Machine clothing: how do the best mills operate?
The "secret" comprises a set of practices and procedures that can make a huge difference for mills trying to improve machine clothing performance. Thanks to the feedback from the machine clothing suppliers that spoke with Solutions! for this article, those "best practices" are not even secret--they are readily available.
Extended machine clothing life is a common goal. Yet experts warn that "longer life is better" is an oversimplification that can do more harm than good. A better goal is to create the conditions that help machine clothing at a mill run efficiently only to the full extent of its maximum designed life. This is a balancing act that requires time and attention. "The risk of a fabric failure with the loss in water removal efficiency of worn clothing is not worthwhile," explained Daniel Hedou, press product business leader for AstenJohnson, Charleston, South Carolina, USA.
Machine clothing manufacturers have answered the call for fabrics with longer designed life, noted David Buchanan, business development manager--board and packaging for Voith Fabrics, Wilson, North Carolina. "Paper machine clothing today is made with advanced structures and materials that allow the fabrics to maintain caliper, resist wear, and maintain void volumes to insure extended high levels of water removal and sheet drying. These advancements and attention to clothing cleaning and machine maintenance also play a big roll in machine clothing life," he said.
"The time to make the clothing run to its greatest potential is while the machine is down," said Randy Kimpfbeck, papermaking services manager, Albany International, Albany, New York. "While a machine is down, all stationary elements must be inspected for condition and replaced as needed. While the machine is down and clothing is off, a complete clean up must also occur." (Editor's Note: Experts from Albany International and Nalco Co., Naperville, Illinois, combined responses to these clothing performance issues. In addition to Albany's Kimpfbeck, Nalco's contributors were Jim Rivard, senior sales representative, David Weinstein, marketing manager, and Pat Sturtevant, principal consultant.)
"Keeping machine clothing clean a key to maximizing performance through the life of the fabric," said Jeff Landry, marketing manager, AstenJohnson. "Better machines will make sure the fabrics are kept clean with proper high pressure needle showers on the paper side. The shower stroke should be twice the nozzle spacing. The oscillation speed should be indexed to the machine speed. All the nozzles should be kept in good condition."
Mills that want longer life for machine fabrics should look first at optimizing clothing efficiency to enhance overall machine efficiency. This may require some bench-marking, according to the experts from Albany International and Nalco. For example, If mills A and B have similarly configured press sections and mill A achieves consistently longer fabric life than mill B, naturally mill B wants to improve fabric life. If mill A has large diameter press rolls with relatively soft covers, and mill B has small diameter rolls with hard covers, mill B may never be capable of achieving the same long life. Benchmark comparisons must be carefully done, they said.
Good mill and supplier communication can help match clothing properties to machine conditions, observed Bill Dunleavy, dryer product business leader for AstenJohnson. "If the prime cause for removal of a dryer fabric on a particular position is hydrolysis, the fabric must be engineered with the proper components to withstand degradation from heat and moisture," he said. "A similar analysis should be done for positions prone to abrasion, contamination, or other specific problems."
Landry emphasized that attention to details is very important. "Many fabrics are damaged on installation, while starting up the machine, or both. Better mills will follow a rigorous installation and start-up procedure to limit or eliminate those instances."
Voith Fabrics' Buchanan agreed. "The importance of monitoring machine clothing by operators cannot be overstated. It can obviate situations that lead to premature removal."
Meticulous monitoring also plays a role in keeping fabrics clean. This is a critical factor for machine clothing efficiency, observed Buchanan. "The furnish is also critical," he added. "As mills increase recycled fiber usage, it will take more diligence and technology to keep clothing clean and open. The introduction of chemicals to the conditioning process is also a big factor. If the chemical showers are positioned in the proper location in the fabric run, this can be an effective means of cleaning the clothing."
AstenJohnson's Hedou added, "In press fabrics, the correct application of a full coverage high pressure needle shower (150 - 250 psi) applied 3 - 4 inches from the surface with proper vacuum usually keeps fabrics clean. Where more contaminants are encountered, the dilution factor can be increased through increased lube shower application," he said.
"Some fabrics run cleaner by altering properties such as components, weave structures, or surface geometry," said Dunleavy. "When contamination is a problem, an all-monofilament, low void construction with perhaps a structured surface could be employed to combat contamination build-up."
Reduced downtime is another "brass ring" mills often reach for in their desire to optimize machine clothing investments, but this oversimplified thinking can cause more harm than good. The only bad downtime is unscheduled downtime, while scheduled downtime can be a mill's best investment in clothing life and machine runnability.
"The downtime related to a press fabric failure is far more costly than taking the press clothing off slightly earlier than its full potential," warned David Buchanan. "An example is a European mill making graphic papers where the inner forming fabric is removed every 21 days for wear. They remove all press clothing at this time because they do not want to risk a press fabric not making a 42-day life cycle. They have optimized their schedule knowing that the pickup and 4th press fabric cannot last 42 days."
Prevention of sheet breaks in the dryer section will also reduce unnecessary downtime said Bill Dunleavy. "At higher machine speeds, dryer fabrics with smooth surfaces should be used to reduce the propensity for air to be carried by the fabric. This often causes breaks. Other causes of downtime can be associated with simple fabric failures. Since most failures are a result of gradual wear, an inspection program during scheduled outages can correct this. If the clothing shows signs of upcoming failure, it should be changed-out during the outage." Mills should also maintain samples of fabrics with shorter-than-expected service life and consult with the supplier to determine the cause of failure and correct out-of-the-ordinary conditions.
"Mills that are committed to best practices for machine clothing ensure that the machinery is maintained properly. They also work to solve machine problems before they become clothing issues," said Buchanan. "For example, excessive forming fabric wear caused by worn table ceramics is not a good reason to go to thicker fabrics. The table ceramics should be replaced and the current design will continue to run."
Performance monitoring, including data collection and analysis, can also make a difference, said the experts from Nalco and Albany International. They added that too often, mills do not have data to understand what the normal operating range is on many variables. Mills cannot say if a value is abnormal. A regular program of collecting grab samples for consistency is a good practice to establish norms. Many mills have installed weir boxes on uhle box water flows, but often overlook weirs on saveall pans. Mills that have water flow measurement on all exiting streams know the complete picture and can better analyze problems. A nip impressions program to maintain nip conditions is important to sheet quality and clothing and machine performance, they stated.
Historical fabric permeability, moisture, filling and wear data provided by PMC and chemical suppliers can also provide insight into performance expectations, they added.
Regular machine inspections should focus on preventing clothing damage due to factors such as improper shower pressures, frozen shower oscillators, stock buildup on vacuum boxes, or improper running tensions. "Do not neglect the details," Buchanan concluded. "Have a schedule of key preventive maintenance measures and stick to it!"
Steve Cole, director, value creation management for Weavexx, Wake Forest, North Carolina, said his company always encourages an "engineering/best practices" approach for maximizing the life and performance of machine clothing. "These best practices, including all the engineering calculations and procedural recommendations, can be downloaded for no cost at www.weavexx.com/technical library."
RELATED ARTICLE: IN THIS ARTICLE YOU WILL LEARN:
* Why long life is not always the best goal.
* Strategies for keeping machine fabrics clean.
* "Best practices" that ensure better machine clothing performance.
* Checklist for boosting clothing efficiencies.
* "A combined future: tracking the trends in machine clothing," Alan Rooks, Solutions!, January 2003.
* "Forming advances promote better clothing," Jim Kenny, Solutions!, April 2003.
* Paper Machine Clothing, S. Adanur, available through TAPPI Press at www.tappi.org/index.asp?rc=1&pid=2906&ch=8&ip=.
RELATED ARTICLE: SOLUTIONS! MACHINE CLOTHING CHECKLIST: Clip and post to improve your mill's clothing efficiency
1. To run clothing longer:
* Eliminate stock throwing at the wet end.
* Invest in modern edge trimming techniques.
* Use correct wash-up procedures.
* Monitor fabric tension.
* Perform routine inspection and maintenance of rolls, showers, and elements in the former.
* Monitor the quality of the HP shower water or use fresh water to clean felts.
* Make sure rolls are not compacting clothing.
* Inspect vacuum box strips and replace when necessary.
* Inspect and calibrate pressure gauges to ensure accurate cleaning pressure.
* Perform routine inspection and maintenance of rolls, uhle box covers, and showers.
* Maintain proper cleaning systems for showers and chemical.
* Closely watch mill water supply (keep chlorine residuals down).
* Use proper installation.
* Maintain guide and stretch systems.
* Use correct design.
* Monitor roll conditions.
* Use proper cleaning systems.
* Provide good sheet break systems that prevent paper wads and heavy wraps in sections.
2. To keep machine fabrics clean & open:
* Ensure proper chemical cleaning for de-inked or ONP stock.
* Provide proper showering sometimes including chemical.
* Maintain showering equipment.
* Use boilouts and chemical cleaning where necessary.
* Use the correct fabric for the furnish.
* Use proper roll doctoring.
* If necessary, flood the edges where the felt runs without stock.
* Develop good batch and continuous chemical cleaning programs.
* Practice proper showering and uhle box conditioning systems.
* Improve chemical cleaning systems and maintain better application intervals.
* Keep suction rolls open and in good shape.
* Pay attention to lubrication and high pressure water supply.
* Have good uhle box condition with proper lubricating shower coverage.
* Use steam boxes in press sections to aid in cleanliness by increasing water flow through temperature.
* Institute a good batch chemical cleaning program and showering system.
* Maintain the pocket ventilation systems.
* Run a continuous needle shower if grade allows.
* Use better wet end chemistry when running recycled furnish.
* Use well-maintained air and vacuum systems.
3. To reduce downtime associated with machine clothing:
* Use regularly scheduled outages to fix runnability problems before they force the machine to go down unscheduled.
* Use pin seam felts where possible.
* Prevent unexpected failure--planned changes are always better.
* Keep fabric clean while on-grade to minimize off-grade and sheet off cleaning.
* Use downtime inspection and surveys to predict remaining life and potential problems.
* Perform proper guiding system maintenance.
4. Critical "best practices" include the following:
* Establish a program to optimize wet-end drainage with particular parameters in mind (stock consistency swings, formation, tear, tensile, stretch, lint count, profile, etc.)
* Treat all clothing damage the same as a mechanical break down (investigate cause and initiate action plan).
* Consider the press section as one unit. Alleviate de-watering expectations on one position by improving another position.
* Set a rigid schedule and adhere to it with an outage frequency of four to seven weeks.
* Install a proper camera system.
* Establish a relationship with a principal clothing supplier and work with them in establishing priorities.
* Think cycles not days (the faster you run the more cycles per day you have.)
* Study machine performance as it relates to clothing life.
* Change press felts as sets (changing one at a time means you will always have at least one worn out felt).
* Change rolls on a set schedule (do not wait for a problem).
* Develop a cleaning program for wire and felts (follow a rigid schedule).
* Change uhle box covers and shower nozzles frequently.
* Realize that machine alignment is critical at any speed.
The following personnel from Weavexx, Wake Forest, North Carolina, USA, compiled this checklist: Roger Mongrain, Sales/Service-Canada; DeWayne Dowdy, Sales/Service-US; Scotty Lamont, Sales/Service-Canada; Norm Kennedy, Sales/Service-US; Bill Perletti, Sales/Service-US; Steve Carmichael, Sales/Service-US
JANICE BOTTIGLIERI, SENIOR EDITOR
ABOUT THE AUTHOR
Janice Bottiglieri, senior editor of Solutions! and editor of TAPPI JOURNAL Contact her at email@example.com.
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|Title Annotation:||Machine Clothing|
|Publication:||Solutions - for People, Processes and Paper|
|Date:||Jan 1, 2004|
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