Data processing: measuring – calibrating – or testing – Measurement system – Dimensional determination
Reexamination Certificate
2000-04-12
2002-10-22
Shah, Kamini (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Dimensional determination
C702S170000
Reexamination Certificate
active
06470294
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a system and method for measuring the rate of application of liquid glue during the manufacture of corrugated board.
In the manufacture of corrugated board a layer of paper referred to as the medium is first passed between two metal, heated and toothed, corrugating rolls that form it into a sinusoidal, fluted shape. A topside layer of paper referred to as the top liner is then bonded with an aqueous, starch-based glue solution to the topside tips of the medium's flutes. This initial fluting and bonding process is typically referred to as singlefacing, and takes place in an area of the corrugating machine that is typically referred to as the singlefacer.
During singlefacing the glue is first delivered to the singlefacer's glue pan through which rotates a glue roll. Glue picked up by this glue roll is then metered off by an adjacent metering roll. The gap between this glue roll and metering roll, which is typically referred to as the singlefacer metering roll gap, may be adjusted to produce a specific glue roll film thickness and resulting topside glue application rate. After the glue is applied the medium is held in contact with the top liner for a brief interval by a suitable loading element, such as a pressure roll or loading belt, to produce the bonded, two-layer, singleface web.
The underside of the singleface web's flutes are then bonded to a second liner, typically referred to as the bottom liner, to form the final three-layer, corrugated board product. This final glue application and bonding process, which is typically referred to as doublefacing, takes place in an area of the corrugating machine that is typically referred to as the glue-machine or glue-unit.
During doublefacing the glue is first delivered to the glue-machine's glue pan, through which rotates a glue roll. Glue picked up by this glue roll is then metered off by an adjacent metering roll. The gap between this glue roll and metering roll, which is typically referred to as the doublefacer metering roll gap, may be adjusted to produce a specific glue roll film thickness and resulting bottom-side glue application rate. During this bottom-side glue application the medium's flutes are typically held in contact with the glue roll by an adjacent rider roll or spring-loaded contact bar that is pressed lightly against the top of the singleface web. Then, after the glue is applied to the underside of the medium's flutes, the medium is subsequently pressed against the incoming bottom liner to initiate the bottom-side bond and complete formation of the three-layered corrugated board.
Some corrugating machines have two or more singlefacers, to form two or more singleface webs, which when bonded together, and to a final bottom liner, permit the formation of a five or more layered corrugated board.
To produce consistent, optimum corrugated board quality, to minimize raw material costs, and to maximize production speeds, glue application rates must be controlled to minimum target levels (across the machine's width), at both the singlefacer and glue-machine.
Producing well-bonded corrugated board to minimize scrap due to delamination requires consistent, uniform glue application to ensure adequate coverage. Producing flat, pliable corrugated board to minimize scrap due to dimensional warp and cracked score lines, requires optimum board moisture levels that also depend upon consistent glue application rates. The paper used to produce corrugated board typically contains about 6.5% water by weight. The paper in a representative three-layer board with a total raw material weight about 120 lbs/1,000 square feet, thus contains close to 8 lbs of water per 1,000 square feet of board. The minimal amount of glue applied to a board of this weight is about 10 lbs of liquid glue per 1,000 square feet, of which about 25% is solids (starch and additives, such as borax) and 75% water (7.5 lbs/1,000 square feet). An application rate of 50 to 100% higher than this is also not uncommon. As indicated by this representative example the amount of water added to the process with the glue is similar and often greater than that entering the process with the paper. Consequently, effective control of final corrugated board moisture requires not only consistent paper moisture levels, but also control of the glue application rate.
A representative corrugating plant produces about 70 million square feet of board per month. This equates to roughly 50,000 tons of board per year, including over 1,000 tons of starch (solids). In this example about 3,000 tons of water per year, introduced along with the starch, would have to be subsequently evaporated from the board during contact with steam-heated vessels. Even a modest 10% reduction in glue consumption, made possible by the on-line measurement and control of the glue application rate, would reduce this representative corrugating plant's glue purchases by 100 tons per year, and it's steam consumption rate by over 300 tons per year.
The conventional means to control and minimize the glue application rate is to control the primary variables, the metering roll gaps, to empirical dimensional targets, to achieve approximate control of the top and bottom-side glue application rates. However, glue application rates are also affected by numerous secondary factors such as the medium's physical properties (i.e. permeability), the glue's characteristics (i.e. viscosity), the machine speed (which affects the amount of glue that is forced through a given metering roll gap), and the gap between the glue roll and the medium's flute tips. An on-line, direct measurement of the glue application rate is needed to facilitate control of the glue application rate to optimum targets, using closed-loop feedback control of the metering roll gaps.
Machine speed on a corrugator varies frequently, often from as high as 800 feet per minute, down to 300 feet per minute, and back up, in less than a minute. Such rapid changes in speed produce concurrent, rapid changes in the glue application rate. To enable closed-loop control of the glue application rate throughout speed changes rapid measurement updates are needed, preferably every second or fraction of a second.
To date, no on-line, direct, rapid measurement of the glue application rate method has been successfully commercialized. U.S. Pat. No. 5,049,216 describes the basic principles of an infrared absorption sensor that with the proper selection of appropriate optical filters and light-sensitive detectors may be used to measure the adjacent quantities of certain organic materials, such as water, cellulose fiber, and starch. However, U.S. Pat. No. 5,663,565 indicates that the basic principle of infrared absorption cannot be used, without enhancement, to directly measure the amount of starch on the board, because the primary absorption bands for starch are the same as for cellulose fiber and because the water in the starch is indistinguishable from the water in the paper. U.S. Pat. No. 5,663,565 subsequently discloses an enhancement that allows the starch component of a direct infrared absorption measurement to be distinguished from the background measurement of the paper's cellulose fiber and water, by exploiting the fact that the starch component of the measurement oscillates at the fluting frequency. However, the method proposed in U.S. Pat. No. 5,663,565 requires complex signal processing and a small light spot size that is tightly focused, depth-wise, on the flute tips, to prevent the undulating medium's depth-sensitive fiber and water signatures from corrupting the measurement.
It is therefore a principle object of the present invention to provide a system and method for measuring the glue application rate on corrugated board.
It is a further object of the present invention to measure the glue application rate on corrugated board during the manufacture of such corrugated board.
SUMMARY OF THE INVENTION
Accordingly the system and method of the present invent
Hale and Dorr LLP
Qualitek-VIB, Inc.
Shah Kamini
Washburn Douglas N
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