Grinding Journal - Summer 2007 - (Page 23)

Summer 2007 Silicon carbide is extremely hard and sharp, like ceramic, but is also very friable. This property allows silicon carbide to perform well on both extremely hard materials (due to its sharpness) and extremely soft materials (due to its friability, or “re-sharpening” property). You will see silicon carbide in applications ranging from carbide re-sharpening to rubber roll grinding. It is quite a versatile grain in environments where the material is either too hard for aluminum oxide to penetrate or too soft to create an environment for aluminum oxide grains to breakdown. Grit size has a direct effect on the rate at which the material is removed as well as the scratch depth that remains afterwards. The first things to consider when selecting a grit size are the required surface finish and any radiuses that need to be ground in the part. The chart below is a good reference, but it’s just a starting point. These factors can vary depending on dressing and grinding parameters. Finish Required Grit Size of Wheel Ra (in) Ra (mm) 60 80 100 120 180 240 24 0.6 20 0.5 16 0.4 12 0.35 10 0.25 8 0.2 6 0.16 4 0.1 3 0.08 0.02 0.016 0.012 0.008 0.005 0.004 Corner Inch Radius 0.5 0.4 0.3 0.2 0.13 0.1 MM Grain Penetration It’s also important to understand grain penetration when considering grit size. In a given operation, the smaller the grit size the higher the unit pressure per grain, as illustrated below: 50 Lbs Down Force on 1 square inch 50 Lbs Down Force on .5 square inch Grit Size: Abrasive Grain Grit Size Grade Structure Bond Type Bond Modification 5SG 60 – L 8 V HP Grit size is the second position in the grinding wheel marking system, and will typically range between 46 and 220 on vitrified bonded abrasive wheels. (There are uses for grits down to 4 and up to over 600 in various bonded abrasive applications.) The lower the grit size number, the larger the grain size. The chart below depicts this relationship: FEPA Grit Size 8 10 12 14 16 20 24 30 36 46 54 60 70 80 90 100 120 150 180 220 Average Particle Size Inches Microns 0.0929 2360 0.0787 2000 0.0666 1700 0.0551 1400 0.0464 1180 0.0334 850 0.0279 710 0.0236 600 0.0196 500 0.0139 355 0.0118 300 0.0098 250 0.0083 212 0.007 180 0.0059 150 0.0049 125 0.0041 106 0.0029 75 0.0024 63 0.00208 53 50 PSI 100 PSI Grinding Journal 2

Table of Contents Feed for the Digital Edition of Grinding Journal - Summer 2007

Contents My Thoughts Exactly When Lives Are at Stake Walter Consolidating Production The Art of Grinding: Knowing the Source of Grinding Errors and How to Fix Them The How and Why of Conventional Vitrified Grinding Wheel Selection Grinding Glass Flat Problem Solver

Grinding Journal - Summer 2007

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