Film blowing forming

Andre, J. M. ct al., 1998. Numerical modelling of the polymer film blowing process. Int. J. Forming Processes 1, 187-210. 

The multilayer film is formed by injection molding, co-injection blow molding, co-injection stretch-blow molding or co-extrusion blow molding techniques. 

A common form of analyzing film blowing is by setting-up a coordinate system, , that moves with the moving melt on the inner surface of the bubble, and that is oriented with the film as shown in Fig. 6.21. Using the moving coordinates, we can define the three non-zero terms of the local rate of deformation tensor as... 

Another class consists of extrusion immediately followed by an additional stage. This includes blow moulding, film blowing, quenched film forming, fibre spinning, and extrusion coating. 

The spherical foam films can be obtained by blowing a bubble from a vertical capillary tube. The principle of formation of such a bubble is illustrated in Fig. 2.22. A vertical capillary tube is placed in a vessel with the surfactant solution so that its upper orifice is close to the solution surface. When a gas (air) with a definite pressure is introduced into the tube over the solution surface a foam film is formed acquiring the shape of a hemisphere. 

During stretching flow, material is drawn from one cross-sectional area to another. This type of flow dominates fibre, film, blow molding, and vacuum forming processes (57). Let us assume that a filament of a molten polymer is hauled off under a force F (see Fig. 13.40). Taking the die of the extruder as the origin of the reference frame, the cross-sectional area A of the filament... 

In this section, examples of films made from polyvinylidene fluoride (PVDF) are discussed. Although most of the pol5winylidene fluoride film is in the form of coating on metal substrates, stand-alone PVDF films and sheets are produced by extrusion and film blowing.1 ] ] Blends of PVDF and a number of other polymers such as polymethylmethacrylate (PMMA) are miscible. Films made from these blends have excellent piezoelectric properties. 

OthersP E[38] jj yg described processes to produce filled and unfilled films and sheets of polyvinylidene fluoride in a wide thickness range. In one invention,conductive PVDF films were formed by slitting a thin wall conductive tube by a film blowing technique which had superior uniformity over a conventionally extruded flat film. The conductive film/ sheet has found application in heaters and circuit protection devices. 

There are several methods for the production of polymeric films (see Table 9.18). The oldest is calendering, but the most common methods are the film blowing and sheet extrusion. Others can be made by post-treating the extruded sheet, e.g., polyimide films [Sweeting, 1971]. Polymer films can also be polymerized onto a substrate from monomers in the vapor state, or formed by the coalescence of polymer dispersions. However, several polymers caimot be formed without dissolving them. 

Cellulose derivatives were the first thermoplastics formed in the film blowing process in the beginning of the 20th century. By the 1930 s, biaxially oriented films of cellulose acetate were commercially available. Forming of synthetic high polymers, especially LDPE, by the film blowing process began only in the 1940 s. 

Polystyrenes are mostly extruded and injection molded to get to the final shape of the products. However, polystyrenes can also form sheets by physical processes such as film blowing and stretching to obtain polystyrene film. In the... 

HPC is soluble in water below 38°C, but is insoluble in warm water. It dissolves in several organic solvents. HPC can be thermoplastically processed, e.g., by blow-forming or injection-molding. These properties are exploited in the manufacture of water-soluble packaging film (capsules for pharmaceutical use, chemicals for swimming pools). Other uses of HPC are as a suspension agent in emulsion polymerizations, as a coating for sweets and tablets, as a stabilizer for artificial whipped cream (in the United States), as a binder for ceramics, etc. 

Film blowing (blown-film extrusion). The process of forming thermoplastic film wherein an extruded plastic tube is continuously inflated by internal air pressure, cooled, collapsed by rolls, and subsequently wound into rolls on thick cardboard cores. The tube is usually extruded vertically upward, and air is admitted through a passage in the center of the die as the molten tube emerges from the die. An air... 

From a pragmatic point of view, the variety of extrudate distortions has little relevance for the industrial practice. For most applications, especially those where free surfaces are formed (e.g. film, blow molding), the first onset of a visually observable extrudate distortion is sufficient to take corrective measures. The possible variables to tinker with are either... 

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