Jun. 24, 2024
In order to choose the right type of press, you first need to know if the machine will be used for:
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You will also need to have a fairly accurate idea of the finished dimensions of the workpiece to be formed, and the dimensions of the parts to be handled for punching or riveting, in particular to be able to correctly choose the dimensions of the worktable and the press opening height.
You will then need to define the tonnage of the machine you require. This will depend on the type of material you will be working with, its thickness and the type of stamping to be performed (for example, the stamping depth or the cutting perimeter). The tonnage of the machine is usually expressed in kilonewtons (kN). There are presses from 5 kN (0.51 metric tons) up to 500,000 kN (50,000 metric tons).
Production requirements are also important to consider, whether they are unitary or small or large series. For one-off needs or small series, you might be interested in manual, mechanical or hydraulic presses, or even electric presses which also exist in portable models. For mass production, it is essential to know whether you need single striking or a repeated striking. In the latter case, you can consider transfer presses that allow you to carry out consecutive striking in a fully automatic manner.
All these criteria will allow you to choose the most suitable technology for your installation, whether it be hydraulic, mechanical or pneumatic.
What should you do to keep your hydraulic press running? Know your press&#;when it is working properly or when it needs attention. You can extend press life and maximize your investment by keeping your eyes and ears tuned and by performing these eight preventive maintenance steps:
1. Keep It Cool. A hydraulic press should run cool&#;typically between 120 degrees F and 140 degrees F, and no higher than150 degrees F.
2. Allow No Leaks. Hydraulic presses that are in good working condition have no leaks. Check around the ram of the press and the O-ring seals on valve seats and hose end fittings, as well as all hydraulic lines. You should refer to the machine operator manual for the specific type of oil that the manufacturer suggests for your press. While you check seals, be sure that sufficient lubrication is applied wherever necessary.
3. Build Pressure Quickly. A press in good working condition takes one-half to one second to build to the maximum required pressure. A pressure buildup of more than two to three seconds may indicate a pump problem. Typically, pressure problems are pump-related; however, occasionally the relief valve may be working too slowly. Perhaps dirt or grit is in the line or the valve is open too wide. Also, if the press's motor is not producing sufficient revolutions per minute (RPM), a drop in pressure could occur.
4. Ensure Smooth Valve Shifts. Valve shifts should be smooth from one speed to another&#;you should not hear any banging noises during speed changes. In fact, any sounds that are not considered normal should be investigated promptly.
5. Check the Electronics. Coils that are located on valves normally have a life cycle of 3 million strokes. Relays normally have a life cycle of 1 million strokes. Replacing the coils before they fail can eliminate or reduce hours of troubleshooting and reduce downtime. Install an hour meter and a nonresettable cycle counter to help maintain accurate records and facilitate maintenance scheduling.
Fix loose wires and fittings and frayed hoses because frayed hoses and incorrectly crimped fittings can cause plumbing failures. Hoses should never touch each other, and fittings should be crimped by an authorized facility to ensure they can withstand the system pressure.
Check the control wiring annually to make sure all connections are tight and that the wiring is in good condition (see Figure 1). Loose wiring should be placed in wire ways or tied with wire ties. All spares or unused wires should be capped off or removed. Dust or dirt should be removed from enclosures.
6. Keep the Oil Clean. Maintaining your press's oil in good condition is a relatively simple way to extend press life. Dirty oil and low oil levels reduce press life rapidly. Dirt and heat are common culprits.
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7. Maintain Optimal Oil Temperature. The ideal operational temperature is about 120 degrees F. Either an air or a water cooler can help maintain the temperature. Probes are inserted into the oil reservoir and temperature maintained with a thermostat. An air cooler uses a radiator to separate the heat with an electric fan, circulating the air through the cooler.
The radiator should be kept clean, as it tends to collect dirt and dust in the vanes, which inhibits airflow. Attaching a common filter, such as the kind used in heating and air-conditioning units, to the heat exchanger is an inexpensive way to help keep the unit clean (see Figure 2).
Water coolers work similarly except that water instead of air travels through the vanes. The water source could be city water, chillers, or rooftop-mounted exchangers. Running city water through an exchanger could be expensive and will tend to rust the inside of the exchanger. Also, many municipalities discourage the use of city water, depending on local water restrictions and codes.
Rooftop-mounted units tend to collect dust and dirt, which can clog the exchanger and perhaps cause rusting. Placing a filter inline will help remove any fine particles. A water chiller is the best way to dissipate heat because the inlet temperature can be adjusted. Also, antirusting agents can be added to the water. Inspection of all of this equipment should be done yearly.
8. Change Filters. The next step in good maintenance is to perform oil samplings to ascertain when you need to change filters and if they are being changed at proper intervals (seeimage at top of page). This should be done at least yearly. The sampling can tell you how many particles of different sizes are in the oil, if the oil has water in it, and the lubricity properties. Usually it is not necessary to change the oil, but certain additives may be needed.
You also can tell from the results if the correct micron level of filtration is being used. Simple hydraulic systems require only code 10 filters, which result in a cleanness level of 20/18/15. More complex systems or those with servo valves require code 03 filters, which have a cleanness level of 16/14/12. Numerous companies can perform this test and maintain the records.
Create a daily (see Daily Checks), monthly, and annual check list for all the equipment in your shop. This allows you to detect problems early and avoid potentially expensive fixes later.
Despite following good maintenance practices to prolong the life of a hydraulic press, sometimes it is necessary for you to replace the press to ensure that part production is accurate and consistent. It's important to recognize critical indicators that signal a new press is required:
The press can no longer build up pressure. Key areas to look into are the pump, press motor, and valves. However, if the pump is faulty, you may be able to replace just the pump.
The frame is cracked. These fractures can be subtle or obvious. A temporary fix is to possibly weld the frame, but ultimately the press will need to be replaced.
Critical hydraulic or electrical problems exist. Intermittent operation problems can signify an electrical short or loose wire. Make sure all wires are tight and have ferrules on the wire ends to prevent cross contact with other electrical components. Some older presses may have outdated electrical controls or hydraulic components that are no longer available. These two factors could be a reason to consider getting a new press rather than upgrading the electrical control or hydraulics package on an old frame that may have performed millions of cycles.
If you ignore any of these warning signs and run the press while it is compromised, performance likely will be sacrificed&#;increased cycle times, longer downtimes, and decreased part accuracy.
In one case example, a manufacturer was trying to press fit a bearing into a seat but it could not be seated properly on a consistent basis. The bearing outside diameter was oversized and the sleeve inside diameter was undersized. When the parts were run on a new press with consistent results, this helped the manufacturer determine that the old press needed to be replaced.
Thomas Lavoie is applications manager and Carl Jean is service manager for Greenerd Press & Machine Company Inc.,41 Crown St., Nashua, NH , 603-889-, .
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