02/24/2015

www.gupta-verlag.de/polyurethanes

Small nozzle with a large impact

[image_0]According to KraussMaffei, processors benefit above all from high flexibility in the system assignment with large and small components, which require correspondingly large and small discharge capacities. This adaptability is made possible by the large adjustment range - the nozzle keeps the pressure in the mixing head constant up to a quantity ratio of 1 : 5. This way it ensures a high mixing quality and a constant mixture ratio. During the process, the Vario nozzle also features high repeatability and particularly good consistency in pressure and quantity, says the company.[image_1_right] Even compared to conventional, spring-loaded nozzles, the Vario nozzle is said to have numerous advantages: Instead of a spring, it operates with a pressure cushion, which counteracts the component pressure. This air cushion has approximately 160 bar of pressure and sits in a gas compartment in the rear part of the nozzle. It acts upon the nozzle needle via a membrane, eliminating the need for moving seals, which are used in the case of the spring-loaded nozzles. These, in turn, are wear-prone and more sensitive to aggressive media and contamination. Moreover, in certain cases the spring and nozzle needle system can begin vibrating.[image_2] By contrast, the design of the Vario nozzle without moving seals significantly reduces the cleaning and maintenance expenses, because the needle can no longer get stuck and become jammed. Thanks to its compact dimensions, the nozzle is also easy and inexpensive to retrofit into existing systems, says KraussMaffei. This requires neither additional control elements nor changes to the control system. The Vario nozzle is compatible with all KraussMaffei mixing heads and systems. According to the company, thanks to its flexibility, the nozzle is particularly suitable for what are called multi-hardness products made of polyurethane, in other words, applications with various hardness zones. For example, if you want to manufacture automotive seat cushions with different output rates and moulds on one system, you need a wide processing window for shot weights and quantity flows. The automotive seats generally consist of zones of different hardness. Usually the seat and back surfaces are soft, while the side parts need more rigidity to provide the occupants with more support. This means that when foaming the various component areas, the output rate of the polyurethane components changes from shot to shot. In order to avoid a loss of quality, pressure differences from these fast and very substantial quantity changes must be kept as close to zero as possible. The mixing head provides the solution; the Vario nozzle is able to compensate for these changes reliably, says KraussMaffei. This guarantees that the components have consistently high quality. The Vario nozzle's range of applications is not limited merely to soft-foam applications. The nozzle has also already proven itself in the realm of major appliances - such as inserting the insulating layers of refrigerators - and when manufacturing fibre-reinforced parts with resin transfer moulding (RTM), says the company.

www.gupta-verlag.de/polyurethanes