Hey! Your stamping press is trying to tell you something
How to read 13 signs of press malfunction
May 10, 2005
Bill Engvall and Travis Tritt teamed up on a humorous little song called "Here's Your Sign." This curious little ditty relates the frustration of dealing with modern man's inability to grasp the obvious in daily living. From the service station attendant who stares at the blown-out tire on your car and asks, "Got a flat?" to the neighbor who leans on your House for Sale sign and asks, "Selling your house?" humankind seems at times unable to process information that is clearly evident.
If your stamping press could sing, it might be singing "Here's your sign." Your press gives you all the signs you need to interpret its condition. As is true with all communication, the key is being aware of how it is attempting to get your attention and understanding what it is saying.
You may contend that your press does not give you clear signs. You may be expecting bells; sirens; flashing lights; and fully automated, programmable logic-controlled equipment. Short of seeing a long-haired, robed, bearded man carrying a doomsday "the world will end tomorrow" placard, you may not be trained to recognize the danger signs your machinery is showing you. But the 13 most obvious and critical signs are those that can be detected with your senses. Your sight, hearing, and sense of smell and touch are your best ways to understand what your press is trying to tell you.
The press's physical condition should be stable; therefore, any visually apparent change should be investigated. Often the most obvious changes in physical characteristics are ignored by operators and maintenance personnel. But if changes are detected, they can point to potential catastrophes and subsequent downtime.
- Leaky Lubrication System. Proper lubrication is critical to a well-maintained press. Because all mechanical presses have both reciprocating and rotary motions, the metal-on-metal components that produce these motions must be lubricated to avoid direct contact, friction, and wear (see Figure 1). Your visual examination should include checking for broken or kinked lines (see Figure 2), lubricant leakage, oil spots on the floor and machine frame (see Figure 3), and contaminants in the lubricant.
- Cracked Frame. Inspect the press's frame and stampings for signs of cracking, warping, and deflection. If you detect cracks anywhere in the press (see introductory photo) or its components (see Figure 4), you would be smart to interpret them as serious signs of overload or fatigue. Not only must you prevent cracks from growing, you need to identify the cause and resultant damages not apparent to the naked eye.
The points where mating machined parts seat together is often the first areas where cracking, warping, and deflection occur. For instance, the split lines on column-to-bed mounting points on a straight-side press often have gaps that may appear to be "breathing" during the press operation. This indicates that an overload condition has occurred and that immediate correction is necessary. Also, bearing caps that gap at the mating surface indicate that bolts are loose or broken.
- Loose or Protruding Fasteners. Loose or protruding fasteners may indicate fatigue. Loose foundation or floor-mount fasteners often indicate that the machine is twisted and is attempting to find its own level.
- Worn Gearing. Analyze wear patterns on gearing. Inspect the gear teeth for wear patterns, indentations, fractures, and signs of abnormal or uneven contact (see Figure 5). A worn gear may fail catastrophically if it is not repaired in time. Although some gear wear may seem normal, it really is not. If all machine systems are functioning properly and the machine is being used within its engineering specifications, gears will roll together and produce machine motion without wear.
- Faulty Operating System. Cycle your press each day so that you can inspect all of its functions visually, especially its safety functions and stopping times. You cannot rely on green and red indicator lights alone to detect safety malfunctions, as shorts or faulty wiring may cause them to malfunction as well. If you cycle the press and it doesn't stop when you test each safety feature—when you put your hand across the light curtain barrier, for example—that is your sign.
A crankshaft angle of more than 3 degrees beyond top dead center indicates a worn or damaged brake system, which is a safety hazard. Improperly functioning electrical systems can damage the machine, its tooling, and the operator. Look closely at each function of the operating system to be sure all signs are noted and scheduled for repairs.
- Excessive Motion Clearances. Watch carefully for signs of excessive motion clearances and jerking. Sudden dropping or wobbling of machine frame or parts or side motions and movements in the ram, shafting, gearing, flywheel, connections, clutch, or brake all are signs that wear or damage has occurred.
- Broken Piping in the Pneumatic System. If your inspection reveals unsupported or broken piping, you should repair the damage immediately. Because the pneumatic system is critical to the safe operation of the machine, any devices that are not Occupational Safety and Health Administration (OSHA)-compliant belong at the top of your repair list. Wobbling rotary unions signal that the threads are in danger of failing, and you need to make corrective repairs immediately.
- Broken or Unattached Electrical Wiring. If you detect bare, broken, or unattached wiring, closer inspection and repairs are necessary (see Figure 6). Missing knobs, switches, burned-out lights, and broken components also are signs that urgent repairs are required.
Review available electrical schematics. If the date on a schematic is earlier than 1980 and the electrical system has not been upgraded since, it is likely that the system does not meet current OSHA/ANSI standards. Further inspection by a qualified industrial electrician is needed.
9. Changes in Noise Patterns. Although a metal forming plant is noisy, you can hear the rhythmic pattern a press produces as it moves through its strokes. A deviation from these healthy sounds during normal operation is a signal that damage or wear has occurred.
Thumping or banging sounds often indicate excessive clearances or broken components. Squeaking and scraping sounds point to a lubrication failure or the loss of adequate clearances in a press's working parts. Electrical humming often means a single phasing or other electrical problem has occurred.
10. Burning Oil and Lubricant Odors. The unmistakable smell of overheating is a sure sign of trouble. Burned grease, oil, and lubricants are easily distinguishable from the normal smells of the fabricating or stamping plant. The usual cause of overheating is inadequate lubrication. Additionally, overcounterbalanced machines can squeeze out lubricants and cause overheating. Often the first sign you will have that a lubrication line is blocked is the smell of overheating lubricant.
Single-stroke applications sometimes cause overheating in a machine's clutch brake system. The clutch brake mechanism can be permanently damaged and may fail if it reaches temperatures above 200 degrees F.
11. Temperature Variations. A machine's normal temperature should not vary dramatically. A departure from the normal temperature warrants concern.
Often a catastrophic failure is preceded by a temperature shift that can be felt by attentive operators or maintenance personnel.
One simple test you can perform is to place your bare hand at each point on the surface of the machine under which a bearing surface is located. These bearing point temperatures should be taken with the press locked out and tagged out to avoid injury.
Once a prior-to-run base test has been done, the same test should be performed after the machine has run for approximately four hours. If the temperature after running exceeds a comfortable level, the bearing or sliding surface is likely overheating. This warrants additional inspection for lack of lubrication, contamination, and broken or bent components.
12. Excessive Vibration. All machinery has moving elements and, therefore, vibration patterns. These can become destructive if they exceed normal levels for the type of machine, its foundation (see Figure 7), the bearing alignments, and aligned machined surfaces. Vibration can damage press components and should be eliminated before it exceeds acceptable levels.
A press that is not sitting level on its base or foundation often vibrates or rocks. Carefully check foundation bolts, vibration pads, and the foundation itself if these signs are present. Ignoring patterns as obvious as rocking or excessive vibration is an invitation to complete system failure.
When vibration becomes a problem, isolate its source. Mechanics once used a technique to isolate a vibration source by holding one end of an extended screwdriver to the machine at various points and the other end near the ear. Today machine stethoscopes often are used to locate the sources of vibration. Other methods used include vibration analysis and balancing equipment.
Typically, the vibration problem occurs when a component—normally a rotating member—is out-of-round or out-of-balance. Other sources of vibration are poor machine setup, loose components, clearances on moving parts that exceed acceptable tolerances, and insufficient foundation.
Another simple test you can perform is to place your hand on the slide or ram of the machine—take care to avoid pinch points and injury—as it travels through its cycle. If you feel a jerking or sudden snap-through motion, an overclearance condition in one of the bearings or connections may be present. You can check this more thoroughly with a lost-motion test.
13. Grainy Lubricant. Whether oil or grease is used to lubricate the bearing points, the lubricant should be clean both when entering and exiting the system. Lubricant samples should be taken as the lubricant enters and exists the bearing and slide surfaces.
You can check the lubricant for signs of contamination by rubbing it between your finger and thumb. If the lubricant feels gritty or shows obvious signs of contamination, the lubrication system should be cleaned, purged, and refilled. If the outgoing lubricant contains bronze particles or other bearing material, the bearings should be disassembled and replaced.
Signs of failure should be taken seriously. If you read the signs—and heed them—you save thousands of dollars in downtime and maintenance. If you address the problems when the signs first show, you can avoid the catastrophic failures of mechanical damage.
If the inspection process is beyond the capabilities of your in-house personnel, inspections and simple testing can be performed by a qualified press service provider.
In addition, specific scheduled checks should be performed by a qualified mechanic at least every six months. Some of the tests that need to be run are level and alignment checks, lost-motion readings, and temperature monitoring. The results should be recorded, and any problems discovered should be scheduled for immediate correction.
Armed with results of thorough testing, a manager or maintenance professional can proceed with confidence to repair, upgrade, or maintain a malfunctioning stamping press.
Robert Kotynski is president of United Machine Corp., 753 Axe Ave., Valparaiso, IN 46383, 219-548-8050, fax 219-548-2053, email@example.com, www.unitedmachinecorp.com. United Machine Corporation is a machine service center that specializes in building and rebuilding metal forming equipment, inspection services, and emergency repair services.