KraussMaffei's PUR spraying process has been recently employed by a German automotive component supplier, Duramotive Bayern GmbH to make acoustic carpet elements-used for soundproofing in passenger compartments-for cars and trucks. The soundproofing PUR layer has a high barium sulphate content is sprayed onto preformed carpet elements in an open mould using a special spray mixing head. The spray head is mounted on an industrial robot which follows a software-controlled spray path. The company claims that this process has distinct cost and process advantages compared with other methods and reduces material consumption, increases flexibility, and results in low mould costs.
Application of the PUR-mix can be restricted to areas where soundproofing is required to minimize material consumption and reduce part weight. The thickness of the layer can be varied, making it possible to spray adjacent areas with different coating weights. Also, the open mould spray process is extremely flexible as the robot can move the spray mixing head in any direction, at any of a range of speeds, enabling it to coat parts with varied and complex geometries. To minimize of polyol/barium sulphate mix, it is metered using piston metering. KraussMaffei's Tandem Hybrid metering machine feeds the abrasive component by means of two pistons moving anticyclically to deliver a steady material flow.
The highly-filled PUR systems used in soundproofing are fairly difficult to mix. To solve this problem, the mixing head is designed for 'T' mixing. This means that the polyol component is discharged into the mixing chamber through two nozzles opposite each other. The jet of isocyanate hits the polyol stream at right angles. This mixing-head design achieves excellent mixing quality and a stable spray jet, even when materials are processed at relatively low pressure and low temperatures.