US3209689A - Reduction of gun barrel wear - Google Patents

Description

Oct. 5, 1965 Filed NOV. 4, 1957 D. E. MGLENNAN 3,209,689

REDUCTION OF GUN BARREL WEAR 2 Sheets-Sheet l Oct. 5, 1965 D. E. MGLENNAN `3,299,689

v REDUCTION OF GUN BARREL WEAR Filed Nov. 4, 1957 2 Sheets-Sheet 2 Ey I Wala/Va@ t United States Patent 3,209,689 REDUCTION 0F GUN BARREL WEAR Donald Elmore McLennan, Carde, Quebec, Canada, assignor to I-Ier Majesty the Queen in the right of Canada as represented by the Minister of National Defence, Ottawa, Ontario, Canada Filed Nov. 4, 1957, Ser. No. 694,453 Claims priority, application Canada, Nov. 14, 1956, 718,214 Claims. (Cl. 102-38) Ever since the introduction of colloidal gun propellants over half a century ago, the wear of gun barrels has represented an important problem. In many instances the service life of a gun barrel is only a few h-undred rounds. As a consequence, frequent costly and inconvenient replacements of the gun barrel become necessary. Furthermore, the compensations made for wear at various stages during the life of a -gun barrel are of an approximate nature and are thus a serious source of inaccuracy.

The excessive wear or erosion of the surfaces of the bore of a gun barrel is due to the high temperature of the propellent gases, which in the case of guns such as 17 and 20 pr.s and heavier artillery is within the range 2000-4000 C. Gun barrels are made of steel which, due to its iron content has the following critical temperature regions, the AC1 transition region between 1340" F. and 1415 F. and the austenitic or gamma region up to the melting point region of 2650-2750 F. The foregoing are typical values for gun barrel steel having an analysis of carbon 0.4%, nickel 1.65-2.0%, chromium 0.7-0.9%, and molybdenum (l5-0.3%. The firing of each round causes a thin surface layer of the bore to be raised to a temperature which exceeds the AC1 transistion point, and may exceed the melting zone causing localized volurne changes which strain and fatigue the metal. This high surface temperature impairs the ability of the steel to withstand the attrition due to the passage of the projectile and the propellent gases. In addition, a variety of chemical reactions such as oxide and nitride formation and localized changes of carbon content causing erosion of the steel take place to an increased extent at high temperatures.

The high temperatures of the propellant gases which are of the order of 3000 C. give rise to an additional problem in that the permissible rate of fire is limited by the temperature of the gun barrel. A high rate of fire results in increased wear, since the bore surface is additionally heated with each successive round. Exceeding the permissible rate of re can result in permanent damage to the gun or may cause a serious accident. A closely related problem is that of length of burst in the case of automatic guns, since their effectiveness against quickly moving targets such as aircraft depends on the permissible length of burst.

The foregoing problems have hitherto been accepted as being incapable of practical and effective solution and considerable effort has been devoted to the improvement of the quality of gun barrel steel, designing driving bands which will reduce and compensate for wear and towards the formulation of cool propellants having iiame temperatures lower than those Iof earlier propellants and therefore causing less wear and permitting a higher rate of re. These formulations have provided merely a highly incomplete partial solution and are accompanied by disadvantages since the use of cool propellants res-ults in a decrease in the propulsion developed by a Igiven weight of charge and sometimes causes ignition difficulties. Also, cool propellants are complex and expensive mixtures the preparation of which requires careful blending. Irregularities in quality and performance 3,209,689 Patented Oct. 5, 1965 are of frequent occurrence and are a source of inaccuracy.

In accordance with this invention a boundary layer of cool inert gases is provided between the surface of the bore and the propellant gases. This boundary layer is formed suiciently rapidly upon the combustion of the charge and is of suicient thickness extent and duration substantially to prevent the sur-face of the bore from being raised by propellant gases having temperatures of about 200G-4000 C. to a temperature at which a deleterious metallurgical transition occurs. The boundary layer will be reasonably effective if it at least halves the bore surface temperature increase. It has ben found that in some cases this reduces wear by factors of 30 or more.

In accordance with a preferred more limited aspect of this invention the boundary layer of cool inert gases is generated by a composition such as an organic high polymer, with or without the inclusion of fillers, which is endothermically decomposed by heat from the burning of the charge and the propellant gases. Preferably this composition has an enlarged surface area and is in the form of a sleeve surrounding the forward end of the charge. The gas generated by the composition forms a laminar insulating boundary layer.

In the drawings which illustrate the preferred embodiments of this invention:

FIGURE 1 is a sectional elevation View of a cartridge case in accordance with this invention.

FIGURE 2 is a detailed perspective view of the sleeve used in FIGURE 1.

FIGURE 3 is a sectional elevation view showin-g part of a gun barrel during the firing of a round of the type illustrated in FIGURE l.

FIGURE 4 is a diagram illustrating the results of tests red with a 17 pr. gun.

In FIGURE 1 of the drawings, a cartridge case 10 contains a propellent charge 11 and an igniter 12, and a projectile 13. A sleeve 14, shown in detail in FIGURE 2, of a coolant gas-forming composition encircles the forward end of the charge, extends back to about the centre of the charge, and is secured to cartridge case 10 by a layer 15 of an adhesive such as a glyptal resin adhesive. Other physically and chemically compatible adhesives may be used. Sleeve 14 preferably includes a neckpiece 14a which is a forward extension of sleeve 14 tapered to conform with the reduced portion 16 of the cartridge case and having a similar function to the main portion of sleeve 14.

FIGURE 3 illustrates part of the gun barrel 17 of, in this case, a breach block obturated gun containing a propellent charge 18. In FIGURE 4 the projectile 13a is shown imediately after ring of the charge 18. The charge provides propellent gases 19 to propel projectile 13a. The heat generated by the burning of charge 18 and from propellant gases 19 decomposes sleeve 1411 causing the formation of a boundary layer 20 of cool inert gases which insulate the bore surface 21 from the heat of propellant gases 19. Since no cartridge case is included in the embodiment shown in FIGURE 3, it is difficult satisfactorily to secure sleeve 14h in position to prevent it from being discharged prematurely with the projectile. Sleeve 14h should extend back to at least the centre of the charge and should closely engage the surface of the bore so that the burning of the charge will tend to force the sleeve against the surface of the bore.

The preferred material for the sleeves 14, 14a and 14b is polyurethane isocyanate foam which has been tested and shown to give improvements :in wear by a factor of from 2 up to 30 or more depending on the type of ammunition. However, other materials such as nylon, silk, wool, polymethyl methacrylate, polystyrene, polyethylene, silicones, silicone rubbers and natural and synthetic rubbers Jce may be used. The polyurethane foam may be combined with a filler such as for example ammonium oxalate which is a gas producer so as to augment the boundary layer, is compatible and has a high decomposition energy to create a cooling effect. The ammonium oxalate in the form of a finely divided powder is blended with the polyurethane monomers. A suitable polyurethane foam has a density of 25 pounds per cubic foot and has the following composition:

Resin pre-polymer yParts by weight Polyethylene glycol 200 10.5 Polypropylene glycol 1200 6.5 `Castor oil (Hydroxyl No. 160-165 Acid No.

1.8 max.) 36.5 2,4-toluene di-isocyanate 46.5

Resin catalyst Part per 100 parts pre-polymer Glycerine, 98% 7.5 Polyethylene glycol 200 3.7 Armeen DM16D 1.0

Where a filler is being used suitable proportions of the resin pre-polymer catalyst and filler are as follows:

Parts per 100 Resin pre-polymer 58.8 Catalyst 7.2 Ammonium oxalate Kmonohydrate 34.0

Almost any material which will decompose endothermically to form gases can be used lfor sleeve 14. However,

it is preferred that an organic high polymer be employed since these have large numbers of chemical bonds, the breaking of which absorbs heat energy and these products on decomposition yield adequate quantities of cooling gas. The breakdown temperature of the material should be as low as possible without being so low as to give rise to lack of stability during storage. If the breakdown temperature is high there will be a delay in the evolution of the gas upon the combustion of the charge and the temperature of the gas in the boundary layer will be high. The preferred breakdown temperature is between about 200 F. and 300 F.

The material used for the sleeves should have no adverse effects on the chemical stability of gun propellants in contact with it and should absorb as little nitroglycerine as possible. `It is undesirable to use materials which will produce toxic or corrosive products of combustion however fea-med polyvinyl chloride has been tested and found to reduce wear by a factor of about ten in spite of the possible corrosive effect of the hydrochloric acid which is one of its decomposition products.

The lmaterial used for the sleeves should have an enlarged surface area because of the importance of providing immediate decomposition. The use of material in the form of foam has been found to be more effective than the use of material in the form of a solid sheet. However, this will depend somewhat on the decomposition temperature of the plastic and on the flame temperature of the propellant.

The sleeve need not extend the full length of the cartridge but should extend rearwardly to the centre of the charge since the boundary layer is poorly formed in the rear portion. The rear portion of the sleeve would be wasted and there would be a fouling up of the igniter if a full length sleeve were used. If the sleeve is located too far forwardly of the centre of the charge it is possible that the sleeve will be expelled from the gun before it has undergone appreciable decomposition. Thus in early ring trials it was found that polyvinyl chloride foam in the form of a doughnut on top of the charge gave a reduction in the total quantity of heat transmitted to the gun of at best only to 15%. Where a cartridge case is |used, an adhesive can conveniently be used to secure the sleeve to the cartridge case. The adhesive will be effective in spite of the high temperatures as the material in the sleeve acts as a thermal insulant for the adhesive and will be decomposed Vbefore the adhesive.

The invention is further illustrated by the following examples:

EXAMPLE 1 A total quantity of 3 oz. of polyurethane foam was applied in the form of a sleeve encircling the charge and adhered within the cartridge case of a 17 pr. gun. The polyurethane foam was applied as an eighth inch thick l0 sheet of 20 lb./cu. ft. foam extending from the front of the charge about half of the distance towards the rear of the charge. Firing trials were conducted of guns using ammunition thus modified in comparison with guns using conventional ammunition. The wear was measured by star gauge both before and after a sequence of rounds and was found to give a factor of improvement of over 30.

EXAMPLE 2 The results of trials with various types of coolant are 20 shown in Table 1.

Table 1-17 pr. trials CFI Rate of wear 9,.. Type ol' ammunition Number of per round 0 rounds (1 C of R),*

inch

Cooled polyurethane, 90 gms 20 0. 0000 *l inch forward of commencement of rifling.

Additional data as to further tests is shown diagrammatically in 'FIGURE 4. In FIGURE 4, pvc refers to polyvinyl chloride and iso refers to polyurethane isocyanate.

l EXAMPLE 3 40 A total quantity of about 3 oz. of polyurethane foam was :applied in the form of a sleeve encircling the charge .and adhered within the cartridge case of a `20 pr, gun. The polyurethane lfoam was applied Ias a one-sixteenth inch thick sheet of 3,0 lb./cu. ft. material, extending from lthe front of the charge about half of the distance towards the rear of the charge. Firing trials were conducted as in Example 1. The results are set out in Table 2.

Table 2.-20 pr. trials (armour piercing discarding sabot ammunition) Rate of wear Type of ammunition Number per round of rounds (1 C of R),

inch

Many 0.0011

The invention is primarily applicable to ordnance ammunition since barrel time is longer than that of small arms and the duration of exposure to the gases is, therefore, longer than in the case of small arms. In small arms the barrel time is less but the avoidance of wear is highly beneficial. The invention can also be applied in the case of small arm-s ammunition to increase the rate of fire by avoiding overheating. In the case of small arms ammunition, it will be particularly important, due to the lower duration of exposure that the sleeve material have a high surface area so that it will readily be decomposed.

The primary advantages of the invention are the saving of wear and increasing the accuracy and rate of fire. Other advantages, however, include the possibility of using hotter propellants to give higher muzzle velocities and the possibility of design improvements for example to the driving bands which previously have been designed with Ithe minimizing yof Wear and the necessity of compensating for wear as controlling factors.

We claim:

1. Ammunition comprising a projectile, an explosive charge :for generating propellent gases 'to propel said projectile through the bore of a gun barrel in which the ammunition is adapated to be used and a sleeve of a compositon having a foam-like cellular structure providing an enlarged surface area encircling at least the forward portion of said charge for generating a boundary layer of cool inert gases between said propellent gases and the surface of said bore substantially immediately upon the burning of said charge and lasting for the duration of the travel of the projectile through the bore, said laminar boundary layer acting at least to halve the bore surface temperature increment, said composition comprising an organic high polymer which decomposes at a temperature between 200 and 300 F.

2. Ammunition as in claim 1 in which said organic high polymer is in the form of a solid foam.

3. Ammunition as in claim 2 in which said organic high polymer is polyethylene isocyanate.

4.-y Ordnance ammunition comprising a cartridge case, a projectile positioned at an open end of said cartridge case, an explosive charge Within said cartridge case for generating propellent gases to propel said projectile through a bore of a steel gun barrel in which the ammunition is adapted to be used, a sleeve of a foam-like cellula-r structure gas generating composition encircling at least the lforward part of .said charge, said composition decomposing upon t-he burning rof said charge to provide a laminar boundary layer of cool inert gases between the propellent gases .and the surface of said bore substantially to .prevent ythe bore surface temperature from rising Ibeyond the alpha-gamma transition temperature of said steel and means for securing said sleeve to .the inner surface of said cartridge oase, -said gas generating composition being an organic high polymer which decomposes at a temperature between 200 and 300 F.

5. Ordnance ammunition as in claim 4 in which said gas generating composition is in the form of a solid foam.

References Cited by the Examiner UNITED STATES PATENTS 45,227 1 1/ 64 Connel 102-97 1,187,779 6/ 16 Patten. 1,842,445 l/ 32 Clyne 102-44 2,180,239 11/39 Holland et al. 102-43 2,188,465 1/ 40 Perrin 102.-43 2,559,275 7/51 Brown 102-95 2,703,529 3/ 55 Tuckerrnan et al. 102-43 2,820,412 l/58 Beeuwkes et al. 102-93 2,897,758 8/59 Miller et al. 102-42 BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL BOYD, ARTHUR M. HORTON, SAMUEL FEINBERG, Examiners.

Claims (1)

1. AMMUNITION COMPRISING A PROJECTILE, AN EXPLOSIVE CHARGE FOR GENERATING PROPELLANT GASES TO PROPEL SAID PROJECTILE THROUGH THE BORE OF A GUN BARREL IN WHICH THE AMMUNITION IS ADAPTED TO BE USED AND A SLEEVE OF A COMPOSITION HAVING A FOAM-LIKE CELLULAR STRUCTURE PROVIDING AN ENLARGED SURFACE AREA ENCIRLING AT LEAST THE FORWARD PORTION OF SAID CHARGE FOR GENERATING A BOUNDARY LAYER OF COOL INERT GASES BETWEEN SAID PROPELLANT GASES AND THE SURFACE OF SAID BORE SUBSTANTIALLY IMMEDIATELY UPON THE BURNING OF SAID CHARGE AND LASTING FOR THE DURATION OF THE TRAVEL OF THE PROJECTILE THROUGH THE BORE, SAID LAMINAR BOUNDARY LAYER ACTING AT LEAST TO HALVE THE BORE SURFACE TEMPERATURE INCREMENT, SAID COMPOSITION COMPRISING AN ORGANIC HIGH POLYMER WHICH DECOMPOSES AT A TEMPERATURE BETWEEN 200* AND 300*F.

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