Manufacture of Braze and Solder Alloy Powders by Atomization
Using This Knowledge
From a cost standpoint, there are several ways to capitalize on the understanding of powder production and the resulting alloy powders. One area to review would be how the method of manufacturing the alloy powders impacts the cost of these materials. As an example, when using a copper-based braze alloy, look for a manufacturer that atomizes in air or water, as these are lower cost processes. Most copper brazing applications do not require the higher cost, gas atomization process, so there is no reason to pay extra for a lower oxide copper powder. On the other hand, if the brazing process involves a base metal that oxidizes readily, such as those that contain aluminum or titanium, it may be more cost effective to use a gas-atomized copper powder even though the initial cost is higher. The dollars that could be saved in the processing of these difficult-to-braze components will more than make up for the higher purchase price.
Another cost consideration is with the mesh size of the alloy powders. When manufacturing powders, the greater the yield, or the more of the "as-atomized" powder that can be used to produce the final product, the lower the cost. For many brazing and soldering applications, no other consideration is necessary beyond that of the lowest cost filler metal. However, there are other applications where the method to apply the filler metal makes it impossible to use the "optimized yield" alloy mesh size. As an example, applications where the powder is sprayed or dusted onto the component could be negatively impacted by a powder that has a high percentage of fine particles as it will tend to clump or clog during these types of applications. The use of the lower priced powder could cost more in lost production time than the upfront cost of the higher priced, restricted mesh size powder.
Understanding the powder size used in a paste can help select the right application equipment for applying the alloy paste. If a coarser powder is used to manufacture the paste, there could be particles as large as 0.006 in. (0.15 mm). But, if the part to be alloyed needs a fine bead of alloy, a typical way to achieve this would be to use a small-diameter needle so only a thin bead of alloy paste is applied. The small-diameter needles measuring from 0.004 to 0.010 in. (0.1 to 0.25 mm) would exclude a lot of the powder particles from passing through. Most often, the larger particles will clog up the entrance to the needle, causing a reaction on the part of the application technician to increase the pressure. The larger particles will yield under the pressure and move aside, resulting in a messy burst of paste from the needle that must be cleaned up. Time and alloy paste are wasted. As if this waste is not bad enough, the larger particles become stuck in the syringe or cartridge and pile up as the smaller particles are extruded. Eventually the syringe or cartridge and the remaining braze or solder material are discarded when no more alloy paste can be pushed from the container.
In a similar situation where a paste or slurry is mixed by the end user, knowing the powder mesh size can help to make the right decision on the amount of binder to add. If a process has been established based on a certain ratio of binder and powder that results in an acceptable viscosity, the process can be upset when the mesh size of a new powder lot is not examined prior to use. To engineering, the most important issue is the ratio by weight between the binder and the alloy powder in order to ensure a specific amount of solder or braze alloy in the joint. Unfortunately, in the real world, the operator has to have a paste viscosity that will extrude through the needle onto the part. When a new powder lot has a higher percentage of fine powder, more binder may be necessary to achieve an acceptable viscosity. The additional surface area of the finer powder particles will yield a thicker, more viscous paste if the same amount of binder is used, which won't go through the needle. This situation is usually fixed by adding enough additional binder so the viscosity is the same as usual. What is rarely measured, unfortunately, is the drop in powder weight this new mix of paste or slurry has. The risk is voids and rework because of the lower alloy weight in the joint.
Using the information provided with each powder certification can help control costs and make it easier to achieve processing goals. Be proactive and talk to the braze and solder manufacturers about specific processes and alternatives they may have to offer that will not only meet the specifications required, but might offer lower costs or higher yields in the brazing or soldering process. There is nothing to loose and a lot to gain with just a little education about the alloy powders being used. u
DIENTJE FORTUNA Deni.Fortuna@ sulzer.com is Braze Product Manager, Sulzer Metco (US) Inc., Troy, Mich.
Based on a paper presented at the 34th International Brazing and Soldering Symposium, 2004 AWS Annual Meeting, April 68, Chicago, Ill. Back [1] [2] [3]
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