Case study: flow stick

Flow meter firm UK Flowtechnik, which is a joint venture between UK Flow and Flowtechnik, supplies flow meters, process sensors and specialist pumping equipment to the process industries.

It also offers technology from companies such as VSE, Flomec and Comeco.

Last year the company was approached by a manufacturer of glue and resin dispensing machines who wanted to find out if UK Flowtechnik had the expertise to accurately measure the flow rate of Araldite AW4804 aluminium-filled adhesive and HW4804 hardener in a hightemperature (210ºC) application.

Andrew Biggs, technical sales manager at UK Flowtechnik, says this was the first time the company had taken on such a project, which also posed two major challenges.

Firstly, the viscosity of 300,000 to 1,000,000 cps and with 55% by weight aluminium filler made this a very difficult media to handle, UK Flowtechnik says.

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, the company says.

In order to overcome these issues and successfully measure the adhesive and hardener’s flow rate, UK Flowtechnik opted for a large RS Series helical screw flowmeter from Germany-based VSE 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.

According to UK Flowtechnik, the helical screw principle allows the resin to move through the flow meter without loss or slippage of flow, while also allowing a high degree of filler without shearing the media.

The RS Series flow meter from VSE is fitted with innovative interpolation electronics that help increase 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.

“We have in the past steered away from aluminium filler as our flow meters run tight tolerances and don’t like big particles,” says Biggs.

“But as it had never been done before, and [as] ‘innovation’ is our watchword, we successfully took on the challenge.”

Biggs says it is a real challenge to measure the flow rates of viscous materials.

“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,” he says.

“But the interpolation electronics allows us to have a large flowmeter with small flowmeter resolution and response time.”