GB2135038A

GB2135038A - Mantle brick for chimney

Info

Publication number: GB2135038A
Application number: GB08333111A
Authority: GB
Inventors: Friedrich Schiedel; Gerhard Hausladen; Werner Munz; Elmer Popelyszyn; Jurgen Vochetzer; Ulrich Wengenroth
Original assignee: Schiedel GmbH and Co
Current assignee: Schiedel GmbH and Co
Priority date: 1982-12-13
Filing date: 1983-12-12
Publication date: 1984-08-22
Also published as: IT1205398B; AT397684B; DE3246078A1; GB8333111D0; IT8368290A0; ATA431283A; FR2537637A1

Abstract

A mantle brick for a multiple- shell chimney has an internal aperture (8) for receiving a chimney fireclay pipe-string (2) and recesses (16) adjacent the aperture defining ducts running parallel to the aperture. The fireclay pipes are surrounded by an insulation layer of mineral fibre mats (4). Start lines (30) for a cutting tool may be located opposite a duct on the surface of the mantel brick, the interval of these start line corresponds to the size of the aperture. Removal of the part of the brick between the start lines provides access to the internal aperture where a chimney cleaning door or branch flue connection may be fitted. Details are provided of joints between the bricks particularly with reference to the joining of the duct. <IMAGE>

Description

SPECIFICATION Mantle brick for chimney The invention relates to a mantle brick for a chimney, and in particular to a mantle brick for a multiple-shell chimney with at least one duct which extends in the mantle brick in the longitudinal dircetion thereof and is open through a cavity towards the internal aperture of the mantle brick, there preferably being a plurality of such ducts distributed round the internal aperture.

Such a mantle brick has been proposed with a plurality of ducts distributed round the internal aperture in an application (published in October 1 982 as German Offenlegungsschrift 32 11 536) by the same applicant. In the case of this mantle brick, the ducts serve as flow paths for a ventialtion gas supplied from the exterior and discharged to the exterior, to enable corrosive gases, steam et cetera which has emerged from the smoke gas to be discharged. Two embodiments of cavities by which the ducts are connected to the internal aperture of the mantle brick are suggested in this context.In one embodiment the cavities extend continuously along the total length of the mantle brick, so that the inside crosssection of duct and cavity is the same at all heights, excepting possibly shaping conicities, and the cavity is included in the flow path of the ventilation gas. In the other embodiment the cavities extend only over a part of the height of the mantle brick and are particularly interrupted at one end face of the latter, so that the cavities are provided only for communication between the actual flow path extending in the ducts and the internal aperture of the mantle brick, but are not included in the flow path of the ventilation gas in the proper sense.

According to a first aspect of this invention there is provided a mantle brick for a multipleshell chimney, having an internal throughaperture for receiving a chimney pipe-string and adjacent said aperture one or more recesses defining a space or spaces respectively open to the through-aperture and on the outside of said mantle brick two start lines to enable cuts to be made extending to said space(s) to allow removal of a portion of the mantle brick between the start lines to provide an access opening to the through-aperture.

Preferably there are a plurality of recesses each extending through the brick to define a duct, and there may be a pair of said start lines associated with each recess, so that the start lines define a set of portions of the mantle brick, one portion between each pair of adjacent recesses, any one of which portions can be cut out to provide said access opening.

According to a second aspect of this invention there is provided a mantle brick for a multiple-shell chimney, the brick having a rounded internal through-aperture for receiv ing a chimney pipe-string, a polygonal exterior wall and associated with each corner of the polygonal exterior wall a recess adjacent said through-aperture with the minimum wall thick ness of the brick between the polygonal exte rior wall and the duct being substantially equal to the minimum wall thickness of the brick between the internal through-aperture and the polygonal exterior wall.

Preferably on at least one face of the poly gonal exterior wall there is a pair of start lines for a cut, each one of said lines being at the or one of the positions of minimum wall thickness of the duct at a respective corner bordering said face of the polygonal exterior wall.

It is particularly convenient if there is a start line for a cut on each side of each corner of the polygonal exterior wall at the or one of the positions of minimum wall thickness of the brick between the polygonal exterior wall and the recess at that respective corner.

The minimum wall thickness is suitably be tween 4 cm and 5 cm. The brick may suitably have a square cross-section.

According to a third aspect of this invention there is provided a mantle brick for a multiple shell chimney having an internal through aperture running from its lower to its upper end and abutment surfaces at its upper and lower ends to allow stacking of the bricks, characterised in that the abutment surfaces are so shaped that when two such bricks are stacked one above the other, the upper abut ment surface of the lower brick projects into the internal through-aperture beyond the lower abutment surface of the upper brick.

This feature may be provided, for example, by having an internal circumferential projec tion at the upper abutment surface of each brick (see Fig. 2), or by internally chamfering the wall at the lower abutment surface (see Fig. Fig. 5).

Embodiments of the invention relate princi pally to those mantle bricks in which the duct and the cavity extend continuously along the total height of the mantle brick. However, it is not intended within the ambit of the invention to exclude the possibility that the duct and/or the cavity is interrupted in the longitudinal direction of the mantle brick, so long as the mass of the material bridges forming the interruptions is relatively small in proportion to the remaining longitudinal extension of the duct and/or of the cavity in the mantle brick.

Accordingly, although the embodiments of the invention particularly contemplate the use of the duct and/or optionally of the cavity as a flow path for a ventilation gas, embodiments of the invention are nevertheless not restricted to this purpose.

A mantle brick according to an embodiment of the invention may further be connected, individually or in assembly with other parts, to form either a finished chimney part or to form either a finished chimney part or to form a complete or finished chimney.

A mantle brick according to an embodiment of the invention, like a simple mantle brick, may be considered particularly for the erection of at least triple-shell chimmeys from finished parts, wherein an internal pipe carrying smoke gas is surrounded by a thermal insulation layer and the mantle brick serves to brace radially the combination of smoke pipe and thermal insulation layer accommodated in it, and in this respect ensures primarily the static strength of the chimney. The peripheral surfaces of the internal aperture of the mantle brick, which are located between the cavities, may serve for the radial bracing of the mats or plates of the thermal insulation layer brought into the corresponding configuration.

Now it is the aim of the development of finished parts for chimney construction, on the one hand to manage with the smallest possible number of types of finished parts, and on the other hand to design the finished parts so that their production is simple and inexpensive, that they can be assembled in simple manner and that they also exhibit optimum functions in the chimney. The invention is based upon the discovery that possible ideas for generic mantle bricks have by no means been exhausted hitherto, but that defects exist in various respects. It is therefore the underlying aim of the invention to improve further the usefulness of mantle bricks.

Various aspects, which when partially or totally combined result in particularly great usefulness of the mantle brick according to embodiments of the invention, but which also appear inventive even individually, are considered within the ambit of the invention.

A first aspect of embodiments of the invention starts from the basis that particular mantle bricks have hitherto been held in stock for those chimney sections in which doors or smoke pipe connections were required for connection to lateral branch spigots of the smoke-carrying internal pipe. Separate stockholding of normal mantle bricks and of the said particular ones was therefore unnecessary. It is a partial aim of one set of embodiments of the invention to enable this separate stockholding to be avoided.

In order to achieve this aim, a mantle brick exhibits the following features: at least two start lines for a parting tool or cutting tool are constructed, each opposite a duct on the mantle surface of the mantle brick, and that the mutual interval of these two start lines corresponds to the width of a housing aperture for a door case or flue pipe connection.

In this case, the fact is utilised that the wall thickness between a duct extending in the mantle brick and the adjacent section of the external mantle surface can be made substantially smaller than the remaining wall thickness of the mantle brick between external mantle surface and internal aperture. In order to make a housing aperture for a door case or flue connection, it is therefore sufficient to sever only the relatively small wall thickness between mantle surface and duct, in order to create the lateral boundaries of the desired housing aperture. In this case the wall between mantle surface and duct is preferably cut through over the total brick height, so that a housing aperture for a door case or flue connection which has the full height of the mantel brick is then created.This is possible in a particularly simple manner in the case of customary commercial mantle bricks of such a height at which three mantle bricks with joints make up approximately one meter (for example, mantle brick height of 32.6 cm for a joint height of 7 mm). In special cases the top and/or bottom boundary of such a housing aperture, which has a smaller height than the mantle brick, may also be created. If both the ducts and also the cavities extend continuously over the total mantle brick height, then cutting through the wall between mantle surface and duct also means simultaneously cutting into the internal aperture. But even if relatively slight material bridges should remain, for example at one end face of the mantle brick, these too can in most cases still be cut additionally with relatively little outlay.

However, the arrangement whereby both the ducts and cavities and also the start lines preforming the cutting zones for a parting or cutting tool extend over the total height of the mantle brick is preferred here, though this is not an essential feature.

The position of the parting zone between mantle surface and duct is preformed by the relevant start line for the parting or cutting tool. If it were desired to provide different widths for a flue connection or a door case, a pair of double lines might be chosen instead of one pair of start lines preforming the lateral boundaries of the housing aperture. However, it has been discovered that it is sufficient to have a pair of single lines, since both types of cases can be made of equal width. This is preferred.

It is conceivable to preform only a single housing aperture by the two start lines. However, such a preformation of a housing aperture is preferably provided on all relevant lateral surfaces, for example, in front, at the back and on both sides in the case of a mantle brick or cylindrical external surface.

The same applies to externally square or rectangular mantle bricks, the external shape of which is preferred. In the case of polygonal mantle bricks with more than four corners, each mantle surface section preferably exhibits such a preformation.

It is not absolutely necessary for each start line to be opposite its own particular duct. For example, both the start lines preforming the same housing aperture may be opposite the same duct. On the other hand, pairs of start lines defining a plurality of housing apertures may also be provided on a single mantle surface section. This applies particularly when the same mantle brick exhibits a plurality of internal apertures for flue pipes, for example in one embodiment where there is an elongate rectangular mantle brick.

In one preferred form the mantle brick has a construction with a circular, or at least rounded, internal aperture, with a polygonal mantle surface and routing of ducts in corner regions of the mantle brick is preferably provided, whilst the polygonal shape is preferably square or rectangular. In the case of such an arrangement, therefore, the ducts are located in wall regions of the mantle brick which are more thickly dimensioned between mantle surface and internal aperture than in the regions between the corners. In this case the will thickness of the mantle brick between the relevant start line and the adjacent duct preferably corresponds approximately to the minimum wall thickness of the mantle brick between the corners.It is then unnecessary to part a greater wall thickness between external mantle surface and duct than in the otherwise narrowest places between mantle surface and internal aperture, but a parting line near the corner, and sufficient distance between the two start lines in order to obtain the necessary width of the housing aperture for a door case or flue connection is then obtained. On the other hand, the wall thickness of the duct, even in the region of the start line, is dimensioned as adequately thickly as is desirable all round in the mantle brick, particularly from static considerations.

The wall thickness of the mantle brick between the relevant start line and the adjacent duct is preferably approximately four to five centimeters. This means, for example if the mantle brick is produced in concrete in the manner widely adopted and preferred here, a statically adequate wall thickness, and nevertheless conforms to the practical engagement depth of customary commercial parting tools, particularly angle grinders, which conveniently permit simple parting down to depths of at least approximately five centimeters.

Accordingly, a preferred method of making a housing aperture for a door case or flue pipe connection in a mantle brick according to the invention preferably provides that the wall of the mantle brick is parted by means of a grinding wheel between the two start lines and the respectively adjacent duct and the wall section located between the parting lines is removed.

A wide spectrum of possibilities for embodying the start line exists. Thus it may be sufficient in individual cases to mark the start line in black or in a colour, continuously or intermittently, along the entire parting line or only along a part thereof, so as to direct the user of the parting or cutting tool spontaneously to the correct parting line.

However, the start line may also, alone or additionally to a coloration, be conformed geometrically differently relative to the surrounding mantle surface, for example as a smoothed or sand-blasted zone in relation to a rough surround. Apart from the fact that such a geometrical conformation also fulfils an optical guide effect, it may also serve directly as a start line for the parting or cutting element of the associated tool.

The latter is possible particularly if the start line is of channel-shaped construction. In this context the widest variety of channel shapes, for example rectangular, triangular or trapezoidal grooves or also rounded channels, particularly semicircular channels or U-shaped channels, may be considered.

From the standpoint of extensive prefabrication, it is further convenient to provide an adapted door case the width of which corresponds to the housing aperture preformed by the start lines and its depth to the wall thickness between one start line and the adjacent duct, whilst its height preferably corresponds to the height of the mantle brick.

Such a door case preferably exhibits a surrounding frame. This frame may exhibit a finished concrete frame, preferably framed by a metal frame part, and may be connectable to the mantle brick by a filling compound, preferably mortar (Fig. 11). With this construction the installation work is minimal despite the case being more complicated.

Alternatively the frame may exhibit an open angle profile, which is preferably formed by a metal frame part, and which, conjointly with the mantle brick cut out along the start line and with the end face of a projecting spigot of a flue pipe inserted into the internal aperture of the mantle brick, forms a housing gap fillable with filling compound, preferably mortar. With the latter construction the prefabrication outlay is smaller, but the installation outlay is somewhat greater. The choice of the suitable alternative depends upon circumstances.

Another partial aspect which restricted the serviceability of the known mantle bricks, was that when placing a mantle brick upon the end face, provided with jointing compound, such as mortar, of a mantle brick located beneath it, jointing compound is forced into the duct and falls down in the latter. This is undesirable, particularly if the relevant duct, optionally with associated cavity, is utilised as a flow path for a ventilation gas supplied from the exterior and discharged to the exterior.

However, this may also be undesirable in other cases.

It is therefore the second partial aim of some embodiments of the invention to counteract the falling of jointing compound into a duct and possibly into a cavity. Embodiments of the invention provide three alternative forms of solution here, which may be embodied individually or in twofold or overall combination The first solution has on at least one end face of the mantle brick a transition from the end face into the internal aperture of the mantle brick which is constructed recessed relative to the end face.

Preferably this feature is combined with the use of a duct and optionally of an associated cavity as flow path for a ventilation gas supplied from the exterior and discharged to the exterior.

The recessing is preferably constructed only on the bottom end face of the mantle brick, suitable as a bevelled surface. Roughly speaking, in this case the relevant duct is in each case provided in the joint region with such an enlargement that this enlargement can accommodate surplus jointing medium which is squeezed out. This involves both the possibility that the end face spread with the jointing medium remains somewhat staggered laterally relative to the normal duct cross-section, and also the possibility that the top end face of the mantle brick remains unmodified and an escape space is created on the bottom side of the next mantle brick located above it.

The second solution is that there is provided a collar upwardly prolonging the contour of the inside cross-section of the duct, and optionally of the cavity, formed at the top end face of the mantle brick.

This collar may be formed by an insert ring, which may have a cross-sectional profile of a recumbent tee.

Thus a kind of dam is formed which prevents the jointing compound from overflowing into the duct.

Lastly, the third possible solution provides a prolongation of the effective end face of the mantle brick with partial overhanging of the duct and/or of the cavity so that the prolongation of this end face constitutes an additional housing plateau for squeezed-out jointing compound.

In all these three solutions, it is possible additionally to adapt to the fact that, when a mantle brick is placed upon one located beneath it, the jointing compound present on it is generally displaced only in a diagonal direction, for example, when an edge of the tilted upper mantle brick is first lowered onto the horizontally arranged top end face of a lower mantle brick in an edge region, and is then tilted down onto the surface. The jointing compound is then displaced towards the aperture of the tilting gap. However, a geometrical adaptation to this possibility presupposes that the mantle brick is given a specific orientation, or that a specific assembly instruction exists, from the outset. In the normal case the arrangement will be made largely invariable as to angle, in order to be able to execute the assembly without additional thought so far as possible.

The third solution mentioned simultaneously creates a throttle position in the duct and/or in the cavity for a ventilation gas flowing therein. Such a creation of a throttle position, optionally also in other regions than in continuation of the top end face of the mantle brick constitutes a third inventive aspect of some embodiments.

Attempts are sometimes made to make a maximum quantity of ventilation gas, generally air, circulate through the relevant flow path in the mantle brick. This presents a maximum quantity of transport medium for undesirable or noxious gases or vapours.

However, it is also desirable sometimes to reduce the quantity of ventilation gas circulated, for example in order to avoid undue lowering of the temperature in the mantle brick. Then if the ventilation gas also has a somewhat higher temperature in the mantle brick, it can partially compensate the quantitative loss by having a higher absorption capacity, for example for steam, at a higher temperature. A throttling of the flow of the ventilation gas may also be desirable, particularly in the case of mantle bricks with ducts where the cavity is included in the flow path and a too vigorous flow leads to a structural deterioration or even gradual damage of an adjacent thermal insulation layer, for example by fibre roughening and ultimately removal from the outside of the thermal insulation layer facing the cavity.

However, throttle positions in the ducts and/or in the cavity may also be useful if the duct-cavity system does not serve as a flow path for a ventilation gas at all; for irrespectively of the ventilation, throttle positions also serve as intercepting cross-sections for lumps of jointing compound which fall down, which, by experience, do not fall down strictly vertically, but describe a more complicated falling arc. When lumps of jointing compound fall down, it is frequently desirable if they do not fall completely to the bottom end of the relevant duct or of the relevant cavity, but are at least partially caught earlier in the duct shaft and thus do not lead excessive material accumulations of hardened jointing compound.

Now it is also inherently possible to adjust the flow of ventilation gas in the region of its supply to or discharge from the chimney.

However, this might give rise to maladaptations, and in any case such an adjustment necessitates additional means. Also, some of the above-mentioned functions cannot be fufilled at all at the inlet or outlet of the ventilation gas, for example the function as a filling compound trap.

According to yet another aspect of the invention, therefore, at least one throttle position constricting the duct and/or the cavity is constructed in the mantle brick.

Such a throttle position may therefore serve, from the outset, not only as an inherent throttling of flow of a ventilation gas adapted to the respective flow conditions in the mantle brick, but may also serve in multiple adaptation to requirements in each case as a jointing compound trap, for example, along the mantle brick. There is also the advantage of being able to adjust the flow of ventilation gas by the throttling and simultaneously to enjoy total freedom otherwise in the duct dimensioning, whether in order to economise masses or to approximate to the external mantle surface in the sense of the first partial aspect of the invention.

By constructing the throttle position only at one end, preferably the top end, it becomes possible to combine this throttling benefit with the benefit of preventing the falling down of jointing compound altogether. Even without this additional benefit, however, a throttle position can be most simply constructed in the end region of a mantle brick, purely from mould removal considerations.

From the same mould removal considerations, in any relevant start line for a parting or cutting tool is conveniently conformed in the mould for the mantle brick, which also characterises the alternative solution of having a channel-shaped start-line.

Even if similar mantle bricks are arranged mutually superposed so that corresponding throttle positions come to lie strictly superposed in position and shape each time, the function of catching falling jointing compound can still be embodied due to the irregular falling path of such compound already mentioned. This makes possible a particularly simple invariable-angle configuration of mantle bricks according to the invention. However, in case of need such a construction of the mantle brick or such a pairing of mantle bricks may be chosen that the throttle positions of mutually superposed mantle bricks are arranged mutually staggered.A preferred embodiment of the last-mentioned type, has the features that the throttle position covers a zone of the duct and/or of the cavity adjoining only one lateral boundary of the duct and/or cavity and the zones are distribured round the internal aperture of the mantle brick so that when the mantle brick is rotated through a given angle, preferably 90 , mutually aligned ducts and/or cavities then change the lateral boundary adjoining the zone.

It is inherently conceivable to provide the throttle position immediately adjacent to the internal aperture of the mantle brick in the region of the cavity, and optionally actually to close the cavity here totally along the peripheral line of the internal aperture, so that then only the duct cross-section, optionally with an adjacent partial cross-section of the cavity, may remain available as cross-section for a ventilation gas.However, the cavity should preferably issue freely into the internal aperture of the mantle brick over the total height of the mantle brick, and the throttling should be provided only in those regions of the duct remote from the internal aperture; this takes into consideration simultaneously the fact that jointing compound is generally displaced by the said tilting process, farther inward from the outside of the end face provided with jointing compound and can then be intercepted by the throttle position present there if the latter serves simultaneously as a catching ledge.

The following are advantageous configurations of the duct with cavity and of a preferred throttle position construction: a mantle brick having a polygonal external mantle surface and construction of the ducts in the corner regions, in which the inside cross-section of the respective duct is bounded externally by two arms of an angle which stands at the same angle as the adjacent corner of the external mantle surface of the mantle brick, and the arms of which are oriented parallel to those sides of the external mantle surface adjacent to the corners.

Suitably the intervals (d) between the respective arms and the sides parallel thereto, of the external mantle surface, are substantially equal to the minimum thickness (d) of the mantle brick in the region between its corners.

Also the lateral boundary lines adjacent to the arms of the horizontal cross-section through the duct may extend straight into the internal aperture of the mantle brick forming the cavity.

The lateral boundary lines may extend parallel mutually and to the angle bisector of the adjacent corner of the external mantle surface of the mantle brick. A throttle position may mask a substantially constant-width zone of the duct adjacent to the two arms. Preferably the width of the zone is between approximately 1/3 and 2/3, preferably approximately 1/2, of the length of the lateral boundary lines of the horizontal cross-section through the duct.

The invention is explained more fully below in a number of exemplary embodiments with reference to diagrammatic drawings, wherein: Figure I shows a horizontal cross-section through a triple-shell chimney employing a first embodiment of a mantle brick according to the invention, the section being made in the region of or just below the top horizontal end face of the mantle brick; Figure 2 shows a vertical radial section of the chimney according to Fig. 1 along the line I-I; Figure 3 shows a detail on a larger scale in a detailed view of the region Z, af Fig. 2; Figure 4 shows a horizontal cross-section through a triple-shell chimney employing a second embodiment of a mantle brick according to the invention, showing the top end face of the mantle brick in plan;; Figure 5 shows a vertical radial section of the chimney according to Fig. 4 along the line lV-lV; Figure 6 shows a detail view on a larger scale of the region Z4 of Fig. 4; Figure 7 shows a vertical radial section through a chimney employing a third embodiment of a mantle brick according to the invention; Figure 8 shows a horizontal cross-section through a triple-shell chimney employing a fourth embodiment of a mantle brick according to the invention, with a plan view of its top end face; Figure 9 shows a horizontal cross-section through a multiple-flue triple-shell chimney employing a fifth embodiment of a mantle brick according to the invention, in a plan view of the top end face of the mantle brick;; Figure 10 shows a horizontal cross-section through a chimney with auxiliary shaft employing a sixth embodiment of a mantle brick according to the invention, in a plan of the mantle brick and with installation of a first embodiment of a door case; Figure ii shows a cross-section through a triple-shell chimney according to Fig. 1, but with an end elevation of the mantle brick and installation of a second embodiment of a door case and Figure 12 shows a horizontal cross-section according to Fig. 11, but with installation of a flue pipe connection instead of the door case.

A triple-shell structure is provided in all the chimneys illustrated. The innermost shell is formed by an internal pipe string carrying smoke gas, which is composed of individual fireclay pipes 2 jointed and cemented together. The fireclay pipes are surrounded by a thermal insulation layer of mineral fibre mats or mineral fibre plates 4, which form the central layer. The outer layer is formed in each case by a mantle brick 6 of light concrete. Further layers are conceivable, for example the inclusion of a vapour diffusion damping layer. It is likewise conceivable, for example, to integrate the thermal insulation layer and the internal pipe string to form a conjoint layer. However, the described construction of at least three, and particularly precisely three, layers is preferred.

The fireclay pipes 2 are pipes with a cylindrical inner surface and a cylindrical outer surface, disregarding shaping conicities in each case. The optionally slitted mineral fibre mats or mineral fibre plates 4 are wrapped round the fireclay pipes 2 so that they encase the latter with the minimum of gaps. The inner pipe string consisting of the fireclay pipes 2, and the thermal insulation layer comprising the mineral fibre mats or mineral fibre plates 4, which have a substantially constant thickness, are braced externally against the unrecessed regions 8 of the internal face--a- gain except for shaping coniciW-of the internal aperture 10 of the mantle brick 6.The mineral fibre mats or mineral fibre plates 4 are thus arranged with some radial play between the inner pipe string comprising the fireclay pipes 2 and the mantle bricks 6, so that the inner pipe spring can firmly expand and contract freely. The bracing against the unrecessed regions 8 gives the statically unstable combination of the two inner shells the required static strength of the chimney against the mantle bricks 6 of statically stable configuration.

All the mantle bricks 6 shown have polygonal outer mantle surfaces 1 2. Their horizontal cross-section is square in each case with the exception of the two exemplary embodiments according to Figs. 9 and 10, and elongate rectangular in the exemplary embodiments according to Figs. 9 and 10, whilst the degree of elongate construction in the embodiment according to Fig. 9 respresents approximately two and a half times, and in the embodiment according to Fig. 10 one and one-half times, the basic square dimension.

The corresponding cross-sections extend substantially coincidently in the longitudinal direction of the mantle brick, again exept for shaping conicities which may possibly be present.

Although the described configuration with a cylindrical inner pipe string, a thermal insulation layer of substantially constant thickness, and an internally cylindrical and externally square or rectangular mantle brick is preferred, nevertheless mantle bricks with a different configuration of internal aperture 10 and external mantle surface 1 2 also fall within the scope of the invention; for example, mantle bricks with a square or rectangular internal aperture configuration and mantle surface configuration, and internally and externally cyclindrical mantle bricks, optionally with constant wall thickness in each case, may be mentioned.

More or less rounded transitional shapes may likewise be considered.

The square basic shape is provided here when the mantle brick exhibits only a single internal aperture 10 to accommodate an inner pipe string carrying smoke gas. As Fig. 9 shows, however, a plurality of such internal apertures 10 may also be present, in the illustrated case two such internal apertures 10 in the same mantle brick 6.

The mantle brick 6 may further also contain shafts 14 for other purposes, for example air shafts, cable shafts or refuse shafts, of which an air shaft 14 is illustrated in each of Figs. 9 and 10. Whereas in Fig. 10 the air shaft 14 is arranged on one side beside the internal aperture 10 in the longitudinal direction of the rectangular extension of the mantle surface 12, in the embodiment of the mantle brick 6 according to Fig. 9 two internal apertures 10 and one additional air shaft 14 are distributed round the longitudinal extension of the rectan gular shape of the mantle brick, the air shaft 14 being arranged centrally and the two inter nal apertures 10 symmetrically on each side of the latter.

It will be clear from the radial sections in Figs. 3, 5 and 7 that the fireclay pipes 2 and the mantle bricks 6 are conveniently mutually axially staggered in the chimney in order to prevent the escape of smoke gas along a common horizontal joint so far as possible.

The mineral fibre mats or mineral fibre plates 4 may likewise be arranged staggered relative to the respective joint. However, it is not excluded in the ambit of the invention that the inner pipe string comprising a plurality of fireclay pipes 2, the thermal insulation layer and the mantle brick conjointly form a prefabricated finished chimney element. However, the individual layers are conveniently constructed step by step from the elements 2, 4 and 6, whilst a plurality of fireclay pipes 3 may make up the length of a mantle brick 6.

In the respective mantle brick 6, ducts 16, four of which in each case are distributed round each internal aperture 10 and communicate respectively through a cavity 1 8 in the mantle brick 6 with the internal aperture 10, extend along the mantle brick 6. The ducts 1 6 with associated cavities 1 8 are arranged in mirror image symmetry to the angle bisectors of the corners of the relevant external mantle surface 1 2 of the mantle brick 6. The cavities 18, like the ducts 16, extend along the total axial height of the relevant mantle brick 6.

Externally the inside cross-section of the relevant duct 1 6 is bounded in each case by two arms 20 of an angle which stands at the same angle as the adjacent corner 22 (compare Figs. 3 and 5 without restricting the generality), whilst the arms 20 are oriented parallel to those sides 24 of the external mantle surface 1 2 adjacent to the corners 22.

The intervals d between the respective arms 20 and the sides 24, parallel to the latter, of the external mantle surface 12, are substantially equal to the minimum thickness d of the mantle brick 6 in the region between its corners (compare Figs. 1 and 4). The lateral boundary lines 26, adjacent to the arms 20, of the horizontal cross-section through the respective duct 1 6 extend straight into the internal aperture 10 of the mantle brick 6, parallel mutually and to the angle bisector of the adjacent corner 22 of the external mantle surface 1 2 of the mantle brick 6, simultaneously forming the cavity 1 8. The junction of the two arms 20 which is opposite the relevant adjacent corner 22 is constructed as a curvature 28, whereas the corners 22 them selves are preferably of sharp-angled construc tion.

In case the ducts 1 6 serve as flow paths for a a ventilation gas supplied from the exterior and discharged to the exterior, the cavities 18 extending continuously with the ducts 1 6 are included in the flow path of the ventilation gas, particularly of ventilation air.

Although the cross-section of duct 1 6 with cavity 1 8 is shown the same, with nuances, in all the exemplary embodiments of mantle bricks 6 illustrated, it may nevertheless have a different shape. Different degrees of curvature of the duct region formed by the arms 20 in each case, and radially different start points of arm 20 and boundary line 26 are illustrated, as immediately apparent from the representa tion in the drawing.

In all the embodiments of mantle bricks 6 illustrated, group of at least two start lines 30 for a parting tool or cutting tool extends along the entire relevant mantle brick 6 on each of the four sides 24 of the mantle brick. Each start line 30 is constructed in the preferred manner as a semicircular or U-shaped chan nel. With the exception of the embodiment according to Fig. 10, the groups or pairs of start lines 30 are associated with an adjacent internal aperture 10 in each case. This pro duces a pair of start lines 30 for each side 24 in all embodiments with the exception of that according to Fig. 9.However, since two inter nal apertures 10 are distributed in the longitu dinal direction of the horizontal cross-section of Fig. 9, two pairs of start lines 30 are also arranged there on the long sides 24 of the mantle surface 12, whereas only one pair of start lines 30 is provided in every other case.

As a general rule the start lines 30 are located opposite the adjacent duct 1 6 in all the exemplary embodiments, so that each start line 30 is then associated with a particu lar duct 1 6. However, this is not absolutely necessary, as the exemplary embodiment of Fig. 10 shows, where a pair of start lines 30 is located opposite a single auxiliary shaft 14 on a narrow side of the external mantle surfsce 1 2. With a different type of configura tion of the ducts 16, a corresponding result may also be obtained in the region of internal apertures 10, including particularly if the in ternal ánd/or external configurations of the mantle brick are differently conformed, for example both rectangular or both cylinderical.

The start lines 30 are conveniently arranged symmetrically to the corners 22 of the mantle brick 6 and extend straight and substantia!ly axially or parallel to the corners. The interval from the relevant corner 22, or the mutual interval of the two start lines 30 is conveni ently chosen so that the start line 30 lies in each case in the region of minimum wall thickness d between external mantle surface 1 2 and adjacent duct 1 6 (or also its adjacent cavity 1 8). It will be seen that with the chosen configuration the wall thickness d remains constant along the total arm length 20 and the condition mentioned can be fulfilled ideally in the same manner in this region.

Because the start lines 30, like the ducts 1 6 and their cavities 18, extend continuously along the total height of the mantle brick 6, it is possible, when parting the wall between the start line 30 and that point of the arm 20 located opposite at right angles to the external mantle surface, to remove the entire wall region of the mantle brick located between the two respective start lines where parting is performed. By a suitable choice of the interval of the two start lines 30, a housing aperture 32 to house a door case 34 (Figs. 10 and 11) or a flue pipe connection 36 (Fig. 12) is thereby obtained. As may be seen from Figs.

10 to 12, the lateral cheeks of this housing aperture then extend each to the arm 20 of the associated duct 16; the housing aperture 32 extending over the total height of the mantle brick 6 is then prolonged freely beyond the duct 1 6 and its adjacent cavity 18 towards the internal aperture 10. In the case of an analogous parting adjoining the auxiliary shaft 14 according to Fig. 10, an analogous housing aperture is then obtained adjacently to this auxiliary shaft 14, which may be utilised for example for a door case of an inspection door, of a refuse disposal door et cetera.

Wherever such pairs of start lines 30 are provided, it is accordingly possible to create a housing aperture 32 by parting the wall regions located behind the relevant start line 30 which extends continuously along the entire mantle brick 6 and permits access to the relevant duct 1 6 or 14 located behind the latter. Because at least one pair of such start lines, and precisely one pair of such start lines in each case of a square cross-section, is present one each side 24 of the relevant mantle brick 6, such a housing aperture 32 can be created on any desired side of the mantle brick.

It is possible to use for example, the grinding wheel of an angle grinder for this purpose, if the dimension d is approximately 4 to 5 cm as preferred. Parting by means of a grinding wheel is still possible even for greater engagement depths, although more time-consuming and generally also more laborious.

Such a fireclay pipe 2 as exhibits a lateral pipe spigot 38, which may have an approximately rectangular cross-section in the case of connecting a door case, but normally has a cylindrical cross-section in the case of a flue pipe connection, is conveniently used in the region of a housing aperture 32 leading to an internal aperture 10. In the former case the pipe spigot 38 conveniently extends into the region of the rear edge of the housing aperture 32 (Figs. 10 and 11), so that the door case 34 can be preassembled within the housing aperture 32, whereas a flue pipe connection is conveniently brought out into the region of the external mantle surface 1 2 (Fig.

12), so that, for example, an onward-leading pipe piece can be inserted telescopically there.

In the latter case it is sufficient to close the flue pipe connection 36 towards the housing aperture 32 by means of an insert 40 shaped from mineral fibres, so that the combination of the lateral pipe spigot 38, serving as a flue pipe, with the preferably one-piece, optionally also multiple-piece, insert 40 produces the flue pipe connection 36.

The two alternative embodiments illustrated with reference to Figs. 10 and 11 may be considered particularly for the construction of the door case 34.

In both embodiments, the door 42 is articulated by a hinge 44 on one side to a onepiece frame-shaped element which is constructed all round as a frame 48. The door 42 carries on its inside a lining 46 of insulating concrete engaging into the frame-shaped element.

In the first embodiment according to Fig.

10, the frame 48 exhibits an open angle profile 50 formed by a cast iron metal frame part. This has a base part 52, which limits the door aperture all round, extends vertically at the sides and otherwise horizontally, has a minor flange 54 parallel to the mantle surface in the region of the mantle surface 12, and a major flange 56 extending parallel to the mantle surface 1 2 and as far as the housing aperture 32, immediately in front of the lateral pipe spigot 38 and the rear region of the housing aperture 32. The region between the base part 52, housing aperture 32 and the two flanges 54 and 56 is filled with a filling compound 58, preferably mortar, which then, due to the configuration, forms a frame of filling compound with an approximately rectangular cross-section of each frame member.

The frame 48 of the second embodiment is fundamentally of the same construction, but exhibits a somewhat shorter major flange 56.

In the limit case the length of the flanges 54 and 56 from the base part 52 may even alternate or be equal.

Here the three frame elements 52, 54 and 56 form an inner retaining enclosure for a finished concrete frame 58 which effects substantially a massive filling of the housing aperture 32, and which, with the housing aperture 32, forms a housing gap 60 enlarging in wedge shape from the inside outwards for joint filling compound, particularly mortar.

Measures are further provided on the mantle bricks 6 to prevent or minimise the dropping out of filling compound, such as jointing mortar, spread upon the top end face of the mantle brick 6, into a duct 1 6 or the adjacent cavity 1 8. Three possibilities are shown here, which may be combined in pairs or also severally.

The first possibility provides that, according to Figs. 4 to 6, at the bottom end face of the mantle brick 6 the transition from the end face into the internal aperture 10 of the mantle brick is constructed recessed as a bevel surface 62 relative to the bottom end face 64 of the mantle brick 6. By this means the jointing compound 66 can collect and at least partly accumulate above the top end face 68 beneath the bevel 62 when the upper mantle brick 6 is placed upon the lower one.

The bottom end face then extends horizontally as far as the internal aperture adjoining vertically downwards, so that an upward displacement can occur at the inner edge of the top end face. This arrangement presents the advantage of not constricting in any way the duct 1 6 or the cavity 18, in case this is undesirable.

The recessed zone 70 formed by the relevant bevel surface 62 then extends along the entire margin of duct 1 6 and cavity 18, that is to say along the arms 20 and the boundary lines 26 with the same depth throughout, for example with a depth between 1/3 and 2/3 of d, preferably with smaller values of this range of dimensions.

According to the second possibility, an insert ring 72 which has approximately the shape of a recumbent tee, is placed upon the top end face of the mantle brick 6. A central flat member 74 then engages partly into the joint, filled with jointing compound 66, between the two mantle bricks 6 arranged mutually superposed, whereas the two arms engage into the lower duct 1 6 or 1 8 and into the upper duct 1 6 or 1 8 respectively. The upper arm 76 then forms a collar against an overflow of filling compound into the duct 1 6 with cavity 1 8. The insert ring 72 is dimensioned internally so that the internal aperture 10 is not covered.

Lastly, the third possibility is illustrated particularly clearly in Fig. 2.

Here the mantle brick has no modification of its bottom end. It is provided at its top end with an inner prolongation 80 of the top end face 68 of the mantle brick partly overhanging the duct 1 6. The prolongation 80 merges bracket fashion, through a bevel 82 in this case, downwards into the normal internal surface of the duct 1 6. The prolongation of the horizontal top end face 68, which partly covers the duct 60, permits the jointing compound 66 to spread out, on the one hand inwards and on the other hand upwards within the unthrottled region of the duct 1 6 in the lower section of the upper mantle brick, without again being constrained to fall into the duct 16.

The normal duct contour with the arms 20 in the unthrottled region is shown by dash lines in Fig. 3, likewise the continuation with the boundary lines 26 beneath the throttle position. The throttle position 82 formed by the overhang of the bracket-like prolongation 80 then covers according to Fig. 3, a zone of the duct 1 6 adjacent to the two arms 20 having a constant width measured along the boundary lines 26. The width of the zone may be between approximately 1/3 and 2/3, preferably approximately 1/2, of the length of the lateral boundary lines 26 of the horizontal cross-section through the duct 1 6 with cavity 18.

By this arrangement of a throttle position, an unthrottled free cross-section of the cavity 1 8 with adjacent section of the channel 1 6 extending continuously along the total height of the mantle brick 6 is obtained; in any case, duct 1 6 and cavity 18 are not strictly mutually separable.

Without restricting the generality, the described construction of a throttle position 82 is also made the basis for the embodiments of Figs. 9 to 12, whilst of course the embodiments of Figs. 4 to 6 may exhibit an enlargement instead of a throttling.

Lastly, Fig. 8 shows an alternative construction of a throttle position 82.

In this case the throttle position 82 adjoins in each case only a lateral boundary 20, 26 of duct 1 6 and cavity 18, whilst the width of the throttle position, measured at right angles to the arm 20, or to the boundary line 26 in each case, is again substantially constant. For example, if viewing from the exterior along the radius towards the internal aperture 10 a "left-hand" boundary 20, 26 and a "righthand" boundary 20, 26 are defined, then in the illustration in Fig. 8 a connection of the throttle position 82 to the lefthand boundary 20, 26 bottom left in the drawing changes clockwise into a connection of the throttle position 82 to the right-hand boundary 20, 26 in the top left corner of the drawing et cetera. This makes it possible, when identical mantle bricks 6 are arranged superposed, but respectively rotated through 90 about their axis, for a path which is formed by superposed ducts with cavities, a throttle position adjacent to a left-hand boundary and a throttle position adjacent to a right-hand boundary alternate one above the other in each case and the throttle positions are thus mutually staggered. By this means, jointing compound which has nevertheless fallen into the duct can optionally be at least partly intercepted if it falls into the duct 1 6 or the cavity 1 8 and even falls vertically downwards.

Claims

1. A mantle brick for a multiple-shell chimney, having an internal through-aperture for receiving a chimney pipe-string and adjacent said aperture one or more recesses defining a space or spaces respectively open to the through-aperture and on the outside of said mantle brick two start lines to enable cuts to be made extending to said space(s) to allow removal of a portion of the mantle brick between the start lines to provide an access opening to the through-aperture.

2. Mantle brick according to claim 1 wherein there are a plurality of recesses each extending through the brick to define a duct.

3. Mantle brick according to claim 2 wherein there is a pair of said start lines associated with each recess, so that the start lines define a set of portions of the mantle brick, ore portion between each pair of adjacent recesses, any one of which portions can be cut out to provide said access openings.

4. Mantle brick for a multiple-shell chimney with at least one duct which extends in the mantle brick in the longitudinal direction thereof and is open through a cavity towards the internal aperture of the mantle brick, whilst particularly a plurality of such ducts are distributed round the internal aperture, characterised in that at least two start lines (30) for a parting tool or cutting tool are con structed, each opposite a duct (16), on the mantle surface (12) of the mantle brick (6), and that the mutual interval of these two start lines (30) corresponds to the width of a housing aperture (32) for a door case (34) or flue pipe connection (36).

5. Mantle brick according to Claim 4, characterised in that the ducts (16) pass through recesses (18) and/or start lines (30) over the height of the housing aperture (32) for the door case (34), preferably over a complete mantle brick height.

6. Mantle brick according to Claim 4 or 5 characterised in that a plurality of, preferably at least four, pairs of such start lines (30) are distributed round the circumference of the mantle surface (12).

7. Mantle brick according to any of Claims 4 to 6 with a rounded internal aperture, a polygonal mantle surface and routing of ducts in corner regions of the mantle brick, characterised in that the wall thickness (d) of the mantle brick (6) between the respective start line (30) and the adjacent duct (1 6) corresponds approximately to the minimum wall thickness of the mantle brick between the corners (22).

8. Mantle brick according to any of Claims 4 to 6 characterised in that the wall thickness (d) of the mantle brick (6) between the respective start line (30) and the adjacent duct (16) is approximately 4 to 5 crn.

9. Mantle brick according to Claim 7 or 8 characterised in that each plane mantle section (24) located between adjacent corners (22) of the mantle brick (6) is provided with a pair each of such start lines (30) for each adjacent internal aperture (10) serving to house a thermally insulated flue pipe.

10. Mantle brick according to any of Claims 4 to 9 characterised in that the start line (30) is constructed as an optically conspicuous guide line.

11. Mantle brick according to any of Claims 4 to 10 characterised in that the start line (30) is constructed geometrically differently from the surrounding mantle surface.

1 2. Mantle brick according to any of Claims 4 to 11 characterised in that the start line (30) is of channel-shaped construction.

1 3. Mantle brick according to any of Claims 4 to 1 2 characterised by a door case (34), the width of which corresponds to the housing aperture (32) preformed by the start lines (30) and its depth to the wall thickness between start line (30) and adjacent duct (16), whilst its height preferably corresponds to the height of the mantle brick (6).

14. Mantle brick according to Claim 13, characterised in that the door case (34) exhibits a surrounding frame (48).

15. Mantle brick according to Claim 14, characterised in that the frame (48) exhibits a finished concrete frame (58), preferably framed by a metal frame part (50), and connectable to the mantle brick (6) by a filling compound, preferably mortar (Fig. 11).

16. Mantle brick according to Claim 14, characterised in that the frame (48 exhibits an open angle profile (50), which is preferably formed by a metal frame part, and which, conjointly with the mantle brick cut out along the start line (30) and with the end face of a projecting spigot (38) of a flue pipe inserted into the internal aperture (10) of the mantle brick (6), forms a housing gap (66) fillable with filling compound, preferably mortar (Fig.

10).

1 7. Mantle brick, particularly according to any of Claims 4 to 16 and preferably with the use of the relevant duct and optionally of the associated cavity as flow path for a ventilation gas supplied from the exterior and discharged to the exterior, characterised in that, on at least one end face of the mantle brick (6), the transition from the end face (64) into the internal aperture (10) of the mantle brick is constructed recessed relative to the end face.

18. Mantle brick according to Claim 14, characterised in that the recessing is constructed only on the bottom end face of the mantle brick (6).

1 9. Mantle brick according to Claim i17 or 18 characterised in that the recessing is constructed as a bevelled surface (62).

20. Mantle brick, particularly according to any of Claims 14 to 1 9 and preferably with the use of the ducts and optionally of the cavities as flow paths for a ventialtion gas supplied from the exterior and discharged t, the exterior, characterised in that at least one throttle position (82) constricting the duct (16) and/or the cavity (18) is constructed in the mantle brick (6).

21. Mantle brick according to Claim 20, characterised in that a throttle position (82) is constructed at at least one end, preferably only the top end, of the mantle brick (6) in each case.

22. Mantle brick according to Claim 21 characterised in that the throttle position (82) enlarges the end face (68) of the mantle brick whilst partially covering the free cross-section of duct (16) and/or cavity (18).

23. Mantle brick according to Claims 1 7 to 22, chacterised by a collar (76) upwardly prolonging the contour of the inside crosssection of the duct, and optionally of the cavity, formed at the top end face of the mantle brick.

24. Mantle brick according to Claim 23, characterised in that the collar is formed by an insert ring (72).

25. Mantle brick according to Claim 24, characterised in that the insert ring (72) forms a recumbent tee profile.

26. Mantle brick according to any of Claims 20 to 25, characterised in that the throttle position (82) is formed in the material of the envelope.

27. Mantle brick according to any of Claims 20 to 26, characterised in that a plurality of throttle positions (82) of the same duct (16) and/or of the same cavity (18) are distributed along the length of the mantle brick (6).

28. Mantle brick according to any of Claims 20 to 27 wherein the ducts and cavities are vertically oriented, characterised by such a construction of the mantle brick (6), or such a pairing of mantle bricks, that when mantle bricks are superposed the throttle positions can be arranged mutually staggered (Fig.

8).

29. Mantle brick according to any of Claims 20 to 28, wherein the cavities are a component of the flow paths, characterised in that the throttle positions (82) in the mantle brick (6) are arranged farther outwards than that region of the respective flow path adjacent to the internal aperture (10) of the mantle brick.

30. Mantle brick according to any of Claims 20 to 29 having a polygonal external mantle surface and construction of the ducts in the corner regions, characterised in that the inside cross-section of the respective duct (16) is bounded externally by two arms (20) of an angle which stands at the same angle as the adjacent corner (22) of the external mantle surface (12) of the mantle brick (6), and the arms of which are oriented parallel to those sides (24) of the external mantle surface adjacent to the corners.

31. Mantle brick according to Claim 30, characterised in that the intervals (d) between the respective arms (20) and the sides (24), parallel thereto, of the external mantle surface (12) are substantially equal to the minimum thickness (d) of the mantle brick (6) in the region between its corners (22).

32. Mantle brick according to Claim 30 or 31 characterised in that the lateral boundary lines (26), adjacent to the arms (20), of the horizontal cross-section through the duct (16) extend straight into the internal aperture (10) of the mantle brick (6), forming the cavity (18).

33. Mantle brick according to Claim 32, characterised in that the lateral boundary lines (26) extend parallel mutually and to the angle bisector of the adjacent corner (22) of the external mantle surface (12) of the mantle brick (6).

34. Mantle brick according to any of Claims 20 to 33, characterised in that the throttle position (82) masks a substantially constant-width zone of the duct (16) adjacent to the two arms (20).

35. Mantle brick according to Claim 34, characterised in that the width of the zone is between approximately 1/3 and 2/3, preferably approximately 1 /2, of the length of the lateral boundary lines (26) of the horizontal cross-section through the duct (1,6).

36. Mantle brick according to any of Claims 28 to 33, characterised in that the throttle position (82) covers a zone of the duct and/or of the cavity adjoining only one lateral boundary (20, 26) of the duct (16) and/or cavity (18) and the zones are distributed round the internal aperture (10) of the mantle brick so that when the mantle brick is rotated through a given angle, preferably 90 , mutually aligned ducts (16) and/or cavities (18) then change the lateral boundary adjoining the zone (Fig. 8).

37. Method of making a housing aperture for a door case or flue pipe connection in a mantle brick according to any of Claims 1 to 1 9 and optionally according to any of Claims 20 to 36, characterised in that the wall of the mantle brick is parted between the two start lines and the respectively adjacent duct by means of a grinding wheel and the wall section located between the parting lines is removed.

38. Mantle brick for a multiple-shell chimney, the brick having a rounded internal through-aperture for receiving a chimney pipestring, a polygonal exterior wall and associated with each corner of the polygonal exterior wall a recess adjacent said through-aperture defining a duct running parallel to the through-aperture with the minimum wall thickness of the brick between the polygonal exterior wall and the duct being substantially equal to the minimum wall thickness of the brick between the internal through-aperture and the polygonal exterior wall.

39. Mantle brick according to claim 38 wherein on each side of each corner of the polygonal exterior wall there is a start line for a cut at the or one of the positions of minimum wall thickness of the brick between the polygonal exterior wall and the recess at that respective corner.

40. Mantle brick according to claim 38 wherein there is a pair of start lines for a cut on at least one face of the polygonal exterior wall, each one of said lines being at the or one of the positions of minimum wall thickness of the duct at a respective corner bordering said face of the polygonal exterior wall.

41. Mantle brick according to one of claims 38 to 40 wherein the minimum wall thickness of the brick between the polygonal exterior wall and the duct is between 4 to 5 cm.

42. Mantle brick according to one of claims 38 to 41 wherein the brick has an exterior wall square in cross-section.

43. Mantle brick for a multiple-shell chimney having an internal through-aperture running from its lower to its upper end and abutment surfaces at its upper and lower ends to allow stacking of the bricks, characterised in that the abutment surfaces are so shaped that when two such bricks are stacked one above the other, the upper abutment surface of the lower brick projects into the internal through-aperture beyond the lower abutment surface of the upper brick.

44. Mantle brick according to claim 43 wherein at the upper abutment surface of each brick there is an internal circumferential projection.

45. Mantle brick according to claim 43 wherein at the lower abutment surface the wall is internally chamfered.

46. Mantle brick substantially as hereinabefore described with reference to the embodiments of Figs. 1 to 3, or Figs. 5 and 6, or Fig. 7 or 8 or 9 or 10, or 11 or 12 of the accompanying drawings.