System and method for testing high-temperature creep property of thermoplastic non-crosslinked insulating material

Abstract

The invention relates to a system and method for testing the high-temperature creep performance of a thermoplastic non-crosslinked insulating material, and relates to the technical field of cable material performance test.The system comprises a temperature control box, a sample bearing frame and a pressure loading mechanism; the temperature control box body is provided with a test chamber which can be closed, a temperature control module is arranged on the temperature control box body, and the temperature control module is used for controlling the temperature of the test chamber and realizing air circulation in the test chamber; the sample bearing frame is fixedly arranged in the test chamber and is used for horizontally bearing at least one sample to be tested; the pressure loading mechanism comprises a pressure applying unit and a weight assembly, the pressure applying unit is arranged on the upper side of the sample bearing frame, and the weight assembly is connected with the pressure applying unit, so that the pressure applying unit applies constant vertical acting force to the surface of the to-be-tested sample. Through a high-precision temperature control and forced circulation system integrated by the temperature control box body and the temperature control module, the temperature fluctuation and gradient in the box are effectively reduced, a more stable thermal environment is provided, and a test temperature field is more uniform.

Description

Technical Field

[0001] This application relates to the field of cable material performance testing technology, and in particular to a high-temperature creep performance testing system and method for thermoplastic non-crosslinked insulation materials. Background Technology

[0002] With the deepening of global energy transition and sustainable development strategies, the power cable industry is facing the dual challenges of energy conservation and environmental protection. Cross-linked polyethylene (XLPE), due to its excellent electrical, mechanical, and heat resistance properties resulting from its chemical cross-linked network structure, has become the preferred insulation material for extruded power cables. However, XLPE is a thermosetting material, which is difficult to recycle after the cables are decommissioned, easily causing environmental pollution. Furthermore, the cross-linking and degassing processes in its production are accompanied by high energy consumption and long production cycles. Therefore, developing recyclable, low-carbon-emission environmentally friendly thermoplastic insulation materials (such as polypropylene and modified polyethylene) has become an important direction for cable technology development. For example, CIGRE established a working group to assess the life-cycle energy consumption costs of new thermoplastic polyolefin materials and traditional XLPE. Through analysis and simulation calculations, from an economic cost perspective, the new thermoplastic insulation materials reduce material costs to a certain extent, and when considering the materials of the entire cable system, the overall cost is reduced to a certain extent. In terms of energy consumption, the extrusion process of new thermoplastic insulation materials for cables does not require energy-consuming processes such as cross-linking and degassing. In terms of carbon emissions, the GWP (global warming potential) is lower than that of XLPE, which illustrates the advantages of thermoplastic polyolefin cable insulation materials in the future development of cables. These materials do not require cross-linking during production, which can shorten the process and reduce carbon emissions. After decommissioning, they can be recycled through melting and remanufacturing, demonstrating significant economic benefits and environmental potential.

[0003] Currently, the main basis for evaluating the mechanical property stability of cable insulation materials at high temperatures is the national standard GB / T2951.21-2008. This standard specifies that a constant stress is applied to dumbbell-shaped specimens at a high temperature of 200°C, and their elongation and permanent deformation after cooling are measured to characterize the thermosetting properties and creep resistance of the material. This method is generally applicable to thermosetting materials represented by XLPE.

[0004] However, this existing standard method is not applicable to emerging thermoplastic non-crosslinked insulating materials: First, the standard test temperature (200°C) is much higher than the melting point of common thermoplastic polyolefin materials (approximately 110-130°C for PE-based materials and approximately 150-160°C for PP-based materials), causing the sample to melt and fail during testing, making it impossible to obtain valid data; second, due to the large temperature difference between the test chamber and the environment, opening the temperature control chamber during the test can easily cause drastic fluctuations in the internal temperature field, affecting the accuracy of the measurement; finally, relying on marking a scale on the sample surface is prone to deformation and blurring of the markings at high temperatures, resulting in large deformation measurement errors. Summary of the Invention

[0005] The purpose of this application is to provide a high-temperature creep performance testing system and method for thermoplastic non-crosslinked insulating materials to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the technical solution adopted in this application is as follows: This application provides a high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials, comprising: The temperature control chamber is equipped with a sealed test chamber. The temperature control chamber is equipped with a temperature control module, which is used to control the temperature of the test chamber and realize the air circulation in the test chamber. The sample support frame is fixedly installed in the test chamber. It includes a support platform and multiple heat-insulating pillars. The support platform is used to horizontally support at least one sample to be tested. The support platform is fixed to the test chamber through the heat-insulating pillars, so that there is thermal insulation between the support platform and the bottom wall of the test chamber. The pressure loading mechanism includes a pressure application unit and a weight assembly. The pressure application unit can be disposed on the upper side of the sample support frame, and the weight assembly is detachably connected to the pressure application unit so that the pressure application unit applies a constant vertical force to the surface of the sample to be tested.

[0007] Furthermore, the temperature control module's temperature control error in the test chamber does not exceed 2℃.

[0008] Furthermore, the temperature control module includes: The heating unit, located on the temperature control chamber, is used to heat the test chamber. A temperature sensor, installed inside the test chamber, is used to monitor the temperature of the test chamber. The ventilation unit, located on the temperature control box and connected to the test chamber, is used to drive the air circulation inside the test chamber.

[0009] Furthermore, the sample support frame also includes a base, which is fixed to the bottom of the test chamber and is horizontally positioned relative to the support platform. One end of the heat-insulating support column is fixedly connected to the base, and the other end is fixedly connected to the support platform, so that there is a gap between the support platform and the bottom wall of the test chamber to form thermal insulation, so as to enable the test sample to exchange heat with the temperature control box through the circulating air in the test chamber.

[0010] Furthermore, a measuring ruler is provided on one side of the support platform, with a minimum scale of 0.1 mm.

[0011] Furthermore, the heat insulation support column is equipped with an adjustment component, which can adjust the support height of the heat insulation support column to level the support platform, and a heat insulation pad is provided between the base and the bottom of the test chamber.

[0012] Furthermore, the support platform is equipped with multiple sample stations to support multiple test samples.

[0013] Furthermore, the pressure application unit includes a cylindrical indenter that contacts the surface of the sample to be tested. The weight assembly transmits gravity to the cylindrical indenter through the pressure application unit. The diameter of the cylindrical indenter is 6.4±0.2mm, and the total gravity of the weight assembly and the pressure application unit is 19.6N.

[0014] This application also provides a test method for a high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials based on any of the above-mentioned methods, comprising the following steps: S1. Measure the melting curve of the insulating material to be tested by differential scanning calorimetry to obtain the melting temperature of the insulating material to be tested, and set the test temperature, which is 10-15℃ lower than the melting temperature; S2. Preheat the test chamber of the temperature control chamber for the first set time and stabilize it at the set temperature, and start air circulation; S3. Place the sample to be tested on the sample support frame and preheat it for the second set time. S4. Measure the initial thickness D1 of the sample to be tested; S5. Place the pressure application unit of the pressure loading mechanism on the surface of the sample to be tested, and connect the weight assembly. Apply constant pressure for 60 minutes at the set temperature. S6. After loading is completed, measure the thickness D2 of the test sample after hot pressing under load; S7. Based on the initial thickness D1 before and after hot pressing, and the thickness D2 after hot pressing, calculate the percentage of deformation of the sample. The calculation formula is as follows: When ε≤50%, the insulation material meets the requirements for high-temperature creep resistance. S8. Remove the weight assembly and pressure application unit, take out the test sample and cool it for 120 minutes, then observe and measure its permanent deformation.

[0015] Furthermore, in S2, the first set time is 60-120 minutes; In S3, the second set time is 60 minutes.

[0016] The beneficial effects of the technical solution provided in this application include at least the following: (1) This application effectively reduces the temperature fluctuation and gradient inside the chamber by integrating a high-precision temperature control and forced circulation system with a temperature control chamber and a temperature control module, providing a more stable thermal environment for testing and making the test temperature field more uniform.

[0017] (2) This application optimizes the thermal design to ensure that the sample mainly exchanges heat with the circulating air through convection, thus simulating real conditions and improving the authenticity of the test.

[0018] (3) This application solves the problem that traditional standards are completely unsuitable for thermoplastic materials due to the fixed high temperature (200℃) by setting the test temperature by floating it downward by 10-15℃ based on the melting point of the material. It specifies a double preheating time to ensure sufficient thermal balance, clarifies the standard loading time and load, and unifies the mechanical conditions of the test, so that the test results conducted at different times and in different laboratories have high comparability and repeatability. Optionally, by statistically analyzing the temperature fluctuation amplitude, maximum temperature difference, and standard deviation or coefficient of variation of the deformation percentage ε at multiple locations in the test chamber, and comparing and verifying with the comparison condition without air circulation, it provides a technical basis for establishing industry-recognized test standards. Attached Figure Description

[0019] The accompanying drawings are provided to further illustrate the present application and form part of the specification. They are used together with the embodiments of the present application to explain the application and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the system in one embodiment of the present invention; Figure 2 This is a front view schematic diagram of the sample support frame in one embodiment of the present invention; Figure 3 yes Figure 2 A side view of the sample support frame in the illustrated embodiment; Figure 4 This is a front view schematic diagram of the pressure application unit in one embodiment of the present invention; Figure 5 yes Figure 4 A side view of the pressure application unit in the embodiment shown.

[0020] Explanation of key figure labels: 10. Sample support frame; 11. Support platform; 12. Insulated support column; 13. Measuring ruler; 14. Base; 15. Insulated pad; 20. Pressure application unit; 21. Cylindrical indenter; 30. Weight assembly; 40. Sample to be tested; 50. Temperature control chamber; 51. Test chamber; 52. Heating unit; 53. Temperature sensor; 54. Ventilation unit. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] In this specification, identical components are represented by the same reference numerals. It should be noted that the terms "front," "rear," "left," "right," "upper," and "lower" used in the following description refer to directions in the accompanying drawings, while the terms "bottom surface," "top surface," "inner," and "outer" refer to directions towards or away from a specific component, respectively. 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 indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this specification, "multiple" means two or more.

[0023] Example 1 Please refer to Figures 1-5 A high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials includes a temperature control chamber 50, a sample support frame 10, and a pressure loading mechanism. The temperature control chamber 50 has a sealable test chamber 51. A temperature control module is provided on the temperature control chamber 50 to control the temperature of the test chamber 51 and to achieve air circulation within the test chamber 51. The sample support frame 10 is fixedly installed in the test chamber 51 and includes a support platform 11 and multiple heat-insulating supports 12. The support platform 11 is used to horizontally support at least one test sample 40. The support platform 11 is fixed to the test chamber 51 through the heat-insulating supports 12, so that the support platform 11 and the bottom wall of the test chamber 51 are thermally isolated. The pressure loading mechanism includes a pressure application unit 20 and a weight assembly 30. The pressure application unit 20 can be installed on the upper side of the sample support frame 10, and the weight assembly 30 is detachably connected to the pressure application unit 20 so that the pressure application unit 20 applies a constant vertical force to the surface of the test sample 40.

[0024] In this embodiment, as Figure 1As shown, the temperature control chamber 50 constitutes the main outer shell of the system, and its interior is a sealable, insulated chamber serving as the test chamber 51. The chamber integrates a temperature control module, a comprehensive system integrating heating, temperature measurement, and airflow driving functions. This module is used to raise the chamber temperature, monitor the temperature in real time, and drive forced air circulation within the chamber to ensure uniform temperature distribution and avoid localized hot spots. The sample support frame 10 is fixedly installed within the test chamber 51 of the temperature control chamber 50. It primarily provides a stable, horizontal platform to support the test sample 40. The platform material must be heat-resistant and have good thermal stability to provide a reliable reference plane for thickness measurement. The pressure loading mechanism enables the application of a constant load and consists of a pressure application unit 20 and a weight assembly 30. The pressure application unit 20 is a contact component that transmits vertical force to the sample surface. It is movably mounted above the sample support frame 10 via a lightweight frame or guide structure. The weight assembly 30 consists of a series of standard mass weights and can be detachably connected to the pressure application unit 20 via suspension or placement. When the weight assembly 30 is connected to the pressure application unit 20, their combined gravity will act vertically and uniformly on the sample surface placed on the support frame through the pressure application unit 20, thereby generating a constant and accurately calculable surface pressure on the sample.

[0025] In practical operation, the temperature control chamber 50 is started, the target temperature is set, and the air circulation function is activated. After a period of operation, the air temperature in the test chamber 51 reaches the set value and remains highly uniform and stable. Simultaneously, the sample support frame 10 and the main body of the pressure loading mechanism are placed inside the chamber for preheating to reduce thermal shock. A pre-prepared, regularly shaped (usually sheet-like) sample is placed horizontally on the platform of the sample support frame 10. The pressure application unit 20 of the pressure loading mechanism is aligned and gently placed at the center of the test area on the sample surface. Then, the pre-configured weight assembly 30 is smoothly applied to the pressure application unit 20. At this point, the sample begins to bear a constant vertical pressure. The system operates continuously under this state (constant temperature, constant pressure) for a standard duration to simulate the creep process of materials under long-term high-temperature service.

[0026] In the aforementioned structure, the high-precision temperature control and forced circulation system integrated with the temperature control chamber 50 and temperature control module effectively reduces temperature fluctuations and gradients within the chamber, providing a more stable thermal environment for testing and resulting in a more uniform test temperature field. The use of independent weight loading ensures a constant and undiminished load, and the sample support frame 10 avoids micro-vibrations and deformation during testing. Furthermore, optimized thermal design ensures that the sample primarily exchanges heat with circulating air via convection, simulating real-world conditions and improving the realism of the test. This system has a clear structure and highly standardized operating procedures, facilitating its adoption across different laboratories and enabling the acquisition of comparable data, thereby improving R&D efficiency.

[0027] Specifically, the temperature control module maintains a temperature control error of no more than 2°C in the test chamber 51. This high-precision temperature control within 2°C solves the problem of inaccurate measurement results caused by ambient temperature fluctuations in traditional testing. It ensures a highly stable thermal environment for the sample throughout the testing period, which can last for several hours, avoiding interference from temperature drift on the viscoelastic behavior of thermoplastic materials. This results in high comparability and repeatability of measurement results for each measurement and for different batches of materials.

[0028] The creep properties of thermoplastic materials are extremely sensitive to temperature; even small temperature changes can lead to significant alterations in the deformation rate. Temperature control accuracy of no more than 2°C suppresses the effects of temperature fluctuations, ensuring that the measured deformation data accurately reflects the material's intrinsic creep resistance at a specific set temperature, thus enhancing the reliability of the test data.

[0029] In the specific structure of the temperature control module, the temperature control module includes a heating unit 52, a temperature sensor 53, and a ventilation unit 54: the heating unit 52 is installed on the temperature control box 50 and is used to heat the test chamber 51; the temperature sensor 53 is installed inside the test chamber 51 and is used to monitor the temperature of the test chamber 51; the ventilation unit 54 is installed on the temperature control box 50 and communicates with the test chamber 51, and is used to drive the air circulation inside the test chamber 51.

[0030] In this embodiment, as Figure 1 As shown, the heating unit 52 typically consists of elements such as heating wires, heating rods, or heating films. These heating elements are positioned at different locations within the temperature control chamber 50, for example, uniformly embedded in the side walls of the chamber or arranged in the interlayer between the bottom and top of the chamber. This allows for the radiation of heat into the test chamber 51 from multiple directions, achieving rapid and uniform initial heating and providing balanced heat replenishment during the constant temperature phase, effectively preventing localized overheating caused by a single heat source. The temperature sensors 53 are distributed and extend into or are fixed within the internal space of the test chamber 51. The temperature sensors 53 can continuously and in real-time feed back the detected actual temperature signal within the chamber to the temperature control circuit. The ventilation unit 54 includes a drive motor and an impeller (fan) driven by it. The ventilation unit 54 is fixedly installed at the rear or top of the temperature control box 50 and is directly connected to the test chamber 51 through a special air duct or grille. When the unit is started, the impeller rotates to drive the airflow, forcing the air in the test chamber 51 to circulate in a forced manner according to a set path (such as being drawn in from one side, passing through the heating area and being blown out from the other side), thereby breaking the temperature stratification formed by the natural rise of hot air and achieving high-speed heat exchange and balance in the entire chamber space.

[0031] The three components mentioned above are connected to form a closed-loop control system through a control circuit (not shown in the figure, which is common knowledge in the field). The temperature sensor 53 sends the monitoring signal to the control circuit, which compares this signal with the user-set temperature and outputs a command to dynamically adjust the power of the heating unit 52 (such as through a PID control algorithm). At the same time, the ventilation unit 54 continues to work, and its role in driving air circulation runs through the entire process of heating and maintaining the temperature.

[0032] In the above structure, the heating unit 52 can provide heat radiation from multiple directions. Combined with the forced air circulation driven by the ventilation unit 54, it can quickly diffuse heat to the entire test chamber 51 during the preheating stage and continuously mix air during the constant temperature stage, effectively eliminating local cold spots and hot spots. This ensures that the sample placed in any position in the chamber is in a highly consistent temperature environment, providing a guarantee for the accuracy and comparability of the test results and effectively solving the problem of measurement inaccuracy caused by uneven temperature.

[0033] In the specific structure of the sample support frame 10, the sample support frame 10 also includes a base 14, which is fixed to the bottom of the test chamber 51 and is horizontally arranged with the support platform 11. One end of the heat-insulating support column 12 is fixedly connected to the base 14, and the other end of the heat-insulating support column 12 is fixed to the support platform 11, so that the support platform 11 and the bottom wall of the test chamber 51 are thermally isolated, so that the test sample 40 can exchange heat with the temperature control box 50 through the circulating air in the test chamber 51. A measuring scale 13 is provided on one side of the support platform 11, and the minimum scale of the measuring scale 13 is 0.1mm. The heat-insulating support column 12 is provided with an adjustment component, which can adjust the support height of the heat-insulating support column 12 to level the support platform 11. A heat-insulating pad 15 is provided between the base 14 and the bottom of the test chamber 51. The support platform 11 has multiple sample stations for supporting multiple test samples 40.

[0034] In this embodiment, as Figure 1 , Figure 2 , Figure 3 As shown, the sample support frame 10 includes a horizontal metal base 14, which is detachably fixed to the bottom wall of the test chamber 51 through mounting holes or brackets at its bottom. At both ends of the base 14, two vertical heat-insulating pillars 12 extend vertically upward. Between these two heat-insulating pillars 12 and parallel to the plane of the base 14, a horizontal support platform 11 is erected. The support platform 11 is fixedly connected to the upper ends of the corresponding heat-insulating pillars 12 at both ends, so that it is suspended above the base 14. This ensures that a certain suspended gap is maintained between the lower surface of the support platform 11 and the upper surface of the base 14, as well as between the support platform 11 and the bottom wall of the test chamber 51, to achieve thermal insulation.

[0035] Each heat-insulating support column 12 integrates an adjustment component (such as an adjusting bolt or wedge block mechanism) inside or at its connection point. By turning it, the effective support height of the support column can be finely adjusted, thereby achieving precise adjustment of the levelness of the upper support platform 11. At the contact point between the base 14 and the bottom wall of the test chamber 51, a heat-insulating pad 15 (such as a ceramic gasket or a high-performance engineering plastic gasket) is placed, ensuring that heat exchange between the support platform 11 and the sample on it and the temperature control chamber 50 is mainly through air convection, greatly reducing the heat conduction path through the solid support.

[0036] The upper surface of the support platform 11 is precision-machined to ensure its flatness. A measuring ruler 13 is fixedly mounted on one side via a bracket. The measuring reference plane of this ruler is flush with or has a fixed positional relationship with the upper surface of the support platform 11. Its minimum scale is 0.1 mm, used to accurately measure the thickness variation of the sample placed on the support platform 11. The support platform 11 is planned with multiple independent sample stations, each corresponding to a placement area for a test sample 40, enabling the system to support simultaneous testing of multiple samples and reducing the influence of errors between samples.

[0037] In the above structure, the thermal barrier chain formed by the thermal insulation support 12 and the thermal insulation pad 15 at the bottom of the base 14, as well as the air gap formed by the suspended design, effectively blocks the path of heat from the bottom wall of the temperature control chamber 50 to the support platform 11 and the sample through solid conduction. This allows the sample to be heated and thermally balanced almost entirely by the controlled circulating air in the test chamber 51, which truly simulates the actual heat dissipation of the cable insulation layer in the air. This avoids local overheating or excessively rapid temperature rise of the sample due to unexpected direct heat conduction, ensuring that the thermal creep test is carried out in a uniform and realistic convective heat transfer environment, and that the data is true and reliable.

[0038] In addition, the adjustment components integrated into the thermal insulation support 12 allow for fine leveling of the support platform 11, ensuring that the pressure application unit 20 is completely perpendicular to the upper surface of the sample and in uniform contact when vertical pressure is applied. This avoids lateral force or uneven contact caused by platform tilt, thus ensuring that the applied stress state meets the requirements and providing a stable and constant geometric reference for the entire testing process.

[0039] The measuring ruler 13 has a minimum scale of 0.1 mm, which improves the consistency and convenience of readings and further enhances the standardization of testing.

[0040] In the specific structure of the pressure application unit 20, the pressure application unit 20 includes a cylindrical indenter 21, which is in contact with the surface of the test sample 40. The weight assembly 30 transmits gravity to the cylindrical indenter 21 through the pressure application unit 20. The diameter of the cylindrical indenter 21 is 6.4±0.2mm, and the total gravity of the weight assembly 30 and the pressure application unit 20 is 19.6N.

[0041] In this embodiment, as Figure 4 , Figure 5 As shown, the main body of the pressure application unit 20 is a rigid rectangular frame, consisting of a horizontal upper frame, a horizontal lower frame, and two vertical connecting columns connecting the upper and lower frames. The lower frame is detachably connected to the connecting columns. The entire frame has sufficient structural rigidity and will not deform significantly when subjected to load. The inner frame dimension of the rectangular frame is larger than the width of the support platform 11 of the lower sample support frame 10, allowing the support platform 11 to pass vertically through the central area of ​​the rectangular frame during testing. The frame itself straddles both sides of the support platform 11, with the bottom surface of its lower frame higher than the surface of the support platform 11, thus providing space for the sample and loading.

[0042] At the center of the upper frame of the rectangular frame, there is a vertically downward cylindrical indenter 21. This cylindrical indenter 21 is made of a high-temperature resistant and high-hardness material (such as stainless steel), and its lower end face is finely ground to ensure a smooth surface. It is used for direct contact with the upper surface of the test sample 40 placed on the support platform 11. The diameter of the cylindrical indenter 21 is 6.4 ± 0.2 mm. To achieve load transfer and adjustment, a mechanical interface for connection, such as a lug or hook with an opening, is specially provided on the lower side of the lower frame of the rectangular frame. The weight assembly 30 (consisting of a series of standard mass weights) is suspended from this opening by a connector such as a rope, chain, or linkage. The total weight of the weight assembly 30, the connector, and the pressure application unit 20 itself is configured to be 19.6 N. When the weights are suspended, their gravity is transferred through the rigid structure of the rectangular frame, and a concentrated load is applied to the sample surface through the cylindrical indenter 21.

[0043] In the above structure, by limiting the diameter of the cylindrical indenter 21 to 6.4±0.2mm and precisely configuring the total weight of the system to 19.6N, the compressive stress applied to the sample surface becomes a standardized, accurately calculable and reproducible physical quantity. This ensures that the mechanical conditions used in different laboratories and different batches of tests are completely consistent, guaranteeing the comparability and fairness of the test data, and is conducive to establishing a unified material evaluation standard.

[0044] The through-hole connection between the rectangular frame and the bearing platform 11 forms a self-centering, highly stable loading structure. The vertical cylindrical indenter 21 ensures that the direction of the force is always strictly perpendicular to the sample surface and the flat bearing platform 11, avoiding the introduction of any lateral force or bending moment, so that the test results reflect the creep characteristics of the material under vertical pressure.

[0045] Example 2 A test method based on a high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials includes the following steps: S1. Measure the melting curve of the insulating material to be tested by differential scanning calorimetry to obtain the melting temperature of the insulating material to be tested, and set the test temperature, which is 10-15℃ lower than the melting temperature; S2. Preheat the test chamber 51 of the temperature control box 50 for a first set time and stabilize it at the set temperature, and start air circulation; S3. Place the test sample 40 on the sample support frame 10 and preheat it for the second set time. S4. Measure the initial thickness D1 of the test sample 40; S5. Place the pressure application unit 20 of the pressure loading mechanism on the surface of the test sample 40 and connect the weight assembly 30, and apply constant pressure for 60 minutes at the set temperature. S6. After loading is completed, measure the compressed thickness D2 of the test sample 40 under load; S7. Based on the initial thickness D1 before and after hot pressing and the thickness D2 after compression, calculate the percentage of deformation of the sample. The calculation formula is as follows: When ε≤50%, the insulation material meets the requirements for high-temperature creep resistance. S8. Remove the weight assembly 30 and pressure application unit 20, take out the test sample 40 and cool it for 120 minutes, then observe and measure its permanent deformation.

[0046] More specifically, in S2, the first set time is 60-120 minutes; In S3, the second set time is 60 minutes.

[0047] In this embodiment, in step S1, differential scanning calorimetry is first used to test the target thermoplastic insulating material to obtain its accurate melt profile, thereby determining its melting temperature. Based on this intrinsic characteristic, the ambient temperature (i.e., the test temperature) in all subsequent test steps is set to be 10-15°C lower than this melting temperature. This ensures that the test is conducted under safe conditions where the material remains in a solid state and is close to the actual maximum operating temperature, thus avoiding material failure due to overheating and melting, and rigorously evaluating its performance at temperature boundaries.

[0048] In step S2, the temperature control chamber 50 is activated, and the target temperature value of the test chamber 51 is set to the test temperature determined in the previous step. Simultaneously, the ventilation device is turned on to initiate air circulation. The system is allowed to run continuously for 60 to 120 minutes (i.e., the first set time). The purpose of this stage is to ensure that the air temperature inside the test chamber 51 not only reaches the set value but also achieves high uniformity and dynamic stability through sufficient circulation, providing a reliable and repeatable thermal environment for subsequent tests.

[0049] In step S3, a pre-cut standard-shaped sample, for example, thermoplastic polyolefin insulation material, is prepared into a 20×20×1mm sample using a sheet press. This sample is then placed horizontally on the designated position of the sample support frame 10. The chamber door is closed, and the sample is allowed to stand in a stable high-temperature environment for 60 minutes (i.e., the second set time). This process allows the sample to reach the same temperature as the environment from the inside out, eliminating internal stress caused by uneven heating and ensuring that subsequent deformation is entirely caused by external loads.

[0050] In step S4, without applying a test load to the specimen, the initial thickness D1 at the center position of the specimen is measured and recorded using a precision measuring ruler 13 (minimum scale 0.1 mm) fixed to the side of the support platform 11. This data serves as the reference for calculating the deformation.

[0051] In step S5, the cylindrical indenter 21 (pressure application unit 20) of the pressure loading mechanism is gently and vertically aligned and placed at the center of the sample surface. Subsequently, a pre-calculated weight assembly 30 with a total weight of 19.6 N is suspended from the loading mechanism, and the system maintains this constant load continuously and uninterruptedly for 60 minutes at a set temperature. This process simulates the continuous mechanical stress state experienced by the material during long-term high-temperature service.

[0052] In step S6, immediately after the loading time reaches 60 minutes, read the compressed thickness D2 of the sample under load using measuring ruler 13. The operation should be rapid to minimize the impact of springback caused by load removal or temperature changes on the reading. If more precise values ​​are required, the thickness D1 can be measured using a micrometer before hot pressing, and the thickness D2 can be measured using a micrometer within 15 seconds after hot pressing.

[0053] In step S7, based on the measured D1 and D2, the deformation percentage ε of the material under this condition is calculated using the formula: ε = (D1 - D2) / D1 × 100%. A clear performance threshold is set: if ε ≤ 50%, the material is deemed to meet the high-temperature creep resistance requirements under this test temperature and stress condition. This quantitative indicator provides a direct and objective basis for material screening and grade determination.

[0054] In step S8, after completing the above test, carefully remove the weight assembly 30 and pressure application unit 20, remove the sample from the high-temperature chamber, and allow it to cool completely at room temperature for 120 minutes. Then, measure the sample thickness again; the difference between this thickness and the initial thickness D1 reflects the permanent deformation of the material. This step can be used to further analyze the viscoelastic recovery properties of the material and assess the reversibility of its deformation.

[0055] The above method addresses the problem that traditional standards, which are limited by a fixed high temperature (200℃), are completely unsuitable for thermoplastic materials by setting the test temperature 10-15℃ downwards from the material's melting point. This method specifies dual preheating times (60-120 minutes for environmental stabilization, and 60 minutes for sample equilibration) to ensure sufficient thermal equilibrium; it clarifies the standard loading time (60 minutes) and load (19.6N), unifying the mechanical conditions for testing; and it employs a fixed precision measuring ruler (13) for thickness measurement, avoiding human error in scribing. This series of standardized operating procedures ensures high comparability and repeatability of test results conducted at different times and in different laboratories, providing a technical foundation for establishing industry-recognized testing standards.

[0056] This method not only provides a quantitative evaluation of a material's creep resistance through the percentage deformation ε, but also offers additional information on the material's elastic recovery characteristics through optional permanent deformation measurement, achieving a more comprehensive characterization of the material's viscoelastic behavior. Furthermore, it supports a design for parallel testing at multiple sample stations, and combined with standardized processes, can significantly improve the efficiency of screening and testing in new material development and formulation optimization.

[0057] In the embodiments disclosed in this application, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; "linking" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments disclosed in this application according to the specific circumstances.

[0058] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials, characterized in that, include: The temperature control chamber has a sealed test chamber. The temperature control chamber is equipped with a temperature control module, which is used to control the temperature of the test chamber and realize the air circulation in the test chamber. A sample support frame is fixedly installed in the test chamber. It includes a support platform and multiple heat-insulating supports. The support platform is used to horizontally support at least one sample to be tested. The support platform is fixed to the test chamber through the heat-insulating supports, so that the support platform is thermally isolated from the bottom wall of the test chamber. The pressure loading mechanism includes a pressure application unit and a weight assembly. The pressure application unit can be disposed on the upper side of the sample support frame, and the weight assembly is detachably connected to the pressure application unit so that the pressure application unit applies a constant vertical force to the surface of the sample to be tested.

2. The high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials according to claim 1, characterized in that, The temperature control module controls the temperature of the test chamber with an error not exceeding 2°C.

3. The high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials according to claim 1, characterized in that, The temperature control module includes: A heating unit is installed on the temperature control chamber and is used to heat the test chamber. A temperature sensor is installed inside the test chamber to monitor the temperature of the test chamber. A ventilation unit is installed on the temperature control box and communicates with the test chamber to drive the air circulation inside the test chamber.

4. The high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials according to claim 1, characterized in that, The sample support frame also includes a base, which is fixed to the bottom of the test chamber and is horizontally arranged with the support platform. One end of the heat insulation support is fixedly connected to the base, and the other end is fixedly connected to the support platform, so that there is a gap between the support platform and the bottom wall of the test chamber to form thermal insulation.

5. The high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials according to claim 4, characterized in that, A measuring ruler is provided on one side of the support platform, and the smallest scale of the measuring ruler is 0.1mm.

6. The high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials according to claim 4, characterized in that, The heat-insulating support column is equipped with an adjustment component, which can adjust the support height of the heat-insulating support column to level the support platform. A heat-insulating pad is provided between the base and the bottom of the test chamber.

7. The high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials according to claim 4, characterized in that, The support platform is equipped with multiple sample stations for supporting multiple test samples.

8. The high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials according to claim 1, characterized in that, The pressure application unit includes a cylindrical indenter that contacts the surface of the sample to be tested. The weight assembly transmits gravity to the cylindrical indenter through the pressure application unit. The diameter of the cylindrical indenter is 6.4 ± 0.2 mm, and the total weight of the weight assembly and the pressure application unit is 19.6 N.

9. A test method for a high-temperature creep performance testing system for thermoplastic non-crosslinked insulating materials based on any one of claims 1-8, characterized in that, Includes the following steps: S1. The melting curve of the insulating material to be tested is measured by differential scanning calorimetry to obtain the melting temperature of the insulating material to be tested, and a test temperature is set, wherein the test temperature is 10-15℃ lower than the melting temperature; S2. Preheat the test chamber of the temperature control box for a first set time and stabilize it at the set temperature, and start air circulation; S3. Place the test sample on the sample support frame and preheat it for a second set time; S4. Measure the initial thickness D1 of the sample to be tested; S5. Place the pressure application unit of the pressure loading mechanism on the surface of the sample to be tested, and connect the weight assembly, and apply constant pressure for 60 minutes at the set temperature; S6. After loading is completed, measure the thickness D2 of the test sample after hot pressing under load; S7. Based on the initial thickness D1 before and after hot pressing, and the thickness D2 after hot pressing, calculate the percentage of deformation of the sample. The calculation formula is as follows: When ε≤50%, the insulation material meets the requirements for high-temperature creep resistance. S8. Remove the weight assembly and the pressure application unit, take out the test sample and cool it for 120 minutes, then observe and measure its permanent deformation.

10. The test method according to claim 9, characterized in that, In S2, the first set time is 60-120 minutes; In S3, the second set time is 60 minutes.

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