Reprinted from the ACJ - November, 1992
There is an old saying that says when something seems to good to be true, it probably is. That's true in politics and for our topic of discussion this month, zinc-free fluxes.
A lot of hoopla has been raised in the recent past concerning the advantages of zinc-free fluxes over the more conventional zinc-chloride (ZnCl2) fluxes. One of the main arguments in favor of the zinc-free fluxes is that they are far safer to use than ZnCl2-based fluxes. To throw out another cliche, "It's six of one, half a dozen of the other."
Although the chemical makeups of the two types of fluxes vary greatly, the fact that they both remove oxidation, clean metal and facilitate soldering indicates that both are aggressive, somewhat corrosive solutions. Similar safety concerns should be raised with both types of fluxes.
Zinc-free fluxes have been around for a long time. They are usually called "organic fluxes" and are used extensively in core production rather than repair. This is due to the fact that they burn off faster and are not quite as efficient as ZnCl2 fluxes. They work well in the controlled, repeatable environment of production, but not as well in the ever-changing world of radiator repair. There isn't as much room for error when using zinc-free fluxes.
These fluxes usually contain an acid—hydrobromic acid is common—but sometimes an organic acid is used. Amines of various types are often incorporated. Glycol ethers are also added along with a dash of wetting agent.
Let's look at the safety matters we need to address with zinc-free fluxes. The health concerns for zinc-free fluxes are similar to those we discussed in a previous column regarding ZnCl2 fluxes. It is a logical conclusion that if the chemicals act the same on metal, they will act the same on your body. After all, "A rose by any other name would smell as sweet."
With all chemical safety, it's important to know how these chemicals can get into your body, also known as routes of entry. Similar to ZnCl2 fluxes, dangerous contact is possible by inhalation and ingestion. Additionally, zinc-free fluxes pose a threat through skin absorption.
The inhalation concern is important because these types of fluxes tend to vaporize during soldering at a faster rate than ZnCl2 fluxes, resulting in more of the flux going into the air. Good ventilation and the proper use of half mask respirators equipped with an organic vapor cartridge will reduce your inhalation exposure.
Ingestion can be controlled easily by good hygiene. Let's see, I must have a cliche for this: "Cleanliness is next to Godliness." Well, that may be a bit strong, but you will get on OSHA's good side by washing up when leaving the work area and before eating or smoking. While it is not common to drink a soldering flux, the majority of contamination is caused by your hands contaminating something that goes into your mouth.
That leads nicely to the next topic, which is skin absorption. Several of the zinc-free flux components are taken into your body directly through the skin. They can cause chronic liver and kidney damage over many years of repeated exposures. Some components are corrosive and can cause irritation, rashes or possibly burns. Still other components can cause what is referred to as sensitization.
When your skin is exposed to certain chemicals, it can develop a sort of allergy to those chemicals. Then, when you are exposed to those types of chemicals in the future, even in much smaller doses, more severe rashes or irritation can occur. This subsequent exposure may be no more than fumes circulating around the shop. It doesn't have to be direct contact. You find yourself with a nasty skin reaction and you haven't even touched the flux at all. Sort of "between a rock and hard place."
For all these reasons, it is very important to wear gloves impervious to the flux solution whenever you handle it. Also, wash up thoroughly whenever you contact it. If you happen to spill or splash flux on your clothes, change them immediately. If you don't, your shirt or pants act as a sponge full of the chemical resting against your body. The skin of your arms, legs or stomach don't have the calluses your hands do, so absorption there is much easier and more rapid.
Zinc-free fluxes don't have the water-grabbing (hydrophilic) tendencies of the ZnCl2 fluxes, so
the physical hazards of using zinc-free fluxes around the shop are mostly problems associated with corrosion. As we discussed before, these fluxes vaporizes readily and a good deal of corrosive fumes are released. Your best defense is a strong offense … sorry it's football season.
Actually, your best defense is good ventilation. Inspection of chains, brackets fixtures is a good idea. Try to keep dirty gloves from contaminating tools, doorknobs, pens, pencils, etc.
In summary, it is best to keep in mind that if a flux acts aggressive, it probably is aggressive and caution is required, no matter how safe it is said to be. A sort of "wolf in sheep's clothing." When comparing zinc-free flux safety to ZnCl2 flux safety, it is a case of "the pot calling the kettle black." Which brings me to another timely cliche: "Quit while you're ahead, Dave."
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