We were approached by a manufacturer of glue and resin dispensing machines to see if it we could accurately measure the flow rate of Araldite AW4804 aluminium filled adhesive and HW4804 hardener in a high temperature (210ºC) application.
Andrew Biggs, Technical Sales Manager at UK Flowtechnik, said: “This was a first for us and we had to start with a clean sheet of paper. We have in the past steered away from aluminium filler as our flow meters run tight tolerances and don’t like big particles. But as it had never been done before, and innovation is our watchword, we successfully took on the challenge!"
The challenge was twofold. Firstly, the viscosity of 300,000 to 1,000,000 cps and with 55% by weight aluminium filler made this a very difficult media. It was crucial that the ratio of resin to hardener was accurately controlled, otherwise the strength of the composite assembly is reduced, or in the worst case the resin does not harden leading to components being scrapped.
Secondly, traditional gear flow meters would be large, expensive, completely impractical and unreliable as they have very low output frequencies which can make them difficult to control.
To solve the problem we used a large we used a large RS Series helical screw flowmeter from VSE in Germany as the best possible solution to give a low pressure drop across the meter yet still provide enough accuracy and resolution for the control system.
The helical screw principle allows the resin to move through the flow meter without loss or slippage of flow whilst also allowing a high degree of filler without shearing the media.
The flow meter is fitted with innovative interpolation electronics which increases the resolution by up to 128 times, giving a high output frequency, allowing a greater degree of control and faster response time to changes in flow rate.
Andrew Biggs, added: “Measuring flow rates of viscous materials is a real challenge so we’re delighted with our success. With the high viscosity of most resins and the smaller ratio of hardener, flow rates are low but the flowmeters themselves are quite large in comparison. But the interpolation electronics allows us to have a large flowmeter with small flowmeter resolution and response time. The perfect mix!”