What is the principle behind a bogie-type annealing furnace?

Car-bottom annealing furnaces (also known as trolley annealing furnaces or car furnaces) are equipment used for the heat treatment of metallic materials, particularly steel. Their primary function is to alter the physical and chemical properties of metals through heating and holding processes, thereby enhancing their performance. This process is commonly referred to as annealing. The annealing furnace manufacturer details the working principle and main components of car-bottom annealing furnaces below:

1. Working Principle

1.1 Fundamental Principles of Annealing

Annealing constitutes a heat treatment process involving heating metal to a specific temperature, maintaining it for a defined duration, followed by gradual cooling. Its primary objectives are:

Improving mechanical properties: By eliminating internal stresses, reducing material hardness, and increasing ductility and toughness.

Relieving internal stresses: Residual stresses within the metal are released during annealing, thereby enhancing machinability.

Refining grain size: Heating and controlled cooling rates promote grain refinement within the metal, thereby enhancing its mechanical properties.

1.2 Heating and Cooling

Heating: Cart-type annealing furnaces utilise fuel combustion or electric heating elements to raise the furnace atmosphere to the required temperature. Furnace temperatures are typically maintained between 600°C and 1000°C, with the specific temperature determined by the material being processed and the target properties.

Soaking: After reaching the target temperature, the material is maintained at that temperature for a specified duration. This phase, known as the soaking stage, ensures uniform internal temperature distribution throughout the material.

Cooling: Annealing furnace manufacturers typically design units to control cooling rates, which may be natural or forced (e.g., using cooling fans). Gradual cooling facilitates the attainment of desired material characteristics.

2. Principal Components

2.1 Furnace Body

Furnace Chamber: The core component of a bogie hearth annealing furnace, typically lined with high-temperature-resistant materials to ensure thermal durability and efficiency. Internal structural design facilitates uniform heating and effective heat transfer.

Furnace Door: The opening used for loading and unloading materials, usually fitted with sealing mechanisms to prevent heat and gas leakage.

2.2 Heating System

Fuel System: Some bogie hearth furnaces utilise gas or liquid fuels for heating. The combustion system comprises burners, fuel supply, and control mechanisms.

Electric Heating Elements: Electric furnaces employ heating elements such as resistance wires or induction coils, which utilise electrical current to heat the furnace atmosphere and metallic materials.

2.3 Bogie

Mobile Car: The car constitutes a critical component of the annealing furnace, serving to carry and transport the metal materials undergoing treatment. Cars are typically engineered for high-temperature resistance and structural stability.

Car Drive System: The drive mechanism enables the car to traverse the furnace chamber, facilitating the loading and unloading of materials.

2.4 Control System

Temperature Control: This system ensures precise regulation of the furnace chamber temperature, typically comprising temperature sensors, controllers, and regulating devices.

Time Control: Sets heating, soaking, and cooling durations for the annealing process to ensure material treatment meets design specifications.

Atmosphere Control: Certain annealing furnaces can regulate the internal atmosphere to prevent metal oxidation or other chemical reactions.

3. Annealing Process

3.1 Material Preparation

Cleaning: Prior to loading into the annealing furnace, manufacturers clean impurities and contaminants from the material surface to avoid compromising annealing quality.

Loading: Materials are placed onto the hearth car, ensuring stable positioning and even distribution for uniform heating.

3.2 Heating

Ramp-up: The heating system is activated to gradually elevate the furnace temperature to the required level. The heating rate must be controlled within a reasonable range to prevent excessive temperature changes on the material surface or internally.

Soak: Materials are maintained at the target temperature for a specified duration, determined by material type and annealing requirements.

3.3 Cooling

Cooling Method: The annealing furnace manufacturer controls the cooling rate to achieve the desired material properties. Cooling speed can be regulated by adjusting the airflow within the furnace or through forced cooling devices.

Unloading: After cooling is complete, remove the material from the furnace. At this stage, the material should maintain a stable annealed state.

4. Application Fields

Baskets annealing furnaces are widely used in the following fields:

Steel Industry: For processing steel to enhance its mechanical properties and workability.

Aluminium Processing: Annealing aluminium to improve ductility and reduce hardness.

Copper Production: Annealing copper alloys to adjust mechanical properties.

Summary

Baskets annealing furnaces alter the physical and chemical properties of metals through heating, holding, and cooling processes to enhance performance. Key components include the furnace body, heating system, baskets, and control system. Correct operation and control are essential for ensuring annealing quality and material properties.