The present invention generally relates to the field of paper converting. In particular, the present invention is directed to a system and method for creping electrical insulating paper.
Paper is used widely in the electrical equipment manufacturing industries as electrical insulation for various electrical conductors and other parts. For example, in the transformer industry, paper is used to insulate the magnet wires that make up the core windings of the transformers. Generally, this paper is wrapped around each magnet wire so as to electrically insulate each portion of the wound wire from other portions of the wire in the winding. Typically, such insulating paper is creped and calendered electrical kraft paper having certain electrical properties so as to provide the necessary insulating properties. In addition to particular electrical properties, the kraft paper used for electrical insulation typically has a relatively high tensile strength, at least along the length of the paper. Often, such kraft paper is made from a furnish having a relative large percent composition, e.g., 70% or more, of virgin softwood fibers, which give the paper much of its tensile strength. Electrical kraft paper often contains 100% unbleached sulfate fibers so as to meet the American National Standards Institute (ANSI) and American Society for the Testing of Materials (ASTM) specification D-1305-99, “Specification for Electrical Insulating Paper and Paperboard-Sulfate (Kraft) Layer Type,” which is an accepted specification for electrical kraft paper.
A common method of creping electrical insulating papers is performed in a continuous-web process wherein a web of roll-base electrical kraft paper is adhered to a creping roll and then creped from the creping roll with a creping blade that imparts a desired creping pattern into the paper. Following creping, the creped web is typically calendered and dried to form a finished insulating paper product. Conventionally, the creping roll has a very smooth peripheral surface for receiving the base kraft paper. During creping, the base kraft paper is supplied to the creping roll from a roll of such paper. As the paper travels toward the creping roll, it is treated with a creping solution for adhering the paper to the creping roll with the adherence necessary to create the desired creping pattern. As those skilled in the art know, the amount of adherence of the paper to the creping roll can be adjusted by changing variables such as the composition of the creping solution, the amount of solution and the amount the solution is dried prior to the web being scraped from the creping roll, among others.
For many years a large portion of the electrical insulating paper creping industry has utilized creping blades made of a metal, e.g., brass, that is softer than the material of the creping roll so as to minimize the damage that the blade causes to the roll. Changing a roll in order to regrind or replace the roll is much more expensive in terms of both time and money than regrinding or replacing a creping blade. Hence, conventional maintenance procedures require periodic regrinding or replacing of the creping blade. Since the creping blade is relatively soft, it wears relatively quickly from both the contact with the surface of the roll and the impact of the kraft paper web on the impact surface of the blade during creping. Consequently, the creping blade needs to be sharpened or replaced very frequently in order for the creped paper to remain within specifications. For example, it is common in the creping of base kraft paper having thicknesses of 2 mils or more to have to sharpen or replace a creping blade after creping only on the order of 13,000 lineal feet, or the amount typically contained in a single roll of base paper. Accordingly, it is common to sharpen or replace a metal creping blade with each new roll of base paper.
Sharpening a used blade is a time-intensive process that requires the creping system to be down for at least 15 minutes to a half hour. In addition, metal blades also require regrinding from time to time and new blades must be “run-in” prior to use. Regrinding and run-in require the creping roll to be run with the creping blade in full contact with the roll, but without the presence of the paper web. Regrinding a used blade after creping a roll of base paper can take about an hour. Grinding a new blade often takes 4 to 6 hours. Replacing a blade with a different blade in order to crepe a different product also requires allowing the creping roll to run against the blade for about an hour. As can be readily appreciated, since the creping roll cannot be used to crepe paper during regrinding, the productivity, e.g., the percentage of time during which a product meeting specifications is being made over a certain period of time, of conventional electrical insulating paper creping machines is severely constrained. What is needed is an electrical insulating paper creping machine having a higher productivity.
In one aspect, the present invention is directed to a method of converting paper. The method comprises the steps of providing a first web of kraft paper and adhering the first web to a roller. The first web is creped from the roller with a creping blade having a ceramic tip.
In another aspect, the present invention is directed to a system for converting paper. The system comprises a first web of kraft paper and a roll having a peripheral surface for adheringly receiving the first web. A creping blade having a ceramic tip engages the peripheral surface. The creping blade removes the first web from the peripheral surface so as to impart a creping pattern into the first web.
In a further aspect, the present invention is directed to electrical insulation comprising an electrical kraft paper having a machine direction and defining a plane. A creping pattern is imparted into the electrical kraft paper along the machine direction and has a plurality of peaks and a plurality of valleys. Each of the plurality of valleys is defined by a pair of walls each having a slope of at least 45° relative to the plane.
For the purpose of illustrating the invention, the drawings show a form of the invention that is presently preferred. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:
Referring now to the drawings,
As discussed in detail below, certain features of creping blade 36 provide a number of substantial benefits heretofore not realized in the kraft paper creping industry. As used herein, the term “ceramic-tipped” and similar terms mean that at least the portion of creping blade 36 that contacts creping roll 28 comprises a ceramic material. As such, this term encompasses the situation wherein only the portion of creping blade 36 that contacts creping roll 28 comprises a ceramic material and the situation wherein the entire blade is made of a ceramic material. Of course, all intermediate situations between these two extremes are encompassed by the term “ceramic-tipped” and like terms. Details of ceramic-tipped creping blade 36 are discussed below.
Creping system 20 may further include a roll feeder 40 for feeding rolls 44, 48, 52 of kraft paper 24 via a plurality of idler and other rollers 56 to creping roll 28. Roll feeder 40 may include one or more roll stations 60 for receiving rolls 44, 48, 52. In the embodiment shown, roll feeder 40 includes three roll stations 60 that may be used to cooperate with an optional auto-splicer 64, e.g., a “zero speed” auto-splicer, that automatically splices two rolls together while creping, calendering and winding remain at full production speed. Zero-speed and other auto-splicers 64 are well known in the paper converting and paper finishing industries, such that a detailed description is not necessary herein for those skilled in the art to understand the present invention. As those skilled in the art will readily appreciate, three roll stations 60 allow one roll station to contain roll 44 presently being creped, one roll station containing roll 48 that will be spliced to the end of roll 44, and one roll station for receiving and containing the next roll 52 to be spliced to roll 48. With three roll stations 60, one station will always be free to receive or contain a new roll 52 that will eventually be spliced to roll 48 that will be spliced into roll 44 presently being processed. Of course, any number of roll stations 60 may be provided, depending upon the design of roll feeder 40.
Upstream of creping roll 28, creping system 20 may include one or more applicators 68 of any suitable type, e.g., spray-type, brush-type or roller-type, for applying one or more creping solutions 72 or other conditioning solution(s) to kraft paper 24 prior to the paper engaging and adhering to the creping roll. In this connection, creping roll 28 may be heated to cure creping solution 72 applied to kraft paper 24 to the desired point to properly effect creping. Those skilled in the art will understand that a variety of solutions 72 may be used in creping system 20 such that further explanation is not required for those skilled in the art to understand and practice the present invention.
Depending upon the application of creped paper 76 made with creping system 20, the system may optionally include a calendering station 80 for calendering the creped paper to a desired finished thickness. Calendering station 80 may include any sort of calendering equipment needed for a particular design, such as soft or hard nip rollers 84. Creping system 20 may also optionally include one or more dryers 88 for drying creped paper 76. A winder 96 may also be provided for winding creped paper 76. Of course, if creped paper requires other, or additional, finishes, creping system 20 may be provided with the required finishing equipment (not shown) at the appropriate location(s).
Referring to
In addition, there is generally a large difference in the composition of the papers used in the tissue paper creping industry and the kraft paper creping industry. This is so due to the differences in the characteristics of the end products. In the tissue paper creping industry, important characteristics of the tissue paper are softness and bulk, whereas in many segments of the kraft paper creping industry, e.g., the electrical insulating paper creping segment, an important feature of the paper is tensile strength. Accordingly, the papers for the two industries are generally made from furnishes having very different compositions. For example, furnishes for tissue paper often contain a relatively large amount of hardwood fibers, which are generally shorter than softwood fibers, that are “cooked” for a relatively long time. The long cooking time and the short fibers tend to yield a soft end product with a relatively low tensile strength. In contrast, furnishes for kraft paper requiring tensile strength as a primary attribute often contain a relatively large amount of softwood fibers that are cooked a relatively short time to maintain their stiffness. Kraft paper particularly suited for use in creping system (
As discussed in the background section above, creping electrical kraft paper with brass blades requires the blades to be changed after relatively short production runs due to wear that detrimentally affects the quality of the creping. For example, for 2 mil and 3 mil thick kraft paper, it is common to sharpen the brass blade every time a new roll of base paper is about to be creped. As a result, conventional kraft paper creping systems had no need for productivity-increasing equipment, such as auto-splicers that allow multiple base paper rolls to be creped in series with one another without shutting down the system. This is so because the system had to be shut down anyway to replace or sharpen the blade.
In contrast, however, the use of ceramic-tipped creping blade 36 greatly increases the length of the kraft paper 24 that creping system 20 can process before the blade must be replaced due to blade wear detrimentally affecting the quality of creped paper 76. For example, with a 2 mil electrical kraft paper, creping system 20 using ceramic-tipped creping blade 36 has been seen to crepe one million lineal feet and more of kraft paper 24 before blade wear detrimentally affects the creping quality. With typical rolls 44, 48, 52 of 2 mil electrical kraft base paper containing about 13,000 lineal feet each, each ceramic-tipped creping blade 36 can be used to crepe 120 or more rolls of paper, i.e., 1.56 million feet or more. Since creping system 20 of the present invention is not constrained to single-roll processing as are conventional creping systems (not shown) using brass blades, the inventive creping system can benefit from the addition of auto-splicer 64 that automatically splices the beginning of new roll 48 to the end of roll 44 presently being processed without shutting, or even slowing, the system down.
Referring to
Referring again to
As mentioned above, ceramic creping blades are well known in the tissue paper creping industry and are available for the tissue creping industry from manufacturers such as BTG Americas, Inc., Norcross, Ga. However, the configuration of ceramic tip 100 may have to be customized for a particular blade setup for kraft paper creping, since, as mentioned above, tissue paper creping systems are typically much different than kraft paper creping systems, such as system 20 of the present invention. The configuration of creping blade 36 discussed in the immediately preceding paragraph was a custom configuration that was specially requested and made.
In contrast,
Whereas
The individual (I) and moving range (MR) charts 132, 136 of
I-chart 132 also shows that the upper control limit (UCL) 140 and lower control limit (LCL) 144 for the brass blade are, respectively, about 63.5 ppi and about 40 ppi. Similarly, UCL 140′ and LCL 144′ for ceramic tipped blade 36 (
In addition to the increases in mean tensile strength and decreases in tensile strength variations relative to creped papers made using brass blades as just discussed, it has been observed that creped kraft papers 76, 76′ made in accordance with the present invention have at times experienced increases in machine direction elongatability (MDE) of about 2% to about 4% or greater relative to creped papers made from the same base kraft paper with the same process parameters, but with a brass blade. It has further been observed that the efficiency and yield of creping roll/blade setup may increase using ceramic-tipped creping blade.
The reduced detriment to tensile strength and greater elongatability relative can have a number of benefits. For example, as mentioned above, increases in tensile strength and elongatability relative to creped paper made using brass blades can result in less breakage since the creped paper is stronger and more forgiving. As a consequence, it is possible to run creping system 20 at speeds higher than could be achieved with a brass creping blade that produces a creped paper having lower strength and elongatability. Similarly, speed gains may also be realized during use of the creped insulation paper, e.g., during winding of magnet wires (not shown).
An additional benefit that may result from the fact that creped paper, e.g., creped paper 76′ of
A further benefit of the present invention is that ceramic-tipped creping blade 36 is less destructive to kraft paper 24 than a brass blade and creped paper 76 can be brought into specifications more quickly as compared to a brass blade. Consequently, the use of ceramic-tipped blade 36 results in less out-of-specifications, startup waste of kraft paper 24 and less time bringing creped paper 76 into specifications.
Yet another benefit particularly important for the electrical insulating paper industry is the elimination of the paper being contaminated with metal dust resulting from a metal blade contacting a metal crepe roll. Ceramic-tipped blade 36 of the present invention virtually eliminates this sort of contamination. In conventional creped insulating papers, the metal dust tends to degrade the dielectric properties of the paper that are critical for electrical insulation.
While the present invention has been described in connection with a preferred embodiment, it will be understood that it is not so limited. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined above and in the claims appended hereto.
This application claims the benefit of priority of U.S. Provisional Patent Application Ser. No. 60/502,683, filed Sep. 12, 2003, and titled “System and Method for Creping Electrical Insulating Paper,” that is incorporated by reference herein in its entirety.
Number | Date | Country | |
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60502683 | Sep 2003 | US |