GB2190166A

GB2190166A - Furnace pipe insulation

Info

Publication number: GB2190166A
Application number: GB08611377A
Authority: GB
Inventors: Thomas James Twort
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-05-09
Filing date: 1986-05-09
Publication date: 1987-11-11
Also published as: GB8611377D0

Abstract

An elongate insulative member for assembly with one or more similar members to cover part or the whole of the surface of an elongate pipe in a furnace to protect the pipe from the effects of furnace heat comprises a plurality of elongate strips 1 of resiliently deformable fibrous refractory material assembled in side by side contiguous relationship, and clamping means including metal brackets 3 and metal rods 2 which pass transversely through the strips in the zone adjacent one longitudinal edge of the assembly to hold the strips 1 assembled and in resilient compression in the said zone. <IMAGE>

Description

SPECIFICATION Furnace pipe insulation This invention relates to means and method for insulating elements mounted within high temperature furnace chambers, particularly water cooled pipes in the supporting structures for work pieces in heat treating furnaces.

A supporting structure within a furnace chamber where temperatures may be in the order of 13000C must be compact in order to leave sufficient combustion space in the chamber, must be strong enough to support heavy metal workpieces being treated in the furnace, and must be protected against injury by the high temperature within the furnace while at the same time not seriously interfering with the efficiency and maximum temperature of a furnace. It must also be strong enough to withstand the stresses and heavy vibration set up by the movement of the heavy workpieces within the heating chamber.

A combination of small size with high strength dictates the use of metals in the supports and the necessity for cooling the metal dictates the use of hollow metal pipes through which cooling water is circulated.

If water cooled pipes with bare outer surfaces are used, however, the absorption of heat through the pipe metal to the cooling water is so great that more fuel is wasted in heating the cooling water than in heating the workpieces. For example, an under fired furnace having bare metal supports in its lower zone requires about three times as much fuel to heat the lower zone of the furnace as the upper zone of the furnace, and no matter how much fuel is supplied to the lower zone it still remains distinctly cooler than the upper zone.

In an endeavour to correct this condition early attempts were made to apply castable refractory insulating material directly to the water cooled support pipes. However, this expedient has not proved very satisfactory because the refractory material tends to crack after some use, principally because of the difference in thermal expansion of the inner and the outer layers of the refractory materials and because of the difference in the thermal expansion characteristics of the refractory materials and the metal pipe which it encloses.

The movement of the supporting structure due to the movement of the heavy workpieces within the heating chamber also contribute significantly to the break up and loss of the refractory material particularly after cracking has occurred.

Various other expedients have therefore been employed in endeavours to prevent loss of the refractory material after cracking has occurred. It has been proposed for example to embed in the refractory material a wire fabric reinforcement which, should damage to the refractory material occur, will hold the refractory material in situ round the piping. It has also been proposed to employ preformed blocks of castable refractory material, with or without wire fabric reinforcement, which blocks are secured together circumferentially around the piping metal connectors or by use of interlocking joints, with the idea that damaged blocks can readily be replaced. However, in practice, this proves to be not always readily possible.

In recent years, fibrous refractory materials which provide a high degree of thermal insulation and are suitable for use at the temperatures prevailing in furnace chambers have become available. These materials, which are flexible and resiliently deformable, are thus able to accommodate movement of these supporting pipe structure due to thermal expansion and vibration without cracking and they are also light in weight by comparison with castable refractory materials. However, while the above properties of the fibrous refractory materials are thus desirable properties for a furnace pipe insulation to possess, the fibrous nature of the materials makes it difficult to attach the materials to the piping in a satisfactory yet simple and reliable manner.

Fibrous refractory materials have thus been used to insulate furnace pipes by wrapping the pipes with blankets of the material secured by circumferential wire ties and covered by a refractory mortar surface coating. Also it has been proposed to sheath the pipes with an inner layer of sheets of refractory fibrous material surrounded by an outer layer of refractory blocks held in place by metal connectors, or by providing an outer layer of interlocked refractory blocks which hold the inner layer of resiliently deformable refractory fibrous material in radial compression and which are in turn held in circumferential stress by the compressed inner layer.However, the above proposals do not utilise the fibrous refractory material to best advantage and the continued employment of castable refractory material has an outer layer or skin means that the disadvantages of the latter material are retained.

Proposals have also been made to use fibrous refractory material as an insulation for furnace pipe work without requiring the use of any castable refractory material in combination. Annular discs have been cut from a web or blanket of fibrous refractory material and have been passed longitudinally over a free end of the pipe work; alternatively, where no free end has been available, a radial slit has been cut in the discs to enable them to be opened out and offered around the pipe work.

By enclosing the pipe with a sufficient plurality of such discs an insulation has been provided.

However, in order to prevent heat penetrating between adjacent discs, the discs must be closed positioned and preferably compressed axially to some extent, and the means necessary to achieve this are complicated and unreliable in action. Installation of the insulation is time consuming and therefore expensive in labour, and replacement of a damaged section of the insulation is difficult without dismantling the entire installation. These disadvantages have hitherto militated against the general adoption of this form of insulation.

It is an object of the present invention to provide an improved method and means for enabling fibrous refractory materials to be employed as insulative materials for furnace pipe work to protect the pipe work from the effects of furnace heat without requiring the use of castable refractory material in combination, by preforming insulative members capable of direct application to the pipe work from fibrous refractory material.

The present invention proposes an elongate insulative member for application to the outer surface of an elongate pipe in a furnace to protect the pipe from the effects of furnace heat, said member comprising a plurality of laminae of resiliently deformable fibrous refractory material stacked one on top of another and compressed longitudinally between two metal end plates which are rigidly connected by longitudinal metal rods that penetrate the laminae.

The metal rods in combination with the metal end plates ensure that the compressed stack of laminae has both longitudinal and circumferential stability.

The rods may be connected to the end plates in any suitable manner, for example by the use of clips, by threaded connections or preferably by welding.

The insulative members are intended for assembly with one or more similar members around a pipe to cover part or the whole of the surface thereof. Circumferentially adjacent such members can be secured together around the pipe by employing interengaging means on or connected to the end plates. The interengaging means may comprise clips which are inserted into preformed holes at adjacent ends of the end face. Alternatively, and if the metal rods project longitudinally beyond the outer faces of the metal end plates at least one end of the elongate insulative member, the interengaging means may take the form of adjustable straps which are positioned over the projecting ends of the rods.

Insulative members may be connected together longitudinally in a convenient manner if one end plate is provided with locating holes and the metal rods extend longitudinally beyond the other end plate to be received in the locating holes in the one end plate of a second, similar insulative member positioned longitudinally adjacent but circumferentially staggered in relation thereto. In this way insulative members can be assembled together and built up to any desired length along the pipe without the need to employ additional retaining means.

The insulative members may be of arcuate form, the radial cross section of the member being part of an annulus, or semi-annular, or may have any desired external configuration determined by the shape of the laminae and the metal end plates.

To prevent heat from penetrating between the abuting radial faces of adjacent assembled members these faces are preferably provided with interlocking tongue and groove formations.

Two embodiments of the invention will now be described by way of example, reference being made to the accompanying drawings in which: Figure 1 is a perspective view of a first embodiment of insulative member, Figure 2 is an exploded view illustrating the method of assembly of the member of Fig. 1, Figure 3 is a perspective view illustrating an assembly of a plurality of the members as shown in Fig. 1, Figure 4 shows one form of a retaining clip, Figure 5 shows an alternative retaining clip, Figure 6 shows an adjustable retaining strap, Figure 7 is a view similar to Fig. 1 showing a second embodiment of insulative member, Figure 8 is a view similar to Fig. 2 but relating to the embodiment of Fig. 7 and Figure 9 is a view similar to Fig. 3 but showing the insulative members of Fig. 7.

With reference to the accompanying drawings, Fig. 1 shows an elongate insulative member 20 comprising a stack of laminae 1 of fibrous refractory material compressed longitudinally between metal end plates 2 and 3 which are connected by longitudinal metal reinforcement rods 4.

The method of assembly of the member 20 is illustrated in Fig. 2. End plates 2 and 3 are semi-annular as shown but could be of any suitable shape e.g. semi-hexagonal. Rods 4 are mounted on end plate 2 e.g. by welding.

A lamina 1 of semi-annular shape cut from a web or blanket of fibrous refractory material, preferably a ceramic fibre material, is located over the free ends of the rods and is passed down thereover until it rests against the end plate 2. The lamina 1 has prepunched holes 5 to accept the rods 4. Other similar laminae 1 are then located successively over the rods 4 until a stack of laminae of sufficient height is built up. End plate 3 is next located over the free ends of the rods 4 and is urged downwardly to compress the fibrous refractory material of the stack of laminae to the desired density.

After compression the plate 3 is secured to the metal rods 4 by welding or in other suitable manner to prevent further movement of the fibrous material. It will be noted that the ends 4' of the metal rods project beyond the end plate 3 for insertion through holes 6 in longitudinally adjacent insulative members 20 during installation as is further explained below.

Assembly of the insulative members 20 on a circular water cooled support pipe in a furnace proceeds as shown in Fig. 3 (the actual pipe is not illustrated). Two members 20 and 20a are positioned circumferentially adjacent to enclose the pipe and are connected together by inserting clips 7 (either Fig. 4 or Fig. 5) into holes 8 in the adjacent ends of the metal plates 2 and 3 of the sections or by positioning a strap 9 (Fig. 6) over the projecting ends 4' of the adjacent metal rods 4 to extend across the juncture between the members. The strap 9 is provided with a plurality of spaced holes 10 so that by selecting appropriate holes to engage over the ends 4' of the rods and members 20, 20a can be drawn together circumferentially to ensure correct tightness and fit around the pipe.

The insulation is extended longitudinally of the pipe by adding longitudinally adjacent members such as member 20b in circumferentially staggered relationship e.g. 90 . The projecting ends 4' of the rods from both members 20 and 20a engage in the holes 6 in the end plate 2 of the member 20b to provide additional circumferential retention of the members 20 and 20a and by penetrating into the fibrous material of the laminae 1 of the member 20b ensuring continuity of insulation in the longitudinal direction. By adding further members the insulation can be extended to any desired length.

The radial ends of the laminae 1 are shaped with interlocking tongue and groove formations 10, 11 to provide an effective heat barrier at the juncture between the circumferentially adjacent members.

Fig. 7 to 9 show an alternative embodiment of insulative member 200, the difference being in the make up of the laminae. Laminae 100 in Figs. 7 to 9 are each composed of three similar interlocking shapes 101 each of which is substantially trapezoidal in plan. The advantage of the shape 101 over the semi-annular shape of the laminae 1 is that shape 101 can be cut out of a web of fibrous refractory material with considerably less wastage. Construction and assembly of member 200 will be apparent from the foregoing description and the drawings. Semi-hexagonal end plates 2 and 3 may be preferred for this embodiment.

Claims

1. An elongate insulative member for application to the outer surface of an elongate pipe in a furnace to protect the pipe from the effects of furnace heat, said member comprising a plurality of laminae of resiliently deformable fibrous refractory material stacked one on top of another and compressed longitudinally between two metal end plates which are rigidly connected by longitudinal metal rods that penetrate the laminae.

2. An insulative member according to Claim 1, wherein the rods project longitudinally beyond the metal end plate at least one end of the member.

3. An insulative member according to Claim 1 or Claim 2, wherein the rods are welded to the end plates.

4. An insulative member according to any one of Claims 1 to 3, wherein the laminae have prepunched holes through which the rods pass.

5. An insulative member according to any one of Claims 1 to 4, wherein each lamina comprises an integral semi-annular piece of fibrous refractory material.

6. An insulative member according to any one of Claims 1 to 4, wherein each lamina comprises a plurality of interlocked pieces of fibrous refractory material each substantially trapezoidal in shape.

7. An insulative member according to any one of Claims 1 to 6, wherein the end plates are arcuate.

8. An insulative member according to any one of Claims 1 to 6, wherein the end plates are semi-hexagonal.

9. A pipe insulation which comprises two or more insulative members for covering a surface of an elongate pipe in a furnace to protect the pipe from the effects of furnace heat, each member comprising a plurality of laminae of resiliently deformable fibrous refractory material stacked one-on top of another and compressed longitudinally between two metal end plates which are rigidly connected by longitudinal metal rods that penetrate the laminae, and means for securing circumferentially adjacent said members together.

10. A pipe insulation according to Claim 9, wherein the circumferential securing means comprise clips which engage with the adjacent end plates of respective circumferentially adjacent members.

11. A pipe insulation according to Claim 9, wherein the metal rods project longitudinally beyond the metal end plates at at least one end of each insulative member, and the circumferential securing means comprise straps positioned over the projecting ends of the rods of circumferentially adjacent members to extend across the juncture between the members.

12. A pipe insulation according to any one of Claims 9 to 11, comprising a plurality of said members arranged in both circumferentially adjacent and end to end longitudinal relationship, with longitudinally adjacent members being circumferentially staggered in relation to each other.

13. A pipe insulation according to Claim 12, wherein for connecting adjacent members together longitudinally the end plates are pro vided with locating poles and the metal rods extend longitudinally beyond the end plates to be received in the locating holes in the respective adjacent end plates of the longitudinally adjacent insulative members.

14. A pipe insulation according to any one of Claims 9 to 13, wherein the abutting radial faces of circumferentially adjacent assembled members are provided with interlocking tongue and groove formations to provide a heat barrier at the juncture between the members.

15. A pipe insulation according to any one of Claims 9 to 14, wherein each lamina of fibrous refractory material comprises an integral semi-annular piece of the material.

16. An elongate insulative member for application to the outer surface of an elongate pipe in a furnace to protect the pipe from the effects of furnace heat, substantially as hereinbefore described with reference to the accompanying drawings.

16. A pipe insulation according to any one of Claims 9 to 15, wherein each lamina of fibrous refractory material comprises a plurality of interlocked pieces of the material each substantially trapezoidal in shape.