Clothing Suppliers Take Holistic Approach to Solve Mill Problems

Paper machine clothing suppliers are approaching mill runnability and quality issues using techniques that account for a wide range of variables

October 2007
By Monica shaw

Paper machine clothing suppliers are going far beyond clothing design to assist mills in achieving their quality and runnability goals, according to a recent Pulp & Paper survey of supplier case studies. In addition to advanced clothing designs, these companies are often providing holistic approaches that examine multiple variables to determine problem origins and help mills improve processes. These tactics can involve the use of laboratory and handheld tools, as well as Six-sigma and other analytical techniques.

The case studies here address issues that have occurred in boxboard, supercalendered (SC), fine papers, linerboard and coated board grades. They show how paper machine clothing suppliers are working with their mill customers to achieve better sheet characteristics and to reduce problems that range from sheet marking to breaks.

This handheld tool was used on the Austrian boxboard machine for fast and simple pulsation studies in the forming section.

FORMING

Handheld, Microwave-Based Tool Analyzes Boxboard Machine Drainage

Problem: An Austrian folding boxboard machine experienced a sudden and uncontrollable production problem that led to poor paper quality, breaks and production losses. Figure 1 shows the paper surface, which indicates paper mass variation and moisture, as well as caliper streaks. These streaks stemmed from fluctuations of the basis weight in the machine direction. The streaks were completely parallel and always the same distance over the paper width. The darker streaks were clearly related to higher basis weight. This led to different paper characteristics in relation to the target basis weight, thickness and moisture.

Figure 1 - Picture of CMD paper defects on a boxboard machine

The paper weight and thickness variations were apparently pulsations, which could involve several types of operating equipment, including mixing pumps (flapping of blades on the traversing wheels, vertical sorter, rotor frequency), random turbulence, mechanical oscillations, air in the stock system, foil set up and vacuum system.

Project: Several investigations and trials were conducted to solve the problem. These involved the control of air at the headbox approach flow system and in the defoamer, bypassing the cleaner, jet angle adjustments and checking the vertical sorter rotation and headbox diffuser.

After all the tests, it was still unclear whether the problem originated in the headbox approach flow system or in the forming section by means of the foil design/layout or the vacuum pumps. One last question was whether the paper streaks were intensified by the vacuum system effect.

In the past, a larger number of diagnostic and measurement tools like ionizing radiation equipment were needed to determine pulsation frequencies. This type of analysis was expensive and required a considerable amount of time. However, Cristini Group offers a new tool for paper machine drainage evaluation, known as FiberScan. This handheld tool uses harmless microwave technology for fast and simple pulsation studies in the forming section. It gives an accurate frequency analysis (Fast Fourier Transform, FFT) that helps diagnostic service engineers find the origin of pulsation and turbulence problems.

The Austrian boxboard mill chose to use FiberScan in its analysis. The instrument was calibrated and adjusted so that immediately after the pulsation measurement (FFT) a standard drainage mass measurement was started. In this way, conditions during the measurements are known for the pulsation study. Therefore, conclusions of the drainage behavior and its influence on the FFT analysis can be taken into consideration.

As shown in Figure 2, it was possible to measure points 1-5. In order to be as accurate as possible, white water consistency samples were taken from every possible element (A, B, C) and then analyzed in the lab. As already mentioned, the FFT and the water mass measurements were taken together.

Results: At the very first measuring point, which was immediately after the forming board, a dominant frequency of around 26 Hz with high-amplitude was evident. This reinforced itself with the work of the Varioline boxes up to an amplitude of more than 150 dB. After the diverter roll, the frequency was substantially weaker, but still clearly obvious.

Figure 2 - White water consistency samples were taken for elements A, B and C on the boxboard machine and sent to the lab for analysis.

With the FiberScan measurements and its FFT analysis, it was possible to define the frequencies and focus on the area where the problem started. Based on the measurements and the frequency of around 26 Hz, it can be clearly stated that the reason for the unstable streaks should be investigated in the approach flow system, particularly in the fan pump.

- Giovanni Cristini is vice president, technology, and Luca Canali is engineer & development leader, FiberScan project, for Cristini Group SpA. Klemens Rauch is sales & service engineer, Cristini Forming GmBH.

Service Work at Fine Paper Mill Boosts Speed, Improves Quality

Problem: A fine paper machine with a fourdrinier plus dandy roll was making writing and base coated papers in basis weights of 45-120 g/m2 at a pre-project speed of 390 mpm using furnish that included GCC. The mill was buying 80% of its forming fabric supplies for the paper machine from Kufferath and 20% from a competitor. The mill needed to improve fabric lifetime and surface quality of the paper, while allowing for the wide basis weight range. This presented a significant challenge, since those requirements impose opposing constraints on the fabric design.

Project: The project consisted of two interlocking approaches. First, Kufferath technical service engineers worked with mill management over a six-month period to conduct dewatering and retention studies at the wet end for all the main paper grades produced by the mill. The supplier's philosophy is that forming fabric is only one part in the complex process of sheet formation, so it is necessary to consider the whole of the wet end when choosing the best fabric design. To this end, the supplier wanted to measure all the variables involved and have its specialists analyze them and make recommendations.

Because of the wide range of paper grades produced, it was especially crucial to the project's success that Kufferath only started the fabric optimization process once studies of dewatering and retention characteristics had been made for all paper grades. The results would then be used to propose changes to the table configuration, if necessary, so that results from the recommended fabric designs were optimized.

The second approach to the project involved analysis of paper samples at Kufferath's German research laboratory to study the sheet markings using the FFT method and determine the origin of the markings. The mill tried running two different forming fabric designs, both of which were triple-layer weft bound SSB fabrics: first, a Geoflex X 325-4 with a weft ratio of 3:2, and next, a Geoflex X 325-2 with a weft ratio of 2:1. The research laboratory evaluated the resulting sheet quality and concluded that fabrics with weft ratios of 3:2 were better suited.

Results: At the end of the project, several changes in the disposition of table elements were made. Speed increased from around 390 mpm to 500 mpm. Also, sheet marking was significantly reduced. As the supplier develops new designs, it continues to work closely with this fine paper mill to make available additional improvements in an ongoing quality improvement process.

- Antonius Kufferath is executive manager, international sales and marketing, for Kufferath.

PRESSING

Kvarnsveden Seeks to Break Its Own SC Speed Record with Clothing Help

Problem: Although Stora Enso Kvarnsveden's No. 12 paper machine in Sweden set a new world speed record of 6,237 fpm for the SC grade in March of this year, beating the old record of 5,955 fpm, the mill wanted to realize even higher speeds. Significantly, this new record was reached during the SC machine's startup phase and only 16 months after the machine went on line.

Also, the March speed trial exceeded all expectations and provided excellent results. The machine ran very smoothly with only one sheet break. During the trial, the No. 12 paper machine was equipped with Tamfelt's Gapmaster PRO F35654 forming fabrics in both inner and outer positions, as well as the Ecomax P2855 pick-up felt.

Tamfelt was one of two main clothing suppliers for the No. 12 paper machine. So far, this supplier's forming fabrics and press felts have run on the machine, as well as the startup belt.

The No. 12 machine produces 420,000 tons/yr in basis weights of 42-60 g/m2. The Metso machine features an OptiFormer LB, SymPress B plus fourth press and SymRun. At first, Tamfelt supplied Gapmaster XT SSB fabrics for both the inner and outer positions in the forming section. The fabrics ran in a very stable way and performed well. However, to improve paper quality and printability while at the same time keeping high drainage properties, these fabrics were replaced by somewhat finer Gapmaster PRO fabrics.

For the press section, Tamfelt supplied Ecomax for the pick-up and Ecostar for the first, third and fourth press. Ecomax is a stable laminated base structure felt that withstands compacting and remains open throughout its lifetime. Ecostar is also a stable laminated base structure felt, but has a smooth paper side base structure to ensure no marking from weave knuckles. For more critical positions, such as the pick-up and the fourth press, the felts are designed with light edge profiling.

During the startup, the No. 12 paper machine was equipped with a Metso Belt supplied by Tamfelt. Featuring a width of 472 in and an area of 678 ft2, it was at that time the largest belt ever made. The belt ran for 66 million nips with excellent performance until it was taken out as planned. A new Tambelt awaits installation.

Project: The Kvarnsveden mill continues to strive for even higher quality on its No. 12 paper machine.

"So far, the machine is well on its starting curve, and today the average speed is 1,750 mpm," says Anders Nordell, production manager for SC paper at Kvarnsveden.

What has been the biggest challenge in the project and startup?

"With regard to paper machine clothing, we've had some edge problems, such as edge flipping in the press section," Nordell describes. "With regard to the product, the challenge is to improve paper quality. It is well accepted by large printing houses, but we want to produce even better quality."

Especially on wide, fast machines, the sheet edge often has a tendency to create runnability problems such as napping after the nip or edge flipping when the felt is at the end of its lifetime. Tamfelt has developed a way to manufacture felts that controls the weight of the felt edges to produce even or slightly lighter felt edge areas. This edge profiling improves runnability.

Open communications between Kvarnsveden, Metso Paper and Tamfelt play an important role in improving machine performance and paper quality. As Nordell puts it: "Close cooperation has provided very good results in the project."

Results: Tamfelt continuously takes samples of the paper produced by the No. 12 paper machine and the fabrics used by it. The samples are analyzed in its Tampere and Juankoski laboratories.

These analyses, together with feedback from machine performance, follow-up measurements and experience from similar machines and by Tamfelt product support groups, contribute to further developing paper machine clothing on the No. 12 paper machine.

- Jonny Karlsson is sales manager, Scandinavia, for Tamfelt PMC.

Coated Board Machine Achieves Improved Smoothness with Seam Fabric

Problem: A major coated food board producer in the southwestern US was running process belts on a 7.87-m-wide machine. The belts on the single-felted bottom press were experiencing frequent damage. During the course of operation, it was not uncommon for the paper sheet to wrap the top press roll, which would in turn "burn" or actually tear the paper machine clothing running on this position.

The papermaker decided to consult with Voith Paper Fabrics to investigate alternatives to the process belts. When running a press fabric as opposed to a process belt, the papermaker has the ability to recondition the fabric in a given burnt area, enabling the fabric to continue to run without marking the sheet. This conditioning is not possible with a process belt.

Process belts are realistically four times the price of a press fabric. Although they have the potential of running well in excess of the life of a press fabric, process belts become cost prohibitive in many cases where damage is frequent.

Installation is also an issue. Endless process belts are extremely difficult and time consuming to install. Even on-machine seamed versions require more time for installation and seaming than do press fabrics, and results with seamed process belts have not been consistent.

The mill's goal in this case was to identify a press fabric that could deliver the same smoothness and bulk as the process belts, but without the susceptibility to damage. Mill managers were seeking a long-life fabric that could handle the sheet properly at startup and during machine breaks.

Project: Voith Paper Fabrics sent in specialists to work with the paper machine superintendent in analyzing and evaluating the needs of the machine, as well as the specific position. These specialists were experts in papermaking and the impact fabrics can have on overall machine performance and productivity.

After considering all factors, the decision was made to install Voith's MultiFlex AS3 Seam with a new engineered surface enhancement designed to increase smoothness, while maintaining water handling and permeability attributes. This fabric has proven to be effective in coated board, board and packaging, and graphics applications.

The MultiFlex AS3 Seam used in this application incorporates Voith's proprietary Vanguard PQ surface technology combined with Vector technology (Figure 3). These solutions are proven to work together to deliver measurable improvements in smoothness characteristics of paper.

Results: Since the press fabric began running on the machine in April, the mill and Voith Paper Fabrics have conducted Sheffield, Emveco and Parker Print tests. The mill has noted improvements in sheet smoothness of up to 10%.

Figure 3 - The MultiFlex AS3 Seam helped a coated food board producer improve smoothness up to 10%.

Other measurable results included a reduction in downtime of 20 min/break because the second press top roll does not have to be cleaned. Sheet handling has been enhanced by the fabric's ability to take the sheet downstairs, reducing roll wraps. In addition, the fabric has reduced burning and damage.

Satisfied that the MultiFlex AS3 had met the goals of the trial, the mill has placed an order for a full set of press fabrics for this machine, which includes a reorder for the second press.

- Cory Stagg is sales manager for Voith Paper Fabrics.

DRYING

Six-sigma Tactics Reduce Linerboard Machine Breaks

Problem: A midwestern linerboard mill had a significant break problem in the unirun second dryer section of one paper machine, with an average of 1.8 breaks/day. This was costing the mill $600,000 to $700,000/yr.

Project: Albany International offered to work with the mill and facilitated a joint Six Sigma project to address this break issue. The goal was to reduce these unirun second section breaks by 1.0/day. A 10-member team was formed, consisting of six people from the mill and four from Albany International.

The first step was a 1.5 day Kaizen-type event focused on process mapping and failure mode analysis. The following procedure was used for this event:

1. Map each step of the papermaking process at the mill, from wood supply to reel
2. At each step of the process, variables that could affect these unirun second section breaks were listed. Table 1 shows a section of the process map
3. At each step of the process, failure modes that could cause these unirun second section breaks were identified
4. Each failure mode was rated by frequency and impact, resulting in a prioritized list of failure modes, as shown in Table 2
5. Action items were developed to address the top failure modes. Completion of these action items were driven by bi-weekly follow-up meetings

In addition to the action items addressing the top failure modes, data was statistically analyzed to identify and confirm impacts of variables from the process map. This resulted in additional action items. Figure 4a-b shows an example of several interesting relationships identified from the analysis. These graphs indicate that lower wood percentages may cause higher breaks.

Results: As a result of completing action items that addressed the failure modes and the statistical analysis, breaks/day were essentially eliminated, as shown in Figure 5, exceeding the project goal. Cost savings attributed to this project were more than $600,000/yr.

- Kevin P. Morgan is a Six-sigma master black belt with Albany International.

Figure 4a-b - Six-sigma tactics revealed that lower wood percentages may have caused more breaks on the linerboard machine.

Figure 5 - By using Six-sigma tactics, average bubble breaks/day were virtually eliminated on a midwestern linerboard machine.

Engineered Approach Achieves Less Sheet Breaks on Linerboard Machine

Problem: A linerboard machine located in the southwestern US was experiencing numerous sheet breaks in the first dryer section, impeding the opportunity for speed and production improvements.

Project: The mill's paper machine superintendent and maintenance engineer worked with AstenJohnson representatives using the supplier's Engineered Approach to analyze the cause of the sheet breaks. Findings concluded that sheet instability and flutter in the first and second sections were the primary culprits.

Figure 6a illustrates the existing configuration. This current configuration resulted in 16 ft of open draw between the first UnoRun and the second section. This open draw, along with the air entrainment associated with the dryer fabric construction, led to significant sheet instability as well as issues with tail threading. Over a seven-month period, there was an average of 31 breaks per month occurring between the UnoRun and the second dryer section. The problem was compounded by an increase in the time to thread up after a sheet break or shutdown.

Figure 6a-b - Configuration of linerboard machine dryer section before (6a) and after (6b) a "pistol grip" arrangement was installed to reduce sheet breaks

The team decided to approach the problem in two ways:

1. Decrease the open draw between the first and second sections
2. Reduce the air carried by the dryer fabrics in these sections

To reduce the open draw between the last dryer can in the first UnoRun (No. 6 dryer) and the first dryer can in the bottom position (No. 7 dryer), a "pistol grip" arrangement was utilized. The pistol grip configuration is considered an easy solution in that it requires very little capital investment as far as new rolls and framework and consists of the top dryer fabric wrapping a dryer can in the bottom position (usually the first or last dryer can in the section). Figure 6b shows where the top dryer fabric was lengthened in order to wrap dryer can No. 7, providing 100% sheet support as the sheet is transferred from the first UnoRun to the second top/bottom. Additionally, felt roll "A" was moved towards the wet end to position the dryer fabric so it "kisses" the No. 6 dryer can, providing further support as the sheet exits the UnoRun.

Figure 7a-7b - Top view (7a) and side view (7b) of UltraClean fabric used to help reduce sheet breaks in linerboard machine’s dryer section

To improve threading and reduce the air carried into the transfer by the dryer fabrics, the surface characteristics of the fabrics were optimized. A dryer fabric's air carrying characteristics and contact area are important considerations when sheet handling is in question.

For this project, AstenJohnson provided its trademarked low permeability UltraClean dryer fabric, the lowest air carrying and highest contact area dryer fabric design available in the industry today. Woven on the trademarked MonoTier platform, the UltraClean fabric uses flat ribbon-shaped monofilament strands in the machine direction (Figure 7a-b). As a result, this high contact area provides a smoother surface that aids in sheet threading (the sheet adheres better to the dryer fabric), and sheet flutter is reduced due to the low amount of air the fabric carries.

Results: The improvements in sheet handling were noticed immediately after startup. The newly configured pistol grip in the second top position, coupled with AstenJohnson's UltraClean dryer fabric, decreased sheet breaks by 73% (down to 8.5 breaks/month) between the UnoRun and second dryer section.

- Blake Farmer is dryer product manager for AstenJohnson.

Monica Shaw is a freelance writer located in Atlanta, GA.

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