WO1991018146A1

WO1991018146A1 - Improvements relating to the manufacture of sheet material

Info

Publication number: WO1991018146A1
Application number: PCT/GB1991/000829
Authority: WO
Inventors: Robert Leighton
Original assignee: Vickerys Limited
Priority date: 1990-05-24
Filing date: 1991-05-24
Publication date: 1991-11-28
Also published as: AU7894391A

Abstract

In order to reduce thermal stressing of granite press rolls in papermaking machines resulting from the injection of steam into the paper prior to its entry into the press nip, an array of spray nozzles (21) capable of selectively spraying wash liquids at heating, cooling and normal roll temperatures are provided in a chamber (32) between twin doctor blades (36, 39) running on the roll surface. A solenoid valve (20) controls the supply to each nozzle (21) from heating, cooling and normal temperature liquid manifolds (22, 23, 24), and the solenoid valves (20a...20n) are controlled in dependence upon differences between an ideal roll temperature profile entered into control apparatus (15) by the machine operator and the actual roll temperature profile as monitored by an infrared camera (11) which tracks back and forward scanning the roll surface. By thus controlling thermal stressing of granite rolls the papermaking machine can safely be operated at maximum speeds and paper quality can be enhanced. The same equipment can also be used with advantage in papermaking machines fitted with synthetic press rolls.

Description

IMPROVEMENTS PTT.aTTNG TO THE MANUFACTURE OF SHEET MATERIAL

FIELD OF THE INVENTION:

This invention generally concerns the manufacture of sheet material and more particularly, though not necessarily exclusively, concerns the manufacture of non-woven sheet material and especially paper and paper-like materials such as card and board materials. BACKGROUND OF THE INVENTION; Pape.rmaking machines, such as the well known Fourdrinier machine, work by continuously depositing an aqueous slurry of fibrous material together with additives such as fillers onto a moving woven wire belt in a thin layer. The wire belt permits some of the water present in the nascent paper layer to drain away and feeds the still very wet paper between two moving endless belts of felt. These absorb yet more of the moisture content of the paper and serve to convey the paper into the nip of a pair of press rolls which have the task of removing a major proportion of the remaining water from the paper before it proceeds to further drying and other processing and finishing stages. Some papermaking machines use a natural granite roll as the upper press roll and such a granite press roll may typically be of the order of 500 to 2000 nuns in diameter and up to 12 m long, and may .run at speeds of anything from 100 to 2000 m of paper throughout per minute. Natural granite is the most favoured material for such press rolls because the mechanical properties of granite are such that a granite roll can span greater widths with minimal deflection and because its naturally porous surface enables maximum water removal, exhibits minimum hydraulic lock and has good sheet release properties. A number of synthetic roll materials are available as substitutes for granite, but none is preferred to granite from a papermaking viewpoint.

To achieve maximum economy in the operation of a papermaking machine, efforts are continuously being made to increase the width of the machine and the speed at which it runs. One of the many factors which imposes a limit on width is the mechanical strength of the press rolls of the machine, and a factor which limits speed increase is the rate at which water can be physically removed from the nip of the press rolls. It has been found that this water removal rate can be increased by raising the temperature of the water in the paper sheet just prior to its entry into the press nip by injecting live steam from so-called steam boxes or steam chests into the sheet. The viscosity of the water falls with increasing temperature and the lower viscosity allows faster ejection of water from the nip. Steam heating of the paper ahead of the nip, however, gives rise to substantial further difficulties as described hereafter.

By elevating the temperature of the water within the paper sheet just prior to the press nip, heat is transferred by conduction into the surface of the upper roll at the press nip and thereafter as the paper runs on the roll surface. Thus the temperature of the upper roll is increased in accordance with the paper sheet temperature. However, because the water content of the paper sheet prior to its entry into the press is not uniform over its width it follows that steam heating of the paper sheet results in a non- uniform temperature profile across the width of the paper sheet. This non-uniformity of the sheet temperature profile results in variations in the roll surface temperature across its width. This temperature variation of the press roll surface over its width results in differential expansion which in turn causes thermal stressing of the roll surface. If a granite roll is employed, the result is that in non- severe cases the press roll life is reduced, and in severe cases the press roll cannot withstand the imposed stresses and disintegrates during operation, 4 occasionally with dangerous, injurious, or even fatal consequences for the machine operator. Non-severe cases of thermal stressing are generally associated with rolls manufactured from synthetic materials, and severe cases have been recorded with rolls manufactured from natural granite. These problems are of such magnitude that many papermaking companies who have traditionally utilized granite rolls are currently voluntarily sacrificing operational speed, achieved through steam injection into the paper just prior to the press nip, by removing or not using steam injection devices or alternatively by changing over to synthetic rolls which have inferior papermaking qualities to those of granite. The non-uniformity of sheet temperature profile which results from steam heating of the paper also results in variations of water viscosity within the sheet and hence gives rise to a non-uniform water removal rate across the sheet width. This has to be corrected either further down the process, which is expensive and inefficient, or by purposely subjecting the press roll to distortion forces which create additional mechanical stresses within the roll which are undesirable from a roll life viewpoint. The temperature gradients that arise in the press roll as a result of steam injection also cause uneven thermal expansion in the press rolls itself thereby giving rise to uneven nip pressures. This in turn leads to uneven moisture content across the width of the paper sheet downstream of the press nip. Since the paper sheet shrinks as water is removed from its bulk and since the speed of the machine is constant at any given point, this uneven moisture content leads to uneven tension being applied to the paper sheet and this can result in the sheet being subjected to creasing and/or tearing during manufacture, thereby giving rise to temporary stoppages during the manufacturing process and consequently reducing the production capacity of the machine. The uneven thermal expansion of the press rolls also results in non-uniform wear of the rolls themselves and of any doctor blades running against them, and this leads to reduced machine running t.imes and correspondingly reduced process profitability.

Finally, as has previously been mentioned, a papermaking machine utilizes a synthetic felt to support the paper sheet up to its entry into the nip of the press rolls and the life of this felt is determined by the ability of the system to maintain uniform cleanliness of the felt over its width and thereby maintain uniform drainage and absorbtion characteristics. A non-uniform press nip will allow some parts of the felt to retain more water than other parts over its width and, since the water contains fillers from the paper (e.g. clay, alum, etc), this leads to non-uniform blinding of the felt, a problem referred to as streaking.

OBJECTS AND SUMMARY OF THE INVENTION;

It is one of the objects of the present invention to enable the production advantages which come from the use of granite rolls and from heating the paper sheet upstream of the press rolls to be preserved, while at the same time eliminating or at least substantially reducing the dangers and adverse consequences which have hitherto resulted from the combination of granite rolls and heating devices. It is a further object of the present invention to enable closer control to be maintained over the operation of the press rolls of papermaking machines, both granite and synthetic, and by so doing to improve the runnability of the machine and increase the paper sheet quality and its speed of production.

According to one aspect of the present invention there is provided an apparatus, in or for a papermaking machine or the like, for controllably and selectively adjusting the temperature profile of a press roll of the machine, such apparatus comprising an array of thermal sources the output flux of each 7 whereof is controllable for selectively heating or cooling an adjoining region of an associated roll surface.

In an exemplary embodiment of the invention which is described in detail hereinafter in the context of controlling the temperature profile of one of a pair of press rolls of a papermaking machine, the temperature control apparatus is conveniently arranged to be mounted adjacent to the surface of the respective press roll within a cavity within the papermaking machine which is occupied by doctoring apparatus operating to clean the respective roll surface. The doctoring apparatus in modern papermaking machinery commonly comprises a pair of doctor blades bearing upon the roll surface at locations circumferentially spaced apart from each other by a short distance, and it has been fairly recent practice to provide between the doctor blades a source of washing liquid which is sprayed onto the roll surface to ensure that any contaminants which pass the first doctor blade are assuredly removed at or before the second blade. In keeping with this established roll cleaning practice, the present invention preferably provides an array of heating/cooling elements within the cavity occupied by the doctoring apparatus and preferably arranged to influence the temperature of the respective roll surface between the two doctor blades, such heating/cooling elements advantageously comprising means for spraying liquid at a selectable temperature onto the adjacent roll surface.

Each heating/cooling element may for example comprise a nozzle adapted to receive a flow of liquid at a selected temperature and to emit it as a spray onto an adjacent part of the surface of the press roll. Each of the heating/cooling elements may thus comprise a temperature control unit which selectively offers heating, cooling and washing liquid as required. This can for example be provided by the use of three liquid manifolds, one to contain cooling liquid, another to contain heating liquid and a third to contain washing liquid, with each nozzle being arranged to be connected through actuator-controlled inlet passages selectively to all three of the manifolds. The actuators can for example be solenoid valves, but this is simply an example and alternative methods could be used to provide the correct liquid temperatures (e.g. mixer valves) .

The invention in another aspect proposes the provision of means for monitoring the temperature of the surface of the press roll over its length, and these means may for example be used to control the operation of the aforementioned temperature control apparatus though, as described hereinafter, they can have wider application. This temperature monitoring means may be mandatory in a papermaking machine if the objective is accident prevention, but may be optional if the objective is increased throughput and/or quality control. Thus, if accident prevention were required, especially in situations utilizing granite rolls, the present invention would propose the fitting of a temperature monitoring means and associated electronics to control the aforementioned heating/cooling means and/or to initiate a procedure to preserve the integrity of the machine, for example a safety shut-down procedure. On the other hand, if machine control for the purpose of increasing sheet quality and/or production rates only were required, and this would be applicable to any roll type situation (e.g. synthetic or non-heated granite), the roll temperature monitoring means may be considered optional and signals supplied from other equipment on the papermaking machine, for example equipment monitoring sheet temperature and/or moisture content, may be used instead to control the roll heating/cooling apparatus of the present invention. By use of such externally supplied control signals, reduced advantages may be obtained but this may be acceptable in certain situations.

The temperature monitoring means may for example be an infra-red camera, or a series of infra-red cameras, set up to observe the roll face. A single infra-red camera might for example be mounted on a carriage arranged to traverse the length of the roll, or other methods of enabling the camera or cameras to view the roll face continuously over its width may be utilized. For example, an optical fibre cable could be arranged to enable the entire width of the roll to be observed simultaneously from a single location. Alternatively, a plurality of fixed temperature sensors could be mounted along the width of the roll, or a single, fixed sensor could be arranged to view the entire roll face across its width through a traversing lens or through a plurality of fixed lenses provided along the length of the roll. No matter what arrangement was utilized, the operation of the heating/cooling/washing elements aforementioned, where such elements were provided, would be arranged to be under the control of apparatus responsive to data received from the temperature monitoring means. Such control apparatus might comprise a computer and might, for example, have inputted thereto a desired temperature profile across the length of the roll, and command signals from the control apparatus to the actuators aforementioned might be established in order to achieve the desired temperature profile at the roll surface.

While the nozzles proposed above for the heating/cooling/washing elements may usefully be confined between the blades of a twin doctor assembly, other heating/cooling elements may not impose the same design constraints. Alternative possibilities for heaters include induction heating pads, radiant heaters, steam jets or even the controlled use of friction between a doctor blade and the surface of the roller, and for cooling refrigerated air flows and other cooling means could be used.

The invention also contemplates adjustment of the temperature profile of a papermaking machine press roll in order to achieve a pre-deter ined press nip load across the length of the roller pair and not solely for temperature profile considerations. By such means it becomes easier to obtain and maintain a desired moisture profile across the width of the paper sheet, and so improve product quality and allow for machine speed increases. Since the speed of a papermaking machine is limited by the rate at which the water content of the paper sheet can be removed by the press rolls and also by the rate of moisture removal in the following driers, and since both these removal rates are proportional to the quantity and viscosity of the water within the paper sheet, therefore it follows that the maximum machine speed attainable is governed by those parts of the paper sheet having the highest moisture content. Accordingly, by achieving a uniform press nip by appropriate practice of the present invention, the average moisture content of the paper sheet over its width can be lower than those peak moisture areas caused by a non-uniform press nip, and this will result in faster water removal at the press and more uniform moisture evaporation in the driers, leading to the possibility of an increase in machine speed and therefore greater production capacity as well as a possible saving in steam consumption.

A more uniform moisture content profile of the sheet leaving the press rolls would also result in a more uniform shrinkage of the paper sheet in the driers, which in turn would reduce paper sheet damage caused by creasing, stretched sheet edges, and paper sheet breaks, which are a cause of machine stoppages and thereby a cause of production loss. Similarly, a uniform sheet moisture profile would reduce the tendency for the initial drier cylinders to damage the sheet face by 'picking', and this would enable the operator to increase the temperature within the driers which, in turn, would lead to faster drying of the sheet and either a saving in steam consumption or an increase in machine speed.

Furthermore, a uniform press roll profile obtained by appropriate practice of the present invention would result in a more uniform pressure on the wood or other fibres from which the paper sheet is comprised. Non-uniformity of the pressure on these fibres can lead to fibre damage or breakage which results in reduced paper quality and/or strength. Therefore, any reduction in the damage caused to these fibres will enhance paper quality, or alternatively, will enable the operator to use less wood fibre to obtain the same paper quality. Since the temperature of the press roll face is related to the moisture profile of the paper sheet, the temperature readings obtained at the press by an apparatus according to the present invention which includes a temperature monitoring means, can be used to adjust and/or control the so-called machine head box slice which is responsible for determining the paper sheet moisture profile in the first instance. By adjusting the machine head box slice in response to signals obtained at the press (instead of from readings obtained just prior to the calender, which is the accepted practice) a better and more meaningful control of sheet quality can be achieved. Similarly, the readings obtained at the press can also be used to correct and/or control other machine functions thereby leading to improved overall machine management. The invention also enables press felt life to be increased, inter alia by decreasing "streaking", which has advantageous effect in regard to felt costs and reduces machine down time caused by felt changes.

Accordingly, in accordance with yet a further aspect of the present invention there is provided a method of operating a papermaking machine or the like, said method comprising monitoring the temperature profile across the length of a press roll of the machine and, in dependence thereon, adjusting one or more process variables and/or operating conditions of the machine. Said one or more process variables and/or operating conditions might for example comprise one or more of;

(i) adjusting the temperature profile of said press roll;

(ii) adjusting the operation of a steam box provided in the machine for heating the paper or other material being manufactured prior to its entry into the press roll nip;

(iii) adjusting the head box slice provided in the machine for determining the supply to the machine of the raw material for manufacturing the paper or other material; and (iv) adjusting the profile of one or more crown controlled rolls provided in the machine. The foregoing and other features of the present invention are set forth with particularity in the appended claims and, together with the advantages thereof, will be clearly understood from consideration of the following detailed description of an exemplary embodiment given with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS;

Fig. 1 is a schematic diagram showing one of a pair of press rolls of a paper making machine, and associated roll surface temperature monitoring and control equipment according to an embodiment of the present invention; and

Fig. 2 is a vertical section through the apparatus depicted schematically in Fig. 1. DETAILED DESCRIPTION OF THE EMBODIMENT;

Referring to Fig. 1 a press roll 10 (which could be formed of synthetic material or of natural granite) of a papermaking machine has a cylindrical surface 16 which is observed by an infra-red camera 11 mounted on a carriage which runs to and fro along the length of the roll 10 on a track 12. There are limit switches 13 and 14 at the ends of the track, connected by means not shown to a control apparatus 15. A command line 16 from the control apparatus 15 controls means (not shown) to move the carriage along the track, and a control line 17 from the carriage provides information to the control apparatus 15 regarding the position of the carriage on the track 12. Temperature data from the camera 11 is fed to the control apparatus 15 through a data line 18. The control apparatus 15 comprises a computer and has the usual input/output peripherals 19 such as a keyboard and display screen so that, for example, a temperature profile across the length of the roll 10 can be displayed on the screen, and a desired temperature profile can be inputted to the apparatus 15. The control apparatus 15 may also be connected to other parts of the papermaking machine, such as for example to the steam box of the machine, for determining the operation thereof.

The temperature of the surface of the roll 10 is arranged to be controlled by controlling the temperature of a spray liquid supplied through a plurality of spray nozzles 21 which are controlled by solenoid valves 20a to 20n. The number of nozzles and solenoid valves shown in Fig. 1 is schematic only and in practice there are likely to be very many more than are shown. Each of the solenoid valves 20 is a three way valve, or alternatively three individual valves, connected in such a manner as to enable liquid selection from any one of three liquid manifolds 22, 23 and 24. Manifold 22 contains hot liquid, manifold 23 contains cool liquid and manifold 24 contains washing liquid having a temperature generally the same as that of the roll surface. Each nozzle 21 is arranged to receive liquid from one of the manifolds 22, 23 and 24 at all times thus ensuring continuous washing of the roll surface with either hot, cool or roll temperature liquid. The solenoid valves are controlled by command lines 25 which run from the control apparatus 15.

Turning now to Fig. 2, a twin doctor assembly 30 has a frame 31 which defines a cavity 32 between a first nose bar 33 of the frame and a second nose bar 34 thereof. A first doctor blade holder 35 is secured to the first nose bar 33 and includes a first doctor blade 36 which runs on the surface 37 of the granite roll 10. The second nose bar 34 carries a second doctor blade holder 38 and blade 39 which again runs on the surface of the roll 10.

The entire doctor assembly provides for pivoting of the frame 31 to carry the blades 36 and 39 well away from the surface 37 of the roll 10. This pivoting movement is under the control of a pair of piston/cylinders 40 in a manner known per se. The prime function of the piston/cylinders is, however, to lock the doctor assembly in its operational position, and to move it away from the roll for maintenance work on the doctor or when it is required to remove the roll from the machine. Within the cavity 32 is housed the spray nozzles 21 shown schematically in Fig. 1. The solenoid valves 20a to 2On, and the three manifolds 22, 23 and 24 are housed within the doctor support frame 31 and are accessible through a plurality of access doors in the front face of the support frame. In other embodiments, they may be housed elsewhere on or in the doctor assembly.

Liquid drains are provided to remove the used wash liquid, and/or heating and cooling liquid from cavity 32 continually during operation. Apart from any roll surface temperature control function, it is necessary to wash the surface of the roll 10 at all times during operation, and for this reason nozzles 21 will receive liquid from one of the manifolds 22, 23 and 24 generally at all times. If no temperature profiling is called for, the nozzles would receive washing liquid from manifold 24 generally at the same temperature as the roll face. The purpose of this washing liquid is to remove from the roll face any particulate matter which may get past the first doctor blade 36.

In operation, the control apparatus 15 causes the camera 11 to effect reciprocating movement on the track 12 so that it performs a double helical scan over the surface of the rotating press roll 10 for every rotational cycle of the press roll. The output from the camera 11 is compared to a desired temperature profile inputted to the control apparatus 15 and any departures from the desired temperature profile are corrected by issuing from the control apparatus 15 command signals down the command lines 25 to the appropriate ones of solenoid valves 20a to 20n thereby causing the respective valves to change over from using wash liquid from manifold 24, to using hot or cool liquid from manifold 22 or 23 whichever is appropriate. Where camera 11 detects an area of the roll having a temperature higher than that desired, it will, via the control apparatus 15, cause the appropriate solenoid valve or valves to select liquid from the cool manifold 23, and similarly where the camera 11 detects a cool area of roll surface, it will cause the control apparatus 15 to instruct the appropriate solenoid valve or valves to draw liquid from the hot manifold 22. The liquid thus selected will be sprayed onto the roll surface 37 with the effect of raising or lowering the roll surface temperature at the respective locations towards the desired temperature.

The temperature profile of the roll face 37 is preferably displayed on the display screen of computer peripheral 19 to provide visual operator information and both desired and actual temperature profiles may be displayed. Further, the control apparatus 15 is preferably pre-programmed with a selection of limit conditions to ensure that safe working conditions are maintained at all times. For example, in the event that camera 11 detects a hot area of the roll and, after causing the control apparatus 15 to instruct respective solenoid valves 20 to utilize cool water from manifold 23, the roll temperature continues to increase, then, at a pre- determined limit programmed into the controller 15, the controller may be arranged to interrupt the steam supply to a corresponding part of the associated steam box and to advise the operator by way of a visual and/or audible alarm. When the roll surface temperature falls, the controller 15 may relinquish its control of the steam supply and continue with temperature control by liquid spray only. In the unlikely event that the controller 15 is unable to reduce the temperature of the roll face by control of both the liquid spray and the steam supply, and the roll temperature approaches a maximum safe working limit pre-programmed into the controller 15, then the apparatus may be arranged to initiate a shut-down procedure for the machine and to warn the operator by an audible and/or visible alarm. The sequences described above are exemplary only and many variations are envisaged to accommodate the multiplicity of features and operating practices employed in different papermaking machines.

The apparatus shown in the drawings is susceptible to modification by use, for example, of compressed air and/or steam in addition to or instead of liquid sprays. The thermal effect of the impingement of a jet of air or steam at any given temperature onto the surface of the press roll is considerably different to that of a liquid spray, and it is possible that by use of such alternative mediums either by themselves or in combination with liquid sprays a finer or speedier control of the roll temperature may be obtainable in specialised instances. Accordingly, it is not intended, in describing the foregoing apparatus, to restrict the invention to use of liquid media only.

It is envisaged that the apparatus hereinbefore described might be employed in any one of four forms, namely:- 1. Primary Automatic Version, to counteract the failure of granite rolls. This version would apply only to papermaking machines employing granite rolls in conjunction with steam boxes. In this version, the apparatus would consist of a twin doctor assembly 30, an integral washing shower 24, a heating/cooling roll^' temperature modification device 22, 23, an infra-red roll temperature scanning device 11, and a controller 15. These components would be arranged to operate automatically whenever the paper machine was in operation, and the controller would be pre-programmed with the operational working limits and the safe working limits of the granite roll. Manual over-ride of the controller would only be possible within the safe working limits of the granite roll, and the controller would, in the ultimate, be pre-programmed to cause machine shut-down in the event that the granite roll approached its safe working limits, regardless of manual over-ride. 2. Secondary Automatic Version, for the enhancement of paper quality and/or production rates. This version of the invention might be employed on papermaking machines which are fitted with granite rolls but do not have steam boxes, or on papermaking machines fitted with synthetic rolls irrespective of whether or not they were used in conjunction with steam boxes.

The apparatus employed would consist of all that described for the Primary Automatic Version, but the controller 15 programme would be different since in this version there would be no necessity to guard against roll failure. The programme would include only those features necessary to achieve maximum paper quality and/or maximum paper machine speed, and the apparatus would control the profile of the press roll accordingly. In this version, the commands from controller 15 could be arranged to be manually over-ridden by the operator through input monitor 19 at any time should this be desirable. This version of the apparatus could be speedily re-programmed to 24 correspond to the Primary Automatic Version abovementioned in the event that the paper machine were ever converted to using a granite roll in conjunction with a steam box (i.e. it could revert to including a safety function) .

3. Manual Version, to enhance paper sheet quality and/or production rates. This version of the invention is applicable to those machines employing granite rolls without steam boxes, or synthetic rolls with or without steam boxes. The apparatus employed in this version would consist of a twin doctor 30, and an integral washing shower 24 plus a heating/cooling roll temperature modification device 22, 23. The infra-red camera 11, tracking mechanism 12, controller 15 and input monitor 19 would not be included. Instead, a manual switching arrangement (not shown for clarity) would be provided to enable the operator to actuate any one (or all) of the solenoid valves 20a to 20n through control lines 25 at will. The machine operator would view an existing machine monitor which displays the moisture profile of the finished paper sheet just 25 before the calendering operation and, based on this visual assessment of the paper moisture profile, he would be able to manipulate the press roll profile by use of the manual switching arrangement in order, to enhance the sheet moisture profile. This manual version of the invention could be up¬ graded to either a Primary or Secondary Automatic version by the addition of the camera and controller etc if and when required.

4. Semi-Automatic Version, to enhance paper sheet quality and/or production rates. This version of the invention is applicable only to those machines employing synthetic crown controlled (profile controlled) rolls used in conjunction with steam boxes. The apparatus employed would consist of a twin doctor 30, an integral wash shower 24, an infra-red temperature sensor and tracking device 11 and 12, control lines 16, 17 and 18, a controller 15 and monitor 19. The heating / coo 1ing roll temperature modification devices 22 and 23 and solenoid valves 20a to 20n would not be employed.

Instead, control line 25 would be connected to a known mechanism incorporated into the roll body and arranged to modify the crown or profile of the roll face, such mechanism being supplied as part of the roll and being outside the scope of the present invention.

In this version, the apparatus relevant to the invention would function in the same manner as already described herein, but instead of using heating, cooling and washing showers to modify the roll profile, it would use the existing equipment built into crown controlled rolls by the roll supplier.

The invention as hereinbefore described is considered to provide the following benefits to manufacturers of non-woven materials such as paper, board and the like, namely:

(i) It will prevent, or at least substantially reduce, the risk of granite roll failure caused by thermo- mechanical stressing as a result of employing steam boxes, and thereby will prevent, or at least substantially reduce, the risk of injury and/or fatality to the machine operator and at the same time allow the machine to 27 be operated at maximum speed;

(ii) It will significantly reduce the frequency of paper sheet breaks by providing a more uniform paper sheet moisture profile and by so doing, will decrease the down-time of the machine and increase its overall output rate;

(iii) It will provide a more uniform paper sheet moisture profile at entry to the driers of the machine and thereby will reduce 'sheet picking', uneven drying, sheet creasing and/or tearing, and will furthermore conserve steam consumption; (iv) By providing a more uniform press nip, it will reduce paper sheet fibre damage and thereby increase paper quality;

(v) It will provide information to enable the machine head box slice to be controlled more effectively and thereby increase sheet quality; (vi) It will increase press felt life by decreasing 'streaking', and thereby save on felt costs and reduce machine down-time caused by felt changes;

(vii) It will increase roll life and doctor 28 blade life and thereby improve production rates by reducing machine down-time necessitated by roll changes; and (viii) It will provide for increased overall machine management and machine runability, and thereby will improve operational efficiency and lead to better paper quality and greater outpu .

In summary therefore the present invention provides an apparatus for paper machine press roll profile control, the apparatus comprising: a twin doctor assembly having a first, upstream doctor blade and blade holder, and a second, downstream doctor blade and blade holder all mounted on a common support frame in such a manner as to define a cavity between the blades which is naturally isolated from the normal activities of the machine operator and which is remote from the influences of the paper making process but is open to the roll surface between the two doctor blades; an integral multi-nozzle shower mounted in or on the twin doctor assembly and capable of delivering washing liquid under pressure to the isolated segment of the press roll surface between the two doctor blades, such washing liquid being delivered at approximately the same temperature as the roll face temperatures; and an additional heating and cooling arrangement mounted in or on the twin doctor assembly, for overriding any one or more of the heated wash shower nozzles and heating or cooling that specific area of the roll face to a higher or lower temperature than the washing shower would otherwise provide. The heating and cooling arrangement as described employs liquids of known temperature to perform its duty of raising or lowering the roll surface temperature in specific areas, but heating and cooling fluxes other than liquid may be utilized and steam, induction heating, radiant heating, heating and cooling air flows or whatever other suitable medium may be available may be employed. Similarly, the profiling of the press roll is not restricted to the use of the heating and cooling system described, and the apparatus may be used in conjunction with existing mechanical apparatus designed for press roll profile manipulation by mechanical, hydraulic or electrical means (crown controlled rolls) . The invention also proposes that the temperature profile of the roll-face or paper sheet, or the moisture content of the paper sheet, may be accurately determined and utilized via a computer to control the press roll profile by adjusting the wash liquid showers, the heating and cooling devices, and/or any other existing paper machine equipment. Temperature measurements of the roll face are described as being determined by one or more infra-red cameras, or bolometers, mounted on a tracking mechanism attached to the twin doctor support frame and arranged to scan the roll face and to feed the derived temperature information to a process controller which controls the heating, cooling and washing mechanisms. However, the gathering of this prime information is not limited to that obtained by one or more infra-red cameras, and may be sourced from a fibre optic system mounted in or on the twin doctor support, or from a completely independent piece of apparatus mounted elsewhere on the papermaking machine (not being part of this apparatus) and producing signals intended primarily for other purposes.

Having thus described the present invention by reference to a specific embodiment, it is to be well appreciated that the invention is not limited to the embodiment described and that modifications and variations will . occur to those possessed of appropriate skills without departure from the spirit and scope of the present invention.

Claims

CLAIMS :

1. Control apparatus in or for a papermaking machine or the like for controllably and selectively adjusting the temperature profile of a press roll of the machine, said apparatus comprising an array of thermal sources the output flux of each whereof is controllable for selectively heating and cooling an adjoining region of an associated roll surface.

2. Control apparatus as claimed in claim 1 wherein said thermal sources are each adapted to provide a fluid flux at a selectable temperature for impingement upon an adjoining region of said surface.

3. Control apparatus as claimed in claim 2 wherein said thermal sources comprise liquid spray nozzles.

4. Control apparatus as claimed in claim 3 wherein each of said liquid spray nozzles has valve means associated therewith for selectively delivering liquid thereto from a plurality of different temperature liquid sources.

5. Control apparatus as claimed in claim 4 wherein said plurality of different temperature liquid sources comprise a source of heating liquid, a source of cooling liquid, and a source whose temperature is between the temperature of said heating and cooling liquids.

6. Control apparatus as claimed in any one of claims 3 to 5 wherein said liquid spray nozzles are arranged to deliver liquid spray onto the associated roll surface at all times that the roll is operating.

7. Control apparatus as claimed in any one of the preceding claims wherein the operation of said array of thermal sources is arranged to be dependent upon a sensed temperature profile.

8. Control apparatus as claimed in claim 7 and including means operative to sense the temperature profile of said roll surface across its width, or to sense the temperature profile of a web conveyed on said roll across its width.

9. Control apparatus as claimed in claim 8 wherein said temperature profile sensing means includes at least one infra-red camera.

10. Control apparatus as claimed in claim 9 wherein said camera is arranged to scan the roll surface in order to sense the temperature profile across the width of the roll or web.

11. Control apparatus as claimed in any one of claims 7 to 10 wherein the sensed temperature profile is compared with a predetermined temperature profile in order to determine the selective operation of said thermal sources.

12. Control apparatus as claimed in any one of claims 7 to 11 and including means for providing a display of the or each said temperature profile.

13. Control apparatus as claimed in any one of the preceding claims wherein said array of thermal sources are mounted in a twin doctor assembly associated with the roll.

14. Control apparatus in or for a papermaking machine or the like, said apparatus comprising means for monitoring the temperature profile of a press roll of the machine, and means responsive to such monitored temperature profile for enabling control of one or more machine functions.

15. Control apparatus as claimed in claim 14 wherein display means are provided for providing to a machine operator a display of the monitored temperature profile.

16. Control apparatus as claimed in claim 15 including means to enable a predetermined temperature profile to be entered and displayed in said display means.

17. Control apparatus as claimed in claim 16 including processing means for computing process command signals as a function of the monitored and predetermined roll temperature profiles.

18. Control apparatus as claimed in claim 17 wherein said command signals include signals adapted or arranged to control the operation of a crown controlled roll of the machine.

19. Control apparatus as claimed in claim 17 or 18 wherein said command signals include signals adapted or arranged to control the operation of a head box slice of the machine.

20. Control apparatus as claimed in claim 17 or 18 or 19 wherein said command signals include signals adapted cr arranged to control the operation of a steam box of the machine.

21. Control apparatus as claimed in any one of claims 14 to 20 wherein the means responsive to the monitored press roll temperature profile includes means responsive to departure of the roll temperature profile or any part thereof from predetermined safe limits for initiating a procedure to preserve the integrity of the machine, for example a safety-shut¬ down procedure.

22. A machine for the manufacture of non-woven web materials such as paper and paper-like materials from a water based fibrous slurry, said machine including a press roll nip for removing moisture from the web material being formed, means for heating the web material prior to its entry into the press roll nip for facilitating the removal of moisture from the web material by reduction of the viscosity of the water content of the web material, means for monitoring the temperature of a press roll defining said press roll nip across the operative length thereof, and control means responsive to the temperature monitoring means for controlling one or more process variables in the machine operation.

23. A machine as claimed in claim 22 wherein said control means is adapted and arranged to adjust the temperature profile of the press roll the temperature whereof is monitored by said monitoring means.

24. A machine as claimed in claim 23 wherein the press roll whereof the temperature profile is monitored has associated therewith a doctor blade assembly and a roll surface washing means adapted and arranged to spray washing liquid onto the roll surface, and said control means comprises means for selectively determining the temperature of the liquid sprayed onto the roll surface at a plurality of locations throughout the length of the roll.

25. A machine as claimed in claim 22 or 23 or 24 wherein the temperature monitoring means comprises an infra-red sensor arranged to scan the surface of the respective roll across the length thereof.

26. A machine as claimed in claim 22, or 23 or 24 or 25 wherein the press roll whereof the temperature is monitored is formed of natural granite.

27. A method of operating a papermaking machine or the like, said method comprising monitoring the temperature profile across the length of a press roll of the machine and, in dependence thereon, adjusting one or more process variables and/or operating conditions of the machine.

28. A method as claimed in claim 27 wherein said one or more process variables and/or operating conditions comprise one or more of: (i) adjusting the temperature profile of said press roll; (ii) adjusting the operation of a steam box provided in the machine for heating the paper or other material being manufactured prior to its entry into the press roll nip; (iii) adjusting the head box slice provided in the machine for determining the supply to the machine of the raw material for manufacturing the paper or other material; and (iv) adjusting the profile of one or more crown controlled rolls provided in the machine.