Search on site
During the hot rolling process, a dark gray to black flaky layer forms on the surface of steel as it exits the furnace. This layer is called tufal in Turkish, or mill scale in English. Mill scale is an iron oxide layer formed on the steel surface due to its reaction with oxygen at high temperatures.
From a geological perspective, tufal is also recognized as a valuable material in both geology and the construction industry. It forms from the fusion of lava, ash, and various mineral compositions during volcanic activity. This natural process determines the unique porous structure and mineral distribution of tufal. Its porosity contributes to the material’s light weight and its thermal and acoustic insulation properties. Due to its structural durability and workability, tufal is widely preferred in architectural and engineering projects. When constructing energy-efficient buildings, tufal stands out for its lightness and insulating properties.
The mineral composition and formation process determine the suitability of tufal for different applications. Some tufal types are dense and hard, while others are lighter and more porous. This variation affects the types of construction projects in which the material can be used. Engineers and architects assess the material’s durability, workability, and response to environmental conditions to make both functional and aesthetic design decisions, ensuring the longevity of the structure.
When steel reaches rolling temperatures (approximately 900–1250°C), it reacts with oxygen in the atmosphere. This reaction produces three primary oxide layers on the steel surface:
FeO (Wüstite) – The innermost layer, formed at high temperatures.
Fe₃O₄ (Magnetite) – The intermediate layer.
Fe₂O₃ (Hematite) – The outermost layer, in direct contact with air.
These layers combine to form a dense, brittle, and black mill scale on the steel surface.
One of the most notable features of tufal is its light weight and porous structure. This porosity provides heat regulation and sound insulation. The material’s durability depends on its mineral content and structural density. Certain types can withstand high pressure and heavy loads, while others offer advantages on supporting systems due to their light weight. These characteristics make tufal a versatile material for modern construction projects.
The chemical composition determines the material’s durability and resistance to environmental effects. Tufal types with high silica and alumina content are resistant to water and abrasion. Its workability allows for easy cutting and shaping, providing design flexibility. Its aesthetic appearance and natural texture make it a preferred material in architectural projects. The porous structure enhances acoustic insulation, increasing indoor comfort and overall building performance.
Tufal has a wide range of applications in the construction and architecture sectors. Its light weight, durability, and insulation properties make it a preferred choice for modern construction projects.
Construction and Building Material: Used in wall blocks, floor slabs, roofing elements, and exterior cladding. Its light weight does not add extra load to structural systems and improves energy efficiency. Porosity provides thermal and acoustic insulation, enhancing interior comfort.
Industrial Structures: High-strength tufal types resistant to pressure and heat are suitable for factories, warehouses, industrial zones, and infrastructure projects. These types maintain durability under heavy loads and harsh environmental conditions.
Landscaping and Environmental Design: Used in garden stones, walkways, flower arrangements, and decorative elements. Its natural texture and aesthetic appearance allow for elegant, nature-integrated landscape designs.
Decorative and Architectural Applications: Serves as a decorative stone for interior and exterior design. Tufal’s natural texture and compatibility with light and shadow enhance visual appeal. Availability in different colors and textures supports architectural creativity and gives projects a unique character.
Energy-Efficient Buildings: Its insulating properties contribute to energy savings in residential and commercial projects by reducing heat loss and maintaining thermal comfort year-round.
Sustainable and Environmentally Friendly Projects: Being natural and recyclable, tufal minimizes environmental impact. Preferred in green building projects and sustainable architectural designs, its durability reduces maintenance needs and optimizes resource use.
Infrastructure and Transportation Projects: Suitable for road construction, bridge support elements, and rail infrastructure. Its light and durable structure maintains long-term structural integrity and reduces maintenance costs.
Tufal is a versatile material due to its numerous advantages. Its porous structure provides thermal and acoustic insulation and contributes to energy efficiency. Its light weight does not burden structural systems and facilitates construction processes. Its durability ensures long-lasting solutions and enhances building safety.
Workability allows for adaptation to different designs and applications. Cutting, shaping, and installation are straightforward, reducing labor time and costs. The natural texture and aesthetic appeal offer advantages in decorative projects. Its environmentally friendly nature makes it a key material in sustainable construction and modern architecture.
Mill scale is considered an unwanted layer on steel surfaces because:
It reduces surface quality and causes roughness.
It necessitates surface cleaning before painting, coating, or welding processes.
It can cause wear and surface defects on rolling mill rollers.
However, in some cases, mill scale can act as a protective layer. For example, it can slow down oxidation during short-term steel storage.
The main methods used to remove mill scale include:
Mechanical Cleaning: Removing the layer by sanding, brushing, or sandblasting.
Chemical Cleaning (Pickling): Dissolving the mill scale in hydrochloric or sulfuric acid baths.
High-Pressure Water Jet (Descaling): Commonly used in rolling mills, where mill scale is removed with a high-pressure water stream.
In modern facilities, mill scale is not considered waste. It can be:
Used as a raw material in the re-melting process due to its high iron oxide content.
Utilized in cement or pigment production.
Tufal is increasingly important as a critical material for sustainable and environmentally friendly construction. Its light weight, insulation properties, and aesthetic appeal provide advantages in modern architectural projects. Its contribution to energy efficiency helps reduce environmental impact. Tufal is valued in the industry as a material that enhances both structural safety and user comfort.
Its industry relevance is reinforced by the benefits it provides across different projects. Industrial buildings, residential projects, and decorative areas can utilize various types of tufal. High-temperature resistant types ensure safety in infrastructure and industrial projects, while aesthetically appealing types stand out in landscaping and architectural designs.
Tufal stands out as an eco-friendly and sustainable material in the construction sector. Its natural origin and recyclability reduce environmental impacts. Its light weight and thermal insulation properties contribute to energy savings and reduce the carbon footprint of buildings, making it ideal for environmentally sustainable projects.
In sustainable projects, tufal offers nature-compatible and energy-efficient solutions. It can be used in landscaping applications and green building designs. Its long lifespan and durability reduce maintenance requirements and promote efficient resource usage. Tufal is a valuable construction material that combines environmental responsibility with modern construction techniques.
Although tufal is a natural byproduct of steel production, it is a critical element that requires careful management for quality control.
Timely and proper removal of mill scale is a crucial step in hot rolled steel production, affecting surface cleanliness, production line efficiency, and final product quality.
