mobile air compressor so making the unit suitable for use in remote areas where there is no electrical power supply. If desired, the unit may include its own air compressor so being entirely self-contained.

It is intended that the unit be manned by a team of two operators in direct contact via a communication system to be described below, but the unit incorporates an override or emergency device which will be referred to herein as a "dead man" valve, under the direct control of the operator handling the hose. The deadman handle is preferably spring loaded so that unless the operator holds down the operating lever the valve automatically reverts to its closed state.

Air under pressure (typically 100-120 psi) enters the unit via a filter 30 along line 32 and is led via a regulator valve 38 (which may be under the control of the operator at the nozzle) to the interior of the blast pot 10 in order to seal the pot and apply pressure above the sand therein, via an air operated shut-off valve 33 under control of the deadman valve 9 to an abrasive control valve 34 at output from the blast pot 10, to the deadman control handle 36 at the end of the hose 20, along line 40 incorporated a poppet valve 42 and regulator 44 on the control panel 22, to drive the agitator 18, and to a control device 46 for the supply of air, also via a poppet valve 48 and regulator 50, to an air drive pump 52.

Motive air is supplied from the regulator 50 to the pump by a so-called "micro-fog" lubricator 54.

The pump control valve 46 incorporates a shut-off valve activated by a diverter valve 56 which is connected by a return line 58 to the air inlet.

Water is delivered to the unit via an air inlet 60 on the control panel 22 which is connected both to the water tank 14 in which the water level is controlled by a float valve or ballcock 62, and via a shut-off valve 64 to the inhibitor tank 1 6 so enabling a concentrated inhibitor solution to be mixed in the tank and enabling the tank to be washed.

Supply lines from the water tank 14 and the inhibitor tank 1 6 are joined at 66 to enable mixing of the water and inhibitor upstream of the inlet to the air drive pump 52 and each supply line is fitted with a shut-off valve 68 and 70 and visible flow meters 72 and 74. In addition, the inhibitor supply line includes a flow control valve 75 by which the flow rate of the inhibitor is continuously variable from zero to a desired maximum value.

The pump 52 is required to deliver a substantially constant output (at a given speed determined by the regulator) and, although in general, any pump which meets this requirement will be satisfactory, we prefer to use a double acting reciprocating pump. Minor fluctuations in the flow are compensated by a surge accumulator 76 in the form of a vertically extending vent pipe 78, connected between the junction 66 and the pump inlet.

This also serves to stabilise the flow meter readings so enabling more accurate setting thereof.

For regulating the pump delivery, a flow control valve 80 is provided, at the control panel 22, in the delivery line 82 leading to an injection coupling 84 in the hose and, typically, 4 metres upstream from the nozzle. This in practice being a convenient distance consistent with the requirement for thorough mixing of the water and abrasive, so that the abrasive is wet, and the need to be able to clear the line of wet abrasive prior to shut down. Water/inhibitor is injected into the hose 20 carrying the air/abrasive stream, via a non-return valve 86 which prevents sand from penetrating the liquid circuit.

In operation, when the air supply in switched on, the blast pot 10 is automatically sealed and pressurised and compressed air is delivered along the hose 20 once shut-off valve 88 is opened. Neither abrasive nor liquid is injected into the air stream until the "deadman" control at the nozzle is opened by the operator.

When this occurs, the shut-off valve 33 opens so admitting air to the abrasive control valve 34 which, in turn opens, to admit abrasive into the stream of air flowing to the nozzle. The quantity of abrasive injected into the air stream and the air flow itself is adjustable by the operator using the regulator valve 38.

At the same time, a pressure signal is applied along line 90, to the diverter valve 56 which activates the shut-off valve to drive the pump at a speed determined by the setting of the regulator 50 on the control panel 22.

Water/inhibitor is supplied to the pump 52 by opening valves 68 and 70 so that the flow rate of water can be set using the flow control valve 80 and flow meter 72 and the control valve 75 is then adjusted until the flow meter 74 indicates the flow rate of inhibitor required to produce the desired mix.

One problem associated with conventional blast pots is the tendency to become blocked due to either an agglomeration of particles or a foreign body, descending through the sand to the outlet, where the blockage occurs.

Becuase the agglomeration or body is heavier than the free particles of sand this invariably occurs when the pot is full of sand so that the pot must be emptied before the blockage can be cleared. This wastes a considerable amount of valuable operating time. To overcome this problem, we propose, connecting at the outlet of the pot, a hollow coupling or block defining a flowpath for the sand and having openings extending therethrough transverse to the sand flow path, removable covers or plugs being fitted in the sand openings. By removing the covers or plugs, it is possible to clear the blockage through the openings, so avoiding the need to empty the pot and considerably reducing down-time.

The wet blast process generates an unhealthy and dangerous environment particularly for the operator at the nozzle and to protect him, it is usual to provide a helmet which covers his face and includes a tough transparent screen. Inevitably, this becomes covered with spray and deposits of grit and dirt so that it has been necessary frequently to interrupt cleaning either to wash or replace a damaged screen.

In the wet blast cleaning unit described above, and more generally in any wet blast cleaning unit of the kind referred to, we provide in accordance with a further aspect of the invention, a cleaning device comprising a dispenser preferably arranged above the transparent screen of the helmet, and control means activated by the operator to supply a quantity of liquid to the dispenser from which the liquid is directed onto the screen. With reference to Figs. 1 and 2, an air line 95 is connected to a tapping 92 on the control panel supplied from the air inlet via a filter 94, to an air activated control valve 96.

Water is tapped at (a) (Fig. 1) from the pump delivery line 82 and supplied via the control valve 96 which may conveniently be attached to the operator's belt, to the dispenser 98, so that a stream of water 100 from the dispenser, which flows down the screen 102 to wash away accumulated grit and dirt, can be produced by the operator when required.

It will be understood, from the foregoing that, although overriding control of the cleaning process lies with the operator of the hose, full advantage can be taken of the versatility of the cleaning unit, only when the operator is able to communicate with the co-operator at the controls. For this purpose, a communication system is installed into the operators helmet. Similar systems have been proposed but these are somewhat bulky making the helmet difficult to use. Also, radio systems are not permitted to be used on certain off-shore installations, so that lengthy cables are required between the two operators. In order to avoid undue interference and electrical noise, we therefore propose a communication system in which the microphone is connected to an amplifier fitted into the helmet. In a similar arrangement an amplifier may be incorporated in the headset or receiver.

Claims (16)

1. A wet blast cleaning unit of the kind in which a regulated volume of a liquid or a mixture of the liquid and one or more liquid additives, in particular water ot a mixture of water and an inhibitor, is introduced into a pressure gas/abrasive line leading to a nozzle, comprising a pump which is connected to a separate supply for each of the said liquids, flow control means being provided for adjusting the relative proportions of the two liquids supplied to the pump.

2. A unit according to claim 1, comprising flow control means fitted in both the liquid and the liquid additive lines.

3. A unit according to claim 1, comprising a flow control valve in the liquid additive line, and a second flow control valve fitted on the outlet side of the pump.

4. A unit according to any one of claims 1 to 3 wherein a visible flow meter is fitted in each of the liquid and liquid additive supply lines.

5. A wet blast cleaning unit of the kind in which a regulated volume of a liquid or a mixture of the liquid and one or more liquid additives, in particular water or a mixture of water and an inhibitor, is introduced into a pressure gas/abrasive line leading to a nozzle, wherein the liquid under pressure is delivered to the pressure gas/abrasive line by a double acting air operated pump.

6. A unit according to any one of claims 1 to 5, having a surge accumulator in communication with the inlet of the said pump.

7. A wet blast cleaning unit of the kind in which a regulated volume of a liquid or a mixture of the liquid and one or more additives, in particular water and an inhibitor, is introduced into a pressure gas/abrasive line, wherein the liquid or a mixture of liquids is introduced into the pressure gas/abrasive line leading to a nozzle, via a hose coupling widely spaced from the nozzle up to a maximum distance so as to ensure adequate mixing and consistent with the available gas pressure being sufficient to clear wet abrasive from the length of hose between the coupling and the nozzle.

8. A unit according to claim 7 and com prising a non-return valve in the liquid/liquid additive line upstream of the hose coupling.

9. A unit according to any one of claims 1 to 4 and according to claim 5 or claim 6.

10. A unit according to any one of claims 1 to 4 and according to claim 7 or claim 8.

11. A unit according to claim 5 or claim 6 and according to claim 7 or claim 8.

1 2. A unit according to any one of the preceding claims, comprising safety control means in the pressure gas circuit responseive to an activator valve located at or near the nozzle on the end of the gas/abrasive line and biased toward a normally closed position.

1 3. A unit according to claim 12, wherein the safety control means is adapted to inhibit means for injecting abrasive into the pressure gas line and to cut off motive power to a pump injecting liquid into the pressure gas/ abrasive line.

14. A unit according to any one of the preceding claims and comprising a regulating valve at or near the nozzle, for adjusting the as flow to the nozzle and the quantity of abrasive injected therein.

1 5. A wet blast cleaning unit of the kind in which a regulated volume of a liquid or a mixture of the liquid and one or more liquid additives, in particular water or a mixture of water and an inhibitor, is introduced into a pressure gas/abrasive line leading to a nozzle, and comprising a cleaning device associated with a helmet for an operator of the unit and having a transparent screen, the device comprising a dispenser on the helmet and control means activated by the operator to supply a quantity of liquid tapped from the liquid supply to the pressure gas/abrasive line, to the dispenser from which the liquid is directed onto the screen.

16. A wet blast cleaning unit according to claim 1 5 and according to any one of claims 1 to 14.

1 7. A wet blast cleaning unit substantially as herein before described with reference to and as illustrated in the accompanying drawings.