Erosion in Large Gun Barrels Report of Committee on Gun Tube Erosion (1975) / Chapter Skim
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DESCRIPTION OF GUN SYSTEM
DESCRIPTION OF GUN SYSTEM
Pages 7-35
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From page 7... ...
However, it appears obvious that the problem of defining the mechanism of erosion cuts across the missions of the various Army arsenals. It is therefore felt that future effort in this area would be more effective if a single leader and a single source of funding devoted exclusively to this technology area be designated.
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From page 8... ...
Ul K co o z z a §5 < O Ul 51?
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From page 9... ...
Classes of Ammunition A-FUZE • -BOOSTER C-FUZE WELL LINER D-SHELL E-OGIVE F-BOURRELET G-BURSTING CHARGE H- ROTATING BAND I-CRIMP 1- BASE COVER K-CARTRIDGE CASE L-PROPELLING CHARGE M-PRIMER N-LIFTINGPLUG O-GROMMET P-COTTER PIN WITH PULL RING Q-IGNITER FIXED AMMUNITION SEMIFIXED AMMUNITION M SEPARATE.LOAMNG AMMUNITION RA PD 40671A Figure 2 Types of Complete Rounds of Artillery Ammunition
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From page 10... ...
Around is the short name for all components of ammunitions necessary to fire a gun once. Erosion is the enlargement and wearing away of the bore interface of gun barrels by the movement of high temperature gases and residues generated from the burning of propellant powder, by chemical action between constituents of propellant powder gases and gun material, and by friction between projectile and bore interface.
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From page 11... ...
The heat check system on lands and grooves is shown in greater detail in Figure 5. The cartridge cases used in these guns act as a rear seal and protect the chamber from the propellant powder gases.
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From page 15... ...
Wear Reducing Additives 5. Firing Conditions No one is independent of the others.
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From page 16... ...
Stellite 21 liners were successful in the caliber . 50 chromium plated and nitrided machine gun barrels.
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From page 17... ...
Considerations of cost and availability indicated the use would be as coatings or liners, if at all. 2'3 Molybdenum base and chromium base hot hard alloys were developed during 2 W
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From page 18... ...
But no change in accuracy life was apparent. Examination of the bore surface of plated and eroded gun liners, and other studies, revealed that the chromium metal was very, although not perfectly, resistant to chemical attack by propellant powder gases.
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From page 19... ...
The same type of test demonstrated that the thicker the chromium plate, the better the erosion resistance, and the less the warping tendency due to heating the substrate steel through its transformation temperature range. Also chromium plate having a Knoop hardness of about 1, 000 performed somewhat better than a softer or harder plate.
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From page 20... ...
Two decades of research failed to find methods of extensively improving the chromium electroplating process-the efficiency of plating, the rate of plating, the elimination of cracks and cracking, the throwing power, the hot hardness, even non-destructive testing for adhesion. The dependance on chromium plate in some large guns has been reduced by the use of wear-reducing additives in the ammunition, which started in the 1950's with the polyurethane Laminar Coolant and in the 1960's with the titanium dioxide -- wax and the talc-wax systems.
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From page 21... ...
The hexafluoride process temperature range, 500-750°C is probably low enough not to seriously affect the structural stability of large gun barrels. The cost of scaling up the process would probably be high but very little is reported in the literature on scaling up CVD processes.
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From page 22... ...
Accordingly, it would be mandatory to evaluate the CVD tungsten coating more definitively before considering scale up. To do this, a small scale but relevant simulation test must be perfected and used both for CVD coatings and for other materials.
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From page 23... ...
Cannelures supply space into which the excess band material can flow without forming fringes and rough edges which would affect the aerodynamic behavior of the projectile. The band rubs on the lands and grooves causing friction and contributing to erosion while at the same time sealing the bore, minimizing the escape of propellant powder gases and rotating the projectile while it passes along the bore.
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From page 24... ...
In order to reduce the access of burning propellant powder gases to the region of the origin of rifling, developmental work with protectors or extensions 1 2 of the cartridge case have been tried. ' " Protectors, the most famous one being the Franklin Institute Small Arms "FISA" protector, were thin steel sleeves over the outside of the neck of the cartridge case and the band of the projectile.
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From page 25... ...
The lack of simple but controlled erosion tests procedures inhibits the establishment of necessary characteristics of plastic products which might be suitable. However, some success has been obtained with plastics in large cannon and it is evident more attention should be given to plastics as a substitute for metal in rotating bands, or for use in combination with metal rotating bands.
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From page 26... ...
Larger diameter gun tubes run cooler. Using the above, one may estimate the tube temperature for different systems as shown on Table I on the following page entitled "Calculated Forcing Cone Temperatures."
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From page 27... ...
27 oo r-.
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From page 28... ...
that is: CF = CnRT = constant o o where- F o = force constant ft Ibs/lb n = gas volume, moles of gas/gm of product T o = isochoric flame temperature R = gas constant C= weight of charge Since C is more or less limited by chamber geometry, at least in high performance systems where erosion is a problem, the only avenue open is the development of propellants with lower flame temperatures and lowered mean molecular weight combustion products i.e., the number of moles of gas/gm is increased. This has been achieved in the triple base cool propellants as shown below: Propellant M6 M5 M30 Type Single base Double base Triple base F , (ft Ibs/lb)
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From page 29... ...
and low flame temperatures (approaching 2500°K)
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From page 30... ...
Evidence of the loss of gun steel by some volatile process is found in the metallographic study of the bore interface of worn plated gun barrels. 2 The CO/CO ratio is higher in the combustion products of single base m cool propellants than it is in the double base (hotter^ propellants.
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From page 31... ...
Additives which are incorporated within the propellant powder, in order to retard deterioration in storage are diphenylamine, ethyl centralite, etc. The additive commonly used to suppress muzzle flash is potassium sulfate.
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From page 32... ...
. One is unable, to date, to predict the degree of success of wear reducing additives in a particular gun system.
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From page 33... ...
The Picard patents specify particles sizes 3 to 60 a No mention is made of particle size in the Jacobson patent. 18 The Navy , as late as 1969.
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From page 34... ...
It is evident that there is a large body of information concerning control of gun tube erosion using additives. These data apparently have never been collated and examined with a view to developing a rationale for understanding the phenomena.
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From page 35... ...
The number of parameters add to the complexities of standardizing erosion testing of any one model especially since large guns are being used in substained firing programs. A high rate of fire raises the temperature that the bore interface can reach and presumably can at times overcome the benefits of cool propellants.
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