Eureka Engineering Design Journal
Continuous fibres wind filter success
Eureka Engineering Design Journal (June 2004)
Improving the design of traditional wound string filters doubles performance and avoids lost bits. Tom Shelley reports
Wound string filters are setting new benchmarks for efficiently catching dirt large amounts of dirt, without risk of introducing stray fibres or other contaminants into the fluid stream being filtered.
Initially made of melt spun polypropylene for the filtration of water, they are now additionally available in polyester and other materials and are finding increasing application in the oil and gas industries.
Manufacturers and inventors, Syntech Fibres in Pakistan started out as a producer of polypropylene textiles. Director, Hamid Omar, told Eureka during a visit, that moving from the fiercely competitive synthetic textile business into manufacturing for engineering customers was a business breakthrough and that the firm was now concentrating its entire business on making filters.
The patent pending innovations of the “Aqua Clear” filters are: the way in which the filters are wound, the way the yarn is made up from continuous filaments and the fact that the filaments are not round, but multi-lobed. The latter ensures a higher dirt holding capacity and lower resistance to flow. The filaments are randomly oriented to each other, intermixed, looped and entwined to produce a bulky yarn. When wound into a cartridge, each filament continues, without a break, throughout the length of the yarn. During winding, the pitch, number of crossings and space between each yarn is continuously varied so that the inner layers are close wound, while the outer layers are more open, but using the same winding tension. Each yarn traps the randomly protruding short loops of adjacent yarns to yield a stable structure.
Diamond shaped voids, typically of conventional wound string filters are avoided, and there are no short fibres that can break away as loose bits. Dirt holding capacity and filter life is said to be about double that of conventional wound filters and pressure drop is halved.
The favoured material is polypropylene, melt spun without use of lubricants, wetting agents, emulsifiers, anti-oxidants or ant-static agents. The products are suitable for uses that include: reverse osmosis pre-treatment and filtering drinking water, beverages, gases, and electronic, electroplating and photographic solutions, applications in oil and gas production for deep well injection of processed water, waste water disposal and cooling tower filtration. Polyester media filter cartridges with stainless steel cores are also available for applications requiring higher temperatures and chemical resistance for the filtration of edible and petroleum oils. Cotton media cartridge are available for use at up to 130 °C. Filter cores are available in polypropylene, stainless steel and galvanised carbon steel.
- Wound string fibres based on a novel continuous fibre process are said to have twice the dirt holding capacity and life of conventional wound string filters and half the pressure drop
- The favoured media is either no or low contaminant polypropylene but cartridges made of polyester or cotton are also available
- Use of continuous fibre avoids the shedding of small fibres into the fluid being filtered