Valves and valve actuation – Hermetic flexible wall seal for actuator – Bellows
Reexamination Certificate
2000-11-14
2002-05-28
Lee, Kevin (Department: 3754)
Valves and valve actuation
Hermetic flexible wall seal for actuator
Bellows
C251S061200, C251S061400, C251S282000
Reexamination Certificate
active
06394418
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an actuator for controlling the amount of fluid delivered through a valve arrangement, and more particularly, to an actuator for independently controlling the application of fluid (e.g. water, steam) in discrete zones across a papermaking machine.
BACKGROUND OF THE INVENTION
Paper Production
In the modern production of paper, a continuous fiber/water slurry is formed as a moving web. As the slurry moves down the paper machine the water is removed to leave the fiber which forms the paper sheet. The first section of the paper machine drains the water under the influence of gravity (on the fourdrinier table) and produces a web with sufficient strength to be self-supporting to feed it into a press section. The second section of the paper machine presses the paper web and squeezes the water from the sheet. This section typically consists of a series of rolls forming press nips between them through which the paper web is fed. After pressing removes all the water that it can, the remaining moisture in the web must be evaporated. The third section of the paper machine evaporates the remaining moisture in the paper web down to the final level desired for the grade of paper being produced.
During the production of paper it is important that a consistent quality be produced and maintained. Of the many paper parameters, the moisture content is probably the most basic. It is not only important that the overall moisture level be controlled, but also that the moisture distribution throughout the sheet be controlled both in the moving (machine) direction (MD) and in the width (cross-machine) direction (CD). Variation in moisture content of the sheet will often affect paper quality as much or more than the absolute moisture content. There are numerous influences on the paper machine that can cause variation of the moisture content; in particular in the cross machine direction. Wet edges and characteristic moisture profiles are common occurrences on paper machines. Thus a number of actuator systems have been developed to offer control of the moisture profile during paper production.
Conventional actuator systems for controlling the moisture profile across the sheet in paper machines work by selectively delivering steam or spraying water onto the paper web during production. If steam is used, it is added before the press nips with the effect of increasing the temperature of all of the moisture in the web. The added temperature makes the water removal by pressing much more effective; the added moisture removal being much greater than the added moisture of steam condensation. If water is sprayed onto the web, it is done in the evaporating section. The added water to the surface can be used to even out the moisture variance across the web. It can have the added effect of locally cooling the web to prevent damaging overheating. Water sprays are generally used for quality improvements while steam showers are used for both production and quality improvements.
Steam Shower Systems
Profiling steam showers deliver a variable distribution of steam in zones across the paper web. Each zone needs an independent actuator to control the volume of flow in that area. Traditionally the actuator used for such a zone control has controlled the steam flow rate by positioning a steam valve in response to a pneumatic signal. The pneumatic signal is varied, typically from 6 psig to 30 psig, to set an amount of valve opening. The pneumatic control portion of the actuator is separated from the steam valve portion.
In this invention a pneumatic signal is varied to directly control the steam pressure at discrete zones across the paper web. An orifice determines the steam flow from its controlled pressure chamber to the paper web area. This approach allows for a smaller actuator and a full shutoff design.
Moisture Spray Systems
Moisture spray actuator systems used in paper machines are designed to apply a profile of moisture spray in the cross-machine direction to counter an undesirable moisture profile in the paper web. Thus these systems consist of a series of actuator modules capable of independently adjusting the amount of spray in discrete adjacent zones in the cross-machine direction. Control of the flow at each zone is made from a logic decision off the machine via a signal sent to that zone position. How this signal is handled becomes an important consideration for such actuator systems.
The moisture spray systems used in paper machines are designed around spray nozzle characteristics. The nozzle is the device that breaks the water particles into a fine droplet size. These nozzles typically use either the hydraulic pressure of the water or use a separate air pressure line to produce the droplets. Other techniques may include such technologies as ultrasonics to produce droplets.
Hydraulic designs use the water pressure directly to break up the water droplets into a spray mist. Typically this technique is limited in how small a particle size it can produce. A change in flow rate affects the mist characteristics (particle size, spray pattern, etc.) of hydraulic nozzles reducing its turndown capability making these nozzles most effective at a single flow rate. These designs need accurately machined tiny openings that become subject to impurities in the feed water. Any partial plugging or blocking of a nozzle opening affects the volume flow as well as the spray pattern and causes the nozzle to lose its mist effect.
Pneumatic designs use compressed air to break up the water droplets into a spray mist. The mist is carried by the compressed air flow to the web surface. The nozzle openings for the water are not as critical to the spray pattern giving them a greater turndown capability. However it is typical that the average particle size will vary (increase) as the water flow is increased. Any partial plugging of the water nozzle opening affects the volume flow but often not the spray pattern. Both the water and air must be provided without impurities to maintain proper operation.
It is of particular interest to make a system that interfaces readily to a programmable logic controller (PLC) or computer. The conventional method of control for each zone has been to use multiple solenoid-operated valves. Each valve can be optimized for spray particle size at a particular water flow rate. Also, solenoid valves give reasonable assurance of 100% shutoff. These multiple valve groupings open the volume flow in a binary manner such that the first solenoid valve allows the minimum flow, the second solenoid valve allows twice the minimum flow, the third solenoid valve allows four times the minimum flow and so on. Thus 4 solenoids are used in combinations to give 16 discrete flow settings while 5 solenoids give 32 discrete flow settings. Nozzles are sized to optimize the spray pattern and particle size for the particular flow.
Locating the zone control solenoid actuators local to the spray nozzles (out over the paper machine) gives the most compact overall design. A common water header (and a common air header when pneumatic designs are used) supplies all zones. Typically a block encompassing the multiple solenoid-operated valves is mounted in each zone. Wiring is fed out to the individual on-machine solenoids. This approach has the disadvantage of placing the electrical solenoids in a very harsh environment. Failures of solenoids are frequent in the very hot and humid environment and replacement of solenoids can require an expensive paper machine shutdown.
Zone control solenoid actuators have, in some systems, been located off the machine with the water piped to the individual zones for spraying. These systems put the electrical solenoids in a controlled environment and give them accessibility. Pressure drops of water (and air) from the control cabinet to the machine zones must be addressed. The space required on the machine is about the same due to the tradeoff of solenoids for individual piping. However, the space required off the machine is greatly increased to accommodate the extra p
Duan Shizhong
Smith Douglas W. P.
ABB Inc.
Lee Kevin
Rickin Michael M.
LandOfFree
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