Carburizing Furnace Cranes: Reliable Handling at 920°C

Gas and pack carburizing furnaces typically operate at 880–940°C with soak times of 6–12 hours. Workpieces still exceed 800°C when extracted for quenching. The core requirements for carburizing furnace cranes are high-temperature resistance and stable lifting. Recommended configuration: LH-type hoist bridge cranes (10–20 t) with asbestos fiber-core heat-resistant wire rope capable of withstanding short-term radiant heat of 300–500°C. All electrical components are housed in a separate, ventilated electrical cabinet positioned away from the furnace opening. Kelude carburizing furnace cranes come standard with high-temperature resistant hoisting limit switches (fluoroplastic housing) and heat-resistant cables (silicone rubber insulation), and are already in service at multiple specialized heat treatment plants. With a typical lifting frequency of 2–4 loads per day for batch and deep carburizing furnaces, durability is a key design driver.

Carburizing baskets typically measure 600×400×300 mm to 1000×800×500 mm with loads of 300–1,500 kg. LH-type cranes fitted with C-hook spreaders allow smooth furnace entry and exit. Recommended hoisting speeds: 5 m/min for main lifting and 0.5–2 m/min creep speed for precise basket positioning onto the furnace guide rails. Remote control is essential for furnace-front operation, allowing the operator to make fine adjustments from a safe distance beside the furnace door. Kelude offers an electrical interlock solution between the crane and furnace door — the crane cannot enter the furnace opening area until the door is fully open, providing dual-redundant safety. Variable frequency drives on the crane bridge are recommended for smooth deceleration and controlled stops, preventing basket sway and impact against furnace walls.

Nitriding Furnace Cranes: Slow, Steady, and Ammonia-Protected

Nitriding processes include gas nitriding (500–570°C) and plasma nitriding (400–560°C), with cycle times ranging from 20 to 80 hours. The unique environmental challenge in nitriding zones is ammonia decomposition gas, making corrosion-resistant design of crane electrical components essential. Recommended configuration: LH-type cranes (10–20 t) with hoisting speeds reduced to 0.5–3 m/min for slow, controlled lifting. Note: nitriding furnaces are well-sealed with heavy lids (500–2,000 kg), so the crane must be equipped with a swivel hook and a dedicated lid-lifting spreader. Kelude offers optional stainless steel hooks (grade 304) for nitriding zones, preventing corrosion from ammonia attack on standard galvanized hooks and eliminating the risk of rust contamination inside the furnace chamber. Electrical cabinets are sealed to IP54 or higher to protect contactor contacts from ammonia corrosion.

Nitriding furnace loading and unloading is characterized by high-frequency, small-batch operations — a single furnace may require multiple load/unload cycles per day. Variable frequency hoisting on LH-type cranes minimizes the impact of frequent start-stop cycles on both equipment and workpieces. Cooling of nitrided parts typically occurs either slowly inside the furnace or in a separate cooling station, so crane transfer efficiency between the cooling and nitriding stations directly affects production capacity. Kelude recommends sizing the crane travel range to cover the full work-cell radius in nitriding zones, ensuring continuous coverage of the triangular path from loading table to nitriding furnace to cooling station without secondary handling. For multiple furnaces in a row, a single large-span crane covering all furnace openings — or one crane shared by every two furnaces — is recommended.

Quenching Cranes: Fast Immersion and Reliable Braking

Quenching is the most demanding heat treatment process for crane performance. Workpieces must be transferred from the heating furnace into the quench medium (water, oil, or salt bath) within 15–30 seconds from furnace opening to quench tank. The QD-type double-girder bridge crane is the optimal choice, rated at 20–50 t. Core configuration: dual-speed hoisting with a high-speed range of 10–20 m/min and low-speed range of 2–5 m/min, dual-brake system (one service brake plus one safety brake), and brake slip distance ≤1 mm at 100% load (per ISO 4301, S ≤ v/100 mm). Kelude quenching cranes come standard with dual brakes and an emergency braking control circuit — even if the main brake fails, the auxiliary brake engages within 0.5 seconds.

Quenching demands precise crane control in three critical areas: ① rapid descent from the furnace opening to 100 mm above the quench liquid surface, then switching to creep speed; ② no brake slippage once the workpiece is submerged — the load must remain stable below the liquid surface; ③ fast lift-out after quenching is complete. Kelude's dedicated quenching control program enables one-touch operation: the operator presses the lower button, and the crane automatically executes the full sequence — high-speed descent, creep speed, immersion, hold, and lift-out — with automatic fallback to safe logic if manual intervention is required. The VFD must be equipped with a braking resistor and DC bus voltage monitoring to prevent overvoltage faults during emergency stops at full load. Wire rope safety factor: ≥9 for quenching duty.

Tempering Furnaces and Loading Stations: Throughput and Flexibility

Tempering is the final controlled-temperature heat treatment step, typically conducted at 150–650°C for 1–4 hours. Cranes in the tempering zone handle furnace loading/unloading of baskets and inter-process transfer. Recommended configuration: LD-type cranes (5–10 t) with hoisting speeds of 4–8 m/min and duty classification A5. Furnace opening temperatures of 100–200°C do not require special heat-resistant design. Cranes work in conjunction with tempering cars: baskets are transferred from the quenching zone to the tempering zone, then lifted into the furnace. Kelude recommends adding an auxiliary electric flat car in the tempering zone for bulk material transfer between quenching and tempering, reducing long-distance crane travel and multiple round trips. KBK workstation cranes (1–3 t) can also be installed in the tempering zone for rapid loading/unloading and inspection of small batches.

Loading stations (material handling areas) see the highest crane usage frequency in any heat treatment workshop. A KBK workstation crane (0.5–3 t) with chain hoist, working alongside an electric flat car, handles basket loading, unloading, and temporary storage across all process stations. The loading area can be divided into four independent KBK rail zones for carburizing, nitriding, quenching, and tempering. Kelude's loading station configuration improves basket turnover efficiency by approximately 35% and reduces floor space requirements by about 20%. For larger heat treatment workshops (monthly capacity above 500 t), a WMS material management system is recommended for the loading area: each basket carries an RFID tag, and the crane automatically scans and records process flow data during lifting, providing full traceability throughout the heat treatment cycle.

Heat Treatment Workshop Crane Configuration Comparison

Heat Treatment Crane FAQ: Safety & Design