EP0053875B1

EP0053875B1 - High temperature insulation panels

Info

Publication number: EP0053875B1
Application number: EP81305119A
Authority: EP
Inventors: Thomas Michael Miller
Original assignee: Eltech Systems Corp
Current assignee: Engineered Thermal Systems Inc
Priority date: 1980-12-05
Filing date: 1981-10-29
Publication date: 1986-12-17
Also published as: EP0053875A1; ATE24351T1; DE3175727D1

Abstract

A high temperature insulation panel comprises a backing element (W) and a heat insulating lining (M), the lining comprising portions of ceramic fibrous material, each portion having two spaced apart leg portions (1, 2) with a space (S) in between, the portions being held together by one leg of one portion being received in the space between the legs of its neighbouring portion. In this way a highly efficient heat insulation panel is formed.

Description

The present invention relates to a heat insulating wall element comprising a heat insulating lining and a backing structure, the lining comprising portions of ceramic fibrous material and being arranged in side-by-side relation, each portion having spaced apart leg portions with a space in between, one leg of one portion being received in the space between the legs of its neighbouring portion, the portions of ceramic fiber material being fastened to a grid-like structural member. Such panels are of value in the heat insulation of high temperature enclosures or parts thereof, examples being (but not limited to) ceramic or refractory kilns, ovens, furnaces such as billet of slab reheat furnaces, forge furnaces: B.O.F. doors, furnace door linings and seals, soaking pit covers and seals, high temperature gasketing, annealing cover seals: glass furnace crown insulation, nuclear insulation and incineration equipment. The insulation may be applied to any wall of the enclosure or part, and the term is intended to cover a side wall, roof or floor, movable or fixed, and the area defining an inlet.
The wall element comprises a backing element and an insulation material which is usually a ceramic fiber. The ceramic fiber material will typically be an aluminosilicate. Such materials are available from many commercial sources: KAWOOL from Babcock and Wilcox, CERA-BLANKET^R or CERAFELT" from Johns Manville and FIBERFRAXR or DURABLANKET^R from Carborundum Corporation: The mat may be in the form of a felt, a.blanket either needled or chemically bonded, a cloth, paper or flexible board.
It is well known to fold a blanket and secure it to the wall of a high temperature enclosure. It is also known that a metal stud or anchor holding the blanket to the wall must be shielded from the heat. Various proposals exist to do these things, see for example US patents 3819468, 3854262, 3940244, 3952470, 3990203, 4083155, 4123886 and 4177616. None of these proposals is totally satisfactory.
French patent application 23 88 197 discloses an insulating wall construction wherein a wall member comprises a grid fastened to the wall member on the side which is intended to be the interior side of an insulated chamber and U-folded or interengaged fiber mats are stacked adjacent to this grid. The fiber mats contain rods in their folds and hooks engage the grid and the rods thereby fastening the fiber mats to the wall member.
It is an object of the present invention to provide a heat insulating wall element for the purpose specified above which is simple and easy to install and repair, efficient in use and which yields economies in the use of the heat enclosure.
This object is met by an insulating wall panel as described at the beginning which is further characterized in that the backing element is constituted by the grid-like member being a lightweight open mesh, and that the heat insulating lining is connected to the backing element by tie wires.
Most preferably, the space of each portion receives two legs from other portions, one leg from the immediate neighbouring portion on one side and one leg from the next to neighbouring portion on the other side. Preferably the legs are so received in the space as to leave a gap in the space to receive a mounting element for holding the lining to the backing element. The mounting element is preferably a rod which is tied by tie wires to the backing element. The backing element is most preferably a lightweight open mesh e.g. of steel.
In a much preferred feature of the invention the portions remote from the backing element and thus in use the so-called hot face, have a lower thermal conductivity from those adjacent the backing element. It is much preferred that each portion comprises a length of flexible ceramic fibrous material folded to have the spaced apart leg portions and an integral bight.
The wall panel of the invention may constitute a part of a heat enclosure of the types specified above.
In use, it is preferred that compressible heat insulating means is arranged to compress the portions together. Such means may be a blanket or sheets of loose fibrous mats. Most preferably the enclosure comprises a forge furnace since, when the sides of such a furnace is formed of the wall panels of the invention the method of manufacture. and economies of use are seen to good advantage. Thus the furnace is lighter in weight, has a fast heat up and short cool down period, and heat leakages can be detected quickly and repaired easily from outside the furnace.
For example, the heating up time can be cut by up to 50%, depending on the operating temperature. When cooling the furnace and speed is important, the furnace may be cooled to a temperature at which an operator can do routine maintenance work four or five times faster than is otherwise the case.
In order that the invention may be well understood, it will now be described by way of example only, with reference to the accompanying diagrammatic drawings, in which

Figure 1 is a perspective view of a portion of a wall panel according to the invention;
Figure 2 is a perspective view of a slot forge furnace incorporating walls panels according to Figure 1;
Figure 3 is a sectional view taken on lines III-III on Figure 2;
Figure 4 is a sectional view taken on lines IV-IV on Figure 3;
Figure 5 is a front elevation view of the furnace with the heat shield removed;
Figure 6 is a plan view, in section, taken along line VI-VI on Figure 3 and showing the corner arrangement between the back and side walls of the chamber; and,
Figure 7 is a plan view, in section, taken along line VII-VII on Figure 5.

The insulation I is held to a mesh wall W which, in the wall panel shown in Figure 1, is substantially vertical. The insulation comprises a vertical stack of mats M each formed of a ceramic fibre blanket. This material may be selected from a variety of commercially available blankets; flexible blankets are preferred. One suitable commercially available material is DURABLANKET (Carborundum Company, New York, U.S.A.). The thermal conductivity and thickness of the blanket will be selected according to use. In the embodiment shown, the mats M1, M3, M5 etc adjacent the wall W have one level of conductivity and those remote from the wall W, M2, M4, M6 etc. and in use the hot face exposed to heat, have a lower level of thermal conductivity. Each mat is folded into generally U-shaped section having two spaced apart leg portions 1 and 2, joined by an integral bight portion 3 and separated by a space S. The mats are arranged alternately so that the exterior of any bight portion 3 faces outwardly of the stack. The mats of the stack are interdigitated as shown by locating the upper leg 1 of each mat M in the facing space S between the legs 1, 2 of its immediate upper neighbour and the lower leg thereof in the space between the legs of the mat next to its lower neighbour. For example the space of the mat M5 receives a leg from each of mat M6 and mat M4. The space S of one mat thus receive one leg from each of two other mats and the stack is held in continuous unbroken relation. A support rod 4 is present in the gap 5 between the inner bight surface of each , of the mats adjacent the wall W and the ends of the legs received in that mat, and the rod 4 is joined to the mesh wall by tie wires 6. The mats M adjacent the wall W are thus prevented from moving vertically or horizontally away from the wall W backing element. The hot face mats M2, M4, M6 etc. are held to the cold face mats M1, M3, M5 etc. adjacent the wall by the interengagement of the legs, and this engagement may be enhanced by vertical compression of the mats by means shown in Figure 4. The support rods 4 may be steel rods or tubes about 5 mm in diameter and the tie wires 6 may be annealed steel alloy. The mats may extend about 30 cm away from the wall which may be unflattened steel sheet, about 6 to 8 mm thick.
The insulated wall of Figure 1 may be used in a wide variety of heat insulating situations e.g. soaking pit lids or covers. In one particularly useful form, several such walls are incorporated in a slot type forge furnace. The forge furnace 10 of Figures 2 to 7 comprises an open frame including upright supports 12_'and horizontal lower front and rear frame members 14 and 16 (Figure 3) and lower side members 18 (Figure 4) and 20. As seen in Figure 4, a floor 22 supports a steel bed plate 24 which in turn supports a refractory brick 26 defining the furnace bottom. The frame includes horizontal upper front and rear frame members 30 and 32, and horizontal upper side members 34 and 36. As seen in Figures 1 and 3, extra upright supports 38 extend between lower supports members 16,18 and 20 and upper supports 32, 34 and 36 respectively.
A removable lid comprises top frame members .40, 42, 44 and 46 having angle iron supports 40a, 42a, 44a and 46a (Figures 3 and 4). Support plates 48 and 50 extend across the top face of the lid and the plates 50 have holes 52 so that the lid can be lifted e.g. by an overhead crane.
The furnace has a rear wall 54, sidewalls 56 and 58 and a topwall 60. These walls each comprise wall panels W according to Figure 1. The walls are welded to the frame members and the extra supports 38 prevent the respective wall panel being deflected out of the furnace frame. The furnace chamber may be about 95 cm high, 95 cm deep and 2 to 3 metres wide.
A burner unit B is mounted in an opening in the sidewalls 56, 58 and the respective support rods 4 are stopped short to allow the unit B to protrude into the interior of the furnace. To prevent damage to the lowermost mats firebricks 80 are present about the periphery of the furnace floor. Figure 6 shows a corner in which adjacent mats M are cut to form vertical walls 86, 87, 88 and 89 whereby the mats interengage to form a Z-path to prevent heat leaking outside the furnace.
To seal the gap between the lid assembly and the walls, a plurality of flat sheets or blankets 82 of fibrous heat insulating material are secured within and below the lid frame by spikes 84 (Figure 3) protruding through holes in the lid sidewalls 40 and 42.
The fibrous insulating material of the mats may shrink slightly during initial operation of the furnace, and the flat or folded sheets pf the insulating material will counteract this. The construction of the wall assemblies with the mats compressed transverse to the planes thereof serves to compensate for shrinkage and shrinkage is further compensated for by compressing the adjacent rows of mats in the direction of the axes of the support rods 4.
The furnace 10 includes a heat shield 90 comprising an angle iron frame defined by top and bottom 92 and 94, and sides 96 and 98; support plates 100 are welded to the top and bottom members. A sheet of open metal mesh material 102, preferably expanded sheet metal W, is welded to the heat shield frame and the underlying flanges of the angle iron. One or more mats of fibrous insulating material 104 overlie the expanded metal 102, and the mats are held on the heat shield frame by an overlying open metal mesh 106 welded to the inner side of the frame. The open metal mesh 106 may be an expanded sheet of metal of lighter gauge material than material 102 or a wire screen.
As seen in Figures 3 to 5, the front wall of the furnace comprises lintel blocks 108 of cast refractory supported above the furnace floor by refractory bricks 110 to define openings 112 into the furnace chamber. The presence of fibrous insulating material enables the use of shorter lintels than previously required. The space between the tops of blocks 108 and top wall assembly 60 is filled with mats of the invention. The mats above lintel blocks 108 are retained against lateral inward displacement relative to the furnace chamber by means of spaced apart wire staves 114 clamped to the frame members 30 and 40.
The lintel in a furnace is generally directly exposed to heat within the furnace chamber. This, together with the massiveness of the lintel and the high heat retention characteristic thereof, directly affects the time required to heat the furnace chamber to an operating temperature upon start up and to cool the chamber upon shut down. The mats of the invention reduce both the heating up and cooling down times for the furnace. As best seen in Figures 3 and 4, the lowermost mats of insulating material overlying lintel blocks 108, designated by numeral 116, are U-shaped mats having parallel juxtaposed outer leg portions 116a between the upper sides of blocks 108 and the undersides of mats and the parallel juxtaposed inner legs 116b extending downwardly along the inner sides of blocks 108 and having an integral bridging portion 116c therebetween and adjacent the lower ends of the lintel blocks. Legs 116b may be bonded to one another and/or to the inner sides of blocks 108, if desired, to assure retention of the inner ends of the mats againstthe lintel blocks. The mats may be of low thermal conductivity..
As best seen in Figures 3 and 6, openings 112 into the furnace chamber are defined by the undersides of lintel blocks 108 and the upperside of refractory brick sill plates 118. Sill plates 118 extend between support bricks,110 for the lintel blocks and have corresponding outer edges 118a and inner edges 118b. The furnace floor for supporting workpieces to be heated is preferably covered by a granular refractory material 120, such as dolomite, which covers refractory material 26 inwardly of inner edges 118b of the sill plates and the inner sides of support bricks 110. Sill plates 118 have a vertical thickness which provides for furnace openings 112 to have a desired maximum vertical dimension, and the sills are retained against lateral outward displacement from the furnace by an angle iron retainer 122 overlying the upper flange of frame member 14. Retainer 122 extends across the front of the furnace for the upright flange of the retaining member to engage outer ends 118a of the sill members. Retainer 122 is removably connected with frame member 14 by bolts 124, and removal of the retainer provides access to the outer ends of sill members 118 to allow shims to be placed between the sills and the underlying refractory material 26 to elevate the sill members and thus reduce the vertical heights of openings 112. Once the shims have been introduced beneath sills 118, the retainer 122 is remounted on flange member 14to engage the outer ends of the sill members against outward displacement relative to the furnace. The vertical heights of openings 112 can of course be reduced by a dimension corresponding to the height of the upright flanges of retaining member 122 without eliminating the retention capabilities thereof. It will be appreciated too that the vertical heights of openings 112 can be reduced beyond the dimension corresponding to the upright flange of retaining member 122 by introducing spacers between the retaining member and the underlying flange of frame member 14, thus to elevate the retaining member. The size of the furnace openings 112 can be thus adjusted without disturbing the positions of the lintel blocks 108. Accordingly, as shown in Figure 7, the lintel blocks can be cast into position. For this recesses 126 are present for vertical alignment of the blocks and when the blocks are in place, this is filled with a cement 128 which bonds the blocks 108 together and seals the joint.
In use of the slot furnace it was observed that there was a fast heat up to a predetermined temperature which may range from about 500°C to about 1600°C. The heat up time was about 30 minutes. When the mats were installed and compressed, there was a compression of about 25 to 35 percent by volume. When the furnace was first used the mats M tended to shrink and this was compensated for by increasing the thickness of the blanket 8. The hot face mats M2, M4, M6 etc. were held tight to the mats M1, M3, M5 etc. secured to the wall and there was no relative movement. Any heat leakages could be observed from outside the furnace by virtue of the open mesh of the wall and these were easily repaired. When routine maintenance work was needed, the heat was switched off and cool air driven through the furnace which cooled very quickly. Fuel consumption was drastically.reduced and slag was eliminated.

Claims

1. A heat insulating wall element comprising a heat insulating lining and a backing structure, the lining comprising portions of ceramic fibrous material and being arranged in side-by-side relation, each portion having spaced apart leg portions with a space in between, one leg of one portion being received in the space between the legs of its neighbouring portion, the portions of ceramic fiber material being fastened to a grid-like structural member, characterized in that the backing element (W) is constituted by the grid-like member being a lightweight open mesh, and that the heat insulating lining is connected to the backing element (W) by tie wires (6).

2. The wall element of claim 1, wherein the legs (1, 2) are received in a space (S) of a portion (M1-M8) such as to leave a gap (5) in the space (S) which receives a mounting element (4) for holding the lining to a backing element (W).

3. The wall element of claim 1 or 2, wherein the portions (M2, M4, M6, M8) remote from the backing element (W), and which in use constitute the hot face of the wall element, have a different thermal conductivity than the portions (M1, M3, M5, M7) adjacent the backing element (W).

4. A heat enclosure or part thereof including a heat insulating wall element according to one of claims 1 to 3.

5. The heat enclosure of claim 4, wherein the portions (M; 82) are arranged in compressed condition to compensate for eventual shrinkage during operation.

6. The heat enclosure of claim 5, being a forge furnace (10), the side walls of said furnace having wall elements according to any one of claims 1-3 and a removable lid including fibrous sheets or blankets (82), the portions (M1-M8) of fibrous material adjacent the side walls (54, 56, 58) of said furnace (10) being compressed by said lid.

. 7. The heat enclosure of claim 6, comprising a lintel (108) which is insulated by mats (116) of said fibrous material.