The present application relates to an off-line finishing apparatus for finishing a fibrous web produced in a paper/board machine, said apparatus comprising an unwinder and a windup station, as well as a calender therebetween, in which apparatus the fibrous web is supplied to the unwinder in reels for unwinding and passed through the calender to the windup station for winding the same for a processed new reel, and said apparatus comprising splicing means for joining the leading end of a new reel fibrous web to the trailing end of a preceding reel fibrous web, and means for cutting the preceding reel fibrous web during the course of splicing. Another object is to provide a method for finishing a fibrous web produced in a paper/board machine, in which method the fibrous web is passed to an off-line finishing apparatus, comprising an unwinder and a windup station, as well as a calender therebetween, the fibrous web being delivered to said apparatus in reels to the unwinder for unwinding and being passed through the calender to the windup station for winding the same for a processed new reel, and said apparatus comprising splicing means for joining the leading end of a new reel fibrous web to the trailing end of a preceding reel fibrous web, and means for cutting the preceding reel fibrous web during the course of splicing.

The subsequent descriptions are examples of prior art calenders. The descriptions are mainly based on the source publication Papermaking Science and Technology, Book 10, Papermaking Part 3, Finishing, edited by Jokio, M., published by Fapet Oy, Jyvaskyla 1999, 361 pages.

Calenders

Soft calender

A soft calender (or soft nip calender) has a soft roll cover on at least one of its two nip rolls. Most commonly, one of the two rolls is a soft roll and the other is a heated hard roll similar to the hard nip calender heated rolls. For matte paper grades, there is a variant where both of the rolls are soft rolls.

Soft calendering process

The soft calendering process is different from the hard nip calendering process in one significant way: the nip backing roll has a soft surface. This difference changes the nature of the whole process. In the soft calendering process, the process variables are:

Linear pressure

Running speed

Hot roll surface temperature

Soft roll cover material - Steaming

Moistening

Soft roll position (against top or bottom side of the web).

The major difference in the nip behavior of soft calenders is that both the web and the roll cover are compressing, which results in a significantly lower actual pressure in the nip compared to hard nip calenders. The nip is longer, allowing better heat transfer and subsequent deformation of the calendered web. Another significant difference is that the compression of the web in both high and low spots is more evenly distributed. The deformation of the soft cover reduces the maximum local nip pressure resulting in more uniform calendering. A hard nip calender tends to equalize the caliper of the paper web resulting in small-scale density variations in the web. The soft calender tends to equalize density of the web resulting in differences in caliper.

Soft calendering offers many benefits over hard nip calendering. Because of the more uniform density, the absorption properties of the web and printing

results are more uniform. As the local high spots are not compressed very hard, there is less gloss mottling in the printed image. Lower maximum pressure allows the web to be calendered to better smoothness without danger of blackening. The strength properties of the web are maintained better compared to hard nip calendering.

The above mentioned benefits have resulted in a change in the calendering method in the majority of new paper machines. Also, in several cases, older machines have been equipped with a soft calender. The capability of soft calendering to be installed on-line has even allowed two- to four-nip soft calenders to replace old supercalenders in processes that do not require the full potential of supercalenders.

Soft calender concepts Gloss calender The predecessor to today's soft calender was the gloss calender. For high basis weight board grades, formation sets limits for hard nip calendering.

Local variations lead to very significant gloss mottling and poor printability.

High-quality board grades were also supercalendered (see the section on moisture) but, as this was an off-line process that resulted in a high amount of reel waste in the high basis weight products, this process was never popular.

High-quality board grades are coated with a heavy coat weight that allows them to be calendered fairly easily to a high surface finish. Temperature is a key parameter in this process. Therefore, a calendering process was developed that used high temperatures (120-150 ⁰ C) and low linear pressures. This is called gloss calendering. Because the backing roll is soft, there is no gloss mottling. For these board grades, the high temperature and low pressure together produce a very good structure. The surface is plasticized for a good printing result, and the rest of the board structure remains less compressed and bulky.

A gloss calender has a polished cylinder heated to a high surface temperature with steam, hot oil, or electricity. The cylinder is usually chrome plated. The calendering nip is formed between this cylinder and a soft covered roll that is pressed against the cylinder. Traditionally, the soft roll material was rubber, but today polyurethane is commonly used. Though the temperature of the hot cylinder is high, soft rolls can be used; because of the thick board, the soft roll has no contact with the hot cylinder surface. Therefore, rubber and polyurethane, which can only withstand temperatures up to 80 ⁰ C, can be safely used.

Since the linear pressures are low, 20—80 kN/m, the soft surface rolls are normally not deflection compensated. The softness of the roll cover and the low pressure do not demand high accuracy. Also, board machines have traditionally been -narrow machines; therefore, the roll deflections are low. For better calendering results, two-nip gloss calenders with two soft covered rolls against one heated cylinder are also used.

Two-roll soft calender Gloss calendering is a good process for board grades, but it cannot be used for paper because the required pressures are higher than can be tolerated by the gloss calender covers. This is due to higher running speeds and less compressible material. Also, the paper is so thin that there would be a direct contact with the hot roll surface and the soft backing roll. However, the benefits that are seen with gloss calendering are so promising that attempts were undertaken to develop a roll cover that could withstand higher linear load and also produce higher specific pressure in the nip. The soft calendering process was first used for all kinds of woodfree specialty papers and matte papers. The .resulting soft-soft calender was called a matte calender or "Matte-on-line" calender as the first major supplier of these calenders, Kusters Corporation, called their product.

As the technology of oil-heated thermo rolls was combined with developing soft cover technology, the soft calender transformed into the very versatile machine for on-line finishing that we know today. The main components of a two-roll soft calender are the deflection compensated soft covered roll and the heated roll with a smooth, polished surface. The linear pressure range of a soft calender is much higher than that of a two-roll hard nip calender; also, the roll diameters are larger. The dimensioning linear pressure of soft calender varies from 150 to 450 kN/m. The surface temperature of the hot roll can be up to 220 ⁰ C -230 ⁰ C.

For two-sided calendering, two nips that have an inverted roll order are combined together, for a total of four rolls. The hot roll is most commonly the top roll in the first nip and bottom roll in the second nip. The roll order is selected by taking into account the two-sidedness of the web, the coating order, and runnability at the calender. The soft calender linear loads can be high, so the hot roll diameter must be large to mechanically withstand the loading and create a straight nip together with the deflection compensated mating roll. In fact, until the early 1990s, the size of thermo rolls was limited and hot soft calenders had to be built with both nip rolls deflection compensated. The hot roll was also deflection compensated. As the chilled cast-iron roll manufacturers increased their capabilities, this technology became obsolete.

Soft calenders are used in a wide variety of layouts. Most simple in design is a true matte calender with two soft 'covered rolls. This concept is an alternative for producing coated matte grades. In this concept, at least one of the rolls is deflection compensated. Most soft calenders are buiit with one soft covered roll and one hard roll. The hard roll can be heated or unheated. It produces higher surface finish and can be either the top or bottom roll, depending on the side to be finished.

Two-roll soft calenders can be combined for higher surface finishing. Normally there are two nips that have inverted roll order, but there are also calenders with two nips finishing the same side twice and calender arrangements with four two-roll soft calenders finishing both sides twice. There are also special calenders combining a hard nip calender and soft calender.

The main design of a two-roll soft calender is very similar to that of a two- roll hard nip calender. However, there are significant differences. Because the deflection compensated roll possesses a soft cover, threading cannot be done with closed nips as with a hard nip calender. In a soft calender during web threading, the nip is opened and the rolls rotate at the same surface speed. When the tail is on the reel, the paper is spread to full width and the nip is then closed. After closing the nip, the calender can be run either in speed difference mode or tension control mode.

The soft roll cover is a critical component in a soft calender. The first soft calenders for paper experienced almost continuous roll failures. This however speeded up the development of roll covers, and today's covers perform very safely when the correct operation and maintenance procedures are performed. In this sense, a soft calender can never be as easy to operate as a hard nip calender. The edge areas are especially critical as there might be direct contact with the hot roll. Because the roll cover cannot withstand this contact, several methods have been developed to cope with this problem. Cooling the edge of the soft cover with cold air is a very frequently used alternative. Another possibility is to taper the edges of the soft roll to eliminate direct contact. The safest method of operation is to use edge slitters after the calender and run overwidth in the calender to prevent contact with the hot roll at the edges. This method loses some trim and can also cause trimming problems if the machine width is critical.

The soft covered roll wears more rapidly than a hard surfaced roll, so the roll change procedure must be efficiently designed. The change time should be minimized, and the roll change 'must be easy and safe. In some cases, the roll change can even be performed while the paper machine is running without shutting down.

Note, the hot roll might be the heaviest component in the paper machine and therefore can dictate the crane capacity, grinding machine capacity, and transport methodology from the machine to the roll maintenance area.

Another important aspect in machine layout is the space requirement for the hydraulic systems, oil-heating systems, electrical drive arrangements, etc. A soft calender is a compact unit, but the peripheral units and systems take up a lot of space; in the case of narrow calenders, the peripheral systems can take more space than the calender itself. In placing the units, there are also limitations regarding the distance to the calender and the relative vertical levels.

The calender frame concept also has a significant influence on the layout. Narrow machines are usually open-faced arrangements allowing roll change with a crane, especially when the nip rolls are not quite vertically arranged but instead are built on a slight angle. In this kind of framing arrangement, room has to be reserved for lifting and transporting both top and bottom rolls. In wider calenders, however, an open-faced arrangement has limitations. The forces that are transferred from the bearing housings to the frame grow rapidly with wider machines, and affixing the bearing housings to the frame becomes critical. This problem can be overcome by two different designs, by having a "nose" in the frame above the top roll bearing housing or by building a frame that is closed. The force transfer from the nip to the frame is easy to arrange in the closed arrangement.

The closed frame, however, has its drawbacks. The bottom rolls can be changed only by using a cart that takes the rolls out sideways from the machine. The cart runs on rails that have to be imbedded either in the floor or on a separate beam that is moved to the calender when changing the rolls. More problematic is the closed frame in existing paper machines because the area for the cart and roll on the side of the machine has to be as wide as the calender itself to allow lifting the roll in this position. In some machine layouts, the machine building is not wide enough or there might already be a control room in this area.

Because of the need for accuracy of the surface speed during threading and the different modes of operation, the drives must have an accurate control system. The dc drives are very often replaced by frequency-controlled ac drives. The mechanical drive arrangement varies depending on the speed and load of the calender. Heated rolls are driven with a universal shaft and a gear reducer. Deflection compensated rolls in narrow and slow calenders are driven with a timing belt drive (toothed belt). In wide and heavily loaded calenders, the deflection compensated rolls are driven with an integrated gear arrangement.

Other major components of a soft calender are spreader rolls before the nips, paper lead rolls, steam showers, doctors, roll edge cooling devices, and caliper actuator. As the soft roll cover can be influenced negatively by the wrinkles entering the nip, the function of the spreader rolls is very important. When operating a calender with a furnish that contains stickies and other impurities, the doctoring of the nip rolls is a key factor for safe operation of the soft rolls. Stickies have to be removed from the surface of the rolls before more fibers, fillers, or other material builds up on the roll surface.

Three-roll soft calender

One nip per side of the paper is not always enough for finishing the sheet. More finishing capacity can be obtained by adding more similar nips. This is, however, an expensive way because the soft calender nip rolls are large in diameter and expensive. The soft calender thermo roll has to be able to withstand the full linear load from one side of the nip. Less stresses are exerted on the thermo roll when there are two soft rolls that are on opposite sides of the thermo roll. In this situation, the nip loads equalize each other and the thermo roll can be dimensioned in a totally different way. However, there are now two nips that consume heat from one roll, and this will limit the maximum surface temperature obtained.

As the paper web passes from the first to the second nip in the same three- roll calender unit, only a one-sided finish can be achieved. By adding another three-roll unit, a serpentine sheet run provides calendering with four nips. This kind of arrangement either with vertical rolls or horizontal rolls is used for finishing woodfree coated papers in some mills. The vertical roll arrangement is used for off-line soft calenders or slow speed on-line calenders. For higher speed on-line calendering, a horizontal roll arrangement is used.

The three-roll unit is a good process tool, especially for one-sided finishing, offering a high finish capability at a reasonable price. It is an interesting unit for two-sided finishing — if the paper web can be plasticized with high temperature and the fairly limited development of smoothness is not a problem. In high temperature soft calendering, high gloss is easier to reach than good smoothness.

Su perca lender

A supercalender is a multiroll calender composed of alternating hard and soft rolls. The soft rolls allow heavy linear loads to be used to obtain good

smoothness without severe blackening or mottling of the web. The control parameters of a supercalender are: -Linear load in the bottom nip

-Surface temperature of heated rolls Hardness and material of filled rolls -Calender speed -Steaming - Moistening -Position at double finisher nip.

The supercalender soft roll is a filled roll. This filled roll has a steel shaft around which specialty paper sheets with a hole in the middle are slid. The paper is then compressed with a hydraulic press. The paper is normally either a blend of wool and cotton or cotton only. When the desired hardness of the roll has been reached, the compressed paper is locked into place with locking nuts. This technology of manufacturing soft filled rolls has been in use for 150 years.

Su perca lenders are always off-machine units, when filled rolls are used. The most common number of rolls is 9-12, but specialty calenders for producing release and grease-proof papers can have up to 16 rolls. If there is an even number of rolls in the supercalender, there will be a double finisher nip in the middle of the stack that has two filled rolls against each other. The side of the paper that is against the hard roll changes in this nip so that the top portion of the calender finishes the opposite side of the web from the bottom portion. The most common number of rolls is 10 or 12.

An uneven number of rolls results in calendering that favors one side of the sheet, i.e., one side will be calendered more than the other. This is desired when making a one-sided product or in a case where the incoming web already shows two-sideness in smoothness or gloss. At one time this was common in North America where the fourdrinier paper machines would

produce a two-sided sheet and final quality was controlled with coating colors and supercalendering. The most common number of rolls in such a case is 9 or 11.

The supercalender roll stack is arranged vertically. When running, the bottom roll, sometimes called the king roll, supports the weight of all the rolls above it. The linear load of the calender is developed by the weight of the intermediate rolls. Because the nature of this load is the weight of the rolls, it is evenly distributed and creates a fairly uniform linear pressure distribution in the cross-machine direction. Since the intermediate roll weight load is not enough for the majority of paper grades, there is a need for extra load to be developed by pressing the top roll bearing housings with hydraulic cylinders. This external force and therefore the linear pressure level of the supercalender can be easily controlled. As each roll adds to the total linear pressure, the maximum pressure is in the bottom nip and the minimum pressure in the top nip. Because the linear pressure range of a supercalender can be fairly wide and the load level quite high, there is a need for deflection compensated rolls in the top and bottom positions. The internal pressure for deflection compensation must be synchronized with the external loading cylinders to have uniformity performing nips.

The supercalender is an off-line operation so, each time the machine reel is changed, the calender is stopped. This operation is the major reason for the low capacity of supercalenders. Some of this lost capacity can be regained by using splicing unwind and windup units. Regardless, each reel change causes loss of production because the reels cannot be run to the end. Another cause of supercalender low capacity is the low running speed. To meet quality targets, in some cases the supercalender speed cannot exceed 500 m/min. Normal maximum production speeds are 750—850 m/min. The major speed- limiting factor is the filled roll. Normally the maximum calender speed, maximum linear pressure, and maximum temperature of the heated rolls

cannot all be used at the same time because of potential filled roll failures in the two bottom positions.

As the surface of the soft filled rolls is marked easily by paper defects, web breaks, or bad profiles, the filled rolls have to be changed fairly often. It is quite normal to change at least one filled roll per day in a given supercalender. When the calendar speed is high, up to three rolls per day have to be changed in one supercalender. This changing of the filled rolls is another factor that addresses calender capacity. To prevent the rolls from being marked by web breaks, supercalenders are equipped with a quickopening feature.

Hydraulic cylinders support the bottom roll. When a web break occurs, the pressure of these cylinders is released very rapidly, causing the bottom roll to drop. When the roll has dropped so far that all the calender nips are open, the bottom roll is softly stopped at the end of the cylinder stroke. This kind of quick opening together with a web-cutting device that cuts the full width of the incoming paper web greatly reduces the risk of marking the filled roll.

After the filled rolls have been changed out of the supercalender, they are left to cool to room temperature. After cooling down, the rolls are refinished by turning or grinding. The refinished rolls, in turn, are put back on the supercalender. In wide calenders, the grinding can take place several times because the grindable surface is 50-65 mm in radius. When the roll diameter is too small to be reground, the roll is sent for refilling to get it back to the original diameter.

Because of this constant variation in filled roll diameters, there must be a way to adjust the nips. This is extremely important with modern calenders with the quick opening of the nips. If the distance the rolls travel during quick opening is too long, the impact forces on the spindles and other

equipment become too high, causing the equipment to fail under fatigue loading. Normally the nip opening between each of the rolls is maintained at 5 mm in wide calenders and 3 mm in narrow calenders. This is accomplished by means of spindles that carry the intermediate rolls when the calender stack is opened.

Basically there are four different ways to support the rolls in an opening situation. The most simple is a one-piece spindle. The nuts on the spindle support each of the intermediate roll housings, and they are manually adjusted. The opening between each of the rolls is 5 mm; therefore, the traveling distance of each roll is an extra 5 mm when opening the stack. The rolls at the bottom portion of the calender travel the longest distance. To quickly get to the adjustment area of the spindle, the support nut can be mechanically adjustable with the help of an electric motor. Spindle adjustment time after roll changing can last up to 1—2 hours.

A more developed version of the spindle adjustment is a split spindle, which has short spindle sections between each of the rolls. The spindle adjustment is accomplished by turning the spindle at each of the rolls to be changed. At each end of the spindle section, there are threads that have a different turning direction. Therefore the spindle is able to open a gap above and below the roll to be changed. With the split spindle calender, operators have a set of keys and test the gap at each spindle nut with the corresponding key. The split spindle section is normally rotated with the help of a pneumatic tool and a built-in gear. The spindle adjustment time after roll change is 15 - 30 minutes. This kind of spindle can also be automated. In that case, every spindle section has its own drive motor and a proximity switch to set the exact gap.

Another widely used automatic spindle system has one drive motor and a one-piece spindle. The exact gap is set using a pneumatic device that either

locks the nut in place or allows it to travel with the spindle. There are proximity switches set for the right gap at each spindle nut. The roll position to be changed is selected with a push button or the automation screen. The automation takes care of the gap for the roll change automatically and, after the roll change, sets the right gaps. Normally, one roll at a time is changed, to prevent gap setting problems. The spindle adjustment time before and after roll change is 1—2 minutes.

One special arrangement for setting the gap is used in closed frame supercalenders with quick opening. The rolls are supported with hydraulic cylinders, and the gap is set automatically as the calender stack is closed. The quick-drop gap is done with an arrangement that has more room for the rolls to drop toward the bottom of the calender. This kind of arrangement is easy to operate on closed frame calenders that would require four spindles for setting the correct gaps.

Because the filled roll change in a supercalender is carried out practically daily, all ¹ other tasks to be performed during a roll change should be easy and fast. The procedure to change the filled rolls includes: adjusting the spindle for the change, lifting the fly roll to the roll stand if it is in front of the roll to be changed, rotating the nip guard out of the way, sliding the crane lifting attachments to the roll journals, and lifting the roll slightly with the crane prior to opening the bearing housing bolts. The roll movements with the crane have to be very careful because, especially in wide calenders, the rolls are heavy and can cause damage to the calender if they are not handled carefully enough. There is also a risk of injury during roll change; therefore, only qualified personnel should perform the roll change. After changing out the roll, a new roll is installed in the calender by reversing the order of tasks. A normal roll change time is 10—30 minutes but can be much longer in the case of closed frame calenders without automated spindles.

Luckily, the development of soft polymer covered rolls has been proceeding rapidly. Today, in almost all supercalenders, polymer rolls can be used in any position with respect to mechanical loading. The only reason that might still require traditional filled rolls to be used is the paper quality. Polymer covered rolls do not require as much mechanical energy to rotate as filled rolls.

Therefore, an equivalent amount of heat is missing from the process. If there is no capacity to increase the surface temperature of the heated rolls or the linear pressure of the calenders, polymer rolls cannot produce the same paper quality as filled rolls. But, even in this case, two or three filled rolls can be replaced by polymer rolls and the same quality can be achieved.

Polymer rolls have a changing interval of 3—4 months; therefore, they substantially increase supercalender capacity. Another benefit of polymer rolls in supercalenders is the improved caliper profile. When filled rolls are used, active profiling cannot be done because the roll is deformed so easily that the Linear pressure profiling is lost within 15—30 minutes. A traditional supercalender, therefore, cannot influence the caliper profile with linear pressure profiling. However, zone-controlled steaming has influence on both gloss and caliper. The incoming profiles must be good, and the filled roll grinding should be accurately performed. Polymer rolls make it possible to influence the paper rolls ¹ profile for a longer time, but the grinding quality of the rolls has to be more precise; the polymer roll is not deformed in the same manner as the filled roll.

The filled roll surface is -rather rough when taken to the calender. The normal Ra roughness is 0.5—0.8 micrometers. This rough surface produces lower gloss values, especially when several rolls are changed at the same time. However, the roll is getting smoother in the calender and, after a few hours of running, the surface roughness is close to the roughness of the hot roll surface (0.2—0.3 microns Ra). The behavior of the polymer roll can be quite different. Some rolls get rougher in the calender, and some become

extremely smooth. This phenomenon has a strong effect on the achieved paper quality.

Swimming-type single-zone rolls provide sufficient control for narrow calenders, but zone-controlled rolls are necessary on wider calenders. Supercalenders have the same linear pressure distribution problem that affects the multiroll hard nip calenders: overhanging loads. Because a supercalender has rolls that have different rigidities and also overhanging loads that vary from nip to nip, the linear pressure CD distribution is never flat unless overhanging load compensation devices are used. These devices are rather new, dating from the late 1980s. The majority of supercalenders are still without these devices. Supercalender slideways experience substantial friction, so only overhanging load compensation devices that operate with pivots tend to work in the long run.

Steam showers are also a part of the calendering process, especially on uncoated SC-grades. The effect of steam showers is based on two factors: heating the paper web and moisturizing the surface. Showers are most effective in the top portion of the calender and can effectively be used for two-sidedness control and gloss CD control. If the coating withstands steaming, it can even be used with LWC and WFC grades but only in small steam quantities. If the steam amount gets too high, the coating is loosened from the surface of the web and sticks on the surface of the calender rolls.

Because the supercalender is a separate process, it is very important that the ¹ machine reel quality after the calender is so good that winder runnability and reel quality after the winder is not influenced by the calender windup. In any case, every winding stretches the paper slightly as it is under tension and consumes the stretch potential of the paper. There still has to be enough stretch potential for the printing machine to ensure the runnability of the printing process. Today, almost solely, center-driven windups with adjustable

rider roll load are used. Center windups without rider rolls have air trapping problems. Surface-driven pope-type windups use very high nip loads to prevent slipping of the smooth paper surface at the reel. The center drive, together with the rider roll, does not have these problems. There are several types of center-driven windups that work basically the same way. In most modern high-speed off-line calenders, there are windups with a driven rider roll for torque adjustment.

Multi-nip calender Until the mid-1990s, almost all calendering was performed with the three previously described basic calendering concepts: hard nip calenders, soft calenders, and supercalenders. Each of these had its advantages and disadvantages. The rapid development that took place with soft calendering technology and its positive influences on paper properties reached physical limits. There was a clear sign that surface properties will not be scarified because of a technology limit. The multi-nip supercalender was still the workhorse to perform the most demanding calendering. But, as paper machine speeds simultaneously were reaching 1600 m/min, there was a severe capacity problem with supercalenders using filled rolls. For speeds above 1600 m/min, three supercalenders would not be enough; there would be a need for a fourth one. This would be very expensive to invest and run.

Luckily, the soft roll technology developed for soft calenders had reached a point so that supercalender filled rolls could be replaced with polymer covered rolls. Experiments were conducted in existing production lines and it was soon determined that, if more than two or three rolls were replaced with polymer rolls, the paper quality was somewhat deteriorated. But, since today's polymer rolls can withstand linear pressures, load cycles, and temperatures that are higher than that of the filled rolls, there are ways to compensate for the heat energy lost from the mechanical drive power. If existing calenders are running at their maximum design limits, some rebuild

is needed; but, for new calenders, this opens totally new possibilities. The major new possibilities are speeds more than twice that of supercalenders and on-line capability due to high speeds and resilient roll covers.

At this point, there are three calender designs in the market that make use of this new technology: the Janus calender from Voith-Sulzer, the Prosoft calender from Kusters-Beloit, and the OptiLoad calender from Valmet.

All these calenders are based on effective use of polymer rolls but are different in their design and process range. All of these calenders can be used in off-line and online processes.

The new multi-nip calendering technology applied in these calenders has become the standard in today's calendering applications. Supercalenders as new machines have vanished and also, in some cases, multi-nip calenders have replaced ¹ soft calenders that would have to run under extreme conditions. Since calendering capacity is no longer a limiting factor, multigrade on-line production lines can be created. One such example is producing paper grades from newsprint to SC-A, when the paper machine and furnish itself is suitable for this kind of operation.

Janus calender

The Janus calender was the first multi-nip calender that could be placed online on a fast paper machine. The primary new concepts used in this application are the polymer rolls and tail threading technology. This calender concept is based on the use of polymer rolls and a higher process temperature than is used with a traditional supercalender. To be able to reach high quality at high speeds, high linear pressures (450600 kN/m) are used. The calender can be built either as a one-stack or two-stack configuration. The normal configurations in one stack are 6—10 rolls and in two stacks 2 x 5 rolls, 2 x 7 rolls, 3 + 5 rolls, or 5 + 7 rolls.

The calender is normally configured to have a so-called inverted roll order (compared to a superca lender) which means that the top and bottom deflection compensated rolls have a soft cover. This allows the first nip to have a hot roll of a higher temperature than that of a normal deflection compensated roll in the normal roll order. Therefore, the first nip is more effective than in a normal multi-nip calender.

The heated rolls are normally peripherally drilled rolls with direct steam heating that produces roll surface temperatures of 150 ⁰ C. As the operating conditions are a combination of high temperature and high linear pressure, the soft roll covers have to be very advanced to be able to perform safely. With these operating conditions, high paper surface quality can be reached with speeds substantially higher than traditional supercalendering speeds.

Since the calender is built for a polymer multi-nip calendering concept, no slideways or spindles are needed. The rolls are supported from their bearing housings with loading arms that incorporate the overhanging load compensation function. There is obviously a trend to reduce the weight of the intermediate rolls and improve soft roll rigidity to be able to reach a higher linear load in the first nip compared to that of the last nip by using aluminum segments on the roll design.

The same benefit is reached with two-stack configurations. A two-stack calender also offers the possibility to adjust paper two-sidedness with the linear pressure difference of the two stacks as well as with the temperature of the heated rolls. The design is low and compact. On the other hand, two stacks have higher investment and operating costs (more deflection compensated rolls) and a more complicated drive arrangement. The free draw between the stacks causes more drying of the paper.

When this multi-nip calender is put on-line with a paper machine, the tail- threading arrangement must perform differently than in a multiroll hard nip calender. A hard nip calender performs tail threading with the nips closed and has no fly rolls between the nips for spreading the web. The Janus calender needs the fly rolls much like the supercalender has, and tail threading is performed with nips open as with a soft calender.

In the first installed calender, this is accomplished with suction conveyors and two ropes that lead the tail threading strip through the calender stack.

Prosoft calender

The typical Prosoft calender configurations are 2 x 3 rolls, 3+ 5 rolls, 2 x 5 rolls, and 2 x 7 rolls. Prosoft calender is similar to the other multi-nip calenders in the characteristics of using polymer rolls and elevated process temperatures. Prosoft calender has drives on all the main rolls to eliminated deflection out of the plane of the nip. This technology is commonly used in all on-line calenders, but the Prosoft calender uses multiple drive points also in off-line calenders.

OptiLoad calender

The OptiLoad calendar came onto the market about the same time as the Janus calender. This concept is also based on polymer rolls and the use of higher temperatures, but uses a special loading arrangement. This multi-nip concept is normally a onestack configuration of 6 — 12 rolls and has inverted roll order (soft top and bottom rolls).

The loading arrangement of the calender is unique. By designing the calender stack with the principle of even deflection, the weight of the intermediate rolls can be completely compensated. The weight of the intermediate rolls does not influence the loading area and the process of the calender.

Because the linear load is created by the external loading cylinders, there is the same Linear load in all the calender nips. This is defined by so-called load angle parameter, which is 90 degrees if there is the same load in all the nips. This compares to a load angle of 45—60 degrees in the case of normal supercalenders where nip load increases as paper goes down the stack.

This loading principle allows the calender to reach the same surface properties at a Linear load level 100—200 kN/m lower than traditionally loaded multi-nip calenders, which means safer operation of the polymer rolls and some savings in bulk. Because this multi-nip calender can have the same load in all the nips, the nip length is also the same in all the nips, allowing this calender concept to reach the required paper surface properties at extremely high speeds.

The load angle of the calender can be adjusted, which allows the calender to have one more control parameter as compared to other multi-nip calenders. This parameter can be used for two-sidedness control by adjusting the linear pressure level between the top and bottom rolls.

Specialty calenders

Wet stack

The wet stack is used as a precalender for a variety of board grades. A wet stack is almost identical with the multiroll hard nip calender, but the process is totally different from standard hard nip calendering. In a wet stack, moisture gradients are effectively used; in fact, the web entering the calender only has 1 %— 2% moisture. On the wet stack calender, there are water boxes on 1—3 rolls to apply a film of water to the surface of the roll before the nip. This film is pressed onto the surface of the web in the nip. The relatively thick web is moistened only from the

surface, so with simultaneous pressure the web is calendered more on the surface as compared to the over-dried interior. This results in a good smoothness to bulk ratio.

The critical factor in a wet stack is runnability. If the nip pressure distribution of the nips with the water boxes is not good enough, water can pass through the nip and form a pocket of water underneath the web. This causes breaks at the next nip. Because the bulk is a critical factor with board grades, there must be a linear pressure range suitable for all the products to be produced with profiles that allow the use of the water boxes. This is normally accomplished with a design that allows running with a varying amount of rolls and by having the position of the deflection compensated roll(s) selected so that the nips used with the water boxes operate with good profiles.

Because the wet stack has runnability problems and requires overdrying of the web before it and drying of the web after the calender, it is only used in those processes that absolutely must have an excellent smoothness to bulk ratio. In other cases, hot hard nip calenders or soft calenders are used.

Breaker stack

A breaker stack is a hard nip calender that is located inside the paper machine drying section. The moisture of the web is about 15%— 20%. Breaker stacks were used commonly with newsprint grades, but many of them have since been removed from operation. The breaker stack produces good smoothness and can also have a positive influence on strength properties of the web. However, on the negative side, the web has a tendency to lose bulk. In some new paper machines with a furnish composed of relatively rough fibers, soft calenders are used in the wet stack

position and at the dry end of the machine. This kind of application develops smoothness with less negative effects on the final product.

Friction calender A friction calender has two rolls, one of which is rotated at a higher speed from the other. The resulting shear forces and slip develop web surface gloss better than a single nip. Friction calenders are rarely used today because they have runnability, control, and linting problems.

Brush finishing

Brush finishing develops surface gloss of the web. Because there is no actual nip, the smoothness is only slightly affected. Brushing of the web is done by rotating brushes made from horsehair against the web. The control parameters are the speed difference between the web and the brush rolls and the direction of brush rotation. There are two ways to do brush finishing: to the web supported by the mating roll or to the free web between supporting rolls. Brush finishing has mainly been used with board grades because it does not reduce bulk, but some paper grades have also been finished with brush units. The use of brushing has become marginal due to dust problems in the finished web and the introduction of hot soft calendering as an alternative.

Long nip calenders

It has been known for a long time that using bigger diameter rolls and roll covers with lower dynamic elastic moduli develops a better surface quality/bulk relationship.

Thus, there has been an interest in moving toward long nip calendering. However, this has not resulted in any major new beneficial results. Now, though, extended nip press rolls and soft calendering belts show promise in this area. The first calenders of this type have shown that surface properties,

especially gloss, can be developed significantly better at the same bulk level as compared to the soft calender.

Another benefit has been very even gloss development that can be clearly seen on the printed image. This type of calendering, with extremely soft belt- type covers and extended nip lengths, will begin to be seen more at mills making board and heavier basis weight grades.

There are two variants of long nip calenders: a shoe roll-type calender with a soft belt as a sleeve around the shoe roll and a roll-type calender with a long belt rotating around one of the nip rolls. Long nip calenders of the shoe roll- type are in use for producing board grades.

Embossing calenders Embossing calenders are special calenders that are designed, not to develop the smoothness or gloss, but to create a desired surface topography of the web. These calenders are used for producing wallpaper, tissue, and some other specialty papers and boards. Embossing can take place either with a hard nip or with a soft nip. In the hard nip process, the rolls that have a special engraved surface rotate synchronously to compress the web. In the soft nip process, rolls can also rotate independently, then the engraving is only in the hard roll.

OptiLoad TwinLine A new generation multinip calender for virtually any printing paper grade. It will drive calendering speed and paper quality to a whole new level. Never before has it been possible to produce so much so fast. In the OptiLoad TwinLine design, we have split the calender into two separate stacks. This configuration offers many significant advantages over one-stack applications: it is now possible to control calendering variables independently for both

sides of the paper. The two-stack design also allows new ideas and equipment installed inside the calendering process.

OptiLoad TwinLine can be installed after the paper machine line in a traditional off-line application or on-line to deliver maximum efficiency and uptime.

•Increased machine uptime •Superior paper quality •High material efficiency -Reduced maintenance and low operating costs •Fast pay Back time

In today's off-line calenders, the continuous process mode has been accomplished by splicing together the webs of a depleting unwinder and the next machine reel by means of a tape splice and by conveying the tape splice at a slow speed all the way to a windup station, at which the web is cut and guided to the next reel spool. Consequently, the web leading end need not be rerun through a calender, resulting in a significant increase in the calender's output. In currently available embodiments, the calender has its running speed dropped to an inching speed (typically 30-50m/min, max lOOm/min) for the duration of splicing and splice run-through. Also, depending on what type of calender is used, the calender nips are either lightened up or opened completely. The reasons for the above running mode are as follows:

- at full running speed and full nip loads, the web splice delivers a powerful shock on rolls with a high likelihood of roll damage

- running at inching speed with nips closed may result in excessive drying of paper, causing breaks - paper quality declines to a broke grade as early as in the decelerating stage, since lightening the load beyond a certain limit does not enable sustaining a desired level of gloss and moisture

- acceleration back to running speed provides at first substandard paper due to difficulties in managing the temperature of thermo rolls, especially when running at high calendering speeds and with hot rolls.

The amount of uncalendered broke produced when running with nips open is attempted to be minimized by dropping the running speed as low as possible. The resulting long deceleration and acceleration ramps increase the time spent for splicing and decline the calender throughput. The faster the calender in question the higher the relative impact. Due to the large mass of calender rolls, a substantial cutback of acceleration and deceleration times is not economically viable. A typical requirement is 2 or 3 off-line calenders for one paper/board machine.

It is an objective of the present invention to provide a solution for achieving an actually continuous off-line finishing process, in which the speed need not be declined to an inching speed for the duration of splicing, whereby the number of off-line calenders can be reduced to just one and the amount of broke resulting from splicing can be substantially diminished and thereby a full quality fibrous web is obtained in a substantially continuous mode of operation.

In order to accomplish this objective, an off-line finishing apparatus of the invention is characterized in that the off-line finishing apparatus is substantially continuous in operation, wherein the splicing of a new reel fibrous web to a preceding reel fibrous web is adapted to take place as flying splicing, and the running speed of a splice through a calender and the nip loads as the splice passes through each nip are adapted to develop in such a way that the quality of a fibrous web, possibly excepting the actual splicing area, does not substantially alter when running the splice through the calender, thus minimizing the amount of broke.

On the other hand, a method of the invention is characterized in that the method comprises running an off-line finishing apparatus in a substantially continuous mode of operation, such that the splicing of a new reel fibrous web to a preceding reel fibrous web is performed as flying splicing, and the running speed of a splice through a calender is such that the quality of a fibrous web, possibly excepting the actual splicing area, does not substantially alter when running the splice through the calender, thus minimizing the amount of broke.

In a solution of the invention, the running parameters of an off-line calender are optimized for a capability of producing full quality, merchantable paper in a continuous mode. This represents a remarkable improvement in a calender capacity and, in off-machine cases, provides the adequacy of production line capacity with a less-than-conventional number of calenders, i.e. typically with one instead of two. In a configuration according to the invention, the running speed and the nip load are reduced for the duration of a splice run-through, such that the rolls receive a milder shock, yet in such a way that the effect of loading and possible extra wetting, which compensates for the declining speed, shall sustain the paper grade at an acceptable level in terms of quality criteria without excessive drying or gloss mottling. The actual splice zone can be run at an even further lightened load, thus allowing the formation of a splice area which does not match all the gloss criteria.

The invention will now be described further with reference to the accompanying drawing, in which:

Fig. 1 shows schematically an off-line finishing apparatus, and

Fig. 2 shows schematically one embodiment for quick splicing in a basic view.

In reference to fig. 1, the off-line finishing apparatus comprises an unwinder 1, a calender 2, and a windup station 3.

Fig. 2 shows schematically one way of splicing the leading end of a new reel fibrous web to the trailing end of a preceding reel fibrous web. The taped-on new reel is designated generally at 10. The splicing stages are depicted in enlarged partial views, wherein stage I comprises adding a sizing agent 12 onto the surface of an old web with a size application device 16 and cutting the web at 14, e.g. with a cutoff tool. In stage II, an old web Wi is pressed over its size-coated zone 12 with a sizing roll 11 against the surface of a new web W2, preferably alongside a taping zone 13. Thus, a portion 13a of the tape 13, which extends beyond the leading end of the new web, is separated from a remaining surface 15 of the new web. This tape portion 13a has its size-coated side passivated in stage III before it comes to contact with calender rolls, thus avoiding adherence of the tape to roll surfaces with its ensuing problems. The passivation can be effected e.g. with passivating chemicals or by using "artificial paper" covering the size-coated portion. The passivating agent may comprise e.g. a tetrafluoride or silicone derivative. The tape may have capsules of passivating agent previously included in its size layer, which break under pressure and heat. The tape may also be provided with a size which adheres poorly to hot steel rolls and polymer rolls, i.e. the size must have its adhesion degrade remarkably as temperature rises to more than 80 ⁰ C.

The optimization of running parameters (speed, calender loading, temperatures, moisture) enables production of full-quality paper throughout the splicing sequence (a principal embodiment) or the amount of broke is reduced so much by the optimization that it fits in the amount of paper to be discarded in the next unwinding, anyway. The running speed of an off-line calender is reduced substantially for splicing (e.g. 5...50%), preferably 10...30%, and other calendering variables are adapted to a control model, such that the calendering result remains constant. During the splicing

sequence, the drying of a web can be compensated for by separate water or steam wetting. The production time used for splicing in an off-line calender is 0,1...2% of the time spent for conventional splicing performed at a web speed of 30...100 m/min.

Web tension is controlled by speed and moment adjustments of the roll assembly and reelers, which are made subject to an adjustment of web tension in machine direction, and the set values of web tension follow the guideline values, which are given to given to the splicing sequence and which are e.g. 5...50% lower than within a standard running range.

Benefits attainable by a solution of the invention include, among others:

- In the principal embodiment, no broke at all is produced during the splicing sequence, while in a second embodiment its maximum production is such that the amount fits within the amount of top or bottom broke to be discarded anyway in the next unwinding (e.g. removing off a piece of surface for sampling)

- the deceleration and acceleration ramps included in splicing are substantially shorter in duration, since the speed of running a splice through a calender is substantially higher than the present inching speed

- the time spent for conveying a splice through a calender is very short, thus contributing significantly to the calender throughput

- particularly the use of a high running speed and hot thermo rolls provides an improved control over roll surface temperatures

- threading is performed in compliance with off-line calender practice (cord threading) after web break or downtime.

In a solution of the invention, both the unwinder and the windup station are structurally designed to handle high-speed splicing and to pass the web over to the next reel spool by means of the windup station.

Applicable implementations may be provided e.g. by technology used in the winders of an off-line coating machine. With regard to the prior art implementation of off-line calenders, the most important differences in winder technology are as follows:

Unwinder

- a brake generator to replace a mechanical brake (adequate capacity)

- a set of articulated rolls to replace a splicing brush (for eliminating variations in web length and a jolt caused thereby in the calender)

- switching gear apt for cutting a high-speed web and air jets for denying access of loose paper and mash to the calender's roll nips

Wind u p station

- switching gear apt for cutting a high-speed web and for conveying to the next reel spool

- reeling equipment apt for precise management of linear load and web tension, as well as for high-speed growth of reel diameter (such as e.g. OptiReel Plus)