GB2061148A - Cleaning metal surfaces - Google Patents

Abstract

This invention consists of a method of cleaning metal surfaces, which is particularly suitable for removing driving band deposits or carbonaceous residues from gun barrels. The method involves bombarding the surface or barrel with particles of a dispersion-hardened plastic material comprising abrasive particles in a plastic material matrix, a preferred material being a glass bead/Nylon 66 composite. In an alternative embodiment the dispersion-hardened particles are produced in-situ in a barrel by fragmentation, on firing the gun of a device inserted into the barrel together with a round and propellant charge, again preferably made of the glass bead/ Nylon 66 composite. Three forms of such a device are described: a sheath to be fitted over the nose of a round in small calibre weapons, a disc to be inserted between the round and propellant charge, and a strip of frangible bags or containers containing pellets of the material, rolled into a ring and inserted between a round and a propellant charge.

Description

SPECIFICATION Cleaning metal surfaces This invention relates to methods and apparatus for removing deposits from metal surfaces and in particular from gun barrels.

To obtain maximum range and accuracy from a gun, it is essential to maintain the inside surface of the barrel of the gun. especially the rifling grooves, in a good condition and as free as possible from pits, deposits etc. which occur as a result of use.

Such pits and deposits are produced by two main routes. Firstly, firing of the gun results in the deposition of various pyrolysis products from combustion of the propellant charge, degradation of oil in the barrel etc. These deposits are hygroscopic, containing metal (particularly calcium) sulphates, oxides, carbonates, nitrates etc and a variety of carbonaceous organic materials, and tend to both lie on the surface of the metal and fill any small cracks etc which already exist in the barrel. When the gun is allowed to cool, cleaned with an oil based solvent, dried, and finally left with a thin film of oil on the surface to protect the surface from rusting, these hygroscopic deposits absorb water from the oil.

Sessile droplets of water therefore form over the deposits which fill the small cracks, and lead to localised electrochemical corrosion. When the gun is next fired, the corroded softened barrel material is eroded away by the passage of the shot, and pitting results. Secondly, the engagement of the soft metal (usually sintered iron or copper) driving band around the shot with the rifling grooves inside the barrel leads to the deposition of metal particles in the grooves. This latter is a cumulative effect, and rapidly results in partial filling of the grooves. If the driving band is made of copper, this will again result in localised electrochemical corrosion of the gun barrel. Both these effects have a highly deleterious effect on the internal surface of the barrel.

It is not easy to remove pyrolysis or driving band deposits from gun barrels. Using conventional cleaning techniques such as that outlined above, it is necessary to wait until the barrel is cool enough to handle, and until there is a convenient time to service the gun. It is found that on cooling the deposits harden and are more difficult to remove.

According to the invention a method for cleaning metal surfaces comprises bombarding said surfaces with particles of a dispersion-hardened plastics material.

The term dispersion-hardened plastics material as used herein refers to abrasive particle/plastics material composites, wherein the plastics material matrix has a breaking strength lower than that of the abrasive particles. In materials of this type, cracks tend to propogate between the dispersed particles, rather than across the bulk of the material, so as to produce a composite substantially less plastic, and harder than the plastics matrix material, but much less brittle than the abrasive material itself.

By the use of dispersion-hardened plastics materials, particles can be manufactured which shatter at a sufficiently high energy to remove deposits when said particles impact with a surface at a sufficient velocity, but which are unlikely to cause scoring of a metal surface.

Dispersion-hardened plastics material may be made by a number of methods, and by choosing appropriate compositions or manufacturing techniques etc, the properties of the particles obtained may be varied to achieve a desired degree of abrasiveness. An additional property which is desirable in a suitable dispersion-hardened material is that it should not contain any substances which are likely to cause further corrosion of a barrel if particles are left in the barrel after a cleaning operation. The material should not contan sulphur or halogens for example, as these may undergo thermal degradation to form corrosive material.

The abrasive particles used may typically be in the size range 100 -150 ttm diameter, and should be of materials which are insufficiently hard to cause scoring of the gun barrel. Suitable particulate abrasive materials include fine sand, fly ash, fused alumina and especially glass beads.

The plastics matrix material should preferably be of a type that is strain-free on hardening to achieve the maximum degree at dispersion hardening. Preferred plastics matrix materials are aliphatic polyamides, especialy Nylon 66, though other common plastics materials may be used. A Preferred composite material is Nylon 66 containing at least 30%, preferably 40-60% by volume of hollow glass beads, preferably of about 100 - 150 um, especially 120 um diameter Other combinations of plastics material and particles will be apparent to those skilled in the field.

The composite material may be made into parti cites suitable for use in the invention by any convenient method, but most conveniently by extrusion into threads and cutting into small pellets. The Nylon 66/glass bead composite described above is suitable for processing on both screw and plunger type moulding machines, and for optimum efficiency in the cleaning method of the invention should be made into equiaxial pellets approximately 1 - 4 mm in each dimension.

The dispersion hardened particles produced as above may be bombarded onto the surface to be cleaned using conventional sand-blasting or peening equipment, suitably adapted to be inserted down a gun barrel and to direct a stream of airborne particles onto the deposits to be removed.

It is necessary that the energy of the composite particles as they bombard the surface to be cleaned should be maintained within certain limits. If the energy is too low debris will not be removed, and in addition, deposits of malleable copper from driving bands may be beaten into a thin film over the surface of the band or driven into pits and cracks in the surface, from which it can only be removed with difficulty. If the energy of the particles is too high, then the integrity of the composite may be destroyed as the particles impact with the barrel surface. This may result in the separation of the abrasive particles from the matrix, and consequent scoring of the metal surface.These limits must be determined experimentally for each application of the method of the invention, but it has been determined that for most commercially available blasting machines, and using the Nylon 66/glass bead composite in pellets of approx 1 - 4 mm size, the upper limit is represented by a working air pressure of 60 psi.

It will be appreciated that in battlefield conditions, when it is most necessary to maintain a gun in a good condition, convenient time for servicing may not be available, and it would be disadvantageous to carry bulky equipment for gun cleaning.

According to a preferred embodiment of the invention there is therefore provided a device for cleaning gun-barrels, said device being shaped for insertion into the barrel together with a round and propellant charge and being constructed to shatter on firing of said propellant charge into fragments capable of cleaning the gun bore by abrasion.

The term "shatter" as used herein refers to fragmentation into a large number of small particles rather than mere fracture into large fragments. The term may also be understood as referring to the disintegration, on firing said propellant charge, of one or more frangible bags or containers containing suitable small particles. These small particles then ricochet within the barrel.

The device according to this embodiment, termed barrel refurbishment ammunition (BRA) -convenient- ly generates abrasive particles in situ which clean the gun barrel during firing, thereby removing newly deposited material while it is still hot, and preventing cumulative build up of layers of deposits. The use of BRA therefore minimises gun servicing, and provides for a relatively erosion free gun barrel.

The device may be made of any material with suitable mechanical properties as described above.

It should be compatible with the propellant, thermally stable to resist barrel temperatures, non hygroscopic, solvent resistant to withstand the effect of oil or cleaning solvents retained in the barrel, and should not contain any substances as mentioned above which are likely to form corrosive products on firing of the gun. The particles formed should not contain any materials which are so hard that scratching of the inside of the barrel is likely.

Although suitable shattering might be achieved with devices made of brittle materials such as ceramics etc, suitable shattering is most conveniently obtained in this embodiment by the use of the plastics material/abrasive particle composites as described above. The propogation of cracks between the dispersed particles in devices made of these composites promotes shattering of the material into a large number of small fragments rather than fracturing into a few large fragments.

The plastics materials suitable for use in this embodiment should again preferably be of a type that is strain-free on hardening, as internal strain in the material may result in undesirable fracture into a small number of larger particles, with a consequent loss of abrading efficiency. In addition the plastics material should preferably be mouldable to facilitate manufacture of said devices.

The particles should be mixed with the plastics material priorto moulding in such a percentage that the final device is neither too plastic to shatter adequately on firing, as a result of too low a particle concentration, nor so friable that it is unlikely to survive rough handling under service conditions as a result of too high a particle concentration. The Nylon 66/glass beads composite material described above is again a preferred material, combining the desir able properties outlined above.

The shape of such a device and the position in which it is mounted within the barrel will depend on the calibre of the weapon, and on the rate of fire. In small calibre automatic fire guns up to about 40mm calibre, the device may be mounted in front of the shot, and conveniently takes the form of a sheath made of the abrasive particle/plastics material composite, fitting over the nose of the shot, so as to be shattered by the dynamic shock as the shot begins to move, and so that the resulting particles spread radially as the moving shot forces them apart. In this case the device should preferably be sufficiently elastic and fitted with equatorial ridges to enable it to grip tightly over the shot, so as not to be detached by rough handling or by vibration, which may cause fouling of a breech mechanism.The device should be moulded as accurately as possible to the contours of the shot it is to fit, to ensure that it shatters uniformly. When the device is fitted to explosive ammunition fitted with a nosefuze, it may be necessary to leave a hole at the top of the device to ensure that the fuze does not impact with the device causing premature detonation in the barrel.

In weapons of calibre greater than 30 mm and especially in weapons where copper driving bands have been used, it may be preferable to mount the device at the front of the cartridge case, immediately behind the shot, so as to be shattered by the explosion of the propellant charge. In this application it is desirable that the device should have a concave rear surface, so that the force of the exploding propellant charge causes radial spread of the fragments. Conveniently the device may be fitted in every round on manufacture.

It has been found that such devices must have a certain minimumweightto ensure boththatthere is sufficient inertial shock when the gun is fired to shatter the device, and to provide efficient abrasion of the barrel. The optimum weight of the device will depend upon the dimensions of the weapon and ammunition.

In an alternative embodiment of the invention which is especially suitable for weapons of larger (eg greater than 40 mm) calibre, mounted as described above between the shot and the cartridge case, the device may be in the form of a plurality of frangible bags or containers containing suitable particles of dispersion-hardened plastics material such as those described above, which are join-ed together to form a strip of pre-cut length or a continuous strip which may be conveniently rolled up for storage. In use, a suitable length of this strip may be cut off, bent into the shape of a ring, and inserted into the gun barrel between the charge holder and the shot, or within the charge holder (eg cartridge case). The forces resulting from the explosion of the propellant causes rupture of the bags and radial scattering of the paticles. This embodiment of the invention may conveniently be manufactured for example by heat sealing a length of flexible thermoplastic tubing of suitable diameter, loading in a quantity of paticulate material, heat sealing the thermoplastic tube so as to enclose the particulate matter, and repeating the operation to form a strip of sachets each containing the particulate material. Other methods of producing a strip of sachets according to the embodiment of the invention will be apparent to those skilled in the art. A preferred combination of materials is a Nylon 66 tube fashioned into sachets containing particles of the Nylon 66/glass bead composite described above, preferably equiaxial and 1 - 4 mm in each dimension. The diameter of the beads used in this embodiment will depend upon the calibre of the weapon, and will normally be between 100-800 Fm.

In a weapon for 40 mm calibre for instance, beads of diameters ranging from 100-200 um are suitable.

It is not necessary that these devices be used on every round fired. It is also unlikely that these devices will be suitable for use in cleaning rifling grooves which are substantially filled with deposits, and it is possible that damage to such a barrel may occur if a BRA mounted in front of a shot is used in an attempt to clean it. In such cases pre-cleaning should be effected by peening with dispersion hardened particles. Thereafter BRA may be used to maintain cleanliness of the barrel. The devices are best used intermittently, say on every thirtieth round fired, and then at the close of firing on the last 3 rounds.

The invention will now be illustrated by way of example only with reference to the following drawings in which: Figure 1 shows a cross sectional view through a device suitable for 30 mm cannon ammunition.

Figure 2 shows a cross sectional view through a 30 mm cannon shell fitted with the device.

Figure 3 shows a cross section through a large calibre shell and cartridge case fitted with the device.

Figure 4 shows a device made frown a number of frangible sachets containing dispersion hardened paticulate material.

EXAMPLE 1 Cleaning with particulate materials Particles of a dispersion hardened material were prepared using Nylon 66 reinforced with 40% by volume of 120 Ftm average diameter glass beads.

This material was moulded into cylindrical pellets 1-4mm long and of the same diameter by extrusion and subsequent cutting, using a barrel temperature of 275-300"C. These particles were then blasted onto the surface of a gun barrel which had become badly fouled through prolonged firing using a commercially available sand-blasting machine with an air pressure of 60 psi. Using a dwell time of 5-7 minutes, this treatment was found to successfully remove the hardened deposits and leave the gun barrel with a bright, lustrous appearance.

Cleaning with barrel refurbishment ammunition The devices illustrated in Figures 1-3 were made using Nylon 66 reinforced with 40% by volume of 120 rtm average diameter hollow glass beads. This material was moulded using a barrel temperature of 275-300"C, a mduld tool temperature of 60-80"C and a screw speed of 50-250 revs/minutes.

EXAMPLE 2 With reference to Figure 1, a device suitable for use with 30 mm cannon ammunition consists of a conical sheath of material. The inner surface 1 is profiled to fit the front surface of the shell or closely as possible, and provided with a number of ridges 2 to grip the round and prevent dislodging. The diameter of the device at its widest point is approximately 28mm, to allow sufficient elastic expansion on fitting without exceeding the barrel diameter. The forward end 3 of the device is thickened to provide sufficient inertial shock on firing, and to provide sufficient material to adequately abrade the barrel.

The weight of material used is approximately 10 g.

At the forward end of the device an aperture 4 allows a nose fuze to project through.

With reference to Figure 2, the device of Figure 1, 11 is shown in position on a 30 mm cannon shell 12 fitted with a nose fuze 13 projecting through the aperture.

-EXAMPLE 3 With reference to Figure 3, a large calibre artillery round consisting of a high explosive shell 21 fitted with a conventional base fuze 22 and on conventional cartridges 23, has a device 24 inserted into the front end of the cartridge case, immediately behind the shell 21 and in front of the propellant charge 25.

The device 24 consists of a disc, with a flat front surface and a concave rear surface to cause radial spreading of fragments. A central hole 26 in the device prevents obstruction of the fuze 22. Similarly, a disc-shaped BRA may be mounted between a shell and a separate charge bag of combustible cartridge case.

EXAMPLE 4 With reference to Figure 4 a device suitable for a 105-120 mm calibre weapon, comprising a plurality of frangible sachets 31 was made by heat-sealing a length of 2" (5 cm) diameter flexible Nylon 66 tubing at one end, pouring in sufficient pellets of the Nylon 66/glass bead composite, prepared as in example 1 using glass beads of diameter 100-800 um to fill about 1" (2 cm) of the tube and then heating the tubing so as to tightly encapsulate the pellets. This operation was then repeated to form a series of sachets containing the pellets, joined by short lengths 32 of closed nylon tubing. In use in a 120 mm calibre gun a strip of the sachets approximately 1 ' 2" (36 cm) long was cut off from the tubing and was dbent into a ring as shown in the drawing of such diameter that it would fit tightly around the bore of the barrel. This ring was then inserted into the barrel between a shell and a cartridge case, for example in a recess in the front of the cartridge case, so as to be disintegrated in firing.

Claims (30)

1. A method for cleaning metal surfaces by bombarding said surfaces with particles of a dispersion-hardened plastics material comprising abrasive particles in a plastics material matrix.

2. A method according to claim 1 wherein the abrasive particles comprise sand, fly ash, fused alumina or hollow glass beads.

3. A method according to claim 1 or claim 2 wherein the abrasive particles are in the size range 100-150um diameter.

4. A method according to claim 3 wherein the abrasive particles are hollow glass beads 120ym mean diameter.

5. A method according to any of claims 1 to 4 wherein the dispersion-hardened plastics material contains at least 30% by volume of hollow glass beads.

6. A method according to claim 5 wherein the dispersion - hardened plastics material contains 40-60% by volume of hollow glass beads.

7. A method according to any of the preceding claims wherein the plastics material is an aliphatic polyamide.

8. A method according to claim 7 wherein said aliphatic polyamide is Nylon 66.

9. A method according to any of the preceding claims wherein the particles of dispersion-hardened material are substantially equiaxial and 1-4mm in each dimension.

10. A method according to any of the preceding claims wherein the particles of dispersion-hardened plastics material are bombarded onto the metal surface by a-jet of gas at a pressure of 60psi or less.

11. A method according to any of the preceding claims wherein the metal surface is part of a gun barrel.

12. A method according to any of claims 1 to 9, and 11 wherein the particles of dispersion-hardened plastics material are produced by the fragmentaion of a device constructed to shatter to give particles of a dispersion-hardened plastics material.

13. A device for cleaning gun barrels, said device being shaped for insertion into the barrel together with a round and propellant charge and being constructed to shatter on firing of said propellant charge to give fragments of a dispersion hardened plastics material comprising abrasive particles in a plastics material matrix.

14. A device according to claim 13 substantially entirely composed of the dispersion-hardened plastics material.

15. A device according to claim 14 in the form of a sheath adapted to fit over the nose of a round.

16. A device according to claim 14 in the form of a disc capable of being mounted between a round and the propellant charge.

17. A device according to claim 16 with a concave rear face.

18. A device according to claim 13 comprising one or more frangible containers or bags containing particles of the dispersion-hardened plastics mate rial capable of cleaning the gun barrel by abrasion.

19. A device according to claim 18 wherein said bags or containers are in the form of a flexible strip of sachets.

20. A device according to any of claims 18 or 19 wherein said bags or containers are made of Nylon 66.

21. A device according to any of claims 18 to 20 wherein said dispersion-hardened plastics material is in the form of substantially equiaxial particles 1-4mm in each dimension.

22. A device according to any of claims 13 to 21 wherein said abrasive particles are sand, fly ash, fused aluminium or hollow glass beads.

23. A device according to claim 22 wherein said abrasive particles are in the size range 100-8001lm.

24. A device according to any of claims 13 to 23 wherein said plastics material comprises an aliphatic polyamide.

25. A device according to claim 24 wherein said aliphatic polyamide is Nylon 66.

26. A device according to any of claims 22 to 25 wherein said dispersion-hardened plastics material contains at least 30% by volume of hollow glass beads.

27. A device according to claim 26 containing 40 to 60% by volume of hollow glass beads.

28. A device according to claim 27 wherein said glass beads are of mean diameter 120Ftm.

29. A device according to any of claims 13 to 28, substantially as hereinbefore defined with reference to the accompanying drawings.

30. A method according to any of claims 1-12 substantially as hereinbefore described with reference to the accompanying drawings.