GB2102106A - Furnace or like thermal insulation - Google Patents

Abstract

A furnace or like lining is formed by an assembled sheet 1 of cut strips 2 of resiliently felted refractory fibres, with an organic binder, secured to furnace wall 5 and arranged so that the fibres predominantly extend in planes perpendicular to the wall. The sheets are held in place by tacky adhesive cement 6 which penetrates key recesses 3 cut in the back surface of the sheet 1. <IMAGE>

Description

SPECIFICATION Furnace or like thermal insulation This invention relates to refractory, thermally insulating linings for the internal walls of furnaces and other high temperature enclosures such as ducts, ovens and kilns.

It is known to make such linings from strips of ceramic fibre blanket arranged perpendicularly to the plane of the furnace wall, so that the fibres have an "end-on" orientation to the hot enclosure, the strips being held together by combustible wrapping or bonded together by an adhesive between the strips of fibre blanket. The wrapping or adhesive holds the strips together for installation and burns away on first firing of the furnace or equivalent heating in use.

The strip lining is sufficiently coherent for the application of cement to secure the lining to a supporting structure, for example the surface of existing firebrick, refractory castable or refractory plastics materials, metal net structures or to another lining where the construction utilises one or more layers of insulation.

A suitable cement is a tacky adhesive cement on the back face of the lining which is then applied to the surface of the wall, the tacky adhesive cement subsequently setting into a stable heatresistant and refractory condition thereby securing the lining to the wall. A suitable tacky adhesive cement is a low silica content air-drying cement based on sodium silicate.

Recently, ceramic fibre materials have been developed in the form of more or less flexible felts, called semi-flexible felts, composed of refractory ceramic fibres and an organic binder and manufactured by vacuum forming. They can be made of uniform density with the possibility of utilising mixed fibre compositions. Such felts have the essential characteristic that the fibres are resilient and are held in intrinsic compression by the organic binder, such that when the binder is burnt out, for example by exposure to furnace operating conditions, the felt tends to expand. The felt can be cut into strips and used in a similar manner to ceramic fibre blanket strips.

The ceramic fibre content of the felt can be of one type, e.g. KAOWOOL (alumina-silicate fibre Trade Mark of Babcock and Wilcox U.S.A.) or a mixture of fibres, e.g. SAFFIL (alumina fibres Trade Mark of l.C.I. Ltd.), and KAOWOOL for instance where the intimate mixture of different fibres makes the felt especially resistant both to temperatures above 1 350or up to 1 6000C and to chemically aggressive atmospheres.

Linings made from semi-flexible felts have been more difficult to attach to furnace walls, using the same adhesive cement, than blanket linings. Great care and attention must be taken to ensure that the cement, which is water-based, is thoroughly manipulated into the organically bonded fibres on the back-face of the felt. This is necessary to achieve adequate adhesion of the lining to the furnace wall when the cement is wet but more importantly to achieve high temperature adhesion of the cement to the lining. The cement must adhere to the lining during combustion or degradation of the organic binder content on initial furnace firing and thereafter in the fired condition.

This fired condition is dependent on temperature and time and may be in a flexible or semi-rigid state, or be changing from the former to the latter in service.

Furnace conditions also affect the rate of state and condition changes of the fibre material described above since temperature and time can vary with different furnace conditions.

In spite of installation with the care and attention set out above, problems have occurred in certain furnace conditions with detachment of flexible felt linings.

To solve the above problem, the present invention provides a thermal insulation lining, of a furnace or like wall, comprising an assembly of cut strips of resiliently felted refractory fibres held in intrinsic compression by an organic binder, the strips having been cut, from a felted sheet, transversely to the plane in which the fibres predominantly lie, and then re-arranged in contact side-by-side and held together to form an assembled sheet in which the fibres predominantly extend in planes perpendicular to the wall, at least the back surface of the assembled sheet facing the wall having formed therein key recesses occupied by tacky adhesive cement forming part of a layer of such cement coating the back surface of the assembled sheet to secure it to the wall surface.

In the case of a multiple layer lining, key recesses may be provided in both faces of an inner or intermediate sheet for keying with an intermediate cement layer.

By providing a positive key for the cement to penetrate into the back of the lining, reliance is no longer placed only on the adhesive bond between the fibrous material and the wall surface.

It will be appreciated that the effectiveness of the provision of key recesses for the cement is very surprising having regard to the fact that the surface of felted fibre material would ordinarily be expected to provide a good key for adhesive.

It is considered probable that the movement of fibres in expansion, recovering from their intrinsic compression when the binder degrades on heating, is sufficient to break down ordinary fibrous surface adhesion of the cement. By providing a positive key, some breakdown of surface adhesion can be tolerated because the interlock of the cement in the key recesses is not reduced, and may even be enhanced, by expansion movement of the fibres in the plane of the assembled sheet of felt strips.

The invention is illustrated by way of example on the accompanying drawing, in which: Fig. 1 is a perspective view of the transversely grooved back surface of part of an assembled sheet of felted fibre strips in accordance with the invention, Fig. 2 is a fragmentary perspective view of an assembled sheet showing an alternative form of key recess, and Fig. 3 is a fragmentary cross-sectional perspective view of a furnace lining in accordance with the invention.

As shown by Fig. 1, an assembled sheet 1 of cut strips 2 of resiliently felted refractory fibres, which lie as indicated predominantly in planes perpendicular to the faces of the sheet, i.e. in the direction of the thickness of the sheet, has dovetai grooves 3 cut across the back surface of the sheet transversely to the strips.

In Fig. 2 an inwardly divergent circular recess 4, formed by drilling or routing, it shown as an alternative shape of key recess. Other closed shapes, such as square or rectangular could be used.

Fig. 3 shows how an assembled felt strip sheet 1 is secured to a furnace wall 5 by a coating layer of tacky adhesive cement 6 which penetrates and keys in the grooves 3. As indicated in dotted lines, key recesses 7, which may be grooves or closed shape recesses, may be provided to key with cement securing another assembled strip sheet to the sheet 1.

The fibre composition, dimensions and details of shape of the felt strips and assembled sheets as well as the size, number and distribution of the key recesses will be selected to suit requirements.

The lining may be assembled from felt strips on site and the key recesses may then be formed.

However prefabrication of assembled sheets is preferred, the felt strips being held together by adhesive or wrapping, and the preferred shapes of dovetail grooves transverse to the strips, or divergent recesses, lend themselves to machine tool cutting in prefabricated sheets.

Claims (5)

1. A thermal insulation lining, of a furnace or like wall, comprising an assembly of cut strips of resiliently felted refractory fibres held in intrinsic compression by an organic binder, the strips having been cut from a felted sheet, transversely to the plane in which the fibres predominantly lie, and then rearranged in contact side-by-side and held together to form an assembled sheet in which the fibres predominantly extend in planes perpendicular to the wall, at least the back surface of the assembled sheet facing the wall having formed therein key recesses occupied by tacky adhesive cement forming part of a layer of such cement securing the back surface of the assembled sheet to the wall surface.

2. A thermal insulation lining according to claim 1, in which the key recesses are dovetail section grooves cut transversely to the strips.

3. A thermal insulation lining according to claim 1, in which the key recesses are inwardly divergent and of circular or other closed shape in cross section.

4. A multiple layer thermal insulation lining according to claim 1, 2 or 3, in which key recesses are provided in both faces of an inner or intermediate sheet for keying with an intermediate cement layer.

5. Thermal insulation lining substantially as described with reference to the accompanying drawing.