8.1 Case Study on Conventional Abrasives Versus Superabrasives for Vitrified Bonded Tools
The user can decide between conventional tools with corundum or silicon carbide or superabrasive tools with diamond or cubic boron nitride. Not only do the tools have different performance profiles, but also different embodied energies, which is important for accounting manufacturing energy to products. Embodied energy is usually understood as the energy that must be used to create 1 kg of usable material measured in MJ/kg [ASHB09]. It is more than the theoretical energy and includes inefficiencies and losses in the processing systems and transport.
Comparing sustainability of conventional and superabrasive grinding tools is of high interest to the research community. However, there is no comprehensive information available on tool manufacturing. To foster understanding of energy use in grinding tool manufacturing, the following case study evaluates the energy for the manufacturing of two different types of vitrified bonded grinding wheel, with CBN and with corundum grits.
This study focuses on vitrified grinding wheels with corundum and cubic boron nitride as abrasive grit material. The raw material production is not analyzed itself, but the available data on embodied energy is reviewed and included in the analysis. The boundaries are from the cradle (i. e. raw material mining and processing) to the tool manufacturer’s outer gate (i. e. the finished grinding tool ready to be shipped to the customer) (Fig. 8.1). Tool manufacturing includes the steps of measuring, mixing, molding, pressing, drying, sintering, and finishing. Transport of material and tools is neglected, even though it might add substantially to the energy used for tool manufacturing. Furthermore, the subsequent use and disposal of the grinding
© Springer International Publishing Switzerland 2016 215
B. Linke, Life Cycle and Sustainability of Abrasive Tools,
RWTHedition, DOI 10.1007/978-3-319-28346-3_8
tools is not analyzed in detail, but the discussion highlights how the tools will be applied and disposed differently.
The functional unit of this study is a single grinding wheel. Figure 8.2 shows the respective grinding wheel designs. The conventional wheel is a monolithic cylinder; the superabrasive wheel consists of a steel body of low carbon tool steel and segments of the abrasive layer. The outer and inner diameters of both wheels are similar.
The results have to be evaluated carefully, because the grinding wheel specification includes various parameters such as abrasive grit type, mean grit size or mesh size, bond type, structure, and effective hardness. Abrasive tools are often adapted to a special application, e. g. high porosity for high material removal processes, CBN for precision grinding of hardened steel, soft bond for internal grinding, etc. Therefore, the comparison of different tools without regarding the application is difficult and not always reasonable. However, this study regards a use case where conventional or superabrasive wheels are interchangeable. For example, in a gear shaft grinding process, vitrified bonded corundum wheels or vitrified bonded CBN wheels can be used. The necessary change of process parameters such as wheel speed, machine periphery or coolant have to be considered.