Continuous Filament Winding process employs a steel mandrel whose surface is made up of a steel tape moving longitudinally with a speed depending upon the tape width and the cam plate. The steel band is elliptically wound on supporting beams placed along the grooved discs which is fixed on the mandrel shaft.
Before applying the raw materials, a special polyester film, mylar aiming to protect the surface and to make extraction of GRP pipe easier, is wound round the mandrel. Then a band of chemical resistant C glass, duly impregnated with resin, is applied. Being rich in resin (90%), it represents the chemical resistant wall of the pipe. The external layer also has the same characteristics as the inner layer.
The other two layers are applied between the inner layer and external layer. One is an anti-diffusion barrier, consisting of 70% resin and 30% chopped roving. The other is a mechanical resistant layer.
The thickness and composition of the mechanical resistant layer depends on the operating conditions the pipe shall withstand. Raw materials like resin, chopped roving, hoop roving and silica sand (if needed) in pre-determined proportions are fed on to the steel tape. As the steel tape moves forward longitudinally, the material on it also moves forward through four different heating zones having radiant heating units where the laminate gets cured. For each area, the heat to be supplied is controlled to maintain the required values of gel time, ISO-thermal peak and post polymerization in the oven.
Hoop roving supplies the required circumferential resistance of the pipe. Such roving, coming from the feeding systems through suitable tensioning device are wound circumferentially and continuously on the pipe wall.On the other hand, the chopped roving, 25-30mm in length, supplies an axial mechanical resistance which is the sum of axial resistance of each yarn.The silica sand has the scope to increase the wall thickness, and therefore the pipe stiffness without using a quantity of glass fiber higher than those foreseen by the design.
The resin represent the GRP composite matrix. It is applied by means of two basins providing to the suitable distribution through gauged holes. The resin delivered to the distribution basins is already mixed in the required percentage with catalyst. The distribution of the resin, catalyst and other raw materials is controlled by a numerical controller according to the mandrel speed.
Curing of resin is carried out in a polymerization oven equipped with infra red lamps installed on four different areas. It is possible to control the power supplied to each area in order to set the gel time, the isothermal peak and the post curing process according to the theoretical curing curve.
The production line is equipped with gauging and automatic cutting devices. The complete process is computer controlled. The pipe cutting at the required length is made by means of a diamond disc tool following the progress of the product.
Nominal size ranging from 25 mm to 2600 mm is manufactured by this process.
