July 19, 2006

Metal Finishing

There is an excellent article in the archives at the website for the e-magazine "The Fabricator". It's called "Choosing the right coated abrasive for plate finishing applications". I'll tease you with a little bit here, but make sure you check out the full article at www.thefabricator.com

Ceramic aluminum, a sharp microcrystalline grain, cuts aggressively under light to moderate pressures. Its quick cutting capability makes it suitable for grinding stainless steel, titanium, and high-nickel alloys. It works well on applications in which high rates of stock removal are required under light pressures, such as when plates require rounding or dimensioning. Ceramic aluminum’s microcrystalline structure gives it a very long life. It is temperature-sensitive, meaning that removing heat from the cut extends the life of the grain. Quite often ceramic products require grinding aids to reduce heat.

Zirconia alumina, although less expensive than ceramic aluminum, also is a single crystal that is very tough and sharp. In fact, this grain is so tough that it withstands heat very well. However, a common problem with zirconia grain is glazing, which occurs when the grains dull from insufficient grinding forces. Rubbing the dulled grains causes the metal to adhere to the tips of the grain. Reducing glazing requires heavier grinding forces to fracture the grain and enable resharpening. Therefore, zirconia lends itself to the higher temperatures and heavier pressures that are present in high-stock-removal applications.

Zirconia’s advantage over ceramic primarily is its performance in high-heat and heavy-pressure applications, such as those characterized by mechanically applied pressures that generate a large spark array. The heavy grinding pressures effectively resharpen the grain, promoting long wear life without adverse effects from the high temperatures. Plate examples are power-pack grinding of castings and automated grinding of fixtured tools.

Aluminum oxide is a single-crystal grain used in most polishing applications because of its durability and longer service life than silicon carbide’s. This grain is less tenacious than ziconia and therefore requires less pressure to prevent glazing. Soft metals, such as aluminum and some carbon and stainless steels, usually are good candidates for aluminum oxide grain products. For the most part, these metals are not as sensitive to the heat that is sometimes generated by the aluminum oxide grain because of its crystalline structure.

Silicon carbide, also a single-crystal grain, is the sharpest and hardest of all grains, but it is also the most brittle of all, resulting sometimes in a short service life. This grain’s advantage is its ability to work well on very hard, tenacious metals such as titanium, cobalt, and INCONEL® alloys. Silicon carbide’s sharp shape and extremely hard properties make it the most suitable grain to work on these metals. Conversely, the “blocky” nature of aluminum oxide grain renders it incapable of penetrating these surfaces efficiently, causing higher heat generation and resulting in a shorter service life.

In addition, because of silicon carbide’s sharp, slender shape, it produces a brighter finish profile on stainless steel and some carbon steels.

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