Hot-runner nozzles are designed to inject and to distribute molten polymer to a number of cavities which give the later plastic component its shape. More cavities improve productivity but also mean more material which has to be melted to required viscosity. Some high performance polymers need fairly high temperatures to ensure proper viscosity. Therefore high temperatures within the nozzle are desired but heat dissipation to the surrounding housing should be as low as possible. These requirements can be realized by combining materials with different heat conductivity [1]. Vacuum brazing enables the design of a sophisticated hot-runner nozzle made of a high-conductive copper alloy, an isolating titanium alloy and a wear resistant hot-work steel. Though the mechanical load is moderate some obstacles during brazing process development have to be removed on the way to a reliable service performance.
展开▼
