01/19/2011

www.gupta-verlag.de/polyurethanes

Pumping and measuring high-viscosity polyurethane components

Polyurethane has many possible uses. Mattresses and car seats are made of flexible polyurethane foams, refrigerator insulation and cladding elements of rigid polyurethane foam. In vehicle manufacturing, parts for the car body and the interior trim are made from polyurethane. A further important field of application for polyurethane is the shoe industry. The global consumption of polyurethane is currently about 15 million t per year. This makes polyurethane one of the most frequently used polymer materials after the so-called standard plastics (polyolefins, PVC, polystyrene). The manufacturing of polyurethane products is different to conventional plastics processing. Thermoplastic polymers can be melted and then formed into products through injection moulding or extrusion. Different laws apply to polyurethane processing. There is a chemical reaction during forming.Put simply, the two components, polyol and isocyanate, are mixed together in their liquid state and, in a cross-linking reaction, form the material polyurethane. This manufacturing process places high demands on the systems used.A crucial criterion of the component quality and the process stability is that the liquid components polyol and isocyanate are made available constantly and are metered with precision. This is particularly challenging for the polyol component. In special applications polyols with a very high viscosity are processed. Even under these conditions Kral screw pumps and flowmeters operate with precision and reliably. Meaning outstanding product quality and high plant availability, even when the materials used are highly viscous.Use of Kral screw pumps.Large quantities of raw materials are often processed during the production of polyurethane products. Usually the raw materials are made available in very large tank farms that are unpressurised. In order to be processed further within the production plant, the raw materials have to be transported from the tank to the plant. Metering plants and tanks are often located at considerable distance from each other. Kral pumps are suited to transporting the raw materials. In plants with continuous production they serve as booster pumps for the reaction components polyol and isocyanate. Pump sets from Kral fulfill all the specifications even in the case of high raw-material viscosities, since they operate with automatic suction and feed the metering pumps continuously and free of pulsations across a wide quantity range. Meaning that the transfer of vibrations to the plant or the pumped liquids is practically excluded.In order not to damage long polymer chains gear pumps have to be operated at low rotational speeds. A screw pump pumps the liquid product-conserving, quietly, with low pulsation and with high output density. Kral screw pumps do not have to be designed larger - they remain compact and inexpensive.Kral volumeter and electronicsHermetically-sealed magnetic coupling.Polyol is highly viscous at low temperatures. In special applications fillers are added to the polyol component. Fillers influence the physical properties such as, for example, the sturdiness and electrical conductivity of the polyurethane products. In order to avoid the risk of damage to the mechanical seals through abrasive fillers, the only solution is to do completely without pumps having a mechanical seal. Kral screw pumps with hermetically-sealed magnetic couplings are conceived so that they can be designed with hardened screws and screw casings for a wide variety of fillers. The lack of a mechanical seals avoids heat reactions caused by friction at the rotary ring surfaces. Increased leakage through damaged sealing surfaces at the mechanical seal is a thing of the past - polyol and isocyanate do not come into contact with the atmosphere.Flow measurement for polyurethanesIn order to manufacture polyurethane products having different property characteristics, it must be possible to meter a wide range of components flexibly. To this purpose the outputs of the individual components are supplied to the mixing head by means of speed-controlled pumps. To ensure that all the reaction partners are available in the stoichiometrically required quantities, the pump outputs are monitored and controlled permanently through Kral precision flowmeters. This guarantees exact adherence to the recipes for quality polyurethane products.

www.gupta-verlag.de/polyurethanes