| Key to Rappold's Wheel Specifications |
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| 5A |
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46 |
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J |
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7 |
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B |
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22 |
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/ 50 |
| Index/Type of Abrasive |
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Grit Size |
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Wheel Grade |
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Wheel Structure |
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Type of Bond |
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Special Symbols |
Peripheral Speed |
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| Resinoid |
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very |
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very |
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very |
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B |
resinoid |
|
works |
|
m/s |
| bonds |
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coarse |
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soft |
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dense |
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bond |
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internal |
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| A |
|
6 |
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E |
|
0 |
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cold pressed |
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symbol |
|
50 |
| 1A |
|
8 |
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F |
|
1 |
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63 |
| 3A |
|
10 |
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G |
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dense |
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BH |
resinoid |
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80 |
| 5A |
|
12 |
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soft |
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2 |
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bond |
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100 |
| 6A |
|
coarse |
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H |
|
3 |
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hot pressed |
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|
125 |
| 7A |
|
14 |
|
I |
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medium |
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| 8A |
|
16 |
|
J |
|
4 |
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BF |
resinoid |
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| 9A |
|
20 |
|
K |
|
5 |
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bond |
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| 77A |
|
24 |
|
medium |
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open |
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reinforced |
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| 29A |
|
medium |
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L |
|
6 |
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| 700A |
|
30 |
|
medium |
|
7 |
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V |
vitrified |
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| ZS |
|
36 |
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N |
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very open |
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bond |
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| ZF |
|
46 |
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O |
|
8 |
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| NZ |
|
54 |
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hard |
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9 |
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| C |
|
60 |
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P |
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porous |
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| 1C |
|
fine |
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Q |
|
10 |
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| 2C |
|
70 |
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R |
|
11 |
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| 3C |
|
80 |
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S |
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highly |
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| 5C |
|
90 |
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very hard |
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porous |
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100 |
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T |
|
12 |
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120 |
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U |
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13 |
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very fine |
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V |
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14 |
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150 |
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W |
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180 |
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eytremly |
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220 |
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hard |
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240 |
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X |
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dust fine |
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Y |
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280 |
|
Z |
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320 |
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360 |
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400 |
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500 |
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600 |
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| |
Hardness
The term "hardness of grinding wheels" does not refer to the abrasive grain, but designates the resistance odf the bond to grains being removed during the grinding process. |
Grain Size
The assignement of numbers to specific grain size distributions has been determined on the basis of an internationally applicable standard. Extremly fine grains (micro-grains: approx. grain 240) are otained by sedimentation. Finer grains are less brittle and harder to break out of a bond. For this reason, a wheel with fine grains appears harder than a wheel within the identical range of wheel hardness but with coarse grains. |
