Rotational molding elasticity

The validity of Frenkel s model is limited to Newtonian flow and can only be used to predict the early stage of the coalescence process, when the diameter of the two spherical particles remains nearly unchanged. The inadequacy of a Newtonian model in describing the coalescence of polymers was also demonstrated in other studies, as reviewed by Mazur, and has led to the development of models as well as alternative methods for the characterization of the coalescence behavior of polymers for rotational molding applications.Based on theoretical and experimental analyses of the coalescence phenomenon, the material properties of primary interest in the evaluation of resin coalescence behavior in rotational molding have been identifled as the resin viscosity, surface tension, and elasticity. 

In addition to zero-shear viscosity, material elasticity plays an important role in determining coalescence behavior in the rotational molding process.For rotational molding grade material, this effect was first recognized from the experimental results obtained with impact modified polypropylenes and is illustrated in Fig. In this work, the relative elasticity of resins... 

Type IV storage tanks (Uner made of polyamide PAG) can be produced more easily and more cost-effectively ( 13 kWh [10]), but suffer from a small leakage of about 2mgh kg ). The production process consists of rotational molding with simultaneous polymerization. The higher elasticity compared with steel tanks potentially offers even better crash worthiness (bursting and impact strength). 

The requirements of the models are strongly influenced by the rotational processing methods, as well as by the inserted component material. For the components that almost always have undercuts, elastic materials (PVC, TPU, and TPO) are used. Additionally, it must be ensured that no mold markings are accepted in the visual area of the component. 

Therefore, single-parted rotational and slush molds are prerequisite and are provided with openings out of which the elastic components are ejected off. Ejecting components in electroplated molding is also done through small mold openings. Therefore, model materials are used that can be mechanically or chemically destroyed. 

---