Manufacturing and Production

Rotational Moulding and Large Container Manufacture

Rotational moulding makes large hollow products from powder with almost no pressure, which makes it forgiving of tooling cost and unforgiving of time and temperature, because the only real control a moulder has is the oven cycle. This course covers using it well. Delegates work through the process cycle and what happens to the powder at each stage, from tumbling and adhesion through coalescence to densification. Material selection is addressed, principally polyethylene grades, powder quality and particle size distribution. Internal air temperature is treated as the central control, since surface readings do not describe what the part is doing. Undercure and overcure are covered, with the mechanical consequences of each. Cooling is addressed, including warpage and shrinkage. Mould design, venting and release follow. Wall thickness control and inserts are covered. Defects are diagnosed: bubbles, pinholes, bridging and poor corner filling. The course closes on tank testing, on ultraviolet stability and on product certification.