Building a Reverberatory Furnace in Adobe, Stone & Wood

Building a Reverberatory Furnace in Adobe, Stone & Wood

The building of reverberatory furnaces (Fortschaufelungsofen) where ordinary brick, fire-brick and iron are comparatively cheap, is quite a different matter from the building of such furnaces in isolated camps, where proper material is only to be obtained at high cost and with long delays. Time is always a large factor in metallurgical operations, and the metallurgist may find himself in a position where it becomes necessary to erect apparatus and have it running in less time than it would take to obtain material from outside. It is here that he must make use of makeshifts.

In Mexico, one of the most important of these is the all useful adobe. Employed from prehistoric times, it still has its sphere of application in a surprisingly large number of instances requiring an article that can be quickly and cheaply produced.

It is quite possible to erect serviceable reverberatory furnaces with no other materials than adobes, stone and wood.

The old Mexican smelting shaft-furnace was an example of what can be done with adobes, and the large number of ruins of this class of furnace scattered through the mining districts of Mexico are silent testimony to the genius of a people who demonstrated their capability of adapting material at hand to their needs.

The present paper will describe briefly the construction of an adobe reverberatory furnace which is giving good results, can be quickly erected at a low cost, and, if properly built and handled, will last a long time.

The material being simply sun-dried, it naturally follows that the construction must be quite heavy. The adobes should be evenly made, with just sufficient straw to hold them together, and not too large in size (9 in. wide, 18 in. long and 4 in. thick is very convenient). The binding-material should be of the same clay as the adobes.

The drawings explain themselves. Fig. 1 is a ground-plan



through the lower hearths; Fig. 2 a longitudinal section; and Fig. 3 a cross-section.

The furnace is double-decked, with three hearths on each deck and an auxiliary fire-place for the upper deck. It is designed for wood firing and chloridizing roasting, and is operated entirely by manual labor.

The ore is charged through a hole in the roof, worked in charges of 1200 kilos, and finally drawn through the last rabbling door into wheelbarrows, to go to the cooling-floor.

Naturally, different ores and conditions would suggest other modes of building and manipulation; but the object of this paper is, simply to show this particular furnace as it is.

The hearths are 10 by 10 ft. in size, with 3-ft. walls, making the furnace 16 ft. wide and about 41 ft. long. The arch springs 9 in. above the hearth floor, and has a 12 in. rise.

The foundation is of stone, well-built on a solid footing, and carried up to the first set of buck-stay rods. These 1-in. iron


rods are placed in pipes or channels, to prevent their burning out, and to permit them to be easily changed if necessary.

The outside walls of adobe are now built up to the top of the lower skew-back, when the floor of the hearth, which consists of a “ fire-stone ” set in clay, is put in. Each hearth is stepped a few inches lower than the preceding one.

The center (of dirt) for the arch is now put in, and curved to templates. A 10-ft. span of arch should not have less than 12 in. rise. When the center has been satisfactorily placed the skew-back is cut, and the arch is built of “ arch ’’adobes, placed upright, and making an 18-in. arch. This arch should be carefully built, using as little mud (made from screened clay) for joints as possible, and hammering adobes in place with a block of wood.

After the arch has been well keyed, the middle buck-stay rods of 1-in. iron are placed in pipes just over it, and the walls are carried up to the top of the skew-back of the upper arch; the upper hearth-floor is put in; the center is placed as before; and the upper arch is built of the same size as the lower one. The upper rods of 1-in. iron, just over the upper arch, need not be put in pipes; however, it is convenient to do so. The top of the furnace is paved with flagstones.

The buck-stays of 10 by 10 in. timbers are now put on; the rods are tightened thoroughly; and the centers are removed by boys, getting into the furnace through the fire-box, after this has been cleaned out.

A light fire is started and kept going one day in the lower firebox, and then in the auxiliary one; the lower fire being increased. After three days of gradually increased firing, during which time steam and water are likely to appear in a few cracks, and the rods are occasionally tightened, a charge of ore is put on each hearth. The sulphur, soon igniting, will in a day or two, with proper firing, bring the furnace up to a temperature sufficient to begin operations. Some 4 or 5 days more are required, however, before the furnace is properly heated, owing to the enormous body of adobe-work that must be brought up to proper temperature.

The rods must be looked after to see that they are kept tight, or, if they burn out, that they be replaced. The enormous weight of the arches will cause their gradual sinking, if not properly held, but they sink very slowly and give abundant notice.