Choice is good. Choice is healthy. Having options allows us to select the most relevant, the most efficient, the most cost-effective, the most attractive, the most compatible option. A “one size fits all” approach is rarely auspicious unless one is purchasing a pair of socks. Sartorial convenience aside, choice is what people want. We want to be presented with options and make our own decisions based on what is best for us. This is particularly apt in the bearings industry today. Choice allows businesses to select the most efficient solution for their specific projects. Manufacturers who are able to provide their customers with a range of products and provide unpartisan advice on the best product range for a given application are surely much more relevant than those who restrict themselves to one material and attempt to “shoe-horn” it into applications where something else is more suited? Here Craig Clydesdale explores the benefits of product choice and the folly of manufacturers who restrict themselves to just one.
Since the very first bearing was patented by the British inventor Philip Vaughan in the 18th century, plain bearings have been made from a multitude of materials to suit a vast range of applications. Typical materials have been wood, bronze, steel/composite, ceramic, glass, sapphire, plastic to name but a few. The list is endless.
Today the most prevalent materials are bronze, metal composites and plastic. Each of these materials has its own unique characteristics which lend them to being more suitable than others for certain applications.
For example; sintered bronze bearings are durable and have good load bearing capabilities, are impregnated with lubricant, can withstand high temperatures, run at high speeds and have excellent corrosion resistance. Hard rolled bronze bearings are durable and can take high loads, can withstand high temperatures, need lubrication and can run at medium to high speeds and have excellent corrosion resistance. Plastic bearings have good sliding properties, are limited on load and temperature and are not good when subjected to high loads when stationary for long periods. They do have excellent corrosion and chemical resistance.
Steel composite bearings mostly are of the wrapped type are usually self-lubricated, can take high loads, can withstand high temperatures and can run at medium to high speeds. Exposure to corrosion needs to be addressed.
Everything in its place
On all projects, multiple considerations are made regarding the bearing application conditions and just what is the best solution to handle such conditions. Temperature, load, lubrication, contamination, speed and interval of use are just a few of these considerations. After these application deliberations, regard needs to be paid to things like ease of maintenance, lubrication and unit cost. The luxury of being able to choose the precise material that will be able to withstand application conditions, lends itself to easy maintenance (or indeed no maintenance) and come within budget is not only convenient but indeed vital to the success of the overall project.
Lets take the purely hypothetical scenario of the installation of a retractable roof onto a sports stadium: The project manager approaches a very reputable manufacturer to install the bearings on the roof. However, this manufacturer can only offer one type of material. Whilst this material is perfectly suited for an array of applications across many industries, the extreme load of the stadium roof causes the bearings to deform after a period of inactivity and the roof to jam the next time it is activated. At great cost and embarrassment, the project manager now needs to remove the previous bearings and approach a supplier who can offer a more suitable material for this bespoke project. This example, whilst hypothetical, is extremely relevant today. Different applications will always require different materials. There is no “one size fits all” range of bearing that is suitable for all applications. If we go back to our clothing analogy for a moment; it is obvious that leather is a fantastic material for all manner of apparel, but there are more appropriate materials when a manufacturer is producing shirts or hosiery.
The point that should to be seriously addressed by engineers and buyers is the need to ensure that when enquiring of manufactures or suppliers, that they do not receive biased advice especially from companies that can only offer one range of product. The “one type fits all” claim can lead to serious design problems and ultimately failure in the field.
Manufacturers who can offer plastic, bronze, steel and composite materials etc. are able to look at each individual project with unbiased eyes. They are not slaves to a particular material and are therefore able to make impartial recommendations as opposed to manufacturers who erroneously state that one range can “do it all”. For the peace of mind to know that you have the correct bearing solution for your project, it is always best to speak to a supplier who can give you a choice of materials.
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?
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.
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