Solder won't stick or flow

B

benjamin2515101

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Oct 1, 2011
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42
I tried soldering some stainless bolsters on my stainless liners, I can't get it to stick at all, and it won't flow into the gap. The surfaces were cleaned with acetone and are flush, sanded to 320 grit. I used flux and tried pre-soldering before connection and soldering with the two pieces touching. Nothing I do is working. Please help or link to a thread that will help.
 
What solder and flux are you using. I use Allstate 430 with good results. Your surfaces must be really, really clean. To clean, I use Ivory liquid soap and hot water and rub the surfaces under hot water till they squeak. I also use a large soldering iron which I feel gives me better control over the heat.
 
I've used stay-brite solder and stay-clean flux to stick 416 bolsters to 410. I've done it the way you mentioned, tinning the pieces before trying to stick them together. Sometimes acetone will leave a film, try soap and water as suggested. What heat source are you using?
 
The question about the solder and flux is because stainless requires different solder, special flux, and very careful heat control.

Using a torch is a really bad way to solder stainless unless it is a Smith or Little torch and you have the skills. A heat gun or iron are far better to learn on.
 
I don't solder much now, but when I did, washing with soap and water seemed to work best. In my case, blue dawn detergent. Heating everything up slow and soft helps. Also, a small stainless pick with a sharp end can sometimes help solder to spread out while hot.
 
The issue with soldering stainless is the surface oxides form at a low temperature. Any overheating or the wrong flux type will create a barrier to the solder adhering and flowing. The solder must be silver bearing solder type. These typically flow at 400F or lower. If the steel is heated above 400F, you are overheating it. A plumbers torch is about 100 times as powerful as what you need to heat a few ounces of steel to 400F.

I wash and scrub with detergent and rinse in hot water.

Acetone will create problems. Denatured alcohol is better if you feel you need a solvent.
 
I mostly use(d) Stay-brite solder and Stay-clean flux. A good combo that sticks well to stainless.
 
I decided to order the Stay-brite kit and try it out, as well as washing with soap for the cleanest surfaces. Thanks for the replies, guys.
 
Make sure you file/sand the areas to be soldered immediately before you start.
 
The trick to silver soldering stainless steel is to use Harris Stay-Clean Liquid Flux part number SCLF4, EDP (electronic data processing?) number of 40002. The UPC (bar code) is 6 84032 00013 1. This is their most active soldering flux formulation. You may be disappointed in the performance of a less concentrated flux. I buy this flux at the local welding shop but it is also available on industrial supply websites and on Amazon as: Harris SCLF4 Stay Clean Soldering Flux, 4 oz.

The solder I use is either Alph Fry 62964 4% silver solder or even better is Kester SN95AG05 #66/44 which is 5% silver. If you don't need 1 pound of the 5% solder you can buy small quantities of it on eBay.

You can get detailed technical information and an MSDS for the flux from:

http://www.harrisproductsgroup.com/en/Products/Alloys/Soldering/Fluxes/Stay-Clean-Liquid-Flux.aspx
(or http://www.harrisproductsgroup.com > alloys > Soldering > Fluxes > Stay-Clean® Liquid Flux)

This flux contains Muriatic Acid which is another name for Hydrochloric acid or hydrogen chloride (HCl) which will produce free chlorine gas when heated.

Wear a respirator mask rated for hydrogen chloride (Hydrochloric acid / HCl) vapor and chlorine gas. The average paint spray mask is probably not rated for these vapors. The 3M 8246 Particulate Respirator available on Amazon and eBay in single quantity is rated for nuisance level acid vapors http://solutions.3m.com > safety and security > personal protective equipment > disposable respiratory protection (picture) > Nuisance Level Acid Gas

Flux residue is corrosive and a post-solder flux removal procedure should be employed. Because of this it is not recommended for use in electrical or electronic applications.

FLUX RESIDUE REMOVAL
Step #1
Thoroughly soak and wash soldered parts in a solution made up of one to two ounces Tri-sodium Phosphate (TSP), Spic and
Span (powdered) or Bicarbonate of soda added to one gallon of water heated to 120° F (49° C) to neutralize the acid residue. Rinse these alkaline cleaning solutions off thoroughly because they are almost as corrosive as the hydrochloric acid.

I keep my bottle of this stuff in an old soup can that gets seriously rusted from the vapor of the flux.
 
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