Bearings are critical to the operation of food processing lines, but can act as traps for bacteria, so must be designed so as not to cause contamination. Phil Burge, marketing and communications manager at SKF UK, explains.
Possibly the worst nightmare for the manager of a food processing factory is a product recall and there is approximately one incident every day in the UK. Many recalls are down to mislabelling, but a significant number are caused by bacterial contamination. Since the start of 2019, there have been separate incidents of salmonella in Polish sausage, tahini and mayonnaise, and one of listeria in cheese.
To avoid these types of incident, food manufacturers follow the principles of hygienic design, which insists that plant and machinery is easy to clean, does not harbour germs, and reduces the risk of cross-contamination (such as by cleaning fluids or other contaminants).
One guiding principle of hygienic design is cleanability, which is why many preparation surfaces are flat and made of stainless steel. However, the rule is often broken at the component level.
Despite their small size in relation to an entire food processing line, bearing units can be a major centre of contamination. For instance, bearing housings can act as tiny incubators for bacteria.
The crevices within a bearing housing are notoriously difficult to clean and can house a variety of food particles, where bacteria can multiply. Once at this stage, an otherwise-rigorous cleaning regime can actually make the problem worse. High-pressure washing can dislodge the bacteria and carry them into the air in the form of aerosols. Once they settle on the floor, they can be spread around the factory. The key task is to stop the bacteria at source.
Food safety is also compromised by the lubrication process. A common problem is over greasing: contaminants that have worked their way into bearings are often removed using grease flushing. However, this has many downsides, including reliability issues, high costs, reduced asset availability and environmental issues.
Relubrication is another problem. Bearings must be lubricated in order to work efficiently, but this raises the risk of contaminating the product with lubricant. Although food grade lubricants are available, they can contain allergens.
The rigorous washdowns used in the food industry can also affect lubricants: the high temperature and pressure of the cleaning water, combined with harsh detergents, can penetrate bearing seals. This is often solved with grease flushing or relubrication and both have already been shown to cause problems.
Upgrading to food safe
The challenge is to redesign food grade bearing units (which can be used in food-contact applications) into food safe bearing units. With rigorous hygienic design principles elevating them to a higher level by the addition of elements such as extra sealability and cleanability, and the use of allergen-free, non-toxic materials.
A prime example of a food safe product is SKF Food Line ball bearing units – Blue Range, which follow the rules of hygienic design. They combine smooth, inert surfaces with a self-draining geometry, superior sealing and a relubrication-free design. These features ensure that microbes cannot penetrate the bearing, while lubricant cannot escape.
Materials are an important factor. The housing is moulded from polypropylene (PP), a highly inert material with high chemical resistance. Inclusion of 40% long glass fibres helps to enhance mechanical properties. The housing is co-injected with a rubber seal, sealing the interface between frame and housing to avoid crevices and empty spaces for bacterial growth. At the same time, the bearing grease used is allergen-free.
The sealed design also ensures that relubrication is not necessary. One example is in the back seal, which stops contamination entering through the shaft inside the bearing unit by providing both static sealing (against the housing) and dynamic sealing (against the shaft).
Another innovative feature is the gutter concept, which boosts cleanability by protecting against detergent ingress. Detergents are designed to pass through anything, so blocking this process is almost impossible. SKF’s gutter concept allows detergent through but guides it towards non-hazardous areas. If water enters the top lip of the seal during washdown, it is guided around and out of the other side by either gravity or centrifugal force, if the bearing is active.
In addition, components are coloured blue for easy optical detectability, while the sealed nature of the bearings means there is no need for relubrication.
One food industry user of the Blue Range bearing units said recently: “Not having to relubricate, and clean excess lubricant from units, is of vital importance to us. In both the appearance of the conveyor lines and the safety around them.”
More carefully designed products usually come with a premium. However, the concept of hygienic design actually saves money for customers through factors such as extended bearing life, reduced need for cleaning and the reduction in re-greasing costs, including the grease itself, and the time taken to apply it.
For instance, a large food industry conveyor system with 200 bearing units may need re-greasing 50 times per year. The cost of grease may be £40/kg, that of labour around £20/hour. Removing these costs can save more than £12,000/year. The labour could be redeployed onto continuous improvement activities.
Third-party tests have also shown that the cleaner state of the Blue Range bearing units means they require around one-third less water to clean them.
Overall, though, the largest saving could be that of creating the necessary conditions to cut the risk of food contamination, and subsequent product recalls, to a minimum – and what factory manager would say ‘no’ to that?
NSK Molded-Oil bearings extend service life in food plant conveyor application
A vegetable processing plant in Germany is enjoying significant benefits following the adoption of Molded-Oil bearings from NSK. Principally, the move has helped the company extend the service life of bearings on a critical conveyor from two weeks, to 40, saving considerable maintenance costs and downtime in the process.
Keen to resolve the question of why its previous bearings were failing at such an unusually fast rate, and eliminate the associated cost and time issues, the company asked NSK to investigate.
During the inspection, NSK experts soon determined the cause. Due to the rigorous hygiene standards demanded by food industry regulations, the system was cleaned thoroughly on a regular basis. However, it was found that the cleaning process prompted considerable quantities of water to penetrate the bearings and, as a result, wash away the lubricating grease.
To help combat the challenges presented by the frequently required wash cycles, NSK recommended the use of its sealed Molded-Oil bearings.
A special tribology concept (tribology is the science of wear, friction and lubrication) has been implemented for Molded-Oil bearings. For instance, the bearings are equipped with NSK’s proprietary oil-impregnated material, which comprises lubricating oil and an oil-related polyolefin resin. This material releases the lubricant, which cannot be washed out due to its consistency, continuously over a long period. At the same time, the carrier material prevents water or solid impurities from penetrating the bearing.
By adopting the bearings, service life at the plant has increased from two weeks to more than nine months. This highly successful outcome once again confirmed NSK’s ´rule of thumb´ that Molded-Oil bearings achieve at least twice the service life of conventional grease-lubricated bearings in water and dust-contaminated environments. In this particular case, service life increased by a factor of 40.
The plant is also experiencing many other benefits. For instance, the operating environment remains clean because no grease escapes and no oil needs to be refilled. Molded-Oil bearings are therefore ideally suited to food industry applications, where thorough and frequent cleaning processes are essential. The use of stainless steel for the bearing components also contributes to this suitability.
NSK supplied the bearings for the vegetable processing plant with highly effective contact seals (DDU) on both sides for even higher levels of protection. This option is available for the standard range of Molded-Oil ball bearings. Molded-Oil is also available on spherical roller bearings and tapered roller bearings.
NSK launches J-Line – a new range of JIS standard bearing units
NSK is expanding its existing RHP branded Self-Lube® range of bearing units to include products made to the JIS standard. With this new J-Line series, NSK also introduces a new packaging design.
The J-Line bearing units comprise six of the most popular housing types: pillow block with/without feet, square and round flange, two-hole flange, and take-up unit. Also available are three pressed-steel housings and five inserts (wide and narrow set screw, wide and narrow lock collar, and adaptor sleeve) covering bore diameters that range from 12 to 90mm. The units are built on demand, offering the highest flexibility for customers.
J-Line bearing units will be easily identifiable in their new, fresh NSK packaging design for the European market.
Ready to ship from April 2019, J-Line bearing units are suitable for use in sectors that include agriculture, cement, construction, food, material handling, packaging, paper, steel, textiles and many others.
To help simplify selection, NSK has published a new Bearing Unit Catalogue containing both J-Line and Self-Lube ranges. An electronic version will be placed on the NSK website ready for download.
NSK Europe Ltd. is the European organisation of the Tokyo-based bearing manufacturer NSK, which was founded in Japan in 1916 and today employs around 31,000 people in its worldwide operations. The products and solutions provided by the industrial and automotive supplier can be found wherever things move. In addition to nearly all types of rolling bearings, the company´s portfolio includes housed bearings, linear technology, wheel bearing units, transmission and engine bearings and steering systems. The company is oriented to perfection in all of its business activities. Its aim is quality leadership in its industry, which it strives for through a continuous process of improvement, excellent product development, optimised production processes and customer-oriented service processes.
NTN-SNR’s SMART TEMP: Parts heated and mounted in complete safety for optimal reliability
NTN-SNR launches SmartTEMP, its new range of induction heaters. They control the temperature whilst mounting, to preserve the integrity of the materials and ensure total safety when mounting components (bearings or gears). Heating gradually and controlling temperature deltas, preserves the functionality of sensitive parts. The touch screen along with the ability to store heating information leads to better traceability. Ease of use and the scope of range make SmartTEMP a very high-performance tool for all industries. With this innovative induction heating device, NTN-SNR furthers the dissemination of good practices concerning the heating and mounting of rotating parts. This is an essential phase when one considers for instance that 17% of bearing failures are caused by incorrect mounting. With the market release of SmartTEMP, NTN-SNR continues to pursue its objective of improving the productivity of its industrial clients by extending the useful life of their parts and machines. Unique cutting-edge functionality The SmartTEMP range offered by NTN-SNR is designed primarily to ensure the safety of the operator and the part being heated. The unique design featuring a coil system beneath the workpiece heats the bearing’s two rings evenly and consistently to prevent any temperature distortions between the different components. Two probes constantly control the difference in temperature between the two rings, thereby ensuring full control of the heating process and the total integrity of the bearing’s physical characteristics. The range comprises seven models that are capable of heating parts with masses ranging from a few grams to 1.6 tons. The RAMP mode allows the rise in temperature to be set evenly over a given period of time in order to heat up sensitive parts very gradually. This innovation is crucial for protecting such parts as gears, whose teeth may become brittle if heated too quickly. The SmartTEMP ensures accurate control over the mounting procedure to fully protect the integrity of the physical characteristics of the materials making up the various parts being heated. It thereby extends the useful life of rotating parts and the machinery.
High performance, user-friendly and a rugged design
The SmartTEMP’s new processor optimises the device’s performance by adapting its power requirement to the characteristics of the part. The current efficiency rises to 0.8 against 0.3 with a traditional heating device. Heating time is thus reduced by 30%, thereby offering significant energy savings. The SmartTEMP features an easy-to-use and intuitive touch screen. The software, which can be set to the operator’s language, downloads the heating data and exports it on a USB stick for full traceability of the mounting of the part. Nowadays this data is essential for connected 4.0 factories, the unit can also carry out self-diagnostics. In order to operate continuously, SmarTEMP’s new design is rugged and highly reliable. The electronic components are located in a separate compartment, and the aluminium frame enable it to bear heavy weights, withstand impacts and extreme temperatures.
Over 17% of bearing failures recorded by NTN-SNR are due to mounting errors, particularly uncontrolled heating of the parts, which is sometimes carried out using a blowtorch or oil bath, which have no accurate temperature control. The recommended heating temperature is generally 110°C, but this can vary according to the materials. Through its Experts & Tools service, NTN-SNR is keen to pass on information regarding good practices, training and the use of the correct tools. The SmartTEMP, is available for all industrial maintenance professionals, ensuring precise mounting of component parts and so increasing the productivity of the machines.
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