FR3101893A1 - EXCAVATION FINGER AND ASSOCIATED EXCAVATION SHOVEL - Google Patents

Abstract

The invention relates to an excavating finger (132) of a shovel (130) for fitting an excavation chain (8) for a ballast excavating device (4) below a railway track ( 2), the finger (132) being in one piece and comprising: a holding portion (132b) having a symmetry of revolution about a reference axis (X) of the finger (132), the holding portion (132b) being intended to be housed in a cylindrical housing (134) of the shovel (130); and a tip (132a) intended to project out of the cylindrical housing (134) of the shovel (130), the excavation finger (132) being characterized in that the holding portion (132b) comprises at least one groove (132c) annular configured to receive at least part of a locking rod (135), intended to ensure axial retention of the retaining portion (132b) in the cylindrical housing (134) so that the finger (132) is free to rotate around its reference axis (X). (Fig. 8)

Description

Excavation finger and associated excavation shovel

Technical field of the invention

The invention relates, in general, to the technical field of shovels intended to be fitted in particular to clearing or excavation chains.

The invention relates more specifically to an excavation finger, or claw, of a shovel intended to equip an excavation chain for a ballast excavation device below a railway track.

We know in the prior art work trains equipped with machines responsible for removing the ballast located under the sleepers of a railway track, and sorting it for possible reuse by dumping it on the track. These machines are commonly referred to as "barners". In a known manner, such work trains generally comprise a machine responsible for screening the ballast to preserve, on the one hand, the sound part of the ballast for its reuse, and on the other hand, to evacuate the worn part of the ballast in wagons provided for this purpose. In this way, the stripper-screener makes it possible to remove, sort the used ballast and replace the entire layer of ballast with the sorted healthy ballast as well as any additional supply of new ballast.

Such works trains are equipped with excavation chains consisting of a succession of links articulated between them, at least part of which is equipped with shovels intended to excavate the ballast. This chain is arranged in a displaceable or height-adjustable manner on the chassis of the railway vehicle. The chain is driven endlessly by a drive mechanism. The path of the chain is configured so that it has a straight portion of excavation located under the sleepers of the railway, the chain working on this portion of excavation transversely to the orientation of the rails of the railway by dragging and transporting with them the ballast. On either side of this rectilinear excavation portion are arranged brackets forming return devices for the excavation chain. These brackets are located at the ends of the rectilinear portion of excavation, the portion along which the ballast is removed, and are generally formed of a fixed angled wall on which the links of the chain slide successively. The chain circulates along a longitudinal arrival path then circulates on the rectilinear portion of excavation after having crossed a first bent portion formed by one of the brackets. The chain which continues on its way then leaves said rectilinear excavation portion to circulate on the longitudinal exit portion after having crossed a second bent portion formed by the other of the brackets. The shovels arrive on this rectilinear portion of excavation being unloaded and come out loaded with ballast towards the longitudinal exit portion. The longitudinal inbound and outbound portions are connected, in an area located above the rail vehicle, by a transverse dumping portion where the ballast is dumped onto conveyor belts. The shovels unloaded from the ballast then continue their journey towards the longitudinal portion of arrival, then repeating these operations.

These excavators are designed to meet many problems. In particular, they must be strong enough to ensure a certain number of predetermined cycles in order to ensure the excavation and transport of ballast with a minimum of maintenance. These shovels must also allow the efficient transport of the ballast to its dumping for the screening operation, this to improve the performance of the stripper by excavating the ballast as well as that of the screener to improve the rate of reuse of sound ballast.

Despite these objectives, and given the considerable stresses undergone by excavators, improving their resistance in order to minimize their maintenance is a constant problem in the continuous search for improvement.

To further improve their lifespan, it is also known to provide these shovels with reinforced fingers forming claws and placed in the extension of the shovel. Such fingers are designed in a very resistant way whose maintenance is easier than the link of the chain itself and which makes it possible to adapt more precisely to localized wear according to the forces undergone. This allows a reduction in the cost of maintenance and maintenance time, therefore machine downtime, which limits costs accordingly.

However, the problem of reducing the wear of the reinforcement fingers is still omnipresent, especially since these fingers have a dual function of protecting and limiting the wear of the shovel on the one hand, and participating with the shovel in the excavation of the ballast on the other hand.

The invention aims to remedy all or part of the drawbacks of the state of the art by proposing in particular a reinforcement finger and an associated excavation shovel which allow a reduction in the wear of the reinforcement fingers so as to be able to reduce maintenance operations aimed at replacing these consumable parts.

• une portion de maintien ayant une symétrie de révolution autour d’un axe de référence du doigt, la portion de maintien étant destinée à être logée dans un logement cylindrique de la pelle, et
• une pointe destinée à être en saillie hors du logement cylindrique de la pelle,

le doigt d’excavation étant remarquable en ce que la portion de maintien comprend au moins une gorge annulaire configurée pour recevoir au moins une partie d’une tige de blocage, destinée à assurer un maintien axial de la portion de maintien dans le logement cylindrique de sorte que le doigt est libre en rotation autour de son axe de référence.To do this is proposed, according to a first aspect of the invention, an excavation finger of a shovel intended to equip an excavation chain for a ballast excavation device below a railway track, the finger being one-piece and comprising:

• a holding portion having a symmetry of revolution around a reference axis of the finger, the holding portion being intended to be housed in a cylindrical housing of the shovel, and
• a tip intended to project out of the cylindrical housing of the shovel,

the excavation finger being remarkable in that the retaining portion comprises at least one annular groove configured to receive at least part of a locking rod, intended to ensure axial retention of the retaining portion in the cylindrical housing of so that the finger is free to rotate around its reference axis.

Thanks to such a combination of characteristics, the finger is configured so as not to be locked in rotation, which allows regular wear thereof. In this way, maintenance for the replacement of fingers is less frequent due to reduced wear.

According to one embodiment, the holding portion comprises a plurality of annular grooves, the annular grooves being parallel to each other and spaced from each other. In this way the excavation finger can receive a locking rod in one or the other of its annular grooves, corresponding to different axial positions of the excavation finger. Once the wear of the finger has been observed by an operator, it is then possible to move the excavation finger in its cylindrical housing by translating it outwards, namely in the direction of an increase in the tip projection out of the cylindrical housing of the shovel. The annular grooves therefore make it possible to index the finger according to a corresponding position, depending on the wear of said excavation finger. Such a characteristic allows prolonged use of the finger and therefore reduces the maintenance consisting in replacing a finger on the one hand, and limits the associated costs.

According to one embodiment, the finger has a symmetry of revolution around the reference axis.

According to one embodiment, the digging finger is formed of steel, preferably. Preferably, the finger comprises, at least at the tip, a reinforcement made of a cutting material, in particular carbon steel, tungsten steel or carbide. In this case, the finger can be formed entirely by this reinforced material. In another embodiment, part of the finger comprising the tip is made of this reinforced material forming a reinforcement, such as carbide, then assembled with a second part formed, for example, of steel, this assembly preferably being made by sintering and/or soldering. In this way, the structure of the excavation finger obtained is perfectly resistant.

According to one embodiment, the annular groove has in section in a plane containing the reference axis a circular arc profile. In general, the profile of the annular groove is configured to match, at least locally, the shape of a zone of the locking rod that it receives.

• un corps comportant au moins un logement cylindrique définissant un axe d’insertion, et un trou de fixation présentant un axe s’étendant dans un plan perpendiculaire à l’axe d’insertion, à distance de l’axe d’insertion, le trou de fixation débouchant dans le logement cylindrique ;
• au moins un doigt d’excavation tel que décrit ci-avant, dont la portion de maintien est logée dans le logement cylindrique, et la pointe est saillante par rapport au corps de la pelle,
• une tige de blocage qui pénètre dans le trou de fixation et dans la gorge du doigt pour maintenir axialement le doigt sur la pelle, le doigt d’excavation étant libre en rotation autour de son axe de référence.

The invention also relates to a shovel intended to equip an excavation chain for a ballast excavation device below a railway track, the shovel comprising:

• a body comprising at least one cylindrical housing defining an axis of insertion, and a fixing hole having an axis extending in a plane perpendicular to the axis of insertion, at a distance from the axis of insertion, the hole fixing opening into the cylindrical housing;
• at least one excavation finger as described above, the holding portion of which is housed in the cylindrical housing, and the tip projects relative to the body of the shovel,
• a blocking rod which penetrates into the fixing hole and into the groove of the finger to hold the finger axially on the shovel, the excavation finger being free to rotate around its reference axis.

According to one embodiment, it comprises a plurality of cylindrical housings each intended to receive an excavation finger. In this way the shovel is better protected by the digging fingers. Preferably, the shovel includes at least three digging fingers.

According to one embodiment, each housing is positioned on a rear part of the shovel so that the associated excavation finger extends in an extension of the shovel. In particular, the excavation fingers are preferably positioned projecting relative to an outer edge of the shovel.

According to one embodiment, the locking rods comprise a screw, the fixing hole or a separate member having a threaded portion so as to receive the screw.

Other characteristics and advantages of the invention will become apparent on reading the following description, with reference to the appended figures, which illustrate:
: a simplified side diagram of a work train equipped with a stripper-screener according to one embodiment;
: a partial diagram of an excavation or clearing device according to this embodiment, seen from the front without an excavation chain;
: a view of a link of an excavation chain carrying a shovel provided with excavation fingers according to one embodiment;
: a view of an excavation finger according to the embodiment of FIG. 3;
: a view of an excavation finger according to another embodiment;
: a top view of a succession of links intended to equip an excavation chain including a link carrying a shovel provided with excavation fingers according to the same embodiment as those illustrated in FIGS. 3 and 4;
: a front view of Figure 5;
: a rear view of a link of an excavation chain carrying a shovel provided with excavation fingers according to one embodiment;
: a sectional view AA of FIG. 7;
: a sectional view BB of figure 8.

For greater clarity, identical or similar elements are identified by identical reference signs in all the figures.

DETAILED description of an embodiment

Referring to Figure 1, there is illustrated a railway vehicle 1 such as a stripper-screener equipped with a clearing or excavation device 4 to clean the ballast of a railway track 2 . This clearing or excavation device 4 is placed between two bogies 3 of the train 1 .

The clearing device4of ballast includes an excavation chain8driven endlessly by a drive mechanism9and guided by ducts including a transverse duct5located under the track2in working position, along which the chain runs over a substantially straight portion of excavation8A. The clearing device4also includes up and down ducts6,7connected on either side of the transverse duct5to which they are connected by angled portions forming references40also known as "brackets" (see Figure 2). It is understood that the excavation portion is globally rectilinear, even if the excavation is ensured in a part of the curve of each of the bevel gears.

The drive device 9 is arranged in height relative to the railway vehicle 1 , above the railway track 2 , on a side longitudinally opposite the transverse conduit 5 , and between the ascent conduit 6 and the descent conduit 7 . The drive device 9 is placed on the path of the excavation chain 8 and comprises a drive wheel 9 ' meshing locally with links 100 of the excavation chain 8 so as to move it. There is thus formed an endless path to guide the chain 8 of excavation. Arrows illustrated in Figure 2 indicate the direction of movement of the chain 8 . At the upper ends of the ascent 6 and descent 7 ducts, on the side of the drive device, idler wheels forming deflection members 40 are provided to ensure the correct movement of the chain 8 at the level of these bent zones.

Once the ballast has been transported in height in the rise conduit 6 , it is unloaded on a conveyor belt 10 and then transported to a screening unit 11 in order to sort the healthy ballast from the used ballast.

The vehicle1further comprises a lifting unit13of the railway2which is connected to a frame14of the vehicle1and which is located upstream of the device4 clearing or excavation in relation to a direction of work12of the vehicle1. A height adjustment device16is also provided and connected to the frame14of the vehicle1, which is configured to move the clearing device4, by training means15, from a raised position to a lowered position under the railway track2and can be connected for example in a removable manner to the transverse duct5by a fitting (not visible in the figures).

Figure 3 illustrates a perspective view, from behind, of an example of a link100intended to compose the chain8of excavation. Chain8of excavation is formed of a succession of links100articulated two by two until the two ends of the chain8are connected end to end to form a chain8closed, endless string type. Some of the links100 chain8, such as that illustrated in FIG. 3, comprise a shovel130allowing the carriage of ballast on the path it travels.

Each of the links100has a body101which extends longitudinally between a front end110and a rear end120each provided with at least one front hole111and a rear hole121crossing right through the link100and configured to receive articulation means160with an adjacent link in the chain8. The longitudinal direction is understood here as the direction of movement of the link100. The front through holes111and back121extend along axes parallel to each other and contained in a reference planeP from the body101.

The link100 illustrated in Figure 3 has a projecting part formed by a shovel130extending from an outer side100Afrom the body101of the link100relative to the reference planeP, opposite the inner side100 Bfrom the body8of the link100, the inner side having a surface configured to come into contact with the return members40clearing device4 when moving the chain8.

The shovel 130 comprises a pallet shape having a working face oriented to the front, that is to say which is oriented in the direction of the direction of advance of the chain 8 and a back oriented to the rear . The shovel 130 extends from the body 101 of the link 100 to an outer end 130a which extends generally along an axis parallel to the reference plane and parallel to the axes of the front 111 and rear 121 through-holes, and has two edges side, lower 130b and upper 130c .

The shovel 130 further comprises excavation fingers 132 projecting outwards from the exterior side 100A with respect to the reference plane P , in the extension of the shovel 130 . In this embodiment, these fingers 132 are three in number: a central finger, a lower finger and an upper finger projecting with respect to the outer side 130a of the shovel 130 .

As illustrated in detail in Figures 4A and 4B, each finger132has a cylindrical body provided with at least one holding portion132bconfigured to fit into a cylindrical housing134correspondent provided for this purpose. Every finger132further includes a tip132aintended to project out of the cylindrical housing134shovel130. In particular, in the position attached to the shovel130, peaks132awith each finger132are disposed protruding from the outer edge130ashovel130 in the extension of the shovel130. Such a protrusion allows each finger132excavation to undergo a large part of the friction stresses instead of the edge130ashovel130from which said finger132excavation protrudes. In this way the edge130amatching shovel130sees its wear greatly reduced.

The holding portion 132b has a symmetry of revolution around a reference axis X of the finger 132 and comprises a body extending along a cylindrical envelope. In this embodiment, the finger 132 as a whole has a symmetry of revolution around the reference axis X.

The retaining portion 132b further comprises at least one annular groove 132c configured to receive at least part of a locking rod 135 , intended to ensure axial retention of the retaining portion 132b in the cylindrical housing 134 so that the finger 132 is free to rotate around its reference axis X. In this way, the locking in translation of the finger 132 is ensured and leaves the finger 132 free in rotation when it is fixed to the shovel 130. The locking rod 135 is fixed in a removable manner with respect to the shovel 130 so to be able to change the finger 132 in the event of excessive wear.

Such fingers 132 are designed in a very resistant way, for example in high-strength steel, the maintenance of which is easier than the link 100 of the chain 8 itself and which makes it possible to adapt more precisely to wear. localized according to the forces undergone. This thus allows a reduction in the cost of maintenance and a shorter maintenance time, and therefore shorter machine downtime.

Specifically, the shovel130includes a body131comprising a plurality of cylindrical housings134, three here, each defining an insertion axisW .To secure the finger132, the shovel130is provided at each cylindrical housing134, a fixing hole136having an axisW'extending in a plane perpendicular to the axis of insertionWcorresponding and at a distance from the axis of insertionW corresponding, the fixing hole136opening into the cylindrical housing134so that the locking rod135that enters the fixing hole136, also partially penetrates the throat132con point132to hold the finger axially132on the shovel130while leaving the finger132free excavation in rotation around its reference axisX.

In such a locking position of the finger 132 , the locking rod 135 comes close to a bottom of the annular groove 132 c associated tangentially with this annular surface. In this way, the blocking rod 135 does not obstruct the rotation of the finger 132 around itself, that is to say around its reference axis X , which coincides with the insertion axis W. Preferably the locking pin 135 is not in contact with the bottom of the annular groove 132c . It can however be, but the support of the locking rod against the annular groove 132c must be relatively low to limit the friction between the locking rod 135 and the annular groove 132c does not create a hindrance for the free rotation of the finger 132 . In FIG. 9, the blocking rod 135 has been illustrated centered on the axis W' of the fixing hole 136 , so that an interference appears between the blocking rod 135 and the bottom of the groove 132c , interference which does not exist in reality, because of the functional games. In this case, it is ensured, taking into account manufacturing tolerances, that there always remains a functional clearance between the locking rod 135 and the bottom of the groove 132c , which gives the finger 132 excavation its freedom of rotation around its reference axis X .

In this embodiment, the locking rods135include for each finger132a screw with a head135b at a first end and a distal end135a, opposite its head135band having a threaded portion135c. In the fixation position, the head135bcomes into contact and bears against a periphery of an inlet of the fixing hole136 ,the threaded portion135c being anchored with a nut135'provided with a threaded hole cooperating with the thread of the threaded portion135c lock rod135. A washer135''East interposed between, on the one hand, a perimeter of an exit from the fixing hole13 6against which it is in contact and bearing against and, on the other hand, the nut135'. The nut135'carrying the tapped hole is here an added part but it is understood that other fasteners can be used. The mounting hole136may for example comprise a cylindrical insert provided with a threaded internal hole. Fixing hole 136 can also be machined to carry a thread. Of course, the locking rod135can also be of different nature, and can include any suitable blocking means such as for example a pin blocked by a pin. However, a screw is easier to change. In addition, the use of a screw as a fixing rod ensures a tight hold without play, reducing noise when using the shovel.130.

The excavation fingers 132 are removably fixed relative to the shovel 130 , the withdrawal of the locking rod 135 , for example by unscrewing it, makes it possible to unlock the finger 132 concerned and to remove it from its cylindrical housing 134 by translating it, or simply moving it axially to index it at another annular groove 132c .

Generally the locking rod135preferably comprises an annular body and the throat132cpresent in section in a plane containing the reference axisXan arcuate profile. This shape is configured to locally match the shape of the fixing rod135 in order to minimize the play between said fixing rod135 And finger132 associated excavation. Preferably the depth of the groove132cin a holding portion132b is greater than 10%, preferably greater than 40% and less than 60%, preferably less than 50% of a finger radius132 associated excavation. Indeed, the annular groove132cmust be deep enough to ensure its axial locking and low enough not to weaken the structural integrity of the finger132of excavation. In this embodiment, the depth of the groove132cin a holding portion132b East sized to match 50% of a finger radius132 associated excavation. Furthermore, the axisW'fixing hole136extends in a plane perpendicular to the axis of insertionWcorresponding and at a distancedof the insertion axisW equal to approximately the radius of the mounting hole136 . This corresponds to a good ratio between the effectiveness of holding the finger132and to limit the fragility of said finger132due to the presence of the annular groove.

Furthermore, the housings 134 are positioned on a rear part of the shovel 130 so that the associated excavation finger 132 extends towards the outside of the shovel 130 , in an extension of said shovel 130 . The front part, or front working face, opposite the rear part of the shovel 130 is configured so as to present a useful surface for the excavation of the ballast. In this embodiment, the locking rod 135 is oriented so that its head is in contact and in support on a part of the front part of the shovel 130 while the nut 135' is in support, indirectly due to the washer 135'' , against a rear face of said shovel 130 . The front part of the shovel 130 has a recess 137 inside which the head 135b of the locking rod 135 can be housed in whole or in part so as to limit its wear (see for example FIG. 8).

As illustrated in FIG. 4B, it is particularly advantageous to provide the holding portion132bwith one finger132of a plurality of annular grooves132c, annular grooves132cbeing parallel to each other and spaced apart so as not to overlap. An overlap would be likely to reduce the effectiveness of the axial locking of the finger132 . Such a plurality of annular grooves132callows finger adjustment132in translation and thus to cause it to translate in its cylindrical housing134to place one of the annular grooves132cfollowing ones in engagement with the locking rod135and thus take predetermined positions according to its wear. The distance between two annular grooves132c may vary depending on the material of the finger132 and the rate of wear relative to the ballast transported. For example annular grooves132care spaced apart by a distance corresponding at least to the axial width of the annular grooves132c, preferably between one and two times the axial width of the annular grooves132c.

The fingers 132 are each oriented along an axis inclined relative to the reference plane P , with an inclination between 65 and 80°, preferably between 70 and 75°.

Fingers132are also oriented in a planeP132inclined with respect to a mean planeP130shovel130extending substantially vertically (see Figure 8), the inclination preferably being between20And35°, and equal here to approximately30° in this embodiment. Such a characteristic allows, in comparison with an equivalent useful working surface of an excavator130 with a greater inclination, to lighten the shovel130 without losing performance or losing rigidity. The useful working surface of the excavator130 is understood here as the surface swept by the shovel130 when moving.

The fingers 132 are all located above a plane Pinf perpendicular to the parallel axes of the front 111 and rear 121 through-holes and tangent to a lower end of said shovel 130 , in particular in this embodiment, also below a plane Psup tangent to an upper end of the shovel 130 (see Figure 7). Given the orientation of the chain 8 and therefore of the shovel 130 on the rectilinear portion of excavation 8A , the planes Pinf and Psup are generally horizontal. This lower end is sensitive in that it is extremely stressed in terms of wear by abrasion against the ballast so that if the wear becomes too great, this can harm the correct attachment of the fingers 132 to the back of the the shovel 130 . With a lower finger 132 located entirely above the Pinf plane, a longer service life is ensured for the link 100 . Preferably, the hardness of the lower surface of the shovel 130 is increased for example by adding chromium/manganese and vanadium by welding or by adding tungsten carbide plates.

The shovel 130 further has an abutment surface 138 located on the back of the shovel 130 , between the body 101 of the link and the cylindrical housings 134 , the abutment surface 138 being configured to receive a counter-stop 140 from an adjacent link rear of the chain 8 so as to limit a relative rotation between the link 100 of chain 8 and the rear adjacent link around the axis of the rear through-hole 121 . Such a position of abutment of the shovel 130 against the counter-stop 140 of the associated rear link 100 is visible in FIG. the ballast which generates a moment on the shovel 130 which tends to tilt the link 100 backwards, this tilting being a pivoting of the shovel 130 around the axis of the rear through-hole 121 configured to receive articulation means 1 6 0 .

Naturally, the invention is described in the foregoing by way of example. It is understood that the person skilled in the art is able to carry out different variant embodiments of the invention without departing from the scope of the invention.

Claims (10)

Excavation finger (132) of a shovel (130) intended to equip an excavation chain (8) for a ballast excavation device (4) below a railway track (2), the finger (132) being one piece and comprising:

• a holding portion (132b) having a symmetry of revolution around a reference axis (X) of the finger (132), the holding portion (132b) being intended to be housed in a cylindrical housing (134) of the shovel (130), and
• a point (132a) intended to project out of the cylindrical housing (134) of the shovel (130),

the excavation finger (132) being characterized in that the holding portion (132b) comprises at least one annular groove (132c) configured to receive at least part of a blocking rod (135), intended to ensure a axial holding of the holding portion (132b) in the cylindrical housing (134) so that the finger (132) is free to rotate about its reference axis (X). Excavating finger (132) according to Claim 1, characterized in that the holding portion (132b) comprises a plurality of annular grooves (132c), the annular grooves (132c) being parallel to each other and spaced from each other. Excavating finger (132) according to Claim 1 or 2, characterized in that the finger (132) has rotational symmetry around the reference axis (X). Excavating finger (132) according to any one of the preceding claims, characterized in that it is formed from steel. Excavation finger (132) according to any one of the preceding claims, characterized in that it comprises, at least at the point (132a), a reinforcement made of a cutting material, in particular carbon steel, tungsten steel or carbide. Excavating finger (132) according to any one of the preceding claims, characterized in that the annular groove (132c) has, in section in a plane containing the reference axis (X), an arcuate profile. Shovel (130) for equipping an excavation chain (8) for a ballast excavation device (4) below a railway track (2), the shovel comprising:

• a body (131) comprising at least one cylindrical housing (135) defining an insertion axis (W), and a fixing hole (136) having an axis (W') extending in a plane perpendicular to the axis insertion (W), at a distance from the insertion axis (W), the fixing hole (136) opening into the cylindrical housing (134);
• at least one excavation finger (132) according to any one of the preceding claims, the holding portion (132b) of which is housed in the cylindrical housing (134), and the tip (132a) projects with respect to the body ( 131) of the shovel (130),
• a locking rod (135) which penetrates the fixing hole (136) and the groove (132c) of the finger (132) to axially hold the finger (132) on the shovel (130), the finger (132) d the excavation being free to rotate around its reference axis (X).

Excavator (130) according to the preceding claim, characterized in that it comprises a plurality of cylindrical housings (134) each intended to receive an excavation finger (132). Shovel (130) according to the preceding claim, characterized in that each housing (134) is positioned on a rear part of the shovel so that the associated excavation finger (132) extends in an extension of the shovel (130 ). Shovel (130) according to any one of Claims 7 to 9, characterized in that the locking rods (135) comprise a screw, the fixing hole (136) or a separate member (135') having a threaded portion of so as to receive the screw.