The pressure control technology of the gas quenching furnace is the core link that determines the quenching quality. Its accuracy and stability directly affect the cooling rate, microstructure transformation and mechanical properties of the workpiece. In the research and development of gas quenching furnaces, Taicang Huarui Vacuum Furnace Industry Co., Ltd. has deeply integrated pressure control technology with material properties and process requirements. Through multi-dimensional technological innovation, it has achieved precise pressure regulation from vacuum state to high-pressure environment, providing reliable pressure guarantee for the gas quenching process of different materials.
The basic principles and core objectives of pressure control
The pressure control of the gas quenching furnace is a dynamic regulation process. Through the coordinated operation of the vacuum system and the gas charging system, the pressure inside the furnace is precisely switched from high vacuum to the target pressure, and the pressure is maintained stable during the cooling stage. The core principle is based on the gas equation of state (PV=nRT), and by controlling the matching relationship between the mass flow rate of the gas and the volume of the furnace, precise pressure regulation is achieved. The primary goal of pressure control is to meet the cooling rate requirements. The continuous cooling transition curves (CCT curves) of different materials have clear requirements for cooling rates. For instance, high-speed steel needs a cooling rate of ≥60℃/s to obtain a martensitic structure, while some alloy steels need to control the cooling rate at 30-40℃/s to reduce stress. Pressure is positively correlated with the cooling rate (within a certain range). By adjusting the pressure, the cooling rate can be indirectly controlled. Huarui gas quenching furnace has established a pressure-cooling rate correspondence model based on experimental data. For example, in a nitrogen environment, 0.3MPa corresponds to a cooling rate of 40℃/s, and 0.5MPa corresponds to 60℃/s. It provides a quantitative basis for the setting of process parameters. Pressure uniformity is another important goal. The pressure deviation in different areas of the furnace should be controlled within ±0.02MPa; otherwise, it will lead to uneven cooling rates in various parts of the workpiece, resulting in performance differences. For instance, when handling large molds, if the pressure difference between the upper and lower parts of the furnace exceeds 0.03MPa, the hardness difference on the mold surface may reach over 3HRC, which will affect the performance in use. The Huarui gas quenching furnace has improved the pressure uniformity inside the furnace to ±0.01MPa by optimizing the layout of the air inlet and the gas circulation structure, ensuring uniform cooling of the workpieces. The response speed of pressure regulation is equally crucial. The time for inflation from a vacuum state (10⁻²Pa) to 0.6MPa should be controlled within 60 seconds. An excessively long pressure build-up time will prolong the workpiece's residence time in the high-temperature zone, resulting in coarse grains. Meanwhile, the overshoot during pressure switching should be ≤5% to prevent sudden high pressure from causing deformation of the workpiece due to airflow impact. The pressure control system of Huarui gas quenching furnace adopts the PID adaptive algorithm, reducing the pressure establishment time to 45 seconds and keeping the overshoot within 3%, meeting the requirements of rapid response.
The core component of the pressure control system
The pressure control system of the gas quenching furnace consists of three parts: the detection unit, the control unit and the execution unit. Each unit works in coordination to form a closed-loop control system, ensuring the accuracy and stability of pressure regulation. The detection unit serves as the "perception center" for pressure control and is composed of high-precision vacuum gauges and pressure sensors. The vacuum gauge is used to monitor the low-pressure section (10⁻³-1Pa), and a capacitive film vacuum gauge is adopted, with a measurement accuracy of ±0.1% FS. The pressure sensor is used in the medium and high pressure section (0.1-1.0MPa), and a diffused silicon pressure sensor is selected. The measurement accuracy is ±0.25% FS, and the response time is ≤10ms. The arrangement of these sensors in the furnace follows the "three-point average" principle, that is, one detection point is set at the upper, middle and lower parts of the furnace respectively. The average pressure is calculated through a data fusion algorithm to avoid single-point measurement errors. The sensor calibration cycle of Huarui gas quenching furnace is every six months. The measurement accuracy is ensured through calibration with a standard pressure source. After calibration, the pressure measurement deviation of the equipment used by a certain aviation enterprise was reduced from 0.015MPa to 0.008MPa. The control unit is the "decision-making core" of pressure regulation, and it realizes logical operations and parameter output based on the PLC control system. Its core algorithm adopts segmented PID control: during the pressure rise stage (0-0.3MPa), PID parameters with a larger proportional coefficient are used to accelerate the pressure rise speed. Switch to a small proportional coefficient parameter at the stage of approaching the target pressure (0.3-0.6MPa) to reduce overshoot. Meanwhile, the system is equipped with an inbuilt pressure compensation algorithm that can automatically correct the pressure setting value based on the ambient temperature (5-40℃) and the type of gas (nitrogen, argon, helium). For instance, the compression coefficient of helium is different from that of nitrogen, resulting in varying actual cooling effects under the same pressure. The compensation algorithm can ensure consistent cooling effect by correcting the pressure value (for example, automatically adjusting from 0.5MPa to 0.48MPa). The actuator is responsible for the "physical actions" of pressure regulation, including vacuum valves, intake valves and exhaust valves. The vacuum valve adopts a pneumatic baffle valve with a leakage rate of ≤1×10⁻⁸Pa · m³/s, ensuring the stability of the vacuum state. The intake valve is a high-precision electric regulating valve, with a flow regulation range of 0-500m³/h and a control accuracy of ± 1%FS, enabling stepless regulation of gas flow. The exhaust valve is used for pressure relief. It adopts a combination of electromagnetic ball valves and throttle valves to achieve the dual functions of rapid pressure relief and fine-tuning pressure relief. The response time of the execution unit of Huarui gas quenching furnace is ≤50ms, ensuring that control instructions can be executed quickly. The usage data of a certain automotive parts enterprise shows that the time for the pressure to be unloaded from 0.6MPa to 0.1MPa can be precisely controlled within 15±1 seconds.
Key technological innovations in pressure control
The innovation of Huarui gas quenching furnace in pressure control technology is reflected in three dimensions: dynamic adjustment strategy, multi-gas adaptation and safety protection mechanism, which has solved the problems of slow response, low precision and poor adaptability existing in traditional pressure control. Dynamic segmented pressure control technology has achieved precise regulation throughout the full range. Pressure control is divided into four stages: vacuum preparation section (10⁻²Pa), low-pressure inflation section (0-0.2MPa), high-pressure stabilization section (0.2-0.6MPa), and pressure relief section (0.6-0 mpa). Each stage adopts independent control parameters. For instance, in the low-pressure inflation section, a "quick filling" strategy is adopted, with the valve opening maintained at 80% to shorten the pressurization time. In the high-pressure stable section, switch to the "fine regulation" strategy. The valve opening is fine-tuned in real time according to the pressure deviation (10%-30%), keeping the pressure fluctuation within ±0.005MPa. After a certain mold factory adopted this technology, the standard deviation of the quenching hardness of the Cr12MoV mold was reduced from 1.2HRC to 0.5HRC, and its stability was significantly improved. The multi-gas pressure adaptation technology has expanded the process range of the equipment. The densities and thermal conductivities of different gases (nitrogen, argon, helium) vary significantly, resulting in different cooling effects under the same pressure. The Huarui gas quenching furnace automatically corrects pressure parameters by establishing a gas characteristic database. For instance, the cooling efficiency of argon is 1.2 times that of nitrogen. When processing materials that require rapid cooling, the system will automatically reduce the pressure from 0.5MPa (nitrogen) to 0.4MPa (argon) to ensure a consistent cooling rate. For mixed gases (such as nitrogen + 20% helium), the system can dynamically adjust the pressure compensation coefficient according to the mixing ratio, ensuring that the pressure control accuracy is not affected by the gas components. Intelligent security protection technology has established a multi-layer protection system. When the pressure sensor detects overpressure (exceeding the set value by 10%), the system immediately opens the emergency exhaust valve, cuts off the heating power supply, and simultaneously issues an audible and visual alarm. If the pressure continuously rises to 0.8MPa (1.3 times the design pressure), the rupture disc will automatically break to relieve the pressure, preventing damage to the furnace body. The Huarui gas quenching furnace also features a redundant design for pressure sensors. When the main sensor fails, the backup sensor automatically switches to ensure that pressure control is not interrupted. A certain aviation enterprise once triggered the switching mechanism due to a main sensor failure, and the equipment completed subsequent pressure control without manual intervention, avoiding the scrapping of batches of workpieces.
The influence mechanism of pressure control on quenching quality
Pressure control indirectly alters the microstructure transformation and performance indicators of workpieces by influencing gas density, flow rate and heat exchange efficiency. Its influence mechanism is reflected in three aspects: cooling rate, stress distribution and surface quality, and performance optimization needs to be achieved through precise control. The influence of pressure on the cooling rate shows a nonlinear relationship. When the pressure rises from 0.1MPa to 0.5MPa, the cooling rate of nitrogen increases from 25 ° C /s to 60 ° C /s (an increase of 140%), but when the pressure exceeds 0.6MPa, the increase in cooling rate tends to be flat (from 0.6MPa to 0.7MPa, the cooling rate only increases by 5 ° C /s). This nonlinear characteristic requires that pressure control be precisely matched with material requirements. For instance, for high-speed steel, the pressure needs to be controlled at 0.5-0.6MPa to achieve sufficient cooling speed, without blindly pursuing higher pressure. The control system of Huarui gas quenching furnace is equipped with a built-in material-pressure matching model, which can automatically recommend pressure ranges to avoid energy waste. Pressure uniformity directly affects the stress distribution of the workpiece. Uneven pressure inside the furnace can lead to differences in cooling rates among various parts of the workpiece, generating thermal stress. For every 0.01MPa increase in pressure deviation, the stress difference may increase by 10MPa. For instance, when dealing with long shaft parts, if the pressure difference between the two ends reaches 0.03MPa, the bending deformation of the shaft may exceed 0.2mm/m. The Huarui gas quenching furnace optimizes the gas intake method (bottom annular gas intake + top central exhaust), creating a spiral upward gas flow inside the furnace. The pressure uniformity is improved to ±0.008MPa, and the deformation of shaft parts is controlled within 0.05mm/m. The influence of pressure fluctuations on surface quality cannot be ignored. Excessive pressure fluctuations can lead to unstable airflow, forming "airflow erosion marks" on the surface of the workpiece, which has a particularly significant impact on the surface roughness of precision parts. The Huarui gas quenching furnace, through a pressure fluctuation suppression algorithm, keeps the fluctuation range within ±0.003MPa. The surface roughness Ra of 316L stainless steel after treatment can be maintained below 0.8μm, meeting the requirements of medical equipment without subsequent polishing.
A typical case of pressure control process for materials
Due to the differences in chemical composition and hardenability, various materials have different requirements for pressure control. Huarui gas quenching furnaces have achieved precise regulation of material properties through customized pressure curves. The following typical cases demonstrate the practical application effects of pressure control technology. High-speed steel (W6Mo5Cr4V2) : The "segmented pressurization" pressure curve is adopted - from vacuum inflation to 0.3MPa (30 seconds), held for 5 seconds to ensure uniform gas distribution, then pressurized to 0.5MPa and maintained until the cooling is completed. This process stabilizes the cooling rate at 65℃/s, ensuring that the austenite is completely transformed into martensite. After treatment, the tool hardness reaches HRC63-65, and the red hardness (600℃×4h) is ≥HRC60. The cutting life is increased by 40% compared with the traditional process. The measurement accuracy of the pressure sensor of Huarui gas quenching furnace in the high-pressure section (0.5MPa) ensures the stability of the cooling rate and is the key to meeting the performance standards of the cutting tools. Die steel (Cr12MoV) : The "stepped pressure reduction" pressure curve is adopted - 0.6MPa (high-temperature section, rapidly passing through the pearlite zone) →0.3MPa (medium-temperature section, reducing stress) →0.1MPa (low-temperature section, slowly completing the transformation). The pressure holding time at each stage is determined based on the thickness of the workpiece (30 seconds per section for 20mm thickness). After treatment, the hardness of the die is HRC58-60, the impact toughness is ≥18J/cm², and the deformation is ≤0.1mm/m, meeting the assembly requirements of precision stamping dies. After a certain automotive mold factory adopted this process, the frequency of mold repair was reduced by 50%, and the production efficiency was significantly improved. Stainless steel (316L) : To prevent nitrogen embrittlement, argon gas is used as the cooling medium, with the pressure controlled at 0.2-0.3MPa and the cooling rate at 25-30℃/s. This pressure range can not only ensure the partial transformation of austenite to martensite (to obtain the appropriate hardness), but also prevent excessive nitrogen from penetrating. The hardness of the treated stainless steel parts is HRC38-42, and their salt spray resistance is ≥72 hours. They are suitable for medical devices and food equipment. The multi-gas matching technology of Huarui gas quenching furnace ensures that the pressure control accuracy of argon gas is consistent with that of nitrogen gas, providing a guarantee for the stable performance of stainless steel. Titanium alloy (TC4) : A low-pressure control strategy is adopted, with a pressure of 0.15-0.2MPa (argon gas) and a cooling rate of 10-15℃/s, to prevent grain coarsening caused by high pressure. The pressure curve remains gentle (fluctuation ≤0.005MPa) to ensure uniform transition of the α+β phase. The tensile strength of the treated titanium alloy is ≥950MPa, and the elongation is ≥12%, meeting the strength and plasticity requirements of aerospace components. Test data from a certain aviation enterprise shows that after adopting the pressure control process of Huarui gas quenching furnace, the fatigue life of titanium alloy parts has increased by 20%.
The development trend of pressure control technology
With the advancement of intelligent manufacturing technology, the pressure control technology of gas quenching furnaces is developing towards intelligence, self-adaptation and integration. The exploration of Huarui gas quenching furnaces in these fields provides technical references for the industry. Intelligent pressure prediction technology optimizes control parameters through machine learning algorithms. The system records the pressure curve, cooling rate and workpiece performance data of each furnace, and through deep learning, establishes a parameter-performance correlation model to automatically recommend pressure curves. For instance, when the system detects that the hardness of a certain batch of Cr12MoV molds is relatively low at a pressure of 0.6MPa, it will automatically fine-tune the pressure to 0.62MPa and record the adjustment effect. After 5 to 8 batches of iterative optimization, the consistency of product performance has been significantly improved. The intelligent control system of Huarui gas quenching furnace already has a basic self-learning function and will incorporate more industrial big data analysis technologies in the future. Adaptive pressure compensation technology enables precise control across all working conditions. Traditional pressure control is significantly affected by environmental temperature and fluctuations in gas source pressure (±5%-8%). Adaptive technology collects environmental parameters (temperature, gas source pressure) in real time and dynamically corrects the pressure setting value. For instance, when the ambient temperature rises from 20℃ to 35℃, the system automatically increases the target pressure from 0.5MPa to 0.52MPa to offset the reduction in cooling rate caused by the decrease in gas density. The initial application of Huarui gas quenching furnace shows that this technology can control the cooling rate deviation within ±3% under different environmental conditions, significantly enhancing the process stability. The pressure-temperature collaborative control technology enables multi-parameter linkage regulation. Combining pressure control with the temperature field control inside the furnace, when a local temperature is detected to be too high, the gas pressure in that area is automatically increased (through the zonal intake valve) to enhance the local cooling rate and achieve dynamic balance of the temperature field. This integrated control technology is particularly suitable for complex-shaped workpieces and can reduce performance defects caused by local overheating. Huarui gas quenching furnaces have attempted this technology in the processing of large molds, reducing the temperature difference between the mold cavity and the outer surface from ±5℃ to ±2℃, and further improving the uniformity of cooling. The pressure control technology of gas quenching furnaces is an interdisciplinary field that combines materials science, control engineering and fluid mechanics. Its development level directly reflects the technical grade of gas quenching furnaces.
Through continuous technological innovation, Taicang Huarui Vacuum Furnace Industry Co., Ltd. has improved the pressure control accuracy from ±0.02MPa to ±0.005MPa.
