The process industry is finding uses for positive displacement pumps that are very different from traditional applications. Eugene McCarthy reports.
A MasoSine SPS series pump from Watson-Marlow Pumps Group has transformed the efficiency and reliability of a bead mill at the Broadstairs, UK, facility of speciality ink producer FSIS. The company previously used an air-operated diaphragm pump but had to battle constantly against excessive friction and heat which had the effect of curing a vital ink component - turning it from liquid to gel - ultimately leading to machine seizure.
FSIS is a global leader in the manufacture of speciality printing inks, producing high performance products for digital, flexographic narrow web and screen print that colour the images on thousands of everyday products - from retail displays, textiles and packaging to CDs and DVDs.
Over the course of the past decade, particularly in the past 3-4 years, changes in the wide format digital ink market have seen FSIS respond to maintain its position as a UV technology leader.
Today, every process at the plant needs to be ultra efficient and 100 per cent reliable in order to meet high customer demands.
"We have a bead/dispersion mill that effectively comprises a six litre capacity, water-cooled horizontal chamber," explains the company's productivity services manager Trevor Cornock. "Inside the chamber are a number of very small beads made of hard-wearing yttrium stabilised zirconium that measure 1.6-2.4 mm in diameter. These beads are deployed to grind the pigment being milled."[Page Break]
Although this sounds straightforward enough, Fujifilm SIS encountered an unexpected problem that due to its repeated nature began to have a significant effect on productivity.
"A certain viscous ink component we use has a UV monomer type base that may cure when exposed to temperatures above 50°C," says Cornock. "Because our previous AOD pump generated a fair amount of friction, this converted to heat and caused the ink component to turn from liquid to gel when temperatures exceeded 60°C, which would eventually bring the bead mill to a halt."
It was clear FSIS required a pump that generated minimal friction and so could avoid the associated heat problems.
As an existing supplier to Fujifilm SIS (formerly Sericol), Watson-Marlow was able to recommend a solution in the form of its MasoSine SPS series, a highly reliable and economical positive displacement pump for industrial applications. Its design features an exclusive sinusoidal rotor that overcomes the limitations of conventional rotary lobe pumps (Fig. 1) to produce powerful suction with low shear, low pulsation, gentle handling - and, most importantly for FSIS, very low friction.
The MasoSine pump has been installed for around nine months and FSIS reports no problems whatsoever. This is aided by the low maintenance design of the SPS series. With a single shaft and rotor, there is no need for the complex timing gears and multiple seals associated with conventional rotary lobe pumps. One rotor, one shaft and one seal equate to simple and economic maintenance.[Page Break]
Wider peristaltic applications
According to Verderflex, the growing awareness of the peristaltic pump's wider potential is leading to its increased use in less arduous fields of application. It is regularly specified by the printing and packaging industries in place of air diaphragm pumps as it is gentle on the product but still able, for example, to handle viscous metallic inks. The food, drink and pharmaceutical industries are also regularly installing this type of pump. This is because the pumped product is isolated from the workings, there's no danger of contamination and it's easy to sterilise.
Another key factor in the rising popularity of the peristaltic pump is its fit-and-forget quality. Its lack of valves, seals and glands makes it inexpensive to maintain.
Indeed the only replacement part on a peristaltic pump is the hose or tube, a relatively low cost item that is easily exchanged.
These, say Verderflex, are important qualities as companies strive to optimise production processes and minimise costly downtime.
As well as improved design, the company says that developments in tube and hose technology have a significant role in the peristaltic pump's wide application scope and high reliability.
The choice includes resistance to high temperatures, corrosive chemicals, oils, fuels, solvent and mineral acids and of course includes special grades for food, drink and pharmaceutical handling tasks. Advances have also been made in the way hoses are manufactured. Historically hoses would fail due to early fatigue.
The rubber layers and the reinforcement layer become dis-bonded, a process that is often accelerated by externally machining the hose to achieve equal wall thickness.
However, a new hose production process has been developed that ensures a uniform wall thickness without the need for secondary machining and this significantly extends the service life of the hose.[Page Break]
As well as its traditional markets, the peristaltic pump is also making its presence felt in other applications. For example, in paper manufacturing where wastewater contains fibrous residues, fillers and chemicals. As the fluid tends to clog when only low flow rates are needed, the efficient working of other pump types is compromised. The low maintenance credentials of a peristaltic pump make it the perfect choice. When the fluid clogs at the suction side, as can happen easily with this application, the simple reverse action of the rotor is the easy solution to the problem.
Verderflex also points to ink handling as another growing application area. A good example in this sector comes from a packaging company that had been using air diaphragm pumps to transfer ink from storage containers to printing machines. However production problems were resulting from the existing pumps' inability to handle the water-based ink gently enough.
As a result, bubbles formed in the ink, ruining the packaging, creating waste and adding expense. A compact peristaltic hose pump proved to be the ideal solution. Ink is dosed gently, eliminating bubbles and as the ink is completely contained within the pump's hose throughout the process there is no mess or wear to moving parts. Colour change is quickly accomplished as the hose is easily exchanged. The pump itself can even run dry without fear of damage.
Another is in yeast pumping, where pumps with a high shear-rate can damage the fragile product. Yeast is also very abrasive and if it is producing gas, can also lead to vapour locks. Peristaltic pumps have no problem with any of these issues.[Page Break]
Wider peristaltic applications
For its part, Eccentric Pumps has created what it describes as a new revolution in peristaltic hose pump design. Its novel approach to building hose pumps employs a single oversized roller that compresses a highly-engineered, low-friction hose through more than 360° of rotation.
The company's peristaltic hose pumps are used at municipal and industrial sites wherever fluids are metered, dosed, or transferred from one place to another. Customers solve wide-ranging and complicated problems such as handling bleach, corrosive and abrasive slurries, acids, alkali, colourants, inks and other difficult-to-pump solutions.
Eccentric's peristaltic hose pump products provide more flow per revolution and only one compression and expansion per cycle. At equal performance points, the Eccentric Pumps peristaltic hose pump runs slower, and the hose lasts longer than pumps with multiple shoes or rollers. This, says the company, gives it a number of other big advantages, including more than 50 per cent more flow per revolution than conventional designs, and cooler running than other hose pumps.
There are performance benefits, too, including a high vacuum for suction lift applications, relatively high discharge pressures, and a compact footprint.