Development of an Obround Polybenzimidazole Nozzle for Cold Gas Dynamic Spray

Abstract

Technoform, a worldwide manufacturer of polymer window frames and window insulation, needs to fulfill customer performance and aesthetic requirements. To this end, they have opted to use the Cold Gas Dynamic Spray (CGDS) process on an industrial scale to coat extruded polymer parts with a thin layer of aluminum. The CGDS process would be an added step in the production line where it would deposit an aluminum coating after the extrusion step, in a single pass. While commercially available equipment can be utilized for this purpose, it is rather inefficient due to the quantity of nozzles required to fulfill Technoform Bautec Ibérica’s requirement of coating the substrate in a single pass. Multiple nozzles placed side-by-side would be required to coat the entire width of the substrate. The focus of this work was to improve and optimise a prototype initially designed by Technoform Bautec Ibérica and Centerline (Windsor) Ltd. This prototype was designed with an obround shape (12.5 x 2.5 mm), to be wider than axisymmetric nozzles and reduce the number of nozzles needed for this specific application. A combination of computational and experimental methods were used to assess the issues with the tungsten carbide (WC) prototype produced by Technoform and Centerline (Windsor). Alternate injection points for the powder feedstock were tested through simulations to improve the particle distribution at the outlet of the nozzle. It was found that a 15° inlet provided a fuller coverage of particles at the outlet when compared to the original inlet, which was at the 90° position. A new, multi-part prototype was designed to be manufactured from polybenzimidazole (PBI) and to utilize the updated inlet position. The WC nozzle produced a single-pass coating of 6.5 mm in width on an aluminum 6061-T6 substrate, while the PBI prototype produced a 7.5 mm wide coating. Further simulations showed that a dual injection approach could provide a wider coating. The PBI prototype was modified for dual injection and produced a 10.5 mm wide coating. With optimised parameters, a 13.6 mm single-pass coating was produced. Different injection gas flow rates were also tested to produce flatter coatings. A gas flow rate of 6.52x10⁻⁴ kg/s (60 SCFH) produced the most even coating in terms of thickness across the entire width of the deposition. Finally, single-pass coatings were deposited on Technoform’s polyamide substrate. The WC nozzle produced an 8.6 mm coating and the dual injection PBI nozzle produced a 13 mm coating.