Hygiene optimized by PUR02/06/2008 With its SIRIUS plansifter, Bühler revolutionized the sifting of milling products years ago. With its new NOVAPUR sieve stack, the developers in the Bühler Milling business unit have now further refined the flour milling process. “Wood is doubtlessly a popular engineering material with a number of good characteristics,” says Urs Dübendorfer, product manager in the Bühler Milling business unit. “But wood poses some problems in terms of food safety and hygiene. We therefore began contemplating the introduction of a new mate-rial for our sieve stacks some time ago.” The intensive search was crowned by success: Bühler has now rolled out an innovative sieve frame made of polyurethane (PUR) with matching frame inserts of stainless steel.
Polyurethane applied as an engineering material offers a number of advantages over wood. Polyure-thane can be given different mechanical properties, depending on its specific composition and produc-tion. The PUR composition chosen by the Bühler engineers is highly tolerant to changes in tempera-ture and air humidity. This means that the new sieve frame will only undergo minimum mechanical changes. Moreover, the PUR surface is abrasion-resistant and of a nature that virtually prevents static friction. In combination with the geometry without corners or edges, this ensures that the foam-molded NOVAPUR sieve frames will hardly show any product adhesions after use and are also very easy to clean. Due to the minimized sliding resistance, the action of the sieve cleaners is also highly effective. Urs Dübendorfer: “The NOVAPUR allows the cleaning requirement to be reduced by one third.”
Matching frame inserts
As part of the further development of the NOVAPUR system, also the frame insert was improved. It is no longer made of aluminum, but of stainless steel. The new frame insert offers higher mechanical resistance, making it easier to remove fabric and adhesive residues when changing the sieve covers. Despite the higher specific gravity of stainless steel, the new NOVAPUR frame insert is not heavier than the previous aluminum insert. “We found a profile that helped us save unnecessary weight,” says Urs Dübendorfer. He immediately goes on to mention another improvement: “The novel rubber lip seals guarantee absolute tightness of the sieve stack.”
Polyurethane and stainless steel offer advantages over wood and aluminium not only as individual materials. “The combination of the two new materials is ideal,” explains Urs Dübendorfer. “PUR and stainless steel have a similar coefficient of expansion. This will be found to be a crucial benefit in ther-mal disinfestation. No undesirable stresses are created anymore.”
The new Bühler NOVAPUR plansifter sieve stack is available in different design versions (standard, control sifting, or vertically subdivided). It can also be incorporated as a retrofit in existing sifters, a job that only requires minor adjustments.