Tool and method for positioning and tightening a nut and tensioning a screw

Abstract

Tool and method for positioning and tightening a nut and tensioning a screw. The method comprises the following steps: placing a screw through the hole of an assembly to be tightened so that its head is against a first face of said assembly; gripping a nut with a tool; positioning the nut with the tool on the free end of the screw and tightening the nut with the tool; gripping the free end with the tool at a gripping part; longitudinally stretching the screw by pulling the free end away from the head with the tool; continuing to tighten the nut with the tool while maintaining the traction exerted by the tool until the nut is against a second face of the assembly opposite the first face; interrupting the traction and gripping exerted on the free end; removing the tool. Figure to be published with the abbreviation: Figure 2

Description

Title of the invention: Tool and method for docking and screwing a nut and tensioning a screw TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of tightening tools allowing precise tension to be applied to a screw.

[0002] The present invention relates to a method for docking and screwing a nut and for tensioning a screw in a bolted assembly, and a tool for implementing said method. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] A screw and its nut can be thought of as a very rigid spring, which can be stretched and maintain tension between its body and the material it is clamping. A screw and its nut form a bolt.

[0004] The tension in a screw is usually applied by means of a torque wrench whose function is to apply to the nut the tightening torque necessary to obtain the desired tension. The thread ensures tightening and stopping in rotation by elliptical deformation of the cylindrical barrel.

[0005] When tightening to the torque, bending and / or torsion phenomena appear in the screw, as well as dispersion phenomena due to friction. The dispersion is usually high at the level of the pre-stressing force because it depends on the coefficient of friction, on the thread and under the head, which is difficult to control.

[0006] Thus, when tightening to torque, it is considered that 40 to 45% of the tightening torque results in a frictional resistance torque under the head of the screw (friction of the screw head against the material it is tightening), that 40 to 45% of the torque results in a frictional resistance torque in the threads (frictional forces of the screw head against the material it is tightening and at the thread level) and that only 10 to 15% of the torque results in a useful tightening torque. Torsion and / or bending phenomena in the screw can amplify this reduction in the useful tightening torque.

[0007] Furthermore, when numerous tightening operations have to be carried out on the same part, for example on a flange, the manual installation of the screws and their nuts is a long and tedious step.

[0008] There is therefore a need for a screwing device making it possible to promote the useful tightening torque of a bolt in order to avoid the effects of torsion on the screw on the one hand and parasitic friction by the screw on the other hand, while making it possible to attach the nut to the screw without manual intervention. Summary of the invention

[0009] The invention provides a solution to the problems mentioned above.

[0010] One aspect of the invention relates to a tool for docking and screwing a nut and tensioning a screw, comprising: • a connection to a pressurized fluid supply; • a main room with a tubular chamber; • a docking and screwing system for nuts housed in the main part; • a screw tensioning system comprising a piston housed sliding in the tubular chamber and equipped with a gripping device, said piston being sliding between a first position resting on the bottom of the tubular chamber and a second position spaced from said bottom.

[0011] According to one aspect of the invention, the tool comprises a first pressurized fluid supply circuit opening into the tubular chamber. The piston is moved into the second position by the fluid coming from said first circuit and present in the tubular chamber.

[0012] According to another aspect of the invention, the nut system comprises: • a movable rotating docking and screwing socket, having an internal housing of a shape adapted to receive a nut and an external circumference equipped with teeth; • a first endless screw housed in a first cylindrical chamber, one thread of which is engaged with the teeth

[0013] According to a further aspect of the invention, the tool comprises a second pressurized fluid supply circuit opening into the first cylindrical chamber. The first worm screw is driven in rotation by the fluid coming from said second circuit and present in the first cylindrical chamber.

[0014] According to one aspect of the invention, the screw tensioning system comprises an elastic return device which pushes the piston into the second position.

[0015] According to another aspect of the invention, the gripping device comprises a set of jaws each comprising a mandrel housed in a mandrel chamber.

[0016] According to a further aspect of the invention, the tool comprises a first pressurized fluid supply circuit opening into each chuck chamber. Each chuck is moved towards each other by the fluid coming from said first circuit and present in each chuck chamber.

[0017] According to one aspect of the invention, the gripping device comprises: • a gripping nut mounted to rotate in the piston, having a threaded internal housing and a gripping part having teeth located on its external periphery, and • a second endless screw housed in a second cylindrical chamber, the thread of which is engaged with said teeth.

[0018] According to another aspect of the invention, the tool comprises a third pressurized fluid supply circuit opening into the second cylindrical chamber. The second worm screw is driven in rotation by the fluid coming from said third circuit and present in the second cylindrical chamber.

[0019] Another aspect of the invention relates to a method for docking and screwing a nut and for tensioning a screw by means of a tool as described previously for tightening an assembly having an orifice, said screw having a head and a free end located opposite the head, the method comprising the following steps: • gripping the nut by the nut system; • docking the nut and screwing it onto the free end of the screw by the nut system so that the free end of the screw protrudes outside the nut; • gripping of the free end by the screw tensioning system; • longitudinal stretching of the screw by moving the piston away from the nut system; • continuation of screwing the nut using the nut system while maintaining the traction exerted by the screw tensioning system until the nut and the head come into contact with the assembly to be tightened.

[0020] According to one aspect of the invention, the step of gripping the free end by the screw tensioning system is carried out by the mutual bringing together of the jaws around a gripping part shaped in the free end of the screw.

[0021] According to another aspect of the invention, the step of gripping the free end by the screw tensioning system is carried out by screwing the gripping nut onto the free end of the screw.

[0022] The tool of the invention makes it possible to dock and screw the nut onto the screw without manual intervention, which in particular provides a considerable saving of time when numerous tightening operations have to be carried out on the same part and also allows the operator to have one hand free.

[0023] The same tool makes it possible to temporarily lengthen the screw in a precise and controlled manner by the fluid pressure used in the tensioning device, which advantageously makes it possible to avoid dispersion phenomena and consequently to very precisely control the tightening force exerted by the screw after removal of the tool.

[0024] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0025] The figures are presented for information purposes only and in no way limit the invention.

[0026] [Fig. 1] is a sectional view of a bolted assembly clamping an assembly formed of two plates.

[0027] [Fig.2][Fig.3] are exploded views of a tool according to a first example of realization of the invention.

[0028] [Fig.4][Fig.5] are exploded views of a tool according to a second example of realization of the invention.

[0029] [Fig.6]-[Fig.l3] are cutaway views illustrating the use of a tool according to the first example of embodiment of the invention.

[0030] [Fig.l4]-[Fig.2O] are cutaway views illustrating the use of a tool according to the second embodiment of the invention, the lower part of the gripping nut being shown cut away in [Fig.l6]-[Fig.l9].

[0031] [Fig.21] is a graph illustrating the ratio Hydraulic force Fh / Tightening force Fo as a function of the ratio of screw length engaged in the bolted assembly L / Screw diameter d for a wide range of different threads.

[0032] [Fig.22]-[Fig.26] are sectional views illustrating examples of part of grip for the screw.

[0033] For reasons of visibility, the assembly to be tightened is not shown in [Fig.2] and following. DETAILED DESCRIPTION

[0034] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0035] By convention, in the present application, the terms "lower", "upper", "on", "under", "vertical" and "horizontal" are defined relative to the position of the tool as shown in the figures. For example, the longitudinal X axis along which the screw and the tool extend is vertical.

[0036] By docking we mean an action aimed at bringing parts together by translation.

[0037] The tool 1 according to the invention is intended to tighten an assembly 4 by a bolted assembly formed of a nut 2 and a screw 3 as shown in [Fig.l].

[0038] The assembly 4 is for example formed of two parts 41 and 42, and has an orifice 43 through which the screw 3 is introduced.

[0039] The screw has a head 33, a threaded rod 32 and a free end 31 located opposite the head 33.

[0040] The nut 2 and the head 33 of the screw 3 shown in the figures are of the bi-hexagonal type with a base, preferred in the aeronautical field. The tool 1 can however be adapted to any type of screw 3 and nut 2.

[0041] The tool 1 according to the invention comprises a main part 11 and is designed to dock and screw the nut 2 onto the free end 31 of the screw 3 and tension said screw 3 in order to tighten the assembly 4. The threaded rod 32 is preferably introduced through the orifice 43 from below so that the head 33 of the screw 3 bears against the lower face 44 of the assembly 4, while the main part 11 of the tool 1 preferably bears against the upper face 45 of the assembly 4, at the free end 31 of the screw 3 to stretch the screw 3 and screw the nut 2. For this purpose, the main part 11 of the tool 1 has, for example, a support skirt 111 having a substantially flat lower face 112.

[0042] In use, the tool 1, the nut 2 and the screw 3 are centered around a vertical axis X.

[0043] The tool 1 according to the invention comprises a pressurized fluid supply or is connected to such a supply. For its pneumatic or hydraulic operation, the tool 1 therefore comprises at least one connection to a pressurized fluid supply (not shown).

[0044] The tool 1 according to the invention also comprises a docking and screwing system for nut 50, hereinafter referred to as nut system 50, and a screw tensioning system 60 which are actuated by the pressurized fluid.

[0045] The system for nut 50. It comprises a socket 51 for docking and screwing, movable in rotation around the axis X in the main part 11, provided for gripping and screwing the nut 2. The socket 51 has an internal housing 511, provided for housing the nut 2, of a shape complementary to that of the external periphery 21 of the nut 2, and an external periphery 512 equipped with teeth 513.

[0046] The nut 2 is preferably held in the sleeve 51 by magnetization, by tight fitting or by an O-ring provided in the internal housing 511 of said sleeve 51. It is however possible to keep the existing conventional tools to preposition the nut 2.

[0047] In order to screw the nut 2 when it is housed in the internal housing 511, the nut system 50 comprises a worm screw 52 housed in a first cylindrical chamber 53 provided in the main part 11. The thread 521 of the worm screw 52 is engaged with the teeth 513 of the sleeve 51 so that when pressurized fluid is supplied to the first cylindrical chamber 53, the worm screw 52 drives the sleeve 51 in rotation. For this purpose, the first cylindrical chamber 53 has an inlet 531 and an outlet 532 for pressurized fluid each opening into the first cylindrical chamber 53 and connected to the pressurized fluid supply.

[0048] The worm screw 52 is driven in rotation by the circulation of the pressurized fluid in the first cylindrical chamber 53. For this purpose, the worm screw 52 may comprise fins or other similar shapes.

[0049] The screw tensioning system 60 comprises a piston 61 having a lower part 611 slidably housed in a tubular chamber 63, for example provided in the main part 11. The piston 61 is preferably a single-acting piston with spring return. The piston 61 is moved upwards when pressurized fluid is injected into the tubular chamber 63, under the lower part 611 of the piston 61, at an inlet 631 for pressurized fluid opening for example into the lower part of the tubular chamber 63 and connected to the pressurized fluid supply. The seal between the piston 61 and the tubular chamber 63 is obtained by a sealing device, comprising for example a first and a second O-ring 613, 614 each housed in a groove 615, 616 respectively provided on the external and internal periphery of the lower part 611 of the piston 61.

[0050] The inlet 531 and the outlet 532 for pressurized fluid of the nut system 50 are preferably independent of the inlet 631 for pressurized fluid of the screw tensioning system 60.

[0051] This system 60 also comprises a gripping device 66, for example located in the piston 61 and provided to grip the free end 31 of the screw 3, either directly at a gripping part 311 provided at said free end 31, or by means of a gripping nut 70 screwed onto this free end 31, said gripping nut 70 comprising a gripping part 71 and an internal housing 72 having a tapping complementary to the thread of the threaded rod 32.

[0052] In its lower part, the gripping nut 70 preferably has a second gripping part 75, for example bi-hexagonal, which is used to set the nut 70 in rotation in the event of failure of the tool 1.

[0053] The screw tensioning system 60 also comprises an elastic return device which tends to push the gripping device 66 of the piston 61 downwards, comprising for example a helical spring 64 housed in an annular groove 6121 provided on the external periphery 612 of the piston 61, the upper part of the helical spring 64 coming to bear against the underside of a stop ring 65 housed in an annular groove 632 in the tubular chamber 63.

[0054] The gripping portion 311 of the screw 3 may be in the form of a raised and / or recessed portion shaped near its free end 31. For example, in [Fig.2], [Fig.3], [Fig.6]-[Fig.13] and [Fig.22], the gripping portion 311 of the screw 3 is in the form of a groove 312, the free end 31 then forming a raised portion relative to the groove 312, which can be grasped by the gripping device 66. Other examples of gripping portions 311 for the screw 3 are shown in [Fig.22], [Fig.23], [Fig.24], [Fig.25] and [Fig.26],

[0055] According to a first variant of the invention shown in [Fig.2], [Fig.3], [Fig.6]-[Fig.13], the gripping device 66 is provided to grip a gripping part 311 provided on the screw 3. According to this variant, the gripping device 66 comprises a set of jaws 661 each comprising a mandrel 6611 housed in a tubular mandrel chamber 662 provided for example in the upper part 613 of the piston 61. The seal between each mandrel 6611 and the tubular chamber 662 where it is housed can be obtained by an O-ring 663 mounted in a groove 6612 provided on the external periphery of each mandrel 6611. The jaws 661 are pushed towards the gripping part 311 to grip the gripping part 311 between them when the tubular chambers 662 are supplied with pressurized fluid, for example through conduits 664 provided in the piston 61 and each connecting the lower part 62 of the piston 61 to a tubular chamber 662.

[0056] During operation of the tool 1, once the jaws 661 are pushed by the pressurized fluid and they grip the gripping part 311 between them, the pressurized fluid then moves the gripping device 66 of the piston 61 upwards, opposing the force of the elastic return device, to stretch the screw 3 upwards.

[0057] The gripping device 66 preferably comprises a lock 67 associated with a spring 68. After gripping the gripping part 311 by the jaws 661, the lock 67 represents an additional safety to the return spring 68 so as not to lose said jaws 661. The spring 68 continuously pushes the jaws 661 to the bottom of the tubular chamber cylinders 662 and allows the return of said jaws 661 to the initial rest position.

[0058] According to a second variant of the invention, the gripping device 66 is provided to grip a gripping part 71 provided on a gripping nut 70 integrated in the tool 1. According to this second variant, the gripping device 66 also comprises a device provided to dock and screw the gripping nut 70 onto the free end 31 of the screw 3 and to unscrew and remove it. Thus, the gripping nut 70 is mounted to rotate in a housing 665, for example cylindrical and provided in the piston 61. The gripping nut 70 has a gripping part 71, for example in the form of a toothed crown 711, having teeth 712 located on the external periphery 73 of the gripping nut 70.

[0059] According to this second variant, the gripping device 66 comprises a worm screw 666 housed in a second cylindrical chamber 666. The thread 6661 of the worm screw 666 is engaged with the teeth 712 of the gripping nut 70 so that when pressurized fluid is supplied to the second cylindrical chamber 666, the worm screw 666 drives the gripping nut 70 in rotation. For this purpose, the second cylindrical chamber 667 has an inlet 6671 and an outlet 6672 for pressurized fluid. pressure each opening into the second cylindrical chamber 667 and connected to the pressurized fluid supply.

[0060] When the gripping nut 70 is rotated, it can approach the free end 31 of the screw 3 and screw onto it. For this purpose, the screw 3 must have a sufficient length, so that after the nut 2 has been approached and screwed onto the screw 3 by the tool 1, the free end 31 of the screw 3 protrudes from the approaching and screwing sleeve 51 so that it can be engaged in the gripping nut 70.

[0061] After the gripping nut 70 has been docked and screwed onto the screw 3 by the tool 1, when the piston 61 equipped with the gripping device 66 is moved upwards, said gripping device 66 carries with it the gripping nut 70, which is in vertical abutment in its housing 665, which stretches the screw 3 upwards.

[0062] It will be noted that the main part 11 has a central tubular part 113 which serves as a hermetic enclosure for the jaws 661 and for the gripping nut 70. For this purpose, the gripping nut 70 and the jaws 661 each have a part 74, 6613 which extends them downwards into the central tubular part 113.

[0063] An example of a method for docking a nut 2 and tensioning a screw 3 using the tool 1 to tighten an assembly 4 is given below. This method uses the tool 1 of the invention, but also a nut 2, a screw 3 and an assembly 4 as described previously.

[0064] This method is suitable for the case where the screw 3 has a gripping part 311 at its free end 31 and in the opposite case, where the tool then comprises a gripping nut 70 having a gripping part 71. It is illustrated in [Fig.6]-[Fig.l3] for the first variant of the invention and in [Fig.l4]-[Fig.2O] for the second variant.

[0065] One step consists of putting the screw 3 in place through the orifice 43 of the assembly 4, for example manually, so that the head 33 of the screw 3 is in abutment against a first face of the assembly 4 to be tightened, for example against the lower face 44 of said assembly 4.

[0066] During this step, the nut 2 is gripped by the tool 1 by making it penetrate into the internal housing 511 of the docking and screwing sleeve 51. In order to facilitate this operation and make it faster, the nut 2 can be placed on a support while the operator moves the tool 1 above said nut and places the tool 1 on the nut 2 ([Fig. 6] and [Fig. 14]).

[0067] The next step consists of docking and screwing the nut 2 onto the free end 31 of the screw 3 by means of the tool 1, for example by rotating the docking and screwing sleeve 51 ([Fig.7], [Fig.8], [Fig. 15] and [Fig. 16]). This screwing must be continued until the nut 2 comes into abutment against a second face of the assembly 4 to be tightened, for example against the upper face 45 of said assembly 4. The free end 31 of the screw 3 is then accessible.

[0068] Then a step takes place which consists of gripping the free end 31 of the screw 3 with the tool 1.

[0069] In the case where the screw 3 has a gripping part 311, this operation is for example carried out by pushing the jaws 661 of the gripping device 66 in the direction of said gripping part 311 ([Fig.9]).

[0070] In the case where the screw 3 does not have a gripping part, this operation is for example carried out by approaching and screwing the gripping nut 70 of the gripping device 66 onto the free end 31 of the screw 3, by rotating the gripping nut 70 ([Fig. 17]).

[0071] The next step consists of exerting traction on the screw 3 by the tool 1 at the gripping part 71, 311 by moving said gripping part away from the head 33 of the screw 3. This causes a longitudinal stretching of the screw 3. This operation is for example carried out by moving upwards the gripping device 66 carried by the piston 61 ([Fig. 10] and [Fig. 18]).

[0072] While the tool 1 maintains the traction exerted on the screw 1, the next step consists of screwing the nut 2 with the tool 1 until it stops against the second face of the assembly 4 to be tightened, for example the upper face 45, for example by rotating the docking and screwing sleeve 51. This final tightening of the nut 2 is preferably carried out without forcing, in order to present only limited friction between the nut and the second face of the assembly 4.

[0073] The traction exerted on the screw 3 by the tool 1 is then interrupted. This is achieved, for example, by ceasing to supply the tool 1 with the pressurized fluid which moves the piston 61 upwards. In parallel, the gripping exerted on the gripping part 71, 311 by the tool 1 is also interrupted. The bolted assembly formed by the nut 2 and the screw 3 then grips the assembly 4 with a tension proportional to the stretching of the screw 3 carried out previously, the amplitude of said stretching being proportional to the pressure of the fluid which moved the piston 61 upwards, this pressure being known precisely. The tension applied by the screw 3 to the tightened assembly 4 is therefore precisely deduced therefrom.

[0074] As an example, in the case where the pressurized fluid is a hydraulic fluid, [Fig.21] illustrates the ratio Fh / FO = f(L / d) for a wide range of different threads, where:

[0075] Fh = Hydraulic force

[0076] Fo = Clamping force

[0077] L = Length of screw engaged in the bolted assembly

[0078] d = Screw diameter.

[0079] In this figure, the upper limit of the range (corresponding to coarse pitch threads) is represented by a dot-and-dash line, while the lower limit of the range (corresponding to fine pitch threads) is represented by a solid line.

[0080] In the case where the screw 3 has a gripping part 311, the operation aimed at interrupting the gripping exerted on it is for example carried out by ceasing to supply the tool 1 with the pressurized fluid which laterally moves the jaws 661, fluid which, preferably, also moves the piston 61 upwards. The jaws 661 then release the gripping part 311 of the screw 3 ([Fig. 12]).

[0081] In the case where the screw 3 does not have a gripping part 311, the operation aimed at interrupting the gripping exerted on the gripping nut 70 is for example carried out by unscrewing the gripping nut 70 and removing it from the free end 31 of the screw 3. The gripping nut 70 however remains housed in the tool 1.

[0082] The elastic return device then moves the gripping device 66 of the piston 61 downwards, into the initial rest position, for example by the thrust force exerted by the helical spring 64 which was compressed while the piston 61 was moved upwards ([Fig. 11] and [Fig. 19]).

[0083] The last step then consists of removing the tool 1. This is done for example by lifting the tool 1 upwards, which disengages the socket 51 from the nut 2 and allows the tool 1 to be moved away to, for example, repeat the previous steps for another bolted assembly ([Fig. 13] and [Fig. 20]).

Claims

Claims

1. Tool (1) for docking and screwing a nut (2) and for tensioning a screw (3), characterized in that it comprises: - a connection to a pressurized fluid supply - a main part (11) having a tubular chamber (63) having a bottom; - a pneumatic or hydraulic docking and screwing system for nut (50) housed in the main part (11); - a pneumatic or hydraulic screw tensioning system (60) comprising a piston (61) housed sliding in the tubular chamber (63) and equipped with a gripping device (66), said piston (61) being sliding between a first position resting on the bottom of the tubular chamber (63) and a second position spaced from said bottom.

2. Tool (1) according to claim 1, characterized in that it comprises a first pressurized fluid supply circuit opening into the tubular chamber (63).

3. Tool (1) according to claim 1 or claim 2, characterized in that the nut system (50) comprises: - a docking and screwing sleeve (51) movable in rotation, having an internal housing (511) of a shape adapted to receive a nut (2) and an external periphery (512) equipped with teeth (513); - a first endless screw (52) housed in a first cylindrical chamber (53), a thread (521) of which is engaged with the teeth (513).

4. Tool (1) according to claim 3, characterized in that it comprises a second pressurized fluid supply circuit opening into the first cylindrical chamber (53).

5. Tool (1) according to any one of the preceding claims, characterized in that the screw tensioning system (60) comprises an elastic return device which pushes the piston (61) into the second position.

6. Tool (1) according to any one of the preceding claims, characterized in that the gripping device (66) comprises a set of jaws (661) each comprising a chuck (6611) housed in a chuck chamber (662).

7. Tool (1) according to claims 2 and 6, characterized in that the first pressurized fluid supply circuit opens into each chuck chamber (662).

8. Tool (1) according to any one of claims 1 to 5, characterized in that the gripping device (66) comprises: - a gripping nut (70) mounted to rotate in the piston (61), having an internal threaded housing (72) and a gripping part (71) having teeth (712) located on its external periphery (73), and - a second worm screw (666) housed in a second cylindrical chamber (667), the thread (6661) of which is engaged with said teeth (712).

9. Tool (1) according to claim 8, characterized in that it comprises a third pressurized fluid supply circuit opening into the second cylindrical chamber (667).

10. Method for docking and screwing a nut (2) and tensioning a screw (3) by means of a tool (1) according to any one of the preceding claims for tightening an assembly (4), said screw (3) having a head (33) and a free end (31) located opposite the head (33), characterized in that the method comprises the following steps: - gripping the nut (2) by the nut system (50); - docking the nut (2) and screwing it onto the free end (31) of the screw (3) by the nut system (50) so that the free end (31) of the screw (3) protrudes outside the nut (2); - gripping the free end (31) by the screw tensioning system (60); - longitudinal stretching of the screw (3) by moving the piston (61) away from the nut system (50);- continuing to screw the nut (2) using the nut system (50) while maintaining the traction exerted by the screw tensioning system (60) until the nut (2) and the head (33) come into contact with the assembly (4) to be tightened.;

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