Wuxi Wondery Industry Equipment Co., Ltd

I. Project Background and Equipment Specifications This case study involves a fully automatic intelligent ion nitriding furnace, model WDL-IV-30A, employing a vertical single-bell-jar single-station structure. The equipment is capable of ion nitriding and soft ion nitriding of titanium alloys, alloy steels, mold steels, and stainless steels. The effective working zone of the furnace body measures 300 mm in diameter and 400 mm in height, with a maximum loading capacity of 100 kg. The common operating temperature range is 500 to 600°C, with a maximum operating temperature of 650°C. The ultimate vacuum degree is no greater than 6.7 Pa, the pressure rise rate is no greater than 5 Pa/h, and the time required to pump from atmospheric pressure to ultimate vacuum does not exceed 30 minutes. The furnace shell surface temperature rise does not exceed 55°C. In the model designation, IV represents the fourth-generation digital control system, 30 represents the maximum average current of the pulse power supply at 30 amperes, and A represents the fully automatic intelligent type. II. Physical Constraints of the Ion Nitriding Process Ion nitriding is conducted in a low-pressure gas discharge environment, and its volt-ampere characteristic curve is non-linear. Ion nitriding of metallic materials generally operates in the "abnormal discharge" segment of the volt-ampere characteristic curve, and the upper limit point G of this segment is a dangerous inflection point. Gas discharge, as a power source, presents a load with negative resistance characteristics. The workpiece, acting as the cathode, has its surface shape and surrounding environment (workpiece stacking) both affecting the surface current density. These physical characteristics determine that the ion power supply must overcome three technical difficulties. The first is arc discharge: when the workpiece surface is not clean, a non-conductive oil film can easily form. When charge accumulates on the surface to a certain extent, it breaks down and forms a momentary high-current discharge, producing high-energy sparks. If not cut off quickly, this will cause power failure and workpiece damage. The second is the hollow cathode effect: when workpieces have holes or slots, gaps between workpieces, or uneven bends, a critical state of glow discharge overlap occurs at certain gas pressures. This manifests as uneven glow discharge brightness across the workpiece surface, corresponding to uneven surface current density, causing uneven temperature distribution. The third is the coupling relationship between current density and gas pressure: gas pressure affects glow thickness, which in turn affects current density – higher pressure produces a thinner glow, beneficial for temperature uniformity; however, when pressure is high enough to uniformly cover all groove and hole surfaces, the current will greatly exceed the power required for workpiece insulation. III. Technical Response Logic of the Pulse Power Supply The pulse power supply configured for this equipment has an output frequency of 20,000 Hz, a square wave output waveform, an output voltage continuously adjustable from 0 to 900 V with no sudden jump above 200 V, a duty cycle continuously adjustable within the range of 10% to 85%, a maximum pulse output average current of 30 A, and an arc extinguishing time of no more than 2 μs. The duty cycle is defined as the ratio of on-time to pulse period. The average heating power equals the peak voltage multiplied by current, then multiplied by the duty cycle. The introduction of an adjustable duty cycle in the pulse power supply effectively resolves the contradiction between the average heating power and the threshold conditions required for workpiece processing – the essence of this contradiction being that, to satisfy the current density required for uniform glow coverage, the heating power may exceed the power required to maintain workpiece temperature, and duty cycle adjustment allows these two to be decoupled. Fast arc extinguishing is achieved by utilizing the principle of electromagnetic induction in the discharge circuit to rapidly detect the arcing signal (with almost no delay), then immediately controlling the high-speed electronic switch of the main current circuit through high-speed digital logic devices, extinguishing the arc within 2 μs. The application of the pulse power supply also yields several process effects: the absolute off-time of the pulse is relatively short, and after power is turned off, the concentration of charged particles does not immediately drop to zero but decreases slowly. Before it has decreased significantly, the next pulse arrives, resulting in a higher average electron concentration and increased ionization rate; the hollow cathode effect is effectively suppressed; and because the pulse power supply widens the adjustment range of nitriding process parameters, with each parameter independently adjustable, it can improve the uniformity of glow coverage on workpieces with complex surface shapes, thereby enhancing infiltration layer quality and surface smoothness. IV. Three-Parameter Closed-Loop Control System The control system uses a programmable logic controller and touch screen as the main control center. The PLC is an FX3G series unit with a program memory capacity of 32K steps, a basic instruction processing speed of 0.21 μs, and two high-speed communication interfaces (RS422 and USB). The touch screen is a 12-inch TFT LCD with a resolution of 1920×1080, four-wire resistive touch, a main frequency of 1 GHz, and pre-installed McgsPro configuration software. The system adopts a multi-task centralized management and distributed control fully digital architecture, capable of simultaneously achieving closed-loop control of three key parameters in ion nitriding: temperature control accuracy of ±1°C, pressure control accuracy of ±1 Pa, and flow control accuracy of ±0.5%. Temperature control employs Japanese Shimaden SRS13 series digital controllers with PID regulation, forming a temperature closed-loop regulation system with the temperature control circuit and thermocouple. Pressure control also employs Shimaden SRS13 digital controllers, forming a pressure closed-loop regulation system with a frequency converter and pressure sensor. Flow control is configured with one dedicated mass flow meter to control gas flow. The pressure closed-loop implementation path is as follows: the pressure transmitter measures furnace pressure and outputs a standard current signal to the digital controller. The controller performs PID calculations based on the set pressure value and real-time sampled values, then outputs a standard current signal to the frequency converter. By adjusting the vacuum pump motor speed, the pumping speed is adjusted, thereby keeping the furnace pressure constant at the process set value. This control method achieves a precision of ±1 Pa, while the combined use of the vacuum pump and frequency converter greatly reduces mechanical wear of the pump body during startup, and long-term low-speed operation can significantly extend service life. Flow control employs Japanese HORIBA S500 series mass flow meters, with a response time of less than 0.3 ±2% seconds from fully closed state to reaching the setpoint when control begins and when the setpoint is changed during control. The control range covers 1 to 100% full scale, operating from a single universal DC24V power supply, with the internal power circuit isolated from input and output circuits. V. Furnace Body System Structural Features The furnace body adopts a vertical bell-jar structure, consisting of two parts: the bell and the base. The bell cylinder adopts a water-cooled double-wall structure and multi-channel water cooling system to ensure furnace temperature uniformity. Six layers of 310S stainless steel heat shields are installed inside the cylinder, and two layers of stainless steel heat shields are installed on the upper part of the furnace base, enabling long-term high-temperature operation and significant energy savings. A layer of aluminum silicate insulation cotton with a thickness of 20 mm is added inside the insulation layer near the furnace wall. The cathode plate is supported on the furnace base by three sets of high-quality cast mica, with adjustable height. The cathode plate is made of 310S stainless steel plate with a thickness of no less than 30 mm; the material tray fixture frame that contacts the workpiece is also made of 310S stainless steel. The cathode connection device is designed as a rigid connection to avoid overheating problems caused by loose quick-connect couplings. Two thermocouples are introduced from the furnace bottom plate and positioned in the middle of the cathode plate to simulate the temperature measuring head. One is used for temperature control by the ion heating pulse power supply, and the other is connected to the alarm instrument for multi-directional temperature monitoring. The base center has a vacuum extraction port and a cathode inlet, connected by flanges, thick-walled stainless steel pipe, and stainless steel bellows, with sealing provided by high-temperature-resistant fluororubber sealing rings. VI. Vacuum and Gas Systems The vacuum system is used for pre-vacuuming of the furnace body and for atmosphere replacement and exhaust gas discharge during the nitriding process. The system is equipped with one 2X15 rotary vane pump as the vacuum unit. The pump set includes one electromagnetic vacuum pump with an inflation valve and one high-vacuum butterfly valve. The rotary vane pump is a Guangdong Xunda 2X series unit, resistant to process gas corrosion, controlled by a frequency converter, and equipped with a GI-50 high-vacuum butterfly valve as the main control valve. Vacuum measurement employs a ZJ-1C type capacitive diaphragm absolute pressure transmitter. This vacuum gauge is not affected by the type and composition of the measured medium, providing accurate and reliable measurement, with the measured value displayed by a digital display instrument and participating in furnace pressure control. The gas distribution system is used to control the introduction of process gas into the furnace, consisting of a gas source, flow meter, and corresponding pipelines. Process gases (such as ammonia) are provided by the user, passing through a mass flow meter and then introduced into the furnace body through a dedicated mixing tank according to the process formula. Gas pipelines are made of stainless steel, with each gas line equipped with a pressure reducing valve, manual shut-off valve, filter, pressure gauge, and solenoid valve. VII. Cooling Water System The cooling water system adopts a circulating cooling method, with the water source provided by the cooling tower and water pump (buyer's responsibility). Cooling water requirements: inlet water temperature not exceeding 31°C, inlet water pressure of 0.15 to 0.25 MPa, and total flow rate of 20 m³/h. Each cooling water branch is equipped with separate inlet and outlet valves for individual flow adjustment. All cooling water pipes, valves, and fittings attached to the equipment are made of stainless steel. An electrical contact pressure gauge is installed on the main inlet pipe for alarms in case of abnormal inlet pressure, and the control system will take corresponding protective actions. A backup water inlet valve is installed at the main water inlet pipe, connected to the user's tap water pipe – in the event of an unexpected power outage or water outage, the furnace body can be cooled by tap water. VIII. Safety Interlock and Alarm Logic The system has alarm functions for over-temperature, over-pressure, thermocouple damage, water shortage, and phase loss, with both audible and visual alarms and control interface alarms, taking corresponding protective actions such as prohibiting power-on, prohibiting heating, cutting off or resuming heating according to specific problems. The control system can realize self-diagnosis of equipment faults, prompting users to check and repair the corresponding fault points. When a fault occurs, the system automatically shuts off all valves. The vacuum system has sequential start and stop functions, equipped with a complete interlocking and mutual interlocking mechanism, with all valves being power-off shut-off type.

I. Project Background and Equipment Application Positioning This case study involves a ladle heating station used for preheating ladle linings after repair and before receiving molten metal. The core function of the equipment is to provide smooth and controllable heating of the lining prior to casting, in order to stabilize the casting temperature regime, reduce metal loss, and ensure process repeatability. The operating environment is an industrial workshop, requiring stable operation across multiple heating cycles. The station is designed to accommodate a conical ladle with a 1-ton molten steel capacity. The ladle has an internal top diameter of 500 mm, internal bottom diameter of 410 mm, and depth of 900 mm; the external top diameter is 770 mm, and the overall height is 1,050 mm. These dimensions establish the geometric boundary conditions for heating element arrangement and station structural design – the conical inner cavity means the radial spacing of heating elements varies along the height direction, precluding the conventional arrangement used for equal-diameter cylindrical furnace chambers. II. Heating System Technical Parameter Requirements The equipment requires electric heating with a total installed power of no less than 30 kW. Heating elements are resistance type, required to withstand high-temperature long-term operation and cyclic thermal loading. The maximum heating temperature must be no less than 800°C, and the heating element temperature must exceed the lining working temperature to ensure sufficient heat transfer intensity without localized overheating. There are inherent constraints among these parameters: an 800°C lining target temperature means the heating element surface temperature must be maintained at a higher level to establish an effective radiative heat transfer differential. If the element surface load is set too high, heat transfer intensity increases but element life under cyclic thermal loading is shortened; if set too low, heating time is extended. Therefore, element material selection and surface load design constitute the core technical trade-off of this project. III. Temperature Uniformity and Control Accuracy Requirements The technical requirements specify two temperature indicators: system temperature stability control accuracy of at least ±10°C, and internal ladle temperature differential not exceeding 50°C. Uniform heating of the ladle inner surface is required along the full height, meaning the type and arrangement position of heating elements must be specifically selected in conjunction with the conical ladle geometry to minimize temperature gradients. The design challenge presented by the conical structure is that the lower section has a smaller diameter while the upper section has a larger diameter. If vertically suspended straight rod elements were used, the spacing between the lower section and the lining would be greater than at the upper section, resulting in insufficient radiative heat transfer intensity at the bottom. Therefore, elements may require segmented arrangement or non-standard geometry to compensate for this geometric difference. The control system must be capable of operating automatically according to a given heating curve, and also allow manual control of main parameters. Temperature control is achieved through real-time thermocouple monitoring, with real-time parameters displayed on the operation panel. Lining heating must be smooth and controllable, eliminating abrupt temperature changes – this requirement points to a heating rate limitation function, meaning the control system requires slope control capability rather than simple on-off temperature regulation. IV. Structural and Safety Design Requirements The heating unit must be insertable into the ladle interior and lockable in the working position. Heating elements must have protective structures to prevent mechanical damage and contact with the lining, such as heat-resistant steel protective mesh or protective sleeves. This requirement stems from actual operating conditions: during ladle lifting and positioning, positional deviation exists, and without protection, elements could be damaged by collision with the lining or ladle wall. Cable routing and connection points must be constructed from high-temperature-resistant materials suitable for high-temperature operation. The equipment structure must facilitate maintenance, allowing heating element replacement without complete disassembly – an important availability indicator, since heating elements are periodic consumables and replacement convenience directly affects equipment downtime. Safety requirements include short circuit, overload, and leakage protection devices, as well as emergency stop, over-temperature protection, and abnormal condition interlock protection functions. Hazardous areas must have structural guards to prevent accidental personnel entry. The equipment must be grounded per code, with no accessible live parts under normal operating conditions. Protection scope covers three risk categories: electric current injury, high-temperature injury, and injury from moving and rotating equipment parts. V. Environmental Adaptability and Power Supply Conditions The equipment is powered by AC 380V, 50Hz. The operating environment temperature range is +5°C to +40°C. The equipment structure must be resistant to dust, vibration, and other factors typical of metallurgical production conditions. This environmental requirement imposes constraints on the protection rating and cooling method of the electrical control cabinet – the dust and vibration environment of a metallurgical workshop is unsuitable for conventional open cooling structures. VI. Scope of Supply and Documentation Requirements The scope of supply includes the complete heating station, comprising heating elements, control cabinet, temperature measurement system, and connecting cables. Supply completeness must ensure the equipment can be directly commissioned without additional procurement of major components. Technical documentation includes operation manual, electrical schematic diagrams, general assembly drawings, and installation instructions, sufficient to ensure safe operation and maintenance of the equipment. VII. Service Life and Technical Support Requirements The warranty period is no less than 12 months from the date of commissioning. During the warranty period, faults and defects attributable to the manufacturer shall be rectified by the supplier. Under compliant operating conditions, equipment service life is no less than 5 years. The equipment must reach the set heating temperature within a reasonable process time agreed with the customer, and ensure parameter stability across multiple heating cycles for repeatable process operation. The control system must have high reliability and resistance to industrial interference. Technical support scope includes operational technical consultation, melting mode setup recommendations, and technical assistance under emergency conditions

I. Project Background and Equipment Specifications This case study involves a vertical aluminum alloy rapid quenching furnace with an effective work zone of 1200×1200×1100 mm (diameter × height). It is a cycle-operated resistance heating furnace primarily used for solution treatment and rapid quenching of aluminum alloy castings and plates. The equipment has a rated power of 135 kW, rated voltage of 380V three-phase 50Hz, and a rated temperature of 650°C with adjustable operating temperature. The structural positioning of this equipment differs from conventional box-type quenching furnaces: workpieces are suspended within the furnace, and the quenching tank is located directly below the furnace body. After the furnace door opens, the workpiece can fall directly into the water – this vertical layout is the physical basis for achieving rapid transfer. II. Temperature Control and Zoning Design The temperature control system employs a two-tier architecture. The upper tier is a 10-inch touch screen responsible for centralized setting, control, monitoring, recording, and storage of heat treatment process curves. The lower tier uses Eurotherm 3504 industrial PID temperature controllers with a control accuracy of ±1°C and furnace temperature uniformity of within ±3°C during the holding stage. The heating zones are configured as 2 zones connected in star configuration. Each zone is equipped with an over-temperature alarm device, program completion indication, audible and visual over-temperature alarm, and automatic current cut-off. The temperature controller features an online self-tuning function that calculates optimal PID parameters based on the actual thermal characteristics of the furnace, balancing heating rate against overshoot. III. Furnace Lining and Heating Element Configuration The furnace lining uses standard refractory fiber cotton, with both walls and roof constructed as all-fiber structures with a total insulation thickness of no less than 240 mm. The fiber folded blocks undergo secondary pre-compression before installation, reaching a compressed density of no less than 230 kg/m³, and are secured to the furnace roof shell with stainless steel round bars. This structure offers low thermal conductivity, low heat capacity, good thermal stability, and thermal shock resistance. Fixing components are stamped from 1Cr18Ni9Ti stainless steel sheet. The heating elements are 0Cr25Al5 alloy resistance strips, pressed with dedicated molds to avoid processing damage. The resistance strips are fixed with special ceramic screws, allowing convenient and rapid maintenance and replacement. During installation, ceramic washers are placed between the fiber wall and the resistance strip to prevent direct contact between the fiber surface and the strip, thereby enhancing heat dissipation from the strip. Both ceramic screws and washers are made of high-alumina material and sintered at high temperatures to ensure sufficient strength and service life. The resistance strips are suspended around the furnace chamber, facilitating heat dissipation and airflow circulation. The heating elements use a star connection, with surface load controlled below 1.6 W/cm² – a value below the conventional design limit for resistance strips, intended to extend element service life under frequent heating and cooling cycles. IV. Hot Air Circulation and Air Guiding System A high-temperature-resistant circulating fan rated at 7.5 kW is installed on the furnace roof. The fan material is designed to withstand prolonged high temperatures without deformation, with air-cooled bearings to accommodate the high-temperature roof environment. The air guiding hood maximizes the longitudinal component of the centrifugal force generated by the fan, pressing hot air downward. The air then bypasses the workpiece and is drawn back into the fan intake from the bottom, forming a closed circulation loop. This airflow path ensures temperature field uniformity within the furnace chamber and is a supporting design for the suspension loading method – workpieces have no obstruction around them, allowing airflow to pass through. V. Material Basket Lifting and Furnace Door Interlock Mechanism The material basket lifting mechanism consists of an electric winch, ring lifting chain, and pulley blocks. The winch is a dual-speed electrically controlled unit with a rope speed of up to 18 meters per minute, meeting the requirement for rapid descent into water; the ascent phase uses slow speed to reduce inertial impact when the workpiece and basket enter the furnace. The winch features inching control and a self-locking device, allowing it to stop at any position. Considering the high-temperature furnace environment, a 16Mn ring chain is used. The pulley system is installed on the upper part of the furnace body, consisting of 4 pulleys and 4 sets of bearings, ensuring smooth basket lifting and lowering. The furnace door is located at the bottom of the furnace body and moves laterally, with guide rails on the side to maintain horizontal movement. Door opening and closing is driven by a cylinder. When closing, the cylinder pushes the door to the closed position and continues to apply pressure, lifting the door upward via a lever mechanism on the side to press it tightly against the furnace body. The lifting mechanism and furnace door mechanism are interlocked: the lifting mechanism can only be powered and operated after the furnace door is fully open (at which point the heating element power has been cut off). This interlock logic prevents equipment damage from misoperation when the door is not open. VI. Quenching Transfer Time and Quenching Tank The quenching transfer time is defined as the time from furnace door opening to full immersion of the workpiece in water, with a design requirement of no more than 10 seconds. This parameter is critical to the aluminum alloy solution treatment process – the shorter the transfer time, the higher the cooling rate through the quench-sensitive range, and the better the aging strengthening effect. The quenching tank is of mobile construction, driven by a 2.2 kW motor. Two 3 kW circulation pumps are installed in the tank to continuously agitate the water during quenching, maintaining uniform water temperature and accelerating heat transfer from the workpiece surface. The tank is welded from 5 mm thick steel plate and tested for leak-tightness. The mobile cart is welded from 12# channel steel, with the front section serving as the material frame worktable area and the rear section as the water tank, with three sets of wheels (one set being drive wheels). VII. Process Action Sequence The complete equipment action sequence is as follows: manual loading → quenching cart moves to below the furnace body → furnace door opens → material frame lifting mechanism descends → manual hooking → material frame rises → furnace door closes → heating and holding according to process time → solution treatment ends → stirring water pump starts → furnace door opens → material frame descends → material frame rapidly enters water for quenching → material frame rises → quenching cart exits → material frame descends → manual unhooking followed by return to furnace opening → furnace door closes → manual unloading → next cycle begins.