Aluminum Oxide Impregnation Article

Question:

I found your article on “aluminum oxide impregnation” most interesting. I have worked in “parts processing” for approximately 10 years, and this question frequently comes up as to what degree of concern there should be when finishing parts to be welded/brazed with ceramic media containing fused aluminum oxide as the abrasive grit.

We specifically make two “cutting” bonds for just these cases—one with aluminum oxide and the other with silicon carbide. Under certain circumstances they both work well, but recently I received parts for test processing tubes made of various types of steel, which after deburring will be welded together to make lawn furniture frames. Our customer’s cutting operation has left very heavy burrs on the end of tubes, which they are presently removing by hand. They would like to go to mass finishing and are not willing to change their cutting operation to minimize the burrs. Under normal circumstances the silicon carbide would be quite effective on this project, but as it stands with the size of their burrs, I would really need to test with one of more abrasive, fast cutting bonds made with the fused aluminum oxide you wrote about in your article.

Over the years I have talked with several customers and have heard a wide variety of advice ranging from people who say “never use media made with fused aluminum oxide on parts to be welded/brazed” and others who call this rule an old wives’ tale. I have always gone along with the first belief. In this case how much of a problem would there be if these steel lawn furniture parts were processed with a very abrasive ceramic media containing fused aluminum oxide in a vibratory tub with a good compound flow through system and well rinsed afterward (some type of inhibitor)? Re: the strength of their weld? As the situation looks now, my only option may be to do my trial tests in this type of abrasive ceramic media, but in doing so, I would like to provide customers with the best information as to what their potential future problems might be. In your article you stated that the weld would be only about 60% as strong as it should be. Would this hold true in this application? I would like to thank you in advance for any consideration you may give this matter and look forward to hearing from you. S.M.

Answer:

I did not recall writing an article or answering any previous questions regarding aluminum oxide contamination of surfaces to be welded or brazed so I did a search on the Products Finishing web site and found out where you got your information. Even though my name appears with that article on the web site, I can’t take credit for it. It originally appeared on page 40 in the October 2000 issue of Products Finishing magazine under the Mass Finishing Forum written by Steve Marcus.

Even though that topic appeared some time ago in a different column, it would be worth covering briefly here again. In my experience with brazing, I would never want to try to braze any ferrous parts that have been finished with an aluminum oxide media. Every effort is made to keep aluminum to a minimum in these processes. The base metal and braze alloys have controlled chemistries to minimize the chance of any aluminum getting into either. Additionally, any mass finishing processes are carried out in just about anything except aluminum oxide. Due to their stability, aluminum oxides can be difficult to reduce unless the flux contains a fluoride additive.

While I do not have the same direct experience in welding, given the problems I see with brazing, I would think that aluminum oxide mechanical finishing could present considerable difficulties. I believe the comments you have heard on the subject are closer to reality than an old wives’ tale.

Having said all this, it still may be worth running preliminary side-by-side tests to show the strength and quality of the welds when finishing using both the aluminum oxide and silicon carbide. This may be worth doing considering the end use of the product. I would think a small amount of porosity and loss of strength in the welds of lawn furniture could be tolerated. This would not be the case if the project had a more demanding end use application.