Detectable breakage screw and associated detection and manufacturing methods

Abstract

Screw with detectable breakage and associated detection and manufacturing methods One aspect of the invention relates to a screw (1) whose breakage is detectable, which comprises a shank (3) enclosing at least one closed cavity (6), in which there is a free substance (12) other than air, in fluid, powdery or granular form, for example a dye or iron filings. Another aspect of the invention relates to a method for detecting the breakage of such a screw, in which it is determined, visually or with a sensor, whether substance is present outside the screw and the condition of the screw is deduced therefrom. Another aspect of the invention relates to a method for manufacturing such a screw by additive manufacturing. Figure to be published with the abstract: Figure 1

Description

Title of the invention: Screw with detectable breakage and associated detection and manufacturing methods TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a screw whose breakage can be monitored, as well as an assembly for detecting the breakage of this screw.

[0002] The present invention also relates to a method for detecting the breakage of such a screw, as well as a method for manufacturing this screw.

[0003] The invention is primarily intended for the aeronautical field, but can also be used in any other field where the condition of screws that are difficult to access or not visible must be monitored. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0004] In many technological fields where complex mechanical systems are used, and in particular in the field of aeronautics, the strength of certain screws is crucial.

[0005] Indeed, the accidental loss of a screw can lead to a serious event, for example a more significant breakage leading to the complete breakdown of the system to which the screw belongs, or even dangerous with a risk of an accident occurring if the screw is linked to a so-called "critical" function or part.

[0006] The condition of these screws must therefore be monitored, in order to detect the possible loss of a screw and to take appropriate action if necessary.

[0007] Such screws requiring monitoring are very common in aeronautics and are found in all highly integrated complex mechanical systems, particularly in engines (reduction box, freewheel, etc.) or in transmission systems (particularly for helicopters).

[0008] Many aeronautical applications in which it is useful to monitor a possible screw breakage can be cited, in particular: • engine and helicopter transmission systems such as main or rear gearbox, transmission shafts, freewheel; • turboprops with transmission / reduction gearbox; or • geared turbojets and their transmission / reduction system ex extremely integrated.

[0009] Currently, this monitoring is done by a visual verification of the presence or absence of these screws, or indirectly by trying to identify the appearance of potential induced behaviors such as vibrations for example.

[0010] However, in many cases the screws to be monitored are not visible or are located in places that are difficult to access. Visual inspection of these screws is not easy and requires prior disassembly, which can only be carried out during long and specific maintenance operations.

[0011] The regular organization of these maintenance operations adds a significant workload to the operators and reduces the availability time of the machine to be checked, while these are only precautionary operations without the need to replace parts most of the time.

[0012] To avoid this, another possibility that complies with regulations is to multiply the number of screws used in order to guarantee the part's hold even in the event of screw loss, and this throughout its lifetime. This redundancy requires a more complex design and generates higher costs, as well as an increase in mass and volume, which is problematic, particularly in aeronautics.

[0013] There is therefore currently no device for monitoring the condition of screws which would be practical, quick and easy to implement, even in the case of hidden or difficult to access screws, and which would avoid having to resort to redundancy of these screws. Summary of the invention

[0014] The invention aims to meet this unmet need.

[0015] For this, a first aspect of the invention teaches a screw intended for an aeronautical propulsion unit, comprising a rod, said rod enclosing at least one closed cavity in which there is a free substance, different from air, in fluid, powdery or granular form.

[0016] Advantageously, this screw is installed in a conventional manner as a replacement for a traditional solid screw and performs the same functions as the latter. They are therefore interchangeable and it is not necessary to modify the parts or the design of the system in which the screw is to be implanted.

[0017] A higher grade material may however be used to produce this screw, in order to obtain mechanical properties at least equivalent to those of a solid screw, in the case where the screw should undergo significant mechanical stresses.

[0018] The screw according to the invention advantageously incorporates a function for monitoring its breakage. Indeed, in the event of breakage of this screw, the free substance initially present in its cavity(ies) spills out of the cavity and spreads outside the screw where it can be detected.

[0019] Depending on the embodiments, this detection can be done by simple visual identification of the substance outside the screw, for example in the lubricating oil, or by means of an appropriate sensor.

[0020] Thanks to this capacity to release a detectable free substance, the rupture of the screw according to the invention can be detected simply, quickly and efficiently, without prior disassembly and even if the screw is hidden or difficult to access.

[0021] Once in place, the condition of this screw can be easily monitored, continuously by means of sensors permanently installed in the machine or punctually during regular routine checks, for example before each use of the machine.

[0022] No disassembly or additional maintenance operation is necessary as long as the substance is not detected outside the screw. And, it is only when the substance is detected that a more in-depth maintenance operation, with disassembly and repair, is planned. Thus, the workload of the operators is reduced and the availability time of the machine is increased.

[0023] Furthermore, since the breakage of the screws according to the invention can be easily monitored, it is not necessary to multiply their number as a precaution. By avoiding this redundancy, an optimized design of the system to which the screw belongs is maintained, by limiting the mass, volume and cost of the assembly.

[0024] The cavity or cavities may extend over a variable rod length, adapted to the failure mode of the screw and depending on the use of the screw, this length being able to range from a few percent to more than 90% of the total length of the rod. Advantageously, the cavity or cavities may extend together over at least 70%, preferably at least 80% and even more preferably at least 90% of the length of the rod.

[0025] Thus, whatever the area of the rod in which the rupture occurs, it impacts a cavity which is then opened, allowing the release of the substance to be detected. The reliability of the detection is thus improved.

[0026] The substance may occupy a variable portion of the cavity depending on the type of detection means and the nature of the substance retained. Advantageously, the substance may occupy at least 50%, preferably at least 70% and even more preferably at least 80% of the volume of the cavity.

[0027] Each cavity is thus filled with a large quantity of substance, which spills more easily and in large quantities in the event of the screw breaking. The substance, present in large quantities, is thus more easily detected outside the screw. The efficiency and sensitivity of the detection are improved.

[0028] Advantageously, the substance may be a dye or a ferromagnetic powder, preferably iron filings.

[0029] When the substance is a colorant, it can be very easily detected by a simple visual check by the operator, for example by checking the color of the lubricating oil which bathes the system.

[0030] In the case of an aircraft, this check can advantageously be carried out at the same time as the daily visual check of the pre-flight oil level.

[0031] When the substance is a ferromagnetic powder, for example iron filings, it can be detected by the conventional iron filing detection system which is usually present in the machine's lubrication system. No additional sensor is therefore required.

[0032] Advantageously, the cavity may comprise an orifice closed by a plug. Such an orifice advantageously makes it possible to fill the cavity with substance, once the screw and the cavity have been produced (for example by a traditional machining process). When the filling is complete, this orifice is preferably closed by a plug to prevent the substance from escaping.

[0033] Alternatively, the cavity(ies) may not have an orifice. In this case, the cavity(ies) are advantageously filled simultaneously with their manufacture, preferably by additive manufacturing.

[0034] A second aspect of the invention relates to a screw breakage detection assembly which comprises at least one screw as described above and a sensor for the presence of said substance outside the screw.

[0035] The presence sensor is chosen in relation to the nature of the substance to be detected. Thus, for example, the substance may be iron filings and the presence sensor may be a detector of the presence of iron filings in the lubricating oil.

[0036] A third aspect of the invention relates to a method for detecting the breakage of a screw as described above, in which it is determined, visually or by means of a sensor, whether substance is present outside the screw and the condition of the screw is deduced therefrom.

[0037] A fourth aspect of the invention relates to a method of manufacturing a screw as described above in which the rod and its cavity(ies) are manufactured by additive manufacturing.

[0038] Additive manufacturing advantageously makes it possible to simultaneously construct the structure of the screw and its internal cavity(ies) in a single step. Additive manufacturing also makes it possible to obtain specific positions, shapes and / or sizes for the cavities that cannot be achieved by conventional machining. The cavities can thus be advantageously optimized and adapted according to the anticipated working profile of the screw.

[0039] Advantageously, during this additive manufacturing, the rod and its cavity are formed by melting a metal powder and the substance located in said cavity is simultaneously formed by leaving unmelted or partially agglomerated metal powder at the location of said cavity.

[0040] It is thus advantageous to manufacture the screw and its cavity(ies) directly filled, in a single additive manufacturing step. Only a final retouching step is then necessary to create the thread.

[0041] Indeed, during additive manufacturing, the screw shaft with its cavity is directly produced by melting the metal powder at the appropriate locations. On the other hand, the powder is left free and not melted at the location of the hollow interior volume of the cavity. The cavity is thus directly filled with metal powder, which can serve as a detectable substance, during the additive manufacturing process.

[0042] The cavity can then be directly closed by creating a sealing wall using the additive manufacturing process. The presence of a plug can thus be avoided.

[0043] Optionally, the metal powder may be partially agglomerated at the location of the interior volume of said cavity, in order to form small clusters of fused powder in the cavity. Filings are thus directly formed by additive manufacturing inside the cavity. Thanks to its larger particle size, these filings are easier to detect by a sensor, in particular a magnetic plug, than a fine metal powder.

[0044] 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

[0045] The figures are presented for information purposes only and in no way limit the invention.

[0046] [Fig. 1] is a longitudinal sectional view of a first example of a screw according to the invention.

[0047] [Fig.2] is a longitudinal sectional view of a second example of a screw according to the invention.

[0048] [Fig.3] is a schematic view of an example of a rupture detection assembly of a screw according to the invention, illustrating its operation when the screw is intact.

[0049] [Fig.4] is a schematic view of the detection assembly of [Fig.3], illustrating its operation when the screw is broken. DETAILED DESCRIPTION

[0050] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0051] In Figures 1 and 2, two examples of screws 1 according to the invention are shown. This screw 1 conventionally comprises a head 2 and a rod 3 of length L which has an external thread 4 at its lower part 5.

[0052] According to the invention, the screw 1 comprises at least one cavity 6 inside its rod 3.

[0053] In the example of [Fig.l], the screw 1 has a single cavity 6 which extends along longitudinally along the entire length L of the stem 3 and continues beyond into a part of the head 2.

[0054] In the example of [Fig.2], the screw 1 comprises two cavities 6a and 6b which extend longitudinally in the extension of one another, over substantially the entire length L of the rod 3, the cavity 6b continuing even into a part of the head 2.

[0055] The rod 3 comprises a solid part 7 interposed between the two cavities 6a and 6b which reinforces the solidity of the assembly. This solid part 7 can advantageously be provided in an area of the screw where greater stresses are expected in operation once the screw is implanted.

[0056] The number, location, size and shape of the cavities 6 can advantageously be adapted to the anticipated working profile of the screw 1 and can therefore be different from the examples shown.

[0057] Each cavity 6 delimits a hollow interior volume 8 which is closed by the walls 9 of the cavity and possibly by a plug 10 or any other similar closing element if necessary.

[0058] Indeed, a cavity 6 may be provided opening at the level of an orifice 11, located for example in the lower part 5 of the screw 1 as shown in [Fig.l], to allow the cavity 6 to be produced (for example by machining or molding) and / or to be filled.

[0059] In this case, the orifice 11 is then closed by any appropriate means, in particular by welding, filling or placing a closing element such as the plug 10.

[0060] Alternatively, the cavity 6 may not have an orifice and be entirely closed by walls 9 as shown in [Fig. 2]. Such a cavity may advantageously be produced and filled by additive manufacturing as explained previously.

[0061] The cavity 6 contains a substance 12, other than air, which is placed in the hollow interior volume 8. This substance 12 is free, that is to say that it is not fixed or linked to the walls 9 of the cavity 6, nor to any other part of the screw 1. It can therefore move freely relative to them.

[0062] Substance 12 is in fluid, powdery or granular form.

[0063] By granular we mean the juxtaposition of a multitude of small solid elements distinct, also called "divided solid" or "bulk", the geometry of these solids can be arbitrary. They can therefore include grains, crystals, particles, balls, flakes, needles, small pieces, aggregates, chips, filings or others.

[0064] The substance 12 can therefore be, for example, a liquid, a gas other than air, a gel, a powder or a set of small solid elements, such as the grains 13 shown in the figures.

[0065] Preferably, it may be ferromagnetic filings, preferably iron filings.

[0066] According to another preferred embodiment, it may alternatively be a colorant, for example in liquid, gel, powder or grain form.

[0067] It can also be any other type of easily detectable substance, for example a suitable chemical reagent.

[0068] In Figures 3 and 4, an example of a screw breakage detection assembly 14 is shown.

[0069] The detection assembly 14 shown comprises a screw 1 corresponding to the variant of [Fig.l] whose state is to be monitored, as well as a sensor 15 for the presence of the substance 12, located outside the screw 1.

[0070] The nature of the sensor 15 is adapted to that of the substance 12 in order to be able to detect the presence of the substance 12. It thus makes it possible to determine whether the substance 12 is present or absent at the sensor 15.

[0071] Thus, for example, when the substance 12 is a ferromagnetic type filing (in particular iron filings), the sensor 15 is a sensor for the presence of ferromagnetic filings, for example of the magnetic plug type or a bipolar detector with two or four conductors. This sensor 15 is preferably placed close to the screw 1 or may be further away if, for example, it is placed in the oil 16 of the lubrication circuit which surrounds the screw(s) 1 to be monitored.

[0072] Advantageously, this sensor 15 can then be the iron filings sensor already present in the lubrication circuit.

[0073] The sensor 15 transmits the information on the presence or absence of substance 12, for example in the form of an electrical signal via wires 17, to a signal processing device 18 which interprets the received signal and triggers an appropriate action. Alternatively, wireless transmission of the signal may be envisaged, for example by means of radio waves.

[0074] When the detection assembly 14 comprises several screws 1 to be monitored, several sensors 15 can be used, for example one sensor 15 per screw 1 or one sensor 15 per group of several screws 1 for example located close to each other or belonging to the same lubrication circuit. In this case, in addition to indicating only the occurrence of the breakage of a screw 1, the detection assembly 14 can give information on the location of the defective screw 1. Preferably, a single signal processing device 18 is used to receive and interpret all of the signals received from the different sensors 15.

[0075] Alternatively, a single sensor 15 can monitor all of the screws 1. In this case, only general information relating to the presence of a defective screw can be given.

[0076] The operation of this detection assembly 14 results from the means described above. It has been illustrated schematically in Figures 3 and 4.

[0077] As shown in [Fig.3], when the screw 1 is intact, the substance 12 is in entirely contained in the cavity 6 which is closed. The sensor 15, placed in the oil 16 of the lubrication circuit surrounding the screw 1, does not detect any substance 12 in the oil 16 outside the screw 1. This information is transmitted to the signal processing device 18, via the wires 17, which interprets it as a normal situation in which the screw is intact.

[0078] As illustrated in [Fig.4], in the event of the screw 1 breaking, an opening 19 is formed in the wall 9 of the cavity 6, thus releasing the free substance 12 which spills out of the cavity 6 by passing through this opening 19. The substance 12 then spreads outside the screw 1 into the oil 16 where it is detected by the sensor 15. This information is transmitted to the signal processing device 18, which interprets it as a situation of breakage of the screw 1 and an alert action is initiated.

[0079] Depending on the applications and the nature of the system in which this device is installed, the alert actions taken may vary. This may involve, for example, the emission of a light or sound signal, the display of an alert message, the programming of a maintenance operation, the transition to degraded safety operation of the system or any other appropriate action desired by the user.

[0080] According to another embodiment, it is not necessarily necessary to use a signal processing device 18, the presence or absence of substance 12 at the sensor 15 being able to be directly determined by an inspection of the sensor 15, for example visual in the case of a magnetic cap, carried out by the operator in particular during a routine check or a one-off maintenance operation.

[0081] According to still other embodiments, the monitoring of the breakage of the screw 1 can also be done without a sensor 15, nor a signal processing device 18.

[0082] For example, a check of the quality or composition of the oil 16 can be carried out by the operator, during a routine check or a one-off maintenance operation, if the substance 12 is a chemical reagent.

[0083] Alternatively, a simple visual inspection of the color of the oil can be carried out by the operator, if the substance 12 is a colorant. This inspection can advantageously be carried out at the same time as regular checks of the oil level.

Claims

Claims

1. Screw (1) intended for an aeronautical propulsion unit comprising a rod (3), characterized in that said rod (3) contains at least one closed cavity (6) in which there is a free substance (12), different from air, in fluid, powdery or granular form.

2. Screw (1) according to claim 1 characterized in that the cavity(ies) (6) extend together over at least 70%, preferably at least 80% and even more preferably at least 90% of the length (L) of the rod (3).

3. Screw (1) according to one of the preceding claims, characterized in that the substance (12) occupies at least 50%, preferably at least 70% and even more preferably at least 80% of the hollow interior volume (8) of the cavity (6).

4. Screw (1) according to one of the preceding claims, characterized in that the substance (12) is a dye or a ferromagnetic powder, preferably iron filings.

5. Screw (1) according to one of the preceding claims, characterized in that the cavity (6) comprises an orifice (11) closed by a plug (10).

6. Screw breakage detection assembly (14) comprising at least one screw (1) according to one of the preceding claims and a sensor (15) for the presence of said substance (12) outside the screw (1).

7. Detection assembly (14) according to claim 6 characterized in that the substance (12) is iron filings and in that the presence sensor (15) is a detector of the presence of iron filings in the lubricating oil (16).

8. Method for detecting the breakage of a screw (1) according to one of claims 1 to 5, characterized in that it is determined, visually or by means of a sensor (15), whether substance (12) is present outside the screw (1) and the state of the screw (1) is deduced therefrom.

9. Method of manufacturing a screw (1) according to one of claims 1 to 5, characterized in that the rod (3) and its cavity (6) are manufactured by additive manufacturing.

10. Manufacturing method according to claim 9 characterized in that, during additive manufacturing, the rod (3) and its cavity (6) are formed by melting a metal powder and the substance (12) located in said cavity (6) is simultaneously formed by leaving unmelted or partially agglomerated metal powder at the location of said cavity (6).

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