As a result of pillow block bearings that were failing every six weeks on the multiple-belt dough-prove section of a process line, a UK-based tortilla wrap manufacturer turned to NSK for help. Investigations by NSK´s expert engineering team attributed the failures to the ingress of flour particulates and set-screw loosening (shaft creep) due to vibration. A recommendation was subsequently made to replace the tortilla wrap manufacturer´s standard pillow block units with Self-Lube Triple-Lip Sealed Units and eccentric locking collars from NSK. The replacement bearing units have successfully extended operating life from six weeks to over one year, resulting in significant cost savings. Flour particulates can be extremely damaging to incorrectly specified bearings on dough-prove belt conveyors
The dough prove at the tortilla wrap manufacturing plant has 42 rollers in total, which prior to the NSK recommendation were each supported by two pillow-block bearing units with a single lip seal and set screw locking arrangement. Rotation speed is around 120-rpm. A belt is wrapped around the rollers to convey the tortilla wraps and retain them for long enough to prove. The tortilla wraps travel from one end of the dough prove, flip over on to the belt below, and travel in the other direction. This sequence is repeated until they enter the oven for baking. Dough-prove conveyors operate in harsh conditions where they are exposed to flour particulates and metallic debris from chain and sprocket wear (a number of rollers on dough-prove conveyors are typically driven by sprockets and chain). For the tortilla wrap manufacturer, this operating environment meant that two mounted bearing units and one 35mm diameter shaft required replacement approximately every six weeks. The bearings were reported as damaged beyond use due to heavy contamination and creep damage to the bore, while the roller had to be replaced due to an undersized shaft diameter at the bearing fitting surface (from wear damage caused by creep). Every failure would require a significant number of man hours to perform the replacement, and bring about substantial machine downtime and costly production losses. In contrast, the introduction of NSK Self-Lube Triple-Lip Sealed Units has produced zero failures over a 12-month period. These bearing units feature a nitrile rubber triple lip that is bonded to a protective pressed-steel shield. As a result, longer bearing life is achieved through superior seal performance. Additionally, the bearing units provide extended re-lubrication intervals, which in turn greatly reduces maintenance costs and increases the productivity of machinery and equipment. In total, the annual savings at the tortilla wrap manufacturer have been calculated at €54,665. Self-Lube Triple-Lip Sealed Units offer simple implementation and represent a ready replacement for existing bearing units. They are available for both set-screw and eccentric locking collar insert options, in metric and imperial bore sizes. Importantly for the application at the tortilla wrap manufacturer, the selection of eccentric locking collars successfully reduced insert loosening in service, without damaging the shaft.
NTN-SNR makes food-processing the flavour of the month
NTN-SNR, a leader in precision mechanics, is pressing ahead with food safety. The company plans to invest in its solutions for the food-processing industry as a way to optimise and strengthen its short-term range. The goal is to achieve optimal production with no risk to the user. This is necessary investment for a sector with increasingly stringent standards…
The average cost worldwide for product recalls in the food-processing industry was €7.92 million between 2012-2017. In 75% of cases, the causes were contamination with bacteria or allergens, or the presence of a foreign body. Despite strict standards, the food-processing market is the French industry leader, with a turnover of € 180 billion in 2017. It also ranks second among industrial sectors most affected by product recalls and withdrawals (16%), after the automotive industry. This presents a risk both to consumers’ health and to companies’ reputations, which are suffering considerable losses.
With this in mind, NTN-SNR, with its 30-year market presence, is pooling its strengths and developing its dedicated teams with a view to making the food-processing business its new battleground. The company’s repositioning brings fresh challenges, including rethinking and reintegrating all of the sector’s constraints, and reidentifying the various segments and ranges to meet each need as accurately as possible, while remaining accessible to all market participants.
A highly constrained environment
With its high-pressure washing, cleaning agents, humidity, fine particles, hygiene standards, high production rates, etc., the food-processing industry is a highly constrained environment.
NTN-SNR relies on its expertise to ensure that health standards-compliant, sustainable production is tailored to each sector of activity.
As of this year, the company is focusing on developing its existing ranges, with Germany and Italy as the main European targets for machine manufacture and France and Spain for maintenance.
NTN-SNR’s short-term food-processing market goals are to eliminate incident risks, reduce maintenance times to increase profitability, and to ensure peace of mind.
Fully suited solutions
To this end, the company offers a wide range of bearings, lubrication solutions, linear guides and stainless steel or thermoplastic self-aligning bearings. NTN-SNR has chosen to offer all-stainless steel bearings, where some market players only offer it for the insert, in combination with an anti-corrosion coated housing. The inserts are equipped with an elastomer seal protected by a shield to counter any impact or mechanical stress. As for the additional protective caps, they are provided with a radial or double-lip seal, offering additional resistance to high-pressure washes, even when in direct contact. These systems are true shields against moisture and dirt.
For added convenience, NTN-SNR inserts are available with Lubsolid® solid food grease. Fifty-five percent of premature bearing failures result from improper lubrication – a fact that led the company to design its flawless lubricant. The polymer matrix containing a large amount of oil completely fills the free space inside the bearing. As a result, neither pollutants nor water can enter.
The grease’s solid state means that it cannot flow, ensuring the cleanliness of your environment.
These properties increase the duration life of the bearing by up to 20 times compared to a part lubricated using a standard high-performance grease.
The appeal of this technology and growing user demand are behind the company’s plans to invest in its solid food grease. The goal is to secure production while increasing its manufacturing capabilities.
3 questions to Kévin Gay, NTN-SNR Market Manager
Why has NTN-SNR decided that this is the time to strengthen its presence in the food-processing industry?
It’s a gigantic market. The food-processing industry is the largest European manufacturing market. Market constraints mean that innovation is a constant, necessary feature.
NTN-SNR is one of the world’s leading bearings manufacturers. It is known in particular for its presence in the automotive, industry and aerospace markets. The company is also a player – albeit a more cautious one – in the food-processing market. Now, however, it seems vital that we emphasise our solutions and further develop our ranges to put forward options that are increasingly adapted to the many demands encountered by today’s manufacturers.
What is NTN-SNR’s added value compared to the competition?
Every experienced market player has high levels of technical skill and specific expertise (bearings, ball bearings, etc.). That being said, while designing reliable, innovative and qualitative products is essential to protect against bacterial growth, you can’t ignore the cost. Certain premium-quality ranges on the market have a rather high price tag. However, of the 300,000 companies making up the European market, 99% are SMEs with sometimes limited maintenance resources. As a result, they are forced to turn to lower cost solutions. For NTN-SNR, guaranteeing the accessibility of quality products in terms of cost to all food-processing stakeholders offers peace of mind.
What do you mean by “peace of mind”?
“Peace of mind” is one of the cornerstones and drivers for how we respond to the constraints of the food-processing business. It has several aspects.
First, there is health-related peace of mind – of the consumer, of course, but also of the manufacturer. On the business side, economic peace of mind is also a key point. With quality equipment, the maintenance manager can increase his operating intervals, thus increasing production. Peace of mind thus equates to saving time, productivity and profitability.
A wide range
- Topline ball bearings
- Thermoplastic mounted units
- Stainless steel mounted units
- Stainless steel ball bearings
- Linear axis and ball bushings
- Lubsolid®, solid food grease
- Lubrication solutions
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.
Hygienic design cuts risk of food contamination
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?
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