| This is the process which relieves all internal strains | | | | be bought which use gas, fuel oils or coal to produce |
| and distortion in the metal and softens it so that it may | | | | the heat and in which the work may be placed on |
| more easily be cut, machined or bent to the required | | | | trays so that the fire will not strike directly on the steel |
| form. In some cases annealing is used only to relieve | | | | being treated. |
| the strains, this being the case after forging or welding | | | | If the work is not very important, it may be withdrawn |
| operations have been performed. In other cases it is | | | | from the fire or oven, after heating to the desired point, |
| only desired to soften the metal sufficiently that it may | | | | and allowed to cool in the air until all traces of red have |
| be handled easily. In some cases both of these things | | | | disappeared when held in a dark place. The work |
| must be accomplished, as after a piece has been | | | | should be held where it is reasonably free from cold air |
| forged and must be machined. No matter what the | | | | currents. If, upon touching a pine stick to the piece |
| object, the procedure is the same. | | | | being annealed, the wood does not smoke, the work |
| The steel to be annealed must first be heated to a dull | | | | may then be cooled in water. |
| red. This heating should be done slowly so that all parts | | | | Better annealing is secured and harder metal may be |
| of the piece have time to reach the same | | | | annealed if the cooling is extended over a number of |
| temperature at very nearly the same time. The piece | | | | hours by placing the work in a bed of |
| may be heated in the forge, but a much better way is | | | | non-heat-conducting material, such as ashes, charred |
| to heat in an oven or furnace of some type where the | | | | bone, asbestos fibre, lime, sand or fire clay. It should be |
| work is protected against air currents, either hot or | | | | well covered with the heat retaining material and |
| cold, and is also protected against the direct action of | | | | allowed to remain until cool. Cooling may be |
| the fire. | | | | accomplished by allowing the fire in an oven or |
| Probably the simplest of all ovens for small tools is | | | | furnace to die down and go out, leaving the work |
| made by placing a piece of ordinary gas pipe in the fire | | | | inside the oven with all openings closed. The greater |
| (Figure 4), and heating until the inside of the pipe is | | | | the time taken for gradual cooling from the red heat, |
| bright red. Parts placed in this pipe, after one end has | | | | the more perfect will be the results of the annealing. |
| been closed, may be brought to the desired heat | | | | While steel is annealed by slow cooling, copper or |
| without danger of cooling draughts or chemical change | | | | brass is annealed by bringing to a low red heat and |
| from the action of the fire. More elaborate ovens may | | | | quickly plunging into cold water. |