Paper making and fiber liberation – Processes and products – With measuring – inspecting and/or testing
Reexamination Certificate
1999-09-20
2001-10-09
Silverman, Stanley S. (Department: 1731)
Paper making and fiber liberation
Processes and products
With measuring, inspecting and/or testing
C162S263000, C162SDIG004, C162SDIG004, C356S431000, C356S430000, C356S429000, C702S127000
Reexamination Certificate
active
06299730
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to paper making machinery and, more particularly, to a method for monitoring web defects which involves scanning the moving paper web and utilizing both a detected defect size parameter and a detected distance from the paper web edge to establish a likelihood of web failure.
BACKGROUND
Productivity and profitability of paper making is determined by the speed of production, that is, the speed with which the paper web progresses through the paper making and paper processing equipment. Production speeds may be as high as 4000 ft/min, but 5000 ft/min or higher would obviously be more profitable. So-called web breaks seriously limit production for two reasons. First, a web break stops production for up to 45 minutes causing a loss of 45×4000=180,000 ft of production (up to 6 tons of paper). Up to 6 web breaks may occur in 24 hours. Second, the higher the production speed, the more web breaks occur, so that production speed is limited by the number of web breaks.
Paper is produced as a continuous sheet of a width often greater than 20 feet. This continuous sheet is commonly referred to as the ‘web’. At the end of the machine the paper is wound on a roll. When a roll has reached a certain size, the web is cut on-the-fly, and a new roll is wound automatically. The rolls so produced are called ‘logs’. In line with the paper machine is the re-reeler in which the logs are rewound. The purpose of the re-reeler will be explained in the following. The logs coming from the re-reeler are fed into the coater, a machine several hundred feet in length in line with paper machine and re-reeler. In the coater the paper is coated, often on both sides, usually with a clay-based material, primarily to improve printability. The initial web coating must be dried, the other side coated and dried and the final product wound up in new logs. Web breaks in the coater are of concern here. If the web breaks paper is spewed all over at 4000 ft/min. The machine has to be stopped and rewound with the associated production loss as explained above. These web breaks are caused by defects in the paper introduced in the paper machine. Control in the production process in the paper machine must detect those defects. In the re-reeler these defects are repaired if serious enough. But repairs are costly and time consuming. In one aspect of the invention proposed here will automatically identify those defects that warrant repair, mark them and make the re-reeler stop automatically at the defect so that a repair can be made and, more important, automatically decide which defects should be repaired, and which should not, depending upon the chance the defect would cause a web break. This allows optimization of production. Alternatively, another aspect of the invention enables those defects that most warrant repair to be marked, such as by automatically marking the paper web in the region of the defect, so that a machine operator can stop movement of the paper web at the re-reeler and repair the marked defect if desired.
As used herein, the terminology “through web defect” refers to any defect which passes completely through the thickness of the paper web such as cracks, circular holes, elliptical holes, and irregular holes. The terminology “web defect” refers to both through web defects and other types of defects including, but not limited to light spots and dark spots caused by significant variances in thickness of the paper web and/or clumps of material. As pointed out in applicant's paper entitled Tenacity, Fracture Mechanics and Unknown Coater Web Breaks TAPPI J. 79(2) Kovalin 233 (1996), such through web defects reduce the strength of the paper web in the region of the defects permitting failure or breaking of the paper web in the region of such defects at a lower tension. The advantage of using fracture mechanics to determine the failure strength of through web defects is likewise described in the subject paper.
Accordingly, a system for real time monitoring of web defects combined with a method to evaluate which defects should be repaired, will be of great benefit.
SUMMARY OF THE INVENTION
In one embodiment, a method for monitoring web defects along a moving web of paper involves determining a dimension of a web defect as the paper web moves along an established paper path in the machine direction. A distance from a side edge of the paper web to a location of the web defect is also determined as the paper web moves along the established paper path. A value indicative of a likelihood of paper web failure at the web defect is then established based at least in part upon both the determined dimension and the determined distance. A determination of whether to repair of the web defect at a subsequent operation, such as a re-reeler, can then be made based at least in part upon the determined failure likelihood indicative value.
Because the most critical dimension of any web defect is the cross machine direction size, it is preferred that such cross machine direction size is determined and used in the subject method. Further, the subject distance used in the method should preferably be the distance from the cross machine direction center of the web defect to the side edge of the paper web in the cross machine direction. However, the distance from the edge of the web defect to the side edge of the paper web could also be used in the subject method. Fracture mechanics is used to establish the relative failure strength (a failure likelihood indicative value), i.e., relative to that of a flawless web under otherwise the same conditions. Depending upon the acceptable relative failure strength—economically acceptable on the basis of anticipated breaks—a decision can then be made whether or not to repair the defect. It should be emphasized that fracture mechanics itself is a general science used in all areas of technology, although it is not accepted as such in paper making technology. In this application the general fracture mechanics equations have been modified on the basis of extensive testing by applicant, to apply specifically to the technology of paper making and coating. This relative failure strength can then be compared to a threshold failure value to determine whether to repair the defect. In this regard, an operator alert is generated so that the operator can consider whether or not the subject web defect should be repaired. By repairing those defects which have the greatest likelihood of causing a paper web break, the productivity of a particular coater can be substantially increased.
In another embodiment, a method for monitoring web defects along a moving web of paper involves establishing a plurality of paper web width regions for the paper web being monitored. A dimension of a web defect is determined as the paper web moves along an established paper path in a machine direction and the web defect is categorized as falling into one of the established paper web width regions. A determination of whether to repair the web defect is then made based at least in part upon the determined dimension and the categorization made.
A system for implementing the subject method includes an optical scanning device having a plurality of CCD cameras arranged to view the entire width of the paper web as the paper web moves along the established paper path. The scanning device produces paper web image signals which are transmitted to a controller which is configured and programmed to analyze web defects utilizing the location of the web defect relative to the side edge of the paper web as a variable. Applicant has conducted a number of tests which show that edge distance is an important variable which, when taken into account, enables improved selection of web defects for repair.
REFERENCES:
patent: 3627944 (1971-12-01), Field
patent: 4728800 (1988-03-01), Surka
patent: 4979029 (1990-12-01), Lemelson
patent: 5389789 (1995-02-01), Nguyen
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patent: 5821990 (1998-10-01), Rudt et al.
pate
Broek David
Connolly Kevin Paul
Swinehart Dirk Everett
Halpern Mark
Silverman Stanley S.
The Mead Corporation
Thompson Hine & Flory LLP
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