A brief analysis of the maintenance and upkeep of hydraulic shears of billet continuous casting machines

This article briefly introduces the maintenance and maintenance of billet hydraulic shears, and conducts research and analysis on the composition, maintenance points, and daily inspection and maintenance of billet hydraulic shears. List the common daily problems of billet hydraulic shears and the reasons that affect the service life, and propose a brief transformation plan.

Keywords: new situation; hydraulic shears; maintenance; equipment modification

Hydraulic shears are very important equipment in continuous casting production. Hydraulic shears are a way for continuous casting machines to cut blanks to fixed lengths. The use of hydraulic shears directly affects the production of continuous casting machines. Hydraulic shears are the main equipment for continuous operation of continuous casting machines. They are in harsh working environment because they are in direct contact with high-temperature cast slabs. High temperature makes the hydraulic shear cylinder, blade, and limiter easily damaged, and the frame easily deformed. However, the life of any equipment cannot be infinite. After a certain period of use, the equipment is likely to have some problems, making it difficult to continue production. In order to extend the service life of the equipment, maintain production and reduce costs, routine maintenance and repair of hydraulic shears is essential.

Composition of hydraulic shears

The hydraulic shears used by our company are 45° suspended billet shears. The lower blade base of the hydraulic shear is connected to the piston rod of the shearing cylinder. The shearing cylinder and the upper and lower blade bases are installed in a water-cooled integral square frame. The upper end of the frame There are four wheels, all of which can run along the track. When the billet touches the fixed-length signal, the traverse hydraulic cylinder pushes the frame to move forward along the horizontal track synchronously with the billet. At the same time, the lower shearing blade moves upwards driven by the shear cylinder to cut the billet. The sheared billet It is sent to the cooling bed by the transport roller. After the shear is in place, the lower cutting edge begins to descend, and the shear is reset by the traverse hydraulic cylinder. This machine has the following features:

1) Using 45° diagonal shearing, the shearing speed is fast (8 seconds to 15 seconds), and the shear section deformation changes little after shearing is completed.

2) A water-cooling tunnel is set up in the entire hydraulic shear equipment body to improve the protection ability of the slab radiation.

3) The grinding sliding bearings and wear-resistant slide rails use specially treated high-nickel-chromium materials, and their service life is 2 to 3 times that of traditional materials.

4) The hydraulic cylinder seal adopts a fully imported combination seal. The guide sleeve is a porous bronze mesh sintered on a steel plate. The mesh is filled with a mixture of lead and polytetrafluoroethylene (PTFE) and other materials.

5) The structure is compact and can be easily replaced as a whole and inspected offline to improve the operating rate and maintenance performance of the hydraulic shear.

6) This equipment is equipped with a dry oil lubrication cup for bearing lubrication.

Hydraulic Shear Maintenance and Maintenance

Maintenance of hydraulic shears

After each team takes over, all connections of the hydraulic shear should be inspected once. The pins should not be loose. If there is any looseness, stop pouring and tighten it in time. Check the hydraulic cylinder pressure and oil pipe for oil leakage. Check the service life of the hydraulic parts blade, check the use of the blade, and whether there is any blockage on the cutting edge. It is necessary to check the inlet rollers, water-cooling guards, metal hoses and other water-passing parts. If any leakage is found, stop pouring and deal with it in time. Inspection is the top priority of equipment maintenance. Every inspection must be carefully inspected to detect and deal with it early to nip all equipment failures in the bud.

Maintenance of hydraulic shears

Hydraulic shear cooling and lubrication

Since hydraulic shears have to work continuously in harsh environments such as high temperature and heavy load during production, the key parts of the hydraulic shears must be cooled and lubricated by water to prevent the hydraulic shears from being damaged due to excessive temperature or severe wear and extend the service life of the hydraulic shears. service life.

The surface temperature of the cast slab in the hydraulic shear area is as high as about 850°C, and radiation will cause damage to all components of the hydraulic shear. The frame of the hydraulic shear should adopt a box-shaped structure to facilitate water cooling, and the hydraulic shear blades should use external spray cooling. Lubrication of hydraulic shears is also essential. Good lubrication can extend the service life of the equipment and reduce the labor intensity of workers.

Adjustment of hydraulic shear blades

The most important thing to adjust the billet shear is to adjust the shearing gap. First loosen the adjusting bolts of the backrest wear-resistant slide rail and the lower support wear-resistant slide rail, so that there is a 2-3 mm gap between the slide rail and the wear-resistant sliding bearing. Start the oil pump motor until the loading pressure reaches the set pressure. Finally, press the “Up Shear” button, release the “Up Shear” button when the upper and lower blades are about to overlap, and stop the motor to adjust the shear gap. The shear gap refers to the sum of the gap between the upper and lower blades and the gap between the wear-resistant sliding bearing and the backrest wear-resistant slide rail. The shear gap is generally 1.0-1.2 mm, and the upper and lower gaps must be consistent in size. Then fix the backrest wear-resistant slide rail, lock the adjusting bolt, and apply grease between the sliding bearing and the slide rail. The adjustment method for the gap between the wear-resistant sliding bearing of the lower bracket and the wear-resistant slide rail is the same as the adjustment method for the shear gap.

Adjustment of hydraulic shear limit

Adjustment of the upper limit: The upper limit of the shear is related to the service life of the shear cylinder. The fixed position of the upper limit should be such that the cylinder piston does not push against the bottom cylinder cover of the cylinder, and the movable blade and the fixed blade should overlap by 3-5 mm.

Equipment modification

The most common failure of hydraulic shear equipment is billet ejection. The main reasons for billet ejection may be the following:

1. The steel billet is not cut;

2. After the cutting is completed, the trolley does not return and starts cutting directly for the second time;

3. The main hydraulic cylinder has a limit failure, and the main hydraulic cylinder does not return to the position after shearing.

We have made several improvements to address the above issues:

1. Optimize the shearing program and confirm that the shearing time does not exceed 18 seconds, so that within a limited time, even if it is not sheared due to various reasons, there will be no ejection failure caused by the failure of the main cylinder rod to return;

2. Add an alarm device for the trolley not returning (under the manual shearing function, the trolley needs to be returned manually. Because the continuous casting machine has a large number of flows and a fast casting speed, the operator sometimes forgets to return or the trolley does not return due to the stuck valve of the translation cylinder reversing valve. If the trolley returns, it will be directly sheared twice and cause the billet to be ejected). If the trolley does not return, promptly remind the operator to confirm the reason and avoid causing the billet to be ejected twice;

3. The hydraulic shear limiter has been working in a high temperature and water bath environment for a long time. Once the limiter is filled with water, it is easy to malfunction. We will modify the limiter with single-side wiring and make the opening facing downward to prevent water from entering and completely solve the problem of the limiter. fault caused.

In addition, the axle structure of the trolley has been mechanically modified to solve the problem of shaft bending due to insufficient strength. In terms of operation, a semi-automatic shearing system has been added to reduce the manual operation process when pouring, and fundamentally solve the problem of cumbersome operations. question.

Common fault analysis

Why does the shear cylinder not move when the shear button is turned on?

1) Check whether the pressure of the system pressure gauge is normal, whether the accumulator pressure is normal, whether the electrical contact setting value is normal, whether the translation pressure is normal, and whether the pressure maintaining state is normal.

2) Check whether the control circuit is normal (when normal, the shear relay indicator lights flash in sequence).

3) Check whether the electromagnetic reversing valve is working (when normal, the reversing valve indicator light flashes and the coil is magnetic).

4) Check the main oil pipeline for oil leakage.

5) Check whether there is any foreign matter stuck in the movable tool holder.

6) Check whether there is any foreign matter blocking the valve core of the solenoid reversing valve.

Why is the steel temperature above 800 degrees, but the shearing is very difficult or the shearing is continuous?

1) Check whether the system shear pressure reaches above 10MPa, and adjust the system shear pressure between 10-15MPa.

2) Check whether the electromagnetic relief valve is stuck, which can be determined by observing the shear pressure. It can be disassembled and cleaned to eliminate it.

3) Check the hydraulic pipeline for oil leakage.

4) Check whether the upper limit of the shear is loose and has slid down, causing the movable blade and fixed blade to fail to overlap.

5) Check whether the blade gap is too large. The normal gap is about 0.2-1mm.

6) Observe whether the upward shearing time of the control panel is too short. Normally it is between 10-15 seconds.

7) If the plunger pump is used for a long time, the flow and pressure of the oil pump will not be sufficient, and the oil pump variable (the small bolt on the top of the pump head) needs to be adjusted.

Why does the hydraulic shear body not automatically move back to its original position after shearing is completed?

1) Check whether there is foreign matter blocking the wheels on the hydraulic shear track.

2) Check whether the cylinder rod of the translation cylinder is strained, leaked or bent.

3) Check whether the pressure gauge corresponding to the translation cylinder has a pressure indication.

4) Check whether the one-way solenoid valve and throttle valve corresponding to the translation cylinder are working properly.

5) Check whether the pipe is broken.

Why does the fault light on the console always light up red?

1) Check whether the upper and lower limit lines of the shear are damaged or broken.

2) Check whether the steel billet is not sheared and the common end does not contact the upper limit.

3) Check whether there are foreign matter, scale and other foreign matter on the metal surface of the upper and lower limit contacts, causing poor contact.

Why oil leakage sometimes occurs in large oil cylinders

1) The oil cylinder expands due to thermal expansion and contraction under high-temperature baking, and the cylinder becomes larger. Check whether the water cooling of the large oil cylinder is normal.

2) Check whether the sealing ring of the large oil cylinder is worn.

3) Check whether the clearance of the backrest sliding bearing of the lower tool holder is too large, causing the cylinder to hold back, and adjust it appropriately.

Why does the shearing suddenly slow down, the oil pump loads frequently or keeps loading, and the vibration of the oil pipe becomes larger?

1) Check the air pressure of the accumulator. If the air pressure is too low (less than 6MPa), add nitrogen to 6-8MPa.

2) Observe the system pressure gauge: whether the pressure disappears quickly after the accumulator is full. If so, check whether there is any foreign matter in the accumulator safety valve, causing the valve to be unable to seal, and the hydraulic oil returns directly to the tank through the return pipe.

3) Observe whether the accumulator is filled instantly. If so, check whether the accumulator has no air pressure or the bladder is damaged.

4) Check whether there is oil leakage in the pipeline

5) The contacts in the electric contact pressure gauge are damaged and have poor contact. The main overflow valve cannot be closed when the pressure reaches a high level, causing the motor to be loaded all the time.

6) The pressure given by the pressure-maintaining overflow valve of the accumulator is lower than the maximum value of the electric contact. The pressure pointer of the electric contact cannot contact the pointer contact with the highest value. The main overflow valve is always in working condition and the motor is always loaded. (You only need to increase the pressure value of the accumulator pressure-maintaining relief valve until it is loaded to the pointer on the electric contact pressure gauge, or reduce the maximum setting value of the electric contact pressure gauge)

 Conclusion

Careful and timely maintenance can extend the service life of each part of the equipment, reduce resource consumption, reduce costs, extend the service life of the equipment, reduce the number of maintenance times, improve efficiency, and bring more considerable economic benefits to the enterprise.

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