Advancing material of indeterminate length – With material-responsive control means – To position material laterally
Reexamination Certificate
2000-03-09
2002-04-16
Mansen, Michael R. (Department: 3653)
Advancing material of indeterminate length
With material-responsive control means
To position material laterally
C137S485000, C137S625210, C251S355000
Reexamination Certificate
active
06371347
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an air switch and palm guide for guiding the high speed fabrics which are used to carry the paper web through papermaking machinery.
BACKGROUND OF THE INVENTION
In the papermaking process, thousands of gallons per minute of liquid pulp or “stock” is poured out of the head box over the forming board and on to the fourdrineer fabric or “wire”. At this point, paper is in liquid form, about 98% water and 2% fiber, filler, and chemicals. The fiber is usually made up from virgin ground wood and or recycled paper. The filler is usually clay and/or pulverized calcium carbonate mined from quarries.
A combination of chemicals are added to the water, fiber, and filler to give the paper certain desired properties. This liquid mixture is commonly referred to as the furnish. The mixture or exact recipe of the furnish will vary with different paper grades and types.
A typical wire can be a 140′ long loop. The term “wire” predates the invention of plastic type monofilament fourdrineer fabrics. Originally, the fourdrineer fabric was actually made of very fine strands of brass or bronze. The fourdineer or wire table is typically about half as long as the wire, since the wire circumscribes the table in a continuous loop.
The first step of the paper machine, with reference to
FIG. 1
, is called the formation. Water drains very quickly though the wire after the headbox. Within the first 20 feet of the wire table, much of the water content of the furnish has drained through the wire into the return trays, and the fibers and fillers have formed together in a layer of very wet paper. The last ⅓ of the wire table includes a series of vacuum boxes that sucks more water out of the furnish. A good even formation, with uniformity of the fibers and fillers is important and will result in a stronger, smoother sheet of paper.
At some point near the first or second vacuum box on the wire table, so much water has been drained or sucked away that the layer of furnish loses its watery shine and takes on a dull haze. The particular area on the wire table where shine turns to haze is commonly referred to as the wet line.
The haze that continues down the last part of the wire table is essentially an unpressed wet sheet of formed paper. At the end of the wire table the wet sheet of paper gets sucked off the wire fabric by a pick up roll and transferred onto the pickup wet press felt. The pick up felt is pressing lightly onto the wire fabric. The transfer of the wet sheet is achieved by the vacuum of the pickup roll turning inside of the pickup felt. The pressing section may include multiple presses.
The function of the wet pressing section of the paper machine is to press down the wet fibers and vacuum out more water from the wet sheet. Also, the wet press can to some degree correct or control the profile of the paper sheet with the use of hydraulic profile rolls in the pressing area.
After being pressed, the wet sheet is now transferred to the drying sections, where the wet sheet is carried by dryer felts over and around a series of dryer cans. After traveling over and around many very hot dryer cans, the paper has only 3 to 4 percent moisture or water content. At this point, the dry sheet is wound up at the end of the paper machine as a reel of paper.
A responsive and well-maintained guiding system is very important for efficient papermaking. A smooth, positive guiding system will properly guide the long wire, felt and fabrics in the center of the papermaking machine and will not let them oscillate from side to side.
The fundamentals for guiding any type of paper machine clothing (i.e. wire, felt, fabric, etc.) are basically the same. The felt always travels at right angles to the axis of the guide roll, as shown in
FIGS. 2A and 2B
. The guide roll generally is pivoted on the backside and movable on the front, and is actuated by a paddle member or palm guide that presses against the felt. This palm senses felt position, and by varying air pressure or mechanical leverage, automatically adjusts the movable side of the guide roll. The felt will move toward the side of the guide roll that it strikes first.
In the process of bumping up speed and efficiency of the paper machine, dryer sections became hooded. Hooded dryers evolved to become completely enclosed dryers. The air temperature inside modern enclosed dryer sections on the. big high speed paper machines can reach well over 300 degrees.
Linked with massive gears and individually weighing many tons, the dryer cans spinning inside the dryer sections are filled with steam temperature of over 400 degrees. Special high temperature monofilament dryer fabrics carry the wet paper over and around the hot dryer cans exceeding 4000 fl/minute. More speed and more heat has caused more problems. Stopping a section of a high speed paper machine can be compared to stopping a fast moving, fully loaded freight train, except the train has a braking system. When a fabric or felt guiding arrangement fails or malfunctions, the fabric or felt can shift its path. Quickly, the felt can run off and into the frame of the machine and become tangled. By the time a section of a huge paper machine can be stopped, the results of any guiding failure or malfunction can be devastating, destructive, and expensive. Guiding failures can be avoided with careful visual observation and routine preventative maintenance. However, the cause of many fabric or felt guiding failure or malfunctions is often the design engineering flaws incorporated into the original auto palm guide.
The auto palm guide is a constantly moving air bleedoff monitoring device controlling the steering action of the fabric or felt guide roll on a paper machine. However, currently available auto palm guides have not evolved enough to meet the demands of the modern high speed paper machine. The high speed paper machine is now in an environment of dust and dirt, 300 degree plus heat, and high moisture. This environment is the enemy of sealed bearings and unlubricated parts in constant movement, such as in the known auto palm guides.
Currently, two types of guiding arrangements are in use on high speed, fine paper machines. One commonly used auto palm guide is a single bleedoff type which utilizes a tapered metal plunger as a bleedoff monitor, usually with a single rubber diaphragm actuating the guiding arrangement. The single bleedoff type of auto palm guide is commonly considered disposable. The use of this tapered plunger device dates back to the early 1950's and is still used as original equipment on machines made in the 1990's. This design has many unlubricated parts and an average life expectancy of about two to six years.
An original single bleedoff tapered plunger type auto palm guide, shown for example in
FIG. 3
, is a simple device. This type of guide is relatively problem free, except for the metal plunger getting dirty and sticking at the “palm in” position or the return spring breaking. The tapered plunger guide is considered disposable. The see-saw action of the plunger wears the round tapered hole of the plunger into an oval. The elongated hole will progressively leak more air.
After much use, the worn guide device can no longer build sufficient pressure in the guide diaphragm to push the guide roll out. Also at this point, the hole located at the top of the cast aluminum palm arm that connects the palm arm to the plunger will be worn excessively as will the palm arm pivotal bushings.
The second commonly used type of original equipment auto palm guide is a double bleedoff type, shown for example in
FIGS. 4A-4D
. The double bleedoff type is used with a twin bleedoff line diaphragm or a positioning cylinder type guiding arrangement. This type of auto palm guide is inherently more complicated, consisting of many more unlubricated moving parts. These parts include triple springs, twin ball and seats, adjustment pins, etc. Although double bleedoff type of devices are considered to be rebuildable, these units require frequent maintenance, and ar
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