Online Encyclopedia


Online Encyclopedia
Originally appearing in Volume V20, Page 208 of the 1911 Encyclopedia Britannica.
Spread the word: it!
SHAFT TO MOTOR cone " de Bange obturator, supported on a carrier arm. This arrangement allows the mechanism (fig. 44) to swing clear of the breech opening immediately the threads of the breech screw are disengaged from those in the breech in a similar manner to the Q.F. guns fitted with a cone screw. The mechanism is actuated by the handwheel L which rotates the hinge pin; this in turn, through gearing, moves a crank arm D connected, by a link B, to the pin on the breech screw. By continuously moving the handwheel the link B is drawn towards the hinge pin until the breech screw threads are disengaged; the catch C then drops into a pocket on the breech screw and fixes it to the carrier arm. The whole of the mechanism then rotates around the hinge pin and leaves the breech open ready for loading. As the breech screw threads are being disengaged the electric or percussion lock W is operated by a cam groove In a similar manner to that already described. In_ the latest modification of this mechanism a roller at the end of the crank arm D works a long lever connected to the breech screw by two pins. This forms what is termed a " pure-couple " mechanism and it is claimed that greater ease of working is ensured by its use. While the loading is going on a new firing tube is placed in the vent, so that on closing the gun, by turning the handwheel in the opposite direction, the gun is ready for firing. For 9.2-in. guns and those of smaller calibre the handwheel is replaced by a hand lever pivoted on the carrier (fig. 45). By giving this lever a single motion from left to right the mechanism is opened. For 6-in. and 4-in. guns a shot support is attached to the breech face which is operated by the breech mechanism so that when the breech is open the shot support is in position for loading, and it falls out of the way when the breech is being closed. In the larger types of all breech mechanisms ball bearings are employed in various parts, such as the hinge pin bearings, &c., to reduce friction and in most of the modern heavy guns on board ship the breech mechanism is arranged to be worked by a hydraulic cylinder placed on the breech face, or by a small hydraulic engine or electric motor placed in some convenient position on the mounting. The hand gear, however, is always retained for emergency and a clutch is provided so that it can be put into action at a moment's notice. The Welin screw is largely used in the United States, but in heavy guns the ordinary cone (not " steep cone ") de Bange obturator is employed. The screw is mounted either in a carrier ring or on a carrier tray. In France the ordinary type of interrupted screw is adopted and this rests in a carrier tray. The operations of opening and closing are very similar to those already described.203 All the recent patterns of mechanism have an extractor fitted to extract the empty cartridge case with Q.F. guns or the fired tube with B.L. guns. In Q.F. field guns it generally takes the form of a lever working on an axis pin. The longer arm of the lever is formed into a jaw which rests on the inner face of the breech opening beneath the rim of the cartridge case, and the short arm is so arranged that when the breech is opened the carrier, in swinging mechanisms, or the breech block itself, in sliding systems, suddenly comes in contact with it; the long arm is thus jerked backwards and extracts the case. In B.L. mechanisms the tube extractor is arranged on the same principle but in this case usually forms part of the box slide, i.e. that portion of the mechanism attached by interrupted collars to the rear end of the vent axial, in which the firing lock slides as it is actuated by the opening or closing of the breech mechanism. When the breech is being opened the firing pin of the lock is drawn back to safety and the lock is moved aside from over the tube; a tripper then actuates the extractor and ejects the fired tube. The extractor and tripper are so contrived that when a new tube is pushed home the extractor is also pushed back into the closed position, or, if the tube is somewhat stiff to insert, the action of closing the mechanism moves the lock over the primer and forces it home. The firing lock used in B.L. guns is an important part of the mechanism. They are all designed on the same principle, with a view to safety and rapidity, and may be regarded as a miniature sliding breech mechanism. In the older types the lock or its substitute was manipulated by hand, and with electric firing the wires from the tubes were joined up to the loose ends of the firing circuit; safety depended therefore on everything being in order and all arranged to be automatic, and wireless electric tubes are used so operations correctly performed. The gun could, however, be fired before the breech was properly secured and a serious accident caused ; to prevent this all the movements of modern locks are that immediately the breech mechanism commences to open, the lock itself is moved in the box slide so as to uncover the vent opening. During the first part of this movement a foot on the striker rides up an incline I (fig. 45) on the box slide and thus pushes back the striker from contact with the tube. The ex-tractor described above is actuated at the same time. Most locks consist of a steel frame with a socket for containing the striker and main spring. They are contrived so as to be capable of firing both electric and percussion tubes, but others are arranged for firing only electric, separate locks being employed for use with percussion tubes. The construction of both is very similar, but with the percussion lock, or the combined lock, a trigger is provided which drops into a notch in the striker when this is pulled back by the lugs E E (fig. 45) on the outer attachment of the striker. On the trigger being pulled by a lanyard the striker is released and fires the tube. For Q.F. guns with interrupted or coned breech screws the striker is contained in the breech screw, but, in order to provide for safety, a small lever cam or other contrivance is fitted which, when the mechanism commences to open, is operated by the hand lever and withdraws the striker from contact with the primer inserted in the cartridge case. The striker consists of a steel needle, with the stem insulated by ebonite or some similar material, contained in an outer steel sheath. The sheath is formed with a foot or lug which is acted upon by the safety gear; a collar is also provided for taking the thrust of the main spring. Another form of lock now much in favour, especially for field-gun mechanisms, is that known as a trip lock. It is mainly used for percussion firing but can also be combined for use with electric tubes. In this pattern the striker is withdrawn, cocked and released by the continuous pull of a hand lever attached to the mounting or by a lanyard attached to the lock. Should a miss-fire occur the striker may be actuated as often as necessary by releasing the hand lever or lanyard and again giving a continuous pull (fig. 46). In all modern heavy guns, especially when firing to windward, there is a tendency, when the breech is opened Back rapidly after firing, for a sheet of flame to issue !lash. from the open breech. It was practically un- known with the old black powders, but is of frequent occurrence with all smokeless propellants. If the gun is loaded immediately after the breech is opened the fresh charge may be ignited and an accident caused. Several serious accidents have already been traced to this cause, notably one on the United States battleship " Missouri " on 13th April 1904, when 33 lives were lost. The flame is due to the large amount of highly heated carbonic oxide remaining in the gun from the explosion of the charge; this mixing with the oxygen of the air when the breech is opened burns rapidly as a sheet of flame in rear of the gun, and should wind be blowing down the gun the action is more intense. By looking into the gun from the muzzle, before the breech is opened, the gas can often be seen burning with a pale-blue flame as it slowly mixes with air and a curious singing noise is heard at the same time. It is now usual to fit a special apparatus on the gun, so that directly the breech is partly opened a blast of compressed air is allowed to enter the rear end of the chamber and thus sweep the whole of the residual gas out at the muzzle. The purpose of the obturator is to render the breech end of the gun gas-tight, and to prevent any escape of gas past the breech mechanism. In the first Obturatora. Armstrong B.L. gun this object was attained by fitting to the breech block a copper ring coned on the exterior; the coned surface was forcibly pressed by screwing up the breech screw against a corresponding copper ring fitted at the breech opening of the gun chamber. It is only possible to use this method when the copper surfaces can be jammed together by a powerful screw. Except the above, all obturators in use are arranged to act automatically, i.e. the pressure set up in the gun when it is fired expands the arrangement and seals the opening; immediately the projectile leaves the bore the pressure is relieved and the obturator, by its elasticity, regains its original shape, so that the breech mechan- ism can be opened or closed with ease. In the French naval service B.L. guns have been in use since 1864, and the system of obturation was arranged on the same expansion principle as the leather packing ring of the hydraulic press. A steel ring A (fig. 47) of cupped form was fastened by a screwed plug to a thick steel plate, carried on the face of the breech screw, so that it could rotate when the breech screw was rotated in opening or clos- ing the gun. The outer lip of the cup fitted against a slightly coned seating formed in the breech end of the gun chamber. When the gun was fired, the gas pressure expanded the cup ring and forced it into close bearing against the seating in the gun and the thick steel plate on the breech screw, thus preventing any escape of gas. Very similar to this was the Elswick cup obturator (fig. 48) intro- duced by the Elswick Ordnance Company in 1881; its rear surface was flat and it was held by a central bolt against the front of the breech screw which was slightly rounded. The cup yielded to the gas pressure until it was supported by the breech screw; this action expanded the lip against a copper seating, let into the gun, which could be renewed when necessary. Many of both types I are still in use and act perfectly efficiently if carefully treated. The use of modern smokeless powder renders them and similar devices, such as the Broadwell ring (fig. 49), &c., peculiarly liable to damage, as a slight abrasion of the lip of the cup or ring, or of its seating, allows gas to escape, and so accentuates the defect with each round fired. Unless, therefore, the fault be immediately remedied considerable damage may be caused to the gun. The Broadwell gas ring is still in use in the French naval service, where it is made of copper (fig. 5o), and also of steel in a modified form (Piorkowski) in the German service (fig. 51) ; in the last-named service, owing to the defect already named, all the latest guns, both light and heavy, use metal cartridge cases. In the French navy, as in most other services, cartridge cases are used for the smaller and medium guns only. One of the most efficient obturators not liable to damage is the plastic device introduced by Colonel de Bange of the French service and adopted by the French army and also by the British and other governments. It consists of a pad (fig. 52) made up of a strong annular-shaped canvas bag A, containing a mixture of asbestos fibre and mutton suet; the bag with its contents is placed in a properly formed die and subjected to hydraulic pressure by which it becomes hard and firm. The pad so made is then placed on the front of the breech, screw B, and it is protected on its faces by disks C, C, of metallic tin or copper having steel wedge rings on the outer edges; the circumference of the complete pad and disks issteel wedge ring into which the axial head fits. On firing the gun the head is forced into the wedge ring and expands it against the seating in the gun. One other means of obturation has to be considered, viz. metallic cartridge cases. These are made of a kind of brass; aluminium cases have been experimented with, but have not proved satisfactory. The case (fig. 54) acts on the same principle as the cup obturation and is extremely efficient for the purpose; more-over, they have certain advantages conducive to rapid firing when used for small guns. The idea has developed from the use of such cartridges in small arms, and larger cartridges of the same type were introduced for 3-pounder and 6-pounder guns by Hotchkiss and Nordenfelt about the year 188o for the purpose of rapid firing against torpedo boats. Then in 1886 the Elswick Company produced a 36-pounder (soon converted to a 45-pounder) of 4.7-in. calibre with the powder charge contained in metallic cases, and about 1888 a 6-in. 100-pounder gun using similar cartridges. A special advantage of the cartridge case is that it contains the firing primer by which the charge is ignited and consequently renders the firing gear of the gun more simple; on the other hand, should a miss-fire occur the gun must be opened to replace the primer. This is a proceeding liable to produce an accident, unless a long enough time is allowed to elapse before attempting to open the breech ; guns having de Bange obturators and firing tubes inserted after the breech is closed are therefore safer in this respect. Some means of extracting the case after firing must be fitted to the gun; this is simple enough with small guns, but with those of heavy natures the extractor becomes a somewhat ponderous piece of gear. Metallic cases of a short pattern have been tried for large calibre guns; although their action is quite efficient, they are difficult to handle, and if a case must be used it is preferable to employ a fairly long one. It was for this reason that in England up to 1898 it was considered that for guns above 6-in. calibre the de Bange obturation was the most advantageous. Since then the de Bange obturator has been employed in guns of 4-in. calibre and above, the cart-ridge case being retained only for 3-in. and smaller guns. Krupp, however, uses cartridge cases with all guns even up to 12-in. calibre, but this is undoubtedly due to the difficulties, which have already been noticed, attending the use of smokeless powder with the ordinary forms of obturation applicable to the wedge breech system. In the most modern Krupp 12-in. guns the charge is formed in two pieces; the piece forming the front portion of the charge is contained in a consumable envelope, while the rear portion is contained in a brass cartridge case, which forms the obturator, about 48 in. long. It will be seen that such large and heavy cases add to the difficulties which occur in handling or stowing the am-munition of large calibre guns, and although the use of cartridge cases with small guns adds to their rapidity of firing this is not the case with heavy guns. It seems, therefore, that the balance of advantages is certainly in favour of the de Bange system, for all guns except those of small calibre. With ordinary field guns cart-ridge cases are now considered obligatory owing to their convenience in loading. While the ordinary types of plastic obturators last for an indefinite time a cartridge case can be used for a limited number of rounds only, depending on the calibre of the gun; with field guns from ten to twenty rounds or even more may be fired from one case if care is taken to reform it after each round; with large guns they will not, of course, fire so many. Cartridge cases are an expensive addition to the ammunition, so that there should be no doubt about the advantages they offer before they are definitely adopted for heavy guns. The rapidity with which modern guns can be fired and the "ioi-taous energy they develop is especially striking when one generally only slightly coned and fits into a corresponding seating formed at the breech end of the chamber, the canvas of the circumference of the pad being in immediate contact with the seat. In the English service the steep cone pattern (fig. 53) of de Bange obturator is used with mechanisms having the Welin screw. In front of the pad is placed a strong steel disk formed with a spindle, and called a mushroom head D, the spindle passing through the hole in the pad and through the breech screw, being secured in rear by a nut. The firing vent is generally drilled through the mushroom head and spindle and the part is then termed a " vent axial." On the gun being fired the gas exerts a great pressure on the mushroom head, which compresses the pad and squeezes it out on the circumference into close contact with the seating, thus forming a perfect gas seal. It is found that this apparently delicate arrangement will stand considerable ill-usage and act perfectly for an indefinite time, and, as it is easily replaced, it is regarded as one of the best and most reliable forms of obturator. In some countries the Freyre obturator is in use; this has a somewhat similar axial head to the de Bange, but the asbestos pad is replaced by a single considers the same facts in connexion with the early guns. Fave states in his Histoire et tactique des trois armes (p. 23) that during the invasion of Italy in 1494 by Charles Range VIII. the guns were so unwieldy and the firing so slow and power. that the damage caused by one shot could be repaired before the next could be fired. The range, too, about too yds. for battering purposes, now seems absurdly short; even at Waterloo 1200 yds. was all that separated the antagonists at the commencement of the battle, but they approached to within 200 or 300 yds. without suffering serious loss from either musketry or gun fire. Nelson fought his ships side by side with the enemy's; and fifty years after Nelson's day a range of 'coo yds. at sea was looked upon as an extreme distance at which to engage an enemy. Contrast this with the range of 12,000 yds. at which the opposing Russian and Japanese fleets more than once commenced a naval battle in 1904, while the critical part of the action took place at a distance of 7000 yds. These long ranges naturally intensified the requirements of the British and other navies, and, so that they shall not be outclassed and beaten by an enemy's long-range fire, guns of continually increasing power are demanded. In 1900 a 12-in. gun of 40 calibres was considered all that was necessary. After the Russo-Japanese War the demand rose first for a 45-calibre gun and then for a 50-calibre gun, and muzzle velocities from about 2400 f.s. to about 3000 f.s. In 1910 greater shell power was demanded, to meet which new type guns of 13.5-in. and 14-in.calibre were being made. In the days of M.L. heavy guns one of the most difficult problems was that of loading. The weight of the shell and powder was such that some mechanical power had to be employed for moving and ramming them home, and as hydraulic gear had by that date been introduced it was generally used for all loading operations. To load, the guns had to be run back until their muzzles were within the turret, or, in the case of the 16-in. 8o-ton guns of H.M.S. "Inflexible," until they were just outside the turret. The guns were then depressed to a fixed angle so as to bring the loading gear, which was protected below the gun deck, in line with the bore; the charge was first rammed home and then the projectile. With this arrangement, and in order to keep the turret of manageable dimensions, the guns had to be made short. Thus the 12.5-in. 38-ton M.L. gun had a length of bore of but 16 calibres, and the largest English .service gun of 16-in. diameter had a bore of 18 calibres in length; while the largest of the type weighing loo tons, built by Sir W. G. Arm-strong & Co., for the Italian navy, had a bore of 17.72 in. and a length of 20 calibres. The rate of fire was fairly rapid—two rounds could be fired from one turret with the t 2.5-in. guns in about three minutes, while it took about four minutes to fire the same number from the 8o-ton and too-ton gun turrets. The possibility of double loading M.L. guns was responsible for the bursting on the 2nd January 1879 of a 38-ton gun in a turret on H.M.S. " Thunderer "; and it was partly due to thisaccident that B.L. guns were subsequently more favourably regarded in England, as it was argued that the double loading of a B.L. gun was an impossibility. With the B.L. system guns gradually grew to be about 30 calibres in length of bore, and they were not made longer because this was considered a disadvantage, not to be compensated for by the small additional velocity which the old black and brown prismatic powders were capable of imparting with guns of greater length. Increase in the striking energy of the projectile was consequently sought by increasing the weight of the projectile, and, to carry this out with advantage, a gun of larger calibre had to be adopted. Thus the 12-in. B.L. gun of about 25 calibres in length gave place to the 13.5-in. gun of 3o calibres and weighing 67 tons, and to the 16 25-in. also of 3o calibres and weighing i r r tons. The 1o,000- or 12,000-ton battleships carrying these enormous pieces were, judged by our present-day standard, far too small to carry such a heavy armament with their ponderous armoured machinery, which restricted the coal supply and rendered other advantages impossible; even the 24,000-ton battleships are none too large to carry the number of heavy guns now required to form the main armament. The weight and size of the old brown prismatic charges had also reached huge dimensions; thus, while with heavy M.L. guns the weight of the full charge was about one-fourth that of the projectile, it had with heavy B.L. guns become one-half of the weight of the shell or even a greater proportion. The introduction of smokeless powder about 189o, having more than three time§ the amount of energy for the same weight of the older powders, allowed longer guns to be used, which fired a much smaller weight of charge but gave higher velocities; the muzzle or striking energy demanded for piercing hard-faced armour could consequently be obtained from guns of more moderate calibre. The 13.5-in. and 16.25-in. guns were therefore gradually discarded and new ships were armed with 12-in. guns of greater power. As the ballistic requirements are increased the weight of the charge becomes proportionately greater; thus for the Lt..* DREW, aacr E W present high velocity guns it has reached a ratio of about 0•4 the case at the present time as regards both projectiles of the weight of the projectile. and armour. As a matter of fact, armour, at the present-day fighting ranges, is rather ahead of artillery—hence the demand for greater power; but even with this the probability of perforation is small, and is usually only obtained when the projectile strikes normally to the surface of the plate; the chance of this happening in action is somewhat re-mote. During the Russo-Japanese War no instance of perforation of the thick belt or turret armour is known; the chief cause of the Russian losses was the bursting of 1z-in. and 6-in.shells inside the unarmoured portions of their ships; it is stated that no ship survived after being struck by ten Iz-in. projectiles. Some authorities have lately sought to increase the F/R/NG WIRE muzzle energy—without adding weight or length to the gun—by in-creasing the weight The progress of artillery and the improvements made in armour of the projectile. This can be done to a limited extent with have been reciprocal; as the protective value of iron and beneficial results, but it is impossible to carry the idea very far, 7 as the projectile becomes very long and difficulties may be encountered with the rifling; or, if these are avoided, the thickness of the walls of the shell is increased so much that
End of Article: SHAFT TO
SHAFT (O. Eng., sceaft, from scafan, to shave; the ...

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click and select "copy." Paste it into a website, email, or other HTML document.