Page:EB1922 - Volume 30.djvu/163

attached to it are withdrawn and the head of the fuze exposed. In this is a needle supported by a copper disc over a detonator. Under this a pivoted shutter, kept in position by a spring, closes a channel leading down to the magazine, which is rilled with a detonating com- position known as " C.E." On firing, the shock of discharge does not

Safety Pin

_ Safety Shutter

Needle Disc Detonator

FIG. i.

affect the relation of the parts but, after a certain small interval of time, the rotation of the shell causes the shutter to swing outwards round its pivot, overcoming its spring and uncovering the fire channel. On impact the needle is crushed down on the detonator, the flash from which, travelling down the now open channel, fires the maga- zine and explodes the shell.

Fuze No. 134 (fig. 2) exhibits some interesting characteristics. It is a " delay-action " fuze, i.e. it is so arranged as to burst its shell about 0-20 of a second after impact. The pellet of this fuze is provided with three inclined projections. The construction of this pellet, of which the upper part is bored out for the reception of the detonator and the lower portion serves as a support for the guard spring, will be best understood from the figure which also shows the position of this pellet before firing and when " armed " after firing.

, Inclined Projection Lower Guar^.___ 1 .Upper Guard

I- Detonator

on OBlonalor PeMet

Sprir-g

FIG. 2.

The action is as follows: Before firing, " ramps " or inclined sur- faces formed on the upper guard bear against the upper portions of the inclined projections on the detonator pellet, and are held there by the creep-spring, while the base of the lower guard is pressed up- wards against the bottom of these projections by the guard-spring. The two guards and the projections being thus locked by the friction of their surfaces, the guards completely mask the detonator. On the shock of discharge the lower guard sets back, compressing the guard- spring. The " ramps " on it ride down the inclined projections on the pellet, giving the guard a slight movement of rotation. The upper guard, impelled by the creep-spring, is then free to follow the lower, and the detonator is unmasked. The guard-spring then reasserts itself, and its upward pressure jams the guards in the set-back posi- tion. On impact the pellet moves forward, overcoming the creep- spring and carrying the detonator on to the needle. The flash from the detonator ignites some mealed powder in the interior of the pellet which communicates with the delay composition, this in turn, after the momentary delay desired, igniting the magazine.

Fuze No. 18 is a simple fuze, the action of which will be understood from fig. 3. It is protected by a strong cap which is removed at the

Detonator

C.E.Pellet

Brass Disc Spun in

Steel/ u Ste!el Shearing Hammer Wire

oose C.E.

FIG. 3.

last moment before loading. The fuze is quiescent in all its parts until direct impact takes place, when the steel hammer is crushed in and, breaking the steel shearing wire, carries its needle-point on to the detonator. The explosion of the detonator fires the loose exploding composition (loose C.E.) in the central channel, which in turn fires the magazine of the fuze (C.E. pellet) and the bursting charge of the shell.

A variation of No. 1 8 , known as No. 45 , has a pivoted safety shutter which is similar to that of No. 44, except that when it rotates, in- stead of merely opening communication between the detonator and the magazine, it brings a patch of composition of its own under the detonator to reinforce the downward flash.

In Fuze, Percussion, No. 106, which is of the instantaneous class, the principal feature is that it is armed by the unwrapping of a steel tape with a weighted end. The general construction will be under- stood from fig. 4 which shows the fuze uncapped and ready for firing. A split steel collar is interposed between the under side of the ham-

Spur Collar

Pellet of C.E.

Weight

ass Tape

Shutter

FIG. 4

Guide Pin

rass tape with weight iteel collar in halves

teel washer

• >pper shearing wire

tonator

mer-head and the top face of the fuze body, and it is round this collar that the tape is wound. On firing, the weight at the end of the tape is gripped by the set-back of the hammer, which receives additional support from the steel split collar. When acceleration ceases that is, when the shell leaves the bore-ythe weight is released, flies off, unwinding, and carrying the tape with it. The segments of the split collar are torn away by the end of the tape, and the hammer is then supported only by a thin shearing wire. On impact (even the slight- est) the hammer is driven in, shearing the copper wire and the detonator is fired. The fuze shown in the figure is a variant, No. 106 E, in which, owing to the inherent sensitiveness of fuzes of this class, a safety shutter is introduced. This shutter, like that of No. 45 alluded to above, carries a composition relay.

No. 106 and its variants were the standard instantaneous fuzes of the British artillery in the World War. Introduced in 1916, some 88,000,000 were made, and at the end of the war they were being turned out at the rate of a million a week, about one-third of those being made of cast iron.

No. 146, also armed by an unwinding tape device, is known as the " All-ways " fuze. It is designed to act and burst its shell at what- ever angle the latter may strike the ground. It is used only for trench-mortar bombs. For rifled shell, which travel nose first, such a fuze is not necessary, but for many trench-mortar bombs, which may fall sideways or on their bases, a percussion fuze is impracticable unless it possesses this characteristic. Fig. 5 shows the final form of the British " All-ways " fuze developed in the war from a crude German archetype. It is called No. 146 MK. V., or the Spigot fuze, as it is screwed on to a spigot which projects from the bomb.

.Bracket Creep Spring with SMeld Safety ,

Split Washer

1 ^jector Spring Detaining Pin

fetonator Holder .-Mud Shutter^

Mud Shutter

Tape

Retaining

ud Shutter i *= \ .

Needle Holder c - , t Magazine & Needle Safet r Bar

itfety Pin

T . withdrawn

Tape Spring b( . fore fi^g

FIG. 5.

On firing, the shock of discharge dislodges the retaining pin and the tape spring causes the tape to unwind, thus permitting the ejector spring to eject the safety bar from the body of the fuze. The " mud shutter " then drops and closes the hole in the body, thus preventing the interior of the body from being filled with mud on falling to the ground. Only a light strip of spring steel now keeps the detonator and the needle apart. On impact one of two things takes place, What- ever the angle of fall. Either the steel ball forces the needle holder down on the detonator, or the latter moves forward carrying its de- tonator on to the needle.

Graze Fuzes rely for their action on the check to the forward movement of the shell that takes place on graze or impact, and not essentially on a blow delivered to any part of the fuze. They are therefore very sensitive and depend for their action on a pellet in- side the fuze which moves forward on graze, causing a needle to come in contact with a detonator. Special arrangements are provided to guard against premature action in transport, handling and loading, on discharge, while the shell is in the bore, and during flight before it strikes or grazes. With these fuzes there is always a slight delay in action, and in some cases an additional delay-action is provided which is sufficient to cause the burst to occur well below the ground surface, or, if the shell ricochets, I o to 50 yd. in front of the graze. In view of the danger to equipment and to personnel in the event of such a shell exploding prematurely there is incorporated with the fuze either a shutter or a " delay," either of which modifications (to be described subsequently) should ensure the burst of the shell not taking place until it is some distance clear of the gun.