Technology and our changing world high Technology

Review questio ns

1. 
   List three types of sheet-metal seams. Make a sketch of each.
   
2. 
   How can seams be made watertight?
   
3. 
   What tool is used to make agrooved seam?
   

FORGING AND HEAT TREATING
Forging is heating metal and hammering or pressing it into a shape. When metal is hot enough to be shaped in this way, we say that it is plastic. The three major operations in forging are drawing, upsetting, and bending.
Years ago the village blacksmith forged metal by heating it in a coal forge. The blacksmith then shaped it over an anvil by pounding it with a hammer. Tod®/, forging is still one of the major methods used by industry. It is used to shape metal parts when great strength is needed. Forging also improves metal by refining thegrain structure and increasing its strength. Forging in the school shop is more like thatdoneby the blacksmith. You can use forging to shape a chisel or a punch. You can use it also to bend heavy pieces of metal that would bedifficult to bend cold.


EQUIPMENT AND TOOLS
The gas-fired forge is used to heat the workpieces. It has largely rep laced the coal forge used by village blacksmiths. It is much cleaner, easier to take care of, and easier to light than a coal forge.
Th eb la cksmith ’s anvil is used as abase for the hand forging operation.
Blacksmith’s hand hammers are used. These are sledge, ball-peen, straight-peen, and cross-peen hammers.
Blacksmith’s tongs are used to pick up toe hot metal. They are made with curved or flat lips.
The hardy cutter (sometimes called the anvil hardy) is a hot and cold chisel made to fit into toe hardy hole of toe anvil. Metal is cut by placing it over toe cutter and then striking it with ahand hammer.


HEATING METAL
Before heating metal, put on your safety glasses and gloves. To light toe furnace, first open toe air valves slightly. Thai place a piece of lighted papa- near toe gas valve. Open toe valve slowly until toe gas begins to bum. Afta^- a few minutes, turn on more air and gas. The flame should turn into a roaring blast of heat that is almost colorless.
For forging, metal must be red hot. Temperatures for forging range between 1300 and 2000°C F. Low carbon or mild steel requires more heat than tool steel.
Heat toe metal slowly until it is bright red. Forging should be done before toe metal begins to lose its color. Use tongs to hold toe metal. Reheat toe metal as necessary.