GB2097304A

GB2097304A - Abrasive cleaning

Info

Publication number: GB2097304A
Application number: GB8110787A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-04-07
Filing date: 1981-04-07
Publication date: 1982-11-03
Also published as: GR75551B; ES8307567A1; KR830009904A; AU8231182A; BE892793A; JPS584359A; GB2097304B; ES511205A0

Abstract

Apparatus for abrasive cleaning comprises a source of compressed air, a source 14 of water, a vessel 18 in which abrasive particles are entrained in compressed air, a mixing zone 34 in which the compressed air carrying abrasive is mixed with liquid, and a compressed air driven pump 22 for pumping water to the mixing zone. The mixing zone is connected to an outlet nozzle by means of a pipeline along which the compressed air/ abrasive/water mixture is passed. The mixing zone is therefore remote from the outlet nozzle, ensuring a homogeneous mix of compressed air with water and abrasive. The water is pumped by a pump which is driven from the common compressed air source, allowing the relative proportions of water and air/abrasive mixture to remain substantially constant despite fluctuations in the air supply. <IMAGE>

Description

SPECIFICATION Abrasive cleaning This invention relates to apparatus for abrasive cleaning employing an abrasive suspended in a liquid medium.

Sand blasting or grit blasting systems are commonly used where it is desired to clean such items as rusted steelwork or stone buildings which have become grimy with age. Grit blasting is normally carried,out by feeding the grit or other abrasive to a nozzle where it is blasted towards the item to be cleaned by means of compressed air. Such systems are effective but the dust produced is disadvantageous both from the point of view of inhalation by the operatives, and, where a building has been cleaned, from the possibility of dust finding its way into the building where it is both a nuisance and can be damaging to sensitive machinery or equipment.

In an effort to overcome this, systems have been proposed in which the abrasive is entrained in a liquid, usually water. Such systems fall into two general types: venturi systems, in which water at extremely high pressure (greater than 7,000 psig) entrains the abrasive article by means of a venturi; and modified air systems in which an air grit blasting system has an additional feed carrying water to the blasting nozzle where it is mixed with the air/grit mixture immediately before leaving the nozzle directed to the articles to be cleaned. The modified air blasting system does not give very good mixing of the water with the grit and it is difficult to control the relative proportions of water, air and abrasive. The venturi system is better in these respects, but requires very high pressure systems and is thus costly.

The invention seeks to provide an apparatus for abrasive blasting in a liquid medium which employs a relatively low pressure system and which is capable of maintaining accurately known relative proportions of materials employed with good mixing.

According to the present invention, there is provided an apparatus for abrasive cleaning which comprises a source of compressed air, a source of water, a vessel in which abrasive articles are entrained in compressed air, a mixing zone in which the compressed air carrying abrasive is mixed with liquid, and a compressed air driven pump for pumping water to the mixing zone.

From the mixing zone the compressed air/ abrasive/water mixture is taken via a pipeline to an outlet nozzle where it can be directed at an item to be cleaned. Having the water supply pumped by a compressed air motor means that, if fluctuations occur in the compressed air supply, these affect equally air/ abrasive mixture and the water so that the relative proportions are unaffected by fluctuations in the supply.

By ensuring that the mixing zone is remote from the output nozzle a homogeneous mix of compressed air with the abrasive and water is obtained which in turn leads to very much better cleaning performance. While the utility of the invention in no way depends on the correctness of the theory, it is believed that the abrasive entrained in the liquid is carried a greater distance over the surface of the article to be cleaned rather than bouncing directly off it and thus the action of the abrasive is enhanced. Consequently, it is possibie to produce the same cleaning action with smaller quantities of abrasive by using the apparatus of the invention.

If desired, chemicals may be added to the water before mixing with the compressed air and abrasive. For example rust inhibitors are often employed when the item to be cleaned is made of iron or steel. Preferably, the chemical is supplied from a separate tank and pump geared to the main water supply pump so that the proportion of chemical in the water supply remains constant despite fluctuations in compressed air pressure.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic plan view of part of apparatus constructed according to the invention; Figure 2 is a diagrammatic plan view of another part of apparatus according to the invention of which part is shown in Fig. 1; and Figure 3 is a side elevational view of the apparatus essentially as shown in Figs. 1 and 2.

Referring to the drawings, the apparatus generally designated 10 comprises a container within which is mounted a water tank 1 2 connected to a water supply by means of a pipe 1 4 through a ball cock arrangement 1 6 so as to maintain a constant head of water within the tank 1 2. A grit vessel 1 8 is also mounted within the container and this is supplied with compressed air from an external source via an air receiver 20 which serves as a reservoir and also smooths small fluctuations in the pressure of the air supply. The vessel 1 8 blends compressed air and grit in a known manner and may indeed comprise a commercially available abrasive blast cleaning machine "pot" such as a Hodge Clemco type scw 2040.

Water from the tank 1 2 is fed to a water pump 22 operated by a compressed air motor 24 fed from the same air supply. A chemical tank 26 is provided which can, if desired, contain a chemical additive in concentrated solution. An agitator motor 28 is provided also driven from the same compressed air supply. Chemical additive is pumped from the chemical tank 26 via a pump 30 geared to the same compressed air motor 24 that drives the main water pump 22. This ensures that the relative proportions of the chemical solution and water remain constant despite fluctuations in air pressure. The water supply and chemical solution are mixed at a Y fork 32.

The output of abrasive/air from the grit vessel 18 and the water from the pump 22 (together with the chemical solution from the pump 30 if desired) are mixed together at a mixing zone which in this case comprises Y tube 34. From the Y tube 34 the air/water/chemical/abrasive mixture is taken along a flexible pipe or tube to an outlet nozzle under the control of the operative.

If, for any purpose, it is desired to revert to conventional air blasting, this is simply achieved by shutting off an isolating valve 36 in the water supply line. A pressure relief valve 38 ensures that the water carrying part of the system is not subject to excess pressure.

In the grit vessel employed, control of the compressed air feed to the vessel is accomplished through a valve arrangement 40 connected to a "dead mans handle" on the operating nozzle. Should the operative release the dead mans handle, the air supply to the grit vessel is discontinued. It is a feature of the apparatus of the present invention that the air supply to the compressed air motor which drives the water pump 22 is down-stream of the valve arrangement 40 so that operation of the dead mans handle cuts off both the supply af compressed air and abrasive and the supply of water on operation.

It has been found that the cleaning efficiency of the apparatus of the invention is extremely high and that less abrasive can be used for a given operation than hitherto.

Furthermore for most purposes the abrasive used may comprise ordinary sand rather than the more expensive abrasive grits available.

The operation of the apparatus entirely by compressed air enables it to be used in hazardous areas, for example petroleum plants where internal combustion or electric motors would not be allowable. Furthermore, since the air, grit, chemical and water supply are all controlled by the same compressed air source, while fluctuations in the pressure of this source will effect the speed of output, the relative proportions of the components will not be effected thereby giving an accurately known mixture.

Apart from the savings gained through being able to use sand fillers prior to grits, the bulk volume of grit consumed is very much lower for a given job than with conventional grit blasting machines of similar capacity.

The relative capacities of the pumps 22 and 30 should be geared to the desired concentration of chemical required in the water flow.

and the concentration of chemical solution within the tank 26. A typical ratio between the volumes pumped by the pumps 22 and 30 would be 100 to 1. The apparatus is designed to be used with a compressed air supply of up to 1 25 pounds psi and in normal use would operate at an air pressure of 100 pounds psi and a water pressure of 105 pounds psi. Relief valves are normally set at 5 pounds psi above these pressures.

If the machine is not being used for a short while, for example during meal breaks, there is a sufficient reservoir of air within the air receiver 20 to continue operating the compressed air driven agitator motor 28, thus ensuring that any chemicals within the tank 26 do not settle out during meal breaks.

Claims

1. Apparatus for abrasive cleaning, the apparatus comprising a source of compressed air, and a source of water, the compressed air source being connected to a vessel in which abrasive particles are entrained in the compressed air, an outlet from the vessel leading from the vessel to a mixing zone, in which the compressed air carrying abrasive is mixed with liquid, a pump for pumping liquid to the mixing zone, the pump being driven by compressed air from the said source, and an outlet nozzle connected to the mixing zone by a pipeline, the nozzle being adapted to direct the abrasive/compressed air/liquid mixture at an item to be cleaned.

2. Apparatus according to claim 1 in which the mixing zone is remote from the outlet nozzle.

3. Apparatus according to claim 1 in which the compressed air driven liquid pump is positive displacement metering pump.

4. Apparatus according to claim 1 in which there is also provided one or more tanks, each for containing a chemical, the or each tank is connected to the mixing zone by means of a pipeline, and in which a pump for pumping the or each chemical to the mixing zone is connected to the main liquid supply pump so that proportion of the or each chemical in the liquid supply remains substantially constant.

5. Apparatus according to claim 4 in which each pump for pumping the chemicals is a compressed air driven positive displacement metering pump.

6. Apparatus according to claim 5 in which each pump forms part of a multiplex pump set having separate pumps for the liquid supply and for the or each chemical.

7. A method of abrasive cleaning in which abrasive particles are entrained in compressed air from a source of compressed air, passed along a pipeline to a mixing zone where they are mixed with a liquid, the liquid being supplied to the mixing zone by means of pump driven by compressed air from the said source, and the liquid/abrasive/compressed air mixture is passed from the said zone to an outlet nozzle and thence onto an item to be cleaned.

8. A method according to claim 7 in which the liquid comprises water and one or more chemicals.

9. A method according to claim 8 in which the chemicals are rust inhibitors or detergents.

1 0. A method according to claim 9 in which the liquid comprises water and one or more chemicals, the water and the or each chemical being pumped each from separate tanks by a part of a multiplex compressed air driven positive displacement metering pump set.