A strain gauge mounting method

Abstract

The present application relates to the technical field of high-temperature pipeline dynamic stress measurement of an aero-engine, in particular to a strain gauge installation method. The method marks a patch area on a high-temperature pipeline to be measured, and performs surface treatment on the high-temperature pipeline in the patch area. After the treatment, the patch area is coated with primer, and pre-solidification is performed. Secondary coating is performed on the primer to form a bonding layer. The stress gauge is attached to the bonding layer, and the bonding layer is solidified. The glass cloth fixing frame on the stress gauge is removed, and the bonding layer is secondarily solidified. The stress gauge is coated to form a cover layer. The cover layer is finally solidified to achieve the installation of the strain gauge. Through detection, the survival rate of the installed strain gauge reaches 80%, solving the problem of low measurement success rate due to the brittleness and damage of high-temperature strain gauges in the existing high-temperature pipeline dynamic stress measurement process.

Description

Technical Field

[0001] This invention relates to the field of dynamic stress measurement technology for high-temperature pipelines in aero-engines, specifically a strain gauge installation method. Background Technology

[0002] Currently, most methods for measuring dynamic stress in aero-engine piping are designed for room-temperature and medium-temperature piping. For small-diameter piping at temperatures above 300°C, strain gauges are primarily used. However, the bonding and curing process for these strain gauges is time-consuming and has a failure rate of up to 75%, resulting in an extremely low survival rate. The main reason is the high brittleness of high-temperature strain gauges, which are easily damaged during bonding and connection in piping. Furthermore, there is limited experience in strain gauge bonding and connection, and no effective method has yet been developed.

[0003] Therefore, there is an urgent need for a strain gauge installation method with a high success rate to meet the requirements of current high-temperature pipeline dynamic stress measurement. Summary of the Invention

[0004] To address the problem of low measurement success rate in existing technologies for measuring dynamic stress in high-temperature pipelines due to the brittleness and susceptibility to damage of high-temperature strain gauges, this invention provides a strain gauge installation method.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] This invention provides a strain gauge installation method, comprising the following steps:

[0007] Step 1) Mark the patch area on the high-temperature pipeline to be tested, and perform surface treatment on the high-temperature pipeline in the patch area;

[0008] Step 2) Apply primer to the patch area of ​​the surface-treated high-temperature pipeline and pre-cure it;

[0009] Step 3) After pre-curing, apply a second layer of adhesive on the base coat to form an adhesive layer;

[0010] Step 4) Attach the stress gauge to the adhesive layer and cure the adhesive layer;

[0011] Step 5) After curing is complete, remove the glass fiber cloth fixing frame from the stress gauge and perform a second curing on the adhesive layer;

[0012] Step 6) After the secondary curing is completed, the stress gauge is coated to form a capping layer;

[0013] Step 7) Perform final curing of the capping layer to complete the installation of the strain gauge.

[0014] Furthermore, the specific operation of step 1) is as follows:

[0015] Step 1.1) Determine the center position of the sensitive grid on the high-temperature pipeline to be tested, and mark the patch area;

[0016] Step 1.2) Shield the high-temperature pipeline to be tested outside the patch area;

[0017] Step 1.3) Use 200-220 mesh alumina sandblasting to sandblast the patch area on the surface of the high-temperature pipeline to be tested. The sandblasting pressure is 0.35-0.45 MPa to remove surface oxides and increase surface roughness; or use sandpaper with a grit greater than 80 to polish the surface of the high-temperature pipeline to be tested, and then use abrasive cloth to cross-grit along the pipeline axis at a 45° angle to create texture to increase surface roughness;

[0018] Step 1.4) After sandblasting or grinding is completed, use a volatile solvent to repeatedly wipe the sandblasted or ground pipe wall until there is no dirt, thus completing the surface treatment of the high-temperature pipeline to be tested.

[0019] Furthermore, the specific operation of step 2) is as follows:

[0020] Apply primer to the patch area of ​​the surface-treated high-temperature pipeline and let it stand in the air for 10-12 minutes;

[0021] Pre-cure the primer after it has been left to stand. The curing conditions are as follows:

[0022] Air dry for 45–50 minutes;

[0023] Heat to 75℃±2℃ and cure for 45~50 minutes;

[0024] Heat to 100℃±2℃ and cure for 30~35 minutes;

[0025] Heat to 230℃±2℃ and cure for 30~35 minutes;

[0026] Heat to 350℃±2℃ and cure for 30~35 minutes to complete pre-curing.

[0027] Preferably, the adhesive used for the second application in step 3) is ceramic adhesive.

[0028] Preferably, the conditions for curing the adhesive layer in step 4) are as follows:

[0029] Allow to cure naturally in air for 45–50 minutes;

[0030] Heat to 75℃±2℃ and cure for 45~50 minutes;

[0031] Heat to 100℃±2℃ and cure for 30~35 minutes;

[0032] Heat to 165℃±2℃ and cure for 30~35 minutes.

[0033] Preferably, the conditions for secondary curing of the adhesive layer in step 5) are as follows:

[0034] Heat to 100℃±2℃ and cure for 30~35 minutes;

[0035] Heat to 230℃±2℃ and cure for 30~35 minutes;

[0036] Heat to 350℃±2℃ and cure for 120~125min.

[0037] Furthermore, the specific operation of step 6) is as follows: after the secondary curing is completed, the temperature is lowered to room temperature;

[0038] Ceramic adhesive is applied to the exposed sensitive grid portion of the stress gauge to form a capping layer.

[0039] Preferably, the final curing conditions in step 7) are:

[0040] Allow to air dry at room temperature for 45–50 minutes;

[0041] Heat to 75℃±2℃ and cure for 45~50 minutes;

[0042] Heat to 100℃±2℃ and cure for 30~35 minutes;

[0043] Heat to 230℃±2℃ and cure for 30~35 minutes;

[0044] Heat to 350℃±2℃ and cure for 30~35 minutes.

[0045] Preferably, the strain gauge is a foil-type high-temperature strain gauge, and the connecting wire of the strain gauge is a high-temperature cable.

[0046] Preferably, two strain gauges are provided, with the grid wires of the strain gauges arranged along the axial direction of the pipeline, the two strain gauges being 90° apart along the circumferential direction of the pipeline, and the distance between the strain gauges and the weld seam on the high-temperature pipeline to be tested being less than 5mm.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] This invention discloses a strain gauge installation method. The method involves marking a patch area on the high-temperature pipeline to be tested and treating the surface of the pipeline in the patch area; applying a primer to the treated patch area and pre-curing it; applying a second layer of adhesive on the primer to form an adhesive layer; attaching the strain gauge to the adhesive layer and curing the adhesive layer; removing the fiberglass cloth fixing frame from the strain gauge and curing the adhesive layer again; coating the strain gauge to form a capping layer; and finally curing the capping layer to complete the strain gauge installation. This method establishes a strain gauge installation method for high-temperature pipelines above 300 degrees Celsius. Testing showed that the survival rate of the installed strain gauges increased from 30%–40% to 80%. Using this method to install strain gauges in measuring the dynamic stress of aero-engine pipelines not only successfully reduces testing and maintenance costs but also improves the accuracy of test results, better meeting the current needs of aero-engine pipeline dynamic stress testing.

[0049] Furthermore, surface treatment of the high-temperature pipeline in the patch area can effectively enhance the roughness of the adhesive surface ears, increase the bonding strength of subsequent installation, and prevent the strain gauge from falling off. Shielding the high-temperature pipeline outside the patch area can prevent damage to the non-bonded parts of the pipeline and ensure the lifespan of the high-temperature pipeline under test. Repeated wiping of the sandblasted or polished pipe wall after surface treatment can prevent impurities such as dirt, oil stains, and dust from affecting the bonding strength.

[0050] Furthermore, by applying a high-temperature resistant ceramic adhesive to the exposed sensitive grid portion of the stress gauge, a high-temperature resistant protective layer can be formed on the stress gauge surface, effectively preventing damage to the stress gauge due to high temperatures and further improving the survival rate of the stress gauge installation.

[0051] The setting of curing conditions not only ensures the bonding strength of the adhesive, but also its bonding properties, which facilitates the installation and fixation of the stress gauge, further ensuring the survival rate of the stress gauge installation. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of a strain gauge installation method according to the present invention.

[0053] Figure 2 This is a schematic diagram of the installation position of a strain gauge according to the present invention.

[0054] Among them, 1-the high-temperature pipeline to be tested, 2-the weld, and 3-the stress gauge. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0056] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0057] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0058] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0059] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0060] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0061] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0062] See Figure 1 This invention discloses a strain gauge installation method, comprising the following steps:

[0063] Step 1) Mark the patch area on the high-temperature pipeline 1 to be tested, and perform surface treatment on the high-temperature pipeline in the patch area. The specific operation is as follows:

[0064] Step 1.1) Determine the center position of the sensitive grid on the high-temperature pipeline 1 to be tested, and mark the patch area;

[0065] Step 1.2) Shield the high-temperature pipeline 1 to be tested outside the patch area. Generally, use 0.07-0.08mm thick Teflon tape to shield and protect the part outside the patch area to avoid damage to other parts during the polishing process.

[0066] Step 1.3) Use 200-220 mesh alumina sandblasting to sandblast the patch area on the surface of the high-temperature pipeline 1 to be tested. The sandblasting pressure is 0.35-0.45 MPa to remove surface oxides and increase surface roughness; or use sandpaper with a mesh greater than 80 to polish the surface of the high-temperature pipeline 1 to be tested, and then use abrasive cloth to cross-grit along the pipeline axis at a 45° angle to create texture to increase surface roughness;

[0067] Step 1.4) After sandblasting or grinding is completed, use volatile solvents such as acetone, alcohol or methyl ethyl ketone to repeatedly wipe the sandblasted or ground pipe wall until there is no dirt, thus completing the surface treatment of the high-temperature pipeline 1 to be tested; note that during the wiping process, avoid repeated wiping, but wipe in the same direction to avoid secondary contamination of the cleaned surface by dirt during repeated wiping.

[0068] Step 2) Apply primer to the patch area of ​​the surface-treated high-temperature pipeline and pre-cur it. Specifically, apply primer to the patch area of ​​the surface-treated high-temperature pipeline and let it stand in the air for 10 to 12 minutes.

[0069] Pre-cure the primer after it has been left to stand. The curing conditions are as follows:

[0070] Air dry for 45–50 minutes;

[0071] Heat to 75℃±2℃ and cure for 45~50 minutes;

[0072] Heat to 100℃±2℃ and cure for 30~35 minutes;

[0073] Heat to 230℃±2℃ and cure for 30~35 minutes;

[0074] Heat to 350℃±2℃ and cure for 30~35 minutes to complete pre-curing;

[0075] Note that during the application of the primer, it is important to ensure the consistency and uniformity of the application to prevent dripping. After allowing it to stand in the air for 10 to 12 minutes, remove any obstructions and then pre-cure the primer.

[0076] Step 3) After pre-curing, apply a second layer of adhesive on the base coat to form an adhesive layer. After pre-curing, evenly coat a layer of ceramic adhesive on the surface of the base coat. Use a blade at an angle of 12-15° and maintain a certain contact pressure to scrape across the entire patch area, so that it forms stripes with a certain angle on the surface of the base coat to increase the adhesive properties of the adhesive and form an adhesive layer.

[0077] Step 4) Attach the stress gauge 3 to the adhesive layer and cure the adhesive layer. The specific operation is as follows:

[0078] Remove the strain gauge, secured to the glass cloth frame, from the glass slide, taking care not to bend the strain gauge leads. Align the strain gauge with the marked mounting area and attach it to the mounting area. See [link to relevant documentation]. Figure 2 Two strain gauges are configured, with the grid wires of the strain gauges arranged axially along the pipeline. The two strain gauges are 90° apart along the circumference of the pipeline, and the distance between the strain gauges and the weld seam 2 on the high-temperature pipeline 1 to be tested is less than 5mm. During this process, it is ensured that the adhesive does not come into contact with the edge of the glass fiber cloth frame to avoid the adhesive causing a decrease in the adhesion of the glass fiber cloth frame, or even warping and detachment, which would affect the positioning of the patch. Finally, ceramic adhesive is applied to the exposed portion of the sensitive grid between the glass fiber cloth fixing frames. After the coating is completed, the adhesive layer is cured under the following conditions:

[0079] Allow to cure naturally in air for 45–50 minutes;

[0080] Heat to 75℃±2℃ and cure for 45~50 minutes;

[0081] Heat to 100℃±2℃ and cure for 30~35 minutes;

[0082] Heat to 165℃±2℃ and cure for 30~35 minutes.

[0083] Step 5) After curing is complete, remove the fiberglass cloth fixing frame from stress gauge 3 and perform a second curing of the adhesive layer. The specific operation is as follows:

[0084] After curing, wait for the temperature to drop to 80℃~75℃, then cut and remove the fiberglass cloth fixing frame, taking care not to pull up or break the sensitive grid; perform a second curing of the adhesive layer under the following conditions:

[0085] Heat to 100℃±2℃ and cure for 30~35 minutes;

[0086] Heat to 230℃±2℃ and cure for 30~35 minutes;

[0087] Heat to 350℃±2℃ and cure for 120~125min.

[0088] Step 6) After the secondary curing is completed, the stress gauge 3 is coated to form a capping layer. The specific operation is as follows: after the secondary curing is completed, the temperature is lowered to room temperature, and ceramic adhesive is applied only to the part of the sensitive grid that is exposed to ensure that a capping layer of uniform thickness is formed on the entire strain gauge.

[0089] Step 7) Perform final curing of the capping layer to complete the installation of the strain gauges. The curing conditions are as follows:

[0090] Allow to air dry at room temperature for 45–50 minutes;

[0091] Heat to 75℃±2℃ and cure for 45~50 minutes;

[0092] Heat to 100℃±2℃ and cure for 30~35 minutes;

[0093] Heat to 230℃±2℃ and cure for 30~35 minutes;

[0094] Heat to 350℃±2℃ and cure for 30~35 minutes.

[0095] After the strain gauge is installed, the strain gauge leads are connected and secured. Due to the high temperature of the high-temperature pipeline 1 being measured, high-temperature cables must be used for the connection. Since the high-temperature cable is made of a different material than the strain gauge, it cannot be welded. A spot welder is used to directly spot weld the strain gauge pins to the high-temperature leads. Preferably, the spot welder current is 0.35–0.37A, and the spot weld depth is 0.1–0.5mm. These current and welding depth parameters were determined through repeated testing to minimize damage to the pipeline. During spot welding, copper foil is placed under the welding leads; copper foil is essential to prevent adhesion and hinder spot welding. The joint is treated for moisture and oil resistance to prevent reduced insulation resistance and adhesion strength, which would affect measurement accuracy. After connection, the leads are fixed by spot welding with the same material as the pipeline or engine casing to the measuring leads. Due to the high resistance of the high-temperature cable, a four-wire connection must be used to eliminate the resistance; otherwise, most instruments cannot perform balance and zeroing.

[0096] During the dynamic stress measurement of high-temperature piping in aero-engines, the engine is subjected to a 3-minute slow scan from ground idle to maximum takeoff speed, and then back to ground idle. The dynamic stress values ​​of the piping and the engine speed are monitored and recorded. The maximum dynamic stress value and frequency of the piping, as well as the corresponding high-pressure and low-pressure speeds, are determined in the FFT frequency domain.

[0097] In summary, this invention provides a strain gauge installation method. This method involves marking a patch area on the high-temperature pipeline 1 to be tested and performing surface treatment on the high-temperature pipeline in the patch area; applying a primer to the treated patch area and pre-curing it; applying a second layer of adhesive on the primer to form an adhesive layer; attaching the strain gauge 3 to the adhesive layer and curing the adhesive layer; removing the fiberglass cloth fixing frame from the strain gauge 3 and performing a second curing of the adhesive layer; coating the strain gauge 3 to form a capping layer; and finally curing the capping layer to achieve strain gauge installation. Testing showed that the survival rate of the installed strain gauges increased from the original 30%–40% to 80%, successfully reducing testing and maintenance costs.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A strain gauge mounting method characterized by, The method comprises the following steps: Step 1) marking a patch area on the high-temperature pipeline to be measured, and performing surface treatment on the high-temperature pipeline in the patch area; Step 2) applying a primer on the patch area of the high-temperature pipeline after surface treatment, and performing pre-curing, specifically, applying a primer on the patch area of the high-temperature pipeline after surface treatment, and standing for 10-12 minutes in air; The pre-curing of the primer after standing is performed under the following conditions: natural drying for 45-50 minutes; heating to 75 DEG C + / - 2 DEG C for 45-50 minutes; heating to 100 DEG C + / - 2 DEG C for 30-35 minutes; heating to 230 DEG C + / - 2 DEG C for 30-35 minutes; heating to 350 DEG C + / - 2 DEG C for 30-35 minutes, completing pre-curing; Step 3) after pre-curing is completed, performing secondary gluing on the primer to form a bonding layer; wherein the glue solution for secondary gluing is ceramic glue, specifically Step 4) sticking a stress gauge on the bonding layer, and curing the bonding layer; wherein the curing conditions for the bonding layer are: natural curing in air for 45-50 minutes; heating to 75 DEG C + / - 2 DEG C for 45-50 minutes; heating to 100 DEG C + / - 2 DEG C for 30-35 minutes; heating to 165 DEG C + / - 2 DEG C for 30-35 minutes; Step 5) after curing is completed, removing the glass cloth fixing frame on the stress gauge, and performing secondary curing on the bonding layer; wherein the secondary curing conditions for the bonding layer are: heating to 100 DEG C + / - 2 DEG C for 30-35 minutes; heating to 230 DEG C + / - 2 DEG C for 30-35 minutes; heating to 350 DEG C + / - 2 DEG C for 120-125 minutes; Step 6) after secondary curing is completed, coating the stress gauge to form a cover layer; Step 7) performing final curing on the cover layer, completing installation of the strain gauge, specifically: after secondary curing is completed, reducing the temperature to room temperature; applying ceramic glue on the part of the stress gauge exposing the sensitive grid to form a cover layer; the final curing conditions are: natural drying at room temperature for 45-50 minutes; heating to 75 DEG C + / - 2 DEG C for 45-50 minutes; heating to 100 DEG C + / - 2 DEG C for 30-35 minutes; heating to 230 DEG C + / - 2 DEG C for 30-35 minutes; heating to 350 DEG C + / - 2 DEG C for 30-35 minutes.

2. The strain gauge mounting method according to claim 1, characterized by, The specific operation of Step 1) is as follows: Step 1.1) determining the center position of the sensitive grid on the high-temperature pipeline to be measured, and marking the patch area; Step 1.2) shielding the high-temperature pipeline to be measured outside the patch area; Step 1.3) using 200-220 mesh alumina sand blasting to sand blast the patch area on the surface of the high-temperature pipeline to be measured, the sand blasting pressure is 0.35-0.45 MPa, the surface oxides are removed and the surface roughness is increased; or using sandpaper with mesh greater than 80 to polish the surface of the high-temperature pipeline to be measured, and then using sandpaper to polish the surface in the direction of 45 DEG to the pipeline axis to increase the surface roughness; Step 1.4) after sand blasting or polishing is completed, repeatedly wiping the sand blasted or polished pipe wall with volatile solvent until there is no dirt, completing the surface treatment of the high-temperature pipeline to be measured.

3. The strain gauge mounting method according to claim 1 or 2, characterized by, The strain gauge is a foil high-temperature strain gauge, and the connecting wire of the strain gauge is a high-temperature cable.

4. The strain gauge mounting method according to claim 1 or 2, characterized by, The strain gauges are arranged in two, the grid wire direction of the strain gauges is arranged along the pipeline axis, the two strain gauges are different by 90° along the pipeline circumferential direction, and the strain gauges are less than 5mm away from the weld (2) on the high-temperature pipeline to be measured.

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