SILVER SOLDER BRAZING

Remember to read and understand the instructions which come with your torch kit, before lighting the torch.

With silver solder brazing, the two metals are joined by the use of a brazing rod which has a lower melting point than the metals to be joined. There are several kinds of brazing rods, however I will deal only with a brazing rod called "SIL-FOS5." This filler rod has 5% silver, 89% copper, 6% phosphorus. On the advice of a sales representitive at Air Liquide, I have used this brazing rod with good success.

A flux is required for most applications. The best flux to obtain is called "Handy Flux". Do not try to go cheap and buy silver solder and flux as I did at a hardware store. It just did not work. Go to your local welding store, like Air Liquide, and talk to the experts, and explain what you are planning to braze.

Now, you will require a torch to heat the metals and brazing rod. The torch I purchased is by Bernzomatic, and is called the Tote Torch. It can produce a flame temperature up to 5300 degrees F. which is much hotter than a standard propane torch. Again, I wasted money by first buying a mini torch which operates on butane fuel. It was suppose to solder and braze, but the temperature was not hot enough to melt the brazing rod. The Tote Torch comes with an oxygen cylinder and a Mapp gas cylinder. The kit does not have any gauges, only a valve for each tank. It also has a 4 ft hose, handle, tip, stand, spark lighter and several brazing rods. This unit can be purchased at stores similar to Home Depot and Rona, for around $75.00 canadian. The replacement tanks of oxygen and Mapp gas cost around $11.00. The handy Flux cost about $8.00 and the SIL FOS5 rods are about $2.50 each. The main complaint with this unit is that the oxygen life is limited.

You will also require at least two fire bricks to work on and some pieces of metal or large bolts to help keep your work in place while brazing. The fire bricks can be obtained at a store which sells wood stoves,etc.

I have used silver solder brazing to join 1/8" steel sq. rod to 1/8" steel sq. rod ; 1/8" sq. steel rod to sheet steel ; 3/32 " diameter drill rod to 1/8" sq. steel rod; sheet steel to copper plate; 1/8" sq. brass rod to 1/8" brass rod, etc. Most of the brazing I do is joining at right angles. So to join 1/8" sq rod to another piece at right angles ( like a "T" ), file one end to a slight chamfer. This end will connect to the top of the "T". By doing this it provides more filler at the joint and you can file the excess away to make a neater looking joint. The resulting joint filler from the SIL FOS5 rod will be difficult to file due to it's hardness. A very strong joint will be made.

Do not get this method of joining metals confused with "soft soldering". Soft solder contains high amounts of soft metals like tin and lead. Soft solder will bridge a gap, whereas with silver solder brazing, the joints should be tight. Soft soldering (without lead) is used to solder household copper piping together where the leak-preventing qualities of soft solder are more important than the strength of the joint. A propane torch is normally used for soft soldering.

Here are a few more rules to follow:

• Clean all surfaces with emery cloth and ensure they are free from grease or oil
• Support the items to be brazed, so you have clear access, and they will not move.
• Have everything ready and in place before lighting the torch
• Always clean your hands after brazing
• Always wear protective clothing and protective welding goggles
• Practice on small pieces of similar metal first
• Read the instruction manual that comes with the torch
• Become very familiar with the lighting and shut-off procedure
• Don't light torch until you are ready to use it, to save oxygen
• Be sure torch is pointed in a safe direction before lighting it.
• Keep combustibles away
• Have a fire extinguisher or bucket of water near the torch
• Work only in a well ventilated area
• Avoid contact of flux with skin or eyes
• Use firebrick to work on, not ordinary brick or concrete which can explode
• Metals and brazing rod to be fluxed
• Have spare tank of Mapp gas and ESPECIALLY Oxygen, on hand
• Best to allow welded joint to cool slowly and naturally

SIL-FOS5 brazing rods have a unique characteristic called "Flow Point". The flow point is designed as the temperature at which the filler metal is fluid enough to capillary through a joint even though not completely liquid.

SIL-FOS 5 brazing rod is designed primarily for applications where close fit-ups cannot be maintained. It has the ability to fill gaps and form fillets without adversely affecting joint strength. Recommended joint clearence: .002" to .005".

There are many different kinds of flux and brazing rods, and this is why I recommend you talk to a sales representitive at a welding supply store. As I said before, I have had excellent results with the Handy Flux and SIL-FOS 5 rods.

It is very important the metal you are brazing is clean. The capillary action of the filler rod into the joint will not work properly if the metal is "contaminated". If this contamination remains, it will form a barrier between the metal surfaces and the brazing filler. Clean any oil and grease off first. Then use an abrasive like emery cloth to further clean the metal. It is a good idea to flux and braze the metal as soon as possible after cleaning. That way, there's less chance of contamination of surfaces by handling, etc.

Flux has special chemicals that clean and prevent freshly cleaned metal from oxidizing. Corrosion is a form of advanced oxidation, and oxidation starts within minutes after metal has been sanded, filed or cleaned.

The use of flux is essential in the brazing process, since heating a metal accelerates the formation of oxides, the chemical combination between the hot metal and the oxygen in the air. These oxides must be prevented from forming or they will inhibit the brazing filler from wetting and bonding to the surfaces. The flux not only forms a barrier from the air, but the flux will also dissolve and absorb any oxides that form during the heating, or that were not completely removed during the cleaning process.

Don't skimp on the flux. It's insurance against oxidation, and an insufficient amount of flux will quickly become saturated and lose it's 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 braze joint is completed.

Flux can also act as a temperature indicator, minimizing the chance of overheating the metal. Handy Flux becomes completely clear and active at 1100 deg F. At this temperature, it looks like water and reveals the bright metal surface underneath, telling you that the metal is just about hot enough to melt the brazing filler.

Handy Flux Paste is an all purpose, low temperature flux for use in brazing both ferrous and non ferrous metals and alloys. It comes in a 227g. plastic jar, and the part number is 73-105. Thin some flux in a small container with water and apply with a small brush or screwdriver.

Silver brazing is probably the most versatile method of metal joining today. Brazed joints are strong, and on non ferrous metals and steels, the tensile strength of a properly made joint will often exceed that of the metals joined. Brazed joints are ductile, able to withstand considerable shock and vibration, and brazing is ideally suited to the joining of dissimilar metals. Brazing does not fuse the metals, but joines them by creating a metallurgical bond between the filler metal and the surfaces of the two metals being joined.

The principle by which the filler metal is drawn through the joint to create this bond is capillary action. In a brazing operation, you apply heat broadly to the base metals. The filler metal is then brought into contact with the heated parts. It is melted instantly by the heat in the base metals and drawn by capillary action completely through the joint.

Now you have everything in place and we are ready to do the actual brazing. The metal parts have been cleaned and flux applied to the metal and to the end of the brazing rod. The basic method of igniting the torch is to slightly crack the gas valve and ignite with a spark lighter. Open the oygen valve slowly and adjust the flame as per instructions with the torch kit. There are different flames, so adjust for the brazing flame. If the flame should go out, turn off the oxygen then the gas, and start over.

With the brazing flame, proceed to heat the two metal parts. The flux will become transparent at 1100 deg F. and the SIL-FOS 5 filler metal melting point is 1185 deg F and it's flow point is 1495 deg F. Heat the metal assembly as quickly as possible to a dark cherry red colour, then apply the SIL-FOS 5 rod to the joint area. If the temperature is correct, the solder will flow almost immediately into the joint. If the heat is too low, the solder will just stick to the surface and not flow, and more heat will be required to melt it. This usually results in too much solder being used, and will have to be filed or ground down later. Heating the joint should be done quickly, otherwise the flux will burn off and fire scale will form. When you apply the solder, make sure it touches both sides of the joint so it will flow into the joint better. Always remember to heat the metal first, then touch it to the heated assembly. Do not heat the solder first. Also, the molten filler metal tends to flow toward areas of higher temperature. If the metals you are joining are for example copper and steel, you will need to apply heat to the steel first then apply less heat to the copper. Also when brazing a thick and thin piece of metal together, heat the thick piece, to prevent burning a hole in the thin piece.

Once you are satisfied with the brazed joint, turn off the oxygen valve, then the gas valve. Wait for the part to cool down, then clean the residual flux on the joint with hot water. File or grind the joint if necessary.

Silver brazing is not an easy skill. It will take patience and practice to master. If you know someone who is skilled at brazing, ask for their assistance, until you are confident enough to do the brazing yourself.

Remember to read and understand the instructions which come with your torch kit, before lighting the torch.

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