Patent Grant
7178582
1. Field of the Invention
The present invention relates to an apparatus for increasing a transfer of thermal energy through an inner surface of a hollow cylindrical dryer of a papermaking machine.
More specifically, the present invention relates to an apparatus for increasing a transfer of thermal energy through an inner surface of a hollow cylindrical dryer of a papermaking machine to a peripheral outer surface of the dryer.
2. Background Information
Paper is normally dried by passing it over a series of steam-heated, cast iron dryer cylinders. These cylinders are typically 4′, 5′, or 6′ in diameter, with some modern dryers being as large as 7′ in diameter. The steam inside the dryer cylinders transfers its heat to the paper through the dryer shell. As the heat is transferred from the hot steam to the wet paper, the steam inside the dryer condenses. The condensate thus formed is then removed from the dryer cylinder through a syphon pipe connected to an external pipe or tank through a rotating seal.
At low rotational speeds, the residual condensate inside the dryer will tend to accumulate in a puddle in the bottom of the dryer cylinder, in a “ponding” state. As the dryer rotational speed increases, the condensate in this puddle will begin to rotate with the dryer shell, and then fall back into the puddle. This is normally referred to as the “cascading” state. At high dryer speeds, the condensate will follow the dryer cylinder around the entire periphery of the dryer shell, in a state that is called “rimming”.
In order to minimize the power required to rotate the dryers in the ponding and cascading states, and to maximize the transfer of heat through the rimming condensate, the dryer syphons are normally designed to minimize the amount of condensate in the dryers.
At high speed, however, even thin residual layers of condensate can form a significant resistance to the transfer of heat from the steam to the dryer shell. At high speed, the rimming layer of condensate is very stagnant and forms an insulating barrier between the steam inside the rimming condensate layer and the inside surface of the dryer shell.
Dryer bars were developed to generate turbulence in the rimming layer, in order to increase the rate of convective heat transfer through the layer. Dryer bars consist of a series of solid metal bars that are located inside the dryer cylinder. The bars are held by various means against the inside surface of the dryer cylinder. The bars tend to generate turbulence in the riming layer of condensate that forms between the individual bars. This increase in condensate turbulence increases the rate of heat transfer and also tends to improve the uniformity of heat transfer from the dryer cylinder.
The concept of dryer bars was first disclosed by Barnscheidt and Staud in U.S. Pat. No. 3,217,426. Specific formulae for predicting the optimum amount of condensate was later added by Appel and Hong as taught in U.S. Pat. No. 3,724,094. Several methods have since been developed for holding these bars to the inside surface of the dryer. One method, for example, uses a series of magnets to hold the bars to the dryer shell surface as described in Mathews U.S. Pat. No. 4,195,417. Another method uses a series of bars that are magnetic as disclosed by Wedel in U.S. Pat. No. 4,486,962. Other methods have been disclosed by Kraus (U.S. Pat. No. 3,808,700), Schiel (U.S. Pat. No. 4,267,644), and Schiel (U.S. Pat. No. 4,282,656), using various types of springs and pins.
In each of these prior art arrangements, the bars have consisted of solid metal bars (normally mild steel, but sometimes stainless steel, for use in corrosive environments). Bars used in commercial embodiments have square or rectangular cross-sections, ranging from 0.25″×0.25″ to as large as 0.5″×0.75″. This cross-section is selected based on the number of rows of bars in the dryer, the amount of condensate that is expected to be rimming inside the dryer, the cost of the bars, the rigidity of the bars, and the ability to handle the bars during installation.
The weight of large cross-section bars makes their installation very difficult, particularly when installed inside existing papermaking dryers that are only 4–6′ in diameter. Bars with small cross-section are much easier to handle, but do not have the structural rigidity to withstand long periods of tumbling of condensate inside the dryer.
Most papermaking dryers have removable cast ports in the front (tending side) head. These ports (“manholes”) are removed to provide access for inspecting the inside of the dryer cylinders and for installing and maintaining syphon equipment. To avoid the very difficult task of removing the dryer heads, dryer bar equipment must fit through these manholes in order to be installed in existing dryer cylinders. This limits the design of the apparatus for holding the bars in place.
Further, modern papermaking machines produce paper up to 400″ in width, running at speeds approaching 6,000 feet per minute. These machines can produce over 1,000 tons of paper per day. The cost of having these machines idled for installation of dryer bars can be very high, often exceeding $15,000 per hour. A reduction in the time required to install dryer bars inside existing dryer cylinders can provide a very significant reduction in the idle time for the machine. Despite this incentive for short installation times, the time required to install prior art dryer bars is still typically 1.5–2.5 hours per drying cylinder. Prior art methods have not provided significant reductions to this installation time.
Most prior art bars are held against the dryer shell using a series of hoop segments. In order to hold the bars tightly against the dryer shell, these hoop segments must be pressed toward the shell surface. In the prior art designs, this force is developed by installing various systems between flanges at the end of the hoop segments, to force the segments apart.
One of these systems is a simple threaded turnbuckle with locking nuts. These turnbuckles are tightened using a pair of open-end wrenches. This is a time-consuming process. The rigid turnbuckles do not provide much resilience to allow for the differential thermal expansion of the dryer shell, with respect to the dryer bar hoops. Without a method for allowing for differential thermal expansion, the stress in the turnbuckle, the stress in the hoop segments, and the stress on the dryer shell will increase. This can cause deformation and long-term loosening of the hoop assembly.
A more sophisticated design uses various types of springs between the hoop segments. These springs have alternately been coil springs, cylindrical springs, and Bellville washers. These springs maintain the design force of the segments against the bars as the dryer is heated up, but the time required to install these systems is much longer. There are more parts to handle and additional hand tools are needed for their installation.
The prior art bars are attached to the hoop segments to prevent them from shifting in the circumferential direction. The bars are normally attached with small threaded fasteners (capscrews). These fasteners require some mechanism to lock them in place, so that they do not come loose inside the dryer cylinder. The locking mechanisms used in prior art dryers include split washers, Bellville washers, flanged self-locking fasteners (WhizLock), and groove lock pins. The threaded fasteners can be difficult to align during installation. It can be difficult to get the fastener started in the threaded holes in the bars, and self-tapping screws can be easily broken. Small diameter pins can be difficult to align, they are easy to break off, and they can come loose inside the dryer.
The present invention provides a method and apparatus for improving the drying capacity of steam-heated cylinders, and in particular cylindrical dryers in a papermaking machine, the apparatus utilizing a series of bars disposed in a generally axial direction inside and adjacent to the shell of the dryer cylinders. The invention more specifically provides for an apparatus which includes hollow rectangular bars, means for holding the bars against the dryer shell, and a method of installing the apparatus. The means for holding includes a fastening system for the bars. The fastening system includes, in combination, a series of hoop segments that are coupled together with special fasteners, a series of bars that are coupled to the hoop segments with special pins, and a unique bar geometry to reduce the time and effort required for their installation.
The dryer bars of the present invention provide a stiffer structure with a lighter weight than existing bar configurations. The apparatus of the present invention can reduce the installation time by approximately a factor of 3. The construction is low in cost and the bar geometry provides heat transfer that equals or exceeds that of the prior art dryer bar configurations.
In order to reduce the weight of the dryer bars, the bars of the present invention are hollow rectangular tubes. These tubes are much lower in weight with much higher bending stiffness than the prior art bars. This greatly improves the ease of handling the bars for installation and makes them less susceptible to bending when subjected to the impact forces of tumbling condensate.
For example, the weight of a typical 0.5×0.75″ solid steel cross-section dryer bar that is 6′ in length is 7.6 pounds. The installation crew must handle 138 pounds of steel bars to install a segment with 18 rows of bars. The weight of one of the bars of the present invention (preferred size is 0.75″×1.00″ with a 0.065″ wall thickness) is only 4.3 pounds and the installation crew must handle only 77 pounds during the installation of a similar segment with 18 rows of bars.
Also, the stiffness of the bars of the present invention is significantly increased. The moment of inertia of the prior art bars in the previous example would be 0.008 in4 in the radial direction and 0.018 in4 in the circumferential direction. By comparison, the moment of inertia of the bars of the present invention, for the preferred size, is be 0.018 in4 in the radial direction and 0.029 in4 in the circumferential direction, that is, 130% stiffer in the radial direction and 60% stiffer in the circumferential direction. All while being lighter in weight.
The bars of the present invention are held against the dryer shell using a series of hoop segments, as is done in most prior art configurations. In order to hold the bars tightly against the dryer shell, these hoop segments are pressed toward the shell surface with a unique threaded fastener. This fastener system consists of a threaded fastener and a threaded nut. The head of the fastener extends through a hole in the end of the hoop segment. This head holds the fastener in place during installation and during operation. The head of the fastener has a socket head. However, the head could alternatively have an external hex shaped configuration. This allows the fastener to be turned using either manual or automatic (electric or pneumatic) ratchets to tighten the fastener, pressing the threaded nut against the flange on the adjacent hoop segment. This greatly speeds up the installation process.
The bars of the present invention are held to the hoop segments using large-diameter pins. These pins are installed in the hoop segment prior to the installation of the bars. This eliminates the time required to find, start, and then engage conventional pins and threaded fasteners. These pins also have a shoulder that prevents them from coming out of the hoop segment, even after the segment has been in service for many years.
A portion of the normal differential thermal expansion between the dryer shell and the bar assembly is absorbed by the radial flexibility of the hollow rectangular tube bars. This, coupled with the flexibility of the hoop segments, allows the bar assembly to handle normal differential thermal expansion without the need for complex systems of springs or flexible hoop couplings.
Because the bars are lighter in weight for a given cross-section, the overall cross-section of the tube bars can be increased to values larger than would be practical with solid bars. This allows the selection of larger bars to optimize the generation of turbulence in the rimming condensate, to gain the maximum heat transfer.
The tube bars can also be manufactured economically in stainless steel, for dryers in which corrosion is a problem. The high cost of stainless steel normally precludes the use of stainless with solid dryer bars, except for very special applications where the high cost would be acceptable. With the lower cross-sectional area of material, stainless steel can be used in place of mild steel while retaining costs that are competitive with respect to solid mild steel bars.
Therefore, it is a primary feature of the present invention to provide an apparatus for increasing a transfer of thermal energy through an inner surface of a hollow cylindrical dryer of a papermaking machine that offers improvemements in performance over that provided by the prior art arrangements.
Another feature of the present invention is the provision of an apparatus for increasing a transfer of thermal energy through an inner surface of a hollow cylindrical dryer of a papermaking machine that is relatively easy to manufacture.
A further feature of the present invention is the provision of an apparatus for increasing a transfer of thermal energy through an inner surface of a hollow cylindrical dryer of a papermaking machine that is of relatively low cost.
Another feature of the present invention is the provision of an apparatus for increasing a transfer of thermal energy through an inner surface of a hollow cylindrical dryer of a papermaking machine that is very easy to install.
Other features and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description of a preferred embodiment of the present invention contained herein.
The present invention relates to an apparatus for increasing a transfer of thermal energy through an inner surface of a hollow cylindrical dryer of a papermaking machine to a peripheral outer surface of the dryer. The apparatus includes a plurality of bars of rectangular cross-sectional configuration, each of the bars extending axially within the dryer. The bars are disposed spaced and parallel relative to each other with each of the bars being urged outwardly against the inner surface of the dryer. A mechanism is provided for urging each of the bars radially outward against the inner surface of the dryer. The mechanism includes a plurality of hoop rings which are spaced axially within the dryer, each hoop ring being disposed normal to an axis of rotation of the dryer. Each hoop ring includes a plurality of segments. The plurality of segments include a first segment which has a first arm extending in a direction from the inner surface of the dryer generally towards the axis of rotation of the dryer, the first arm defining a first orifice. A second arm extends in a direction from the inner surface of the dryer generally towards the axis of rotation of the dryer, the second arm defining a second orifice. A second segment includes a first limb which extends in a direction from the inner surface of the dryer generally towards the axis of rotation of the dryer, the first limb defining a first aperture. A second limb extends in a direction from the inner surface of the dryer generally towards the axis of rotation of the dryer, the second limb defining a second aperture. An adjuster has a first and a second end, the adjuster extending through and being guided by the second orifice of the first segment and the first aperture of the second segment such that the first end of the adjuster is disposed adjacent to the second orifice and the second end of the adjuster is disposed adjacent to the first aperture. The adjuster further includes a radially extending collar which is disposed between the first and second ends of the adjuster. The collar bears against the first limb when the second end of the adjuster is extending through the first aperture. A guide portion extends between the collar and the second end of the adjuster for guiding the second end of the adjuster within the first aperture. A threaded portion extends between the collar and the first end of the adjuster such that the threaded portion extends through the second orifice. Also, a movable member threadably cooperates with the threaded portion so that the movable member bears against the second arm when the threaded portion extends through the second orifice. The arrangement is such that when the threaded portion is rotated relative to the movable member, the movable member and the collar move away from each other so that the second arm of the first segment is urged away from the first limb of the second segment such that the hoop ring is expanded for urging each of the bars radially outward away from the axis of rotation of the dryer towards the inner surface of the dryer.
In a more specific embodiment of the present invention, each of the bars is fabricated from metallic material. More particularly, each of the bars is fabricated from steel. The steel in one embodiment is low-carbon steel and in a preferred embodiment, the steel is stainless steel.
Moreover, the plurality of bars is within a range of 12 to 30 bars and more specifically, within a range of 15 to 24 bars.
In one embodiment, the plurality of bars is 18 bars and in another embodiment, the plurality of bars is 21 bars.
Preferably, the plurality of bars is within a range which is 3 to 4 times an outside diameter of the dryer when the outside diameter is expressed in feet. So the number of bars could be over 24. Also, each of the bars is equally spaced relative to an adjacent bar.
Each of the bars has a cross-sectional dimension within a range of 0.25″ width by 0.25″ depth to 1.50″ width by 1.00″ depth. In one embodiment, each of the bars has a square cross-sectional configuration.
Additionally, each of the bars has an outside width and an outside depth and an inside width and an inside depth. The arrangement is such that:
1) a total cross-sectional area of a bar is a product of the outside width and the outside depth. Also, 2) a cross-sectional area of the enclosure is a product of the inside width and the inside depth. Therefore, 3) a cross-sectional area of the metallic bar is the total cross-sectional area (1) less the cross-sectional area (2) of the enclosure. The arrangement is structured such that the cross-sectional area (3) of the metallic bar is at least alternatively 25%, 50% and 75% respectively less than the total cross-sectional area (1).
The apparatus also includes a mechanism for urging each of the bars radially outward against the inner surface of the dryer
More particularly, the mechanism includes a plurality of hoop rings which are spaced axially within the dryer, each hoop ring being disposed normal to an axis of rotation of the dryer.
Moreover, each hoop ring includes a plurality of segments. The plurality of segments include a first segment which includes a first arm extending in a direction from the inner surface of the dryer generally towards the axis of rotation of the dryer, the first arm defining a first orifice. A second arm extends in a direction from the inner surface of the dryer generally towards the axis of rotation of the dryer, the second arm defining a second orifice. A second segment has a first limb which extends in a direction from the inner surface of the dryer generally towards the axis of rotation of the dryer. The first limb defines a first aperture. A second limb extends in a direction from the inner surface of the dryer generally towards the axis of rotation of the dryer. The second limb defines a second aperture.
Also, an adjuster has a first and a second end, the adjuster extending through and being guided by the second orifice of the first segment and the first aperture of the second segment. The arrangement is such that the first end of the adjuster is disposed adjacent to the second orifice and the second end of the adjuster is disposed adjacent to the first aperture.
In a preferred embodiment of the present invention, each hoop ring includes three segments.
The guide portion defines a socket structured for receiving therein a driving attachment of a power tool. Alternatively, the guide portion defines an external hex type arrangement structured for receiving thereover a driving attachment of a power tool.
The apparatus also includes a pin which extends between a bar of the plurality of bars and an adjacent hoop ring of the plurality of hoop rings for supporting the bar relative to the hoop ring.
More specifically, the pin includes a first portion for insertion thereof within a hole defined by the bar. The first portion has a first and a second extremity such that when the first extremity of the first portion is inserted into the hole, the first portion is disposed within the enclosure and the second extremity of the first portion is disposed adjacent to the hole. A second portion of the pin has a first and a second end and an outer surface, the second portion extending from the second extremity of the first portion. The second portion is inserted into a further hole defined by the hoop ring.
In a first embodiment of the present invention, the outer surface of the second portion defines at least one barb which engages the further hole of the hoop ring when the second portion is inserted therein so that connection of the bar to the hoop ring is permitted.
In a second embodiment of the present invention, the outer surface of the second portion defines at least one groove lock which engages the further hole of the hoop ring when the second portion is inserted therein so that connection of the bar to the hoop ring is permitted.
In a third embodiment of the present invention, the outer surface of the second portion provides an interference fit with the further hole of the hoop ring when the second portion is inserted therein so that connection of the bar to the hoop ring is permitted.
Moreover, the first portion has a greater diameter than the second portion so that when the second portion is inserted into the further hole of the hoop ring, insertion of the first portion of the pin into the further hole of the hoop ring is inhibited.
Also, the first portion has a diameter of at least 0.25″ and preferably has a diameter which is equal to the thickness of the hoop rings. In one specific arrangement, the diameter is 0.375″.
The present invention also includes a method for installing a plurality of hollow rectangular bars inside a dryer cylinder of a papermaking machine such that the bars extend parallel and spaced relative to each other so that the bars extend axially within the cylinder. The method includes the steps of inserting pins into unconnected segments of a hoop ring. The segments are then located within the dryer cylinder. Next, a plurality of hollow bars are located within the dryer cylinder.
The pins are then inserted within corresponding holes defined by the bars so that a segment and corresponding bars are connected to each other. An adjuster is disposed between adjacent segments so that the adjacent segments with the adjuster therebetween cooperate together to generate the hoop ring, the bars being disposed between the hoop ring and an inner surface of the dryer cylinder. At least one of the adjusters is rotated so that the hoop ring is expanded for urging the bars against the inner surface of the dryer cylinder.
The step of positioning the adjuster further includes positioning an adjuster between adjacent lower segments of the hoop ring and subsequently, positioning further adjusters between the lower segments and at least one upper segment for completing the hoop ring.
Also, the step of inserting the pins within corresponding holes defined by the bars further includes, pulling the segment away from the inner surface of the dryer cylinder by a distance such that the pins are located adjacent to corresponding holes defined by the bars for facilitating engagement of the pins within such holes while preventing pins which have previously been located and engaged within corresponding holes from becoming disengaged from such holes.
Many modifications and variations of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings which show a preferred embodiment of the present invention. However, such modifications and variations fall within the spirit and scope of the present invention as defined by the appended claims.
Similar reference characters refer to similar parts throughout the various embodiments and views of the drawings.
In a more specific embodiment of the present invention, each of the bars 18–35 is fabricated from metallic material. More particularly, each of the bars 18–35 is fabricated from steel. In one embodiment of the present invention the steel is low-carbon steel and in a preferred embodiment of the present invention, the steel is stainless steel.
Moreover, the plurality of bars is within a range of 12 to 30 bars and more specifically, within a range of 15 to 24 bars.
In the embodiment shown in
Preferably, the plurality of bars 18–35 is within a range which is 3 to 4 times an outside diameter D of the dryer 14 when the outside diameter D is expressed in feet as shown in
As shown in
As shown in
The arrangement is structured such that the cross-sectional area (3) of the metallic bar 18 is at least alternatively 25%, 50% and 75% respectively less than the total cross-sectional area (1).
As shown in
More particularly, the mechanism 40 includes a plurality of hoop rings 42, 43, 44, 45 and 46 spaced axially within the dryer 14, each hoop ring 42–46 being disposed normal to an axis of rotation 48 of the dryer 14.
In a preferred embodiment of the invention, each hoop ring 42–46 includes three segments 50–52 as shown in
Additionally, as shown in
As shown in
A second portion 100 of the pin 90 has a first and a second end 102 and 104 respectively and an outer surface 106, the second portion 100 extending from the second extremity 98 of the first portion 92. The second portion 100 is inserted into a further hole 108 defined by the hoop ring 42.
In a first embodiment of the present invention as shown in
Moreover, as shown in
Also, the first portion 92 has a diameter of at least 0.25″ and preferably has a diameter which is equal to the thickness of the hoop rings.
The present invention also includes a method for installing a plurality of hollow rectangular bars 18–35 inside a cylindrical dryer 14 of a papermaking machine such that the bars 18–35 extend parallel and spaced relative to each other so that the bars 18–35 extend axially within the dryer 14. The method includes the steps of inserting pins such as pin 90 into unconnected segments 50, 51 and 52 of a hoop ring such as hoop ring 42. The segments 50–52 are then located within the dryer 14. Next, the plurality of hollow bars 18–35 are located within the dryer 14.
The pins 90 are then inserted within corresponding holes such as hole 94 defined by the bar such as bar 18 so that a segment such as segment 50 and corresponding bars 18–23 are connected to each other. An adjuster 70 is disposed between adjacent segments such as segments 50 and 51 so that the adjacent segments 50 and 51 with the adjuster 70 therebetween cooperate together to generate the hoop ring 42, the bars 18–35 being disposed between the hoop ring 42 and the inner surface 12 of the dryer 14. At least one of the adjusters 70 is rotated by the driving attachment so that the hoop ring 42 is expanded for urging the bars 18–35 against the inner surface 12 of the dryer 14.
Additionally, the step of positioning the adjuster 70 further includes positioning the adjuster 70 between adjacent lower segments 50 and 51 of the hoop ring 42 and subsequently, positioning further adjusters 70′ and 70″ as shown in
In operation of the apparatus according to the present invention a 5′ diameter dryer is equipped with 18 hollow rectangular steel bars, each disposed in an axial direction and positioned adjacent to the inside surface of the paper drying cylinder. The equivalent number of bars for a 6′ diameter dryer cylinder is 21.
One of these hollow rectangular bars is shown in
In the preferred embodiment, the hoop ring segments are attached to the rectangular dryer bars with pins. In the preferred embodiment, the hoop has a thickness of ⅜″ and the pins have a diameter of ⅜″ also. Where the pins engage the hollow rectangular tube bars, the pin diameter in the preferred embodiment is larger than the diameter of the pin where it engages the hoop segment. This larger diameter is preferably 1/16″ larger than the smaller diameter of the pin. One of these pins is shown is
In the preferred embodiment, the pins have raised ridges or barbs on the circumference of the pins in the portion that engages in the holes in the hoop segments. These raised portions lock the pins in the hoop segments until the bars have been installed in the dryer.
Also included in this invention is the method for installing the bars. With the following procedure, the time for bar installation can be reduced to about ⅓ of the time required for assembly of prior art type configurations:
In the method according to this invention, the first two hoop segments of each hoop assembly are positioned in a circumferential direction along the bottom portion of the dryer. Threaded fasteners are positioned between these two segments, with adjusting nuts turned onto the fasteners.
Hollow rectangular bars are then slipped under the two partial hoop assemblies, one at a time, and sequentially engaged with the pins in the hoops, beginning with the bottom bar positions.
Once all of the bars have been installed in the lower two hoop segments, the top (last) segments of the hoop assemblies are placed into position, with threaded fasteners between them and their adjacent hoop segments. The last group of bars is then installed, one at a time, beginning at one end of the segment and continuing until the rest of the bars are installed.
Then the threaded fasteners are tightened, beginning with the lower two. Each fastener is tightened with a manual, electric, or pneumatic ratchet, while holding the nut with an open-end wrench. The fasteners are adjusted until the distance between the segments are about equal, then the fasteners are tightened to the final specification. This completes the installation of one axial segment. The time for this installation is about 5–10 minutes with a two-man crew.
The present invention provides a unique apparatus for increasing the heat transfer from within a dryer to the outer surface thereof while additionally providing a relatively simple system for installing such apparatus.
This application is a continuation of application U.S. Ser. No. 10/151,407 filed May 17th 2002 now U.S. Pat. No. 7,028,756. All of the disclosure of the aforementioned U.S. Ser. No. 10/151,407 is incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 1640019 | Young | Aug 1927 | A |
| 3724095 | Appel et al. | Apr 1973 | A |
| 4195417 | Mathews | Apr 1980 | A |
| 4267644 | Schiel | May 1981 | A |
| 4542593 | Viitanen et al. | Sep 1985 | A |
| 4674196 | Means | Jun 1987 | A |
| 5528838 | Timm et al. | Jun 1996 | A |
| 7028756 | Ives et al. | Apr 2006 | B2 |
| Number | Date | Country |
|---|---|---|
| 2 032 056 | Oct 1980 | GB |
| 63-165594 | Jul 1988 | JP |
| 9307864 | Aug 1993 | KR |
| Number | Date | Country | |
|---|---|---|---|
| 20060157226 A1 | Jul 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10151407 | May 2002 | US |
| Child | 11301356 | US |
