A silicone rubber curing stress testing method and tooling

Abstract

The present invention discloses a method and tooling for testing the curing stress of silicone rubber, and belongs to the technical field of adhesive index testing; the method comprises the following steps: selecting isotropic optical materials as force-sensitive elements; polishing one side of the optical material as an interferometer test area; roughening the back of the polished surface as a bonding area; placing the optical material on a metal base, with the roughened surface facing the metal base; fixing the fixed end of the optical material by a pressing plate, and providing a gap adjustment unit between the optical material at the fixed end and the metal base, so that the free end of the optical material is suspended on the metal base; squeezing silicone rubber into the gap between the free end of the optical material and the metal base, and then waiting for it to be completely cured; testing the surface type PV value of the polished surface of the optical material; and calculating the curing shrinkage force of the silicone rubber according to the measured surface type PV value of the polished surface and the bending strength of the optical material. The present invention solves the problems of complex preparation work for silicone rubber curing stress testing and large differences in test results.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesive index testing, and in particular relates to a silicone rubber curing stress testing method and tooling. Background Art

[0002] Silicone rubber is widely used in bonding optical components in optical systems due to its strong weather resistance, aging resistance, and low curing stress. Under the premise of ensuring bonding strength and rigidity, the lower the curing stress of silicone rubber, the more conducive it is to ensuring the performance indicators of the optical system. Therefore, in engineering applications, a simple and accurate method is needed to test the curing stress of various silicone rubbers and select silicone rubber products with curing stress that meets the requirements.

[0003] Existing silicone rubber stress testing methods all require the use of resistance strain gauges to convert the structural deformation caused by the curing shrinkage of silicone rubber into changes in resistance and voltage for measurement. When measuring, it is necessary to build a test bridge and connect the data acquisition system, which is a relatively complicated preparation work; the difference in the bonding state of the resistance strain gauge will also affect the accuracy of the test results, resulting in large differences in the test results obtained by different systems built according to this test method. Summary of the invention

[0004] Technical issues to be solved:

[0005] In order to avoid the shortcomings of the prior art, the present invention provides a silicone rubber curing stress testing method and tooling, which uses a special tooling to convert the curing shrinkage force of silicone rubber into crystal deformation, which is then measured by an interferometer, thereby solving the problems of the complexity of the existing silicone rubber curing stress testing method and poor test repeatability.

[0006] The technical solution of the present invention is: a silicone rubber curing stress testing method, the specific steps are as follows:

[0007] Step 1: Select isotropic optical materials as force-sensitive elements;

[0008] Step 2: Polish one side of the optical material as the interferometer test area; roughen the back side of the polished surface as the bonding area;

[0009] Step 3: placing the optical material on the metal base with the roughened surface facing the metal base; fixing the fixed end of the optical material by a pressing plate, and providing a gap adjustment unit between the optical material at the fixed end and the metal base, so that the free end of the optical material is suspended on the metal base;

[0010] Step 4: Squeeze silicone rubber into the gap between the free end of the optical material and the metal base, and wait for it to fully cure;

[0011] Step 5: Test the surface PV value of the polished surface of the optical material;

[0012] Step 6: According to the measured PV value of the polished surface and the various parameters of the optical material sample, calculate the curing stress of the silicone rubber:

[0013]

[0014] Where E is the elastic modulus of the material, I z is the moment of inertia of the specimen about the y-axis, λ is the surface PV value, S is the area of ​​the silicone rubber spot, and L is the length from the fixed end to the end of the specimen.

[0015] A further technical solution of the present invention is: the optical material is a strip structure, and its bending modulus is less than 60Mpa.

[0016] A further technical solution of the present invention is: the optical material is a crystalline material, including zinc selenide, calcium fluoride and barium fluoride.

[0017] A further technical solution of the present invention is that the roughness of the polished surface of the optical material is 0.05, and the roughness of the roughened surface is 3.2.

[0018] A further technical solution of the present invention is that the gap adjustment unit is a series of copper gaskets, and the gap between the optical material and the metal base is adjusted by adjusting the copper gaskets of different thicknesses.

[0019] A further technical solution of the present invention is that the surface PV value of the polished surface of the optical material is tested by using an interferometer, and the surface PV value reflects the displacement of the free end of the optical material after the silicone rubber is cured.

[0020] A silicone rubber curing stress testing tool, comprising a metal base, an optical material placed on the metal base, a pressing plate for fixing a fixed end of the optical material on the metal base, a copper gasket for adjusting a gap between the fixed end of the optical material and the metal base, and an interferometer;

[0021] The metal base is provided with a through hole at a position relative to the free end of the optical material, which serves as a glue injection hole, and the silicone rubber is squeezed into the gap between the free end of the optical material and the metal base through the glue injection hole;

[0022] The copper gaskets are used to adjust the gap between the fixed end of the optical material and the metal base by adjusting the quantity and thickness.

[0023] A further technical solution of the present invention is that the optical material can transmit visible light, and the diameter of the silicone rubber spot can be observed during testing; its size is 150mm long, 25mm wide, and 3mm thick.

[0024] A further technical solution of the present invention is that the area of ​​the pressing surface between the pressing plate and the optical material is 20mmx20mm.

[0025] A further technical solution of the present invention is: the interferometer is a 632.8nm laser interferometer with a PVr calculation function; the PVr indicator is used instead of the PV to reduce the measurement error and improve the test accuracy; the measured PVr calculation formula is as follows:

[0026] PV r =PV 36Zernikes +3×σ 36ZernikeResid

[0027] In the formula, PV 36Zernikes is the PV of the surface fitted by 36 Zernike terms, σ 36ZernikeResid It is the RMS of the surface residual after removing the 36-item Zernike fitting surface.

[0028] Beneficial Effects

[0029] The beneficial effects of the present invention are: the new method of measuring silicone rubber curing stress improves the measurement accuracy and reduces the measurement cost compared with the measurement method of resistance strain gauges. The specific advantages are as follows:

[0030] 1) The 632.8nm laser interferometer used in the present invention is a conventional device in an optical assembly workshop, which is easy to use, has high measurement accuracy, small repeatability error, and can accurately reflect the curing stress of silicone rubber;

[0031] 2) The optical crystal material used in the present invention has a much lower rigidity than the stainless steel base. The curing and shrinking process of the glue can eliminate the influence of the base deformation and simplify it to a single-direction deformation of the end of the optical material, which is easy to calculate;

[0032] 3) The glue injection and glue cleaning operations of the present invention are convenient, and the tooling can be reused after glue cleaning, thereby reducing the measurement cost;

[0033] 4) The curing shrinkage force of silicone rubber is greatly affected by the diameter-thickness ratio of the glue spot. The gap between the optical crystal and the stainless steel base of the present invention can be adjusted, the injection diameter can be observed, and the curing shrinkage force of silicone rubber under a specific glue spot diameter-thickness ratio can be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the appearance of the tooling dedicated to the embodiment;

[0035] Figure 2 It is an enlarged schematic diagram of the details of the tooling used in the embodiment;

[0036] Explanation of the reference numerals: 1. optical material, 11. glue injection hole, 2. metal base plate, 3. pressure plate, 4. copper gasket. DETAILED DESCRIPTION

[0037] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0038] Based on the fact that the prior art requires the use of resistance strain gauges for testing, it is necessary to build a test bridge and connect the data acquisition system during measurement, and the preparation work is relatively complicated; the difference in the bonding state of the resistance strain gauge will also affect the accuracy of the test results, resulting in large differences in the test results obtained by different systems built according to the test method. The present invention provides a method for measuring the curing stress of silicone rubber, and the specific steps are as follows:

[0039] Step 1: Select a long strip of isotropic optical material with a bending modulus of <60Mpa as a force-sensitive element;

[0040] Step 2: Polish one side of the optical material as the interferometer test area, and roughen the back side as the bonding area;

[0041] Step 3: Fix the optical material on the metal base with a pressing plate, with the roughened surface facing the base; press the pressing plate on one end of the optical material, and leave the other end of the material hanging in the air; add a copper foil gasket under the end of the optical material pressed by the pressing plate to control the gap between the optical material and the base;

[0042] Step 4: Squeeze silicone rubber into the gap between the suspended end of the optical material and the metal base, and wait for it to fully cure;

[0043] Step 5: Use an interferometer to test the surface PV value of the polished surface of the optical material;

[0044] Step 6: According to the measured PV value of the polished surface and the various parameters of the optical material sample, calculate the curing stress of the silicone rubber:

[0045]

[0046] Where E is the elastic modulus of the material, I z is the moment of inertia of the specimen about the y-axis, λ is the surface PV value, S is the area of ​​the silicone rubber spot, and L is the length from the fixed end to the end of the specimen.

[0047] Specifically, the optical material sample is transparent to visible light, the diameter of the silicone rubber spot can be observed during the test, and crystalline materials such as zinc selenide, calcium fluoride, and barium fluoride are selected.

[0048] Specifically, the size of the optical material sample is 150 mm in length, 25 mm in width, and 3 mm in thickness.

[0049] Specifically, the area of ​​one end of the optical material sample pressed by the pressing plate is 20 mm x 20 mm.

[0050] Specifically, the interferometer used is a 632.8nm laser interferometer, and the interferometer used has a PVr calculation function. The PVr indicator can be used instead of PV to reduce measurement errors and improve test accuracy. The measured PVr calculation formula is as follows:

[0051] PV r =PV 36Zernikes +3×σ 36ZernikeResid

[0052] In the formula, PV 36Zernikes is the PV of the surface fitted by 36 Zernike terms, σ 36ZernikeResid It is the RMS of the surface residual after removing the 36-item Zernike fitting surface.

[0053] Specifically, the calculation process of the silicone rubber curing shrinkage force can be performed with the aid of finite element analysis software.

[0054] After the measurement is completed, the pressure plate can be removed and the test fixture can be soaked in ether or gasoline. After the silicone rubber is fully swollen and loses its strength, a blade can be used to clean the silicone rubber attached to the optical material and the metal substrate to restore the fixture to its original state.

[0055] A special tool for measuring the curing stress of silicone rubber, comprising a metal base 2, an optical material 1, a pressure plate 3, and a copper gasket 4; the main body of the metal base 2 is a rectangular flat plate, one end of which is provided with a threaded hole for mounting the pressure plate 3, and the other end is provided with a through hole for injecting glue. The material of the metal base 2 is preferably stainless steel. The copper gasket 4 is placed between the fixed end of the optical material 1 and the metal base 2, so that the free end of the optical material is suspended.

[0056] The present invention is further described in detail with reference to specific embodiments:

[0057] This embodiment provides a method for measuring the curing shrinkage force of silicone rubber, and the materials and operation process used are as follows:

[0058] 1) Select 3 pieces of barium fluoride optical material with a length of 150 mm, a width of 20 mm and a thickness of 3 mm, and polish one side to a roughness of The other side is roughened to a rough surface

[0059] 2) Place the three optical materials with the roughened surface facing down and the coated surface facing up on a 1Cr18Ni9Ti stainless steel base. Figure 1 As shown, a 0.5 mm copper foil gasket is inserted between the two. Figure 2 As shown;

[0060] 3) Further, if Figure 1 As shown, the optical material is pressed with a pressing plate to fix it and the stainless steel base as a whole;

[0061] 4) Further, if Figure 2As shown, use a syringe to inject silicone rubber into the injection hole of the stainless steel base, observe and measure through optical materials, and stop injecting glue when the diameter of the glue spot reaches 15mm. Lay the test tool flat and wait for the silicone rubber to be completely cured.

[0062] 5) Use a 632.8nm laser interferometer to test the polished surface of the optical material, and take the average PVr value of the test results of three samples as the end displacement of the optical material;

[0063] 6) The curing shrinkage force of silicone rubber is calculated based on the end displacement of the optical material and the Young's modulus of the barium fluoride material.

[0064] 7) After the measurement is completed, the pressure plate can be removed and the test fixture can be soaked in ether or gasoline. After the silicone rubber is fully swollen and loses its strength, use a blade to clean the silicone rubber attached to the optical material and the metal substrate to restore the fixture to its original state. The test fixture can be reused.

[0065] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for testing the curing stress of silicone rubber, characterized in that The specific steps are as follows: Step 1: Select isotropic optical materials as force-sensitive elements; Step 2: Polish one side of the optical material as the interferometer test area; roughen the back side of the polished surface as the bonding area; Step 3: placing the optical material on the metal base with the roughened surface facing the metal base; fixing the fixed end of the optical material by a pressing plate, and providing a gap adjustment unit between the optical material at the fixed end and the metal base, so that the free end of the optical material is suspended on the metal base; Step 4: Squeeze silicone rubber into the gap between the free end of the optical material and the metal base, and wait for it to fully cure; Step 5: Test the surface PV value of the polished surface of the optical material; Step 6: According to the measured PV value of the polished surface and the various parameters of the optical material sample, calculate the curing stress of the silicone rubber: Where E is the elastic modulus of the material, I y is the moment of inertia of the specimen about the neutral axis in the y direction, λ is the surface PV value, S is the area of ​​the silicone rubber spot, and L is the length from the fixed end to the free end of the specimen.

2. A silicone rubber curing stress testing method according to claim 1, characterized in that: The optical material is a strip structure, and its bending modulus is less than 60Mpa.

3. A silicone rubber curing stress testing method according to claim 1, characterized in that: The optical material is a crystalline material, including zinc selenide, calcium fluoride and barium fluoride.

4. A silicone rubber curing stress testing method according to claim 1, characterized in that: The roughness of the polished surface of the optical material is 0.05, and the roughness of the roughened surface is 3.

2.

5. A silicone rubber curing stress testing method according to claim 1, characterized in that: The gap adjustment unit is a series of copper gaskets, and the gap between the optical material and the metal base is adjusted by adjusting the copper gaskets of different thicknesses.

6. A silicone rubber curing stress testing method according to claim 1, characterized in that: The surface PV value of the polished surface of the optical material is tested by using an interferometer, and the surface PV value reflects the displacement of the free end of the optical material after the silicone rubber is cured.

7. A silicone rubber curing stress test tool, characterized in that: Used to implement the silicone rubber curing stress testing method according to any one of claims 1 to 6; the testing tool comprises a metal base, an optical material placed on the metal base, a pressing plate for fixing the fixed end of the optical material on the metal base, a copper gasket for adjusting the gap between the fixed end of the optical material and the metal base, and an interferometer; The metal base is provided with a through hole at a position relative to the free end of the optical material, which serves as a glue injection hole, and the silicone rubber is squeezed into the gap between the free end of the optical material and the metal base through the glue injection hole; The copper gaskets are used to adjust the gap between the fixed end of the optical material and the metal base by adjusting the quantity and thickness.

8. The silicone rubber curing stress testing tool according to claim 7, characterized in that: The optical material can transmit visible light, and the diameter of the silicone rubber spot can be observed during testing; its size is 150 mm long, 25 mm wide, and 3 mm thick.

9. A silicone rubber curing stress testing tool according to claim 8, characterized in that: The area of ​​the pressing surface between the pressing plate and the optical material is 20mmx20mm.

10. The silicone rubber curing stress testing tool according to claim 7, characterized in that: The interferometer is a 632.8nm laser interferometer with a PVr calculation function. The PVr indicator is used instead of the PV to reduce the measurement error and improve the test accuracy. The measured PVr calculation formula is as follows: PV r =PV 36Zernikes +3×σ 36ZernikeResid In the formula, PV 36Zernikes is the PV of the surface fitted by 36 Zernike terms, σ 36ZernikeResid It is the RMS of the surface residual after removing the 36-item Zernike fitting surface.

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