EP0874114B1 - Security cylinderlock having an increased picking resistance - Google Patents

Abstract

The lock has a protective sleeve (1) containing a safety barrel with a stator (8) and rotor (9) controlled by a key. Between the forward end of the barrel and the sleeve the lock incorporates an anti-drilling plate (10) with a slot (11) for the key, and a guard ring (18) with a series of inserts (17). The inserts can be conical or curved in shape, having their pointed or curved faces towards the front of the lock and their axes parallel to that of the ring, which is fitted to a step (10) on the anti-drilling plate.

Description

The present invention relates to a safety cylinder intended for the operation of a lock, said cylinder comprising a safety barrel arranged inside a protective sleeve intended to protect the barrel against attempted break-ins.

We know that a safety barrel intended for the maneuver a lock consists of a stator inside which can turn a rotor, the rotor having a key housing; ways to keying are provided between the rotor and the stator, so that the declaving occurs when the appropriate key is inserted in the key housing. When the correct key is used, the rotor can therefore rotate relative to the stator and drive a rotating member which causes the operation of the lock with which the barrel is associated. Ways of keying interposed between the rotor and the stator are generally arranged in planes which are radial with respect to the rotor. For tamper with the lock, specialists are looking to destroy the keying means with a drill driven by a drill parallel to the axis of the rotor, in which case, if the means of are destroyed, the perpetrator can rotate freely the rotor relative to the stator and cause the opening of the lock. It is therefore necessary to protect the front face of the barrel to avoid this type of break-in.

French patent 2,690,192 has already proposed place an anti-drilling disc in front of the key entry of a rotor safety barrel. This pellet is free to rotate inside a protective sleeve into which the safety barrel to be protected is inserted; the patch is crossed by a slot allowing the introduction of the key to the key housing of the barrel rotor. When attacking drilling such a pellet, the drill drives the pellet in rotation, which prevents drilling. Of course, such a tablet must be likely to resist impact, otherwise it would be enough to break the pellet, extract the pieces out of the protective sleeve and then attack the barrel rotor with a drill. All the difficulty of developing such a tablet therefore lies in the fact of finding a compromise between resistance to drilling, which is all the better that the hardness of the material is higher, and the impact resistance, which unfortunately decreases when the hardness of the material used. In the aforementioned French patent, it has been proposed to insert inserts in the pellet material with a hardness greater than that of the tablet: the material of the tablet can thus be of a hardness moderate to be able to withstand shocks and if the pellet undergoes attempt to drill, the drill used breaks when it comes into contact with a very hard insert. Unfortunately, the anti-drilling tablet thus proposed does not have the expected effectiveness due to the fact that the inserts are put in place by the rear face of the burglar-resistant disc, so that if they are exposed by a start of drilling, they can be chased with a pin punch, the barrel retreating under the blows transmitted by the pin punch and the inserts then falling between the face front of the barrel and the rear face of the pellet. It should be noted just remove one of the inserts from the pellet described in the aforementioned patent so that there is sufficient passage to allow the drilling. To avoid this inconvenience, one could imagine brazing the inserts in the pellet, but, in this case, the cost price of the tablet increases considerably due to labor costs of work.

In addition, the tablet described in the French patent 2,690,192 has two external diameters in its thickness, the shoulder between the two diameters allowing the retention of the tablet inside the protective sleeve. The connection between two diameters is made at a right angle and is in the vicinity immediate pastille inserts; this results in a weakening of the patch at the connection angle.

The object of the invention is to improve the burglar-proof characteristics a safety cylinder.

The invention relates to a safety cylinder for lock having improved burglary protection, said cylinder comprising a safety barrel arranged inside a chamber formed in a protective sleeve, said chamber being delimited by a bottom on the side of the front face of the protective sleeve, said barrel comprising a rotor capable of rotating around its axis at inside a stator, keying means being arranged between rotor and stator and can be operated by a key inserted in a rotor key housing, said protective sleeve bearing on its front face, facing the rotor, an anti-drilling pad in which is provided a key passage.

According to a first characteristic, the invention relates to a safety cylinder of the type defined above, in which the anti-drilling pad includes, on both sides of the key passage, at least one pellet insert made of a material with a hardness greater than that of material constituting the pellet, this cylinder being characterized by the fact that each pad insert constitutes a pin arranged substantially parallel to the plane of the key passage and substantially perpendicular to the axis of the patch.

It is clear that, according to this provision, the inserts do not cannot be driven out with a pin punch in the direction of the barrel and the positioning of the pins in the pad prevents a drill from cross said patch without damage.

According to a preferred embodiment, the anti-drilling tablet is free to rotate and has a front face facing the outside, of smaller diameter than its rear face facing the barrel rotor, the outer side wall of the pellet comprising a frustoconical zone between its front and rear faces: the front face of the protective sleeve surrounds the anti-drilling disc and the presence of the frustoconical zone makes it possible to significantly strengthen the resistance to deformation of the front face of the protective sleeve in the area where the pellet increases in diameter; indeed if in this area the front face is too thin, it is possible to deform the face frontal enough to open a hole allowing the extraction of the anti-drilling tablet. In addition, the shape of the frustoconical area above proposed allows the drill to be deflected when the drilling attack takes place at the right of the said zone. In addition, to further reduce the risk of extraction of the pellet, it is proposed, according to the invention, that the the patch has, on its rear face, a peripheral flange which, preferably does not connect directly to the frustoconical area and which constitutes an additional retention element of the pellet.

Advantageously, the pellet includes a pin each side of the key passage, the axes of the two pins being symmetrical with respect to the mean plane of the key passage; the axes pins are preferably arranged relative to the area frustoconical of the pellet, on the side of the rear face of said pellet.

We can plan to spare, between the frustoconical zone and the flange of the patch, a cylindrical seat in which are made the two parallel bores where the two are arranged lozenge pins; advantageously, the two pins are inserted in blind bores made upside down in the pellet. This head-to-tail arrangement of the pin bores is particularly interesting due to the fact that there are necessarily a weakening of the patch between the key passage and the area where a pin bore opens; if the bores are not not arranged upside down, the break-in action may break of the pellet in the weakened areas, which gives rise to a free sector of low angular opening which can be extracted at the relatively easily clamps, which makes extraction easier of the lozenge. On the contrary, by adopting a head to tail arrangement, the break-in action will break the wafer substantially according to a diametral plan, which will no longer allow easy extraction of a small angular sector.

According to an advantageous embodiment, the rear face of the pad has a recess making it possible to accommodate the front face of the barrel rotor, which projects slightly from the face front of the stator; the front face of the patch is curved, in particular in the shape of a spherical cap, and has its convexity towards the outside; the area of the front face of the protective sleeve, which surrounds the front face of the patch, forms a depression, by example of a conical shape, the concavity of which faces outside.

According to another characteristic of the invention, which can possibly be taken in combination with the characteristics previous relating to the anti-drilling pad, the safety cylinder of the previously defined type is characterized by the fact that a plurality of protector inserts is placed in a crown around the anti-drilling tablet, in housings in the sleeve protector, at the bottom of the room where the barrel is housed. We observed, indeed, that one of the ways to overcome the difficulty corresponding to the presence of an anti-drilling tablet consists of present the drill on the side of the pad at an angle by relative to the axis of the safety cylinder, so that the drill can reach the area behind the patch without it being necessary destroy or extract the anti-drilling tablet. By having the crown inserts around the patch in the protective sleeve, we creates obstacles in the path of such a bias drilling and, by therefore, the burglary protection is greatly improved.

According to a preferred embodiment, the inserts of protector have a frustoconical shape, the small base of which is directed towards the front of the protective sleeve. This advantageous form of inserts to prevent them from being released from their housing; indeed, if we insert balls in the drilling area, the drill which happens on a broken ball, but the ball is thus exposed and can be extracted from its housing, which is not the case with an insert frustoconical whose large base is arranged opposite the face front of the protective sleeve. We can predict that the small base of protector inserts are rounded, for example in the shape of a cap spherical, and has its convexity towards the front face of the sleeve protector; in this way, the attempt to gripping an insert, assuming that the insert was exposed by a drill bit.

Advantageously, all of the protector inserts are integral with a circular ring; indeed, the installation of inserts frustoconical in the bottom of the protective sleeve chamber is difficult to achieve with an automatic assembly machine. We have so thought to link all the inserts together with a circular ring to form a ring, the handling of which is easier. We can provide that all protector inserts have their axes parallel to the axis of said ring and protrude outside the ring of this Ring. Preferably, the ring of the protector inserts is put in place on a cylindrical surface of the anti-drilling tablet; advantageously, if an anti-drilling tablet is used according to the first characteristic of the invention, as defined above, the cylindrical reach can be that in which the two open pellet pin bores.

Advantageously, the protector inserts are not put in places that opposite the angular barrel sectors comprising the keying means to be protected.

According to a preferred embodiment, the sleeve chamber protector where the barrel is located is cylindrical and has, on its side wall, parallel to its generator direction, grooves allowing the installation of the ring at the bottom of the chamber of the protective sleeve by sliding inserts in said grooves towards the bottom of the chamber, a sheath being interposed between the stator of the barrel and the sleeve chamber on at least part of the sector occupied by said grooves. The scabbard may have on its external face of the ribs complementary to the grooves of the chamber, which allows its easy positioning on an angular sector determined from the room to the right of the protector inserts. The scabbard may have, at its end intended to come from the side of the face front of the sleeve, a flat crown positioned around a cylindrical bearing surface of the anti-drilling disc, said crown being in support on the bottom of the chamber and having as external contour the internal cross section of said chamber; in case we use a anti-drilling tablet according to the first characteristic of the invention, as defined above, the flat crown can be positioned around the flange of the patch.

Provision may be made for the axis of the rotor to be offset from the axis of the stator, the sleeve then extending over a sector close to 180 ° arranged below the plane which contains the axis of the rotor and which is perpendicular to the plane containing the axes of the rotor and the stator, i.e. on the side of this plane where the axis of the stator is not located.

To better understand the object of the invention, we will now describe them as purely illustrative examples and not limiting an embodiment shown in the accompanying drawing.

• la figure 1 représente en perspective éclatée les différents éléments d'un cylindre de sûreté selon l'invention ;
• la figure 2 représente, en coupe, le cylindre de sûreté de la figure 1 monté sur une porte pour la commande de la serrure de ladite porte ;
• la figure 3 représente, en élévation, le manchon protecteur du cylindre de la figure 1 ;
• la figure 4 représente une vue selon IV-IV de la figure 3 ;
• la figure 5 représente une coupe selon V-V de la figure 4 ;
• la figure 6 représente une coupe selon VI-VI de la figure 3 ;
• la figure 7 représente une vue frontale de la pastille anti-perçage du cylindre de la figure 1 ;
• la figure 8 représente une coupe selon VIII-VIII de la figure 7 ;
• la figure 9 représente une vue selon IX-IX de la figure 7 ;
• la figure 10 représente une vue arrière selon X-X du fourreau du cylindre de sûreté de la figure 1 ;
• la figure 11 représente une coupe selon XI-XI de la figure 10 ;
• la figure 12 représente une vue selon XII-XII de la figure 11.

On this drawing :

• Figure 1 shows in exploded perspective the different elements of a safety cylinder according to the invention;
• 2 shows, in section, the safety cylinder of Figure 1 mounted on a door for controlling the lock of said door;
• Figure 3 shows, in elevation, the protective sleeve of the cylinder of Figure 1;
• Figure 4 shows a view along IV-IV of Figure 3;
• Figure 5 shows a section along VV of Figure 4;
• Figure 6 shows a section on VI-VI of Figure 3;
• 7 shows a front view of the anti-drilling pad of the cylinder of Figure 1;
• Figure 8 shows a section along VIII-VIII of Figure 7;
• Figure 9 shows a view along IX-IX of Figure 7;
• 10 shows a rear view along XX of the sheath of the safety cylinder of Figure 1;
• Figure 11 shows a section along XI-XI of Figure 10;
• FIG. 12 represents a view along XII-XII of FIG. 11.

Referring to the drawing, we see that designated by 1, as a whole, the protective sleeve of a safety cylinder according to the invention. The sleeve 1 has a front face 1 a and an external flange 1 b which surrounds its rear zone, that is to say the zone which is opposite to the front face 1 a . The protective sleeve 1 externally has a generally cylindrical shape and its front face is that which appears outside a door which is equipped with such a safety cylinder. In a known manner (see in particular French patent 2,576,626), the protective sleeve is, at its front face, surrounded by a counter plate 2, which is kept applied to the door 3 by three screws 4 bearing on the lock 5 of the lock 6 with which the safety cylinder according to the invention is associated. 4 screws pass freely through the collar 1b of the protective sleeve 1 and cooperate with bores in the thickness of a tube 2 welded to the rear against the plate 2. Furthermore, the edges of the counter plate 2 are held by screw 4 has also taking support on the Foncet 5 and screwing into the terminals 2b which are secured against the plate 2 to the back thereof.

The protective sleeve 1 internally defines a chamber 7 of cylindrical shape but of non-circular cross section. Inside the chamber 7, is arranged the stator 8 of a safety barrel, whose rotor 9 causes, by its rear end, the operation of the lock 6, the front end of the rotor being that which is neighboring of the front face 1 a of the protective sleeve 1. The stator 8 of the barrel is secured, by its rear face, to the pin 5 of the lock 6.

The chamber 7 is open at its rear end and, on the side of the front face 1 a , it has a bottom 7 a . In the barrel, the axis of the rotor 9 is offset by 4 mm relative to the axis of the stator 8. The front face of the protective sleeve 1 has a circular orifice where the front part of a designated anti-drilling disc is arranged. by 10 as a whole.

The pad 10 includes a key passage 11, which allows the key associated with the safety cylinder to pass through the pad 10; it is delimited externally by a side wall made up of four successive parts: a cylindrical front part 10 b , which is connected to the front face 10 a of the patch; a rear part 10 e , which constitutes a circular peripheral flange; a frustoconical zone 10 c , which connects with the cylindrical part 10 b ; and a part 10 d , which constitutes a cylindrical bearing surface connecting the conical part 10 c to the base of the collar 10 e . A recess 12 is formed on the rear face of the flange 10 e and is intended to receive the front face of the rotor 9, front face which is slightly projecting relative to the front face of the stator 8.

Parallel to the mean plane of the key passage 11, two blind holes 13 a , 13 b are arranged head to tail in the cylindrical surface 10 d , the axes of these two bores being symmetrical with respect to the mean plane of the passage of key 11. In these two bores 13 a , 13 b , pins are inserted, respectively 14 a , 14 b , and the pins are held in place by a slight crimping made in 15. The pins 14 a , 14 b are made of a material harder than that of the anti-drilling pad, this material can be brittle: it can be, for example, highly hardened steel, carbide or ceramic.

The front face 10 a of the pad 10 is disposed at the bottom of a frustoconical depression 1 c , which has the front face 1 a of the protective sleeve 1. The part 10 b of the pad 10 projects very slightly at the bottom of the depression 1 c , but the material of the sleeve 1 follows the outline of the parts 10 b , 10 c of the patch 10 and constitutes a retaining lip of said patch, this lip having, due to the frustoconical shape of the part 10 c , a increasing thickness, when following its contour from the front face 1a in the direction of the interior of the protective sleeve.

In the bottom 7 a of the chamber 7, seven frustoconical housings 16 have been formed, the small bases of which are shaped according to a spherical cap and are arranged on the side of the front face 1 a of the protective sleeve 1. The housings 16 are arranged in crown around the axis of the rotor 9, over a sector of approximately 260 °, said sector being symmetrical with respect to the plane which contains the axes of the rotor 9 and the stator 8. In these housings 16, inserts are inserted of protector 17 having a shape corresponding to that of the housings 16, the inserts 17 therefore comprising a frustoconical side wall and an end wall in the form of a spherical cap. All the inserts 17 are arranged in a crown on the outer edge of a circular ring 18, all of the inserts 17 and the ring 18 constituting a ring 19. The ring 18 is housed in a recess 20 of the protective sleeve 1, said recess being situated immediately behind the zones where the parts 10 b and 10 c of the pad 10 are placed. The ring 18 of the ring 19 is therefore placed around the cylindrical surface 10 d of the pad 10 and the peripheral flange 10 e of the patch 10 comes to bear against the ring 18 of the ring 19.

To set up the ring 19 against the bottom 7 a of the chamber 7, it is necessary to practice on the side wall of the chamber 7 grooves 21, which allow the passage of the frustoconical inserts 17 in relief on the outside of the ring 18. These grooves are formed parallel to the generatrices of the chamber 7, that is to say parallel to the axis of the rotor 9 or of the stator 8 of the barrel placed in the chamber 7.

Given the offset of the axes of the rotor 9 and the stator 8, it is necessary to support the stator 8 in the chamber 7 in order to bring the rotor 9 opposite the pellet 10, so as to allow the setting in position of the key passage 11 vis-à-vis the key housing made in the rotor 9. A sheath 22 is therefore put in place, which has the shape of a cylindrical sector, the inner wall of which has a circular cross section centered on the axis of the stator 8 and the outer wall of which has ribs 23 having profiles complementary to that of the grooves 21. The sheath 22 extends over approximately 180 ° around the axis of the rotor and is provided, at its end intended to come against the bottom 7 a of the chamber 7, of a flat crown 24, the thickness of which is substantially equal to that of the peripheral flange 10 e ; the flat crown 24 delimits a circular orifice whose diameter is equal to that of the peripheral flange 10 e which is therefore housed inside the crown, this orifice therefore being centered on the axis of the rotor 9. A its lower part, the crown is formed by the front end of the sheath 22 and, at its upper part, it is delimited by a circular external contour centered on the axis of the stator 8.

It can be seen that the mounting of the safety cylinder which has just been described is extremely simple: the pad 10 is first assembled in the ring 19; from the rear opening of the chamber 7, this sub-assembly is then put in place in the front part of the protective sleeve 1, so that the front face 10 a is flush with the bottom of the depression 1 c , the ring 18 of the ring 19 coming to bear at the bottom of the recess 20. The sheath 22 is then put in place, said sheath coming to lock the pellet 10 in position by resting on the rear of the peripheral flange 10 e , the crown 24 from surrounding said peripheral flange. The barrel is then put into place inside the chamber 7, the front face of the rotor 9 coming to engage in the recess 12 of the pad 10.

This security cylinder is particularly effective against break-ins for the various reasons which have been previously detailed. A piercing action acting directly on the pad is hampered by the fact that this pad is free to rotate; if, nevertheless, the drill enters the pellet, it breaks when it comes into contact with the pins 14 a , 14 b . If one seeks to pass on the side of the anti-drilling pad to reach the rotor / stator keying means at an angle, the drill bit falls on the inserts 17 and breaks, since the ring 19 is made of a very hard of the same type as that of pins 14 a , 14 b .

Maintaining the barrel in abutment against the peripheral flange 10 e and the crown 24 is obtained by virtue of the fact that the barrel is carried by the bolt 5 and that the protective sleeve 1 is subjected to the action of springs (not shown), which are inserted between the tube 2 a and the collar 1 b of the protective sleeve 1. The greater or lesser compression of these springs makes it possible to adapt the assembly to doors of slightly different thicknesses for a barrel stator of given length, by playing on the play existing between the collar 1 b and the tube 2 a . The extraction of the protective sleeve 1 towards the outside is limited by the stroke existing between the tube 2 a and the collar 1 b .

Claims (24)

1. Safety cylinder for a lock with improved protection against forcing, the said cylinder comprising a safety barrel located inside a chamber (7) made in a protective sleeve (1), the said chamber (7) being delimited by an end wall (7a) at the same end as the front face (1a) of the protective sleeve (1), the said barrel having a rotor (9) capable of turning about its axis inside a stator (8), keying means being located between rotor and stator and being operable by a key introduced into a key housing in the rotor (9), the said protective sleeve (1) carrying, on its front face (1a), facing the rotor (9), a drill-proof pellet (10) in which a keyhole (11) is made, characterized in that a number of protective inserts (17) are placed in a ring around the drill-proof pellet (10) in housings (16) formed in the protective sleeve (1) at the end of the chamber (7) in which the barrel is housed.
2. Cylinder according to Claim 1, characterized in that the protective inserts (17) have a frustoconical shape, the small base of which faces towards the front face of the protective sleeve (1).
3. Cylinder according to Claim 2, characterized in that the small base of the protective inserts is domed and its convex side faces towards the front face of the protective sleeve (1).
4. Cylinder according to one of Claims 1 to 3, characterized in that all the protective inserts (17) are secured to a circular annulus (18) to form a ring (19).
5. Cylinder according to Claim 4, characterized in that all the protective inserts (17) have their axes parallel to the axis of the annulus (18) which connects them and project on the outside of this annulus (18).
6. Cylinder according to one of Claims 4 and 5, characterized in that the ring (19) of protective inserts (17) is fitted onto a cylindrical bearing surface (10d) of the drill-proof pellet (10).
7. Cylinder according to one of Claims 1 to 6, characterized in that the protective inserts (17) are fitted only facing angular sectors of the barrel which have the keying means that need protecting.
8. Cylinder according to Claim 5 taken alone or in conjunction with one of Claims 6 and 7, characterized in that the chamber (7) of the protective sleeve (1) in which the barrel is housed carries, in its side wall, parallel to its generatrix direction, grooves (21) allowing the ring (19) to be fitted to the end of the chamber (7) of the protective sleeve (1) by sliding the protective inserts (17) along the said grooves (21) towards the end (7a) of the chamber (7), a sheath (22) being inserted between the stator (8) of the barrel and the chamber (7) of the sleeve (1) over at least part of the sector occupied by the grooves (21).
9. Cylinder according to Claim 8, characterized in that the sheath (22) comprises, on its outer face, ribs (23) which complement the grooves (21) of the chamber (7).
10. Cylinder according to one of Claims 8 and 9, characterized in that the sheath (22), at its end intended to be on at the same end as the front face (1a) of the sleeve (1), has a flat roundel (24) positioned around a cylindrical bearing surface (10e) of the drill-proof pellet (10), the said roundel (24) resting against the end (7a) of the chamber (7) and having, as its external profile, the internal cross section of the said chamber (7).
11. Cylinder according to one of Claims 8 to 10, characterized in that the axis of the rotor (9) is offset with respect to the axis of the stator (8), the sheath (22) extending over a sector close to 180° arranged, with respect to the plane containing the axis of the rotor (9) and which is perpendicular to the plane containing the axes of the rotor (9) and of the stator (8), on the side that does not contain the axis of the stator (8).
12. Cylinder according to one of Claims 1 to 11, characterized in that the drill-proof pellet (10) comprises, on each side of the keyhole (11), at least one pellet insert (14a, 14b) made of a material that is harder than the material of which the pellet (10) is made.
13. Cylinder according to Claim 12, characterized in that each pellet insert constitutes a pin (14a, 14b) arranged roughly parallel to the plane of the keyhole (11) and roughly perpendicular to the axis of the pellet (10).
14. Cylinder according to one of Claims 12 and 13, characterized in that the drill-proof pellet (10) is free to rotate and has a front face (10a) facing outwards, with a smaller diameter than its rear face which faces towards the rotor (9) of the barrel, the exterior side wall of the pellet (10) having a frustoconical zone (10c) between its front and rear faces.
15. Cylinder according to Claim 14, characterized in that the drill-proof pellet (10) comprises, on its rear face, a peripheral flange (10e) which does not connect directly with the frustoconical zone (10c).
16. Cylinder according to Claim 13, taken alone or in conjunction with one of Claims 14 and 15, characterized in that the pellet (10) has a pin (14a, 14b) on each side of the keyhole, the axes of the two pins (14a, 14b) being symmetric with respect to the mid-plane of the keyhole (11).
17. Cylinder according to Claim 14 taken alone or in conjunction with one of Claims 15 and 16, characterized in that the axes of the pins (14a, 14b) are arranged, with respect to the frustoconical zone (10c) of the pellet (10) , on the same side as the rear face of the said pellet (10).
18. Cylinder according to Claims 14 to 16 taken simultaneously, characterized in that, between the frustoconical zone (10c) and the flange (10e) of the pellet (10) there is a cylindrical bearing surface (10d) in which are made two parallel bores (13a, 13b) in which the two pins (14a, 14b) are placed.
19. Cylinder according to Claim 16 taken alone or in conjunction with one of Claims 17 and 18, characterized in that the two pins (14a, 14b) are inserted in blind holes (13a, 13b) formed head-to-toe in the pellet (10).
20. Cylinder according to one of Claims 12 to 19, characterized in that the rear face of the pellet (10) has a counterbore (12) to accommodate the front face of the rotor (9) of the barrel, which projects slightly with respect to the front face of the stator (8).
21. Cylinder according to Claim 14 taken alone or in conjunction with one of Claims 15 to 19, characterized in that the front face (10a) of the pellet (10) is domed and its convex side faces outwards.
22. Cylinder according to Claim 14 taken alone or in conjunction with one of Claims 15 to 20, characterized in that the zone of the front face (1a) of the protective sleeve (1) which surrounds the front face (10a) of the pellet (10) forms a depression (1c), the concave side of which faces outwards.
23. Cylinder according to Claims 6 and 18 taken simultaneously, characterized in that the ring (19) of protective inserts (17) surrounds the cylindrical bearing surface (10d) in which the two bores (13a, 13b) for the two pins (14a, 14b) are made.
24. Cylinder according to Claims 10 and 15 taken simultaneously, characterized in that the flat roundel (24) of the sheath (22) is positioned around the peripheral flange (10e) of the drill-proof pellet (10).

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