Reprinted from the ACJ - June, 1994
In the past, we have all seen the demonstrations where a hole in a pop can is sealed up effortlessly with various fluxes, alloys, torches, etc. You don't see that demo much anymore. I guess the failure rate for pop cans isn't what it used to be.
Now, actual radiators are being repaired right before our very eyes, not only lending to the validity of the repair but also the ease with which it can be done. I mean, if an uncoordinated engineer like myself can do it, it should be a snap for a skilled repair guy.
The explosion of aluminum cores in the market, and now the aftermarket and repair industry, has brought brazing and high temperature soldering to the forefront of the radiator repair industry. With it has come a plethora of repair products from which to choose and, as always seems to be the case in this column, a number of new hazards and health concerns for us all to think about.
The health concerns associated with brazing are similar to those of soldering. The major difference is the increased variety of chemicals to which you are exposed. Whereas soldering operations usually involve a tin/lead solder with maybe a little antimony thrown in for good measure, brazing alloys can contain an alphabet soup of various metals: silver (Ag), copper (Cu), zinc (Zn), nickel (Ni), manganese (Mn), cadmium (Cd), phosphorus (P), lithium (Li) and tin (Sn), among others.
Put all these letters together and it looks like a Scrabble hand from hell. Inhale this spelling lesson and the toxicity ranges from relatively harmless for zinc to acute toxicity bordering on poison for cadmium.
If the metals aspect seems daunting, the variety of fluxes used is even more so. Unlike soldering, where zinc chloride is predominant and organic acids and amines round out the field, brazing fluxes can contain all of these components as well as cadmium, boron, tin and aluminum salts.
The reason all these folks are invited to the party is because the guest of honor, aluminum, is one tough customer when it comes to opening up and joining with others (boy, that's a bad analogy, but you get the point). Aluminum oxide is very tenacious and these aggressive fluxes and alloys are required to lift the oxide and adhere to the aluminum itself.
The aluminum oxide is in and of itself a nasty toxin. The "Hazardous Chemical Desk Reference" by N. Irving Sax lists it as a possible carcinogen and a contributing agent to a lung disease known as Shaver's Disease. I don't know who Mr. Shaver is, but I'm sure he would rather be remembered for something less distasteful, perhaps as inventor of the electric razor.
Even the aluminum alloys themselves are a cause for concern when it comes to health aspects. Little of the aluminum we contact everyday is pure. Magnesium (Mg), silicon (Si), nickel and others are added for strength and workability purposes. Hey, adding those letters with the others I think I can get a double word score!
These elements add to the complex makeup of the fumes coming off of the work piece, and aluminum fumes themselves are linked to pulmonary ailments and have been theoretically linked with Alzheimer's disease.
I suppose mentioning the paint, oil, grease and dirt fumes that will burn off of the radiator during the brazing process might be like throwing gasoline on a house fire. But what the hey, "Burn Baby, Burn." I'm sorry, just a quick flashback to the sixties.
The need for increased heat that I mentioned above is a strong contributing factor to the toxicity of the brazing process. A good deal more heat is required to activate the fluxes, break the oxides and flow the filler metal than for soldering. Usually, temperature above 840° F is considered brazing, while high temperature soldering pushes 800° F itself. Because of this high heat, some or all of the elements we mentioned above are going to volatilize and be in the air for you to breath. The simple safety answer is don't breath it, and here's how.
In order to make a quality aluminum repair, we have to accept these conditions and work to minimize their impact on our health. Minimize the exposure and you minimize the possible detrimental health effects. One way is to use minimal flux. That's hard for a flux manufacturer to say, but it's the truth and I can't lie to you. Going to a fluxless process involving abrasion is safer still.
More important, in my opinion, is knowing the chemical makeup of the alloy you are using. Use of alloys containing cadmium should be eliminated if at all possible due to its toxicity. There are dozens of great brazing alloys out there that contain no cadmium.
By reducing the temperature you use to make the braze, you can benefit in several ways. The tip
of a torch flame can be well over 2000° F - if possible, control your heat at lower levels. This helps reduce the fume levels and keeps the aluminum surface from pulling that disappearing act it seems so fond of when I try a high heat torch repair. Softer torch flames and/or use of a hot plate, as has been promoted lately, is an excellent way to reduce the amount of flux and metal fumes being released.
Always work under an exhaust system if flux or cadmium fumes are liberated. It is a good idea even in a fluxless operation, but a well ventilated area is necessary regardless. Try not to place your head directly above the work area, thus reducing the amount of fumes going into your eyes and lungs. Safety glasses are a given, and a half-mask respirator with a HEPA filter can never hurt. Be sure to wash thoroughly after handling the radiator and repair products to avoid ingesting the chemicals with your lunch.
Generally speaking, less is best when it comes to these operations. Less flux and less heat means less fumes and less exposure. Coupled with the proper protective equipment, this can enable what used to be nearly impossible: a simple and impressive repair procedure.
Oh my! With that last literary flourish my hand slipped and the pencil went sailing right through my pop can. Soda is gushing everywhere! It's getting on the Scrabble board! Is there anybody out there who still remembers how those demos worked?
The above article was written by David M. Brown, Chief Engineer of Johnson Manufacturing Company, Inc. and is published by JOHNSON with the expressed approval of the National Automotive Radiator Service Association and the Automotive Cooling Journal. Other reproduction or distribution of this information is forbidden without the written consent of JOHNSON and NARSA/ACJ. All rights reserved.
JOHNSON MANUFACTURING COMPANY
114 Lost Grove Road / PO Box 96 / Princeton, Iowa 52768-0096
Phone 563-289-5123 or Fax 563-289-3825