INDUSTRY FOCUS FOOD & BEVERAGE BLUE BEARINGS ENGINEERED WITH HYGIENE IN MIND


Phil Burge, PR and Brand Awareness Manager at SKF, looks at the challenges of food grade bearing design and describes some important breakthroughs in tackling cleaning and contamination problems


D


espite increasing consumer and regulatory demand for product safety,


contamination-related recalls and alerts continue to be a fact of life in the food and beverage industry. One of the key contaminant sources is processing machinery. While machine surfaces may be


gleamingly clean and hygienic, the crevices in bearings and their housings often harbour microbes. Ironically, efforts to sanitise equipment by washing can make the situation worse, by pushing water past bearing seals and widening the contamination’s spread. During washdowns, food residues and


bacteria land on bearing housings and work their way into even the tiniest of spaces behind them. Driven by high- pressure sprays, they can reach further still – creeping through the bearing shaft


Engineers have addressed all these issues


in developing SKF’s Blue Range of Food Line ball bearing units, to which six new patent submissions and three design protections apply. They are relubrication- free, protected by effective sealing, and contain a purpose-designed, food-grade, allergen-free, detergent-resistant grease. Their blue housing is formed from inert,


chemical-resistant, hydrophobic polypropylene (PP), with smooth surfaces and self-draining shapes. A high (40%) long glass fibre content gives extra mechanical strength, and any fragments released by damage are easy to detect optically thanks to their blue colour. Their rubber base seal, featuring closed


bushes, is injected into the housing and co-moulded with it, so that all space between this structure and the machine frame is filled. A stop limiter around the


A blue PP end cover, securely twist-locked into place, with indicator dots to confirm correct positioning, provides both anchoring and sealing


have been proven by rigorous in-house and third-party testing. One test by RISE (Research Institute of Sciences and Engineering) in Sweden involved brushing sour milk onto bearing housings and then pressure-cleaning with detergent. Compared to their predecessors, Blue Range units retained less milk residue, needed less cleaning water and gave better end cover and back seal performance. In a high-pressure detergent wash test


developed by SKF engineers for the base seal, no water passed through. The same was true in similar tests for the end cover


gap and entering the housing. These sheltered, permanently moist environments provide allow micro- organisms to breed, and for allergens and other contaminants to accumulate. Each time the machinery is pressure-


washed, some of the accumulated microbes and materials are flushed out, along with contaminated lubricant and moved around the processing plant. Use of jet sprays can lift them high into the air, where they may be suspended in aerosols for several hours before landing and contaminating every surface. To protect against corrosion and poor


performance caused by water and detergents in their cavities, bearings may have to be regularly relubricated. Excess lubricant is another contaminant, and a carrier of bacteria. It spreads not only through washdowns but via towels, cloths and gloves used for dry-cleaning. Non- food-safe constituents in some lubricants and bearing construction materials may add to the contaminant mix.


26 MAY 2020 | PROCESS & CONTROL


housing bushes allows optimum bolt tightening torque while maintaining a hygienic seal. A blue PP end cover, securely twist-


locked into place, with indicator dots to confirm correct positioning, provides both anchoring and sealing. Also moulded from blue PP is the back seal, which prevents entry of contaminants into the bearing unit via its shaft. It uses a combination of static sealing against the housing and dynamic, rotary sealing against the shaft. There are no spring components with the potential to fall into food. A new approach, the ‘gutter concept’, is


used for the bearing seal system. Here, detergents cannot be totally excluded, as they are specifically formulated to pass through barriers. Instead, the small amounts entering as drops via its top lip are directed away from sensitive bearing structures and allows them to exit via the other side. Low heat generation avoids degradation of lubricant grease. The new bearing units’ hygienic benefits


The hygienic design of the Blue Range of Food Line ball bearing units helps avoid the considerable expense and reputational damage of product recalls arising from contaminated machinery


and back seal. Most competitors’ end covers failed, as did the market standard back seal. SKF also devised a ‘droplet test’ for


bearing sealing systems, in which water and detergent were constantly dripped over 500 hours of operation. Compared to the industry standard unit, SKF’s new product emerged with less contamination of its grease and with its raceway in visibly better condition. In addition, friction torque testing confirmed the gutter sealing concept’s lower energy consumption and operating temperature. Not surprisingly, SKF Blue Range bearing


units come at a slightly higher price, but the resulting operational savings can quickly repay that investment. These result from longer service life, reduced cleaning requirements, and elimination of relubrication-related labour, downtime and material costs.


SKF www.skf.co.uk 


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