Sheet extrusion process

Sheet Extrusion Processing Guide, Nature Works LLC, Minnetonka, MN, 2005. 

In the blown sheet extrusion process, after leaving the extmder, gear pump and screen pack, the resin moves to a circular spiral mandrel die in which a tube of molten material is formed and inflated with air from the inside. The tube is then lifted in a haul-off tower up to 40 m high where it is cooled by an internal and external flow of cool air. It then proceeds to... 

Solventless Extrusion Process. The solvendess process for making double-base propellants has been used ia the United States primarily for the manufacture of rocket propellant grains having web thickness from ca 1.35 to 15 cm and for thin-sheet mortar (M8) propellant. The process offers such advantages as minimal dimensional changes after extmsion, the elimination of the drying process, and better long-term baUistic uniformity because there is no loss of volatile solvent. The composition and properties of typical double-base solvent extmded rocket and mortar propellant are Hsted ia Table... 

Melt Extrusion. By far the most important method for producing film and sheeting materials reties on one or another of the various melt extmsion techniques (5). The main variations of melt extmsion are the slot (or flat) die-cast film process, the blown films process, and the flat die sheeting-stack process. These may be combined with one or more steps such as coextmsion wherein multilayer film or sheet is formed, biaxial orientation, and in-line coating (6). 

Extrusion processes can generate several types of scrap, including out-of-specification material, material generated when the process is not running at steady state, and edge trim when sheet or film is trimmed to the required width. In extrusion, the scrap can be reintroduced to the material stream and reincorporated into the manufactured products. As with injection molding, the form of the scrap often differs substantially from the starting resin. 

Polypropylene film is found in a variety of applications. Films are thin plastic sheets with thicknesses less than 250 pm. Applications for these films include candy mappers, plastic label material, electrical capacitors (which requires very pure polymer), and fiber glass insulation backing. There are two general categories of polypropylene films unoriented and oriented. Films are manufactured through either a cast or a blown film extrusion process. Oriented films exhibit improved strength relative to unoriented films. This means that they can be... 

The advantage of calendering over direct sheet extrusion is that a complicated and expensive die is not required. Some additional mixing can be done as part of the calendering process, as well, and a surface finish can be applied by the final roller, if desired. Sheet up to a few millimeters thick and a meter wide can be made using calendering. 

With mixed aramid fibre/particulate flake compositions in polycarbonate, however, the previously mentioned processing operations significantly reduced the levels of fibre and flake orientation relative to corresponding observations with single particle compounds [167]. For example, in sheet extrusion and injection moulding, the flakes oriented perpendicular to the fibres losing their biaxial orientation parallel to the surrounding machine surfaces. 

In a 2-year study, the emissions produced during the processing of a series of thermoplastic materials were investigated. In the case of HIPS, the emissions at sheet extrusion and injection molding processes were monitored. Sheet extrusion was done at 193°C, whereas, injection molding was done at 225°C. 

Polyethylene is readily fabricated by all methods of thermoplastic processing. The principal methods used are film and sheet extrusion, extrusion coating, injection molding, blow molding, pipe extrusion, wire and cable extrusion coating, rotomolding, and hot melt and powder coatings. 

Another possibility is to extrude foam into sheets the pressure within the extruder prevents foam formation only after leaving the die the pentane evaporates to form the foam. In most cases the extrusion process is carried out with normal PS granules in the cylinder pentane or another blowing agent is injected, where it mixes into the polymer and brings about foam formation after leaving the die. 

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