Roller for pressure treatment of webs

Details Roller for pressure treatment of webs Roller for pressure treatment of webs

1991-11-18

1993-11-02

Eley, Timothy V.

Roll or roller

With antideflection means

492 40, 492 42, 492 47, 492 56, B21B 2700, B21B 1302

Patent

active

052579654

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a roller according to the introductory part of claim 1. Rollers of this kind have a diameter of 0.3 to 1.50 meters and a length of up to 9 meters; the shell of the roller in the case of press rollers consists usually of granite, and, in the case of hard calender rollers, it consists of special cast iron with a sometimes chromium plated surface. As it is known, granite is an igneous rock which has a granular, speckled appearance, and consists usually of tightly packed crystals of quartz, feldspar, mica and a number of smaller components such as magnesite and iron pyrites which can be seen only with a microscope. The following material characteristics are found in the literature on granite:


______________________________________ Important Material Characteristics: ______________________________________ Tensile strength 10-20 N/mm.sup.2 Compressive strength 160-240 N/mm.sup.2 Compressive fatigue limit approx. 110 N/mm.sup.2 Modulus of elasticity 15,000-71,000 N/mm.sup.2 Poisson's number 0.2 Density 2.62-2.85 g/m.sup.2 Specific heat capacity 710-840 J/kgK Thermal conductivity 2.9-7.5 W/mK Thermal change of length 5-9 m/mK ______________________________________
In recent times it has emerged that the most critical of these material characteristics is the tensile strength, which is very low in all rock. Also, the tensile strength test is very complicated, since the shape, size and loading method have a great influence on the results and also, when considering its properties, it must be taken into consideration that granite, as a natural product, varies greatly, and local flaws in the structure can never be ruled out. With increasing size of the roller diameter and increasing speed of paper machines, the centrifugal force involved approaches the limit, and the first destructions of granite rollers have already been published, which not only resulted in severe disturbances of production but also constituted great danger to personnel in the vicinity of the machine.
To avoid the known disadvantages it has already been proposed to use press rolls whose outer periphery consists of plastic admixed with pulverized rock as filler--EP Patent 53 804.
It is likewise known to form the shell of the roller form a mixture of metal powder and a powder of inorganic substances, using as metals steel, nickel, chromium, titanium, copper or bronze, and, as the inorganic substances, quartz, feldspar, aluminum oxide, zirconium oxide, titanium oxide, titanium carbide, silicon carbide, magnesium oxide, silicon nitride, chromium oxide, tungsten carbide, niobium carbide, vanadium carbide, chromium carbide, or mixtures thereof--German Patent Disclosure Document 35 46 343.
It has furthermore been proposed to build up the shell of the press roller in the form of a hardened body of a hydraulic composition, i.e., from cements and mineral materials, and to cure it so that a compressive strength is achieved of not less than 1,000 kp/cm.sup.2 and a density of not less than 2.5. Portland cements, oil cements, silica cements and fly ash cements as well as blast-furnace cements have been proposed as the cements, and, as mineral materials, alite (CA.sub.3 SiO.sub.5), blast furnace slag, fly ash, and particles of crushed rock, such as granite, quartz, and feldspar, and additives, activators etc. are added in addition to water--German Patent Disclosure Document 36 17 316.
It is furthermore known to apply a coating to a shell of the roller made of metal, the coating consisting of chromium or stainless steel to which one or more components of a ceramic substance have been added. Al.sub.2 O.sub.3, SiO.sub.2, TiO.sub.2, ZrO.sub.2, SiC,TiC, Cr.sub.3 C.sub.2, WC, NbC, VC, and Cr.sub.7 C.sub.3 have been proposed as ceramic additive materials.
An additional proposal for the production of a press roll is contained in European Patent Disclosure Document 207,921. According to this proposal, first a metal intermediate layer of a lower coefficient of expansion than that of the ro

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