Dr. E. B. Prupis, Engineer I. L. Kaplinsky, and Engineer T. S. Karacharov

Air Showering in Open-Hearth Shops¹

From the Dnepropetrovsk All-Union Scientific Research Institute of Occupational Safety in Ferrous Metallurgy and Coke Chemistry (Director: Dr. L. N. Shcheglova)

The use of air showers in open-hearth shops is hampered by the crowding of the shops with transport equipment (cranes, winches, and charging machines), the presence of large quantities of red-hot metal on the working platforms, and the need for substantial space for the main production processes.

For these reasons, it was necessary to abandon the installation at workplaces of ventilation units that direct air onto the surface exposed to radiant heat, as recommended by several authors (Arnautov, Veller, Davydov, and others), and to confine the installation to units that supply air to the entire work area. The effectiveness of such air delivery was confirmed not only by our investigations, conducted

¹ The work was carried out by the occupational health research station at the Moscow “Sickle and Hammer” plant, a branch of the Dnepropetrovsk institute.

not only directly in the workshops, but also by the experimental data of Dr. N. I. London, A. I. Levina, and E. Ya. Zak (Moscow Institute of Occupational Safety of the All-Union Central Council of Trade Unions).

Air Showering of Charging Platforms

Although charging is performed mainly by special machines, certain tasks on the charging platform are carried out by hand. These include feeding in the rabble during metal tapping, operations associated with repairing the furnace, adding supplementary materials, and others. During this work, the workers are 1–2 m from the charging doors. Since the door must be kept open to between one-quarter and three-quarters of its opening, heat radiation reaches 9 cal per cm² per minute. On the days of the survey, the actual air temperature reached 38.4° when the outdoor temperature was 22°; thus, in summer the difference reached 16°.

The operations listed are characteristically intermittent and individually of short duration. Between operations, the steelworkers and their assistants remain on the working platform 2–6 m from the charging doors.

On the basis of these data, the following principles can be recommended for the design and construction of air showers on the charging platform.

Air should be supplied to the charging platform in a concentrated jet perpendicular to, or at an angle to, the longitudinal axis of the furnace. Under no circumstances should the jet be directed away from the furnace or parallel to it, so as to avoid drawing hot gas into the air supplied by the shower.

In workshops where charging platforms are well ventilated by aeration—that is, where there is sufficient air exchange, with used air removed through roof monitors and replaced by outdoor air entering through openings in the longitudinal wall—ventilation units that circulate the room air may be used for air showering. In this case, the shower creates air movement to improve thermoregulation. It is assumed that aeration alone already produces an acceptable temperature difference in the working zone. Where there is a bay with racks for charging boxes, as when charging is performed by crane-mounted machines, we recommend installing stationary air-shower units and attaching them to the columns between the charging platform and the charging-box bay.

A schematic of an air-shower unit on an open-hearth platform is shown in Fig. 1.

The unit consists of a TsAGI No. 10 four-bladed axial fan mounted on a common shaft with an electric motor rated at 2.3 kW and 960 rpm. The unit is mounted in an iron casing 0.7–0.8 m long. To produce a concentrated flow and regulate it in the vertical plane, a nozzle with guide vanes at its outlet is provided downstream of the fan. The nozzle outlet measures \(0.7 \times 1.0\ \text{m}^2\). The total length of the assembled unit is 1.5 m. To achieve an adequate hygienic effect, physiological laboratory studies and workplace observations have established that air velocity under working conditions on open-hearth platforms should range from 5 to 2 m/s, averaging 3–4 m/s.

It should be noted that, for a given unit capacity, its effectiveness in producing maximum air volumes and velocities at the working platform depends primarily on the length of the nozzle. Therefore, where structural conditions permit, the length of the nozzle downstream of the fan should be 1.5–2 times the diameter of the fan casing.

In addition, a flow-straightening grille can be recommended to make the flow more uniform.

On the basis of the principles listed above, eight fans were installed at the Serp i Molot plant in Moscow, in accordance with specifications developed by the branch of the Dnipropetrovsk Institute of Occupational Safety in the Ferrous Metallurgy Industry of the All-Union Central Council of Trade Unions, to supply air to the working platforms at four furnaces.

Fig. 1. Diagram of the air-shower unit on the open-hearth platform at the Serp i Molot plant.

A 4 m wide crane-winch bay is located between the columns and the exterior wall. Outdoor air entering through the window openings in the longitudinal wall is drawn in by the fans and conveyed to the working platform.

Tests of the effectiveness of these units during the summer of 1939 yielded the data presented in Table 1.

Table 1

Effectiveness of air showers on the charging platform of the open-hearth shop, with two fans each supplying 20,000 m³/h of air at a nozzle exit velocity of 12 m/s

It should be noted that in the open-hearth shop of the Serp i Molot plant, unfavorable aeration conditions cause the openings in the longitudinal wall to operate unreliably as air inlets,

As a result, the fans circulate heated air within the shop. Air intake through window openings can therefore be recommended only where aeration is good.

When the shop is equipped with floor-mounted charging machines and there is no aisle for the crane hoist, the units may be installed on special platforms supported by posts along the outside wall, or mounted on the wall columns (the Krasny Oktyabr and Dzerzhinsky plants).

Where openings are available in the lower part of the outside wall, high-capacity portable ventilation units may also be used to provide air showers. The fans must be positioned so that they draw air from a cooler zone. American portable Perkins-type fans installed at the Petrovsky plant in Dnepropetrovsk proved very effective.

When stationary ventilation units are installed, the choice of intake location for the air showers is of considerable importance. In such cases, all local conditions that might cause air contamination must be taken into account.

Depending on the equipment and layout of the shop, the following arrangements for drawing in and conveying outdoor air are possible:

1. The air inlet of the shower unit is located along the outside wall of the building, 2–2.5 m above ground level. The duct is attached to the wall. This arrangement is feasible when the charge is loaded by floor-mounted machines and there is no aisle for the crane hoist.

2. The air inlet of the shower unit is located along the outside wall of the building, 2–2.5 m above ground level. The duct runs through the upper part of the space beneath the open-hearth platform and passes through the floor structure, then follows a column to the discharge nozzle. This arrangement is recommended when a crane-mounted charging machine is used for charging and an aisle is provided for the hoist, provided that the nozzles and their supply ducts do not obstruct the movement of the charging machine.

3. Only in exceptional cases, when routing the duct from below presents very serious difficulties, may air be drawn from above, beneath the shop roof.

4. The air inlet of the shower unit is located at the end of the building, and the duct runs along the outside or inside face of the exterior wall. This arrangement is recommended when a space in which gases are released—for example, a gas-generator department—adjoins the wall of the open-hearth shop (open-hearth furnace No. 2 at the Dzerzhinsky plant).

Air showers for trough platforms

The unfavorable thermal conditions at workplaces where the troughs are serviced—high air temperatures and intense radiation from both sides, from the rear wall of the open-hearth furnace and from the trough—make air showers necessary at trough platforms in all cases, regardless of the shop’s aeration conditions.

The intense radiation on the platform, 1.5–7 small calories per cm² per minute, requires relatively high air velocities at the workplaces, averaging 6–7 m/s, to achieve a sufficient shower effect. Convective currents from the heated surfaces of the equipment and the trough itself make it necessary, when designing the system and selecting the method of supplying the air shower, to consider the possibility of hot air being blown undesirably from one workplace to another. Therefore, when the trough is serviced from both sides, a vertical downward supply of air is most appropriate.

The shower air should be supplied to the area of the platform immediately adjacent to the trough, since the principal operations carried out on the platform—opening and plugging the furnace tap hole, preparing the trough, and so forth—are usually performed near the troughs.

The shower nozzles should be installed 0.4–0.5 m from the edge of the trough, at a height of 2–2.2 m above the platform floor.

The work area requiring air showers on each side of the trough usually measures \(1 \times 0.5\) m. Accordingly, the nozzle outlet should preferably have a rectangular cross section, with its longer side parallel to the trough. The nozzle’s position between the furnace wall and the platform railing, as well as the distance from the floor to the lower edge of the nozzle, should be chosen so as not to interfere with normal work in the shop.

On the trough platform in the open-hearth shop of the “Hammer and Sickle” Works, air-shower outlets are installed on both sides of the trough (Fig. 2), each serving an area of approximately \(0.5\ \text{m}^2\). For cooling the air in summer, a humidifying chamber is provided, reducing the air temperature by \(3\)–\(5^\circ\). The principal data on the effectiveness of this installation are given in Table 2.

It should be noted that, despite the thermal insulation provided, the air was heated by \(2.5\)–\(5^\circ\) as it passed through the ducts, particularly in sections farthest from the fan. When designing similar installations, efforts should be made to reduce the heating of the air along its path from the fan to the outlet. To this end, it is desirable to: (a) minimize the lengths of ductwork close to highly heated surfaces, especially above the furnaces; and (b) insulate, wherever possible, all sections of ductwork, including the pipes supplying the nozzles. The most expedient arrangement is to provide decentralized air-shower installations, each serving no more than two open-hearth furnaces at a time.

Fig. 2. Air-shower outlets on the trough platform of an open-hearth furnace at the “Hammer and Sickle” Works.

The main duct serving two furnaces should, if possible, be located in the passage between the furnaces on the first floor, beneath the open-hearth platform, with risers supplying air to each furnace passing through the platform floor.

If work is carried out on one side of the trough, air showers can be provided by supplying air from the side, with the airflow directed from the workers toward the trough. With lateral air supply and workstations on one side of the trough, there is no danger of convective heat currents, smoke, and dust being blown from the trough toward the worker. The resulting wide area covered by the airflow is highly advantageous, since the work area becomes larger when the trough is serviced from one side. This method of air showering requires air velocities at the workstation of approximately \(5\)–\(6\ \text{m/s}\). The quantity of air supplied by each nozzle and the outlet velocities may be the same as for outlets with vertical air supply.

The main supply duct of the ventilation installation for the troughs, located in the bay of the open-hearth platform along …

…of the columns at the furnace itself, must be covered along its entire length with a heat-insulating layer.

In modern American-type open-hearth shops, the troughs are usually removable. Slag is cleaned from the troughs and the troughs are prepared away from the trough platform; only the removal and installation of troughs and the opening and plugging of the tap hole are carried out on the platform. This considerably reduces the time workers spend on the platform. Moreover, the meteorological conditions at workplaces in such shops are considerably better because there is no casting pit.

Table 2

Effectiveness of air showering on the trough platform of the open-hearth shop at the Serp i Molot plant
(Based on observations in 1938 and 1939)

Fig. 3. Mobile air-cooling unit

For these reasons, there is little need for fixed supply nozzles here, and it is advisable to provide air showers at workplaces using mobile ventilation units, which have proved effective in industrial trials. Fig. 3 shows an air-shower cooling unit designed by the Moscow Institute of Occupational Safety.

Air Showering of Workstations in the Casting Pit

The principal workstations in the casting-pit building that require air-shower ducting are the work platforms along the pits. At these locations, workers prepare and clean bottom plates and fit them with siphons; prepare hot tops in shops casting high-quality steels; and clean and blow out ingot molds.

Hot convection currents and intense radiation from red-hot ingots and molds, combined with strenuous muscular work, make it necessary to supplement general ventilation with intensified air showering. At casting-pit workstations, the actual air temperature during the removal of hot metal reaches 47° in summer, approximately 27° above the outdoor air temperature.

When siphons are prepared along an exterior wall containing openings, portable ventilation units can provide substantial air movement.

When a hot bay of an adjoining shop, often a rolling mill, abuts the longitudinal side of the casting-pit building, air showering should be provided with outdoor air through nozzles fitted with guide vanes. The same principle should be applied to the workstations of siphon workers located between the furnaces and the pit, and to areas where plates are cleaned and hot tops prepared; these operations are also performed on the work platforms along the pits. The method described, supplying a stream of air to workstations, came into use at the casting pit of the Serp i Molot plant in Moscow as early as 1938 and produced favorable results (Table 3).

Table 3

Effectiveness of air showering in the casting pit of the open-hearth shop at the Serp i Molot plant
(Based on observations in 1938–1939)

Figure 4 shows the arrangement of air-shower nozzles (of the Baturin system) in the casting-pit area of the open-hearth shop at the Serp i Molot plant. The nozzles are 2 m above the shop floor. Tests showed that the ducts do not provide air-shower coverage for the entire work area. With an air supply of 2,000–2,500 m³/h and an outlet velocity of 7 m/s, velocities at the center of the work area, 2–2.5 m from the duct, are low, averaging 1 m/s. This forces the foundry workers to approach the high-velocity zone during short breaks in their work. To provide full coverage of workstations with outside air, air-shower nozzles should be installed with an outlet opening measuring at least \(0.5 \times 0.3\) m and an outlet velocity of approximately 10 m/s. A wider, higher-velocity air jet is also advisable because these nozzles can be used to serve workers employed directly at the pit during short breaks in their work.

Fig. 4. General view of the air-shower ducts at the pit in the open-hearth shop of the Serp i Molot plant.

One possible design for air-shower nozzles serving workers—primarily siphon operators and, to some extent, workers employed at the pits—is to place the nozzles in the passages between the furnaces, with air drawn in along the outside wall of the charging platform at a height of up to 4 m above ground level, as in the casting pit of the open-hearth shop at the Krasny Oktyabr plant. This installation was highly effective. A drawback of the nozzle design is the limited vertical spread of the jet due to its slot-like shape. Therefore, where it is structurally feasible to install systems of this type, the following recommendations should be observed:

1. The nozzles should not be slot-shaped, but should have a rectangular cross-section measuring at least \(0.7 \times 0.4\text{–}0.5\) m.
2. The nozzles should have guide vanes at the outlet. TsAGI axial fans are recommended for supplying the air; the fan type and size should be selected according to the required capacity and back pressure.
3. An axial fan has advantages over a centrifugal fan in compactness, low cost, and economy of operation.

The greatest difficulty is providing air-shower ventilation for workers employed directly at the pit, particularly when the pit is located in the center of the building. In such cases, maximum use of mobile air-cooling units can be recommended—for example, those designed by the Moscow Institute of Occupational Safety of the All-Union Central Council of Trade Unions.

If air showers cannot be provided directly at the workstations beside the pit, every structural opportunity should be used to install air-shower nozzles along the longitudinal walls, thereby serving the workers during short breaks in their work.

A further task is to develop methods of providing air showers for the workplaces of the caster’s assistants directly at the casting pit.

For all the air-shower methods described above, the most advisable approach is to draw air from an uncontaminated area outside the building. To reduce the heating of the air inside the ducts, the ducts should be covered with thermal insulation.

The effectiveness of the air-shower ventilation units described above can be increased substantially by cooling the supplied air during hot weather.