New spray machine for PU skin applications from Cannon
Cannon USA has annonced that the company has developed a new machine for processing PUR spray skin parts used in automotive applications such as door interiors, seats, dashboards or instrument panels. Cannon has developed a mixing head and process specifically designed for this market, which gives the manufacturer the ability to produce economic imitation leather parts while maintaining excellent quality and performance. The spray skin technology uses a Polyurethane-based elastomer, which is sprayed into heated open moulds, with a surface texture which gives a leather look and feel to the finished parts. This elastomeric „skin“ is intended to act as a substitute for PVC materials currently being used in production in many vehicles. Several chemical companies have developed specific formulations for the processing of these skins, and Cannon USA has adapted and developed a system for processing these chemicals. The Cannon spray machine is described as a compact single-frame design, complete with pressurised day tanks, radial piston pumps, magnetic couplings for both the isocyanate and polyol components, temperature control, closed loop controls with volumetric flow meters and frequency drives, low and high pressure chemical filters, flow display and MMI, and a compact, hydraulically-operated mixing head. Chemical temperatures are controlled independently by combining water-jacketed day tanks and in-line heat exchangers. This enables the chemicals to be heated for processing at the mixing head while keeping the chemicals cooler, if necessary, in the day tanks. A stand alone control cabinet houses a PLC, which is the “brain” of the whole system. The machine processes the chemicals independently through individual circuits and combines them through impingement mixing in the mixing head. The components are then directed through a hollow tube or wand, which does not contain any mixing element, to a spray tip, which applies the urethane to the mould. Following the urethane spray, in order to prepare the mixing head for the next shot and for cleaning purposes, solvent is flushed at high pressure to the mixing head nozzle, wand and tip. This type of application has many advantages, one of which is that the length of the wand can be varied to virtually any size without having to change the static mixer elements or have elements custom made to fit the respective application. Also, because there is no mixing element in the wand, cleaning of the tube is much more efficient, the cost of replacing the wand is minimal, and the tubing used is commercially available. The mixing head used for the spray system is a modified version of the Cannon LN-5 style mixing head, which utilizes a simple piston action and is hydraulically operated. Trials at Cannon USA’s lab facility - consisting of successful testing with multiple chemical suppliers - included processing the systems and spray testing on both a small heated plaque mold as well as on a full sized prototype IP mold Process parameters during testing included runs with very high chemical temperatures at the mixing head and mixing pressures up to 3000 psi. The small, lightweight mixing head and spray system has proven very flexible in trials, and - due to the geometry of the specially-designed mixing chamber - successful spray skins have been produced at a variety of mixing pressures and flow rates. The chemical flows, and consequently pressures, were varied by as much as +/-20% throughout the shot, and the mix remained excellent throughout the entire part. This can be a major advantage due to the fact that it is usually necessary to vary the flow of the Polyurethane throughout the pour to accommodate the varying features of typically intricate automotive parts. Again, the versatility of the Cannon mixing head has allowed the introduction of a third component - a pigment - during the spray process which permits the processed skin to be produced in colour variations as desired by the customer. In addition, the colour injection could be turned on and off at will allowing more versatility in final skin production. The success of this testing has resulted in Cannon producing two separate versions of their spray skin mixing head: a two component head and a three component head. While both incorporate the same basic components that have produced superior mixing capability, each head has unique differences. However, both heads are small in design, capable of handling a third component for adding additional elements such as pigment or other components, and both utilize the hollow wand for the spray applications.