Three 5.4-meter tunnel furnaces for Malaysian customers have been debugged and are ready for shipment.

1. General Description

2. Working Principle

2.1 Heat Transfer Mechanisms

• Conduction: Heat is transferred through the solid materials within the furnace, such as the furnace walls, conveyor belts, and the products themselves. The materials with higher thermal conductivity facilitate faster heat transfer. For example, in a metal - processing tunnel furnace, the metal parts being heated conduct heat from the hot furnace environment to their inner parts.
• Convection: In the furnace chamber, hot gases circulate. These gases are either generated by combustion (in gas - fired furnaces) or heated by electrical elements and then circulated by fans. The hot gases transfer heat to the products as they flow around them. In a food - baking tunnel furnace, hot air blown over the food products helps in evenly cooking the food.
• Radiation: Heat is emitted in the form of electromagnetic waves from the heated surfaces such as heating elements or the hot inner walls of the furnace. This radiant heat is absorbed by the products, raising their temperature. Infrared heating elements in some tunnel furnaces work mainly based on radiation, which is efficient for quickly heating products as infrared rays can penetrate the surface to a certain depth.
  

2.2 Conveyor - Based Operation

3. Types of Tunnel Furnaces

3.1 Electric Tunnel Furnaces

• Heating Elements: These furnaces use electric heating elements such as nichrome wire, silicon carbide rods, or infrared lamps. Nichrome wire elements are commonly used for lower - temperature applications (up to around 1200°C), while silicon carbide rods can withstand higher temperatures (up to 1600°C). Infrared lamps are used for rapid heating and surface - focused heating applications.
• Advantages: They offer precise temperature control, as the power to the heating elements can be accurately regulated. They are also clean - burning, producing no emissions during operation, which is ideal for applications where a clean environment is required, such as in the electronics and food industries.
• Disadvantages: Higher electricity consumption compared to some gas - fired furnaces, and the initial cost of the heating elements and electrical control systems can be relatively high.

3.2 Gas - Fired Tunnel Furnaces

• Combustion Systems: Gas - fired tunnel furnaces use natural gas, propane, or other gaseous fuels. The combustion system typically consists of burners, air - fuel mixing devices, and ignition systems. The burners can be designed for direct - firing (where the combustion gases directly contact the products) or indirect - firing (where the combustion gases heat a heat exchanger, and the heated air is then used to heat the products).
• Advantages: They are generally more cost - effective in terms of energy consumption for high - volume and high - temperature applications. They can also provide high heating rates, making them suitable for processes that require rapid heating.
• Disadvantages: The combustion process can produce emissions such as carbon dioxide, nitrogen oxides, and particulate matter, which may require additional pollution control measures. Temperature control may not be as precise as in electric furnaces, especially in direct - firing systems.

3.3 Vacuum Tunnel Furnaces

• Vacuum Chambers: These furnaces are equipped with vacuum chambers to create a low - pressure environment. Vacuum pumps are used to evacuate the air from the chamber. In some cases, an inert gas such as argon or nitrogen can be introduced into the chamber after evacuation to create a controlled atmosphere.
• Applications: Vacuum tunnel furnaces are mainly used for heat - treating processes where oxidation or contamination of the products needs to be avoided. They are commonly used in the aerospace industry for heat - treating high - performance alloys, in the semiconductor industry for processing wafers, and in the production of high - quality metals and ceramics.
• Advantages: By eliminating oxygen and other reactive gases, the risk of oxidation, decarburization, and other chemical reactions that can degrade the quality of the products is greatly reduced. The low - pressure environment also allows for lower processing temperatures in some cases, which can save energy and improve the quality of heat - treated materials.
• Disadvantages: The cost of the vacuum system, including the vacuum pumps, valves, and associated instrumentation, is high. The operation and maintenance of the vacuum system require specialized knowledge and skills.

4. Key Technical Parameters

4.1 Temperature Range

• Different tunnel furnaces are designed to operate within specific temperature ranges. For example, some food - baking tunnel furnaces may have a temperature range from 50°C to 300°C, suitable for baking bread, cakes, and cookies. In the electronics industry, tunnel furnaces used for soldering and curing may operate in the range of 150°C to 400°C. High - temperature tunnel furnaces for ceramic sintering or metal heat - treating can reach temperatures as high as 1600°C or even higher.

4.2 Temperature Uniformity

• Temperature uniformity is a crucial parameter as it directly affects the quality of the heat - treated products. A well - designed tunnel furnace should have a temperature variation within a specified tolerance across the width and length of the furnace chamber. For many industrial applications, a temperature uniformity of ±1°C to ±5°C is desirable. This is achieved through proper design of the heating elements, gas distribution systems (in gas - fired furnaces), and the use of insulation materials to minimize heat loss.

4.3 Conveyor Speed

• The speed of the conveyor can be adjusted according to the heat - treatment requirements of the products. For processes that require a short exposure to high temperatures, such as flash - drying or rapid sintering, a higher conveyor speed may be used. In contrast, for processes that need a longer and more gradual heat treatment, like slow - baking of certain foods or stress - relieving of metals, a lower conveyor speed is selected. The conveyor speed is typically controlled by a variable - speed drive system, which can be adjusted manually or programmed through an automated control system.

4.4 Load Capacity

• The load capacity of a tunnel furnace refers to the maximum weight or volume of products that can be processed at one time. It depends on the size of the furnace chamber, the strength of the conveyor system, and the heating capacity of the furnace. For example, a small - scale tunnel furnace used in a laboratory may have a load capacity of a few kilograms, while a large - scale industrial tunnel furnace can handle several tons of products per hour.

5. Control Systems

5.1 Temperature Control

• Thermocouples and RTDs: Temperature sensors such as thermocouples (made of different metal alloys) and resistance - temperature detectors (RTDs) are used to measure the temperature inside the furnace. Thermocouples are suitable for a wide range of temperatures and are relatively inexpensive, while RTDs offer higher accuracy in a more limited temperature range.
• PID Controllers: Proportional - Integral - Derivative (PID) controllers are commonly used to regulate the temperature. The PID controller compares the measured temperature from the sensor with the set - point temperature. Based on the difference (error), it calculates the appropriate control signal to adjust the power to the heating elements (in electric furnaces) or the fuel - air ratio (in gas - fired furnaces) to maintain the desired temperature.