Rotational molding parameters

Rotational molding (process parameters) oven temperature °C 364-391... 

Compared with blow molding, rotational molding offers lower equipment and mold costs and broad design parameters. Blow molding, however, provides a quicker... 

The viscosity of the polyethylene material at very low shear-rate is an important parameter for the type of polyethylene used in the rotational molding process because of the very low shear rate that is present during the molding process. This property is referred to as zero-shear viscosity of the resin. 

Earlier studies showed that the rotomoldability of resins is affected by several parameters. Material properties and powder properties are the most important key factors. Because the virtually zero shear and pressme free nature of the rotational molding process there are special requirements about the polymers which could be used in the process. For example low viscosity is required... 

Research Module 2 Understanding the fundamental mechanisms and critical parameters governing the extrusion-assisted processing of lightweight fine-celled foams in rotational molding. 

A fundamental study was conducted to determine the root causes of the orange peel in rotational molding. The effects of material properties such as density, rheological, thermal and powder properties, and process parameters were investigated. In addition, comparisons are made between the dry blended and melt blended samples in terms of orange peel development. 

A fundamental study was conducted to determine the parameters causing OP in rotational molded parts made from blended polymers. The study of the effects of process conditions showed that increasing heating time and temperature resulted in lower crystallinity and lower surface roughness. Some thermal degradation was also observed. 

The Fracture behavior of Medium Density Polyethylenes (MDPE) with different melt flow indexes (1.9 to 5.0 dg/min) employed in rotational molding were studied by Essential Work of Fracture (EWF). The EWF parameters obtained were equivalent for all samples examined regardless of their differences in comonomer content and molecular weights. Annealing of samples resulted in lower ductility values according to EWF parameters, in spite of minimum crystallinity changes. 

In order to understand potential problems and their solutions, it is helpful to consider the relationships of machine capabilities, plastics processing variables, and part performance (see Chapter 7). A distinction should be made between machine conditions and processing variables. Machine conditions are basically temperature, pressure, and processing time (such as screw rotation/rpm, and so on) in the case of a screw plasticator, die and mold temperature and pressure, machine output rate (Ib./hr.), and the like. Processing variables are more specific as parameters than are machine conditions, as the melt in the die or the mold temperature, the flow rate, and the pressure used. 

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