Film and Sheet Making Process

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  Film and sheet making process Shahbaz ali 15MME-S1-321Semester 5 th Department of Metallurgy and Materials engineeringUniversity of the Punjab    Introduction Plastic film is a thin continuous polymeric material. Thicker plastic material is often called a “sheet”. These thin plasticmembranes are used to separate areas or volumes, to hold items.  Raw material used for film making ã Polyethylene ã Polypropylene ã Nylon ã The most common plastic film is made of one of the varieties of polyethylene;Low-densit   y polyethylene,Medium-densi   ty polyethylene,High-density  polyethylene, andLinear low-density polyethylene.   Whyweusepolymerfilms?D ependingonrawmaterialsomepropertiesofpolymerfilmsarelistedbelow  HDPE is more rigid and stronger than LDPE and has good impact strength  Largest volume commodity thermoplastic(LDPE)  PE film is soft, very flexible, clear and glossy and has good tear resistance  LLDPE is selected for its higher tensile and impact strength and better heat seal ability  ULDPE is a soft and very flexible thermoplastic and is ideal for applications where excellent optics, and high tear resistance is required   Method to produce polymer film  Blown Film Process The process involves extrusion of a plastic through a circular die, followed by bubble-like expansion.   At the film manufacturing plant, thepolyethyleneresin is loaded into hoppers, and heated to approximately 400 degrees, melting the resin.  The melted polyethylene is passed through a horizontal extrusion ring.   Air is blown upward through the center of the ring, and a bubble of molten polyethylene begins to rise, like a large soap bubble.  The bubble is pulled upward by machinery, more air is constantly pumped in from below, and the polyethylene bubble forms a tall vertical tube as it continues to rise.   Air is blown against the outside of the tube, to cool the polyethylene to its solid state.
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