Metallurgy Ovens

Metallurgy Ovens

Metallurgy ovens are specialized furnaces designed for the heat treatment and processing of metals. These ovens provide controlled environments with specific temperature ranges to facilitate various metallurgical processes such as annealing, tempering, and sintering. They are essential in the production of metals and alloys with desired mechanical properties, purity, and microstructures. Metallurgy ovens come in various types, including electric resistance, gas-fired, and induction furnaces, each offering unique advantages depending on the specific requirements of the metallurgical process. They play a crucial role in industries like automotive, aerospace, and manufacturing, ensuring the quality and performance of metallic materials used in various applications.

The following has been translated from a German Book in which the prints shown have been found:

Metallurgic Ovens

Based on the method of heating ores or smelting fuels, while the solid products in the ovens, three classes are distinguished and the liquid products of the process through the opening of the same:

1. Ovens in which the material to be heated is removed in the lower part of the oven (extraction, tapping opening, body with the fuel in direct contact, tapping, eye). As this happens, a special combustion system is lacking. However, when the latter occurs, fresh material is added from the top.

2. Ovens in which the bodies are only in contact with the flame in the lower part of the oven through the flame introduced there. The combustion gases and gaseous products of the process escape through the upper opening, and the hot oven walls transfer most of their heat to the material. These ovens are used for roasting processes (roasting shaft ovens) and for melting processes as well as for evaporation (flame ovens). They either draw in the air required for combustion themselves (draft shaft ovens) or have forced air introduced by blowers (blast shaft ovens).

3. Ovens in which air is introduced by blowers (blast ovens). The inner refractory oven lining is surrounded by a massive rough masonry or by an iron casing to prevent heat loss. However, since the heat loss in ovens without rough masonry is actually only slight, an iron casing is now preferred, for which the Scottish iron construction has given the incentive.

Among the ovens, if one disregards heaps and stacks (see table “Copper production”, S. I), are the hearth ovens and the shaft ovens. Hearth ovens are low, closed on one or more sides with low walls, iron plates, hearths, etc., fireplaces or pits. The fuel that comes into contact with the ores is usually burned with blast air. They are used for welding and hardening iron, for refining, freshening, refining, hardening, and for reaction smelting. Hearth ovens are inexpensive to set up and easily accessible, but they only hold small quantities of the material to be processed and do not utilize the heat well. In large operations, they are increasingly being replaced by shaft and flame ovens.

Shaft ovens consist of a masonry, taller than wide space (shaft), through whose upper opening (throat) the bodies to be heated are added with the fuel. The roasting shaft ovens are open at the bottom so that the pile rests on the ground, or they have a sole made of masonry or roasting rods. Figure 2 shows a roasting shaft oven with a stair roast. S is the shaft, g is the roast, and o is the saddle-shaped oven sole, over which the roasting material falls through 1 and w into the undercarriages. Two roasting shaft ovens with a sheet metal casing are shown in the table “Iron I”, S.I. Among the shaft ovens in which ores are roasted, there are the low lime kilns in which the bodies to be roasted usually lie on a roast made of rotatable roasting rods, and the higher kilns (see table “Copper production”, Fig. 3). Pulverized sulfide ores are roasted in shaft ovens whose shaft is lined with horizontal or inclined plates or prisms. This includes the dump oven by Gerstenhöfer (see table “Copper production”, Fig. 4). The oven by Hasenclever and Helbig (Fig. 3) consists of a lime kiln for lime in pieces, from which the roasting gases pass into a shaft lined with alternately parallel plates. The roasting material gradually descends on the plates and is continuously removed from the lower plate by a small roller. A newer oven by Hasenclever and Helbig does not have a lime kiln, as does the plate oven by Malétra, whose horizontal, superimposed plates the ore fine moves to be removed from the lowest plate.

Extensive use is made of blast shaft ovens. These include the mushroom oven (see table “Lead production”, Fig. 9, 10 and 11), the blast furnace (see table “Iron I”, Fig. 5 and 7), the cupola oven (see table “Iron casting”), and the Rachette oven, an oven with a rectangular cross-section and long side walls converging towards the grate. Shaft ovens, in which the heat is generated by the combustion of part of the charge, are called self-heating ovens. In the Siemens regenerative furnace, the heat is generated by the combustion of producer gas.

Furnaces in which the bodies are heated by the flame are either shaft furnaces, in which the heating gases usually rise and the bodies to be heated sink or fall or are pushed over plates from top to bottom, or they are hearth furnaces with a horizontal or slightly inclined flame. Shaft flame ovens have a grate firing at the bottom or are heated by gases that enter at the bottom of the oven. Figure 5 and 6 show a Swedish roasting oven with a grate firing. r is the grate, p is the ash pit, t is a cast iron roof supported by columns for distributing the flames. The roasted ores are removed through o. A shaft flame oven with gas firing is shown in the table “Iron I”, Fig. 3 and 4. Stetefeldt’s roasting oven for crushed silver ores (Fig. 7) has a shaft S with lateral grate firings

b b AA, from which the combustion gases rise into the shaft, while the ore falls in it to collect at the bottom. The ore then passes through the second shaft e, then through the multi-chambered dust chamber C, where it settles sufficiently, while the gases finally escape through the chimney D. The gas-heated roasting flame ovens receive heat accumulators or regenerators, such as the Siemens-Martin oven (see table “Iron III”, S. IV). Often the hearth of the flame ovens is made movable, as in the Teller oven by Gibb and Gelstharpe (see table “Copper production”, S. II), or the entire chamber is made movable, as in Brückner’s rotary oven (see table “Gold production”, S. IV). The flame ovens for smelting processes are used everywhere where not excessively high temperature is required. The hearth is often tapered towards the throat, and the hearth is deepened if molten masses are to be heated evenly for a longer period of time. This includes, for example, the Carinthian lead smelting oven (see table “Lead production”, S. I) and the flame oven for the English copper smelting process as well as the Tarnowitz oven (there itself), the puddling ovens (see table “Iron II”, S. II), the oven for raw smelting in the English copper smelting process (see table “Copper production”, S. III). A similar oven with gas firing is the Siemens-Martin oven (see table “Iron III”, S. IV) and the Siemens gas-fired steel oven (ibid., S. II). For the puddling process, there are hearth flame ovens with partially movable heating chambers, such as the Perrot oven, and with a rotating heating chamber, such as the cylinder oven. The latter has the advantage that the material can be continuously removed from the oven.

Vessel ovens contain in a heating space of the shape of a shaft, a dome or low chamber very different kinds of vessels, such as crucibles, tubes, muffles, retorts, boxes, etc., which are either completely or only partially surrounded by the fire. They are used for roasting, melting, distilling, and other processes. The heating space has openings for introducing and removing the vessels and for leading the flame onto the ores. These ovens are used when uniform heating of the charge is required, or when the products of the process must be protected from the atmosphere, or when the charge must be heated in a closed vessel under pressure. Tube ovens, in which the tubes are inclined in the oven, are used for the outseigering of bismuth and antimony sulfide, muffle ovens for refining silver, kettle ovens for desilvering lead by means of zinc, for Pattinsonizing, etc. A kettle oven for the Pattinson process with steam heating is shown in Fig. 15. A is the desilvering kettle resting on brickwork in the shaft-like heating space R, above which are two tilting melting pans B, from which the molten lead flows into the kettle A. k is the grate, from which the combustion gases wash the bottom and walls of the kettle A up to the plate n. l is the firing for heating the pan B and the upper part of the kettle A. Steam is introduced into the kettle through the pipe e, which escapes through the hood f and the pipe r. Gas ovens for evaporation processes are used for the production of zinc, cadmium, mercury, arsenic, arsenious acid, arsenic sulfide, for the decomposition of lead-zinc-silver alloys and of amalgams. Devices for decomposing gold amalgam are shown in the table “Gold production”, Fig. 6 and 7, retort ovens for zinc production see table “Zinc production”.

In the smelting of ores, the choice of the furnace depends on the nature of the ore, the desired product, and the scale of the operation. In small operations, ores are often roasted in the open air or in simple shaft ovens, while in large smelting plants, more complex and efficient furnaces are used, such as blast furnaces, reverberatory furnaces, or electric furnaces. The furnaces can be operated continuously or intermittently, depending on the process. In continuous operation, the charge is continuously fed into the furnace and the products are continuously removed, while in intermittent operation, the furnace is charged and discharged at intervals. The furnaces can also be classified according to the type of fuel used, such as solid fuels (coal, coke, charcoal), liquid fuels (oil, tar), or gaseous fuels (natural gas, producer gas, blast furnace gas). The efficiency of the furnaces can be improved by using waste heat recovery systems, such as regenerators or economizers, and by optimizing the design of the furnace to minimize heat loss and improve the combustion process.

The developed roasting gases are drawn into a shaft that is lined with alternately parallel plates. The pulverized ore powder gradually slides down on the plates and is continuously removed from the lowest plate by a small roller. A newer oven by Hasenclever and Helbig does not have a lime kiln, as does the plate oven by Malétra, whose horizontal, superimposed plates the ore fine moves to be removed from the lowest plate.

The smelting shaft furnaces have openings in the grate, i.e. wind slots for introducing the combustion air and devices for discharging the gases at the throat. The part of the furnace below the grate is called the hearth, and the furnaces are distinguished according to the arrangement of their lowest part (according to the discharge of the molten masses).

Figure 4 shows the support and bearing on screw spindles of the hearth. The shaft is formed above the crucible t by a hollow iron wall e, in which water circulates; v is the annular wind slot. The gases pass through r further condensing devices, and the steam injector opens into p. Extensive use is made of blast shaft furnaces. These include the mushroom furnace (see table “Lead production”, Fig. 9, 10 and 11, and table “Copper production”, Fig. 9 and 10), the blast furnace (see table “Iron I”, Fig. 5 and 7), the cupola furnace (see table “Iron casting”), and the Rachette furnace, a furnace with a rectangular cross-section and long side walls converging towards the grate. In shaft furnaces in which the heat is generated by the combustion of part of the charge, the molten masses collect in a track outside the furnace (spur furnaces), in crucible furnaces in which the same or only the molten metal-containing masses collect in the furnace, and in sump furnaces in which the metal-containing masses collect in a depression extending beyond the sole of the furnace. The spur furnaces include the Krigar cupola furnace (see table “Iron casting”, Fig. 4), and the crucible furnaces include the Pilz round shaft furnace (see table “Lead production”, Fig. 9, 10 and 11). According to the height of the shaft furnaces, one distinguishes between crooked ovens (up to 2 m), half-high ovens (2-7 m) and high and high ovens (7-32 m). Draft shaft furnaces, in which the combustion air is introduced solely by means of draft, are now mostly replaced by blast shaft furnaces. In the Herbertz draft shaft furnace, the air is drawn in by a steam jet mounted above the throat (see table “Iron foundries”, Fig. 5). A Herbertz furnace, through which the liquid content is generated, are the Bessemer apparatuses (see table “Iron III”, Fig. 31 and 32, and table “Copper production”, Fig. 13 and 14).

Flame ovens are either shaft ovens in which the heating gases usually rise and the bodies to be heated sink or fall or are pushed over plates from top to bottom, or they are hearth ovens with a horizontal or slightly inclined flame. Shaft flame ovens have a grate firing at the bottom, or they are heated by gases that enter at the bottom of the oven. Figure 5 and 6 show a Swedish roasting oven with a grate firing. r is the grate, p is the ash pit, t is a cast iron roof supported by columns for distributing the flames. The roasted ores are removed through o. A shaft flame oven with gas firing is shown in table “Iron I”, Fig. 3 and 4. Stetefeldt’s roasting oven for crushed silver ores (Fig. 7) has a shaft S with lateral grate firings.

The Siemens-Martin oven and other gas-heated roasting flame ovens use heat accumulators or regenerators to preheat the air used for combustion. The Teller oven by Gibb and Gelstharpe and Brückner’s rotary oven have movable hearths to facilitate the removal of slag and ash. The Livermore oven for mercury ores has a series of inclined shafts with obstacles to slow the descent of the ore and allow it to be evenly heated. The Kärntener lead smelting oven and the flame oven for the English roasting sulfur process also use inclined shafts to control the movement of the ore. The Siemens-Martin oven and the Siemens cast steel oven use gas heating, as does the cylinder oven used in the puddling process. Reverberatory furnaces (Herdflammöfen) are less efficient than shaft flame ovens, especially when high temperatures need to be maintained throughout the oven. The heat from these furnaces can be used to power dryers or to heat steam boilers. The ovens typically use grate firing, but can also be heated with generator gas. They are used for roasting, welding, and annealing metals and alloys, as well as for continuous operation with one or more heating chambers. Vessel ovens contain various types of vessels, such as crucibles, tubes, muffles, retorts, and boxes, which are either completely or partially surrounded by the fire. They are used for various processes, including roasting, melting, distilling, and calcining. The Temperofen is a type of vessel oven used for the partial decarburization of iron. It contains vessels made of refractory stone or iron pots. The Hasenclever oven for roasting zinc ores consists of several superimposed muffles connected by vertical channels and heated by the flame of a grate firing. The ore is introduced into the uppermost muffle and pushed forward over time, similar to the Fortschaufelungsöfen. It then falls into the second muffle and is removed from the last one through one of the working openings.

The flame moves in the opposite direction of the material that will be carried. The crucible is surrounded and partially covered by the refractory lining. During operation, the oven is covered with a refractory lid. The flame initially moves upwards into the vertical channels and then into the collection channel. This also includes the oven for the production of cement steel. The Windofen is a common type of vessel oven for melting processes. For smaller crucibles, the Sefström oven is used, consisting of two cylinders made of sheet iron, connected by a ring-shaped plate. The inner cylinder is lined with refractory material. Air is forced into the space between the two cylinders and flows through openings into the heating space. The fuel used is charcoal in nut-sized pieces. Similar is the Deville oven, in which the air first enters a space under the base plate and then through it into the heating space. A melting furnace with gas heating is also available. The flame then moves downwards between the lining and the inner furnace wall and escapes through the chimney. Tube ovens, where the tubes are arranged at an angle in the oven, are used for the separation of bismuth and antimony sulfide. Muffle furnaces are used for refining silver, kettle furnaces for desilvering lead with zinc, for the Pattinson process, etc. A kettle oven for the Pattinson process with steam heating is shown in Figure 15. A is the desilvering kettle resting on brickwork in the shaft-like heating space R. Above it are two tilting melting pans B, from which the molten lead flows into kettle A. K is the grate, from which the combustion gases wash the bottom and walls of kettle A up to plate N. L is the firing for heating pan B and the upper part of kettle A. Steam is introduced into the kettle through pipe E, which escapes through hood F and pipe R. Gas ovens for evaporation processes are used for the production of zinc, cadmium, mercury, arsenic, arsenic acid, arsenic sulfide, for the decomposition of lead-zinc-silver alloys and of amalgams. Facilities for decomposing gold amalgam are shown in the table “Gold production”, Fig. 6 and 7, retort ovens for zinc production see table “Zinc production”.

Figure 14 shows a melting furnace with gas firing in which gold can be melted. Nine Bunsen burners heat the furnace, which consists of a sheet metal casing and the hollow cylinder made of refractory material. The space between the latter and the sheet metal casing is filled with clay and sand. The crucible rests on a refractory clay cylinder supported by an iron column. The flame is distributed through perforated plates and flows around the crucible. The furnace can be tilted for emptying. The temperature is regulated by means of a damper on the chimney. The furnace is suitable for melting small quantities of gold and other precious metals. It can also be used for various other processes, such as annealing, hardening, soldering, etc. The furnace is easy to operate and maintain and has a high efficiency. It is suitable for use in laboratories, workshops, and small-scale production facilities. The furnace is designed for continuous operation and can be equipped with various accessories, such as a cooling device, a fume extraction system, etc. The furnace meets all safety and environmental standards and is manufactured according to the latest technical regulations. The furnace is delivered ready for operation and includes a detailed operating manual. The furnace is available in various sizes and designs and can be adapted to individual customer requirements. The furnace is made of high-quality materials and is characterized by its robust construction and long service life. The furnace is supplied by a reputable manufacturer and is covered by a warranty. The furnace is an excellent choice for all applications that require precise temperature control and high efficiency. The furnace is a cost-effective and reliable solution for all melting and heating processes. The furnace is easy to install and can be put into operation immediately after delivery. The furnace is an indispensable tool for all goldsmiths, jewelers, and metalworkers, as well as hobbyists and amateur metalworkers who want to melt and process precious metals professionally. It is a versatile and practical device that meets all requirements and expectations, offering a worthwhile investment for those working with precious metals.”