processes The following
processes The following example shows that the comparatively easier-to-grind bearing steel can be ground by the tested grinding wheels of the specification with the hardness and structure “I8” without any issues up to the last blank, so without a drop in spindle power or an increase in wheel wear. In the case of carbon steel all wheels reach their performance limit at the fourth blank, while this limit is already reached at the second blank in the case of high chromium steel with difficult grindability, resulting in high wheel wear and a significant drop in spindle power. *The tests on the 100Cr6 were carried out with ten (instead of four) plunges, whereby the first plunge, analogous to the tests on the C60 and X100, was carried out with 1/10 of the total infeed on blank #1; blanks #2, #3 and #4 each received 3/10 of the total infeed, also analogous to the tests on the C60 and X100 Selection of the grinding wheel specifications The seven investigated specifications were selected according to different structures (open, medium, closed) and grades (soft, medium, hard) in order to represent different grain retention forces. This ensured that a representative spectrum of specifications was analyzed and mapped. In the example shown, all wheels from soft (I8) to hard (Q5) show almost optimum stock removal at both material removal rates on the 100Cr6 workpiece: ➢ the harder the grinding wheel, the higher the power/energy/force ➢ good cutting behaviour for all specifications ➢ soft specification (I8) shows optimum removal It can also be seen that the selected specifications, which differ in their grain retention forces, also operate at different specific grinding energies, as shown in the following diagram: The grinding energy increases with increasing grain retention forces or – in other words – with increasing hardness and density of the grinding wheel, which means that the harder wheels (red and green) have a higher energy consumption in order to remove an equivalent volume. It is important to note that the harder wheels tend to reach their performance limit earlier on the more difficult-to-grind workpieces (C60 and X100) than softer wheels, as the latter have a higher cutting ability. Differentiation of equivalent grinding wheels When it comes to the question of which HT bond is optimally substituted by which LT bond in which application, a wholistic view is required, considering all measured data and observations. All three workpiece qualities must be taken into consideration, as the following example illustrates. The soft specification with the hardness and structure “I8” was tested on the three different workpiece materials presented. The red bars in the diagrams represent the reference HT grinding wheel with the bond designation VC.1, the blue and green bars represent the two LT grinding wheels of the same specification with the bond designations VC.2 and VC.3. The Grinding Technology Centre Europe (EGTC) of Saint-Gobain Abrasives Since 2001 the Grinding Technology Centre Europe (EGTC) in Norderstedt near Hamburg has played a key role in the development of innovative grinding solutions to support the customers of Saint-Gobain Abrasives GmbH. In addition to the development of new process technologies for diamond, cBN and bonded grinding tools, a further focus is on application technology research and the dialogue with experts and end users, with the clear aim of offering customers modern, sustainable grinding solutions that are tailored to their processes. As one of Saint-Gobain Abrasives‘ four Grinding Technology Centres worldwide, the EGTC in Norderstedt plays a fundamental role in the design and investigation of innovative grinding solutions and technologies for all product families. Together with end users, machine manufacturers and various scientific institutions, new grinding solutions are developed and optimized there. Trendsetting customer-specific application projects are also regularly launched in Norderstedt. In addition the EGTC offers a wide range of seminars and training programs to facilitate a practice-oriented transfer of knowledge for industrial grinding processes – supported by measuring technology, the latest generation of grinding machines and state-of-the-art training technologies. 32 no. 4, November 2024
processes *The tests on the 100Cr6 were carried out with ten (instead of four) plunges, whereby the first plunge, analogous to the tests on the C60 and X100, was carried out with 1/10 of the total infeed on blank #1; blanks #2, #3 and #4 each received 3/10 of the total infeed, also analogous to the tests on the C60 and X100. With the 100Cr6 bearing steel, both the HT reference wheel and the two LT wheels show a stable spindle power curve and only low wheel wear as well as similar material removal – a differentiation is therefore not yet possible at this point. Accordingly it is necessary to analyze the grinding tests with analogous engagement conditions on the C60 and X100 workpieces, which are more difficult to grind. This shows that with carbon steel C60 there is a drop in spindle power from blank 3 onwards and thus correlates with higher wheel wear. In the case of the high chromium steel X100 a similar spindle power curve can be seen, but this results in a more intense decrease. This is accompanied by even higher wheel wear. Furthermore it can be seen that the VC.2 grinding wheel with the highest material removal in the grinding process produces intense chatter marks on the X100 workpiece, which also correlates with the consistently higher spindle power of this wheel. Therefore, in this specific case, the wheel with the second-highest material removal (VC.3) should be selected as a substitute, as this corresponds to the grinding behaviour of the HT bond. No chatter marks occur here and at the same time the wheel wear is significantly lower, compared to the HT grinding wheel. A further argument is the fact that the HT reference wheel operates at almost the same level of spindle power as the VC.3 and therefore a very similar energy consumption can be expected. Based on the results obtained in this way, Saint-Gobain Abrasives could replace almost all vitrified HT bonds with LT bonds by the end of 2023 without any loss of performance. An exception are (still) a few specialty products, which only account for 3 % of the total range. Summary The tests were carried out over a period of five months and were designed to ensure the comparability of the bond systems and maximize time efficiency: ➢ same engagement conditions for all trials ➢ test setup with high reproducibility ➢ dressing and grinding parameters for rapid attainment of the quasi-stationary grinding window ➢ internal grinding investigation with around 230 trials ➢ supplemented by external trials at customer sites, accompanied by application engineers (the results obtained there were in line with the internal trials) The results are therefore characterized by a high level of conclusiveness and were also validated comprehensively with the support of other Saint-Gobain Grinding Technology Centres regarding different grinding applications. Hence, a complete representation of different grinding conditions could be reached as much as possible. The most important fact at the end: By almost completely replacing HT bonds with LT bonds, the Saint-Gobain Abrasives GmbH was able to reduce CO 2 emissions from production in Europe by around 1,700 tons per year, and gas consumption was reduced by around 800,000 m 3 per year. Another important step towards achieving the ambitious scope 1 and scope 2 targets! further information: www.nortonabrasives.com no. 4, November 2024 33
