GB1562296A

GB1562296A - Paper-making machine stock supply system

Info

Publication number: GB1562296A
Application number: GB4424576A
Authority: GB
Original assignee: Beloit Corp; BOLOIT CORP
Current assignee: Beloit Corp; BOLOIT CORP
Priority date: 1975-10-29
Filing date: 1976-10-25
Publication date: 1980-03-12
Also published as: SU797598A3; DE2649458C3; JPS5527199B2; MX146729A; JPS5270104A; DE2649458B2; ES453229A2; PL117899B1; IT1074034B; DE2649458A1; CA1053047A

Description

(54) PAPER-MAKING MACHINE STOCK SUPPLY SYSTEM (71) We, BELOIT CORPORATION, a Corporation organised and existing under the laws of the State of Wisconsin, United States of America, of Beloit, Wisconsin 53511, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to improvements in paper-making machines, and more particularly to a stock supply system, for use in a paper machine headbox installation and located between a stock supply pump and a slice chamber, wherein sudden pressure changes or surges in the system are damped.

The invention provides modificaions and improvements to the invention described in our Patent Specification No. 1,533,865.

In commercial paper-making machines, the stock slurry is usually delivered from a fan pump under pressure through a supply system, through a headbox into a slice chamber, and out through a slice opening.

The supply system and the headbox are designed to give uniform flow characteristics across the entire width of the headbox and to avoid any local deviations or nonuniformities which are caused by nonuniform flow. One of the objectives is to avoid any nonuniformity which might be caused by sudden pressure changes or pulses in the stock flow. Such pressure pulses or surges are caused by normal hydraulic problems of operating machinery, and for example, are caused by normal vibrations or pulsations of the fan pump. They are also introduced by cleaners, screens, stock system resonances, valves and other structures which are required in the stock supply system which conducts the stock under pressure through the piping and headbox and through the slice opening onto a forming wire.Unless the surges and pulsations in pressure are reduced or eliminated, they can cause basis weight fluctuation, particularly in a machine direction (that is, in the direction of stock flow) and possibly in a crossmachine direction.

In a high speed commercial paper-making machine the phenomena of hydraulic surges and pressure fluctuations cannot be predicted by advance design. Furthermore, optimum operation with a minimum of hydraulic surge fluctuation can occur at one set of conditions where the machine is operating at a certain pressure and flow rate and with a certain type of stock, and with change in any one of the factors, surging or pulsation can begin occurring. It is therefore highly desirable to provide an arrangement which will automatically function to damp the pressure pulses which can occur and to achieve this damping over the wide range of operational circumstances expected during operation of a commercial machine.

It is accordingly an object of the present invention to provide a stock supply system which will maintain uniform pressure and which will attenuate pressure surges and fluctuations which occur during operation of the paper-making machine, so that substantially uniform pressure will be maintained in the pressurized stock flow from the stock supply system thus improving uniformity of paper web formation, According to the invention there is provided a paper-making machine stock supply system for conducting stock from a supply pump to a slice opening and including conduit means having an inlet for connection to the supply pump and an outlet for connection to the slice opening, characterised in that said conduit means include a stock flow chamber, and in that there is provided a pressure chamber for containing air under pressure, which chamber is separated from the stock flow chamber by a yieldable wall, means being provided for controlling the air pressure in said pressure chamber, whereby pressure fluctuations in the stock flow chamber will be absorbed by movement of said yield able wall.

Our above-mentioned Specification No.

1,533,865 describes and claims a headbox system in which a yieldable wall is disposed between a pressure chamber and a stock distribution chamber which is associated with a headbox leading to a slice opening.

In the modification according to the present invention, on the other hand, there is provided a structure for maintaining uniform pressure comprising conduit means which may be disposed anywhere in the stock supply system between the supply pumps and- the slice opening. The structure may therefore be readily introduced into an exist ing paper stock system with few changes in the design of the system.

The following is a more detailed description of one embodiment of the invention reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic side elevation of a portion of a paper-making machine stock supply system according to the invention; Figure 2 is a horizontal section taken substantially along the line II-II of Figure 1; Figure 3 is an enlarged fragmentary vertical section taken substantially along the line III-III of Figure 1; Figure 4 is an enlarged fragmentary vertical section taken substantially along the line IV-IV of Figure 2; Figure 5 is a plan view taken substantially along line V-V of Figure 1; and Figure 6 is a fragmentary vertical section taken substantially along the line VI-VI of Figure 5.

As illustrated in Figure 1, a stock supply system is provided for conducting stock from pressure stock supply 10, such as a fan pump to a headbox 12. The stock supply system includes conduit means indicated generally at 11, which comprises circular piping with the stock flowing through the interior at 20. Circular pipes lla and lib are fitted with intervening conversion piping sections 13 and 14 which convert the circular piping to a rectangular section for fitting a pulse attenuator housing 15 in place, and convert the section back to circular through the fitting 14.

The pulse attenuator housing 15 defines a chamber 17 therein, as shown in Figures 3 and 4. Because the housing may be formed of various structural framing pieces suitable for attachment to a rectangular section of piping, the details of the housing construction need not be described, and variations will be apparent to those versed in the art from the teachings contained herein.

The attenuator is arranged so that a flexible diaphragm 18 forms one wall of a rectangular chamber 21 through which the stock flows. The diaphragm 18 is rectangular in shape and forms the entire wall facing transversely of the direction of the stock flow. The diaphragm is backed over its entire surface by air under pressure and pulsations or surges in stock pressure are absorbed by the air backed diaphragm. The air is compressible, and forms a resilient overall support. Generally, fluctuations in pressure in the stock as it flows through the rectangular chamber 21 will be absorbed by the diaphragm 18, and if the stock pressure decreases, the diaphragm 18 will move toward the stock flow, and if the stock pressure increases, the diaphragm will move away from the stock flow to attenuate these pressure changes.For improving the attenuation function and avoiding fluttering or pulsation of the diaphragm, the air chamber 17 is divided into a first diaphragm support compartment 17a and a second supply com- partment 17b. These compartments are separated by an attenuator wall 19 which includes an attenuator felt which prevents surges of air between the two compartments.

The attenuator wall 19 can take different forms to permit passage of air between the compartments 17a and 17b, but prevent rapid surges therebetween. In the preferred form shown, the wall 19 is in the form of a felt 19a supported between perforate plates or screens 19b and 19c.

The screens are clamped between plates 23 and 24 which have circular holes 19d therein, as illustrated in Figures 2, 3 and 4.

Control of the attenuation of the flow of air between the compartments 17awl and 17b may be obtained by selecting plates with holes of a different size or by changing the character of the felt. However, a change in the attenuation effect during operation may be provided by furnishing plugs 24a which can fit into the holes, and the number of plugs which will be inserted will determine the overall open area between the compartments.

The diaphragm 18 is formed of a material such as rubber, suitably clamped at its edges to prevent leakage of air into the stock stream and leakage of stock into the air compartment. A clamping arrangement is shown at 25 at one edge in Figure 3, and an alternative form of clamping arrangement is shown at 26 at another edge in Figure 4.

Air is supplied to the air chamber 17 through a fitting at 29 (Figure 5) to maintain a continuous supply at a predetermined reference pressure. Normally a continual flow of air will be maintained in the chamber at a reference pressure, and excess air will be bled out from the chamber through an air release valve 30 (Figure 5).

Additional vents 27 and 28, Figure 5, may be provided having valves which may be quickly opened for quick discharge of air from the system should this become necessary.

The air release valve 30 is operated by the diaphragm 18, and for this purpose has an opening 32, as shown in Figure 6, which is normally just barely maintained in a closed position by the diaphragm resting against the opening 32.

A duplicate valve 31, identical to the valve 30, is provided in the air chamber, also controlled by the diaphragm, and may be connected to operate in parallel with the valve 30, if required, in order to have a second valve available for better control, and for a backup should one of the valves fail to operate correctly. Only the operation of the valve 30 will be described.

In operation, air will be introduced continually into the chamber 17 through the supply fitting 29 until the pressure in the air chamber equals the pressure in the stock flow chamber 21 on the other side of the diaphragm. At that point, the diaphragm is barely touching the valve head of the valve 30 to barely maintain the valve port 32 in a closed position. Any unintended excess pressure in the air chamber will tend to move the diaphragm away from the valve opening 32 to bleed the air out through the relief valve 30. The stem of the relief valve leads to atmosphere, passing through the wall 16 of the housing 15. Thus, equilibrium conditions and an equilibrium position of the diaphragm 18 is maintained during operation.

This permits the diaphragm to perform its intended purpose of reducing the air pressure rapidly within the chamber 17 when the fluid pressure in the stock flow chamber 21 suddenly drops. This maintains the flow rate and the pressure in the stock supply as constant as possible. Similarly, any surges and increases in pressure in the stock flow chamber 21 will distend the diaphragm forcing it toward the air chamber com- pressing the air therein so that the pressure surge is taken up by the diaphragm to maintain the stock supply pressure and stock flow rate as uniform as possible. Circular support members 35 of foam material are positioned above the diaphragm on the plate 23.

The air supply to the inlet fitting 29 is provided by suitable mechanism, not shown, which is provided with a controllable pressure regulator so that a constant supply of air is available which may be admitted only intermittently, but maintains a reference pressure based on the desired stock fluid flow pressure.

The air supply is constant only up to the reference pressure.

The principles of operation are also disclosed and described in our above-mentioned Patent Specification No, 1,533,865.

The arrangement described herein is a preferred construction wherein the attenuation of the stock flow pressure is maintained in a supply line elading from the fan pump 10 to the headbox 12, but the principles of the concept are also employed wherein the diaphragm support is utilized at other points in the stock supply system, such as the headbox itself, as described in Specification No. 1,533,865. In the arrangement disclosed herein wherein the attenuator is positioned in a section of the stock inlet pipe, restrictions are avoided which are imposed by having the attenuator integral wlith the headbox distributor as described in the above-mentioned specification. In that arrangement, the attenuator extended for the width of the machine. In the present arrangement the attenuator diaphragm extends for the full width of the flow, forming one complete wall of the rectangular flow chamber.An attenuator diaphragm of the order of 183 cm long may be used and will give the diaphragm sufficient exposure to the stock flow and provide a size of air chamber large enough to provide a desired amount of yield in the diaphragm. The quick and easier the diaphragm reacts to surge pressure pulsations, the more effective it will be. Yet, with the division of the air chamber into compartments and an attenuator arrangement between compartments so as to provide a relatively more shallow diaphragm support compartment, effective control of surges is attained without danger of introducing fluctuations due to air surges or flutter or unstable conditions.

With the present arrangement, a broad range of frequencies are attenuated, and these broadranges are encountered due to inherent requirements of the design of the paper machine stock supply pressure system.

A low mass, large area diaphragm accomplishes the attenuation and in combination with the damping of the flow of air between the compartments of the air chamber, it is wholly effective. The arrangement handles expeditously the surges caused by rotational frequency of a constant speed centrifugal pump which has heretofore been a problem.

Also, the only moving part, which is the attenuating diaphragm, is smooth and forms a portion of the stock flow chamber wall so that no projections or recesses are formed which would - tend to adversely affect the stock flow and cause fibres to gather.

The operating valve parts are exposed only to air and thus, do not need servicing or cleaning. It has been found that the structure meets the objectives and advantages above set forth and solves problems encountered in existing and newly designed paper machine stock distribution systems.

The surges and fluctuations in pressure which are in part in the form of compressional waves have been a problem in reduction of quality of the web formed. With the elimination of these compressional waves, more uniform basis weight formation can be achieved and improved fibre distribution and reduction of flocculation result. Elmination of compressional waves eliminates variations in velocities, and therefore, ensures a more uniform product.

WHAT WE CLAIM IS: 1. A paper-making machine stock supply system for conducting stock from a supply pump to a slice opening and including conduit means having an inlet for connection to the supply pump and an outlet for connection to the slice opening, characterised in that said conduit means include a stock flow chamber, and in that there is provided a presure chamber, for containing air under presure, which chamber is separated from the stock flow chamber by a yieldable wall, means being provided for controlling the air pressure chamber, for containing air under pressure, which chamber is separated from ber will be absorbed by movement of said yieldable wall.

2. A paper-making machine stock supply system according to claim 1 characterised in that said stock flow chamber is rectangular in cross-section and said yieldable wall extends the full width of said stock flow chamber tranversely of the direction of flow of stock through said chamber.

3. A paper-making machine stock supply system according to claim 1 or claim 2 characterised in that said yieldable wall comprises a flexible diaphragm.

4. A paper-making machine stock supply system according to any of claims 1 to 3 characterised in that said means for controlling air pressure in the pressure chamber include an inlet port for connection to means for supplying air under pressure to said pressure chamber, an air valve for releasing air from the pressure chamber, and means for operating the air valve in response to changes in pressure in the stock flow chamber.

5. A paper-making machine stock supply system according to claim 4 characterised in that said air valve includes a port controlled by movement of said yieldable wall so that movement of the wall due to increase in pressure in the stock flow chamber restricts air flow through said port, and movement of the wall due to decrease in pressure in the stock flow chamber increases the air flow through said port.

6. A paper-making machine stock supply system according to claim 5 characterised in that a part of the yieldable wall cooperates directly with said valve port so that increase in pressure in the stock flow chamber moves said part of the wall towards the valve port to restrict flow of air therethrough.

7. A paper-making machine stock supply system according to any of claims 4 to 6 characterised in that there is provided a second air valve for releasing air from the pressure chamber in response to changes in pressure in the stock flow chamber.

8. A paper-making machine stock supply system according to any of claims 1 to 7 characterised in that said pressure chamber comprises a support compartment exposed to said yieldable wall, and a supply compartment for connection to a source of air under pressure, and damping means restricting air flow between said compartments so as to damp movement of the yieldable wall.

9. A paper-making machine stock supply system according to claim 8 characterised in - that said damping means comprise a plate separating said compartments with opening through said plate and air flow damping material across said openings.

10. A paper-making machine stock supply system according to claim 9 characterised in that there are provided removable plug means for selectively closing said openings.

11. A paper-making machine stock supply system according to any of claims 1 to 10 in combination with a stock supply pump connected to the- inlet of the conduit means for delivering a continuous flow of stock under pressure therethrough, and a slice chamber connected to the outlet of the conduit means and leading to a slice opening.

12. A paper-making machine stock supply system according to any of claims 1 to 11 in combination with means for continually delivering air under pressure to said pressure chamber.

13. A paper-making machine stock supply system substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. above set forth and solves problems encountered in existing and newly designed paper machine stock distribution systems. The surges and fluctuations in pressure which are in part in the form of compressional waves have been a problem in reduction of quality of the web formed. With the elimination of these compressional waves, more uniform basis weight formation can be achieved and improved fibre distribution and reduction of flocculation result. Elmination of compressional waves eliminates variations in velocities, and therefore, ensures a more uniform product. WHAT WE CLAIM IS:

1. A paper-making machine stock supply system for conducting stock from a supply pump to a slice opening and including conduit means having an inlet for connection to the supply pump and an outlet for connection to the slice opening, characterised in that said conduit means include a stock flow chamber, and in that there is provided a presure chamber, for containing air under presure, which chamber is separated from the stock flow chamber by a yieldable wall, means being provided for controlling the air pressure chamber, for containing air under pressure, which chamber is separated from ber will be absorbed by movement of said yieldable wall.