Soldering Stainless Steel

[K5HM]

I'm working on an 2M antenna project that requires soldering the end of a stainless steel whip into the center of a PL259 connector. I used a Dremel tool to taper the end of the whip so it fits in the hole. I am going to use a 300 watt Radio Shack soldering gun and some lead/silver solder. But I cannot find an acid flux in a small quantity. The ones at the hardware store specifically say not for stainless steel. Any ideas where I can find a small quantity of acid flux? The article in QST says to use Hydrochloric Swimming Pool Acid but i can't find that stuff inthe stores either. Through some googling on the internet , I learned that muriatic acid is really Hydrochloric diluted to 30% but I think that is still too strong. I'm open . . .

[VK2HHS]

A quick search brought up the following; seems hydrochloric acid flux is not recommended!

Soft Soldering
All grades of stainless steel can be soldered with lead-tin soft solder. Leaded solders should not be used when the product being soldered is used for food processing, serving or transport. Soldered joints are relatively weak compared to the strength of the steel, so this method should not be used where the mechanical strength is dependent upon the soldered joint. Strength can be added if the edges are first lock-seamed, spot welded or riveted. In general welding is always preferable to soldering.

Recommended Procedure for Soldering
Recommended procedure for soldering:

· 1. The steel surfaces must be clean and free of oxidation.

· 2. A rough surface improves adherence of the solder, so roughening with grinding wheel, file or coarse abrasive paper is recommended.

· 3. Use a phosphoric acid based flux. Hydrochloric acid based fluxes require neutralising after soldering as any remnant traces will be highly corrosive to the steel. Hydrochloric acid based fluxes are not recommended for soldering of stainless steels.

· 4. Flux should be applied with a brush, to only the area being soldered.

· 5. A large, hot iron is recommended. Use the same temperature as for carbon steel, but a longer time will be required because of stainless steel's low thermal conductivity.

· 6. Any type of solder can be used, but at least 50% tin is recommended. Solder with 60-70% tin and 30-40% lead has a better colour match and greater strength.

Brazing (Silver Soldering)
When welding is impractical and a stronger joint than soft soldering is required, brazing may be employed. This method is particularly useful for joining copper, bronze, nickel and other non-ferrous metals to stainless steel. The corrosion resistance of the joint will be somewhat lower than that of the stainless steel, but in normal atmospheric and mildly corrosive conditions brazed joints are satisfactory. Because most brazing operations involve temperatures at which carbide precipitation (sensitisation) can occur in the austenitic grades, low carbon or stabilised grades (304L, 316L or 321) should be used. Ferritic grades such as 430 and 3CR12 can be quenched from the brazing temperatures, but hardenable martensitic grades (410, 420, 431) should not be heated above 760°C when brazing. The free machining grades 303, 416 and 430F should generally not be used as a dark scum forms on the surface when fluxing and heating, which adversely affects the appearance of the steel.

Recommended Procedure for Brazing
Recommended procedure for brazing:

· 1. Use silver brazing alloys with melting points from 590-870°C. Select the alloy for best colour match.

· 2. Remove dirt and oxides from the steel surfaces and apply flux immediately.

· 3. A slightly reducing flame should be played across the joint to heat uniformly.

· 4. For high production work use induction heating or controlled atmosphere furnaces (argon, helium or dissociated ammonia with dew point of about -50°C).

· 5. After brazing remove all remaining flux with high pressure steam or hot water.

· 6. When brazing grade 430 use a silver solder with 3% nickel. This alloy also helps to minimise crevice corrosion when used with austenitic grades.

[M0DSZ]

My father made some cake tins and baking trays from scrap stainless steel at least 20 years ago, we still use them regularly. He used brazing solder but it's quite in order to use a lower temperature silver solder if you're not going to subject them to oven temperatures.

[K5HM]

Well, I did it.

I couldn't find any flux in the local hardware stores that was recommended for stainless steel. The article in QST recommended the use of Hydrochloric Swimming Pool Acid, which I found out was basically muriatic acid. Nasty stuff. Muriatic acid is basically HCL diluted to 30%. Spa and pool supply stores carry it but I had to buy 2 gal!!!.

I used the "flux" to help tin the end with lead-tin-silver solder from Radio Shack. Once I had the whip tinned, i could solder the PL259 tip to the whip without a problem.

Oh well, I will probably use the rest of the nasty stuff to clean up the oil stains in my driveway. i hear it makes a good concrete cleaner too.

[K8ERV]

I make 2m whips the same way, no problem with regular solder and paste.

TOM K8ERV Montrose Colo

[N5RLR]

...I will probably use the rest of the [muriatic acid] to clean up the oil stains in my driveway. i hear it makes a good concrete cleaner too.

It does. Just be sure to wear shoes that you'll consider sacrificing to the cause.

[KB5PN]

Oh well, I will probably use the rest of the nasty stuff to clean up the oil stains in my driveway. i hear it makes a good concrete cleaner too.

It does a good job. Wet the concrete first and then don't let the acid sit too long before scrubbing and rinsing as it will etch the concrete.
BTW, don't use your wifes best broom to scrub with....don't ask how I know!!

[KI4QFL]

It does a good job. Wet the concrete first and then don't let the acid sit too long before scrubbing and rinsing as it will etch the concrete.
BTW, don't use your wifes best broom to scrub with....don't ask how I know!!

Opps, Sounds like someone has done that before.

[K5HM]

Thanks for the tip. I would have probably forgotten about the shoes until it was too late.

[AE5JU]

Well, I did it.

(trimmed)

The article in QST recommended the use of Hydrochloric Swimming Pool Acid, which I found out was basically muriatic acid. Nasty stuff. Muriatic acid is basically HCL diluted to 30%. Spa and pool supply stores carry it but I had to buy 2 gal!!!.

(trimmed)

Do all below OUTDOORS.

HCl is not diluted to 30%. 30% is about as high as you can concentrate HCl, depending on temperature. HCl is most active at 15%, so the 30% swimming pool acid will have to be cut 50%-50% with water.

DO NOT pour water into acid. The water will heat up and cause a steam explosion, splattering acid all over you.

Pour the acid very slowly into the water.

When you do this wear a slicker suit, rubber gloves, rubber boots, goggles and face shield. No, I am not being overly protective here. Do it.

Have a running water hose nearby. Do NOT do this by yourself, but have someone standing by to hose you down if necessary. Do not worry about neutralizing with baking soda, etc. If you are splashed you will not have time for that. Just dilute and wash away with lots of water. If in your eyes rinse under running water for 10 minutes. It will probably be necessary for your assistant to forceably open your eyelids to rinse your eyes. Then see a doctor.

I have mixed and used literally many thousands of gallons of HCl and other acids and chemicals in my job. In just the past year, probably 3000-4000 gallons of HCl alone.

Paul
AE5JU