Old-fashioned overload protection devices in mechanical presses, such as crush-type, have gradually been eliminated because they cannot accurately signal and effectively protect the machine, and replacement is very troublesome. Instead, it is a hydraulic overload protection system with rapid unloading and quick recovery.
1 The composition and working principle of the system
Hydraulic overload protection system generally consists of pneumatic pumps, unloading valves, pressure relays, solenoid valves, pressure gauges and other components. As shown below.
1. Air supply 2. Lubricator 3, 4. Solenoid valve 5, 14. Pressure reducing valve 6. Pneumatic pump 7. Muffler 8. Fuel tank 9. Oil filter 10. Shut-off valve 11, 12. Inlet and outlet oil one-way Valve 13. Non-return check valve 15. Unload valve 16. Pressure relay 17. Pressure gauge and buffer valve 18. Hydraulic cylinder
When the die height is not properly adjusted or double, the pressure is overloaded. At this time, the pressure in the hydraulic cylinder rises sharply, the pressure in the high pressure chamber of the unloading valve is greater than the back pressure in the back pressure chamber, and the piston is pushed downward to open the oil return port, and the hydraulic oil is quickly drained back to the fuel tank. Under the action of the balancer, the slider moves upwards by 20mm to protect the press and the mold from damage; at the same time, the pressure relay and the stroke switch act to cut off the clutch control circuit and the press stops; the solenoid valve 3, 4 closes the air source and is quickly discharged. The unloading valve back pressure chamber air, "normal" indicator light off, "unloading" indicator light, the press can not start.
After troubleshooting of the press, the hydraulic protection switch of the control station is turned to the position of “resetâ€, the “inch†stroke is started, and the slider is raised to the top dead point. At this time the solenoid valve 3, 4 connected to the air source, the compressed air into the lower chamber of the unloading valve, so that the piston rise reset, close the hydraulic cylinder return channel; while compressed air into the pneumatic pump, pushing the pneumatic piston reciprocating motion, thereby driving the hydraulic column The plug reciprocated. As a result, the low-pressure oil is drawn into the tank, and it is output to the hydraulic cylinder via the one-way valve, gradually raising the pressure to the specified pressure. At this point, the hydraulic pad is reset, the pressure relay and the unloading valve's stroke switch act, the hydraulic protection “unloading†indicator light is off, the “normal†indicator light is on, and the hydraulic overload protection system returns to normal. Turn the hydraulic protection selector switch to the “normal†position and the press will work properly. Each restoration of the hydraulic overload protection system takes only about 3 minutes to meet the requirements for general high efficiency stamping production.
2 common faults and troubleshooting
Due to the frequent reciprocating action of the press slider and the severe vibration during the work, the hydraulic and pneumatic components that make up the system may often cause some failures and cause the press to stop. At the same time, the use of seals and other materials for hydraulic and pneumatic components, long-term use will cause wear, aging or failure, failure. This article will introduce some common faults and their elimination methods based on our experience in producing and debugging hydraulic overload protection systems for many years.
2.1 Pneumatic pump The pneumatic pump is a functional part that provides the specified pressure of the hydraulic overload protection system. It consists of a pneumatic part and a hydraulic part. When analyzing faults, first listen to the sound of the pneumatic pump. If it is a normal, regular rhythmic commutation sound and the pressure does not increase, then basically you can determine that the aerodynamic part is not faulty. You should focus on the hydraulic part of the analysis; if the sound is not rhythmical, or the pneumatic pump is connected to the wind source If there is no action or obvious air leakage, it can be basically determined that the fault is in the pneumatic part.
The hydraulic part of the pneumatic pump is mainly composed of a plunger and a seal, a check valve for oil inlet and outlet, an oil suction pipe and an oil filter, a cylinder block, and the like. The easy-to-failures are:
(1) The suction pipe seal is not good or loose, resulting in inhalation of air in the cylinder and cannot be ruled out. The pneumatic pump is idle and does not come out of oil. Remedy: Remove the suction tube, re-apply and fasten, and fill the cylinder with oil.
(2) Oil filter plugging. Should be removed and cleaned.
(3) Seal wear or aging failure at the plunger. Should be removed for replacement.
(4) Incoming and outgoing check valves The dirt or plugging of the check valve makes it impossible to reset the steel ball or loosen the spring seat. Remove the cleaning fastening.
The pneumatic part of the pneumatic pump consists of a reversing valve, a pilot reversing valve, a valve body, a valve cover, a cylinder block, a piston, an air pipe, and a fastening bolt. The pilot directional valve is equivalent to the limit switch of the piston up and down position, and controls the switching of the directional valve. The prone to failure of the pneumatic part is:
(1) Seal failure at pilot reversing valve. Since the main reversing valve uses the pressure difference between the two sides of the reversing plunger to reverse the direction, the reversing valve cannot be reversibly switched when the seal is failed, and the pneumatic pump has no action or air leakage.
(2) The spring at the pilot reversing valve is subjected to pressure for a long time and the elastic force is reduced. The force required for resetting the pilot reversing needle plunger cannot be provided.
If the above pilot valve malfunctions, it will leak from the pilot valve of the valve cover and it is easier to judge. Remedy: Remove the inspection and replace the corresponding parts.
(3) Pilot valve pin plunger is adhered by moisture and dirt in the compressed air and is rusted and does not operate normally.
(4) The main reversing valve consists of a reversing sleeve, a reversing plunger, a sealing ring, a guide ring, a cushion, and a compression ring (namely, a muffler joint). The reversing sleeve and the reversing plunger adopt gap sealing. The gap value is generally less than 0.015mm, so it is sensitive to impurities and dirt and has a higher requirement for lubrication. This requires that the air line must be provided with clean oil mist lubrication to ensure its normal operation; its outlets should be blocked during storage and transportation to prevent the entry of dirt; after long-term storage, oil guns should be used to inject cleanliness. Lubricant, and hook the plunger hole with a special tool, gently push and pull a few times. If you push it lightly, it means there is no problem here. It is recommended not to dismantle it easily.
2.2 Unloading valve The unloading valve is mainly composed of a valve body, a piston, a cushion, a lower cover, and a travel switch. The high pressure chamber of the valve body is connected with the hydraulic cylinder (or high pressure pipeline). The low pressure chamber is connected with the fuel tank. The high pressure oil is sealed through the 100° cone surface of the valve body and the 100° cone surface of the piston. The back pressure is provided by the compressed air in the lower chamber of the piston. . The main failure of the unloading valve is that the pressure oil leakage cannot reliably maintain the pressure, and is mostly caused by the contaminants and contaminants in the oil that damage the 100° cone surface. The judgment method is as follows: the sound of the pneumatic pump is normal, the oil at the outlet is pressured, and the system pressure cannot meet the requirements, and the pneumatic pump is frequently compensated. The exclusion method is: disassemble the unloading valve and check the cone of 100°. If the injury is minor, use a grinding paste to remove it. Otherwise, replace the unloading valve and clean the internal dirt of the system.
2.3 Pressure relays Pressure relays are also components that are prone to failure in the system. Its common faults are:
(1) Pressure oil leaks. The pressure relay is mainly composed of a valve body, a plunger, a micro switch, and a spring. Under the effect of hydraulic pressure, the axial movement of the plunger touches the micro switch to switch the electrical signal. The clearance between the plunger and the valve body is sealed. If the manufacturing quality cannot be guaranteed, excessive leakage will inevitably cause the system pressure to drop, causing the pneumatic pump to compensate too frequently and affect its life. Judgment method: In the case of pressure in the system, check whether the oil return port is too much, and replace the pressure relay if necessary.
(2) The micro switch cannot be reset and cannot be linked with the electric. Due to long-term use, the reset spring of the micro switch gradually loses its elasticity and cannot be reset. The solution is to replace fatigue-failed reeds with copper sheets that are the same thickness (or thicker than the original ones).
2.4 Electromagnetic valve solenoid valve faults are:
(1) The electromagnetic coil burns for a long time.
(2) In-valve seal fails to leak air, or dirt adheres to the spool and does not move.
Due to the simple structure of the solenoid valve, it is possible to remove the above check and replace the new solenoid valve.
2.5 Regulator Valve Regulators cannot be adjusted due to corrosion of internal parts or have no output. Should be removed for replacement.
3 Use and maintenance precautions
(1) Before the main line of the workshop or the total gate of the press, set up the water diversion device, and do the draining of the water in the device before use. Otherwise, it will have an adverse effect on the system, causing corrosion and failure of all components and reducing the service life. This is particularly important in wet areas.
(2) Always check the oil level on the tank and compensate it in time to avoid emptying the pneumatic pump. Change the hydraulic oil and clean the fuel tank and piping regularly. Use hydraulic oil that meets the requirements; filter measures when refueling; always check the system. Whether oil spills, take timely measures.
(3) When the hydraulic overload protection system fails, do not dismantle it easily. Observe it more. If necessary, ask a qualified person to repair it.
(4) Pneumatic pumps require good lubrication during operation. Always check and supplement clean lubricants.
(5) Be sure to take care not to carry any dirt such as iron swarf, cotton yarn, etc. into the system during maintenance. Wipe the device with a clean cotton gauze before reinstalling it. Otherwise, components may not work properly due to clogging. Do not force a component reset until the cause of the fault is found. In particular, some of the imported pumps, valves, and gas-liquid safety valves have magnetic properties in their magnetized pistons, which are prone to adsorb iron scraps in the oil and cause the system to malfunction. They must be dismantled and thoroughly removed before they can be removed.