Double-stroke hydraulic cylinder capable of step-by-step control, working method thereof, and application thereof

Abstract

The present invention discloses a two-stroke hydraulic cylinder capable of step-by-step control, as well as its operating method and application. In the hydraulic cylinder, the tail end seal of the secondary cylinder barrel slides in the primary cylinder barrel, while the head end seal passes through the primary cylinder barrel. The tail end seal of the push rod slides in the secondary cylinder barrel, while the head end seal passes through the secondary cylinder barrel. The tail and head of the primary cylinder barrel are respectively provided with oil ports 1 and 2. The tail of the secondary cylinder barrel is provided with an oil hole, while the head is provided with oil port 3. One working interface of a two-position four-way solenoid reversing valve is connected to oil port 1 through a first pipeline, while the other working interface is blocked. One working interface of the three-position four-way solenoid reversing valve is connected to oil port 2 through a second pipeline, while the other working interface is connected to oil port 3 through a third pipeline. A superimposed one-way throttle valve and a one-way sequence valve are provided on the second pipeline, and a superimposed one-way throttle valve is provided on the third pipeline. The hydraulic cylinder can achieve reliable and stable extension of the first working stroke without the need for position detection and control, and is economical and convenient.

Description

Technical Field

[0001] The present invention relates to a hydraulic cylinder, in particular to a double-stroke hydraulic cylinder capable of step-by-step control, a working method thereof and an application thereof. Background Art

[0002] Driven by high-pressure oil, hydraulic cylinders offer high driving force and fast response, making them widely used in heavy industries such as metallurgy. However, in certain special working conditions, a two-step fixed stroke or workstation is required to complete the work, and the load inertia is large, and speed requirements are high. However, due to the limited space available for equipment installation, only short-stroke hydraulic cylinders can be used. To meet these requirements, there are currently two approaches to controlling the first step of the hydraulic cylinder's stroke or workstation: 1) Using proximity switches and ordinary electromagnetic hydraulic valves for control. However, due to the high speed and large load inertia of the hydraulic cylinder, the proximity switches are unable to capture the signal in time, resulting in frequent detection failures and failing to meet the working conditions; 2) Using closed-loop control methods using proportional valves and displacement sensors. This not only requires a large investment, but also has poor anti-contamination properties for the hydraulic system. Furthermore, due to individual differences in proportional valves, these valves often fail after a period of use. Summary of the Invention

[0003] The purpose of the present invention is to provide a two-stroke hydraulic cylinder capable of step-by-step control, a working method thereof, and an application thereof. The hydraulic cylinder can realize reliable and stable extension of the first working step without the need for position detection and control, is economical and convenient, avoids the impact of the cylinder structure caused by retracting too quickly, has a simple structure, is small in size, and is easy to install.

[0004] The technical solution adopted in the present invention is:

[0005] A double-stroke hydraulic cylinder capable of step-by-step control comprises a hydraulic cylinder body and a hydraulic control system; the hydraulic cylinder body comprises a primary cylinder barrel, a secondary cylinder barrel and a push rod, the tail end of the secondary cylinder barrel is slidingly fitted in the primary cylinder barrel through a piston structure seal, and the head end seals and passes through the primary cylinder barrel, the tail end of the push rod is slidingly fitted in the secondary cylinder barrel through a piston structure seal, and the head end seals and passes through the secondary cylinder barrel, the tail and head of the primary cylinder barrel are respectively provided with oil port 1 and oil port 2, the tail of the secondary cylinder barrel is provided with an oil hole separated from the oil port 1, and the head is provided with oil port 3 located outside the primary cylinder barrel; the hydraulic control system comprises two A four-way solenoid directional valve and a three-position four-way solenoid directional valve, one working interface A of the two-position four-way solenoid directional valve is connected to oil port one through the first pipeline, and the other working interface B is blocked, one working interface A of the three-position four-way solenoid directional valve is connected to oil port two through the second pipeline, and the other working interface B is connected to oil port three through the third pipeline, the oil inlet interface P and the oil outlet interface T of the two-position four-way solenoid directional valve and the three-position four-way solenoid directional valve are respectively connected to the oil supply pipeline and the oil return pipeline, a superimposed one-way throttle valve and a one-way sequence valve are provided on the second pipeline, and a superimposed one-way throttle valve is provided on the third pipeline.

[0006] Furthermore, the first end of the first cylinder is sealed with a sealing cover through its own flange, bolts, nuts and gaskets, and the second cylinder passes through the sealing cover and is sealed with the dust ring and sealing ring at the outlet hole; the first end of the second cylinder is sealed with a sealing cover through its own flange, bolts, nuts and gaskets, and the push rod passes through the sealing cover and is sealed with the dust ring and sealing ring at the outlet hole.

[0007] Furthermore, a seal that cooperates with the primary cylinder is provided at the piston structure at the tail end of the secondary cylinder; and a seal that cooperates with the secondary cylinder is provided at the piston structure at the tail end of the push rod.

[0008] Furthermore, a hinged joint for external connection is provided at the front end of the push rod.

[0009] Furthermore, a trunnion for installation is provided on the first-stage cylinder.

[0010] Furthermore, the oil supply pipeline, the first pipeline, the second pipeline and the third pipeline are all provided with high-pressure ball valves, and the oil return pipeline is provided with a one-way valve.

[0011] Furthermore, the oil supply pipeline, the oil return pipeline, the first pipeline, the second pipeline and the third pipeline are all provided with pressure measuring joints, and the pressure measuring joints can measure pressure through an external pressure measuring hose and a pressure gauge.

[0012] The working method of the above-mentioned double-stroke hydraulic cylinder capable of step-by-step control is:

[0013] In the initial position: the two-position four-way solenoid reversing valve switches to the TA port being conductive and the P port being blocked, and the three-position four-way solenoid reversing valve switches to the PB port being conductive and the TA port being conductive, so that the high-pressure hydraulic oil in the three-way oil port, the return oil in oil port 1, and the return oil in oil port 2 are brought back by the back pressure through the one-way sequence valve, driving the secondary cylinder and the push rod to fully retract in succession, completing the initial position;

[0014] During the first working advance: the two-position four-way solenoid reversing valve switches to the PA port to be conductive and the T port to be blocked, and the three-position four-way solenoid reversing valve switches to the PB port to be conductive and the TA port to be conductive, so that the oil port 1 and the oil port 3 pass high-pressure hydraulic oil, and the oil port 2 returns oil, the secondary cylinder extends outward, and the push rod is pressed at the tail end of the secondary cylinder and does not move relative to the secondary cylinder until the secondary cylinder moves to the limit position and is blocked by the head end of the primary cylinder, completing the first working advance or stroke;

[0015] During the second working step: the two-position four-way solenoid reversing valve is switched to the PA port being conductive and the T port being blocked, and the three-position four-way solenoid reversing valve is switched to the PA port being conductive and the TB port being conductive, so that the oil port one and the oil port two are connected to the high-pressure hydraulic oil and the oil port three returns the oil, the push rod is extended outward, and the secondary cylinder is pressed against the head end of the primary cylinder and does not move until the push rod moves to the limit position and is blocked by the head end of the secondary cylinder, completing the second working step or stroke.

[0016] An application of the above-mentioned double-stroke hydraulic cylinder capable of step-by-step control is used on the cooling bed of a bar production line. Multiple cylinders are used in parallel to drive the full-length synchronous lifting and lowering of the brake skirt through a long shaft and several connecting rod mechanisms. When producing small-sized bars with high-speed rolling, the brake skirt is switched in sequence between low, middle and high positions through the hydraulic control system. When producing large-sized bars with low-speed rolling, the middle position is cancelled and the brake skirt is switched between low and high positions through the hydraulic control system.

[0017] Low position action: the two-position four-way solenoid reversing valve switches to the TA port being conductive and the P port being blocked, and the three-position four-way solenoid reversing valve switches to the PB port being conductive and the TA port being conductive, so that the high-pressure hydraulic oil of the three-way oil port, the return oil of oil port 1, and the return oil of oil port 2 are returned with back pressure through the one-way sequence valve, driving the secondary cylinder and the push rod to fully retract in succession, completing the retraction to the initial position;

[0018] Neutral action: The two-position four-way solenoid directional control valve switches to the PA port being conductive and the T port being blocked; the three-position four-way solenoid directional control valve switches to the PA port being conductive and the TB port being conductive, so that ports 1 and 2 are connected to high-pressure hydraulic oil and port 3 returns oil, the push rod extends outward, and the secondary cylinder is pressed against the head end of the primary cylinder and does not move until the push rod moves to the limit position and is blocked by the head end of the secondary cylinder, completing the neutral stop;

[0019] High-position action: the two-position four-way solenoid directional control valve is switched to the PA port being conductive and the T port being blocked; the three-position four-way solenoid directional control valve is switched to the PA port being conductive and the TB port being conductive, so that the oil ports one and two are connected to the high-pressure hydraulic oil and the oil port three returns the oil. The push rod extends outward and the secondary cylinder is pressed against the head end of the primary cylinder and does not move until the push rod moves to the limit position and is blocked by the head end of the secondary cylinder, completing the high position.

[0020] The beneficial effects of the present invention are:

[0021] The hydraulic cylinder can be designed into two fixed strokes according to specific stroke requirements. It can be extended in two steps under the control of the hydraulic control system to meet two working positions, and then quickly retracted. The hydraulic cylinder can achieve reliable and stable extension of the first working position without the need for position detection and control, which is economical and convenient. The hydraulic cylinder avoids the impact of the cylinder structure caused by excessive retraction. The hydraulic cylinder has a simple structure, small size and is easy to install. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of a double-stroke hydraulic cylinder capable of step-by-step control in an embodiment of the present invention.

[0023] Figure 2 Schematic diagram of the structure of the hydraulic cylinder body in an embodiment of the present invention.

[0024] Figure 3 This is a schematic diagram of the brake skirt in the low position when an embodiment of the present invention is applied to a cooling bed of a bar production line.

[0025] Figure 4 It is a schematic diagram of the neutral position state of the brake skirt when an embodiment of the present invention is applied to a cooling bed of a bar production line.

[0026] Figure 5 This is a schematic diagram of the high-position state of the brake skirt when an embodiment of the present invention is applied to a cooling bed of a bar production line.

[0027] In the figure: 1-high-pressure ball valve; 2-check valve; 3-pressure measuring joint; 4-two-position four-way solenoid reversing valve; 5-three-position four-way solenoid reversing valve; 6-superimposed one-way throttle valve; 7-one-way sequence valve; 8-pressure gauge; 9-pressure measuring hose; 10-hydraulic cylinder body; 11-dust ring; 12-sealing ring; 13-sealing cover; 14-secondary cylinder; 15-bolts, nuts and washers; 16-first-stage cylinder; 17-seal; 18-oil port 1; 19-trunnion; 20-oil hole; 21-oil port 2; 22-push rod; 23-oil port 3; 24-articulated joint; 25-long shaft; 26-connecting rod mechanism; 27-roller drive motor; 28-input roller; 29-protective cover; 30-brake skirt; 31-rod; 32-stepping rack. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings and examples.

[0029] like Figure 1 and Figure 2 As shown, a double-stroke hydraulic cylinder capable of step-by-step control comprises a hydraulic cylinder body 10 and a hydraulic control system; Figure 2 As shown, the hydraulic cylinder body 10 includes a primary cylinder 16, a secondary cylinder 14 and a push rod 22. The tail end of the secondary cylinder 14 is slidingly fitted in the primary cylinder 16 through a piston structure seal, and the head end is sealed and passes through the primary cylinder 16. The tail end of the push rod 22 is slidingly fitted in the secondary cylinder 14 through a piston structure seal, and the head end is sealing and passes through the secondary cylinder 14. The tail and head of the primary cylinder 16 are respectively provided with an oil port 18 and an oil port 21. The tail of the secondary cylinder 14 is provided with an oil hole 20 separated from the oil port 18, and the head is provided with an oil port 3 23 located outside the primary cylinder 16. Figure 1As shown, the hydraulic control system includes a two-position four-way solenoid reversing valve 4 and a three-position four-way solenoid reversing valve 5. One working interface A of the two-position four-way solenoid reversing valve 4 is connected to the oil port 1 18 through the first pipeline, and the other working interface B is blocked. One working interface A of the three-position four-way solenoid reversing valve 5 is connected to the oil port 2 21 through the second pipeline, and the other working interface B is connected to the oil port 3 23 through the third pipeline. The oil inlet interface P and the oil outlet interface T of the two-position four-way solenoid reversing valve 4 and the three-position four-way solenoid reversing valve 5 are respectively connected to the oil supply pipeline and the oil return pipeline. A superimposed one-way throttle valve 6 and a one-way sequence valve 7 are provided on the second pipeline, and a superimposed one-way throttle valve 6 is provided on the third pipeline.

[0030] like Figure 2 As shown, in this embodiment, the first end of the first-stage cylinder 16 is sealed with a sealing cover 13 through its own flange and bolts, nuts and washers 15, and the second-stage cylinder 14 passes through the sealing cover 13 and is sealed with the dust ring 11 and the sealing ring 12 at the outlet hole; the first end of the second-stage cylinder 14 is sealed with a sealing cover 13 through its own flange and bolts, nuts and washers 15, and the push rod 22 passes through the sealing cover 13 and is sealed with the dust ring 11 and the sealing ring 12 at the outlet hole.

[0031] like Figure 1 As shown, in this embodiment, a high-pressure ball valve 1 is provided on the oil supply pipeline, the first pipeline, the second pipeline and the third pipeline, and a one-way valve 2 is provided on the oil return pipeline, which improves safety performance and facilitates the protection of major equipment and precision components in emergency situations.

[0032] like Figure 1 As shown, in this embodiment, pressure measuring joints 3 are provided on the oil supply pipeline, the oil return pipeline, the first pipeline, the second pipeline and the third pipeline. The pressure measuring joints 3 can measure the pressure 8 through an external pressure measuring hose 9 and a pressure gauge, thereby improving safety performance and facilitating maintenance and detection of system status.

[0033] like Figure 2 As shown, in this embodiment, a seal 17 cooperating with the primary cylinder 16 is provided at the piston structure at the tail end of the secondary cylinder 14 ; a seal 17 cooperating with the secondary cylinder 14 is provided at the piston structure at the tail end of the push rod 22 .

[0034] like Figure 2 As shown, in this embodiment, the front end of the push rod 22 is provided with a hinged joint 24 for external connection.

[0035] like Figure 2 As shown, in this embodiment, a trunnion 19 for installation is provided on the first-stage cylinder 16.

[0036] The working method of the above-mentioned double-stroke hydraulic cylinder capable of step-by-step control is:

[0037] In the initial position: the two-position four-way solenoid reversing valve switches 4 (the electromagnet in position a loses power) to the TA port being conductive and the P port being blocked, and the three-position four-way solenoid reversing valve 5 switches (the electromagnet in position a is energized) to the PB port being conductive and the TA port being conductive, so that the oil port three 23 passes through the high-pressure hydraulic oil, the oil port one 18 returns the oil, and the oil port two 21 returns the oil with back pressure through the one-way sequence valve 7 (the pressure can be set), driving the secondary cylinder 14 and the push rod 22 to fully retract in succession, completing the initial position; because the one-way sequence valve 7 provides back pressure for the return oil of the oil port two 21, the secondary cylinder 14 without back pressure retracts first, and the push rod 22 retracts after it is fully retracted, avoiding the impact of retraction too quickly on the primary cylinder 16 and the secondary cylinder 14.

[0038] During the first working advance: the two-position four-way solenoid reversing valve 4 is switched (the electromagnet is energized in position a) to the PA port being connected and the T port being blocked, the three-position four-way solenoid reversing valve 5 is switched (the electromagnet is energized in position a) to the PB port being connected and the TA port being connected, so that the oil port 18 and the oil port 3 23 are connected to the high-pressure hydraulic oil, and the oil port 2 21 returns the oil, the secondary cylinder 14 is extended, and the push rod 22 is pressed at the tail end of the secondary cylinder 14 and is immovable relative to the secondary cylinder 14 until the secondary cylinder 14 moves to the limit position and is blocked by the head end of the primary cylinder 16, completing the first working advance or stroke; the oil port 3 23 is connected to the high-pressure hydraulic oil, on the one hand to maintain the pushed rod 22 in a pressed state, and on the other hand to provide a certain back pressure for the secondary cylinder 14, thereby improving its stability when extending. The secondary cylinder 14 is limited by the structure of the primary cylinder 16 itself, and the working position of the first step is stopped reliably, and no position detection and control are required, which is economical and convenient.

[0039] During the second working step: the two-position four-way solenoid reversing valve 4 is switched (the electromagnet is energized in position a) to the PA port being conductive and the T port being blocked, the three-position four-way solenoid reversing valve 5 is switched (the electromagnet is energized in position b) to the PA port being conductive and the TB port being conductive, so that the oil port 18 and the oil port 2 21 pass the high-pressure hydraulic oil, and the oil port 3 23 returns the oil, the push rod 22 extends outward, and the secondary cylinder 14 is pressed against the head end of the primary cylinder 16 and does not move until the push rod 22 moves to the limit position and is blocked by the head end of the secondary cylinder 14, completing the second working step or stroke.

[0040] As can be seen from the above, the hydraulic cylinder of the present invention can be designed into two fixed strokes according to specific stroke requirements. It can be extended in two steps under the control of the hydraulic control system to meet two working positions and then quickly retracted. The hydraulic cylinder of the present invention can achieve reliable and stable extension of the first working position without the need for position detection and control, which is economical and convenient. The hydraulic cylinder of the present invention avoids the impact of retracting too quickly on the cylinder structure. The hydraulic cylinder of the present invention has a simple structure, small size, and is easy to install. The hydraulic cylinder of the present invention has excellent functions and good working effects, and has good application prospects. The following is an application example:

[0041] Application Examples

[0042] The cooling bed is an indispensable equipment in the bar production line. It is mainly used to transport the cut bars 31 to the stepping rack 32 for slow cooling, so that its temperature drops from 900°C to 100-300°C, and then output it to the downstream equipment; the cooling bed generally includes a long shaft 25, a connecting rod mechanism 26, a roller drive motor 27, an input roller table 28, a protective cover 29, a brake skirt 30 and a stepping rack 32, among which the brake skirt 30 has a fast lifting rhythm and is driven by a hydraulic cylinder. Multiple hydraulic cylinders are used in parallel, and the brake skirt 30 is driven to rise and fall synchronously along its entire length through a long shaft 25 and several connecting rod mechanisms 26 in turn.

[0043] Currently, the brake skirt 30's lifting and lowering control uses two operating modes: one for large-gauge, low-speed rolling, where the brake skirt 30 descends from a high position to a low position, then rises from a low position to a high position after a delay. This reciprocating motion constitutes one cycle. The other for small-gauge, high-speed rolling, where the brake skirt 30 descends from a high position to a low position, then rises from a low position to a mid-position after a delay. It pauses at the mid-position for a delay to allow sufficient time for the bar 31 to brake on the brake plate, and then continues to rise to the high position. This completes one cycle. The brake skirt 30's initial position is always high. The high position is the skirt's steel feeding and steel ejection position, the low position is the steel lowering position, and the mid-position is the steel separation and braking position during high-speed rolling.

[0044] At present, the high position, middle position and low position of the brake skirt 30 are detected by proximity switches. When the in-position signal is detected, the PLC gives a command signal to the hydraulic reversing valve to control the reversing of the reversing valve. However, the hydraulic cylinder has a short stroke (about 80 to 150 mm), a large load inertia and a fast speed requirement (100 mm / s to 200 mm / s). When the middle position stop is adopted in high-speed rolling, the proximity switch often does not have time to capture the middle position, and the hydraulic cylinder rushes through the middle detection position, and the steel separation and simultaneous braking in the middle position cannot be achieved. Therefore, the working conditions of high-speed steel rolling cannot be met, and the middle position is often abandoned, which greatly limits the steel feeding rhythm of the cooling bed and seriously affects the production capacity.

[0045] In order to solve the above problems, the hydraulic cylinder 10 of the present invention can be used on the cooling bed of the bar production line, and multiple cylinders can be used in parallel to drive the brake skirt 30 to rise and fall synchronously along its entire length through a long shaft 25 and a plurality of connecting rod mechanisms 26. When small-sized bars 31 are produced by high-speed rolling, the brake skirt 30 is switched in sequence between low, middle and high positions through the hydraulic control system. When large-sized bars 31 are produced by low-speed rolling, the middle position is cancelled, and the brake skirt 30 is switched between low and high positions through the hydraulic control system.

[0046] like Figure 3As shown, the low position (brake position) action: the two-position four-way solenoid reversing valve 4 is switched (the electromagnet in position a is de-energized) to the TA port being conductive and the P port being blocked, and the three-position four-way solenoid reversing valve 5 is switched (the electromagnet in position a is energized) to the PB port being conductive and the TA port being conductive, so that the oil port 3 23 is connected to the high-pressure hydraulic oil, the oil port 18 is returned, and the oil port 2 21 is returned with back pressure through the one-way sequence valve 7 (the pressure can be set), driving the secondary cylinder 14 and the push rod 22 to be fully retracted in succession, completing the retraction to the initial position;

[0047] like Figure 4 As shown, in the neutral position (steel and brake positions), the two-position four-way solenoid directional control valve 4 is switched (the electromagnet is energized in position a) to connect the PA port and block the T port; the three-position four-way solenoid directional control valve 5 is switched (the electromagnet is energized in position b) to connect the PA port and connect the TB port, so that the oil port 18 and the oil port 2 21 pass the high-pressure hydraulic oil, and the oil port 3 23 returns the oil, the push rod 22 extends outward, and the secondary cylinder 14 is pressed against the head end of the primary cylinder 16 and does not move until the push rod 22 moves to the limit position and is blocked by the head end of the secondary cylinder 14, completing the neutral stop;

[0048] like Figure 5 As shown, the high position (steel feeding and throwing position) action: the two-position four-way solenoid reversing valve 4 is switched (the electromagnet is energized in position a) to the PA port being conductive and the T port being blocked, the three-position four-way solenoid reversing valve 5 is switched (the electromagnet is energized in position b) to the PA port being conductive and the TB port being conductive, so that the oil port 18 and the oil port 2 21 pass the high-pressure hydraulic oil, and the oil port 3 23 returns the oil, the push rod 22 extends outward, and the secondary cylinder 14 is pressed against the head end of the primary cylinder 16 and does not move until the push rod 22 moves to the limit position and is blocked by the head end of the secondary cylinder 16, completing the high position.

[0049] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A two-stroke hydraulic cylinder capable of step-by-step control, characterized in that: It includes a hydraulic cylinder body and a hydraulic control system; the hydraulic cylinder body includes a first-stage cylinder, a second-stage cylinder and a push rod, the tail end of the second-stage cylinder is slidingly fitted in the first-stage cylinder through a piston structure seal, and the head end is sealed and passes through the first-stage cylinder, the tail end of the push rod is slidingly fitted in the second-stage cylinder through a piston structure seal, and the head end is sealed and passes through the second-stage cylinder, the tail and head of the first-stage cylinder are respectively provided with oil port 1 and oil port 2, the tail of the second-stage cylinder is provided with an oil hole separated from oil port 1, and the head is provided with oil port 3 located outside the first-stage cylinder; the hydraulic control system includes a two-position four-way electromagnetic reversing valve And a three-position four-way solenoid reversing valve, one working interface A of the two-position four-way solenoid reversing valve is connected to oil port one through the first pipeline, and the other working interface B is blocked, one working interface A of the three-position four-way solenoid reversing valve is connected to oil port two through the second pipeline, and the other working interface B is connected to oil port three through the third pipeline, the oil inlet interface P and the oil outlet interface T of the two-position four-way solenoid reversing valve and the three-position four-way solenoid reversing valve are respectively connected to the oil supply pipeline and the oil return pipeline, a superimposed one-way throttle valve and a one-way sequence valve are provided on the second pipeline, and a superimposed one-way throttle valve is provided on the third pipeline.

2. The dual-stroke hydraulic cylinder capable of step-by-step control according to claim 1, characterized in that: The first end of the first-stage cylinder is sealed with a sealing cover through its own flange, bolts, nuts and washers. The second-stage cylinder passes through the sealing cover and is sealed with the dust ring and sealing ring at the outlet hole; the first end of the second-stage cylinder is sealed with a sealing cover through its own flange, bolts, nuts and washers. The push rod passes through the sealing cover and is sealed with the dust ring and sealing ring at the outlet hole.

3. The dual-stroke hydraulic cylinder capable of step-by-step control according to claim 1, characterized in that: A seal that cooperates with the primary cylinder is provided at the piston structure at the tail end of the secondary cylinder; and a seal that cooperates with the secondary cylinder is provided at the piston structure at the tail end of the push rod.

4. The dual-stroke hydraulic cylinder capable of step-by-step control according to claim 1, characterized in that: The front end of the push rod is provided with a hinged joint for external connection.

5. The dual-stroke hydraulic cylinder capable of step-by-step control according to claim 1, characterized in that: A trunnion for mounting is provided on the first-stage cylinder.

6. The dual-stroke hydraulic cylinder capable of step-by-step control according to claim 1, characterized in that: The oil supply pipeline, the first pipeline, the second pipeline and the third pipeline are all equipped with high-pressure ball valves, and the oil return pipeline is equipped with a one-way valve.

7. The dual-stroke hydraulic cylinder capable of step-by-step control according to claim 1, characterized in that: The oil supply pipeline, oil return pipeline, first pipeline, second pipeline and third pipeline are all provided with pressure measuring joints, which can measure pressure through external pressure measuring hoses and pressure gauges.

8. A method for operating a dual-stroke hydraulic cylinder capable of step-by-step control according to any one of claims 1 to 7, characterized in that: In the initial position: the two-position four-way solenoid reversing valve switches to the TA port being conductive and the P port being blocked, and the three-position four-way solenoid reversing valve switches to the PB port being conductive and the TA port being conductive, so that the high-pressure hydraulic oil in the three-way oil port, the return oil in oil port 1, and the return oil in oil port 2 are brought back by the back pressure through the one-way sequence valve, driving the secondary cylinder and the push rod to fully retract in succession, completing the initial position; During the first working advance: the two-position four-way solenoid reversing valve switches to the PA port to be conductive and the T port to be blocked, and the three-position four-way solenoid reversing valve switches to the PB port to be conductive and the TA port to be conductive, so that the oil port 1 and the oil port 3 pass high-pressure hydraulic oil, and the oil port 2 returns oil, the secondary cylinder extends outward, and the push rod is pressed at the tail end of the secondary cylinder and does not move relative to the secondary cylinder until the secondary cylinder moves to the limit position and is blocked by the head end of the primary cylinder, completing the first working advance or stroke; During the second working step: the two-position four-way solenoid reversing valve is switched to the PA port being conductive and the T port being blocked, and the three-position four-way solenoid reversing valve is switched to the PA port being conductive and the TB port being conductive, so that the oil port one and the oil port two are connected to the high-pressure hydraulic oil and the oil port three returns the oil, the push rod is extended outward, and the secondary cylinder is pressed against the head end of the primary cylinder and does not move until the push rod moves to the limit position and is blocked by the head end of the secondary cylinder, completing the second working step or stroke.

9. An application of a step-controlled dual-stroke hydraulic cylinder according to any one of claims 1 to 7, characterized in that: Used on the cooling bed of the bar production line, multiple are used in parallel, and a long shaft and several connecting rod mechanisms are used to drive the brake skirt to rise and fall synchronously along its entire length. When small-sized bars are produced by high-speed rolling, the brake skirt is switched in sequence between low, middle and high positions through the hydraulic control system. When large-sized bars are produced by low-speed rolling, the middle position is cancelled and the brake skirt is switched between low and high positions through the hydraulic control system. Low position action: the two-position four-way solenoid reversing valve switches to the TA port being conductive and the P port being blocked, and the three-position four-way solenoid reversing valve switches to the PB port being conductive and the TA port being conductive, so that the high-pressure hydraulic oil of the three-way oil port, the return oil of oil port 1, and the return oil of oil port 2 are returned with back pressure through the one-way sequence valve, driving the secondary cylinder and the push rod to fully retract in succession, completing the retraction to the initial position; Neutral action: The two-position four-way solenoid directional control valve switches to the PA port being conductive and the T port being blocked; the three-position four-way solenoid directional control valve switches to the PA port being conductive and the TB port being conductive, so that ports 1 and 2 are connected to high-pressure hydraulic oil and port 3 returns oil, the push rod extends outward, and the secondary cylinder is pressed against the head end of the primary cylinder and does not move until the push rod moves to the limit position and is blocked by the head end of the secondary cylinder, completing the neutral stop; High-position action: the two-position four-way solenoid directional control valve is switched to the PA port being conductive and the T port being blocked; the three-position four-way solenoid directional control valve is switched to the PA port being conductive and the TB port being conductive, so that the oil ports one and two are connected to the high-pressure hydraulic oil and the oil port three returns the oil. The push rod extends outward and the secondary cylinder is pressed against the head end of the primary cylinder and does not move until the push rod moves to the limit position and is blocked by the head end of the secondary cylinder, completing the high position.

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