Stem the flow01 December 2005

These days, industrial lubrication has two main purposes: first, to ensure by some mechanical, electronic or outsourced human means that machine mechanisms receive timely lubrication; and, secondly, that this lubrication should be as environmentally friendly as possible.
This can mean reducing toxicity, locking up lubricants in the bearing material, choosing bearing materials that are lifetime lubricated or doing away with the need for lubrication altogether.
Centralised lubrication systems that pump grease into bearings without human intervention are attached to the main axle bearings on many UK passenger trains. And while this may add cost in capital terms, the savings achieved in terms of reduced maintenance costs and enhanced reliability are enormous.

Centralised lubrication systems that pump grease into bearings without human intervention are attached to the main axle bearings on many UK passenger trains. And while this may add cost in capital terms, the savings achieved in terms of reduced maintenance costs and enhanced reliability are enormous.

SKF has recently acquired German lubrication specialist Willy Vogel AG. The company offers centralised lubrication in its KF range. In operation, an electronic control unit switches the pump unit on and off at pre-selected intervals. If a lubrication point becomes blocked, a pressure-relief valve on the pump indicates the fault. In the case of electronically monitored installations, the fault is signalled via an indicator light on the dashboard.

Pumps can be supplied with grease reservoir capacities of 1, 2, 6 or 10 litres to suit the size of the machine. Topping up is done with a drum pump, grease gun or grease cartridges via a filling cylinder.

SKF has found that the system increases bearing life at least fourfold, cutting repair and maintenance costs, as well as non-productive machine and personnel time, by typically 20%. At the same time, lubricant consumption drops by as much as 40%.

For construction machinery and farm vehicles, Vogel has developed an inexpensive centralised lubrication unit called KFA. The units have a 1-litre capacity for lubricating grease up to NLGI grade 2 and the reservoir is made from clear plastic that provides a ready indication of fill level. Two independent lubrication circuits can be fed from a couple of outlet ports, allowing the direction of lubricant to the chassis and steering mechanisms on one circuit, and to mounted implements and attachments via the other. Three delivery rates can be selected for each circuit, according to need. They are able to work down to -20°C, thanks to a 300bar operating pressure.

On the fixed manufacturing plant scale, it is becoming increasingly common to place the management of lubrication in the hands of a specialist supplier. Such is the case at the Tate and Lyle Thames refinery at Silvertown, London, the largest cane sugar refinery in the world. Around a thousand people work there, while several hundred machines - including gearboxes, centrifuges and large rotary driers - produce 1.1m tonnes of sugar per year in a 365-day, 24-hour operation.
Prior to Castrol's involvement six years ago, the company managed its own lubrication, which engineering and projects manager Glenn Clarke admits wasn't structured as effectively as it could be. "We didn't have the expertise to maintain effective lubrication schedules or compliance monitoring, so we decided it was time to bring in a specialist."

Commenting on the benefits of outsourcing, Clarke explains: "Castrol introduced a structured regime that gave us immediate gains in plant reliability from fewer lubrication-related failures, and we experienced a dramatic reduction in bearing and gearbox failures. Castrol also introduced oil and vibration analysis as the contract developed, which helped us to pre-empt equipment failures and identify where we could make positive changes within the plants. To ensure that food-compatible lubricants are used wherever necessary, we worked with Castrol to develop a HACCP audit that identified areas that could be a potential risk. Wherever it was possible to completely remove the risk of contamination, we use standard lubricants, but where there remained an element of risk, we changed to Castrol food grade lubricants."

Another food-related business embracing outside management is Cranswick Country Foods in Hull, which operates a state-of-the-art abattoir and cutting plant, and a factory that specialises in sausage production. After some years of using a number of Rocol Foodlube lubricants alongside those from other suppliers, Cranswick's chief engineer Keith Richardson decided to switch completely to Rocol and its 'Rocolcare' lubrication management programme.

"We wanted to ensure that only food grade lubricants are used across our production facilities," he explains. "Our abattoir and cutting plant has been recently refurbished to significantly increase capacity, with butchery work taking place here, both for our own group as well as a large number of manufacturers in the UK and export markets. Our excellent reputation depends on safe, efficient processing and we cannot afford to take risks with contamination. Previously we were using lots of different lubricants and it made a lot of sense to standardise across the plants. Being familiar with the quality of the Foodlube products from Rocol, and their comprehensive service and support, it was an obvious choice."

As part of the service, an in-depth site survey recommended correct lubricants for the various applications, the exact levels of lubrication required and the frequencies. Rocol has also provided comprehensive training and signage to ensure operators avoid errors.

"The signage for our plants is particularly useful. The use of photos to show exactly how the lubricant should be applied is second only to having someone demonstrate the procedure in person," adds Richardson. To improve lubrication further at its facility, Cranswick has also appointed a dedicated preventative maintenance engineer whose primary role is to lubricate machinery throughout the plant over a night shift, instead of relying on individual machinery operators.

Bearing up

Solid state bearings - which either contain lubricant or work without lubrication - avoid the need for greases or oils, of food grade or any other grade.

NSK's Molded-Oil bearings are filled with a plastic containing lubricating oil. These bearings have been chosen to replace drive end bearings in food processing machines re-engineered by Peter Cox Marketing. "When we were considering a new design of vegetable peeler," says managing director Peter Cox, describing the design process, "we focused on several key areas that would benefit customers over the life of the machines. What we were particularly keen to achieve was a combination of higher overall levels of reliability and reduced cost of ownership.

"The reliability issue really centres on the operation of the rough-coated horizontal roller, which is the main element in our range of peeler machines. The roller is up to 3m long; it is electrically driven and supported by rolling element bearings at both its drive and non-drive ends. This arrangement generally works well. However, in the worst of operating environments, wear on the roller can result in misalignment, a condition that impairs the life of the bearings, often causing them to fail prematurely. The result is costly downtime, which is unacceptable in the pressurised food-processing environments in which vegetable peelers are employed."

Cox adds: "In our new design, we wanted to solve this problem once and for all. At the same time, we also needed to find a solution to the maintenance problem of relubricating the drive-end bearings. Relubrication took time and was not a good solution environmentally, both in terms of the operating environment for the bearings (food) and the disposal of lubricant. NSK offered advice and support on both of these problems and, more importantly, provided us with solutions."

The same benefits are also being enjoyed on the non-drive end of the vegetable peeler machine; in this area, spherical roller bearings equipped with Molded-Oil replace balls bearings. The new bearings also permit a higher load capacity and are more tolerant to the misalignment that occurs as the roller wears.

Higher load with zero maintenance is a feature of a number of polymer-based solid state bearings, lubricated rolling element bearings only being unavoidable at very high speed/load combinations, where polymer-based bearings fail from excessive heat. There are several suppliers of these products. Igus has solved design and maintenance problems for many companies with its Iglide plastic bearings, DryLin linear bearings and guide systems, and Igubal all-polymer rod ends. Railko has been supplying heavy-duty solid state bearings since 1936 when the company began with a plastic railway bogie centre pivot liner, designed to overcome problems of friction and wear associated with metal parts which had led to derailments. Finally, the largest manufacturer of metal-polymer plain bearings in the world is GGB, formerly Glacier Garlock Bearings, founded as Findlay Motor Metals in 1899, and renamed as the Glacier Antifriction Metal Company in 1901.

Development of these products continues apace. Asbestos, at one time deemed irreplaceable as fibre reinforcement, has not only been totally replaced, but superseded. The latest concepts eliminate contact altogether by suspending shafts in magnetic fields.

Such bearings are already in use in aerospace. Nexans SuperConductors, based in Hürth, Germany, has supplied the world's first contactless bearing based on high-temperature superconductors (HTS) to go on test for use in an industrial application. The customer for this prototype is Siemens Corporate Technology division, which is evaluating it for use in electrical machinery.

Siemens is carrying out intensive research on high-temperature superconductors and recently started operation of a 4 MVA generator designed for ships, containing a rotor with an HTS magnet. The HTS' high current densities result in more compact designs for engine and generator applications. With the help of a magnetic field, the HTS bearing holds a rotor equipped with permanent magnets in contactless suspension and can bear a nominal load of 500kg.

"HTS bearings are inherently safe, something which distinguishes them from other contactless bearings," explains Dr Joachim Bock, managing director of NSC. Permanent magnets alone cannot produce a stable state. Bearings based on electromagnets (active magnetic bearings) require a constant current supply to make the control adjustments to balance the load. The passive HTS bearing does not require this type of regulation, as the YBCO (yttrium barium copper oxide) crystals react individually when they approach the rotor's permanent magnets, here arranged in a ring form. The super conductor effectively becomes a permanent magnet under the influence of an external magnetic field.

The HTS cylinder consists of 270 individual YBCO bulk crystals produced by NSC, arranged on a copper body with a diameter of around 325 mm and height of 305 mm. A refrigerating machine cools the copper cylinder containing the superconductors to around -210°C. A 10-7 mbar vacuum in the bearing prevents the icing that would occur due to freezing of moisture in the atmosphere. The stator's copper mass retains the low temperature, enabling the bearing to bear its load for several more hours, even if the refrigerating machine breaks down.

SOE

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