Forge Work

by William L. Ilgen

Both of these and all interior portions that come in contact with the heat and metal are constructed of fire brick. The bridges are built over hollow iron castings, through the openings of which there is a circulation of water provided to keep them cool. The bottom of the hearth is formed of iron plates rabbeted together; this and the sides are sometimes provided also with hollow castings for water circulation.

The hearth is lined with blue billy and the sides with bulldog. The former is a fusible silicate, chiefly ferric oxide, and is produced from tap cinder; it does not readily unite with silica when heated. Bulldog is made from burnt pyrites, a quality of ore used for the manufacture of sulphuric acid; the resulting oxide is sometimes called blue billy, but more frequently bulldog, to distinguish it from the former class of oxides. Both of these linings are known as fettlings.

The flue slopes down toward the stack; the draft is regulated with a damper, located in the top and connected by a chain, which hangs within reach of the operators. Various forms of furnaces are used, such as stationary and rolling furnaces; but whatever the style of furnace, the process is based on the decarbonization of the metal, and the charge of pig iron does not come in direct contact with the fuel, as in the open-hearth process. An advantage gained in using the puddling furnace is that various kinds of fuel can be employed without injury to the product of iron, also various labor-saving devices, which have recently been invented, can be better used.

In the pig-boiling process the furnace is first lined with the fettlings and charged with about 500 pounds of white foundry or forge pig iron. The refining process is divided into four distinct stages known as melting down, mixing, boiling, and balling.

A very high temperature is desired during the first stage, which usually lasts about thirty-five minutes. During this time the melting down occurs, and a partial removal of the silicon from the pig iron is effected.

In the second or mixing stage, which lasts about seven minutes, a comparatively low temperature is maintained by lowering the damper in the stack, while the charge is being thoroughly mixed with the oxidizing fluxes or cinders that are added. The puddler draws down the metal from around the sides into the center, where it will become more rapidly refined and mixed.

During the third or boiling stage the damper is raised to increase the temperature. At this time a violent reaction occurs, caused by the release of carbonic oxide, which is formed when the oxygen unites with the carbon in the pig iron. The gas escapes through the slag on the surface of the metal, thus causing it to appear as though it were boiling, from which action the process derives its name. During this stage, which lasts from twenty to twenty-five minutes, a large portion of the manganese, sulphur, and phosphorus contained in the pig iron is removed.

The oxidation is assisted by the constant stirring or rabbling of the metal by the puddler, done for the purpose of bringing it under the oxidizing influence of the air. The boiling gradually ceases, and the surface of the charge “drops,” as it is called, and the whole mass lies in a pasty state on the bed of the furnace, where it is worked by the puddler as thoroughly as possible so as to allow the flames to pass uniformly over it.

The fourth or balling stage requires from fifteen to twenty minutes. This consists of breaking up the contents into balls weighing from 60 to 80 pounds each. After they have been formed, they are rolled near the fire bridge to receive a final welding heat before they are removed to the squeezer, or hammer, where the slag is expelled and the bloom formed.