Wuxi Wondery Industry Equipment Co., Ltd

I. Project Background and Equipment Specifications This case study involves the WDL-RG series elliptical resistance crucible furnace, available in 400 kg, 600 kg, and 800 kg capacity configurations. The equipment is designed for factory workshop environments with an ambient temperature of 0 to 60°C and relative humidity of 40% to 70%. The rated aluminum liquid temperature is 650 to 700°C. All three configurations achieve a full-load melting time of no more than 4 hours. Heating power increases with capacity: the 400 kg model is rated at 66 kW, the 600 kg model at 90 kW, and the 800 kg model at 105 kW; corresponding heating currents are 99 A, 135 A, and 158 A respectively. The input power supply is uniformly 380V AC, 50Hz, three-phase five-wire. The control cabinet measures 650×600×400 mm, with an S7-200smart PLC and touch screen as the main control system. Temperature measurement uses 2 channels with a range of 0 to 1300°C. Aluminum liquid temperature control accuracy during the holding stage is ±5°C. Protection mechanisms include leakage protection and over-temperature protection. II. Cascade PID Temperature Control Architecture The core feature of this equipment's temperature control is the adoption of a cascade PID control structure rather than single-loop PID. There are two temperature measurement channels in the system: one for furnace atmosphere temperature and one for aluminum liquid temperature. The cascade control action path is as follows: the outer loop uses aluminum liquid temperature as the main control parameter, and the inner loop uses atmosphere temperature as the auxiliary parameter. The setpoint of the inner loop is dynamically generated by the PID output of the outer loop. The engineering significance of this architecture lies in the fact that aluminum liquid temperature changes with relatively large lag, while atmosphere temperature responds faster. If the heating power were adjusted directly based on aluminum liquid temperature deviation, overshoot or sluggish response would be likely. With atmosphere temperature introduced as the inner loop, the system can respond quickly through the inner loop before the aluminum liquid temperature deviates significantly, ensuring both response speed and overshoot suppression. The PID control interface on the touch screen provides three independent input boxes for P, I, and D parameters, with a real-time temperature curve displayed at the top of the interface, supporting sliding of the time axis to view historical data within 0.5 hours. When parameters are adjusted, the temperature curve provides real-time feedback to help operators judge the adjustment effect. III. Three Process Modes Related to the Crucible The equipment has three preset working modes, switched via a drop-down menu on the touch screen. The design of all three modes revolves around thermal stress management of the graphite crucible. The sintering and solidification mode is a dedicated program for the first heating of a new crucible. This program is divided into 6 heating steps, with the starting setpoint rising progressively from 50°C to 800°C, and the corresponding heating rate decreasing progressively from 36°C/s to 6°C/s. The design logic of this decreasing heating rate is that faster heating can be tolerated in the low-temperature stage, while the rate must be reduced near the sintering temperature to avoid thermal stress cracking of the crucible caused by excessive temperature differential between the interior and exterior. The upper right corner of the interface verifies operating prerequisites in real time, with items that do not meet the standards warned in black font and items that pass marked in green font. The preheating mode is a secondary preheating program after the equipment completes the first sintering and solidification. Its running time is shorter than that of the sintering and solidification mode, but the temperature curve settings, condition verification rules, and temperature monitoring parameters are completely consistent with the sintering and solidification mode. This design enables the equipment to restore working temperature along a controlled heating path when restarted after shutdown, avoiding direct full-power startup from a cold furnace. The working mode is the standard state after the equipment enters normal production. When the furnace temperature reaches the preset operating threshold and the thermal field uniformity meets the requirements, the system confirms the state switch through audible and visual prompts. IV. Parameterized Requirements for Crucible Installation and Preheating The selection of the crucible base directly affects crucible life. The base shape should match the crucible bottom, with a size approximately 2 cm larger. Crucible bases of appropriate height should be selected for different types of crucible furnaces. Using discarded crucible bases will greatly shorten the crucible's service life. For installing a resistance furnace crucible, the crucible should be placed in the center of the furnace, with the bottom of the crucible higher than the bottom row of heating elements. Insulation cotton should be used to seal the area between the top of the crucible and the furnace rim. The parameter path for the first preheating of the crucible is as follows: without adding any material, preheat to approximately 200°C for 30 minutes, then dry for 4 hours. The purpose of this step is to evaporate moisture adsorbed on the crucible surface, preventing cracking during initial use. After preheating, the crucible should be heated to 800 to 900°C (about 2 hours) as soon as possible and held at that temperature for 1 hour, then raised or lowered to the working temperature. This rapid passage through the temperature range is designed to move the graphite crucible quickly through the oxidation-prone temperature band. After the first preheating, the crucible usually does not need to be preheated again unless the crucible becomes damp again. V. Thermal Stress Constraints in Charging and Operating Procedures The metal material must be dried before it is added. When adding materials, place them gently; do not throw or pour metal ingots into the crucible. Place the metal ingot vertically into the crucible, ensuring sufficient space between the ingot and the crucible wall for expansion. Do not place the ingot horizontally in the crucible, as the expansion of the ingot during heating may damage the crucible. You can first add some small pieces of metal into the crucible as a base for the larger ingot. During continuous smelting, some molten metal can be retained in the crucible to accelerate the melting process. However, large pieces of metal should be avoided incorporating into small amounts of solution, as this could cause the solution to cool rapidly or solidify, damaging the crucible. When adding liquid metal, avoid overfilling; generally, the crucible should not be filled to more than 80% capacity. Additives should only be added after the metal has completely dissolved. Additives should never be added to an empty crucible or to solid metal, nor should they be allowed to directly contact the crucible wall or outer rim. The prescribed dosage must be strictly followed, as excessive use of additives will significantly shorten the lifespan of the crucible. The size of the crucible tongs must match the size and shape of the crucible, and they must not squeeze the upper edge of the crucible. The crucible tongs should be clamped in the lower middle part of the crucible – if too high, the crucible may fall off or be damaged; if too low, it will be difficult to operate during pouring. When moving a hot crucible, it should be placed on a high-temperature resistant plate or transport tool. Do not place a hot crucible on a cool surface to avoid damaging the bottom of the crucible. When it is necessary to temporarily stop using the crucible for reasons such as removing slag or repairing the crucible furnace, the molten metal inside the crucible should be emptied. If the molten metal is left to solidify inside the crucible, it will burst due to expansion during the next heating. VI. Slag Removal Frequency and Crucible Corrosion Control During the smelting process, additives and impurities in the molten metal will form slag, which adheres to the crucible wall. Because the slag contains additive components, it will corrode the crucible wall, so the slag should be removed once a day. Specialized tools should be used to remove molten slag before it solidifies. Solidified slag will be difficult to remove. When removing slag, avoid scratching the crucible wall. When multiple layers of slag solidify and remain on the crucible wall, they will corrode the crucible, affect its thermal conductivity, and cause the crucible to crack during heating and expansion, thus shortening the crucible's service life. VII. Control System Interface and Data Recording The control cabinet panel is equipped with a three-color indicator light: red for Level 1 error alarm, yellow for Level 2 warning alarm, and green for automatic operation indication. The LED digital display shows the current ambient temperature during preheating and sintering modes, and the current aluminum liquid temperature during operating mode. The touch screen system features hierarchical user permissions, with different permission levels corresponding to different operating scopes. The main interface displays equipment status, heating system status (including power regulator contactor open/closed state and regulator readiness status), real-time three-phase current monitoring values, and the current and set values of atmosphere temperature and aluminum liquid temperature. The atmosphere temperature setpoint upper limit is 950°C, and the aluminum liquid temperature setpoint upper limit is 900°C. The energy consumption statistics interface records the cumulative electricity consumption since the equipment was put into use, as well as the daily electricity consumption of the last two weeks. The I/O monitoring interface displays the real-time action status of PLC input points. The alarm event interface sounds the buzzer immediately when a fault occurs; if the fault cannot be eliminated temporarily, clicking the mute button silences the buzzer, and a new fault will automatically unmute and sound again. After the fault is cleared, clicking the reset button clears the current alarm.

I. Project Background and Equipment Specifications This case study involves a fully automatic intelligent ion nitriding furnace, model WDL-IV-75A, employing a vertical single-bell-jar single-station structure. The equipment is capable of ion nitriding and soft ion nitriding of alloy steels, mold steels, and stainless steels. The effective working zone of the furnace body measures 600 mm in diameter and 800 mm in height, with a maximum loading capacity of 400 kg. The common operating temperature range is 500 to 600°C, with a maximum operating temperature not exceeding 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 evacuate 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, 75 represents the maximum average current of the pulse power supply at 75 amperes, and A represents the fully automatic intelligent type. II. Matching Relationship Between Large-Volume Chamber and Power Supply Capacity From the 30A model to the 75A model, the maximum average current of the pulse power supply increases by a factor of 1.5, while the effective chamber volume expands from approximately 28 liters to approximately 226 liters, a factor of about 8. This non-proportional change reveals a design principle of ion nitriding equipment: expansion of chamber volume does not require the power supply current to increase proportionally with volume, because the heating power for ion nitriding depends primarily on the workpiece surface area and the required current density, rather than the chamber spatial volume. The abnormal glow discharge current density range given in the proposal is 0.1 to 5 mA/cm². Based on this range, for a workpiece combination with a loading capacity of 400 kg and a relatively large surface area, the maximum average current of 75 A provides a clear design margin for the upper limit of supportable workpiece surface area. Meanwhile, the pulse power supply output voltage is continuously adjustable from 0 to 800 V with no sudden jump above 200 V, and the duty cycle is continuously adjustable within the range of 10% to 85%. III. Duty Cycle Adjustment Logic of the Pulse Power Supply Gas discharge, as a power source, presents a load with negative resistance characteristics. The workpiece, acting as the cathode, has its surface shape and stacking method both affecting the surface current density. Ion nitriding has a minimum threshold condition: to satisfy the current density required for uniform glow coverage, the heating power may exceed the power required to maintain workpiece temperature. This contradiction is particularly prominent for thin-walled, lightweight workpieces. After the pulse power supply introduces an adjustable duty cycle, the average heating power equals the peak voltage multiplied by current, then multiplied by the duty cycle. By reducing the duty cycle, the average heating power can be lowered while maintaining sufficient peak voltage to sustain glow coverage, thereby resolving the aforementioned contradiction. This mechanism is the core reason why this series of equipment can simultaneously process heavy workpieces and thin, lightweight workpieces. The implementation path for fast arc extinguishing is as follows: utilizing the principle of electromagnetic induction in the discharge circuit to rapidly detect the arcing signal, 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. IV. Thermal Insulation and Temperature Uniformity Design of the Large-Volume Furnace Body The bell cylinder adopts a water-cooled double-wall structure and multi-channel water cooling system to ensure furnace temperature uniformity. The inner insulating liner of the cylinder is made of stainless steel, while the inner and outer cylinder walls are made of high-quality carbon steel plates. The furnace body is equipped with two layers of 304 stainless steel heat shields, each layer 2 mm thick, and two layers of 304 stainless steel heat shields are also installed on the upper part of the furnace bottom plate. Compared with the six-layer heat shield configuration of the previous case, this model has fewer heat shield layers. This difference stems from the change in the ratio of chamber volume to surface area – a large-volume chamber has a relatively smaller heat dissipation area, and the heat loss proportion decreases accordingly, so the number of insulating layers can be appropriately reduced while ensuring long-term high-temperature operation. 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 carbon steel plate with a thickness of no less than 30 mm; the material tray fixture frame in contact with the workpiece is also made of high-quality carbon steel. The cathode connection device is designed as a rigid connection to avoid overheating problems caused by loose quick-connect couplings. The cathode structure includes cathode PTFE insulation, cathode insulating mica, cathode conductor connection socket, cathode connection fitting, and M10 stud bolt fixed connection cable lug. 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. Three observation windows are arranged on the outer circumference of the furnace shell for multi-directional observation of conditions inside the furnace. V. Vacuum System and Pressure Closed-Loop Control 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 pump set consists of one 2X-15 rotary vane pump, 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. The pressure closed-loop control principle 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 pressure control accuracy of ±1 Pa. 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. Vacuum measurement employs a ZJ-1C type capacitive diaphragm absolute pressure transmitter, with a range of 0 to 1000 Pa, output of 4 to 20 mA, and power supply of 15 to 30 VDC. This vacuum gauge is not affected by the type and composition of the measured medium, and the measured value is displayed by a digital display instrument and participates in furnace pressure control. VI. Gas Distribution and Cooling Water Systems The gas distribution system is used to control the introduction of process gas into the furnace. Gas sources include nitrogen, hydrogen, and other process gases, provided by the user. The gases pass through mass flow meters and are then introduced into the furnace body through a dedicated mixing tank according to the process formula. This model is equipped with two dedicated mass flow meters, controlling nitrogen and hydrogen flow separately – this is the main difference from the single flow meter configuration of the 30A model, corresponding to the higher requirements for atmosphere composition adjustment precision in a large-volume chamber. The mass flow meters are Japanese HORIBA S500 series units, 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. 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. 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. A backup water inlet valve is installed at the main water inlet pipe, connected to the user's tap water pipe, so that the furnace body can be cooled by tap water in the event of an unexpected power outage or water outage. VII. Three-Parameter Closed-Loop Architecture of the Control System The control system uses an FX3G series programmable logic controller and a Kunlun Tongtai TPC1231Ni touch screen as the main control center. The PLC has 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. In automatic operation mode, the system automatically starts the maintaining pump and pre-evacuation pump, opens the baffle valve and solenoid valve to extract a vacuum. Once the vacuum reaches the working pressure for glow discharge activation, the glow discharge voltage and resistance-assisted heating are automatically activated to perform the initial workpiece arcing and cleaning process. After arcing ends, the system automatically enters the heating stage, automatically adjusting flow rate, pressure, voltage, duty cycle, and current according to the process curve design steps. When the temperature reaches the process temperature, the system enters the temperature maintenance stage, maintaining according to the set process holding time. After the holding period, the system shuts down the vacuum pump and all valves on the extraction pipeline. Once the furnace temperature drops to the set temperature, all switches automatically turn off, and the system enters a stop state.

I. Project Background and Equipment Application Positioning This case study involves a cart-type degreasing and carbonization furnace, model RT3-360-5, a cycle-operated furnace with a chamber working dimension of 6,000 mm in length, 2,000 mm in width, and 2,000 mm in height. The equipment serves two purposes: first, degreasing metal cylinders and pipes of different diameters; second, burning off rubber insulation and lining inside cylinders and pipes of varying diameters in carbonization processes. The common feature of these two processes is that the workpieces contain organic or polymer materials inside that need to be removed, and the combustion products must be discharged promptly. The workpieces themselves are elongated cylindrical structures, imposing relatively high requirements on furnace temperature uniformity. The rated temperature of the equipment is 500°C, with adjustable operating temperature. II. Main Technical Parameters and Power Configuration The rated power of the equipment is 500 kW, adjustable within a percentage range; rated voltage 380V, three-phase 50Hz. The full-load heating rate is adjustable from 20 to 80°C per hour, and the empty furnace heating time does not exceed 90 minutes. Furnace temperature uniformity during the holding stage does not exceed ±5°C. The temperature control instrument is a Japanese Shimaden SRS13A with an accuracy of no more than ±1°C. The temperature control method combines a touch screen human-machine interface with the Shimaden intelligent instrument and a power regulator for PID voltage regulation control. The heating elements are 0Cr25Al5 high-resistance alloy resistance strips produced by Shougang Group, processed into a waveform structure using a special mold, and arranged on five surfaces: both sides of the furnace, the furnace door, the rear wall, and the furnace bottom. The number of temperature control zones is set at 4, with each zone independently equipped with an ammeter, voltmeter, and on/off indicator for ease of fault localization. The furnace body insulation material is standard aluminum silicate refractory fiber cotton with a thickness of 240 mm. The furnace air guiding mechanism material is 304 stainless steel with a thickness of 2 mm. The furnace bottom plate material is CrMnN cast steel with a thickness of 30 mm, in strip form. III. Lining Structure and Energy-Saving Logic The lining uses standard aluminosilicate refractory fiber blankets, specially processed into large plate structures with a density of 230 kg/m³, finally assembled into a lining with a thickness of 240 mm. The fiber cotton modules are anchored to the steel structure of the furnace body using SUS304 stainless steel round bar anchors. The weight of an all-fiber lining is approximately one-thirtieth that of a refractory brick furnace body. The direct consequence of this weight difference is a substantial reduction in steel structure load. The comparison reference given in the proposal is that, under the same specifications, the all-fiber structure saves approximately 30% more energy than a brick-based resistance furnace. This figure is an engineering empirical value; actual energy savings depend on operating conditions such as furnace sealing condition, heating curve, and loading rate. All-fiber refractory structures have good thermal shock resistance, can withstand rapid heating and cooling, and have a longer service life than brick structures. IV. Heating Device and Suspension Structure The heating elements adopt an advanced suspension structure with high radiation efficiency, enhancing heat exchange within the furnace, improving furnace thermal efficiency, and extending heating element life. The resistance strips are processed from 0Cr25Al5 into a waveform structure, convenient for installation and maintenance. V. Furnace Door Structure and Sealing Mechanism The furnace door adopts a steel frame structure with refractory fiber as the heat insulation material, installed in the same manner as the furnace body. The furnace door is equipped with a 2-ton electric lifting mechanism, with the electric hoist installed above the furnace door gantry frame. The door lifting speed is 8 m/min. The furnace door sealing employs a cam mechanism for automatic clamping combined with a soft-edge sealing device, ensuring the door automatically seals against the furnace body. The function of this sealing mechanism is to guarantee furnace sealing throughout production, prevent the escape of high-temperature furnace gases, improve the working environment, and also ensure furnace temperature uniformity and enhance energy efficiency. This sealing device is simple in structure, safe, reliable, and easy to maintain, having been verified over years in the production of all-fiber cotton cart-type furnaces. Regarding safety protection, both upper and lower travel of the furnace door are equipped with double safety limit mechanisms, along with an interlocking device with the furnace car. Heating power is automatically cut off the moment the furnace door opens. Limit switches are Omron brand. VI. Trolley and Traction Mechanism The trolley consists of a frame, trolley furnace lining, furnace bottom plate, and trolley traction mechanism. The frame is welded from channel steel, with 10 mm side plates and 5 mm bottom plates (Q235), firmly and reliably constructed, not easily deformed or warped. The bottom insulation layer of the trolley furnace base consists of two layers of alternating diatomaceous earth bricks and lightweight straight bricks, while the refractory layer is constructed using heavy bricks. The trolley perimeter uses irregularly shaped bricks to prevent furnace gas from directly contacting the trolley side plates. The refractory layer on the trolley is constructed in a groove shape for placing heating elements, which also serves as a support for the furnace bottom plate. The furnace bottom plate is made of CrMnN cast steel with a total thickness of 30 mm, resting above the groove where heating elements are placed to prevent oxides from falling onto the heating elements after the workpiece is heated. The furnace bottom plate is equipped with a snap-fit design to prevent movement. The rear of the trolley is equipped with RT0 moving and stationary contacts for power connection, completing the power supply to the heating elements on the trolley. This contact method has a large and sufficient contact surface, good contact, and no electric sparks or overheating after long-term use. The traction device uses a frame structure for load-bearing and movement. The frame is mainly welded from 16 channel steel and steel plate. The wheels are forged from 45# steel with strong wear resistance. The drive is a motor plus a reducer, with an entry/exit speed of 6 to 8 m/min, driven by one motor. Both furnace entry and exit are equipped with double safety limit mechanisms and interlocking mechanisms – if the trolley does not reach the correct position, the furnace door cannot be opened or closed, and the entire furnace body cannot be powered. Synchronous geared motors make the trolley entry and exit flexible, stable, and accurately positioned. VII. Hot Air Circulation System To achieve uniform furnace temperature, 4 centrifugal circulating fans are installed at the top of the furnace along its length, each rated at 7.5 kW, 4-stage motors. The fan blades and shaft are made of 304 stainless steel. The fan is a one-piece design, with the motor rotor and fan shaft as a single unit, providing stable speed, low noise, and strong airflow. The furnace air guiding mechanism is made of heat-resistant SUS304 steel plate, with convection walls on both sides. Considering that the workpieces are plate-shaped or cylindrical, the hot air circulation direction is designed as horizontal – air flows horizontally from one side of the convection wall to the other, that is, air passes through the middle of each layer of workpieces. This airflow path ensures even heating and uniform temperature of the workpieces, further improving product performance.