Increase equipment efficiency with preventive and predictive maintenance.

As bottom-line cost pressures increase, foundries must follow effective maintenance programs to ensure maximum production and casting quality.

As a foundry's casting production and quality is pushed to its limits to meet increased OEM cost-improvement demands, the condition of its equipment is paramount. Breakdowns and downtime clog production, increase costs and leave a plant with idle personnel. In addition, only properly maintained equipment is capable of producing castings that can survive in today's competitive arena.

As a result, many foundries have embraced preventive and predictive maintenance (PM and PdM) programs to increase equipment uptime and productivity. The old philosophies of "When it breaks down, fix it" and "If it ain't broke, don't fix it" have been replaced by "If it ain't broke, keep it from breaking."

This article looks at PM and PdM and provides guidelines for establishing foundry programs.

PREVENTIVE MAINTENANCE 

PM is the inspection and repair of equipment before it fails. It is accomplished using the inspector's physical senses - sight, hearing, smell and touch - in addition to some basic tools (machine levels, amp meters, pressure gauges, etc.) to make equipment adjustments (such as leveling and lubrication) to prevent deterioration.

The PM of equipment must start when it is installed. This allows inspectors to know the condition of the equipment upon installation and maintain the equipment running in this condition. In many foundries, maintenance mechanics and electricians are assigned to perform PM on a machine or area that is critical to production. Another option is to have a specialized group of workers who are assigned as full-time PM equipment inspectors. A third option is to train the workers who operate the equipment to perform PM.

If your foundry is just establishing its PM program, the first step is to assemble all available data on downtime for existing equipment. In many cases, the production department keeps maintenance records. It is important to have concrete records, as opposed to relying on people's memories, as workers tend to remember critical breakdowns and not short-term problems. The short-term problems can be more disruptive over an extended production schedule then the critical breakdowns.

Downtime maintenance is an important tool. It can be entered into a computer database for analysis and can help determine if recurring problems indicate:

* the equipment is out of adjustment or unlevel;

* excessive wear on specific equipment areas;

* operator error, including cycle times that are too fast;

* a malfunction that isn't readily apparent, requiring a check of all equipment parts and root cause analysis.

The next step is to check the equipment supplier's recommendations for maintenance and return to the basics, such as cleaning the equipment. Excess dirt can cause problems and hide many of the causes and failures. For example, it is difficult to trace an electrical problem when the wiring is covered in oil and grease. As a general rule, the production department is responsible for cleaning the outside of equipment and the maintenance personnel perform the internal cleaning.

The equipment must be properly leveled and/or aligned. While basic, this is often overlooked as a cause of early breakdown or improper operation. Also, the equipment must be checked for any loose parts, missing bolts or fasteners, loose or worn drive belts or chains, and other "minor" problems.

Lubrication

The heart of any PM program is lubrication. Without proper lubrication, maintenance personnel will be so busy repairing equipment failures that the other PM responsibilities will go unmet.

When implementing a lubrication program (or upgrading an existing plan), begin by contacting your lubricant vendor, who can assist in worker training, engineering, testing for worn gear reducers and hydraulic systems, and locating special lubricants designed for specific systems. Bearing manufacturers can supply charts indicating the frequency and type of lubrication to be used on their products. The recommended frequency is given in relation to the operating environment of the bearing.

If the bearing is operating in an area with elevated temperatures, a magnetic thermometer must be used to determine ambient air temperature. This information must be compared to the temperature characteristics of the lubricant to ensure against breakdown. If the bearing is operating in dusty or dirty areas, a lubricant with high surface tension must be used.

The frequency of lubrication is not an exact science. Following are four uses of lubricants and guidelines to keep in mind:

Bearings - When a bearing fails, it should be disassembled to determine the cause. Bearing failure can be caused by over-lubrication as well as under-lubrication. Also, failure can occur through the use of greases that contain base materials that aren't compatible with the system. By tracking bearing failure, lubricants and the frequency of lubrication can be altered to maximize bearing life.

Gear reducers - The use of lubricant with gear reducers is recommended by equipment manufacturers, however, the use of synthetic lubricants (to reduce friction in the reducer and allow operation at a reduction in power) has become prevalent. When switching to synthetics, it is vital to contact the equipment manufacturer to determine compatibility. Instead of discarding the lubricant, another option is to use the synthetic fluid as a replacement when testing determines that the reducer fluid must be replaced.

Hydraulics - Equipment manufacturers specify hydraulic fluids for their systems. [n some situations, as with CNC machines, fluids that are nearly free of contaminant particles are required. If this is required, maintenance must find a fluid to meet the requirements or use a filter device to transfer the fluid to the equipment. The fluid filtering interval is dependent upon the operating environment and the equipment run time.

Electric motors - The lubrication of electric motors must be performed by an electrician. It is vital to check with the motor manufacturer to determine lubricant specifications. When a motor is sent out to a repair shop, lubricant specifications should be provided to maintain consistency in motor care.

Another area of concern is systems or components of a system that aren't easily accessible (resulting in improper lubrication). An option is an automatic lubrication system, which uses air to deliver lubrication from a reservoir to the component at proper intervals and amounts. Maintenance then must check only the reservoir to make sure lubricant is used at the proper rate.

PM Implementation

Due to the differing complexity and level of maintenance required on each foundry system, PM scheduling is done on a daily, weekly, monthly and in "special case" circumstances.

Daily run shift - These inspections are performed with the equipment running and on equipment components that can be observed easily. The inspector uses sight, hearing and touch for observation, and notifies a supervisor of problems to take action and repair.

Daily down shift - Performed while equipment isn't running, this inspection looks at the components that weren't checked in the daily run shift. Minor problems that can be fixed before the equipment is scheduled to operate are fixed, but major problems that will cause breakdown are left and scheduled during downtime.

Weekly inspection - This inspection is more involved than the daily inspections and require adjustments, alignment and the repair of any faulty conditions found during the week. If major repairs must be made, the supervisor determines whether to do them immediately or create a work order. It often is better to spend extra overtime on the weekend than risk a breakdown during the week's production.

Monthly, semi-annual and annual inspections - These inspections are complete maintenance checks on every component of every system and require a full shift (or more) to complete. Maintenance performs inspect/adjust/repair steps as well as draining, cleaning and refilling of various fluids and their reservoirs. These inspections are scheduled on weekends or when equipment is not scheduled for production for at least three shifts [ILLUSTRATION FOR FIGURE 1 OMITTED].

OSHA, EPA, hazardous material and other safety-related inspections - These inspections are required by a government agency and must be properly documented for compliance.

Quality audit inspection - If a facility is required by a customer or management to perform quality audits of equipment to document quality production, these inspections can be incorporated as part of a weekly or monthly check.

Inspections also can be based on equipment operating hours. This can prevent over- and under-inspecting equipment due to changes in production. Also, it is vital that maintenance personnel do not fall into the trap that an inspection is "too simple to be done" and that "it can be done without an inspection form." Following a printed inspection form [ILLUSTRATION FOR FIGURE 1 OMITTED] designates the responsibility for performing the inspection and also establishes regular documented maintenance records.

The documentation in a PM program is the key. After the program has been running for 3 months, perform a comparative analysis with downtime before the program start-up. Do the same after 6 months and 1 year. The expected results [ILLUSTRATION FOR FIGURE 2 OMITTED] of the PM program are:

* less production downtime due to maintenance-related causes (this is translated into dollars saved);

* less scrap due to properly adjusted equipment and replaced worn parts;

* better utilization of personnel resulting in less overtime and fewer maintenance employees (after 1 year);

* reduced cost of repair parts;

* 85-90% of corrective work orders generated by PM inspections result in a reduction in emergency repairs.

PREDICTIVE MAINTENANCE

PdM is the natural extension of a PM program. PdM techniques are emerging as the leading edge of productivity-solutions and are expanding to include the continuous monitoring of equipment and checking for equipment design concurrence with specifications.

PdM is the use of graphic representation of measured parameters to indicate new or used equipment condition, and then correcting the unsatisfactory conditions before excessive deterioration or breakdown occurs. As a result, measurements and data collection are of the utmost importance, and it is recommended that a single PdM technician be assigned to the program in each foundry.

The frequency of performing various PdM inspections is dependent upon experience. If a foundry determines through its records that the bearings on a muller fail every 6-9 months, then a vibration analysis should be conducted every 6 months to avoid the failure and subsequent downtime. The same experience timeline can be applied to each of the PdM techniques.

Vibration Analysis

Vibration is the movement of equipment or parts of equipment back and forth from a resting position. All rotating machinery and all machinery that uses electric motors for power are subject to vibration. The total distance of movement is the peak-to-peak displacement of vibration and the number of cycles during a given time is the frequency.

Causes of vibration include:

* out-of-balance equipment - The most common cause of vibration, this shows up as radial displacement and occurs at a frequency equal to the rotating speed of the part. It can be repaired in place, without major disassembly of the equipment.

* misalignment/bent shaft - Both conditions are common and characterized by high axial vibration occurring at a frequency of 1, 2 or 3 times the rotating speed of the part.

* mechanical looseness of parts - Often caused by loose bearing mounting bolts, this condition is a common source of vibration. It is detected by radial vibration at twice the radial speed of rotation.

* bad anti-friction bearings - Worn or bad bail-and-roller or tapered bearings are detected by vibration at a high frequency.

* bad gears - This type of vibration is detectable because the frequency is equal to the gear teeth on the bad gear multiplied by the rotational speed.

* aerodynamic and hydraulic forces - This vibration is associated with fans, pump impellers and centrifugal compressors. The vibration frequency is equal to the number of blades multiplied by the rotational speed.

Vibration readings are taken by an analyzer/data collector in conjunction with the appropriate software. The collector is equipped with a probe thai is placed against the equipment to measure vibration. The measurement points (x, y and z axes) must be marked in the equipment for future testing, and the measurement instrument should have a small display for simple field checks. Continuous monitoring vibration analysis equipment also is available.

The vibration analyzers show where a problem exists, and actual inspection shows the real cause of the problem. All vibration analysis equipment must produce quality, easily-understood representations of the conditions found. Any tabular information can be used by technicians, but graphics are the best way to present the information to management. In addition, vibration analysis specifies the limits of vibration that are acceptable on a piece of equipment.

Tribology 

As the science of lubrication, tribology is the use of oil and wear particle analysis PdM tools. These analysis inspections are performed by taking lubricant samples on a semi-annual basis. Samples are taken from the oil reservoirs on the equipment and must be taken from the bottom of the reservoir to ensure the sampling of sludge.

The samples then are sent to the manufacturer's laboratory for testing. At the laboratory, an oil analysis is performed to determine if the oil is within original specification, and, if not, what the reason for breakdown was. Wear particle analysis is performed to determine the composition of any particulate found. If a sample contains dirt or dust, this indicates worn or broken seals. If metallic particles are present, further testing can determine the metallic's composition and from what part of the equipment it came.

The laboratory's report determines if the lubricant was satisfactory, marginal or poor. Because the cost of lubricant is minimal compared to equipment cost, a foundry must change any lubricant that reads marginal or lower. To change the lubricant, the oil reservoir must be flushed with a cleaning agent before refilling. In equipment with hydraulic reservoirs, the oil must be pumped out of the reservoir into drams, and then the reservoir must be cleaned thoroughly. The oil is pumped back with a filtering pump.

Thermography 

Thermography, or infrared scanning, is the detection of flaws in electrical equipment and wiring by detecting hot spots that are caused by poor or deteriorated insulation. Since this technique requires expensive equipment and technical expertise, it is normally performed annually by an outside firm.

Another use of thermograph inspection is ensuring that all newly installed electrical components pass specification before payment. In addition, the inspection technique can be used to uncover faults in mechanical systems and roofs, and it can be used to scan outside surfaces of a boiler and furnace to determine where insulation has deteriorated.

Ultrasonic Analysis

Ultrasonic technology falls into two categories: airborne ultrasonic, which is the use of sound waves to detect leaks in pressurized gas systems and vacuum systems, and pulse echo, which is used to determine the thickness of materials.

Airborne ultrasonic testing must be specified for any equipment purchases that include pressurized and vacuum lines. It is particularly applicable to equipment using heat exchangers to ensure that there aren't leaks in the tube bundles.

Pulse echo ultrasonic testing primarily is used as a diagnostic tool. When there is an indication of low flow in a pipeline, pulse echo determines the thickness of the pipe wall for corrosion buildup. If vibrating conveying equipment with metal decks is used by a foundry, the pulse echo can determine deck thickness wear (without drilling holes) for possible deck replacement.

Results from PdM

PdM programs pay for themselves and the cost of their equipment within 1.5 years. The benefits of the program include:

* prolonged equipment life - PdM keeps the equipment from deteriorating prematurely, and often extends equipment beyond normal service life;

* minimum unscheduled downtime - By predicting equipment failure, PdM allows the equipment to be repaired before breakdown;

* personnel utilization - Because equipment problems are isolated before they become major, maintenance can be scheduled to eliminate overtime and use fewer workers;

* eliminates unnecessary equipment rebuilds - The repairs are made before excessive wear and breakage occurs;

* eliminates back-up equipment - Back-up systems are expensive to install and operate, but PdM eliminates this redundant service;

* enhances machine safety - By minimizing breakage due to vibration shorts in electrical systems and other malfunctions, operator and plant safety improves;

* enhances quality - PdM eliminates the equipment problems that produce substandard components. Thus, scrap is reduced and systems become more efficient.

This article was adapted from chapters in Achieving Six Sigma Maintenance, which is available from AFS Publications at 800/537-4237.

RELATED ARTICLE: Performing PdM at Internet

The job of maintenance is to keep equipment running. In 1992, an Internet foundry, which already had an effective and welt-established PM program, decided to take the next step and begin PdM - to attempt to solve all its equip, merit problems before they occurred.

In this foundry's PdM program, two techniques dominate equipment analysis - vibration analysis and tribology (lubricant analysis).

Vibration Analysis

In a PdM program, the most powerful tool is vibration analysis. This technique, which can be performed in-house or by an outside service, is used to test pumps/motors, environmental equipment (fans, motors), elevator gearboxes, air compressors, belts/conveyor drives, blowers and any rotating equipment.

The foundry used an outside service to check more than 70 pieces of critical equipment every month via vibration analysis. During the first 6 months of the program, the foundry averted more than 40 hr of potential downtime because it was alerted to equipment failures by vibration analysis before breakdown.

Examples of prevented downtime include the foundry's muller motor and hydraulic pumps.

Muller motor - By sight and sound, a 200-hp muller motor was operating to specification. However, during a routine vibration analysis ([ILLUSTRATION FOR FIGURE A OMITTED] left), it was determined that there was an irregular vibration in the spectrum of a bearing defect. On the weekend (during shutdown), maintenance evaluated the motor and its front shaft bearing and determined that it was about to fail. Maintenance replaced it and averted a breakdown of the motor. shift and in-belt and a loss of 4 hr downtime,

Hydraulic pumps - Experience in PM doesn't always pay off. Foundry records indicated that one of its eight hydraulic pumps (regardless of age) would fail every 13 months due to vein wear. As a result, the foundry changed all eight pumps annually to avoid a breakdown foundry began vibration analysis, it was able to pinpoint a failing pump before it died, leaving the other seven in place to be changed as needed. The result was an annual savings of $16,000.

Tribology

At the start-up of its Prim lubrication analysis, the foundry tested 74 critical points, including blast gearboxes, pour-off crane gearboxes, conveyor gearboxes, and air compressor oil systems.

Through spectrographic and ferrographic analysis of oil samples, the foundry checked for viscosity, oxidation, water, metal content from wear and other components that cause irregular lubricant levels. The results of its testing saved the foundry downtime and money as 67.6% of all oil samples at the outset of analysis were unsatisfactory. Although the PM program had the foundry watching the lubricant levels, the analysis revealed high oxidation and wear metal buildup, excess silicon and high or low viscosity. Following are two examples that illustrate the benefits of oil analysis.

Muller gear box - In oil analysis, a muller gear box oil sample showed heavy metal sediments. This contradicted the PM findings that showed no problem. If left unfound, these sediments would have destroyed the gears and bearings. The foundry drained and flushed the gearbox and added new lubricants. Repeat testing and vibration analysis showed no additional accelerated wear. The foundry saved its gearbox, which would have cost $50,000-65,000 to replace.

Air compressor - An oil sample indicated high water content. If the unit continued to operate, failure would occur. As a result, the unit was shut down and the oil changed. Repeat testing proved that there wasn't an internal water leak. The foundry saved $10,500.

S. Reid Vass, Intermet Corp., Lynchburg, Virgina