Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
2000-04-27
2001-07-17
Wilson, Pamela (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S456000, C034S114000, C034S117000, C034S119000
Reexamination Certificate
active
06260287
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
This invention relates to a method and apparatus for carrying a delicate wet paper web on a high speed paper drying machine in the first and second dryer sections.
(b) Description of the Prior Art
On high speed paper drying machines, single felts or fabrics are often used to carry the delicate paper web in the first and second dryer sections. Although the web is fully supported, it can become detached from the felt or fabric at the vacuum wedge as the web adheres to the dryer cylinder, and because of the small vacuum formed as the two surfaces separate. The greater potential problem is at the compression wedge formed between the felt or fabric and the dryer. A large volume of air is carried by the boundary layer on the felt or fabric and this is forced into the nip and pushed through the permeable felt or fabric, to detach the web.
Instabilities in the sheet run in the single-felted paper drying machines are mainly caused by the following mechanisms. Moving surfaces create an under-pressure at the nip of the sheet and the top dryer. This under-pressure creates air flows which tend to lift the sheet off of the felt or fabric. These air flows are directed from the edges of the sheet towards the centre of the sheet. This is one reason for sheet-edge flutter between the top and bottom dryers of the single-felted section.
Moving surfaces create an overpressure at the nip of the felt or fabric and at the bottom dryer. If the felt or fabric is open (i.e., if it has high permeability), the air easily flows through the felt or fabric and lifts the sheet off of the felt or fabric, often across the entire sheet width. If the felt or fabric permeability is low, the air which has entered between the sheet and the felt or fabric at the nip of the sheet and the top dryer cannot escape fast enough through the felt or fabric, and an “air bubble” is created at the nip of the sheet and the top dryer. This bubble is a reason for wrinkles on the sheet.
There are a number of techniques to address this problem, e.g., blasting air out of the compression wedge to create a vacuum or using parallel jets with curved surfaces to generate a negative pressure using the Coanda effect.
One recent technique which was alleged to solve this problem involved blowing air away from the bottom of the nip of the felt or fabric and the bottom dryer and against the boundary layer carried by the felt or fabric at the nip of the felt or fabric and the top dryer. A nozzle in each end of the blow box was alleged to make it possible to maintain a slight vacuum from top to bottom dryer. The vacuum was created by the high velocity air flow from the nozzles based on ejector principles. The result was that the sheet was said to be held steadily to the felt or fabric from both of these nips. This was said to prevent the air build-up between the sheet and the felt or fabric, and to prevent the air bubble from being created at the top nip.
SUMMARY OF THE INVENTION
(a) Aims of the Invention
One object of the invention is to solve the problem of instability in the sheet run on a single-felted dryer by the use of a Venturi which is used to generate a negative pressure in the compression wedge, and using the “exhaust” to generate a negative pressure across for the vacuum wedge.
Another object of the invention is to provide such solution which provides double the air to control the problem compared to the previous solutions where the air must be split using the other techniques.
Yet another object of the invention is to provide such solution using a Venturi which is easier and offers more exact control.
(b) Statements of Invention
The present invention provides a sheet stabilizer for a dryer section of a paper-making machine of the type which conveys a wet sheet of paper by way of a felt or fabric, the dryer section including a leading upper dryer roller, a lower dryer roller, and a trailing upper dryer roller, the sheet stabilizer comprising a Venturi system for stabilizing the wet sheet of paper which is being conveyed on the dryer section of the paper-making machine by way of the felt or fabric by drawing air away from the nip between the felt or fabric and the lower dryer roller, the Venturi box being disposed between a leading upper dryer roller and a trailing lower dryer roller.
The Venturi System includes two Venturi boxes, namely an upper Venturi box and a lower Venturi box. The upper Venturi box is defined by a fixed outer lateral surface and a fixed inner lateral surface, to provide a pair of spaced-apart, substantially-parallel, lateral surfaces which are configured to be at a fixed spatial relationship to one another. Those spaced-apart substantially-parallel lateral surfaces are disposed substantially-parallel to the plane of the felt or fabric. The outer lateral surface is configured to be in sliding contact with the wet sheet of paper when the felt or fabric supporting the wet sheet of paper is moving. The upper Venturi box includes means for generating a flow of a first jet of air into the space between the fixed, spaced-apart, substantially-parallel, lateral surfaces, the flow of the first jet of air thereby generating a negative pressure at the upper Venturi box. The first jet of air is then discharged into the space between the pair of spaced-apart substantially-parallel lateral surfaces, in a direction which is opposite to the direction of movement of the felt or fabric. This draws air away from the nip between the wet sheet of paper and the lower dryer roller and into the space between the pair of spaced-apart, substantially-parallel lateral surfaces, to be discharged along with the first jet of air. The lower Venturi box is defined by a fixed outer bottom surface and a fixed inner bottom surface, to provide a pair of spaced-apart, substantially-parallel, lower surfaces which are configured to be at a fixed spatial relationship to one another. These spaced-apart, substantially-parallel lower surfaces are angularly-disposed to the plane of the felt or fabric. The lower Venturi box includes means for generating a flow of a second jet of air into the space between the spaced-apart, substantially-parallel, lower surfaces. The flow of the second jet of air thereby generates a negative pressure at the lower Venturi box. The second jet of air is then discharged from the space between the spaced-apart, substantially-parallel lower surfaces, in an angular direction away from the felt or fabric supporting the wet sheet of paper. This draws air away from the nip between the wet sheet of paper and the lower dryer roller and into the space between the spaced-apart, substantially-parallel lower surfaces, to be discharged along with the second jet of air.
The present invention also provides a method for stabilizing a wet sheet of paper which is being conveyed through a dryer section of a paper-making machine by way of a moving felt or fabric. The dryer section includes a leading upper dryer roller, a lower dryer roller and a trailing upper dryer roller. The method includes generating a flow of a first jet of air in a space between a fixed outer lateral surface and a fixed inner lateral surface which define spaced-apart, substantially-parallel, lateral surfaces which are configured to be at a fixed spatial relationship to one another and which are disposed parallel to the moving felt or fabric. The wet sheet of paper is supported on the moving felt or fabric and is in sliding contact with the outer lateral surface. The flow of the first jet of air thereby generates a negative pressure at an upper Venturi box. The first jet of air is then discharged into the space between the pair of spaced-apart substantially-parallel lateral surfaces in a direction which is opposite to the direction of movement of the felt or fabric. This thereby draws air away from the nip between the wet sheet of paper and the lower dryer and into the space between the pair of spaced-apart, substantially-parallel surfaces, to be discharged along with the jet of air. A flow of a second jet of air is generat
Mancini Raffaele
Walker Peter
Birch, Stewart, Kolash & Birch LLP
Wilson Pamela
LandOfFree
Wet web stability method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wet web stability method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wet web stability method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2542259