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Abrasive Water Suspension Jet (AWSJ) cutting
The Abrasive Water Suspension Jet (AWSJ) - often called “Slurry Jet” or “Water Abrasive Suspension (WAS) jet” - is a specific type of the abrasive water jet, which is used for waterjet cutting. In contrast to the abrasive water injector jet (AWIJ), the abrasive water suspension jet (AWSJ) is characterised by the fact that the mixing of abrasive and water takes place before the nozzle. This has the effect that, in contrast to AWIJ, the jet consists of only two components (water - abrasive).

Since there are only 2 components (water and abrasive) in the AWSJ, the acceleration of the abrasive grains by the water takes place with a significantly increased efficiency compared to the AWIJ. The abrasive grains become faster with the WASS than with the WAIS for the same hydraulic power of the system. Therefore, comparatively deeper or faster cuts can be made with the AWSJ.

AWSJ cutting, in contrast to the AWIJ cutting process described below, can also be used for mobile cutting applications and cutting under water, in addition to machining demanding materials. Examples include bomb disposal s well as the dismantling of offshore installations or the dismantling of reactor pressure vessel installations in nuclear power plants.

Abrasive Water Injector Jet (AWIJ) cutting
The AWIJ is generated by a water jet that passes through a mixing chamber (a cavity) after exiting the water nozzle and enters a focusing tube at the exit of the mixing chamber. The interaction of the water jet in the mixing chamber with the air inside creates a negative pressure, the water jet entrains air particles. This negative pressure is used for the pneumatic transport of the abrasive into the chamber (the abrasive is led to a lateral opening (bore) of the mixing chamber by means of a hose).

After contact of the abrasive material in the mixing chamber with the water jet, the individual abrasive grains are accelerated and entrained in the direction of the focusing tube. The air used as a carrier medium for transporting the abrasive into the mixing chamber also becomes part of the AWIJ, which now consists of three components (water - abrasive - air). In the focusing tube, which is (should be) optimised in its length for this purpose, the abrasive is further accelerated (energy transfer from the water to the abrasive grain) and the AWIJ ideally leaves the focusing tube at the maximum possible abrasive grain speed.

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The Abrasive Water Suspension Jet (AWSJ) - often called “Slurry Jet” or “Water Abrasive Suspension (WAS) jet” - is a specific type of the abrasive water jet, which is used for waterjet cutting. It has to be distinguished from the Abrasive Water Injection Jet (AWIJ).

History
As early as 1924, a technical system was patented by the inventors Jakob Maurer and Heinrich Friedrich Jakobsen, which was describing a tool for grinding and drilling teeth. According to the patent description, a press water with added abrasive is used (Preßwasser mit Schleifmittelzugabe). This technology was limited in terms of the pressure level used, but the method of generating the jet already corresponded to the AWSJ principle.

Technological characteristics of abrasive water suspension jet cutting
In contrast to the abrasive water injector jet (AWIJ), the abrasive water suspension jet (AWSJ) is characterised by the fact that the mixing of abrasive and water takes place before the nozzle. This has the effect that, in contrast to AWIJ, the jet consists of only two components (water - abrasive).

In the development of AWSJ, three different ways of admixing abrasive to water have been investigated and applied so far.

One method is to mix the suspension (= water - abrasive mixture) at ambient pressure and pump it directly through a nozzle (in this case, diaphragm pumps are used, for example). Although this method is very easy to use, it has not yet gained economic importance, mainly because of the high abrasive wear in the pump while the suspension is pressurised [Figure below "Direct pumping"].

The second way of generating AWSJ is indirect pressurisation of a premixed suspension [Figure below "Indirect pumping"]. Water is pressurised and drives a piston in a pressure vessel. This forces the premixed suspension out of a high-pressure reservoir and then accelerates the suspension in the nozzle.

The third method of admixing is the so-called bypass principle [figure below "Bypass principle"]. In this case, water is pressurised in the pump. Part of the flow is directed through a bypass line to a high-pressure container that was filled with abrasive in a previous process under ambient pressure (this container is thus filled with a water-abrasive mixture = suspension). The other part of the water quantity, which is in the system from the pump, flows past the pressure vessel in the so-called main stream. The water flowing through the pressure vessel now entrains abrasive particles and thereby reduces the abrasive content in the vessel. This is an important aspect because, due to this property, AWSJ generation used to be a discontinuous process. When the abrasive content in the tank is used up, the AWSJ process must be interrupted. To do this, the system is relieved and brought back to ambient pressure so that the container can be refilled with abrasive. Recent developments in system technology have offered the following solutions for bypassing a discontinuous cutting process:
 * Two pressure vessels are integrated in the system. Via a so-called switch box, the supply of high-pressure water can be switched between the two tanks in so-called shuttle operation . This means that when the abrasive in one tank is used up, the other tank, which has already been refilled, is available for immediate further use. In this case, the cutting process only has to be interrupted for the short moment of switching over. This is a quasi-continuous process. This system is mainly used in the dismantling of offshore plants, usually as part of a complete system certified for offshore applications.

Regardless of the technical variants mentioned above, the highly concentrated suspension (high proportion of abrasive) transported out of the container is reunited with the main flow at the so-called mixing piece. From there is transported to the nozzle in a lower concentrated mixture. Within the nozzle (e.g. made of hard metal) the potential energy (pressure) is converted into kinetic energy (speed). In the process, the abrasive grains are also accelerated. Since there are only 2 components (water and abrasive) in the AWSJ, the acceleration of the abrasive grains by the water takes place with a significantly increased efficiency compared to the AWIJ. The abrasive grains become faster with the AWSJ than with the AWIJ for the same hydraulic power of the system. Therefore, the AWSJ can cut deeper and faster.
 * The pressure vessel can be filled with abrasive during operation via a patented sluice system (ConSus) and without the need to lower the pressure[8]. By implementing this technology, the AWSJ can be used as a continuous process for the first time, so that the technological and economic advantages can also be used in industrial production.

ConSus – The abrasive water suspension jet system with continuous abrasive supply
The patented abrasive water suspension jet system "ConSus“ (Continuous Suspension) enables a continuous supply of the abrasive (without air supply) into the pressurised high-pressure vessel via an intermediate vessel by means of a lock process.

The actual high-pressure vessel with the premixed suspension is level-monitored. If the fill level has dropped to a predefined lower level, suspension (abrasive water) is added via a valve from the intermediate vessel under the same high pressure. When the intermediate tank is empty, the valve and the high-pressure water supply line are closed and the intermediate tank is depressurised.

Then a ball valve is opened and the "refill" water-abrasive suspension flows into the intermediate container without air via a hopper. After the ball valve is closed, the intermediate tank is pressurised again via the high-pressure water line so that suspension can be added again as soon as the level in the high-pressure tank drops. In this pressure vessel, there is then a further mixture between water and abrasive suspension.

The water flushes the abrasive out of the high-pressure vessel and carries it up to the suspension nozzle (carbide nozzle), where it is then accelerated together with the abrasive and emerges as a 2-component abrasive water jet for cutting.

Sustainability through improved recyclability of the abrasive used
Modern waterjet cutting machines are equipped with water and abrasive treatment and the water can be circulated within the system. . The abrasive can reused again after cleaning (removal of the joint discharge material) and after appropriate screening and particle size classification (recycling).

The abrasive can also be filled into the pressure vessel in a moist state for cutting in the was process. In contrast to the AWIJ process, it is not necessary for the abrasive to be in dry and free-flowing form. This process advantage enables the abrasive residue to be processed directly at the machine, i.e. directly at the point of origin and reuse.

Industrial manufacturing
As early as the 1990s, water-abrasive suspension jet cutting technology was used sporadically in the machining of metallic and non-metallic flat components. In the initial phase, however, the system components were often home-made. As part of a European-funded development project in cooperation with the University of Hanover, a so-called job shop, i.e. a cutting service provider, from Denmark was convinced of the advantages of AWSJ technology at an early stage and carried out cutting tasks with a specially developed system Currently, AWSJ technology is used in the field of manufacturing technology, especially for the production of parts made of materials that are difficult to cut or with a large cutting depth (advantage of the high cutting performance of AWSJ) as well as for cutting tasks with a necessary small cutting jet diameter or where sparking must be avoided. In addition to the technical advantages, the ecological and economic advantages of the simple reuse of partial quantities of the abrasive used will become increasingly important in the future. In this context, it is to be expected that the users of AWIJ plants will seek a AWSJ system extension or additional AWSJ plant in order to be able to reuse the abrasive waste that has so far been produced as residual material.

A water abrasive suspension jet (WAS or AWSJ or slurryjet) cutting system achieves numerous advantages over AWIJ systems:

With the water abrasive suspension jet system "ConSus" (Continuous Suspension), which enables the uninterrupted use of AWSJ technology in industrial production as described above, existing AWIJ systems can be upgraded to a water abrasive suspension cutting system or a complete AWSJ system is offered, in each case optionally with an abrasive recycling system and/or water treatment systems.
 * even the hardest materials with a material thickness of up to 1,000 mm can be cut through precisely
 * up to 3 times the cutting speed or an increase in productivity of up to 300 % compared to conventional AWIJ technology
 * up to 70 % lower energy consumption and wear due to the low pressure of only 1,500 bbar
 * improved occupational health and safety due to reduced noise and particle emissions
 * Energy-efficient recycling of 80 % of the abrasive and direct reuse without drying

Cutting of fine structures
According to the current state of the art, jet diameters of 200 micrometres and more are used for industrial part production using AWIJ. Therefore it is possible to produce the most filigree, previously unfinishable contours on high-performance materials. The machining qualities can be compared to those of wire EDM, whereby a minimum electrical conductivity is not a prerequisite for the machining of the semi-finished product.

For this purpose, a fully integrated AWSJ machine is offered, which has the following features:


 * Manufacture of the most filigree, previously unfinishable contours on high-performance materials through reduced beam diameter down to 0.2 mm with significantly higher performance
 * fully integrated system technology (incl. high-pressure pump) with a total installation area of 2.5 square metres
 * universal applicability for different processing tasks
 * Lower energy consumption through the use of pump technology with reduced drive power and a max. required water pressure of 1500 bar (150 MPa). (In the AWIJ process, pressure levels of up to 6000 bar (600 MPa) are used as standard )
 * Resource conservation through recycling of consumables (see above).

Disassembly of components in nuclear power plants
The AWSJ was already used in an early trial at the Kahl experimental nuclear power plant with regard to its applicability and reliability in the dismantling of thick-walled components under water cover. The results of the cutting operations carried out there subsequently led to further applications in the dismantling of nuclear facilities in Europe.t   n advantage is that the mobile cuttindevises c can be operated remotely and are spatially separated from the other central components of thAWSJ systemntandathus t only a few components can be contaminated by radioactive radiation. Since the water cover and the abrasive reflecting from the kerf lead to a rapid clouding of the surrounding water and thus to poor visual monitoring of the cutting process, sensory monitoring devices and processes were developed especially for this area of application which can now also be used in maritime underwater operations.

Bomb disposal
During missions of the Explosive Ordnance Disposal Service, situations occur time and again in which the fuse of unexploded ordnance to be defused can not at all or only at an unacceptable risk be removed from the bomb with the standard tools available. Under these operating conditions, safe access to the detonator can be cut free by means of a mobile, remotely handled AWSJ cutting device.

In addition to its MACE systems, the Lübeck-based company ANT AG also provides the necessary cutting devices, to meet the special requirements for accessing and defusing bombs, grenades, improvised explosive devices such as pipe bombs, suitcase bombs, gas cylinders and car bombs. These cutting guidance systems can be mobile multi-axis handling systems to be set up at the site of operation, controlled e.g. with MACE from a distance of up to 500 m, or also robot-controlled remote handling tools which arrive at the site of operation by means of a "remote operated vehicle" (ROV).

Decommissioning of offshore structures
The slurryjet (AWSJ) is used for the dismantling of thick-walled components or surface and underwater components made of steel or a mixture of materials (e.g. steel and concrete) for offshore structures such as rigs. . The air-free supply of the jet components by means of high-pressure hoses from above the waterline (from a ship or from the offshore platform ) to the respective subsea deployment sites is a decisive success factor. The slurry jet cannot jam or get stuck during cutting. The AWSJ system can be used by means of (remote-controlled) handling systems, but also as a hand-guided system by divers. .

In particular, cutting through multistring casings, downhole pipes and platform piles from the inside using a WAS cutting tool (e.g. DCH Downhole Cutting Head or PCH Pile Cutting Head) is a typical area of application in the dismantling of offshore installations in the oil and gas industry. . The base structures of offshore wind turbines are dimensioned accordingly large due to the tower heights and the high forces introduced by the rotor blades. When dismantling such structures above and below the waterline (for repair purposes or also when the service life is reached), cutting tools are required that can be used without any problems both in terms of the material thickness present and in terms of any material mix (steel and concrete).

Cutting free a stuck tunnel drilling machine
In 2015, the steel shield of the tunnel boring machine "Giulia", which had become jammed with a 1.20 metre thick bored pile wall on a construction site in Karlsruhe, was cut free using a water abrasive suspension jet. . The mobile AWSJ system was supplemented on site with the necessary handling components.

Submarine (KURSK)
The accident of the nuclear-powered Soviet submarine "KURSK" is remembered by many people due to the intensive media presence at the time. In order to rescue the injured seamen from the submarine or to lift the submarine safely, it was necessary to cut 26 holes in the hull to attach special lifting equipment. According to reports, a water abrasive jet was also used in the process. The abrasive used, with the background of maximum cutting performance, was reported to be diamond grit. .Due to the conditions of use, it can be assumed that the abrasive water jet used was a slurry jet.

COBRA extinguishing lance
The extinguishing system "Cobra" of the company ColdCut-Systems from Sweden works with a pressure of up to 300 bar (30 MPa). The handling system (the so-called lance) is carried by the firefighter directly to the scene of the fire and can be used there to penetrate solid bodies such as doors, walls or metal sheets. The system is used when a fire has ignited in a locked room, container, etc. and no other mechanical solution for access can be realised. A WASS is used for cutting or drilling through the wall, where the abrasive supply can be shut off immediately after the jet exits the inside of the wall. Thus, only pure water is then sprayed through the lance into the cavity. The small droplet size due to the high pressure and the speed of the droplets result in a very high heat absorption capacity. After about seven metres, the jet disintegrates into a cloud of water droplets. The cooling and thus extinguishing effect of the system is greatest at this distance.