Water turbine top cover double-end large bolt pre-tightening force detection device and pre-tightening method

Abstract

The invention provides a water turbine top cover double-end large bolt pre-tightening force detection device. The water turbine top cover double-end large bolt pre-tightening force detection device comprises a first force bearing plate, a second force bearing plate, an adjusting mechanism and a pre-tightening force sensor. The first bearing plate is provided with a first mounting hole for mounting a to-be-detected nut; the second bearing plate is provided with a second mounting hole for mounting a to-be-detected screw rod; the adjusting mechanism is operably connected with the first force bearing plate and the second force bearing plate, and the distance between the first force bearing plate and the second force bearing plate is adjusted to adapt to different bolt lengths. The pre-tightening force sensor measures the axial pre-tightening force borne by the bolt in the testing period and generates pre-tightening force data so as to draw a pre-tightening force-rotation angle characteristic curve. Lifting of the upper force bearing plate is achieved through the position adjusting screw rod, and the device adapts to different bolt lengths; an anti-rotation pin hole prevents relative rotation under large torque; the replaceable gasket is matched with different bolt diameters; the device is simple in structure, light in weight, convenient to carry to a water turbine site, rapid to disassemble and assemble, high in universality and suitable for bolts of various specifications.

Description

Technical Field

[0001] This invention belongs to the field of water turbine technology, specifically a device for detecting the preload force of double-headed large bolts on the top cover of a water turbine and a preload method. Background Technology

[0002] As a core basic connection method in industrial equipment, the precision of bolted connections directly determines the structural integrity and service safety of large rotating machinery. The connection system between the turbine top cover and the seat ring needs to withstand hundreds of tons of water thrust and dynamic loads. The M40-M60 grade double-headed large bolts used in this system are designed with a preload of 60-300 tons, forming the lifeline for the safe operation of the unit.

[0003] These types of bolts require a huge preload during assembly, and the accuracy of this preload has a decisive impact on the anti-loosening, sealing, and fatigue resistance performance of the connection. If the preload deviation of these bolts is too large, it will cause a chain of failures such as seal failure, fretting wear on the flange surface, and even bolt fatigue fracture, which has historically led to several turbine lift-up accidents.

[0004] The existing industry uses torque control to implement pre-tightening, but due to the coupled effects of factors such as the friction coefficient of the thread pair, lubrication status, and gasket deformation, the actual pre-tightening force fluctuates significantly from the design value, which cannot meet the pre-tightening requirements of the double-headed large bolts on the turbine top cover. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for detecting the preload of large bolts on the top cover of a water turbine that is easy to install and can measure the preload of large bolts with small error.

[0006] The present invention provides a preload force detection device for a large double-headed bolt on a turbine top cover, comprising a first support plate, a second support plate, an adjustment mechanism, and a preload force sensor; the first support plate has a first mounting hole for mounting a nut to be tested; the second support plate has a second mounting hole for mounting a bolt to be tested; the adjustment mechanism operably connects the first support plate and the second support plate, adjusting the distance between them to accommodate different bolt lengths; the preload force sensor measures the axial preload force on the bolt during the test and generates preload force data to plot a preload force-rotation angle characteristic curve.

[0007] In one embodiment of the above-mentioned device, the first support plate and the second support plate are respectively provided with a plurality of evenly distributed adjustment mechanism mounting holes, and the adjustment mechanism includes at least one adjustment screw, which passes through the adjustment mechanism mounting hole.

[0008] In one embodiment of the above-mentioned device, the first support plate and the second support plate are respectively provided with a plurality of evenly distributed anti-rotation pin holes and anti-rotation pins are inserted therein.

[0009] In one embodiment of the above-mentioned device, the first support plate and the second support plate are respectively provided with a plurality of evenly distributed sensor mounting holes, and the preload sensor is installed in the sensor mounting holes. The preload sensor is a strain gauge load sensor, which includes an elastic body, a strain gauge, a signal amplification circuit and a data output interface.

[0010] In one embodiment of the above-described device, a replaceable pad is further included, which is installed on the first mounting hole and the second mounting hole, and the center diameter of the replaceable pad can be replaced to match bolts of different diameters.

[0011] In one embodiment of the above-described device, a base plate is further included, which is fixed below the second load-bearing plate to provide a stable base and ensure that the device remains level during testing.

[0012] In one embodiment of the above-described device, the elastic body of the strain gauge load sensor is made of high-strength alloy steel, the strain gauge is configured using a Wheatstone bridge, the signal amplification circuit converts the strain gauge signal into a standard voltage or current output, and the data output interface is connected to an external data acquisition system.

[0013] A method for pre-tightening large bolts using the aforementioned pre-tightening force detection device comprises the following steps:

[0014] S1. Preparation of the testing device: Select and install a matching replaceable pad according to the diameter of the bolt to be tested, adjust the distance between the first bearing plate and the second bearing plate through the adjustment mechanism to adapt to the bolt length, insert the anti-rotation pin to lock the relative position, and install the preload sensor.

[0015] S2. Bolt installation and alignment: Insert the bolt to be tested into the second mounting hole and fix it. The top of the bolt passes through the first mounting hole. Use a level to check the parallelism between the first load-bearing plate and the second load-bearing plate.

[0016] S3. Actual measurement of preload characteristic curve: Screw the nut into the top of the bolt and tighten the nut at a constant speed. Collect the preload and rotation angle data simultaneously. Continue loading until the preload reaches 110% of the design value. Plot the torque-rotation angle characteristic curve. Repeat the test after unloading to obtain the average value.

[0017] S4. Installation Parameter Determination: Based on the torque-rotation angle characteristic curve, identify the threshold torque corresponding to point B, the starting point of the linear segment. and rotation angle And the threshold torque corresponding to the design preload point m and rotation angle Calculate the actual preload rotation angle ;

[0018] S5. On-site bolt installation: During the formal installation, first load the bolts to the aforementioned threshold torque. Then rotate the bolt to the actual preload rotation angle. After installation, allow the equipment to stand still and retest the preload. If the attenuation value is ≤5%, the equipment is considered qualified.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. The upper support plate is raised and lowered by adjusting the position screw to accommodate different bolt lengths; the anti-rotation pin hole prevents relative rotation under high torque; the replaceable shim matches different bolt diameters; the device has a simple structure, is lightweight, easy to carry to the turbine site, is quick to assemble and disassemble, and is highly versatile, suitable for various bolt specifications;

[0021] 2. First, use the device to measure the bolt preload characteristic curve, and determine the threshold torque accordingly. and actual preload rotation angle Then, bolts are installed; the preload control accuracy is significantly improved, avoiding sealing failure or fatigue fracture caused by large deviations in preload from the design value during installation, thus improving assembly quality and reducing rework rate. Attached Figure Description

[0022] Figure 1 This is a front cross-sectional view of an embodiment of the present invention.

[0023] Figure 2 for Figure 1 Top view of the upper and middle load-bearing plates.

[0024] Figure 3 for Figure 1 Top view of the lower load-bearing plate.

[0025] Figure 4 This is a schematic diagram of the torque-angle control method curve in this invention.

[0026] The attached figures are labeled as follows:

[0027] 1—Upper support plate, 2—Lower support plate, 3—Adjusting screw, 4—Inspection nut mounting hole, 5—Screw mounting hole, 6—Anti-rotation pin hole, 7—Sensor mounting hole, 8—Base plate, 9—Pad plate, 10—Inspection screw mounting hole. Detailed Implementation

[0028] The relevant technical solutions will now be clearly and completely described with reference to the accompanying drawings of the embodiments of the present invention. The described embodiments are only a part of the embodiments, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] like Figure 1 As shown in this embodiment, the double-headed large bolt preload testing device for turbine top cover includes an upper support plate 1, a lower support plate 2, and an adjusting screw 3. These components work together to form an adjustable-height frame for installing and testing large bolts. The device achieves height adjustment and quick assembly / disassembly through the combined design of the upper and lower support plates; it is also equipped with anti-rotation pin holes 6 and replaceable pads 9 to adapt to the preload testing requirements of bolts of different specifications.

[0030] The upper support plate 1 serves as the upper support component of the device. It has a hole 4 for mounting the nut to be inspected in the center. Its edge planar structure effectively holds the bolt head to prevent rotation during the loading process. It is used to install the nut to be inspected and the pad 9.

[0031] like Figure 2 As shown, the upper support plate 1 is also provided with three evenly spaced adjusting screw mounting holes 5 for fixing the adjusting screw 3; three evenly spaced anti-rotation pin holes 6 for inserting anti-rotation pins to prevent relative rotation; and three evenly spaced sensor mounting holes 7 for mounting preload sensors. These holes are evenly distributed on the plate surface to ensure uniform force distribution and structural stability.

[0032] like Figure 3 As shown, the lower support plate 2 serves as the lower support component of the device. Its structure is symmetrical to that of the upper support plate 1. It is also provided with screw mounting holes 5, anti-rotation pin holes 6, sensor mounting holes 7, and screw mounting holes 10.

[0033] The lower support plate 2 is aligned with the upper support plate 1 through the anti-rotation pin hole 6, ensuring that the two remain in a fixed relative position during operation. The edge of the mounting hole 10 for the screw under test is flat, which facilitates fixing the screw under test and prevents rotation.

[0034] The adjusting screw 3 connects to the upper support plate 1 and the lower support plate 2 through the adjusting screw mounting hole 5 and is mounted on the base plate 8. The adjusting screw can be rotated to adjust the raising and lowering of the upper support plate to accommodate different bolt lengths.

[0035] A preload measuring sensor is installed in sensor mounting hole 7. It is a strain gauge load sensor, which includes an elastic body, strain gauge, signal amplification circuit and data output interface.

[0036] The elastomer, made of high-strength alloy steel, is cylindrical and undergoes minute deformation when subjected to axial force. Strain gauges are bonded to the surface of the elastomer using a Wheatstone bridge configuration. As the elastomer deforms, the resistance of the strain gauges changes, generating an electrical signal. A signal amplification circuit amplifies the weak electrical signal and converts it into a standard voltage or current output. The data output interface is connected to a data acquisition system.

[0037] The base plate 8 provides a stable base, ensuring that the entire device remains level during testing.

[0038] The pad 9 is installed on the nut mounting hole 4 and the screw mounting hole 10 to be inspected. The diameter of its center hole can be changed to match bolts of different diameters, thus achieving versatility.

[0039] A method for inspecting and applying preload to large double-ended bolts on the top cover of a water turbine using this device, the specific steps of which are as follows:

[0040] S1. Preparation of detection equipment;

[0041] Select a matching shim plate according to the diameter of the bolt to be measured, and ensure that the center hole diameter of the shim plate matches the bolt tolerance; adjust the height of the upper support plate by adjusting the screw to make the distance between the two support plates match the length of the bolt to be measured, and lock the relative position of the upper and lower support plates by inserting a pin through the anti-rotation pin hole; finally, select a preload measuring sensor with a suitable range according to the design preload range, and install it in the sensor mounting hole of the upper and lower support plates;

[0042] S2. Bolt installation and alignment;

[0043] Insert the bolt to be tested through the mounting hole of the lower support plate and use the plane structure at the edge of the hole to clamp the bolt head; the bolt passes through the center hole of the lower support plate and the upper support plate in sequence; use a level to check the parallelism of the two support plates to ensure that there is no off-center load under axial loading.

[0044] S3, Actual measurement of preload characteristic curve;

[0045] Screw the nut into the top of the bolt and press the washer. Tighten the nut at a constant speed, simultaneously collecting data on the preload force F and rotation angle φ. Continue loading until the preload reaches 110% of the design value, then stop. Plot the results as shown below. Figure 4 The torque-angle characteristic curve is shown; unload the bolts and record the springback data, repeat the test three times and take the average value to eliminate assembly errors.

[0046] S4. Determine installation parameters;

[0047] Identify the starting point B of the linear segment in the torque-rotation characteristic curve and the bolt design preload point m, and record the threshold torque corresponding to point B. and rotation angle The threshold torque corresponding to point m and rotation angle Finally, the actual preload rotation angle was obtained. The specific steps are as follows:

[0048] The installation of large bolt fasteners is guided by the torque-angle control method, that is, the installation is based on the axial preload F and the tightening angle of the nut. The relationship between the two factors determines the angle at which the nut is tightened, as shown in the following formula:

[0049]

[0050] In the formula: F is the design preload; E is the system stiffness of the threaded connection; Pitch; For the corner;

[0051] During assembly, the axial preload is indirectly controlled by adjusting the angle of the tightening nut; for example... Figure 4 As shown, in reality, during the bolt tightening process, the preload F and the tightening angle are related. It's not a simple linear relationship; normally, the bolt tightening process can be divided into three stages:

[0052] Phase 1: Initial screwing in of the nut; during this phase, no axial preload is generated before the nut contacts the fastener, such as... Figure 4 Middle 0-A segment;

[0053] The second stage: initial pre-tightening process; Pre-tightening force only begins to be generated after the nut contacts the fastener. At this stage, due to the small contact area and incomplete tightening, the pre-tightening force is small and its increase is slow; for example... Figure 4 Middle AB segment;

[0054] Third stage: Linear preload process; the nut ensures a tight fit between the fasteners, and the axial preload F is related to the tightening angle. The relationship is linear: bolt axial preload F, axial elongation The angle of rotation as the nut is tightened Increase proportionally, such as Figure 4 Middle BC section;

[0055] Generally, the preload of large bolts is designed to be before the material's yield point, and the entire process consists of the three stages mentioned above. However, if the bolt is tightened further after reaching the yield point, the bolt elongation will be greater under the same rotation angle increment. With the addition of force, the change in preload F is minimal;

[0056] Therefore, based on the bolt preload characteristic curve measured in step S3, the threshold torque corresponding to point B can be determined. and rotation angle The threshold torque corresponding to point m and rotation angle Actual pre-tightening rotation angle .

[0057] S5. On-site bolt installation;

[0058] During the actual installation, first load the bolts to be installed to the threshold torque. Then switch modes and continue tightening the bolts on top of the initial loading until the precise rotation angle is achieved. After installation, let it stand for 30 minutes and then retest the preload. If the attenuation value is ≤5%, it is considered qualified.

[0059] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A device for detecting the preload of double-headed large bolts on the top cover of a water turbine, characterized in that: Includes a first load-bearing plate, a second load-bearing plate, an adjustment mechanism, and a preload sensor; The first support plate is provided with a first mounting hole for installing the nut to be tested; the second support plate is provided with a second mounting hole for installing the screw to be tested; the adjustment mechanism is operablely connected to the first support plate and the second support plate, and the distance between them is adjusted to accommodate different bolt lengths; the preload sensor measures the axial preload force on the bolt during the test and generates preload force data to plot the preload force-rotation angle characteristic curve.

2. The device for detecting the preload of double-headed large bolts on the turbine top cover as described in claim 1, characterized in that: The first support plate and the second support plate are respectively provided with a plurality of evenly distributed adjustment mechanism mounting holes. The adjustment mechanism includes at least one adjustment screw, which passes through the adjustment mechanism mounting hole.

3. The device for detecting the preload of double-headed large bolts on the turbine top cover as described in claim 1, characterized in that: The first load-bearing plate and the second load-bearing plate are respectively provided with a plurality of evenly distributed anti-rotation pin holes and anti-rotation pins are inserted therein.

4. The device for detecting the preload of double-headed large bolts on the turbine top cover as described in claim 1, characterized in that: The first load-bearing plate and the second load-bearing plate are respectively provided with a plurality of evenly distributed sensor mounting holes. The preload sensor is installed in the sensor mounting holes. The preload sensor is a strain gauge load sensor, which includes an elastic body, a strain gauge, a signal amplification circuit and a data output interface.

5. The device for detecting the preload of double-headed large bolts on the turbine top cover as described in claim 1, characterized in that: It also includes a replaceable pad, which is installed on the first mounting hole and the second mounting hole, and the center diameter of the replaceable pad can be changed to match bolts of different diameters.

6. The device for detecting the preload of double-headed large bolts on the turbine top cover as described in claim 1, characterized in that: It also includes a base plate, which is fixed below the second load-bearing plate to provide a stable base and ensure that the device remains level during testing.

7. The device for detecting the preload of double-headed large bolts on the turbine top cover as described in claim 4, characterized in that: The elastic body of the strain gauge load sensor is made of high-strength alloy steel, the strain gauge is configured with a Wheatstone bridge, the signal amplification circuit converts the strain gauge signal into a standard voltage or current output, and the data output interface is connected to an external data acquisition system.

8. A method for pre-tightening large bolts using the pre-tightening force detection device according to any one of claims 1-7, characterized in that, The specific steps are as follows: S1. Preparation of the testing device: Select and install a matching replaceable pad according to the diameter of the bolt to be tested, adjust the distance between the first bearing plate and the second bearing plate through the adjustment mechanism to adapt to the bolt length, insert the anti-rotation pin to lock the relative position, and install the preload sensor. S2. Bolt installation and alignment: Insert the bolt to be tested into the second mounting hole and fix it. The top of the bolt passes through the first mounting hole. Use a level to check the parallelism between the first load-bearing plate and the second load-bearing plate. S3. Actual measurement of preload characteristic curve: Screw the nut into the top of the bolt and tighten the nut at a constant speed. Collect the preload and rotation angle data simultaneously. Continue loading until the preload reaches 110% of the design value. Plot the torque-rotation angle characteristic curve. Repeat the test after unloading to obtain the average value. S4. Installation Parameter Determination: Based on the torque-rotation angle characteristic curve, identify the threshold torque corresponding to point B, the starting point of the linear segment. and rotation angle And the threshold torque corresponding to the design preload point m and rotation angle Calculate the actual preload rotation angle ; S5. On-site bolt installation: During the formal installation, first load the bolts to the aforementioned threshold torque. Then rotate the bolt to the actual preload rotation angle. After installation, allow the equipment to stand still and retest the preload. If the attenuation value is ≤5%, the equipment is considered qualified.

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