A stress relieving method for epdm elastomer for capacitor with wide temperature range

Abstract

The application discloses a stress relieving method for EPDM elastomer for capacitors in a wide temperature range, which comprises the following steps: S1, a high-temperature stress releasing stage: placing the EPDM elastomer to be stress relieved in an oven, controlling the oven temperature to rise to a preset first temperature, and keeping the temperature for a preset first time length; S2, a high-temperature adapting stage: slowly lowering the oven temperature to a preset second temperature, and keeping the temperature for a preset second time length; S3, a slow relaxation stage: continuously slowly lowering the oven temperature to a preset third temperature, and keeping the temperature for a preset third time length; and S4, a normal-temperature stabilizing stage: slowly lowering the oven temperature to a preset fourth temperature, and standing for a preset fourth time length, so as to finally complete the stress relieving operation on the EPDM elastomer. The application can effectively relieve the stress of the EPDM elastomer for capacitors in a wide temperature range (-40 DEG C to 70 DEG C), so that the EPDM elastomer is adapted to the wide temperature working condition, and has great practical significance.

Description

Technical Field

[0001] This invention relates to the field of capacitor manufacturing technology, and in particular to a stress relief method for EPDM elastomers with a wide temperature range (-40℃ to 70℃). Background Technology

[0002] Ethylene propylene diene monomer (EPDM) rubber is widely used in the sealing, buffering, and insulation structures of capacitors due to its excellent high and low temperature resistance, aging resistance, and elasticity. It is especially suitable for wide temperature range working scenarios from -40℃ to 70℃, such as automotive capacitors, industrial control capacitors, and outdoor energy storage capacitors.

[0003] During the vulcanization process of EPDM elastomer, residual stress is generated internally due to uneven cross-linking reaction of polymer chain segments, changes in molding temperature gradient, and rapid shrinkage during cooling. At the same time, there is a difference in the coefficient of thermal expansion between EPDM and components such as capacitor core and metal shell. Under the long-term operation of capacitors in a wide temperature range of -40℃ to 70℃, the residual stress will be superimposed with the thermal stress, causing problems such as uneven shrinkage, warping, and cracking of EPDM elastomer. This can lead to interface delamination between EPDM and capacitor components, decreased airtightness, and even capacitance drift and capacitor failure, seriously affecting the service life and operational stability of the capacitor.

[0004] However, existing traditional stress treatment processes cannot meet the stress relief requirements of EPDM elastomers for wide-temperature-range capacitors.

[0005] Therefore, there is an urgent need to develop a method that can effectively eliminate the stress of EPDM elastomers for capacitors with a wide temperature range (-40℃ to 70℃), so that EPDM elastomers can be adapted to wide temperature conditions. Summary of the Invention

[0006] The purpose of this invention is to address the technical deficiencies of existing technologies by providing a stress relief method for EPDM elastomers used in wide-temperature-range capacitors.

[0007] Therefore, the present invention provides a stress relief method for EPDM elastomers used in wide-temperature-range capacitors, which includes the following steps: Step S1, High-temperature stress release stage: Place the EPDM elastomer to be stress-relieved in an oven, control the oven temperature to rise to a preset first temperature, and keep it at that temperature for a preset first time; Step S2, High Temperature Adaptation Stage: Slowly reduce the oven temperature to the preset second temperature and keep it warm for the preset second duration; Step S3, slow relaxation stage: Continue to slowly reduce the oven temperature to the preset third temperature and keep it warm for the preset third time; Step S4, room temperature stabilization stage: slowly reduce the oven temperature to the preset fourth temperature and let it stand for the preset fourth time to finally complete the stress relief operation on the EPDM elastomer.

[0008] As can be seen from the technical solution provided by the present invention above, compared with the prior art, the present invention provides a stress relief method for EPDM elastomers for wide temperature range capacitors. Its design is scientific and can effectively eliminate the stress of EPDM elastomers for wide temperature range capacitors (-40℃ to 70℃), making EPDM elastomers suitable for wide temperature conditions, which has great practical significance.

[0009] The technical solution of this invention is a method developed to address the stress relief requirements of EPDM elastomers for capacitors in a wide temperature range (-40℃ to 70℃). This method can completely eliminate residual stress, adapt to wide temperature conditions, avoid the generation of secondary stress, and improve the compatibility between EPDM and capacitor components, thereby ensuring the long-term stable operation of capacitors in a wide temperature range.

[0010] To address the issue that traditional processing techniques cannot meet the stress relief requirements of EPDM elastomers for wide-temperature-range capacitors, leading to problems such as cracking, interface peeling, and capacitor failure under thermal cycling at -40℃ to 70℃, the method of this invention, through a stepped temperature gradient design, precisely matches the wide-temperature operating conditions of the capacitor, completely eliminates residual stress and thermal history stress from EPDM molding, avoids the generation of new stress during cooling, improves the dimensional stability and interface compatibility of the EPDM elastomer, and thus ensures the reliability and service life of the capacitor over a wide temperature range.

[0011] After testing, the method of the present invention is applicable to the treatment of EPDM elastomers in various capacitors with an operating temperature range of -40℃ to 70℃. It can effectively eliminate residual stress after EPDM molding and improve the reliability of capacitors under wide temperature and thermal cycling conditions. Attached Figure Description

[0012] Figure 1 The flowchart illustrates a stress relief method for EPDM elastomers used in wide-temperature-range capacitors provided by this invention. Detailed Implementation

[0013] 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. 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.

[0014] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this 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. Therefore, they should not be construed as limitations on this invention.

[0015] In the description of this patent, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this patent according to the specific circumstances.

[0016] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0017] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0018] See Figure 1 This invention provides a stress relief method for EPDM elastomers used in wide-temperature-range capacitors, comprising the following steps: Step S1, High-temperature stress release stage: Place the EPDM elastomer to be stress-relieved in an oven, control the oven temperature to rise to a preset first temperature, and keep it at that temperature for a preset first time; In step S1, specifically, the EPDM elastomer to be stress-relieved is a vulcanized EPDM elastomer with residual stress inside.

[0019] In step S1, specifically, the preset first temperature is 100℃±5℃ (i.e., 95℃~105℃), and the preset first duration is 1h~5h.

[0020] Preferably, in step S1, the oven temperature is controlled at 100°C and kept at that temperature for 3 hours.

[0021] It should be noted that, for this invention, by performing a high-temperature stress release stage: placing the vulcanized EPDM elastomer in an oven, controlling the oven temperature to rise to 100℃±5℃, and holding it at that temperature for 1h~5h, it can perform a special function: to eliminate the internal stress of the polymer chain segments and the residual stress generated during the vulcanization process of the EPDM elastomer.

[0022] Step S2, High Temperature Adaptation Stage: Slowly reduce the oven temperature to the preset second temperature and keep it warm for the preset second duration; In step S2, specifically, the second temperature is preset to be equal to the highest operating temperature of the capacitor ± N℃, where N is a natural number greater than 0 and less than or equal to 5.

[0023] Furthermore, in step S2, the maximum operating temperature of the capacitor is 70℃, and N℃ is 5℃, that is, the preset second temperature is 70℃±5℃ (i.e. 65℃~75℃). In step S2, specifically, the second duration is preset to be 2h to 6h.

[0024] Preferably, in step S2, the oven temperature is controlled at 70°C and kept at that temperature for 4 hours.

[0025] It should be noted that, for this invention, a high-temperature adaptation stage is performed: the oven temperature is slowly reduced to 70℃±5℃ and kept at that temperature for 2h~6h. Here, 70℃ corresponds to the highest operating temperature of the capacitor. The function of this stage is to allow the EPDM elastomer to pre-adapt to the highest operating temperature environment of the capacitor, eliminate creep stress under high-temperature conditions, and improve the dimensional stability of the EPDM elastomer under high-temperature conditions.

[0026] Step S3, slow relaxation stage: Continue to slowly reduce the oven temperature to the preset third temperature and keep it warm for the preset third time; In step S3, specifically, the preset third temperature is 50℃±5℃ (i.e., 45℃~55℃), and the preset third duration is 3h~8h.

[0027] Preferably, in step S3, the oven temperature is controlled at 50°C and kept at that temperature for 5 hours.

[0028] It should be noted that, in this invention, the slow relaxation stage involves slowly reducing the oven temperature to 50℃±5℃ and holding it at that temperature for 3 to 8 hours. The function of this stage is to gradually relax the stress inside the EPDM elastomer through slow cooling and heat preservation, thereby avoiding the generation of thermal stress caused by rapid cooling.

[0029] Step S4, room temperature stabilization stage: slowly reduce the oven temperature to the preset fourth temperature and let it stand for the preset fourth time to finally complete the stress relief operation on the EPDM elastomer.

[0030] In step S4, specifically, the preset fourth temperature is 25℃±5℃ (i.e., 20℃~30℃), and the preset fourth duration is 4h~10h.

[0031] Preferably, in step S4, the oven temperature is controlled at the room temperature assembly temperature of the EPDM elastomer, and the oven is left to stand for 6 hours. More preferably, the room temperature assembly temperature of the EPDM elastomer is 25°C.

[0032] It should be noted that, for this invention, the room temperature stabilization stage involves slowly lowering the oven temperature to 25℃±5℃ (room temperature) and letting it stand for 4h to 10h. The function of this stage is to stabilize the molecular chain segment morphology and fix the size of the EPDM elastomer, thereby completing the stress relief treatment.

[0033] In this invention, specifically, the preset first temperature, preset second temperature, preset third temperature and preset fourth temperature decrease sequentially.

[0034] In this invention, specifically, EPDM elastomer is applied to capacitors with an operating temperature range of -40°C to 70°C. The capacitors include any one of film capacitors, aluminum electrolytic capacitors, power capacitors, and energy storage capacitors.

[0035] In this invention, specifically, EPDM elastomer is used in the sealing, buffering, or potting structure of capacitors.

[0036] In this invention, specifically, the thickness of the EPDM elastomer is 0.5mm to 5mm, and the Shore hardness is 50 to 80HA.

[0037] In step S1, specifically, the heating rate of the oven is controlled to be 2℃ / min~5℃ / min; Preferably, the heating rate of the oven is controlled at 3℃ / min.

[0038] In steps S2 to S4, specifically, the cooling rate of the oven is controlled to be 2℃ / min to 5℃ / min; Preferably, the cooling rate of the oven is controlled at 3℃ / min.

[0039] It should be noted that, in this invention, the heating and cooling rates of the oven in steps S1 to S4 are controlled at 2°C / min to 5°C / min, which can effectively avoid the generation of new thermal stress due to sudden temperature changes.

[0040] It should be noted that, in order to further optimize the process and improve the performance of the pretreated EPDM elastomer, the present invention provides the following preferred solutions: 1. In the high-temperature stress release stage of step S1: the oven temperature is controlled at 100℃ and kept at that temperature for 3 hours. This temperature can quickly break the stress balance inside EPDM and eliminate residual stress from molding, without causing degradation of EPDM molecular chain segments, thus ensuring the original elasticity and temperature resistance of EPDM. 2. In the high-temperature adaptation stage of step S2: the oven temperature is controlled at 70℃ and kept at that temperature for 4 hours. This temperature is precisely matched to the maximum operating temperature of the capacitor, allowing the EPDM elastomer to fully creep at this temperature and eliminate potential stress under high-temperature conditions. 3. In the slow relaxation stage of step S3: the oven temperature is controlled at 50℃ and kept at that temperature for 5 hours. This temperature is in the transition range between high and low temperatures, which can achieve stable relaxation of stress and avoid stress concentration. 4. In the room temperature stabilization stage of step S4: the oven temperature is controlled at 25℃ and left to stand for 6 hours, so that the EPDM elastomer slowly returns to the room temperature state, the molecular chain segments are stably arranged, and the size is fixed, ensuring that there will be no deformation due to stress release after subsequent assembly. It should be noted that, in this invention, the heating or cooling rate is controlled at 3℃ / min in steps S1 to S4, which can ensure process efficiency and avoid new thermal stress caused by sudden temperature changes.

[0041] To better understand the technical solution of the present invention, the following specific embodiments will be used to illustrate the technical solution of the present invention.

[0042] Example 1 In this embodiment 1, the present invention provides a stress relief method for EPDM elastomers used in wide-temperature-range capacitors. The EPDM elastomer is an EPDM sealing gasket with a thickness of 2 mm and a Shore hardness of 65 HA. This EPDM sealing gasket is used for sealing supercapacitors with an operating temperature of -40℃ to 70℃. The method includes the following processing steps: Step S1, High-temperature stress release stage: Place the vulcanized EPDM sealing gasket in a precision oven, control the oven to heat up to 100℃ at a rate of 3℃ / min, and keep it at that temperature for 3 hours to eliminate the internal stress of the polymer chain segments and the residual stress generated during the EPDM molding process. Step S2, High Temperature Adaptation Stage: Control the oven to slowly decrease to 70℃ at a rate of 3℃ / min, and keep it at this temperature for 4 hours to allow the EPDM sealing gasket to pre-adapt to the maximum operating temperature of the vehicle capacitor and eliminate high temperature creep stress. Step S3, slow relaxation stage: Control the oven to continue to drop to 50℃ at a rate of 3℃ / min and keep it at that temperature for 5 hours to gradually relax the internal stress of the EPDM gasket and avoid thermal stress caused by rapid cooling. Step S4, room temperature stabilization stage: control the oven to cool down to 25°C at a rate of 3°C / min, and let it stand for 6 hours to stabilize the molecular chain segments of the EPDM gasket, fix its size, and complete the stress relief treatment.

[0043] Example 2 In this embodiment 2, the present invention provides a stress relief method for EPDM elastomers used in wide-temperature-range capacitors. The EPDM elastomer is an EPDM buffer pad with a thickness of 0.5 mm and a Shore hardness of 50 HA. This EPDM buffer pad is used in industrial control aluminum electrolytic capacitors with an operating temperature of -40℃ to 70℃. The method includes the following processing steps: Step S1, High-temperature stress release stage: Place the vulcanized EPDM cushioning pad in a precision oven, control the oven temperature to rise to 95℃ at a rate of 2℃ / min, keep it at that temperature for 1 hour to eliminate residual molding stress; Step S2, High Temperature Adaptation Stage: Control the oven to slowly decrease to 65℃ at a rate of 2℃ / min, keep it at that temperature for 2 hours, adapt to the highest operating temperature of the capacitor, and eliminate high temperature creep stress; Step S3, slow relaxation stage: Control the oven to continue to drop to 45℃ at a rate of 2℃ / min, and keep it at that temperature for 3 hours to achieve slow stress relaxation; Step S4, room temperature stabilization stage: control the oven to cool down to 20℃ at a rate of 2℃ / min, let stand for 4 hours to complete the stress relief treatment.

[0044] Example 3 In this embodiment 3, the present invention provides a stress relief pretreatment method for an EPDM elastomer used in wide-temperature-range capacitors. The EPDM elastomer is a potted EPDM elastomer with a thickness of 5 mm and a Shore hardness of 80 HA. This potted EPDM elastomer is used in outdoor energy storage capacitors with an operating temperature of -40℃ to 70℃. The method includes the following processing steps: Step S1, High-temperature stress release stage: Place the vulcanized EPDM potting elastomer in a precision oven, control the oven to heat up to 105℃ at a rate of 5℃ / min, and keep it at that temperature for 5 hours to completely eliminate residual molding stress and polymer chain segment stress. Step S2, High Temperature Adaptation Stage: Control the oven to slowly decrease to 75℃ at a rate of 5℃ / min, and keep it at that temperature for 6 hours to adapt to the highest operating temperature of outdoor capacitors and improve high temperature stability. Step S3, slow relaxation stage: Control the oven to continue to drop to 55℃ at a rate of 5℃ / min, and keep it at that temperature for 8 hours to ensure that the stress is fully relaxed; Step S4, temperature stabilization stage: control the oven to cool down to 30°C at a rate of 5°C / min, and let it stand for 10 hours to stabilize the dimensions of the EPDM potting elastomer and complete the stress relief treatment.

[0045] Effect verification.

[0046] To verify the effectiveness of the method of the present invention, the EPDM gasket from Example 1 above was selected as the experimental group, and an EPDM gasket of the same specification without any treatment was selected as control group 1. An EPDM gasket of the same specification treated with a conventional annealing process of holding at 80°C for 4 hours was selected as control group 2. The following tests were performed on the three groups of samples: Test items: -40℃~70℃ thermal shock test (each cycle: first hold at -40℃ for 1 hour, then raise the temperature to 70℃ and hold for 1 hour, 1000 cycles). After the test, the deformation rate, interfacial peel strength, air tightness, and capacitance drift rate of the corresponding capacitors of the three groups of samples were measured. The test results are shown in Table 1 below.

[0047] Table 1:

[0048] As shown in Table 1 above, the test results indicate that, using the stepped stress relief method of the present invention, the deformation rate and capacitance drift rate of the experimental group EPDM gasket are significantly lower than those of control group 1 and control group 2. The interfacial peel strength and airtightness of the experimental group EPDM gasket are significantly better than those of control group 1 and control group 2. This shows that the method of the present invention can effectively eliminate the residual stress of EPDM elastomer, improve its dimensional stability and interfacial adaptability in a wide temperature range, and thus ensure the working reliability of the capacitor. The effect is far superior to the prior art.

[0049] Compared with the prior art, the stress relief method for EPDM elastomers used in wide-temperature-range capacitors provided by the present invention has the following beneficial effects: 1. Highly targeted and adaptable to a wide temperature range: The stress relief method of this invention is a stepped stress relief method. The stepped temperature gradient (100℃→70℃→50℃→25℃) of this invention is not a general annealing process, but is designed to strictly correspond to the wide temperature range of capacitors from -40℃ to 70℃. Among them, 70℃ corresponds to the highest operating temperature of the capacitor, 50℃ is the high and low temperature transition range, and 25℃ is the room temperature assembly temperature. It can accurately eliminate various stresses of EPDM elastomers under wide temperature conditions, and solve the defect of existing single-temperature annealing that cannot adapt to a wide temperature range. 2. Thorough stress elimination with no secondary stress generation: This invention employs a stepped design, using high temperature to release residual molding stress, medium temperature to adapt to working conditions, low temperature for slow relaxation, and room temperature for stable shaping. This not only completely eliminates the polymer chain segment stress and residual molding stress inside the EPDM elastomer, but also prevents the EPDM elastomer from generating new thermal stress during the cooling process, ensuring uniform stress distribution in the treated EPDM elastomer.

[0050] 3. Improve capacitor reliability: After testing, the dimensional stability of EPDM elastomer after stress relief treatment is significantly improved. It is less prone to shrinkage, warping, cracking and other problems under thermal cycling at -40℃ to 70℃. It can effectively improve the interface compatibility between EPDM and capacitor core and shell, improve the airtightness and insulation performance of capacitor, reduce capacitance drift and extend the service life of capacitor. 4. Reasonable process and strong operability: This invention only requires step temperature control through an oven, without the need for complex equipment and special reagents. The process parameters are clear, which facilitates industrial mass production. The cost is low, making it suitable for large-scale application in the production process of wide-temperature-range capacitors.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for stress relief using EPDM elastomer for wide-temperature-range capacitors, characterized in that, Includes the following steps: Step S1, High-temperature stress release stage: Place the EPDM elastomer to be stress-relieved in an oven, control the oven temperature to rise to a preset first temperature, and keep it at that temperature for a preset first time; Step S2, High Temperature Adaptation Stage: Slowly reduce the oven temperature to the preset second temperature and keep it warm for the preset second duration; Step S3, slow relaxation stage: Continue to slowly reduce the oven temperature to the preset third temperature and keep it warm for the preset third time; Step S4, room temperature stabilization stage: slowly reduce the oven temperature to the preset fourth temperature and let it stand for the preset fourth time to finally complete the stress relief operation on the EPDM elastomer.

2. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 1, characterized in that, In step S1, the preset first temperature is 100℃±5℃, and the preset first duration is 1h~5h.

3. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 1, characterized in that, In step S2, the second temperature is preset to be equal to the highest operating temperature of the capacitor ± N℃, where N is a natural number greater than 0.

4. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 3, characterized in that, In step S2, the maximum operating temperature of the capacitor is 70°C, and N°C is 5°C. The preset second temperature is 70℃±5℃.

5. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 1, characterized in that, In step S3, the preset third temperature is 50℃±5℃, and the preset third duration is 3h~8h; In step S4, the preset fourth temperature is 25℃±5℃, and the preset fourth duration is 4h~10h.

6. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 1, characterized in that, In step S1, the oven temperature is controlled at 100℃ and maintained for 3 hours; In step S2, the oven temperature is controlled at 70℃ and maintained for 4 hours; In step S3, the oven temperature is controlled at 50℃ and maintained for 5 hours. In step S4, the oven temperature is controlled at the room temperature assembly temperature of the EPDM elastomer, and the oven is left to stand for 6 hours. The room temperature assembly temperature for EPDM elastomers is 25℃.

7. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 1, characterized in that, The preset first temperature, preset second temperature, preset third temperature, and preset fourth temperature decrease in value sequentially.

8. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 1, characterized in that, EPDM elastomers are used in capacitors with an operating temperature range of -40℃ to 70℃; The thickness of EPDM elastomer is 0.5mm to 5mm, and the Shore hardness is 50 to 80HA; Capacitors include any one of the following: film capacitors, aluminum electrolytic capacitors, power capacitors, and energy storage capacitors.

9. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 1, characterized in that, In step S1, the heating rate of the oven is controlled to be 2℃ / min~5℃ / min; In steps S2 to S4, the cooling rate of the oven is controlled to be 2℃ / min to 5℃ / min.

10. The stress relief method for EPDM elastomers used in wide-temperature-range capacitors as described in claim 9, characterized in that, In step S1, the heating rate of the oven is controlled at 3℃ / min; In steps S2 to S4, the cooling rate of the oven is controlled at 3℃ / min.

Images