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Contaminants in your weld? Here's how to prevent them

Topics: Laser welding

 

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Sandwiches don't mix well with welding.

I mentioned in blog 4 that contamination is a topic in itself.  Well, why not follow that train of thought?

Anything and everything that is not the “stuff” being welded is a potential contaminant.  Whether it be oil from machining, paper fibers, soapy water from a wash cycle, a sliver of plastic from your expensive non-marring table top, or even brown mustard from that London broil sandwich you had for lunch, these are going to put something unexpected into your end product.

Now, if you enjoy the smell of toasted brown mustard (yes, it has happened) and don’t much care about the quality of your welded parts, then don’t read anything more.  You’re done -- wait for blog 6! 

If you want to know the implications of weld contamination and what to do about it, let’s go!

Let’s simplify things by breaking this down into 3 categories:

  • Organics – If it was ever alive, it will have carbon in abundance along with hydrogen, oxygen and nitrogen. Basically hydrocarbons.  Each of these components has its own effect on your weld. Carbon typically hardens iron-based alloys, increasing crack susceptibility.  Hydrogen often leads to embrittlement, oxygen has all sorts of effects good and bad, and nitrogen can be anything from harmless to utterly destructive. Examples are paper fibers, hydraulic oil, hair, a breadcrumb (really).
  • Inorganics – Things that aren’t primarily carbon. Silicon-based contaminants, dirt, silt, sand, glass – these all end up in parts, leading to porosity, cracking, and sometimes complete lack of fusion.  Ceramics from abrasives – some of these are innocuous, and others can lead to severe weld degradation and cracking, pitting, and general weakening of your precious parts.
  • Atmospherics – If your part is reactive, gasses and compounds floating around can wreak havoc in all kinds of ways through corrosion and conversion. These are complex problems and can really be tough to troubleshoot. 

What to do about weld contaminants

How you deal with a contaminant depends greatly on what it is.  Simple organic compounds can often be removed with an organic solvent like acetone, isopropyl alcohol, MEK, or something similar.  Soapy water can be effective for oils as long as no soap residue is left behind.  For some of the more persistent organics, an aggressive acid or alkaline cleaner may be necessary.

Inorganics like abrasive dust can be easy to remove by a quick dry wipe or with a lint free cloth and DI water.  However for embedded particles, usually following a grinding operation, the solution can be quite challenging.  Often progressive polishing or machining is in order and will entail removing enough of the weld surface to ensure all of the inorganics are gone.

Of course, the best way to deal with contaminants is to NEVER introduce them to begin with.  My primary recommendation is to expose your parts to as few contaminants as possible.  Clean them thoroughly after inspection, then seal them in clean packaging so they can’t come in contact with anything until it’s time to weld.

As always, talk to a pro before putting those parts on a truck to your welder.   I’m sure we’ll touch on this topic again soon.  See you in blog 6.

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