Supporting the forming fabric on a paper machine is a series of drainage elements designed to form and drain the stock slurry that is delivered from the headbox. At this point, the stock slurry is 99% water and 1% wood fiber. The initial part of the forming zone is critical in determining the final characteristics of the sheet of paper. The first drainage element in the process is aptly called the forming board. Its placement relative to the headbox has a major impact on how the initial fibers are formed on the top surface of the forming fabric. The structural integrity of the forming board is a significant consideration in its design because it must withstand the impact of thousands of gallons of water per minute. It must withstand this hydraulic load without vibration or deflection.

Through the years, Johnson Foils has manufactured forming boards for the most demanding applications, including some of the widest and fastest paper machines in the world.

Beyond the forming board is a series of drainage elements used to form the sheet of paper. The type of element depends on the grades of paper being produced. On white paper applications, printing, writing, newsprint and other publication grades, high frequency foils are used to initiate and control beneficial stock activity during the sheet forming process. While the papermaking foil was not invented by Johnson Foils, we are the undisputed leader in the refinement of its design and application. Beginning with the patented T-bar mount, followed by the placement of foils on harmonics and, most recently, the high frequency forming concept, all have been major developments by Johnson Foils.

Unique foil designs are also used for specific applications. One such blade is the agitator. The agitator is generally used on paper grades containing a high percentage of recycled fiber or mixed waste. The positive pressure pulses developed across the blade minimize sheet sealing tendencies during the forming process.

On board grades -- both bleached board and unbleached grades such as linerboard and corrugating medium -- a different system is used for forming and draining. The ISOFLO®, another Johnson Foils patented system, is designed to impart beneficial stock activity while draining large volumes of water. It was originally developed for use on bleached board machines where foils were ineffective in generating stock activity because of the heavy sheet weights and slow machine speeds. Its high success rate quickly made it the standard within the industry. Today, over 90% of the bleached board machines in North America are equipped with ISOFLOs. High speed linerboard machines are the single most demanding application from a water removal standpoint. Headbox flow rates on these machines can easily be three to four times greater than on a fine paper machine operating at comparable speeds. The ISOFLO is used on several of the highest producing linerboard and corrugating medium machines in the world. Further ISOFLO developments included another patented concept, which is the ISOFLO PLATFORM. This approach allows the ISOFLO structures to be physically joined together to form a continuous platform. This "system" is used on fourdriniers with limited table space.

The DELTAFLO™ is the newest pulsative drainage device. It is a vacuum augmented unit that incorporates a new cover concept. The cover consists of pulsative blades that can be adjusted "on the run" in order to optimize stock activity. The DELTAFLO is a relatively large unit, about 48" (1,219 mm) wide, with multiple adjustable cells. A cell is a series of pulsative blades that can be adjusted to accommodate machine conditions. The DELTAFLO tends to operate at very low vacuum levels, so the airflow requirements are very low as well. Several DELTAFLO Systems have been installed on board machines ranging in speed from 800 feet per minute (245 meters per minute) to 2,700 feet per minute (825 meters per minute). The objectives have varied from increasing production, reducing basis weight while maintaining the board's physical properties, improving formation and improving smoothness. All of these objectives have been accomplished with the installation of a DELTAFLO System.

To quantify the above:

• On linerboard, 10 to 20 gsm reduction in basis weight
• On linerboard, 5% increase in production (15% on corrugating medium)
• On folding boxboard, 30% improvement in Sheffield smoothness
• On linerboard, 10% improvement in formation
• Once the sheet leaves the forming section, the next concern is strictly drainage. We want to achieve the highest possible dryness to the couch roll without disturbing the mat that was previously formed.

The next series of drainage devices are low vacuum units (lovacs). A lovac is a sealed unit connected to an external vacuum source. When "vacuum" is applied, the pressure within the unit is lowered. It is the differential pressure between the sealed chamber and atmosphere that allows water to be squeezed into the unit. The drained water is then removed through integral drainage ducts or an external air/water separator system.

The ORTHOFLO® (single chamber lovac) and the DUOFLO® (two chamber lovac) are the two common designs offered by Johnson Foils. The ORTHOFLOs with integral style ducts are used in high drainage applications where operating vacuums are relatively low. Other ORTHOFLO designs and the DUOFLO have single end discharges (SEDs) that connect to an external separator. These are used in dryer table positions where the available water is much less and the vacuum requirements are higher.

ORTHOFLOs and DUOFLOs are commonly used for many important functions, including:

• Consistency control ahead of a top wire unit
• Consistency control entering a dandy (those used for formation or watermark)
• Capturing the wetline and dryline at the lowest possible load

On a fourdrinier, when the sheet takes on a dry looking appearance or when a top wire unit exists, then suction boxes (hivacs) are used to maximize sheet dryness to the couch. These are high vacuum units that operate under the same principle as lovacs.

The application and design of these units is critical. Too many hivacs or improperly designed covers can create excessive drag or, in severe cases, can cause the ceramic surfaces to become so hot that they will melt the forming fabric.

Being part of a clothing company, Johnson Foils has devoted tremendous resources to the research and development of hivac cover design and materials. Our objective is to provide the driest possible sheet to the couch at the lowest dragload with no detrimental effects to clothing.

One of our most significant early developments was the TRIVAC®, a three chamber high vacuum unit. The TRIVAC has many inherent benefits:

• Maximum sheet dryness due to more efficient use of the available airflow
• Compact size; requires less table space than three individual boxes
• Reduced installation time and cost; fewer structures to mount

For the more demanding applications, such as linerboard, Quadrivacs (four chamber) and Quintivacs (five chamber) are also available. In addition to the above benefits, these large structures can also provide the continuous application of vacuum under a steamhood.

In addition to the vacuum augmented units, Johnson Foils provides ancillary equipment to complete the vacuum systems. We also provide engineering services to assist with the complete system design from vacuum source to drainage unit.

Forming Products Section