WO2000018551A2

WO2000018551A2 - Improvements in and relating to fluid cutting operations

Info

Publication number: WO2000018551A2
Application number: PCT/GB1999/003035
Authority: WO
Inventors: Jonathan Barlow
Original assignee: British Nuclear Fuels Plc
Priority date: 1998-09-29
Filing date: 1999-09-29
Publication date: 2000-04-06
Also published as: GB9821025D0; WO2000018551A3; AU6098999A

Abstract

The invention provides a method and apparatus relating to fluid cutting in which a cutting jet of fluid (8) is directed through a nozzle (2) on a jet path, the jet path passing through a cutting zone in which a work piece (10) is placed in use and subsequently to a baffle area (16), the baffle area providing a baffle element which deflects the jet from the jet path on to a deflected path, the atmospheric pressure being greater in the area of the cutting jet path prior to deflection than in the area of the jet on the deflected path. In this way, the invention provides for reduced generation of spray or aerosols and/or assists in containing and removing such spray and/or aerosols from the air.

Description

IMPROVEMENTS IN AND RELATING TO FLUID CUTTING OPERATIONS

This invention concerns improvements in and relating to fluid cutting operations and particularly, but not exclusively, to fluid cutting of hazardous materials or materials contaminated therewith.

Fluid and particularly water cutting has many attractions for cutting articles into smaller components. It is particularly appropriate for use in hostile environments including those processing real or potential radioactivity, chemical or biohazards, where mechanical or flame cutting devices carry a significant risk of igniting materials present.

A number of operations in the nuclear and other industries, including decommissioning, reguire articles to be cut up. The articles may be cut to facilitate handling, storage or disposal. Equally articles may be cut to gain access to their interior. In many cases the articles may contain or carry on their surfaces radioactive materials. Whether these materials are alpha, beta or gamma emitters their containment is of a high priority.

In any cutting operation small parts of the article will come away from the two parts of the article formed by the cut. In water cutting this is a particular problem as fine water droplets from the cutting jet are also sprayed into the air. These water droplets, or particles suspended in them may be contaminated. The particles of the article may also become buoyant in this environment due to the water droplets.

Any containment vessel in which cutting of hazardous materials is undertaken is usually presented with one or more filters for air entering and leaving the vessel. To prevent clogging of these filters and the escape of aerosol droplets as cut articles are removed through an air lock, for instance, the effective suppression of the aerosol droplets is desirable. This applies whether the hazard comes from the material forming the article which is being cut, materials present on the cut article or associated contaminants. The hazard may be a chemical and/or radiological and/or biohazard and / or toxic hazard. According to a first aspect of the invention we provide a method of fluid cutting in which a cutting jet of fluid is directed from a nozzle on a jet path, the jet path passing through a cutting zone in which a workpiece is placed in use and subsequently to a baffle area, the baffle area providing a baffle element which deflects the jet from the jet path onto a deflected path, the atmospheric pressure being greater in the area of the cutting jet path prior to deflection than in the area of the jet on the deflected path.

In this way a net flow of the atmosphere in which the cutting occurs towards the post deflection part of the flow path.

Preferably the area of the jet path prior to deflection refers to the area including the 10cm, or even 5cm, of the jet path immediately prior to deflection.

Preferably the area of the jet path on the deflected path refers to the area including the 10cm, or even 5cm, of the path immediately after deflection.

Preferably the pressure differential is generated by the jet flow. This provides a simpler construction than applying an elevated pressure externally of the baffle gap and/or a depressed pressure internally of the baffle gap through means such as pumps .

According to a second aspect of the invention we provide fluid cutting apparatus comprising a nozzle connected to a supply of cutting fluid, a cutting zone for the workpiece to be cut and to which the nozzle directs a cutting jet along a cutting jet path, the cutting zone being between the nozzle and a baffle area, the baffle area providing a baffle element on to which the cutting jet is directed, the baffle element directing the jet onto a deflected path, the atmospheric pressure being greater in the area of the cutting jet path prior to deflection than in the area of the jet on the deflected path.

The baffle area may comprise the first baffle element and a second baffle element. The second baffle element may be provided on the nozzle side of the first baffle element. The baffle area preferably extends over at least the lateral and/or vertical travel distance of the nozzle. Preferably the baffle area configuration is substantially constant throughout this travel distance.

The first baffle element and second baffle element may define a recess into which the cutting jet is directed. The portions of the first and second baffles opposing one another in defining the recess may be further apart towards the nozzle than they are towards the impact location of the cutting jet on the baffle. A V-shaped recess may be provided. In this way mildly deflected cutting jets and / or energy depleted jets on divergent paths are redirected towards the deflecting location.

The first baffle element may provide the deflection of the cutting jet at a deflecting area. The deflecting area may comprise or consist of a location at which the jet impacts on the baffle, the impact location. Preferably the deflecting area extends away from the impact location. In this way further deflection or change in flow path direction may be provided beyond that generated by the impact. The cutting jet may be deflected increasingly away from the cutting jet path as it progresses over the deflecting area away from the impact location .

The first baffle element may comprise a first portion extending away from the impact location in a first direction and a second portion. The second portion may also extend away from the impact location. Preferably the first and second portions extend away in opposite directions, but most preferably also towards the nozzle. The first baffle element may thus define an -shaped baffle element. The impact location may be provided at the transition between the arms of the L-shape. The transition may be curved, most preferably to define the deflecting area.

Preferably the surface of the first baffle element at the impact location is angled relative to the cutting jet path, i.e. not perpendicularly provided. The angle defined between the cutting jet and surface of the first baffle element at the impact location is preferably less than 45° and more preferably less than 30°. It is preferred that the angle is less than 15°. In this way the initial impact is substantially tangential to minimise cutting of the baffle.

Preferably the angle between the projection of a tangent to the deflecting area and the undeflected cutting jet path increases as progression is made along the deflecting area away from the impact location. The angle may increase to 70°, 90° or even to 120°. The deflected jet may be angled back towards the nozzle by the end of the deflecting area.

The second baffle may comprise a first and second portion. The first portion may define, with the first portion of the first baffle element, the recess into which the cutting jet is directed. The second portion of the second baffle may extend away from the first at an angle and/or away from the recess .

The first and second portions of the second baffle element may define a general L-shape. The angle between the first and second portion of the second baffle element may be between 80° and 120°. The first and/or second portions may be linear.

The first portion of the second baffle element may be angled at between 45° and 15° to the cutting jet path.

The second portion of the second baffle element may be angled at substantially 90° to the cutting jet path.

The first portion of the second baffle element may be angled towards the impact location and/or deflecting area on the first baffle element. The first portion of the second baffle element may be generally provided between the first and second portions of the first baffle element.

Preferably the end of the first portion of the second baffle element is proximate to the first baffle element and in particular the deflecting area and/or impact location. Preferably the end of the first portion of the second baffle element is separated from the first baffle element by a maximum of 8.0cm and more preferably by a maximum of 5.0cm. Preferably the end of the first portion of the second baffle is separated from the first baffle by a minimum of 0.5cm and more preferably a minimum of 0.8cm.

Preferably the separation between the first and second baffle elements increases along the deflected jet path away from the impact location and/or deflecting area. Preferably the increase occurs at least between 5 to 15cm along the deflected path from the impact location.

The distal end of the second portion of the first baffle element may extend toward the distal end of the second portion of the second baffle element and/or vice versa. The ends of the second portions of the first and second baffle elements may be separated by a distance of between 0.8cm and 5.0cm.

The first and second baffle elements may be generally L- shaped with the end of the foot of the second baffle element proximate to the junction of the foot and stem of the first baffle element and with the end of the stem of the first and second baffle elements proximate to one another.

The first and/or second baffle elements may be provided with a through passage connecting the volume between the baffles to the external space.

The lower part of the second portions of the first and/or second baffle may extend into a fluid collection trough and/or below the surface of a liquid. Preferably the first and/or second baffle lower portions extend below the surface of a liquid contained in a trough.

The level of liquid in the trough may be controlled by balancing the input of liquid against the rate of drainage from the trough. The balance may arise from the dimensions of holes in the base of the trough.

The fluid is preferably water. Preferably the grit loading for the fluid is between 20 and 160 g/1, more preferably between 60 and 100 g/1.

The nozzle is preferably movably mounted, most preferably on a linearly moveable mounting.

The work pieces may be pipes, rods, bars, containers, fuel rods, plates and the like. The cutting location is preferably open at one, or more preferably both, ends so as to allow movement of the workpiece into and out of the cutting jet path. Preferably the workpiece is provided aligned perpendicularly to the cutting jet.

Preferably the entrance and/or exit to the cutting location for the workpiece is provided with means for preventing aerosol escape. The means may surround the workpiece. The means may be flexible. The means may comprise a plurality of elongate elements, such as brush hairs/filaments. Two opposing sets of means may be provided for each opening. The ends of the means may abut or overlap or be spaced from one another. The means preferably comprise nylon brushes.

Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings in which :-

Figure 1 illustrates a plan view of a water cutting apparatus; and

Figure 2 illustrates a side view of the apparatus of Figure 1.

Water jet cutting generally uses a grit impregnated jet of water to cut through materials. The jet is provided at very high pressure, around 4000 bar, to provide the cutting force necessary to cut through metallic articles and articles of other materials.

The jet is typically provided at a flow rate of around 2 litre/min for a 10 thousandths of an inch nozzle. Such a jet normally includes around 160 g/min of grit.

The pressures involved generally result in a substantial amount of aerosol formation as the jet impacts on the article being cut. The aerosols typically entrain grit and/or bits of the article from the cut. Thus if the article carries hazardous materials, for instance radioactive sources, there is a risk these will become suspended with the aerosols too. Whilst the vessels which contain such cutting operations for hazardous materials include air filter systems to remove such aerosols, very high levels of aerosols can swamp the filters.

A cutting apparatus is illustrated in Figure 1 and comprises a moveable nozzle 2 fed with high pressure grit impregnated water. The nozzle 2 can be moved from side to side to progress the cut and avoid the risks from cutting for too long at any one location.

The nozzle 2 is mounted on a support frame 4 which includes, opposing the nozzle 2, a baffle area 6. The baffle area 6 provides impact resistance for the jet 8 originating from the nozzle 2 when this passes through a cut in the workpiece 10. The workpiece 10 being cut is placed between the nozzle 2 and baffle area 6.

As illustrated in Figure 2 the baffle area 6 comprises a first, back baffle 12 and a second, front baffle 14 space therefrom. Both baffles 12, 14 extend downward into a collection trough 15.

The first baffle 12 is provided with a curved surface 16 opposing the nozzle 2 and is the intended impact location for an unopposed water jet 8. The curved surface 16 is formed from a first linear portion 18, a second linear portion 20 and a curved transition surface 22 between the two. Both the first 18 and second 20 linear portions extend towards the nozzle as they extend away from the transition surface 22. The actual impact location is on the transition surface 22.

The second baffle 14 is formed of a linear portion 24 and a second, dog legged, linear portion 26 which extends towards the transition surface 22 on the first baffle 12.

The relative positions of the two baffles 12, 14 is such that a converging channel 28 is formed between portions 18 and 26 so as to encourage any mildly deviated spray towards the intended impact location. The end 30 of portion 26 is closer to the nozzle 2 than the actual impact location on transition surface 22. In this way the impacting jet is deflected by the baffle 16 downward and through the gap 32. The transition surface 22 is shaped to promote the passage of the deflected jet through the gap 32. A significant volume 34 exists between the lower portion 20 and lower portion 24 of the respective baffles. This volume 34 provides a location for the aerosol droplets formed at the impact to stagnate and coalesce and drip down into the trough 15.

Water descending into the trough 15 forms a reservoir 36 which closes off the lower part of the volume 34. The level of the reservoir 36 is controlled by the drainage rate from holes 38 in the bottom of the trough 15 through which the water and grit flows for subsequent recovery.

The pressure of the water jet 8 and the configuration of the baffles 12, 14 around the impact location is such that a lower pressure forms at a location just inside the gap 32, towards volume 34, compared with a location just outside the gap 32, towards passage 28. This has the effect of retarding any attempt by aerosols to escape into the space 40 between the baffle system 6 and the nozzle location 2.

The pressure differential is maintained via a passage 100 in one or both of the baffle 12, 14, or elsewhere, which allows air flow back to volume 40.

Via a system provided in this way the overall level of aerosols in the air in the apparatus is very significantly reduced so reducing the problems with the ventilation system filters .

Inevitably some aerosol formation will occur in the space 40 due to impact on the workpiece during cutting and where the jet 8 is deflected during cutting away from the impact location. To reduce the risk of these aerosols being drawn into the ventilation filters the top and bottom of the space 40 is provided with mutually opposing and interlocking brushes 42. The nylon bristles of these brushes 42 form a dense mat on which aerosols collect and coalesce to form heavy drops. The brushes 42 have the advantage that they reform readily around the periphery of workpieces introduced into the cutter, so as to maintain the aerosol suppression.

Claims

CLAIMS :

1. A method of fluid cutting in which a cutting jet of fluid is directed from a nozzle on a jet path, the jet path passing through a cutting zone in which a workpiece is placed in use and subsequently to a baffle area, the baffle area providing a baffle element which deflects the jet from the jet path onto a deflected path, the atmospheric pressure being greater in the area of the cutting jet path prior to deflection than in the area of the jet on the deflected path.

2. A method according to claim 1 in which the pressure differential is generated by the jet flow.

3. Fluid cutting apparatus comprising a nozzle connected to a supply of cutting fluid, a cutting zone for the workpiece to be cut and to which the nozzle directs a cutting jet along a cutting jet path, the cutting zone being between the nozzle and a baffle area, the baffle area providing a baffle element on to which the cutting jet is directed, the baffle element directing the jet onto a deflected path, the atmospheric pressure being greater in the area of the cutting jet path prior to deflection than in the area of the jet on the deflected path.

4. Apparatus according to claim 3 in which the baffle area comprises the first baffle element and a second baffle element, the first baffle element and second baffle element defining a recess into which the cutting jet is directed.

5. Apparatus according to claim 4 in which the first baffle element provides the deflection of the cutting jet at a deflecting area, the deflecting area comprise or consist of a location at which the jet impacts on the baffle, the impact location, and the deflecting area extending away from the impact location and the cutting jet being deflected increasingly away from the cutting jet path as it progresses over the deflecting area away from the impact location.

6. Apparatus according to claim 5 in which the surface of the first baffle element at the impact location is angled relative to the cutting jet path, the angle defined between the cutting jet and surface of the first baffle element at the impact location being less than 45°.

7. Apparatus according to claim 5 or claim 6 in which the separation between the first and second baffle elements increases along the deflected jet path away from the impact location and/or deflecting area.

8. Apparatus according to any of claims 3 to 7 in which the entrance and/or exit to the cutting location for the workpiece is provided with means for preventing aerosol escape, the means surrounding the workpiece and the means being flexible.