Heating and holding device for all-ceramic ball bearing testing machine

Abstract

This invention provides a heating and insulation device for an all-ceramic ball bearing testing machine, which at least solves the problem that existing high-temperature testing machine insulation structures cannot meet the requirements of wide temperature range, high uniformity, low heat loss, and long-term sealing reliability. The heating and insulation device for the all-ceramic ball bearing testing machine includes: a testing machine frame; a test chamber body, located on the testing machine frame and having openings at both axial ends; a multi-layer insulation structure, located at the openings at both axial ends of the test chamber body, and enclosing the test chamber body to form a test chamber; and a mounting base, located inside the test chamber, for mounting the all-ceramic ball bearing to be tested. The heating and insulation device provided by this invention has strong adaptability to a wide temperature range, covering the testing requirements of all-ceramic ball bearings from 100℃ to 1200℃; the heating components are arranged around the bearing, resulting in rapid heating, high thermal efficiency, and uniform temperature distribution; the multi-layer gradient insulation structure and the double-effect high-temperature sealing components work synergistically to significantly reduce heat loss and ensure good long-term sealing reliability.

Description

Technical Field

[0001] This invention relates to the field of all-ceramic ball bearing testing technology, and more specifically, to a heating and heat preservation device for an all-ceramic ball bearing testing machine. Background Technology

[0002] All-ceramic ball bearings, with their superior properties such as high temperature resistance, low coefficient of thermal expansion, wear and corrosion resistance, antimagnetic insulation, and oil-free self-lubrication, are widely used in special fields such as aerospace engines, metallurgical furnaces, chemical reactors, and high-temperature equipment in new energy. High-temperature environments (typically above 300℃, with silicon nitride ceramic bearings reaching 800℃ and silicon carbide ceramic bearings even exceeding 1200℃) are the core service scenarios for all-ceramic ball bearings. Their performance in these environments directly determines the operational safety and stability of related high-temperature equipment, thus requiring specialized testing machines for precise high-temperature performance testing.

[0003] Thermal insulation is one of the core technologies of high-temperature all-ceramic ball bearing testing machines, and its insulation effect and temperature field stability directly affect the validity of test data. Existing high-temperature testing machines often have the following defects in their thermal insulation structures:

[0004] 1. The insulation temperature range is relatively narrow, making it difficult to meet the testing requirements of all-ceramic ball bearings in a high-temperature, wide-temperature range of 100℃ to 1200℃, resulting in poor adaptability;

[0005] Second, the temperature uniformity within the cavity is poor, with obvious thermal gradients in different areas, resulting in uneven heating and inconsistent stress and wear conditions in different parts of the bearing, which affects the objectivity of the test results.

[0006] Third, the insulation layer has insufficient thermal insulation performance, and the heat inside the cavity is quickly conducted outward. At the same time, low-temperature air from the outside can easily penetrate in, resulting in large temperature fluctuations and making it impossible to stably maintain the target test temperature.

[0007] Fourth, the sealing structure has poor high temperature resistance. Under high temperature, the sealing components are prone to aging, deformation, and sealing failure, which aggravates heat exchange and may also affect the normal operation of the external electrical control components of the testing machine, posing a safety hazard.

[0008] Fifth, the lack of an effective heat radiation barrier mechanism makes the heat radiation from the bearings and heating components prone to causing local overheating. At the same time, the heat radiation loss from the cavity wall is large, increasing the energy consumption of the equipment.

[0009] Therefore, developing a high-temperature insulation structure with a wide insulation temperature range, good insulation effect, uniform temperature field, high temperature resistance and sealing, and adaptable to the high-temperature testing requirements of all-ceramic ball bearings has become the key to solving the relevant technical pain points. Summary of the Invention

[0010] The present invention aims to at least solve the problem that the existing high-temperature testing machine insulation structure cannot meet the requirements of wide temperature range, high uniformity, low heat loss and long-term sealing reliability in related technologies.

[0011] The first aspect of this invention provides a heating and insulation device for a testing machine for all-ceramic ball bearings, comprising: a testing machine frame; a testing chamber body disposed on the testing machine frame and having openings at both axial ends; a multi-layer thermal insulation structure disposed at the openings at both axial ends of the testing chamber body and enclosing the testing chamber body to form a testing chamber; a mounting base disposed within the testing chamber for mounting the all-ceramic ball bearing to be tested; a heating assembly disposed inside the testing chamber and surrounding the all-ceramic ball bearing to be tested; a high-temperature sealing assembly including a ceramic fiber seal and a metal magnetic seal, wherein the ceramic fiber seal fills the connection gap between the testing chamber body and the multi-layer thermal insulation structure, and the metal magnetic seal is disposed at the outer splice of the multi-layer thermal insulation structure; a temperature monitoring assembly including multiple temperature sensors electrically connected to the heating assembly, at least some of the temperature sensors being disposed corresponding to the all-ceramic ball bearing to be tested, and at least some of the temperature sensors being disposed within the multi-layer thermal insulation structure; and a buffer assembly disposed between the multi-layer thermal insulation structure and the testing machine frame for dispersing the thermal expansion stress of the multi-layer thermal insulation structure.

[0012] Specifically, the testing machine frame serves as the supporting foundation for the entire device. The testing chamber body is fixed to the testing machine frame, with openings at both axial ends. Multiple layers of thermal insulation structures are installed at these openings, together forming a closed testing chamber. A mounting base is located inside the testing chamber to secure the all-ceramic ball bearing to be tested. The heating assembly is located inside the testing chamber and arranged around the all-ceramic ball bearing, directly heating the bearing and its surrounding environment. The high-temperature sealing assembly consists of two types of seals: ceramic fiber seals fill all the connection gaps between the testing chamber body and the multiple layers of thermal insulation structures, providing high-temperature resistance and blocking heat convection; metal magnetic seals are installed at the joints on the outside of the multiple layers of thermal insulation structures, using magnetic attraction to achieve rapid closure and external airtightness. The temperature monitoring assembly includes multiple temperature sensors. Some sensors are positioned corresponding to the all-ceramic ball bearing to be tested, used to monitor the bearing's own operating temperature in real time; other sensors are embedded inside the multiple layers of thermal insulation structures (e.g., between different insulation layers), used to monitor heat leakage and interlayer temperature. All temperature sensors are electrically connected to the heating assembly, forming a closed-loop temperature control circuit. The buffer assembly is placed between the multi-layer insulation structure and the test machine frame. It uses its elastic deformation to absorb the thermal expansion stress generated by the multi-layer insulation structure at high temperatures, thus preventing structural damage.

[0013] This invention achieves systematic heating and insulation from three dimensions: thermal radiation, thermal conduction, and thermal convection. It involves placing a heating assembly around a bearing inside the test chamber, employing a multi-layered thermal insulation structure arranged at both axial ends, combined with a dual-effect high-temperature sealing system consisting of ceramic fiber seals and metal magnetic seals, as well as a distributed temperature monitoring assembly and a thermal stress buffer assembly. Compared with related technologies, the advantages of this invention include: strong adaptability to a wide temperature range, covering 100℃ to 1200℃; the heating assembly is arranged close to the bearing, resulting in rapid heating and high thermal efficiency; significantly improved temperature uniformity within the test chamber; substantial reduction in heat loss and equipment energy consumption; long-term stable and reliable sealing at high temperatures; and the buffer assembly prevents structural cracking due to thermal stress, improving the lifespan of the device and the reliability of test data.

[0014] In the above technical solution, optionally, the heating component includes: a reflective heat shield, which is made of multi-layer aluminum foil ceramic fiber composite material and is arranged around the all-ceramic ball bearing to be tested, and a heating element is arranged inside the reflective heat shield; a protective sleeve, which is made of silicon carbide ceramic material and is fitted on the outside of the reflective heat shield; and a radiation blocking layer, which is a composite layer of ceramic coating and reflective heat insulation film and is arranged around the outside of the protective sleeve.

[0015] In this technical solution, the heating assembly comprises, from the inside out, a reflective heat shield, a protective sleeve, and a radiation blocking layer. The reflective heat shield is a composite structure made of alternating layers of aluminum foil and ceramic fiber cloth, surrounding the outer circumference of the all-ceramic ball bearing under test. Heating elements (such as resistance wires or silicon carbide rods) are installed inside. Part of the heat generated by the heating elements is directly radiated to the bearing, while the other part is reflected back towards the bearing by the multiple layers of aluminum foil, reducing outward radiation. The protective sleeve is made of silicon carbide ceramic material and is fitted over the reflective heat shield. Silicon carbide has high thermal conductivity and high temperature resistance, enabling it to evenly diffuse the heat from the heating elements and prevent localized overheating. The radiation blocking layer uses a ceramic coating (such as zirconium oxide) as a base, covered with a reflective heat-insulating film (such as an aluminum film or a gold-plated film), and is coated on the outermost layer of the protective sleeve to reflect residual heat radiation back to the center of the test chamber. To further enhance heating uniformity, a heat-diffusing graphite film can be added between the reflective heat shield and the bearing.

[0016] In this technical solution, by integrating the heating element inside a reflective heat shield and sequentially setting a silicon carbide protective sleeve and a radiation blocking layer, high-efficiency and highly uniform surround heating is achieved. The reflective heat shield reduces heat loss through radiation, the silicon carbide protective sleeve ensures uniform heat distribution, and the radiation blocking layer further blocks radiation loss to the cavity wall. The synergistic effect of these three elements concentrates heat on the all-ceramic ball bearing under test, resulting in rapid heating, uniform temperature field, and a significant reduction in heating power requirements.

[0017] Optionally, in the above technical solution, a heat-spreading channel is provided on the surface of the mounting base near the all-ceramic ball bearing to be tested, and the heat-spreading channel is filled with thermally conductive ceramic filler.

[0018] In this technical solution, a heat-spreading channel is formed on the surface of the mounting base facing the all-ceramic ball bearing to be tested (i.e., the bearing mounting surface). This channel can be an annular groove, a spiral groove, or multiple radial grooves. The heat-spreading channel is filled with thermally conductive ceramic filler, such as alumina ceramic particles, silicon carbide powder, or boron nitride fibers. The heat generated by the heating element is first transferred to the mounting base, and then rapidly and evenly conducted to the entire bearing mounting surface through the thermally conductive ceramic filler, and then to the outer ring of the bearing. The high thermal conductivity of the thermally conductive ceramic filler eliminates local hot spots within the channel, while the tiny gaps between its particles also play a role in uniform airflow distribution and buffering. The heat-spreading channel can be formed by machining or casting, and the filler is fixed in the channel by compaction or high-temperature sintering.

[0019] This technical solution significantly improves the heat transfer efficiency and temperature uniformity of the bearing mounting surface by setting heat-equalizing channels filled with thermally conductive ceramic filler on the surface of the mounting base. Compared with flat mounting bases without channels, this solution reduces the temperature difference between various points on the outer ring of the bearing to within ±1℃, avoiding local temperature differences caused by the thermal conductivity limitations of the mounting base itself. This ensures consistent heating of all parts of the bearing, resulting in more objective and accurate test data.

[0020] In the above technical solution, optionally, the multi-layer thermal insulation structure includes: a thermal insulation buffer layer made of ceramic fiber cotton, connected to the axial end face of the test chamber body; a high-temperature resistant fire-resistant layer made of refractory castable, located on the side of the thermal insulation buffer layer away from the test chamber; and a vacuum insulation layer made of vacuum insulation board, located on the side of the high-temperature resistant fire-resistant layer away from the test chamber.

[0021] In this technical solution, the multi-layer thermal insulation structure consists of a thermal insulation buffer layer, a high-temperature refractory layer, and a vacuum insulation layer, arranged sequentially from the side closest to the test chamber towards the side furthest away from the test chamber. The thermal insulation buffer layer, made of ceramic fiber cotton with a thickness of 50mm-80mm, is directly bonded to the axial end face of the test chamber body. Its soft and compressible properties absorb the stress generated by the high-temperature expansion of the test chamber body, while also initially blocking heat conduction. The high-temperature refractory layer is integrally cast using lightweight refractory castable (such as high-alumina castable or mullite castable), with a thickness of 80mm-120mm and a thermal conductivity ≤0.08W / (m·K). It can withstand ultra-high temperatures of 800℃ to 1200℃, providing thermal protection for the outer vacuum insulation layer. The vacuum insulation layer uses a vacuum insulation panel (VIP), whose interior is a high-porosity core material evacuated to a vacuum state. Its thermal conductivity can be as low as 0.004 W / (m·K), and an excellent insulation effect can be achieved with a thickness of only 20mm-30mm. These three layers can be bonded together using high-temperature resistant adhesives or mechanical fasteners. Furthermore, a stainless steel protective shell can be added to the outside of the vacuum insulation panel to prevent mechanical damage.

[0022] This technical solution achieves highly efficient thermal insulation over a wide temperature range by employing a gradient composite structure consisting of a thermal insulation buffer layer, a high-temperature resistant fire-resistant layer, and a vacuum insulation layer. The thermal insulation buffer layer disperses thermal stress and provides initial insulation, the high-temperature resistant fire-resistant layer withstands ultra-high temperatures and blocks most of the heat, and the vacuum insulation layer, with its extremely low thermal conductivity, blocks the conduction of remaining heat. The synergistic effect of these three elements significantly increases the total thermal resistance of the insulation structure, bringing the outer surface temperature of the cavity close to room temperature and reducing equipment energy consumption by more than 30%.

[0023] In the above technical solution, optionally, at least some temperature sensors are disposed between the vacuum insulation layer and the high-temperature resistant fire-resistant layer; and / or at least some temperature sensors are disposed at the connection between the heat insulation buffer layer and the test chamber body.

[0024] In this technical solution, some temperature sensors are installed in the gap between the vacuum insulation layer and the high-temperature refractory layer. Specifically, shallow grooves can be made on the outer surface of the high-temperature refractory layer to embed thermocouple sensors, which are used to monitor the real-time temperature of the vacuum insulation layer and determine whether the high-temperature refractory layer effectively protects the vacuum insulation layer and prevents high temperature intrusion that could cause the vacuum layer to fail. Other temperature sensors are installed at the connection between the heat insulation buffer layer and the test chamber body, such as at the interface between the axial end face of the test chamber body and the ceramic fiber cotton, to monitor the temperature of this interface and determine whether the heat insulation buffer layer is working properly and whether there is heat leakage. The sensor signal lines are led out to an external data acquisition system via high-temperature resistant leads.

[0025] In this technical solution, temperature sensors are installed at key interfaces of the multi-layer thermal insulation structure to achieve real-time monitoring of the working status of the thermal insulation layer. Once the high-temperature resistant and fire-resistant layer shows signs of aging and damage or the thermal insulation buffer layer experiences heat leakage, the sensors can detect the abnormality immediately and issue an early warning, preventing the vacuum insulation layer from failing due to overheating. At the same time, the service life of the thermal insulation buffer layer can also be assessed, thereby ensuring the long-term reliability of the thermal insulation structure and the safety of the testing process.

[0026] Optionally, in the above technical solution, the high-temperature sealing assembly further includes: a bellows compensator, and bellows compensators are provided at the connection between the ceramic fiber seal and the test chamber body, and at the connection between the ceramic fiber seal and the multi-layer thermal insulation structure. The bellows compensator is used to compensate for the thermal expansion deformation between the test chamber body and the multi-layer thermal insulation structure.

[0027] In this technical solution, one or more corrugated compensators are installed at the connection between the ceramic fiber seal and the test chamber body, and at the connection between the ceramic fiber seal and the multi-layer thermal insulation structure. The corrugated compensators are made of a high-temperature alloy and have a corrugated tubular structure. When the temperature inside the test chamber rises, the test chamber body and the multi-layer thermal insulation structure will experience different degrees of thermal expansion due to differences in materials and heating processes. The corrugated compensators absorb these differences in expansion through their axial or radial corrugated deformation, preventing the ceramic fiber seal from cracking or failing due to excessive compression. The number of corrugations, wall thickness, and material of the corrugated compensator can be calculated based on the design temperature range and the amount of expansion. Furthermore, flexible ceramic fibers can be filled inside the corrugated compensator to enhance its thermal insulation effect.

[0028] This technical solution effectively solves the problem of sealing failure caused by the difference in thermal expansion coefficients between different structural components at high temperatures by installing corrugated compensators at both ends of the ceramic fiber seal. The corrugated compensators can adaptively absorb the thermal expansion deformation of each structural component, keeping the ceramic fiber seal in a suitable compression state at all times. This ensures the long-term stability of the sealing performance, avoids heat leakage and cold air intrusion caused by aging or deformation of the seal, and significantly improves the high-temperature operation reliability of the equipment.

[0029] In the above technical solution, optionally, the all-ceramic ball bearing to be tested includes an inner ring, an outer ring, and rolling elements; at least one temperature sensor is disposed on the surface of the inner ring; at least one temperature sensor is disposed on the surface of the outer ring; at least one temperature sensor is disposed near the rolling elements; and at least two temperature sensors are disposed in different areas of the test chamber.

[0030] In this technical solution, the temperature monitoring component includes multiple temperature sensors. At least one sensor is fixedly attached to the inner ring surface for real-time monitoring of the bearing's inner ring operating temperature; at least one sensor is fixedly attached to the outer ring surface for monitoring the outer ring temperature; at least one sensor is located in the rolling element area for monitoring the temperature of the rolling elements and the lubricating film; in addition, at least two sensors are respectively arranged in different areas of the test chamber (e.g., near the front and rear walls of the chamber) for monitoring the overall temperature field distribution of the chamber. All sensors are led out to an external data acquisition system using high-temperature resistant wires.

[0031] In this technical solution, temperature sensors are installed in different areas of the inner ring, outer ring, rolling elements, and test cavity to achieve comprehensive temperature monitoring of all key parts of the bearing and the cavity environment. This distributed multi-point monitoring method can accurately reflect the actual heating state of the bearing at high temperatures and the uniformity of the cavity temperature field, promptly detect abnormal temperature gradients, and provide accurate feedback data for the heating control system, thereby ensuring the stability of the temperature field and the repeatability of test results during the heating and heat preservation process.

[0032] In the above technical solution, optionally, the buffer component includes: a ceramic fiber buffer pad connected to a multi-layer thermal insulation structure; and an alloy spring connected between the ceramic fiber buffer pad and the test machine frame.

[0033] In this technical solution, the buffer assembly consists of two parts: a ceramic fiber buffer pad and an alloy spring. The ceramic fiber buffer pad is made of high-purity ceramic fiber felt and has excellent compression resilience and high-temperature resistance. One side of the pad is fixed to the outer surface of the multi-layer insulation structure using high-temperature resistant bolts or adhesives. One end of the alloy spring abuts against or connects to the ceramic fiber buffer pad, and the other end is connected to the corresponding mounting base on the testing machine frame. When the multi-layer insulation structure undergoes thermal expansion at high temperatures, the ceramic fiber buffer pad is first compressed to absorb some of the displacement, and then the alloy spring is further compressed, together playing a role in buffering and limiting the movement.

[0034] In this technical solution, a combined cushioning assembly of ceramic fiber buffer pads and alloy springs effectively disperses the thermal expansion stress generated by the multi-layer insulation structure at high temperatures. The ceramic fiber buffer pads maintain good elasticity at high temperatures, avoiding hard contact; the alloy springs provide controllable elastic recovery force, preventing the multi-layer insulation structure from damaging the frame or cracking due to excessive expansion. This structure significantly improves the durability and structural stability of the heating and insulation device during repeated heating and cooling cycles.

[0035] In the above technical solution, optionally, the mounting base is made of silicon carbide ceramic material, and the difference between its coefficient of thermal expansion and the coefficient of thermal expansion of the all-ceramic ball bearing to be tested is less than or equal to 5%. The all-ceramic ball bearing to be tested is a silicon nitride ceramic bearing or a silicon carbide ceramic bearing.

[0036] In this technical solution, the mounting base is integrally sintered or machined from silicon carbide ceramic material. The coefficient of thermal expansion of the silicon carbide ceramic mounting base is very similar to that of the ceramic bearing, typically within 5%. This thermal matching design ensures that excessive installation clearance will not occur between the mounting base and the bearing due to differences in expansion at high temperatures.

[0037] In this technical solution, by selecting a silicon carbide ceramic mounting base that closely matches the coefficient of thermal expansion of the all-ceramic ball bearing under test, the installation accuracy issues and additional thermal stress caused by differences in thermal deformation at high temperatures are eliminated. This ensures that the bearing's installation state during testing is consistent with its design state, avoiding abnormal stress and wear caused by installation clearances or interference fits, thereby guaranteeing the objectivity and accuracy of the test data.

[0038] Optionally, in the above technical solution, the heating and heat preservation device further includes: an alarm device electrically connected to the temperature monitoring component, the alarm device having a preset temperature threshold, used to issue an alarm signal when the temperature in the test chamber exceeds the temperature threshold; the alarm device is also electrically connected to the heating component, used to send a control signal to the heating component to adjust the heating power or stop heating when the temperature in the test chamber exceeds the temperature threshold.

[0039] In this technical solution, the heating and insulation device also includes an alarm device. The alarm device is electrically connected to each temperature sensor of the temperature monitoring component via wires and has multiple preset thresholds, including a temperature threshold. The alarm device is also electrically connected to the heating component. When the temperature at any monitoring point inside the test chamber exceeds the corresponding threshold, the alarm device automatically triggers an audible and visual alarm signal (such as a buzzer and a red indicator light) and simultaneously sends a control command to the heating component to adjust the heating power or directly stop heating according to the over-temperature level. The alarm device can also be configured with a remote communication interface to send alarm information to a monitoring center.

[0040] In this technical solution, by setting up an alarm device and linking it with the temperature monitoring component and the heating component, real-time monitoring and active protection against abnormal temperature rises in the test chamber and insulation structure are achieved. Once situations such as excessive temperature, aggravated heat leakage, or seal failure occur, the alarm device can promptly issue a warning and automatically adjust the output power of the heating component or cut off the heating source, effectively preventing equipment damage and safety accidents, and ensuring the safety of the test sample and the testing machine itself.

[0041] Optionally, in the above technical solution, the inner wall corner of the test cavity body is a rounded transition structure.

[0042] In this technical solution, the inner wall corners of the test chamber body adopt a rounded transition structure instead of right angles or sharp corners. The radius of curvature of the rounded transition is ≥50mm, which can be achieved by casting or machining the rounded corners. This rounded transition structure significantly reduces the stress concentration coefficient at the inner wall corners. Under high-temperature conditions, when the test chamber body expands due to heat, the rounded transition can evenly distribute the thermal expansion stress over a larger area, avoiding stress concentration at sharp corners that could lead to cracking.

[0043] Optionally, in the above technical solution, the temperature monitoring component also includes a data filtering module, which is electrically connected to the temperature sensor and is used to filter high-temperature interference signals in the temperature data.

[0044] In this technical solution, the temperature monitoring component further integrates a data filtering module based on the temperature sensor. This data filtering module is implemented through circuitry or embedded software and is electrically connected to the signal output terminals of each temperature sensor. Due to high-temperature environments (especially with frequent switching of heating elements or high-power electromagnetic interference), the raw signals acquired by the temperature sensors may contain high-frequency noise, spikes, or electromagnetic coupling interference. These interference signals can cause temperature readings to fluctuate and control logic to misjudge. The data filtering module uses one or more combinations of low-pass filters (such as RC filters) and digital filtering algorithms (such as moving average filtering, median filtering, or Kalman filtering) to filter out high-frequency interference signals and retain the low-frequency components of the true temperature change. The filtered, clean temperature signal is then transmitted to the heating control system and alarm device.

[0045] In this technical solution, by setting up a data filtering module, noise interference in the temperature sensor's acquired signals under high-temperature electromagnetic environments is effectively eliminated, significantly improving the stability and accuracy of temperature monitoring. This avoids frequent fluctuations in heating power or false alarms caused by signal jumps, resulting in smoother and more precise temperature control, further improving constant temperature accuracy, and enhancing the overall anti-interference capability of the heating and insulation device in industrial environments.

[0046] Optionally, in the above technical solution, the test chamber body is made of high-temperature resistant alloy material, and the inner wall and / or outer wall of the test chamber body are provided with a high-temperature anti-oxidation coating.

[0047] In this technical solution, the test chamber body is made of a high-temperature resistant alloy (such as a nickel-based high-temperature alloy), which maintains good mechanical properties and creep resistance even at temperatures above 1000℃. Furthermore, the inner and / or outer walls of the test chamber body are coated with a high-temperature anti-oxidation coating. The coating can be applied to the inner or outer walls alone, or to both. The high-temperature anti-oxidation coating can be one of the following materials or a combination thereof: aluminide coating, ceramic coating, or enamel coating. The coating thickness is typically 50μm-200μm and can be applied using chemical vapor deposition, physical vapor deposition, plasma spraying, or slurry coating methods. This coating can form a dense alumina or chromium oxide protective film at high temperatures, preventing oxygen from diffusing into the base metal, thereby significantly slowing down the high-temperature oxidation and corrosion rate. In addition, the coating can reduce the thermal radiation absorption rate of the inner wall of the test chamber, assisting the radiation barrier layer in its function.

[0048] In this technical solution, by employing a high-temperature resistant alloy and applying a high-temperature anti-oxidation coating, the oxidation resistance and service life of the test chamber body under long-term high-temperature operation conditions are significantly improved. The coating effectively prevents high-temperature oxidation and spalling of the base metal and intergranular corrosion, avoiding sealing failure and heat leakage caused by the deterioration of the chamber material, ensuring the reliability of the test chamber in long-term stable operation at 1200℃, and reducing the frequency of equipment maintenance and replacement costs.

[0049] In the above technical solution, optionally, the heat dissipation channel includes an inner ring heat dissipation channel and an outer ring heat dissipation channel, wherein the inner ring heat dissipation channel corresponds to the position of the inner ring of the all-ceramic ball bearing to be tested, and the outer ring heat dissipation channel corresponds to the position of the outer ring of the all-ceramic ball bearing to be tested.

[0050] In this technical solution, the heat dissipation channel on the mounting base is further subdivided into an inner ring heat dissipation channel and an outer ring heat dissipation channel. The inner ring heat dissipation channel is located in the corresponding area of ​​the inner ring of the mounting base, and its position matches the axial and radial positions of the inner ring of the bearing under test. This partitioned heat dissipation design can effectively compensate for the temperature difference between the inner and outer rings caused by differences in bearing structure, so that the inner and outer rings of the bearing maintain a highly consistent temperature during high-temperature testing, avoiding changes in preload and additional thermal stress caused by the temperature difference between the inner and outer rings, and further improving the accuracy and reliability of the test data.

[0051] Optionally, in the above technical solution, the heating and heat preservation device also includes a thermal stress buffer sleeve, which is located at the connection between the test chamber body and the test machine shaft, which can reduce the heat conduction between the shaft system and the chamber, and at the same time compensate for the amount of high temperature deformation. Attached Figure Description

[0052] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0053] Figure 1 One of the structural schematic diagrams of the heating and heat preservation device of the all-ceramic ball bearing testing machine according to an embodiment of the present invention is shown;

[0054] Figure 2 This is the second schematic diagram of the heating and heat preservation device of the all-ceramic ball bearing testing machine according to an embodiment of the present invention;

[0055] Figure 3 A schematic diagram of the heating assembly according to an embodiment of the present invention is shown;

[0056] Figure 4 A schematic diagram of the structure of a high-temperature sealing assembly according to an embodiment of the present invention is shown;

[0057] Figure 5 This is the third schematic diagram of the heating and heat preservation device of the all-ceramic ball bearing testing machine according to an embodiment of the present invention;

[0058] Figure 6 A schematic diagram of the structure of the buffer component according to an embodiment of the present invention is shown;

[0059] Figure 7 A schematic diagram of the structure of the all-ceramic ball bearing to be tested according to an embodiment of the present invention is shown.

[0060] The components include: 1. Test machine frame; 2. Test chamber body; 3. Multi-layer thermal insulation structure; 32. Thermal insulation buffer layer; 34. High temperature and fire resistant layer; 36. Vacuum insulation layer; 4. Test chamber; 5. Mounting base; 52. Heat distribution channel; 6. Heating component; 62. Reflective heat insulation cover; 64. Heating element; 66. Protective sleeve; 68. Radiation barrier layer; 7. High temperature sealing component; 72. Ceramic fiber seal; 74. Metal magnetic seal; 76. Corrugated compensator; 8. Temperature monitoring component; 82. Temperature sensor; 9. Buffer component; 92. Ceramic fiber buffer pad; 94. Alloy spring; 100. All-ceramic ball bearing to be tested; 102. Inner ring; 104. Outer ring; 106. Rolling element; 11. Alarm device; 12. Rotating shaft. Detailed Implementation

[0061] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0062] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0063] like Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, the first aspect of the present invention provides a heating and insulation device for a testing machine for all-ceramic ball bearings, comprising: a testing machine frame 1, a testing chamber body 2, a multi-layer heat insulation structure 3, a mounting base 5, a heating assembly 6, a high-temperature sealing assembly 7, a temperature monitoring assembly 8, and a buffer assembly 9. The testing chamber body 2 is disposed on the testing machine frame 1 and has openings at both axial ends; the multi-layer heat insulation structure 3 is disposed at the openings at both axial ends of the testing chamber body 2 and surrounds the testing chamber body 2 to form a testing chamber 4; the mounting base 5 is disposed inside the testing chamber 4 for mounting the all-ceramic ball bearing 100 to be tested; the heating assembly 6 is disposed inside the testing chamber 4 and surrounds the all-ceramic ball bearing 100 to be tested. 00 Setup; High-temperature sealing assembly 7 includes a ceramic fiber seal 72 and a metal magnetic seal 74. The ceramic fiber seal 72 fills the connection gap between the test chamber body 2 and the multi-layer thermal insulation structure 3, and the metal magnetic seal 74 is located at the outer splice of the multi-layer thermal insulation structure 3; Temperature monitoring assembly 8 includes multiple temperature sensors 82 electrically connected to the heating assembly 6. At least some of the temperature sensors 82 are set to correspond to the all-ceramic ball bearing 100 to be tested, and at least some of the temperature sensors 82 are located inside the multi-layer thermal insulation structure 3; Buffer assembly 9 is located between the multi-layer thermal insulation structure 3 and the test machine frame 1 to disperse the thermal expansion stress of the multi-layer thermal insulation structure 3.

[0064] Specifically, the testing machine frame 1 serves as the supporting foundation for the entire device. The testing chamber body 2 is fixed to the testing machine frame 1, with openings at both axial ends. Multi-layer thermal insulation structures 3 are installed at each opening, together forming a closed testing chamber 4. A mounting base 5 is provided inside the testing chamber 4 to fix the all-ceramic ball bearing 100 to be tested. The heating assembly 6 is located inside the testing chamber 4 and arranged around the all-ceramic ball bearing 100 to be tested, directly heating the bearing and its surrounding environment. The high-temperature sealing assembly 7 consists of two types of seals: a ceramic fiber seal 72 fills all the connection gaps between the testing chamber body 2 and the multi-layer thermal insulation structure 3, providing high-temperature resistance and blocking heat convection; a metal magnetic seal 74 is installed at the joint on the outside of the multi-layer thermal insulation structure 3, using magnetic attraction to achieve rapid closure and external airtightness. The temperature monitoring component 8 includes multiple temperature sensors 82. Some temperature sensors 82 are configured to monitor the operating temperature of the all-ceramic ball bearing 100 under test in real time; other temperature sensors 82 are embedded inside the multi-layer insulation structure 3 (e.g., between different multi-layer insulation structures 3) to monitor heat leakage and interlayer temperature of the insulation structure. All temperature sensors 82 are electrically connected to the heating component 6, forming a closed-loop temperature control circuit. The buffer component 9 is located between the multi-layer insulation structure 3 and the testing machine frame 1, using its elastic deformation to absorb the thermal expansion stress generated by the multi-layer insulation structure 3 at high temperatures, preventing structural damage.

[0065] This invention achieves systematic heating and insulation from three dimensions: thermal radiation, thermal conduction, and thermal convection. It employs a multi-layered thermal insulation structure 3 arranged at both axial ends, a dual-effect high-temperature sealing system consisting of ceramic fiber seals 72 and metal magnetic seals 74, a distributed temperature monitoring component 8, and a buffer component 9. Compared with related technologies, the advantages of this invention include: strong adaptability to a wide temperature range, covering 100℃ to 1200℃; the heating component 6 is arranged close to the bearing, resulting in rapid heating and high thermal efficiency; significantly improved temperature uniformity within the test chamber 4; substantial reduction in heat loss and energy consumption; long-term stable and reliable sealing at high temperatures; and the buffer component 9 prevents structural cracking due to thermal stress, improving the lifespan of the device and the reliability of test data.

[0066] Understandably, the test cavity body 2 and the multi-layer thermal insulation structure 3 of the present invention together form the test cavity 4, rather than the test cavity 4 being formed by a single complete test cavity body. This is to reduce the manufacturing difficulty and cost of large-size integrated cavities while ensuring efficient axial thermal insulation.

[0067] In the above technical solution, optionally, the heating component 6 includes: a reflective heat shield 62, which is made of multi-layer aluminum foil ceramic fiber composite material and is arranged around the all-ceramic ball bearing 100 to be tested, and a heating element 64 is arranged inside the reflective heat shield 62; a protective sleeve 66, which is made of silicon carbide ceramic material and is sleeved on the outside of the reflective heat shield 62; and a radiation blocking layer 68, which is a composite layer of ceramic coating and reflective heat insulation film, and is arranged around the outside of the protective sleeve 66.

[0068] In this technical solution, the heating assembly 6 comprises, from the inside out, a reflective heat shield 62, a protective sleeve 66, and a radiation blocking layer 68. The reflective heat shield 62 is a composite structure made of alternating layers of aluminum foil and ceramic fiber cloth, surrounding the outer periphery of the all-ceramic ball bearing 100 to be tested. A heating element 64 (e.g., a resistance wire or silicon carbide rod) is installed inside. Part of the heat generated by the heating element 64 is directly radiated to the bearing, while the other part is reflected back towards the bearing by the multiple layers of aluminum foil, reducing outward radiation. The protective sleeve 66 is made of silicon carbide ceramic material and is fitted over the reflective heat shield 62. Silicon carbide has high thermal conductivity and high temperature resistance, enabling it to evenly diffuse the heat from the heating element 64 and prevent localized overheating. The radiation blocking layer 68 uses a ceramic coating (e.g., zirconium oxide) as a base, with a reflective heat-insulating film (e.g., an aluminum film or a gold-plated film) covering its surface. It is coated on the outermost layer of the protective sleeve 66 to reflect residual heat radiation back to the center of the test chamber 4. To further enhance heating uniformity, a heat-diffusing graphite film can be added between the reflective heat shield 62 and the bearing.

[0069] In this technical solution, by integrating the heating element 64 inside the reflective heat shield 62, and sequentially setting the silicon carbide protective sleeve 66 and the radiation blocking layer 68, high-efficiency and highly uniform surround heating is achieved. The reflective heat shield 62 reduces heat radiation loss to the outside, the silicon carbide protective sleeve 66 ensures uniform heat distribution, and the radiation blocking layer 68 further blocks radiation loss to the cavity wall. The synergistic effect of these three elements concentrates heat on the all-ceramic ball bearing 100 under test, resulting in rapid heating, uniform temperature field, and significantly reduced heating power requirements.

[0070] Optionally, in the above technical solution, a heat dissipation channel 52 is provided on the surface of the mounting base 5 near the all-ceramic ball bearing 100 to be tested, and the heat dissipation channel 52 is filled with thermally conductive ceramic filler.

[0071] In this technical solution, a heat-spreading channel 52 is formed on the surface of the mounting base 5 facing the all-ceramic ball bearing 100 to be tested (i.e., the bearing mounting surface). This channel can be an annular groove, a spiral groove, or multiple radial grooves. The heat-spreading channel 52 is filled with thermally conductive ceramic filler, such as alumina ceramic particles, silicon carbide powder, or boron nitride fibers. The heat generated by the heating component 6 is first transferred to the mounting base 5, and then quickly and evenly conducted to the entire bearing mounting surface through the thermally conductive ceramic filler, and then transferred to the outer ring 104 of the bearing. The high thermal conductivity of the thermally conductive ceramic filler eliminates local hot spots in the channel, while the tiny gaps between its particles also play a role in uniform airflow distribution and buffering. The heat-spreading channel 52 can be formed by machining or casting, and the filler is fixed in the channel by compaction or high-temperature sintering.

[0072] In this technical solution, by setting a heat-equalizing and heat-conducting channel 52 filled with thermally conductive ceramic filler on the surface of the mounting base 5, the heat transfer efficiency and temperature uniformity of the bearing mounting surface are significantly improved. Compared with a flat mounting base without a channel, this solution reduces the temperature difference between various points of the bearing to within ±1℃, avoiding local temperature differences caused by the thermal conductivity limitation of the mounting base 5 itself, thus ensuring that all parts of the bearing are heated uniformly, and the test data are more objective and accurate.

[0073] In the above technical solution, optionally, the multi-layer thermal insulation structure 3 includes: a thermal insulation buffer layer 32, made of ceramic fiber cotton, connected to the axial end face of the test chamber body 2; a high-temperature resistant fire-resistant layer 34, made of refractory castable, located on the side of the thermal insulation buffer layer 32 away from the test chamber 4; and a vacuum insulation layer 36, made of vacuum insulation board, located on the side of the high-temperature resistant fire-resistant layer 34 away from the test chamber 4.

[0074] In this technical solution, the multi-layer thermal insulation structure 3, from the side closest to the test chamber 4 towards the side furthest from the test chamber 4, consists of a thermal insulation buffer layer 32, a high-temperature resistant refractory layer 34, and a vacuum insulation layer 36. The thermal insulation buffer layer 32 is made of ceramic fiber cotton with a thickness of 50mm-80mm and is directly attached to the axial end face of the test chamber body 2. Its soft and compressible properties can absorb the stress generated by the high-temperature expansion of the test chamber body 2, while initially blocking heat conduction. The high-temperature resistant refractory layer 34 is integrally cast using lightweight refractory castable (such as high-alumina castable or mullite castable), with a thickness of 80mm-120mm and a thermal conductivity ≤0.08W / (m·K). It can withstand ultra-high temperatures of 800℃ to 1200℃, providing thermal protection for the outer vacuum insulation layer 36. The vacuum insulation layer 36 uses a vacuum insulation panel with a high-porosity core material evacuated to a vacuum state. Its thermal conductivity can be as low as 0.004 W / (m·K), and an excellent insulation effect can be achieved with a thickness of only 20mm-30mm. These three layers can be bonded together using high-temperature resistant adhesives or mechanical fasteners. Furthermore, a stainless steel protective shell can be added to the outside of the vacuum insulation panel to prevent mechanical damage.

[0075] In this technical solution, a gradient composite structure consisting of a thermal insulation buffer layer 32, a high-temperature resistant fire-resistant layer 34, and a vacuum insulation layer 36 achieves efficient thermal insulation over a wide temperature range. The thermal insulation buffer layer 32 disperses thermal stress and provides initial thermal insulation, the high-temperature resistant fire-resistant layer 34 withstands ultra-high temperatures and blocks most of the heat, and the vacuum insulation layer 36, with its extremely low thermal conductivity, blocks the conduction of remaining heat. The synergistic effect of these three elements significantly increases the total thermal resistance of the insulation structure, bringing the outer surface temperature of the cavity close to room temperature and reducing equipment energy consumption by more than 30%.

[0076] In the above technical solution, optionally, at least some of the temperature sensors 82 are disposed between the vacuum insulation layer 36 and the high-temperature resistant and fire-resistant layer 34; and / or at least some of the temperature sensors 82 are disposed at the connection between the heat insulation buffer layer 32 and the test chamber body 2.

[0077] In this technical solution, some temperature sensors 82 are installed in the gap between the vacuum insulation layer 36 and the high-temperature resistant refractory layer 34. Specifically, shallow grooves can be made on the outer surface of the high-temperature resistant refractory layer 34 to embed thermocouple sensors, which are used to monitor the real-time temperature of the vacuum insulation layer 36 and determine whether the high-temperature resistant refractory layer 34 effectively protects the vacuum insulation layer 36 and prevents high temperature intrusion that could cause the vacuum layer to fail. Some temperature sensors 82 are installed at the connection between the heat insulation buffer layer 32 and the test chamber body 2, such as at the contact interface between the axial end face of the test chamber body 2 and the ceramic fiber cotton, to monitor the temperature of this interface and determine whether the heat insulation buffer layer 32 is working properly and whether there is heat leakage. The signal lines of the temperature sensors 82 are led out to an external data acquisition system through high-temperature resistant leads.

[0078] In this technical solution, temperature sensors 82 are installed at key interfaces of the multi-layer thermal insulation structure 3 to achieve real-time monitoring of the working status of the thermal insulation layer. Once the high-temperature resistant and fire-resistant layer 34 shows signs of aging and damage or the thermal insulation buffer layer 32 experiences heat leakage, the temperature sensor 82 can detect the abnormality immediately and issue an early warning, preventing the vacuum insulation layer 36 from failing due to overheating. At the same time, it can also assess the service life of the thermal insulation buffer layer 32, thereby ensuring the long-term reliability of the thermal insulation structure and the safety of the testing process.

[0079] Optionally, in the above technical solution, the high-temperature sealing assembly 7 further includes: a corrugated compensator 76. The connection between the ceramic fiber seal 72 and the test chamber body 2, and the connection between the ceramic fiber seal 72 and the multi-layer thermal insulation structure 3 are all provided with corrugated compensators 76. The corrugated compensators 76 are used to compensate for the amount of thermal expansion deformation between the test chamber body 2 and the multi-layer thermal insulation structure 3.

[0080] In this technical solution, one or more corrugated compensators 76 are installed at the connection between the ceramic fiber seal 72 and the test chamber body 2, and at the connection between the ceramic fiber seal 72 and the multi-layer thermal insulation structure 3. The corrugated compensator 76 is made of a high-temperature alloy and has a corrugated tubular structure. When the internal temperature of the test chamber 4 rises, the test chamber body 2 and the multi-layer thermal insulation structure 3 will experience different degrees of thermal expansion due to differences in materials and heating processes. The corrugated compensator 76 absorbs these differences in expansion through its axial or radial corrugated deformation, preventing the ceramic fiber seal 72 from cracking or failing due to excessive compression. The number of corrugations, wall thickness, and material of the corrugated compensator 76 can be calculated based on the design temperature range and expansion amount. Furthermore, flexible ceramic fibers can be filled inside the corrugated compensator 76 to enhance its thermal insulation effect.

[0081] In this technical solution, by installing corrugated compensators 76 at both ends of the ceramic fiber seal 72, the problem of sealing failure caused by the difference in thermal expansion coefficients between different structural components at high temperatures is effectively solved. The corrugated compensators 76 can adaptively absorb the thermal expansion deformation of each structural component, keeping the ceramic fiber seal 72 in a suitable compression state at all times. This ensures the long-term stability of the sealing performance, avoids heat leakage and intrusion of cold air caused by aging or deformation of the seal, and significantly improves the high-temperature operation reliability of the equipment.

[0082] In the above technical solutions, optionally, such as Figure 7 As shown, the all-ceramic ball bearing 100 to be tested includes an inner ring 102, an outer ring 104, and rolling elements 106; at least one temperature sensor 82 is disposed on the surface of the inner ring 102; at least one temperature sensor 82 is disposed on the surface of the outer ring 104; at least one temperature sensor 82 is disposed near the rolling elements 106; at least two temperature sensors 82 are disposed in different areas of the test chamber 4.

[0083] In this technical solution, the temperature monitoring component 8 includes multiple temperature sensors 82. At least one temperature sensor 82 is fixedly attached to the surface of the inner ring 102 for real-time monitoring of the operating temperature of the bearing inner ring 102; at least one temperature sensor 82 is fixedly attached to the surface of the outer ring 104 for monitoring the temperature of the outer ring 104; at least one temperature sensor 82 is located in the area where the rolling element 106 is located (e.g., on the cage or near the rolling element 106) for monitoring the temperature of the rolling element 106 and the lubricating film; in addition, at least two temperature sensors 82 are respectively arranged in different areas of the test chamber 4 (e.g., near the front and rear walls of the chamber) for monitoring the overall temperature field distribution of the chamber. All temperature sensors 82 are led out to an external data acquisition system using high-temperature resistant wires.

[0084] In this technical solution, temperature sensors 82 are installed in different areas of the inner ring 102, outer ring 104, rolling elements 106, and test cavity 4, enabling comprehensive temperature monitoring of key parts of the bearing and the cavity environment. This distributed multi-point monitoring method can accurately reflect the actual heating state of the bearing at high temperatures and the uniformity of the cavity temperature field, promptly detect abnormal temperature gradients, and provide accurate feedback data for the heating control system, thereby ensuring the stability of the temperature field and the repeatability of test results during the heating and heat preservation process.

[0085] In the above technical solutions, optionally, such as Figure 6 As shown, the buffer assembly 9 includes: a ceramic fiber buffer pad 92, which is connected to the multi-layer thermal insulation structure 3; and an alloy spring 94, which is connected between the ceramic fiber buffer pad 92 and the test machine frame 1.

[0086] In this technical solution, the buffer assembly 9 consists of two parts: a ceramic fiber buffer pad 92 and an alloy spring 94. The ceramic fiber buffer pad 92 is made of high-purity ceramic fiber felt and has excellent compression resilience and high-temperature resistance. One side of it is fixed to the outer surface of the multi-layer thermal insulation structure 3 by high-temperature resistant bolts or adhesives. One end of the alloy spring 94 abuts against or is connected to the ceramic fiber buffer pad 92, and the other end is connected to the corresponding mounting base of the testing machine frame 1. When the multi-layer thermal insulation structure 3 undergoes thermal expansion at high temperatures, the ceramic fiber buffer pad 92 is first compressed to absorb part of the displacement, and then the alloy spring 94 is further compressed, together playing a role in buffering and limiting.

[0087] In this technical solution, the combined buffer assembly 9, consisting of a ceramic fiber buffer pad 92 and an alloy spring 94, effectively disperses the thermal expansion stress generated by the multi-layer insulation structure 3 at high temperatures. The ceramic fiber buffer pad 92 maintains good elasticity at high temperatures, avoiding hard contact; the alloy spring 94 provides controllable elastic recovery force, preventing the multi-layer insulation structure 3 from damaging the frame or cracking due to excessive expansion. This structure significantly improves the durability and structural stability of the heating and insulation device during repeated heating and cooling cycles.

[0088] In the above technical solution, optionally, the mounting base 5 is made of silicon carbide ceramic material, and the difference between its coefficient of thermal expansion and the coefficient of thermal expansion of the all-ceramic ball bearing 100 to be tested is less than or equal to 5%. The all-ceramic ball bearing 100 to be tested is a silicon nitride ceramic bearing or a silicon carbide ceramic bearing.

[0089] In this technical solution, the mounting base 5 is integrally sintered or machined from silicon carbide ceramic material. The thermal expansion coefficient of the silicon carbide ceramic mounting base is very similar to that of the ceramic bearing, typically within 5%. This thermal matching design ensures that there will not be an excessively large installation gap between the mounting base 5 and the bearing due to the difference in expansion at high temperatures.

[0090] In this technical solution, by selecting a silicon carbide ceramic mounting base that closely matches the coefficient of thermal expansion of the all-ceramic ball bearing 100 under test, the installation accuracy issues and additional thermal stress caused by differences in thermal deformation at high temperatures are eliminated. This ensures that the bearing's installation state during testing is consistent with its design state, avoiding abnormal stress and wear caused by installation clearances or interference fits, thereby guaranteeing the objectivity and accuracy of the test data.

[0091] Optionally, in the above technical solution, the heating and heat preservation device also includes an alarm device 11, which is electrically connected to the temperature monitoring component 8. The alarm device 11 has a preset temperature threshold, which is used to issue an alarm signal when the temperature in the test chamber 4 exceeds the temperature threshold. The alarm device 11 is also electrically connected to the heating component 6, which is used to send a control signal to the heating component 6 to adjust the heating power or stop heating when the temperature in the test chamber 4 exceeds the temperature threshold.

[0092] In this technical solution, the heating and insulation device also includes an alarm device 11. The alarm device 11 is electrically connected to each temperature sensor 82 of the temperature monitoring component 8 via wires, and has multiple preset thresholds, including a temperature threshold. The alarm device 11 is also electrically connected to the heating component 6. When the temperature at any monitoring point inside the test chamber 4 exceeds the corresponding threshold, the alarm device 11 automatically triggers an audible and visual alarm signal (such as a buzzer + red indicator light), and simultaneously sends a control command to the heating component 6 to adjust the heating power or directly stop heating according to the over-temperature level. The alarm device 11 can also be configured with a remote communication interface to send alarm information to the monitoring center.

[0093] In this technical solution, by setting up an alarm device 11 and linking it with the temperature monitoring component 8 and the heating component 6, real-time monitoring and active protection against abnormal temperature rise in the test chamber 4 and the insulation structure are achieved. Once the temperature exceeds the limit, heat leakage intensifies, or the seal fails, the alarm device 11 can issue a warning in a timely manner and automatically adjust the output power of the heating component 6 or cut off the heating source, effectively preventing equipment damage and safety accidents, and ensuring the safety of the test sample and the testing machine itself.

[0094] Optionally, in the above technical solution, the inner wall corner of the test cavity body 2 is a rounded transition structure.

[0095] In this technical solution, the inner wall corners of the test chamber body 2 adopt a rounded transition structure instead of right angles or sharp corners. The radius of curvature of the rounded transition is ≥50mm, which can be achieved by casting or machining the rounded corners. This rounded transition structure significantly reduces the stress concentration coefficient at the inner wall corners. Under high temperature conditions, when the test chamber body 2 expands due to heat, the rounded transition can evenly distribute the thermal expansion stress to a larger area, avoiding stress concentration at sharp corners that could lead to cracking.

[0096] In this technical solution, by setting a rounded transition structure at the corner of the inner wall of the test chamber body 2, the risk of thermal stress concentration at high temperatures is effectively eliminated, preventing cracks or even ruptures in the test chamber during repeated heating and cooling cycles, and significantly improving the structural strength and long-term service life of the test chamber body 2. At the same time, the rounded transition also helps to achieve a uniform distribution of the temperature field inside the chamber, avoiding local overheating or overcooling that may occur at sharp corners.

[0097] Optionally, in the above technical solution, the temperature monitoring component 8 also includes a data filtering module, which is electrically connected to the temperature sensor 82 and is used to filter high-temperature interference signals in the temperature data.

[0098] In this technical solution, the temperature monitoring component 8 further integrates a data filtering module based on the temperature sensor 82. This data filtering module is implemented through circuitry or embedded software and is electrically connected to the signal output terminals of each temperature sensor 82. Due to high-temperature environments (especially when the heating element 64 is frequently switched on and off or there is high-power electromagnetic interference), the raw signals collected by the temperature sensor 82 may contain high-frequency noise, spikes, or electromagnetic coupling interference. These interference signals can cause temperature readings to fluctuate and control logic to misjudge. The data filtering module uses one or more combinations of low-pass filters (such as RC filters) and digital filtering algorithms (such as moving average filtering, median filtering, or Kalman filtering) to filter out high-frequency interference signals and retain the low-frequency components of the true temperature change. The filtered, clean temperature signal is then transmitted to the heating control system and alarm device 11.

[0099] In this technical solution, by setting up a data filtering module, noise interference in the signal collected by temperature sensor 82 under high-temperature electromagnetic environment is effectively eliminated, significantly improving the stability and accuracy of temperature monitoring. This avoids frequent fluctuations in heating power or false alarms caused by signal jumps, resulting in smoother and more precise temperature control, further improving constant temperature accuracy, and enhancing the anti-interference capability of the entire heating and insulation device in industrial environments.

[0100] Optionally, in the above technical solution, the test chamber body 2 is made of high-temperature resistant alloy material, and the inner wall and / or outer wall of the test chamber body 2 are provided with a high-temperature anti-oxidation coating.

[0101] In this technical solution, the test chamber body 2 is made of a high-temperature resistant alloy (such as a nickel-based high-temperature alloy), which can maintain good mechanical properties and creep resistance even at temperatures above 1000℃. Furthermore, the inner and / or outer walls of the test chamber body 2 are also provided with a high-temperature anti-oxidation coating. The coating can be applied to the inner or outer walls alone, or to both. The high-temperature anti-oxidation coating can be one of the following materials or a combination thereof: aluminide coating, ceramic coating, or enamel coating. The coating thickness is typically 50μm-200μm and can be applied by chemical vapor deposition, physical vapor deposition, plasma spraying, or slurry coating. This coating can form a dense alumina or chromium oxide protective film at high temperatures, preventing oxygen from diffusing into the base metal, thereby significantly slowing down the high-temperature oxidation and corrosion rate. In addition, the coating can also reduce the thermal radiation absorption rate of the inner wall of the test chamber 4, assisting the radiation blocking layer 68 in its operation.

[0102] In this technical solution, by employing a high-temperature resistant alloy and applying a high-temperature anti-oxidation coating, the oxidation resistance and service life of the test chamber body 2 under long-term high-temperature operation conditions are significantly improved. The coating effectively prevents high-temperature oxidation and spalling of the base metal and intergranular corrosion, avoids sealing failure and heat leakage caused by the deterioration of the chamber material, ensures the reliability of the test chamber in long-term stable operation at 1200℃, and reduces the frequency of equipment maintenance and replacement costs.

[0103] In the above technical solution, optionally, the heat dissipation channel 52 includes an inner ring heat dissipation channel and an outer ring heat dissipation channel. The inner ring heat dissipation channel corresponds to the position of the inner ring 102 of the all-ceramic ball bearing 100 to be tested, and the outer ring heat dissipation channel corresponds to the position of the outer ring 104 of the all-ceramic ball bearing 100 to be tested.

[0104] In this technical solution, the heat dissipation channel 52 on the mounting base 5 is further subdivided into an inner ring heat dissipation channel and an outer ring heat dissipation channel. The inner ring heat dissipation channel is located in the corresponding area of ​​the inner ring of the mounting base 5, and its position matches the axial and radial positions of the inner ring 102 of the bearing under test; the outer ring heat dissipation channel is located in the corresponding area of ​​the outer ring of the mounting base 5, and its position matches the position of the outer ring 104 of the bearing under test. This partitioned heat dissipation design can effectively compensate for the temperature difference between the inner and outer rings caused by the differences in bearing structure, so that the inner ring 102 and the outer ring 104 of the bearing maintain a highly consistent temperature during high-temperature testing, avoiding changes in preload and additional thermal stress caused by the temperature difference between the inner and outer rings, and further improving the accuracy and reliability of the test data.

[0105] In this technical solution, by setting up inner ring heat dissipation channels and outer ring heat dissipation channels corresponding to the inner ring 102 and outer ring 104 of the bearing, independent temperature control of the inner ring 102 and outer ring 104 regions is achieved. This zoned heat dissipation design can effectively compensate for the temperature difference between the inner and outer rings caused by the differences in bearing structure, so that the inner ring 102 and outer ring 104 of the bearing maintain a highly consistent temperature during high-temperature testing, avoiding changes in preload and additional thermal stress caused by the temperature difference between the inner and outer rings, and further improving the accuracy and reliability of the test data.

[0106] Optionally, in the above technical solution, the heating and heat preservation device also includes a thermal stress buffer sleeve, which is located at the connection between the test chamber body 2 and the test machine shaft 12, which can reduce the heat conduction between the shaft system and the chamber, and at the same time compensate for the amount of high temperature deformation.

[0107] In this technical solution, the heating and insulation device is also equipped with a thermal stress buffer sleeve, which is installed at the connection between the test chamber body 2 and the test machine shaft 12. Specifically, the shaft 12 passes through the wall of the test chamber body 2 and enters the interior of the test chamber 4 to support the inner ring 102 of the all-ceramic ball bearing 100 to be tested or to rotate in conjunction with the bearing. Due to the different materials of the test chamber body 2 and the shaft 12, their coefficients of thermal expansion differ, resulting in relative displacement and thermal stress at high temperatures. The thermal stress buffer sleeve is made of elastic or flexible high-temperature resistant materials, such as ceramic fiber braided sleeves, expanded graphite rings, or high-temperature alloy corrugated sleeves, and is fitted around the outer circumference of the shaft 12 while simultaneously contacting the inner wall of the shaft hole of the test chamber body 2. The buffer sleeve absorbs the difference in thermal expansion between the two through its own compression deformation or interlayer slippage, preventing jamming, wear, or seal failure caused by hard interference. The buffer sleeve can also contain a lubricant (such as graphite powder) to reduce friction. In addition, the buffer sleeve can be designed as a split structure for easy replacement.

[0108] In this technical solution, a thermal stress buffer sleeve is installed at the connection between the test chamber body 2 and the rotating shaft 12, effectively solving the problem of interference or leakage caused by thermal expansion mismatch between components made of different materials. The buffer sleeve absorbs the axial and radial expansion differences, ensuring smooth rotation and precise positioning of the rotating shaft 12 at high temperatures, while preventing damage to the connection due to excessive thermal stress, further improving the reliability and testing accuracy of the device during wide-temperature-range cyclic operation.

[0109] In addition, the rotating shaft 12 passes through the multi-layer thermal insulation structure 3 and is connected to the all-ceramic ball bearing 100 to be tested. The high-temperature sealing component 7 is also provided at the connection between the rotating shaft 12 and the multi-layer thermal insulation structure 3.

[0110] Another embodiment of the present invention provides a heating and insulation device for a high-temperature all-ceramic ball bearing testing machine, which consists of a test chamber 4, a heating component 6, a multi-layer insulation structure 3, a high-temperature sealing component 7, and a temperature monitoring component 8. The temperature monitoring component 8 is electrically connected to the heating component 6 and is installed inside the test chamber 4; the heating component 6 is placed inside the test chamber 4; the high-temperature sealing component 7 connects all structural components and achieves sealing and insulation. The specific structure and implementation scheme of each system are as follows:

[0111] Test chamber 4 serves as the high-temperature test carrier for the all-ceramic ball bearing. It is made of a high-temperature resistant alloy and treated with a high-temperature anti-oxidation coating. Inside, there is a silicon carbide ceramic mounting seat 5 adapted to the bearing under test. This mounting seat 5 matches the thermal expansion coefficient of the all-ceramic ball bearing 100 (silicon nitride / silicon carbide) under test, preventing installation gaps or stress caused by high-temperature thermal deformation and ensuring installation accuracy. The mounting seat 5 has a heat-spreading channel 52 inside, filled with highly thermally conductive ceramic filler, which evenly conducts heat to all parts of the bearing, improving the temperature uniformity around the bearing. The heat-spreading channel 52 enables precise heating and high-temperature maintenance of the all-ceramic ball bearing 100 under test. The internal corners of test chamber 4 adopt a rounded transition structure (radius of curvature ≥ 50mm) to disperse thermal expansion stress under high temperature and prevent cracking of the chamber due to stress concentration. A thermal stress buffer sleeve is provided at the connection between test chamber 4 and the rotating shaft 12 to reduce heat conduction between the shaft system and the chamber, while compensating for high-temperature deformation.

[0112] The heating component 6 includes a reflective heat shield 62, a protective sleeve 66, and a radiation blocking layer 68, all made of high-temperature resistant, low thermal conductivity, and high reflectivity materials. Their specific structures and functions are as follows:

[0113] Reflective heat shield 62: It adopts a multi-layer aluminum foil ceramic fiber composite structure and wraps around the outside of the all-ceramic ball bearing 100 to be tested. It reflects the heat radiation of the bearing itself and the heating component 6, reduces local overheating and heat radiation loss of the bearing, and avoids the heating medium from directly impacting the bearing surface and causing thermal shock damage.

[0114] Protective sleeve 66: Made of silicon carbide ceramic material, it is fitted on the outside of the heating element 64 of the testing machine to achieve uniform diffusion of heating heat and prevent excessive local heat radiation from the heating element 64, which could lead to disorder in the temperature field of the cavity.

[0115] Radiation blocking layer 68: It adopts a composite structure of high emissivity ceramic coating and reflective heat insulation film, which is attached to the inner wall of test cavity 4 to reduce the heat radiation absorption and outward radiation loss of the test cavity 4 wall and improve the temperature field stability of the cavity.

[0116] The multi-layer thermal insulation structure 3 consists of, from the inside out, a thermal insulation buffer layer 32, a high-temperature resistant and fire-resistant layer 34, and a vacuum insulation layer 36. It adopts a gradient thermal insulation structure design to adapt to the thermal insulation requirements of different high-temperature ranges. The specific structure and functions are as follows:

[0117] Thermal insulation buffer layer 32: Made of ceramic fiber cotton, it is closely attached to the outside of the test chamber 4 with a thickness of 50mm-80mm. Its main function is to disperse the thermal expansion stress of the test chamber 4, and at the same time, to initially block the heat conduction of the chamber and prevent high temperature from directly impacting the outer thermal insulation structure.

[0118] High-temperature refractory layer 34: Made of lightweight refractory castable, with a thickness of 80mm-120mm, suitable for heat insulation in the ultra-high temperature range of 800℃ to 1200℃, with a thermal conductivity of ≤0.08W / (m·K), effectively blocking high-temperature heat conduction and providing high-temperature protection for vacuum insulation layer 36.

[0119] Vacuum insulation layer 36: It adopts a vacuum insulation panel structure, and the thermal conductivity is reduced to below 0.004W / (m·K). It is wrapped around the outside of the high temperature and fire resistant layer 34 to reduce heat conduction in the medium and low temperature range and the intrusion of external heat, while reducing the overall volume of the equipment. Temperature sensor 82 is installed inside the vacuum insulation layer 36 to monitor the interlayer temperature in real time and prevent high temperature from entering and causing the vacuum layer to fail.

[0120] The high-temperature sealing assembly 7 includes a ceramic fiber seal 72, a metal magnetic seal 74, a sealing connector, and a high-temperature elastic compensation structure (bellows compensator 76), achieving all-around high-temperature sealing of each structural component and preventing the exchange of hot and cold air. The specific structure and function are as follows:

[0121] Ceramic fiber seal 72: Made of high silica ceramic fiber, it fills the connection gap between the test chamber 4 and the heating component 6 and the multi-layer thermal insulation structure 3. It can withstand temperatures up to 1200℃ and has good high-temperature sealing and thermal insulation performance.

[0122] Metal magnetic sealing element 74: It adopts a stainless steel magnetic frame and high-temperature silicone sealing strip structure, and is set at the outer splice of the multi-layer thermal insulation structure 3. The air leakage rate of the door gap is less than 0.5%, which realizes external sealing and prevents the infiltration of low-temperature air from the outside.

[0123] Corrugated compensator 76: A high-temperature alloy corrugated compensator is used and arranged at the connection between the ceramic fiber seal 72 and each structure to compensate for the thermal expansion deformation of each structure under high temperature, prevent the ceramic fiber seal 72 from being squeezed and damaged due to deformation, and ensure long-term stable sealing performance.

[0124] The temperature monitoring component 8 consists of multiple high-temperature-adaptive temperature sensors 82 (adaptive temperature range from room temperature to 1300℃) and a data filtering module, enabling real-time monitoring of the cavity temperature field and heat exchange with the insulation structure. Its specific structure and functions are as follows:

[0125] Temperature sensors 82 are arranged in a distributed manner. Some of them are evenly distributed inside the test chamber 4, corresponding to the inner ring 102, outer ring 104, rolling element 106 and different areas of the cavity of the all-ceramic ball bearing 100 to be tested, respectively, to collect the temperature field data of the cavity in real time. The other part is arranged in the gaps and sealing connections of the multi-layer thermal insulation structure 3 to monitor heat exchange and heat loss.

[0126] Data filtering module: Filters high-temperature interference signals in temperature data, improves the stability and accuracy of temperature monitoring. The processed temperature data is transmitted to the heating control system of the testing machine to realize the coordinated adjustment of heating power and insulation status. On the other hand, it is transmitted to the alarm device 11 to provide data support for abnormal early warning.

[0127] Buffer component 9: An alloy spring 94 and a ceramic fiber buffer pad 92 are arranged at the connection between the multi-layer thermal insulation structure 3 and the test machine frame 1 to disperse the thermal expansion stress of the thermal insulation structure under high temperature and prevent the thermal insulation layer from cracking and falling off.

[0128] The alarm device 11 is electrically connected to the temperature monitoring component 8. It has a preset temperature threshold. When the temperature field of the cavity fluctuates beyond the range or the temperature of the insulation layer gap rises abnormally (indicating increased heat exchange and sealing failure), it automatically issues an audible and visual alarm signal and sends a command to the testing machine control system to adjust the heating power or cut off the heating source in a timely manner.

[0129] The overall workflow of the heating and heat preservation device of the all-ceramic ball bearing testing machine in this embodiment is as follows:

[0130] Preset parameters: The test target temperature, insulation accuracy, heating rate and other related parameters are preset through the test machine controller, and the alarm device 11 is set to the temperature and heat exchange warning threshold simultaneously.

[0131] Sample installation: Install the all-ceramic ball bearing 100 to be tested on the silicon carbide ceramic mounting base of the test chamber 4, and cover it with a reflective heat shield 62, a protective sleeve 66 and a radiation blocking layer 68. Close and fix the heating component 6 and the end cover of the test chamber 4.

[0132] Sealing and thermal insulation: The ceramic fiber seal 72 and the metal magnetic seal 74 of the high-temperature sealing component 7 are installed in sequence to ensure that the connection gaps are well sealed and the multi-layer thermal insulation structure 3 is in normal working condition.

[0133] Heating and monitoring start-up: Start the heating system of the testing machine to heat up the test chamber 4. The temperature monitoring component 8 collects the temperature data of each monitoring point in the chamber and the gap of the insulation layer in real time, and transmits it to the heating control system and alarm device 11 after filtering.

[0134] Constant temperature insulation: When the real-time temperature reaches the target temperature, the heating control system dynamically adjusts the heating power according to the temperature monitoring data. The multi-layer insulation structure 3 achieves efficient insulation from the dimensions of heat conduction and heat convection. The heating component 6 blocks heat radiation loss and together maintains the high temperature and constant temperature of the cavity. The constant temperature accuracy is controlled within the preset range.

[0135] Abnormal warning: If the temperature exceeds the preset range or the gap temperature of the multi-layer insulation structure 3 rises abnormally during the test (seal failure / intensified heat exchange), the alarm device 11 will automatically issue an audible and visual alarm, and at the same time adjust the heating power or cut off the heating source according to the abnormality level.

[0136] Test completed: Turn off the heating system and control the equipment to slowly cool down to room temperature through the testing machine control system. After the temperature drops to a safe range, open the high-temperature sealing component 7 and the multi-layer thermal insulation structure 3, take out the test sample, and complete the test.

[0137] The heat insulation structure of the high-temperature all-ceramic ball bearing testing machine provided in this embodiment has the following advantages compared with related technologies:

[0138] Wide temperature range and high insulation accuracy: It achieves high temperature insulation and heat preservation from room temperature to 1200℃, with constant temperature accuracy controlled within ±1℃, meeting the testing requirements of all-ceramic ball bearings from 100℃ to 1200℃.

[0139] Excellent temperature uniformity: Through the synergistic effect of the heat dissipation channel 52, the distributed temperature sensor 82, and the heating component 6, local thermal gradients are avoided, thus improving the objectivity of the test results.

[0140] High thermal insulation efficiency and low energy consumption: The composite thermal insulation structure, combined with a double sealing method and a reflective heat insulation cover 62, reduces equipment energy consumption by more than 30%.

[0141] Reliable sealing and good high temperature resistance: The double sealing structure, combined with the bellows compensator 76, can maintain a good seal for a long time at 1200℃, and an alarm device 11 is set up to ensure safety.

[0142] High installation accuracy and low test interference: The thermal expansion coefficient of the silicon carbide mounting base is matched, and the arc transition and buffer components reduce thermal stress interference.

[0143] Stable structure and long service life: High temperature resistant materials and buffer components prevent cracking and deformation, ensuring high stability of the equipment during long-term operation.

[0144] Highly adaptable and versatile: The mounting base 5 is replaceable, the multi-layer thermal insulation structure features a 3-gradient design, and the temperature monitoring component 8 supports multiple parameter presets, making it suitable for a wide range of applications.

[0145] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one embodiment or example.

[0146] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A heating and heat preservation device for an all-ceramic ball bearing testing machine, characterized in that, include: Testing machine frame; The test chamber body is located on the frame of the testing machine and has openings at both axial ends; A multi-layer thermal insulation structure is provided at the openings at both ends of the test cavity body along the axial direction, and together with the test cavity body, forms a test cavity; A mounting base is provided inside the test cavity for mounting the all-ceramic ball bearing to be tested; A heating assembly is disposed inside the test chamber and surrounds the all-ceramic ball bearing to be tested; A high-temperature sealing assembly includes a ceramic fiber seal and a metal magnetic seal. The ceramic fiber seal fills the connection gap between the test chamber body and the multi-layer thermal insulation structure, and the metal magnetic seal is located at the outer splice of the multi-layer thermal insulation structure. The temperature monitoring component includes a plurality of temperature sensors electrically connected to the heating component, at least some of the temperature sensors being disposed corresponding to the all-ceramic ball bearing to be tested, and at least some of the temperature sensors being disposed within the multi-layer thermal insulation structure; A buffer assembly is disposed between the multi-layer thermal insulation structure and the test machine frame to disperse the thermal expansion stress of the multi-layer thermal insulation structure.

2. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to claim 1, characterized in that, The heating component includes: The reflective heat shield is made of multi-layer aluminum foil ceramic fiber composite material and is arranged around the all-ceramic ball bearing to be tested. The reflective heat shield is equipped with a heating element. The protective sleeve, made of silicon carbide ceramic material, is fitted onto the outside of the reflective heat shield; The radiation blocking layer is a composite layer of ceramic coating and reflective heat insulation film, which is surrounded on the outside of the protective sleeve.

3. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to claim 2, characterized in that, The mounting base has a heat-spreading channel on its surface near the all-ceramic ball bearing to be tested, and the heat-spreading channel is filled with thermally conductive ceramic filler.

4. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to claim 1, characterized in that, The multi-layer thermal insulation structure includes: A heat insulation buffer layer, made of ceramic fiber cotton, is connected to the axial end face of the test chamber body; The high-temperature resistant refractory layer is formed by refractory castable and is located on the side of the heat insulation buffer layer away from the test chamber; The vacuum insulation layer, made of vacuum insulation board, is located on the side of the high-temperature resistant and fire-resistant layer away from the test chamber.

5. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to claim 4, characterized in that, At least a portion of the temperature sensor is disposed between the vacuum insulation layer and the high-temperature resistant and fire-resistant layer; and / or At least a portion of the temperature sensor is located at the connection between the heat insulation buffer layer and the test chamber body.

6. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to claim 1, characterized in that, The high-temperature sealing assembly also includes: The corrugated compensator is provided at the connection between the ceramic fiber seal and the test chamber body, and at the connection between the ceramic fiber seal and the multi-layer thermal insulation structure. The corrugated compensator is used to compensate for the thermal expansion deformation between the test chamber body and the multi-layer thermal insulation structure.

7. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to claim 1, characterized in that, The all-ceramic ball bearing to be tested includes an inner ring, an outer ring, and rolling elements; At least one of the temperature sensors is disposed on the surface of the inner ring; At least one of the temperature sensors is disposed on the surface of the outer ring; At least one of the temperature sensors is positioned close to the rolling element; At least two of the temperature sensors are located in different areas of the test chamber.

8. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to claim 1, characterized in that, The buffer component includes: A ceramic fiber cushioning pad is connected to the multi-layer thermal insulation structure; An alloy spring is connected between the ceramic fiber buffer pad and the test machine frame.

9. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to any one of claims 1 to 8, characterized in that, The mounting base is made of silicon carbide ceramic material, and the difference between its coefficient of thermal expansion and that of the all-ceramic ball bearing to be tested is less than or equal to 5%. The all-ceramic ball bearing to be tested is either a silicon nitride ceramic bearing or a silicon carbide ceramic bearing.

10. The heating and heat preservation device for the all-ceramic ball bearing testing machine according to any one of claims 1 to 8, characterized in that, Also includes: An alarm device is electrically connected to the temperature monitoring component. The alarm device has a preset temperature threshold and is used to issue an alarm signal when the temperature in the test chamber exceeds the temperature threshold. The alarm device is also electrically connected to the heating component and is used to send a control signal to the heating component to adjust the heating power or stop heating when the temperature in the test chamber exceeds the temperature threshold.

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