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A car manufacturer was looking for a solution to prolong the service life of spindle bearings in their machining centres. Following a thorough analysis of the situation, the problem was solved by using sealed high-precision bearings: The service life of the bearings has now more than tripled.
The bearings of spindles in modern machining centres are subject to high stresses, yet at the same time they are required to provide maximum running precision. This is necessary to produce high quality workpieces even with high axial and radial loads and production based dimensional variances.
High demands on precision and service life
This is why the bearings have to absorb high radial and axial forces and still guarantee a high rigidity. What’s more, machine reliability is a key requirement in the automotive industry and the bearing plays an important role in achieving this. This is particularly true of machining centres, which are often integrated in fully automated lines, common in the automotive industry. An unscheduled machine failure here leads to costly and time-consuming rescheduling that has several consequences for the productivity of the entire line.
Initial situation: unscheduled failures of spindle bearings
A car manufacturer was experiencing early failures of spindle bearings in his machining centres. The average service life was only 12 months and this caused major problems for the plant management. The manufacturer contacted the bearing experts at NSK who have developed the ‘Added Value-Programme’ for instances such as this. The objective of this programme is to increase the profitability and reliability of customer machines and systems by reducing bearing-induced failures and subsequence lost production to a minimum.
Contamination - a cause of bearing failure
The AIP programme follows a set procedure that begins with a thorough analysis of the actual situation. In this case, the ambient conditions as well as the bearings themselves were investigated. It was discovered that the premature failures of the high-precision angular-contact ball bearings were caused by external contamination.
Recommendation: sealed precision bearings
NSK’s recommendation for the car manufacturer was to use sealed bearings. NSK offers bearings with non-contact seals for this application. On the one hand, this type of seal guarantees a longer service life for the bearings by reducing the wear on the raceways and surface of the balls and ensuring a uniform lubrication. On the other hand, it does not inhibit the rotational speed of the bearings or introduce any friction. This is an important aspect, particularly for very fast-running spindle bearings.
The recommendation was implemented as a trial on one machining centre. The AIP programme also produced further information that showed the contamination had been introduced into the bearing during assembly. NSK therefore trained the customer engineers in the correct handling and installation of precision bearings. Furthermore the first sealed bearings were installed under the technical supervision of NSK with the customer.
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| Product Model | Inside Diameter | Outside Diameter | Thickness |
| 2212SK NTN | 60 | 110 | 28 |
| 1212SK NTN | 60 | 110 | 22 |