Large-torque hydraulic angle actuator for butterfly valve

Abstract

The invention relates to the technical field of valve actuators, and discloses a large-torque hydraulic angle actuator for a butterfly valve, which comprises a box body, a hydraulic cylinder mounted at the upper end of the box body, and a shifting fork mounted in the box body and sleeved at the end part of a main shaft, a guide rod is mounted in the box body, and a piston rod of the hydraulic cylinder extends downwards into the box body and is provided with a movable block; one end of the movable block is provided with a sliding block through a main pin, the sliding block is arranged in a guide groove formed in the shifting fork in a sliding mode, and the other end of the movable block is assembled with the guide rod in a sliding mode. The piston rod of the hydraulic cylinder drives the movable block to ascend and descend along the guide rod and drives the sliding block to slide in the guide groove of the shifting fork, so that the shifting fork drives the main shaft to rotate, the structure can provide basic conditions for an actuator to achieve large-torque acting, and a valve can be quickly opened and closed under special working conditions such as high temperature and high pressure; the requirement for safety production in the petrochemical industry field is met, and the problem that a conventional actuator is insufficient in torque is effectively solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of valve actuators, in particular to a large-torque hydraulic angular actuator for a butterfly valve. BACKGROUND

[0002] At present, valves are widely used in controlling the flow, pressure, temperature and flow rate of fluid, ensuring the safe, reliable and efficient operation of equipment and pipeline systems, and actuators play a role in driving the valve in the pipeline system. The actuators can be divided into three categories according to their energy forms, namely, pneumatic, hydraulic and electric. The hydraulic actuator uses hydraulic transmission as power, and its significant feature is large pushing force, which is suitable for many application scenarios in the petroleum and chemical industry.

[0003] At present, the butterfly valve is widely used due to its simple structure, light weight and rapid opening and closing advantages, and the corresponding actuator is required, and the hydraulic angular stroke actuator can meet the requirements.

[0004] In the petroleum and chemical industry, the working environment of the butterfly valve is often accompanied by high-temperature and high-pressure fluid, which requires the structure of the actuator to be resistant to high temperature and high pressure, and the actuator needs to have the ability to drive externally with large torque to realize the rapid opening and closing of the valve in the production process. At the current stage, the driving torque of the conventional hydraulic actuator is insufficient, which makes it difficult to open the valve in special situations. The production of large-torque actuators is relatively insufficient in China. In order to realize the safe production in the petroleum and chemical industry, the application provides a large-torque hydraulic actuator to solve the above problems. SUMMARY

[0005] In order to solve the technical problems in the background art, the application provides a large-torque hydraulic angular actuator for a butterfly valve.

[0006] The large-torque hydraulic angular actuator for the butterfly valve comprises a box body, a hydraulic cylinder mounted on the upper end of the box body, a yoke mounted in the box body and sleeved on the end of a main shaft, a guide rod mounted in the box body, a piston rod of the hydraulic cylinder extending downward into the box body and mounted with a movable block, a sliding block mounted on one end of the movable block through a kingpin, and the sliding block being slidingly arranged in a guide groove formed in the yoke, the other end of the movable block being slidingly assembled with the guide rod, the movable block being driven to ascend and descend along the guide rod by the piston rod of the hydraulic cylinder, and the sliding block being driven to slide along the guide groove, so that the yoke drives the main shaft to rotate and controls the opening and closing of the valve. The unique transmission structure is designed, the guide rod provides stable guidance for the movement of the movable block, and the accuracy of the lifting movement of the movable block is ensured, the hydraulic cylinder is used as a power source, the piston rod of the hydraulic cylinder is retracted and extended to drive the movable block to move along the guide rod, the slider at one end of the movable block slides in the guide groove of the yoke, the linear movement of the movable block is converted into the rotary movement of the yoke, and then the rotary movement of the main shaft is driven, the opening and closing of the valve are realized, the structure can effectively increase the torque output through the ingenious mechanical transmission, the requirement of the butterfly valve for being quickly opened and closed under special working conditions, such as high temperature and high pressure, is met, and the problem that the conventional actuator is difficult to open the valve due to insufficient torque is solved.

[0007] As a further optimized scheme of the present application, the number of yokes is two and they are symmetrically distributed on the two sides of the movable block, the guide grooves are arranged on the two yokes along the length direction of the yokes, the sliders are slidably assembled in each guide groove, and the main pin penetrates through the two sliders and the movable block between the two yokes and is locked by the elastic retainer ring. The two symmetrically distributed yokes, the movable block and the sliders are connected through the main pin and the elastic retainer ring, the stability of the transmission is enhanced, the power of the movable block can be more uniformly transmitted to the two sides through the symmetrically distributed yokes, the component wear or movement deviation caused by uneven force is avoided, the main pin penetrates through multiple components and is locked by the elastic retainer ring, the firmness of the connection between the components is ensured, the components are prevented from loosening during the operation of the equipment, the shaking and deviation during the movement are reduced, the reliability of the actuator is ensured, the risk of failure caused by unstable structure is reduced, and the actuator can more stably provide large torque drive for the butterfly valve.

[0008] As a further optimized scheme of the present application, the movable block and the slider are provided with the movable holes, one end of the main pin is provided with the annular protrusion, the other end of the main pin penetrates through the three movable holes in sequence and is provided with the annular groove, and the elastic retainer ring is clamped in the annular groove and is attached to the surface of the slider. The movable holes on the movable block and the slider cooperate with the main pin, the installation and positioning of the main pin are facilitated, the annular protrusion at one end of the main pin can limit the axial displacement of the main pin during the installation process, the accurate installation of the main pin is ensured, the annular groove at the other end of the main pin cooperates with the elastic retainer ring, the elastic retainer ring is clamped in the annular groove and is attached to the surface of the slider, the stability of the connection between the main pin and the slider is further enhanced, the main pin is prevented from falling off during the work process, the stability of the whole transmission structure is ensured, the connection between the components of the actuator can be reliable during the long-term operation process, and the normal work of the actuator is ensured.

[0009] As a further optimized scheme of the present application, the guide rod is vertically arranged in the box body and is parallel to the piston rod of the hydraulic cylinder, and the upper and lower ends of the guide rod are fixed in the upper and lower end reserved holes of the box body through the sealing plates and the fasteners. The guide rod is vertically arranged and parallel to the hydraulic cylinder piston rod, and provides accurate guide for the lifting of the movable block, the movable block slides on the guide rod, and the accuracy of the movement direction of the movable block can be ensured, the movable block is prevented from deviating during the movement, the stable sliding of the sliding block in the guide groove of the fork is ensured, and the fork stably drives the main shaft to rotate, the upper and lower ends of the guide rod are fixed in the reserved holes of the box body through the sealing plates and fasteners, the stability of the guide rod is ensured, the guide rod will not shake or displace when bearing the pressure and friction of the movable block, and reliable support is provided for the stable operation of the entire actuator. It should be noted that spring washers are arranged between the upper ends of the guide rod and the adjacent sealing plates and are fixed through the inner hexagonal bolts.

[0010] As a further optimized scheme of the present application, a shaft sleeve is mounted on the side of the movable block away from the main shaft, and the shaft sleeve is slidably sleeved on the guide rod, the shaft sleeve is a copper alloy composite graphite bearing, has good self-lubricating property and wear resistance, and the bottom of the shaft sleeve is provided with a retaining ring for facilitating subsequent maintenance. The shaft sleeve adopts the copper alloy composite graphite bearing, has good self-lubricating property and wear resistance, can effectively reduce the friction between the movable block and the guide rod, can reduce the heat and energy loss generated by the friction during the frequent lifting of the movable block during the operation of the actuator, and improves the transmission efficiency, and the good wear resistance can prolong the service life of the shaft sleeve itself and reduce the replacement frequency of components.

[0011] As a further optimized scheme of the present application, a slide rail parallel to the guide rod is mounted on the inner wall of the box body, and the shaft sleeve is slidably assembled with the slide rail. The slide rail mounted on the inner wall of the box body is slidably assembled with the shaft sleeve, further enhances the stability of the movement of the movable block, and during the lifting of the movable block, the slide rail and the guide rod jointly act on the shaft sleeve to constrain the shaft sleeve, so that the movement of the movable block is more stable, and the shaking and deviation are reduced, which not only improves the accuracy of transmission, but also reduces the additional wear of other components caused by the unstable movement of the movable block, and further improves the reliability and service life of the actuator.

[0012] As a further optimized scheme of the present application, first and second limiting sleeves are mounted on the inner wall of the box body, the first and second limiting sleeves are centrally arranged and are arranged above and below the fork respectively, and are used to limit the rotation angle of the fork. The first limiting sleeve and the second limiting sleeve are arranged, so that the rotation angle of the fork can be accurately controlled, and then the opening and closing angle of the valve can be accurately controlled, in the petroleum and chemical pipeline system, the opening and closing precision of the valve is crucial to the normal operation of the system, by limiting the rotation angle of the fork, the valve opening and closing can be avoided, the flow, pressure and other parameters of the fluid in the pipeline system are stable, the stability and safety of the whole pipeline system are improved, and the production accident risk caused by improper valve angle control is reduced.

[0013] As a further optimized scheme of the present application, the lower end of the piston rod of the hydraulic cylinder is connected with the upper end of the movable block through a connecting flange, and the upper end of the connecting flange is provided with a spring washer sleeved on the lower end of the piston rod of the hydraulic cylinder and mounted through bolts. The connecting flange is used for connecting the piston rod of the hydraulic cylinder and the movable block, ensuring the firmness and stability of the connection between the two, so that the power of the hydraulic cylinder can be reliably transmitted to the movable block, the spring washer is mounted on the upper end of the connecting flange and sleeved on the piston rod, which can play a loosening prevention role, during the working process of the actuator, the bolts may be loose due to vibration and other factors, the spring washer can always maintain the pre-tightening force of the bolts through its elastic deformation, preventing the bolts from loosening, ensuring the reliability of the connection and the normal operation of the actuator.

[0014] As a further optimized scheme of the present application, the fork is in the shape of a cam, the front end of the fork has an assembly groove for sliding assembly of the movable block, and the rear end of the fork is assembled with the main shaft through a spline; The fork is designed in the shape of a cam, the assembly groove at the front end of the fork is used for cooperation with the movable block, facilitating the sliding of the sliding block in the guide groove and realizing the conversion of the linear motion of the movable block into the rotary motion of the fork, and the rear end is assembled with the main shaft through a spline, the spline connection has the advantages of high centering accuracy and large torque transmission, which can ensure reliable torque transmission between the fork and the main shaft, so that the fork can stably rotate the main shaft, and then accurately control the opening and closing of the valve, meeting the requirements of the butterfly valve for large torque driving and precise control.

[0015] As a further optimized scheme of the present application, the box body and the fork are both made of ZG450-630 cast steel material, the ZG450-630 cast steel material has good comprehensive mechanical properties, including high strength, hardness and toughness, and the use of this material to make the box body and the fork can make the actuator maintain stable structural strength in a high temperature and high pressure environment, resist the impact and pressure of fluid, and is not easy to deform or be damaged, which improves the high temperature and high pressure resistance of the actuator, ensures its long-term stable operation in special working conditions such as petroleum and chemical industry, and meets the strict requirements of reliability and durability in this field.

[0016] The large torque hydraulic angle actuator for butterfly valves provided by the present application has the following beneficial effects: (I) The movable block is driven to ascend along the guide rod by the piston rod of the hydraulic cylinder, the slider is driven to slide in the guide groove of the fork, and the fork drives the main shaft to rotate, so that the actuator can provide basic conditions for large torque work, the valve can be quickly opened and closed under special working conditions such as high temperature and high pressure, the safety production demand of the petroleum and chemical industry field is met, and the problem of insufficient torque of the conventional actuator is effectively solved; (II) The two symmetrically distributed forks are connected with the movable block and the slider through the kingpin and the elastic retainer, the stability of transmission is enhanced, the guide rod is vertically arranged and fixed at both ends of the box body, stable support is provided for the lifting of the movable block, the shaking and deviation in the movement process are reduced, the reliability of the actuator in the working process is ensured, and the fault risk caused by unstable structure is reduced; (III) The shaft sleeve installed on the movable block is a copper alloy composite graphite bearing, has good self-lubricating property and wear resistance, and is slidingly assembled with the guide rod and the sliding rail, so that the friction of the movable block in the movement process is effectively reduced, the energy loss is reduced, the transmission efficiency is improved, the actuator is more efficient in the running process, the component wear caused by friction is reduced, and the service life of the equipment is prolonged.

[0017] Additional aspects and advantages of the application will be set forth in part in the following description, will become apparent from the following description, or will be learned through practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0018] Fig. 1 It is an internal structure diagram of the box body of the application; Fig. 2 It is a first perspective view of the application. Fig. 3 It is a second perspective view of the application.

[0019] BRIEF DESCRIPTION OF DRAWINGS: 1, box body; 2, hydraulic cylinder; 3, fork; 4, main shaft; 5, guide rod; 6, movable block; 7, kingpin; 8, shaft sleeve; 9, retainer; 10, sliding rail; 11, cover plate; 12, first limiting sleeve; 13, second limiting sleeve; 14, elastic retainer; 15, connecting flange; 16, spring washer; 17, guide groove; 18, slider. DETAILED DESCRIPTION

[0020] The embodiments of the application are described in detail below, examples of which are shown in the drawings, wherein the same or similar symbols represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the application, and cannot be understood as a limitation on the application.

[0021] In the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature "on", "above" and "above" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the first feature is higher than the second feature in horizontal height. The first feature "under", "below" and "below" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the first feature is less than the second feature in horizontal height.

[0022] In the field of valve actuator technology, the butterfly valve in the petrochemical industry has special requirements for the actuator. The traditional conventional actuator has the problem of insufficient torque, and it is difficult to meet the demand of the butterfly valve for rapid opening and closing in a high-temperature and high-pressure environment. The large-torque hydraulic angular actuator for butterfly valves of the present application is designed to solve these problems, and the specific implementation is as follows: As Figs. 1-3 shown, the actuator mainly consists of a box body 1, a hydraulic cylinder 2, a yoke 3 and a main shaft 4, etc. The box body 1 serves as the support frame of the entire actuator, and a guide rod 5 is installed inside it. The guide rod 5 is vertically arranged inside the box body 1 and is parallel to the piston rod of the hydraulic cylinder 2. Its upper and lower ends are fixed in the reserved holes at the upper and lower ends of the box body 1 through end plates 11 and fasteners, providing stable guidance for the movement of the movable block 6. When installing the guide rod 5, spring washers are arranged between the upper ends of the guide rod 5 and the adjacent end plates, and are fixed by internal hexagonal bolts, further ensuring the stability of the guide rod 5 and preventing it from shaking or shifting during use.

[0023] The hydraulic cylinder 2 is installed at the upper end of the box body 1, and its piston rod extends downward into the box body 1 and is installed with a movable block 6 at the end. One end of the movable block 6 is installed with a sliding block 18 through a kingpin 7, and the sliding block 18 can slide in the guide groove 17 of the yoke 3. The other end is slidingly assembled with the guide rod 5. The side of the movable block 6 away from the main shaft 4 is also installed with a shaft sleeve 8, which is made of copper alloy composite graphite bearing and has good self-lubricating property and wear resistance. It is slidingly assembled on the guide rod 5, effectively reducing the friction between the movable block 6 and the guide rod 5. In order to facilitate subsequent maintenance, a retaining ring 9 is installed at the bottom of the shaft sleeve 8. The retaining ring 9 serves as a limiting buckle, facilitating the replacement of the vulnerable parts in the shaft sleeve 8. At the same time, the inner wall of the box body 1 is installed with a sliding rail 10 parallel to the guide rod 5. The shaft sleeve 8 is slidingly assembled with the sliding rail 10, further enhancing the stability of the movement of the movable block 6 and reducing shaking and deviation. The hydraulic cylinder 2 has a design pressure of 32 MPa, a buffer stroke of 50 mm, meets the valve 75° closing buffer requirement, has a design service life of 10 years, can meet stable work in a petrochemical working scene, and all the sealing rings in the hydraulic cylinder 2 are imported sealing rings, effectively reducing the oil tank leakage situation; Further, the hydraulic cylinder 2 adopts a large oil amount design, the oil pipe diameter is designed through calculation, and the requirement of valve 0.5s quick closing in an emergency is ensured; Further, in order to realize the convenience of disassembly and maintenance in actual operation, process holes are added to the side wall of the box body 1, facilitating the maintenance of the sliding block main pin.

[0024] The fork 3 is sleeved on the end of the main shaft 4, the number is two and is symmetrically distributed on both sides of the movable block 6, a guide groove 17 is formed on each fork 3 along the length direction, a sliding block 18 slides in the guide groove 17, the main pin 7 penetrates the two sliding blocks 18 and the movable block 6 between the two forks 3, and is locked through the elastic retainer 14, ensuring that the components are connected firmly; The movable block 6 and the sliding block 18 are both provided with a movable hole, the annular protrusion at one end of the main pin 7 is used to limit the axial displacement, and the annular groove at the other end cooperates with the elastic retainer 14, thereby enhancing the stability of the connection between the main pin 7 and the sliding block 18, and preventing the main pin 7 from falling off during work.

[0025] When the piston rod of the hydraulic cylinder 2 extends and retracts, it drives the movable block 6 to move up and down along the guide rod 5, since the sliding block 18 is connected with the movable block 6 through the main pin 7 and the sliding block 18 is located in the guide groove 17 of the fork 3, the linear motion of the movable block 6 drives the sliding block 18 to slide in the guide groove 17, the fork 3 is designed in a cam shape, the front end has an assembly groove for sliding assembly of the movable block 6, and the rear end is assembled with the main shaft 4 through a spline, the sliding of the sliding block 18 in the guide groove 17 makes the fork 3 rotate around the main shaft 4, thereby driving the main shaft 4 to rotate, realizing the opening and closing operation of the valve; This fork and sliding block structure is designed according to 1.5 times the torque, the rated torque is ≥100000 Nm, and the maximum bearing torque is ≥150000 Nm, which converts the linear motion of the hydraulic cylinder 2 into the rotary motion of the fork 3, provides a basis for the large torque work of the actuator, effectively solves the problem that the conventional actuator torque is insufficient and difficult to open the valve under special working conditions, and meets the demand of the petrochemical field for quick opening and closing of the butterfly valve.

[0026] In order to accurately control the opening and closing angle of the valve, the first limiting sleeve 12 and the second limiting sleeve 13 are arranged on the inner wall of the box 1, the two limiting sleeves are arranged in pairs, are located above and below the fork 3 respectively, are used for limiting the rotation angle of the fork 3, the first limiting sleeve 12 plays an upper limiting role, prevents the piston rod from exceeding the stroke to cause the valve plate to open too large, and the second limiting sleeve 13 plays a lower limiting role, prevents the piston rod from exceeding the movement stroke to cause the valve plate and the pipeline inner wall to be too large to produce abrasion; In the actual operation process, when the fork 3 rotates with the movement of the movable block 6, once touching the first limiting sleeve 12 or the second limiting sleeve 13, the rotation is stopped, thereby ensuring the accuracy of the opening and closing angle of the valve, avoiding that the valve is opened or closed excessively or insufficiently, guaranteeing that the flow, pressure and other parameters of the fluid in the pipeline system are stable, and improving the safety and stability of the entire pipeline system.

[0027] The lower end of the piston rod of the hydraulic cylinder 2 is connected with the upper end of the movable block 6 through the connecting flange 15, the firmness and stability of the connection between the two are guaranteed, the power of the hydraulic cylinder 2 can be reliably transmitted to the movable block 6, the spring washer 16 sleeved on the lower end of the piston rod of the hydraulic cylinder 2 is installed on the upper end of the connecting flange 15 through bolts, the spring washer 16 always maintains the pre-tightening force of the bolts by using the elastic deformation of itself, prevents the bolts from loosening due to vibration and other factors in the working process of the actuator, ensures the reliability of the connection, and guarantees the normal operation of the actuator.

[0028] The box 1 and the fork 3 are made of ZG450-630 cast steel material, and the connecting size of the box 1 and the valve support meets the ISO40F40 standard, the material has good comprehensive mechanical properties, including high strength, hardness and toughness, can withstand the impact and pressure of the fluid in the high temperature and high pressure petroleum chemical environment, is not easy to deform or damage, improves the high temperature and high pressure resistance of the actuator, ensures that the actuator can stably operate for a long time in harsh working conditions, and meets the strict requirements of reliability and durability of the actuator in the field.

[0029] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A butterfly valve with a large torque hydraulic angular actuator, comprising a box (1), a hydraulic cylinder (2) mounted on the upper end of the box (1), and a yoke (3) mounted inside the box (1) and sleeved on the end of a main shaft (4), characterized in that: a guide rod (5) is mounted inside the box (1), the piston rod of the hydraulic cylinder (2) extends downward into the box (1) and is provided with a movable block (6), one end of the movable block (6) is provided with a sliding block (18) through a kingpin (7), the sliding block (18) is slidingly arranged in a guide groove (17) formed on the yoke (3), the other end of the movable block (6) is slidingly assembled with the guide rod (5), the movable block (6) is driven to ascend and descend along the guide rod (5) by the piston rod of the hydraulic cylinder (2), thereby driving the sliding block (18) to slide along the guide groove (17), so that the yoke (3) drives the main shaft (4) to rotate and controls the opening and closing of the valve.

2. A large torque hydraulic angle actuator for butterfly valves as claimed in claim 1, wherein, The number of yokes (3) is two and they are symmetrically distributed on both sides of the movable block (6), the two yokes (3) are each provided with a guide groove (17) arranged along the length direction thereof, each guide groove (17) is slidingly assembled with a sliding block (18), and the kingpin (7) penetrates through the two sliding blocks (18) and the movable block (6) between the two yokes (3) and is locked by an elastic retainer (14).

3. A large torque hydraulic angle actuator for butterfly valves as claimed in claim 2, wherein, The movable block (6) and the sliding block (18) are each provided with a movable hole, one end of the kingpin (7) has an annular protrusion, the other end of the kingpin (7) penetrates through the three movable holes in sequence and has an annular groove, and the elastic retainer (14) is clamped in the annular groove and is attached to the surface of the sliding block (18).

4. A large torque hydraulic angle actuator for butterfly valves as claimed in claim 1, wherein, The guide rod (5) is vertically arranged in the box (1) and is parallel to the piston rod of the hydraulic cylinder (2), and the upper and lower ends of the guide rod (5) are fixed in the upper and lower reserved holes of the box (1) through an end plate (11) and fasteners.

5. A large torque hydraulic angle actuator for butterfly valves as claimed in claim 1, wherein, The side of the movable block (6) away from the main shaft (4) is provided with a shaft sleeve (8) which is slidingly sleeved on the guide rod (5).

6. A large torque hydraulic angle actuator for a butterfly valve as claimed in claim 5, wherein, The inner wall of the box (1) is provided with a sliding rail (10) parallel to the guide rod (5), and the shaft sleeve (8) is slidingly assembled with the sliding rail (10).

7. A large torque hydraulic angle actuator for butterfly valves as claimed in claim 1, wherein, The inner wall of the box (1) is provided with a first limiting sleeve (12) and a second limiting sleeve (13), the first limiting sleeve (12) and the second limiting sleeve (13) are centrally arranged and are arranged above and below the yoke (3) respectively, for limiting the rotation angle of the yoke (3).

8. A large torque hydraulic angle actuator for butterfly valves as claimed in claim 1, wherein, The lower end of the piston rod of the hydraulic cylinder (2) is connected with the upper end of the movable block (6) through a connecting flange (15), and the upper end of the connecting flange (15) is provided with a spring washer (16) sleeved on the lower end of the piston rod of the hydraulic cylinder (2) through bolts.

9. A large torque hydraulic angle actuator for butterfly valves as claimed in claim 1, wherein, The yoke (3) is in the shape of a cam, the front end of the yoke (3) has an assembly groove for slidingly assembling the movable block (6), and the rear end of the yoke (3) is assembled with the main shaft (4) through splines.

10. A high torque hydraulic angle actuator for butterfly valves according to any one of claims 1-9, characterized in that, The box (1) and the yoke (3) are both made of ZG450-630 cast steel.

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