US3077924A

US3077924A - Paper making system

Info

Publication number: US3077924A
Application number: US654194A
Authority: US
Inventors: George Garnet M Eastwood
Original assignee: Spruce Falls Power and Paper Co Ltd
Current assignee: Spruce Falls Power and Paper Co Ltd
Priority date: 1957-04-22
Filing date: 1957-04-22
Publication date: 1963-02-19
Anticipated expiration: 1980-02-19

Description

Feb. 19, 1963 a. s. M. EASTWOOD 24 PAPER MAKING SYSTEM I 3 Sheets-Sheet 1 Filed April 22. 1957 \Q uw G. G. M. EASTWOOD 3,077,924

PAPER MAKING SYSTEM Feb. 19, 1963 5 Sheets-Sheet 2 Filed April 22, 1957 \N .w mm mm mm kw MNN w 1 9 R m m 3 mmw km \W. NW 5 km whw MS he \Q o \Q Q9 1963 e. s. M. EASTWOOD 3,077,924

PAPER MAKING SYSTEM 3 Sheets-Sheet 3 Filed April 22, 1957 ilnited. tates Fatent 3,677,924 PAPR MAKENG SYSTEM George Garnet M. Eastwood, Neenah, Win, assign-or to Spruce Falls lower a haper (30., Ltd, Toronto, Gutario, Qanada, a corporation of Canada Filed 22, l5i, Ser. No. 654,194 6 Claims. (lCl. l62259) The present invention relates to a system for controlling the application of a furnish of cellulosic fibers to the Fourdrinier wire of a papermaking or like machine. More particularly, the invention pertains to means for automatically correlating the Fourdrinier wire speed with the velocity at which the furnish is applied to the wire in a papermaking operation.

In a Fourdrinier paparmaking operation, a dilute suspension of cellulosic fibers and in some instances fillers, which is called a furnish, is applied to the surface of a moving endless wire screen which is called a Fourdrinier wire by means of a head box or other suitable distributing means. As the wire moves from the point at which the furnish is applied thereto, the water drains from the portion of the pulp which has been retained by the wire. When the resulting web on the wire has been sufiiciently drained, it is transferred to a moving felt or similar belt and thereafter to a suitable drying apparatus which usually includes rolls, to reduce the moisture content of the resulting web to the desired level. The speed of the Fourdrinier wire and the speed of the felts and drying rolls are correlated in operation so as to provide the proper tension or draw on the web between the various machine elements, the proper draw or tension varying for papers having difierent basis weights and different characteristics.

In the known papermaking machines, the control of the so-called wet end of the machine, i.e., the Fourdrinier wire and head box, is effected manually by the operator of the machine who controls the rate or delivery of the furnish to the wire and the speed of the wire in response to certain observations and measurements which are made from time to time upon the finished paper and upon the stock on the wire. While this procedure involving manual control has been used for many years, it has not been entirely satisfactory as evidenced by the difiiculties encountered in day-to-day operation with even a highly experienced papermaking crew.

In most papermaking operations there are a number of breaks in the Web each day. For example, in a mill making newsprint at moderate speeds there may be an average of 8 to 10 breaks each day. In the case of book-paper as many as 35 or more breaks may occur. While a few of the breaks may be attributed in some instances to changes in furnish, most breaks in the Web may be attributed to the fact that the amount of furnish supplied to the wire is not the proper amount for the wire speed being employed. Each of the breaks in the web is extremely costly because of the labor and lost production involved. For example, starting a papermaking machine after a break requires from about -20 minutes Work for the full crew of the machine; this compares with a period of from about 30-40 minutes to initially start-up the machine after it has been shut-down completely for a vacation or clean-up period. During the start-up tirne after a break no usable paper is pro duced which results in a large loss in production. Also, the large quantites of paper which are produced during any start-up period must be reworked because of the fiaws in the paper occasioned by feeding the sheet or web through the equipment and this occasions a considerable loss. Moreover, in the case of a break during operation, the partial rolls or" finished paper which are on the take up roll of the machine at the time the break occurs must be handled separately because they include odd lengths. In the case of all breaks in the web, the machine may get out of balance, the drier temperatures may rise unduly, the pulp supply becomes loaded with broke, and in short, the machine and its auxiliary equipment all require extensive adjustment.

It would appear at first glance that it should be a simple matter to control a papermaking machine by getting it up to any given speed and then locking the controls on the wire drive, stock pump, etc. after optimum operation is obtained. In actual practice, however, control of the wet end of a papermaking machine to minimize break-s is extremely difficult to accomplish because of various factors. Even the slight normal variations in line voltage on the electrical drive motors for the Fourdrinier wire and other electrical variations will result in a cyclic variation in the speed :of the Fourdrinier wire of from 40 to 60 feet per minute or even more when the wire is operating in the range of from about 1000 to 1500 feet per minute, and even greater speed variations occur when operating at higher speeds.

It can be readily seen that an increase in speed of this magnitude tends to attenuate the furnish supply to the wire and if the machine is running close to a critical limit the Web will be so weakened that it will break. In any event, an increase in wire speed without a corresponding increase in the volume and the velocity of furnish delivered to the Wire will reduce the thickness of the sheet. Conversely, if the wire slows down, the sheet being formed will become heavier with a consequent loss in uniformity and the possibility of causing difliculty in subsequent operations unless the furnish supply and velocity is decreased with the decrease in speed of the wire. Also, non-uniform operation occurs in the fan pump in the stock supply system and in various other or" the driving units with similar consequences.

Changes of wire speed without efiecting a corresponding change in the volume and velocity of furnish delivered to the wire also has a serious effect upon the fiber lay or formation which, in turn, changes the appearance of the sheet and its finish. The printing trade requires sheets which have strength and uniformity and it has been found that sheets which have non-uniform fiber lay as is caused by uncompensated speed variations, are diflicult to handle during printing and especially when they are employed in special-elfect work.

Accordingly, it is the principal object of this invention to provide a control system and a method of control adapted to be applied tothe operation of the wet end of a Fourdrinier papermaking or like machine so as to minimize breaks thereby increasing the daily output of the machine. It is a further object of this invention to provide a method of control and a control system which will increase the uniformity and quality or" the web being formed. Other objects and advantages of the invention will become apparent by reference to the accompanying drawing and the following description.

in the drawing:

FIG. 1 shows in diagrammatic form a papermaking system which embodies various of the features of the invention; and,

FIGS. 2 and 3 are diagrams respectively showing modifications of the papermaking system.

Like characters of reference designate like parts in the several views.

In general, the control of the papermaking machine is effected by the linking together by a control system or" a measurable element which is related to and which varies with the velocity of the furnish at the point that it is ap plied to the wire, and a measurable elementwhich is related to and which varies with the wire speed. The control system in response to these two measurable elements may be made operable to automatically change speeds,

velocities, etc., so that substantially the optimum rate of delivery of furnish to the wire is accomplished for any wire speed desired or the optimum wire speed is automatically provided for any desired rate of furnish delivery or velocity. With this system, a variation in or the manual control of either the wire speed or the velocityof the furnish atfthe point at which it is applied to the wirecan automatically adjust the. other element to the optimum value.

Basically, the control of the papermaking system isettected by converting an element which is related to and which varies with the velocity of thestock at the point it is applied to the wire into a control signal, and anVelement which is related to and which varies with wire speedto another control signal.- The two control signals ,gener,

ated by the wire speed and the stock velocity or a function of the two signals is then applied to a controller means in either the furnish supply system or the wire speed sys-;

tem to cause the two generated control signals to be auto matically brought into a predetermined relationship atwhich pointanoptimum furnish delivery rate. or velocity will be insured for the given speed.

In the embodiment of the invention illustrated in FIG. 1", a control system ofttheclass described is shown in co'nnectionwith a Fo'urdr'inier papermaking machine'of conventional construction. The machine, whose main parts:

are schematically illustrated, includes an endless formingscreen or Wire 3 which is'supported upon a breast roll 5 and a couch roll 7 which are located at opposite ends of n sump in which the furnish and water are collected to be recycled in the stock system as will hereinafter appear.

The furnish is supplied to the wire 3 adjacent the breast roll 5 in the conventional manner through a headbox 13 which in the illustrated embodiment is of the open or non-pressure type, i.e., the furnish flows onto the wire? under the action of the head of furnish in the head box 13, However, the control system of the invention is equally applicable to any head box of the spouting type which may be of the gravity head type as described above or the type which employs an air pad to enhance the actual head so as to obtain higher spouting velocities.

The furnish is continuously circulated from the sump in the wire pit it to the head box 13 by a conventional furnish supply system which includes a suitable fan-type or other pump 15 for circulating the furnish or stock. The fan pump 15 is connected to the sump at the bottom of the wire pit 11 by means of a suitable set of conduits represented schematically by the conduit 17, and to the head box 13 by means of a suitable set of conduits represented schematically by the conduit 19. The system also includes means for introducing make-up furnish continuously into the furnish system, the means and equipment for accomplishing this being well known in the art and being shown, for example, in FIG. 122, page 208, in the book Pulp and Paper Manufacture, volume 4, Auxiliary Paper Mill Equipment (1. N. Stephenson, Editor-in-Chief), McGraw-Hill, 1955. Such makeup furnish supply means and equipment includes a stock supply conduit A connected to the conduit 17 and having a valve B in the conduit A. Also, suitable screens (not shown) may be provided intermediate the, fan pumplS and the head box 13 as is usual in an open head box type construction and in some machines there may be provided a flow spreader.

As has been indicated previously, means are'provided in a Fourdrinier machinefor driving the Fourdrinicr wire at variable speeds. In the illustrated embodiment, the

couch roll 7 is driven by an electric motor 21 which is connected by" means of a shaft 23 to the couch roll 7. The speed of the motor 2 1 is controlled by a motor speed controller 25 which may be either manually or automatically controlled as will be hereinafter described. The motor controller "25 is connected to the motor 21 and to a suitable source of electrical power by means of

suitable conduits

27 and 29, respectively. The driving means for the couch roll 7 which has been described, is but one of several driving means which may be employed, and as will be seen from the subsequent description, the exact rnannerof rotating the roll 7 or for effecting the movementof the wire 3 from the head box 13 to the couch roll 7 is not a critical feature of this invention. Various otherdriving; arrangements known to the art maybe employed, e-.g.-, a constant speed motorwith a variable speed r v tc.

Means are also provided in thesys-tem for controlling I therate of delivery ofthe furnish to the head box. In

3 volume of furnishflowing to the head box.

the illustrated system this is accomplishedby providing the fan pump 15 with a driving motor 31, which is controlled by a suitable rnotor controller 33. The motor controller isconnected to the-motor 31 anclto asuitable source of electrical power by means of conduits- 35 and 37;,respective'ly; Instead of this arrangement, a constant speed pump may be employed and a control valve 39 may beintroduced into the conduit 19 to control the Either of these control methods may be employed or in some instances a bypass system may be employed wherein a portion of the furnish from the fan pump is recycled to a point in the system ahead of the fan pump.

The control system illustrated in FIG. 1 includes a signal producing unit 41 which is responsive to the wire speed so as to provide a signal which is related to the wire-speed; a signal producing unit 43 which is responsive to the head of furnish in the head box 13 which is one ,measure of the velocity of the furnish at the point that itis applied to the wire' 3; and a controller 45 which is connected to and adapted to be operated by the signal producing units 41 and 43 so as to control one or more of the

drive motor controllers

25 and 33 and the valve 39.

vThe illustrated system is preferably a pneumatic-mewith suitable moisture-proofing, an electrical system or an electrical-mechanical system may be employed instead of the pneumatic-mechanical system which is illustrated and suitable electrical units having equivalent functions may be employed in place of the pneumatic-mechanical units which will be described.

As has been pointed out, the papermaking machine. illustrated includes anopen head box 13. It has been determined that the optimum operation of an open head box machine is obtained when the speed of the wire 3 is approximately the same as the spouting velocity of the furnish as it leaves the head box 13. The spouting velocity is shown by the formula:

where:

v is the spouting velocity in feet per second g is the acceleration constant 32.2 feet per second It is head in feet When thisis converted to the units used in papermalting, i.e., velocity in feet per minute and head in inchesv (ft. min.) 93 tnehes 13 so thatla'measure of head which is a convenient-.varia.-

ble to measure will reflect the square of the velocity as expressed by the formula p (ft./min.) 19320 The control aspects of the relationship, if head is to be used as a measure of spouting velocity which is to be correlated with wire speed, are simplified when one of the signal units d1 or if; is adapted to either square or to abstract the square root of its measured variable as appropriate, in accordance with the foregoing formula.

We have found that it is convenient to have the control signal from the signal unit as which measures the speed of the wire 3 produce a signal which varies as the square of wire speed so that this squared signal may be compared directly with the end signal produced by the signal unit 43. Of course, if another variable in the system is employed as a measure of furnish velocity, it may not be necessary to either square or abstract the square root of that variable, depending upon the nature of the signal which is the measure of the other variable in the system.

Preferably, the signal producing unit 41 is a pneumatic speed transmitter of the pneumatic force-balance type. A transmitter of this type may be of conventional construction and include a fly ball governor arrangement which controls a pneumatic valve so as to transmit a pressure signal which varies as the square of the speed. The pneumatic valve in the unit opens until the pneumatic pressure transmitted equals the pull of the rotating fiy balls. The details of such transmitters are known in the art so that the working details thereof are not shown in the drawings. in the illustrated structure a speed input shaft 47 in the pneumatic speed transmitter 41 is operatively connected by means of a sprocket and chain drive to the drive shaft 23 between the couch roll '7 and the driving motor 21. The sprocket and chain drive 49 includes a sprocket 51 in the input shaft 47, a sprocket 53 in the drive shaft 23, and a chain 55 connecting the two sprockets. The drive 49 thus provides a positive drive connection between the shaft 23 and the speed transmitter input shaft 47. While a chain and sprocket drive connection is shown, the drive connection may be effected by any suitable mechanical drive arrangement.

Pressure air at the desired pressure for forming the transmitted pressure signal is supplied through an air supply pipe 57 which is connected to a suitable source of pressure air (not shown}. The air supply pipe 57 preferably includes an air cleaner assembly 5%, a shut-01f valve 61, and a pressure-regulating valve 63 so that the pressure supplied to the pneumatic speed transmitter 41 is at the proper pressure for producing a transmitted signal in the desired range and is free from objectionable moisture, oil, and dirt so as to insure efficient operation of the system. The pneumatic signal which varies as the square of the speed is transmitted to the controller 45 and to one pen of a two pen continuous recording pressure indicator 65 by means of a conduit 67, as illustrated.

As has been indicated heretofore, the velocity of the furnish at the point that it is applied to the wire 3, is determined by the head of furnish in the open head box 13. Measurement of the head is accomplished by a pres sure-sensing element 6% which is located inside of the head box 13 and positioned adjacent the lower portion thereof so as to be responsive to the head of furnish in the box. Various types of pressure-sensing devices may be provided as the sensing element 69. For example, the element 69 may take the form of a pressure sensitive diaphragm, a liquid column, or a bubble tube arrangement which is adapted to supply a measured amount of air through a tube one end of which is open adjacent the bottom of the head box, the head bein measured by the pressure required to force the measured amount of air through the tube. Regardless of what type of pressure sensing element 69' is employed, it is connected to the signal producing unit 4-3 by means of a suitable conduit 71.. The signal producing unit 43 in the illustrated system may desirably comprise a simple pneumatic pressure transmitter which converts the pressure head in the head box 33 to a pneumatic signal pressure which bears direct proportion to the head in the head box 13. The transmitted pressure should be of such magnitude that the head signal provided will be at the proper range to be compared with the signal producing unit 41 which transmits a signal proportioned to the square of the speed of the Wire 3. In the event that a unit ll is employed which transmits a signal which is directly proportional to the speed of the wire 3, the signal producing unit 43 should be of the type which transmits a signal proportional to the square root of the head in the head box 13.

Pressure air for the pneumatic pressure transmitter 43 is supplied by a suitable air supply pipe '73 which is connected to a suitable source of pressure air (not shown). The air supply pipe preferably includes an air cleaner 75, a shut-off valve 77, and a pressure regulating valve 79, so as to provide clean air at the proper pressures for supplying the signal from the unit 43. The signal from the unit 43 which is proportional to the head in the head box 13 and thereby proportional to the square of the spouting velocity as previously indicated, is transmitted through conduits $1 to the second pen of the continuous indicator 65 and to the controller 45.

Instead of measuring head, other variables in the furnish supply system which reflect the velocity or the furnish at the point it is applied to the wire may be employed to monitor the pneumatic transmitter unit 43 so as to provide a signal which is proportional to the velocity of the furnish or a function thereof. For example, a set of pressure taps may be employed in the conduit 19 from the fan pump so as to determine the velocity in the conduit and thereby the volume of furnish being supplied to the head box or if the efiiciency curve of the fan pump 1'5 is known, a speed transmitter may be connected to the pump to provide an indication of the volume being pumped. Furnish velocity at the head box outlet at the point the furnish is applied to the wire will then be determined by the area of the head box outlet. Of course, the area of the head box outlet must be maintained constant if the pressure drops in the conduit 19 or the fan pump speed are to be employed as a measure of velocity since an increase or decrease in head box outlet area with a given flow will produce a velocity change which varies inversely with the change in area.

The controller 45 in the illustrated pneumatic mechanical system is preferably what is known as a two-pressure controller. This type of controller receives two transmitted sign-a1 air pressures and responds to differences between the two signal pressures by diaphragm movements to supply a machine control air supply of varying pressure on either side of a control point. The control air supply is operable to adjust the motor drives or valves to bring the furnish velocity and speed of the wire into equilibrium which will balance the two pressures which are received by the controller. If electrical control means are employed, a suitable electrical controller may be used which has the same function.

in the illustrated apparatus, the pressure air signal transmitted by the pneumatic transmitter 43 is carried through the conduit 61 to one signal receiving inlet of the controller 45. The pressure air signal from the pneumatic speed transmitter 41 is conducted to the other signal receiving inlet of the two-pressure controller 46 by means of a conduit 83a, 8312 which is connected to the conduit 67.

In order to permit a controlled variation between the theoretical relationship wherein the furnish velocity equals the speed of the wire, so that various furnish conditions, velocity ratios, and the like can be better accommodated, it is desirable to provide means for varying the automatic, mathematical correlation between the furnish velocity and the wire Speed. In the illustrated system, a biasing pneumatic pressure relay 85 is provided between the sec-- tious 83a and 83b of the conduit which carries the speed signal to the controller 45, so as to enable an operator to vary the set point somewhat from the theoretical furnish velocity required for a given wire speed or the theoretical wire speed for a given furnish velocity. A. suitable type of pneumatic biasing control 85 is what is known as an addition-subtraction pneumatic relay. This type of relay transmits through its outlet a pressure which is equal to the pressure received at its inlet conduit plus or minus a given pressure. This is accomplished by a pneumatic force-balance system in the relay. Pressure air for addition to the pressure transmitted through the conduit is fed to the relay by an air supply system which includes an air inlet pipe 87 which is connected to a suitable source of pressure air (not shown) and which includes an air cleaner 89, a shut-oil valve 1, and a pressure regulating valve 93 which is adapted to supply clean air for the desired pressure range of operation. An-exhaust conduit 95 is also provided from the relay unit 35' for exhausting air from the relay in the event that the pressure is to be lowered by a given value. In order that anoperator may see what biasing action is being accomplished by the relay 85, a pressure gauge 97 is connected between the conduits 83a and 83b around the relay 8% so that biasing setting of the relay may be readily determined. Under some conditions it may be desirable to provide a biasing control 85 which will multiply the received signal pressure by a desired factor. In any event, the biasing control 85 can be adjusted to compensate for the variables in the system such as changed in the coefilcients of discharge at the slice, wire slip or creeping, and to control the fiber lay and characteristics of the web.

Pressure air for providing a machine control air supply is conducted into the two-pressure controller 45 by means of an air supply pipe 1 51 which includes an air cleaner 1&3, a shut-oil valve H95, and a pressure-regulating valve 3&7. The outlet for the machine control air may be connected as is illustrated in PEG. 1 to the stock supply valve 39 by a conduit 169 whereby the volume of stock flowing to the head box 13 may be increased or decreased to efiect a variation in furnish velocity as required by the speed of the wire 3 in response to changes in pressure in the control air supplied to the valve 39. Similarly, a valve (not shown) could be controlled to vary the amount of stock recycled through the fan pump to accomplish the same result. In the alternative, referring to FIG. 2, the machine control air may be used to control the speed of the tan pump 15 and in this instance, the outlet of the controller is connected to the fan pump speed control 33 by a con duit 1659 to increase or decrease the speed of the fan pump 15 so as to vary the level of the stock in the head box thereby bringing the signals transmitted by the signal producing units 41 and 43 into a given predetermined relationship. Another way to control the paper making machine, referring to FIG. 3, is to connect the machine control air to the wire drive control 25 by a conduit 109" so as to effect an increase or decrease in wire speed in response to variations in furnish velocity.

When the valve 39 in the stock control system is automatically controlled to correlate stock velocity and wire speed, the control system and the paper making machine are operated in the following manner. Wire speed is 0011 trolled manually on the motor control 2.5 by the operator as desired. The rotation of the drive shaft 23 effects a corresponding rotation of the input shaft 47 on the pneu matic speed transmitter 41. Rotation of the speed transmitter input shaft causes the operation of the signal control valve in the unit 41 to supply pressure air at a pressure which is proportional to a factor of the speed of the wire 3'.

One convenient range of pressure signals correlates wire speed from 0 feet per minute to 1000 feet per minute with air pressures varying from 3 to 15 pounds per square inch, the pressure increments with increased speeds in the given range varying as the square of the speed increases. For example, a speed of 0 feet per minute will provide a base pressure of 3 p.s.i.; a speed of 200 f.p.m. will provide a signal of approximately .5 psi. above the base pressure or a total signal pressure of about 3.5 p.s.i.; a speed ot-400 tpm. will provide a signal or approximately 2.0 p.s.i. above the base pressure or a total signal pressure of about 5.0 p.s.i.; and a speed or" 800 f.p.m. will provide a signal of approximately 3.0 psi. above the base pressure or a total of about 11.0 psi.

if it is desired to magnify the control signal the operating speed range of the machine may be solely employed to produce the signal. For example, if the machine operates at a speed between 1,000 and 1,200 f.p.m. the base pressure can be 3 psi. at 1,000 f.p.m. and the signal pressure can be increased as the square of the speed.

The wirespeed pressure signal is transmitted to one inletot thecontroller 45 through the pipes 67, 83a and 83b and to'the recorder 65 through the pipe 67 where it is balanced with the furnish velocity signal as will hereinafter appear;

The furnish supply system is adjusted by setting the speed of the fan pump 15 with the motor controller 33 so that it is capable of supplying all of the furnish necessary for the desired wire speeds, and as has been pointed out, the flow of furnish is controlled by the valve 39 which is preferably pneumatically controlled when a pneumaticmechanical system is employed. Measure of the head of furnish in the head box 13 is accomplished by the sensing device 69 whose signal is transmitted to the pneumatic transmitter unit 43 through the conduit '71. The pressures transmitted by the unit 43 are correlated with the pressures transmitted by the unit 41 so that the pressure signals may be more readily compared by the controller 45. With the speeds referred to in connection with the speed transmitter 41 and the signal pressures which have been referred to, it has been found convenient to have a head pressure from 0 to 50 inches of furnish supply a signal of from 3 to 15 p.s.i., the transmitted signal varying directly with the variation in head. For example, 0 inches of head will transmit a base pressure of 3 p.s.i., and each 10 inch increment in head serving to increase the base pressure by about 2.4 psi. The head pressure signal can be amplified by starting with a base pressure in the operating range of the machine, as has been outlined in connection with the speed signal.

The head signal which is proportional to the square of the spouting velocity of the furnish from the head box is transmitted to the second inlet of the controller 45 and to the recorder 65 by a conduit 81.

In the controller 45 any dillerence in pressure between signals from the units 41 and 43 is operable to vary the pressure in the line ltl by connecting it to the air supply pipe 101 or to'exhaust air from the pipe 199. The air in line 109 is operable to change the opening of valve 39 thereby bringing the level of furnish in head box 13 to a point where the transmitted signal from the unit 43 is equal to the signal from the unit 41 at which point the controller 15 is operable to stabilize the air pressure in line it to hold the valve 39 at the desired opening.

In operating a system of this type, all that an operator need do is to manually control the speed of the wire and the proper velocity of furnish is automatically supplied. When it is desired to hold a difference between the velocity of furnish and the speed of the wire, the biasing relay may be employed to raise or lower the pressure of the signal transmitted by the unit 41 enough to provide the desired amount of dilference between furnish velocity and the wire speed so as to vary the characteristics of the web.

It has been found that in operation a unit controlled in the manner which has been described, may be started in initial operation in a period of about 6 minutes as compared to the ordinary 30 to 40 minute period which is required to start the machine. Moreover, in daily operation the number of breaks in the web are reduced by the automatic correlation of furnish velocity and speed to a small fraction of'those' occurring prior to the time automatic correlation was instituted. Obviously, the amount of breaks or material to be reworked is substantially reduced. It will be seen that this will result in considerable economy in a papermaking operation.

As an alternative means of control, the control air from the controller 45 may be conducted to the control unit for the fan pump instead of the valve 39 (see FIG. 2). In this instance, the fan pump is operated at varying speeds to supply the varying head required for the various speeds instead of operating the fan pump at a con stant speed as described in the previous mode of operation. In this instance, the pressure air is conducted to the controller 33 by means of the conduit 109 instead of through the pipe 109.

Similarly, if it is more convenient to have the furnish velocity govern the operation of the Fourdrinier section, the furnish level may be controlled manually by adjusting the fan pump motor controller 33. In this instance, the air output controller 45 is conducted through the pipe 109" to the wire drive motor controller 25 (see FIG. 3) so as to etfect automatic speed control of that unit in response to manually controlled variations in the furnish velocity.

In the foregoing there has been described a control system and method of control which is effective to markedly reduce operating costs on a papermaking machine and to increase the uniformity of the product. These economies and increases in quality result from the automatic delivery of the right amount of furnish at the proper velocity for application to the Wire so as to effectively control the thickness of the web formed with a consequent reduction in the number of breaks in the web. While the system described in detail has been described as a pneumatic system because of the inherent difliculties in waterproofing an electrical system, electrical components may be readily substituted for the pneumatic-mechanical components which have been described with no appreciable change in the operating characteristics of the control system.

I claim:

1. In a machine for making a Web of sheet material, a movably supported web forming screen, a screen pit into which the liquid draining from a web formed on said screen may drain, a first mechanism for driving said screen, a head box for spouting a mixture of makeup furnish and said liquid onto said screen in the direction of screen movement, a second mechanism for pumping said liquid to said head box from said pit and connected to a supply of makeup furnish to provide said mixture in the head box, a sensing device sensing changes in the velocity of said mixture spouting from said head box onto said screen, a sensing device sensing changes in speed of said screen, and control means operable to control one of said mechanisms and under the control of both of said sensing devices so as to correlate the rate of supply of said liquid to said head box and thereby the velocity of said mixture spouting from said head box onto said screen with the speed of the screen.

2. In a machine for making a web of sheet material, an endless forming screen, a plurality of rolls for movably mounting said screen, a screen pit into which liquid draining from a web formed on said screen may drain, a first mechanism for driving one of said rolls to thereby drive said screen, a head box adapted to spout a mixture of makeup furnish and said liquid onto said screen in the direction of screen movement, a second mechanism for pumping said liquid to said head box from said pit and connected to a supply of makeup furnish to provide said mixture in the head box a sensing device sensing changes in the head of said mixture within said head box,

a sensing device sensing changes in speed of said screen, and control means operable on said second mechanism and under the control of both of said sensing devices so as to change the rate at which said liquid is supplied to said head box and thereby change the velocity of said mixture spouting from said head box onto said screen with changes in speed of the screen.

3. In a machine for making a web of sheet material, a movably supported web forming screen, a screen pit into which the liquid draining from a web formed on said screen may drain, a head box for spouting a mixture of make up furnish and said liquid onto said screen in the direction of screen movement, a system for transferring liquid from said pit to said head box and connected to a supply of makeup furnish to provide said mixture in the headbox and including a pump hydraulically connected to said pit and head box, means for controlling the output of said pump, a sensing device sensing changes in the head of said mixture within said head box, a sensing device sensing changes in speed of said screen, and means operable on said pump controlling means and under the control of both of said sensing devices so as to change the rate at which said liquid is supplied to said headbox and thereby change the velocity of said mixture spouted onto said screen With changes in speed of the screen.

4. In a machine for making a web of sheet material, a movably supported web forming screen, mechanism for driving said screen, a screen pit into which the liquid draining from a web formed on the screen may drain, a head box for spouting a mixture of makeup furnish and said liquid onto the screen in the direction of screen movement, a system for transferring said liquid from said screen pit to said head box and connected to a supply of makeup furnish to provide said mixture in the headbox and including a pump hydraulically connected to said pit and head box, means for driving said pump at variable speeds so as to change the pump output, a sensing device sensing changes in the head of said mixture within said head box, asensing device sensing changes in speed of the screen, and a control means operable on said pump driving means and under the control of both of said sensing devices so as to change the rate at which said liquid is supplied to said head box and thereby change the velocity of said mixture spouted onto said screen with changes in speed of the screen.

5. In a machine for making a web of sheet material, a movably supported web forming screen, mechanism for driving said screen, a screen pit into which the liquid draining from a web formed on said screen may drain, a head box for spouting a mixture of makeup furnish and said liquid onto said screen in the direction of screen movement, a system for transferring liquid from said screen pit to said head box and connected to a supply of makeup furnish to provide said mixture in the headbox and including a pump hydraulically connected to said pit and head box, a valve for controlling the output of said pump, a sensing device sensing changes in head of said mixture within said head box, a sensing device sensing changes in speed of said screen, and a control means operable on said valve and under the control of both of said sensing devices so as to change the opening or" the valve and change the velocity of said mixture spouted from said headbox onto said screen with changes in speed of the screen.

6. In a machine for making a web of sheet material, an endless web forming screen, a screen pit into which liquid draining from a web formed on said screen may drain, a plurality of rolls for movably mounting said screen, a first mechanism for driving one of said rolls for thereby driving said screen, a head box for spouting a mixture of makeup furnish and said liquid onto said screen in the direction of screen movement, a second mechanism for pumping said liquid to said head box from said pit and connected to a supply of makeup furnish to provide said mixture in the headbox a first signal generating unit which is responsive to the head of said mixture in said head box to generate a first signal of pressure air whose pressure is directly related to the head of said mixture, a second signal generating unit which is responsive to the speed of said screen to generate a second signal of pressure air whose pressure is related to the speed of said screen, and a control means operable to control said second mechanism and under the control of both of said pressure air signals: so as to change the rate at which said liquid is supplied to said head box and to change the velocity of said mixture spouting onto said screen with changes in speed of the screen.

References Cited in the file of this patent UNITED STATES PATENTS Donaldson Apr. 13, Witham July 17, Lewellen June 24, Ware Aug. 26, De Mers Nov. 21, Lang May 12, Staege June 3 Gade Aug. 25,

FOREIGN PATENTS Great Britain Nov. 22,

Claims

1. IN A MACHINE FOR MAKING A WEB OF SHEET MATERIAL, A MOVABLY SUPPORTED WEB FORMING SCREEN, A SCREEN PIT INTO WHICH THE LIQUID DRAINING FROM A WEB FORMED ON SAID SCREEN MAY DRAIN, A FIRST MECHANISM FOR DRIVING SAID SCREEN, A HEAD BOX FOR SPOUTING A MIXTURE OF MAKEUP FURNISH AND SAID LIQUID ONTO SAID SCREEN IN THE DIRECTION OF SCREEN MOVEMENT, A SECOND MECHANISM FOR PUMPING SAID LIQUID TO SAID HEAD BOX FROM SAID PIT AND CONNECTED TO A SUPPLY OF MAKEUP FURNISH TO PROVIDE SAID MIXTURE IN THE HEAD BOX, A SENSING DEVICE SENSING CHANGES IN THE