25 May 2004
25 May 2004
Polymat “Hi-Flow” has been developed by Flemings Textiles (a subsidiary of Scott & Fyfe Ltd) for use in closed mould processes and is being heralded as the next generation of closed mould structural fabrics.
“We have created a fabric that is a breakthrough for closed mould applications. Tests have shown that our Polymat “Hi-Flow” has an outstanding permeability characteristic that allows resin to fill a mould cavity at twice the rate of other mats as well as using up to 20% less resin in VARTM systems (due to no recorded back pressure). We are providing production cost benefits to moulders worldwide,” says Scott & Fyfe’s Managing Director Robert Martin.
Enabling controlled infusion with a wide range of resin formulations, Polymat “Hi-Flow”, a mechanically stitch bonded reinforcement consisting of a deformable engineered thermoplastic core sandwiched between two layers of chopped strand glass fibre can, offer a number of benefits.
According to Scott & Fyfe, Hi-Flow can provide up to 50% reduction on fill time with the ability to handle filled and high viscosity resins with ease and lower resin requirement to fill medium to large VARTM moulds due to reduced flow restriction. Hi Flow is claimed to offer improved control of finished part thickness under vacuum film infusion and improved ability to withstand higher RTM pressures than current materials in use. There is also uniform compressibility across surface area giving consistent gauge.
Plastech, UK who have experience in running trials on many mats for manufacturers and suppliers have been carrying out tests at their new Manufacturing and Technology Centre in Cornwall to prove the effectiveness of this breakthrough.
The mould tool utilised to run tests with Polymat “Hi-Flow” (450gms of glass either side of the M01 core) and compare directly to a similar weight product from a leading competitor, had Plastech’s new PVSensor incorporated to control the input rate of resin as the sensor picked up back pressure readings. It would prove to be an effective control mechanism for confirming the promoted flow characteristics of the new Polymat “Hi-Flow”.
Using the Polymat “Hi-Flow”, the mould was vacuum clamped, the machine counter zeroed and the PVSensor system set at 1010mb. Prior to injection the in mould vacuum reading displayed on the PVSensor system's LCD read 460mb (absolute). The machine was signalled to commence injection and the flow was seen to circumvent the cavity and proceed to fill towards the mould's central vacuum catch point in the conventional manner. However, the low build up of backpressure was immediately apparent as it slowly increased towards atmospheric pressure. It was only towards the end of the injection with around 80% mould fill, that sufficient back pressure was reached (at the pre-set point of 1010mb) at which point the system throttled the machines output back to a new slower rate, finally achieving a total mould fill in 210 seconds for 5.8 litres of catalysed resin.
After cure and release the mould was reloaded using a leading manufacturer's glass mat of the same weight and dimension. No machine or vacuum levels were altered and a second injection made. Within 90 seconds, the back pressure had built up to the set point and the machine slowed. The fill at this stage had only reached 50% and it was very evident that greater resistance was preventing the resin flowing as easily as it had in the previous test. It could be argued that the fibre mat under test this time was less resilient to the fixed vacuum level and as such was squeezed tighter by the flexible mould thus offering more resistance. However, one would have immediately deduced that had this been the case a lower volume of resin would be needed. Surprisingly 20% more resin was consumed and took over 50% longer to fill the mould (Fill time460 seconds for 7 litres of catalysed resin).
“Polymat's success is sure to offer production moulders the opportunity to increase their output considerably by using this product in their existing moulds, as quicker gel times can now be set allowing overall faster cycle times with the same resin system” says Plastech Managing Director Alan Harper.