Panoramic Analysis of Heating Methods in Multi purpose Furnace Production Lines: Technical Principles, Application Comparisons, Selection Strategies
Multi purpose furnace (a heat treatment production line that can perform various processes such as carburizing, carbonitriding, quenching, tempering, cleaning, etc.) is the core equipment of modern batch heat treatment production. The choice of heating method directly determines the process capability, product quality, energy efficiency, operating costs of the production line. The current multi-purpose furnace production line mainly adopts two technical routes: gas fuel heating electric heating, various specific implementation forms have been derived on this basis. This article will systematically analyze compare these heating methods.
1、 Deep analysis of the technical principles characteristics of mainstream heating methods
（1） Gas fuel heating method
Gas fuel heating is currently a widely used technologically mature heating method, especially suitable for large-scale continuous production.
1. Radiant tube heating
Working principle: The burner burns inside a heat-resistant alloy steel tube (radiation tube), heating the tube wall to a high temperature (usually 900-1100 ℃), the heat is transferred to the workpiece in the furnace in the form of thermal radiation. The combustion exhaust gas is discharged through another channel to achieve complete isolation between combustion furnace gas.
Key configuration:
Radiation tube type:
U-shaped/W-shaped/straight tube: U-shaped tube has a compact structure is widely used; W-shaped tubes have higher thermal efficiency but are more complex to manufacture; Straight pipes are easy to maintain.
Gas/air preheating: Advanced regenerative radiation tubes (RRT) self preheating radiation tubes (SRT) use flue gas waste heat to preheat combustion air to above 500 ℃, with a comprehensive thermal efficiency of over 75%.
Combustion control system: using proportional adjustment (automatic tracking of air-fuel ratio) burner to achieve high-precision temperature control (± 5 ℃) low excess air coefficient combustion.
Advantages:
The process has extremely wide applicability: the furnace has a pure process atmosphere (such as RX gas, nitrogen methanol), without interference combustion products, which is very suitable for precision chemical heat treatment such as carburizing carbonitriding.
Good uniformity of furnace temperature: By arranging the radiation tubes reasonably, a uniform radiation heat field (Class 2 even Class 1) can be achieved inside the furnace.
Good fuel adaptability: can use various clean gas fuels such as natural gas, city gas, liquefied petroleum gas, etc.
Disadvantages:
The initial investment is relatively high: the cost of radiation tubes combustion systems is expensive.
There is thermal inertia: the heating rate is relatively slow.
Maintenance requirement: The radiation tube is a high-temperature pressure bearing component that poses risks of oxidation, deformation, burning after long-term use, requires regular inspection replacement.
2. Open flame direct combustion heating
Working principle: The burner flame is directly sprayed into the furnace, the workpiece is heated by convection radiation of the flame high-temperature flue gas.
Application Features:
Main applications: It is mainly used for simple heating processes such as quenching, normalizing, tempering, etc. that do require high furnace gas composition, for some carburizing processes that do require high requirements (by controlling the furnace gas carbon potential through special combustion technology).
Advantages: High thermal efficiency, fast heating rate, low investment cost.
Fatal disadvantage: Combustion products (H ₂ O, CO ₂) can seriously interfere with the carbon potential control of the furnace atmosphere, making it difficult to meet high-precision carburizing requirements; Direct impact of flames on the workpiece may cause local overheating.
（2） Electric heating method
Electric heating plays an important role in high-quality highly flexible production due to its clean, accurate, easy to control characteristics.
1. Resistance strip/resistance wire heating
Working principle: Nickel chromium (Cr20Ni80) iron chromium aluminum (such as 0Cr27Al7Mo2) alloy resistance strips/wires are wound arranged on the refractory material groove ceramic support of the furnace, heat is generated after being powered on.
Layout form: Usually arranged on the side back walls of the furnace, large furnaces are also arranged on the top of the furnace.
Advantages:
Simple structure low cost.
Extremely accurate control: PID regulation is achieved through solid-state relays (SSRs) thyristors (SCR), with a temperature control accuracy of ± 1 ℃.
Clean environment: No combustion noise exhaust emissions, good workshop environment.
Small thermal inertia: fast heating speed flexible adjustment.
Disadvantages:
High operating costs: Completely dependent on electricity, in areas with high industrial electricity prices, the unit heat cost is usually significantly higher than that of gas.
Component lifespan: Resistance strips are prone to oxidation embrittlement at high temperatures (especially in carburizing atmospheres), limiting their service life.
Power density limitation: Single zone power should be too high, otherwise components are prone to damage.
2. Heating with electric radiation tube
Working principle: This is a combination of electric heating radiation tube form. Encapsulate the resistance alloy wire (tape) in a heat-resistant alloy tube filled with inert protective gas, transfer heat through the tube wall radiation.
Core advantages:
Combining the accurate control of electric heating with the purity of furnace gas protection of heating elements through radiation tubes.
Very suitable as a substitute for gas radiation tubes in chemical heat treatment that requires a high cleanliness atmosphere.
Disadvantages: The initial installation cost operating cost (electricity) are both high, making it one of the high-end heating solutions.
2、 Emerging special heating methods
1. Pulse combustion technology (applied to gas radiation tubes)
Principle: The burner does burn continuously, but performs "on-off" pulse combustion at high frequencies (such as 50-100Hz). Control power by adjusting pulse frequency duty cycle.
Advantage:
Leap in furnace temperature uniformity: High speed pulse airflow generates strong disturbances inside the radiation tube, making the temperature of the tube wall highly uniform.
Extremely high thermal efficiency: close to stoichiometric combustion intense convective heat transfer, with a comprehensive efficiency of over 80%.
NOx emissions are extremely low.
Application: Belonging to gas radiation tube technology, it is a choice for pursuing uniformity energy efficiency.
2. Induction heating (for local rapid heating applications in multi-purpose furnaces)
Principle: Place the workpiece in an alternating magnetic field use electromagnetic induction to generate eddy currents for heating.
Application in multi-purpose furnaces:
the mainstream furnace heating method.
Potential application scenarios: Used as a rapid preheating station for production lines, it quickly heats workpieces to a certain intermediate temperature before entering the main furnace, shortens the heating time of the main furnace, improves overall production capacity energy efficiency.
3、 Selection strategy systematic consideration
Choosing a heating method is simply a matter of technical comparison, but should be based on systematic decision-making according to the company's strategy.
Process requirements are the fundamental starting point:
If the core process is precision carburizing carbonitriding, it is necessary to choose radiation tube heating (gas electric heating) that can ensure the purity of the furnace gas. Open flame heating is basically feasible.
If it is only for quenching, tempering, normalizing, all methods can be considered, a comprehensive cost balance is required.
Energy economy accounting (TCO total cost of ownership):
Conduct a detailed full lifecycle cost analysis. Compare the long-term price trends of local natural gas electricity. Even though the investment in electric heating equipment may be slightly lower, the high electricity costs may quickly offset its advantages within 3-5 years.
Considering the potential for waste heat recovery: The flue gas waste heat gas radiation tubes can be used to preheat combustion air (self preheating type), generate process atmosphere (such as preparing endothermic atmosphere), for heating cleaning machines tempering furnaces, greatly improving system energy efficiency. Electric heating does have this advantage.
Production scale flexibility requirements:
Large scale continuous production: Gas radiant tube heating has obvious advantages in operating costs is the mainstream choice.
Multi variety, small batch, research development nature: Electric heating (resistance strip electric heating tube) may have more advantages due to its fast temperature rise fall, accurate control, flexible start-up.
Environmental Protection Workshop Conditions:
In areas with strict environmental requirements limited ventilation conditions in the workshop, zero emissions electric heating are a significant advantage.
Gas equipment needs to consider meeting smoke emission standards arranging exhaust pipes.
Technological foresight reliability:
Pulse combustion gas radiation tubes represent the forefront of high efficiency uniformity technology.
Electric heating radiation tubes are the choice for achieving ultra pure atmosphere nanoscale control.
Evaluate the supplier's technical expertise, successful cases, after-sales service capabilities in this heating method.
