CN219985779U - Hydraulic system for anti-tear rollers in leveling decoilers - Google Patents

Abstract

The utility model is a hydraulic system for anti-tear rollers in leveling decoilers, which includes a hydraulic pump station, a proportional directional valve, an electromagnetic reversing valve, a proportional pressure reducing valve and a hydraulic cylinder. The piston rod end of the hydraulic cylinder is used to be fixedly connected to the anti-tear roller. The hydraulic pump station is connected to the rodless cavity and rod cavity of the hydraulic cylinder through the oil supply pipe and the oil return pipe respectively. The proportional directional valve is connected to the oil supply pipe and return pipe. The oil pipes are all connected and can control the extension or retraction of the piston rod. The electromagnetic directional valve is located between the hydraulic cylinder and the proportional directional valve. It is connected to both the oil supply pipe and the oil return pipe, and can control the oil supply pipe and the oil return pipe to be in passage or cut off at the same time. The proportional pressure reducing valve is connected in series to the oil supply pipe and is located between the hydraulic cylinder and the electromagnetic reversing valve. A pressure sensor or pressure relay is connected to the oil supply pipe and close to the rodless cavity. The hydraulic system of the utility model can be used in conjunction with the anti-tear roller to prevent strip tearing caused by shaking of the strip.

Description

Hydraulic system for anti-tear rollers in leveling decoilers

Technical field

The utility model relates to the field of cold-rolled strip production, and in particular to a hydraulic system for anti-tear rollers in leveling uncoilers.

Background technique

In cold-rolled strip production, a single-stand four-roller smoothing unit improves the mechanical properties of the strip and improves the surface quality, flatness, and surface roughness of the strip through smoothing the cold-rolled and annealed steel coils. The bell-type furnace performs recrystallization annealing on steel coils. When the steel coils in the furnace begin to cool, the outer layer of the steel coils cools faster while the inner layer cools more slowly due to poor heat dissipation. The temperature difference between the inside and outside of the steel coils will produce a significant High radial pressure will cause bonding between steel coil layers. During flat uncoiling, the bonding of the strip can cause the strip to tear or break. An anti-tear roller is installed at the outlet of the decoiler. By adjusting the position or pressure of the roller, the stress state of the strip can be optimized to prevent strip tearing caused by shaking of the strip. In order to realize the movement of this machine, a new matching hydraulic control system needs to be designed.

Therefore, relying on many years of experience and practice in related industries, the inventor proposes a hydraulic system for anti-tear rollers in leveling decoilers to overcome the shortcomings of the existing technology.

Utility model content

The purpose of this utility model is to provide a hydraulic system for an anti-tear roller in a leveling uncoiler, which can be used in conjunction with the anti-tear roller to prevent strip tearing caused by shaking of the strip.

The purpose of this utility model is achieved as follows: a hydraulic system for anti-tear rollers in leveling decoilers, including a hydraulic pump station, a proportional directional valve, an electromagnetic reversing valve, a proportional pressure reducing valve and a hydraulic cylinder; a hydraulic cylinder The end of the piston rod is used to be fixedly connected to the anti-tear roller. The hydraulic pump station is connected to the rodless cavity and rod cavity of the hydraulic cylinder through the oil supply pipe and the oil return pipe respectively. The proportional directional valve is connected to the oil supply pipe and the oil return pipe. connection, and can control the extension or retraction of the piston rod; the electromagnetic reversing valve is located between the hydraulic cylinder and the proportional directional valve. It is connected to both the oil supply pipe and the oil return pipe, and can control the oil supply pipe and the oil return pipe to be passages at the same time. Or cut off at the same time; the proportional pressure reducing valve is connected in series to the oil supply pipe and is located between the hydraulic cylinder and the electromagnetic reversing valve. A pressure sensor or pressure relay is connected to the oil supply pipe and close to the rodless cavity.

In a preferred embodiment of the present invention, a displacement sensor is installed on the rodless cavity.

In a preferred embodiment of the present invention, the proportional directional valve is a three-position four-way valve and has a first pressure oil port, a first return oil port, a first working oil port and a second working oil port. The oil port and the first working oil port are both connected in series to the oil supply pipe and the first working oil port is set close to the electromagnetic reversing valve. The first oil return port and the second working oil port are both connected in series to the oil return pipe and the second The working oil port is located close to the electromagnetic reversing valve.

In a preferred embodiment of the present invention, the proportional directional valve is a high-frequency response proportional valve or a proportional servo valve.

In a preferred embodiment of the present invention, the electromagnetic reversing valve includes four actuating oil ports, two of which are connected in series to the oil supply pipe, and the other two actuating oil ports are connected in series to the oil return pipe.

In a preferred embodiment of the present invention, the electromagnetic reversing valve is an electromagnetic ball valve.

In a preferred embodiment of the present invention, a first manual valve is provided on the oil supply pipe between the rodless chamber and the proportional pressure reducing valve, and a first manual valve is provided on the oil return pipe between the rodless chamber and the electromagnetic reversing valve. There is a second manual valve between them.

In a preferred embodiment of the present invention, a first pressure measuring joint is connected to the oil supply pipe between the rodless chamber and the proportional pressure reducing valve, and a first pressure measuring joint is connected to the oil return pipe between the rodless chamber and the electromagnetic reversing valve. A second pressure measuring joint is connected between the valves.

In a preferred embodiment of the present invention, the hydraulic pump station includes a hydraulic pump set and an oil tank. The oil supply pipe and the oil return pipe are both connected to the oil tank, and the hydraulic pump set is located on the oil supply pipe.

In a preferred embodiment of the present invention, a one-way valve is provided on the oil return pipe and close to the hydraulic pump station.

From the above, the hydraulic system of the present invention can be used in conjunction with the anti-tear roller. The proportional directional valve can be used to move the piston rod of the hydraulic cylinder to the preset position. The pressure sensor can be used to detect the pressure of the rodless chamber in real time, and then the proportional directional valve can be used to detect the pressure of the rodless chamber in real time. The pressure reducing valve adjusts the pressure of the rodless chamber to achieve closed-loop control of the force of the anti-tear roller, effectively ensuring that the pressure exerted by the anti-tear roller on the strip is constant, thereby effectively preventing strip tearing caused by the shaking of the strip. .

Description of the drawings

The following drawings are only intended to schematically illustrate and explain the present invention, and do not limit the scope of the present invention. in:

Figure 1: A schematic structural diagram of the hydraulic system for the anti-tear roller in the leveling decoiler provided by the present utility model.

Explanation of reference numbers:

1. Hydraulic pump station; 11. Hydraulic pump group; 12. Oil tank; 13. Oil supply pipe; 131. Pressure sensor; 132. First manual valve; 133. First pressure measuring joint; 14. Oil return pipe; 141. No. Two manual valves; 142. Second pressure measuring joint; 143. One-way valve;

2. Proportional directional valve; P3, first pressure port; T1, first return port; A1, first working port; B1, second working port;

3. Electromagnetic reversing valve; C1, first execution port; C2, second execution port; C3, third execution port; C4, fourth execution port;

4. Proportional pressure reducing valve; P4, second pressure port; T2, second return port; A2, third working port;

5. Hydraulic cylinder; 51. Rodless cavity; 511. Displacement sensor; 52. Rod cavity.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention will now be described with reference to the accompanying drawings.

As shown in Figure 1, this application provides a hydraulic system for anti-tear rollers in leveling decoilers, including a hydraulic pump station 1, a proportional directional valve 2, an electromagnetic reversing valve 3, a proportional pressure reducing valve 4 and a hydraulic cylinder. 5; The piston rod end of the hydraulic cylinder 5 is used to be fixedly connected to the anti-tear roller, and the hydraulic pump station 1 is connected to the rodless cavity 51 and the rod cavity 52 of the hydraulic cylinder 5 through the oil supply pipe 13 and the oil return pipe 14, respectively. The proportional directional valve 2 is connected to both the oil supply pipe 13 and the oil return pipe 14, and can control the extension or retraction of the piston rod; the electromagnetic directional valve 3 is located between the hydraulic cylinder 5 and the proportional directional valve 2, and is connected to the oil supply pipe 13 Both are connected to the oil return pipe 14, and can control the oil supply pipe 13 and the oil return pipe 14 to be in passage or cut off at the same time; the proportional pressure reducing valve 4 is connected in series to the oil supply pipe 13 and is located between the hydraulic cylinder 5 and the electromagnetic reversing valve 3 A pressure sensor 131 or a pressure relay is connected to the oil supply pipe 13 and close to the rodless cavity 51 (that is, between the hydraulic cylinder 5 and the proportional pressure reducing valve 4) for real-time feedback of the rodless cavity of the hydraulic cylinder 5. 51 pressure.

The hydraulic pump station 1 gives the pressure P1 to the rodless chamber 51 through the oil supply pipe 13 to overcome the friction of the hydraulic cylinder 5 and the hydraulic valves (the hydraulic valves mentioned here include the proportional directional valve 2, the electromagnetic reversing valve 3 and the proportional pressure reducing valve 4) The pressure P2 of the rod cavity 52 is the pressure loss of the pipe, and the pressure P2 of the rod cavity 52 is the back pressure. The area of the rodless cavity 51 is A1, and the area of the rod cavity 52 is A2. The force F1 of the rodless cavity 51 is P1×A1, and the force F2 of the rod cavity 52 is P2×A2. The resultant force F formed by the sum of F1 and the self-weight G of the movable parts of the anti-tear roller, minus the sum of F2 and the action friction force f of the anti-tear roller, acts on the strip. The resultant force F changes with the strip specifications. For a certain specification of strip steel, the resultant force F is kept at a constant value during the rolling process, so that the anti-tear roller can follow the strip steel.

The hydraulic system can be used to adjust the resultant force exerted by the anti-tear roller on the strip so that the resultant force value remains constant. Specifically, during use, the piston rod of the hydraulic cylinder 5 and the anti-tear roller are fixed. The above-mentioned electromagnetic reversing valve 3 has a connecting working position and a cutting working position. During normal rolling, the electromagnetic reversing valve 3 is in the connecting working position, and the oil supply pipe 13 and the oil return pipe 14 are both passages; in an emergency, the electromagnetic reversing valve 3 is in the connecting working position. The reversing valve 3 is in the cutting position, and both the oil supply pipe 13 and the oil return pipe 14 are cut off to cut off the hydraulic oil. After the strip is threaded, the proportional directional valve 2 is used to control the piston rod of the hydraulic cylinder 5 to extend to the preset position. The pressure sensor 131 can feedback the pressure P1 of the rodless chamber 51 in real time and transmit the signal to the corresponding controller (PLC). ), the pressure F of the anti-tear roller is calculated by the controller; after comparing this value with the target value of the anti-tear roller pressure F, the command signal of the difference is given to the proportional pressure reducing valve 4, and passed through the proportional pressure reducing valve 4 The pressure P1 of the rodless cavity 51 is adjusted to ensure that the pressure of the rodless cavity 51 is stable, thereby ensuring the constant force F and realizing a force closed loop.

Therefore, the hydraulic system can be used in conjunction with the anti-tear roller. The proportional directional valve 2 can be used to move the piston rod of the hydraulic cylinder 5 to the preset position. The pressure sensor 131 can be used to detect the pressure of the rodless chamber 51 in real time, and then reduce the pressure through the proportional directional valve 2. The pressure valve 4 adjusts the pressure of the rodless cavity 51 to achieve closed-loop control of the force of the anti-tear roller, effectively ensuring that the pressure exerted by the anti-tear roller on the strip is constant, thereby effectively preventing strip tearing caused by the shaking of the strip. crack.

In a specific implementation, a displacement sensor 511 is installed on the rodless cavity 51 .

The proportional directional valve 2 can adjust the amount of oil entering the rodless chamber 51. When it is necessary to increase the oil in the rodless chamber 51, the proportional directional valve 2 is in the first working position (right position), and the pressure oil in the hydraulic pump station 1 It enters the proportional directional valve 2 through the oil supply pipe 13, and then enters the rodless chamber 51 through the left passage of the electromagnetic reversing valve 3 and the proportional pressure reducing valve 4, which can cause the piston rod of the hydraulic cylinder 5 to extend; at the same time, there is a rod chamber The oil in 52 is returned to the hydraulic pump station 1 through the right passage of the electromagnetic reversing valve 3, the proportional directional valve 2 and the oil return pipe 14. When it is necessary to reduce the oil in the rodless cavity 51, the proportional directional valve 2 is in the second working position (left position). The pressure oil enters the proportional directional valve 2 through the oil supply pipe 13, and then enters through the right passage of the electromagnetic reversing valve 3. In the rod cavity 52, the piston rod of the hydraulic cylinder 5 is retracted; at the same time, the oil in the rodless cavity 51 passes through the proportional pressure reducing valve 4, the left passage of the electromagnetic reversing valve 3, the proportional directional valve 2 and the oil return pipe 14 Return oil to hydraulic pump station 1.

The displacement sensor 511 can actually measure the position of the hydraulic cylinder 5 and transmit the signal to the controller. After comparing this value with the target value of the displacement, the difference command signal is sent to the proportional directional valve 2 to ensure that the position of the hydraulic cylinder 5 is constant and achieve Position closed loop.

More specifically, the proportional directional valve 2 is a three-position four-way valve and has a first pressure oil port P3, a first return oil port T1, a first working oil port A1 and a second working oil port B1. The first pressure oil port P3 and the first working oil port A1 are connected in series to the oil supply pipe 13 and the first working oil port A1 is located close to the electromagnetic reversing valve 3 (the first pressure oil port P3 is located close to the hydraulic pump station 1), the first oil return port T1 and the second working oil port B1 are both connected in series to the oil return pipe 14 and the second working oil port B1 is located close to the electromagnetic reversing valve 3 .

The proportional directional valve 2 has a normal position (that is, the middle position shown in Figure 1), the above-mentioned first working position (that is, the right position shown in Figure 1) and the above-mentioned second working position (that is, the right position shown in Figure 1) (out of the left position), the proportional directional valve 2 is in the normal position when power is lost. At this time, the first pressure port P3 is closed, and the first working oil port A1 and the second working oil port B1 are both connected to the first return port T1. When the proportional directional valve 2 is powered and in the first working position, the first pressure oil port P3 is connected to the first working oil port A1 so that the pressure oil can enter the rodless chamber 51, and the second working oil port B1 is connected to the first working oil port A1. The oil return port T1 is connected, so that the oil in the rod chamber 52 can be returned through the first oil return port T1. When the proportional directional valve 2 is powered and in the second working position, the first pressure oil port P3 is connected to the second working oil port B1 so that the pressure oil can enter the rod chamber 52, and the first working oil port A1 is connected to the first working oil port B1. The oil return port T1 is connected, so that the oil in the rodless cavity 51 can be returned through the first oil return port T1.

For the above-mentioned proportional directional valve 2, an ordinary proportional directional valve can be used, and a high-frequency response proportional valve or a proportional servo valve is more preferably used. The high-frequency response proportional valve has higher accuracy, and the proportional servo valve has faster response speed and better accuracy. . For ordinary proportional directional valves, high-frequency response proportional valves and proportional servo valves, they are all existing structures and will not be described again here.

Furthermore, the electromagnetic reversing valve 3 includes four actuating oil ports, two of which are connected in series to the oil supply pipe 13 , and the other two actuating oil ports are connected in series to the oil return pipe 14 .

Referring to Figure 1, these four execution oil ports are respectively marked as the first execution oil port C1, the second execution oil port C2, the third execution oil port C3 and the fourth execution oil port C4. The first execution oil port C1 and the third execution oil port are The execution oil port C3 is connected in series to the oil supply pipe 13, the first execution oil port C1 is close to the proportional directional valve 2, the third execution oil port C3 is close to the proportional pressure reducing valve 4; the second execution oil port C2 and the fourth execution oil port C4 is connected in series to the oil return pipe 14 , the second actuating oil port C2 is close to the proportional directional valve 2 , and the fourth actuating oil port C4 is close to the rod chamber 52 . When the electromagnetic reversing valve 3 is in the connected working position (that is, the right position shown in Figure 1), the first execution oil port C1 is connected to the third execution oil port C3, and the second execution oil port C2 is connected to the fourth execution oil port C4. connected to realize the passage of the oil supply pipe 13 and the oil return pipe 14 here; when the electromagnetic reversing valve 3 is in the cut-off working position (ie, the left position shown in Figure 1), the first execution oil port C1 and the third execution oil port C1 The oil port C3 is disconnected, and the second execution oil port C2 and the fourth execution oil port C4 are disconnected, so that the oil supply pipe 13 and the oil return pipe 14 are disconnected here.

The electromagnetic reversing valve 3 can specifically be an electromagnetic ball valve. Of course, other types of electromagnetic reversing valves 3 that can achieve the above functions can also be used as needed. The structures of the electromagnetic ball valve and the electromagnetic reversing valve 3 are both existing structures. This will not be described again.

Referring to Figure 1, the above-mentioned proportional pressure reducing valve 4 has a second pressure oil port P4, a second oil return port T2 and a third working oil port A2. The second pressure oil port P4 and the third working oil port A2 are both connected in series. On the oil supply pipe 13, and the second pressure oil port P4 is set close to the electromagnetic reversing valve 3, the second oil return port T2 is bypassed on the oil return pipe 14 through the corresponding pipeline to realize oil return. The specific structure of the proportional pressure reducing valve 4 is an existing structure and will not be described again here.

Further, a first manual valve 132 is provided on the oil supply pipe 13 between the rodless chamber 51 and the proportional pressure reducing valve 4 , and a first manual valve 132 is provided on the oil return pipe 14 between the rodless chamber 52 and the electromagnetic reversing valve 3 A second manual valve 141 is provided.

During normal production, the first manual valve 132 and the second manual valve 141 are both open; when maintenance work is required, the first manual valve 132 and the second manual valve 141 are both closed to facilitate maintenance by the operator.

In order to facilitate the detection of pipeline pressure during maintenance, a first pressure measuring joint 133 is connected to the oil supply pipe 13 and is located between the rodless chamber 51 and the proportional pressure reducing valve 4. A first pressure measuring joint 133 is connected to the oil return pipe 14 and is located in the rod chamber. A second pressure measuring joint 142 is connected between 52 and the electromagnetic reversing valve 3. The first pressure measuring joint 133 is provided between the proportional pressure reducing valve 4 and the first manual valve 132, and the second pressure measuring joint 142 is provided between the electromagnetic reversing valve 3 and the second manual valve 141; when in use, the first Corresponding pressure measuring instruments, such as pressure gauges, can be installed on the pressure measuring joint 133 and the second pressure measuring joint 142 to facilitate detection of the pressure at this location.

Further, the hydraulic pump station 1 includes a hydraulic pump set 11 and an oil tank 12 . The oil supply pipe 13 and the oil return pipe 14 are both connected to the oil tank 12 . The hydraulic pump set 11 is provided on the oil supply pipe 13 . The entire hydraulic pump station 1 is a power source, which includes a fuel tank 12 and its accessories, a hydraulic pump group 11, etc. The specific structure of the hydraulic pump station 1 is an existing technology and will not be described again here.

Generally, a one-way valve 143 is provided on the oil return pipe 14 and close to the hydraulic pump station 1 . The one-way valve 143 is located between the proportional directional valve 2 and the oil tank 12 and can prevent oil from flowing back from the oil tank 12 .

The entire hydraulic system can realize double closed-loop control of the position and force of the anti-tear roller. During rolling, the force closed loop can be put in alone, the position closed loop can be put in alone, or the two closed loops can be put in together. The three specific control methods can be selected according to actual needs. The working principles are as follows:

(1) Single input force closed loop: the displacement sensor 511 does not work in this mode

During operation, after the strip is threaded, a pressure target value is given through the proportional pressure reducing valve 4. The proportional directional valve 2 is energized and is in the first working position, and the pressure entering the rodless chamber 51 of the hydraulic cylinder 5 is adjusted through the proportional directional valve 2. oil, until the data detected by the pressure sensor 131 reaches the pressure target value, the hydraulic rod of the hydraulic cylinder 5 remains stationary at this position;

Then the pressure sensor 131 is used to detect the pressure P1 of the rodless chamber 51 in real time, and compares P1 with the pressure target value. According to the difference, the proportional pressure reducing valve 4 is controlled to adjust the pressure P1 of the rodless chamber 51 until the pressure target value is reached. A closed force loop is used to ensure that the force exerted by the hydraulic rod is constant.

During the entire adjustment process, if the actual measured value P1 of the pressure sensor 131 is greater than the pressure target value, the proportional directional valve 2 is energized and is in the second working position; if the actual measured value P1 of the pressure sensor 131 is less than the pressure target value, the proportional directional valve 2 is energized and is in the first working position. Working position; the solenoid ball valve is always powered and in the connected working position. In the event of a strip emergency, the proportional directional valve 2 is in the normal position, and the solenoid ball valve is in the cut-off position when it is powered. At this time, no hydraulic oil enters the hydraulic cylinder 5, and the hydraulic cylinder 5 remains motionless.

(2) Single input position closed loop: the pressure sensor 131 does not work in this mode

During operation, after the strip is threaded, a position target value is given, and the proportional directional valve 2 is energized and is in the first working position, and the oil entering the rodless chamber 51 of the hydraulic cylinder 5 is adjusted through the proportional directional valve 2 until the displacement sensor Until the data detected by 511 reaches the position target value, the hydraulic rod of the hydraulic cylinder 5 remains stationary at this position;

Then the displacement sensor 511 is used to detect the position of the hydraulic cylinder 5 in real time, and the position is compared with the displacement target value. According to the difference, the proportional directional valve 2 is controlled to adjust (specifically, the proportional directional valve 2 is powered to be in the first working position, and the hydraulic pressure The displacement of cylinder 5 increases; or the proportional directional valve 2 is energized and is in the second working position, and the displacement of hydraulic cylinder 5 decreases) until the current position of hydraulic cylinder 5 reaches the position target value, the position of the hydraulic rod is kept constant through the position closed loop.

The entire adjustment process adjusts the proportional directional valve 2 to be in the first working position or the second working position as needed, and the solenoid ball valve is always powered in the connected working position. In the event of a strip emergency, the proportional directional valve 2 is in the normal position, and the solenoid ball valve 05 is in the cut-off position when the power is supplied. At this time, no hydraulic oil enters the hydraulic cylinder 5, and the hydraulic cylinder 5 remains stationary.

(3) The force closed loop and the position closed loop are put into use at the same time: the position closed loop is put into use first. After the hydraulic cylinder 5 reaches the set position, the position closed loop is closed and the force closed loop is put into use.

During operation, after the strip is threaded, a position target value is given, and the proportional directional valve 2 is energized and is in the first working position, and the oil entering the rodless chamber 51 of the hydraulic cylinder 5 is adjusted through the proportional directional valve 2 until the displacement sensor Until the data detected by 511 reaches the position target value, the hydraulic rod of the hydraulic cylinder 5 remains stationary at this position;

Then a pressure target value is given through the proportional pressure reducing valve 4, the pressure sensor 131 is used to detect the pressure P1 of the rodless chamber 51 in real time, and P1 is compared with the pressure target value. According to the difference, the proportional pressure reducing valve 4 is controlled to adjust the pressure. The pressure P1 of the rod chamber 51 until P1 reaches the pressure target value is used to ensure that the force exerted by the hydraulic rod is constant through a force closed loop.

During the entire adjustment process, if the measured displacement value is greater than the position target value or the measured pressure value is greater than the pressure target value, the proportional directional valve 2 is energized in the second working position, otherwise it is energized in the first working position; the solenoid ball valve is always energized in the connected working position. . In the event of a strip emergency, the proportional directional valve 2 is in the normal position, and the solenoid ball valve is in the cut-off position when it is powered. At this time, no hydraulic oil enters the hydraulic cylinder 5, and the hydraulic cylinder 5 remains motionless.

The above are only illustrative embodiments of the present invention, and are not intended to limit the scope of the present invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present utility model shall fall within the scope of protection of the present utility model.

Claims (10)

1. The hydraulic system for leveling the tearing-proof roller in the uncoiler is characterized by comprising a hydraulic pump station, a proportional directional valve, an electromagnetic directional valve, a proportional pressure reducing valve and a hydraulic cylinder;

the end part of a piston rod of the hydraulic cylinder is fixedly connected with the anti-tearing roller, the hydraulic pump station is respectively connected with a rodless cavity and a rod cavity of the hydraulic cylinder through an oil supply pipe and an oil return pipe, and the proportional direction valve is connected with the oil supply pipe and the oil return pipe and can control the extension or retraction of the piston rod; the electromagnetic reversing valve is positioned between the hydraulic cylinder and the proportional direction valve, is connected with the oil supply pipe and the oil return pipe, and can control the oil supply pipe and the oil return pipe to be simultaneously in a passage or be simultaneously cut off; the proportional pressure reducing valve is connected in series to the oil supply pipe and is positioned between the hydraulic cylinder and the electromagnetic reversing valve, and a pressure sensor or a pressure relay is connected to the oil supply pipe and is close to the rodless cavity.

2. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

and a displacement sensor is arranged on the rodless cavity.

3. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

the proportional direction valve is a three-position four-way valve and is provided with a first pressure oil port, a first oil return port, a first working oil port and a second working oil port, wherein the first pressure oil port and the first working oil port are connected in series on the oil supply pipe and close to the electromagnetic directional valve, and the first oil return port and the second working oil port are connected in series on the oil return pipe and close to the electromagnetic directional valve.

4. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

the proportional direction valve is a high-frequency response proportional valve or a proportional servo valve.

5. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

the electromagnetic reversing valve comprises four execution oil ports, wherein two execution oil ports are connected in series on the oil supply pipe, and the other two execution oil ports are connected in series on the oil return pipe.

6. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

the electromagnetic reversing valve is an electromagnetic ball valve.

7. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

the oil supply pipe is provided with a first manual valve which is positioned between the rodless cavity and the proportional pressure reducing valve, and the oil return pipe is provided with a second manual valve which is positioned between the rod cavity and the electromagnetic reversing valve.

8. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

the oil supply pipe is connected with a first pressure measuring joint which is positioned between the rodless cavity and the proportional pressure reducing valve, and the oil return pipe is connected with a second pressure measuring joint which is positioned between the rod cavity and the electromagnetic reversing valve.

9. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

the hydraulic pump station comprises a hydraulic pump set and an oil tank, wherein the oil supply pipe and the oil return pipe are connected with the oil tank, and the hydraulic pump set is arranged on the oil supply pipe.

10. A hydraulic system for levelling a tear-resistant roll in an unwinder as claimed in claim 1,

and a one-way valve is arranged on the oil return pipe and close to the hydraulic pump station.