BASF has developed its first polyamide for the rotomoulding technology. This un-reinforced polyamide 6 (PA6) is sold under the brand name Capron BR30HS. The plastic’s first serial production application is in the automotive sector and additional projects are on the drawing board.
The new Capron® in powder form can be employed wherever there is a need to produce a small series of liquid containers used in motor vehicles. This includes tanks for hydraulic oil or diesel fuel as well as coolant equalizing reservoirs. Other possible components are air supply conduits and covers for trucks, construction machinery, forklifts and tractors. Thanks to its stabilisation and flow properties, which have been optimised for rotomoulding, this material also makes it possible to create shapes with rim holes. Metal inserts such as sleeves or screw threads can be readily integrated into the parts. The inner surface of components made of the new Capron is very smooth, which is a prerequisite for liquid-carrying vessels. The plastic is available in uncoloured form and in black.
“Polyethylene, one of the materials most commonly used for rotomoulding, reaches its limits when it comes to combining high heat resistance with good mechanical properties. On the other hand, a high-performance plastic like PA12, which is also used for this application, is very expensive. The new Capron® can fill this gap,” explains Werner Budinger, specialist for Capron brands and rotomoulding at BASF’s Engineering Plastics.
Rotomoulding is a plastics processing technique that is particularly well-suited for small production series. This method is employed in the manufacture of hollow components and stands out for its virtually tension-free workpieces. The tool costs are just one-tenth of the costs of an injection moulding tool. Due to the long cycle times, however, this method is only economical up to an annual production volume of about 50,000 units. If the production runs are larger, rotomoulding – which has been in commercial operation for 50 years – has to compete with blow moulding and injection moulding. Typical applications outside of the automotive sector are slides for children’s playgrounds, underground tanks, cisterns and other large-volume liquid containers.
The two halves of the hollow mould are filled with the plastic powder, shut tightly and heated up in a heating chamber until the material melts; in the case of polyamide 6, this happens at about 220°C [428°F]. During the heating and melting process, the hollow mould is rotated around several axes so that its entire inner surface is covered with the viscous plastic compound. As soon as the wall is completely coated with a melt film, the mould is taken out of the heating chamber and cooled off. The finished hollow part can then be removed.