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Lubrication without contamination

11 March 2019

Automated machinery brings with it the potential for contamination by lubricants. This risk can be mitigated through the use of appropriate design and technology argues Phil Burge

To operate efficiently and to avoid premature wear bearings need to be well lubricated. In the food and drink sector, an obvious requirement is that any lubricant must be a food-grade product and it is best to use the brand specified by your bearing supplier to ensure optimum performance and also to meet safety and hygiene requirements.

The next step is to keep the lubricant sealed inside the bearing. In wet or humid environments, there is a danger of moisture breaching a bearing’s seals. This may be exacerbated by the effects of detergents used to keep the equipment clean, or of aggressive substances such as citric acid, if present. Frequent washdowns, often under high pressure, add to the sealing challenge for the food industry.

If liquids can reach into the bearing cavity from outside, the lubricant may also leak in the opposite direction and regular relubrication will be needed to purge the bearing of water and contaminants. This adds to the risk of polluting the process and the environment. Even with this extra maintenance, the service life of the bearing may be shortened.

A solution is to seal the bearing and lubricant so effectively that no liquid is able to enter or leave. Then there will be virtually no need for relubrication within the bearing’s lifetime. This thinking led to the creation of the SKF’s Food Line Y-bearing units, where a single pre-fill of food-grade grease can last for a number of years.

The time and lubricant savings, when compared with relubrication of, say, 100 bearing positions, can easily be 100 minutes a week and 78kg of lubricant every year. 

In the past a poultry processing plant, which has now switched to sealed bearings, would need to replace hundreds of nickel-plated cast iron bearing units every few months because of leaks and corrosion. Its bearings now last four times longer and it has also benefitted from  labour cost savings.

Solid solutions
To avoid contaminant ingress and lubricant leakage in very challenging situations, one alternative is to use Solid Oil. In this scenario, the bearing cavity is filled by an oil-saturated polymer matrix which remains firmly trapped within it. It is also resistant to high-pressure washing – even with caustic cleaning agents – and to corrosion. Food-grade oil can be specified in the pre-filled bearings and there is no need for relubrication. 

One customer switching to Solid Oil had suffered water penetration and lubricant leakage from bearings which were supposedly greased for life. Bearing service life increased from 12 weeks to two years, maintenance costs were reduced and lubricant leakage was virtually eliminated.

Dry lubrication
The most radical alternative, perhaps, is to lubricate without grease or oil. Dry graphite-based lubrication is particularly suited to use in very hot applications where grease tends to melt and leak leading to potential contamination issues. Leak-free, relubrication-free graphite solutions avoid consumption of expensive high-temperature grease and overcomes restrictions on oven temperatures.

In the case of a confectionery producer’s wafer-baking oven, using deep groove ball bearings, relubrication with high temperature grease was required every 16 weeks. Following replacement with graphite-lubricated units, which ran for four years around the clock, gave the company a saving of 26 hours of planned downtime every 16 weeks, as well as 150 hours of labour annually.

Phil Burge is marketing and communications manager at SKF. 

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