Introduction
The pusher-type heating furnace is a critical piece of equipment in the steel rolling industry, designed to heat steel billets to the required temperature before they enter the rolling mill. This guide provides a detailed, factual overview of the pusher furnace based on standard training materials, covering its main systems, operational control, and key parameter calculations. Whether you are an engineer, operator, or student, this article will help you understand the structure, fonction, and technical specifications of a pusher heating furnace.
1. Charging System (Material Handling System)
The charging system is responsible for transporting steel billets to the front of the furnace. It consists of:
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Run-in table rollers that convey the billets
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A pusher mechanism that pushes the billets into the furnace
The system ensures a continuous and controlled supply of cold billets into the furnace interior, where they will be heated to rolling temperature.
2. Furnace Body (Heating Furnace Proper)
The furnace body includes the following structural components:
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Furnace foundation – supports the entire furnace weight
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Furnace walls – made of refractory materials to contain heat
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Furnace roof – also refractory-lined, often arched or suspended
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Masonry work – the brickwork and castable refractory lining
These components form the enclosed space where combustion and heat transfer occur, protecting the surroundings from high temperatures and minimizing heat loss.
3. Circuit de refroidissement
The cooling system is essential to protect furnace components from overheating. It includes:
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Cooling of water pipes inside the furnace – this is the primary cooling requirement, as internal water-cooled skid pipes support the billets and must withstand intense heat
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Cooling of the front and rear end walls – prevents structural damage
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Fan cooling – for auxiliary equipment
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Cooling of the front roller table (before the pusher)
Parmi ceux-ci, le internal water pipe cooling system is the most critical, as it directly affects the operational life and safety of the furnace.
4. Combustion System
The combustion system determines the heating capacity of the furnace. Its key components are:
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Burners (nozzles) – where fuel and air mix and ignite
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Air blower and air piping – supplies combustion air
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Fuel gas piping – delivers gas fuel to the burners
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Reversing device (reverser) – used in regenerative or recuperative burners
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Induced draft fan (ID fan) – helps remove flue gases
The performance of the combustion system directly impacts the furnace’s heating rate, uniformité de la température, and fuel efficiency. A properly tuned system can significantly increase productivity.
5. Exhaust System (Flue Gas System)
The exhaust system manages the removal of flue gases from the furnace. It comprises:
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Induced draft fan (ID fan)
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Flue gas ductwork
Furnace pressure is controlled by adjusting a damper or valve in front of the ID fan. Proper pressure control is crucial to prevent cold air infiltration or flame rollout, ensuring stable combustion and energy savings.
6. Automatic Control System
Modern pusher furnaces are equipped with an automatic control system that typically includes:
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Primary instrumentation – sensors for temperature, pression, flow, etc..
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API (Contrôleur logique programmable) – receives signals from the instruments
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Actuators and final control elements – regulate process variables
The system automatically adjusts température, pression, et flow to maintain optimal heating conditions. This closed-loop control improves consistency, reduces fuel consumption, and minimizes manual intervention.
7. Heating Control Strategy
Proper heating control is key to product quality and furnace efficiency. The control strategy is based on the rolling mill’s production rhythm. Key parameters and guidelines:
Under Normal Production
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Heating zone temperature – set according to process requirements
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Soaking zone temperature – typically set about 50°C lower than the heating zone
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Discharge temperature – 1150–1250°C (billet exit temperature)
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Flue gas temperature – 90–170°C
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Air-to-fuel ratio – controlled at 0.8:1 (air:carburant)
During Production Stoppage (Holding)
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Furnace temperature – maintained at 1000–1100°C to prevent sticking (adhesion) between billets
This temperature range avoids “sticking steel” – a condition where overheated billets fuse together, causing push line obstructions and damage.
8. Pusher Furnace Parameter Calculation
Proper design and operation require several key calculations. Below are the formulas and empirical values based on standard practices.
8.1 Furnace Internal Width
B=L+2CB = L + 2C
Où:
- BB = Furnace internal width (mètres)
- LL = Steel billet length (mètres)
- CC = Gap between billet and furnace wall (typiquement 0.15–0.30 m)
This ensures the billet can move freely without excessive side clearance that would waste fuel.
8.2 Furnace Length
Furnace length is primarily determined by the desired taux de production. It is expressed through the push ratio:
Push ratio=Push length (furnace length)Minimum billet thickness (height)\text{Push ratio} = \frac{\text{Push length (furnace length)}}{\text{Minimum billet thickness (height)}}
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Good conditions (well-lubricated, straight billets): push ratio = 250–300
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Poor conditions (rough billet ends, désalignement): push ratio = 200–250
A higher push ratio allows a longer furnace for the same billet height, increasing capacity but also pushing force.
8.3 Pusher Thrust Force Calculation
P=Q×FP = Q \times F
Où:
- PP = Thrust force (tons or kN)
- QQ = Weight of the steel being pushed (tonnes)
- FF = Friction coefficient (typiquement 0.5–0.6)
This force must overcome friction between billets and water skids, as well as between billets themselves.
8.4 Pusher Speed
Pusher speed is selected based on billet cross-section height:
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For small billets (30–60 mm height): 0.05 – 0.08 MS
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For large billets (100–300 mm height): 0.10 – 0.12 MS
Slower speeds reduce impact and wear, while higher speeds increase productivity. The speed must match the rolling mill’s intake rhythm.
Summary Table of Key Parameters
| Paramètre | Valeur / Gamme |
|---|---|
| Discharge temperature | 1150 – 1250 °C |
| Flue gas temperature | 90 – 170 °C |
| Soaking zone offset | ~50 °C below heating zone |
| Air-to-fuel ratio | 0.8 : 1 |
| Holding temperature (stoppage) | 1000 – 1100 °C |
| Furnace side clearance (C) | 0.15 – 0.30 m |
| Push ratio (good conditions) | 250 – 300 |
| Push ratio (poor conditions) | 200 – 250 |
| Friction coefficient (F) | 0.5 – 0.6 |
| Pusher speed (small billets, 30–60 mm) | 0.05 – 0.08 MS |
| Pusher speed (large billets, 100–300 mm) | 0.10 – 0.12 MS |
Conclusion
The pusher-type heating furnace is a robust and widely used technology in steel reheating applications. Its performance depends on the proper integration of multiple systems: chargement, corps de four, refroidissement, combustion, exhaust, and automatic control. Understanding the heating control rules and the basic parameter calculations—such as furnace width, longueur, thrust force, and pusher speed—enables engineers to design, operate, and troubleshoot these furnaces effectively.
By adhering to the temperature guidelines (1150–1250°C discharge, 1000–1100°C during stoppages) and maintaining the correct air-fuel ratio (0.8:1), operators can achieve high production rates while avoiding common issues like billet sticking and excessive fuel consumption.
For further training or operational manuals, always refer to your specific furnace manufacturer’s documentation and site-specific conditions.