FR2791404A1 - Electrical connection calibrated force locking screw having screw thread profiled sections and inner ring with protrusion outer head nut section driven/set force ceasing. - Google Patents

Abstract

The calibrated force locking screw has an upper section (20) movement head with side skirt (22) surrounding a main screw section (4). There is an intermediate ring (30) with a polygonal profile which engages with the skirt section and having protruding profiled sections contacting profiled sections on the screw, so that the screw tightens to a set force, and then the upper body rotates without screw movement.

Description

The invention relates to a calibrated clamping screw, to a system for

  electrical connection incorporating at least one

  such a screw and a method of manufacturing such a screw.

  In electrical connection systems, as known for example from FR-A-2 670 614, from FR-A-2 715 775 or from FR-A-2 751 465, it is possible to use screws with breakable heads to immobilize and electrically connect two elements of an electrical circuit. The operating principle of these known screws is based on the fact that the head of the screw breaks when the desired tightening torque is reached. The manufacturing tolerances of these screws are such that the tightening torque obtained is relatively imprecise. In addition, at least for certain uses, it is sometimes necessary to dismantle the electrical connection thus produced, then reassemble it. If the screw already used is kept, its breakable head is no longer available, so that it must be maneuvered thanks to its conventional hexagonal head which remains integral with the body of the screw and that it is no longer possible to guarantee a tightening torque with a predetermined value. If a new screw is used, the

  cost of each intervention is increased accordingly.

  It is to these drawbacks that the invention more particularly intends to remedy by proposing a calibrated clamping screw which can be tightened and loosened several times, its torque

  nominal tightening remaining the same after the first use

tion.

  In this spirit, the invention relates to a calibrated clamping screw, including a rod with a threaded part and a section with a polygonal profile. This screw comprises a cap forming an operating head and extending by a skirt surrounding the polygonal profile section of the rod and provided, on its internal face, with reliefs. This screw also comprises an elastic ring housed between the polygonal profile section of the rod and the skirt of the cap, this ring being provided, on its external radial surface, with reliefs capable of cooperating with the reliefs of the skirt for the drive. in rotation of the ring. On its internal radial surface, this ring is provided with at least one lug capable of transmitting a rotational movement from the ring to the rod, at the level of the section with a polygonal profile, and of sliding on this profile when the force

  rod resistance is greater than a predetermined value.

  Thanks to the invention, the sliding movement of the ring relative to the polygonal profile section of the rod results in a limitation of the torque transmitted to the rod without breaking part of the screw, so that the screw can be tightened and loosened several times in succession up to or from its nominal tightening torque. The invention takes advantage of the elastic deformation of the ring which is provided in a suitable material, in particular spring steel. The invention also makes it possible to obtain greater precision in the definition of the nominal tightening torque of the screw, in the

  measure o this does not depend on possible homogeneity faults

  birth of the material of the threaded rod.

  According to advantageous aspects of the invention, the screw incorporates one or more of the following characteristics:

  - the cover is mounted free to rotate and immobilize

  sée in translation relative to the main axis of the rod. In particular, the rod can be provided with a peripheral groove

  external receiving an internal collar of the cap.

  - the rod is extended by a nipple with overall section -

  circular shape forming a core for the operating head of the cap.

  the profile of the rod comprises, in cross section

  the, several ramps, each connecting a hollow nose and heel. In this case, the lug and the profile of the rod are advantageously shaped so that, when the screw is tightened, the lug is able to slide on one of the ramps and to

  exceed the neighboring nose by elastic deformation of the ring.

  It can also be provided that during the loosening of the screw, the lug is able to lock against a surface of a heel in

neighboring hollow.

  The invention also relates to an electrical connection system which comprises at least one calibrated clamping screw as described above. Such a system is easier to use by an operator, since it is not necessary to maneuver a screw with a head of low height such that it remains on the screws with breakable head after their rupture. In addition, it is not necessary to change the screw after each disassembly and the tightening torque calibration function remains, even if the operator forgets to carry out a

calibrated tightening.

  The invention finally relates to a method of manufacturing a screw as previously described which consists in mounting a cap, forming an operating head and extending by a skirt surrounding a polygonal profile section of a threaded rod, free to rotate and fixed in translation relative to the main axis of this rod, and to insert an elastic force transmission ring between the internal surface of

  this skirt and this polygonal profile section.

  According to an advantageous aspect of the invention, the method consists in overmolding the cap on the rod, which allows

  to obtain a particularly effective and resistant assembly.

  The invention will be better understood and other advantages thereof will appear more clearly in the light of the

  description which will follow of an embodiment of a screw

  calibrated tightening according to the invention, given solely by way of example and made with reference to the accompanying drawings in which: - Figure 1 is a partial exploded perspective view of a screw according to the invention; - Figure 2 is a partial longitudinal section of the screw of Figure 1 mounted; - Figure 3 is a cross section along line III-III in Figure 2; - Figure 4 is a section similar to Figure 3 during a screw tightening step; - Figure 5 is a section similar to Figure 3 during a step of loosening the screw and Figure 6 is a partial detail view to more

  large scale of the profile of the screw rod of Figure 1.

  The screw 1 shown in the figures comprises a rod 2

  in steel having undergone a zinc-plated type surface treatment

  bichromate or equivalent. The rod 2 comprises a threaded part 3 intended to cooperate with a thread or a nut, not shown. The rod 2 also comprises a section 4 with a polygonal profile, the geometry of which appears more clearly in FIG. 6. The profile P of the section 4 has, in top view or in section in the plane of FIGS. 3 to 7, a shape such that it fits into a hexagon H shown in phantom in Figure 6, so that it can cooperate with a conventional operating key, the distance d between two parallel edges of hexagon H having a normalized value , for example from mm. Profile P is divided into six angular sectors around the main axis XX 'of the rod 2 of the screw 1. Each angular sector comprises a ramp 5, at least partially rectilinear, and the distance of which from the axis XX 'varies between an r value and an r value, the r value being less than the r value. At a first edge 5a of each ramp 5 of radius r, the profile P defines a nose 6 connected, by a transition surface 7, to a hollow heel 8 formed in the vicinity of the second edge 5b of each ramp 5 of which the distance

  r with respect to the axis XX 'is minimal.

  Each ramp 5 is partially coplanar with one of the sides of the hexagon H. The ramps are offset two by two by an angle of 120 corresponding to the hexagon of the hexagon H. The profile P comprises six ramps 5, six nose 6 and six hollow heels 8, the noses 6 being defined at the tops of

the aforementioned hexagon H.

  The rod 2 also comprises a groove 9 formed between the section 4 and a flange 10 of diameter substantially equal to that of the threaded part 3 and less than or equal to the distance d. The end of the rod 2 opposite the threaded part 3 is formed by a stud 11 with a generally cylindrical section and of

  diameter smaller than that of the collar 10.

  A cap 20, made of insulating plastic, is provided to be mounted on the part of the rod 2 which is not threaded, that is to say on the elements 4 to 11. This cap forms an operating head 21 with hexagonal external profile

  adapted to cooperate with a conventional operating key.

  The operating head 21 is hollow, so that the stud 11 constitutes the central core, which allows it to withstand the compression and torsional forces exerted by a key. In addition, the fact of making the head 21 in a hollow form avoids molding a mass portion of plastic material of relatively large section, which is generally difficult. From the head 21, the cap 20 is extended by a skirt 22 provided to surround the section 4 and whose surface

  internal carries grooves 23. The cap 20 also includes

  an internal collar 24 adapted to penetrate into the groove 9. The internal diameter D of the skirt 22 is substantially

greater than distance d.

  The cap 20 can be molded in a mold provided for this purpose, then placed on the rod 2 by elastic deformation of the flange 24. However, according to a particularly advantageous aspect of the invention, provision is made to overmold the cap 20 directly on the end of the rod 2, so that the flange 24 is perfectly adapted

  to the dimensions of the groove 9 and that the locking in transla-

  tion of the cap 20 parallel to the axis XX ′ is particularly

  rement effective, because the section of the flange 24 can be provided large enough to avoid any deformation thereof parallel to the axis XX '. A suitable drawer allows, during the injection of the cap 20, to provide a free space between the skirt 2 and the section 4 of the rod 2. When the cap has been molded onto the rod 2, the cap is therefore free in

  rotation and immobilized in translation relative to the X- axis

  x '. A ring 30 made of spring steel is then inserted between the skirt 22 and the section 4 of the rod 2. On its external radial surface, the ring 30 carries grooves 33 whose geometry corresponds to the grooves 23 of the skirt 22, of so that a rotational movement of the cap 20 around

  the axis XX ′ is efficiently transmitted to the washer 30.

  On its internal peripheral surface, the ring 30 carries three pins 34 adapted to come to bear sliding on three non-adjacent ramps 5. The three pins 34 are regularly distributed over the internal peripheral surface of the ring 30,

  so that they define angles of 120 between them.

  The contact between the surfaces 35 of the lugs 34, intended to come into contact with the ramps 5, and the ramps 5 is a metal / metal contact, the materials of the rod 2 and of the ring 30 being suitable for this contact, in particular thanks to a Treatment of

suitable surface.

  The operation is as follows: When the screw 1 is tightened, the operating head 21 is driven by means of a key not shown, so that the skirt 22 which is integral with the head 21 drives, in the direction

  of arrow F in FIG. 4, the ring 30 thanks to the cooperation

  tion of the grooves 23 and 33. As long as the resistive torque exerted by the rod 2 remains low, the lugs 34 remain in the position of FIG. 3. When this torque increases and reaches a predetermined threshold value, the rod 2 no longer rotates around the axis XX ′, so that the pins 34 slide along the ramps 5 on which they are supported, until they come to the level of the noses 6, as shown in FIG. 4. In this position, if the operator continues to rotate the head 21, each lug 34 exceeds the corresponding nose 6 and enters the next heel 8, so that the cap 20 has made a rotation of one sixth of a turn relative to the rod 2 , which an operator perceives by passing a "hard point" at the level of the noses 6. As the apparent radius of each ramp 5 increases progressively from Lr to r in the direction of the arrow F, the effort which must be exerted by l operator to move the lugs 34 towards the noses 6 gradually increases, pu is suddenly reduced as soon as the nose passes 6. The operator therefore feels the passage

of a "hard point".

  The internal diameter of the ring 30, defined at the level of the surfaces 35 of the lugs 34, increases during the passage of the noses 6, which occurs by elastic deformation of the ring 30. The nominal tightening torque of the screw is then reached 1 without

  rupture of one of its constituent elements.

  If the operator continues to exert a force on the head 21 in the direction of the arrow F in FIG. 4, the pins slide on the following ramps and pass the following noses without driving the rod 2. It is no longer possible to d 'drive the rod 2 in the direction of arrow F. In the position of Figure 4, in addition to a slight elastic deformation of the lugs 34 the assembly of the ring 30 is deformed into a "curvilinear triangle", this deformation being transmitted to the skirt 22. This deformation is however of small amplitude and non-destructive, taking into account the materials used. When it is necessary to loosen the screw 1, it suffices to exert on the operating head 21 a force in the direction of the arrow F 'in FIG. 5, this force having the effect of pressing the pins 34 in the heels recessed 8, against

transition surfaces 7.

  The geometry of the heels 8 is such that an effective blocking is obtained, which makes it possible to exert a loosening torque.

  significantly greater than the predetermined tightening torque.

  After loosening screw 1, a new tightening remains

  possible, the operation being identical to that described above

  above. The fact that the profile P is inscribed in a hexagon H also makes it possible to envisage, in the event of a rupture of the cap 20 or of plastic deformation of the washer 30, to remove these elements and to operate the rod 2 with a conventional key by cooperation with the P profile. Calibration of the tightening torque is then no longer possible, but this at least makes it possible to remove the screw from the assembly to which it belongs. In addition, the particular aspect of section 4 reminds the operator that the screw

  1 is not in normal operating condition.

  The number of pins 34 of the ring 30 depends on a choice of embodiment within the reach of those skilled in the art and the shape of the

profile P of the rod 2.

  It suffices that the ring 30 is provided with at least one lug to perform the desired function. However, the distribution of the forces on the ring 30 is better when several

  regularly spaced pins are provided.

  The invention is particularly suitable for tightening electrical connection elements or for immobilizing one or more electrical cables in a connector. It also finds application in the field of mechanics and, more generally, in any field where a screw must be

tightened with nominal torque.

  In electrical applications, the invention has the additional advantage that the operation of the screw is carried out by an insulating plastic part, which makes it possible to guarantee the operator's safety and to avoid short circuits. The screw of the invention is interchangeable with existing screws, so that it allows upgrading of existing systems, in particular connection devices

electric, by standard exchange.

Claims (10)

  1. Calibrated tightening screw including a rod with a threaded part and a polygonal profile section, characterized in that it comprises: - a cap (20) forming an operating head (21) and extending by a skirt (22 ) surrounding said section (4) with polygonal profile (P) and provided, on its internal face, with reliefs (23), and - an elastic ring (30) housed between said section (4) with polygonal profile (P) and said skirt (22), said ring being provided, on its external radial surface, with reliefs (33)   able to cooperate with the reliefs of said skirt for training   in rotation of said ring, and, on its internal radial surface, of at least one lug (34) capable of transmitting a rotational movement (F, F ') of said ring to said rod at its profile section polygonal (P) and to slide on said polygonal profile (P) of said rod when the resistance force of said rod (2) is greater than a predetermined value. 2. Calibrated clamping screw according to claim 1, characterized in that said cap (20) is mounted free in rotation and immobilized in translation relative to the axis   main (X-X ') of said rod (2).   3. Calibrated clamping screw according to claim 2, characterized in that said rod (2) is provided with a groove (9) external device for receiving an internal flange (24) of said cap (20).   4. Calibrated clamping screw according to one of claims   above, characterized in that said rod (2) is extended by a stud (11) of generally circular section forming a core   for the operating head (21) of said cap (20).   5. Calibrated clamping screw according to one of claims   previous, characterized in that said profile (P) of said rod (2) comprises, in cross section, several ramps (5)   each connecting a nose (6) and a hollow heel (8).   6. Calibrated tightening screw according to claim 5, characterized in that said lug (34) and said profile (P) are shaped so that, when tightening (F) of said screw, said lug is able to slide on one of said inclined ramps (5) and beyond the neighboring nose (6), by elastic deformation of said ring.   7. Calibrated clamping screw according to one of claims 5   or 6, characterized in that said lug (34) and said profile (P) are shaped such that, when loosening (F ') of said screw, said lug is capable of locking against a   surface (7) of a neighboring hollow heel (8).   8. Electrical connection system, characterized in that it comprises at least one screw (1) with tightening calibrated according to   one of the preceding claims.   9. Method of manufacturing a calibrated clamping screw from a rod comprising a threaded part and a polygonal profile section, characterized in that it consists in mounting   a cap (20), forming an operating head (21) and extending   giant by a skirt (22) surrounding said section (4) with polygonal profile (P), free in rotation and fixed in translation relative to the main axis (X-X ') of the rod (2) and to insert a elastic ring (30) for transmitting forces between the internal surface of said skirt and said polygonal profile section. 10. Method according to claim 9, characterized in that it consists in overmolding said cap (20) on said rod (2).