GB2042398A

GB2042398A - Method and apparatus for penetrating a body of material or treating a surface

Info

Publication number: GB2042398A
Application number: GB8001142A
Authority: GB
Original assignee: BOC Ltd
Current assignee: BOC Ltd
Priority date: 1979-01-15
Filing date: 1980-01-14
Publication date: 1980-09-24
Also published as: GB2042398B

Abstract

Liquefied gas is subjected to a pressure of at least 5 MPa by a pump 8. The pressurised liquefied gas is passed through a pipe 12 to a nozzle 14 which forms a jet of the liquid and directs it towards, for example, a sheet of leather whose surface is to be treated eg: cut or which is to be penetrated by the liquefied gas. Suitable liquefied gases include liquid argon, liquid neon, liquid krypton, liquid xenon and liquid carbon dioxide. The materials to be treated may be metal, plastics, elastomers, textiles, paper, foodstuffs. <IMAGE>

Description

SPECIFICATION Method and apparatus for penetrating a body of material or treating a surface This invention relates to a method of and apparatus for treating a surface or penetrating a body of (solid) material by means of a jet of liquid. The invention is particularly concerned with the following methods of penetrating a body of (solid) material, cutting, shearing, boring, gouging and piercing, and the term "penetrating a body of solid material" as used herein encompasses such methods. The invention is also concerned with the following methods of treating a surface: finishing (eg.

planing, deburring, or deflashing) cleaning and polishing and the term "treating a surface" as used herein encompasses such methods.

It is known to use jets of liquid to perform various processes of treating surfaces or penetrating solid bodies. The ability of a liquid jet to perform such processes depends in part on the momentum of the liquid as it strikes the surface or solid body. A high velocity jet may be created by subjecting a stream of liquid (typically water) to a high pressure and then passing the stream under the high pressure through a nozzle. As the stream passes out of the nozzle so the pressure is translated into velocity. For a given nozzle, the higher the pressure, the greater the velocity of the resultant jet and therefore the greater its ability to deform a surface. In order to create a high pressure, a special kind of pump, called an intensifier, may be used.

The ability to penetrate a solid body may be greatly enhanced by subjecting the surface not to a jet of constant kinetic energy but instead to one whose kinetic energy repeatedly varies from a maximum to a minimum and back to the maximum (ie. is effectively pulsed). One method of achieving such a variation in the kinetic energy is to feed particles of hard material into the jet or stream of liquid from which it is formed. Another method is to interrupt the jet so as to form individual slugs of liquid. The flow of liquid may be physically interrupted by a suitable mechanical device. Alternatively, the nozzle may be so designed as to induce cavities to form in the jet.

Jets of liquid have been used to claim surfaces, for example, of marine structures.

Jets of liquid have also been used to cut, shear or pierce such various materials as metals, textile, elastomers, plastics, laminates and other composite materials, particularly fibre reinforced plastics, leather and paper. Jets of liquid have also been used to mine materials, particularly coal. The uses of jets of liquid in treating surfaces and penetrating solid bodies mentioned in this paragraph are merely illustrative and by no means exhaustive.

The jet of liquid is commonly formed of water.

According to the present invention, there is provided a method of treating a surface or penetrating a body of (solid) material, comprising the steps of forming a stream of liquefied gas, subjecting the stream to a pressure of at least SMPa, and passing the pressurised stream though a nozzle to form a jet of liquefied gas, and directing the jet of liquefied gas at the surface or body.

The invention also provides apparatus for treating a surface or penetrating a body of (solid) material, comprising a source of a liquefied gas having a greater density than water; a pump operable to subject a stream of the liquefied gas to a pressure of at least 5 MPa, and a nozzle which is in communication with the outlet of the pump which is capable of forming a jet of the liquefied gas.

The term "body of (solid) material" as used herein encompasses hollow bodies, porous bodies, and bodies with interstitial voids (such as foamed plastics materials), as well as solid bodies that are monolithic.

The liquefied gas may be selected from the following which all have densities greater than water: liquid oxygen, liquid argon, liquid neon, liquid krypton, liquid xenon, and liquid carbon dioxide.

Of the above mentioned liquefied gases, we recommend that oxygen not be used. A high pressure jet of pure liquid oxygen would, in many circumstances, give rise to grave risks of fires or explosions.

Liquid carbon dioxide and liquid argon are the preferred liquefied gases as they are plentifully available. Liquid carbon dioxide has a density of 1.1 78 kg per litre and liquid argon has a density of 1.395 kg per litre. Liquid krypton or liquid xenon may, however, be used as an alternative to liquid argon or liquid carbon dioxide. Liquid krypton and liquid xenon are not in such plentiful supply as liquid argon and liquid oxygen but have higher densities and at a given velocity therefore have greater momentum than a comparable jet of water. Liquid krypton has a density of 2.458 kg per litre, and liquid xenon has a density of 3.063 kg per litre.The use of liquid krypton or liquid xenon might be particularly attractive for an automated cutting process performed in a closed chamber, in which instance the gaseous xenon and krypton formed on evaporation of the liquid would be collected and recycled for reuse.

Forming the jet of one of the aforementioned liquefied gases may make possible attaining one of the following advantages. First the liquefied gas may owing to its low temperature, cause a local embrittlement of the body to be penetrated. This would facilitate cutting of plastics materials and resins (whether or not reinforced or strengthened) by the method according to the invention. In order to achieve this advantage, the density of the liquefied gas is immaterial, and liquid nitrogen which has a relative density of less than 1 (at atmospheric pressure) may be chosen as the liquefied gas.Second, the liquid gas, owing to its low temperature, may tend to evaporate in the jet or upstream of the outlet of the nozzle (or such evaporation may be induced by suitable heating means), thus forming bubbles or pockets of vapour which may grow in size sufficiently for individual slugs or bodies of liquid separated from one another by the vapour may be formed in the jet. Liquid nitrogen may, we believe, offer this advantage as well as the aforementioned liquefied gases.

Third, the liquefied gas on striking the surface or body may evaporate rapidly without being absorbed by the material of which the surface or body is made. Thus, a liquefied gas (for example, liquid nitrogen) may be employed in, for example, processes of cutting materials that would be damaged by absorption of moisture and which therefore would present difficulties if they were to be cut by a jet of water. Paper and "Turkish Delight" are examples of such materials. Another disadvantage of using water which it is possible to overcome by the invention is that the water may react chemically with the body or surface. A suitably inert liquid may generally be chosen from those mentioned herein particularly liquid nitrogen and liquefied noble gases.

The liquefied gas may be one not to be found in the atmosphere in gaseous state. For example, the liquefied gas would be a fluorocarbon or halofluorocarbon (for example of the kind sold under the Registered Trademarks "Arcton" and "Freon"), boron trifluoride, or sulphur hexafluoride.

A conduit of flexible material may connect the nozzle to the outlet of the pump. The pump is preferably of the intensifier kind.

Such pumps are described in the literature relating to jet cutting. The nozzle may conform to any one of a number of alternative shapes. Both the nozzle and the intensifier are desirably fabricated of material which is not rendered brittle to any great degree by the liquefied gas. The nozzle may, for example be formed of artificial sapphire, a cermet or ceramic. The parts of the pump that come into contact with the liquefied gas may be formed of a stainless steel of the kind conventionally used in cryogenics.

The nozzle may, for example, have a hollow cylindrical upstream portion meeting a conical downstream portion which converges in the downstream direction and ends in a small circular orifice. Alternatively, the nozzle may have an annular outlet. Another alternative is for the nozzle to be formed with a convergent upstream part and a divergent downstream part, both parts meeting in a throat.

The nozzle may be designed so as to cause cavitations in the jet of liquefied gas. Such nozzles are described in the literature.

The pump may typically generate a pressure from 5 to 1000 MPa (or 5 to 500 MPa). If the method and apparatus according to the invention are to be used to clean surfaces, the pump preferably generates a pressure in the range of 5 to 25 MPa. The nozzle may, for example, have an outlet orifice having a diameter of 0.5 mm or less.

When precision cutting by the method according to the present invention, it is preferred to keep the nozzle fixed and to move the work. To this end, the work may be mounted on a suitably controlled carriage. Metals, plastics (whether reinforced or strengthened or not), confectionery, leather, paper, ice, frozen fish, meat and bread, are examples of the wide range of materials that may be cut. The invention is particularly suitable for cutting materials that are conventionally cut by blades. For example, it may be used to slice bread.

The method and apparatus according to the invention will now be described by way of example with reference to the accompanying drawing, which is a schematic view of a jet cutting apparatus.

With reference to the drawing, a source of liquid carbon dioxide 2 communicates via a conduit 4 with the inlet 6 of a pump 8. The pump 8 is of the intensifier kind and those parts of it which come into contact with the liquid carbon dioxide are formed of a nickelcontaining cryogenic steel. The pump 8 has an outlet 10. Connected to the outlet 10 is a pipe 1 2 of material which is not rendered brittle by the liquid carbon dioxide. A nozzle 14 is secured in the end of the pipe 1 2 remote from the pump 8. The nozzle 14 has a hollow cylindrical upstream portion 1 6 which terminates in a conical downstream portion 1 8 which converges in the downstream direction and ends in a small orifice 20.The nozzle 14 is mounted with its axis vertical such that the orifice 20 points towards a sheet of leather 22. The sheet of leather 22 is mounted on a carriage 24 which has means (not shown) for precisely controlling the position of the leather sheet so that a precise cut can be made.

In operation, the liquid carbon dioxide is supplied from the source 2 and subjected to a pressure in the range of 100 to 500 MPa in the pump 8. A pressurised stream of liquid carbon dioxide passes through the nozzle 14 which it leaves in the form of a fine jet.

Typically, the nozzle 14 is mounted 20mm above the sheet of leather. The impact of the jet of liquid on the leather causes its surface to be breached, and the liquefied gas penetrates through the leather. The carriage is driven along a predetermined path so that a cut of chosen shape may be made. The liquid carbon dioxide evaporates after it passes through the leather. Unlike cutting with a jet of water, problems caused by liquid "splashing back" onto the back of the leather do not arise. If there is any splash back, the liquid carbon dioxide will evaporate without being absorbed by the leather.

Claims

1. A method of treating a surface or penetrating a body of (solid) material, comprising the steps of forming a stream of liquefied gas, subjecting the stream to a pressure of at least 5 MPa, passing the pressurised stream through a nozzle to form a jet of liquefied gas, and directing the jet of liquefied gas at the surface of the body.

2. A method as claimed in claim 1, in which the liquefied gas is liquid carbon dioxide.

3. A method as claimed in claim 1, in which the liquefied gas is liquid argon.

4. A method as claimed in claim 1, in which the liquefied gas is liquid xenon.

5. A method as claimed in claim 1, in which the liquefied gas is liquid krypton.

6. A method as claimed in claim 1, in which the liquefied gas is liquid nitrogen.

7. A method as claimed in claim 1, in which the liquefied gas is a halofluorocarbon, fluorocarbon, boron trifluoride or sulphur hexafluoride.

8. A method as claimed in any one of the preceding claims, in which the liquefied gas is subjected to a pressure in the range 5 to 1000 MPa.

9. A method as claimed in any one of the preceding claims, in which a material is cut by the jet.

10. A method as claimed in claim 9, in which the material is a composite material, a resin, plastics material, reinforced or strengthened plastics material, paper, leather, a metal, meat, bread, ice, frozen fish or confectionary.

11. A method of penetrating a body of solid material, substantially as herein described with reference to the accompanying drawing.

1 2. Apparatus for treating a surface or penetrating a body of (solid) material, comprising a source of liquefied gas having a greater density than water; a pump operable to subject a stream of the liquefied gas to pressure of at least 5 MPa, and a nozzle which is in communication with the outlet of the pump and which is capable of forming a jet of the liquefied gas.

1 3. Apparatus for treating a surface or penetrating a body of (solid) material described with reference to, and as shown in, the accompanying drawing.