The Continuous Filament Winding (CFW) process involves the use of three primary raw materials: reinforcing fibers, resin and silica sand. These materials are combined to create composite products with specific mechanical properties and performance characteristics.
Here's a breakdown of these raw materials:
Reinforcing Fibers
- Fiberglass Rovings: Fiberglass is the most common type of reinforcing fiber used in the CFW process. It consists of thin glass filaments bundled together into rovings. These rovings provide tensile strength, stiffness, and durability to the composite product. Fiberglass is chosen for its excellent strength-to-weight ratio, corrosion resistance, and cost-effectiveness.
Resins
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Terephthalic resins, a resin containing primarily terephthalic acid are known as a Terephthalic resin which is commonly used in GRP Pipe manufacturing. It is often prepared for buried pipeline applications where weathering effects are kept away. Terephthalic resins are used when high modulus and strength are desired, but the low colour properties of an Iso resin are not necessary. Terephthalic acid is generally lower cost than isophthalic acid, but both give similar strength characteristics to a GRP product.
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Orthophthalic resins, which are the general-purpose resins used in water conveying and sewerage applications. They are used for manufacturing laminates, which are not supposed to undergo strong chemical attacks or weathering. From the thermal point of view, orthophthalic resins are employed at ambient or medium-low temperatures. They should not be used for the making of the internal liner of a fiberglass pipe.
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Isophthalic resins, the most suitable end-use are in the manufacturing of pipes conveying waste liquids, drinking water and seawater above or below ground. They are more resistant to corroding substances present in the ground, to most salts, and medium concentrations of oxidizing acids.
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Vinylester resins, combine a greater resistance to chemicals with a high mechanical strength, which is also true at high temperatures. Isophthalic and Vinylester resins are mostly used for the internal liner of the pipe. They are also used for the transportation of hot water up to 80°C (for example in the heating systems), as well as for the transportation of water in the cooling systems, sea water outfalls from power plants, desalination plants, etc.
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Bisphenolic resins, have lower mechanical properties compared to vinylester resins, but they are characterized by high resistance to the chemicals.
Silica sand
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Silica sand is mainly added to the structural part of the laminate in order to increase the thickness and the stiffness of the pipes with a minimal cost increase. In case of a low pressure pipe or “gravity pipe”, where the strength required to sustain the internal pressure is quite low, the pipe wall is less thick, while a thicker wall would be necessary to give the required pipe stiffness. The wall thickness is increased by means of adding silica sand, dispersed in the core layer of the pipe wall. At the same time, a certain amount of the resin needs to impregnate the silica sand.
In the Continuous Filament Winding process, the sand, together with the glass fibres and resin, is one of the main components of the pipe structural wall.
In the CFW process, these raw materials are carefully selected based on the specific requirements of the end product.