A manufacturing method and forming mold for a coated strain gauge

Abstract

The present invention discloses a method for manufacturing a coated strain gauge and a molding die. A rectangular cavity is provided at the top of the mold body. The cavity depth is 30 to 50 times the thickness of the strain gauge, and the cavity area is 4 to 10 times the area of ​​the strain gauge. A wire slot for lead wires is provided on the side of the cavity at the top of the mold body. The strain gauge base is attached downward to the center of the bottom surface of the cavity of the molding mold using a thermoplastic polymer material or a temporarily fixed pressure-sensitive resin. An enameled wire is led out from the strain gauge pad, and the free end of the enameled wire is connected to a waterproof lead wire, which is then clamped into the wire slot of the mold body. A coating material is injected into the mold cavity until the cavity is full, and the coating material is cured and formed. The mold is demolded and the thermoplastic polymer material or temporarily fixed pressure-sensitive resin is removed to obtain a coated strain gauge. Using this strain gauge can shorten the protection time, avoid problems such as bubbles in the protective layer, insufficient curing, and uneven thickness, make the overall thickness uniform, and improve test accuracy.

Description

Technical Field

[0001] The invention belongs to the field of strain gauge production, and relates to a production method and a forming die for a coated strain gauge. Background Art

[0002] At present, in order to cope with stress testing in underwater and humid environments, the most commonly used method is to first waterproof the conventional strain gauge patch. The specific steps are: ① First, mount the conventional strain gauge and lead out the lead at its solder point; ② Then, use multiple protective adhesives to seal the area 4 to 10 times the surface of the strain gauge in multiple times (usually 3 to 4 times), and each time you apply the protective adhesive, you need to wait for the previous coating to completely cure.

[0003] The above method mainly has the following problems:

[0004] ①The protection process is complicated. Each layer of protective glue takes about 24 hours to fully cure, and the overall protection time is about 3 to 4 days.

[0005] ② Affected by the construction workers' operating level and operating environment, the protective rubber layer is prone to bubble defects, making the insulation strength after protection substandard;

[0006] ③ There may be a situation where the curing reaction is affected by improper matching between the protective adhesive layer materials, resulting in low curing degree and interlayer bonding strength of the protective adhesive layer;

[0007] ④ The coating layer is relatively thick, with thickness varying from 2 to 5 mm at different locations, which affects the test accuracy. Summary of the Invention

[0008] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for manufacturing a coated strain gauge and a molding mold, which can shorten the protection time, is not prone to bubbles, avoids the matching problems between the protective adhesive layer materials, reduces the thickness of the coating layer, and makes the overall thickness uniform.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A mold for forming a coated strain gauge, comprising a mold body;

[0011] A rectangular cavity is provided on the top of the mold body. The depth of the cavity is 30 to 50 times the thickness of the strain gauge, and the area of ​​the cavity is 4 to 10 times the area of ​​the strain gauge. A wire groove for lead wires is provided on the side of the cavity at the top of the mold body.

[0012] Preferably, the width of the wire clamping groove is 0.2 mm shorter than the width of the lead wire, and the depth of the wire clamping groove is 0.5 mm greater than the diameter of the lead wire.

[0013] Preferably, the mold is made of PTFE, mold steel or aluminum alloy.

[0014] A method for manufacturing a coated strain gauge includes the following steps:

[0015] S1, using thermoplastic polymer material or temporary fixing pressure-sensitive resin to attach the strain gauge base downward to the center of the bottom surface of the cavity of the molding die;

[0016] S2, lead out the enameled wire from the strain gauge pad, connect the free end of the enameled wire to the waterproof lead wire, and clamp the waterproof lead wire into the wire clamping groove of the mold body;

[0017] S3, injecting the coating material in a fluid state into the mold cavity until the cavity is full, and after degassing and removing bubbles, solidifying the coating material into a shape;

[0018] S4, demolding the conventional strain gauge with the coating layer, removing the thermoplastic polymer material or the temporarily fixed pressure-sensitive resin on the base surface, and obtaining the coated strain gauge.

[0019] Preferably, the lead wire is made of waterproof PVC or TPE.

[0020] Preferably, after S2 is completed and before S3 is performed, the cavity in the mold body, the upper surface of the strain gauge and the enameled wire are subjected to corona or plasma treatment.

[0021] Preferably, the coating layer material is epoxy, polyurethane three-proof glue or epoxy molding compound.

[0022] Preferably, after S2 is completed and before S3 is performed, the entire mold is preheated to 40-80°C.

[0023] Preferably, in S2, the enameled wire is led out from the strain gauge pad by welding, and the free end of the enameled wire is located in the cavity after it is completely straightened.

[0024] Preferably, in S4, manual demoulding is adopted.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The mold described in the present invention is provided with a cavity inside, and the volume of the cavity is many times larger than that of the strain gauge, so that the strain gauge can be directly coated with a coating layer at one time, so that there is only one coating layer, which shortens the protection time, is less likely to cause bubbles, avoids the matching problem between the protective rubber layer materials, reduces the thickness of the coating layer, makes the overall thickness uniform, and ensures the test accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart for manufacturing the coated strain gauge of the present invention;

[0028] Figure 2 A top view of a strain gauge according to a first embodiment of the present invention;

[0029] Figure 3 A side view of a strain gauge according to an embodiment of the present invention

[0030] Figure 4 A top view of a mold according to embodiment 1 of the present invention;

[0031] Figure 5 This is a side sectional view of a mold according to embodiment 1 of the present invention;

[0032] Figure 6 This is a top view of a mold with a strain gauge placed therein according to embodiment 1 of the present invention;

[0033] Figure 7 This is a side sectional view of a mold with a strain gauge placed therein according to embodiment 1 of the present invention;

[0034] Figure 8 This is a top view of a strain gauge according to a second embodiment of the present invention;

[0035] Figure 9 A side view of a strain gauge according to embodiment 2 of the present invention

[0036] Figure 10 This is a top view of the mold of Example 2 of the present invention;

[0037] Figure 11 This is a side sectional view of the mold of Example 2 of the present invention;

[0038] Figure 12 This is a top view of the mold with the strain gauge 2 placed in the second embodiment of the present invention;

[0039] Figure 13 This is a side sectional view of a mold with a strain gauge 2 placed therein according to embodiment 2 of the present invention.

[0040] Among them: 1-coating layer; 2-strain gauge; 3-enameled wire; 4-lead wire; 5-cavity; 6-wire slot. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to directions in the accompanying drawings, and the words "inside" and "outside" refer to directions toward or away from the geometric center of a specific component, respectively.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] The mold for forming the coated strain gauge of the present invention is as follows: Figure 4 and Figure 10 As shown, it includes a mold body.

[0045] The mold body as a whole is in the shape of a rectangular cube, and a rectangular cavity 5 with rounded corners is opened on the top surface. The number of cavities 5 can be multiple. In this embodiment, the number of cavities 5 is two, and the two cavities 5 are arranged in parallel. The depth of cavity 5 is 30 to 50 times the thickness of strain gauge 2, and the area of ​​cavity 5 is 4 to 10 times the area of ​​strain gauge 2.

[0046] A wire clamping groove 6 for the lead wire 4 is opened on the side of the cavity 5 at the top of the mold body. The width of the wire clamping groove 6 should be 0.2mm shorter than the width of the lead wire 4 to firmly clamp the lead wire 4. The depth of the wire clamping groove 6 is 0.5mm larger than the diameter of the lead wire 4 to ensure that the lead wire 4 can be completely inside the covering layer 1.

[0047] The material of the mold body can be PTFE, mold steel or aluminum alloy.

[0048] like Figure 1 FIG. 1 shows a method for manufacturing a coated strain gauge according to the present invention, which includes the following steps:

[0049] First, according to the stress and strain measurement requirements, a suitable strain gauge 2 is selected. The strain gauge 2 can be a uniaxial strain gauge, a biaxial strain gauge 2 or a multi-axial strain rosette.

[0050] Using a thermoplastic polymer material or a temporary pressure-sensitive resin, attach the strain gauge 2, base-side down, to the center of the bottom surface of the mold cavity 5. A length of enameled wire 3 is then welded from the pad on the strain gauge 2. The length of the enameled wire 3 should be such that, after fully straightening, the free end of the wire remains within the mold cavity 5. Next, connect the free end of the enameled wire 3 to a waterproof PVC or TPE lead wire 4, which is then clipped into the wire slot 6 in the mold.

[0051] The mold, fitted with the conventional strain gauge 2, is then placed on the workbench of a surface treatment machine. Corona or plasma treatment is then performed on the cavity, the upper surface of the strain gauge 2, and the enameled wire 3 according to the set parameters to increase the surface activity of the cavity, the upper surface of the strain gauge 2, and the enameled wire 3. The entire mold is then preheated to 40-80°C to improve the wettability and bonding strength of the coating 1. Next, the coating 1 material, heated to a fluid state, is injected into the mold cavity 5 until it fills the cavity. Degassing and degassing are performed by increasing the temperature and applying a vacuum. Curing and molding are then performed according to the specific characteristics of the selected coating 1 material. The coating 1 material can be epoxy, polyurethane, or epoxy molding compound.

[0052] Finally, the conventional strain gauge 2 with the coating layer 1 is manually demoulded, and the thermoplastic polymer material or the temporarily fixed pressure-sensitive resin on the base surface is manually removed to obtain an integrated coated strain gauge with complete waterproof and moisture-proof functions.

[0053] The present invention prefabricates an integrated waterproof coating layer 1 for the strain gauge 2, thereby shortening the overall protection time of the strain gauge 2 when used underwater in a humid environment by 2 to 3 days.

[0054] The strain gauge 2 is flexible and uniform, and can fit perfectly with any curved surface. It does not require multiple layers of waterproofing when in use, which greatly reduces the complexity of the process and greatly increases the efficiency.

[0055] The coating layer 1 has a regular shape and uniform thickness, which improves the test accuracy.

[0056] Figure 2-Figure 7 In the first embodiment of this patent, the structure of the strain gauge 2 is as follows Figure 2 and Figure 3 As shown, the specific production method is as follows:

[0057] First, if Figure 4 and Figure 5 As shown in the figure, based on the stress and strain measurement requirements, a 1.5mm uniaxial strain gauge 2 was selected. The rear waterproof lead wire 4 is a 3P TPE cable with a total width of 3mm and a single strand diameter of 1mm. Furthermore, a mold for forming the coating 1 was designed and fabricated based on the dimensions of the strain gauge 2 and lead wire 4. The mold is a rectangular cube with a 1.5mm rectangular cavity 5 with rounded corners on one side. The cavity 5 is 2mm deep. The lead wire 4 retaining groove 6 is 2.8mm wide and 1.5mm deep. The mold material can be PTFE, mold steel, or aluminum alloy. Multiple cavities 5 and retaining grooves 6 can be arranged in one mold.

[0058] Secondly, if Figure 5 and Figure 6As shown, a strain gauge 2 is attached, base-side down, to the center of the bottom surface of the mold cavity 5 using a thermoplastic polymer material or a temporarily fixed pressure-sensitive resin. A length of enameled wire 3 is first soldered to the pad of the strain gauge 2. The length of the enameled wire 3 should be such that, after being fully straightened, its free end remains within the mold cavity 5. In this embodiment, a 5mm long φ0.15mm enameled wire 3 is used. The free end of the enameled wire 3 is then connected to a waterproof PVC or TPE lead wire 4, which is then clipped into a wire slot 6 in the mold.

[0059] Then, follow the Figure 1 As shown in the process flow, the mold with the conventional strain gauge 2 attached is placed on the workbench of the surface treatment equipment, and the cavity, the upper surface of the strain gauge 2, and the enameled wire 3 are subjected to corona or plasma treatment according to the set parameters. Then the mold is preheated to 40-80°C, and the three-proof glue or the molding compound heated to a fluid state is injected into the mold cavity 5 until it fills the mold cavity 5. Degassing and defoaming are carried out by heating and vacuuming. Curing and molding are carried out according to the specific characteristics of the selected coating layer 1 material. The coating layer 1 material can be epoxy, polyurethane three-proof glue or epoxy molding compound. The epoxy three-proof glue selected in this embodiment needs to be kept at 80°C for 2-3 hours to complete the curing molding.

[0060] Finally, the conventional strain gauge 2 with the coating layer 1 is demoulded, and the thermoplastic polymer material or the temporarily fixed pressure-sensitive resin on the base surface is removed to obtain an integrated coated strain gauge with complete waterproof and moisture-proof functions.

[0061] Figures 8-13 In the second embodiment of this patent, the structure of the strain gauge 2 is as follows Figure 8 and Figure 9 As shown, the specific production method is as follows:

[0062] First, if Figure 10 and Figure 11 As shown in the figure, a φ10mm triaxial strain gauge rosette was selected to meet the stress and strain measurement requirements. The waterproof lead wires 4 at the rear end are 2P TPE cables with a total width of 2mm and a single strand diameter of 1mm. Furthermore, a mold for forming the coating 1 was designed and fabricated based on the dimensions of the strain gauge 2 and lead wires 4. The mold is a rectangular cube with a 2mm rectangular cavity 5 with rounded corners on one side. The cavity 5 is 2mm deep. The lead wire 4 retaining groove 6 is 1.8mm wide and 1.5mm deep. Similarly, the mold material can be PTFE, mold steel, or aluminum alloy, and multiple cavities 5 and retaining grooves 6 can be arranged in a single mold.

[0063] Secondly, if Figure 12 and Figure 13As shown, a strain gauge 2 is attached, base-side down, to the center of the bottom surface of the mold cavity 5 using a thermoplastic polymer material or a temporarily fixed pressure-sensitive resin. A length of enameled wire 3 is first soldered to the pad of the strain gauge 2. The length of the enameled wire 3 should be such that, after being fully straightened, its free end remains within the mold cavity 5. In this embodiment, a 5mm long φ0.15mm enameled wire 3 is used. The free end of the enameled wire 3 is then connected to a waterproof PVC or TPE lead wire 4, which is then clipped into a wire slot 6 in the mold.

[0064] Then, follow the Figure 1 As shown in the process flow, the mold with the conventional strain gauge 2 attached is placed on the workbench of the surface treatment equipment, and the cavity, the upper surface of the strain gauge 2, and the enameled wire 3 are subjected to corona or plasma treatment according to the set parameters. Then the mold is preheated to 40-80°C, and the three-proof glue or the molding compound heated to a fluid state is injected into the mold cavity 5 until it fills the mold cavity 5. Degassing and defoaming are carried out by heating and vacuuming. Curing and molding are carried out according to the specific characteristics of the selected coating layer 1 material. The coating layer 1 material can be epoxy, polyurethane three-proof glue or epoxy molding compound. The epoxy three-proof glue selected in this embodiment needs to be kept at 80°C for 2-3 hours to complete the curing molding.

[0065] Finally, the conventional strain gauge 2 with the coating layer 1 is demoulded, and the thermoplastic polymer material or the temporarily fixed pressure-sensitive resin on the base surface is removed to obtain an integrated coated strain gauge with complete waterproof and moisture-proof functions.

[0066] The finished coated strain gauge was patched with room temperature curing adhesive and tested according to the following indicators. The results are shown in Table 1:

[0067] Table 1 Test results of strain gauge 2 indicators

[0068]

[0069] It can be seen from the above test values ​​that this patent solves the current problem of strain gauge 2 protection in underwater and humid environments. The produced coated strain gauge has excellent waterproof and moisture-proof performance and meets the stress testing requirements in underwater and humid environments.

[0070] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0071] It should be understood that the above description is for illustration and not for limitation. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this patent should not be determined with reference to the above description, but rather with reference to the preceding claims and the full scope of equivalents to which such claims are entitled. For the purpose of completeness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein from the preceding claims is not a disclaimer of such subject matter, nor should it be considered that the applicants did not consider such subject matter to be part of the disclosed inventive subject matter.

Claims

1. A method for manufacturing a coated strain gauge, characterized in that: The molding die comprises a molding die body; A rectangular cavity (5) is provided on the top of the mold body. The depth of the cavity (5) is 30 to 50 times the thickness of the strain gauge (2). The area of ​​the cavity (5) is 4 to 10 times the area of ​​the strain gauge (2). A wire slot (6) for the lead wire (4) is provided on the side of the cavity (5) at the top of the mold body. The production method includes the following steps: S1, using thermoplastic polymer material or temporary fixed pressure-sensitive resin to attach the strain gauge (2) base downward to the center of the bottom surface of the cavity (5) of the molding die; S2, lead out the enameled wire (3) from the pad of the strain gauge (2), connect the free end of the enameled wire (3) to the lead wire (4), and clamp the lead wire (4) in the wire clamping groove (6) of the mold body; The lead wire (4) is made of waterproof PVC or TPE; Performing corona or plasma treatment on the cavity in the mold body, the upper surface of the strain gauge (2) and the enameled wire (3); S3, injecting the coating layer (1) material in a fluid state into the cavity (5) until the cavity (5) is filled, and after degassing and removing bubbles, solidifying the coating layer (1) material into a shape; S4, demoulding the strain gauge (2) with the coating layer (1), removing the thermoplastic polymer material or the temporarily fixed pressure-sensitive resin on the base surface, and obtaining a coated strain gauge.

2. The method for manufacturing a coated strain gauge according to claim 1, wherein: The width of the wire slot (6) is 0.2 mm shorter than the width of the lead wire (4), and the depth of the wire slot (6) is 0.5 mm larger than the diameter of the lead wire (4).

3. The method for manufacturing a coated strain gauge according to claim 1, wherein: The mold body is made of PTFE, mold steel or aluminum alloy.

4. The method for manufacturing a coated strain gauge according to claim 1, wherein: The covering layer (1) is made of epoxy, polyurethane three-proof glue or epoxy molding compound.

5. The method for manufacturing a coated strain gauge according to claim 1, wherein: After S2 is completed and before proceeding to S3, the entire mold body is preheated to 40-80°C.

6. The method for manufacturing a coated strain gauge according to claim 1, wherein: In S2, the enameled wire (3) is led out from the pad of the strain gauge (2) by welding, and the free end of the enameled wire (3) is located in the cavity (5) after it is completely straightened.

7. The method for manufacturing a coated strain gauge according to claim 1, wherein: In S4, manual demoulding is adopted.

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