A taste for reliability
Published: 02 June, 2016
Food and beverage manufacturing facilities are tough environments for bearings. The avoidance of premature failures calls for smart approaches to their selection, operation and maintenance. PWE spoke to David Oliver, channel and platform development manager bearings and units at SKF.
Almost every machine used in food and drinks production relies on bearings in its operation. In many instances, however, bearings fail prematurely. A wide range of factors can cause this, but the unusually demanding operating conditions in food and beverage plants are a primary contributor.
Water, humidity and chemicals
Many areas of food plants are exposed to water, humidity and chemicals, either as part of the production process itself, or during wash-down operations. Wet, chemically aggressive environments create a host of problems for bearings. Corrosion and chemical damage can harm bearing surfaces, shortening their life and pushing up replacement costs. Flaking corrosion can contaminate food. And unexpected failures can lead to unplanned stoppages and loss of production.
Wet environments are also tough on lubrication. Wash-downs can displace the grease from bearings, for example, meaning maintenance staff has to re-lubricate on a regular basis. That drives up labour costs and has an impact on sustainability too. Grease contamination of wastewater increases effluent treatment costs, and the contaminated gloves, wipes and containers used in the re-lubrication process typically end up in landfill.
Bearings don’t just suffer in the wash-down process, they can also make it harder to implement. Bearing housings with cavities, tight radius corners and rough surfaces are difficult and time-consuming to clean, and they provide a habitat for bacteria, creating a food safety risk.
The hot conditions in and around ovens, grills, dryers and fryers can reduce lubricant viscosity, allowing grease to escape from the bearing, another source of potential product contamination. High temperature lubricants are costly, and re-lubrication is even more time consuming than in room temperature environments, since operators must wait for equipment to cool, or risk personal injury during re-greasing. The temperature limits of bearing lubricants can also put a ceiling on output, since manufacturers can’t increase operating temperatures to accelerate production.
At the opposite end of the temperature scale, freezers and chillers generate another set of problems. Regular cycling between sub-zero and ambient temperature can lead to condensation inside the bearing, increasing the risk of corrosion and the potential for lubricant to be displaced into the production environment. Lubricants can stiffen or freeze at low temperatures, increasing friction, driving up energy costs and potentially causing bearing components to crack and fail.
In response to these challenges, bearing manufacturers have developed a range of specialist solutions for food and beverage producers. Let’s look at a few examples.
One poultry processing plant was being forced to replace hundreds of nickel-plated cast iron bearing units every two or three months due to grease washout and corrosion. The company replaced these bearings with SKF composite Y-bearing units with stainless steel bearing inserts and a special multi-lip seal that prevents grease displacement or water ingress, even under high-pressure washing. The composite housing of these bearings is designed to resist damage by disinfectants, cleaning chemicals, acids and fats, while simple geometry, suitably radiused corners and smooth, non-porous surfaces simplify cleaning and resist bacterial growth. After the change, bearing service life was extended by a factor of four, and the company also enjoyed significant labour savings thanks to reductions in lubrication and replacement.
In the event of the failure of a bearing or seal in service, the ability to spot potential product contamination is an increasing priority for food manufacturers and regulators.
David Oliver, channel and platform development manager bearings and units at SKF explained that SKF’s latest Food Line range of stainless steel deep groove ball bearings uses seals made from synthetic rubber compliant with US Food and Drug Administration (FDA) as well as European Community (EC) requirements, and are coloured blue for optical detectability, should they be damaged.
Oliver added that another company, this time in the baked goods sector, needed to shut its ovens for two days every four months to re-grease the bearings on its oven conveyors. The company replaced conventional grease lubricated bearings with SKF high temperature bearings that use a self-lubricating graphite cage. The consequent reduction in maintenance shutdowns saved the company £53,000 a year over the expected four and half year lifespan of the new bearings in continuous production. As a further benefit, the higher temperature rating of the new bearings allowed it to run its ovens 10 to 15 C hotter, enabling a significant increase in throughput.
He also highlights that smart lubrication technology was the key to big maintenance cost reductions for an ice-cream maker. The bearings on its freezer conveyors were prone to early failure due to moisture ingress during cleaning, when their temperature would cycle rapidly between -40 and +25 C. In this case the company adopted SKF bearings with Solid Oil, which replaces conventional grease with a polymer matrix, impregnated with food grade oil, which completely fills the internal space in the bearing. The lack of internal voids in this design prevented the breathing effect that had previously led to water ingress, and the polymer material provided a sufficient reservoir of oil to eliminate re-lubrication during the life of the bearing – around three years in this application.
Installation and maintenance
Environmental conditions are not the sole difficulty for bearings in food production environments, however. Premature failure can also be caused by incorrect installation and poor maintenance procedures.
Companies often experience problems with rotating equipment in the form of excessive vibration and noise levels, seal failure, and elevated housing temperatures. These issues can lead to excessive energy consumption, potential contamination due to oil and grease leakage, premature bearing failure, and ultimately costly unplanned downtime. Frequently, the root cause is shaft misalignment, and in the case of belt-driven machinery, incorrect tensioning.
Traditional alignment methods – involving a straight edge, thickness gauge, dial indicator, or the naked eye – are time consuming and do not provide the precision needed for accuracy. A more effective modern solution is the use of laser alignment systems. These devices are easy to set up and use, with no operator training required and can ensure proper alignment first time, every time.
Keeping conventional bearings properly lubricated is another challenge. Oliver says one major food processing plant relied on manual lubrication to keep its bearings in proper operating condition, for example. But, with 150 hardtoreach critical lubrication points throughout the plant, it was difficult to maintain the proper lubrication and to monitor equipment lubrication needs. Bearings were often over- or under-lubricated, resulting in frequent bearing failures, shutdowns and costs related to machine repairs and maintenance. The challenges of reaching some lubrication areas also presented a continual risk of operator injury.
Oliver explained that SKF recommended the installation of its SYSTEM 24 LAGD series automatic lubricators for all 150 lubrication points. The system provided an easytomanage lubrication process and proper lubrication 24 hours a day, seven days a week. As a result, Oliver says downtime was reduced and productivity increased. Savings were realised in grease costs, and in parts and labour previously needed for machine lubrication and repairs.
Oliver concludes by highlighting that once bearings are appropriately selected, properly installed and effectively lubricated, they should have a long trouble-free service life. Problems can still arise, however, and an increasing number of food and beverage companies are adopting condition monitoring technologies to keep a close eye on machinery performance. One popular and cost effective solution is the use of hand-held data collection and recording devices. These systems can be used by front line staff to regularly check temperatures, vibration levels and other plant parameters. Faster and easier to use than paper-based systems, such devices allow deviations from normal levels to be easily identified, prompting early investigation and appropriate mitigating actions.
For further information please visit: www.skf.co.uk