A pit type heat treatment furnace for machining parts

Abstract

The application provides a part processing well type heat treatment furnace, and relates to the technical field of heat treatment furnaces.The well type heat treatment furnace comprises a furnace body, and the middle position of the furnace body is in a cylindrical structure, so that when workpieces are heat treated, the utilization rate of the internal space can be effectively adjusted according to the height of the annular workpieces, the problem of 'large furnace cavity empty burning' caused by small and delicate workpieces in traditional furnace bodies can be avoided, the temperature rising time is shortened, the nozzles on the heating pieces can be shielded by the lifting piece, the heat treatment effect is ensured, energy is further saved, and the problem that the size of the furnace body of the current part processing well type heat treatment furnace is usually much larger than the size of the actual processing workpiece is solved, especially when small and delicate workpieces are faced, in order to meet the processing requirements, the temperature in the whole large furnace cavity space has to be raised to the process requirements, this process not only significantly reduces the energy utilization efficiency, causes a large amount of heat to be wasted, but also greatly prolongs the temperature rising time, and seriously hinders the production rhythm.

Description

Technical Field

[0001] This invention relates to the field of heat treatment furnace technology, and in particular to a pit-type heat treatment furnace for parts processing. Background Technology

[0002] In the current booming development of the machinery manufacturing industry, ring-shaped parts made of steel and other metal materials play a crucial role as core basic components in various mechanical equipment. Among them, bearing housings are particularly representative. The performance of these parts directly affects the stability and reliability of the entire mechanical equipment during operation, and is one of the key factors to ensure the efficient and long-term operation of the equipment. Heat treatment process, as the core link to enhance the comprehensive mechanical performance of ring-shaped parts, is of great significance. By precisely applying heating, heat preservation and cooling processes to the parts, it deeply optimizes the internal structure of the material, thereby comprehensively improving the key performance indicators such as strength, hardness and toughness of the parts, laying a solid foundation for the stable service of the parts under complex working conditions. In recent years, with the profound adjustment of the global energy landscape and the growing popularity of environmental protection concepts, natural gas has rapidly emerged in the field of industrial heating due to its clean, efficient and relatively economical characteristics, becoming a favored energy choice. However, looking at the current design and application status of pit-type heat treatment furnaces for parts processing, many design defects seriously restrict their efficiency and industry development.

[0003] However, there are some shortcomings in the current design of pit furnaces:

[0004] First, the furnace body size of the current pit-type heat treatment furnace used for parts processing is usually far larger than the actual size of the workpiece being processed. Especially when dealing with relatively small workpieces, in order to meet the processing requirements, the temperature in the entire huge furnace cavity has to be raised to the process requirements. This process not only significantly reduces energy utilization efficiency and causes a lot of heat to be wasted, but also greatly prolongs the heating time, seriously hindering the production rhythm and increasing production costs.

[0005] Secondly, in the workpiece transfer process, due to the furnace structure and operating characteristics, the current stage relies heavily on lifting devices to transport the workpieces into the furnace. However, due to the limited operating space and difficulty in controlling the lifting accuracy, the lifting devices frequently collide with the furnace interior. Over time, this causes significant damage to the furnace's internal precision structure, directly affecting the furnace's service life and the stability of heat treatment quality. At the same time, the high-temperature airflow inside the furnace tends to concentrate at the top of the furnace due to natural convection. When the workpiece is lifted from the top, the hot airflow rushes out, causing a large amount of heat to dissipate, further exacerbating energy waste, which runs counter to the current requirements of energy conservation and emission reduction. Summary of the Invention

[0006] In view of the above problems, one object of the present invention is to overcome these shortcomings, and more specifically, to provide a pit-type heat treatment furnace for parts processing, which can adjust the utilization rate of the internal space of the furnace body according to the size of the workpiece, and can also solve the drawbacks caused by hoisting the workpiece from the top of the furnace body.

[0007] In a first aspect, the present invention provides a pit-type heat treatment furnace for parts processing, specifically comprising: a furnace body; the furnace body having a cylindrical structure in the middle; a ring-shaped docking hole inside the furnace body; a support plate disposed below the furnace body, wherein an insert sleeve at the upper end of the support plate is inserted into and engaged with the bottom of a support rod below the furnace body, and a push plate above the support plate is slidably engaged with the support rod; a fixing ring is installed at the upper end of the furnace body, wherein a limiting hole inside the fixing ring is penetrated by a connecting pipe on a heating element inside the furnace body, and a lifting element inside the fixing ring extends into the heating element. The lifting component is fitted to the inner wall of the heating component. A material tray is slidably installed inside the push plate. Two sets of frustum-shaped structures are provided above the material tray. Each set of frustum-shaped structures can be inserted into the furnace body from the bottom. The two sides of the guide rod inside the material tray slide in cooperation with the guide groove inside the push plate. The retaining rod at the upper end of the material tray can extend into the heating component. The upper end of the retaining rod can penetrate the lifting component. The push plate on the retaining rod can contact the bottom of the lifting component. When the retaining rod is inserted into the heating component, the push plate can push the lifting component to move inside the heating component.

[0008] Preferably, the inner side of the furnace body has a ring-shaped connecting hole, and the furnace body is fitted with an inner liner. Support rods are provided at the lower ends of the four corners of the furnace body.

[0009] Preferably, a heating element is inserted inside the furnace body. The outer end of the heating element is in contact with the inner lining. The heating element has a hollow structure inside. The inner end of the heating element is provided with an inclined nozzle in a spiral shape. The upper end of the heating element is provided with a connecting pipe that can be connected to a gas supply pipe. The bottom of the heating element is provided with a bottom rod in a ring shape. The bottom rod can be inserted and matched with the docking hole inside the furnace body.

[0010] Preferably, the support plate has four corners at the top and a hydraulic rod at the top, and a push plate is fixedly installed on the hydraulic rod. The push plate has a T-shaped through groove inside and guide grooves are symmetrically opened on both sides.

[0011] Preferably, circular limiting holes are symmetrically opened on both sides of the inside of the fixing ring.

[0012] Preferably, a lifting component is slidably installed inside the fixed ring, and positioning holes are provided vertically at equal intervals on both sides of the lifting component.

[0013] Preferably, the fixed ring has side grooves at both ends, and a pin is slidably installed inside the side groove. The end of the pin can penetrate the inside of the fixed ring and be inserted into the positioning hole.

[0014] Preferably, the upper frustum-shaped structure of the material tray has an installation hole inside, and a guide rod is inserted into the middle of the material tray, with the guide rod extending from both sides of the material tray.

[0015] Preferably, a retaining rod is installed on the frustum-shaped structure at the upper end of the material tray. The bottom of the retaining rod is inserted into the mounting hole, and the inner side of the upper end of the retaining rod is provided with horizontally arranged inner holes at equal intervals.

[0016] Preferably, a push plate is slidably mounted on the retaining rod, and a slidable stop bar is inserted inside the push plate, the stop bar passing through the inner hole inside the retaining rod.

[0017] This invention provides a pit-type heat treatment furnace for parts processing, which has the following beneficial effects:

[0018] 1. This invention incorporates a fixing ring and a lifting component. The fixing ring is installed at the upper end of the furnace body, and the lifting component is installed inside the fixing ring. The lifting component extends into the interior of the heating element and is fixed inside the heating element by a pin. This allows for effective adjustment of the internal space utilization based on the height of the ring-shaped workpiece during heat treatment, avoiding the problem of "empty furnace chamber" caused by small workpieces in traditional furnaces, and shortening the heating time. At the same time, the lifting component can also block the nozzles on the heating element, further saving energy while ensuring the heat treatment effect.

[0019] 2. This invention features a material tray with a retaining rod inserted into it. A push plate is slidably mounted on the retaining rod. The push plate is moved to a position close to the workpiece and fixed with a stop bar. When the workpiece is fed into the furnace, the push plate pushes the lifting component upward, thereby creating a suitable space for workpiece processing inside the heating element. Through the lifting action of the lifting component, the utilization rate of the furnace's internal space can be adaptively adjusted, effectively reducing ineffective heat consumption and significantly improving energy efficiency.

[0020] 3. This invention features a material tray and a pusher plate. The material tray is slidably installed within the pusher plate, allowing the guide rod to slide along the guide groove. During processing, a set of frustum-shaped structures on the material tray delivers the workpiece into the furnace body, while another set of frustum-shaped structures places the annular workpiece to be processed. When the workpiece inside the furnace body is finished, the pusher plate moves downward, and the positions of the two sets of workpieces are swapped by sliding the material tray within the pusher plate. Then, the support plate is reset by a hydraulic rod. This allows for unloading at the bottom of the furnace body while simultaneously refilling the furnace body, optimizing the production process and improving production rhythm and efficiency. Furthermore, by setting up this bottom-loading structure, it not only avoids the risk of collisions that are easily caused by traditional loading methods but also prevents heat loss from the top when the furnace body is completely open for material replacement. Attached Figure Description

[0021] The following accompanying drawings will provide a better understanding of the invention by those skilled in the art, and will more clearly demonstrate the advantages of the invention. The drawings described herein are for illustrative purposes only, representing selected embodiments and not all possible implementations, and are not intended to limit the scope of the invention.

[0022] In the attached diagram:

[0023] Figure 1 A three-dimensional structural schematic diagram according to an embodiment of the present invention is shown.

[0024] Figure 2 A cross-sectional structural schematic diagram according to an embodiment of the present invention is shown.

[0025] Figure 3 An exploded view is shown according to an embodiment of the present invention.

[0026] Figure 4 A schematic diagram of the connection structure between the push plate and the tray according to an embodiment of the present invention is shown.

[0027] Figure 5 A schematic diagram of the cross-sectional structure of the furnace body according to an embodiment of the present invention is shown.

[0028] Figure 6 A schematic diagram of the internal structure of the furnace body according to an embodiment of the present invention is shown.

[0029] Figure 7 A schematic diagram of the connection structure between the fixing ring and the lifting component according to an embodiment of the present invention is shown.

[0030] Figure 8 A schematic diagram of the connection structure between the retaining rod and the push plate according to an embodiment of the present invention is shown.

[0031] List of reference numerals

[0032] 1. Furnace body; 101. Connecting hole; 102. Liner; 103. Support rod; 104. Heating element; 1041. Connecting pipe; 1042. Bottom rod;

[0033] 2. Support plate; 201. Insertion sleeve; 202. Push plate; 2021. Guide groove;

[0034] 3. Fixing ring; 301. Limiting hole; 302. Lifting component; 3021. Positioning hole; 303. Side groove; 3031. Pin;

[0035] 4. Material tray; 401. Mounting hole; 402. Guide rod; 403. Holding rod; 4031. Inner hole; 404. Push plate; 4041. Stop bar. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1: Please refer to Figures 1 to 8 As shown:

[0038] This invention provides a pit-type heat treatment furnace for parts processing, comprising: a furnace body 1; the furnace body 1 has a cylindrical structure in the middle; the interior of the furnace body 1 has an annular connecting hole 101; a support plate 2 is provided below the furnace body 1, the upper end of the support plate 2 has an insertion sleeve 201 that is inserted into the bottom of the support rod 103 below the furnace body 1, and the upper part of the support plate 2 has a push plate 202 that is slidably engaged with the support rod 103; a fixing ring 3 is installed at the upper end of the furnace body 1, the limiting hole 301 inside the fixing ring 3 is penetrated by a connecting pipe 1041 on the heating element 104 inside the furnace body 1, the lifting element 302 inside the fixing ring 3 extends into the interior of the heating element 104, and the exterior of the lifting element 302 is in contact with the heating element 104. The inner wall of component 104 is fitted together, and a material tray 4 is slidably installed inside the push plate 202. Two sets of frustum-shaped structures are provided above the material tray 4. Each set of frustum-shaped structures can be inserted into the furnace body 1 from the bottom. The two sides of the guide rod 402 inside the material tray 4 are slidably engaged with the guide groove 2021 inside the push plate 202. The retaining rod 403 at the upper end of the material tray 4 can extend into the interior of the heating element 104. The upper end of the retaining rod 403 can pass through the lifting element 302. The push plate 404 on the retaining rod 403 can contact the bottom of the lifting element 302. When the retaining rod 403 is inserted into the interior of the heating element 104, the push plate 404 can push the lifting element 302 to move inside the heating element 104.

[0039] As a second embodiment of the present invention, based on embodiment 1, such as Figure 5 and Figure 6 As shown, the inner side of the furnace body 1 has a ring-shaped docking hole 101, and the furnace body 1 is fitted with an inner lining 102. Support rods 103 are provided at the lower ends of the four corners of the furnace body 1. A heating element 104 is inserted into the furnace body 1. The outer end of the heating element 104 is in contact with the inner lining 102. The heating element 104 has a hollow structure inside. The inner end of the heating element 104 has an inclined nozzle arranged in a spiral shape. The upper end of the heating element 104 is provided with a connecting pipe 1041 that can be connected to a gas supply pipe. The bottom of the heating element 104 has a ring-shaped bottom rod 1042, which can be inserted and matched with the docking hole 101 in the furnace body 1.

[0040] This invention fixes the furnace body 1 to the support plate 2 by inserting the support rod 103 on the furnace body 1 into the insertion cylinder 201. The inner lining 102 is inserted into the furnace body 1 to effectively prevent heat loss during heat treatment. The annular heating element 104 is inserted into the furnace body 1, and the bottom rod 1042 is inserted into the docking hole 101. The connecting pipe 1041 on the heating element 104 is connected to the gas supply pipe. After the gas inside the heating element 104 is ignited, it can be sprayed out through the inclined nozzle inside the heating element 104 to heat treat the workpiece inside the furnace body 1. By setting the nozzle to be inclined, the nozzle can avoid directly heating the workpiece, thereby increasing the overall temperature inside the furnace body 1 and ensuring the uniformity of heat treatment of the workpiece.

[0041] As a third embodiment of the present invention, based on embodiment 1, such as Figure 3 As shown, plug-in cylinders 201 are provided at the four corners of the upper end of the support plate 2, and a hydraulic rod is installed at the upper end of the support plate 2. A push plate 202 is fixedly installed on the hydraulic rod. A T-shaped through groove is opened inside the push plate 202, and guide grooves 2021 are symmetrically opened on both sides of the push plate 202.

[0042] This invention involves inserting the connector 201 into the support rod 103 to fix the furnace body 1 onto the support plate 2. The push plate 202 then moves the material tray 4, allowing material to be fed from the bottom of the furnace body 1. The guide groove 2021 and guide rod 402 are slidably engaged, allowing the material tray 4 to slide within the push plate 202 and also limiting its range of motion.

[0043] As a fourth embodiment of the present invention, based on embodiment 1, such as Figure 7As shown, circular limiting holes 301 are symmetrically opened on both sides of the inside of the fixed ring 3. A lifting component 302 is slidably installed inside the fixed ring 3. Positioning holes 3021 are vertically and equidistantly opened on both sides of the lifting component 302. Side grooves 303 are opened at both ends of the fixed ring 3. A pin 3031 is slidably installed inside the side groove 303. The end of the pin 3031 can penetrate the inside of the fixed ring 3 and be inserted into the positioning hole 3021.

[0044] This invention installs a fixing ring 3 on the upper end of the furnace body 1, allowing the connecting pipe 1041 to pass through the limiting hole 301, thus limiting the fixing ring 3 on the furnace body 1. A cylindrical lifting member 302 is set inside the fixing ring 3, extending into the interior of the heating member 104. The internal space of the furnace body 1 can be adjusted according to the size of the workpiece. By controlling the utilization of space, the efficiency of heat treatment of the workpiece can be improved. Positioning holes 3021 are opened on both sides of the lifting member 302, and side grooves 303 are opened at both ends of the fixing ring 3. The pin 3031 is slidably installed into the side groove 303. By inserting the pin 3031 into the positioning hole 3021, the lifting member 302 can be fixed inside the furnace body 1, thereby controlling the size of the internal space of the furnace body 1. At the same time, by covering the nozzle on the heating member 104 with the lifting member 302, the amount of gas used can be adjusted according to the size of the workpiece.

[0045] As a fifth embodiment of the present invention, based on embodiment 1, such as Figure 4 and Figure 8 As shown, the upper frustum-shaped structure of the material tray 4 has an installation hole 401 inside, and a guide rod 402 is inserted into the middle position of the material tray 4. The guide rod 402 extends from both sides of the material tray 4. A retaining rod 403 is installed on the upper frustum-shaped structure of the material tray 4. The bottom of the retaining rod 403 is inserted into the installation hole 401. The upper inner side of the retaining rod 403 has horizontally arranged inner holes 4031 at equal intervals. A push plate 404 is slidably installed on the retaining rod 403. A slidable stop rod 4041 is inserted into the push plate 404. The stop rod 4041 can pass through the inner hole 4031 inside the retaining rod 403.

[0046] In this invention, the material tray 4 is slidably installed inside the push plate 202, and the material tray 4 slides along the inside of the push plate 202 via the guide rod 402. The push plate 202 delivers the workpiece on the material tray 4 to the inside of the furnace body 1, enabling material feeding from the bottom of the furnace body 1. By sliding the material tray 4 inside the push plate 202, the positions of the two sets of workpieces on the push plate 202 can be quickly switched, allowing material to be unloaded and then loaded into the furnace body 1. The retaining rod 403 is inserted into the upper end of the material tray 4, and the push plate 404 is slidably installed on the retaining rod 403. The push plate 404 is slid to a position close to the top of the workpiece, and the stop rod 4041 passes through the inner hole 4031, fixing the push plate 404 on the retaining rod 403. In this way, when feeding material into the furnace body 1, the push plate 404 supports the lifting member 302 to a certain height, allowing the workpiece to complete the heat treatment process in the appropriate space of the heating member 104.

[0047] The specific usage and function of this embodiment are as follows:

[0048] In this invention, such as Figures 1 to 8As shown, the furnace body 1 is inserted above the support plate 2 via the support rod 103. A push plate 202 is installed on the upper end of the support plate 2 via a hydraulic rod. The push plate 202 is slidably engaged with the support rod 103. The material tray 4 is inserted into the push plate 202. The ring-shaped part is placed on the frustum-shaped structure of the material tray 4. The retaining rod 403 is inserted into the upper end of the material tray 4 through the mounting hole 401. The push plate 404 is moved to a position close to the workpiece. The stop rod 4041 is passed through... The inner hole 4031 allows the push plate 404 to be fixed on the retaining rod 403. The inner lining 102 and the heating element 104 are sequentially inserted inside the furnace body 1. The fixing ring 3 is installed above the furnace body 1, allowing the connecting pipe 1041 on the heating element 104 to pass through the limiting hole 301. The lifting element 302 is slidably installed inside the fixing ring 3, extending into the interior of the heating element 104. The push plate 202 is pushed upwards via a hydraulic rod, sending the annular workpiece on the material tray 4 from its lower end into the furnace body 1. The workpiece is placed inside the heating element 104. While pushing the workpiece, the push plate 404 supports the lifting element 302 inside the heating element 104, thereby forming a space inside the heating element 104 suitable for processing workpieces of this size. Then, the pin 3031 is inserted into the positioning hole 3021 to fix the lifting element 302 on the fixing ring 3. Gas is supplied to the heating element 104 through the gas supply pipe. After the gas is ignited in the combustion chamber inside the heating element 104, it is sprayed out through the nozzle and heats the inside of the furnace body 1, so that the heat treatment is completed in the heating element 104 inside the furnace body 1. While processing the workpiece, the part to be processed is placed on the circular platform on the material tray 4 outside the furnace body 1. The push plate 202 is driven down by the hydraulic rod to remove the processed workpiece from the bottom of the furnace body 1. The two sets of workpieces are swapped by pushing the material tray 4 inside the push plate 202. The push plate 202 is then reset by the hydraulic rod and the next set of annular workpieces is heat treated.

[0049] The following points should be noted in this article:

[0050] 1. The accompanying drawings of the embodiments of the present invention only involve the structures involved in the embodiments of the present invention; other structures can refer to general designs.

[0051] 2. Where there is no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other to obtain new embodiments.

[0052] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A pit-type heat treatment furnace for machining parts, comprising: Furnace body (1); the furnace body (1) has a cylindrical structure in the middle; the furnace body (1) has a ring-shaped docking hole (101) inside; characterized in that a support plate (2) is provided below the furnace body (1), the insertion cylinder (201) at the upper end of the support plate (2) is inserted into the bottom of the support rod (103) below the furnace body (1), and the push plate (202) above the support plate (2) is slidably engaged with the support rod (103), a fixing ring (3) is installed at the upper end of the furnace body (1), the limiting hole (301) inside the fixing ring (3) is penetrated by the connecting pipe (1041) on the heating element (104) inside the furnace body (1), the lifting part (302) inside the fixing ring (3) extends into the interior of the heating element (104), and the outside of the lifting part (302) is connected to the heating element (104). The inner wall of the push plate (202) is fitted together. The inside of the push plate (202) is slidably installed with a material tray (4). The material tray (4) has two sets of frustum-shaped structures above it. Each set of frustum-shaped structures can be inserted into the furnace body (1) from the bottom. The two sides of the guide rod (402) inside the material tray (4) are slidably engaged with the guide groove (2021) inside the push plate (202). The retaining rod (403) at the upper end of the material tray (4) can extend into the interior of the heating element (104). The upper end of the retaining rod (403) can penetrate the lifting element (302). The push plate (404) on the retaining rod (403) can contact the bottom of the lifting element (302). When the retaining rod (403) is inserted into the interior of the heating element (104), the push plate (404) can push the lifting element (302) to move inside the heating element (104).

2. The pit-type heat treatment furnace for parts processing according to claim 1, characterized in that: The furnace body (1) has a ring-shaped connecting hole (101) on its inner side, and an inner liner (102) is inserted inside the furnace body (1). Support rods (103) are provided at the lower ends of the four corners of the furnace body (1).

3. A pit-type heat treatment furnace for parts processing according to claim 2, characterized in that: A heating element (104) is inserted inside the furnace body (1). The outer end of the heating element (104) is in contact with the inner lining (102). The heating element (104) has a hollow structure inside. The inner end of the heating element (104) is spirally provided with an inclined nozzle. The upper end of the heating element (104) is provided with a connecting pipe (1041) that can be connected to a gas transmission pipe. The bottom of the heating element (104) is annularly provided with a bottom rod (1042). The bottom rod (1042) can be inserted into the docking hole (101) inside the furnace body (1).

4. A pit-type heat treatment furnace for parts processing according to claim 1, characterized in that: The support plate (2) has four corners at the top and is equipped with plug tubes (201). A hydraulic rod is installed on the top of the support plate (2). A push plate (202) is fixedly installed on the hydraulic rod. A T-shaped through groove is opened inside the push plate (202), and guide grooves (2021) are symmetrically opened on both sides of the push plate (202).

5. A pit-type heat treatment furnace for parts processing according to claim 1, characterized in that: The fixed ring (3) has symmetrical circular limiting holes (301) on both sides inside.

6. A pit-type heat treatment furnace for parts processing according to claim 1, characterized in that: The fixed ring (3) has a lifting component (302) slidably installed inside it, and the lifting component (302) has positioning holes (3021) vertically spaced at equal intervals on both sides.

7. A pit-type heat treatment furnace for parts processing according to claim 6, characterized in that: The fixed ring (3) has side grooves (303) at both ends. A pin (3031) is slidably installed inside the side groove (303). The end of the pin (3031) can penetrate the inside of the fixed ring (3) and be inserted into the positioning hole (3021).

8. A pit-type heat treatment furnace for parts processing according to claim 1, characterized in that: The material tray (4) has an installation hole (401) inside the frustum-shaped structure above it, and a guide rod (402) is inserted in the middle of the material tray (4). The guide rod (402) extends from both sides of the material tray (4).

9. A pit-type heat treatment furnace for parts processing according to claim 8, characterized in that: A retaining rod (403) is installed on the frustum-shaped structure at the upper end of the material tray (4). The bottom of the retaining rod (403) is inserted into the mounting hole (401), and the inner side of the upper end of the retaining rod (403) is provided with horizontally arranged inner holes (4031) at equal intervals.

10. A pit-type heat treatment furnace for parts processing according to claim 9, characterized in that: A push plate (404) is slidably mounted on the retaining rod (403), and a slidable stop bar (4041) is inserted inside the push plate (404). The stop bar (4041) can pass through the inner hole (4031) inside the retaining rod (403).

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