Biswapriya Nandi

The timeless beauty of zinc as a cladding material has always fascinated architectural firmament across the globe, driving it to give the world many impressive buildings with zinc facades. The introduction of Zinc Composite Panel (Z-A) - which is more cost-efficient and has some technical advantages, too - has further encouraged the industry to explore the myriad aesthetic possibilities offered by the metal. ZCP (Z-A) has zinc as the top surface and aluminium as the bottom. The trend is fast catching on in India as well. A. Handling: Protective Film: The ZCP surface is covered with a strippable film during the manufacturing process to protect the surface from dirt, moisture, and scratches during handling, fabrication, and installation. This film should be removed immediately after installation. Leaving the film for an extended period after installation may cause extreme difficulty in removing the film. Handling: While handling the ZCP panel, the middle of the panel and both ends should be held as well, as it is heavier than standard ACP and tends to have extensive warping owing to its dead load. Support: Flat and fabricated ZCP panels should be transported in secure packing configurations to avoid abrasion and scratches. Special care should also be taken to store and transport ZCM (Z-A) panels on flat, well-supported surfaces to avoid material deflection and potential permanent sets. Protection from Water & Moisture: ZCP panels must be transported and stored under dry, ventilated condition. Direct contact of the top zinc surface with the wet surface should be avoided. One of the advantages of Aludecor’s ZCP is that the aluminium on its back surface resists corrosion from the accidental accumulation of water beneath the panels. Fingerprint: Gloves and long sleeves should be used while handling ZCP. Handling the unprotected surface of the material with bare hands may leave fingerprints on the surface, which over time will get absorbed into the patina and thereby discolour the metal due to the acidity in perspiration. B. Design: Dimensional Tolerance & Width Limitation: Due to the lamination of dissimilar metals, the BOW tolerance of ZCP is 0.8% which is slightly higher than that of laminations of similar metals. Generally, the bow of ZCP is not a partial distortion, but a gradual warping of the entire panel. Also according to manufacturing process parameters, ZCP is limited to a width of 1000mm. With standard rout and return system, panel modules of a maximum of 950mm in width are recommended. Physical Properties: The coefficient of thermal expansion/contraction of ZCP differs significantly from Aluminium Composite Panel. There is an equal longitudinal and transverse expansion and contraction of the metal grains in aluminium. But the titanium zinc alloy used in ZCP expands and contracts differently in each direction. Therefore, while performing thermal movement calculation for a particular “run” of panels on an elevation or façade, it is essential that the calculations take into account both vertical and horizontal directions. Mechanical Properties: Zinc composite panel’s mechanical properties are similar to ACP. However, it has been tested that ZCP has a peculiar elastic behaviour owing to zinc's lower tensile yield strength than aluminium. Namely, a ZCP panel, loaded even within the elastic limit, still has a residual deflection after the load is eliminated. But the aluminium at the back of Aludecor’s ZCP counteracts the residual deflection of zinc. Processing Method: As the machining performance of zinc is quite similar to that of aluminium, we can process ZCP with the same machines and tools we use for ACP. The working parameters are also the same as long as the processing is in the usual range. Namely, we can cut ZCP with circular saws, fold it through the route and return, and bend it with a 3-roll bender and a press brake. ZCP, as an exception, when it is bent to a concave shape (zinc skin lying inner, aluminium skin lying outer), shows a larger bendable limit. Also, we can rectify the panel bow by 3 roll benders - ZCP panels passing through 3 roll benders before grooving - or by stiffening the panel with the aluminium profile. C. Installation: Fixing Method: ZCP has most of its characteristics similar to that of ACP. Therefore, the exact fixing details of ACP also apply to ZCP. However, screws, rivets and attachment extrusion made of stainless steel & aluminium should only be used for assembling ZCP panels. This is because contact between dissimilar metals causes an electrochemical reaction under moist conditions. As zinc has a lower corrosion potential than copper & iron, galvanic corrosion accelerates the corrosion of zinc alloy upon contact with these metals. Accumulation of water/moisture/rainwater and weeping condensation on the installed panel: While Zinc Composite Panel necessitates installation in adherence to design specifications for weeping condensation or rainwater drainage to avoid accumulation, no such precaution is required in the case of Aludecor’s ZCP again owing to the aluminium surface on its back. It also gives a 100% clear water run-off, having no free particles which can mix with rainwater and thereby contaminate it. Façade Cover: If covers are used to protect panel areas during construction or staging it is critical that the covering: a. Should not be placed over wet or damp ZCP panels. b. Should not be used if the cover material is damp. c. It Should be installed in a manner that ensures proper ventilation of all the covered panels. Silicone Sealant: In order to ensure the waterproofing of joints between panels, normally a sealing material is used. ZCP reacts well with neutral or slightly alkaline silicon sealant (Ph<12). Systems with an acid reaction, such as acetoxy or acetic acid system, should not be used since, upon contact with ZCP, they may initiate corrosion.

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