Worry-free turnkey package for polyurethane production

Individually designed fluid feeder stations

Worry-free turnkey package for polyurethane production

Plastics in the polyurethane family are versatile and can be found almost anywhere in everyday life, e. g. in cold-foam mattresses, shoe soles and car seats. Their production, however, is complex and requires detailed know-how – especially in terms of feeding. Brabender meets these requirements by providing specifically designed feeder stations.

Polyurethanes are something of an all-rounder amongst plastics. They are made from liquids – diols and polyisocyanates. The sensitivity of these liquid products makes handling them especially precarious and feeding them a demanding task. When planning and designing a fluid feeder system, Brabender Technologie always comes up with an individual solution to provide the best feeding result. The heart and lungs of every feeder station are the feed unit, the weighing system and the pump. The measurement and control technology forms the neural pathways. The basic set-up also includes the filling valve, which prevents dripping. Coriolis flow meters are also used as an alternative to the weighing system in a PU feeder station at the customer’s request. Continuously operating gear pumps are normally selected, as they can cope with high pressure and high temperatures and are both precise and compact.

One of the pitfalls of PU production is the formulation: it must be exactly right from the outset, because the ongoing process cannot be stopped or adjusted. In case of an error, the extruder has to be emptied and the batch will be rejected. This delicate situation necessitates a sophisticated control system. Brabender uses its own M-CON multi-component system together with the Congrav control module, which can be connected to a higher-level process control system (host/PLC). Among the visible consequences of this are the relatively large control cabinets that are part of every PU feeder system. In contrast to this, most cables are invisible, as they are concealed in the hollow sections. Many also have plug connections in key places to make replacing them as easy as possible. Since the wiring involved in the numerous control loops is complex, it is assembled in the factory. Brabender’s PU feeder stations are thus delivered practically like a plug-and-play device: after being connected to the extruder, they are immediately ready to use.

The chemicals used in PU production react very sensitively to changes in temperature. The ideal production conditions lie within a narrow temperature range of ±5 °C. To ensure this continuously without risking the formation of cold or warm thermal bridges, the entire feeder system has to be heated. Two heating options are offered here for the fluid feeders. Firstly, the entire structure can be given a double-walled configuration, meaning that the system can be heated using water or thermal oil. This is a good choice if, for example, waste heat is generated by another application or explosive substances are processed or handled. For PU feeding stations, however, electric heating is generally preferred. For this purpose, all modules and flexible tubes are wrapped in tailor-made heating sleeves, which are closed using Velcro fasteners. Each sleeve is fitted with an individual, pluggable control loop, in order to make replacement as easy and convenient as possible and facilitate precision control. The benefit of this method is that each component has its own heating, so that, for example, the piping leading from the pump can be heated to a greater extent than the feeder unit. All in all, this can add up to between 10 and 15 control loops.

During the ongoing production process an additional agitator in the hopper ensures continuous mixing of the liquid, so that the temperature remains as constant as possible. If the liquid is not being conveyed, it flows through a bypass in the loop back into the hopper. If the source materials were to sediment, they would clog the system, which is why they must always remain in motion. The PU feeding stations offer another benefit: they always run with powerful servo motors. These are actually oversized for what they are intended to do, but they operate at an absolutely constant speed for this reason. The motors are also able to compensate any pressure fluctuations, which in turn allows the gear pump to work with optimal precision.

In a static mixer, which can be incorporated in a heat exchanger, the source chemicals and their catalyst are mixed. Here, the chemicals flow through double-walled heat pipes until they reach the ideal processing temperature and are ready for mixing and extrusion. At the customer’s request, not only the feeder system itself but also the peripheral equipment with all the necessary connections and the automation can be planned by Brabender Technologie – as a worry-free turnkey package for PU production facilities.

Hall 10, Booth A41

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Adrian Baron

Mechanical engineer,

Brabender Technologie

Thomas Neuhaus

Mechanical engineer, Brabender Technologie

Facts & Figures

Up to 16 metering feeders controlled in one line

For liquid feeding, Brabender Technologie uses control components in the Congrav product family from the M-CON multiple feeder controller line. This modular system includes feeder control modules for control cabinet installation and the appertaining touch screen operator interfaces. However, direct communication is also available for most host/PLC systems via a variety of standard interfaces. Control systems can be configured for up to 16 metering feeders, ensuring perfect feeder interaction and accurate metering.

The same control components are used for liquid feeders as for the bulk feeding systems shown here