Patent Grant
7776183
The present invention concerns a twin fabric gap blade type forming section of a papermaking machine and an apparatus for improving sheet formation therein.
The modern two fabric (or twin wire) papermaking machines in which the papermaking stock or furnish is delivered from the headbox slice lip into the gap between two converging forming fabrics is often referred to as a gap former. In a gap former, one of the two forming fabrics is supported either by wrapping it around a rotating roll surface, or by wrapping it over the fabric support surfaces comprised of a series of blades mounted on a supporting stationary shoe. There are two types of gap formers.
In the first type of gap former, referred to as a gap roll former, initial impingement of the stock jet is onto a fabric supported on a roll surface; this arrangement provides for constant pressure drainage, with excellent fiber retention, excellent tolerance to impingement angle variations, but poor sheet formation due to the absence of the beneficial pressure pulses provided by blade edges.
In the second type of gap former, known as a gap blade former, the initial impingement of the stock jet is onto a fabric which is supported by a series of blade surfaces. The strong pressure pulses generated by fabric deflection at the edges of each blade surface results in excellent sheet formation, but poor fiber retention and an almost zero tolerance for variations in the angle of impingement of the stock jet from the headbox slice.
Recent advances in two fabric forming technology have included the introduction of stationary curved impingement shoe technology, for example, as shown in US 2003/0173048 to Buchanan et al. The stationary curved impingement shoe, which is partially wrapped by both fabrics, replaces the roll or blade impingement zones described above. The curved impingement shoe provides an impingement zone that dewaters the sheet in a manner similar to that obtained with a curved roll surface as in the gap roll former, but combined with a series of much gentler pressure pulses than are possible with the traditional bladed stationary shoe as in the gap blade former. In gap formers equipped with the stationary curved impingement shoe such as those described in the present invention, a fabric lead-in roll is present immediately upstream to the impingement shoe.
Following the initial impingement zone in any of these aforementioned roll, blade or impingement type gap former arrangements, the two forming fabrics together with the papermaking furnish sandwiched between them pass over a stationary bladed forming shoe for further dewatering and formation enhancing pressure pulses provided by the blade edges. This formation shoe is most often placed on the inside run of the opposite fabric to that on which the impingement occurs to provide for a balancing of the drainage. It is also known to use adjustable pressurized blades that can be loaded by means of hydraulic or air pressure so as to push them into the fabrics, such as are described by U.S. Pat. No. 6,361,657, that are mounted opposite the stationary bladed forming shoe so that the individual pressurized blades can press into the two fabrics (with the stock sandwiched between them) in the gaps between the stationary blades on the forming shoe.
The adjustable pressurized blades provide a further degree of adjustment and control over the magnitude of the pressure pulses occurring at each stationary blade edge. These adjustable blades are capable of providing dramatic improvements in sheet quality, but only if the sheet consistency entering this portion of the forming section is within a very narrow range that permits beneficial fiber realignment. If the consistency is too high or too low, then the use of these blades can be detrimental to sheet quality, rather than providing an improvement.
The consistency of the embryonic sheet entering the opposed blade section is determined by many factors, including: basis weight of the product being manufactured, consistency of the stock exiting the headbox slice, composition of the stock and, most importantly, the amount of drainage occurring in the initial impingement zone. The drainage occurring in the initial impingement zone, whether it be in a gap roll, gap blade or curved impingement shoe forming arrangement, is also dependant on the above mentioned factors as well as the fabric tension and the angle of wrap (i.e. the amount of the curved surface over which the two fabrics wrap in the impingement zone). It is well known that the angle of wrap in the impingement zone is fixed by machine geometry and therefore the consistency entering the opposed blade section will change if any of the operational variables fluctuate, and consequently paper quality will suffer.
The headbox is a massive object and, although so-called slice lips are provided which may be used to direct the stream of stock being ejected from the headbox onto a desired location on the impingement shoe, fine control of these lips is imprecise and cumbersome. It is very difficult in practice to precisely direct the stock jet onto the impingement shoe so that it impacts at a specific location with precision.
U.S. Pat. No. 4,523,978 discloses the use of a forming shoe in a twin wire former. The forming shoe is located downstream of the initial single wire portion of the forming section so that it only acts after some degree of felting of the embryonic paper web has taken place and the fibers are no longer able to move relative to each other. The position or attitude of the forming shoe is adjustable in order to adjust the dewatering capability of the forming section as well as web formation. This arrangement is not indicated as effecting fiber distribution in the embryonic paper web.
Briefly stated, the present invention is directed to an improved forming section of the type in which the stock jet is delivered from a headbox slice onto a first of a pair of moving forming fabrics at a location where the first fabric (known as the conveying fabric) passes in sliding contact over an impingement shoe. The impingement shoe is followed by a forming shoe upon which are mounted a plurality of fixed formation blades. Preferably, an opposing blade unit is provided with a plurality of resiliently mounted formation blades located opposite the forming shoe so that the blades are positioned in between the blades of the forming shoe and press into the fabrics to provide a series of pressure pulses which provide energy to randomize fiber distribution and improve sheet formation. Opposing blade units are preferable for most, but not all, paper grades. At least one of the impingement shoe and the forming shoe, and more preferably both the impingement shoe and forming shoe, are mounted in an adjustable manner. This allows the effective drainage length of the stock sandwiched between the forming fabrics at the impingement shoe, and thus a consistency of the stock, to be adjusted prior to the formation shoe based on the effective wrap angle, and also allows the fabric deflection angle of the forming fabrics between the impingement shoe and the formation shoe to be adjusted to prevent overstressing and damage to the embryonic web being formed as it is carried to the formation shoe.
Through the ability to adjust a position of the impingement shoe and/or formation shoe in a quick and efficient manner, stock consistency can be optimized so as to maximize the benefit obtained from the pressure pulses provided by the impingement and formation shoes. This allows the papermaking machine to efficiently produce a wider variety of paper products with a shorter turnaround time than has hitherto been possible.
The invention is based, in part, on the determination that the consistency of the stock entering the forming section can be controlled by altering the location of the point of impingement of the stock jet onto the forming fabric which wraps the curved impingement shoe. This changes the effective drainage length without having to move the headbox structure. Unlike the roll former with its fixed structure, the impingement point of the stock jet on the impingement shoe in a gap former can be moved according to the invention by combining a very small but controlled amount of rotation and/or linear movement of the impingement shoe while leaving the trajectory of the headbox jet unchanged. In one preferred embodiment, a pivot point is provided for the impingement shoe and is located such that the fabric path between the trailing edge of the impingement shoe and the leading edge of the formation shoe remains in approximately the same position, while the lower (upstream) portion of the curved impingement shoe is caused to rotate so that the jet impinges further downstream onto the impingement shoe, thus reducing the effective drainage length.
The lead-in roll is preferably also moved in a linked manner with the impingement shoe as an assembly to ensure that the position of the front edge of the shoe remains constant relative to the lead-in roll.
Additionally, an effective wrap angle of the sandwiched forming fabrics with the stock located therebetween about the impingement shoe can be increased, maintained or diminished in a precisely controlled fashion during normal operation of the papermaking machine so as to provide more or less dewatering for adjustment to various sheet properties.
These features of the invention allow the consistency of the stock entering the opposing blade portion of the forming section to be more precisely controlled than has previously been possible by altering the location of the point of impingement of the stock jet, thereby changing the effective drainage length of the stock and forming fabrics over the impingement and forming shoes, without having to move the huge headbox structure. By using the features of the present invention, it is now possible to quickly and efficiently alter the position of the impingement point of the stock jet on the impingement shoe. This is accomplished by imparting a very small, but precisely controlled amount of movement, such as by rotation and/or linear movement to either the impingement shoe, the forming shoe, or both the impingement and forming shoe, while leaving the trajectory of the headbox jet unchanged.
In a second aspect of the present invention, the downstream forming shoe assembly is also moveable, preferably by incorporating another pivot point and/or transverse adjustment, which would allow for movement by rotation or transverse adjustment at a position immediately downstream of the impingement shoe. This assists in controlling a fabric deflection angle of the forming fabrics as they pass from the impingement shoe to the forming shoe in instances where the position of the fabrics at the trailing edge of the impingement shoe require adjustment to optimize paper formation properties.
In one embodiment, both the impingement shoe and the forming shoe are moved cooperatively so as to provide the necessary adjustments to formation properties, if necessary. Alternatively, the impingement shoe and the forming shoe are moved independently using separate controls or adjustments.
In another aspect of the invention, the forming shoe is linked to the impingement shoe by a linkage arrangement or via logic programmed into one or more controllers so that movements of the impingement shoe provide cooperative movements of the forming shoe.
The foregoing summary, as well as the following detailed description of the preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:
a show the trailing edge of the impingement shoe and leading edge of the forming shoe in a first position for use in connection with a thin papermaking stock.
a show a thick papermaking stock being delivered from the head box with the impingement shoe and forming shoe being in the same location as in
a show the impingement shoe and forming shoe after an adjustment of the position of the impingement shoe and the forming shoe from that shown in
Certain terminology is used in the following description for convenience only and is not considered limiting. The words “lower”, “upper”, “left” and “right” designate directions in the drawings to which reference is made. The terms “a” and “one” are defined as including one or more of the referenced item unless specifically noted. The term “effective wrap angle” refers to the wrap angle from the jet impingement point to the trailing edge of the impingement shoe. The term “fabric deflection angle” refers to the angle formed by the fabric at the trailing edge of the impingement shoe and/or the leading edge of the forming shoe.
Referring now to
A forming shoe 40 is located immediately downstream of the impingement shoe 30. The backing forming fabric 20 slides over the forming shoe 40 to further distribute fibers in the papermaking stock and dewater the web. The two forming fabrics 18, 20 with the embryonic paper web sandwiched therebetween preferably encounter a series of blade edges 42 on the forming shoe which create pressure pulses to enhance dewatering. An oppositely mounted series of adjustable pressurized blades 50 are preferably also provided and can be loaded by means of hydraulic or air pressure so as to push them into the fabrics 18, 20, as described in U.S. Pat. No. 6,361,657, which is incorporated herein by reference as if fully set forth.
According to the invention, the impingement shoe 30 is mounted for at least one of pivoting and transverse (left-right) movement so that a position of the point of impingement 16 of the jet of papermaking stock 14 on the conveying fabric 18 in an area of sliding contact over the impingement shoe 30 is adjustable by at least one of rotating the impingement shoe 30 about a first pivot point 32 and transversely shifting the impingement shoe 30. In the embodiment shown in
The lead-in roll 18 is preferably linked to the impingement shoe 30 so that adjustments in the position of the impingement shoe 30 provide corresponding adjustments to a position of the lead-in roll in order to maintain a desired lead-in angle for the conveying fabric 18 to the leading edge of the impingement shoe 30.
Still with reference to
In a preferred embodiment, the forming shoe 40 is linked to the impingement shoe 30 such that movement of the impingement shoe 30 provides a corresponding movement of the forming shoe 40. This is preferably accomplished via a linkage 46 which is connected to the impingement shoe 30 and causes movement of the forming shoe 40 as well as the structure for supporting the oppositely mounted series of adjustable pressurized blades 50. This can be in the form of a simple linkage 46 or, if necessary, a more complex linkage may be provided to provide a desired movement characteristic between the trailing edge of the impingement shoe 30 and the leading edge of the forming shoe 40.
Referring now to
The impingement shoe 130 is preferably also mounted for a pivoting movement about the first pivot point 132 which is controlled via actuator 136. The first pivot point 132 can also be transversely shifted via actuator 139. The actuators 136 and 139 are preferably also controlled via the controller to allow a desired position and holding of the impingement shoe 130 at a desired angle so that a desired impingement point 116 and effective wrap angle can be achieved. The controller may provide a logical linkage between movement of the impingement shoe 130 and the forming shoe 140 based upon control signals to one or more of the actuators 136, 139, 148 and 154 to provide a linked movement between the impingement shoe 130 and the forming shoe 140.
Referring now to
In order to ensure that the embryonic paper web formed between the backing and conveying fabrics 18, 20 is not damaged due to too high or too low of a wrap angle between the trailing edge of the impingement shoe 30, 130 and the leading edge of the forming shoe 40, 140, the forming shoe 40, 140 can be moved in connection with an adjustment of the position of the impingement shoe 30, 130. This can be done separately, or through a linked or controlled movement of both the forming shoe 30, 130 and impingement shoe 40, 140 which can be accomplished via a mechanical linkage, such as the mechanical link 46 shown in
Preferably, the range of motion of the leading edge of the impingement shoe to obtain beneficial effects on the stock is in the range of from about 0.5 mm to about 5 mm in normal operation, depending on grade of product being made by the paper machine. Heavier basis weights will have a thicker fabric-slurry-fabric sandwich. In extreme cases of basis weight changes, it may necessary to move the leading edge of the impingement shoe up to about 10 mm or more although movement in the range of up to 15 mm may be necessary depending on the papermaking variables.
Similarly, movement of the leading edge of the forming shoe should normally be in the range of from about 0.5 mm to about 5 mm, but may include movement of the leading edge by as much as 20 mm.
Referring now to
a show the impingement shoe 30, 130 and the forming shoe 40, 140 in the same locations as in
Referring to
It is noted that a thickness of the sandwiched fabrics 18, 20 and papermaking stock can be adjusted by a number of factors, including changing the impingement point 16 on the impingement shoe 30, 130 and the effective wrap angle. For example, for a thicker stock, providing an impingement point 16 closer to a leading edge of the impingement shoe 30, 130 with a greater wrap angle would result in more drainage being carried out on the impingement shoe 30, 130 and result in a reduced sandwiched thickness. However, for a thin stock, in order to maintain a proper tension and fabric deflection angle between a trailing edge of the impingement shoe 30, 130 and a leading edge of the forming shoe 40, 140, it may be desirable to have less drainage carried out on the impingement shoe 30, 130. Therefore it could be desirable to adjust the impingement point 16 to a position closer to the trailing edge of the impingement shoe 30, 130, for example as shown in
According to the invention, adjustments in a location of the impingement point 16 on the impingement shoe 30, 130 as well as the fabric deflection angle between the trailing edge of the impingement shoe 30,130 and a leading edge of the forming shoe 40, 140 can be easily adjusted via one or more of the actuators 36, 136, 139, 148 and 154, preferably using a controller for easy adjustment during changeovers to mill runs of different types of paper. This used to entail a laborious process of shutting down the equipment and manually adjusting the impingement and/or forming shoe locations prior to restarting the equipment. Only when the equipment was restarted would it be possible to determine whether the proper adjustment had been made. In accordance with the invention, the moveable impingement shoe 30, 130 and/or forming shoe 40, 140 can both be easily moved to adjust the forming section for forming different types of paper webs. This can be carried out prior to or during operation of the papermaking machine allowing for minute adjustments on the fly in order to improve the quality of the paper web being formed. The result is that the papermaking machine can efficiently produce a wider variety of paper products with a shorter turnaround time than has hitherto been possible.
A variety of mechanisms are available which will impart sufficient accurate movement (rotational and/or linear) of the leading edge of either or both the impingement shoe and forming shoe. Selection of any one of these will be dictated by machine design and layout (the mechanism should not interfere with any other units, showers, pans or mountings) as well as papermaking conditions and customer requirements. The actual mechanism may include a simple single pivot arrangement, a double sliding mechanism, where each end is moved linearly along a fixed path, or a combination of both, or other suitable arrangements. Rotational movement can be provided by a drive actuator, such as a cross shaft and screw jack arrangement driven by an electric motor. Alternatively, hydraulic or pneumatic actuators or drives could be utilized.
Those skilled in the art will recognize from the present disclosure that some or all of the benefits of the invention can be obtained by utilizing a movable impingement shoe, a movable forming shoe, or both.
It will be recognized by those skilled in the art that changes can be made to the above-described embodiments of the invention without departing from the broad inventive process thereof which provides an impingement shoe and/or a forming shoe which can be moved, either independently or in a linked manner, in order to allow adjustments to both the impingement point of the jet of papermaking stock and the effective wrap angle, as well as the fabric deflection angle between a trailing edge of the impingement shoe and a leading edge of the forming shoe in order to provide improved paper web formation. It is understood therefore that the invention is not limited to the particular embodiments disclosed, but is intended to cover all modifications which are within the spirit and scope of the invention as defined by the appended claims.
This application is a 371 National Phase of PCT/US2005/041455, filed on Nov. 16, 2005, which claims the benefit of U.S. Provisional Application 60/630,393, filed Nov. 23, 2004.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2005/041455 | 11/16/2005 | WO | 00 | 5/23/2007 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2006/057871 | 6/1/2006 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3997390 | Kankaanpaa | Dec 1976 | A |
| 4523978 | Pullinen | Jun 1985 | A |
| 4648943 | Malashenko et al. | Mar 1987 | A |
| 4684441 | Ibrahim | Aug 1987 | A |
| 5635032 | Bubik et al. | Jun 1997 | A |
| 6117271 | Page | Sep 2000 | A |
| 6361657 | McPherson | Mar 2002 | B2 |
| 6372091 | Wildfong et al. | Apr 2002 | B2 |
| 6712941 | Sherril | Mar 2004 | B2 |
| 7364643 | Poikolainen et al. | Apr 2008 | B2 |
| 20030173048 | Buchanan et al. | Sep 2003 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20070295468 A1 | Dec 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60630393 | Nov 2004 | US |
