Are you in the brazing business or in the heat-treating-of-fixtures business? Many brazing companies claim they are a brazing job shop doing lots of brazing for their clients, when in actuality they are only doing the brazing work for their clients in order to generate some income to pay for their real business (i.e., heat treating of furnace fixtures). Does that seem strange? Let’s take a deeper look at this.
It is important that every brazing shop measure and know the weights of whatever they put into their furnaces for a brazing cycle they wish to perform for a client. This measurement includes the weights of the component parts being brazed for the client. It also includes the weight of all the fixturing put into that furnace to hold the client’s parts in proper alignment, etc.
Here's a real-life example. A brazing shop was planning to vacuum-braze some aerospace components for their client and intended to process approximately 20 components in each furnace load. The client component assemblies weighed about 4 pounds (1.8 kg) each. The components were carefully placed in a large basket made from heavy-steel bar stock. The basket measured approximately 3 feet x 2 feet x 8 inches deep (1 meter x 0.5 meter x 150 mm), weighing almost 120 pounds (50 kg). The furnace grate onto which the basket was laid weighed 210 pounds (95 kg), and the furnace floor posts onto which the grate was laid were estimated to weigh about 50 pounds (23 kg). When the weight of the fixturing used was added up, it totaled about 380 pounds (over 170 kg). The weight of the parts being brazed totaled about 80 pounds (36 kg).
As could be seen, the weight of the parts being brazed represented about 21% of the total weight going into the furnace to be heated up to brazing temperature (everything that was being heated by the heating elements in the vacuum furnace). Thus, 79% of the load represented “fixturing” weight.
IMPORTANT: There is no “free ride” in any brazing furnace. Every pound (kilogram) heated up to brazing temperature costs money. Thus, far more heat was required to heat up the fixturing to brazing temperature than was needed to heat the components to brazing temperature based on the weight of the parts. If you were to add in the thermal conductivity of all the components being heated, it can make the problem worse. If the metals of the client components are thermally conductive (aluminum or copper) then even more heat would be required for that cycle since highly conductive metals radiate heat rapidly (as well as absorb heat) as they get hotter, and more energy is needed to get them up to temperature.
Have you ever taken the time to analyze the loading of your furnaces for brazing? Perhaps you will also discover (as did the brazing shop just described) that you are actually in the heat-treating-of-fixtures business rather than in the brazing business!
A goal that is worthy of being strived for is to keep the total weight of the fixturing to no more than half the weight of the parts being brazed. Many shops have taken that to heart and are now achieving this goal. How about you?
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