Oven-ready bearings enable maintenance reduction for bakers

11 May 2020

Commercial scale, conveyor-fed baking and proving ovens present a particularly challenging environment for bearings. But, by using modern high temperature bearing technologies and novel lubrication techniques, the industry can solve many of its maintenance problems.

Baking on an ‘industrial’ scale usually involves the operation of conveyor ovens, which must be capable of running for extended periods of time at elevated temperatures in order to satisfy daily, high-volume market demands. Such are the pressures of modern bakery production that conveyor ovens are frequently run at the limits of their specified operating parameters, where faster conveyor speeds and higher oven temperatures combine to increase the stresses on vulnerable components, not least being the conveyor bearings themselves.

At high humidity and temperatures that frequently exceed 180 °C, conventional bearing grease rapidly deteriorates, increasing metal-to-metal contact within the bearing and accelerating wear. Moreover, prolonged exposure to high temperatures can even cause grease hardening, ultimately leading to bearing seizures. High humidity, in particular, poses challenges for bearings used in bread dough proving ovens, which, although working at lower temperatures, have atmospheric moisture levels that actually create conditions of precipitation within the oven.

Bearing and/or lubricant failure in these applications have a big impact on maintenance budgets. In applications where traditional grease lubricated bearings are used, ovens must first be shut down and allowed to cool before maintenance staff can safely access the equipment to remove any faulty bearings, clean off existing or hardened grease and re-lubricate. The entire process can shut down production for upwards of three days – and must be repeated every few weeks to keep the ovens functioning at peak performance.

Lost production, however, is just part of the cost penalty associated with bearing/lubricant failure; the cost of the grease itself is not insignificant. The perfluorinated grease used in these applications, which offers non-flammability and high temperature stability, is an expensive commodity, and as there may be thousands of bearings supporting the conveying system, performing routine service on just a single oven becomes a costly task.

While our intuition would tend to support the premise that high temperatures are always likely to degrade bearing performance, the question arises: is there any possibility that a high temperature environment can actually improve a bearing’s performance? Exploring the answer to this particular conundrum drove SKF engineers to develop a novel bearing technology that not only tolerates but actually thrives under high temperature operating conditions.

SKF high temperature deep groove ball bearings feature an adjusted high temperature bearing radial internal clearance and optional integral shields, together with a fully crowned, pure graphite cage. The graphite medium permits just enough contact between the ball and cage to create a fine powder that coats the bearing’s rolling elements, avoiding metal-to-metal contact and the need for additional lubrication. Because graphite can tolerate extreme temperatures – and need the oven’s inherent humidity to function properly – provide optimum performance at temperatures up to 350 °C. With these bearings, producers are able to run their ovens hotter than they could with traditional bearings (thereby increasing throughput), while avoiding the need for repeated re-lubrication and its cost implications.

Where proving ovens are concerned, the problems are more to do with very high levels of humidity within the oven rather than high temperatures and SKF has a solution for this as well – bearings with ‘Solid Oil’ lubrication technology. Solid Oil is an encapsulated lubricant technology, which can be applied to virtually any bearing, uses a polymer matrix saturated with lubricant that completely fills the internal space, encapsulating the cage and rolling elements. SKF bearings with Solid Oil do not require re-lubrication and can be considered virtually maintenance-free.

Since installing SKF bearings with Solid Oil more than a decade ago, one of SKF's bakery customers has completely avoided unplanned stoppages, saving in excess of 300 hours of maintenance activity and more than £4,000 in yearly bearing-related expenses. Eliminating unexpected production halts also helped the bakery avoid the financial losses associated with scrapped and wasted ingredients.

Bakers - and food manufacturers in general - are keen to increase the efficiency of their ovens while coping with the time and financial consequences of elevated temperatures, high humidity and extended running times that place such high stresses on oven conveyor bearings. Fortunately, thanks to some innovative developments in bearing technology by SKF, many of the maintenance challenges that food producers face every day can be virtually eliminated.

https://www.skf.com/uk/industries/food-and-beverage/products-and-solutions/high-temperature-bearings-and-units#cid-496021