QUESTION: Can I make my own brazing paste by mixing a gel binder with a brazing filler-metal powder, or should I only purchase pre-mixed pastes from filler-metal suppliers?
ANSWER: The answer is both “yes” and “no,” depending on the specific end-use application for which the paste will be used. If you are desiring to make your own brazing paste that you can dispense from a cartridge by hand onto the base-metal parts that you want to braze together, then yes. This can be easily done, and it is widely being done across the entire brazing industry worldwide.
Brazing engineer Torstein Grosted of Hoganas (a brazing filler-metal manufacturer) described some specialized applications. If your brazing needs include roller coating or screen printing, then specialized gel-binders that can maintain a specific and preferred viscosity versus shear-rate profile are required. These properties cannot merely be achieved by mixing an off-the-shelf gel-binder with any brazing filler metal (BFM) that you may want to use. Some manufacturers of gel-binder systems, such as Fusion Inc. in Ohio, claim to have in excess of 400-450 different gel formulations depending on very specific end-use requirements.
Therefore, please understand that blending your own brazing paste may be simple and may be OK in a wide range of applications, but it is certainly not applicable in all situations and should never be assumed to be a universal technique that everyone can use. You should experiment to see if it works for you. If so, then go ahead and use it because it can be a very cost-effective method for making good, reliable brazing paste for many different applications. I have done it for many years in a variety of different applications, but they all involved making pastes for direct application by hand using paste cartridges for laying beads of BFM paste along brazed joints.
How do you make your own paste? If you intend for it to be used for hand application of beads of BFM paste (either continuous or intermittent) onto surfaces to be brazed, then this is a simple and easy way to do it.
- First, procure the desired BFM)in powder form and a gel-binder from one of the BFM manufacturers. I show a listing of such manufacturers on my website and each company’s name is a hotlink to that company’s website. As mentioned earlier, some manufacturers do sell gel-binders as separate items, whereas other manufacturers will only offer their gel-binder as part of a pre-blended system with the BFM. Those manufacturers who do offer gel-binders will usually sell them in a variety of container sizes, ranging from about a quart up to gallon-size containers.
- Find a good paint shaker for blending the BFM and the gel-binder, such as the one shown in Fig. 1. Such paint shakers can usually be found in company labs or maintenance areas. They can also be found at your local paint store, or you can purchase a good used one online from a place such as eBay.
- Procure empty containers (plastic bottles with secure caps are preferred, but glass or metal containers also work fine) in which you will mix the materials to make your brazing paste and from which you will pour the paste into the dispensing cartridges.
- Lastly, procure the plastic cartridges into which you intend to load the brazing paste that you make. These dispensing cartridges are usually packaged in boxes that also contain end caps and pistons for the cartridges.
We'll learn the procedure for making brazing paste in Part 2.