Alfred Zenczak
Illustration 1: Different types of rolling bearings
In the production of rolling bearings (Illustration 1), grinding is one of the most important process steps which affects the raceways as well as all other functional surfaces and diameters. In this context, not only shortest machining times are paramount, but also the accuracies of the components according to the international APEC classification. The latter require a high degree of constant surface quality and exact compliance with the dimension-, form- and position tolerances. An improved tool life, which is achieved by a high dressing interval and low dressing amounts, is the prerequisite for an economical machining process. The present article is dedicated to the two most important processes, internal cylindrical grinding of the bore of rolling bearing inner rings with oscillation and the plunge-cutting process for machining the outer ring raceway with Meister Abrasives’ CERALOX grinding tools.
CERALOX @ Meister Abrasives
Meister CERALOX tools have been an indispensable part of the rolling bearing industry for decades. But what makes these tools so special and why are these proprietary Meister Abrasives tools so well suited for this high-performance process?
Illustration 2: CERALOX Structure
Over 30 years ago, with the first presentation of synthetic sintered grits, manufactured according to the Sol-Gel process, the use of this abrasive grit in coated abrasives (sandpaper) was certain to triumph. High stock removal rates coupled with long service life were the outstanding properties of this new abrasive grit. In combination with resin-bonded tools on a backing, the properties of the new miracle grit were incomparable. However, due to the high firing temperatures of corundum tools, the use in conventional ceramic bond systems posed a problem. All the advantages of the fracture/breakage behavior and the formation of new grinding- and fracture- edges of sintered corundum are vanished if the firing temperature is too high.
The development approach at Meister Abrasives was, therefore, focused on maintaining 100% of the grain properties of the sintered aluminum oxide abrasive and achieving maximum bond strength in the ceramic bond. Due to the many years of developing CBN and diamond tools in ceramic bond systems, Meister Abrasives had an outstanding reserve of available raw materials and formulations. Coupled with a specially developed and optimized firing program, the development engineers at Meister Abrasives succeeded in introducing a unique tool line to the market. The outstanding grain properties are retained by the elaborately developed CERALOX bond, while the adapted flow behavior and the wettability of the bond components also allow for complex wheel shapes in highly porous structures (Illustration 2).
Machining Technology
Illustration 3: CNC Internal cylindrical grinding machine for the rolling bearing industry
New highly modern CNC grinding machines with CF control (constant force control) or adaptive grinding force control, are today state of the art technologies (Illustration 3). The feed rates are programmed through an appropriately set maximum spindle load of usually 40-50%. Depending on the cutting ability of the grinding tools, this also allows for very high infeed rates of up to 120µm/sec (roughing range) and thus, for achieving a high metal removal rate Q’w of up to 12mm³/s/mm. These high values are, of course, dependent on the cooling lubricant used and the dressing tools employed. Many older machines are operated with emulsion which makes the metal removal rates significantly lower. The rigidity of the workpiece holder – component – grinding spindle system, as well as the available spindle power, is another important factor influencing the optimum utilization of Meister Abrasives CERALOX tools.
Illustration 4: Bearing wheel with a CERALOX high-performance grinding wheel
One of the fascinating properties of sintered corundum is its high toughness. This is far higher than that of fused alumina/corundum which is why the sintered corundum requires a higher grinding pressure in order to form new cutting edges. If the rigidity in the machine system is not adequate or if the drive power of the grinding spindle is not sufficient, the advantages of CERALOX tools cannot be fully exploited. An opinion often shared in practice is that sintered corundum causes high wear on the dressing tool, however, this must be disproved by the fact that under optimum conditions the dressing interval can be three or sometimes even more times higher compared to tools with fused corundum.
In the field of dressing technology, Meister Abrasives has achieved another breakthrough with the development of a new dressing tool in cDD technology. The availability of optimally matched grinding and dressing tools makes Meister Abrasives the ideal system supplier.
In practice, the processes are discussed with the customer and the application engineer.
Meister CERALOX tools have been the benchmark in the high-performance grinding processes from their very first appearance on the market and it is impossible to imagine the highly competitive rolling bearing industry without them (Illustration 4).
Case Studies for Meister CERALOX Tools
