Pre-tightening force verification for critical fasteners

Abstract

A female fastener (40) for receiving and engaging a threaded male fastener, the female fastener (40) comprising a threaded body (1), a load measuring device (42) having an electrical switching mechanism sealingly disposed and housed inside the threaded body (1) for measuring a compressive load on the female fastener (40), and for transmitting a signal representative of the measured compressive load to an external system (44).

Description

Technical Field

[0001] The present invention relates to a female fastener, an arrangement, and a method of use. Background Art

[0002] Tightening a threaded fastener below its preload in operation may quickly lead to its fatigue failure or leakage of liquid from a pressure joint. Therefore, it is very important to tighten the fastener to a safe preload (i.e., a preload exceeding any load experienced in operation). Equally important is that any relaxation in the joint after assembly does not cause the preload to drop below the above-mentioned safe minimum preload.

[0003] Tightening a fastener is typically performed using a torque wrench or a hydraulic tensioner. It is well known in the industry that both of these methods have poor control over the preload. For a torque wrench, the thread friction is an unknown factor that directly affects the final bolt tension. For a hydraulic tensioner, the final fastener load is uncertain because the load transfer loss between the tensioner tool and the bolt can only be estimated. Neither of these methods provides any way to check the bolt load after assembly.

[0004] WO 2014 / 106752 A2 uses a gauge pin assembled into the side of a nut and orthogonal to the threaded hole of the nut. This orthogonal design necessarily introduces several measurement errors. The diameter of the orthogonal hole limits the strain that can be measured. The precision 90-degree coupling mechanism required to operate the gauge rod introduces clearance errors. Operability is a problem because sliding a tightening socket or wrench over the nut can easily damage the gauge mechanism assembled in the side of the nut.

[0005] US 2830486 shows a nut with an elongated indicating pin fixed at one end and freely slidable within a hole at its other end, where compression of the nut relative to the set level of the pin causes the pin end to move from a first state to a second state. These two states are distinguished by a visual inspection of the position of the pin end relative to the top of the nut. The load-bearing capacity of this nut is low and is severely limited by the necessary internal grooves.

[0006] GB 2112725.3 shows a nut with an elongated indicating pin fixed at one end and freely slidable within a hole at its other end, where compression of the nut relative to the set level of the pin causes the pin end to move from a first state to a second state. These two states are distinguished by checking with a fingertip whether the rotor can rotate freely. This is a mechanism operated by finger pressure and is thus not connected to other nuts or tightening control devices. Summary of the Invention

[0007] An object of the present invention is to provide a reliable fastener for ensuring a safe joint.

[0008] To achieve the above object, a female fastener, an arrangement, and a method of use according to the independent claims are provided. Other embodiments are provided by the dependent claims.

[0009] According to an exemplary embodiment of the present invention, there is provided a female fastener for receiving and engaging a threaded male fastener, wherein the female fastener includes a threaded body and a load measuring device having an electrical switching mechanism (e.g., a two-state (e.g., on or off) electrical switching mechanism), the load measuring device being sealed and housed inside the threaded body for measuring the compressive load on the female fastener and for transmitting a signal representative of the measured compressive load (which may be, for example, an electrical signal or an electrically detectable signal) to an external system.

[0010] According to another exemplary embodiment of the present invention, there is provided an arrangement including the female fastener having the above characteristics and an external system that receives the signal when coupled to the female fastener.

[0011] According to yet another exemplary embodiment of the present invention, the female fastener having the above characteristics or the arrangement having the above characteristics is used in a wind turbine, for example, in an offshore wind turbine.

[0012] Thus, there can be provided a female fastener for receiving and engaging a threaded male fastener, the female fastener including a force sensor device that is completely sealed and housed inside the body of the fastener for sensing the compressive force on the female fastener and for outputting a signal representative of the compressive force to an external data collection device.

[0013] Embodiments of the present invention seek to alleviate the above problems by providing a reliable means of measuring the compressive load in a nut and referencing it to a preset safe minimum load. It enables interconnecting large groups of nuts and transmitting their pre-tensioning force conditions for remote monitoring. Thus, it can be detected at an early stage when relaxation in an assembled joint causes the pre-tensioning force to drop below the safe minimum pre-tensioning force, so that countermeasures can be taken in a timely manner. It can also be detected during assembly that the joint has not provided sufficient pre-tensioning force, so that the assembly process can be continued until sufficient strength of the joint can be ensured.

[0014] Exemplary embodiments can provide a female threaded load indicating nut for engaging with a threaded male fastener.

[0015] Exemplary embodiments of the present invention relate to a female threaded nut fastener that can measure its own pre-tensioning force, can use the measured value to control its own tightening process, and can transmit the pre-tensioning force measurement value to a remote monitoring station.

[0016] Exemplary embodiments of the present invention relate to a nut having its own built-in load measuring device. This can accurately measure and indicate the pre-tightening force. It can control any tightening system in use, such as a wrench or a tensioner. It can indicate when its own pre-tightening force drops below a preset safe minimum load using a simple hand-held tool. It can be easily connected to other nuts in the surrounding group, such as the large nut groups found in wind turbines, and transmit the status of all groups to a remote monitoring station via a single transmitter.

[0017] The load measuring mechanism can be set deep inside the nut body where it can avoid physical and environmental damage. This is an advantageous feature that enables the fastener to work in challenging environments but be completely reliable.

[0018] When the female fastener is connected to the corresponding male fastener, especially by screwing the male fastener with an external thread into the inner hole of the female fastener with an internal thread (which may cause the male fastener to press against the internal thread of the female fastener), the female fastener may be subjected to a compressive load, while the male fastener may be subjected to a tensile load. Too small a compressive load in the female fastener (e.g., during the assembly process) or an excessive reduction in the compressive load (e.g., over time due to loosening forces) may indicate that the nut is loose and thus unsafe, which may lead to reliability problems. According to the exemplary embodiments of the present invention, such unexpected conditions of the female fastener and the joint as a whole can be detected precisely and early, so that measures can be taken to increase the connection strength to remedy the reliability problems.

[0019] For example, female fasteners or arrangements can be used in wind turbines to identify loose or unsafe nuts. The female fasteners of a wind turbine (e.g., those connected at the wind turbine blades) may be difficult to reach or access. With the exemplary embodiments, the corresponding signals indicating loose or unsafe nuts can be transmitted reliably and automatically without dispatching engineers to the installation locations of the nuts that may be difficult to reach.

[0020] Although wind turbines may be a preferred application area of the exemplary embodiments of the present invention, the female fasteners or arrangements can also be used for other purposes, such as in petrochemical plants (e.g., to prevent leaks due to loose nuts).

[0021] Hereinafter, other exemplary embodiments of the female fasteners, arrangements, and usage methods will be explained.

[0022] In an embodiment, the load measuring device includes an electrical switch configured to change its switching state when the measured compressive load drops below a preset minimum compressive load level. In particular, the female fastener may include a single electrical switch that operates when the compressive load drops below a preset minimum level. For example, in the case of meeting the preset minimum compressive load level, the electrical contacts of the electrical switch may be closed, while in the case of not meeting the preset minimum compressive load level, the electrical contacts of the electrical switch may be open. Thus, detecting the electrical signal at the electrical switch allows the detection of the compressive load level.

[0023] For example, the switch may be implemented as an on-off switch that switches between two switching states, i.e., on and off. The corresponding electrical signal may be an analog signal or a digital signal. A digital signal (e.g., having two different voltage levels) may allow highly accurate signal transmission.

[0024] In an embodiment, the load measuring device includes at least two electrical switches configured to change their switching states at different preset compressive load levels. Thus, the female fastener may include two or more electrical switches that are preset to switch at different compressive loads. Providing two or more switches may allow for an improved compressive load detection function of the load measuring device, as at least two different compressive load levels can be detected.

[0025] In an embodiment, the female fastener includes an internal sealed chamber that contains the load measuring device and contains a fluid, particularly a liquid, that is configured to protect the load measuring device from environmental damage, particularly from corrosion and / or vibration. Thus, the female fastener may contain an internal sealed chamber that contains one or more load sensing devices that contain a fluid (e.g., oil) to protect the load sensing devices from environmental damage. This may allow the female fastener to be implemented even under harsh conditions, such as a corrosive environment and / or an environment where vibration is applied to the female fastener.

[0026] In an embodiment, the female fastener includes a coupling unit for communicatively coupling, particularly in a wired or wireless manner, the female fastener to at least one other female fastener. For example, the coupling unit may include a cable or a set of cables that electrically connect multiple female fasteners to each other. Thus, the female fastener may include means for connecting to other similar or identical fasteners via a wire or a wifi device. By coupling multiple female fasteners to the coupling unit, signals indicating the compressive loads applied to each individual female fastener can be combined and transmitted as an overall signal to an external system via a transmitter. For example, a common signal may include the compressive load information of multiple female fasteners connected by one or more coupling units.

[0027] In an embodiment, the female fastener is configured as a nut. However, other configurations of the female fastener are also possible. When the female fastener is implemented as a nut, holes can be formed in the flange surface of the nut, and the switch-rod pair can be inserted into the holes. Then the lateral surface of the nut can remain intact and closed, and there is no need to provide holes for inserting components of the load measuring device therein. This can maintain the mechanical integrity of the nut and thus strengthen the nut-bolt joint.

[0028] In an embodiment, the female fastener is configured to be waterproof, especially configured for subsea operations. When made waterproof (especially by corresponding sealing and by manufacturing the female fastener from non-corrosive materials), the female fastener can be used under conditions where it is exposed to water (such as rainwater in outdoor applications or seawater in offshore wind power applications). For subsea operations, the female fastener can also be formed to be pressure-resistant up to at least the subsea pressure relevant to the application (such as at least up to 100 bar).

[0029] In an embodiment, the female fastener is configured to indicate via the signal when its own pre-tightening force drops below a preset safe minimum load. The corresponding switch of the female fastener can be configured such that at a predefined safe minimum load applied to the female fastener, the switching state changes between a closed state (which can be a low-ohm state) and an open state (which can be a high-ohm state).

[0030] In an embodiment, the load measuring device includes at least one switch that is triggered to change its switching state when the compressive load on the female fastener sufficiently compresses the female fastener to move the switch to contact the rod in the threaded body. In the absence of a compressive load, the rod is set at a preset distance from the switch. When the compressive load acting on the female fastener is sufficient, the switch is moved to physically contact the rod, thereby establishing an electrical connection therebetween. In the absence of a compressive load acting on the female fastener or when the compressive load acting on the female fastener is insufficient, the switch remains separated from the rod, with no direct physical contact therebetween, thereby disabling the electrical connection therebetween. These two different switching states can be detected in the form of an electrical signal of the switch-rod pair, which indicates a low-ohm state when there is direct physical contact between the switch and the rod, and a high-ohm state when there is no direct physical contact between the switch and the rod. Therefore, by measuring the electrical signal generated by and detected at the load measuring device of the external system, the compressive load state of the female fastener can be reliably detected. The signal representing the measured compressive load can be generated based on the electrical response of the switch-rod pair in response to an electrical stimulation signal applied by the external system to the switch-rod pair.

[0031] In an embodiment, the female fastener includes a socket for inserting a probe of an external system, wherein said insertion triggers the transmission of said signal representing the measured compressive load to the external system. The socket may be a recess and the probe may be a protrusion. The socket and the probe may be adapted to match each other (e.g., by form closure). When the probe is inserted into the socket and the probe transmits an electrical stimulation signal through the socket to a switch, an electrical response signal can be detected at the load measuring device, which electrical response signal indicates the compressive load applied to the female fastener.

[0032] In an embodiment, the female fastener does not have an energy supply unit, in particular no battery. However, the external system may include an energy supply unit (in particular a battery), which is configured to supply power to the load measuring device when coupled to the external system. The female fastener may be powered by electrical energy provided by the connected external device. For example, when a hand tool of the external system is connected to the female fastener to read the electrical signal at the switch - lever pair, the formation of the mechanical connection between the socket of the female fastener and the probe of the external system may also connect the female fastener to the energy supply unit (e.g., a battery) of the external system, thereby powering the female fastener during the signal reading process.

[0033] In an embodiment, the external system includes a tightening tool, in particular a torque wrench, which is configured to compare a signal representing the transmission of the measured compressive load with the torque applied by the tightening tool to the female fastener to achieve this compressive load, and to adjust the applied torque based on the result of said comparison. Thus, the female fastener may include means for signalling its compressive load state to the torque wrench, such that the torque wrench can compare the compressive load achieved in the fastener with the torque applied to the fastener to achieve this compressive load. Then, the applied torque can be automatically adjusted accordingly to achieve the desired final load. Thus, the operation of the tightening tool can become more reliable, as it can ensure that the correct amount of torque is applied to the female - male fastener arrangement to ensure a sufficiently strong connection therebetween.

[0034] In an embodiment, the external system includes a tightening tool, in particular a hydraulic tensioner, which applies said compressive load and is configured such that if the compressive load transmitted by signal to the tightening tool deviates from a target load level, the tightening tool adjusts the applied compressive load towards the target load level. In such an embodiment, the female fastener may include means for signalling its compressive load state to the hydraulic tensioner for applying the load. If the compressive load signalled by the fastener is not as desired, the hydraulic tensioner can be adjusted automatically or manually to achieve the desired load.

[0035] In an embodiment, the external system includes a hand-held tool that can be manually connected to the load measuring device to obtain, in particular display (e.g., visually or audibly), information indicating the measured compressive load. Thus, the female fastener can be equipped with means for checking whether its compressive load is correct by using a simple hand-held tool.

[0036] In an embodiment, the hand-held tool is configured for subsea operations. In such an embodiment, the female fastener that can then also be installed subsea can include, for example, means for a diver to check whether there is a safe pre-tensioning force in the fastener using a simple hand-held tester.

[0037] In an embodiment, the external system includes a remote monitoring station that is configured to analyze the transmitted signal representing the measured compressive load and to take action, in particular output a warning of pre-tensioning force loss, when the measured compressive load drops below a preset minimum compressive load level. The corresponding female fastener can include an internal force sensor that can be connected to other similar fasteners and one or more data collection networks. Then the inspection of the fastener can be performed remotely. For example, further detailed analysis of the data can provide an early warning of pre-tensioning force loss in the joint due to any reason, including initial cracking of the mating male fastener.

[0038] In an embodiment, at least a part of the external system is located at a remote location relative to the female fastener. For example, the female fastener can be positioned and installed at a technical device (e.g., a wind turbine), while at least a part of the external system can be arranged at a control site away from the technical device (e.g., in a control room for controlling the wind turbine). Thus, one or more female fasteners can be monitored from a remote location, which is extremely advantageous when the female fasteners are located in hard-to-reach positions (e.g., installed on a wind turbine).

[0039] In an embodiment, the arrangement includes at least one additional female fastener having the above-described features, wherein the female fastener and the at least one additional female fastener are coupled for transmitting signals representing the measured compressive loads of the female fastener and the at least one additional female fastener to the external system. This connection can be established by a coupling unit that can create a physical (preferably conductive) connection or a wireless communication connection (e.g., via Bluetooth or wifi coupling) between the individual female fasteners. Thus, the individual signals from the female fasteners can be bundled and can be sent as a common signal from the female fasteners and the coupling unit to the external system, which for example includes a wireless transmitter.

[0040] In an embodiment, the load measuring device includes an electrical switch configured to complete a circuit between a probe of an external system on the one hand and an additional contact of the female fastener on the other hand when the probe of the external system is inserted into a socket on the female fastener. The electrical switch may include two conductive parts (e.g., a movable switch body and a fixed part (e.g., a rod)) that may be electrically coupled to each other or separated from each other, depending on whether the measured compressive load of the female fastener is above or below a predefined threshold. Thus, a machine voltage compressive load detection can be achieved, which can be read out by an external system by directly detecting an electrical signal at the electrical switch.

[0041] In an embodiment, the external system includes an indicator indicating a predefined state of the measured compressive load, in particular a light-emitting diode (LED) that lights up when the switch of the load measuring device changes its switching state. In another embodiment, the external system includes a flashing warning light module to be inserted into the socket of the female fastener, which is configured to flash when the female fastener is at a safe load indicated by the signal. Such an external system may be permanently or temporarily attached to the female fastener for visually indicating a critical load state.

[0042] In an embodiment, the external system includes a wireless transmitter (e.g., a wifi transmitter and / or a Bluetooth transmitter) to be inserted into the socket of the female fastener and configured to wirelessly signal (e.g., to a remote monitoring station) the switching state of the switch of the load measuring device. Such a wireless transmission system allows monitoring of the compressive load state of one or more female fasteners from a remote location. This is particularly advantageous when the female fasteners are installed in locations that are not easily accessible.

[0043] Uniquely, an exemplary embodiment may have an electrical switch mechanism disposed deep within the body of the nut that continuously, repeatedly, and / or occasionally measures the compressive load in the nut and checks whether it has dropped below a preset safe minimum. Such an electrical mechanism can signal a series of actions associated with the nut. First, during an initial tightening operation, it can automatically adjust a torque wrench to compensate for variations in thread friction. It can also signal a hydraulic tensioner to adjust the hydraulic pressure to compensate for errors in final tension. Then, during the working operation of the joint, it can transmit data regarding the nut preload condition to a remote site for monitoring and analysis to ensure that the nut load does not drop below the safe minimum.

[0044] Field inspectors can also easily check the nut load using a simple hand-held test unit. A subsea version of this tester is also disclosed, which can be manually operated by a diver or automatically operated by a deep submergence vehicle.

[0045] In operation, the precision electrical switch completes the circuit between a plug or probe inserted into a socket in the nut and the body of the nut. The switch is triggered when the force on the nut sufficiently compresses the nut such that the switch moves to just contact a reference bar that is a preset distance from the switch. The preset distance corresponds to the desired minimum compression load in the nut. The operation of the switch causes the connected equipment inserted into the switch to operate. It will be appreciated that this provides several new and original control options that are beneficial for the safe operation of the fastener.

[0046] An advantageous feature of an exemplary embodiment of the present invention is that a preset minimum safety strain value in the nut is associated with the formation of the circuit, so that the switch not only senses when the preset load is reached, but also simultaneously controls other external systems that can be a wrench, a tensioner, an indicator, a data storage system, a transmitter, to send information about the nut load state to a remote computer, etc.

[0047] Another important feature that results in high accuracy of strain measurement is that the reference bar does not move or bear any load, so it remains completely stable. The switch is the only moving part, and when the nut compresses, it moves towards the fixed reference bar.

[0048] In another embodiment, the switch can have two or more switching points that operate at different loads, thereby allowing the nut to switch at two different loads in the nut. Typically, this option is used to provide minimum and maximum load measurements to assist the tightening procedure. However, it can also have completely different uses. In some applications, the minimum load setting can be set very low, for example only 50% of the safety minimum load. In this case, if the minimum setting is triggered and it is the only nut in the group that is triggered, it can indicate a fault, such as a bolt breakage. The monitoring station can immediately receive a warning not only about bolt relaxation but also about possible bolt breakage that requires urgent attention.

[0049] Note that the reference pin and the switch can be located inside a hole in the body of the nut, the hole is completely sealed, and can be pre-filled with fluid during initial assembly to prevent corrosion and attenuate any vibrations. This creates reliability and avoids having the fragile measurement parts located on the outside of the fastener where they would be prone to corrosion and damage.

[0050] The state of the switch can be signaled through an electrical socket mounted in the top surface of the switch. Signals from the switch can activate a variety of equipment. If the signals are saved over time, it can also provide a record of the ongoing nut state. An advantageous feature of the system is that the socket in the switch can take a variety of different plug-in options.

[0051] The external system of the embodiment uses a handheld indicator tool that can show when a switch is made. The tool is manually held in the socket, and typically an LED light in the tool lights up when a switch is made. The operator can check regularly and stop tightening the nut when the minimum safe load is reached. For subsea work, a handheld waterproof version of the indicator tool can be used.

[0052] Another option is to insert a flashing warning light module into the socket. This can typically be held by a magnet on the end of the nut, freeing the hands. The flashing warning light module will flash when the nut is at the safe load and is an option for holding a manual tester on the nut.

[0053] Another option is to insert a removable Wi-Fi transmitter into the switch unit to signal the switch state, which can be used in situations where it is difficult to reach with a manual tool indicator (such as when using a hydraulic tensioner tool).

[0054] Another embodiment involves inserting a Bluetooth transmitter into the socket, which can then control the tightening process of a hydraulic torque wrench. When the nut has reached its safe load, the transmitter signals the receiver on the wrench to tell the wrench to stop tightening. Alternatively, when the nut load is known to be at a given torque, the applied torque can then be automatically adjusted up or down to allow for thread friction. Note that once the torque is at the set load of the nut, the thread friction is automatically known.

[0055] An advantageous embodiment of the present invention is that multiple groups of nuts can be electrically hard-wired together in a chain, which can then be connected to a transmitter via Wi-Fi or hard-wire. Then, a single transmitter can send data about all the nuts in the group to a remote monitoring station via that single transmitter. The wire chain designed to connect the nuts is arranged such that it is clear which nuts have dropped below the minimum safe load (if any). This is a very simple, reliable, and low-cost way to monitor the safety of large groups of nuts commonly found in, for example, wind turbines.

[0056] The reliability of the bolt load monitoring device is crucial. Such nuts do not require batteries or electronic components, and have a fully protected mechanism inside the nut, which means it can provide an unprecedented level of practical safety, which is advantageous for critical fasteners.

[0057] In an exemplary embodiment, an electrical switch may be provided inside the nut body to prevent physical or environmental damage. In an embodiment, a minimum pre-tightening force warning may be issued. In an embodiment, minimum and / or maximum pre-tightening force monitoring may be implemented. The embodiment may provide a fluid-filled chamber. In an embodiment, the nuts may be combined using hardwiring or wifi connection. According to an embodiment, the tightening of a torque wrench may be controlled. According to another embodiment, the tightening of a hydraulic tensioner may be controlled. A manual pre-tightening force check may be performed. In an embodiment, a subsea pre-tightening force check may be performed. Data analysis may be performed in an embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The present invention will now be described only by way of example and with reference to the accompanying drawings, but the present invention is not limited thereto:

[0059] Figure 1 A plan view of a female fastener configured as a nut according to a first embodiment is shown.

[0060] Figure 2 A cross-section of a nut according to a first embodiment is shown.

[0061] Figure 3 A detailed cross-section of a switch unit of a female fastener according to a first embodiment is shown.

[0062] Figure 4 A detailed cross-section of a switch unit of a female fastener according to a second embodiment is shown.

[0063] Figure 5 An arrangement of a plurality of female fasteners to be implemented as nuts connected together according to an exemplary embodiment is shown, and a connection via a wifi transmitter for remote monitoring is shown.

[0064] Figure 6 A cross-section of a nut-type female fastener with a wifi plug according to an exemplary embodiment is shown.

[0065] Figure 7 A plan view of a nut-type female fastener with a wifi plug used together with a hydraulic torque wrench according to an exemplary embodiment is shown.

[0066] Figure 8 A side view of an external system in the form of a handheld test unit used together with a nut-type female fastener according to an exemplary embodiment is shown.

[0067] Figure 9 A side view of a subsea embodiment of an external system in the form of a handheld test unit implemented to cooperate with a female fastener is shown.

[0068] Figure 10A side view of a warning light assembled near a female fastener implemented as a nut according to an exemplary embodiment is shown.

[0069] Figure 11 A switch unit and a corresponding female fastener according to an exemplary embodiment are shown in detail. Detailed Description

[0070] The illustrations in the drawings are schematic. In different drawings, similar or identical elements are provided with the same reference numerals.

[0071] Figures 1 to 3 A first embodiment of a nut-type female fastener 40 is shown in different views. Figure 1 A top view is shown, Figure 2 A cross-sectional view is shown, and Figure 3 Details of the female fastener 40 are shown.

[0072] The shown female fastener 40 is configured as a nut for receiving and engaging a male fastener having an external thread, which is not shown and may be implemented as, for example, a bolt or a screw. The female fastener 40 includes a threaded body 1, which may be an annular body having a through-hole 62 and an internal thread 64.

[0073] A load measuring device 42 is disposed in a hole 3 formed in the threaded body 1 for measuring a compressive load applied to the female fastener 40 due to the connection of the female fastener 40 with the male fastener. The load measuring device 42 is sealed and accommodated inside the threaded body 1 for measuring the compressive load on the female fastener 40 and for transmitting an electrical signal representing the measured compressive load to an external system (see Figures 5 to 10 reference numeral 44 in the drawings).

[0074] More specifically, the load measuring device 42 includes an electrical switch 6, which is configured to change its switching state (particularly between on and off) when the measured compressive load drops below a preset minimum compressive load level. An internal sealed chamber 60 of the female fastener 40 houses the load measuring device 42 and houses a fluid (such as oil), which is configured to protect the load measuring device 42 from environmental damage (such as corrosion and vibration). Due to its sealed construction, the female fastener 40 is waterproof and can thus be implemented, for example, in an offshore wind turbine. It is even possible that the female fastener 40 is configured for subsea operation, for example, to withstand the hydrostatic pressure at the subsea level.

[0075] The load measuring device 42 can be configured to indicate via the electrical signal when the self-preloading force of the female fastener 40 drops below a preset safe minimum load. More specifically, the load measuring device 42 includes the above-mentioned switch 6. When the compressive load on the female fastener 40 sufficiently compresses the female fastener 40 to move the switch 6 to contact the fixed rod 4 in the threaded body 1, the switch 6 is triggered to change its switching state. In the absence of a compressive load, the rod 4 can be set at a preset distance from the switch 6 (see the distance D in Figure 11 ). In the presence of a compressive load that can be, for example, at least at the level of a preset minimum compressive load, the distance D decreases to zero, such that the switch 6 and the rod 4 are in direct physical contact with each other.

[0076] In addition, the female fastener 40 includes a recessed socket 7 for receiving the insertion probe of the external system 44 (see the reference numeral 20 in Figure 5 、 Figure 6 、 Figures 8 to 10 ). Advantageously, the insertion can establish a connection between the probe 20 and the switch 6, and this connection can trigger the transmission of the electrical signal representing the measured compressive load to the external system 44.

[0077] Still more advantageously, the shown female fastener 40 can be without an energy supply unit, for example, it may not require its own battery. When the probe 20 of the female fastener 40 is inserted into the socket 7 of the female fastener 40, the female fastener 40 can be powered by the battery of the external system 44 or any other energy supply unit. This simplifies the design and maintenance work of the female fastener 40.

[0078] Still referring to Figures 1 to 3 , the nut body 1 is shown as a typical threaded hexagonal nut. More generally, the nut can be any threaded female fastener and can take other shapes, such as circular, square, double hexagonal. The nut has an extended annular collar 2, and the annular collar 2 both increases the strength of the nut and increases the compression length of the nut. A hole 3 (which can be a single through hole or a blind hole extending along the tightening axis of the nut-type female fastener 40) is formed through the nut. The reference rod 4 passes through the hole 3 and is fixedly fixed in the nut at its lower end 5. The electrical switch 6 is at a preset gap above the reference rod 4 and adjacent to the reference rod 4, and the electrical switch 6 is fixedly mounted in the hole 3. Both the switch 6 and the rod 4 extend along the tightening axis of the nut-type female fastener 40 (which is the vertical axis in the illustrations of Figure 2 and Figure 3 ). The socket 7 for connection by a connector plug is located in the top of the switch 6. Through this socket 7, when the safe preset load is reached, there will be current flowing, which indicates that the nut has exceeded the minimum safe load.

[0079] Figure 4Details of the female fastener 40 according to another embodiment of the present invention are shown. In this embodiment, there are two plug sockets 7, 7, and the two plug sockets 7, 7 allow two connections indicating the presence of a minimum load or a maximum load in the indicating nut. This is achieved by providing two sets of contacts in the switch body for slightly different loads. For example, two electrical switches 6, 6 with different distances D can be formed in the load measuring device 42 (see Figure 10 ). Thus, the load measuring device 42 according to Figure 4 includes two electrical switches 6, 6 and two corresponding sockets 7, 7. The switches 6, 6 are configured to change their switching states at different preset compressive load levels. One of the switching states can correspond to minimum load measurement, and the other of the switching states can correspond to maximum load measurement. This can assist the user during the tightening procedure. The different load measurements associated with different pairs of switches 6 and sockets 7 can be defined by different distances (see Figure 11 for "D") for each pair.

[0080] Figure 5 An arrangement including a plurality of female fasteners 40 and an external system 44 is shown. The external system 44 receives an electrical signal from the female fasteners 40, and the electrical signal represents the measured compressive load applied to each of the female fasteners 40. More precisely, Figure 5 the arrangement shows a set of female fasteners 40, which are implemented as nuts and are connected together by hard-wired wires 9 and simple plugs 10, thereby connecting any number of nuts in a set together. The status of the entire set is sent to a remote monitoring station 52 via a wireless transmitter 11 or hard-wired. The wiring circuit is designed such that if any of the nuts drops below the minimum required load, the identity of the specific unit can be displayed remotely or locally on the nut itself.

[0081] Thus, Figure 5 it is shown that the external system 44 can include a remote monitoring station 52, and the remote monitoring station 52 can be configured to analyze the transmitted signal representing the measured compressive load. In addition, the remote monitoring station 52 can be programmed to take a predefined action when the measured compressive load drops below a preset minimum compressive load level. For example, such an action can be to output a warning of preload loss.

[0082] Advantageously, the part of the external system 44 in the form of the remote monitoring station 52 can be located at a remote location relative to the female fasteners 40 and the transmitter 11. For example, the female fasteners 40 and the transmitter 11 can be attached to one or more blades (not shown) of a wind turbine, while the remote monitoring station 52 can be arranged away from the blades of the wind turbine, such as in a control room.

[0083] According toFigure 5 The arrangement includes a plurality of female fasteners 40 connected to each other by a coupling unit 46. This enables signals representing the measured compressive loads of each of the plurality of female fasteners 40 to be transmitted to an external system 44. To this end, the external system 44 includes a wireless transmitter 11 which can be inserted into a socket 7 of one of the female fasteners 40 and which can be configured to wirelessly signal the switching state of a switch 6 of a load measuring device 42 to a remote monitoring station 52. The above-mentioned coupling unit 46 can be configured to communicatively couple the individual female fasteners 40 to each other in a wired manner. For example, the wireless transmitter 11 can be a wifi transmitter and / or a Bluetooth transmitter. As described above, Figure 5 the arrangement is particularly suitable for use in wind turbines, such as offshore wind turbines.

[0084] Figure 6 shows an arrangement including a female fastener 40 and an external system 44 which, when coupled to the female fastener 40, receives from the female fastener 40 a signal representing the measured compressive load applied to the female fastener 40. Thus, Figure 6 shows another embodiment in which a plug-in, removable Wi-Fi or Bluetooth unit in the form of a transmitter 11 will transmit a signal that the load in a warning nut has dropped below a preset minimum value. This can be particularly useful when the nut is located on a moving structure, such as a wind turbine blade.

[0085] Figure 7 shows an arrangement including an external system 44 and a female fastener 40 according to another exemplary embodiment. Figure 7 shows another important way in which this minimum load indication signal can be used. The signal can be used to control the initial tightening process of a nut-type female fastener 40. In this example, a hydraulic torque wrench 15 is used to tighten a nut having a plug in a Bluetooth transmitter 11. When the nut reaches its preset load, it then sends a signal to the torque wrench 15 telling it to stop tightening. The unique feature is that when the nut reaches its preset load, the torque reading on the torque wrench 15 can be recorded and used to automatically calculate the true friction on the thread. If desired, this true coefficient of friction can be used to add an accurate additional tightening. For example, by this method, an accurate additional 10% load (or another predefined value) can be added above the nut set load in order to allow some relaxation in the joint before the nut signals a low, unsafe load. Generally, when thread friction is found by this method, any load replacing the preset load can be accurately applied to the nut by the torque wrench.

[0086] According to Figure 7, the external system 44 thus includes a tightening tool 48 implemented as a torque wrench 15. The torque wrench 15 is configured to compare a transmitted compressive load indication signal representing the measured compressive load from the transmitter 11 assembled on the female fastener 40 with the torque applied by the tightening tool 48 to the female fastener 40 to achieve that compressive load, and to adjust the applied torque based on the result of the comparison.

[0087] In another embodiment, the tightening tool 48 can be a hydraulic tensioner (not shown) that applies the compressive load and is configured such that if the compressive load transmitted to the tightening tool 48 deviates from a target load level, the tightening tool 48 adjusts the applied compressive load towards the target load level.

[0088] Figure 8 An arrangement including a female fastener 40 and an external system 44 is shown according to yet another exemplary embodiment. More specifically, Figure 8 A method of checking the bolt load using a simple handheld tester is shown. Such a simple device is portable and immediately available for checking any nut. The body 16 contains a battery or any other supply unit 54 as well as an LED 17 and a sound alarm 18. The ground connection 19 is magnetic and can be connected to the nut itself or to any conductive location on the flange. The probe 20 enters the nut socket 7, and if there is a load above a minimum acceptable preset value, the LED flashes and the buzzer sounds.

[0089] More generally, the load measuring device 42 of the female fastener 40 includes an electrical switch 6 that is configured to complete a circuit between the probe 20 of the external system 44 on the one hand when the probe 20 of the external system 44 enters the socket 7 on the female fastener 40 and another contact of the female fastener 40 on the other hand. Here, the external system 44 is equipped with a handheld tool 50 that can be manually connected to the load measuring device 42 for outputting information indicating the measured compressive load visually, for example, through the LED 17 and / or auditorily, through the sound alarm 18.

[0090] Therefore, Figure 8 The external system 44 shown includes an energy supply unit 54 in the form of a battery that is configured to power the load measuring device 42 when the female fastener 40 is coupled to the external system 44. Advantageously, the female fastener 40 does not require any of its own energy supply unit, which simplifies its construction and makes the female fastener 40 maintenance-free.

[0091] Furthermore, according to Figure 8 the external system 44 includes an indicator 56 that indicates a predefined state of the measured compressive load. In Figure 8In it, the indicator 56 is implemented as a light-emitting diode 17 (which lights up when the switch 6 of the load measuring device 42 changes its switching state) and a sound alarm 18 (which outputs an audio signal when the switch 6 of the load measuring device 42 changes its switching state).

[0092] In an embodiment of the arrangement according to Figure 9 a hand tool 50, which can be implemented in a manner similar to that according to Figure 8 is configured for subsea operations. Figure 9 A special version of a hand-held tester for subsea applications is shown. Since seawater is a good conductor, there is no need for Figure 8 the ground terminal 19 shown. This terminal is replaced by a metal boss 21, which conducts the current through the seawater to the nut, thus completing the circuit to operate the LED 23. When the probe 20, which can be implemented as the detection point 25 in Figure 9 is correctly positioned in the nut through the waterproof seal 26, the waterproof button 22 activates the unit.

[0093] Figure 10 An arrangement of a female fastener 40 and an external system 44 according to yet another exemplary embodiment is shown. In this embodiment, the external system 44 includes a flashing warning light module 58 to be inserted into the socket 7 of the female fastener 40. The flashing warning light module 58 is configured to flash when the female fastener 40 is at the safe load indicated by the signal.

[0094] More specifically, Figure 10 a warning light 29 connected to the nut socket 7 through a cable 28 and a removable plug 27 that can form the probe 20 is shown. The warning light can be mounted, for example, on the end of a bolt (such as a male fastener 90 with an external thread 92) by a magnet or on a tightening wrench or a hydraulic tensioner used during the assembly process ( Figure 10 not shown in

[0095] When the minimum load is reached in the nut, then the light flashes. This is a particularly useful device for a hydraulic tensioner because the stud and bolt are very likely to be completely inaccessible at the tightened end, so the device can be assembled at the other end of the stud, where, if the final assembly load is too low, it can give a warning. Figure 5 When any of the above tightening control methods have been used, then a simple procedure is to connect a hard-wired coupling mechanism for long-term remote monitoring, as

[0096] Figure 11 shown. Figure 11On the left side, a part of the female fastener 40 is shown. On the right side, details of the female fastener 40 are shown, which further show in more detail the construction of the load measuring device 42 with the switch 6.

[0097] In addition, according to Figure 11 , the shown female fastener 40 is configured to receive and engage a threaded male fastener (not shown). The female fastener 40 includes a threaded body 1 that can be made of any metallic material (such as steel). The load measuring device 42 is hermetically arranged and accommodated within the threaded body 1. The load measuring device 42 is used to measure the compressive load on the female fastener 40 and to transmit a signal representing the measured compressive load to an external system 44 ( Figure 11 not shown in). Advantageously, the load measuring device 42 includes a switch 6 that is triggered to change its switching state when the compressive load on the female fastener 40 compresses the female fastener 40 sufficiently to move the switch 6 into contact with a rod 4 in the threaded body 1. In the absence of a compressive load, the rod 4 is arranged at a preset distance D from the switch 6. The distance D can be, for example, in the range of 10 μm to 100 μm, such as 40 μm to 50 μm. By adjusting the distance D, the minimum compressive load level at which the switch 6 switches can be preset.

[0098] Hereinafter, the construction of the load measuring device 42 with the electrical switch 6 according to Figure 11 will be described in more detail.

[0099] The protective cap 70 of the load measuring device 42 can include a socket 7 for inserting a probe 20 ( Figure 11 not shown in). For example, the protective cap 70 can be made of a plastic material (such as PEEK (polyetheretherketone)). The socket 7 can be adapted to cooperate with a connector or for manual testing. Advantageously, the protective cap 70 inserted into the nut body 1 can protrude beyond the upper main surface of the nut body 1 by, for example, 0.5 mm. This can have a positive impact on the sealing performance of the female fastener 40. In addition, the sealing of the load measuring device 42 can be further promoted by, for example, one or more sealing rings 72 assembled at the protective cap 70.

[0100] A ring insert 74 can be arranged below the protective cap 70. The insert 74 can be made of a plastic material (such as PEEK). In addition, the insert 74 can have an internal thread. For example, the insert 74 can be press-fitted and riveted in place in the hole 3 of the nut body 1.

[0101] The plunger 76 of the switch 6 (such as a spring plunger) can be assembled in the hole of the insert 74. For example, the plunger 76 can be made of stainless steel so that it will not be damaged by seawater. For example, the plunger 76 can be locked and sealed in the hole of the threaded insert 74.

[0102] A gap 78 with a distance D is provided (e.g., preset during manufacturing) between the bottom of the plunger 76 and the top of the contact member 80 of the rod 4. In the absence of a compressive load acting on the female fastener 40, the distance D will be maintained. In the presence of a compressive load acting on the female fastener 40, the distance D will decrease and will become zero when the preset minimum compressive load level is reached. Thus, the size of the gap 78 sets the switching load at which the switch 6 switches. Additionally, the gap 78 can be filled with oil to inhibit corrosion and vibration.

[0103] The rod 4 with its contact member 80 can be installed at a fixed position in the hole 3 of the female fastener 40, and the switch 6 can be installed at a preset position in the hole 3, where the positions are set during manufacturing according to the level of the compressive load applied to the female fastener 40.

[0104] The contact member 80 can be made of, for example, tungsten carbide, which is very hard and not easily worn. The contact member 80 can be fitted into the top of the body of the rod 4. Preferably, the material of the rod 4 is the same as the material of the body 1, such as steel. This ensures that the rod 4 and the body 1 have the same coefficient of thermal expansion (CTE). Thus, when the temperature changes, the gap 78 and the corresponding distance D remain unchanged. Therefore, no thermal mismatch occurs, and the accuracy of load measurement can be very high.

[0105] An optional spherical washer 82 can be provided at the bottom side of the load measuring device 42.

[0106] It should be noted that the term "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Elements described in different embodiments can also be combined.

[0107] It should also be noted that the reference signs in the claims should not be construed as limiting the scope of the claims.

[0108] The implementation of the present invention is not limited to the preferred embodiments shown in the figures and described above. Instead, even in the case of fundamentally different embodiments, it is possible to use the solutions shown and various variants based on the principles of the present invention.

Claims

1. A female fastener (40) for receiving and engaging a threaded male fastener, the female fastener (40) comprises: a threaded body (1); a load measuring device (42) having an electrical switching mechanism hermetically disposed and housed inside the threaded body (1), the load measuring device being configured to measure a compressive load on the female fastener (40) and to transmit a signal representative of the measured compressive load to an external system (44).

2. The female fastener (40) according to claim 1, wherein the load measuring device (42) comprises an electrical switch (6), the electrical switch being configured to change a switching state of the electrical switch when the measured compressive load drops below a preset minimum compressive load level.

3. The female fastener (40) according to claim 1 or 2, wherein the load measuring device (42) comprises at least two electrical switches (6, 6), the at least two electrical switches being configured to change switching states of the at least two electrical switches at different preset compressive load levels.

4. The female fastener (40) according to any one of claims 1 to 3, comprising an internal sealed chamber (60) that houses the load measuring device (42) and houses a fluid, in particular a liquid, the fluid being configured to protect the load measuring device (42) from environmental damage, in particular from corrosion and / or vibration.

5. The female fastener (40) according to any one of claims 1 to 4, comprising a coupling unit (46) for communicatively coupling, in particular wired or wirelessly, the female fastener (40) to at least one additional female fastener (40).

6. The female fastener (40) according to any one of claims 1 to 5, the female fastener being configured as a nut.

7. The female fastener (40) according to any one of claims 1 to 6, the female fastener being configured to be waterproof, in particular for subsea operations.

8. The female fastener (40) according to any one of claims 1 to 7, the female fastener being configured to indicate via the signal when a self-preloading force of the female fastener (40) drops below a preset safe minimum load.

9. The female fastener (40) according to any one of claims 1 to 8, wherein the load measuring device (42) comprises at least one switch (6), the switch being triggered to change a switching state of the switch when a compressive load on the female fastener (40) sufficiently compresses the female fastener (40) to move the switch (6) into contact with a rod (4) in the threaded body (1), wherein the rod (4) is disposed at a preset distance (D) from the switch (6) in the absence of a compressive load.

10. The female fastener (40) according to any one of claims 1 to 9, comprising a socket (7) for inserting a probe (20) of the external system (44), wherein the insertion triggers transmission of the signal representative of the measured compressive load to the external system (44).

11. The female fastener (40) according to any one of claims 1 to 10, said female fastener having no energy supply unit, in particular no battery.

12. An arrangement, comprising: the female fastener (40) according to any one of claims 1 to 11; and the external system (44) which receives the signal when coupled to the female fastener (40).

13. The arrangement according to claim 12, wherein the external system (44) comprises a tightening tool (48), in particular a torque wrench, the tightening tool being configured to compare a transmitted signal representing the measured compression load with the torque applied by the tightening tool (48) to the female fastener (40) to achieve that compression load, and to adjust the applied torque based on the result of the comparison.

14. The arrangement according to claim 12 or 13, wherein the external system (44) comprises a tightening tool (48), in particular a hydraulic tensioner, the hydraulic tensioner applying the compression load and being configured such that if the compression load transmitted to the tightening tool (48) by the signal deviates from a target compression load level, the tightening tool (48) adjusts the applied compression load towards the target compression load level.

15. The arrangement according to any one of claims 12 to 14, wherein the external system (44) comprises a hand-held tool (50), the hand-held tool being capable of being manually connected to the load measuring device (42) for outputting information indicating the measured compression load, for example visually and / or audibly.

16. The arrangement according to claim 15, wherein the hand-held tool (50) is configured for subsea operations.

17. The arrangement according to any one of claims 12 to 16, wherein the external system (44) comprises a remote monitoring station (52), the remote monitoring station being configured for analyzing a transmitted signal representing the measured compression load and for taking action, in particular outputting a warning of preload loss, when the measured compression load drops below a preset minimum compression load level.

18. The arrangement according to any one of claims 12 to 17, wherein at least a part of the external system (44) is located at a remote location relative to the female fastener (40).

19. The arrangement according to any one of claims 12 to 18, comprising at least one further female fastener (40) according to any one of claims 1 to 11, wherein the female fastener (40) and the at least one further female fastener (40) are coupled for transmitting a signal representing the measured compression load of the female fastener (40) and the at least one further female fastener (40) to the external system (44).

20. The arrangement according to any one of claims 12 to 19, wherein the load measuring device (42) comprises an electrical switch (6) configured to complete an electrical circuit between a probe (20) of the external system (44) when inserted into a socket (7) on the female fastener (40) on the one hand and a further contact of the female fastener (40) on the other hand.

21. The arrangement according to any one of claims 12 to 20, wherein the external system (44) comprises an energy supply unit (54), in particular a battery, configured to power the load measuring device (42) when the female fastener (40) is coupled to the external system (44).

22. The arrangement according to any one of claims 12 to 21, wherein the external system (44) comprises an indicator (56) indicating a predefined state of the measured compressive load, in particular a light emitting diode (17) that lights up when the switch (6) of the load measuring device (42) changes its switching state.

23. The arrangement according to any one of claims 12 to 22, wherein the external system (44) comprises a flashing warning light module (58) for insertion into the socket (7) of the female fastener (40) and configured to flash when the female fastener (40) is at a safe load as indicated by the signal.

24. The arrangement according to any one of claims 12 to 23, wherein the external system (44) comprises a wireless transmitter (11), such as a wifi transmitter and / or a bluetooth transmitter, for insertion into the socket (7) of the female fastener (40) and configured to wirelessly signal the switching state of the switch (6) of the load measuring device (42).

25. A method of using the female fastener (40) according to any one of claims 1 to 11 or the arrangement according to any one of claims 12 to 24 in a wind turbine, such as an offshore wind turbine.

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