Concrete precast slab forming device

Abstract

The utility model relates to the technical field of precast slab forming, in particular to a concrete precast slab forming device, which is characterized in that an overturning component comprises an arc plate fixed on a side die and a wedge block fixed on a bottom die; the wedge block is positioned on the rear side of the side die and forms an upward inclined guide surface facing the side die; an arc surface is formed on the arc plate; the driving end of the sliding driving piece is hinged to the side die along the first axis, and the axis of the arc face coincides with the first axis. Along with driving of the sliding driving part, the side die can be switched between the forming state that the side die abuts against the bottom die and the tilting state that the arc face is supported on the guide face, and the side die overturning mechanism has the beneficial effects that under the action of the overturning assembly, when the sliding driving part continuously pulls the side die, the side die can be switched to the tilting state, and then the bottom face of the side die is exposed; and a worker can conveniently and quickly finish cleaning operation of the top surface of the bottom die and the bottom surface of the side die, so that the maintenance efficiency of the forming device is improved, and the production efficiency of the prefabricated slab is further improved.

Description

Technical Field

[0001] The utility model relates to the technical field of prefabricated board forming, in particular to a concrete prefabricated board forming device. Background Art

[0002] In the prior art, during the forming process of a precast concrete panel, two side molds that can move closer to or further away from each other are used in conjunction with a fixed end mold. Both the side mold and the end mold are set on a bottom mold to form a concrete pouring frame.

[0003] Since the side mold can slide relative to the bottom mold, small particles of concrete can easily enter the gap between the two. After the contact surface is scratched, the sliding seal between the two will fail excessively, which will lead to concrete leakage during the concrete molding process, reducing the reliability of the molding device.

[0004] In order to avoid the above problems, it is necessary to regularly clean and maintain the side molds and the bottom molds. However, since the side molds are attached to the bottom molds, they have to be removed during maintenance and then assembled after maintenance is completed. This greatly reduces the maintenance convenience of the forming device and is not conducive to improving the production efficiency of precast panels. Utility Model Content

[0005] (1) Technical issues to be resolved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a concrete precast panel forming device, which solves the technical problem that the forming device in the prior art has poor maintenance convenience, thereby leading to low production efficiency of precast panels.

[0007] (2) Technical solution

[0008] In order to achieve the above-mentioned purpose, the main technical solutions adopted by this utility model include:

[0009] In the first aspect, the utility model provides a concrete precast panel forming device, comprising a bottom mold, a side mold and a sliding drive member; the bottom mold extends laterally, and the sliding drive member drives the side mold to move laterally on the bottom mold, and also includes a flip assembly; the flip assembly includes an arc plate fixed on the side mold and a wedge block fixed on the bottom mold; the wedge block is located on the rear side of the side mold and faces the side mold to form an upwardly inclined guide surface; an arc surface is formed on the arc plate; the driving end of the sliding drive member is hinged to the side mold along a first axis, and the axis of the arc surface coincides with the first axis; as the sliding drive member is driven, the side mold can switch between a forming state in contact with the bottom mold and a tilted state in which the arc surface is supported on the guide surface.

[0010] In one technical solution of the present invention, in the forming state, the bottom surface of the side mold is kept in contact with the top surface of the bottom mold; in the tilted state, the side mold is supported on the guide surface by the arc surface and tilted upward; in the process of the sliding drive member driving the side mold in the forming state to move backward, the arc surface abuts against the guide surface and rolls upward along the guide surface, thereby driving the side mold to rotate around the first axis so that the bottom surface of the side mold separates from the bottom mold and rotates to tilt upward.

[0011] In one technical solution of the present invention, it also includes a connecting component, which connects the side mold and the sliding drive member; the connecting component includes a connecting plate connected to the side mold, and a hinge head connected to the sliding drive member, and the connecting plate and the hinge head are hinged along a first axis; a sub-limiting portion is formed on the connecting plate, and a mother-limiting portion opposite to the sub-limiting portion is formed on the hinge head; when the side mold is in a forming state, the sub-limiting portion and the mother-limiting portion can abut against each other when the end of the side mold close to the bottom mold swings toward the direction of the hinge head, so as to limit the swinging tendency of the end of the side mold close to the bottom mold toward the direction of the hinge head; the sub-limiting portion is a limiting flange, and the mother-limiting portion is a limiting groove.

[0012] In one technical solution of the present invention, a supporting surface is formed on the wedge block, which is continuous with one end inclined upwardly from the guide surface, and the supporting surface extends horizontally; the side mold can also be switched to a supporting state. In the supporting state, the side mold rolls the arc surface onto the supporting surface under the traction of the sliding drive member, so that the supporting surface bears the weight of the side mold.

[0013] In a technical solution of the present invention, in the supporting state, the center of gravity of the side mold is located directly above the supporting surface.

[0014] In one technical solution of the present invention, a contact layer is provided on the contact surface of the arc plate and the wedge block.

[0015] In one technical solution of the present invention, a sealing strip extending along the length direction of the side mold is detachably connected to the bottom surface of the side mold.

[0016] In a technical solution of the present invention, a plurality of the flipping components and the sliding driving components are provided at intervals along the length direction of the side mold.

[0017] In a technical solution of the present invention, the side molds are arranged as two spaced apart, the two side molds can approach or move away from each other, and the sliding drive member and the flip assembly are arranged as two groups corresponding to the two side molds.

[0018] In a technical solution of the present invention, it further includes two end molds that are spaced apart. The bottom mold, the two side molds and the two end molds can enclose a molding space with an open top.

[0019] (3) Beneficial effects

[0020] The beneficial effect of the present invention is that the concrete precast slab forming device of the present invention, under the action of the flip assembly, when the sliding drive member continues to pull the side mold, the side mold can be switched to a tilted state, thereby exposing the bottom surface of the side mold, so that the staff can conveniently and quickly complete the cleaning operation of the top surface of the bottom mold and the bottom surface of the side mold, thereby improving the maintenance efficiency of the forming device and thus improving the production efficiency of the precast slab.

[0021] It is precisely because the forming device can be reliably and conveniently maintained that it can prevent impurities such as concrete trapped between the bottom mold and the side mold from affecting the normal sliding of the side mold, and can also prevent concrete leakage from the gap between the side mold and the bottom mold during the concrete pouring process, thereby ensuring the reliability of the use of the forming device.

[0022] The flip assembly consists of a curved plate and a wedge. The curved surface of the curved plate mates with the guide surface of the wedge. This design cleverly achieves flipping of the side mold by leveraging the traction of the sliding drive, greatly simplifying the flipping process. The exposed bottom surface of the side mold also improves maintenance efficiency. The flip assembly allows the side mold to be easily tilted, making it easier for workers to clean the top surface of the bottom mold and the bottom surface of the side mold. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is one of the structural schematic diagrams of the concrete precast panel forming device of the present utility model;

[0024] Figure 2 This is the second structural diagram of the concrete precast panel forming device of the present utility model;

[0025] Figure 3 For this utility model Figure 1 Schematic diagram of the local enlarged structure at A in the middle;

[0026] Figure 4 For this utility model Figure 2 Schematic diagram of the local enlarged structure at B in the middle;

[0027] Figure 5 This is a partially enlarged structural diagram of the connection assembly position of the present invention;

[0028] Figure 6 This is a structural diagram of the hinged joint and the sliding drive member of the utility model.

[0029] [Description of Reference Numerals]

[0030] 1. Bottom mold;

[0031] 2. Side mold;

[0032] 3. Sliding drive member;

[0033] 4. Flip the component;

[0034] 41. Arc plate; 410. Arc surface;

[0035] 42. Wedge; 420. Guide surface; 430. Support surface;

[0036] 5. Connect components;

[0037] 51. Connecting plate; 510. Sub-limiting portion;

[0038] 52. hinged joint; 520. female limiting part;

[0039] 6. End mold. DETAILED DESCRIPTION

[0040] In order to better explain the present invention, and to facilitate understanding, the following Figures 1-6 , through the specific implementation method, the utility model is described in detail. Among them, the directional nouns such as "upper" and "lower" mentioned in this article are Figure 1 The orientation is referenced.

[0041] Example 1:

[0042] Reference Figures 1-6 , an embodiment of the present invention provides a concrete precast panel forming device, including a bottom mold 1, a side mold 2 and a sliding drive member 3; the bottom mold 1 extends laterally, and the sliding drive member 3 drives the side mold 2 to move laterally on the bottom mold 1, and also includes a flip assembly 4; the flip assembly 4 includes an arc plate 41 fixed on the side mold 2 and a wedge block 42 fixed on the bottom mold 1; the wedge block 42 is located at the rear side of the side mold 2 and faces the side mold 2 to form an upwardly inclined guide surface 420; an arc surface 410 is formed on the arc plate 41; the driving end of the sliding drive member 3 is hinged to the side mold 2 along a first axis, and the axis of the arc surface 410 coincides with the first axis; as the sliding drive member 3 is driven, the side mold 2 can switch between a forming state in contact with the bottom mold 1 and a tilted state in which the arc surface 410 is supported on the guide surface 420.

[0043] Specifically, the rear side in this embodiment is the side of the edge form 2 facing away from the concrete pouring space.

[0044] In the forming state, the bottom surface of the side mold 2 remains in contact with the top surface of the bottom mold 1; in the tilted state, the side mold 2 is supported on the guide surface 420 by the arc surface 410 and tilts upward; in the process of the sliding drive member 3 driving the side mold 2 in the forming state to move backward, the arc surface 410 abuts against the guide surface 420 and rolls upward along the guide surface 420, thereby driving the side mold 2 to rotate around the first axis so that the bottom surface of the side mold 2 separates from the bottom mold 1 and rotates to tilt upward.

[0045] In this embodiment, the sliding drive 3 can drive the side form 2 to slide, thereby forming a concrete pouring space in conjunction with other molds, or completing the demolding operation after pouring. Under the action of the flip assembly 4, when the sliding drive 3 continues to pull the side form 2, it can switch to a tilted state, thereby exposing the bottom surface of the side form. In other words, the bottom surface of the side form 2 can rotate away from the bottom form 1 and away from the sliding drive 3, thereby tilting the bottom surface of the side form 2. Workers can quickly and easily complete the cleaning operation of the top surface of the bottom form 1 and the bottom surface of the side form 2, thereby improving the maintenance efficiency of the forming device and thus the production efficiency of precast panels.

[0046] It is precisely because the forming device can be reliably and conveniently maintained that it can prevent impurities such as concrete sandwiched between the bottom mold 1 and the side mold 2 from affecting the normal sliding of the side mold 2, and can also prevent concrete leakage from the gap between the side mold 2 and the bottom mold 1 during the concrete pouring process, thereby ensuring the reliability of the use of the forming device.

[0047] Specifically, the bottom form 1 serves as the foundation for forming the precast concrete slab. It extends laterally, providing sufficient surface area to support the installation of the side forms 2 and sliding actuators 3, as well as the pouring of concrete. The side forms 2 define the edge shape of the precast concrete slab. The sliding actuators 3 drive the side forms 2 to slide on the bottom form 1. This not only helps to create the required pouring space in conjunction with other molds before pouring, but also facilitates demolding after pouring.

[0048] The flip assembly 4 comprises an arc plate 41 and a wedge 42. The arc surface 410 on the arc plate 41 cooperates with the guide surface 420 on the wedge 42. When the sliding drive 3 pulls the side mold 2, the arc surface 410 rolls upward along the guide surface 420, driving the side mold 2 to rotate about the first axis, causing the bottom surface of the side mold 2 to separate from the bottom mold 1. This design cleverly achieves the flipping of the side mold 2 by leveraging the traction of the sliding drive 3, greatly simplifying the flipping process. The exposed bottom surface of the side mold 2 also improves the maintenance efficiency of the side mold 2. The flip assembly 4 allows the side mold 2 to be easily tilted, making it easier for staff to clean the top surface of the bottom mold 1 and the bottom surface of the side mold 2.

[0049] More specifically, the lower end of the guide surface 420 should be lower than the horizontal center line of the arc surface 410 to ensure that it plays a guiding role for the arc surface 410 .

[0050] The bottom surface of the side form 2 is detachably connected to a sealing strip extending along its length. This improves the seal between the bottom surface of the side form 2 and the top surface of the bottom form 1, thereby enhancing the reliability of the forming apparatus when forming precast concrete panels. Because the side form 2 can be switched to a tilted position, the sealing strip can be easily and quickly maintained.

[0051] The side molds 2 are spaced apart, allowing them to move toward or away from each other. The sliding drive members 3 and the tilting assembly 4 are arranged in two groups corresponding to the two side molds 2. The bottom mold 1, the two side molds 2, and the two end molds 6 are spaced apart to form a molding space with an open top, thereby enabling the molding of precast concrete panels. The two side molds 2 can be arranged parallel to each other, and the two end molds 6 can also be arranged parallel to each other, with the side molds 2 and end molds 6 being perpendicular to each other.

[0052] When the device is in use, the side mold 2 serves as the movable mold and the end mold serves as the fixed mold. Concrete is poured within the aforementioned forming space. After the concrete is initially formed, the side mold 2 is pulled backward relative to the concrete by the sliding drive member to allow demolding. Furthermore, after the side mold 2 is switched to the tilted position, the bottom surface of the side mold 2 and the top surface of the bottom mold 1 can be maintained.

[0053] Example 2:

[0054] Reference Figures 1-6 In addition to all the technical solutions of the above embodiments, the embodiments of the present invention further have the following technical solutions:

[0055] It also includes a connecting component 5, which connects the side mold 2 and the sliding drive member 3; the connecting component 5 includes a connecting plate 51 connected to the side mold 2, and a hinge head 52 connected to the sliding drive member 3, and the connecting plate 51 and the hinge head 52 are hinged along a first axis; a sub-limiting portion 510 is formed on the connecting plate 51, and a mother-limiting portion 520 opposite to the sub-limiting portion 510 is formed on the hinge head 52; when the side mold 2 is in a forming state, the sub-limiting portion 510 and the mother-limiting portion 520 can abut against each other when the end of the side mold 2 close to the bottom mold 1 swings toward the hinge head 52, so as to limit the swinging tendency of the end of the side mold 2 close to the bottom mold 1 toward the hinge head 52.

[0056] In this embodiment, when the sliding drive member 3 pushes the side form 2, friction will be generated after the side form 2 contacts the bottom form 1. This friction will cause the bottom end of the side form 2 to tend to swing toward the sliding drive member 3. However, due to the action of the connecting component 5, the torque generated by the friction that causes the side form 2 to rotate will be offset by the abutment between the sub-limiting portion 510 and the main limiting portion 520, thereby ensuring the stability of the side form 2 during the pushing process, and thus ensuring the stability and reliability of the forming device in the process of forming concrete precast panels.

[0057] Specifically, the connecting plate 51 is used to be hinged to the hinge head 52 , so that the side mold 2 can rotate around the first axis while maintaining a stable connection with the sliding drive member 3 .

[0058] More specifically, the sub-limiting portion 510 is a limiting flange, and the female limiting portion 520 is a limiting groove.

[0059] Example 3:

[0060] Reference Figures 1-6 In addition to all the technical solutions of any of the above embodiments, the embodiments of the present invention further have the following technical solutions:

[0061] A supporting surface 430 is also formed on the wedge block 42, which is continuous with one end of the guide surface 420 that is inclined upward, and the supporting surface 430 extends horizontally; the side mold 2 can also be switched to a supporting state. In the supporting state, the side mold 2 rolls the arc surface 410 onto the supporting surface 430 under the traction of the sliding drive member 3, so that the supporting surface 430 bears the weight of the side mold 2.

[0062] In this embodiment, the supporting surface 430 is a plane. When the wedge block 42 has the supporting surface 430, the wedge block 42 can be configured as a trapezoid, with the bottom surface of the trapezoidal wedge block 42 connected to the bottom mold 1. After the arc surface 410 passes the guide surface 420, it can continue to slide under the traction of the sliding drive member 3 and be supported on the supporting surface 430, thereby improving the stability of the side mold 2 and facilitating maintenance work on the side mold 2.

[0063] Specifically, the support surface 430 is a horizontally extending plane on the trapezoidal wedge 42, which is continuous with the upwardly inclined end of the guide surface 420. When the side mold 2 rolls across the guide surface 420 under the traction of the sliding drive member 3, the arc surface 410 can smoothly transition and be supported on the support surface 430.

[0064] The side mold 2 can be switched to a supporting state, ensuring its stability, facilitating maintenance, and preventing problems caused by shaking. It also allows staff to more easily operate the side mold 2 during maintenance, reducing safety risks.

[0065] The contact surfaces of the arc plate 41 and the wedge block 42 are provided with a contact layer. The contact layer can be provided on the guide surface 420 and the supporting surface 430 to prevent the wedge block 42 from impacting the arc plate 41, thereby increasing the service life of the arc plate 41 and the wedge block 42 and reducing the operating noise of the molding device. The contact layer can be provided as a rubber layer.

[0066] Alternatively, the contact layer may be provided on the arc surface 410 to achieve the same effect.

[0067] Example 4:

[0068] Reference Figures 1-6 In addition to all the technical solutions of any of the above embodiments, the embodiments of the present invention further have the following technical solutions:

[0069] In the supporting state, the center of gravity of the side mold 2 is located directly above the supporting surface 430, which can reduce or even eliminate the tendency of the side mold 2 to swing along the first axis under the action of gravity, so that the supporting surface 430 can more reliably and effectively support the side mold 2, and reduce the load received by the sliding drive member 3 when the side mold 2 is maintained on the supporting surface 430.

[0070] Example 5:

[0071] Reference Figures 1-6 In addition to all the technical solutions of any of the above embodiments, the embodiments of the present invention further have the following technical solutions:

[0072] Multiple flip assemblies 4 and sliding drive members 3 are provided at intervals along the length of the side mold 2 to ensure operational stability and uniform force distribution of the side mold 2 during use. Furthermore, one or two flip assemblies 4 may be provided near each sliding drive member 3, preferably one flip assembly 4 on each side of a sliding drive member 3, to further ensure force distribution stability of the side mold 2 and improve operational stability.

[0073] Example 6:

[0074] Reference Figures 1-6 In addition to all the technical solutions of any of the above embodiments, the embodiments of the present invention further have the following technical solutions:

[0075] The side molds 2 are spaced apart, allowing them to move toward or away from each other. The sliding drive members 3 and the tilting assembly 4 are arranged in two groups corresponding to the two side molds 2. The bottom mold 1, the two side molds 2, and the two end molds 6 are spaced apart to form a molding space with an open top, thereby enabling the molding of precast concrete panels. The two side molds 2 can be arranged parallel to each other, and the two end molds 6 can also be arranged parallel to each other, with the side molds 2 and end molds 6 being perpendicular to each other.

[0076] It can be understood that, except for any conflicting parts, the above-mentioned embodiments 1-6 can be freely combined to form other implementation methods of the present invention.

[0077] In the description of this utility model, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of this utility model, "plurality" means two or more, unless otherwise specifically defined.

[0078] In this utility model, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on specific circumstances.

[0079] In the present invention, unless otherwise expressly specified or limited, when a first feature is “above” or “below” a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, when a first feature is “above,” “above,” or “above” a second feature, it may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is “below,” “below,” or “below” a second feature, it may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0080] The term "comprise" or any other similar term is intended to cover non-exclusive inclusion, such that a process, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, article, or apparatus / device.

[0081] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

Claims

1. A concrete precast panel forming device, comprising a bottom mold (1), a side mold (2) and a sliding drive member (3); the bottom mold (1) extends laterally, and the sliding drive member (3) drives the side mold (2) to move laterally on the bottom mold (1), characterized in that: Also included is a flip assembly (4); The flip assembly (4) comprises an arc plate (41) fixed on the side mold (2) and a wedge block (42) fixed on the bottom mold (1); the wedge block (42) is located at the rear side of the side mold (2) and faces the side mold (2) to form an upwardly inclined guide surface (420); a circular arc surface (410) is formed on the arc plate (41); The driving end of the sliding driving member (3) is hinged to the side mold (2) along a first axis, and the axis of the arc surface (410) coincides with the first axis; as the sliding driving member (3) is driven, the side mold (2) can switch between a forming state in contact with the bottom mold (1) and a tilted state in which the arc surface (410) is supported on the guide surface (420).

2. The precast concrete panel forming device according to claim 1, wherein: In the molding state, the bottom surface of the side mold (2) and the top surface of the bottom mold (1) are kept in contact with each other; In the tilted state, the side mold (2) is supported on the guide surface (420) by the circular arc surface (410) and tilted upward; in the process of the sliding drive member (3) driving the side mold (2) in the forming state to move backward, the circular arc surface (410) abuts against the guide surface (420) and rolls upward along the guide surface (420), thereby driving the side mold (2) to rotate around the first axis, so that the bottom surface of the side mold (2) is separated from the bottom mold (1) and rotated to tilt upward.

3. The precast concrete panel forming device according to claim 2, wherein: It also includes a connecting assembly (5), wherein the connecting assembly (5) connects the side mold (2) and the sliding drive member (3); The connecting assembly (5) comprises a connecting plate (51) connected to the side mold (2), and a hinged joint (52) connected to the sliding drive member (3), wherein the connecting plate (51) and the hinged joint (52) are hingedly connected along the first axis; A sub-limiting portion (510) is formed on the connecting plate (51), and a female limiting portion (520) opposite to the sub-limiting portion (510) is formed on the hinge joint (52); When the side mold (2) is in the forming state, the sub-limiting portion (510) and the female limiting portion (520) can abut against each other when the end of the side mold (2) close to the bottom mold (1) swings toward the hinge joint (52), so as to limit the swinging tendency of the end of the side mold (2) close to the bottom mold (1) toward the hinge joint (52); The sub-limiting portion (510) is a limiting flange, and the female limiting portion (520) is a limiting groove.

4. The precast concrete panel forming device according to claim 3, wherein: The wedge block (42) is further formed with a supporting surface (430) which is continuous with one end of the guide surface (420) that is inclined upward, and the supporting surface (430) extends horizontally; The side mold (2) can also be switched to a supporting state. In the supporting state, the side mold (2) is pulled by the sliding drive member (3) so that the arc surface (410) rolls onto the supporting surface (430), so that the supporting surface (430) bears the dead weight of the side mold (2).

5. The precast concrete panel forming device according to claim 4, characterized in that: In the supporting state, the center of gravity of the side mold (2) is located directly above the supporting surface (430).

6. The precast concrete panel forming device according to claim 4, wherein: A contact layer is provided on the contact surfaces of the arc plate (41) and the wedge block (42).

7. The precast concrete panel forming device according to claim 2, wherein: The bottom surface of the side mold (2) is detachably connected to a sealing strip extending along the length direction of the side mold (2).

8. The precast concrete panel forming device according to any one of claims 1 to 7, characterized in that: The turnover assembly (4) and the sliding drive member (3) are both provided in multiple numbers spaced apart along the length direction of the side mold (2).

9. The precast concrete panel forming device according to claim 8, characterized in that: The side molds (2) are arranged as two spaced apart, and the two side molds (2) can move closer to or farther away from each other. The sliding drive member (3) and the flip assembly (4) are arranged as two groups corresponding to the two side molds (2).

10. The precast concrete panel forming device according to claim 9, wherein: It also includes two end molds (6) arranged at intervals. The bottom mold (1), the two side molds (2) and the two end molds (6) can enclose a molding space with an open top.

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