Checking on a hydraulic press to keep it in good working order is more than just smart operating procedure - it can actually pay off for manufacturers. By knowing when a hydraulic press is running well or is in need of attention, and by consistently conducting preventative maintenance, the lifespan of a press can be significantly increased. The key is to get to know the machinery and develop a written preventive maintenance schedule that will help keep the equipment in peak condition for many years to come.
Oil Maintenance
Not maintaining proper oil levels and quality will quickly reduce the life of a machine. Dirt and heat are especially destructive to a press. Keeping oil in new condition is fairly easy to do. Best operation temperature is about 120° F. Oil temperature can be maintained by either air or water coolers. Probes are inserted into the oil reservoir and temperature maintained by the use of a thermostat. The air coolers use a radiator to separate the heat with the use of an electric fan moving the air through the cooler. Dirt and dust tend to collect in the vanes of the radiator and prevent the airflow from traveling at maximum capacity, so it is important to keep the radiator clean.
To help keep the unit clean, attach a common filter, like the ones used for heating and air conditioning, to the heat exchanger.
The results can also indicate if the correct micron level of filtration is being used. Simple hydraulic systems only require code 10 filters, which result in a cleanliness level of 20/18/15. More complex systems that have proportional or servo valves require code 03 filters, which have a cleanliness level of 16/14/12. Several companies can perform this test and maintain records.
Pressure
If the press is in good working condition with no leaks, it should build to the maximum required pressure in one-half to one second. A pressure buildup of two to three seconds may indicate a problem with a pump, valve or motor. Pressure problems are usually pump related, although the issue could also stem from the relief valve working too slowly. Look for dirt or grit in the line and also check to see that the valve is not open too wide. Additionally, if the press motor is not producing sufficient revolutions per minute (RPM), a drop in pressure could occur.
Electrical Maintenance
Electronics today are very dependable, but do not last indefinitely. Coils that are located on valves normally have a life cycle of three million strokes, and relays typically have one million strokes. Replacing them before they fail can decrease or eliminate hours of troubleshooting, resulting in less down time. Installing an hour meter and non re-settable cycle counter will help to maintain accurate records and can help with scheduling maintenance. Check the control wiring annually to make sure all connections are tight and that the wiring is in good condition. Place loose wiring in wire ways or tie them with wire ties. Unused wires or spares should be capped off or removed. Remove any dust or dirt from enclosures.
Developing a preventive maintenance checklist - daily, monthly and yearly - that is right for the press is the key to detecting issues at an early stage to avoid potential costly fixes later on and keeping the press at optimal performance for years to come.
A Quick Check a Day
The daily maintenance checklist below provides examples of small tasks that can be performed to keep the equipment up and running:
- Look for oil leak on all hydraulic lines. A small leak can be a big mess. Tighten fittings and clean up excess oil. Keep the press clean to help locate leaks as they develop and to help keep the press cooler.
- Measure fluid levels and top off as necessary. Most presses have an oil tag on the machine describing the type of oil to be used.
- Check for loose bolts. Some dies can cause vibrations that can loosen bolts over time.
- Make sure there is lubrication on the guided plates. Some bushings will have greased fittings to keep lubrication over the rod. Do not over grease, this causes dirt accumulation and the bearings will wear. Other bushings have a check valve-type fitting, which have graphite impregnated into the bronze and require little maintenance. Use Mobil Viscolite (or similar) to spread graphite onto rod. The rod will be somewhat dry. Never put grease on this type of rod.
- Let the machine warm to operating temperature. Check that the oil is at 120° F.
- Check light curtain function. Break beam while ram is traveling down; the press should stop. Breaking beam on the upward stroke may not stop the press. See owner's manual for proper function.
- Keep area clean for safety and accident prevention.
Yearly Inspection
Additional measures performed throughout the year will help maintain a healthy press. Yearly inspection is recommended for:
- Water-cooled systems function much in the same way as air coolers except that water travels through the vanes. The method for the water could be city water, chillers or roof top mounted exchangers. To inspect, remove the end caps to check for clear passages and flush with cleaning solvent if necessary.
- Roof top mounted units tend to collect dust and dirt. That can result in clogging of the exchanger and produce rust. Placing a filter in line will help remove any fine particles.
- Water chillers dissipate heat well because the inlet temperature can be adjusted and anti-rusting agents can also be added to the water.
- Oil sampling needs to happen to determine when filters need to be changed. This sample will tell how many particles of different sizes are in the oil, if the oil has water in it, as well as the lubricity properties. In most cases it is not necessary to change oil but certain additives may be needed. The oil sampling can be used to determine if the oil filters are being changed at proper intervals.
Authored by: Engineers at Greenerd Press & Machine Co., Inc.
For more information contact:
Greenerd Press & Machine Co., Inc.
P.O. Box 886
Nashua, NH 03060
603-889-4101
www.greenerd.com