9.3.1 Types of Grain Wear
Overlap between the above-mentioned wear mechanisms leads to changes in the abrasive grain. These wear types are depicted in Figure 9.2. They basically can be divided into [3]
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Process |
Tool |
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Single grain force |
Grain holding force |
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Load impulse |
Toughness of the bond |
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Load direction |
// Flattening |
Heat conductance |
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Contact zone |
‘ of the bond |
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temperatures • Temperature gradient |
Microcrystalline splintering |
‘ Absorbtion of cooling lubricant V Geometry |
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Relative speed • . |
Partial grain break-off |
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Complete grain break-off |
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Grain properties |
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Structural conditions of grains |
thermal diffusivity of the grinding wheel bond. Additionally, the basic porosity of the bond has a crucial influence on lubricant absorption and thus on the thermal conditions within the working zone. The abrasive grains of the abrasive medium differ in terms of hardness, tensile strength, and ductility. The fracture and splintering behavior can thereby be controlled by screening procedures during abrasive manufacture and the synthesis process [Juchem and Martin 1989, Jackson and Hayden 1993, Uhlmann and Stark 1997].
9.3.3 Grain Hardness and Temperature
Hardness of the abrasive grains also depends on the process conditions. Figure 9.3 shows the hardness of polycrystalline sintered corundum grains with changing process temperature. With increasing temperature, abrasive grain hardness declines. At 800°C, it is approximately 25% compared to room temperature. The wear resistance of the grains depends not only on the hardness at ambient temperature, but more importantly on the hardness at the operating contact temperatures.