Sealed Roller Bearings
Bearings are precision components, capable of giving millions of smooth revolutions, while absorbing all the wear and tear that the machine will be subjected to without it. A smooth running bearing ensures energy efficient operation. However, a small defect, either in the shaft or in the housing, can lead to misalignment. A misaligned bearing will not run smoothly and will also damage the bearing overtime reducing the machine´s performance. At times, the machine is subject to loads that may cause the misalignment or the equipment just may not be worth enough to be machined with high precision. In such cases self-aligning bearings come to rescue. SKF invented the first self-aligning ball bearing back in 1907. In-fact, all self-aligning bearings have been invented and introduced by SKF. These bearings allow for small deviations in the rotating axis, without affecting the performance of bearing or the machine.
The company introduced spherical roller bearings in 1919, and since then they have been continuously improved. Roller bearings have higher load carrying capacity. They are used in heavy equipments. Rotating cement kilns for example use roller bearings. Roller bearings find applications in grinders, screeners, crushers and such machines where bearings have to perform under tough conditions.
One of the recent developments in self-aligning roller bearings was a new heat treatment process that improves service life. The upgraded Explorer has better service life (almost double) in both contaminated, as well as poorly lubricated conditions. The upgrade increases service life of the bearing boosting the C-value by 15 per cent.
With its designs and material properties perfected, SKF took another leap in the bearing technology. It introduced the worlds first sealed roller bearing. Sealed roller bearings ensure that the contaminants stay out of the bearing lubricant, thus extending the bearing life almost four fold. It also eliminates the need for maintenance shutdowns for replacing bearing lubrication. As a result, there is no used grease to be treated, saving oil and grease treatment cost to the company, while being environment friendly.
For example, pinion gear drives at a mining plant required frequent relubrication. The company had its 100 bearings relubricated with 10 tonnes of grease per year, and the drives still failed prematurely. The dust and contamination was too high to handle for the bearings. Finally, the company switched to sealed bearings, which lasted twice as long, and the grease consumption was reduced by more than 95 per cent.
Self-aligning sealed bearings have definite application in material handling equipment that have to perform under dust laden environment. The company offers about 104 types of sealed bearings as of today.
Seal the performance
Henrik Wickberg, Project Manager, Spherical Roller Bearings (SRB), SKF Henrik Wickberg, in an interaction with ICR elaborates on the factors that influence bearing performance and how the seal extends bearing life even in harsh conditions.
How does the housing impact bearing performance?
Bearing performance depends on both internal and external factors. Internal factors are the roundness of bearing, the surface roughness of bearing components and the interaction between internal geometries. External factors include the roundness of the shaft and the housing in which the bearing is fixed. These factors will influence bearing performance.
Even if the bearing is round and perfect, if you put it in a housing that is not, the bearing will deflect and will lead to uneven load distribution. That will lower bearing performance. So I recommend using high quality housing to get the best from your bearing.
How do you compare a sealed bearing with an open bearing in the same genre for similar application?
SKF has always been looking for ways to further improve bearing performance. One way is to look at new designs and exploring new materials. The other way is to protect the bearing, which also improves the performance. One such way is the use of seal for bearing protection.
While a quarter of our bearings operate in good conditions, such as proper lubricant, free of contaminants, etc., the remaining bearings are used in harsh to very harsh environments. Use of seal protects the bearing from contaminants and allows the bearing to perform, as it should even in such conditions.
As the bearing is lubricated at the factory itself, the quality is assured, and in most cases it is lubricated for life. Sealed bearings have rating life 2-4 times more than open bearings.
What is C value, and the a SKF factor?
C value helps in projecting the bearing life. It is determined as per the ISO standards and is a function of the number of rollers or balls in a bearing, function of effective length of roller that will bear the load, diameter of the roller, angle of race way, etc. The calculation looks at the life of bearing for one million revolutions.
C value is very important for engineers as it helps in judging the performance of a bearing. However, different manufacturers present the C value in different ways. For example, while working out the C value you have to factor the lubrication in the calculation, which is given as the Kappa value. Now some manufacturers use Kappa value as 4. It is the highest value representing absolutely clean lubricant and no friction at all. That will give you a very high C value. Now that is not exactly against the rule book, but it might confuse the buyer. Not many people have the catalogue or read the catalogue that carefully. One must understand that if you factor poor lubrication or contaminants, the bearing performance drops drastically. So calculating high C value based on high kappa value is incorrect.
We use Kappa value of ´1´ to match the conditions in reality as much as possible, while some use Kappa 2. We also give performance as per the aSKF factor, which is more accurate in stating the bearing performance. The aSKF factor is peer reviewed by experts to be a better way of indicating bearing life and performance.
How do you detect bearing issues? And can bearings be refurbished?
There are a few indicators of bearing failure. Temperature is the most commonly observed parameter. High temperature indicates friction in the bearing. Another factor is vibration, which could be due to defective shaft, housing, or misalignment between these components. It could also be due to uneven load distribution. Worn out bearings at the end of life do vibrate, otherwise it could be due to a defective bearing itself.
Worn out bearings could be refurbished, depending on the extent of damage. At times the surface could be refurbished or the rollers could be replaced. It is more profitable to refurbish large bearings rather than small ones, depending on the application. We have a solutions factory where we refurbish bearings and re-certify that bearing for its extended life.
Positioning it right
Dinesh Mirjurkar, General Manager, Marketing and Business Excellence, Regional Sales and Services, SKF India
SKF has a strong market reputation. Clients by default have high expectations not just from the products but also from after-sales service. The company ensures that the customers are satisfied at every stage and that the products are positioned suitably. Dinesh Mirjurkar talks more about this with ICR.
Where do these large size bearings find applications?
These bearings have applications in the mining and mineral processing industries, in paper pulp processing, steel and cement manufacturing plants, coal crushing machines, etc.
Who are your leading customers in cement industry?
We are supplying bearings to FLSmidth, Loesche, etc. The bearings have multiple application areas and are consumed through a network of distributors.
They are used in cement manufacturing equipment such as vertical grinding mill, cement mill, crushers, screeners, etc.
How do sealed and open bearings compare cost wise?
Sealed SRB is only slightly costlier than the open bearing. So the cost advantage is very high when compared to open bearings. Besides, you are avoiding system shut down to replace the bearing or to do any bearing maintenance job. The bearing does not require re-lubrication and so there is no cost associated with the disposal of used grease from the bearings. That too is a saving. We have positioned it where, though it is a bit costlier than open bearing, it encourages our customers to try the new variant.
How are you tackling counterfeiting issues?
We are dealing with it at various levels. We are educating our customers about what to look for when they source bearings. We have improved the packaging, making it difficult to copy for fake part manufacturers and makes it easier for buyers to spot the difference.We are also fighting it at legal levels, taking legal measures to ensure that counterfeiting is discouraged.
Delivering with perfection
Ajay Naik, Factory Manager, SKF Ahmedabad
SKF has technologically advanced manufacturing facilities across the globe that conform to uniform standards all over. Ajay Naik talks with pride about the SKF India plant. Excerpts.
Tell us a bit about your plant.
The SKF factory at Ahmedabad was inaugurated in 2009. Currently, the factory is spread over around 26,700 sq.m, and has an additional 20,400 sq.m of land for further expansion. The facility is ISO 14001 certified and has won the coveted LEED (Leadership in Energy and Environmental Design) Gold certification conferred by IGBC (India Green Building Council). The Ahmedabad factory is the first bearing factory in India to be certified by LEED rating and the third SKF facility, amongst all 140 plus plants across the globe to get the LEED Gold certification.
Medium to large scale bearings are manufactured at this plant.The facility for heat treatment is unlike you will see at other plants. It is a completely automated facility with state-of-the-art technology. Operators can man the furnace from their cabins and monitor each activity closely. The plant has facilities for black oxidation and phospating.
How many units are manufactured by SKF every month?
It depends on the size and the kind of bearing that we are manufacturing at a given point. As a ballpark figure, we are manufacturing around 4000-5000 units a month.
How do you maintain uniform standards across all plants in several countries?
Everything right from approval of steel to the testing of the final product is centrally driven. All plants of SKF across the globe are allowed to purchase steel only from the centrally approved steel supplier. The vendor qualification is a rigorous process and takes around 9 to 18 months. This is to ensure that the raw material quality, the metallurgical characteristics are uniform and as per the set standards across all SKF plants.The final product too is tested and approved at the central facility. Hence, there are absolutely no variations in product.