Pulling all the right strings
New solutions to old problems
The company recently developed a reinforced pultruded cable for underground pipe inspections. The challenge was to produce a product stiff enough to be pushed up a pipe but flexible enough to negotiate bends and resist abrasion. A specialised protective sheathing surrounds the cable and houses wires that the operator can use to detect and locate faults, or link to a tiny front-end camera to carry out pipe inspections. The company's efforts paid off and the cable is now used extensively throughout New Zealand and in other countries overseas.
With an almost endless range of uses for pultrusions and the global resources boom making inroads into the cost competitiveness of rival products made from metal, Pultron Composites looks likely to keep growing and proving New Zealand companies can overcome isolation with a strong commitment to research and innovation.
Richard Worrall is a Christchurch-based freelance journalist.
Manufacturing a pultrusion
To turn fibreglass into a tough, durable product such as a reinforcing bar, Pultron Composites starts with literally thousands of separate fibreglass strands. To produce a 10-millimetre-diameter rod, for example, requires no less than 80,000 separate fibre filaments drawn together, each only 20 microns in diameter.
Fibreglass arrives at the factory in large rounds called "cheeses", each weighing roughly 20 kilograms. Each cheese has a "tow" – 4,000 fibreglass filaments combined into a single strand that pulls from the cheese's centre. The cheeses are stored in 10 roving bays (essentially racks), with up to 1,200 cheeses per bay. Special islets guide the tows to the end of the bay and into the manufacturing process.
Prior to entering the heated die, sensing devices measure the tension of the running tows. A "wet-out" occurs when the glass fibres become soaked with the resin prior to entering the curing section inside the heated die. Feeding additional cross-bound fibres (like a woven mat) into the heated die along with the tows gives varying degrees of axial or transverse strength.
The hot pultrusion profiles emerge from the die fully cured. Once the profiles cool sufficiently to manipulate, an extraction machine pulls – rather than pushes – the profiles from the die to prevent the fibres becoming misaligned. The puller uses twin reciprocating hydraulic clamping patterns with a 16-tonne clamping pressure and a six-tonne pulling force. These combine to extract the profiles in a hand-over-hand pulling process.
A flying cut-off saw cuts the profiles to length. From there they move to finishing, where a grinding or over-moulding machine shapes them to the final application.
