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.