INDUSTRIAL TECHNOLOGY-METAL ASSOCIATED THEORY

1. INDUSTRIAL TECHNOLOGY-METALASSOCIATED THEORY TOPIC 5. WELDING & BRAZING SAFETY PRECAUTIONS ELECTRIC ARC WELDING WELDING EQUIPMENT WELDING & BRAZING BLOWPIPE GAS FUSION WELDING BRAZING

2. WELDING EQUIPMENT After steel components have been cut and shaped they can be joined together. This is known as fabrication. It may be achieved by using mechanical fasteners, such as bolts & rivets, or the parts may be joined together by various soldering and welding methods. All of these processes involve heating the metals to be joined, the varying, according to the particular process. The heat may be applied by the burning of or by using Compressed gases are kept in strong steel–walled They are rented from gas companies, who are responsible for and the cylinders on a regular basis to guarantee their safety. temperature GAS WELDING EQUIPMENT gases electricity. Spark arrestor cylinders. This safety device is fitted between the hose and the blowpipe. filling testing

3. SAFETY PRECAUTIONS The cylinders are available in several sizes, e.g., , and each cylinder is colour coded to indicate the type of gas they contain. The threads on fuel gas fittings are handed and the threads on non-fuel gas fittings are handed. What precautions should be taken with cylinders?  What particular precautions should be taken with oxygen cylinders? What particular precautions should be taken with acetylene cylinders? Cylinder taps should only be turned on   turn to enable them to be turned off quickly in an emergency. Hoses and fittings should be checked  regularly for and wear & tear. E or D Cylinders should be chained upright. Valves must be closed when not in use. left right Keep oil away from oxygen fittings. Contents gauge Pressure gauge Acetylene bottles must remain upright. Adjusting knob one full Hose connection damage Cylinder connection

4. WELDING & BRAZING BLOWPIPE Handle Tip Mixing chamber Fuel valve Oxygen valve CARBURISING FLAME Lighting the Blowpipe • Point the tip upwards and away from flammable objects. • Turn on the fuel and light with a flint. • Slowly open the oxygen valve and adjust to a neutral flame. feather NEUTRAL FLAME Small cone OXIDISING FLAME ALWAYS WEAR GOGGLES WHEN USING THE BLOWPIPE

5. BRAZING Clear goggles are suitable when brazing. Brazing (also known as bronze welding) is a non fusion weldingprocess.This is because the parent metals do not melt, only the metal.  Brazing is a popular method of joining metals, and thin metals. It does not require as much heat as welding. Describe the preparation needed to make a successful brazed joint. What is the filler rod used for brazing, at what temperature does it melt, and how does it work. How do you know when the parent metal is hot enough to apply the filler rod? What purpose does the flux perform? filler dissimilar Tobin bronze melts above 5500 and flows into the grain boundaries of the parent metal. • Shape the parts to be brazed so they are a good “fit”. • Clean the metal in the vicinity of the join with abrasive cloth. • Apply a suitable flux where the filler is to be applied. When it is dull red it will melt the bronze as it is touched to the joint. It cleans the metal and prevents further corrosion.

6. GAS FUSION WELDING Describe the procedure for lighting the oxy-acetylene torch. Gas fusion welding requires temperatures than brazing because the parent metal melts as well as the filler metal. For this reason oxy-acetylene equipment is used. The parent metal and the metal must be the  composition. What type of eye protection should be used when gas fusion welding? • Point the tip upwards and away from flammable objects. • Turn on the fuel and light with a flint. • Slowly open the oxygen valve and adjust to a neutral flame. higher filler same 50kPa 50kPa Approved shaded welding goggles protect the eyes against sparks, heat and bright light. Oxygen Acetylene

7. GAS FUSION WELDING Filler rod blowpipe GAS WELDING A BUTT JOIN

8. ELECTRIC ARC WELDING This type of welding uses electricity to melt the parent metal and a filler metal. A transformer converts the mains power supply by the voltage, and the amperage. decreasing increasing +ive transformer • SAFETY • Use a full-faced helmet with the correct shaded lens. • Cover unprotected skin to avoid burn from ultraviolet rays. • Avoid welding in damp conditions. • Shield your work from other workers, children and pets. -ive What function does the flux coating on the welding electrode/rod perform? It prevents oxidisation of the metal during the welding process.

9. ELECTRIC ARC WELDING DOWN-HAND ARC WELDING THE FOUR MAIN VARIABLES TO A SUCCESSFUL WELD Core wire Flux coating Gaseous shield • The Amperage. In general, the higher the amperage the higher the temperature. • Angle of Rod. This will influence the depth of penetration and the effective strength. • Speed of Traverse. If the rod is moved too quickly the parent metal will not melt sufficiently. • Length of the Arc. A shorter arc produces a neater, penetrating weld with minimal distortion. Arc stream slag Molten pool CROSS-SECTIONAL VIEW 200-300 Tack weld electrode Tack weld PICTORIAL VIEW