Common contamination detection methods for hydraulic systems mainly include: the microscope contrast counting method uses vacuuming to filter a known volume of working fluid sample through a filter membrane printed with squares, so that pollutant particles are filtered and accumulated on the surface of the filter membrane. Examine the filter membrane with a microscope to determine the size and count of the dirt particles by particle size.

The basic principle of the hydraulic press system pollution detection method is that when the oil passes through the sensor, the particles in the oil cover part of the laser beam and reduce the light intensity, so as to detect the total number and size of the particles in the unit volume of oil. And this particle technology method is also divided into shading type, scattering type, resistance type, and so on. The shading type liquid particle counter is the most widely used type in oil pollution analysis.

The reliability of the hydraulic press system depends largely on the pollution degree of the medium. Therefore, the pollution degree should be monitored from multiple angles, the working environment of the components should be optimized, and the maintenance of the system should be strictly implemented, especially the replacement of hydraulic oil and filter elements. Monitor the chemical composition of the oil to avoid failures and unnecessary losses.

In the installation and commissioning stage of the hydraulic press, on the one hand, the hydraulic press system should be protected from secondary pollution, and on the other hand, it should be ensured that the pollution degree of the external pipeline meets the product requirements before it can be connected to the hydraulic system.

1. It is not allowed to use the hydraulic press system in the equipment to circulate and flush the external pipeline. The external pipeline must be flushed separately, and the pollution degree test is qualified before it can be connected to the hydraulic system. This is also one of the most important links between pollution degree and quality control.

2. During commissioning, when adding hydraulic oil to the hydraulic system, the oil filter must be used to refuel. At the same time, pay attention to the grade of the filter element of the oil filter and replace the filter element regularly. It is not allowed to directly add hydraulic oil to the hydraulic system.

3. The pipelines and cylinder interfaces of the hydraulic system must be well protected, and they must be installed and disassembled at any time to avoid pollution of the pipelines.

70%-80% of the failures of the hydraulic press system are caused by hydraulic oil contamination. The oxidation of the hydraulic oil produces sludge, colloid, and other substances, which will cause the hydraulic system to work abnormally, block the oil circuit, and corrode the metal.

Hydraulic oil contamination is mainly manifested in two aspects:

1. Particle pollution of hydraulic oil;

2. Deterioration of oil's physical and chemical properties (such as viscosity, acidity, alkalinity, oxidation degree, etc.).

The main sources of particle pollution are:

(1) Original pollution: originates from the manufacturing, testing, transportation, installation, and other stages of hydraulic system products;

(2) The pollution brought to the system by the medium during the process of transportation, storage, oil replenishment, etc.;

(3) Particles produced by the hydraulic system after it is put into use.

The deterioration of the physical and chemical properties of hydraulic oil mainly includes:

(1) The mixing of different types of media causes chemical reactions, making the media deteriorate;

(2) During the production process, the oil temperature is too high or the oil is used for too long due to oxidation and deterioration, resulting in medium pollution;

(3) When water is mixed into the medium, the oil becomes an emulsion, which reduces the lubricating and anti-corrosion effects of the lubricating oil, and easily causes cavitation;

(4) The quality of hydraulic oil is low or inferior sealing materials are used, which will cause damage to the sealing materials and cause hydraulic oil contamination.

Hydraulic press system cleaning is absolutely necessary for hydraulic systems that are being assembled or newly put into use. After strict cleaning, it can reduce and avoid system debugging and failures in early operation, shorten the system debugging cycle, and reduce unnecessary losses. The following introduces the matters needing attention when cleaning the hydraulic system:

(1) When cleaning the general hydraulic press system, use working hydraulic oil or test oil instead of kerosene, gasoline, alcohol, steam, or other liquids to prevent corrosion of hydraulic components, pipelines, fuel tanks, and seals.

(2) During the cleaning process, the hydraulic pump runs, and the cleaning medium is heated at the same time. When the temperature of the cleaning oil is 50~80°C, the rubber residue in the hydraulic press system is easy to remove.

(3) The intermittent operation of the hydraulic pump is beneficial to improve the cleaning effect, and the intermittent time is generally 10-30 min.

(4) A filter or screen should be installed on the circuit for cleaning the oil circuit. At the beginning of cleaning, because there are many impurities, an 80-mesh filter can be used, and a filter of 150 mesh or more can be used in the later stage of cleaning.

(5) The cleaning time is generally 48~60h, which should be determined according to the complexity of the hydraulic press system, filtration accuracy requirements, pollution degree, and other factors.

(6) In order to prevent corrosion caused by external moisture, the hydraulic pump will continue to run at the end of cleaning until the temperature returns to normal.

(7) After cleaning the hydraulic press system, the cleaning oil in the circuit should be drained.

Servo hydraulic presses have a wider application range than traditional hydraulic presses and have high added value. They can be applied to precision forming processes such as sheet metal stamping, isothermal forging, powder pressing, rubber vulcanization, fiberboard hot pressing, straightening, press fitting, and injection molding. The system introduction of the servo-hydraulic press is as follows:

1. High-power AC servo motor and drive control system:

At present, the servo-hydraulic press mainly uses the switched reluctance motor (SMR), which has the advantages of simplicity, reliability, high-efficiency four-quadrant operation in a wide speed and torque range, fast response speed, and low cost.

2. Special control system:

The closed-loop control technology of the pressure and position of the servo-hydraulic press is realized through the change of the servo motor speed. Traditional hydraulic machines are controlled by proportional valves and positions, and it is necessary to study a special control algorithm for the pump control system so that the hydraulic system has high stability and high precision between 1 and 25 MPa.

3. Energy recovery and energy management system:

In order to reduce energy loss as much as possible, it is necessary to recover and reuse the potential energy of the sliding block's own weight and the energy generated by the pressure relief of the cylinder. In terms of energy management, since the instantaneous power is many times larger than the average power, it is necessary to do a good job in energy allocation in large servo-hydraulic machines to avoid impact on the power grid.

1. Solvent heating and immersion

Immerse the parts to be cleaned in a cleaning tank with heating equipment (the heating temperature is generally 35~85°C), and pass compressed air or steam into the cleaning solution to make the cleaning solution dynamic, and the immersion time is 0.5~2h.

2. Spray washing

It is cleaned by a pressure jet machine, which is suitable for continuous operation in large and medium-sized factories and workshops. The prepared heated aqueous solution is sprayed and cleaned by a hydraulic press machine at a pressure of 0.3MPa through a corrosion-resistant pump.

3. Motorized scrubbing

Dirt can be removed with soft bristles to maintain component precision and low roughness. If the mesh oil filter uses a hard wire brush, it will sometimes damage the filter element or change the filter accuracy of the hydraulic press machine.

4. Ultrasonic cleaning

Ultrasonic waves of appropriate power are injected into the cleaning liquid to form tiny dot-shaped cavities. When the cavity expands to a certain extent, a partial vacuum is formed, and the circulating fluid fills the vacuum at a high speed, generating super strong sound pressure and mechanical impact force (i.e. cavitation) peels off the contaminants on the surface of the hydraulic system parts.

5. Acid treatment method

Different metal materials use different pickling solutions. After removing the pollutants on the surface of the hydraulic system of the hydraulic press machine, dip them in a solution composed of CrO3, H2SO4, and H2O to form a corrosion-resistant film on the surface.

1. Intelligent: The slider movement curve can be optimized online according to different production processes and mold requirements (such as blanking, stretching, sheet metal extrusion, progressive die stamping, etc.), and unique working characteristic curves can be designed to carry out Difficult and high-precision processing.

2. High efficiency: the smart hydraulic press machine can set the number of strokes of the slider in a wide range, the speed, and stroke of the slider can be adjusted easily, and the slider can work at the minimum stroke according to the forming process, with the help of multi-station technology and automatic feeding technology, the Increase productivity.

3. High precision: Through the servo control technology, the movement of the hydraulic press can be precisely controlled. Generally, it is equipped with a slider displacement detection device, and any position of the slider can be accurately controlled.

4. Composite functions: For new technologies such as isothermal forging and superplastic forming, the slider and mold space are used to build a temperature-controllable heating environment, and the forging, stamping process and heat treatment process are combined to achieve a multi-purpose machine and ensure product quality.

5. Low noise: The smart hydraulic press simplifies the transmission system and reduces noise. Helps reduce punching noise by setting the low-noise motion profile of the slider.

From the perspective of hydraulic power components, the periodic change of the working volume of the hydraulic pump makes the instantaneous flow pulsating. Flow pulsation generates pressure pulsation under the action of the hydraulic system pipeline and load impedance, and at the same time generates wave reflection, refraction, and interference.

From the perspective of hydraulic control components, in the case of sudden changes in system states such as start-stop, reversing, and shifting, the reverse pressure pulsation generated by the control valve due to inertial action will increase the pulsation amplitude of the system.

From the perspective of the hydraulic system, resonance will occur when the natural frequency of components and pipelines is the same or similar to the frequency of the coupled pulsation. The resonance will increase the pulsation and noise of the system, reduce the life of the mechanical structure, and affect the control performance of the system. In severe cases, major accidents may occur.

In addition, the vibration of the hydraulic system is the main source of the noise. Strong noise will accelerate the fatigue damage of the mechanical structure, or even break it, and will also cause adverse effects on the human auditory tissue and central nervous system.

Hydraulic press systems generally have high nonlinear and uncertain dynamic characteristics. Simple linear or nonlinear differential equations cannot fully express the corresponding actual systems, so the control algorithms based on accurate models are not suitable. The control algorithms commonly used in hydraulic press systems are as follows:

1. The hydraulic press system adaptive control algorithm, which is suitable for systems with certain uncertainties, can automatically adjust the model parameters according to the data characteristics in the process of analysis and processing, and finally approach the target in the best state.

2. The hydraulic press system seeks the optimal control algorithm by itself. It is suitable for the controlled system without a precise mathematical model but with nonlinear characteristics. During the control process, the real-time optimal state can be obtained through continuous measurement, understanding, calculation, and judgment.

3. The neural network control algorithm of the hydraulic press system does not require a thorough understanding of the system. Through learning and training with a certain amount of input and output samples, it can approximate any complex nonlinear mapping with extremely high precision and has a strong self-learning ability. , adaptive capability, and nonlinear mapping capability.

4. The fuzzy control algorithm of the hydraulic press systems is suitable for complex nonlinear systems with inaccurate or uncertain known information. It summarizes control rules based on theoretical and empirical analysis and then controls the system through reasonable reasoning based on the rules. It has strong robustness.

A complete hydraulic power unit consists of five parts, namely the working medium, power part, execution part, control part, and auxiliary part. The working medium is used to transmit motion and power in the hydraulic power unit, and the commonly used working medium is hydraulic oil. The core component of the power part is the hydraulic pump, which converts the mechanical energy output by the prime mover into liquid pressure energy and inputs it into the hydraulic power unit. The core element of the executive part is the hydraulic cylinder or hydraulic motor, which converts the pressure energy of the liquid into mechanical energy to drive the working mechanism.

The control part is mainly composed of three types of control elements, which are used to control or adjust the pressure, flow, or direction of the oil in the hydraulic power unit to ensure that the execution device completes the expected work. In the currently commonly used hydraulic transmission system, various movements of the hydraulic power unit are mainly realized by the hydraulic control element controlling the hydraulic actuator to change the direction of movement, the carrying capacity, and the speed of the movement.

The control elements mainly include directional control elements, pressure control elements, and flow control elements. Auxiliary components connect the previous parts together to form a system, which mainly plays the roles of oil storage filtration, measurement, and sealing in the hydraulic power unit.