The hydraulic press relief valve has two main functions, which are to maintain the pressure stability of the hydraulic system and to limit the high pressure of the system. It is installed at the outlet of the hydraulic pump. If the hydraulic oil circuit is overloaded, the hydraulic oil can return to the tank from the relief valve to realize the unloading of the system to protect the hydraulic system.

The following is the fault analysis of the hydraulic press relief valve.

(1) The damping hole of the hydraulic press relief valve is blocked

The damping hole is blocked, which is a common and easy-to-be-ignored problem, is due to the hydraulic oil is not pure, and oil impurities caused by too much. In this case, first, check whether the relief valve is blocked, clean the relief valve, and then return the spool to the position, reset and open the pressure according to the load required by the machine.

 (2) hydraulic press relief valve spring problem

If the spring is not firmly fixed or the spring is deformed or broken, it will cause the pressure of the relief valve to decrease, so that the hydraulic actuator can not work normally. The operator needs to re-secure the spring or replace it with a new spring.

(3) The poppet valve of the hydraulic press relief valve is seriously worn

The loss of pressure in the hydraulic system is closely related to the serious wear of the poppet valve. Too much wear of the poppet valve causes a serious leakage of the hydraulic system, resulting in pressure drop or loss of pressure failure of the hydraulic press system. In this case, a new relief valve should be replaced immediately.

The leakage of liquid is a problem that cannot be ignored in the transmission of a four-post hydraulic press machine. If the leakage is not solved, it will affect the normal application of hydraulic equipment and the development of hydraulic technology.

Specifically, the impact caused by the leakage has the following aspects:

1. The system pressure is not high;

2. The speed of the actuator is unstable;

3. System heating;

4. The volume efficiency of components is low:

5. Waste of energy and oil;

6. Pollution of the environment;

7. May cause control failure;

8. Disaster elimination may occur.

Generally speaking, the causes of leakage of the four-post press include design, and manufacturing problems, as well as equipment maintenance, maintenance, and other management problems.

In order to reduce the failure of the four-post hydraulic press machine system, improve the efficiency of the hydraulic system, prevent environmental pollution, and reduce the loss of hydraulic media, we must pay attention to the leakage problem, analyze the causes, take corresponding measures to reduce leakage and avoid leakage.

Common faults of the four-column hydraulic press machine are analyzed as follows:

1. The oil temperature is too high is the biggest cause of the four-column hydraulic press system, it brings harm: hydraulic oil viscosity, volume efficiency, and efficiency of the hydraulic system are decreased, leakage increases, and even make the equipment cannot work normally.

2. The parts of the four-column press system expand because of overheating, which destroys the original normal clearance of the relative moving parts, leading to the increase of friction resistance and the hydraulic valve is easy to get stuck.

3. The rubber seal of a four-column hydraulic press deteriorates, shortens its life, and even loses its sealing performance so that the hydraulic system leaks seriously.

4. Four-column hydraulic press machine oil vaporization, water evaporation, easy to cause cavitation erosion of hydraulic components; The oxidation of oil to form gelatinous deposits, easy to plug the filter and hydraulic valve hole, so that the hydraulic system can not work normally.

Therefore, the high oil temperature will seriously affect the normal use of the four-column press, reduce the service life of hydraulic components, and increase the maintenance cost of the hydraulic press.

The related factors causing the leakage of the four-pillar hydraulic press system are as follows:

1. Work pressure

Under the same conditions, the higher the pressure of the four-pillar hydraulic press system, the greater the possibility of leakage, so the size of the system pressure should be in line with the best value needed by the hydraulic system.

2. Working temperature

Most of the energy lost by the hydraulic system is converted into heat energy. Some of this heat energy is released into the atmosphere through the surface of the hydraulic components themselves, pipelines, and oil tanks, and the rest is stored in the hydraulic oil, which will make the oil temperature rise.

3. Cleaning procedure of oil

The hydraulic oil of the four-pillar hydraulic press often contains various impurities. The impurities in the hydraulic oil will aggravate the wear on the surface of the hydraulic components, the spool of the hydraulic valve is blocked, the hole is blocked, and the seal is damaged, which causes damage to the hydraulic valve and causes the leakage of hydraulic oil.

4. Selection of sealing device

The correct selection of sealing device is very important to prevent leakage of the four-pillar hydraulic press system. Reasonable selection of sealing devices can improve the performance and efficiency of the equipment, and prolong the service life of the sealing device, so as to effectively prevent leakage.

In the use of a four-post hydraulic press, due to the poor working environment, long operation time, frequent oil conversion movement, and system failures multiple, the reasons are various, fault judgment and elimination are also more complex, do a good job of fault diagnosis to do:

1. Familiar with the working characteristics of the four-post hydraulic press components and the structure of the hydraulic system, working principle, master the configuration relationship of hydraulic components, accessories, system, working conditions, and environmental requirements.

2. Establish and improve the equipment technical condition inspection, maintenance, repair system, and fault technical files, and accumulate the data and operation records of the four-post hydraulic press.

3. Familiar with the fault phenomena and fault inspection methods of all kinds of hydraulic components of four-post hydraulic press, and must have certain field practical experience and equipment management knowledge.

4. Familiar with the four-post hydraulic press and the use of hydraulic system fault diagnosis and analysis methods and reasonable selection, with the necessary detection instruments and certain detection means, pay attention to learning and application of modern advanced diagnostic technology.

1. Subjective diagnostic technology: it refers to the maintenance personnel using simple diagnostic instruments to analyze and judge the causes and locations of four-column hydraulic press failures based on their personal practical experience. It is convenient and fast and has low reliability. It belongs to simple qualitative analysis, including the intuitionistic empirical method, logical analysis method, parameter measurement method, cut-off method, and so on.

1) Intuitive experience method refers to the maintenance personnel with their senses and experience, through seeing, listening, touching, smelling, asking, and other methods to determine the cause of failure.

2) Logic analysis method refers to the logical relationship and fault phenomenon of four-column hydraulic press components, systems, and equipment, through the study of hydraulic schematic diagram and component structure, logic analysis, to find out the fault location.

3) Parameter measurement method means to determine whether the parameters are normal or faulty by measuring the working parameters at the required points in the system loop and comparing them with the normal working value of the system.

4) Cut-off method refers to the composition of the hydraulic press system and fault phenomenon selection cut-off point, cut-off method is to observe the change of pressure and flow, so as to find out the fault method.

2. instrument diagnosis technology: according to the pressure, flow, temperature, noise, vibration, oil pollution, the speed of the execution parts of the hydraulic press system, through the instrument display or computer calculation to judge the results.

3. Intelligent diagnosis technology: it refers to the simulation of human brain function, the effective acquisition, transmission, processing, regeneration, and utilization of fault information, and the use of a large number of unique expert experiences and diagnosis strategies.

In the design of the hydraulic cylinder structure, the selection of its structure form generally depends on the hydraulic cylinder in the hydraulic machine support, and the specifications of the hydraulic cylinder is determined according to the total pressure of the hydraulic machine.

1. Overview of hydraulic cylinder structure design

Hydraulic cylinder structure design including hydraulic cylinder type, size, and support mode. Because the hydraulic cylinder is the executive component of the hydraulic machine, the output power is to bear the load, and the hydraulic machine is easy to fail. The selection of a suitable cylinder structure, specifications, and support mode can not only ensure the accurate action of the hydraulic cylinder but also extend the service life of the hydraulic cylinder.

2. Structural design of blank holder cylinder

Small hydraulic press chooses to install a block thickness of 150 mm steel plate on the movable beam, steel plate processing through the hole, hydraulic cylinder flange and steel plate connected together, hydraulic cylinder wall cylindrical surface, and steel plate through the hole with installation.

3. Structural design of lateral forming hydraulic cylinder

The lateral forming cylinder adopts the piston cylinder with symmetrical Settings, the rod support connection, the cylinder is fixed on the lateral support seat, and the lateral support seat and the hydraulic press base are connected. The nominal pressure of the lateral forming cylinder is 1000 kN and the liquid pressure is 25 MPa.

Hydraulic pressure relief actions usually rely on opening the charging valve of the oil cylinder end to achieve, under the condition of ultrahigh-pressure liquid， the valve core could be stuck and could not be opened. Once the charging valve cannot open, the pressure relief will not be able to be realized automatically, but only through manually loosening the oil inlet pipe of the cylinder cavity on injection pressure relief. It is not only very dangerous but also a waste of oil.

The following describes the safety settings of the hydraulic press system：

Hydraulic press emergency stop through the safety controller control, in addition to the button rotation, reset also added a special reset button and indicator light; The two-hand operation button is controlled by the two-hand special function module in the safety controller, and there is a clear requirement for the synchronization action time difference between the two buttons (≤0.5s). Because the working table of the press is long, there are two mobile button stations, and the operation buttons on the two mobile button stations have synchronization action time differences in addition to themselves. The operation between the two moving button stations is also set with the synchronous action time difference to ensure the safety of the operation; In addition, there is an emergency return button for mandatory return action in the state of emergency.

The control method of the hydraulic press is optimized and improved on the basis of the original design, and the pleasant forming special process control is added, which can reduce the labor intensity of the operator and improve production efficiency at the same time. From the perspective of safety, the corresponding changes are made to protect the life safety of the operator.

Recently, Shuntec Press has designed and built a 6-cylinder hydraulic press for a client from Australia. A total of 6 cylinders are used to drive the slider movement, and the inlet and outlet of the middle 4 cylinders are combined to supply oil through the hydraulic system, and the inlet and outlet of the two cylinders are controlled by a separate hydraulic system driven by a motor proportional pump. The system composition of the 6-cylinder hydraulic press is described as follows:

1. Setting of bottom cylinder material supporting function

The hydraulic press usually enters the pressure relief return automatically after the end of the slide pressing, and the top cylinder is pushed out to facilitate the operator to take the material. However, the bottom plane of the workpiece is often deformed because of the notch of the die. Therefore, the customer requires the ejection action of the ejection cylinder at the same time as the return journey of the press slider to ensure the forming of the workpiece.

2. Automatic blanking device

A hydraulic press longer on forming will be tightly attached to the mold, the operator needs to spend a long time through a crowbar and other tools to make it out. The automatic feeding device can facilitate the workpiece demoulding, reduce the working intensity, and improve the working efficiency.

3. Selection of short and long material forming

For customized hydraulic press longeron have a variety of specifications and lengths is different, and the effective work of a machine tool table 12 meters long, 6 cylinders is also a uniform layout, the suppression of length 8 m or less will appear when the longitudinal beam of two sides because of the lower cylinder without artifacts support continued to press, on both sides of the sliding block caused by partial load, can cause the connection bolt snap even serious damage of oil cylinder.

With the rapid development of the automobile industry, especially the continuous expansion of the scale of light truck production, the main structure of its chassis - longitudinal beam primary forming equipment demand is also expanding. The traditional production process is the use of dozens of drilling press drilling and then forming, and now most manufacturers have used beam CNC punch punching processing, and efficiency has been greatly improved.

The Shuntec hydraulic press system is mainly composed of Siemens S7-300 PLC, Siemens TP1200 touch screen, Germany NOVO displacement sensor, Rexroth proportional flow valve, Jining Taifeng hydraulic system, high proportion pump, and so on.

Set relevant parameters in the touch screen, according to the feedback signal of the displacement sensor, S7-300 PLC after operation and processing control hydraulic components and proportional pump action, achieve process control requirements.

In addition, a proportional flow valve is arranged on the pipeline of the lower chamber of the oil cylinder. When the slider moves from fast to slow, the control signal of the proportional flow valve is changed to realize the adjustment of the valve port, so as to realize the smooth transition of the speed of the slider from fast to slow without impact.