Classification and Application of Trolley Furnaces

1. Classification of Trolley Furnaces

1.1 Classification by Heating Method

• Electric Resistance Trolley Furnaces: These furnaces use electric resistance heating elements (usually made of high-quality materials like Kanthal or Nichrome) to generate heat, which is then transferred to the workpiece through radiation and convection. They feature precise temperature control, uniform heating, and clean operation without exhaust gas emissions, making them suitable for scenarios requiring high heating accuracy. The heating elements are arranged on the furnace walls, door, and trolley to ensure consistent temperature distribution throughout the chamber. They are widely used in the heat treatment of metals, ceramics, and glass, especially for processes like annealing, tempering, and stress relieving of small to medium-sized heavy workpieces.

• Fuel-Fired Trolley Furnaces: These furnaces use fossil fuels such as natural gas, diesel, or coal as energy sources, with combustion chambers generating high temperatures to heat the workpiece. They are further divided into gas-fired and oil-fired trolley furnaces. Compared with electric resistance types, fuel-fired trolley furnaces have higher heating efficiency and lower operating costs, making them suitable for large-scale heating of heavy workpieces such as steel ingots, billets, and large castings. Some advanced models are equipped with regenerative burners that reuse waste heat from exhaust gases to improve energy efficiency and reduce emissions.

• Induction Trolley Furnaces: A specialized type that uses electromagnetic induction to heat metals directly, without heating the furnace chamber first. This results in rapid heating, high energy efficiency, and precise temperature control, making them ideal for the foundry industry for melting and casting metals, as well as for heat treatment of high-demand metal components.

1.2 Classification by Working Atmosphere

• Atmosphere Trolley Furnaces: These furnaces are filled with a specific protective atmosphere (such as nitrogen, argon, or hydrogen) to prevent oxidation, decarburization, or carburization of the workpiece during heat treatment. They are widely used in the heat treatment of high-precision components in industries such as aerospace, automotive, and medical devices. For example, bright annealing furnaces, a type of atmosphere trolley furnace, use inert gases to maintain a clean, bright surface of the workpiece without scale formation.

• Vacuum Trolley Furnaces: These furnaces operate in a high-vacuum environment, which effectively avoids oxidation and chemical reactions between the workpiece and air. They are suitable for heat treatment of high-value, high-precision components such as titanium alloys, superalloys, and semiconductor materials, as well as for processes like vacuum brazing and vacuum annealing.

• Ordinary Air Trolley Furnaces: These furnaces operate in a normal air atmosphere, with a simple structure and low cost. They are mainly used for general heating processes where the workpiece surface quality requirements are not high, such as pre-forging heating of steel ingots and annealing of ordinary castings.

1.3 Classification by Temperature Range

• Low-Temperature Trolley Furnaces: With a maximum temperature of 600°C, they are mainly used for low-temperature processes such as stress relieving, aging treatment, and drying of workpieces. Common applications include the heat treatment of welded structures and the drying of non-metallic materials.

• Medium-Temperature Trolley Furnaces: Operating at 600°C to 1000°C, they are the most widely used type, suitable for processes like annealing, normalizing, and tempering of most metals (such as carbon steel, alloy steel, and cast iron). They are widely used in machinery manufacturing, metallurgy, and other industries.

• High-Temperature Trolley Furnaces: With a maximum temperature exceeding 1000°C (some up to 1700°C), they are used for high-temperature processes such as sintering of ceramics and refractory materials, high-temperature annealing of superalloys, and melting of special metals. They feature high-quality insulation materials to reduce heat loss and ensure stable high-temperature operation.

1.4 Other Special Classifications

2. Applications of Trolley Furnaces

2.1 Metallurgical Industry

• Heating of steel ingots and billets: Fuel-fired or high-temperature electric trolley furnaces are used to heat steel ingots, billets, and steel plates to the required temperature for forging or rolling processes. The large load-bearing capacity of the trolley allows for the handling of heavy steel ingots weighing tens of tons.

• Heat treatment of castings and forgings: Medium-temperature trolley furnaces are used for annealing, normalizing, and tempering of castings and forgings to eliminate internal stresses, refine grains, and improve mechanical properties. For example, large steel castings such as turbine casings and rolling mill frames undergo annealing in trolley furnaces to avoid cracking during subsequent processing.

• Uniformization of special alloys: High-temperature trolley furnaces are used for uniformization treatment of titanium alloy and superalloy ingots, heating them to high temperatures and holding them for a long time to eliminate component segregation and ensure uniform performance of the material after subsequent processing.

2.2 Machinery Manufacturing Industry

• Heat treatment of large components: Large mechanical parts such as machine tool beds, large gears, and generator spindles (weighing up to several tons) are heat-treated in trolley furnaces. Processes such as quenching and tempering (modulation treatment) are used to obtain excellent comprehensive mechanical properties, including high strength and toughness.

• Stress relief of welded parts: Large welded structures such as engineering machinery booms and mine machinery bucket frames have concentrated internal stresses after welding. Trolley furnaces are used for stress relief annealing, heating the workpiece to 500-650°C and cooling slowly to release internal stresses and prevent cracking of welded parts.

• Heat treatment of molds and tools: Large molds (such as automobile panel molds and household appliance shell molds) are annealed and preheated in trolley furnaces to reduce hardness, eliminate internal stresses, and facilitate subsequent precision processing. Some large cold-work molds also undergo quenching heating in trolley furnaces to improve surface hardness and wear resistance.

2.3 Aerospace and Automotive Industries

• Aerospace industry: Vacuum or atmosphere trolley furnaces are used for heat treatment of high-precision components such as aircraft engine parts, aerospace fasteners, and titanium alloy structural parts. The vacuum or protective atmosphere ensures that the components do not oxidize during heat treatment, maintaining their high precision and mechanical properties.

• Automotive and rail transit industry: Trolley furnaces are used for heat treatment of large automotive and rail transit components. For example, the frame longitudinal beams and axle housings of heavy trucks undergo annealing to eliminate processing stresses, ensuring structural stability during operation. High-speed rail bogie beams and subway wheel hubs are normalized or modulated in trolley furnaces to meet the strength and fatigue resistance requirements of high-speed operation.

2.4 Other Industrial Fields

• Ceramics and refractory materials industry: High-temperature trolley furnaces are used for sintering large ceramic components (such as refractory bricks and ceramic filter tubes) and batch ceramic products. The stable high-temperature environment and uniform heating ensure the sintering quality of the products, avoiding defects caused by uneven heating.

• Chemical industry: Some special chemical materials require a controlled high-temperature environment for synthesis or decomposition reactions, which can be provided by trolley furnaces with precise temperature control and good sealing performance.

• Metal powder metallurgy: Large powder metallurgy structural parts (such as large gear rings) are sintered in atmosphere trolley furnaces, which are filled with inert gases to avoid oxidation during sintering and ensure the density of the products.

3. Conclusion