GB2056333A

GB2056333A - Wet sand blasting

Info

Publication number: GB2056333A
Application number: GB8007126A
Authority: GB
Original assignee: MYERS EUROPE PUMPEN GmbH
Current assignee: MYERS EUROPE PUMPEN GmbH
Priority date: 1979-08-22
Filing date: 1980-03-03
Publication date: 1981-03-18
Also published as: DE2934023A1; EP0025156A1

Description

SPECIFICATION Wet sand blasting The invention relates to a wet sand blasting method, in particular for underwater use, in which a mixture of water and sand is fed to a nozzle in measured quantities and emerges from the nozzle in a stream under high pressure, and to an apparatus for carrying out such a method. A method of this type is known in which dry sand is stored in a container which is connected to a nozzle via a valve and a sand supply pipe. The nozzle is connected to a high-pressure water pump which delivers a powerful jet of water and creates a reduced pressure in the sand supply pipe so that the sand is sucked out of the container. In this process the sand enters the high-pressure jet of water sufficiently evenly provided that the sand has been introduced into the container in an extremely dry state and maintained dry. In addition to the high-pressure water pump an air compressor is necessary if work is to be carried out under water at depths below 5 m. This involves considerable installation and running costs.In addition, air bubbles are fed to the nozzle with the sand and escape from the water/sand stream emitted from the nozzle during underwater work, thus considerably reducing visibility. An object of the present invention is to provide a wet sand blasting process, particularly for underwater use, which is both economic and efficient. According to the present invention there is provided a method of wet sand blasting in which a supply of sand is substantially saturated with water, the resultant sand/water mixture is introduced with the aid of gravity into a stream of water and the stream of water is then combined with a high-pressure water flow and exits through a nozzle as a high-pressure water jet. The invention utilises the known phenomenon that sand, which in a damp state conglomerates into a solid mass, tends to flow when a sufficiently large quantity of water is added to it. As used herein the term saturated is used to mean that water is added to a given quantity of sand until it can absorb substantially no more water and preferably the quantity of water is such that even the uppermost particles of sand are covered with water. In this state the sand can flow under the effect of gravity and can then be introduced into a stream of water which conveys it to a sandblasting nozzle. If the process according to the invention is to be carried out underwater, the sand can be stored underwater without any further treatment and can even, in suitable cases, be obtained on site from the seabed. Preferably the stream of water and the highpressure water jet are combined at the outlet of the said nozzle. In one embodiment of the invention the stream of water flows downwardly at the point where the sand/water mixture is introduced, and is caused to flow by a reduced pressure created in the nozzle by the high-pressure water jet. However, in an alternative embodiment the stream of water flows upwardly at the point where the sand/water mixture is introduced, and is caused to flow at least partially by the high pressure of the high-pressure water flow. The invention also embraces an apparatus for carrying out such a method including a container for preparation of a substantially saturated mixture of sand with water having at its lower end a liquid connection and containing an upwardly extending pipe through which water can flow, the pipe communicating at its lower end with the liquid connection and with the interior of the container and a nozzle connected to the liquid connection by means of a first supply pipe and to a high-pressure water pump by means of a second supply pipe, the nozzle being constructed such that, in use, a stream of water will flow through the pipe in the container carrying with it sand from the container, be mixed with the high-pressure flow from the pump and ejected in a high-pressure water jet. Preferably the lower portion of the container is conical and converges downwardly and the pipe is coaxially disposed within the lower portion. The container may include a mixing chamber with which the pipe within the container, the liquid connection and the interior of the container communicate. In one embodiment the lower end of the pipe within the container defines together with the container an annular slot through which the pipe communucates with the interior of the container. However, the communication may alternatively be through openings in the pipe itself. In both cases the cross-section of the communication between the pipe and the interior of the container can easily be adjusted by known means and thus adapted to various operating conditions and sand grain sizes. When intended for underwater use, the container is preferably open-topped and includes suspension gear by means of which it can be suspended under water from a ship, oil platform or the like so that, in use, the container will be full with sand and water. For sand blasting work under water the container can be suspended, also under water, near to the working place so that the supply pipe leading from the container to the nozzle can be relatively short and the flow losses occurring in the pipe can thus be kept small. Of the entire apparatus conveniently only the high-pressure water pump and its drive means are arranged on board the ship, the oil platform or the like. If the method is to be carried out in such a way that the stream of water at the point where the saturated sand is introduced into it flows downwards, then the upper end of the pipe in the container is preferably open-ended so that, in use underwater, water will flow downwardly through the pipe. This embodiment has the advantage of being particularly simple, above all for underwater use, since water from the surroundings enters through the upper end of the pipe and flows down the pipe without any assistance as soon as highpressure water from the second supply pipe is expelled from the nozzle and creates a reduced pressure there which then acts via the first supply pipe on the water in the pipe in the container and produces a flow of water to the nozzle. However, if the method is to be carried out in such a way that the stream of water at the point where the saturated sand is introduced into it flows upwards then preferably both the fluid connection and the upper end of the pipe within the container are connected to the nozzle such that, in use, part of the high-pressure flow from the pump flows upwardly through the pipe within the container and thence back to the nozzle. In this embodiment a supply pipe connects the upper end of the pipe within the container to the nozzle and the container has at its lower end below the mixing chamber an inlet which is connected by means of a third supply pipe to the high-pressure water pump. The additional cost of the third supply pipe is justified in many cases, primarily because it makes it possible to work with the nozzle at a location which is considerably higher than the container.At such a location the work can be interrupted without danger of a blockage in the first supply pipe. The sand which is on the way from the container to the nozzle when work is interrupted gradually sinks back down into the pipe and when work is recommenced is then carried along with the high-pressure waterflowing out of the third supply pipe through the inlet of the container. In contrast to this, in the embodiment of the invention described previously in which the water/sand mixture leaves the container downwards, if work is interrupted care must be taken that a sand blockage does not form in the first supply pipe as a result of sagging of the pipe, since such a blockage may not clear by itself when work is recommenced if the only means available for moving the sand in the first supply pipe were the reduced pressure created at the nozzle as described above. The cost of the third supply pipe, which is, therefore, justified in many cases, can be kept low since the third supply pipe does not necessarily have to be connected to the high-pressure water pump. In accordance with the invention it is sufficient for the third supply pipe to be connected to the high-pressure water pump via a gun on which the nozzle is arranged and via the second supply pipe which terminates at the gun. The quantity of water per unit of time which is fed through the third supply pipe into the mixing chamber need only be a small fraction, for example a tenth, of the quantity of water supplied to the nozzle by the second supply pipe. Further features and details of the invention will be apparent from the following description of two specific embodiments which is given by way of example, with reference to the accompanying schematic drawings, in which:- Figure 1 shows a first embodiment of apparatus in accordance with the invention for wet sand blasting under water; Figure 2 is a vertical section through part of the apparatus of Figure 1 on a greatly enlarged scale; Figure 3 is a view similar to Figure 1 of a second embodiment for sand blasting under water; Figure 4 is a vertical section through part of the apparatus of Figure 3 on a greatly enlarged scale; and Figure 5 is a still further enlarged vertical section of part of the apparatus shown in Figures 3 and 4. The apparatus shown in Figures 1 and 2 is intended to carry out sand blasting work from a ship 10 on underwater parts of a drilling rig 12, for example in order to clear those parts for nondestructive examination of mussel growth or the like. An open-topped container 20 is suspended from a derrick 14 on the ship 10 by means of a cable 16 and suspension gear 18. The container 20 has a circular section upper portion 22 and a funnel-shaped lower portion 24 connected to the lower end thereof and having an outlet 26. The outlet 26 is connected via a first supply pipe 28 comprising a conventional hose to a nozzle 30 which forms part of a blasting gun 32. The gun 32, which, in use, is held by a diver 34, has an inlet 36 to which is connected a second supply pipe 38. The second supply pipe 38 comprises a high-pressure hose and connects the gun 32 to a high-pressure water pump 40 on board the ship 10 which is driven by a motor 42. Between the inlet 36 and the nozzle 30 the gun 32 has a junction 44 to which is connected a propulsion nozzle 46 which is coaxial with the nozzle 30 but directed in the opposite direction and which, in operation, produces a reactive force which is equal to and thus balances the force produced by water leaving the nozzle 30. As shown in Figure 2, a hose connection 48 with a wear-resistant lining 50 is screwed into the outlet 26 from below. In the container 20 above the lining 50 a pipe 52 is arranged which.is vertically adjustable in a boss 54 secured to the wall of the cylindrical portion 22 and is clamped therein by'means of a screw 56 (which is merely schematically indicated) at such a height that an annular slot 60 remains between the lower end 58 of the pipe 52 and the adjacent wall of the funnelshaped portion 24 of the container 20. The pipe 52 is open both at its lower end 58 and at its upper end 62, so that water from the surroundings can flow unimpeded through the pipe. The interior space in the container 20 around the pipe 52 constitutes a storage space 64 for a supply of sand 66. The container 20 is open at the top, and because of this and the fact that the container is underwater the stock of sand 66 is permanently soaked with water. The annular slot 60 connects the storage space 64 to a mixing chamber 68 formed between the lower end 58 of the pipe and the upper end of the lining 50. A vibrator 70 may be mounted on the container 20 and connected by means of an electrical, pneumatic or hydraulic line (not shown) to the ship 10 to vibrate the container by electromechanical, pneumatic-mechanical or hydraulic-mechanical means if required, for example, to loosen the stock of sand 66 at the commencement of work. Figure 2 also shows some details of the nozzle 30 which includes a hose connection 72 screwed axially into the nozzle and connected to the hose connection 48 via the first supply pipe 28. On the other side, which in operation is the front and in Figure 2 is the upper end, a nozzle extension 74 is screwed into the nozzle 30 and between this and the hose connection 72 a nozzle insert 76 is tightly clamped. The nozzle insert 76 has an axial channel 78 which has a wear-resistant lining 80 which also extends through the hose connection 72. An annular channel 82 is formed around the nozzle insert 76 and is connected to the inlet 36 via an angled pipe 84 and the junction 44 and to the interior of the nozzle extension 74 by several generally axially extending channels 86. The channels 86 are regularly arranged around the axis of the nozzle 30 and converge at an acute angle. When water supplied from the high-pressure water pump 40 on the boat reaches the nozzle 30 via the bent pipe 84 and emerges from the annular channel 82 through the channels 86 in strong jets, a reduced pressure is formed in the interior of the nozzle extension 74 around the axial channel 78, and this is transmitted via the first supply pipe 28 to the mixing chamber 68 and results in water being sucked from the surroundings above the container through the pipe 52 and into the mixing chamber 68. This flow of water assists the effect of gravity acting on the saturated supply of sand 66 which therefore flows out of the storage space 64 through the annular slot 60 and into the mixing chamber 68 in a metered quantity per unit time.A water/sand mixture is formed in the mixing chamber, and this passes through the lining 50, the first supply pipe 28 and the lining 80 to reach the nozzle extension 74 and is then carried along with the jets of water emerging at high pressure from the channels 86. These jets of water combine at the free end of the nozzle extension 74 into one common jet 88 which is indicated in Figure 1. The apparatus shown in Figures 3 to 5 has numerous components which are the same as those described with reference to Figures 1 and 2 and these are designated by the same reference numerals. Those components which are equivalent to components in Figures 1 and 2 are designated in Figures 3 to 5 by the same reference numerals with a prime. In the embodiment shown in Figures 3 to 5 the container 20 has at its lower end, instead of the outlet 26 shown in Figures 1 and 2, an inlet 90 which is connected via a third supply pipe 92 to an additional junction 44' on the gun 32, which junction is in turn connected via the first supply pipe 38 to the high-pressure water pump 40. The inlet 90 defines the bottom of the mixing chamber 68 and contains a water-jet nozzle 94 which is arranged in the middle of the mixing chamber 68 and directed axially upwards. A hollow cylindrical spacer 98 is fixed around the inlet 90 with grub screws 96 and extends upwards surrounding the mixing chamber 68 and carries a Venturi tube 100. The Venturi tube 100 is arranged coaxially with the water-jet nozzle 94 and the spacer 98 and defines the top of the mixing chamber 68. In the apparatus shown in Figures 3 to 5 the vertical pipe 52 is also arranged inside the container 20, and as shown in Figures 4 and 5 this pipe is rotatably slid onto the cylindrical outer surface of the spacer 98 and/or the Venturi tube 100. The grub screws 96 extend through slots 102 extending in the peripheral direction in the pipe 52 so that the pipe is free to rotate through a predetermined angle, but can only be withdrawn from the container 20 together with the inlet 90. Instead of the annular slot 60 shown in Figure 2, holes 60' are provided in the pipe 52 and in the spacer 98, and these holes are aligned with each other in pairs as shown in Figure 5 and define a limited cross-sectional area connecting the storage space 64 to the mixing chamber 68. This cross-section can be reduced by rotation of the pipe 52 and can even be completely closed, which is of value when work is interrupted, for. example in order to refill the storage space 64. In order to rotate the pipe 52 a spoked wheel 104 is mounted on its upper end as shown in Figure 4, centred within the inner surface of the upper portion 22 of the container 20 and adapted to be clamped in position by a clamping screw 106 (which is illustrated schematically). The vertical pipe 52 may also be vertically adjustable as described in connection with Figure 2 in order either to leave open or partially or completely obstruct the holes 60' with its lower end. Secured around the Venturi tube 100 is a supply pipe 28' which corresponds to the first supply pipe 28 in Figures 1 and 2 since it leads to the nozzle 30 in the same manner as the supply pipe 28 and has the function of delivering the water/sand mixture formed in the mixing chamber 68 to the nozzle 30. The supply pipe 28' may be connected to the upper end of the pipe 52, however, in the preferred embodiment the supply pipe 28' is mounted on the Venturi tube 100 as shown in Figures 4 and 5, for example with a hose clip 108, since this facilitates adjustment of the pipe 52. In both embodiments the gun 32 has a trigger 110 with which a diver 34 can open an inlet valve 112 which is biased in the closing direction. This arrangement is shown schematically in Figure 4 to make it clear that in the embodiment shown in Figures 3 to 5 the junction 44' (like the branch pipe 44) is arranged between the inlet valve 112 and the nozzle 30. In use, water flows under high pressure through the third supply pipe 92 into the mixing chamber 68 only when a high-pressure stream of water simultaneously reaches the nozzle 30 through the bent pipe 84 and emerges through the channels 86 in powerful jets. The cross-sections of the supply pipes are of such dimensions that the quantity of water emerging through the water-jet nozzle 94 per unit of time amounts to approximately 10% of the quantity of water emerging through the channels 86. The stream of water from the water-jet nozzle 94 flows through the Venturi tube 100 and creates a reduced pressure which causes the water/sand mixture to be sucked out of the storage space 64 into the mixing chamber 68 whence it is carried along into the supply pipe 28' to the nozzle 30.

Claims

1. A method of wet sand blasting in which a supply of sand is substantially saturated with water, the resultant sand/water mixture is introduced with the aid of gravity into a stream of water and the stream of water is then combined with a high-pressure water flow and exits through a nozzle as a high-pressure water jet.

2. A method as claimed in Claim 1 in which the stream of water and the high-pressure water jet are combined at the outlet of the said nozzle.

3. A method as claimed in Claim 1 or Claim 2 which is carried out under water.

4. A method as claimed in any one of the preceding claims in which the stream of water flows downwardly at the point where the sand/water mixture is introduced, and is caused to flow by a reduced pressure created in the nozzle by the high-pressure water jet.

5. A method as claimed in any one of Claims 1 to 3 in which the stream of water flows upwardly at the point where the sand/water mixture is introduced, and is caused to flow at least partially by the high pressure of the high-pressure water flow.

6. A method of wet sand blasting substantially as specifically herein described with reference to Figures 1 and 2 or Figures 3, 4 and 5 of the accompanying drawings.

7. Apparatus for wet sand blasting including a container for preparation of a substantially saturated mixture of sand with water having at its lower end a liquid connection and containing an upwardly extending pipe through which water can flow, the pipe communicating at its lower end with the liquid connection and with the interior of the container and a nozzle connected to the liquid connection by means of a first supply pipe and to a high-pressure water pump by means of a second supply pipe, the nozzle being constructed such that, in use, a stream of water will flow through the pipe in the container carrying with it sand from the container, be mixed with the high-pressure flow from the pump and ejected in a high-pressure water jet.

8. Apparatus as claimed in Claim 7 in which the lower portion of the container is conical and converges downwardly and the pipe is coaxially disposed within the lower portion.

9. Apparatus as claimed in Claim 7 or Claim 8 including a mixing chamber with which the pipe within the container, the liquid connection and the interior of the container communicate.

10. Apparatus as claimed in any one of Claims 7 to 9 in which the lower end of the pipe within the container defines together with the container an annular slot through which the pipe communicates with the interior of the container.

11. Apparatus as claimed in any one of Claims 7 to 10 for underwater use in which the container is open-topped and includes suspension gear by means of which it can be suspended under water from a ship, oil platform or the like so that, in use, the container will be full with sand and water.

12. Apparatus as claimed in any one of Claims 7 to 11 in which the upper end of the pipe within the container is open, so that in use underwater, water will flow downwardly through the pipe.

13. Apparatus as claimed in any one of Claims 7 to 11 in which the fluid connection and the upper end of the pipe within the container are connected to the nozzle such that, in use, part of the high-pressure flow from the pump flows upwardly through the pipe within the container and thence back to the nozzle.

14. Apparatus for wet sand blasting substantiaHy as specifically herein described with reference to Figures 1 and 2 or Figures 3, 4 and 5 of the accompanying drawings.