Fabrication processes rotational molding

Important are behaviors associated and interrelated with plastic materials (thermoplastics, thermosets, elastomers, reinforced plastics, etc.) and fabricating processes (extrusion, injection molding, blow molding, forming, foaming, rotational molding, etc.). They are presented so that the technical or non-technical reader can readily understand the interrelationships. 

The term dispersion refers to how well the pigments are wetted out in the plastic matrix (see below), whereas distribution refers to the uniformity of color in the part. Finally, in referring to the parts fabrication process, the term molder is used below to represent any the following pieces of equipment injection molding machine, injection or extrusion blow molding machine, or rotational molding machine. 

Perfiuoroalkoxy (PFA) pol mier is the most difficult to fabricate by rotomolding because of its high melt viscosity. Table 6.33 shows the temperature and oven (fusion) time ranges for processing PFA. Some specific examples of rotational molding and lining are described here. 

Aside from PTFE and PCTFE, copolymers of TFE and a few other fluorocarbon polyuners are processed by melt-processing methods. Commercial fluoropolymers that have found application in chemical processing industries include PFA, FEP, ETFE, ECTFE, and PVDF. These plastics are fabricated into parts by common techniques such as injection molding, transfer molding, blow molding, compression molding, rotational molding, and extrusion (Table... 

The range of processes that may be used for fabricating a plastics product is determined by the scale of production, the cost of the machine and the mold, and the capabilities and limitations of the individual processes. For example, complex and precise shapes can be achieved by injection molding, hollow objects via blow molding and rotational molding, and continuous lengths by extrusion. 

Although the rotational molding process is carried out with very little shear on the polymer melt, the cooling rate of the polyethylene after the fabrication step remains important in order to avoid excessive shrinkage and warpage. This is due to the crystallization process that takes place as the polymer melt cools from an amorphous, less dense state to a solid, semicrystalline state, higher density solid. 

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