Rare earth metal casting mold

Abstract

The invention discloses a rare earth metal casting mold which is of a containing groove structure with an upper opening. The containing groove structure comprises a bottom wall and a side wall, the bottom wall and the side wall define the containing groove structure, and a containing space of the containing groove structure is used for containing a rare earth metal melt and enabling the rare earth metal melt to form a rare earth metal block in a corresponding shape; a first cavity is formed in the bottom wall, and a second cavity is formed in the side wall; the first cavity and the second cavity are communicated or not communicated; and the accommodating space is not communicated with the first cavity and the second cavity. The mold can slow down the cooling and solidification speed of the rare earth metal melt, so that electrolyte impurities in the rare earth metal melt fully float on the surface, the separation of slag formed by the electrolyte from the rare earth metal in the subsequent process is facilitated, the purity of the rare earth metal product is improved, the loss of the rare earth metal is reduced, and the heat treatment energy consumption of the mold is saved. The production cost of rare earth metal is reduced.

Description

Technical Field

[0001] The invention relates to a rare earth metal casting mold, in particular to a casting mold used for preparing rare earth metals and alloys thereof by molten salt electrolysis. Background Art

[0002] Molten salt electrolysis is one of the main methods for industrial preparation of rare earth metals and their alloys. It is a metallurgical process in which rare earth metal salts are melted and used as electrolytes for electrolysis to extract and purify rare earth metals.

[0003] Casting molds are equipment for producing rare earth metals and their alloys by electrolysis. Casting molds are used for casting rare earth metals. Rare earth metal casting is a process in which rare earth metal melt is poured into a mold, cooled and solidified, and cleaned to obtain rare earth metal castings with predetermined shapes, sizes and properties.

[0004] In the actual electrolysis process, rare earth metals are reduced on the cathode and deposited together. The deposited rare earth metal melt needs to be taken out and cast into a mold. After cooling and solidification, the desired rare earth metal product is obtained. In the process of taking out the rare earth metal melt and casting it into the mold, the electrolyte will be brought into the rare earth metal melt. However, due to the different densities of the electrolyte and the rare earth metal melt, the electrolyte will float on the upper layer of the rare earth metal melt and become slag. The slag and the rare earth metal can then be separated by cutting. However, during the solidification process of the rare earth metal melt, and also during the process of the electrolyte floating up to become slag, the casting mold will absorb a large amount of heat from the rare earth metal melt, causing the rare earth metal melt to cool rapidly. However, the electrolyte has not yet fully floated up, resulting in some slag mixed in the solidified rare earth metal.

[0005] The Chinese patent application with application number 202022437553.7 discloses a rare earth metal casting mold, comprising a first surface portion and a second surface portion; the first surface portion and the second surface portion enclose a holding area capable of holding the rare earth metal; the holding area has an opening, the opening is located above the first surface portion and parallel to the first surface portion, and the opening is used to inject the rare earth metal into the holding area; a groove is provided at the center of the first surface portion, the groove is located in the holding area, the depth of the groove is greater than or equal to one sixth of the thickness of the first surface portion and less than or equal to one half of the thickness of the first surface portion; the cross-sectional area of ​​the groove is greater than or equal to one tenth of the area of ​​the first surface portion and less than or equal to one half of the area of ​​the first surface portion. The mold facilitates demolding of rare earth metals.

[0006] The Chinese patent application with application number 201010553758.X discloses a mold for high-purity rare earth metal casting profiles, wherein a half-combined profile casting mold is provided between an outer titanium plate mold body and an intermediate titanium plate mold body that are close to each other, and the joint surface of the outer titanium plate mold body and the intermediate titanium plate mold body is the half-combined parting surface; the mold upper ring is inserted into the upper end of the titanium plate casting mold with a gap, and one side frame of the mold upper ring and the mold lower ring is provided with a first bolt that engages with the frame; and a graphite plate is placed on the lower end surface of the titanium plate casting mold. The mold is easy to disassemble and demould.

[0007] The Chinese patent application with application number 202410908135.1 discloses a casting mold for rare earth metals, including a top mechanism, a mold body mechanism and a bottom support mechanism; the mold body mechanism includes a mold body, and a casting cavity is arranged in the mold body; the top mechanism is configured to be able to adjust the distance between it and the mold body; the top mechanism includes a top body, and the top body is provided with a liquid outlet joint; the liquid outlet joint is configured to match the casting cavity; the top body is provided with a first fluid port and a second fluid port; the distance between the bottom support mechanism and the mold body can be adjusted; the bottom support mechanism includes a casting cavity sealing end; the casting cavity sealing end is configured to match the casting cavity. The mold is easy to demould.

[0008] The above molds all focus on whether they are easy to demold. In the atmospheric environment, the above molds still absorb a lot of heat from the rare earth metal melt, causing the rare earth metal melt to cool too quickly. The residual electrolyte impurities in the rare earth metal melt have not fully floated up, and the rare earth metal melt in the mold has cooled and solidified, which is easy to cause residues formed by electrolyte wrapped inside the rare earth metal product, affecting the purity of the rare earth metal product.

[0009] The Chinese patent application with application number 202220199313.4 discloses a casting mold for rare earth metal production that can be cooled rapidly, including a mold body and a limit rod, the limit rod is arranged on the outside of the mold body, a casting groove is provided on the side close to the mold body, a liquid cooling groove is provided in the mold body and at a position corresponding to the casting groove, both ends of the liquid cooling groove pass through the side away from the mold body, the four corners of the mold body away from the side are fixedly connected to the support frame, the upper end of the support frame away from the mold body is fixedly connected to the mounting plate, and the mounting plate is fixedly connected to the circulating pipe. The mold uses the coolant to flow in the liquid cooling groove to quickly dissipate the heat of the mold body, so that the rare earth metal melt is quickly cooled, and it is even more impossible for the electrolyte to fully float.

[0010] In order to allow the rare earth metal melt to cool slowly and allow the electrolyte to fully float, in actual production, the casting mold is generally preheated in an oven before casting, but this increases the operating steps and energy loss. Summary of the invention

[0011] In view of this, the object of the present invention is to provide a rare earth metal casting mold, which can slow down the cooling and solidification rate of the rare earth metal melt, so that the electrolyte impurities in the rare earth metal melt can fully float to the surface, which is beneficial to the subsequent process of separating the slag impurities formed by the electrolyte from the rare earth metal.

[0012] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0013] The present invention provides a rare earth metal casting mold, which is a receiving groove structure with an upper opening; the mold comprises a bottom wall and a side wall, wherein the bottom wall and the side wall enclose the receiving groove structure, and the receiving space of the receiving groove structure is used to receive rare earth metal melt and form the rare earth metal melt into a rare earth metal block of a corresponding shape;

[0014] A first cavity is disposed inside the bottom wall, and a second cavity is disposed inside the side wall; the first cavity and the second cavity are connected or not connected;

[0015] The accommodating space is not connected with the first cavity and the second cavity.

[0016] The rare earth metal casting mold according to the present invention is preferably:

[0017] The first cavity is connected to the second cavity;

[0018] An air hole is arranged on the top of the side wall, and the air hole is communicated with the second cavity and with the outside atmosphere.

[0019] The rare earth metal casting mold according to the present invention preferably further comprises a pore control device, which is arranged on the top of the side wall and is used to adjust the opening size of the pore.

[0020] According to the rare earth metal casting mold of the present invention, preferably, the pore control device is configured as a ball valve structure.

[0021] According to the rare earth metal casting mold of the present invention, preferably, the first cavity and the second cavity are connected, and the first cavity and the second cavity are both filled with gaseous refractory.

[0022] According to the rare earth metal casting mold of the present invention, preferably, the first cavity and the second cavity are connected, and the first cavity and the second cavity are both filled with solid refractory.

[0023] According to the rare earth metal casting mold of the present invention, preferably, the first cavity and the second cavity are connected, and the air pressure in the first cavity and the second cavity is lower than the external atmospheric pressure.

[0024] According to the rare earth metal casting mold of the present invention, preferably, the second cavity is arranged in an annular direction, and its central axis coincides with the central axis of the accommodating space.

[0025] According to the rare earth metal casting mold of the present invention, preferably, the cross-section of the accommodating space is in an inverted trapezoidal shape.

[0026] According to the rare earth metal casting mold of the present invention, preferably, the cross-section of the accommodating space is rectangular, square or elliptical.

[0027] The rare earth metal casting mold of the present invention can reduce the heat loss during the cooling process of the rare earth metal melt, slow down the cooling and solidification speed of the rare earth metal melt, so that the electrolyte impurities in the rare earth metal melt can fully float to the surface, so that it is easy to remove the slag impurities formed by the electrolyte in the subsequent process, which is conducive to separating the slag impurities from the rare earth metal, thereby reducing the loss during the separation of the rare earth metal and improving the purity of the rare earth metal product. In addition, it can also save the energy consumption of mold heat treatment and reduce the production cost of rare earth metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure is a schematic structural diagram of a rare earth metal casting mold according to an embodiment of the present invention.

[0029] Figure 2 for Figure 1 Schematic top view of .

[0030] Figure 3 for Figure 1 Schematic diagram of the left side.

[0031] Figure 4 It is a schematic structural diagram of a rare earth metal casting mold according to another embodiment of the present invention.

[0032] Figure 5 The figure is a schematic structural diagram of a rare earth metal casting mold according to another embodiment of the present invention.

[0033] The following are the descriptions of the reference numerals:

[0034] 100-bottom wall, 110-first cavity; 200-side wall, 210-second cavity, 220-air hole;

[0035] 300-accommodation space;

[0036] 400-Porosity control equipment. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0038] The rare earth metal casting mold of the present invention comprises a bottom wall and a side wall, wherein a first cavity is arranged inside the bottom wall, and a second cavity is arranged inside the side wall. Preferably, a pore is arranged on the top of the side wall. Preferably, the mold further comprises a pore control device. The following is a detailed description.

[0039] <Bottom Wall, Side Wall, First Cavity, and Second Cavity>

[0040] The rare earth metal casting mold of the present invention is a receiving tank structure with an upper opening. The receiving space of the receiving tank structure is used to receive rare earth metal melt and form the rare earth metal melt into rare earth metal blocks of corresponding shapes.

[0041] The rare earth metal casting mold of the present invention includes a bottom wall and a side wall, and the bottom wall and the side wall enclose the containing groove structure. The shape of the containing space is not particularly limited and can be set according to actual needs. According to a specific embodiment of the present invention, the cross-section of the containing space is an inverted trapezoid. According to another specific embodiment of the present invention, the cross-section of the containing space is a rectangle. According to yet another specific embodiment of the present invention, the cross-section of the containing space is a square. According to yet another specific embodiment of the present invention, the cross-section of the containing space is an ellipse.

[0042] In the present invention, a first cavity is provided inside the bottom wall, and a second cavity is provided inside the side wall. The thickness of the first cavity and the thickness of the second cavity can be set according to the thickness of the bottom wall and the side wall. The cross-sectional area of ​​the first cavity and the cross-sectional area of ​​the second cavity can be set according to the cross-sectional area of ​​the bottom wall and the side wall.

[0043] In the present invention, the accommodating space is not connected with the first cavity and the second cavity.

[0044] In certain embodiments, the first cavity and the second cavity are not in communication.

[0045] In a preferred embodiment, the first cavity is connected to the second cavity. By designing the cavity structure inside the mold, the heat absorption of the rare earth metal melt by the mold itself can be reduced, thereby reducing the heat loss during the cooling process, extending the cooling time of the rare earth metal melt, and allowing the electrolyte to fully float on the surface of the rare earth metal melt to form slag, which is beneficial to improve the purity of the rare earth metal product, reduce the loss of rare earth metal and impurities in the later separation, and save energy consumption for mold heat treatment, reducing the production cost of rare earth metals. If the electrolyte cannot fully float, the slag or residue formed by the electrolyte will be dispersed inside the rare earth metal product, affecting the purity of the rare earth metal product.

[0046] In the present invention, the second cavity can be a large cavity, or a plurality of small cavities, wherein the plurality of small second cavities are evenly distributed.

[0047] According to one embodiment of the present invention, the second cavity is arranged circumferentially, and its central axis coincides with the central axis of the accommodating space. In this case, the second cavity is a large cavity.

[0048] In the present invention, the heat preservation effect can be improved and the cooling speed of the rare earth metal melt can be slowed down by making the air pressure in the first cavity and the second cavity lower than the external atmospheric pressure.

[0049] In the present invention, the mold can be manufactured in a negative pressure environment so that the air pressure in the first cavity and the second cavity is lower than the external atmospheric pressure.

[0050] According to a specific embodiment of the present invention, the first cavity is connected to the second cavity, and the air pressure in the first cavity and the second cavity is lower than the external atmospheric pressure.

[0051] In the present invention, the first cavity and the second cavity may also be filled with a low thermal conductivity material. For example, the low thermal conductivity material may be a gaseous refractory or a solid refractory. A gaseous refractory refers to a material whose thermal conductivity is less than that of air and is refractory. Gaseous refractory materials include, but are not limited to, carbon dioxide. Solid refractory materials are heat storage materials. Solid refractory materials include, but are not limited to, porous zirconium oxide fibers and porous aluminum oxide fibers. In this way, it is beneficial to further reduce the mold itself from absorbing the heat of the rare earth metal melt, further improve the thermal insulation effect, further slow down the cooling rate of the rare earth metal melt, so that the electrolyte fully floats on the surface, thereby improving the purity of the rare earth metal product.

[0052] In certain embodiments, the first cavity and the second cavity are connected, and both the first cavity and the second cavity are filled with gaseous refractory.

[0053] According to a specific embodiment of the present invention, the first cavity and the second cavity are connected, and both the first cavity and the second cavity are filled with carbon dioxide.

[0054] In other embodiments, the first cavity and the second cavity are connected, and both the first cavity and the second cavity are filled with solid refractory.

[0055] According to one embodiment of the present invention, the first cavity and the second cavity are connected, and the first cavity and the second cavity are both filled with porous alumina fibers. According to another embodiment of the present invention, the first cavity and the second cavity are connected, and the first cavity and the second cavity are both filled with porous zirconia fibers.

[0056] The rare earth metal casting mold of the present invention can be made of cast steel or cast iron.

[0057] <Blowhole>

[0058] The top of the side wall of the present invention is provided with an air hole, which is connected to the second cavity and to the outside atmosphere. The present invention finds that by providing such an air hole, the cooling and solidification speed of the rare earth metal melt can be better slowed down, so that the electrolyte in the rare earth metal melt can fully float. The rare earth metal casting mold with such a structure is relatively easier to manufacture.

[0059] When the rare earth metal melt produced by the molten salt electrolysis method is cast into the mold, the temperature of the rare earth metal melt is transmitted to the inside of the mold, and the gas in the first cavity and the second cavity expands due to the heat and is discharged to the outside atmosphere through the pores at the edge of the upper opening, thereby reducing the density of the gas inside the first cavity and the second cavity, thereby further reducing the heat conduction rate, further slowing down the cooling and solidification speed of the rare earth metal melt, allowing the electrolyte in the rare earth metal melt to fully float, thereby improving the purity of the rare earth metal product, and at the same time saving the energy consumption of mold heat treatment and reducing the production cost of rare earth metals.

[0060] According to a specific embodiment of the present invention, the first cavity is connected to the second cavity; the top of the side wall is provided with one or more air holes, which are connected to the second cavity and to the outside atmosphere.

[0061] <Blowhole Control Equipment>

[0062] The pore control device of the present invention is arranged on the top of the side wall to adjust the opening size of the pores, so that the gas content in the mold cavity can be controlled, thereby adjusting the cooling speed of the rare earth metal melt.

[0063] In the present invention, the structure of the pore control device is not particularly limited. According to a specific embodiment of the present invention, the pore control device is configured as a ball valve structure. By turning the ball valve handle, the opening size of the pore can be adjusted, thereby adjusting the gas content in the first cavity and the second cavity, and further controlling the cooling rate of the rare earth metal melt in the casting mold.

[0064] Example 1

[0065] Figure 1 The figure is a schematic structural diagram of a rare earth metal casting mold according to an embodiment of the present invention. Figure 2 for Figure 1 Schematic top view of . Figure 3 for Figure 1 Schematic diagram of the left side.

[0066] like Figure 1 , Figure 2 and Figure 3As shown, a rare earth metal casting mold of this embodiment is a receiving groove structure with an upper opening. The rare earth metal casting mold includes a bottom wall 100 and a side wall 200, and the bottom wall 100 and the side wall 200 enclose the receiving groove structure. The receiving space 300 of the receiving groove structure is used to receive the rare earth metal melt and form the rare earth metal melt into a rare earth metal block of a corresponding shape.

[0067] A first cavity 110 is disposed inside the bottom wall 100. The thickness of the first cavity 110 is smaller than that of the bottom wall 100. A second cavity 210 is disposed inside the side wall 200. The thickness of the second cavity 210 is smaller than that of the side wall 200. The first cavity 110 and the second cavity 210 are connected.

[0068] The accommodation space 300 is not connected to the first cavity 110 and the second cavity 210. The first cavity 110 and the second cavity 210 are not connected to the outside atmosphere.

[0069] In this embodiment, the second cavity 210 is arranged in an annular direction, and the central axis thereof coincides with the central axis of the accommodating space 300 .

[0070] In this embodiment, the cross-section of the accommodation space is an inverted trapezoid, that is, the top area of ​​the accommodation space is larger than the bottom area of ​​the accommodation space.

[0071] Such a mold can reduce the heat loss of the rare earth metal melt during the cooling process, slow down the cooling and solidification speed of the rare earth metal melt, so that the electrolyte impurities in the rare earth metal melt can fully float to the surface, making it easier to remove the slag impurities formed by the electrolyte in the subsequent process, reducing the loss when separating the rare earth metal and the slag impurities, and improving the purity of the rare earth metal product. In addition, it can also save the energy consumption of mold heat treatment and reduce the production cost of rare earth metals.

[0072] Example 2

[0073] Figure 4 It is a schematic structural diagram of a rare earth metal casting mold according to another embodiment of the present invention.

[0074] like Figure 4 As shown, a rare earth metal casting mold of this embodiment is a receiving groove structure with an upper opening. The rare earth metal casting mold includes a bottom wall 100 and a side wall 200, and the bottom wall 100 and the side wall 200 enclose the receiving groove structure. The receiving space 300 of the receiving groove structure is used to receive the rare earth metal melt and form the rare earth metal melt into a rare earth metal block of a corresponding shape.

[0075] A first cavity 110 is disposed inside the bottom wall 100. The thickness of the first cavity 110 is less than that of the bottom wall 100. A second cavity 210 is disposed inside the side wall 200. The thickness of the second cavity 210 is less than that of the side wall 200. The first cavity 110 and the second cavity 210 are connected. The accommodation space 300 is not connected to either the first cavity 110 or the second cavity 210.

[0076] In this embodiment, the second cavity 210 is arranged in an annular direction, and the central axis thereof coincides with the central axis of the accommodating space 300 .

[0077] In this embodiment, the top of the side wall 200 is further provided with an air hole 220, which is connected to the second cavity 210 and communicates with the outside atmosphere. The air hole 220 may be one or more, for example, one, so that the first cavity 110 and the second cavity 210 communicate with the outside atmosphere.

[0078] The mold of this embodiment can further reduce the heat conduction rate, further slow down the cooling and solidification speed of the rare earth metal melt, make the electrolyte in the rare earth metal melt float more fully, improve the purity of the rare earth metal product, and at the same time save the energy consumption of mold heat treatment and reduce the production cost of rare earth metal.

[0079] Example 3

[0080] Figure 5 FIG. 1 is a schematic structural diagram of a rare earth metal casting mold according to another embodiment of the present invention. Figure 5 As shown, a rare earth metal casting mold of this embodiment is a receiving tank structure with an upper opening. The rare earth metal casting mold includes a bottom wall 100, a side wall 200 and a pore control device 400. The bottom wall 100 and the side wall 200 enclose a receiving tank structure, and the receiving space 300 of the receiving tank structure is used to receive rare earth metal melt and form the rare earth metal melt into a rare earth metal block of a corresponding shape.

[0081] A first cavity 110 is disposed inside the bottom wall 100. The thickness of the first cavity 110 is less than that of the bottom wall 100. A second cavity 210 is disposed inside the side wall 200. The thickness of the second cavity 210 is less than that of the side wall 200. The first cavity 110 and the second cavity 210 are connected. The accommodation space 300 is not connected to either the first cavity 110 or the second cavity 210.

[0082] In this embodiment, the second cavity 210 is arranged in an annular direction, and the central axis thereof coincides with the central axis of the accommodating space 300 .

[0083] In this embodiment, a pore 220 is further provided on the top of the side wall 200, and the pore 220 is connected to the second cavity 210 and to the outside atmosphere. There may be one or more pores 220, for example, one.

[0084] The pore control device 400 is disposed at the top of the side wall 200 and is used to adjust the opening size of the pore 220. The pore control device 400 may be a ball valve structure. By turning the handle of the ball valve structure, the opening size of the pore 220 may be adjusted, thereby adjusting the gas content in the first cavity 110 and the second cavity 210, and further controlling the cooling speed of the rare earth metal melt in the casting mold.

[0085] When the hollow part of the ball valve structure is not connected to the pore 220, the pore 220 is completely closed, and the gas content in the first cavity 110 and the second cavity 210 is constant. When the hollow part of the ball valve structure is connected to the pore 220, the pore 220 is completely opened, and during the casting of the rare earth metal melt, the gas in the cavity expands due to heat and diffuses from the pore 220 to the atmosphere, reducing the gas content in the first cavity 110 and the second cavity 210, thereby achieving the control of the cooling rate of the rare earth metal melt by controlling the gas content in the first cavity 110 and the second cavity 210.

[0086] Example 4

[0087] The only difference from the first embodiment is that the air pressure in the first cavity 110 and the second cavity 210 is lower than one standard atmospheric pressure (ie, lower than 0.1 MPa), for example, it can be 0.5 standard atmospheric pressure, which is beneficial to reduce the thermal conductivity.

[0088] Example 5

[0089] The only difference from the first embodiment is that the first cavity 110 and the second cavity 210 are filled with gaseous refractory, such as carbon dioxide gas, so as to reduce thermal conductivity and reduce the cooling rate of the rare earth metal melt.

[0090] Example 6

[0091] The only difference from Example 1 is that the first cavity 110 and the second cavity 210 are filled with a solid refractory with low thermal conductivity, such as a porous zirconia fiber refractory or a porous alumina fiber refractory, which can further reduce the thermal conductivity and the cooling rate of the rare earth metal melt.

[0092] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A rare earth metal casting mold, characterized in that: It is a receiving tank structure with an upper opening; it includes a bottom wall and a side wall, the bottom wall and the side wall enclose the receiving tank structure, and the receiving space of the receiving tank structure is used to receive rare earth metal melt and form the rare earth metal melt into rare earth metal blocks of corresponding shapes; A first cavity is disposed inside the bottom wall, and a second cavity is disposed inside the side wall; the first cavity and the second cavity are connected or not connected; The accommodating space is not connected with the first cavity and the second cavity.

2. The rare earth metal casting mold according to claim 1, characterized in that: The first cavity is connected to the second cavity; An air hole is arranged on the top of the side wall, and the air hole is communicated with the second cavity and with the outside atmosphere.

3. The rare earth metal casting mold according to claim 2, characterized in that: It also includes an air hole control device, which is arranged on the top of the side wall and is used to adjust the opening size of the air hole.

4. The rare earth metal casting mold according to claim 3, characterized in that: The air hole control device is configured as a ball valve structure.

5. The rare earth metal casting mold according to claim 1, characterized in that: The first cavity is communicated with the second cavity, and both the first cavity and the second cavity are filled with gaseous refractory.

6. The rare earth metal casting mold according to claim 1, characterized in that: The first cavity is communicated with the second cavity, and both the first cavity and the second cavity are filled with solid refractory.

7. The rare earth metal casting mold according to claim 1, characterized in that: The first cavity is connected to the second cavity, and the air pressure in the first cavity and the second cavity is lower than the external atmospheric pressure.

8. The rare earth metal casting mold according to any one of claims 1 to 7, characterized in that: The second cavity is arranged in an annular direction, and a central axis thereof coincides with a central axis of the accommodating space.

9. The rare earth metal casting mold according to claim 8, characterized in that: The cross section of the accommodating space is in an inverted trapezoidal shape.

10. The rare earth metal casting mold according to claim 8, characterized in that: The cross section of the accommodation space is rectangular, square or elliptical.

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