Grinding and polishing tools - joke Technology GmbH - #7

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94 2 N1 N2 N3 N4 N5 N6 N7 N8 D181 D126 D91 D54 D46 D30 D15 K120 K600 K220 K320 K400 K180 P40 P80 P120 P180 P220 P320 P400 P600 P800 P120 P1200 P1000 P800 P400 P600 P220 P320 P180 100ì 80ì 60ì 40ì 30ì 15ì 9ì K120 K600 K220 K320 K400 K180 45ì 25ì 14ì 8ì 6ì 0,025 0,1 0,05 0,2 0,4 0,8 1,6 3,2 Tel. +49 (0) 22 04 / 8 39-0 • Fax +49 (0) 22 04 / 8 39-61 • info@joke.de 2. Grinding and polishing tools Surface roughness Overview of the surface roughness of the preliminary processing methods and the different grinding medium grit sizes in linear processing When selecting the correct grit size, a surface improvement by 1.5 roughness classes (coarse surfaces) to 0.5 roughness classes (fine surfaces) should be taken into account. The tips of the wedges of preliminary processing are max. attainable values under good working conditions. The stock removal dimensions are usually higher than the absolute surface roughness (errors in the macro form and removal of the erosion skin). It may therefore be advisable to begin with a coarser grit size. Degree of roughness Grinding Surface roughness Ra Turning Milling VDI 18 VDI 21 VDI 24 Diamond tools with galvanic bonding Abrasive files with ceramic bonding Abrasive files with synthetic resin bonding Ceramic fibre abrasive files Abrasive cloths Abrasive paper Grinding film Diamond compound with lapping wood Light brown orange dark brown blue white red Surface roughness in mould building Ra In by far the most cases, the surface roughness is indicated as an Ra value. The height root mean square surface finish Ra is the height of the fictitious surface over the midline, the magnitude of which corresponds to the sum of the individual surfaces above and below. The visual appearance may markedly deviate from the indication of the Ra value: e.g. smaller Ra value with visible isolated scratches. Rt The Rt value is considerably more meaningful for assessment of very fine surface finishes in mould making: the maximum peak-to-valley height Rt is the vertical distance between the highest and lowest point within the measuring section. For surface roughness indications in this catalogue, the maximum peak-to-valley height Rt is generally used. Roughness classes The roughness classes according to DIN/ISO 1302 are indicated as Ra values. The Rt values listed in the table are estimated values that are not contained in the standard. The ratio Ra:Rt corresponds to approx. 1:8 to 1:12 during manual working. As a result of the evenness of manual working and also less pressure and good lubrication, the ration Ra:Rt can be reduced to 1:6. All the values indicated in this catalogue are empirically determined on steel 1.2767 with 53 HRC and represent nonbinding guideline values. Ra Lm = measuring section Lm = measuring section Rt Roughness classes according to DIN/ISO 1302 Degree of Roughness Roughness roughness No. value Ra (ìm) value Rmax (ìm) N 12 50 ~ 500 N 11 25 ~ 250 N 10 12.5 ~ 125 N 9 6.3 ~ 60 N 8 3.2 20 ... 40 N 7 1.6 10 ... 20 N 6 0.8 6 ... 10 N 5 0.4 2 ... 6 N 4 0.2 1.5 ... 2.5 N 3 0.1 0.75 ... 1.25 N 2 0.05 0.3 ... 0.7 N 1 0.025 0.1 ... 0.3