An Introduction to Brazing
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An Introduction to Brazing

How brazing differs from silver soldering and welding

Brazing has always been one of the most versatile and useful methods to join metals but until recent years, the equipment was bulky and expensive. Back in the days when I started brazing and welding metals one could expect to pay $500 or more just for the torch, tips, hoses and gauges. Then one would have to put out several hundred dollars mores for the tanks and the acetylene and oxygen gasses.

Today one can get started with a MAPP gas/Oxygen torch set that will cost less than $80. The Benzomatic Oxygen MAPP gas brazing/welding/cutting torch 2V8 is a good starter rig. Granted this outfit doesn’t have the brazing/welding/cutting capacity of a full size oxy-acetylene rig but it perfectly capable of cutting metals up to ¼” thick. It’s perfect for the hobbyist and occasional metal worker. Besides the Benzomatic torch set you will need the following basic tools and supplies

  1.  Wire brush (hand or powered) for cleaning the metal
  2.  Emery cloth for cleaning and prepping the metal
  3.  Assorted clamps for securing the metal parts to be brazed
  4.  Hacksaw (hand or powered)
  5. Brazing rods
  6. Brazing flux
  7. Flux filler rods
  8. Goggles
  9. Welding gloves

Before I get into how brazing is different from soldering, silver soldering and welding, I want to spend a few minutes talking about general safety practices when using a torch. I may have covered some of these rules in my article on working with copper pipes and in my article on silver soldering but a little refresher never hurt anyone.

1. Read the instruction manual that comes with your torch. The instruction booklet that comes with the 2V8 gives detailed instructions on how to set the torch up and how to adjust the flame for various soldering, brazing, welding and cutting tasks. Do not attempt to use the torch before reading the instructions

2. This may seem like common sense but I feel compelled to mention this safety rules because, as someone once said, “common sense is the most uncommon thing in the world.” Always keep torches out of the reach of children; never use them to light a cigarette; and never point them at anyone

3. Always disconnect the torch from the fuel tanks when not in use

4. Never attempt to modify a torch or used it with fuels that it was not designed to be used with

5. Be especially careful when using a torch on a bright sunny day because the bright sunlight can make the flame invisible

6. Be especially careful when using a torch in a windy environment because the wind can carry the flame back towards you, the hoses, or towards some other flammable substance

7. When using a torch near combustible materials, like a wood wall or wood framing members, use a heat shield

8. Never use a damaged or leaking torch

9. Always wear goggles having an ANSI Z87.1 1979 shade No.4 or No.5 lens when brazing

10. Always work in a well-ventilated area. Always avoid inhaling the fumes from the flux rods and the fumes given of by the metal being brazed. Wear a respirator if necessary

11. Avoid skin contact with the flux

12. Always place your work piece on fire bricks or some other noncombustible material

13. Always wear welding gloves and other protective clothing

14. Never ever, use a torch to repair a gas tank or some other container that held combustible materials. Gas tanks can be repaired but it’s best left to the professionals who have the proper equipment to pressurize them with nitrogen gas before welding or brazing them. Nitrogen is a combustion suppressor

15. Always have a fire extinguisher close at hand

16. Never use a torch with the tank setting at less than a 60 degree angle

How does brazing differ from welding

Unlike welding, brazing doesn’t involve melting the base metal, the metal being joined, therefore it’s performed at much lower temperatures. Brazing temperatures vary in the range of 1150°F to 1600°F (620°C to 870°C) whereas when welding the temperatures vary from 1981°F to 2500°F (1083°C to 1370°C). Welding joins the work pieces by melting the base metals and then fusing the two pieces together. Brazing, on the other hand join the work pieces by creating a metallurgical bridge between the filler rod material and the two work pieces being joined. In brazing, the heat is applied directly to the base metals. When the base metal is at the proper temperature the filler metal rod is touched to the metal where it immediately melts and it’s drawn into the joint by capillary action. In that respect brazing is quite similar to the silver soldering process where the silver solder is drawn into the joint by capillary action.

The advantages of a brazed joint

1. A brazed joint, like a properly welded joint, is a great deal stronger than a silver solder joint. When properly brazed a joint is as strong as the base metal itself, and in many cases the joint can be stronger than the base metal

2. Since the base metals doesn’t melt during the brazing process there’s less chance of causing irreparable damage to metals being joined

3. Unlike welding, most people can master the basics after only a few hours of practice whereas with welding it can take days or weeks to master the basics

4. Brazing requires less expensive equipment

5. Brazed joints are much neater appearing than welded joints

Hands-on practice

Before tackling an actual repair job get in a few hours practice using scrap metal that can be found around your shop or purchased at a salvage yard. Start with a few pieces of 1/8” scrap boilerplate (sheet iron). Make several different joints during practice. Join two pieces in the same plane. Join two pieces so one is perpendicular to the other. I’ll walk you through the first one. Then you are on your own to learn at your own pace.

1. Clean both pieces of metal to be joined with a wire brush or emery paper. Dirty metal cannot be brazed properly

2. Clamp the two cleaned work pieces tightly together making the seam to be brazed as tiny as possible. Double check the alignment and tightness before proceeding because once the metal is heated it will be too hot to make any kind of adjustments

3. Light and adjust the flame of your torch according to the instructions that came with it. The flame should be small

4. Holding the torch tip 1” from the metal, begin heating while moving the torch tip in a circular motion

5. After heating the joint for a few seconds, use a flux rod to sprinkle flux over the area to be joined. This flux will remove all the oxides from the metal

6. When the metal has reached the proper temperature to be brazed, it and the flame will glow a dull red

7. Touch the metal filler rod to the metal and direct the flame ahead of the melting rod

8. Continue heating the joint evenly, moving the flame in a zigzag pattern while depositing flux until the two pieces mold together

9. After the pieces cools, chip away the excess hardened flux

After making a few practice runs on scrap, you should be ready for your first real project.


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Comments (2)

Yes, Clairsie, you do run the rod all the way around the outside of round pieces to be joined because because you want an even bond/bridge covering the exposed break of the metal. It looks neater and the joint has greater strength when the outer bead runs completely around the work piece.. Capillary action will assure that the metal completely bonds between the two mating pieces. As for Sy's article, "The Mystical Donut," I can honestly tell you that I didn't read it. My article was prompted by my wife bringing the holiday to my attention and by my desire to write something different at that moment in time when I wrote it. I'll have to read it now, especially since I don't believe in all that mystic stuff.

Good morning Clairsie. Glad I could be of help. My wife never knows what to get me for Father's Day either. The way we solved that problem is I give her a sales flier from some place like Harbor Freight with a bunch of stuff circled and tell her to surprise me. That way she knows what I could use in or around the shop and she still gets to surprise me. That Benzomatic torch set will be a great Father's Day gift. I have a full size rig but I also have one of those Benzomatic rigs which gets a lot of use when I'm working in tight quarters.