Aluminum oxide
Aluminum oxide
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Written by tom   
Tuesday, 26 February 2008
Aluminum oxide wheels are used for grinding materials of high tensile strength. Silicon carbide is harder but is not as strong as aluminum oxide It is used for grinding metals that have dense grain structure and for stone. Vitrified wheels are made by molding under heat and pressure. They are used for general and precision grinding where the wheel does not exceed a speed of 6,500 surface ft/min (33 m/s).
The rigidity gives high precision,and the porosity and strength of bond permit high stock removal. Silicate wheels have a silicate binder and are baked. The silicate bond releases the grains more easily than the vitrified, and is used for grinding edge tools to reduce burning of the tool. Synthetic resins are used for bonding where greater strength is required than is obtained with the silicate, but less openness than with the vitrified. Resinoid bonds are used up to 16,000 surface ft/min (81 m/s), and are used especially for thread grinding and cutoff wheels. Shellac binder is used for light work and for high finishing. Rubber is used for precision grinding and for centerless-feed machines.Grading of abrasive wheels is by grit size number from No. 10 to No.600, which is 600 mesh; by grade of wheel, or strength of the bond, which is by letter designation, increasing in hardness from A to Z; and by grain spacing or structure number. The ideal condition is with a bond strong enough to hold the grains to accomplish the desired result, and then release them before they become too dull. Essential qualities in the abrasive grain are: penetration hardness, body strength sufficient to resist fracture until the points dull and then break to present a new edge, and an attrition resistance suitable to the work. Som: wheels are made with a porous honeycombed structure to give free cutting and cooler operation on some types of metal grinding. Some diamond wheels are made with aluminum powder mixed with a thermosetting resin, and the diamond abrasive mix is hot-pressed around this core wheel. Norton diamond wheels are of three types: metal bonded by powder metallurgy, resinoid bonded, and vitrified bonded.
Last Updated ( Saturday, 01 March 2008 )