NSK, Motion & Control
Bearing News
11/11/2011
Choosing the right bearings
Expert advice can cut costs dramatically
There are many factors to take into account when selecting bearings. Designers in the machine-tool and plant construction industry should consider their options carefully if they want to guarantee maximum availability and productivity for machine users. Three examples of NSK consultancy projects show that it is possible to significantly reduce costs and enhance both efficiency and productivity, even by optimising the choice of bearings retrospectively.
The people who use a machine or plant equipment are often the ones who recognise the need for optimisation due to the bearings’ service life falling short of the mark under operating conditions. Users are quite right to question a shortcoming of this kind because bearing manufacturers offer the right component for (almost) every application and all kinds of environments. Given the range on offer, it is advisable to choose bearings carefully and seek extensive advice from a bearing expert. This is true whether you are looking for initial equipment or seeking to optimise machinery and plant equipment retrospectively.
Production machine for concrete floors: new bearing concept
A manufacturer of prefabricated concrete floor sections took up NSK’s offer of advice. The company manufactures the slabs on steel formwork using a slip-form construction method on production lines with a length of approximately 100 metres. One of the slip-form machines , which are operated by a cable drive, repeatedly experienced bearing failures at the same point. One of the drive elements had two reciprocal tapered roller bearings which were not fixed centrally. These bearings failed up to 20 times a year, resulting in plant downtime on each occasion.
Efficient seal prevents failures
NSK analysed the operating conditions and environment and found that moisture and contamination easily penetrated the bearings, which was causing bearing failure and unplanned downtime. Based on these findings, a new bearing concept was produced with an efficient seal and a higher load rating.
The new bearing is mounted on a journal as a wheel bearing unit. It features a bearing that can be fixed axially using two snap rings. Bearing units of this kind have also proved invaluable in applications where safety is of prime importance, such as crane construction, as rope pulley bearings.
Annual savings of €68.600
The new bearings have now been in place for 12 months and they have not failed once. The bearings and planned maintenance cost a total of €625; the previous bearing and maintenance expenses amounted to around €7.600 plus €61.650 of downtime costs. This means that the manufacturer can now save €68.600 – every year – thanks to NSK’s engineering advice and replacement bearings.
Woodworking: prompt replacement of bearings safeguards availability
A manufacturer of glue-laminated timber contacted NSK’s application technology team with an urgent request. Several roller elements – known as solid rollers – on a machine used to process the laminated beams had ground to a halt because their tapered roller bearings were faulty. Spares were no longer available. It had become necessary to stop production, and restarting the machine as quickly as possible was the manufacturer’s number one priority.
Engineering support within 24 hours
Within 24 hours, an NSK engineer visited the site to assess the situation and recommended replacing the existing tapered roller bearings with a simpler design featuring an RHP Self-Lube® bearing insert. These mounted units consist of a sealed, single-row deep-groove ball bearing with a spherical outer ring and a wide inner ring. The component is mounted in a pillow block or flanged bearing housing and can be installed and removed very quickly. The spherical fit accommodates any initial misalignment. These bearings are supplied prelubricated sealed and also boast a relubrication facility. A protector cap can also be supplied, which offers additional protection for the Self-Lube insert.
Savings of €80.000 thanks to simplified maintenance and longer service life
Integrating the new bearings into the surrounding structure was straightforward, meaning that the machine could start operating again very quickly. Ever since, it has only been necessary to replace the solid rollers’ mounted units during planned servicing. The plant has not experienced any unplanned downtime since the switch. On top of all this, it now takes just one hour rather than three to replace the bearing on a roller. This enabled the user to slash bearing costs and make downtime a thing of the past. Overall, that equates to annual savings of €79.000.
Bakery machines: high-performance spherical roller bearings for high mechanical loads
A large-scale bakery also had a problem with a particular bearing’s service life. The spherical roller bearings in the kneader of a dough kneading machine were subject to high mechanical loads and had to be replaced every two or three months. This was associated with considerable production downtime on each occasion. The high loads that sometimes occurred were identified as the reason behind the wear and tear and subsequent downtime of the machine.
The company asked NSK to develop suggestions for improving the bearings’ service life. NSK’s food and beverage industry specialists analysed the operating conditions and environment and recommended the use of HPS™ spherical roller bearings, whose service life is twice as long as that of conventional spherical roller bearings. The HPS™ components also have a 20% higher speed limit. The whole design of the inner and outer ring – and that of the cages – was structurally optimised to enable the bearings to absorb very high loads.
Nine months ago, the user followed NSK’s recommendation. They have not needed to replace the bearings since. This means the bearings’ service life has already been trebled. In this case, the annual savings come to no less than €128.000 as a result of lower expenses for servicing and parts along with reduced production losses.
Conclusion: ask for expert advice!
All three case studies show that it is well worth asking for expert advice when choosing bearings – both when designing a machine and in order to extend the bearings’ life during machine operations. It is highly likely that there is a standard or special bearing that will deliver a longer service life in a specific set of conditions. The cost of replacing bearings is often low, and any expenditure is quickly recouped by the increase in availability of the machine or production line.