Introduction

Rock wool, also known as mineral wool or stone wool, is a highly efficient and versatile

insulation material made from volcanic rock, primarily basalt and diabase. It is widely used in

construction and industrial applications for its excellent thermal, acoustic, and fire-resistant

properties. As one of the most advanced and sustainable insulating materials available today,

rock wool plays a crucial role in improving building performance and energy efficiency.

The origins of rock wool date back to the early 20th century when researchers discovered a

method to melt volcanic rock and spin it into fibers. The process mimics a natural phenomenon

where volcanic eruptions produce fibrous ash when lava interacts with cool air or moisture.

Today, modern manufacturing methods use high-temperature furnaces to melt raw materials,

which are then spun into fine, interwoven fibers resembling wool.

The primary raw material for rock wool is basalt, a dense and hard volcanic rock. Other

materials like dolomite and recycled slag may also be included. These components are heated to

temperatures exceeding 1,500°C (2,732°F) until they melt into a lava-like consistency. This

molten rock is then rapidly spun and cooled to form thin, wool-like fibers. The resulting product

is lightweight, yet robust, with a complex, open structure that traps air and resists heat transfer.

One of the defining characteristics of rock wool is its outstanding thermal insulation. Its fibrous

structure creates countless tiny air pockets, which significantly reduce heat conduction. This

makes it an ideal material for insulating buildings, helping to maintain comfortable indoor

temperatures and reduce energy consumption for heating and cooling.

In addition to thermal performance, rock wool excels in sound insulation. Its dense, irregular

structure absorbs sound waves, reducing noise transmission between rooms and from external

sources. As a result, it is commonly used in offices, studios, homes, and industrial facilities to

improve acoustic comfort.

combustible stone, rock wool can withstand temperatures above 1,000°C without melting or

releasing toxic fumes. This makes it a preferred material in fireproofing applications, especially

in high-rise buildings, tunnels, and industrial complexes where safety is paramount.

Rock wool is also resistant to moisture, mold, and mildew. Unlike organic materials, it does not

rot or decay when exposed to humidity. This ensures long-term performance and durability,

especially in damp or humid environments. It also contributes to healthier indoor air quality, as

it does not support microbial growth.

Environmentally, rock wool is considered a sustainable insulation choice. It is made from

abundant natural resources and often includes recycled industrial waste, such as slag.

Furthermore, rock wool insulation can significantly reduce energy use in buildings, thereby

cutting carbon emissions over the lifespan of a structure. It is also recyclable at the end of its

use.

The installation of rock wool is relatively straightforward. It is available in various forms, such

as batts, boards, rolls, and loose-fill. These products are easy to cut and fit between studs, joists,

and rafters in walls, roofs, and floors. Some variants are also faced with foil or other membranes

for specific vapor or thermal control requirements.

Compared to other insulation materials, such as fiberglass, polyurethane foam, and polystyrene,

rock wool offers superior fire resistance and sound insulation. While it may be heavier and

slightly more expensive, its durability and multi-functional performance often justify the

investment.

In industrial settings, rock wool is used for insulating pipes, boilers, storage tanks, and process

equipment. Its ability to maintain thermal performance at high temperatures makes it ideal for

power plants, chemical factories, and refineries.

systems. The material provides excellent water retention and air circulation, helping plants grow

efficiently in soilless environments.

Architects and engineers appreciate rock wool for its design flexibility and its contribution to

energy-efficient building envelopes. It helps meet modern building codes and green building

certifications such as LEED and BREEAM. It also supports goals for net-zero energy buildings

and sustainable development.

Despite its many advantages, there are some considerations. Handling rock wool may cause

temporary skin or respiratory irritation due to loose fibers. Therefore, protective gear is

recommended during installation. However, modern formulations have improved fiber stability,

reducing these effects significantly.

Over the past decades, the demand for rock wool has grown significantly as awareness of energy

conservation and building safety has increased. Countries with strict energy efficiency

standards, such as those in the EU, promote the use of rock wool in both residential and

commercial construction.

Research and development continue to improve rock wool products, making them thinner,

lighter, and more efficient without compromising performance. Innovations include high-density

panels for façade insulation, acoustic ceiling tiles, and sandwich panels for prefabricated

buildings.

Rock wool manufacturers often emphasize closed-loop recycling in their operations. Waste rock

wool generated during production or construction is collected and reused, minimizing

environmental impact. This circular economic approach aligns with global efforts to reduce

waste and promote sustainable building practices.

In summary, rock wool is a high-performance insulation material with exceptional thermal,

acoustic, and fire-resistant qualities. Its durability, sustainability, and safety features make it a
top choice in both construction and industrial applications. As the world moves toward more

energy-efficient and resilient buildings, rock wool continues to play a central role in achieving

those goals.
The definitions of Wool Rock

Rock wool, or mineral wool, is an insulation material made by melting volcanic rock—usually

basalt or diabase—at around 1,500–1,600 °C, then spinning it into fine, wool-like fibers These

fibers are bonded (often with small amounts of resin) into batts, rolls, boards, or loose-fill

forms for versatile applications.

Thanks to its fibrous structure, rock wool excels in thermal insulation—its trapped air pockets

significantly reduce heat transfer. It also provides excellent acoustic insulation, absorbing and

dampening sound waves, ideal for quiet and comfortable spaces.

A major benefit is its outstanding fire resistance—being non-combustible, it can withstand

temperatures over 1,000 °C, making it a preferred choice for fire-safe constructions.

Rock wool is moisture-resistant and mold-proof, as it’s inorganic and doesn’t support

microbial growth—this ensures long-lasting performance even in damp environments.

It's also valued for being sustainable and recyclable: manufactured from abundant natural

minerals (and often recycled industrial slag), it’s eco-friendly and reusable.

Common forms include batts, rigid boards, and loose-fill, which are used in walls, roofs,

floors, industrial equipment, and even HVAC systems.

Comparatively, rock wool is more dimensionally stable over time—it doesn’t sag or lose R-

value and maintains insulation quality throughout its lifespan.

Although it can be slightly more expensive than alternatives like fiberglass, its durability, fire

safety, and acoustic performance often justify the cost

Due to fine fibers, protective gear (gloves, masks) is recommended during installation—

modern versions are designed to reduce irritation.

treatments, and fire protection systems—valued in residential, commercial, and industrial

settings alike.

MELTING THE RAW MATERIALS

Cupola furnace operation

The cupola furnace is an apparatus designed to melt magma rocks and their supplements,

utilizing coke as its fuel source. It is loaded from the top with pre-prepared bundles of magma

rocks and coke. Inside the furnace, various chemical and thermal reactions occur. The

melting process is affected by the composition and quantity of the materials fed into it, as

well as the under draft.

The under draft is essential for the optimal operation of the cupola furnace, acting as a

regulator for the melting speed and impacting the properties of the melt directly. It is

achieved through the use of concentric nozzles positioned around the furnace's periphery,

which deliver air in a precisely regulated manner regarding both volume and temperature.
This air can also be enriched with oxygen. The under draft enhances the combustion of coke,

generating extremely hot gases that ascend through the furnace, transferring heat energy to

the magma rocks and coke. The exhaust gases exit the cupola furnace at around 400°C.

Thanks to the heat transfer, the materials located above the nozzles start to melt and flow

downward toward the bottom of the cupola, where the melt level is controlled using a siphon.

The cupola furnace can be categorized into various zones based on its operation, as illustrated

in Fig. 2.1 [8]. The initial zone is known as the heating zone, where the raw materials are

heated, leading to the loss of moisture and gas. The indirect reduction of iron oxide begins at

temperatures between 300–400°C, and this zone operates within a temperature range of 200–

800°C. The second zone is referred to as the re-formation zone for the added materials, as

depicted in Fig. 2.1. The temperature in this zone ranges from 800°C to 1250°C. Here,

dolomite (CaC𝑂3 , MgC𝑂3) decomposes, releasing CO2. Amphibolite can be broken down as

it becomes more brittle at elevated temperatures. Additionally, iron oxide undergoes further

reduction. Casting coke remains inactive until it attains a temperature of 1000°C. The direct

reduction of iron oxide (FeO) is achievable.

materials, as depicted in Fig. 2.1. Magma rocks and dolomite usually begin to melt at

temperatures ranging from 1250 to 1350°C. The melting process of magma rocks is

influenced by the types of minerals present and their granulation. At such elevated

temperatures, the solidity of amphibolite diminishes. The significant weight above the

furnace causes the material beneath to crush, making it easier to melt. A similar process

occurs with dolomite, which decomposes at approximately 800°C, releasing CO2. Grains of

CaO and MgO ignite at around 1200°C before melting at even higher temperatures. When

briquettes are melted, additional unknown quantities, including thin calcinated bauxite and

non-fiberized crushed melt, are produced. These substances combine, held together by

cement, to form a solid structure. Briquettes mainly consist of waste materials generated

during production, with a significant portion made up of previously fiberized mineral

materials and products from the fiberization process occurring within the furnace. Cement

phases bond with each other and sublimate at about 600°C.

The fourth zone, where coke burning occurs, is situated above the nozzles (illustrated in Fig.

2.1) and concludes at the melting bed. In this area, coke reaches the temperature required for

combustion with oxygen, around 600–700°C. The underdraft may be cold or heated, which

accelerates the coke burning process. It is understood that coke can burn to produce carbon

dioxide (CO2) and carbon monoxide (CO). The full oxidation release of heat energy is

substantially greater in the case of CO2, which occurs when there’s sufficient underdraft for

the coke. Above 600°C, thermodynamic conditions favor the generation of CO, which can

form from CO2 as it passes through the base coke. This reaction depends on temperature, the

contact surface area between CO2 and coke, and the duration the gases remain in contact with

the base coke. However, from a thermal perspective, this reaction is undesirable as it

consumes casting coke and is endothermic. An increase in CO promotes an atmosphere of

reduction, enhancing the ability of Fe2O3 to reduce into pig iron. Caster and mineral wool
manufacturers prefer using casting coke in cupola furnaces due to its reduced reactivity. CO

is generated more readily with casting coke, which also produces a greater thermal effect.

Within the fourth zone, temperatures reach their peak just above the melting bed,

distinguishing between the highest temperatures of gases, coke, and the incoming melt.

Research from Danish scientists [8] indicates peak temperatures of approximately 1500°C for

the melt, around 1800°C for the coke, and over 2000°C for the gas. It has been established

that the melt’s temperature elevates to between 1300–1500°C while traversing this zone and

maintains this temperature upon exiting the cupola furnace (as shown in Fig. 2.1)

The fifth zone, located at the bottom of the cupola furnace, is referred to as the separation

zone. In this area, due to physical principles, pig iron separates from the silicate melt (slag)

and sinks due to its higher density.

Processes and chemical reactions in the cupola furnace