processes Roadmap for
processes Roadmap for the decarbonization of grinding processes Development and grinding technical investigation of a vitrified bond formulation for low-temperature firing written by Dr. Alexander Nashed (Senior Research Engineer), Jörg Rucker and Lutz Gaida Saint-Gobain Abrasives GmbH Industrial companies throughout Europe are currently busy identifying potential for massive CO 2 savings and getting closer to their defined scope 1 and scope 2 targets through optimized processes. The Saint-Gobain Group – and with it the abrasives specialist Saint-Gobain Abrasives – is no exception. The target: by 2030 the aim is to achieve a 33 % reduction in emissions for scope 1 and 2 (direct and indirect) and a 16 % reduction in scope 3, i.e., across the entire value chain (absolute reduction compared to 2017). The target for 2050 is “net zero carbon”! This way all process steps are being examined for any potential for optimization and conversion. Saint-Gobain Abrasives has now taken a decisive step by almost completely switching from high-temperature to low-temperature bonds in vitrified bonded abrasive tools. If the ambitious targets set by the European Union and others are to be achieved, three pillars must be considered in parallel and driven forward accordingly: ➢ decarbonization of customer processes ➢ development and distribution of maximally sustainable product solutions ➢ massive reduction in CO 2 emissions during their production At Saint-Gobain Abrasives the question arose early, as part of the research and development work in the Grinding Technology Centre Europe (EGTC) in Norderstedt near Hamburg, on how to noticeably increase the energy efficiency, particularly in the production of vitrified bonded grinding tools. Looking at the usual firing temperature range for vitrified bonds, which is between around 900 ° C and 1260 ° C, it quickly becomes clear that the greatest potential, the greatest impact on scope 1, lies in reducing the firing temperature and therefore the (gas) energy supply. Accordingly it makes sense to replace all high-temperature bonds (HT) in the product portfolio of conventional grinding tools, which are generally manufactured in the upper temperature range, with low-temperature bonds (LT) – while retaining both the mechanical properties and the required grinding behaviour. Saint-Gobain Abrasives launched the first vitrified LT bond back in 1985 and has been developing new solutions exclusively based on LT since 1990, building up a wealth of experience in this area over the years. The obvious next step was to replace all HT bonds in Europe as completely as possible by the end of 2023. To realize this project a general approach was pursued that takes all relevant physical properties into account in the development of the vitrified LT bond formulation and generates reliable and representative results in the subsequent grinding investigation. Aspects of the development of LT bonds When manufacturing vitrified bonded abrasive tools it is essential to match the bond chemistry to the respective application: network formers, network modifiers and intermediate oxides, for example, have a direct influence on the physical properties of the bond, such as its strength, melting and crystallization behaviour. Therefore they also influence the mechanical properties and performance of the finished grinding wheel. The mechanical properties considered include modulus of elasticity, flexural strength, hardness and density – these should be in the same range as the reference wheel containing the HT bond. Approach to the grinding inspection The main task of the EGTC was to develop a grinding method in which different grinding parameters are used to determine characteristic values that enable a comparative analysis of the grinding tools. By selecting different workpiece and grinding wheel specifications, a wide range of applications was mapped, which can be processed in a timeefficient manner using the aforementioned methos. During the tests at the EGTC the following data was measured and analyzed in detail: ➢ power consumption of the grinding spindle ➢ grinding wheel wear ➢ material removal ➢ surface quality R a and R z To ensure the (geometric and dynamic) comparability of the results, the following values were kept constant: ➢ equivalent diameter d eq => constant contact length l g at related infeed a e ➢ workpiece speed v w ➢ cutting width a p ➢ cutting speed v c 30 no. 4, November 2024
processes Experimental setup and execution For the tests at the EGTC external cylindrical plunge grinding was selected, whereby the plunge cuts were carried out with defined grinding parameters on four workpiece blanks of the same quality. Seven different wheel specifications from hard to soft were tested on three different workpiece qualities. Grinding was performed in counter direction and two different material removal rates were run per specification in order to load the grinding wheels to different levels of stress. ensure that the spindle power consumption increases sharply in the normal case during the initial cut and to avoid premature loss of performance of the grinding wheel. On the other hand the wheel should not be dressed too roughly to ensure that the quasi-stationary working window is reached quickly (in plunges two to four). Based on extensive preliminary tests and empirical data from research, the following parameters were therefore established for a suitable "dressing method": About the grinding method As already mentioned, a moderate specific material removal rate of 3.2 mm 3 /mms and a high specific material removal rate of 7.5 mm 3 /mms were selected. When selecting the specific material removal rates care was taken to ensure that grinding was neither carried out at a too low radial feed rate (high specific grinding energy) nor at a too high radial feed rate. Because too drastic radial feed rate leads to increased grain pull-out and excessive wear of the grinding wheel. A cutting speed of 45 m/s was identified as a standard cutting speed for customer processes. It should also be mentioned that a total infeed of 3.0 mm was sufficient to cause significant wheel wear. The following diagrams show examples of spindle power measurements at moderate (left) and high material removal rates (right). The grinding wheels have a width of 10 mm, the blanks of 5 mm. The plunge is done in the center of the grinding wheel width so that wear creates a measurable profile on the grinding wheel. The plunge into the first blank is done with 1/10 of the total infeed, plunges two, three and four are each done with 3/10 of the total infeed. After each plunge the wheel profile generated by wear is projected onto a graphite coupon, which is then measured optically in order to record the radial grinding wheel wear. Using this method the initially high grain protrusion caused by dressing can be reduced to such an extent that a load is applied to the bond at the plunges in blanks two, three and four, which has a dominant effect compared to the grain wear. This ensures that the grinding wheel ideally reaches its quasi-stationary working window at blanks two to four and therefore grinds outside the uncontrolled statistical range. In addition the measured values can be correlated with each other after each plunge, which also makes it easier to analyze the development of the measured values within the overall infeed. Workpiece selection For the grinding tests, two LT specifications per workpiece were always compared with an HT reference wheel. In order to compare the behaviour of the wheel specifications, three different workpiece qualities with different grindability were defined: About the dressing method The speed quotient q d , the infeed a ed and the overlap ratio U d are the main factors influencing the topography of the grinding wheel generated during rotary dressing. These parameters were selected so that the grinding wheel is rough enough (with correspondingly low grinding forces at the start) to no. 4, November 2024 31
