Congratulations ! ! HiTo new project---a continuous hot dip galvalume line successfully put into production in Dubai

In China, factories equipped with 55% Al-Zn-Si production lines (Galvalume Line) are generally large in scale, featuring high production line capacity, sufficient technical talents of various types, and stable product quality. By 2025, over 50% of their products are exported to global markets, which has far exceeded domestic market sales.

Now, capital from more and more countries is investing in galvanizing production lines (including Galvanizing Line, Galvalume Line, and ZAM Production Line).

The UAE client has installed the first continuous coil Galvalume line in the Gulf region. After comprehensive assessment, HiTo (Sea Route) has taken the following factors into consideration:

1. The client lacks a professional and experienced production operation team.
2. The natural environment of the UAE (hot and humid in the hot season).
3. Energy conservation and environmental protection from the client's perspective.

At the initial design stage, HiTo's technical team has designed the production line to be simple and easy to operate, so as to reduce the requirements for process operators, achieve energy conservation and environmental protection, ensure stable production operation and produce high-quality products. The specific selection of corresponding process equipment is as follows:

1. The structure and function of single drive equipment adopt those that have been well-proven in the Chinese market to ensure reliability and durability.
2. A C-type narrow lap welder is selected, which features high automation, high welding quality, short welding time, and simple maintenance.
3. The cleaning section is equipped with an electrostatic degreasing section, whose main function is to efficiently remove rolling oil, iron powder, dust, and other contaminants from the surface of the steel strip through the synergistic effect of electrostatic adsorption and chemical degreasing, thereby providing a clean substrate surface for the subsequent hot-dip coating process.
Key configurations and equipment:
① The degreasing tank body must be corrosion-resistant and insulated.
② High-voltage electrostatic system - Core components: high-voltage electrostatic generator, electrode plate.
③ Degreasing agent circulation system - Composed of circulation pumps and pipeline valves. The degreasing agent is updated in real time according to actual conditions (usually, the replacement cycle of the degreasing agent is 14-25 days).
④ Steel strip guiding and stabilizing device:

- Steering combination roll system: Prevents the steel strip from deviating, ensures uniform spacing between the steel strip and the electrode plate, and avoids local electrostatic field imbalance.
- Squeeze rolls: Located at the exit of the degreasing section, they squeeze the residual degreasing fluid on the surface of the steel strip to reduce the amount of fluid carried into the rinsing section.

4. A full radiant tube furnace (RTF) is selected as the annealing furnace. It realizes the recrystallization annealing of the steel strip through indirect heating by radiant tubes, and precisely controls the temperature and microstructure properties of the steel strip, laying a foundation for the uniform adhesion and stable quality of the subsequent galvanized coating. The following is a detailed explanation from the aspects of core functions, working principles, key structures, process characteristics, and application precautions:

⑴ Core functions
The core goal of the full radiant tube annealing furnace is to heat, insulate, and cool (anneal and reduce) the cold-rolled steel strip in a protective atmosphere (to avoid oxidation of the steel strip). The specific functions include:
① Microstructure control: Through precise heating (usually at a temperature of 650-850℃), the grains inside the steel strip are recrystallized, the cold-rolling work hardening is eliminated, and the required mechanical properties such as yield strength and elongation (e.g., soft or semi-hard steel strip) are obtained.
② Surface protection: Nitrogen (N₂) or a nitrogen-hydrogen mixture (with H₂ content of 5%-20%) is introduced into the furnace as a protective atmosphere to isolate air, prevent the formation of iron oxide on the surface of the steel strip due to oxidation, and ensure good bonding between the zinc liquid and the steel strip during subsequent galvanizing.
③ Temperature homogenization: Through the uniform arrangement of radiant tubes and furnace temperature control, the temperature deviation in the width and length directions of the steel strip is ensured to be ≤±5℃, avoiding differences in the thickness of the galvanized coating or deformation of the steel strip caused by local temperature unevenness.

⑵ Working principle
The full radiant tube annealing furnace works through an indirect heating method of "fuel combustion (or electric heating) → radiant tube heating → radiant heat transfer → steel strip heating". The specific process is as follows:
① Heat source supply: Fuel (such as natural gas, liquefied petroleum gas) is mixed with air and burned inside the radiant tube, or electric heating elements (such as resistance wires, induction coils) are used for heating, so that the wall temperature of the radiant tube rises to 800-1000℃.
② Radiant heat transfer: The high-temperature radiant tube wall transfers heat to the steel strip passing through the furnace chamber through thermal radiation (the main method) and thermal convection of the protective atmosphere in the furnace. The steel strip runs continuously in the furnace (at a speed of 45-150m/min) and passes through the preheating section, heating section, and heat preservation section in sequence to gradually reach the target annealing temperature.
③ Cooling and temperature control: After the microstructure transformation of the steel strip is completed in the heat preservation section, it enters the cooling section in the furnace, and the temperature is reduced to 450-580℃ (adapting to the zinc liquid temperature for subsequent galvanizing) through cooling gas (such as cooling nitrogen), and finally the annealing process is completed.

⑶ Key structural components
The structure of the full radiant tube annealing furnace needs to be adapted to the steel strip specifications (thickness 0.15-1.0mm, width 700-1250mm) and production rhythm. The core components include:
① Furnace chamber and furnace shell:

- Furnace chamber: Built with high-temperature resistant refractory materials (such as high-alumina bricks, ceramic fibers) to form a closed space and reduce heat loss; steel strip guide rolls are arranged inside to ensure the stable operation of the steel strip.
- Furnace shell: The outer layer is a steel plate, and the middle is filled with thermal insulation materials (such as rock wool, aluminum silicate wool), so that the surface temperature of the furnace body is ≤60℃ and energy consumption is reduced.
② Radiant tube assembly:
- Radiant tube: The core heating element, mostly made of heat-resistant steel (such as Cr25Ni20) or ceramics, with shapes of U-type, W-type, and straight tube type (W-type is the most commonly used because of its high power and ease of installation and maintenance). It is evenly arranged on the upper and lower sides of the furnace chamber (with a spacing of 100-200mm) to ensure uniform heating of the upper and lower surfaces of the steel strip.
- Combustion system (fuel type): Including burners, gas pipelines, and air preheaters (recovering flue gas heat to improve combustion efficiency); the electric heating type is equipped with a power control cabinet and a heating element junction box.
③ Protective atmosphere system:
- Gas generation device: Such as nitrogen generators and ammonia decomposition furnaces (producing nitrogen-hydrogen mixture), to ensure the purity of the protective atmosphere (O₂ content ≤10ppm, H₂O content ≤20ppm).
- Gas circulation and exhaust system: A circulation fan is arranged in the furnace to make the protective atmosphere flow evenly; an exhaust port is set at the tail to discharge a small amount of waste gas generated by combustion (for fuel type) or leaked air.

④ Temperature and tension control system:

- Temperature control: Thermocouples are arranged in the furnace chamber to monitor the temperature of each section in real time, and the fuel supply (or electric heating power) is adjusted through the PLC system to achieve precise temperature control.
- Tension control: Tension rolls are set at the inlet and outlet to control the tension of the steel strip in the furnace (usually 50-200N/mm²) and prevent the steel strip from deviating or wrinkling.

⑷ Process characteristics
Compared with other annealing furnaces (such as open-flame heating furnaces and induction heating furnaces), the core advantages of the full radiant tube annealing furnace are:
① Good heating uniformity: The indirect heating of radiant tubes avoids direct contact between open flames and the steel strip, reduces local overheating or temperature difference, results in small temperature deviation of the steel strip, and improves the uniformity of the galvanized coating thickness by 10%-15%.
② Excellent surface quality: No oxidation occurs in the protective atmosphere, the surface of the steel strip is clean, and the zinc coating adhesion is stronger during subsequent galvanizing, reducing defects such as "missing plating" and "zinc particles".
③ Balance between energy consumption and maintenance: Fuel-type radiant tubes can reduce energy consumption through waste heat recovery (thermal efficiency 60%-70%); electric heating type has no exhaust gas emission and simpler maintenance, which is suitable for scenarios with high environmental protection requirements.

⑸ Operation and maintenance precautions
① Safe operation:

- For fuel-type furnaces, the tightness of gas pipelines must be checked regularly to avoid gas leakage.
② Daily maintenance:
- Radiant tubes: Check the wall thickness every 3-6 months (to prevent burnout), and replace them in time if deformation or damage is found; for fuel-type ones, clean the burner nozzles to avoid blockage.
- Protective atmosphere system: Detect the gas purity daily, and replace the filter element regularly to prevent impurities from entering the furnace chamber.
③ Process parameter control:
- Annealing temperature: Adjust according to the steel strip material (such as low-carbon steel, high-strength steel). For example, the annealing temperature of low-carbon steel is 700-750℃, and that of high-strength steel needs to be increased to 800-850℃.
- Steel strip speed: Match with the annealing temperature. Excessively fast speed may lead to insufficient heating, while excessively slow speed affects production efficiency. It needs to be adjusted dynamically according to the production line rhythm.

5. The equipment in the zinc pot area is also specially configured according to the zinc liquid composition required by the client. Since the client produces 55% Al-Zn-Si products, our selection is as follows:
① Zinc pot body: The internal corners of the zinc pot are usually arcs with R600, which facilitates the flow of zinc liquid in the pot and temperature conduction, and prevents the formation of cold dead corners. Its capacity is generally 70-90 tons, which is conducive to making the temperature and composition more uniform through magnetic stirring and reducing heat loss at the same time.
② Inductor: Due to the special solidification temperature range of the 55% Al-Zn-Si alloy liquid, when the pot temperature is lower than 595℃, aluminum in the alloy liquid will crystallize and precipitate first. Therefore, the inductor needs to work frequently or continuously at high power to flush the internal molten channel of the inductor, prevent blockage of the molten channel or reduction of the cross-section of the molten channel until the inductor is damaged, and at the same time make the temperature and composition of the zinc pot uniform. HiTo has configured 4 inductors for the main zinc pot of the client's production line, with a maximum power of 350-400KW, which are arranged on the four sides of the zinc pot respectively.
③ Pre-melting pot: Generally, a 55% Al-Zn-Si production line is equipped with a pre-melting pot, which is a small-capacity power-frequency ceramic induction heating pre-melting pot with two inductors and a power of 400KW×2. An overflow port is left on the upper edge of the wall, which is connected to a chute (55Al-Zn-Si liquid launder) leading to the main zinc pot. The alloy liquid flows into the main pot by adding alloy ingots to increase the zinc liquid level of the main pot.
④ Auxiliary devices: Including sinking rolls, stabilizing rolls, and their adjustment devices, which are usually called "three rolls, six arms, and one zinc snout". Specifically, they consist of one sinking roll, one correction roll, one stabilizing roll, six arms that support the three rolls to be immersed in the zinc pot, and one zinc snout that guides the steel strip into the zinc pot. In addition, in order to remove zinc dross on the rolls, an electric scraper device is installed on the arm beam to improve the use effect and service life of the sinking rolls.
6. The cooling process section is specially equipped with forced air cooling (mobile air cooling) equipment. After the strip exits the zinc pot, it passes through a strong cooling section for air-blast cooling. The strip temperature is reduced from 600°C to 450°C within 3-5s, and the required cooling rate is not less than 30°C/s.
7. A high-end wet skin-pass mill is configured.
① Main functions: By calendering the surface of the steel plate after it exits the zinc pot, the skin-pass mill can flatten the surface of the steel strip, enabling the zinc coating to adhere better to the surface of the steel strip. It can also improve the surface finish and smoothness of the steel strip, eliminate tiny uneven defects, eliminate internal stress and yield platform of the material, improve processing performance, improve the plate shape to a certain extent, and transfer roughness, making the calendered steel strip easier to undergo anti-rust treatment.
② Basic structure: The skin-pass mill is mainly composed of a housing, a stand, rolls, a hydraulic system, and other components and mechanisms. The rolls are the core components, usually adopting a four-roll structure, including upper work rolls, lower work rolls, upper backup rolls, and lower backup rolls.
8. One passivation coater is configured for passivation and anti-rust treatment on the surface of the strip, and one anti-fingerprint coater is configured for coating the surface of the strip with an anti-fingerprint coating.