- Buyer's Guide
Preventive maintenance methods are often promoted but rarely put into practice. This article will attempt to encourage a paradigm shift in maintenance thinking with prevention driving most of the activities. The main thrust will be on leadership and not simply management.
The classic definition of management is to do things right. The definition of leadership is to do the right things. The difference may be subtle but very important. How often have you witnessed someone planning a repair job to be completed within an allotted timeframe when no one was asking why this repair needed to be made so frequently?
A manager attempts to get work done on time, while a leader attempts to minimize or eliminate the required work. A manager continually asks for more people, while a leader tries to maximize the effectiveness of his or her staff. A manager tackles problems as they arrive, while a leader asks why continual problems are tolerated.
Without proper leadership, problem prevention is very difficult to achieve. The following case studies illustrate a variety of situations in which preventive techniques were used effectively in a typical mill environment.
In this mill, steel slabs issuing from a caster started as a long, continuous hot metal strand. A torch cutter sliced off 30-foot slabs from the front end as the strand moved at a slow pace. The slabs were lifted off the table rolls and stacked for delivery to a storage yard by a carrier. The tongs resembled two pairs of giant 10-foot scissors operated by hydraulic cylinders and fed by a hydraulic system mounted near the top of the scissor arms. The system had a vertical tank with a pump mounted beside it. Due to space limitations, the valves, tubing and hoses were located directly over the pump and motor, making for a very congested design. The entire assembly hung from a crane. When an O-ring blew or a valve needed changing, quite a bit of disassembly was required to access the bad part. A lot of time was also wasted with repairs on this equipment due to the design.
The cause of the problem was obvious, and only a redesign would suffice. The supplier of the tongs was contacted and told the system design was inadequate. With “manifolding” technology, much of the pipe, tubing and hoses could be eliminated as well as the congestion in the confined spaces. The supplier agreed to redesign this part of the system, which solved the problem. This case exemplified a unique issue where only prevention of future problems would suffice. Learning to live with the problem was not an option.
At this particular company, lubricants and hydraulic fluids were purchased by individual departments with no coordination between them. Consequently, the number of brands proliferated, increasing the chances of duplication. Products were procured by brand name, and the purchasing department had no choice but to buy what was requested. Because lubricants were purchased by brand name with no competition, suspicions arose that prices might be excessive. When a problem arose, quality was blamed and another supplier was brought in to solve it.
It was suspected that the company was living with a problem that could be resolved. Because ASTM and other test methods could help determine product quality, a committee was formed to decide how to purchase lubricants based on these tests. A strategy was soon developed. All products would be tested for important parameters to uncover duplicates. Products would be separated by categories such as petroleum hydraulic fluids, fire-resistant hydraulic fluids, general-purpose greases, electric-motor bearing greases, petroleum turbine oils, gear oils, anti-friction bearing oils, petroleum circulating oils and synthetic oils.
Specifications were also written for each lubricant type based on the test results of the higher grades in each category. Every specification was assigned a unique number, and equipment throughout the plant was tagged with the number of the product it was to receive.
The specifications were sent out for bids from various suppliers. The lowest bidder was awarded the business for one year. The prices received were markedly lower than the comparable branded products.
After the initial groundwork was completed, the system began to function well. The inventory shrank because so many locations used the same products. Purchasing in bulk became possible due to consolidation, which also resulted in a reduction in drums and costs. Samples of incoming products were taken periodically to ensure quality. Gradually, the overall quality improved.
The goal of the system was to purchase high-quality products at the least possible cost and to eliminate as many empty drums as possible. Mistakes related to applying the wrong lubricant were also reduced. Once the system was in place, it took very little time to maintain it.
This was an example of a plant living with a problem that not many thought was a problem. It was only after some penetrating questions were asked that most were convinced that there might be a better way of doing things. How the plant was purchasing lubricants was costing much more than necessary both in dollars and in manpower.
In this hot mill, as the steel strand issues from the last finishing stand, a long series of rolls conveys it at high speed to the coilers. Each roll is individually driven by an electric motor. Water cascades down from sprays to cool the strip as it speeds toward the coilers. Despite elaborate splash guards, it is almost impossible to keep water off the motor shafts. The shaft seals were not adequate to keep water out of the motors, and trying different seal designs did not help. The motor repair shop could barely keep up with all the failures. Finally, a seal company recommended adding flingers on the shaft. These consisted of a rubber device that looked much like a shaft seal but with a hole in the center slightly smaller than the shaft diameter. As a motor was repaired and ready to ship, the repairman would slip a flinger onto the shaft up to the housing. When the motor was installed in this wet environment, any water that migrated toward the seal area would be flung off due to the rotating flinger. In this way, water could not get to the seal. Motor bearing life increased tremendously. In this instance, a serious problem was prevented with a simple device but only after someone asked why this was being tolerated.
As steel mill technology improved, more and more servo valves were being used on the mill’s hydraulic systems to gain precision. Because of dirt sensitivity, systems with servo valves must be filtered to extreme cleanliness. Despite great efforts, servo-valve losses were becoming excessive at the mill. Costs were also high since the repairs could not be done in-house.
To prevent these failures, a non-bypass duplex filter separated by a three-way valve with an electrical alarm was installed ahead of each valve. The filters had a cleanliness level of 1 to 2 microns. When the alarm sounded, maintenance personnel knew they had only a few minutes to switch the three-way valve to the clean side before a shutdown occurred. A clean filter element was always on standby. The result was that the servo-valve failures virtually ceased.
Once again, a simple design change prevented a serious problem. However, the difference with the servo-valve issue was that production was being affected as well as repair costs.
Oil losses were becoming excessive in the mill’s hydraulic and lubrication systems. The millwrights dutifully kept the systems filled and operating but did not report all the oil additions as they were made. When additions were reported, there was no good method for determining the amount. Therefore, it was difficult to establish where the bad leaks were and to schedule repairs. Prevention or reduction of these oil losses was the goal, but they could only be attacked when they occurred.
The decision was made to mount small water meters on the fill lines to each system. These meters had some internal friction, but since the oil was being pumped in as makeup oil, the pressure required was adequate. In cases where the oil flowed by gravity from an upper to a lower floor, low-friction meters were required. Each day, an inspector read the meters to determine if any leaks had gone unreported. If so, action was taken. This was an example of taking preventive action (reading the meters) to prevent further losses. No action could be taken without proper information supplied by the meters.
The plant’s coke oven doors are approximately 20 feet tall and 4 feet wide. They are made of steel, lined with firebrick and weigh about 1,000 pounds. Each is mounted vertically on each end of the oven and must be lifted off by a huge machine so the red-hot coke can be pushed out. The doors are held in place by two steel arms that are rotated into place behind vertical “buckstays.” In the center of the arms is a hexagonal nut that is 5 inches in diameter. The arms are rotated by a large socket that fits the hexagonal nut and is operated by a motor and gear reducer mounted on the machine. The arms often become wedged behind the buckstays, so an electrician must hold in the overload relays to get the motor to turn. Frequent motor burnouts were attributed to this practice.
Rather than increase the size of the motors, the decision was made to convert the operation to hydraulic motors due to the inherent overload protection in such a system. Relief-valve adjustment serves this purpose.
Because of the large amount of dirt inherent in the coke plant and the dirt sensitivity of the hydraulic motors, the hydraulic systems were redesigned. This redesign was so successful that no hydraulic motor failures occurred for the first five years. The improved cleanliness also increased pump life. This case was an example of prevention involving a radical design change with which not everyone agreed.
At another hot mill in the Pittsburgh area, the challenge was determining the cause of losing several back-up bearings. It seemed to be a case of the oil overheating, but when the coolers were examined, none of the thermometers was working. It also appeared that no one was checking the key system parameters, such as temperature, water content, flow, tank levels and cleanliness.
When the thermometers were replaced, oil temperatures of 175 degrees F were observed. Evidently, the coolers were having no effect. Once the coolers were replaced, the problem ceased.
This was a case of not paying attention to signs that can warn of impending problems. Management hastily instituted a form to be completed on each shift that forced someone to watch those important system parameters.
Oil purchased for the mill’s back-up bearing system needed to be able to drop out water quickly. The purchasing specifications gave a very strict number that had to be obtained from the ASTM D-2711 test. ASTM D-1401 is another test for demulsibility, but it is used for light oils. The heavier oils utilized for these back-up bearings had to be tested with the former test, although it took much longer than the ASTM D-1401 test.
The mill was experiencing a rise in water levels with samples tested from new loads of oil. Samples taken from in-service oil were having the same problem. Under normal conditions, the water levels should have remained under 5 percent but were now 20 percent. The lab assured the mill that the samples of new oil were within the specification. This situation continued for several months as an investigation was conducted. There were concerns that back-up losses would soon begin rising.
As luck would have it, the lab shut down, which meant the mill had to find another one. When the next sample was sent to the new lab, the mill immediately received a call that the demulsibility was below specification. The load had been pumped out and replaced with a load from another company. It turned out that the old lab had been using the ASTM D-1401 test because it was quicker than the D-2711 test but did not inform the mill. The oil supplier didn’t even have the equipment to perform the D-2711 test but was relying on its additive supplier to provide the percentage to use. This was a case of having all the needed tools in place but still getting bad information.
These case studies encompass preventive actions for three types of situations: an obvious situation, a change of methods situation and an unseen situation. Each of these is described below.
These situations are like the poorly designed hydraulic system or the electric motor bearing issue. The problem is very costly, and the solution is either obvious or requires a design change. The solution will also require time, money and the will to do it. Most agree that solving the problem is worth a try since it is easily seen. These situations are usually designated as “crises.” The alternative is to learn to live with the problem.
These situations involve a long-standing way of doing things, such as each department buying lubricants with no attempt at consolidation or not reporting system fluid additions. Although the problems are seen, not everyone envisions a solution or agrees one is needed. Personnel have learned to live with the problem. Basically, the way things are done must be changed.
Many times actions can be taken to prevent bad things from happening. These include condition monitoring, regular inspections, close monitoring of system gauges and oil sampling for laboratory tests. Every plant system has parameters that must be checked periodically. These checks consist of people making an assessment of the condition and filing accurate reports. When these people do their jobs correctly, bad things are prevented.
Short-sighted managers only “see” the people who repair things. Those focused on prevention work in a less dramatic environment. Consequently, when the economy is poor, these jobs often are eliminated.
Leaders not only must ensure the “seen” is handled efficiently but also that the “unseen” is not neglected. The “unseen” typically requires recognizing the indications of bad things about to happen, which can often be identified in regular inspections by sight, feel, smell or hearing. However, most of the “unseen” must be detected by equipment. This would include temperature, vibration, sound and lab tests.
The “unseen” also involves a conviction that technology can be used to predict events in order to avoid or plan for them. This conviction is an important leadership attribute. Remember, managers don’t see the “unseen,” but leaders do.