Joining parts by welding
Joining metal items to each other by high temperature is called welding. By heating method, welding is gas welding or electric welding. In gas welding a combustible gas (for example acetylene) burns in oxygen and gives heat; the textbook says the flame of an acetylene–oxygen mixture can reach 3150 °C. In electric-arc welding, current from the welding machine creates an electric arc between the electrode and the part; the electrode melts and the molten metal fills the joint. Electrodes have a coating that protects the metal from oxidation. Welding is very dangerous: arc light burns the eyes, sparks and hot metal burn the skin, and gas cylinders can explode. So welding is done only by a specially trained welder in a protective helmet, gloves and work clothes. A child never goes near welding equipment and never looks at the arc.
Safety poster: the group makes a poster on welding hazards (“Don’t look at the arc!”, “Don’t touch the cylinder!”, “Welding – experts only”) using only pencils and coloured paper. Any demonstration is given by a welder in a workshop, with the class standing at a distance behind a shield.