Reducing tissue breaks with digital event recording technology

Kari Hilden, Papertech

Breaks are typically classified as coming from either known or unknown sources. Breaks coming from known sources can usually be eliminated, but the unknown sources can cause significant losses in machine operating speeds and efficiencies. For example, a tissue machine producing 100 tons/day, with ten breaks per day, lasting on average five minutes each, results in over US$250,000 in efficiency losses per year.

BREAK RECORDING TECHNOLOGY. To help increase production and product quality while reducing operating costs, the WebVision® Plus system has been developed to provide tissue makers with tools to capture and diagnose events. This allows them to identify the root cause of breaks, sheet defects and runnability issues, often before they result in downtime.

Tissue makers can use the real-time analysis tools to monitor and alarm trouble spots such as the pick-up felt, suction pressure roll, Yankee adhesive build-up, creping blade, reel turn-up, etc. often preventing breaks before they occur.

In general WebVision® Plus offers the following:

·Designed specifically for tissue machine operating conditions;

·Optimal camera enclosures – single handed, no tools operation & 360º internal image rotation;

·Small, powerful and efficient lighting technology with fully adjustable light beam angle;

·Latest NIR-based, high resolution, high speed cameras capable of 120 images/second to capture events at tissue making speeds;

·Compact, highly reliable, full featured interface cabinet with the latest non-proprietary computer technology;

·Advanced software modules including several leading edge features to pinpoint the root cause of defects and machine issues;

·Easily upgradeable;

·Ability to download and upload data from a mill wide system.

Page 110 illustrates the general layout of a digital event capturing system. All components must be matched to ensure no weak links limit its overall performance. Generally cameras on machines wider than 4 meters (150”) are mounted in pairs (front side, back side).

SYSTEM COMPONENTS CAMERAS.

Cameras form a critical part of an event capturing system. If they are not sensitive enough or designed to withstand the tissue machine operating conditions, the system will be insufficient for root cause analysis (see page 111).

CCD based video camera technology has dramatically improved over the last 10 years and now offers high sensitivity (below 0.1 lux, using high quality lenses) with shutter speeds of up to 1/100,000 of a second. The fast shutter ensures minimal sheet travel and improves the image sharpness as shown in Table 1.

The image frequency of cameras is a function of the line frequency. In North America the image frequency is 60Hz and with non-interlacing (separates the odd and even fields in the image) this allows 60 images/second to be viewed, instead of the NTSC broadcast standard of 30 images/second. As the following table illustrates, the image frequency defines the distance that the sheet travels during 1/60th of a second. For example, at 1400 m/min (4600 ft/min) the sheet travels 38 cm (15”) between each image. The cameras therefore need to be properly located, allowing at least this much sheet in the machine direction to be visible (Table 2).

Lighting is also very important. There must be enough lighting, and the right type, to ensure maximum shutter speeds and prevent so called “fade-in / fade-out” problems that result when the light line frequency interferes with the camera image frequency.

In addition, a large selection of mounting brackets is essential for the best web viewing positions and to ensure the cameras do not interfere with any routine machine maintenance.

EVENT CAPTURING. The method that is used for recording the events is just as critical as the cameras. The main objective is to record at the highest possible resolution.

Techniques are now available that keep the camera image history both in RAM and hard drive memory. This allows both instantaneous access to the event following a break (no blackout period) as well as partial RAM based downloads when the system is, for example, triggered by a hole detector.

OPERATOR INTERFACE AND SOFTWARE. A critical factor to any break analysis system is the user interface. It must be simple to use, trouble-free and allow complete analysis and break storage.

WebVision® Plus can download and store hundreds of events. With the system’s high image resolution and frame rate, the images are clear and offer tissue makers a powerful tool to identify the root cause of runnability problems (Figures 1 & 2).

The software makes it easy to store the information following each break. A rapid event download allows the operator to view the break immediately after it occurs with all the cameras active and at the same time store the event in the software and note the reason for it. The operator can rapidly analyze the most recent event and compare it with a previous one by clicking on it.

CAMERA LOCATIONS. Cameras that have been designed for high temperature applications, together with sufficient cleaning technology and lights, can be located in all sections of a tissue machine. Typical camera locations are trim squirts, pick-up, pressure roll, creping blade, reel and various converting applications.

RESULTS. To date, event monitoring systems have provided tissue makers with an effective new tool to reduce breaks. With a sufficient number of cameras correctly placed, a nearly complete picture of the event can be achieved.

A world-class tissue mill documented substantial reductions in breaks using WebVision® Plus. With its proven benefit, the mill is now purchasing additional systems for a number of tissue machines. Out of the 500 breaks that were analyzed by the system:

·57% of the breaks were found to be a result of an event that took place at the back-side of the machine;

·30% due to loose edges;

·25% due to winder/spreader;

·20% due to Yankee coating problems;

·15% due to edge breaks;

·10% unknown.

The mill had 20-70 breaks a day and was able to trace many of the breaks that were occurring at the Yankee, creping blade and reel to problems that were originating at the wet-end. The operators were previously unaware that the problems were starting at this part of the machine.

The problem was discovered with bubbles in the sheet at the wet-end which collapsed through the press and drying process, causing breaks at the reel. They found that the bubbles were caused in the transfer of the sheet from the wire to the pick-up felt at the wet-end (Figure 3).

CONCLUSIONS. Minimizing all sources of paper machine breaks has a major effect on increasing tissue machine operating efficiencies and production rates. Event capturing technology has been found to reduce breaks by 20% to over 80%.

In summary, automated break recording systems today are able to:

-Automatically, in real-time monitor and record all critical locations on the tissue machine;

-Use easy-to-operate PC Windows® based software that allows the operators to fully view and manipulate all of the image information;

-Allow environmentally enclosed, high resolution cameras to be placed in all of the critical locations;

-Provide a permanent record of each event that can be easily viewed, printed, tagged and compared to other breaks;

-Allow operators to be given early warning of a change such as trim build-up, Yankee adhesive build-up, creping blade, reel turn-up;

-Interface to mill-wide systems for complete reporting.

With a typical payback of less than six months, and an average increase in machine efficiency of 2-5%, it is expected that in the next five years, the use of this technology will grow rapidly to ensure that maximum tissue machine efficiency, production and tissue quality is maintained. •

Kari K. Hilden, Papertech Inc. #108-245 Fell Avenue, North Vancouver, B.C. Canada, V7P 2K1 (604-990-1600)