HYDRAULICS & PNEUMATICS FEATURE A sticky situation A
lthough pumps and flow meters have been used for many years in the
painting and coating of products, with more complicated fluids such as resins, carbon fibres and plastics being used, the technology has had to advance. Not only are resins thick and sticky so can lose pressure when pumped through a pipe, but they also have a tendency to harden in the pipe. In addition, they can become runnier if too hot, or set if too cold. So, for applications where the
pumping of viscous liquids is needed, UK Flowtechnik uses Beinlich pumps. Manufactured in Germany, the company offers positive displacement pumps specifically designed to deal with both high and low viscosity, thereby making the pumping of thick and sticky resins much easier. There are a number of benefits to this
pump range, the company explains. They operate at a constant flow and pressure at a given viscosity, so they can be very accurate, and are ideal for dispensing and dosing as the flow rate will remain proportional to the speed. Although capable of coping with a wide range of viscosities, these are especially suited to thicker fluids as the volumetric efficiency actually increases, improving its accuracy. Added to this, the pumps can cope with pressures up to 200 bar.
VISCOSITIES Typically, viscous resins range from one to one million centipoise (cPs). Distilled
water measures one centipoise, and more viscous liquids such as motor oil will measure between 1,000 to 2,000 cPs. Resins like window putty will measure around 1,000,000 cPs. No matter what the viscosity, however, when pumping and metering viscous resin, it’s essential that
Pumping viscous resins can be a difficult task, but selecting the
right pump can help to overcome the challenges. UK Flowtechnik looks at the problems faced and suggests a solution
accurately controlled, or the strength of the composite assembly is reduced or the resin does not harden.
UK Flowtechnik offers positive displacement pumps
specifically designed to deal with both high and low viscosity
FACING THE CHALLENGE Resin Transfer Moulding (RTM) is a manufacturing process used to make components ranging in size from very small to large carbon fibre parts such as wing panels, car doors and components, and wind turbine blades. Any pump used in RTM must have the ability to be fine-tuned, so it can fill moulds over a range of speeds – ensuring the resin doesn’t cure before it goes into the mould,
the materials that make up the resin are mixed to the correct ratio and their combined flow rate must be spot on. As the Beinlich pump starts at flow rates
of just two millilitres per minute, rising up to 3,000 litres per minute, it works well when used as part of a closed-loop- control system, allowing engineers to check the output via the speed of the flow meter against the pump, so they can adjust the flow of the resin and hardener until the right ratio is achieved. The ratio of resin to hardener must be
VALIDATING THE USE OF PUMPS FOR SEED TREATMENT
A seed treatment company has been involved in the validation of Watson-Marlow Fluid Technology Group’s new Qdos 120 peristaltic metering pump. According to the company, the pump offers flows of up to 120 l/hr at a maximum pressure of four bar, double that of existing models in the Qdos range. As the pump maintains the same common interface, connectivity and functionality of the existing models,
it is said to be easy for customers to upscale to the higher flow rate model. In addition, its peristaltic operating principal enables the pump to deliver continuous, smooth flow for optimal fluid mixing, while high accuracy provides chemical savings and increased process quality. Furthermore, there are no valves or seals to clog, leak, gas-lock or corrode; and its one consumable part, the ReNu pumphead, can be replaced in 60 seconds. The fully contained pumphead also ensures no spillage or exposure to chemicals. Since adopting the pump, the seed treatment company has seen improved flow capability and accuracy at
a higher viscosity. In addition, the company was previously limited to the chemical types it could run on its existing Qdos 60. The application involved pumping viscous and shear-sensitive polymer chemicals from 11 litre packaged containers to a 1,200 litre tote (via a 3m pipe run) ready for seed coating. Here, any pulsation would affect consistency because the pump is feeding an air-powered atomiser. The flow range of the Qdos 120 is ideal for this application because different seed is treated with different levels of chemical, on demand. The company does not want to make up large batches of treatment which would then go to waste. Here, the self-priming and dry running capabilities of the Qdos pump play a vital role. The new pump has also been used successfully at an electroplating business for metering various
chemicals, including sodium hydroxide (NaOH) at 50% and calcium fluoride. Watson-Marlow Fluid Technology
www.wmftg.com
but also not too quickly which can leave voids in components. Furthermore, when bonding parts, it’s imperative that the right amount of resin is in the right place, so a high accuracy flow is essential. According to the company, this is done by fitting the VSE flow meter with innovative interpolation electronics. This produces extra signals and pluses, so the engineer can control the variables in a more responsive way and alter the amount of resin that is pumped out. An additional challenge is that varying the temperature of a viscous resin also changes its dynamics – a reduction of just 10 to 20 degrees can have a big impact on viscosity. The Beinlich pump, however, has a closed loop control sensor which is specifically designed to monitor and adjust the temperature as required.
UK Flowtechnik T: 0115 901 7111
www.ukflowtechnik.com
DESIGN SOLUTIONS | JUNE 2016 23
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