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| after forging or welding operations have been | | | | withdrawn from the fire or oven, after |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