Paper making and fiber liberation – Apparatus – Web creping or crinkling type
Reexamination Certificate
1998-12-02
2001-03-27
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Apparatus
Web creping or crinkling type
C015S256510, C034S120000
Reexamination Certificate
active
06207021
ABSTRACT:
The present invention relates to a creping blade for the detachment of a travelling paper web from a rigid dryer cylinder to form a porous paper product, so called tissue.
BACKGROUND OF THE INVENTION
Scrapers or doctor blades are extensively used in the paper industry for different purposes but in most of the cases their function is to clean or scrape off material or residues from the surface of a rotating roll. A specific application of blades is constituted by their use as creping blades for the manufacture of tissue. Such blades have for a purpose to detach a paper web from a rigid dryer cylinder, usually a cast iron cylinder, by scraping the surface of the cylinder. At the same time the top or edge surface of the blade exerts a compressive action on the paper thereby creating the typical crepe structure of a tissue product.
Since creping blades are subjected to extensive wear different techniques to increase their life time are being used, such as adding wear resistant material onto the section of the blade engaging the cylinder. As an example of such reinforcement of the top or edge surface of the blade ceramic hardfacings are currently used as a practical solution to reduce the blade wear. Such ceramic coatings are usually applied to blades made of hardened and tempered carbon steel and can be applied by thermal spraying, such as plasma spraying or plating.
Examples of techniques for the provision of such wear resistant coatings onto doctor blade or scrapers are found in UK patents 978,988, 1 289 609, and 2 130 924. All this prior art is directed to the provision of a wear-resistant coating on the part of the blade engaging the surface of a rotating cylinder.
SUMMARY OF THE INVENTION
The present invention is based on an entirely different concept relating to the creping blade design, said concept allowing the blade to be used for a longer period of time while maintaining a substantially constant tissue quality.
Accordingly, one object of the invention is to provide a new creping blade having a substantially extended lifetime yet allowing the provision of a high tissue quality.
Another object of the invention is to provide a creping blade provided with a wear resistant coating at the location of the blade hit by the travelling paper web.
Yet another object of the invention is to leave those parts of the blade engaging the moving cylinder substantially uncovered by such wear resistant coating to provide for a certain amount of wear of said uncoated part.
Still another object of the invention is to provide a creping blade designed in such a manner that inspite of the blade wear a substantially constant engagement specific pressure of the blade against the cylinder can be maintained.
For these and other objects which will be clear from the following description the invention provides for a creping blade for the detachment of a travelling paper web from a dryer cylinder, wherein said blade has an edge or tip section engaging said cylinder and also is constantly hit by the travelling web during its detachment from the cylinder. The improvement according to the present invention is constituted by the fact that said edge or tip section is provided with a wear resistant coating on a first part of said second hit by the web, whereas the other part of said section engaging the cylinder is uncoated or coated with a non-wear-resistant material so that said other part is subjected to sliding wear.
In a preferred embodiment of the invention the creping clade has a thickness of at least about 0.5 mm. The upper extreme of the thickness of the blade is not particularly critical but usually does not exceed 2 to 3 mm. A particularly practical range is from about 0.8 to about 1.2 mm.
The wear-resistant coating used to reduce the wear on the part of the blade which is hit by the travelling paper web during detachment can suitably be comprised by a ceramic material, but also other wear-resistant materials, such as metallic or composite materials, can be used. It is particularly preferred to use a ceramic material applied by thermal spraying, such as plasma spraying or by a PVD (physical vapour deposition) or CVD (chemical vapour deposition) process.
The wear-resistant coating is preferably comprised of a thermally sprayed material and is suitably selected from metal oxides, silicates, carbides, borides, nitrides and mixtures thereof.
Particularly preferred ceramic materials are selected from alumina, chromia, zirconiz, tungsten carbide, chromium carbide, zirconium carbide, tantalum carbide, titanium carbide and borides.
The wear-resistant coating applied in accordance with the present invention has preferably a thickness varying within the range of about 1 to 100 &mgr;m. However, the coating can have a thickness even exceeding that upper limit.
The material used in the creping blade according to the present invention is preferably a metal in the form of a strip of metal, polymeric material or composite material, and it is particularly preferred that such metal strip is comprised of hot or cold rolled steel. It is suitable to use hardened and tempered carbon steel as a material for the blade.
In another preferred embodiment of the invention the creping blade is comprised of a substantially flat strip having a top or edge surface, a side surface facing the cylinder, a junction section between said surfaces engaging said cylinder and a recess in said side surface extending along said junction section and forming a narrow wear land on the junction section, said land being subject to conformation to the moving cylinder surface.
In such embodiment it is preferred that said recess is designed in such a manner that the wear land surface engaging the cylinder surface remains essentially constant throughout the operative cycle of the blade.
Further, in relation to such embodiment the surface of the blade opposite to the wear land is provided with wear-resistant coating to broaden said top or edge surface of the blade. This will increase the depth of wear, yet maintaining the creping efficiency and a constant tissue quality.
The recess may be filled with a non-wear-resistant material. In the alternative said other section is uncoated.
REFERENCES:
patent: 3688336 (1972-09-01), Costello, Jr. et al.
patent: 3703019 (1972-11-01), Bratt
patent: 4247196 (1981-01-01), Ogawo
patent: 978988 (1965-01-01), None
patent: 1289609 (1972-09-01), None
patent: 2130924 (1984-06-01), None
patent: WO86/07309 (1986-12-01), None
Eriksson Tore
Freti Silvano
BTG Eclepens S.A.
Burns Doane Swecker & Mathis L.L.P.
Hastings Karen M.
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