DD299952A5 - PROCESS FOR PRODUCING ASBEST FREE FLAT SEALING PLATES - Google Patents

Abstract

The invention relates to the production of asbestos-free flat gaskets on two-roll calenders. It is known that the substitution of asbestos by another raw material is not easy, as no raw material having the complex properties of asbestos has yet been found. The low storage capacity of solvents of the previously known substitutes leads to the adhesion of mixture components to the cooled roller of the calender. Through the use of bloated in organic solvents Xonotlits as a mixture component, the object of the invention is achieved. Main claim: Item 1. {Flat gasket plate, asbestos-free; two-roll calender; Xonotlit; Speichervermoegen; Solvent; Mix component; Verstaerkungsmittel; calcium silicate hydrate; Core layer}

Description

Field of application of the invention

The invention relates to the production of asbestos-free flat gaskets, which are produced on a two-roll calender.

Characteristic of the known technical solutions

Flachdichtungsplatteii, u, o be prepared on a two-roll calender, consist of 3 layers, a shoulder layer, a core layer and a cover layer. In this case, one roll of the two-roll calender is cooled and the second roll is heated. On this heated roll, the flat sealing plate is built up of different mixtures in layers. Conventional flat gaskets mainly contain asbestos in addition to rubber, fillers and vulcanizing aids. Asbestos is an excellent reinforcing raw material, however, recent research has shown that asbestos in rubber-bound and / or resin-bound products are much more positive properties, including those that have a significant impact on the processability of such mixtures.

Since it has since been proven that asbestos can cause severe health problems in humans, bans have been issued in many countries for the processing of asbestos, or at least aggravating orders on the handling of asbestos. Therefore, an attempt is made to find suitable substitutes for the asbestos. In the opinion of the experts, it has come to the realization that the asbestos with its complex properties can not be replaced by a single substitute. The substitution of asbestos is based on a combination of fillers and fibers with which to simulate the complex property spectrum of asbestos is tried.

In addition to the problems related to the thermal instability of organic fibers and / or the dispersion of some fillers and fibers and / or the lack of adhesion of predominantly synthetic fibers in the rubber dressing and / or the high prices of some raw materials, there are also still considerable Processing difficulties in the shaping of asbestos-free flat gaskets on. These processing difficulties consist in the fact that, during the construction of the initially mentioned layer structure of the flat sealing plate, parts of the core layer under construction adhere to the cooled roller. By means of these adhering mass particles, the cooled roll is practically profiled, which leads to local impressions in the flat gasket plate under construction. A homogeneous plate structure is prevented. This leads to a corrugated plate surface in the end result. A FlachdichtungsplattG made in this way is completely unusable due to their uneven surface and must be discarded. From this, the role of asbestos in the plate forming process of the core layer was further investigated, and it was found that the morphology of the asbestos fibers - contrary to the previous opinion of the art, according to which the asbestos fibers are primarily responsible for application properties such as thermal resistance and tear resistance and the like - Also essential for the processability of the core mass. It has been known that, due to its fibrillar hollow fiber structure, the asbestos fiber is able to store and deliver sufficient quantities of solvent required for the preparation of the rubber. " That the cooled roller is wetted with a solvent film and that until the construction of the gasket plate is completed. Such solvents include, for example, gasoline, benzene, toluene, methylene chloride, methyl ethyl ketone, and others.

This solvent film prevents the adhesion of mixture parts to the cooled roll. Many of the previously known and used substitutes lack this property of the storage capacity of solvent, so that it evaporates quickly in the course of Flachdichtungsplattenaufbaues on the heated roll. In order nevertheless to be able to produce asbestos-free flat sealing plates on a two-roll calender, a water film or a film of a water-alcohol mixture is applied as release agent after or during the evaporation of the solvent on the cooled roll. This is done, for example, by spraying the release agent from a corresponding atomizer nozzle by hand. The disadvantage of this method is obvious. The release agent spraying means an additional process step, which has to take place simultaneously with the plate calendering. In addition, the environment of the two-roll calender and this itself is constantly wetted. It is up to the skill of the operator to decide how successful this procedure is.

Object of the invention

It is the object of the invention to provide a process for the production of asbestos-free flat gaskets of two-roll calenders, with which the adhesion of mixture components to the cooled roll is prevented.

Darloyung the Wet ons of the invention The object of the invention is a process for the production of asbestos-free flat gaskets on two-roll calenders

to provide that in the mixture such an amount of solvent over the time of the plate assembly is stored, that the object of the invention is achieved.

It has been found that the acicular calcium silicate hydrate "xonotlite" which is known for the production of Thermal insulation materials is used, which occurs when substituting the asbestos Eliminate processing difficulties. Although the cause of this effect is not yet fully understood and Subject of further investigations, it is assumed that the cause can be explained as follows: Xonotlite forms due to its fine needle-like grain shape and that, for example, during its manufacture

agglomerates consisting of three-dimensionally toothed needles which are difficult to destroy and which also occur in organic solvents, such as gasoline, xylon and the like, remain stable during the comminution process occurring during the comminution process. The hydrophobic nature of the aforementioned solvents enhances them

Agglomerisationsneigung considerably, while hydrophilic solvents such as water or alcohol, dispersing effect. These agglomerates are due to their large internal cavity (porosity) suitable organic liquids through Capillary action to save. The technical effect of the invention consists in the fact that during the construction of the flat gasket plate on the heated Roll these agglomerates are deformed in the nip, the stored solvent at least partially

is released and deposited on the cooled roller. This continuous wetting of the cooled roll forms the desired release layer, which is constantly maintained by the deformation of further agglomerates in the nip and the associated release of solvents. This prevents the adhesion of mixture components to the cooled roll. Another positive effect is that the remaining after the evaporation process Xonotlitneln represent an excellent filler for the core layer mixture. The needle-shaped form of the Xonotlite also acts as a reinforcing agent.

Under the calcium silicate hydrate is a mined or industrial by hydrothermal conversion of SiOy dust and quicklime produced acicular mineral. Since ultimately the inventively stored amount of solvent, the processing of the core layer mixture essential

It is necessary to introduce an appropriate amount of xonotlite into the mixture. It is 5 to 50 parts by mass in%, depending on the other components of the composition of the flat gasket plate, whereby the optimum amount of xonotlite can easily be determined experimentally taking into account the total composition of the mixture.

The mass ratio of xonotlitol to solvent should be in order to utilize the storage capacity of xonotlite agglomerates

about 1 to 1.5 to 1 to 3.3, preferably 1 to 2 to 1 to 2.5. For the rubber binder v / ird recommended: NBR, SBR,

EPDM or similar. Suitable solvents are all customary organic solvents for rubbers, such as gasoline, benzene, toluene, Methylene chloride, methyl ethyl ketone and / or mixtures hidraus. Suitable reinforcing agents are: glass fibers, carbon fibers, PAN fibers, pre-oxidized PAN fibers, cellulose fibers,

aromatic polyamide and polyester fibers.

As vulcanization aids are recommended: sulfur, peroxides, accelerators, activators, pigments. Fillers are: slate flour, kaolin, carbon black, graphite, talc, silicic acid, mica, bentonite, barite, wollastonite. Ausführungsbolsplele The invention will be explained in more detail below by exemplary embodiments. Embodiment 1 The following starting materials were used for an asbestos-free core mixture for flat sealing plates:

(Figures in% by weight)

13TeileSBR

10 parts PAN fibers 3 parts vulcanization agent 1

59 parts of a mixture of kaolin, silica and mica in equal parts 15 parts of xonotlite

100 parts solid + 60 parts gasoline based on the dry weight of the mixture components

In one part of the total amount of solvent, the rubber was swollen for at least 24 hours and then made into a homogenous mixture in a high speed mixer with the remaining mixture components and the remaining solvent. This mixture was calendered on a two-roll calender to an asbestos-free seal plate.

Implementation Bills 2

For a further, higher temperature resistant gasket sheet, the following ingredients were used:

(% Mass in% by weight) 15 parts 12 parts of aromatic polyamide fiber, 3 parts of aluminum silicate fiber (non-melted) 3 parts of vulcanization aid 57 parts of a mixture of kaolin, calcium silicate hydrate, bitonite and heavy spar

in equal parts 10 parts of xonotlite

100 parts solids + 60 parts toluene based on the dry matter of the mixture components

In both cases, gasket parameters were achieved which are in the area of asbestos-containing gasket sheets. There were no technological difficulties due to the adhesion of mixture components to the cooled top roll.

Claims (2)

1. A process for producing asbestfteler gasket sheets on a two-roll calender, wherein a roller is heated and a roller is cooled.und on the heated roller a flat sealing plate is constructed with a shoulder layer, a core layer and a cover layer, characterized in that in the mixture for the core layer is incorporated into the conventionally obtained or industrially produced acicular calcium silicate hydrate xonotlite, to a proportion of 5 to 50% by weight, based on the solids content of the total mixture. 2. The method according to claim 1, characterized in that the ratio of used xonotlite to the amount of solvent used is 1.5 to 3.3, preferably 1 to 2 to 1 to 2.5.