Servo hydraulic presses are generally driven by a plunger pump to supply oil to the hydraulic cylinder to achieve slider movement. In order to realize the fixed-range and constant-pressure process of the hydraulic press slider, the oil flow in the input cylinder must be precisely controlled.

The basic working principle of the servo-hydraulic press is introduced as follows:

The internal meshing pump driven by two groups of AC servo motors is directly connected to the upper and lower chambers of the master cylinder, and a safety module is connected between the pump and the cylinder. The pump outlet, the safety module, and the upper and lower chambers of the master cylinder are respectively connected with pressure sensors to detect the pressure of the system, and the input control system is used to servo control the speed of the AC servo motor.

When the servo hydraulic press system overpressures, the cartridge valve spool of the safety module opens to release the pressure into the oil tank. The outlet of the pump is equipped with a safety device, which also releases pressure to the tank in case of overpressure.

The control valve group of the servo-hydraulic press adopts proportional servo constant pressure control technology, which is conducive to improving the reaction speed of the filling valve. The pressure sensor is used to detect the pressure, and the input control system is used to control the proportional servo valve for the pressure supplement.

1. Prevent external gas from entering the hydraulic system. In use, the oil quantity of the tank should be checked regularly to avoid the phenomenon of air suction.

2. During maintenance and installation, the air in the hydraulic components and pipelines must be discharged, and the suction pipe and pump body should be filled with oil to maintain good sealing of the tubing.

3. During the operation of the hydraulic press, it is necessary to check whether the oil suction filter is blocked, so as to avoid the air separation phenomenon caused by the low pressure of the oil suction port caused by the poor oil suction.

4. Each part of the hydraulic system should be kept full of oil. The way is to install a check valve at the outlet of the hydraulic pump and set up a back pressure valve on the oil return road.

5. Try to prevent the pressure in the hydraulic system from being lower than the atmospheric pressure. At the same time, a good sealing device should be used.

6. Select the appropriate viscosity of the working medium, the viscosity of the oil is too high, the reaction to the control has a tendency to slow down, and will also cause the increase of fluid friction so that the oil temperature of the hydraulic system rises, or cause the hydraulic pump suction, so as to increase the formation of foam.

The main causes of excessive vibration in hydraulic systems are:

1) Hydraulic vibration shock when the liquid flow channel is rapidly closed;

2) The moving parts are suddenly stopped in high-speed motion;

3) Hydraulic vibration impact caused by air in the fluid.

Take the following measures to eliminate the excessive vibration in hydraulic systems:

(1) Try to change the complete vibration to incomplete vibration, which can be achieved by slowing down the valve opening and closing speed or reducing the shock wave distance;

(2) In the hydraulic system, limit the flow rate of oil in the tubing;

(3) can be used in the hydraulic system with a rubber hose or an accumulator at the vibration source;

(4) where the hydraulic system is prone to vibration, install a safety valve to limit the pressure rise;

(5) The piston of a high-speed cylinder with a large load is prohibited to stop or reverse suddenly in the middle of the stroke.

There must be no free air in the hydraulic system. Air will have a negative impact on the operation of the hydraulic system. What are the specific hazards to the hydraulic system?

1. Hydraulic oil mixed with air, will produce bubbles and a hole formation phenomenon, in the high-pressure area, under the impact of pressure oil, bubbles will be broken, and sharply compressed so that the hydraulic system noise;

2. When the gas in the hydraulic oil is suddenly compressed, a lot of heat will be released, causing local overheating, which damages the hydraulic components and hydraulic oil;

3. Because of the compressibility of the air, the working organs of the hydraulic system crawl, destroy the stability of the work, and sometimes even cause vibration, affecting the normal work of the machine tool;

4. If a large number of bubbles are mixed into the hydraulic press system, it is easy to cause oil deterioration, thereby reducing the service life of hydraulic oil.

Hydraulic system design, the system of temperature control, pressure control, level control, and so on have some fixed configuration. But sometimes the mechanical and hydraulic vibration is not considered carefully, resulting in some accidents caused by system vibration shock. It shows that the mechanical components are damaged, the motion precision is reduced, and the noise pollution is serious, which directly affects the life of the hydraulic system.

1. Mechanical vibration in the hydraulic system

Due to the increasing complexity of modern mechanical structures and the increasing speed of movement, the harm of vibration is more prominent. The hydraulic system is mainly reflected in the motor hydraulic pump, the hydraulic motor shaft running at high speed, will produce a frequency and speed corresponding to the forced vibration. This vibration will be transmitted to other pipelines, oil tanks, and valves through the pump station foundation or pipeline. During the use of motor hydraulic pumps and hydraulic motors, due to wear and other reasons, the matching clearance increases and the bearing position moves in series.

2. Fluid vibration in the hydraulic system

Fluid vibration is the vibration shock phenomenon caused by the instantaneous pressure change of oil. The impact pressure can be as high as 3~4 times the normal working pressure, so that the components, pipes, and instruments in the hydraulic system are destroyed; The hydraulic shock causes the pressure relay to send the wrong signal, interferes with the normal work of the hydraulic system, and affects the working stability and reliability of the hydraulic system; Hydraulic impact causes vibration and noise, loose connectors, resulting in oil leakage, pressure valve adjustment pressure change; Hydraulic impact comes quickly, often make the operator avoid, causing personal injury.

Like all tools, the hydraulic press machine can become damaged over time through heavy usage. Here are common problems associated with hydraulic press machines and solution tips that should help you fix them.

1. The pressure of the main cylinder of the hydraulic press machine does not rise enough

The damping hole of the main spool of the hydraulic press machine has the phenomenon of blockage, and the main spool valve will open the overflow at a lower pressure. The main spool stuck in the opening position may also lead to the pressure of the main cylinder can not rise.

Solution: carefully check the position of the flow valve of the hydraulic press machine, and then analyze the causes of various possible failures in detail to find out the reasons for certain treatments. The relief valve damping hole and each part must be cleaned to ensure a smooth state. When replacing the main spool, the sealing ring should be processed with the valve seat hole to avoid oil leakage.

2. The spring of the filling valve of the master cylinder of the hydraulic press machine is broken, and the sealing degree is not up to the standard

Solution: replace the spring, and grind the sealing surface of the liquid filling valve to ensure no leakage phenomenon.

3. The sealing ring of the main cylinder is damaged, and the pressure oil in the upper and lower chambers colludes

Solution: replace the sealing ring. If there is a strain on the inner wall of the main cylinder, it should be repaired to grind the surface, so as to prevent the sealing ring from being damaged.

4. The sound of the hydraulic press machine system is abnormal, and the vibration is relatively large

The possible reason is that the filter of the tank is blocked by unknown substances, and the suction of the hydraulic pump is blocked.

Solution: clean the filter, in the process of inspection, not only to check if the oil is polluted but also to filter the oil pollution or directly replace the oil with new oil.

1. Pay attention to the inspection and maintenance of the hydraulic system

To prevent external gas from entering the system, the oil quantity of the tank should be checked regularly during use to avoid air suction phenomenon, and the oil condition should be checked in time to avoid oil deterioration; Often check whether the oil filter is blocked, so as to avoid the low pressure of the oil port and the inhalation of air.

2. Improve the structure of a hydraulic system

The exhaust device should be set up in the upper part of the hydraulic cylinder and pipeline to release the air in the system: some large hydraulic actuators in the movement due to sudden stop or reversing, will form holes in the oil inlet cavity, in order to prevent the formation of holes, should be set up oil filling circuit;

The bottom of the oil suction side of the oil tank of the hydraulic press can be covered with a layer of 60~100 purpose-defoaming metal mesh from the middle partition to the wall of the box to separate the gas in the oil;

The suction pipe with a larger diameter is used to reduce the local resistance of the pipeline and prevent the cavitation of the hydraulic pump. At the same time, the oil suction filter with a large capacity is used to prevent the oil from mixing with the air.

The suction pipe of the hydraulic pump and the return pipe mouth of the system should be lower, the distance should be as far as possible, and the baffle or defoaming net should be added between the two.

1. The hydraulic system is not working well

In the hydraulic transmission system, oil is the transmission medium of power. Once the oil is mixed with air, its compression rate will be greatly increased, seriously endangering the reliability of the system, such as automatic control failure, intermittent movement, and so on.

2. Oil temperature of the hydraulic press rises

After the bubble is compressed instantaneously by the pump and other components, its temperature will rise sharply. The hazards of rising oil temperatures are as follows:

(1) Accelerate the oxidation of the oil

When the oil temperature is above 60℃, the oxidation rate will increase exponentially with every increase of 10℃. After oxidation, the viscosity of the oil will increase and acidic compounds will be generated, which will cause corrosion of metal parts in the system and easily produce slag and mud.

(2) The lubricating property of oil decreases

The oil film strength of the deteriorated oil is not enough to withstand the pressure of the working load, causing the metal surface to contact each other, resulting in a sharp increase in friction, and accelerating the wear of parts in the hydraulic system.

(3) Accelerate the aging of seals

If the oil temperature exceeds the normal heat resistance temperature of the seal, it will accelerate the aging of the seal, lose its elasticity, and lead to premature loss of sealing performance.

3. Lead to cavitation of hydraulic system

When the bubbles in the oil are brought to the high-pressure area by the oil, the volume shrinks sharply, so that the vacuum is formed in the local area, and the particles collide with each other to produce local high pressure, forming hydraulic impact, and making the local pressure rise sharply.

1. Strengthen the management of hydraulic oil

Hydraulic press failure caused by hydraulic oil pollution accounts for about 70% of the total faults, so we must strictly control the hydraulic oil pollution, and maintain the normal and stable operation of machinery, in order to reduce the incidence of faults, prolong the service life of equipment, reduce operating costs, so as to achieve an increase in profits.

2. Strengthen the maintenance of hydraulic press components

A hydraulic press system is a set of systems that need to operate under high pressure. In hydraulic components in long-term high-speed operation, the clearance will become larger, component leakage will increase. Therefore, we must pay attention to the maintenance of the hydraulic press, the regular disassembly and inspection of components, and cleaning and maintenance by professionals.

3. Strengthen the training of operators

A hydraulic press system is composed of many high-precision components, the connection of each pipeline is a ring buckle a ring, and the structure of the system is very complex. Therefore, it is necessary to strengthen the training of operators, improve the business level and maintenance management ability, and timely solutions and troubleshooting, to ensure the normal operation of a hydraulic press, so as to minimize hydraulic press failure.

The hydraulic press is a combination of mechanical, hydraulic, electrical, and other devices, so the failure is also diverse, so it is difficult to find the fault of the hydraulic press system.

Fault diagnosis of hydraulic press system needs to continue to analyze, explore, verify, timely and accurate troubleshooting causes. Common fault diagnosis methods are described as follows:

1. Regional analysis method

The area analysis method is to divide the whole system diagram of the hydraulic press, through the appearance of the fault, find out the area where the fault may occur, check these areas, analyze and judge the factors of the fault, and put forward the method to solve the fault.

2. Comprehensive analysis

The comprehensive analysis method is the comprehensive analysis of hydraulic press system faults, including the cause of the failure and the development process, and the testing system, using the modern information processing method of the hydraulic press data processing, to obtain accurate results, so as to find out the root cause of the failure, make the right judgment and solution is put forward.