A mechanical grate furnace fixed frame

Abstract

The present invention discloses a mechanical grate furnace fixed frame, including a basic frame and several columns of fixed grate frames installed in each section of the basic frame, the basic frame including a drying section, a combustion section and a burnout section surrounded by columns and main beams, the main beam is transversely arranged between two columns, two adjacent main beams have different setting heights and the setting height of the main beam gradually decreases along the drying section, the combustion section and the burnout section; a plurality of first positioning plates are arranged at intervals on the side surface of the main beam and / or a plurality of second positioning plates are correspondingly arranged on the top surface, the first positioning plate is installed with an articulated support capable of realizing rotation connection, and the second positioning plate is installed with a sliding support capable of realizing sliding guidance; several columns of fixed grate frames are arranged side by side in each section of the basic frame, the fixed grate frames are connected to the articulated support through the end cover at the upper end and contact the sliding support through the slider at the lower end. The present invention solves the thermal expansion problem from the source through a modular design concept.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, and more particularly to a fixing frame of a mechanical grate furnace for garbage incineration. Background Art

[0002] Waste incineration treatment has the advantages of harmlessness, resource utilization and volume reduction. Currently, more than 90% of the world's waste incinerators use mechanical grate furnaces. Mechanical grate furnaces have stable operation, wide adaptability, stable combustion, less fly ash, low slag thermal loss rate, and high equipment availability. Therefore, they are welcomed by the vast majority of waste power plants.

[0003] However, mechanical grate furnaces will inevitably experience thermal expansion during operation. If the expansion displacement cannot be effectively released, it will lead to problems such as uncoordinated deformation, excessive gaps, and thermal stress damage. In severe cases, the entire grate will lose its working ability. Summary of the invention

[0004] In view of the problem in the prior art that the overall thermal expansion of the grate cannot be effectively released, resulting in uncoordinated grate deformation, excessive gaps, and thermal stress damage, the present invention proposes a mechanical grate furnace fixing frame that takes the expansion displacement into consideration as a whole, and solves the thermal expansion problem of the grate furnace from the source through a modular design concept.

[0005] The present invention provides a mechanical grate furnace fixed frame, comprising a basic frame and a plurality of rows of fixed grate frames installed in each section of the basic frame, wherein:

[0006] The basic frame includes a drying section, a combustion section and a burnout section which are connected and surrounded by columns and main beams. The main beam is transversely arranged between two columns. Two adjacent main beams have different setting heights and the setting height of the main beam gradually decreases along the drying section, the combustion section and the burnout section. A plurality of first positioning plates are arranged at intervals on the side surface of the main beam and / or a plurality of second positioning plates are correspondingly arranged on the top surface. A hinged support capable of realizing rotational connection is installed on the first positioning plate, and a sliding support capable of realizing sliding guidance is installed on the second positioning plate.

[0007] The plurality of rows of fixed grate frames are arranged side by side in each section of the basic frame, and the fixed grate frames are connected to the hinged support through the end cover at the upper end and contact with the sliding support through the slider at the lower end.

[0008] According to an embodiment of the mechanical grate furnace fixed frame of the present invention, each fixed grate frame is installed at the preset positions of the drying section, the combustion section and the burnout section in the basic frame through two hinged supports and two sliding supports.

[0009] According to an embodiment of the mechanical grate furnace fixed frame of the present invention, the hinged support includes a fixed ear plate, a movable ear plate and a pin shaft, the movable ear plate is arranged between two fixed ear plates, the end cover of the fixed grate frame is connected to the movable ear plate, and the pin shaft passes through the fixed ear plate and the movable ear plate for fixing, wherein there is a gap between the movable ear plate and the fixed ear plate, and the gap is set between 1 mm and the lateral thermal expansion displacement of the fixed grate frame.

[0010] According to an embodiment of the mechanical grate furnace fixed frame of the present invention, the sliding support includes a support plate, a slide plate and a limit block, the support plate is vertically arranged on the second positioning plate, the slide plate is arranged on the top of the support plate, and the limit block is arranged on the slide plate at a location where the lateral displacement of the slider of the fixed grate frame needs to be limited so that the slider can only slide obliquely upward and downward along the slide plate, and the surface of the slide plate is coated with a polytetrafluoroethylene coating.

[0011] According to an embodiment of a mechanical grate furnace fixed frame of the present invention, the fixed grate frame includes end covers, cross beams, inclined beams, sliders, a fixed grate shaft and a fixed grate shaft supporting steel plate; two fixed grate shaft supporting steel plates are arranged in parallel, two cross beams are arranged between the two fixed grate shaft supporting steel plates and a plurality of fixed grate shafts are arranged at intervals on the two fixed grate shaft supporting steel plates; the end covers are arranged on the upper ends of the two fixed grate shaft supporting steel plates, two inclined beams are respectively arranged on the lower bottom surfaces of the two fixed grate shaft supporting steel plates, and two sliders are respectively arranged on the lower bottom surfaces of the two inclined beams.

[0012] According to an embodiment of the mechanical grate furnace fixed frame of the present invention, a slide rail for supporting the movable grate frame is arranged on the inner side of the inclined beam, and the sliding line direction of the slide rail is parallel to the movement direction of the movable grate frame.

[0013] According to an embodiment of the mechanical grate furnace fixed frame of the present invention, a hydraulic system fixing device is provided at an appropriate position on the fixed grate frame or the main beam, and each row of fixed grate frames is correspondingly provided with a group of hydraulic system fixing devices for installing a hydraulic drive device.

[0014] According to an embodiment of the mechanical grate furnace fixed frame of the present invention, both ends of the column are connected to the columns of the mechanical grate furnace, and both ends of the main beam are connected to the columns; the surface of the slider of the fixed grate frame is coated with a polytetrafluoroethylene coating.

[0015] According to an embodiment of the fixed frame of the mechanical grate furnace of the present invention, at least three rows of fixed grate frames are arranged in each section of the basic frame.

[0016] According to an embodiment of the mechanical grate furnace fixed frame of the present invention, the two sides of the first and last rows of fixed grate frames are fixed so that they can expand toward the middle, and the left side of the middle row of fixed grate frames is fixed so that it can expand toward the right.

[0017] Compared with the prior art, the design of the mechanical grate furnace fixed frame in the present invention follows the modular design concept, and the size of each fixed frame and the number of columns of each section can be adjusted according to the daily garbage processing volume of the grate, providing a basis for the serialization of grate design and the convenience of production, transportation and installation. The design of the fixed frame fully considers the overall layout of the grate, and provides convenience for fixing the grate shaft, grate sheet, grate lower wind scoop, grate drop sealing material, compensation mechanism, movable grate frame, hydraulic drive device, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the overall structure of a mechanical grate furnace fixing frame according to an exemplary embodiment of the present invention is shown.

[0019] Figure 2 A schematic structural diagram of a fixed grate frame in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0020] Figure 3 A schematic structural diagram of a sliding support in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0021] Figure 4 A structural schematic diagram showing the sliding of a sliding support in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0022] Figure 5 A schematic structural diagram of a hinged support in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0023] Figure 6 A schematic structural diagram of the sliding of an articulated support in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0024] Figure 7 A structural schematic diagram of a hydraulic system fixing device in a mechanical grate furnace fixing frame according to an exemplary embodiment of the present invention is shown.

[0025] Figure 8 A schematic structural diagram of the transverse arrangement of sliding supports in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0026] Fig. 9 A schematic structural diagram of an expansion system of a fixed grate frame in a mechanical grate furnace fixed frame according to an exemplary embodiment of the present invention is shown.

[0027] Description of reference numerals:

[0028] 1-column, 2-main beam, 3-first positioning plate, 4-fixed grate frame, 4-1-end cover, 4-2-slider, 4-3-fixed grate shaft, 4-4-fixed grate shaft supporting steel plate, 4-5-slide rail, 4-6-inclined beam, 4-7-cross beam, 5-hinged support, 5-1-fixed ear plate, 5-2-movable ear plate, 5-3-pin shaft, 6-sliding support, 6-1-support plate, 6-2-slide plate, 6-3-limiting block, 7-second positioning plate, 8-hydraulic system fixing device. DETAILED DESCRIPTION

[0029] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0030] Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0031] Figure 1 A schematic diagram of the overall structure of a mechanical grate furnace fixing frame according to an exemplary embodiment of the present invention is shown.

[0032] like Figure 1 As shown, according to an exemplary embodiment of the present invention, the mechanical grate furnace fixed frame includes a basic frame and a plurality of fixed grate frames 4 installed in each section of the basic frame. The basic frame includes a drying section, a combustion section and a burnout section connected and surrounded by columns 1 and main beams 2, and the drying section, the combustion section and the burnout section correspond to the corresponding functional sections of the mechanical grate furnace.

[0033] Specifically, the main beam 2 is transversely arranged between two columns 1, and both ends of the columns 1 are connected to the columns of the mechanical grate furnace, and both ends of the main beam 2 are connected to the columns. Two adjacent main beams 2 have different setting heights and the setting height of the main beam 2 gradually decreases along the drying section, the combustion section and the burning section. A plurality of first positioning plates 3 are arranged at intervals on the side surface of the main beam 2 and / or a plurality of second positioning plates 7 are arranged correspondingly on the top surface, and a hinged support 5 capable of realizing rotational connection is installed on the first positioning plate 3, and a sliding support 6 capable of realizing sliding guidance is installed on the second positioning plate 7.

[0034] When the main beam 2 is arranged at the upper end of the basic frame, the main beam 2 is only provided with a plurality of first positioning plates 3 at intervals on the side surface; when the main beam 2 is arranged at the lower end of the basic frame, the main beam 2 is only provided with a plurality of second positioning plates 7 correspondingly on the top surface; when the main beam 2 is arranged at the middle of the basic frame, the main beam 2 is provided with a plurality of first positioning plates 3 at intervals on the side surface and a plurality of second positioning plates 7 correspondingly on the top surface. The first positioning plates 3 and the second positioning plates 7 are used to locate the installation position of each column of the fixed grate frame 4.

[0035] Among them, several rows of fixed grate frames 4 are arranged side by side in each section of the basic frame. The fixed grate frames 4 are connected to the hinged support 5 through the end cover 4-1 at the upper end and are in contact with the sliding support 6 through the slider at the lower end.

[0036] Figure 2 A schematic structural diagram of a fixed grate frame in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0037] like Figure 2 As shown, the fixed grate frame 4 is the minimum supporting unit for realizing the independent function of the grate, providing a root for fixing the fixed grate shaft, grate sheet, grate lower wind scoop, grate drop sealing material, compensation mechanism, movable grate frame, hydraulic drive device and other components, and is the "collector" for realizing the independent use function of the grate. Among them, the inclination angle of the fixed grate frame is preferably within the range of 14° to 26°, and the inclination angles of the three sections (drying section, combustion section, and burning section) can be the same or different.

[0038] According to the present invention, the fixed grate frame includes an end cover 4-1, a crossbeam 4-7, an inclined beam 4-6, a slider 4-2, a fixed grate shaft 4-3 and a fixed grate shaft supporting steel plate 4-4. Two fixed grate shaft supporting steel plates 4-4 are arranged in parallel, two crossbeams 4-7 are arranged between the two fixed grate shaft supporting steel plates 4-4, and a plurality of fixed grate shafts 4-3 are arranged at intervals on the two fixed grate shaft supporting steel plates 4-4; the end cover 4-1 is arranged at the upper end of the two fixed grate shaft supporting steel plates 4-4, two inclined beams 4-6 are respectively arranged on the lower bottom surfaces of the two fixed grate shaft supporting steel plates 4-4, and two sliders 4-2 are respectively arranged on the lower bottom surfaces of the two inclined beams 4-6. In fact, the fixed grate frame 4 is a rectangular frame, and its basic components are H-shaped steel or other forms of components. As long as the arrangement form of the fixed grate frame conforms to the form of 3 sections × N columns, it falls within the scope of the technical solution of the present invention.

[0039] Figure 7 A structural schematic diagram of a hydraulic system fixing device in a mechanical grate furnace fixing frame according to an exemplary embodiment of the present invention is shown.

[0040] like Figure 7As shown, a hydraulic system fixture 8 is provided at an appropriate position on the fixed grate frame 4 or the main beam 2, and each row of fixed grate frames 4 is provided with a set of hydraulic system fixtures 8 for installing a hydraulic drive device. The hydraulic drive device can realize the movement of the movable grate frame driven from the bottom of the fixed grate frame. The hydraulic system fixture fully follows the modular design concept and can realize the independent drive of 3×N grate units.

[0041] The inner side of the inclined beam of the fixed grate frame is provided with a slide rail for supporting the movable grate frame, and the sliding line direction of the slide rail is parallel to the movement direction of the movable grate frame. This arrangement forms the fixed grate frame and the movable grate frame into a compact organic whole, and can realize the linear reciprocating motion of the movable grate frame.

[0042] The basic frame is divided into three sections and each section is provided with N rows of fixed grate frames, a total of 3×N independent fixed grate frame units (N=3 is used as a typical example here). Each unit can expand independently, and the coordination between the expansions is considered as a whole.

[0043] like Figure 1 and Figure 2 As shown, each fixed grate frame 4 is installed at the preset positions of the drying section, the combustion section and the burnout section in the basic frame through two hinged supports 5 and two sliding supports 6. One end of each fixed grate frame 4 is connected to the hinged support 5 through the end cover 4-1, and the other end is in contact with the sliding support 6 through the slider 4-2. The hinged support has the functions of supporting, releasing the rotation constraint, and releasing the displacement constraint. The sliding support has the functions of supporting, guiding, and releasing the displacement constraint. Through the combined action of the hinged support and the sliding support, the displacement constraint and the rotation constraint of the grate after heating can be released, and the problems of incoordination of deformation, excessive gap, thermal stress damage, etc. caused by the thermal expansion of the grate can be solved.

[0044] Figure 5 A schematic diagram of the structure of a hinged support in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown. Figure 6 A schematic structural diagram of the sliding of an articulated support in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0045] like Figure 5 and Figure 6 As shown, the hinged support 5 includes a fixed ear plate 5-1, a movable ear plate 5-2 and a pin 5-3, the movable ear plate 5-2 is arranged between two fixed ear plates 5-1, the end cover 4-1 of the fixed grate frame 4 is connected to the movable ear plate 5-2, and the pin 5-3 passes through the fixed ear plate 5-1 and the movable ear plate 5-2 for fixing. There is a gap between the movable ear plate 5-2 and the fixed ear plate 5-1, and the gap is set between 1mm and the lateral thermal expansion displacement of the fixed grate frame.

[0046] Specifically, there are circular openings on the ear plates. During assembly, the movable ear plates are placed between the two fixed ear plates, the circular openings of the three ear plates are aligned, and the pins are inserted and fixed. There are two main installation gaps between the fixed ear plates and the movable ear plates: when the displacement here needs to be limited, the gap is equal to zero (considering the manufacturing and installation errors, a gap of 1mm is left on each side); when the displacement here is to be released, the gap is equal to the thermal expansion displacement of the fixed grate frame (considering the margin, the gap is slightly larger). That is, the articulated support 5 determines whether the upper end of the fixed grate frame 4 undergoes lateral displacement by whether a gap is reserved. The width of the gap is set according to the size of the lateral thermal expansion displacement, and the position of the gap is set according to the preset expansion position; the rotational expansion constraint is released by the pin 5-3.

[0047] Figure 3 A schematic structural diagram of a sliding support in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown. Figure 4 A structural schematic diagram showing the sliding of a sliding support in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown.

[0048] like Figure 3 and Figure 4 As shown, the sliding support 6 includes a support plate 6-1, a slide plate 6-2 and a limit block 6-3. The support plate 6-1 is vertically arranged on the second positioning plate 7, the slide plate 6-2 is arranged on the top of the support plate 6-1, and the limit block 6-3 is arranged on the slide plate where the lateral displacement of the slider of the fixed grate frame needs to be limited so that the slider can only slide obliquely upward and downward along the slide plate. The surface of the slide plate 6-2 is coated with a polytetrafluoroethylene coating, and the surface of the slider 4-2 of the fixed grate frame 4 is also preferably coated with a polytetrafluoroethylene coating to ensure smooth sliding, thereby the longitudinal expansion constraint is released by the relative sliding of the slide plate 6-2 and the slider 4-2.

[0049] The fixed grate frame 4 is installed between the hinge support 5 and the sliding support 6. The specific installation method is: the upper end of the fixed grate frame 4 is installed with an end cover 4-1, and the lower end is installed with a slider 4-2. The end cover 4-1 is connected to the movable ear plate 5-2 of the hinge support 5, and the slider 4-2 is in contact with the slide plate 6-2 of the sliding support 6. In this way, each fixed grate frame 4 is installed at the set position of the main beam 2 through two hinge supports 5 and two sliding supports 6.

[0050] The axial clearance of the hinged support can release the horizontal expansion displacement constraint of the fixed grate frame, and the hinged action of the hinged support itself can release the rotation constraint of the fixed grate frame. The contact and sliding between the slide plate and the slider at the sliding support can realize the horizontal and vertical free expansion of the fixed grate frame in the inclined surface of the grate. At the sliding support where the horizontal displacement needs to be restricted, a guide block can also be set so that the fixed grate frame can only expand along the grate inclination direction.

[0051] Figure 8 A schematic diagram showing a structure in which sliding supports are arranged transversely in a fixed frame of a mechanical grate furnace according to an exemplary embodiment of the present invention is shown. Fig. 9 A schematic structural diagram of an expansion system of a fixed grate frame in a mechanical grate furnace fixed frame according to an exemplary embodiment of the present invention is shown.

[0052] like Figure 8 and Fig. 9 As shown, according to the present invention, at least three rows of fixed grate frames are arranged in each section of the basic frame. For each section, the two sides of the first and last rows of fixed grate frames are fixed so that they can expand toward the middle, and the left side of the fixed grate frame in the middle row is fixed so that it can expand toward the right.

[0053] By setting the above expansion method, on the one hand, the docking problem between the fixed grate frame and the fixed two side walls can be well solved by fixing on both sides, and the gaps between the rows can be compacted by expanding toward the middle; on the other hand, for each row, the upper end is fixed and the expansion is obliquely downward, which can ensure that the expansion direction is consistent with the oblique downward direction of the gravity component, making the expansion easy to achieve.

[0054] The fixed grate frame 4 of the present invention bears the load transmitted by the entire grate body, including garbage load, grate plate load, movable grate frame load, hydraulic drive system load, ash hopper load, etc., and must be ensured to have sufficient strength and rigidity. Finite element modeling and calculation can be used to ensure that the strength and rigidity of the fixed grate frame 4 of the present invention meet the requirements.

[0055] In addition, since the hinged support 5 and the sliding support 6 are weak parts, especially whether the strength of the ear plate and the pin connection is sufficient will affect the safety of the grate, finite element modeling and calculation can be used to ensure that the strength of the hinged support 5 and the sliding support 6 meets the requirements.

[0056] In summary, the mechanical grate furnace fixed frame of the present invention fully releases the displacement constraint of the grate during hot operation, solves the problems of incoordination of deformation, excessive gaps, thermal stress damage, etc. caused by thermal expansion of the grate, and its structural arrangement is beneficial to the overall design of the entire grate. Through a reasonable limiting device, the expansion of each fixed grate frame is coordinated, the fixed grate frame and the two side walls are tightly connected, and the fixed grate frame columns are tightly pressed together, so that the expansion problem and sealing problem of the fixed frame are solved at the same time. The entire fixed frame is divided into three sections and N columns, with a total of 3×N independent fixed grate frame units. The size of each section and the number of columns of each section can be adjusted according to the amount of garbage processed by the grate, providing a basis for the serialization and modularization of the design and the convenience of production, transportation, and installation.

[0057] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A mechanical grate furnace fixed frame, characterized in that: It includes a basic frame and several rows of fixed grate frames installed in each section of the basic frame, wherein: The basic frame includes a drying section, a combustion section and a burnout section which are connected and surrounded by columns and main beams. The main beam is transversely arranged between two columns. Two adjacent main beams have different setting heights and the setting height of the main beam gradually decreases along the drying section, the combustion section and the burnout section. A plurality of first positioning plates are arranged at intervals on the side surface of the main beam and / or a plurality of second positioning plates are correspondingly arranged on the top surface. A hinged support capable of realizing rotational connection is installed on the first positioning plate, and a sliding support capable of realizing sliding guidance is installed on the second positioning plate. The plurality of rows of fixed grate frames are arranged side by side in each section of the basic frame, and the fixed grate frames are connected to the hinged support through the end cover at the upper end and contact with the sliding support through the slider at the lower end; The hinged support includes a fixed ear plate, a movable ear plate and a pin, wherein the movable ear plate is arranged between two fixed ear plates, the end cover of the fixed grate frame is connected to the movable ear plate, and the pin passes through the fixed ear plate and the movable ear plate for fixing, wherein a gap is provided between the movable ear plate and the fixed ear plate, and the gap is arranged between 1 mm and the lateral thermal expansion displacement of the fixed grate frame; The sliding support comprises a support plate, a slide plate and a limit block, wherein the support plate is vertically arranged on the second positioning plate, the slide plate is arranged on the top of the support plate, the limit block is arranged at a position on the slide plate where the lateral displacement of the slide block of the fixed grate frame needs to be limited so that the slide block can only slide obliquely upward and downward along the slide plate, and the surface of the slide plate is coated with a polytetrafluoroethylene coating; The fixed grate frame includes end covers, cross beams, inclined beams, sliders, fixed grate shafts and fixed grate shaft supporting steel plates; two fixed grate shaft supporting steel plates are arranged in parallel, two cross beams are arranged between the two fixed grate shaft supporting steel plates and a plurality of fixed grate shafts are arranged at intervals on the two fixed grate shaft supporting steel plates; the end covers are arranged on the upper ends of the two fixed grate shaft supporting steel plates, two inclined beams are respectively arranged on the lower bottom surfaces of the two fixed grate shaft supporting steel plates, and two sliders are respectively arranged on the lower bottom surfaces of the two inclined beams.

2. The mechanical grate furnace fixing frame according to claim 1, characterized in that: Each fixed grate frame is installed at the preset position of the drying section, the combustion section and the ember section in the basic frame through two hinged supports and two sliding supports.

3. The mechanical grate furnace fixing frame according to claim 1, characterized in that: The inner side of the inclined beam is provided with a slide rail for supporting the movable grate frame, and the sliding line direction of the slide rail is parallel to the moving direction of the movable grate frame.

4. The mechanical grate furnace fixing frame according to claim 1, characterized in that: A hydraulic system fixing device is arranged at an appropriate position on the fixed grate frame or the main beam, and each row of fixed grate frames is correspondingly provided with a group of hydraulic system fixing devices for installing a hydraulic drive device.

5. The mechanical grate furnace fixing frame according to claim 1, characterized in that: The two ends of the column are connected to the columns of the mechanical grate furnace, and the two ends of the main beam are connected to the columns; the surface of the slider of the fixed grate frame is coated with a polytetrafluoroethylene coating.

6. The mechanical grate furnace fixing frame according to claim 1, characterized in that: At least three rows of fixed grate frames are arranged in each section of the basic frame.

7. The mechanical grate furnace fixing frame according to claim 6, characterized in that: Fix both sides of the first and last rows of fixed grate frames so that they can expand toward the middle, and fix the left side of the fixed grate frame in the middle row so that it can expand toward the right.

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