GB2135917A - Apparatus and method for shot blasting - Google Patents

Abstract

A transport vehicle (1) carries a shot material reservoir (3, 4) having a shot-material outlet at the bottom. A source of compressed air (2) is conveyed by a conduit arrangement for supplying the air to a shot-blasting nozzle (12, 13) together with shot material collected from the outlet. The size of said reservoir is such that it can accommodate an amount of shot-material at least sufficient to supply the nozzle with said mixture for a period of at least four hours. Control valves (10, 11) for the compressed air and shot-material are remotely actuated by a handle (16, 17) on the nozzle (12, 13).

Description

SPECIFICATION Apparatus and method for shot blasting The present invention relates to shot blasting.

Shot blasting involves directing a shot material entrained in a jet of air on to a surface to be treated and is used in various applications, for example the removal of paint, dirt or corrosion products (e.g.

rust). The most commonly used shot material is sand, and another material is copper slag. The choice depends upon the particular application and is well understood in the art.

Besides being used in factories, shot blasting is also applied to the on-site treatment of structures as, or as the first step of, a renovation operation. Objects of the present invention are to provide improved appratus for, and an improved method of, such on-site use.

In accordance with the present invention, there is provided apparatus for shot blasting which comprises a transport vehicle having positioned thereon a shot-material reservoir, a shot-material outlet at the bottom region of said reservoir, a source of compressed air and conduit means adapted and arranged for conveying a flow of compressed air from said source to a shot-blasting nozzle whilst collecting shot material from said outlet so that said nozzle is supplied with a shot blasting mixture of air and shot material, the size of said reservoir being such that it can accommodate an amount of shotmaterial at least sufficient to supply the nozzle with said mixture for a period of at least four hours.

On-site shot blasting has heretofore been carried out using portable equipment. In a typical case the reservoir holds a supply of shot material sufficient for 20 minutes of blasting. When this reservoir is exhausted it is de-pressurized and refilled manually, usually from a sack. The resulting interruptions of the blasting operation account for a loss of on-site time of as much as 60% and an economically significant proportion of the sand or other shot material is lost by spillage. With the present apparatus, the interruptions are reduced subtantially with consequent saving. In addition, the intervals of four hours or more between refilling operations enable the refilling to be done in the form of mechanised filling from a supply tanker with substantial elimination of loss by spillage.It is not necessary for the tanker to remain on or in the neighbourhood of the working site, as would be necessary for refilling at intervals of 20 minutes or other short duration.

In practice the reservoir may be made much larger than is required to give a four hour working period, a reservoir of such volume as to accommodate at least 4000 Kg of sand (or substantially 5300 Kg of copper slag which is more dense than sand) being preferred.

According to a preferred arrangement the transport vehicle has at least four driving wheels and is advantageously a low-load truck or low-load vehicle of the articulated type. Such vehicles can be driven to the majority of working sites, including sites at a distance from a roadway.

It is found that best results are obtained by having a pair of reservoirs mounted on the vehicle. They are readily accommodated within the rectangular loading space and can be (a) of such volume as to hold a supply of the shot material which is large and yet within the load capacity of suitable available vehicles and (b) also of a height which gives reasonable centres of gravity and does not interfere substantially with the passage of the vehicle under bridges.

Advantageously, the or each reservoir is provided with valve means for halting the flow of the compressed air at a position upstream of the outlet of the or each reservoir. It happens in practice that a blockage can occur in the flow of the sand or other shot material from a reservoir to the conduit means aforesaid. Halting the flow of compressed air to the shot-material outlet of the reservoir, at least assists the clearance of the blockage especially if the reservoir is of the pressu rised type and the flow of compressed air thereto is maintained. An especially useful arrangement is to have the valve means provided with a remotely operable actuator.When, as preferred, the actuator is mounted with the blasting nozzle or otherwise so mounted as to be accessible to the operator at the blasting site, the clearance of most blockages can be effected with little loss of blasting time.

The following description in which reference is made to the accompanying diagrammatic drawings is given in order to illustrate the invention. In the drawings: Figure 1 is a side elevation of an embodiment of an apparatus provided in accordance with the invention, Figure 2 shows a modification of the apparatus of Figure 1, Figure 3 shows part of the apparatus of Figures 1 and 2 in further detail, and Figure 4 is a cross-section showing the form of remote-controlled valves employed in the apparatus.

In Figure 1, a 6-wheeled vehicle 1 with all wheels driven has permanently mounted thereon a pair of diesel engined air-compressors 2 each giving an ouput of 250 cubic feet (7 cubic metres) per minute.

Two shot material reservoirs 3 and 4 are mounted on the low-loader platform 5 of the vehicle. Each reservoir has a volume sufficient to hold 8000 Kg. of sand. A conduit system 6 is provided for pressurising the reservoirs via remotely actuated valve devices 7 & 8. A second conduit system 9 with remotely actuated devices 10 & 11 provides an air supply to one or both of a pair of shot blasting nozzles 12 & 13 via pick-up arrangements of conventional design, positioned at the bottoms of the reservoirs, for feeding the sand or other shot material to flexible connectors 14 & 15 and thence to the nozzles 12 & BR< 13. Valve levers 16 & 17 on the nozzles open valves 10 and 11 when released by the operator thereof. An electrical or pneumatic system, not shown, links these levers with their valves.

Using sand as the shot material, the sand content of the stream ejected from a nozzle on to the surface 18 to be treated typically has a sand content of 10% by volume and a velocity of the order of 200 Km per hour.

For typical blasting operations, the reservoirs require replenishment only at intervals of 10 mandays. In a modified form of the apparatus, each reservoir is divided internally into two parts, each of which communicates with a nozzle. With the two nozzles operated by a pair of operators, replenishment is required at 5 man-day intervals.

Replenishment of the reservoir is by a tanker vehicle specially driven to the site, only a small fraction of the tanker's available operational time being required for this purpose.

Examples of surfaces which can be treated with the apparatus are the exterior surfaces of gas-holers and cargo containers of the kind carried by container ships.

The shot blasting operation can be commenced, without significant delay, upon arrival of the vehicle with the reservoirs already containing the sand or other shot material. It is not necessary for the loading to be complete. Thus a residual load from another working site can be employed, at least for starting the blasting operation.

Having a multi-sheel drive on the vehicle gives useful access to working sites over a wide range of terrains, virtually independently of the weather.

Wastage such as occurs in manual filling is substantially avoided. Also avoided is the cost of sacks or other packaging provided for manual filling.

Figure 2 shows a reservoir 116 which replaces the reservoirs 3 & 4 of Figure 1. Each of these reservoirs has a manhole arrangement 17 and a tubular shot material entrance 18 with a cover 19 which is removable for connection of a supply conduit 20 for shot material 21.

Entrance 18 is fitted after supplying the shot material with a silica gell cartridge 22 for the absorption of moisture during periods when the filled reservoir is not in use.

An air compressor 2 supplies a conduit 23 provided with a non-return valve 24. A branch conduit 25 supplies compressed air to reservoir 116 via a branch 26 beyond which the conduit has an extension fitted with a pressure relief valve 27 which is opened manually in preparation for filling the reservoir. Advantageously, valve 27 is provided in combination with a pressure gauge.

Beyond branch conduit 25, conduit 23 extends to shot nozzle 12a. Shot material is collected from reservoir 116 via a passageway 28 positioned downstream of a constriction 29.

Mounted in an assembly with nozzle 12a is a valve 30 operable by a handle 1 6a and shown in further detail in Figure 3. Valve 30 has an internal air passageway 31 leading to a port 32. A handle 16, pivotally mounted at 33 carries a rubber gromet 34 which is brought into sealing arrangement with port 32 by the blasting operator at his working position.

Air at two atmospheres pressure above atmosphere is supplied to valve 30 by a flexible tube 35 connected with an inlet 36. This tube leads from a manifold 37 fed from conduit 23 via a regulator 38, positioned as shown, and a line 39. A branch 40 controls a shot delivery valve 41 which is closed to prevent the passage of shot material in the absence of an air flow through conduit 23.

Another branch, 41 of line 39 leads to manifold 37 via a two-way valve arrangement 42 which diverts the flow from the compressor via an outlet 43 to atmosphere in the absence of a pressure build-up produced by closure of valve 30. Also connected with manifold 37 is a line 38 leading via a valve 44.

The pneumatic arrangements prevent the supply of compressed air to the reservoir or nozzle 12a when handle 16a is released.

For optimum safety of operation those parts of the apparatus controlled by the handle 16a preferably function to permit the shot blasting only when the pressure in the control system exceeds a minimum, e.g. one atmosphere (i.e. two atmospheres absolute).

The form of the remote-controlled valves, such as valve 38 is shown in Figure 4. A rubber hose part 50, which may be part of the conduit itself, has metal components 51 and 52 secured on opposite sides.

Component 52 is formed with an apex part 53 shaped to provide a recess 54. A plunger 55 extends into recess 54 from a pneumatic actuator 56 of the diaphragm type and holds hose part 50 pinched to a fully closed state by component 52 except when an opening pressure is received by a controi line such as line 39.

It will be understood that the foregoing description is given by way of example only and that various departures from the apparatus and its method of use can be made by those skilled in the art without departing from the ambit of the invention claimed.

Claims (16)

1. Apparatus for shot blasting which comprises a transport vehicle having positioned thereon a shotmaterial reservoir, a shot-material outlet at the bottom region of said reservoir, a source of compressed air and conduit means adapted and arranged for conveying a flow of compressed air from said source to a shot-blasting nozzle whilst collecting shot material from said outlet so that said nozzle is supplied with a shot blasting mixture of air and shot-material, the size of said reservoir being such that it can accommodate an amount of shotmaterial at least sufficient to supply the nozzle with said mixture for a period of at least four hours.

2. Apparatus according to Claim 1 in which said reservoir is of such volume as to accommodate at least 4000 Kg of sand.

3. Apparatus according to either of Claims 1 or 2 having a valve means for halting the flow of the compressed air at a position up-stream of the outlet of the or each reservoir.

4. Apparatus according to Claim 3 in which said valve means is provided with a remotely operable actuator.

5. Apparatus according to Claim 4 in which said actuator is so mounted as to be accessible to the operator at the blasting site.

6. Apparatus according to Claim 5 in which said actuator is mounted with the blasting nozzle.

7. Apparatus according to any one of Claims 1 to 6 in which said reservoir is a pressure vessel and is arranged to be pressurized by said source of com pressed air.

8. Apparatus according to any of Claims 1 to 7 in which said reservoir is one of a set of reservoirs positioned on the vehicle.

9. Apparatus according to Claim 8 in which said reservoir is one of a pair of reservoirs positioned on the vehicle.

10. Apparatus according to any one of Claims 1 to 9 in which the reservoirs are of such size as to accommodate at least 7000 Kg of sand.

11. Apparatus according to any one of Claims 1 to lOin which said transport vehicle has at least four driving wheels.

12. Apparatus according to any one of Claims 1 to 11 in which the vehicle is a low-load truck or a low load vehicle of the articulated type.

13. Apparatus for shot blasting substantially as hereinbefore described and illustrated by reference to the accompanying drawings.

14. A method of shot blasting an installation in which apparatus according to any one of Claims 1 to 13 is driven to the site of the installation with the reservoir or reservoirs loaded with the shot material.

15. A method of shot blasting an installation substantially as hereinbefore described and illustrated by reference to the accompanying drawings.

16. An installation when treated by shot blasting buy a method according to either of Claims 14 or 15.