Driving Bands

Published on February 2017 | Categories: Documents | Downloads: 24 | Comments: 0 | Views: 163
of 14
Download PDF   Embed   Report

Comments

Content

These are the bands placed around projectiles to prevent the forward loss of gas around the projectile. They are usually made from copper, gilding metal and sometimes sintered iron. The modern day has intruded here also and they will now be encountered in plastic versions. Their use and introduction can be traced back to the time when cylindrical projectiles first appeared. The original round cannonball because of its requirement to be loaded from the muzzle had no method of sealing the bore. In fact had the ball been tight enough to seal the bore you wouldn't have been able to load the weapon at all. All this changed when the Cylindro-ogival projectile arrived on the scene along with the not-new breech loading weapons. (They had been tried many years before but failed through the inability of the gunners to adequately seal the breeches). A round cannonball needs no stabilizing. Because of its spherical shape it is inherently stable. Ask any cricketer, golfer or baseballer. On the other hand the Cylindro-ogival projectile is inherently unstable. It will not fly very well at all unless it is stabilized in some way. The two basic methods of stabilizing an elongated projectile are: •



Fin stabilization and, Spin stabilization.

Both of these methods are in current use in the world today.

To provide adequate stability for a projectile using fins there needs to be some sort of protection for the fins. The arrow of your ancient bowman would not survive in the bore of a cannon without some form of protection. In fact the Manuscript depicting the Vase Gun shows just this fact. The gun is shown firing what appears to be an arrow with its fins wrapped in some form of leather. The latest technique is to provide a discarding sabot which protects and carries the projectile up the bore and is then discarded at the muzzle. The drawbacks are obvious, they are expensive and more complicated to make. One great advantage is that the weapon can be made smooth bore as spin is not necessary. FIN STABILISATION.

Providing spin to a cylindrical projectile introduces gyroscopic forces which keep the projectile flying point first. To provide this spin you must arrange some form of rifling in the bore of the weapon and then devise some method of transfering the spin from the rifling to the projectile. This adds considerably to the cost and complexity of the weapon and requires some device on the projectile for accepting the forces applied to create the spin. I.e. a driving band. SPIN STABILISATION

Many steps were tried before the driving band of today was arrived at. The steps in roughly chronological order are: • • • • Twisted projectiles. Studded projectiles. Lead coated projectiles. Studded projectiles with gas checks. Gas checks with supporting and driving bands. Driving Bands.

• •

TWISTED PROJECTILES

The two efforts at producing a smooth bored twisted projectile were by two different men. Mr. Josheph Whitworth and a Mr. Lancaster. They both came up with the idea to produce a projectile with several faces twisted along the length. The bore of the weapon was likewise twisted. The great problem arising from the use of these types of projectiles was the difference between a laboratory and the mass produced weapon at the front. In the laboratory where the conditions were pristine and each round was individually produced the system works well. At the front where the ammunition had been mass produced by unskilled labour and the weapon was also mass produced the tolerances were a little more generous giving rise to the projectiles jamming in the bore with distressing frequency.

An example of a Whitworth hexagonal shrapnel shell. Photo courtesy of the Artillery museum, Woolwich.

STUDDED AND RIBBED PROJECTILES

It occurred to inventive minds that providing studs on the outside of the projectile engaging in the grooves of the rifling would impart spin to the projectile as it passed through the bore. Tolerances being what they were in those days there was still a gas loss forward past the studs and the rifling.

An example of a studded projectile. Photo courtesy of the Artillery museum, Woowhich. An example of a ribbed projectile. Photo courtesy of the Artillery museum, Woolwich.

Lead coated projectiles.

If you coated a projectile in a sheath of lead the whole thing would act as a complete seal for the bore. The drawback is that the quantity of lead being driven through the bore leaves large amounts of lead fouling behind. But is certainly sealed the bore and showed the way forward to the solution of the problem of obturation.

An Armstrong lead coated projectile.

Gas check designs

It is clearly evident from these designs that the designers had begun to get the hang of this obturation business. It needed just a little refining and they were there.

Driving bands

At last the solution is achieved, the humble driving band. A simple ring of soft metal press fitted to the body of a projectile that seals the bore, imparts spin and is relatively easy to provide.

An example of a double driving band. Photo courtesy of the Imperial War Museum, London.

An example of a single wide driving band. Photo courtesy of the Imperial War Museum, London.

The functions of a driving band are as follows: To prevent the escape of propellant gasses past the projectile. To transfer the twist of the rifling to the projectile as spin. To a lesser extent to retain the projectile in the bore when high angles of elevation are applied.

To centre the projectile in the bore.

In addition to these main functions there are several considerations which must be borne in mind when selecting the type of band and the material thereof. 1. It should not wear the bore excessively. 2. It should compensate for the normal wear in a bore. 3. It should remain attached to the projectile throughout the internal and external ballistic phases. 4. After engraving has occurred the engraving process should not degrade the ballistic properties. 5. It should be cheap. 6. It should be easy to affix.

The forces being applied to the driving band during the passage through the bore are such that the driving band must be prevented from moving around the body of the projectile. To ensure the security of the driving band during its passage up the bore and while in flight, ribs are cut or milled into the groove where the driving band is pressed. In the case of ribs chisel cuts have to be provided to prevent air being trapped underneath during the pressing operation.

Grommets

It was soon found that the band itself was quite susceptible to damage in storage and transport. Damage to the driving band negates the reasons for it being there in the first place. The answer was to provide a protective piece around the driving band. These are called variously grommets or grummets. Originally these were made from rope and canvas. Once again modern technology has crept in and they are now made from plastic.

An example of a canvas grommet. Photo courtesy of the Australian Logistics Training Centre, Bandiana.

An example of a modern plastic grommet. Photo courtesy of the Australian Logistics Training Centre, Bandiana, Victoria.

BRITISH DRIVING BAND DESIGNS

GUN TYPE No. 1 This type was known as the "Gas check" design. It was used on 6 inch, 12 inch, 13.5 inch and 15 inch guns. Theoretically the gas pressure under the lip forced it outwards into the rifling thus giving an improved seal. The raised portion was susceptible to damage in transport and handling, particularly in the conditions prevailing on the Western front.

GUN TYPE No. 2 This type was used for 9.2 and 7.5 inch guns and was in the nature of an experimental driving band in that the gas check idea was modified so that only a raised portion was used to seal the bore. The shape gave rise to the name "Hump band" for this type. Because of its very solid nature this type was suitable for service conditions.

GUN TYPE No. 3 This type was introduced for use with naval 6-inch high velocity projectiles. The band was made from Cupro-nickel.

GUN TYPE No. 4 This type was known as the EOC band as the Elswick Ordnance Company made it. It was applied to 5.5 and 4 inch guns.

GUN TYPE No. 5 This was a simplified Hump band being very easy to make and very robust. It was applied to naval 4.7 and 5.2 inch guns.

GUN TYPE No.6 Originally introduced for use with BL 60 pr and QF 4.7 inch guns and designed as a strong and simple driving band suitable for field service.

GUN TYPE No.7 This was a very simple band very much like the early Vavasseur bands. Like these early bands it was prone to fanning.

ECONOMY BANDS

To economize on the use of copper the width of some bands was reduced and these bands were known as "Economy bands". To compensate for the smaller surface area and to provide a better seal the bands were made a little deeper. The accuracy with this type of band was slightly poorer and they were very susceptible to fanning.

An example of an economy driving band. Photo courtesy of the Artillery Museum, Woolwich.

DOUBLE DRIVING BANDS With some high velocity equipments such as Anti-tank and Anti-aircraft a broad driving band is necessary to provide good quality sealing and a large surface area to support the high pressures and velocities encountered in these weapons. A difficulty arises in that the pressing of a very wide band onto the projectile is difficult. This can be overcome by making the band in two pieces. By placing the second band well forward on the projectile a very steady movement through the bore is achieved.

An example of double driving bands.

AUGMENTING STRIPS. As the rifling on a weapon wears the projectile gets rammed further and further forward into the barrel of the weapon. This changes the ballistics to a marked degree. To overcome this, an augmenting strip was introduced. It consisted of a strip of pure copper of roughly square section with one side curved. The strip was hammered into a cannelure in the band with the curved side down and was cut off when the strip filled the cannelure all round. The strip also acted as a gas check.

Augmenting strip

PROBERT BAND. This was a system designed by the Research Department (of RDX fame) in which the breech of the weapon is of greater diameter than the barrel and is tapered. The rear band in this system is of considerable width to fill this tapered space. The rifling of the barrel commences forward of the front bands, of which there are two. This arrangement ensures that any gas losses around the rear driving band occur only in the smooth tapered section thus no erosion of the rifling takes place. The rifling is progressively reduced as it approaches the muzzle and the last portion is smooth bore and swages the driving bands down to the diameter of the projectile. The forward bands are grooved to prevent highpressure gasses building up between the bands during the passage through the bore. An overly complicated system which is not often encountered today.

SEALING CUPS AND RINGS. Another method of imparting spin and sealing bores is to attach expanding rings and/or cups to the base of the projectile. This method is especially suitable for Armour Piercing Discarding Sabot projectiles as the base is discarded at the muzzle (hence the name). The method is not, as one might imagine, a new one. Some of the very earliest projectiles were fitted with sealing cups and were successfully used in the American Civil War (1861 to 1865).

SKIRT TYPE

This is the simplest of the sealing cup systems to be found. The action of the propellant gasses simply expands the cup outward, which forces the driving band into the rifling.

SANDWICH TYPE SEALING RING With this type the gas pressure acting on the cup shaped driving band causes the driving band to expand and force the sealing ring into the rifling to seal the bore.

HINGED TYPE DRIVING BAND AND SEAL

This is a German development and is simple and efficient as most German ammunition items are. The Driving Band is affixed directly to the projectile body. The sealing cup is quite often found with different coatings such as copper, rubber, plastic and, the most common, tinned plate.

PRE-ENGRAVED DRIVING BANDS Projectiles fired in Recoilless (RCL) weapons have their driving bands pre-engraved so that the energy required to engrave the driving band is not supplied by the propellant. This preengraving ensures that the velocity is not degraded. I believe that the frictional forces An example of a pre-engraved driving band. Photo courtesy of the Artillery museum, Woolwich. offered by a standard driving band in an RCL weapon might ensure that all the propellant gasses would exit to the rear through the venturi. Pre-engraving a driving band means that the projectile must be loaded in such a manner as to line up the rifling in the weapon and the preengraving on the band. This is achieved by providing locating studs on the ogive of the projectile.

OBTURATING BANDS FOR MORTAR PROJECTILES

For smooth bore weapons such as Mortars, which are muzzle loaded, the projectile has to be small enough to pass down the bore to the base of the tube. This provides a large gap through which the propellant gasses can escape. To overcome this problem the designers have developed what are called "obturating" bands. These consist of a ring applied to the middle of the mortar body and are such a shape that when gas pressure is applied to them, they expand and seal the bore to a large extent, the usual material being plastic or nylon.

Clearly seen on this 81mm inert mortar round is the obturating band around the middle of the body.

DRIVING BANDS FOR RIFLED MORTARS Not all mortars are smooth bored, some are rifled, and this gives the designer the opportunity to utilize the spin provide by the rifling. It can be used to arm the fuze in the conventional way and it adds a little to the range and accuracy of the mortar bomb. The designers need to be a little tricky as the usual problem of having the bomb small enough to drop down the tube and yet still seal the bore. One method is to make the mortar a breechloader, which has been done, successfully on several mortars in the past. This has the disadvantage of slowing the loading considerably.

The Japanese Army came up with a novel method for sealing the bore of a rifled mortar. This consists of placing the propellant inside a container that has the driving band on the outside. The propellant gas pressure causes the container to expand and force the driving band into the rifling thus sealing the bore.

Sponsor Documents

Or use your account on DocShare.tips

Hide

Forgot your password?

Or register your new account on DocShare.tips

Hide

Lost your password? Please enter your email address. You will receive a link to create a new password.

Back to log-in

Close