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Vario-Nozzle for Polyurethane Output

Flexible Output Rates at Constant Pressure

With its Vario nozzle, KraussMaffei Technologies GmbH in Munich, Germany, presents a possibility for processing polyurethane (PU). The pressure in the mixing head is kept constant, even with fast changes in the discharge rate of the PU component. This permits components with different sizes and hardnesses to be produced with consistently high quality.

According to the manufacturer, this flexible adaptation to small and large discharge rates is ensured by the nozzle’s wide adjustment range, which maintains a constant pressure in the mixing head up to a quantity ratio of 1 : 5. During processing, the Vario nozzle also features high repeatability and particularly good consistency in pressure and quantity.

Vario nozzle without hydraulic closure (figure: KraussMaffei Technologies)

Contrary to conventional spring-loaded nozzles, the Vario nozzle operates with a pressure cushion that counteracts the component pressure. At a pressure of some 160 bar, this air cushion is located in a gas compartment in the rear part of the nozzle. It acts on the nozzle needle via a membrane, thereby eliminating the need for movable seals, as used in spring-loaded nozzles. The latter are subject to higher wear and are more sensitive to aggressive media and contamination. Moreover, under certain conditions, the spring and nozzle needle system can start to vibrate.

The design of the nozzle without moving seals reduces cleaning and maintenance costs, as the needle can no longer get stuck or jammed. Thanks to its compact dimensions, the nozzle can be retrofitted easily into existing systems. This requires neither additional control elements nor changes to the control system, and the Vario nozzle is compatible with all KraussMaffei mixing heads and systems.

The nozzle is also suited for multi-hardness PU products with different hardness zones, e. g. for the manufacture of automotive seat cushions with differing output rates and molds on a single system. Hereby, a wide processing window is required for shot weights and flow quantities.

In general, automotive seat cushions consist of zones with different hardness. Mostly, the seat and backrest areas are soft, while the side supports exhibit higher stiffness to provide the necessary support for occupants. For this, the output rate for the different areas of the PU components must vary from shot to shot during foaming.

The nozzle’s application range is not limited to soft-foam applications. The product can also be used in the white goods field – e. g. for inserting the insulating layers of refrigerators – and in the manufacture of fiber-reinforced moldings using the resin transfer process.

Translated from Kunststoffe 6/2015, p. 12.

Company profile

KraussMaffei Technologies GmbH

Krauss-Maffei-Str. 2
DE 80997 München
Tel.: 089 8899-0
Fax: 089 8899-2206

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