Metal Brazing Procedures

Paweł Chodaczek
Niezależna firma R&D działająca w Warszawie
proceduresMetal Brazing Procedures
The Phos-Copper family of brazing alloys permits the brazing of copper to copper without use of a brazing flux.  Brazing of stainless and carbon steels; nickel alloys such as Monel 400, Inconel 600, and Hastelloys; lead-free brasses; OFHC copper; beryllium-copper and other base metals. We excel at difficult and complex assemblies of OFHC copper, stainless and Monel or other components which must be assembled by step-brazing using multiple filler metals. The lower melting point of the brazing rod is key, because the heat that causes it to melt (flow) comes from the heated metal pieces being joined, not directly from the torch, as with soldering.Soldering: A process where similar or dissimilar metals are joined using an alloy that typically includes a base of tin combined with lead, silver, antimony, bismuth and indium.  According to Merriam-Webster, brazing means to solder with a nonferrous alloy having a lower melting point than the metals being joined.” But you don`t use solder in the sense that we usually discuss solder; for brazing, it`s referred to as a brazing rod or filler metal. Brazing is very similar to pick soldering, in that you apply the solder” or brazing rod after heating the metal components, not before applying the torch. Then that hot metal heats the brazing rod, causing it to melt and flow” like solder flows. Brazing joins are strong and permanent, like soldering joins, they just rely on a slightly different process.I always like to pay attention to different tools and methods that others use to make anything so that I can learn and adapt the methods that work for myself.  I once heard someone describe the difference like quilting and sewing, with soldering being more like quilting and brazing being more like sewing. In her new video Beginner Brazing for Copper Jewelry Making, Kim St. Jean describes it well with her fingers, as shown below, with the type of join achieved by soldering on the left and brazing on the right.Brazing is a metal -joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the adjoining metal. However, with brazing, the molten brazing rod material doesn`t flow into the heated metal to be joined but rather it binds or attaches the two metal surfaces (at the fingertips, above), similar to how glue binds two objects together-but much stronger. Silver based alloys Cadium Free are used wherever Cadmium is inadmissible due to its properties. We offer three-layer materials called Trimetals, where two layers of brazing material are clad onto Copper core.As everyone is pitching in with methods, I take this opportunity to mention practical soldering - lead/tin soldering, that is, rather than brazing (brass rod), silver solder (4%-50% silver), bronze welding, MIG & TIG methods.  Alloys with Nickel content help to join hard to join surfaces such as: stainless steel, tool steel and tungsten carbide, nickel and nickel alloys. Copper layer reduces vibrations asising during operating of tools and prevents cracking. Phosphorous Copper / Phosphorous Copper Silver alloys are widely used primarily for joining components of Copper and its alloys in manufacture of instalation of refrigeration, air conditioning or heating and electrical engineering. Addition of Phosphorus to Copper decreases melting temperature and creates self-refining effect that eliminates using fluxes during soldering.
Due to Phosphorus share these alloys are not suitable for brazing materials containing Iron and Nickel because of chemical reaction. This is well-developed group of materials such as brass, bronze, copper-nickel and other multi-component alloys. Variety of chemical composition and technical properties make these alloy suitable for many applications with various brazing techniques. Brazing, as we`ve seen, uses the principle of capillary action to distribute the molten filler metal between the surfaces of the base metals.Therefore, during the brazing operation, you should take care to maintain a clearance between the base metals to allow capillary action to work most effectively. The following chart is based on brazing butt joints of stainless steel, using Handy & Harman`s Easy-Flo filler metal. By the time you reach brazing temperature, the more rapid expansion of the brass creates a suitable clearance. Heating a metal surface accelerates the formation of oxides, the result of chemical combination between the hot metal and oxygen in the air.To help you in planning proper clearances in brazing dissimilar metals, the COE`s Comparison of Materials chart furnishes the coefficient of thermal expansion for a variety of metals and alloys. These oxides must be prevented from forming or they`ll inhibit the brazing filler metal from wetting and bonding to the surfaces. A coating of flux on the joint area, however, will shield the surfaces from the air, preventing oxide formation. And the flux will also dissolve and absorb any oxides that form during heating or that were not completely removed in the cleaning process.Since flux is conventionally made in a paste consistency, it`s usually most convenient to brush it on. But as production quantities increase, it may be more efficient to apply the flux by dipping - or dispensing a pre-measured deposit of high viscosity dispensable flux from an applicator gun. Many companies find the repeatable deposit size improves joint consistency, and because typically less flux is used, the amount of residue entering the waste stream is also reduced.That way the flux has least chance to dry out and flake off, or get knocked off the parts in handling. Choose the one formulated for the specific metals, temperatures and conditions of your brazing application. There are fluxes formulated for practically every need; for example - fluxes for brazing at very high temperatures (in the 2000°F/1093°C area), fluxes for metals with refractory oxides, fluxes for long heating cycles, and fluxes for dispensing by automated machines.
Fortunately, your inventory problem is considerably simplified by the availability of general-purpose fluxes, such as Handy & Harman`s Handy Flux, which is suitable for most typical brazing jobs. Keep in mind that the larger and heavier the pieces brazed, the longer the heating cycle will take - so use more flux. An insufficient amount of flux will quickly become saturated and lose its effectiveness.A flux that absorbs less oxides not only insures a better joint than a totally saturated flux, but it is a lot easier to wash off after the brazed joint is completed. Flux can also act as a temperature indicator, minimizing the chance of overheating the parts. Bright metal surface is visible underneath, At this point, test the temperature by touching brazing filler metal to base metal.You can join copper to copper without flux, by using a brazing filler metal specially formulated for the job, such as Handy & Harman`s Sil-Fos or Fos-Flo 7. (The phosphorus in these alloys acts as a fluxing agent on copper.) And you can often omit fluxing if you`re going to braze the assembly in a controlled atmosphere. A controlled atmosphere is a gaseous mixture contained in an enclosed space, usually a brazing furnace. Then the flux becomes totally saturated with oxides, usually turning green or black.If you have a number of assemblies to braze and their configuration is too complex for self-support or clamping, it may be a good idea to use a brazing support fixture. However, if you`re planning to braze hundreds of identical assemblies, then you should think in terms of designing the parts themselves for self-support during the brazing process. The simplest mechanical holding device is the best, since its only function is to hold the parts together while the permanent joint is made by brazing.Best bet is to immerse them while they`re still hot, just making sure that the filler metal has solidified completely before quenching. If they`re a little stubborn, brush them lightly with a wire brush while the assembly is still in the hot water. The only time you run into trouble removing flux is when you haven`t used enough of it to begin with, or you`ve overheated the parts during the brazing process. A 25% hydrochloric acid bath (heated to 140- 160°F/60-70°C) will usually dissolve the most stubborn flux residues.