IMPROVEMENTS RELATING TO CUTTING APPARATUS

Abstract: The invention provides cutting apparatus which is in the nature of a high pressure jet cutter. Water (16) at high pressure is supplied to a mixing head (14) and also supplied to the mixing head is a suspension (18) including abrasive particles, the particles being held in the suspension. The respective components are fed to a mixing head at different speeds, the water at high speed and the abrasive suspension at slow speed. The suspension is accelerated to match the water speed in the mixing head to ensure mixing. The advantage of the arrangemet is that if the supply of materials to the jet cutter is stopped, the abrasive particles remain in suspension and do not settle out so that the apparatus can be restarted without difficulty. The invention also provides a mixing head enabling the above to be achieved.

Description: IMPROVEMENTS RELATING TO CUTTING APPARATUS This invention relates to cutting or abrading apparatus, and relates specifically to a jet cutting or abrading apparatus wherein a cutting fluid comprising a liquid carrier and abrasive is jetted in a fine stream to act as a cutting lance for cutting, for example, rigid sheet materials. A " particular application for the present invention comprises the cutting of linings of pipes (such as underground sewers) where such linings block connections between lateral connecting pipes and the main sewer. The invention may also be used for cutting obstructions in pipes. It is known for example from British Patent No. 1449455 to line a sewer to repair or rehabilitate same using soft flexible lining material which is in the nature of a fibrous felt impregnated with a curable synthetic resin. The lining tube is applied to the sewer surface and is then held in position until the resin cures to a hard condition froming a rigid lining pipe. In this process, the lining tube must be applied over the lateral connecting pipes, and these laterals must re re¬ opened using a cutting means which is placed in the lined pipe. The cutting apparatus of the present invention is particularly suitable for this cutting operation in that the fine high pressure cutting jet can be used to cut a "coupon" from the lining in register with the lateral connection to be re-established by appropriate manipulation of the cutting jet. According to the present invention there is provided a method of high pressure jet cutting comprising feeding high pressure liquid carrier and an abrasive composition comprising abrasive particles in suspension to a mixing head, delivering the resulting mixture to a nozzle from which said issues as a high pressure cutting jet or jets. , The carrier fluid preferably is water at a pressure in the order of up to 4,000 psi. It is known that water jet cutting can be enhanced if abrasive particles such as sand particles can be entrained in the water, and this has already been proposed according to one arrangement as disclosed in European patent no. 0 152 223. In the said European patent, it is proposed to carry the abrasive particles to the nozzle along a separate supply line, and using air as a carrier medium to transport the abrasive particles. Immediately prior to mixing of the abrasive particles with the water at a mixing head, the carrying air and sand are separated, the air being vented, and the sand being carried through to the mixing head to mix with the water to become entrained therein and the mixture is expelled from a nozzle. This system works satisfactorily, but if there is failure of the air supply, the sand simply settles in the supply tube and is not satisfactorily taken up by the nozzle head. The present invention provides for the delivery of abrasive particles to the mixing head, in a fluent medium of such as to form with the abrasive particles a suspension in which the abrasive particles are suspended in such a fashion that if there is failure in the supply pressure delivering the mixture to the nozzle head, the particles will not fall out of suspension. This arrangement also has the considerable advantage that the supply of the abrasive composition can be stopped and restarted without any deleterious effects. It will be understood therefore that if there is a failure of the pressure supplying the mixture to .the nozzle head, even if this is a negative inducing pressure, " the mixture will simply remain in the supply line with the particles in suspension until such times as the pressure is re-established, when the mixture will be carried forward to the nozzle head as if there had been no breakdown in the supply pressure. Typically, the abrasive material may be sand, and a suitable fluent material for suspending sand is water with a thickening thixotropic agent. The mixture may be drawn into the high pressure water at the mixing head by virtue of venturi action. Preferably, . the abrasive composition is delivered at a slower speed than the water to the mixing head, but at said mixing head the abrasive composition is acceletated up to the speed of the water so that there is effective mixing, for delivery to the nozzle. Preferably, the ratio of the throat restrictor for the abrasive compositions to that for the water, at the mixing head, as in the order of 3:20. The abrasive composition is preferably delivered to the mixing- head by a twin piston pump arrangement the pistons being connected in a back to back or push-pull configuration. The water may be delivered by means of a high pressure water pump. The instant invention is also concerned with the apparatus for providing the fluid cutting jet, and also in accordance with the present invention, a high- pressure fluid cutting jet apparatus comprised an outlet nozzle for the jet, means supplying a carrier liquid under pressure to the nozzle and means for supplying a fluent composition comprising or containing the abrasive particles in suspension to said jet so that the liquid and composition mix in a ' mixing head to form the final cutting jet, said means for supplying the fluent composition comprising a pump means driven by the pressure of the carrier liquid. The said pump means preferably comprises a pair of piston pumps arranged back to back so as to have a common piston rod, with appropriate valving providing that the pressurised carrier liquid is applied alternately to the crown side of the piston of each pump, whilst the fluent composition is pumped by the rod side of the respective piston pumps and alternately, thereby to provide augmentation of the pressure in the fluent composition. The fluent composition is preferably supplied to the mixing head through a passage which is a fraction of the area of the passage through which the carrier liquid is supplied in order that the carrier liquid can be applied in substantially greater volume to the jet than the fluent composition, but so that the composition and carrier liquid are supplied to the jet at substantially the same velocity in order to ensure homogenous mixing of carrier liquid and fluent composition. The apparatus may embody a control shuttle valve controlling the supply of the carrier liquid under pressure to the alternate piston pumps, so that as one pump is pressurised, the other is exhausted, the shuttle valve being switched by a means coupled to the said common piston rod, and the outlets from the crown sides of the piston pumps being provided with appropriate one¬ way valves to ensure that as fluent composition is being pumped from one of said rod sides to the nozzle, the other is drawing in a fresh supply of the fluent composition ready to be charged to the nozzle at the next stroke of that pump. The mixing head and nozzle may be as set forth in British Patent Application No. 9009072.1. Embodiments of the present invention will now be described by way of example, with reference to the accompanying diagrammatic drawings, wherein:- Fig. 1 is a ciruit diagram of the hydraulic circuit of apparatus according to a first embodiment of the present invention; Fig. 2 is a view of an apparatus according to a second embodiment of the invention. Referring to Fig. 1, the hydraulic circuit of the apparatus according to the embodiment of the invention comprises a water tank 10, water forming the pressurised liquid component of the system, a tank 12 for the composition of carrier matrix and abrasive, and a mixing head 14 to which a pressurised water line 16 and a pressurised fluent composition line 18 lead so that in the head 14, pressurised water and fluent material under pressure are mixed and together then pass along pipe 15 to an outlet nozzle 14A from which 14A and head 14 may be combined into a single unit to perform the cutting operation. The water travels in line 16 at greater speed than the composition in line 18 but in the head 14 are restrictors x and y for the composition flow and water flow in order to ensure that the composition and water meet at substantially the same velocity. Suitably, the composition restrictor x may be 3/20ths of the cross- sectional area of the water restrictor y. The water is drawn from tank 10 by means of a pump 22 which may supply water at 21 litres per minute at a pressure in the order of 2,000 psi. The output line 24 from the pump 22 leads directly to the nozzle 14, but also has a branch line 26 containing a flow control valve 28 to divert say in the order of 3 litres per minute through a shuttle valve 30 depending upon its position as • will be explained hereinafter. The fluent composition is drawn from the tank 12 to either one of a pair of pumps 32, 34 which comprise piston and cylinder devices, and the pistons 36, 38 are arranged on a common piston rod 40 so that pumps 32 and 34 are arranged back to back. A centralising spring arrangement serves to bias the piston rod to the centralised position shown in Fig. 1. The composition is drawn from the tank 12 through a line 44 and either of two non-return valves 46, 48 in lines 50, 52 leading to the rod sides of pumps 32 and 34. Two outlet pipes from pumps 32 and 34 indicated by reference numerals 54 and 56 contain non-return valves 58 and 60 and lead to an outlet line 62 which in turn couples with the fluent composition outlet pipe 18. Operation of the apparatus of Fig. 1 will be understood from the above. When the apparatus is operational, the pistons 36 and 38 will be displaced back and forth in the pumps 32 and 34 and will operate the shuttle valve 30. Assume that the shuttle valve 30 is to the right- hand side of the blocking position shown in Fig. 2. In this case high pressure water from the pump 22 is charged into the crown end of pump 34 displacing the piston 38 to the right of Fig. 2 and forcing the composition in the rod side of the piston through line 52, valve 60, line 56 and line 62 to the nozzle 14. At the same time high pressure water is pumped via the line 24 to the nozzle 14. As regards the pump 32 during this operation, water on the crown side of the piston 36 is forced through line 64 and the shuttle valve 30 to a return line 66 so that the water is returned to the tank, and at the same time a fresh supply of the fluent composition is drawn from tank 12 through line 44, valve 46 and line 50 into the rod side of the pump. The piston pair moves to the left until a detent on the rod 40 engages an operating leg of the shuttle valve displacing the shuttle valve to its extreme right hand position in which piston 32 and the movement of the piston assembly reverses so that the fluent composition im pump 32 is now discharged through line 50 of valve 58 and into line 62. A continuous supply of the fluent composition and water through nozzle is therefore ensured, but the system can be stopped by stopping the pump 22. The amount of water which is used for displacing the pistons can be controlled by adjustment of the flow control valve 28.. In an embodiment of the invention in Fig. 2, the apparatus comprises a nozzle head 10X containing a nozzle outlet 12X from which the high velocity jet of water issues, the water being supplied via a high pressure water hose 14 at a pressure in the order of 3,000 P.S.I, at 4 gallons per minute. In the nozzle head 10X, the pipe 14X leads to a venturi chamber 16X which is traversed by a feed pipe 18X for the mixture of the abrasive composition. The composition is drawn in accordance with well-established venturi principles into the venturi chamber 16X in use through a small aperture 20X in the pipe 14X and facing the nozzle 12X. The abrasive composition is pumped by means of a motor 22X which drives a feed auger 24X, in a chamber 26X, to which the material is fed from a storage hopper 28X. The source of the material in hopper 28X and the source of high pressure water may be located remotely from the nozzle head 10X which typically will be loctated in the pipeline where cutting is to take place. A cross-connecting pipe 30X couples the feed pipe 18X for the composition and the water pipe 14X and contains a flushing valve 32X which is normally closed, but which can be opened when it is required to pump water through the pipe 18X in order to flush same of residual composition and/or abrasive. The composition is such that the carrier medium and the abrasive are of like density and/or specific gravity so that the abrasive particles will remain in suspension in the carrier even in the event of failure of the pump 22X. In other words a ' s in the Fig. 1 embodiment there will be minimum or no settling out of the abrasive even when the system is not operational, distinguishing the method and apparatus from the known arrangements. Various materials may be used as the abrasive compositon, depending upon the natural interval being cut, provided that the abrasive particles do not settle out of suspension too quickly (if at all) when the composition is left standing. If the particles settle out within one hour the composition being left standing, that would be considered too quick. A suitable compo'sition may comprise, by weight, the following:- a) Water 200 parts b) Sand 200 parts c) Thickening agent 8 parts d) Lubricating agent (to lubricate pump) 7 parts This composition may be mixed by weight with the water in the retes of 1 to 6 (one part composition to six parts water) .

Claims: CLAIMS 1. A method of high pressure jet cutting comprising feeding high pressure liquid carrier and an abrasive composition comprising abrasive particles in suspension to a mixing head, delivering the resulting mixture to a nozzle from which the mixture issues as a high pressure cutting jet or jets. 2. The method according to Claim 1, wherein the carried fluid is water at a pressure in the order of up to 4,000 psi. 3. A method according to Claim 1 or 2, wherein the abrasive composition comprises a mixture of water, abrasive particles and a thickening agent . 4. A method according .to any preceeding Claim, wherein the abrasive composition is delivered at a slower speed than the water to the mixing head, but at said mixing head the abrasive composition is accelerated up to the speed of the water so that there is effective mixing for delivery to the nozzle. 5. A method according to Claim 4 wherein the ratio of the throat restrictor for the abrasive composition to that for the water at the mixing head is in the order of" 3 to 20. 6. A method according to any preceeding Claim, wherein the abrasive composition is delivered to the mixing head by a twin piston pump arrangement, the pistons being connected in a back-to-back or push- pull configuration. 7. A method according to any preceeding Claim wherein the water is delivered to the mixing head by means of a high pressure water pump. 8. Apparatus for providing a high pressure cutting jet comprising an outlet nozzle for the jet, means supplying a carrier liquid under pressure to the nozzle and means for supplying a fluent composition comprising or containing abrasive particles in suspension to said jets so that the liquid and composition mix in a mixing head to form the final cutting jet, said means for supplying the fluent composition comprising a pump means driven by the pressure of the carrier liquid. 9. Apparatus according to Claim 8, wherein the pump means comprises a pair of piston pumps arranged back-to-back so as to have a common piston rod, with appropriate valving providing that the pressurised carrier liquid is applied alternatively to the crown side of the piston of each pump, whilst the fluent composition is pumped by the rod side of the respective piston pumps and alternately, thereby to provide augmentation of the pressure in the fluent composition. 10. Apparatus according to Claim 9, wherein the fluent composition is supplied to the mixing head through a passage which is a fraction of the area of the passage through which the carrier liquid is supplied in order that the carrier liquid can be applied in substanaially greater volume to the jet than the fluent composition, but so that the composition and carrier liquid are supplied to the jet at subastantially the same velocity in order to ensure homogeneous mixing of the carrier liquid and fluent composition. 11. Apparatus according to Claim 10 wherein the apparatus includes a shuttle bob controlling the supply of the carrier liquid under pressure to the alternate piston pumps, so that as one pump is pressurised, the other is exhausted, the shuttle valve being switched by means coupled to said common piston rod, and the outlets from the crown sides of the piston pumps being provided with appropriate one-way valves to ensure that as fluent composition is being pumped from one of said rod sides to the nozzle, the other is drawing in a fresh supply of the fluent composition ready to be charged to the nozzle at the next stroke of that pump. 12. A mixing head for use in the apparatus according to any Claims 8 - 11, said mixing head comprising a coupling for connection to an abrasive composition supply, and a coupling for connection to a high pressure water supply, said coupling including restrictors, the restrictor in the composition coupling being a fraction of the area of the restrictor in the water coupling.

Inventors: WOOD ERIC, WOOD, ERIC
Applicants: INSITUFORM GROUP LTD, INSITUFORM GROUP LIMITED
Application year: 1990
Main classification: B24C7
IPC codes: B24C5, B24C7