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SANDWICH PANEL MECHANICAL STRENGTH

Used as a cladding material in building roofs, exteriors, interiors, or cold rooms, sandwich panels are featured in architectural preferences thanks to its quick assembly, high insulating properties as well as load capacity. Various factors such as dead weight, wind load, temperature affect buildings on its own or in combination with each other. ASSAN PANEL roof and exterior wall system load-bearing tables offer various products suitable for any specific architectural project requirements. As sandwich panels are composite materials consisting of polyurethane filling material between two metal sheets, their behavior against the exposed loads should be evaluated with caution. Although each of metal surfaces and polyurethane filling material has individual bearing capacity, they have difficulty in even carrying their own weight due to low young’s modulus (elasticity) values. On the other hand, since composite form offers high shear strength and bending strength, each layer provides a new system having a better load bearing capacity. Due to homogeneous distribution and high adherence in joints, only the metal surfaces account for the bending moment, which directly affects buckling on the surface. On the other hand, most of the shear effect is compensated by the filling material which is thicker than the metal surfaces. For this reason, composite system offers various advantages to sandwich panels due to increased shear capacity. In conclusion, corrugated form of panels and filling material strength greatly affect the bearing capacity.

SANDWICH PANEL FILLING MATERIALS

The most preferred inner core filling materials in sandwich panel applications consist of various materials such as Polyurethane, PIR, Polystyrene, Phenolic Foam, and Rock Wool. These materials are categorized under two groups: all materials such as Polyurethane, PIR, Polystyrene, Phenolic Foam are categorized as Plastic Foam whereas Rock Wool is categorized as an inorganic fiber. People often ask and wonder about how they are different from each other or what kind of performance advantages are offered by each of these materials. Although sandwich panels are used in a wide range of applications, there are significant misconceptions about their technical specifications in addition to the lack of reliable information flow. The type of core material plays a very crucial role in choosing the right composite sandwich panels taking into consideration the mechanical strength, insulation, fire performance, and manufacturing processes in line with the building physics. From this perspective, it is highly crucial to correctly identify all performance criteria expected from the materials and compare them to each other in a reliable manner. PUR/PIR (Polyurethane), namely, Polyurethane (PUR) and Polyisocyanurate (PIR) are among the plastic foams that are most used in the production of sandwich panels. Generally preferred in laminated lines, they offer significant advantages as this type of plastic foams has outstanding adhesion properties during the foaming process. In recent years, their chemical properties have been improved leading to increased fire performance. In their production, environmentally friendly n-Pentane gas is used. Having been used for over 50 years in sandwich panel production, polyurethane is known as the most reliable insulating material to date.

SANDWICH PANEL PERFORMANCE ADVANTAGES

With the development of manufacturing technologies coupled with high quality materials, sandwich panels with high load bearing capacity can be manufactured. Load bearing capacity not only depends on the density and thickness of the core filling material, but it also depends on the form of the metal surfaces and such panels are able to effortlessly carry loads that are significantly higher than their own weights. With these capabilities, sandwich panels are preferred as a cladding material in roof and exterior wall applications. Sandwich panels are the most ideal building material that can be used in essentially all buildings with steel, wooden, or reinforced concrete construction. In addition, sandwich panels allow for cost savings from construction materials thanks to increased purlin spacing with the selection of suitable sandwich panels as well as saving time in terms of total time of assembly. With the use of sandwich panels in buildings with custom production of panels available up to 18 meters in length, the assembly works as well as the number of joints in the covered surface will be reduced significantly. Sandwich panels are mounted on large exteriors and roof surfaces in a relatively short period of time thanks to improved shipment and transportation facilities. A rough estimate of assembly times of 10 minutes/m2 for exteriors and 8 minutes/m2 for roofs can be provided as reference data. Whereas sandwich panels do not restrict construction volume or building height, limit values are determined based on the supporting structure. Despite their standard components and limited availability of length options, sandwich panels offer limitless design opportunities for designers. Horizontal, vertical, or angular installation of panels or using varying color options allow for visual dynamics in exterior wall structures. In addition, potential design options for designers increase even more thanks to panels that can be used for multiple purposes in interior sections of buildings. Joint details include joints connecting panels and those connecting panels to the supporting structure. Tight joint providing insulating functions is ensured by using double tongue-and-groove joints in exterior wall panels and generally tongue-and-groove joints together with lateral joints in roof panels. The main requirement expected from joints is to provide airtightness, thermal insulation, and easy assembly. Easy assembly basically means that the components fully fit into each other easily during installation.

Recent studies have shown that panels offer 100 times better airtightness properties than even the highest quality windows. In addition, panels used in exterior walls are manufactured with hidden screws and therefore providing an aesthetic appearance without exposing any screws. With careful planning, large-scale expanding and renovations can be carried out without causing any disturbance to indoor activities in the building. Sandwich panels allow for longitudinal and transverse extensions based on the building structure. In addition, they offer economic and practical advantages for application as panels may be removed and reassembled elsewhere for reuse.

Sandwich panels redeem their cost within a short period of time. In addition to economic advantages provided during assembly, these panels offer more distinct amortization advantages with the energy efficiency provided by thermal insulation as compared to other building materials. By checking thermal conductivity values of the materials, energy efficiency provided can be easily identified in comparison with other materials. As PUR sandwich panels has a lower thermal conductivity coefficient compared to all other similar thermal insulation materials, they offer high insulation and energy efficiency. Therefore, they allow for preservation of resources. In addition, generating electricity using solar power by installing solar skylights on the panels is also possible. In addition to the reduced shipment time and costs, the lightweight design of sandwich panels allows for decrease in basic construction costs as it offers lower load transmission to the supporting system of the building, thus providing a positive effect. Moreover, they have low maintenance cost with a long-lasting use life. Durability of sandwich panels is ensured by modern finishing used in the panels that offers protection against high-level corrosion and UV lights.

Contrary to concrete and gas concrete used in building exteriors, PUR sandwich panels provide the same thermal insulation with very low thickness. Therefore, the total available space and volume within the building are measurably expanded.

Also known as condensability capacity, the contribution of the material to spreading fire or even the fire resistance of the material is defined as fire performance. A panel system consisting of a non-flammable metal surface and polyurethane is defined as B, s2, d0 (i.e., almost non-flammable) according to EN 13501 standard; however, potential fire behavior in buildings may not be evaluated simply based on the resistance to fire of the exterior coating material as various other factors play a role in fire behavior. Materials such as textile, furniture, PVC joinery, etc. present in the buildings are generally highly sensitive to fire and cause the fire to spread throughout the building. Therefore, each of fire safety parameters before and after fire plays a crucial role in taking necessary measures. Corrosion developing over time as water comes into contact with certain materials such as steel leads to various problems in terms of load bearing in addition to visual issues in buildings. Moreover, serious financial losses may occur as a result of water leakage from roof or exterior walls damaging materials such as fixtures and furniture, etc. located inside the building. Potential water leakage may be prevented by double tongue-and-groove joints system used in exterior wall panels. Roof panels are determined based on roof gradients in order to ensure waterproofing. The required waterproofing is ensured even in case of roof panels installed by a 5% gradient thanks to capped roof panels. High waterproofing is ensured by membrane panels in roof applications installed in roofs with a gradient lower than 5%. On the other hand, water vapor due to condensation affects the building, causing chemical degradation and deterioration of comfort conditions. Water vapor risk does not play a significant role in sandwich panels. This is because insulated metallic surfaces serve as a strong stabilizer in buildings.

Polyurethane (PUR) sandwich panels provide satisfactory levels of acoustic absorption in normal industrial buildings based on the requirements of the building; however, these are not adequate for other locations or offices that are too sensitive to noise whereas additional solutions such as vibration dampers can be used in such cases. In the production of polyurethane, which is the core filling material of sandwich panels, fully green systems are used, and production procedures are carried out using environmentally conscious systems. n-Pentane, a type of gas which is currently used to blow out polyurethane is not harmful to the environment. In addition, polyurethane can be reprocessed into powder to be reused as a thermal insulation material. Sandwich panels to be installed in roofs and exterior walls, which are defined as the building envelope, ensure protection of the building against external factors and thus ensuring long service life, energy efficiency as well as providing more comfortable living conditions.

SANDWICH PANEL AND ENVIRONMENT

Environmental compliance of building components consisting of various materials is one of the most crucial topics that need attention. An overview of the physical characteristics of sandwich panels indicates that all components of sandwich panels including metal surfaces, organic finish, polyurethane (PUR) core filling materials etc. are safe components. Such components remain safe from the assembly of the materials to the building up to the entire use in the building after assembly. The safety of this cladding system which has been in use for over 50 years except for minor revisions is already evident from previous experience.

Including applications that require food safety, all materials used in sandwich panels easily meet the requirements for good hygiene practices. Polyurethane as the core filling material offers significant advantages with its biological properties such as being odorless in addition to being highly resistant to contaminants, mold, and decay. In addition, a high level of insulating capacity also makes it the ideal core filling material. The ecological effects of gases used to blow out polyurethane are one of the important issues required to be addressed. Based on various studies conducted, it was found that gases previously used within this scope had adverse effects in the ozone layer. With an aim to find a solution to this problem, environmentally conscious sandwich panel manufacturers have made great efforts and begun using environmentally friendly n-Pentane gas.

In a natural cycle, any form of energy consumption has a certain effect on the environment. Although the content of these effects is complex in nature, they are often related to emissions released into the atmosphere. The amount of energy used for heating purposes has a direct effect on ecological balance. For such reasons, high-capacity insulating materials used in buildings provide significant environmental advantages in addition to economic contribution. In conclusion, insulating materials used in buildings for a long period help protect energy resources as well as contributing to reduction of emissions in the atmosphere.

Sandwich panels are the most effective cladding system in terms of economic and ecological aspects thanks to its polyurethane core filling with high insulation capacity as well as its technology that does not create a thermal bridge. Although there is energy consumption during the production processes of sandwich panels, it is considered to have a minimum impact as compared to the energy efficiency provided during their use. The greatest advantage of sandwich panels within the energy cycle is their long service life. Their polyurethane filling material has commonly been used as an insulating material for about 50 years. Since the beginning of 1960s, polyurethane has proved to be the most effective insulating material used in cold room systems despite the significant differences between the interior and exterior temperatures.

Today, whether materials are recyclable is among the most crucial parameters in terms of environmental concerns. Thanks to its long service life, the unused portions of polyurethane materials used in buildings remain negligible as compared to the production volumes. Provided they are disassembled carefully without causing any damage, sandwich panels can be reused. In case the polyurethane material that has been used for many years is not suitable for reuse due to damage or being no longer required, then there are three different recycling methods are available. Since older versions of polyurethane materials still contain CFC gas which is harmful to the ozone layer, such materials and raw materials are not suitable for recycling, and therefore, only the energy recovery is considered. Polyurethane materials containing CFC gas and that have been used over the years may be used in new materials only under special conditions. Recycling of the metal surfaces of sandwich panels is often preferred in the metal industry.

SANDWICH PANEL AND ACOUSTIC INSULATION

Acoustic insulation should be used in areas where protection against the harmful effects of noise is required or areas where prevention of noise emissions to the surrounding environment is required. Many countries have their own regulations on noise emissions issued based on the following factors:

  • Environmental exposure to noise from industrial premises
  • Traffic noise exposure in buildings
  • Indoor noise levels in buildings

The required parameters and calculation methods for acoustic insulation between the rooms as well as acoustic insulation of roof and exterior wall cladding can be determined during the design stage. Some portion of the sound wave hitting on a surface is reflected while another portion is absorbed, and the remaining portion is transmitted. The rates of reflection, absorption, and transmission depend on various factors such as the shape of the surface, sound absorbing properties of the materials, and the audio frequency. Sound absorption materials consist of porous, or fiber materials and they are effective in the transformation of some portion of acoustic energy into thermal energy by causing friction losses in the air entering in the pores found in their structures.

Polyurethane (PUR) sandwich panels provide satisfactory levels of acoustic absorption in normal industrial buildings based on the requirements of the building; however, these are not adequate for other locations or offices that are too sensitive to noise whereas additional solutions may be required in such cases.

Example for calculation:

What is the acoustic transmission loss of 70 dB noise of 630 Hz frequency in polyurethane (PUR) sandwich panel? Using the table showing the change of acoustic absorption coefficient based on frequency:

70 dB x 0.49 = 34.3 dB 70 dB – 34.3 dB = 35.7 dB (resulting sound level).

FIRE TESTS AND CLASSIFICIATION IN SANDWICH PANELS

Many countries have introduced regulatory requirements with an aim to determine the acceptable minimum level for fire protection. These requirements serving as guidelines may not answer all questions of the designers; however, they provide insights. Fire regulations are considered crucial for EU whereas it is not paid enough attention in Turkey. To sum up, regulatory provisions related to fire safety have been drafted based on the following requirements (without limitation):

Fire outbreak and spread of fire and fumes inside the building should be limited (Reaction to Fire). Load bearing capacity of the constructed building should not be decreased for a certain period (Fire Resistance). Spread of fire to surrounding buildings should be limited (Active Safety Systems). Building occupants should be able to evacuate the building or rescued by various means (Fire Detection Systems). The safety of rescue teams should be taken into consideration.

Each of fire safety parameters before and after fire plays a crucial role in taking necessary measures. However, the reaction to fire properties (Fire Performance) of building materials included in the architectural discipline should be evaluated in particular. The contribution of the material to spreading fire or even the fire resistance of the material is defined as fire performance.

Reaction to Fire testing is performed using small-scale models suitable for final use. Exterior wall and roof lines where the fire spreads the most in the building are modeled and subjected to fire testing. All standards and test methods for polyurethane (PUR) sandwich panels are set out in detail in TS EN 14509. In this standard in which fire performance is also included, building materials have been classified under 6 different classes from A1 to F. Other classes of the material are also determined based on the amount of smoke and burning droplets resulting from fire in line with the test reports of the material as follows:

TS EN ISO 11925-2: Small Flame Test (SFI): This fire test method consists of simulating a fire by placing a lighter-sized flame source on a corner or surface of the sample for 15 or 30 seconds. The time until ignition or until the fire exceeds 150 mm is documented. Based on the test results, the fire class is determined as D, E, or potentially F. The fire classes of materials for B, C, and D are not determined only using this test method. In addition to this test, SBI test is also required.

TS EN 13823: REACTION TO FIRE TESTS (SBI)

Based on the principles of this test method, reaction to fire of materials in B, C, and D classes is determined. This test is performed in addition to SFI test. SBI test is a test method carried out by directing a flame source of 30 KW size from a corner of the room to the material. Although internal corner detail is actually used less in exterior wall applications, test results can be obtained by simulating as if an internal corner detail existed. Oxygen consumption, carbon dioxide release, and temperature values are determined in SBI test. By calculating these values obtained, the Total Heat Release (THR) and Fire Growth Rate (FIGRA) data for the first 10 minutes of the sample subject to fire are obtained. This test provides crucial insights about the fire growth for the first 10 minutes and how the material would react to fire in the buildings. The fire classes of the materials (B, C, and D) are determined based on the data obtained. In addition, it is also observed whether the flame spreads laterally (Lateral Flame Spread (LFS)) in the material subject to fire for 20 minutes. If lateral flame spread occurs, such material is classified as D. On the other hand, classification called as d0, d1, and d2 is determined based on whether burning droplets are formed within the first 10 minutes and whether such burning droplets burn for more than 10 seconds. Based on the smoke produced during the first 10 minutes, Total Smoke Production (TSP) and Smoke Growth Rate (SMOGRA) values are determined and then classification as s1, s2, and s3 is assigned based on these values.

REGULATIONS ON FIRE PROTECTION OF BUILDINGS

he objective of these Regulations is to minimize fire that may occur during the stages of design, construction, operation, maintenance, and use of any kind of structures, buildings, facilities, and enterprises used by public institutions and organizations, private institutions, and natural persons as well as preventing loss of life and property due to fire that may occur for any cause in any manner whatsoever.

In our country, the reaction to fire section of the standard on fire protection of buildings was prepared in reference to the German DIN 4102 standards. Upon adoption of the European fire classes, the member states were required to amend their national legislation in line with the EU fire classes. For that reason, TS EN 14509 standard, which also includes provisions on the reaction to fire of Polyurethane (PUR) sandwich panels, has been implemented in our country within the scope of harmonization of the EU technical legislation. A direct comparison of reaction to fire classes as contained in TS EN 13501-1 and DIN 4102 standards may not provide conclusive results as they are different standards; however, the following comparison table designed based on the flammability properties of the materials can be used as reference data.

SANDWICH PANEL ASSEMBLY DETAILS

Manufactured using ideal materials for thermal and acoustic insulation as well as waterproofing and using state-of-the-art technologies, polyurethane (PUR) sandwich panels offer numerous advantages to users as compared to other alternative materials. High-grade quality production is achieved through meticulous and precise control processes. However, users are also required to exercise due care in certain conditions during assembly in order to ensure the highest efficiency in using top-quality panels:

  • One of the most crucial points to pay attention before beginning panel assembly is to determine the predominant wind direction. Panel assembly should be carried out in the opposite direction of the predominant wind direction.
  • The number of screws to be used in assembly should be determined based on the wind conditions and as required by the details.
  • Special attention must be paid to avoid crushing the metal coatings on top of the panels during assembly and shoes with rubber soles should be worn if possible.
  • Panel longitudinal joints should be minimum 25 cm, sealant tape should be used in-between two metal components with joints, and the joint site should be reinforced by applying a pop rivet or puller screw.
  • Components such as fringes and corners that are exposed to wind effect should be fixed to each purlin.
  • In roofs with a low gradient, silicone should be used in joints.
  • During assembly, contact of materials such as steel purlins, concrete, or plaster etc. to panel coating should be prevented by using suitable insulating material or paint.
  • Aluminum materials should be protected against water, snow, and moisture from shipment from the production plant until the time of assembly (to avoid oxidation).
  • When removing panels to be installed on the roof, panels should be placed in a manner to distribute the load throughout the entire roof surface rather than placing them to close proximity to each other as a package. Packages should be placed on the truss rather than in the middle of purlins as much as possible.
  • In order to prevent panels from detachment from the roof due to wind especially in case of windy weather, the exposed panels and panel packages should be firmly fixed to the structure (in case the exteriors of the construction where the panels are intended to be assembled are exposed in the open, wind suction force should always be taken into consideration).
  • Two or more people should try not to stand on the same location during panel assembly works (As this load is considered as point charge and is not considered in panel load bearing tests as indicated by deflection especially in roof ridges and stream sides).
  • Panel pliers should always used during panel assembly to prevent any air transfer between two panels.
  • Panels must always be fixed to all load bearing purlins and horizontal beams.
  • Accessories of a minimum thickness of 0.50 mm should be used for the durability of the works and for aesthetic purposes.
  • As much as possible, all purchase orders for accessories should be placed following measurement on-site after completion of the panel assembly rather than ordering based on the project specifications. In case the time is of the essence, then wing length of such accessories should be kept longer.
  • At joint locations as required between the panels, the joint length should be minimum 250 mm taking into consideration the roof gradient (double-row waterproofing should be provided at joints).
  • The best mechanical way to resolve water problem in roof ridges and fronts is to fold down the edges of the panel left inside the accessory. Subsequent solutions consist of chemical solutions to improve safety and that are inevitable to be provided.
  • Especially in roof ridges and roof front, silicone or foam should never be used in-between the joints of the accessories.
  • It is an ideal solution to use self-drilling steel screw to install panels to steel construction and twisted steel screw to install panels to precast concrete construction during assembly.
  • When installing accessories, using a puller screw to join sheet to sheet and a pop rivet to join sheet to aluminum give better results than other alternative solutions.
  • Screws to be used in assembly must be reinforced by wide flange sleeve with EPDM sealing, which would both prevent water leakage into screws and expand the screw connection surface in roofs and exterior walls in wind suction position.
  • A uniform insulation must be provided in roof ridges by bringing together both panel edges as closely as possible and placing glass wool or rock wool in-between the edges.
  • Flat upper roof ridges should be designed based on the roof gradient to extend minimum 200 mm under the panel edges to prevent wind and water intake inside the building and bitumen-impregnated foam must always be used after folding down the panel edges.
  • When placing purchase orders for accessories (accessories to connect the roof panel to the exterior wall) of exterior building facades (front and back), make sure that such accessories return from the roof panel pitches as much as possible, otherwise, it would be too difficult to prevent water problem.
  • In case of assembly of panels with craft paper, it was observed that panel packages have changed form when exposed to sunlight for a long period, therefore, it is required to assemble such panels as soon as possible from the moment they are delivered on the site and finish coating (membrane layer finish) should immediately be performed (for panels changing its form due to exposure to sunlight for a long period, the panels should be dampened to gain its flexibility just a few hours prior to installation).
  • Especially, painted sheet panels coated with protective film should be protected against sunlight. As the protective thin polyethylene films on the painted sheet would stick to the panels more if exposed to sunlight for a long period of time, it would be difficult to remove them during assembly.
SANDWICH PANEL COLORS

Sandwich panels are categorized under different color groups based on thermal load effects.

Sandvic Panel Renkleri

Color Classes

As compared to light color panels, dark color panels absorb more heat on their surfaces. As a result, significant temperature differences (Δt) arise between the interior metal and exterior metal temperatures especially in high temperature regions. Due to this temperature difference, thermal stresses may occur which could affect the sandwich panel performance, cause corrugation/undulation on exterior metal surfaces, and even may result in detachment in the worst-case scenario.

EN 14509: 2010 standard sets out the applicable requirements.

Maximum exterior surface temperatures for color groups are determined as follows: +55°C for extra light colors, +65°C for light colors, and +80°C for dark colors. Indoor temperature inside buildings as used in calculations is determined as +20°C. While maximum allowable temperatures are used in the summer months in calculations, the assumed temperature in the winter months is determined as -20°C. Therefore, the following temperature gradients are used in calculations.

For each color group:

  • Extra Light Colors Δt = 40°C
  • Light Colors Δt = 45°C
  • Dark Colors Δt = 60°C

Dark Color Panels

Applicable Principles for Dark Color Panels Compared to light color panels, dark color panels are exposed to more thermal stress and due to such stress, they may be subject to deformation and partially lose its original form. Taking this fact into account, the designer is responsible for preventing any potential deformation and changes in form. In such cases, it is recommended to find a solution that would meet the following 3 key requirements:

  • Determination of fixing method based on the purlin distances and load bearing tables;
  • Reduction of maximum panel lengths; and
  • Taking into consideration the temperature on the site during assembly of the panels.

Supporting Structure and Fixing Method

For the design of both wall and roof panels, static calculations taking into consideration deflection and stress analyses as well as temperature parameters should be used. Even though the selected panel is to be installed on a protected side of the structure, dark color panels are recommended for application in a single span system. In multispan systems, minimal surface undulations in the central support are possible due to high thermal stress. Even though it is permitted in the product standards, such surface undulations may cause aesthetic problems. Choosing thick sheets with a thickness of 0.6 mm and above in dark color panel productions would make positive contribution to the surface performance. Unless otherwise provided in writing, Assan Panel does not provide any warranty as to the surface smoothness of dark color panels installed in multispan systems.

Maximum Panel Length

The maximum length of manufactured dark color exterior wall panels is determined to be 6,000 mm. Assan Panel does not provide any warranty as to the surface smoothness of custom panels exceeding this maximum length. On the other hand, sinus form exterior wall panels have no length limitation.

Assembly Temperature

Since the assembly of dark color panels in low temperatures would increase the stress on the panel surface, assembly in ambient temperatures below 10°C is not recommended. Unless otherwise provided in writing, Assan Panel does not provide any warranty as to the surface smoothness of dark color panels installed during the days in which the average ambient temperatures were below 10°C.

POLYURETHANE (PUR)

As an efficient thermal insulation material, polyurethane has been used in buildings since 1950s. Polyurethane (PUR) sandwich panels are ever-increasingly preferred by more investors and designers all around the world. Having the best insulating values among the insulating materials used in buildings, polyurethane provides energy savings up to 40% in ever-increasing heating and air conditioning costs. Use of fossil fuels comprises 80% of CO2 emissions in the world. Use of polyurethane is a rational approach to help reduce CO2 emissions which is also the primary cause of global warming. Investors always seek high performance with low costs and the best solution to this expectation is polyurethane. Polyurethane is (plastic) polymers produced as a result of reactions between isocyanates in NCO group and polyols of OH group.

Contribution reaction is completely a polymerization reaction, and it is a sub-group of plastics. Polyurethane foam is produced by mixing the following 4 raw materials

:
  • Polyol
  • Isocyanate
  • Blowing gas (N-Pentane)
  • Catalyst

In addition to two fluids, i.e., isocyanate and polyol, the ideal closed cell polyurethane foam is produced as a result of chemical reactions of activators. Foam production rates are regulated by the catalyst. With the correct formulation of two raw materials and the control of the foam reaction, the following characteristics of polyurethane are determined:

  • Density
  • Mechanical Endurance
  • Closed Cell Structure
  • Heat Resistance
  • Resistance to Solvents
  • Reaction rate
  • Bonding strength

Roughly, chemical reactions can be described at 4 stages. The first stage consists of mixing Polyol formulation with isocyanate. In this case, a fluid is immediately produced, and foam begins to be produced at the second stage. At the third stage, the foam mixture creates heat and expands in volume by a factor up to 25 times more than its initial volume. At this stage, due to high adhesive properties of the foam, the foam tightly and continuously binds to various materials. At the fourth stage, free foaming creates a resistant layer on the exterior surface. In case there are still fluids at this stage, foaming process continues, and these fluids move to small gaps to fill up. Polyurethane only achieves the most homogeneous foaming process with homogeneous sections. After completion of the foaming reactions, millions of small, closed cells are created. Each cell is filled with blowing gas-originated gas. The underlying reason for polyurethane foam provides the perfect thermal insulation is intracellular gases with low thermal conductivity and polyurethane material with relatively low thermal conductivity. Identifying itself as “Eco-Friendly”, Assan Panel uses HC Pentane (n) gas, which is not harmful to ozone, as a blowing gas in its products.

Thanks to the closed cell form of polyurethane, it does not absorb water due to capillary effect. Water intake is only possible due to diffusion effect based on application. Moisture balance is affected by the ambient temperature and relative humidity. Even under ambient conditions of 100% Relative Humidity (RH), polyurethane is not affected more than 5% in weight and more than 0.15% in volume as these are the maximum limits. In this case, the fact that metal surfaces of sandwich panels create closed surfaces particularly reduce the practical importance of moisture activity. When the high heat transmission of water (i.e., 0.60 W/mK) is considered, such surfaces would also contribute to the thermal insulation properties of polyurethane which does not allow moisture intake. Water vapor permeability is highly crucial for comfort in buildings. Water vapor diffusion resistance (μ) and diffusion equivalent thickness (Sd) are two key characteristic values. Water vapor diffusion resistance (μ) value is specific to the material and determined by comparing it to the air diffusion resistance, which is considered to be 1. Water vapor permeability in sandwich panel systems is dependent on the density of polyurethane, manufacturing process, and the type of metal surface.

TYPES OF COATING

Rapid developments in coating materials in recent years offer quality advantages and high-performance opportunities in organic coating materials. The layer consisting of a combination of galvanized coating and organic coating forming the metal surfaces of sandwich panels provides an ideal solution specially against corrosion and increases the material life cycle. Depending on the type and degree of corrosion, the thickness of metal surfaces of sandwich panels facing exterior sections is typically 45 mm (25 mm organic coating and 20 mm galvanized coating); however, this thickness may be increased up to 300 mm based on the user requirements.

On the other hand, coating is expected to be highly resistant to UV lights, chemical activity, atmospheric activity, humidity, and physical effects. In addition, a wide range of color scale offered by organic coating provides significant design advantages in architectural solutions.

Coating materials are categorized under 3 groups as liquid coating, film coating, and powder coating materials. Finish coating of various qualities and colors as used on galvanized sheet or aluminum is preferred by users based on the application site and user requirements.

Aluzinc (AZ), also known as galvalume, is a coating application of aluminum-zinc alloy on steel sheet on both sides and Zinc (Z) is a coating application of zinc alloy on sheet on both sides. Assan Panel recommends a minimum of Z100 / AZ70 coating for its products. Polyester provides high resistance to external environmental conditions, high flexibility, and thermal balance. It is the most commonly used type of paint. It can be used for various purposes indoors and outdoors.

Polyurethane

Perfect surface hardness is ensured by polyamide reinforcement. It provides high resistance against scratches and stains. It is suitable for deep drawing and twisting. It can be used for various purposes indoors and outdoors.

PVdF

It is resistant to external environmental conditions, having high corrosion resistance, and resistance against chemical oils. It is highly resistant to chemicals and UV lights. It is a type of coating with the highest color durability and brightness resistance. It can be used in prestige buildings, roofs, and exterior wall coating applications.

Plastisol

It is capable of taking the perfect form. It is resistant to humidity and corrosion, and suitable for use in food-grade applications. It delivers an outstanding performance in cold and humid climatic conditions.

PVC Film

It is applied by lamination method. It is suitable for applications that require intensive forming and high flexibility. It can safely be used in food-grade applications in compliance with food regulations thanks to its hygienic and easy to clean properties.

ROCK WOOL

Rock wool is a type of mineral wool produced from a mixture of rocks such as basalt, diabase, and dolomite. Delivering perfect results in fire resistance and acoustic insulation, rock wool has lower values in thermal insulation as compared to plastic foams. Rock wool sandwich panels are used in roof, exterior wall, or partition coating in buildings with a high risk of fire. The insulating material is expected not to be directly affected by water. In addition, the thermal conductivity value of the materials should not increase indirectly through capillarity.

The fibers present in rock wool do not get wet; however, the air spaces between the fibers may fill up with water if they come in contact with water and the wet rock wool fails to function as an insulating material. For airborne-sound insulation, open pore materials (e.g., glass wool, rock wool, acoustic foam, etc.) are used. Sound absorbing materials are either porous or fiber materials and they exert their effect by transforming some portion of acoustic energy into thermal energy by causing friction losses in the air entering in the pores found in their structures. Contribution of rock wool sandwich panels to acoustic insulation is relatively better than other types of panels. On the other hand, high load bearing capacity values should not be expected from rock wool panels in case of conditions where high acoustic performance is required, and low-density rock wool should be used in such cases.

As a result of their internal structure, rock wool sheets have lower resistance values lengthwise as compared to widthwise. Nevertheless, its non-flammable properties have allowed for various activities to improve its low mechanical values. As a simple method, rock wool sheets are divided into lamella, in other words, they are cut into lines of desired thickness. This lamella is joined to create panels by using an adhesive. Therefore, mechanical properties are relatively improved while panels with high fire resistance are produced.

Mineral wools are quite stable materials as both fibers and bonding materials maintain their properties for a long period. Temperature has minimal effect on the mechanical properties of the material. Strength increases by an increase in density; however, it is more dependent on the internal structure. Compressive strength is between 0.005 and 0.08 N/mm2 for 60-150 kg/m3 limits. Tensile strength is low and typically between 0.001 and 0.01 N/mm2. The strength is higher in the direction of fibers. Similarly, shear strength varies between 0.03 and 0.20 N/mm2 based on the direction of fibers. In buildings where fire resistance is of critical importance, rock wool sheets consisting of inorganic fibers are used sandwich panel core material. Also defined as flammability capacity, fire resistance of the material is defined as fire performance. Fire resistance tests are carried out by a small-scale modeling of exterior wall and roof lines where the fire spreads the most in the building. Materials are categorized under 6 different fire classes beginning from A1 up to F. Other fire classes of the material are determined based on the amount of smoke and burning droplets due to fire. Rock wool sandwich panels deliver the best performance in fire-resistant exterior wall, roof, or interior partition wall applications.

Fire resistance of rock wool sandwich panels vary between 30 to 120 minutes depending on the type, thickness, and joint details of rock wool. Ignition temperature is 850°C. The structure of rock wool is open cell as compared to rigid foams. Open porosity structure of rock wool causes rock wool sheets to be more susceptible to water and vapor diffusion. However, this risk is minimized in sandwich panels due to metal surfaces that do not allow for diffusion.

 

PVC MEMBRANE

Membrane sandwich panels are used in low-gradient deck roof coating. The lower surface of the panel is manufactured as a metal (painted galvanized sheet) and upper surface is manufactured with a membrane. Therefore, no additional waterproofing material is required for coating on site after assembly, which ensures saving time and labor.

Advantages of PVC Membrane

  • It has a laminated layer resistant to any kind of atmospheric conditions, sunlight, and plant roots.
  • It has high dimensional stability and high tear resistance due to polyester fitting.
  • It has excellent adhesion properties in panel manufacturing due to geotextile felt lamination.
  • It has high quality due to strict follow-up by accredited laboratories during manufacturing.
  • It is vapor permeable.

Craft Paper

Assan Panel roof panels can be manufactured using craft paper instead of metal on one surface. Sandwich panels with craft paper is used as an alternative in deck roof coating applications. The lower surface of the panel is manufactured as a metal (painted galvanized sheet) and upper surface is manufactured as craft paper. Craft paper is cellulose-based and suitable for fitting bitumen waterproofing sheet on deck roofs. Panels are screwed in purlins with craft paper surface on top and fitted to the supporting load-bearing system with self-tapping screws.

FITTINGS

Fittings of various dimensions and types are used in a number of details with accessories, including fitting sandwich panels and single-layer corrugated sheets to supporting load-bearing structures in exterior wall and roof coating applications. Fittings should be chosen carefully during the design stage due to various factors such as resistance, waterproofing, appearance, etc.

Key points to consider while choosing sandwich panel fittings:

  • In choosing fittings to be used, make sure that static values of screws are certified. In calculations to be made, certified shear and tensile strength values should be used.
  • Sandwich panel external metal would be subject to various deformations over time due to temperature effects. Fittings used during such deformation should not lose its static characteristics and should be elastically resistant to such effects.
  • Sandwich panel screws may be exposed to intensive corrosion effects due to their environment. It is recommended that sandwich panel screws to be used have organic coating providing high corrosion resistance or to be of stainless type.
  • Tightening screws more or less than it is actually required during assembly leads to leakage. For correct assembly, EPDM seal should be tightened by 25%. Using a depth control apparatus ensures that the assembly is properly performed as required.
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