Utilizing PM and PdM techniques: five ways to help maximize paper machine efficiency.

The use of preventive and predictive maintenance techniques (PM and PdM) is nothing new to the paper industry. They cover a broad range including vibration analysis, ultrasonic inspections, temperature readings, amperage readings, thermographic inspections, and simple measurements and visual inspections.

It may be necessary to use several of these techniques on each piece of equipment within your facility to ensure that each operates reliably. Below are five specific examples where we have used these techniques to maintain maximum machine efficiency.

SCREEN BASKET INSPECTION

The maintenance department partnered with our screen basket supplier to develop a program to monitor the performance of our screen baskets through the entire life cycle. The intent was to minimize basket maintenance cost while maximizing the performance of our screening process.

Each screen basket is replaced on a three- or six-month interval depending on the location within the process. After removal, each basket is power washed to remove debris, slot widths are measured in detail, and an impression is taken of the profile.

The slot width information and the profile impression are sent to the OEM, where a representative analyzes them and uses them in combination to calculate the actual efficiency of the basket. Recommendations are then made to the mill representative as to whether the basket should be a) returned to inventory, b) returned for chrome replacement, c) rebuilt or replaced.

This program is managed entirely by one maintenance or production employee and a representative from the screen basket supplier. It is best to assign this program to one specific individual who can take ownership of the program. It is also more effective to have direct contact with the screen basket representative who actually performs the analysis of the screen data.

The cost savings of the program can be measured as shown in the following example using a position in our process that I classify as a fairly aggressive application.

Before we began the program it was common practice to install a screen basket and then run until it was obvious that the basket had worn to a point that it caused production issues; typically about 18 months for this particular position. A new basket would be installed and production employees would have to re-learn how to run the process. The old basket would be sold for scrap with a total life-cycle cost of US$40,000.

The inspection program extends the life cycle of a typical basket in the same position. The basket in this position will have a "1st run life" of 12 months, during which time it will be inspected four times. At that point, the basket profile will normally have worn to a point that it has begun to affect process efficiency. The basket is then returned to the OEM to be re-chromed at an average cost of 10% of the cost of a new basket--in this example $4,000. The basket is then returned to service and typically has a "2nd run life" of nine months, with three inspections.

Normally after the "2nd run life" the slot widths of the basket have increased to a point where the basket begins to affect process efficiency, although this effect is not easily identified by production operators. In this case, the average slot width increased from its original 0.008-in. to 0.010-in.

The effect on your particular process can be determined by your screen basket supplier. Just keep in mind that profile changes need to be considered when calculating the effect of increased slot width. At this point, the basket should either be refurbished or scrapped depending on the design. In this case, we are able to refurbish the basket to original OEM standards for two-thirds the original cost, or US$26,400. The basket would then be returned to service at a "1st run life" capacity.

As you can see, this program is very effective in cutting maintenance costs when using screen baskets that can be refurbished. But the real savings comes from maintaining uniformity and efficiencies in the papermaking process.

RE-WETTING SHOWER MAINTENANCE PROGRAM

The rewetting shower helps control the cross directional moisture profile as paper is produced. In our mill, we have a Measurex Aquatrol system comprised of multiple zones oriented in the machine direction, with four spray nozzles in each zone. The spray nozzles are graduated in size from A to D, with A being the smallest nozzle and D the largest. As sheet properties are recorded by the online scanner, the paper machine control system (DCS) makes adjustments to each zone to "smooth" the moisture profile of the sheet.

In September 2006, it was deemed unsafe to service this system on the run due to heat and humidity in the service area. The I & E department decided to identify specific items that contributed to the need for service. A log sheet helped keep track of each time a service technician was called and the results can be seen in Figure 1.

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Upon analysis of the data, the I & E department found that the system worked correctly the majority of the time, but because it had been deemed unreliable by most production crews, it was the first step in troubleshooting a moisture profile issue. Close inspection of the system revealed that the unreliable status was somewhat justified.

The findings included:

1. Most of the A nozzles were plugged due to buildup on the valve plunger

2. Several other nozzles were either plugged or not working

3. The spray nozzle solenoids would fail with out warning

4. The wire connectors and water connectors would fail or plug

To address the situation and return the system to a reliable status, the following initiatives were taken:

1. Lights were added to the work area so the system could be easily inspected and repaired

2. The department replaced 10 zones during each scheduled outage, until all zones were replaced

3. The removed zones were disassembled and cleaned and worn parts were replaced and reassembled

4. A detailed function check of the system was performed on each outage. Any non-functioning zones were replaced or repaired at that time.

5. The resistance across the nozzle actuator coils was checked on a periodic basis to identify degradation

6. The department established a six-month change-out schedule for all zones

This program has resulted in reduced maintenance parts cost, more reliability and increased efficiency. Figure 2 illustrates the reduction in repair parts costs and the number of calls per month.

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As can been seen, this program was very effective in saving maintenance costs, although this was not intuitively obvious in the beginning. The resources required to maintain this program are two I & E technicians--for two hours on each scheduled outage--to verify each zone and repair as necessary. It also takes one I & E technician about one hour to disassemble, clean and repair a zone after removal.

The real saving came in the form of improved sheet quality and increased efficiency of the re-wetting shower system. Figures 3 and 4 show cross machine profile graphs before and after the start of the program. Notice that the moisture profile variance is maintained below 0.200, while the percent shower usage is reduced significantly resulting in increased dryer efficiency and reduced energy costs.

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ROTATING STEAM JOINT PROGRAM

The department began a rotating steam joint preventive maintenance program in early 2006, beginning with the installation of quick disconnect fittings on the inlet and outlet of each rotating steam joint. Differential readings were then taken across each steam joint. The results were logged and any steam joint that was not performing to OEM specifications was replaced at the next opportunity.

A mechanic was selected to manage this program and sent to Kadant's Three Rivers, MI, research facility for training in proper maintenance techniques of the rotating steam joints. The mechanic takes bi-monthly differential pressure readings across each steam joint and also measures carbon rings and monitors them for wear on each scheduled outage. Once the carbon ring wears beyond OEM specifications, a work order is written and the joint is removed from service on the next scheduled outage.

This program can be easily set up and maintained by one maintenance person. The initial cost of the quick disconnects, gauges and safety equipment is less than US$3,000. Kadant periodically offers training sessions at its facility at little or no charge.

The saving in maintenance repair costs can be seen in Figure 5. We have also observed increased joint reliability and, as a result, increased dryer efficiency.

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THERMAL IMAGING PROGRAM

The department purchased a thermal imaging camera in early 2007 to perform biannual inspections of electrical equipment within the facility. We also found several secondary opportunities to use the camera including: 1) identify plugged steam lines in our disperser shredder and pre-heater unit, 2) verify storage tank levels, 3) identify plugged stock lines and 4) inspect steam traps.

Figure 6 shows a thermographic image of a valve train that has a tendency to plug. It is inspected biweekly, plugged lines are identified, and work orders are written to unplug the valves on the next outage.

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The resources required to create and manage this program include one l&E technician trained in the use of a thermal imaging camera. If a camera is not available, a simple inexpensive infrared thermometer can also be used with similar results. The cost saving in this case is the increased efficiency of the equipment due to the increased steam supply to the process.

EQUIPMENT AMPERAGE LOG PROGRAM

In 2004, the I&E department began logging motor amperage on process pumps that were identified as critical components of the stock prep system. The amperage was logged three times a week and the data was used to: 1) track pump wear, 2) identify process changes, and 3) confirm or deny energy saving initiatives.

We observed that as the production rate of the paper machine increased, the efficiency of the equipment in the stock prep system decreased. Figure 7 illustrates how a pump can wear over time. This data was used to justify the purchase of a pump casing in Stainless Steel CD4 material. Historically, the mill had used a cast-iron casing for this application at a cost of US$7,000. The CD4MU casing cost US$35,000. During a recent inspection, after 18 months of service the CD4 material showed no signs of wear.

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Amperage readings can also be used to verify energy saving initiatives. The mill recently installed a new type of press roll cover that required no internal cooling water. The vendor had observed a 5%-8% reduction in energy usage. The mill actually experienced a 14% reduction in the top position and a 10% reduction in the bottom position, as can be seen in Figure 8.

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The resources required to set up and maintain the Equipment Amperage Log Program are a standard amp meter, any safety gear that might be required to obtain the readings, a computer program for logging data, and approximately 10 hours per week of an I&E technician.

Our department uses a combination of Microsoft Excel and SKF Machine Analyst to log and analyze the data. The I&E department worked with production to develop minimum acceptable amperage levels to use as triggers to create work orders to repair the equipment.

The cost savings for this project is in the increased efficiency of the stock preparation process. As pump performance decreases, so does the efficiency of the equipment to which it is pumping the material. Identifying these decreases helps production employees understand why gradual changes in equipment operation become necessary and what changes need to be made when the pump is repaired and returned to original design specifications. It is also an effective troubleshooting tool in identifying process changes, equipment issues and cost savings initiatives.

CONCLUSION

The illustrations included in this paper can be tailored to almost any production facility or process. In most cases the programs resulted in decreased repair parts expense and a reduction in maintenance hours to repair equipment. In all cases they resulted in increased process efficiency and reduced process variability. When developing these types of programs it is vital to consider who will take ownership of the program and how the data will be collected and used to add value to the production process.

The owners of the programs should be encouraged to communicate with production employees and other maintenance employees when issues are found. It is not uncommon in our program to have the person in charge of amperage readings working with the vibration technician, the thermographic technician and production employees to help identify the root cause of an issue. The key to these types of programs is establishing standards, continually improving your process and adding value back to the production process.

ACKNOWLEDGEMENTS

I would like to thank the employees at Corrugated Services Inc. for their support, input and involvement in the programs outlined in this article. I would also like to thank the following companies and their representatives for assisting in developing and maintaining the programs: Advanced Fiber Technologies (AFT) for its involvement in the Screen Basket Inspection Program, and Kadant Inc. for its involvement in developing the Rotating Steam Joint Program.

Chris M. Jackson is maintenance manager at Corrugated Services Inc. Contact him at cjackson@csipaper.com.