Dan Kay on Brazing Stop-Off Materials

Dan Kay:

Hi Mike —

Yes, there are a number of brazing filler metal (BFM) manufacturers who also produce and supply brazing stop-off materials that can be painted onto graphite surfaces such as you mention in your note to Doug Glenn.  Here are just a few:  Surface Flow Technologies (Div. of LSN Diffusion Int’l) in Michigan, Wall Colmonoy Corp in Michigan, Vitta Corp in Connecticut, and Wesgo Metals (Div. of Morgan Advanced Materials) in California are some of the primary ones.  

Stop-off materials come in different colors, the coloring of them being merely to identify its manufacturer, since all stop-off materials use metallic oxide materials to create their “stop-off” capabilities, and all these oxide powders are essentially white, to begin with.  Thus, to differentiate the various stop-offs they began to color them so that people would learn to associate green stop-off with company A, pink stop-off with company B, red stop-off with company C, etc.

White stop-off products are essentially the weakest of all the colored stop-offs out there and are primarily aluminum-oxide products in a paint-like consistency.  The binders/gels used to make the stop-offs vary considerably from manufacturer to manufacturer are proprietary, and you’ll not get any of them to actually tell you about all the ingredients in them.  People are often surprised to hear that a product such as Phillips Milk of Magnesia, available in lots of stores or pharmacies, is actually a decent stop off (magnesium oxide) for a number of applications.

But you are correct to say that you can make your own in many different ways by merely mixing some aluminum-oxide powder, or titanium-oxide powder, etc., in with a variety of quick-drying solvents, perhaps also with a thin acrylic type cement to give it adherence, paint it onto graphite surfaces, and after evaporation you would be left with an adherent layer of that protective oxide barrier, so that it prevents direct contact of a metal (especially any iron-containing metals) with the graphite, since an iron-carbon reaction is to be avoided.  

I’d be happy to assist you further with this, if you have additional questions, since I’ve had much direct manufacturing experience over my 45+years in the brazing world, a lot of it involved in making BFMs, brazing stop-offs and cements, etc., and am pretty much aware of the companies today who make and supply such materials.

On my website at http://www.kaybrazing.com, you will see a tab on the homepage that shows “Brazing Suppliers”. By clicking on that tab you can see a listing of the different companies who produce these materials, and in that tabular section the name of each company (such as those I mentioned above) is a hotlink that will bring you directly to that company’s website so that you can search it for a specific type of product that you might desire.  It part’s of the service that I want to provide to users of my website.  I hope you will find it useful.

Let me know how I can help you further.