process Filament winding of twisted glass bundles for drainage pipe filters and aerators The Ukraine-based company Polistok produces GRP pipe filters by winding twisted glass-fibre bundles impregnated with epoxy resin By ilyA kryzhAnovsky consultAnt frp consulting T he bundles are wound so as to form a grid on the mandrel surface, and a filtering material is then fixed between two cylindrical GRP layers. These pipe filters are used in water wells. Protected design Polistok’s pipe filter design is protected by Ukraine patent No.7071 (1993) Fig. 1: GRP pipe filter wound from twisted glassfibre bundles impregnated with epoxy resin (source: Polistok) and by Russian Federation patents Nos. 2153574 (1998) and 2171339 (1999). The pipe filter can be further reinforced by an internal metal skeleton, as shown in Figure 2. Polistok’s hybrid metal-GRP design (see Figure 3) imparts even higher strength to the well filter. High filter efficacy can be achieved by positioning the filtering layer some height above the surface of the perforated metal pipe, so that practically all the filtering layer surface will take in water. The experience gained from the practical application of such STF-SK (SK = steel skeleton) filters shows that a GRP filtering shell can resist mechanical loads during the extraction of the filter from the well, independently of the soil structure and pumping regime (continuous or discontinuous). The properties of Polistok pipe filters are summarized in the table below. While Polistok uses a hot-cured epoxy binder for the production of GRP-only and metal-GRP well filter designs, other binders that are curable in Fig. 2: Well filter with internal steel reinforcing skeleton (source: Polistok) 110 jec composites magazine / No79 March 2013 outdoor conditions (such as polyester or epoxy resins) are used for hybrid thermoplastic-GRP designs (see Figure 6). A long experience Polistok pipe filters already benefit from more than 12 years of practical Fig. 3: (a) interior and (b) exterior views of STF-SK hybrid metal-GRP well filter (source: Polistok)