Sandwich Panels

Sandwich panels are composite materials manufactured with inner core material (PIR, PUR, Rockwool) between two painted Galvanized or Aluminum corrugated sheets for thermal insulation.

Used as a coating material in building roofs, exterior walls, and interiors or cold rooms, sandwich panels ensure efficiently high thermal, water, and acoustic insulation as well as preventing humidity concentration and condensation.

Additionally, it is mainly preferred in architectural applications for its excellent bearing capacity. The bearing capacity of sandwich panels depends on the fatigue and thickness characteristics of the inner core material of the panel as well as the form of metal surfaces. Sandwich panels offer an economical solution based on cost-benefit analysis.

The thickness of metals (i.e., painted galvanized sheet metal, aluminum, etc.) and inner core materials is determined in line with the application surface and the load to be applied onto the surface. Climatic conditions in the region for application are also taken into consideration to determine the thickness of the inner core material. Sandwich panels ensure thermal, water, and acoustic insulation without requiring any additional coating such as plaster, paint, etc., and form the building envelope aesthetically and cost-effectively. It is procured with the best available rates and used in building structures having a load-bearing system made of steel or prefabricated reinforced concrete such as industrial buildings, military buildings, community facilities, agricultural structures, sports facilities, construction site buildings, silos, hypermarkets, shopping malls, cold storage rooms, and marketplaces.

In Assan Panel plants, products to meet the requirements of any kind of architectural project are manufactured by aluminum or painted galvanized sheet metals in any desired quantity and custom dimensions.

Sandwich Panel Materials

Materials are categorized under two groups wherein all materials such as polyurethane, PIR, polystyrene, phenolic are called Plastic Foam and Rockwool falls under inorganic fiber material.

People often wonder about the differences or performance variations between these materials. In terms of technical specifications of sandwich panels being used in a wide range of applications, it is a fact that there are still some misunderstandings as well as a lack of accurate information in general.

The type of core material plays a crucial role in choosing the right composite sandwich panel by taking into consideration other key factors such as mechanical strength, insulation, fire performance, and production processes in line with the building physics.

From this viewpoint, it is also important to correctly identify all performance expectations for these materials and compare to one another.

PUR / PIR (Polyurethane): Polyurethane (PUR) and Polyisocyanate (PIR) are plastic foams which are most commonly used in the production of sandwich panels. Having preferred mostly in laminated lines, these types of plastic foams provide superior advantages thanks to their binding properties during the foaming process. In recent years, its chemical properties have been further improved allowing for increased fire performance advantages. For its production, eco-friendly n-pentane is used as a blowing agent. Polyurethane has been used for about 50 years in the production of sandwich panels and considered as the most reliable insulation material.

XPS / EPS (Polystyrene): Polystyrene foam is found in two forms as Extrude (XPS) and Expanded (EPS). It is bound to metal surfaces by using additional adhesives in sandwich panel applications. Categorized as thermoplastic, polystyrene foam melts in low temperatures.

Phenolic Foam (PF): As compared to other plastic foams, phenolic foam is considered a relatively new material. It is rarely used in sandwich panels. Phenolic foam offers the best fire performance among plastic foams.

Rockwool: It is a type of mineral wool obtained by melting and spraying of various minerals such as basalt, dolomite, and diabase, etc. followed by mixing with bakelite and then undergoing special treatment processes. Giving excellent results in terms of fire resistance and acoustic insulation, rockwool has relatively lower insulation properties compared to plastic foams in thermal insulation.

Sandwich Panel Technical Specifications

Aşağıda sunulan teknik bilgiler özel bir üreticiye özgü olmayıp, fikir vermek amacıyla ifade edilen genel karşılaştırma verileridir:

1. Mechanical Strength

Variables such as compressive, tensile, and shear strength as well as shear modulus, etc. are key elements to determine mechanical strength advantages of composite materials. In addition, resistance or strength in composite materials is directly correlated to interactions of components with one another. Materials such as polystyrene foam and rockwool are bound to metal surfaces using additional polyurethane-based adhesives while polyurethane, PIR, and phenolic foams are bound to metal surfaces on their own by expanding from its liquid mixture state. Although EPS and XPS are good insulating materials with highly cost-effective production processes, their need for additional adhesives causes them to be used less in sandwich panel applications. Even though the tensile strength of the adhesive on metal surfaces is generally higher than the tensile strength of polystyrene inner core material, analyses require that this value should not go below 0.10 N/mm2. Otherwise, potential stresses may cause surface distortions. In addition to ambient temperatures and potential exposure to moisture, viscoelastic behavior (i.e., creep factor) of foam materials as a result of sustained loads should also be taken into consideration during the careful assessment of properties of this type of materials containing polymers, especially during designing stages of sandwich panels. The mechanical properties of sandwich panel plastic foams are directly correlated to density while they are not the primary factor in materials such as rockwool and may vary based on production processes such as those related to the characteristics of fibrous structure. PIR foams differ from PUR polyurethane foams only in terms of the variation in proportion of ingredients used in production. Therefore, mechanical and physical characteristics of both types of foam as well as foaming process are quite similar to each other.

Having been developed to further improve the fire performance of polyurethane since 1970s, phenolic foam's mechanical strength has been found to be associated with certain problems in recent years. Early panel disintegrations which are reasonably believed to arise due to decomposition of the phenolic structure over time have been observed in sandwich panels containing phenolic foam, which are mainly used in roof applications especially when there is considerable pedestrian traffic. Inner core material characteristics of sandwich panels should be paid great attention especially in structures repeatedly undergoing sustained loads.

2. Thermal Insulation

Thermal conductivity coefficient (λ) is specific to each material. It is an expression of heat flow in Watt (W) arising when the temperature difference between internal and external surfaces is 1 Kelvin for a material of 1 m thickness with a surface area of 1 m². Thermal conductivity values of typical insulating materials are provided in the table below. Lower thermal conductivity values mean higher thermal insulation achievement and the desired performance can easily be achieved by an insulating material with less thickness. Thermal conductivity in all insulating materials varies based on temperature. However, this is generally a linear relationship. When determining material thickness in calculations, temperature is assumed to be 10°C in typical applications and thermal conductivity design values are determined based on this temperature.

Although the initial heat transmission value is a key variable in selecting the optimal thermal insulating material, insulation properties in aged material should also be taken into account due to the fact that insulating capacity decreases over time, especially in plastic foams. Comparing their low values for insulating properties in addition to taking into consideration their multi-purpose use and long-lasting performance, PUR/PIR foams offer the optimal solution. While the closed-cell structure of plastic foams provides better water resistance, inorganic materials such as rockwool may cause a significant decrease by up to 75% in thermal performance when such inorganic materials come into contact with water.

3. Water Absorption Capacity

Insulating materials are expected to be not directly vulnerable to water exposure. In addition, their thermal conductivity should not increase due to indirect water absorption through capillarity. Fibers found in rockwool don't actually get wet; however, rockwool absorbing water due to air circulation affected by capillary absorption between fibers may cause a decrease in its insulating performance.

4. Density

Consumed material quantity may be reduced efficiently only by aiming for the best performance to the greatest extent possible with the lowest density by taking into consideration the production costs. Especially in plastic foams, density has a direct impact on mechanical strength. On the other hand, sandwich panels manufactured using rockwool with high densities cause installation challenges as well as introduce additional loads on load-bearing structures in buildings due to increased weights. The thermal conductivity coefficient varies based on various factors that are not time-dependent. Such factors include, for instance, closed-cell percentage, sample thickness, longer diffusion time, slower change in thermal conductivity coefficient, cell size, type of foaming agent as well as other factors as applicable. The following table shows the effects of density on thermal conductivity coefficient.

5. Temperature Resistance

Each thermal insulating material has a temperature point at which it begins to undergo deformation by losing its underlying properties. For this reason, the maximum temperatures to which the material will be exposed on application site must be determined in advance and material suitable for this temperature must be selected.

6. Water Vapor Permeability

Water vapor permeability is an important factor to ensure comfort in buildings. Water vapor diffusion resistance (µ) and vapor diffusion thickness (sd-value) are two key characteristic values. Water vapor diffusion resistance (µ) value is specific to each material and calculated by comparing the air resistance value taken as 1. In sandwich panel systems, water vapor permeability also varies based on the density of the material, connection details, manufacturing process, and the type of metal surface. As the vapor diffusion resistance increases, the quantity of vapor to pass through the material decreases. Thermal insulating materials are expected to have a high vapor diffusion resistance coefficient.

7. Acoustic Insulation

Variables and calculation methods required for acoustic insulation of roof and exterior wall cladding are determined during the design stage. A portion of acoustic waves hitting a surface is reflected, some of them are absorbed, and the rest of them are transmitted. Reflection, absorption, and transmission rates vary based on the shape of the surface, acoustic absorption of the material, and audio frequency. Closed-cell plastic foam materials are essentially used as thermal insulating materials. Open-pore materials (e.g., fiberglass, rockwool, acoustic foam, etc.) are used for airborne-sound insulation. Materials with acoustic absorbing capabilities are made of porous or fibrous materials and they act by transforming a portion of acoustic energy into thermal energy by causing friction losses in air entering in capillary spaces within structures. Characteristics of rockwool sandwich panels contributing to acoustic insulation are way more advantageous as compared to other types of panels.

8. Dimensional Stability

Volumes of all plastic foams are affected by changes in temperature. The pressure of gases contained in cells increases as the foam temperature increases and this causes expansion. The exact opposite condition (i.e., contraction) arises in case of a sudden decrease in temperature. Due to negative pressure, foam structure may potentially be damaged. This must be taken into consideration, especially during the cooling process after the production of PUR foams.

9. Chemical Resistance

Due to corrosion, materials may lose all of their functions such as mechanical strength in addition to disruption in visual characteristics. At all times, all building materials and components are required to be either resistant to corrosion or otherwise additional measures are required to be taken to protect such materials against corrosion. From this perspective, just like metal surfaces, the inner core materials of sandwich panels should also be resistant to corrosion. Used as a catalyst in the production of phenolic foams, aromatic sulfonic acid may dissolve when it comes into contact with water. Sulfuric acid dissolved through phenolic foam with high volume of water absorption and infiltrating through metal surfaces may cause corrosion of metal.

10. Fire Performance

Categorized in inorganic materials, rockwool is included in Non-combustible class. Sandwich panels in which rockwool is used as the core material offer the best advantage in fire-resistant exterior wall, roof, or interior wall applications. In addition, considering the fire resistance of rockwool sandwich panel of 100 mm thickness, it varies between 30 and 120 minutes based on the type of rockwool and connection/fitting details as applicable. On the other hand, rockwool and polyurethane-based adhesives allowing for binding to metal surfaces demonstrate an equivalent behavior similar to PUR sandwich panels at the early stages of fire. All plastic foams are organic. Therefore, all of them are combustible. Fire resistance of such materials varies based on selection of suitable raw materials, foaming process, fire-retardant additives, and inorganic components used in formulations. General characteristic features of plastic foam are as follows. PUR/PIR: The right chemical formulation in plastic foams may offer advantages in terms of fire performance. High percentages of isocyanate content and fire-retardant additives used in formulation are determinative factors in fire performance of polyurethanes. PUR materials begin to decompose at 150-200°C and cause combustion and emission of fumes at temperatures over 300°C. For instance, polyurethane foam of 60 mm in thickness achieves up to 30 minutes for critical fire resistance time in tests conducted. XPS/EPS: Both expanded polystyrene (EPS) and Extruded polystyrene (XPS) are pastic foams with the lowest fire resistance values. They begin to melt at 100°C and create droplets during fire. Phenolic Foam: With its polymeric structure, phenolic foam provides better performance against fire as compared to PUR/PIR foams. In addition, it results in low emission of fumes equivalent to those of PUR/PIR foams. On the other hand, phenolic foam, which has been developed in order to improve fire resistance of plastic foams, may have certain disadvantages. Main disadvantages include low mechanical strength especially for the acid used in production process as well as being fragile and relatively low thermal insulating capabilities.

Sandwich Panel Prices

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