Abstract:
Integration of clothing performance into production planning, scheduling and execution of papermaking machines yields paper products with consistent acceptable quality with minimum downtime and inventory. Linking the selection and operation of papermaking machines to their respective clothing performances improves clothing life cycle. Selected operating parameters of a papermaking machine and historical clothing data are indicative of the machine&#39;s clothing condition. Order scheduling engine identifies manufacturing times for particular grades of product and generates order blocks. Papermaking machines are assigned to execute specific order blocks with provision that each machine completes execution of the assigned orders without any anticipated breakage of the wire or felts.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the manufacturing of paper and board products and in particular to novel techniques of evaluating the condition of machine clothing and the integration of clothing performance into the production planning and execution of customer orders for such products. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the manufacture of paper on continuous papermaking machines, a web of paper is formed from an aqueous suspension of fibers on a traveling mesh wire or fabric and water drains by gravity and vacuum suction through the fabric. The web is then transferred to the pressing section where more water is removed by dry felt and pressure. The web next enters the dryer section where steam heated dryers and hot air completes the drying process. The wire or fabric and felt are commonly referred to as papermaking clothing which is conditioned (or cleaned) periodically and replaced as required. Substandard clothing leads to poor web formation on the machine which ultimately results in lower quality paper products exhibiting streaks, pinholes and poor mechanical and optical properties. 
         [0003]    Techniques for regulating papermaking by monitoring the condition of the felt and/or affecting the moisture level of the felt are known. For example, EP 2198278 describes infrared measurement of the paper machine clothing condition to control paper production. U.S. Pat. No. 7,811,417 describes a cross-direction actuator system for maintaining the moisture level on press felt in order to affect the moisture content in the sheet of paper produced. EP 1342839 describes measuring the hardness or compactness of clothing to determine its condition and performance. EP 1329551 describes monitoring the cross-direction dewatering profile in the wet section to determine when replacement of the felt was necessary. 
         [0004]    The average felt life is approximately 40 to 45 days and the average wire life is approximately 90 to 100 days, with both being dependent on the type of paper machine and nature of raw material processed. To avoid interruptions and downtime caused by unexpected clothing breakage during production, papermakers often replace the felt and wire more frequently than is required. In addition, papermakers will change the grades of paper being produced in order to reduce the likelihood of breakage. For instance, a changeover from a lower basis weight paper to a higher basis weight paper can be implemented as the wire fabric becomes impregnated with fiber and debris. The basis weight is the paper&#39;s weight per area and is typically designated in the industry by grams per square meter (gsm). Unscheduled changeovers generate excess inventory of unplanned paper grades. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is based in part on the recognition that considering clothing performance as a strong input during production planning significantly improves the operations of individual papermaking machines. Integration of the clothing performance (ageing of machine clothing) reduces the frequency of clothing breakages and attendant shutdowns, maximizes the use of the clothing, and produces consistently better paper and paperboard products. Furthermore, papermaking machine operators will be able to deliver paper product orders on time, with less waste and at lower costs. With prior art practice, clothing performance was not considered during production planning and, as a result, the frequent unplanned shutdowns of the papermaking machines required re-planning of many orders which caused inevitable delays and related problems. 
         [0006]    In one aspect, the invention is directed to a method of operating a papermaking machine with enhanced clothing life wherein a sheet of wet stock comprising fibers is initially formed on a water permeable moving wire of a forming section of a de-watering machine and thereafter a sheet of partially de-watered web stock is transferred to a press section of the de-watering machine, wherein the press section comprises at least one continuously circulating press felt, the method including the steps of: 
         [0007]    (a) operating the machine to produce a selected quantity of first grade paper product; 
         [0008]    (b) monitoring the condition of the wire and generating wire data; 
         [0009]    (c) monitoring the conditions of the felt and generating felt data; 
         [0010]    (d) calculating the remaining useful life of the wire; 
         [0011]    (e) calculating the remaining useful life of the felt; 
         [0012]    (f) operating the papermaking machine to produce a selected subsequent quantity of subsequent grade of paper product, wherein the subsequent grade of paper produced could be the same as the grade of previously made paper product, with the proviso that the amount of selected subsequent quantity of subsequent grade paper product produced does not cause the papermaking machine to exceed either the remaining useful life of the wire or the remaining useful life of the felt; and 
         [0013]    (g) repeating steps (b) through (f) until the useful life of either the wire or felt is reached with the provision that neither the wire nor felt breaks upon termination of operations of the papermaking machine. 
         [0014]    The present invention allows for robust optimized production planning of customer orders that require manufacturing multiple grades of paper and/or paperboard products with different delivery schedules where the planner can select from a plurality of papermaking machines which are located at different mills to make the products and complete the orders. The papermaking machines include machines of various designs. The only limitation being that the machine is capable of producing one or more grades of paper product in the customer order. 
         [0015]    In another aspect, the invention is directed to a method of manufacturing paper products that includes the steps of: 
         [0016]    (a) monitoring the condition of the clothing on a plurality of papermaking machines and estimating the life of the clothing for each papermaking machine; 
         [0017]    (b) obtaining customer orders for paper products; 
         [0018]    (c) assigning one or more of the plurality of papermaking machines to produce the paper products with the objective of limiting costs; 
         [0019]    (d) identifying the warehousing requirements for the paper products; and 
         [0020]    (e) identifying the delivery date for each customer order. 
         [0021]    The present invention which links the selection and operation of one or more papermaking machines to their respective clothing performance will improve clothing life cycle. It is expected that the wire life and the felt life will both be raised to at least 90% of normal. Moreover, the paper products produced will have a consistently better quality resulting in fewer production rejections and excess inventory. Furthermore, with the attendant improved production and delivery times, there will be significantly reduced warehousing requirements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  depicts a papermaking machine; 
           [0023]      FIG. 2  illustrates the press arrangement of the papermaking machine; and 
           [0024]      FIG. 3  is a production model that integrates clothing performance in customer order planning scheduling. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    The integration of clothing performance in dynamic planning optimization will be illustrated by implementing the technique in a sheet or web making system  10  that includes papermaking machine  2 , control system  4  and network  6  as illustrated in  FIG. 1 . The papermaking machine  2  produces a continuous sheet or web of paper material  12  that is collected in take-up reel  14 . The paper material  12 , having a specific width, is produced from a pulp suspension, comprising of an aqueous mixture of wood fibers and other materials, which undergoes various unit operations that are monitored and controlled by control system  4 . The network  6  facilitates communication between the components of system  10 . 
         [0026]    The papermaking machine  2  includes a headbox  8 , which distributes a pulp suspension uniformly across the machine onto a continuous moving screen or wire  30  that moves in the machine direction (MD). The wire  30  is typically an open mesh material that can be made of metal such woven bronze or copper. Alternatively, the wire can be made of synthetic materials such as plastics (polyamides), in which case the wire is often referred to as a fabric. Headbox  8  includes any suitable structure for distributing a pulp suspension and includes a slice opening through which the pulp suspension is distributed onto moving screen or wire  30  which comprise a suitable structure such as a mesh for receiving a pulp suspension and allowing water or other materials to drain or leave the pulp suspension. The slice jet speed is the speed at which pulp stock exits the headbox. Besides the composition, consistency and temperature of the stock, the jet-to-wire speed ratio is another important operating variable. As used herein, the “wet end” forming portion of sheetmaking system  10  comprises headbox  8  and wire  30  and those sections before the wire  30 , and the “dry end” comprises the sections that are downstream from wire  30 . 
         [0027]    Sheet  12  enters a press section  32 , which includes multiple press rolls where sheet  12  travels through the openings (referred to as “nips”) between pairs of counter-rotating rolls. In this way, the rolls in press section  32  compress the pulp material forming sheet  12 . This may help to remove more water from the pulp material and to equalize the characteristics of the sheet  12  on both of its sides. 
         [0028]    As sheet  12  travels over a series of heated rolls in dryer section  16 , more water in sheet  12  is evaporated. A calendar  18  processes and finishes sheet  12 , for example, by smoothing and imparting a final finish, thickness, gloss, or other characteristic to sheet  12 . Other materials (such as starch or wax) can also be added to sheet  12  to obtain the desired finish. An array of induction heating actuators  24  applies heat along the cross direction (CD) to one or more of the rollers to control the roll diameters and thereby the size of the nips. Once processing by calendar  36  is complete, sheet  12  is collected onto reel  14 . 
         [0029]    Sheetmaking system  10  further includes an array of steam actuators  20  that controls the amount of hot steam that is projected along the CD. The hot steam increases the paper surface temperature and allows for easier cross directional removal of water from the paper sheet. Also, to reduce or prevent over drying of the paper sheet, paper material  14  is sprayed with water in the CD. Similarly, an array of rewet shower actuators  22  controls the amount of water that is applied along the CD. 
         [0030]    In order to control the papermaking process, the properties of sheet  12  are continuously measured and the papermaking machine  2  adjusted to ensure sheet quality. This control may be achieved by measuring sheet properties using one or more scanners  26 ,  28  that are capable of scanning sheet  12  and measuring one or more characteristics of sheet  12 . For example, scanner  28  could carry sensors for measuring the dry weight, moisture content, ash content, or any other or additional characteristics of sheet  12 . Scanner  28  includes suitable structures for measuring or detecting one or more characteristics of sheet  12 , such as a set or array of sensors. Scanner  28  can measure the dry end dry weight, ash content, or other physical properties of the paper product. Measurements from scanner  28  are provided to control system  4  that adjusts various operations of papermaking machine  2  that affect MD and/or CD characteristics of sheet  12 . An MD characteristic of sheet  12  generally refers to an average characteristic of sheet  12  that varies and is controlled in the machine direction. 
         [0031]    In this example, control system  4  is capable of controlling the dry weight of the paper sheet by adjusting the supply of pulp to the headbox  8 . For example, control system  4  could provide information to a stock flow controller that regulates the flow of stock through valves and to headbox  8 . Control system  4  includes any hardware, software, firmware, or combination thereof for controlling the operation of the sheetmaking machine  2  or other machine. Control system  4  could, for example, include a processor and memory storing instructions and data used, generated, and collected by the processor. Scanner measurements control operations of the papermaking machine with both the dry end control and wet end control loops operating. 
         [0032]      FIG. 2  depicts a representative press section which is situated between the end of the forming section and beginning of the dryer section. The press section consists of a number of cooperating endless circulating loops, through which a sheet of wet stock is transformed into a sheet of partially de-watered wet-stock. This exemplary press arrangement includes three separate closed loops that include: (1) upper press felt  40 , (2) lower press felt  42 , and (3) dryer felt  44 . Press felts  40 ,  42  serve as reservoirs to collect (absorb) water from the sheet of wet stock by pressing and capillary action. The forming wires, press felts, and dryer felts are collectively referred to as papermaking clothing. Dryer felt  44  is heated and water evaporates from the partially de-water wet stock as it is carried by the dryer felt. Upper and lower press felt  40 ,  42  are typically made of synthetic materials whereas dryer felt  44  is typically made of cotton or synthetic materials. The structure of the felts used in the dryer section can have very high open areas to afford rapid evaporation. Coarse or grainy characteristics, chocking of felts, sticky materials on the felts, degraded porosity and excessive hardness on the press and dryer felts can cause marks or imperfections on the paper formed. 
         [0033]    A sheet of aqueous wet stock  46  is transported from wire  30  of the forming section onto the wet-press section. Vacuum devices  62 ,  64  referred to as Uhle boxes (vacuum boxes) under the wire and press felt remove water from the web. A sheet of wet stock  46  is transferred by suction to the bottom side of upper press felt  40  that is held by suction roll  62  and is thereafter retained and supported by surface tension on the upper press felt  40  as the sheet becomes disposed between the upper press felt  40  and the lower press felt  42 . The sheet of wet of stock, which is sandwiched between the two felts, advances toward a press nip that is created by press rolls  48  and  50  where compression forces water from the wet stock and into the felts. Papermaking machine can have multiple press sections depending on the machine configuration. Upon exiting the wet-press step, the partially de-watered and consolidated sheet is transferred onto the first dryer felt  44  which carries and supports the sheet as it passes over dryer cylinders  52  and  54  where some residual water is removed by evaporation. The sheet is then transferred onto the second dryer felt  58  which is heated by dryer cylinder  56 . Only one dryer cylinder is shown whereas a commercial papermaking machine typically has thirty to sixty, depending on the paper machine configuration. At this stage in the process, the relatively thin sheet dried paper product  60  is available for further papermaking processing, such as coating and calendaring, where the moisture content is reduced. 
         [0034]    Forming wire  30  is washed and repaired offline whereas press and dryer felts can be cleaned and washed, wherein the process is generally referred as conditioning, using chemicals and/or water either online or offline. For example, as shown in  FIG. 2 , upper press felt  40  is equipped with sensor  70  which measures characteristics of the fabric such as moisture level, porosity of the clothing materials and the like. A spray device  72  directs cleaning fluid onto the fabric as necessary and vacuum device  74  removes the cleaning fluid. Lower press felt  42  is similarly conditioned with sensor  82 , spray device  84  and vacuum device  86  and dryer felt  44  is equipped with sensor  76 , spray device  78  and vacuum device  80 . The quality of machine clothing is maintained in order to produce acceptable paper and paperboard products. Lighter basis weight paper products are preferably made when the felt is new or just cleaned offline whereas the highest basis weight products are produced later when the felt is less porous. 
         [0035]    The operating parameters of the papermaking machine are tuned to produce paper products having specific characteristics such as paper grade. With the present invention, empirical operating data of the papermaking machine collected during actual production can be employed to develop a mathematical model to predict the useful life of the wire and press and dryer felts. The collected operating data forms a database that correlates actual useful lives of clothing to machine operating parameters. In this fashion, for any papermaking machine that is available for production, the expected remaining useful life the wire and felts can be calculated based on its operation history. 
         [0036]    Operating parameters that are particularly suited for predicting useful clothing lives include, but are not limited to, press felt Uhle box vacuum, suction roll vacuum, clothing thickness, felt water permeability, felt air permeability, hardness of felt or wire, dryer section steam demand, wire speed, and MD and CD physical characteristic profiles of the felts. Felt air permeability measures the air flow rate through the felt while the felt is stationary or as the machine is operating. Felt water permeability measures the flow rate of water that is injected into the stationary or moving felt. Other attributes which can be employed with the collected operating parameters to predict the remaining clothing life are historical clothing data which consist of data of how the clothing was used previously. Exemplary historical clothing data include, for instance, clothing mounting date, average life of clothing, length of operation of clothing on machine, online conditioning regiment for clothing, offline conditioning schedule for clothing, type of clothing such as single or multi-layer fabrics and different grades and basis weights of paper products manufactured on a particular papermaking machine. 
         [0037]    Typical attributes of an order for paper products are customer, a due date (ship date), production specifications (grade, basis weight), physical specifications (width, product roll diameter range or sheet length, core diameter and customer specific requirements) and order quantity with given tolerances. When an order has more than one product, in terms of physical and production specifications, the individual product is referred to as an order item. A typical large paper manufacturing enterprise has a number of paper mills in various locations, with each mill having one or more papermaking machines. A feature of the present invention order allocation process pertains to production planning and scheduling to decide where each order item will be produced. Orders can also include forecasted order items, which are standard orders that are based on forecasted quantities based on historical data. 
         [0038]    Each papermaking machine can be tuned to produce different products at different production rates. The production costs, which comprise the major portion of the selling price, are usually different for different papermaking machines for the same product. To the reduce transportation cost, which is another major component to the selling price, it is preferable to produce order items in mills close to the order&#39;s final destination. Order allocation in the prior art that focused on production, fixed grade change time (the cost associated with change over production time loss and does not consider clothing performance), inventory and transportation costs without taking clothing performance into account often resulted in schedules with poor performance in on-time delivery, setup changeovers and trimming. The setup changeover cost, trim loss and on time delivery depend on how the production runs get form on individual machines. 
         [0039]    A continuous papermaking machine makes one product at a time. A production run or time slot is the period of time over which the machine produces the same product. It should be noted that production runs or time slots can be of different time widths depending upon the quantities of the order items being processed simultaneously. When the product on a machine is changed, the machine can continue to operate but the paper produced is usually of lower quality for an initial period of time. This “transition time” or “grade change time” depends on the machine and on the products being manufactured before and after the changeover. 
         [0040]    Planning and scheduling begins with obtaining customer orders to be delivered within a specific time frame and equipment availability. Customer orders can also include forecasted or anticipated future orders. Planning entails collecting standard or conventional order planning parameters which includes for example: (1) order details such as customer name, consignee, mode of transportation, stock or making order, order quantity, (2) order type such as roll, sheet, and cartons, (3) production route such as papermaking machine, winder, rewinder, sheeter, warehouse, and combination of different paper making, converting and wrapping machines (4) grade specification details such as writing and printing, paperboard, packaging, cartons, kraft, copier, newsprint, laser paper, tissue, and specialty papers (5) ship promise date and delivery date, (6) papermaking machine availability and downtime, and (7) different types of costs such as manufacturing, trimming, warehousing, opportunity lost, and freight cost. Next, for each papermaking machine that is available for production, it is necessary to measure and collect for each machine the above-mentioned operating parameters and ascertain the historical clothing data. 
         [0041]      FIG. 3  shows the production process where the clothing performance of individual papermaking machines is considered in the planning stages so that orders for paper products are assigned to selected papermaking machines such that upon executed of the orders, the products are delivered on time and with minimal costs. The standard order planning parameters, operating parameters and ascertained the historical clothing data are inputs into a Planning and Scheduling Engine which employs a mathematical model that analyzes the data and generates solutions that identify the manufacturing time associated with each ordered item. For example, a plurality of time blocks is generated with each time block corresponding to a paper product having specific grade, quantity, and delivery time. Any planning tool generates a production plan that identifies the papermaking machines, order execution dates, type, size and quantity of paper products required. The trim planner fine tunes the production plan with external constraints that include, but are not limited to, the following parameters: (1) papermaking machine parameters such as throughput, machine configuration and specifications, (2) optional and urgent (hot) orders, (3) stock orders, (4) quantity tolerances, and (5) future orders. Production tracking monitors and controls the production process. The produced products are warehoused and thereafter shipped. 
         [0042]    The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus, the above-described embodiments should be considered as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.