Conveying device for conveying piece goods

Abstract

A conveying device (1) is provided to increase the life of conveyor screws (3, 3b), in particular in rotary hearth furnaces, above all to prevent high wear of the blades (6) and permit a continuous conveying of the piece goods (10). The conveying device (1) for conveying piece goods (10) consists of a conveyor (2) which, during operation of the conveying device (1), conveys the piece goods (10) in a conveying direction (F) in a conveying space (FR), and at least one conveying screw (3, 3b) which, during operation of the conveying device (1), conveys the piece goods (10) in a screw conveying direction (S, Sb) along an axial axis of rotation (RA), wherein the pitch (k) of the number of blades (6) of the at least one conveying screw (3, 3b) increases in the screw conveying direction (S, Sb) and an axial end of the conveying portion (A) with the number of blades (6) with the greater pitch (k) extends into a region at a lateral edge (7) of the conveyor (2).

Description

[0001] Conveyor system for conveying piece goods

[0002] The present invention relates to a conveyor device for conveying piece goods, comprising a conveyor which, during operation of the conveyor device, conveys the piece goods in a conveying direction in a conveying chamber, wherein the conveying chamber is delimited laterally on both sides by an edge as seen in the conveying direction, so that the conveying chamber has a width, and at least one conveyor screw which, during operation of the conveyor device, conveys the piece goods in a screw conveying direction along an axial rotation axis, wherein the screw conveying direction is dependent on a direction of rotation about the axial rotation axis, wherein the at least one conveyor screw consists of a shaft with two axial ends and a number of blades which are arranged spirally with a pitch on the outer circumference of the shaft and project radially outwards from the outer circumference in an axial conveying section between the two axial ends of the shaft,A screw conveyor chamber of the at least one screw conveyor is formed between the blades, the screw conveyor direction running transversely to the conveying direction of the conveyor, and the at least one screw conveyor being arranged such that the conveyor chamber of the conveyor and the screw conveyor chamber of the at least one screw conveyor at least partially overlap. The present invention further relates to an arrangement of the conveyor device in a reduction furnace.

[0003] In conveyor technology, screw conveyors, also known as screw conveyors, are known in various designs for transporting or conveying a wide variety of materials (e.g. bulk or piece goods). A screw conveyor basically consists of a shaft and a number of blades (e.g. made of sheet steel) that are attached spirally to the outer circumference of the shaft with a pitch and project essentially radially outwards. These blades form an axial conveying section with a screw conveying direction. A screw conveying chamber for the material is formed between the blades. The fill level describes the extent to which the screw conveying chamber is filled. As the screw conveyor rotates around a rotational axis, the material is moved between the blades in the screw conveying direction.The screw conveyor can also be arranged in a trough or in a pipe to prevent the material being conveyed from escaping or escaping during conveying.

[0004] Such screw conveyors are used in a wide variety of applications, for example in agriculture (e.g., for grain silos), in plastics processing machines (e.g., extruders), or in metallurgical processes such as pig iron and steel production. Depending on the application, the screw conveyor is designed to convey any piece of material made of different materials (wood, various ores, etc.) and in various shapes (round, cylindrical, square, etc.). For example, the piece of material can be produced by pelletizing (pellets) or by extrusion and subsequent cutting to length.

[0005] In pig iron production, reduction furnaces, such as rotary hearth furnaces, are used for the so-called direct reduction of iron ore. A rotary hearth furnace is basically a rotating ring-shaped or plate-shaped furnace, as described, for example, in US Pat. No. 4,597,564 A. The iron ore, e.g. in the form of lump material, is fed to the rotary hearth furnace together with a reducing agent, such as coal or natural gas. The lump material can be, for example, iron ore balls with a diameter of approximately 0.5 to 2 cm. However, the use of reduction furnaces is not limited to pig iron production and to iron ore as lump material. Other materials, in particular other ores such as manganese, chromium, etc., can also be mined and reduced as lump material in reduction furnaces.

[0006] In a rotary hearth furnace, the lump material is conveyed in a conveying direction on a conveyor which is designed as a rotating ring-shaped furnace plate. Viewed in the conveying direction, the conveyor is limited on both sides by a lateral edge. During direct reduction, the lump material (e.g. iron ore) is heated to the temperature required for the chemical reaction to take place. The required temperature fundamentally depends on the material of the lump material. In the case of iron ore as lump material, the required temperature is in any case below the typical melting point of iron ore and is typically in the range between 1000 and 1200°C. When the lump material is heated, the carbon in the reducing agent reacts with the oxygen in the material of the lump material and dissolves or reduces it, which in the case of iron ore produces pig iron (reduced iron ore).The pig iron is then conveyed as lump material, also known as sponge iron, over the sides of the annular furnace plate. The pig iron can then be used for steel production.

[0007] A screw conveyor is typically used to transport the piece goods over the side edges of the annular furnace plate. Due to the high temperatures and the aggressive gases and materials in rotary hearth furnaces, the screw conveyor often fails. US 4,636,127 A therefore discloses a screw conveyor with hollow, water-cooled blades to increase service life. The screw conveyor is designed with a constant pitch and is arranged across the width of the annular furnace plate of the rotary hearth furnace to transport the piece goods from the furnace plate, out of the rotary hearth furnace and, for example, into a container. Despite the complex cooling system, the service life of the screw conveyor is no longer than five months before it must be removed for maintenance, thus shutting down the rotary hearth furnace. In US 5,863,197 A, the blades of the screw conveyor are solid, and cooling is provided inside the shaft.The blades are sometimes double or reinforced, and are made of a corrosion- and erosion-resistant alloy. Due to the arrangement of the screw conveyor across the width of the annular furnace plate, the piece goods enter the screw conveyor chamber via the entire axial conveying section of the screw conveyor. The quantity of piece goods to be conveyed increases steadily over the axial conveying section in the screw conveyor direction. This can cause the piece goods to accumulate between the blades at the far end in the screw conveyor direction, resulting in greater wear on the blades. Consequently, the blades are reinforced in this area, as described above. The service life of the screw conveyor for this design is approximately twelve months.

[0008] A short service life of the screw conveyor results in long downtimes of the rotary hearth furnace and high maintenance and personnel requirements, which in turn result in high costs.

[0009] It is therefore an object of the present invention to extend the service life of screw conveyors, in particular in rotary hearth furnaces, and above all to prevent excessive wear of the blades and to enable continuous conveyance of the piece goods.

[0010] According to the invention, the object is achieved with a conveyor device for conveying piece goods in that the pitch of the number of blades of the at least one conveyor screw increases in the screw conveying direction and an axial end of the conveying section with the number of blades with the greater pitch extends into an area on a lateral edge of the conveyor. The problems associated with arranging the at least one conveyor screw across the width of the conveying space of a conveyor are thus prevented, since the screw conveying space between the blades or the fill level increases with the increasing pitch. High wear of the blades at the axial end of the at least one conveyor screw with the number of blades with the greater pitch and possible blocking due to the constant increase in the quantity of piece goods to be conveyed over the length of the at least one conveyor screw in the screw conveying direction are avoided.

[0011] In an advantageous design of the conveyor device, the second axial end of the conveyor section with the number of blades with the smaller pitch extends into an area on the opposite lateral edge of the conveyor. This ensures that the piece goods reach the screw conveyor across the entire width of the conveyor. In an advantageous design of the conveyor device, the axial conveyor section extends at least to one lateral edge of the conveyor or beyond one lateral edge of the conveyor. This ensures that no piece goods get back onto the conveyor.

[0012] In an advantageous embodiment of the conveying device for conveying piece goods, the gradient in the screw conveying direction in the axial conveying section of the at least one screw conveyor increases linearly because the quantity of piece goods to be conveyed also increases linearly over the length of the at least one screw conveyor.

[0013] With an advantageous arrangement of the at least one screw conveyor, the screw conveying direction runs perpendicular to the conveying direction of the conveyor. This results in the shortest possible axial conveying section of the at least one screw conveyor, which allows less bulk material to accumulate, especially at the far end of the screw conveying direction.

[0014] In an advantageous embodiment of the conveyor system for conveying piece goods, an additional screw conveyor is arranged, wherein the screw conveyor directions of the respective screw conveyors extend transversely to the conveying direction of the conveyor and to a different lateral edge of the conveyor, and wherein the screw conveyors are arranged such that their screw conveyor chambers at least partially overlap with the conveyor chamber of the conveyor. This also allows the axial conveying section per screw conveyor to be shortened. This is particularly advantageous if the width of the conveyor chamber of the conveyor exceeds a certain value, e.g., 4 m.

[0015] With an advantageous arrangement of the conveying device for conveying piece goods in a reduction furnace, the pitch of the number of blades of the at least one screw conveyor increases in the screw conveying direction, with the screw conveying direction running toward the annular outer wall or the annular inner wall of the reduction furnace. This easily avoids the problems mentioned above when using a screw conveyor in a reduction furnace, and the service life of the at least one screw conveyor is extended.

[0016] The present invention will be explained in more detail below with reference to Figures 1 to 3, which show exemplary, schematic and non-limiting advantageous embodiments of the invention.

[0017] Fig. 1 shows the basic structure of the conveying device according to the invention, Fig. 2 shows the conveying device according to the invention with two conveyor screws, and Fig. 3 shows a simplified rotary hearth furnace with the conveying device according to the invention. In Fig. 1, the basic structure of the conveying device 1 for conveying piece goods 10 (only indicated in Fig. 1) according to the invention is shown in a plan view. The piece goods 10 is conveyed during operation of the conveying device 1. The piece goods 10 comprises, for example, as described in the introduction, raw or reduced iron ore, but also other materials, in particular other ores, such as ores containing manganese, chromium, etc. The conveying device 1 comprises a conveyor 2 and at least one conveyor screw 3. In Fig. 1, a conveyor 2 with a conveying direction F is shown as an example, wherein the conveying direction F is linear.Depending on the type of conveyor 2, the conveying direction F can also be radial, as, for example, on an annular furnace plate in a rotary hearth furnace (shown in Fig. 3). The conveyor 2 can also be designed as a conveyor belt, for example.

[0018] The conveyor 2 forms a conveying chamber FR, in which the piece goods 10 are received and continuously conveyed during operation of the conveyor device 1 while being conveyed on the conveyor 2. The conveying chamber FR can be formed, for example, on a conveyor belt or an annular conveyor plate. The conveying chamber FR is bounded laterally (as seen in the conveying direction F) on both sides by an edge 7, so that the conveying chamber FR has a width B. The lateral edge 7 can be formed by a wall of a conveyor belt or a conveyor plate.

[0019] The at least one conveyor screw 3 basically consists of a shaft 4 with two axial ends 5 and a number of blades 6. The shaft 4 can be designed as a hollow or solid shaft (e.g. made of steel), wherein the two axial ends 5 can be designed as bearing journals, which serve to support the shaft 4 (not shown in Fig. 1). The shaft 4 of the conveyor screw 3 can be rotated about a rotation axis RA. Furthermore, a drive (e.g. an electric motor with a gearbox) can be provided on at least one of the two axial ends 5, which is connected to the shaft 4, for example via a shaft coupling (not shown in Fig. 1), in order to set the shaft 4 and thus the at least one conveyor screw 3 in rotation about the rotation axis RA for conveying the piece goods 10. In the case of a hollow shaft, cooling can be provided inside the shaft 4.The shaft 4 can also be designed with a corrosion and erosion-resistant alloy or coating to improve protection against aggressive media and environmental conditions in the respective application.

[0020] The number of vanes 6 are arranged spirally with a pitch k on the outer circumference of the shaft 4 and projecting radially outwards from the outer circumference in an axial conveying section A between the two axial ends 5 of the shaft 4.

[0021] In Fig. 1, the axial conveying section A is shown extending continuously over the entire length of the shaft 4. The axial conveying section A also has two axial ends. Depending on the application or the width B of the conveying chamber FR of the conveyor 2, the axial conveying section A can also be formed over only part of the length of the shaft 4. In particular, the axial conveying section A can extend only on one side of the shaft 4 to the axial end 5 of the shaft 4, or it can also be provided on both sides spaced from the axial ends 5 of the shaft 4.

[0022] The vanes 6 can, for example, be made of sheet steel and welded to the outer circumference of the shaft 4. The vanes 6 can also be hollow (e.g., for cooling), partially double or reinforced (as mentioned in the introduction), and coated with a corrosion- and erosion-resistant alloy or coating.

[0023] Between the blades 6, a screw conveyor chamber SR of the at least one screw conveyor 3 is formed, which depends on the pitch k. The greater the pitch k, the larger the screw conveyor chamber SR between the blades 6 and the more piece goods 10 can be conveyed therein. According to the invention, the pitch k of the number of blades 6 increases in the screw conveyor direction S, preferably linearly. Depending on the application, other courses of the pitch k can also be provided in order to continuously convey the piece goods 10.

[0024] The screw conveying direction S depends on the direction of rotation of the at least one screw conveyor 3 around the rotation axis RA. However, for the screw conveyor 3 according to the invention, the screw conveying direction S is always in the direction of the axial end of the conveying section A with the number of blades 6 with the larger pitch k.

[0025] The at least one conveyor screw 3 is designed to convey piece goods 10 in the screw conveying direction S in the axial conveying section A upon rotation of the at least one conveyor screw 3, wherein the screw conveying direction S runs transversely, preferably normally (as shown in Figs. 1 and 2), to the conveying direction F of the conveyor 2, “transversely” preferably means an angle in the range of ±45° to the normal to the conveying direction F.

[0026] The at least one screw conveyor 3 is arranged in the conveyor device 1 such that the conveying space FR of the conveyor 2 and the screw conveyor space SR of the at least one screw conveyor 3 at least partially overlap and that the axial end of the conveyor section A with the number of blades 6 with the greater pitch k extends into an area at the lateral edge 7 of the conveyor 2. As a result of this arrangement, the piece goods 10, which are conveyed in the conveying space FR of the conveyor 2 during operation of the conveyor device 1, pass from the conveyor 2 into the screw conveyor space SR of the at least one screw conveyor 3. The at least one screw conveyor 3 then conveys the piece goods 10 further in the screw conveyor direction S along the axial conveyor section A during operation of the conveyor device 1. At the end of the conveying section A, the piece goods 10 are ejected by the at least one screw conveyor 3, for example into a container (not shown in Fig. 1).

[0027] Preferably, the axial conveying section A of the at least one conveyor screw 3 extends to the lateral edge 7 of the conveyor 2 or beyond the lateral edge 7 of the conveyor 2, as shown in Fig. 1. In principle, the area on a lateral edge 7 of the conveyor 2, up to which the axial conveying section A of the at least one conveyor screw 3 extends, extends at least far enough into the vicinity of the lateral edge 7 within the width B of the conveying space FR, so that a conveying of the piece goods from the conveyor 7 over the lateral edge 7 is still possible according to the invention, ie that no piece goods from the at least one conveyor screw 3 get back onto the conveyor 2. For example, an individual piece of the piece goods is cylindrical with a length of 5 cm, then an axial conveying section A, which e.g.2 cm within the width B of the conveying space FR from the lateral edge 7 of the conveyor 2, nor ensure that the individual piece is conveyed over the lateral edge 7 of the conveyor 2 (e.g. by pushing the following pieces).

[0028] The at least one conveyor screw 3 can also be designed to be height-adjustable in order to be optimally positioned in the conveying space FR of the conveyor 3, e.g. when used in a rotary hearth furnace just above the annular furnace plate, so that the wings 6 do not touch the annular furnace plate.

[0029] Fig. 2 shows the conveyor device 1 according to the invention with an additional conveyor screw 3b, wherein the screw conveying directions S and Sb of the respective conveyor screws 3, 3b run transversely to the conveying direction F of the conveyor 2 and to a different lateral edge 7 of the conveyor 2. The screw conveying directions S, Sb of the conveyor screws 3, 3b are thus essentially opposite. Both conveyor screws 3, 3b are arranged such that their screw conveying chambers SR, SRb each at least partially overlap with the conveying chamber FR of the conveyor 2. As a result, the piece goods are conveyed from the conveyor 2 by the two conveyor screws 3, 3b over both lateral edges 7 of the conveyor 2.

[0030] The arrangement of the two conveyor screws 3, 3b is shown offset in Fig. 2, however, depending on the application, it is also possible to arrange the two conveyor screws 3, 3b with their screw conveying directions S, Sb in a line, for example to convey the piece goods 10 at the same height over the lateral edges 7. It can also be advantageous to provide guides 8 in the area of ​​the conveyor 2, which direct the piece goods 10 on the conveyor 2 in a more targeted manner in the direction of the conveyor screws 3, 3b, particularly if the axial conveying section A does not extend over the entire length of the shaft 4. As described above and shown in Fig. 1, the pitch k of the number of blades 6 of at least one of the, preferably both, conveyor screws 3, 3b increases in the respective screw conveying direction S, Sb, preferably linearly. Otherwise, the above statements regarding the conveyor screw 3 according to Fig. 1 apply analogously to both conveyor screws 3, 3b.

[0031] 3 and 4 each show an example of a reduction furnace 11 for the direct reduction of, for example, iron ore, but also other ores such as manganese, chromium, etc., with a conveying device 1 according to the invention in a plan view. For the sake of clarity, only the reduction of iron ore will be described below. The reduction furnace 11 comprises two outer walls 12, with a conveyor 2 arranged between the two outer walls 12. The conveyor 2 conveys the piece goods 10 in a conveying direction in a conveying chamber FR with a width B during operation of the reduction furnace 11. At least one conveyor screw 3, 3b is arranged, which conveys the piece goods 10 in a screw conveying direction S, S during operation of the reduction furnace 11. The pitch k of the number of blades 6 of the at least one conveyor screw 3, 3b increases in the screw conveying direction S, Sb, wherein the screw conveying direction S, Sb runs in the direction of one of the two outer walls 12 of the reduction furnace 11.

[0032] Fig. 3 shows a schematic plan view of a rotary hearth furnace as an annular reduction furnace 11 with a conveying device 1 according to the invention. The reduction furnace 11 is constructed from two annular outer walls 12, with the conveyor 2, in this case an annular turntable, being arranged between the annular outer walls 12. The lateral edges 7 of the conveyor 2 each extend preferably close to the respective annular outer wall 12 so that the conveying chamber FR of the conveyor 2 has the largest possible width B. During operation, the conveyor 2 moves in a conveying direction F in the circumferential direction to convey piece goods 10. In the reduction furnace 11, for example, iron ore, for example in the form of pellets or extrudate parts, is conveyed as piece goods 10 into the conveying chamber FR of the conveyor 2, with the piece goods 10 reaching the conveyor 2, for example, through an opening 14 in the reduction furnace 11, e.g. by means of a conveyor belt.In addition to the piece goods 10, a reducing agent for the reduction of oxygen from the iron ore can also be conveyed. At least one heat source can also be provided at the reduction furnace 11 (not shown in Fig. 3), which heats the piece goods 10 to the necessary temperature for the reduction of oxygen (as described in the introduction). The at least one screw conveyor 3 is arranged at the end of the reduction section of the reduction furnace 11 and, according to the invention, is arranged such that the conveying chamber FR of the conveyor 2 and the screw conveying chamber SR of the at least one screw conveyor 3 at least partially overlap. Of course, more than one screw conveyor 3 and / or guides 8 can also be arranged in the region of the conveyor 2 in a reduction furnace 11, as shown in Fig. 2.After the oxygen has been reduced from the iron ore, the piece goods 10 pass from the conveyor 2 into the screw conveyor chamber SR of the at least one screw conveyor 3, wherein the piece goods 10 are conveyed in the screw conveyor direction S. The screw conveyor direction S runs, as shown in Fig. 3, transversely to the conveying direction F of the conveyor 2 and radially outwardly towards one annular outer wall 12 of the reduction furnace 11, wherein the pitch k of the number of blades 6 of the at least one screw conveyor 3 increases in the screw conveyor direction S according to the invention. Depending on the application, the screw conveyor direction S can also run radially inwardly towards the other annular outer wall 12. The axial conveying section A of the at least one screw conveyor 3 extends, as shown by way of example in Fig. 3, across the width B of the conveying chamber FR of the conveyor 2.The axial ends 5 of the shaft 4 are spaced from the axial conveying section A and extend over the annular outer walls 12, where, for example, a bearing for the axial ends 5 or the shaft 4 or a drive for the at least one conveyor screw 3 can be provided (not shown in Fig. 3). Furthermore, depending on the application, an outlet can be provided on one of the two annular outer walls 12 or on both annular outer walls 12, through which outlet the piece goods 10 are ejected at the end of the axial conveying section A by the at least one conveyor screw 3 from the screw conveying chamber SR, for example into a container (not shown in Fig. 3). Furthermore, a type of partition wall 15 can be provided in the reduction furnace 11 (e.g. suspended in the reduction furnace 11), which spatially separates the opening 14 from the at least one conveyor screw 3.

[0033] The reduction furnace 11 can also be designed linearly, as shown in Fig. 4, wherein the conveyor 2 is correspondingly constructed linearly and is arranged between two outer walls 12. The conveyor 2 conveys the piece goods 10 during operation of the reduction furnace 11 in a linear conveying direction F in a conveying chamber FR with a width B. At least one conveyor screw 3, 3b is also arranged, which conveys the piece goods 10 during operation of the reduction furnace 11 in a screw conveying direction S, Sb. The pitch k of the number of blades 6 of the at least one conveyor screw 3, 3b increases in the screw conveying direction S, Sb, wherein the screw conveying direction S, Sb runs in the direction of one of the two outer walls 12 of the reduction furnace 11.

[0034] However, the reduction furnace 11 is not limited to a linear or annular structure, but other conceivable designs are also possible.

Claims

Patent claims 1. Conveying device (1) for conveying piece goods (10), comprising a conveyor (2) which conveys the piece goods (10) in a conveying direction (F) in a conveying chamber (FR) during operation of the conveying device (1), wherein the conveying chamber (FR) is delimited laterally on both sides by an edge (7) as seen in the conveying direction (F), so that the conveying chamber (FR) has a width (B), and comprising at least one conveyor screw (3, 3b) which conveys the piece goods (10) in a screw conveying direction (S, Sb) in the direction of a rotation axis (RA) during operation of the conveying device (1), wherein the at least one conveyor screw (3, 3b) consists of a shaft (4) with two axial ends (5) and a number of blades (6) which are arranged spirally with a pitch on the outer circumference of the shaft (4) and projecting radially outwards from the outer circumference in an axial conveying section (A) between the two axial ends (5) of the shaft (4). are arranged,wherein a screw conveyor chamber (SR, SRb) of the at least one screw conveyor (3, 3b) is formed between the blades (6), wherein the screw conveyor direction (S, Sb) runs transversely to the conveying direction (F) of the conveyor (2) and the at least one screw conveyor (3, 3b) is arranged such that the conveying chamber (FR) of the conveyor (2) and the screw conveyor chamber (SR, SRb) of the at least one screw conveyor (3, 3b) at least partially overlap, characterized in that the pitch (k) of the number of blades (6) of the at least one screw conveyor (3, 3b) increases in the screw conveyor direction (S, Sb), and an axial end of the conveyor section (A) with the number of blades (6) with the greater pitch (k) extends into a region on a lateral edge (7) of the conveyor (2).

2. Conveyor device (1) according to claim 1, characterized in that the second axial end of the conveyor section (A) with the number of blades (6) with the smaller pitch (k) extends into a region on the opposite lateral edge (7) of the conveyor (2).

3. Conveying device (1) according to claim 1 or 2, characterized in that the axial conveying section (A) extends at least as far as a lateral edge (7) of the conveyor (2) or extends beyond a lateral edge (7) of the conveyor (2).

4. Conveying device (1) according to claims 1 to 3, characterized in that the pitch (k) in the screw conveying direction (S, Sb) increases linearly in the axial conveying section (A) of the at least one conveyor screw (3, 3b).

5. Conveying device (1) according to claims 1 to 4, characterized in that the screw conveying direction (S, Sb) runs normal to the conveying direction (F) of the conveyor (2).

6. Conveying device (1) according to claims 1 to 5, characterized in that a further conveyor screw (3b) is arranged, wherein the screw conveying directions (S, Sb) of the respective conveyor screw (3, 3b) run transversely to the conveying direction (F) of the conveyor (2) and to a different lateral edge (7) of the conveyor (2), and wherein the conveyor screws (3, 3b) are arranged such that their screw conveying space (SR, SRb) each overlaps at least partially with the conveying space (FR) of the conveyor (2).

7. Reduction furnace (11) with a conveying device (1) according to claims 1 to 6, wherein the reduction furnace (11) is preferably constructed in a linear or annular manner, wherein the reduction furnace (11) comprises two outer walls (12), wherein a preferably linear or annular conveyor (2) is arranged between the two outer walls (12), which conveyor conveys the piece goods (10) during operation of the reduction furnace (11) in a conveying direction, preferably in a linear conveying direction or in a conveying direction (F) in the circumferential direction, in a conveying chamber (FR) with a width (B), and at least one conveyor screw (3, 3b) is arranged, which conveys the piece goods (10) during operation of the reduction furnace (11) in a screw conveying direction (S, Sb), characterized in that the pitch (k) of the number of blades (6) of the at least one conveyor screw (3, 3b) increases in the screw conveying direction (S, Sb), where the screw conveying direction (S,Sb) in the direction of one of the two outer walls (12) of the reduction furnace (11).

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