Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2001-10-17
2004-07-13
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S343000, C162S298000
Reexamination Certificate
active
06761801
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. § 119 of German Patent Application No. 100 51 802.2, filed on Oct. 18, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lamella of a headbox in, e.g., a paper, cardboard or tissue machine.
2. Discussion of Background Information
A lamella of a multi-layered headbox is known to the Applicant from European Patent Application No. EP 0 681 057 A2. In the nozzle of the disclosed headbox, at least one lamella is provided, which maintains the distance of two adjacent suspension flows down to a region of an exit nip. The lamella is formed of plastic with its modulus of elasticity preferably being smaller than about 80,000 N/mm
2
.
As is generally known, the plastic can be a polycarbonate (PC) which has been extremely successful as a material for many modern and technically demanding applications due to its specific characteristics. For example, the high-tech polycarbonate by the company Bayer AG with the trade name Makrolon®, and that of General Electric with the trade name Lexan®, have a global reputation.
The polycarbonate is used for inexpensive lamellae of applications in which the use of expensive lamellae is impossible or not suitable for economic reasons, e.g., in one-layered headboxes in which the lamellae end within the nozzle.
When polycarbonate is used as the material for lamellae, it is disadvantageous that the connection between the lamella and the headbox (or turbulence generator) must be constructed larger than sometimes desired due to the low stability of the polycarbonate. Additionally, polycarbonate has mechanical, chemical, thermal, and processing disadvantages as well.
Carbon fiber composite materials are better, yet also more expensive materials for lamellae, by which lamellae are produced in several components. The carbon fiber composite materials are particularly suitable in applications with very high requirements concerning shape stability and constancy of the crosswise thickness profile of the streams, in particular in multi-layered headboxes.
Until now, all materials known and used for lamellae for use in headboxes for producing a material web, such as a paper or cardboard web, by at least one fibrous stock suspension, have had in common the fact that they render the lamellae sensitive to the influence of mechanical forces, such as, e.g., during handling. Furthermore, they have a low resistance to high temperatures and alkaline solutions during cleaning of the headbox by “boil out.” Additionally, the service life of the lamellae is reduced due to the cited properties of the materials mentioned above.
SUMMARY OF THE INVENTION
Therefore, the present invention provides a headbox of the type generally discussed at the outset in which a lamella is provided with a better expense/effectiveness ratio for all possible utilizations and better withstands different operating conditions.
Accordingly, the present invention is directed to a headbox that includes a lamella constructed of at least one high-performance polymer, having high stability, high heat resistance, and good to very good resistance to alkaline solutions and/or acids.
High-performance polymers belong to the thermoplastic plastics, called “thermoplastics,” for short, and are characterized by a very high maximum operational temperature according to UL 746 B (U.S. testing regulations of the Underwriters' Laboratories) and/or IEC 216, among other things, being in the range of about 160° C. to about 260° C., i.e., which exhibits a very good heat resistance, a good to very good resistance to alkaline solutions, and increased stability values.
Due to these characteristics (mechanic, thermal, and chemical), mentioned as examples, high-performance polymers are quite optimally suitable for use as the material for lamellae. They have an improved expense/effectiveness ratio and are able to withstand worsened operating conditions for longer.
In order to increase the mechanical characteristics of the lamella and to reduce its sensitivity to the influence of mechanical forces, the high-performance polymer has a tensile strength R
m
(DIN 53455) in the range of about 50 N/mm
2
to about 150 N/mm
2
, preferably about 70 N/mm
2
to about 110 N/mm
2
, and a breaking elongation A
s
(DIN 53455) in the range of about 20% to about 80%) preferably about 30% to about 60%. Furthermore, the high-performance polymer has a modulus of elasticity module E (DIN 53457, ISO 527-2) in the range of about 500 N/mm
2
to about 10,000 N/mm
2
, preferably about 1,000 N/mm
2
to about 5,000 N/mm
2
.
The connection between the lamella and the turbulence generator may be constructed in a smaller fashion, if the high-performance polymer has an impact strength when notched (ISO 179) of about 40 kJ/m
2
to about 100 kJ/m
2
, preferably about 45 kJ/m
2
to about 90 kJ/m
2
.
The behavior of the lamella concerning moisture and water (hydrolysis resistance) is decisively improved if the high-performance polymer has a moisture acceptance FA (ISO 62) in the range of about 0.05% to about 2%, preferably about 0.2% to about 12%.
In order to allow an efficient and inexpensive cleaning of a lamella, the high-performance polymer has a heat resistance WB (DIN 53461) in the range of about 120° C. to about 230° C., preferably about 170° C. to about 220° C., and a good to very good resistance to alkaline solutions. With these values, the performance of cleaning the headbox by “boil out” is possible, i.e., the presence of temperatures in the range of about 100° C. and, simultaneously, the use of sodium hydroxide (NaOH) of about 20%.
In order to ensure the dimensional stability even during operation, the high-performance polymer has a low swelling Q, in particular, a low linear swelling Q
L
, in the preferred range of about 0.02% to about 0.2%.
Out of the group of high-performance polymers that perform the above-mentioned requirements during operation and during cleaning of the headbox in an excellent fashion, polyphenylene sulphone (PPSU), polyether sulphone (PES), polyetherimide (PEI), and polysulphone (PSU) are recommended. The first three mentioned high-performance polymers, which were not developed until most recently, exhibit water absorption characteristics (DIN 53495) of 1.10% for PPSU; 2.00% for PES and 1.25% for PEI and heat resistance (DIN 53461) of 214° C. for PPSU; 214° C. for PES and 200° C. for PEI, which are superior to those of PSU, i.e., 0.8% for DIN 53495 and 181° C. for DIN 53461.
Depending on the use in question, the lamella reaching to the region of the nozzle may, on its structure less end region viewed in the flow direction, have a dull lamella end having a height less than about 0.4 mm, preferably less than about 0.3 mm, or have on its structured end region viewed in the flow direction, a dull lamella end having a height of more than about 0.5 mm. In another embodiment, a structured end region can be provided with a grooved structure having a rectangular and/or wedge-like and/or parabolic and/or round shape with a constant and/or varying depth.
In an advantageous embodiment, the lamella is completely constructed of one high-performance polymer in a homogenous design; in an alternative embodiment, the lamella end only is formed from at least one high-performance polymer. Thus, both embodiments ensure that at least the critical region of the lamella, i.e., the lamella end in the preferred embodiment of a lamella tip, has the advantageous characteristics of the high-performance polymer.
Furthermore, the lamella according to the invention may be embodied in a headbox with sectioned stock density control (dilution water technology). In this embodiment of the headbox, the possibility is created of allowing the sectional control of throughput, stock density, and, thus, basis weight and orientation of the fibers in the presence of the optimized lamellae.
In order to take into account present and future requirements of
Loser Hans
Ruf Wolfgang
Greenblum & Bernstein P.L.C.
Griffin Steven P.
Hug Eric
Voith Paper Patent GmbH
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