3.6.1 Technological Dimension
Bond composition and structure define the self-sharpening ability of the tool and process stability. The main bonding systems for grinding tools are resin, vitrified and metallic bonds (Table 3.2). Each type has a huge variety in its specifications, manufacturing, and ingredients. For polishing and lapping processes also different kinds of slurry or pasteous binders exist, described in Sects. 4.4 and 4.5.
The bond composition has to enable strong grit retention, optimum grit protrusion, and optimum self-sharpening abilities. The tool manufacturer has to find
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Table 3.2 Overview on bonds after [COLL88, p. 869 f.]
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Bonding type
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Chemistry
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Manufacturing
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Use
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Resin bonds
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Thermoset macro molecules (Duroplast) of crosslinked phenol, epoxy, or urethane resins
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Dry mixture process with liquid resin and powder resin, hot or cold pressing, hardening in oven at 140-200 °C; or wet processing with two component system of resin and hardener, hardening in mold at 20-80 °C
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Insensitive against impact, shock, and lateral pressure; high toughness; high cutting speeds and material removal rates possible for cut-off and roughing operations; high elasticity enables finishing operations with high surface quality
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Vitrified bonds
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Aluminum silicates of kaoline, quartz, fieldspars and glass frits as fluxing agents
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Casting or forming with temporarily binders and pressing, sintering process at 1000-1300 °C
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High porosity; good resistance against cooling lubricants; cool cutting; wet and dry grinding
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Sintermetallic
bonds
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Metals of steel, bronze, carbide powder
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Sintering after pre-compressing in oven with reduced atmosphere, then pressing at high temperatures
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High toughness; often used for diamond and CBN to machine hard and brittle material
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Rubber bonds
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Natural and synthetic caoutchouc
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Mixture of vulcanization agent and grits between rolls, punching out of tools, hot pressing and vulcanization
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Thin cut-off wheels of up to 0.05 mm thickness; precision grinding tools; control wheels for centerless grinding
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Table 3.3 Mechanical properties for most utilized bonds after [MARI04, METZ86, p. 51]
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Bonding type
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Brinell Hardness (HB)
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Rupture strength (N/mm2)
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Elasticity modulus (N/mm2)
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Resin bonds
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228
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7.21
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1196.24
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Vitrified bond
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380
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8.57
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4133.41
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Sintermetallic
bond
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278
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14.29
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5460.65
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the appropriate compromise between hardness and erosion resistance [STOC86]. In the past, resin bonded wheels were preferred over vitrified bonded tools for working at higher speeds. This was due to the higher tensile strength of resin bonded wheels, but this limitation has been overcome [WHIT72]. Example mechanical properties of resin, vitrified and metallic bonds are shown in Table 3.3.
