Time to Update Technology

Q. We have an 8 cu ft tub-style vibratory finisher. We use #00 aluminum oxide media to debur and radius large (about 10 × 14 inches) pieces that are laser cut from 1/2-inch steel plate. The process takes three or more hours.

Recently, a vendor suggested an abrasive compound to reduce cycle time. We tried that but cycle time is not much shorter, and the added compound cost is not justified. In addition, the abrasive compound quickly overwhelms our wastewater filter.
Have you any other advice? C.W.

 

A. Yes. Get rid of the random-shaped fused aluminum oxide media, and the abrasive compound. That technology is at least 40 years old.

Allow me to present some history about mass finishing media. In the early days of tumble finishing the most common media was natural stone. Anything from river rocks to granite to Novaculite was used. The river rocks wore out very quickly; granite polished very well but had no cut; and Novaculite was somewhere in between.

For your information, Novaculite is microcrystalline quartz, also known in some variations as flint. It is very popular as whetstone for honing knives to a fine edge; you can buy Arkansas whetstone at many hardware and sporting good stores that sell cutting edge tools and knives.

Synthetic abrasives, such as fused aluminum oxide, had been around for industrial use since the very early 1900s, but did not find their way into tumbling until the early 1930s. The large pieces of manufactured fused aluminum oxide were crushed in ball mills. The jagged, random shapes were screened to various sizes for tumbling. This is a very tough product, less friable than most rocks, and it rapidly replaced the various rocks for mass finishing, except that granite continued to be the choice for polishing and burnishing.

Because fused aluminum oxide is an abrasive, and because the same homogeneous crystal structure is consistent throughout the nuggets, this product was touted in those days as “fast-cutting, 100% pure abrasive.”
The big drawback to any random shape is that it lodges easily and is difficult to remove from the parts. In the case of fused aluminum oxide, it also glazes very quickly and loses its cutting ability. It is only a little better than rocks.
Preformed ceramic media was introduced in the 1950s; it cut faster and greatly reduced lodging problems. While it solved many problems, it had a very high wear rate and, as a result, got off to a bad start.

A popular mass finishing guide circulated from 1956–1966 said random media is preferred for most applications. By the last part of the ’60s, the wear problem was under control, and the popularity of preformed ceramic media soared. Today’s preformed ceramic media are so good that there is almost no justification for continuing to use random shapes.

As to the abrasive compound, you will find that an average-cutting preformed media, if kept clean and free cutting, will cut just as fast, or faster, than random media with added abrasive compounds. In our lab tests we have demonstrated that there is no advantage to the use of abrasive compounds, with very few exceptions.

One notable exception is when the parts are to be deburred or radiused followed by burnishing. In that case, you can use a polishing or burnishing media with abrasive compound followed by rinsing and burnishing in the same media. This is often preferable to two machines in series, one for cutting and one for burnishing. And, it is very preferable to changing media in the same machine.

For starters, if you try preformed media, I suggest one of the heavier (100+ lbs/cu ft) medium- cutting compositions, in a blocky shape approximately the same size as the random media. The shape of the media is important, as well. Without seeing the parts, I am inclined to recommend a shape called, variously, V-cut cylinders, double dut Cylinders, or WEJ (a trademark of Markee).