GB2190167A

GB2190167A - Furnace pipe insulation

Info

Publication number: GB2190167A
Application number: GB08611378A
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
Anticipated expiration: 2006-05-09
Also published as: GB2190167B; GB8611378D0

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 a 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 by 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 thus 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 closely 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.

Fibrous refractory materials are relatively expensive, and in cutting out annular discs (or even part-annular discs) from a web or blanket of such material there is considerable wastage. It is accordingly a further object of the present invention to provide a construction of insulative member capable of employing the material in shaped which can be cut from a web with little or no wastage.

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 elongate strips of resiliently deformable fibrous refractory material assembled in side by side contiguous relationship, and clamping means for holding said strips assembled and in resilient compression in a zone adjacent one longitudinal edge of the assembly, said clamping means including at least one metal rod which passes transversely through the strips in the said zone.

The strips may be designed and configured in various ways according to the particular application of the insulative member and the cross sectional shape of the furnace pipe to which the insulative member is intended to be applied. In one form of member the strips comprise sub-assemblies each composed of two individual similar strips, preferably rectangular in outline, and a filler member or insert of lesser width sandwiched between the two strips of the pair adjacent to the other longitudinal edge. In another form, the strips are folded in half lengthwise around a filler member or insert so that the longitudinal edges of the strip are in a common plane. The insert or filler member may be a fibrous refractory material, or a solid cylindrical or tubular refractory insulating material or indeed may have any desired shape.

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. The clamping means may include metal brackets which have a shape conforming to part of the outer surface of the pipe, the metal rods, for preferably at least two rods are employed, having their ends secured to the brackets.

In another construction the metal rods are secured intermediate their ends to a support member, metal end plates being connected to the end of the rods to retain the strips assembled and under the desired compression.

The support bracket may be extended at its ends to project longitudinally clear of the fibrous refractory material so that the insulative member can be secured to the furnace pipe.

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 a perspective view of a component strip of fibrous refractory material, Figure 3 is a perspective view of a metal rod, Figure 4 is a perspective view of a bracket, Figure 5 is a perspective view illustrating an assembly for a plurality of the members as shown in Fig. 1, one insulative member being shown partly broken away.

Figure 6 is a perspective view of a composite strip of fibrous refractory material of a different form, Figure 7 is a perspective view of a second embodiment of insulative member, Figure 8 is a perspective view of a support member used in the embodiment of Fig. 7, and Figure 9 is a perspective view illustrating an assembly of a plurality of the members shown in Fig. 7.

With reference to the accompanying drawings, Fig. 1 shows an elongate insulative member 20 comprising a plurality of elongate strips 1 of fibrous refractory material assembled on two metal rods 2 the ends of which are secured to respective metal clamping brackets 3.

Each strip 1 comprises, Fig. 2, a rectangular piece of fibrous refractory material 4, preferably a ceramic fibre material, folded in half lengthwise around a longitudinally extending insert 5 so that the longitudinal edges of the material 4 are in a common plane. The mating faces of the material are preferably adhesiveiy bonded to assist in handling of the folded strip. The strip 1 has two pre-punched holes 6, 7 to accept the metal rods 2. The rods 2 are semi-circular, Fig. 3, and may have threaded ends. The clamping brackets 3, Fig.

4, comprise a main semi-circular portion 8, Ushaped portions 9 and end flanges 10 bent outwardly into a common diametral plane. The end flanges 10 are provided with holes 11 to receive the ends of the rods 2.

Insulative member 20 is assembled by threading a rod 2 transversely through each of the holes 6 and 7 of a member 1, and then assembling other members 1 similarly onto the rods 2 in contiguous side by side relationship until the desired total number of strips 1 is positioned on the rods. Next the clamping brackets 3 are fitted over the ends of the rods 2, and a circumferential force is applied to draw the ends of the rods 2 outwardly of the holes 11 in the brackets and thus to compress the fibrous refractory material of the strips 1 in the inner zone surrounding the holes 6, 7 adjacent the inner longitudinal edge of the strips to a desired density and to draw the strips up against the outer faces of the semi-cylindrical portions 8 of the brackets 3 as well as against the flanges 10.

The inner circumference of the member 20 is less than the outer circumference because the member 20 has a finite radial thickness; the difference in circumference is allowed for by the incorporation of the inserts 5 which prevent the fibrous refractory material in the outer zone compressing to the same extent as in the inner zone.

When the member 20 has assumed the desired shape with the desired compression and density of the fibre material in the inner zone, the projecting ends of the rods 2 are suitably secured to the brackets 3, such as by positioning nuts (not shown) on the threaded ends of the rods 2, by welding or by use of securing clips as shown at the lower right hand side of Fig. 1.

Assembly of the insulative members 20 on a circular water-cooled support pipe in a furnace proceeds as shown in Fig. 5 (the actual pipe is not illustrated). Two members 20 and 20a are positioned circumferentially adjacent to enclose the pipe. The holes 6 and 7 in the strips 1 and thus the brackets 3 are at different distances from the end faces of the members 20, 20a so that adjacent brackets 3 lie side by side and the U-shaped portions 9 cooperate to define a channel through which metal wires or rods 12 can be inserted to connect the members 20, 20a together circumferentially.

The brackets 3 may have extensions 13 as illustrated in Fig. 4 which project beyond the longitudinal end faces of the members 20 so that the members can be secured to the pipe by welding or by clips.

The insulation is extended longitudinally of the pipe by adding longitudinally adjacent members such as 20b and 20c in circumferentially staggered relationship e.g. 900.

For clarity of the above description a circular water-cooled support pipe has been assumed, thus the rods 2 and the brackets 3 shown are semicircular. However, wafter-cooled supports in furnaces can be of any shape, such as rectangular, in which case the rods and brackets would be of a conformable shape.

Fig. 6 illustrates an alternative construction of an elongate strip 51 of fibrous refractory material. Strip 51 comprises a composite or sub-assembly of two individual similar rectangular strips 52 and a flat insert 53 of lesser width sandwiched between them adjacent what will be the outer face of the strip in the assembled insulative member. The strips 52 and inserts 53 are adhesively bonded together. The thickness of the insert 53 can be varied to suit the radius of the pipe to which the insulative member is to be applied. Strip 51 may be used instead of or in combination with the strip 1 in any embodiment of insulative member according to the invention.

Strips 51 are used in the second embodiment shown in Figs. 7 to 9, now to be described. The second embodiment of insulative member 120 is based on a support member 58 illustrated in Fig. 8 which is of T-section.

The rods 2 pass through and are welded to the web 54 of the member 58. The flange 55 is longer than the strips 51 to be used. Strips 51 are assembled onto rods 2 as described previously in connection with the first embodiment, and when the inner zones are compressed to the desired density clamping plates 56 are fitted over the ends of the rods 2 and secured as previously described.

Assembly of the insulative members 120 onto a circular water-cooled support pipe in a furnace proceeds as shown in Fig. 8 and is generally as previously described, except that the projecting ends of the flanges 55 serve to enable the members 120 to be secured to the pipe by welding or by clips. The clamping plates 56 of each member 120 include additional holes 57 to receive the projecting ends of the rods 2 of the circumferentially adjacent insulative member. The projecting ends of the flanges are protected by the longitudinally adjacent members.

The strips of fibrous refractory material described can be cut from a larger web or blanket of material to use the material substantially completely with minimum wastage.

The thickness and/or diameter of the inserts 5, 53 can be varied to suit the desired difference between the inner and outer circumferences of the insulative member and by appropriate choice of insert insulative members can be constructed to insulate substantially any shape of furnace pipe that will be met with in practice, including rectangular shapes with radiused corners.

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 elongate strips of resiliently deformable fibrous refractory material assembled in side by side contiguous relationship, and clamping means for holding said strips assem bled and in resilient compression in a zone adjacent one longitudinal edge of the assembly, said clamping means including at least one metal rod which passes transversely through the strips in the said zone.

2. An insulative member according to Claim 1, wherein the clamping means comprise at least two said metal rods longitudinally spaced apart and a clamping bracket secured to the respective ends of each rod.

3. An insulative member according to Claim 2, wherein the clamping brackets each comprise a shaped central portion having at each end thereof a U-shaped portion and an end flange, the end flanges lying in a common plane and been provided with holes to receive the ends of the rods.

4. An insulative member according to Claim 3, wherein the ends of the rods are secured to the end flanges of the clamping brackets by welding or by securing clips fitted over the end of the rods.

5. An insulative member according to any one of Claims 2 to 4, wherein the brackets carry extension pieces which project beyond the longitudinal end faces of the member.

6. An insulative member according to Claim 1, wherein the clamping means comprises at least two said metal rods longitudinally spaced apart and secured intermediate their ends to the web of a longitudinally extending T-shaped support member, and metal end plates connected to the ends of the rods to retain the elongate strips assembled under compression.

7. An insulative member according to Claim 6, wherein the flange of the support member extends longitudinally beyond the longitudinal end faces of the strips of fibrous refractory material.

8. An insulative member according to any one the preceding claims, wherein each said elongate strip comprises a sub-assembly composed of two individual similar strips of fibrous refractory material and a filler member sandwiched between the two strips adjacent to the other longitudinal edge.

9. An insulative member according to any one of Claims 1 to 7, wherein the elongate strips of fibrous refractory material comprise strips folded in half lengthwise around a filler member so that the longitudinal edges of the strip are in a common plane.

10. An insulative member according to Claim 8 or Claim 9, wherein the filler member is a refractory material.

11. A pipe insulation which comprises two or more elongate insulative members for application to the outer surface of an elongate pipe in a furnace to protect the pipe from the effects of furnace heat, wherein said insulative members are as claimed in any one of the previous claims and are positioned circumferentially adjacent relative to the surface of the pipe to cover part or the whole of the surface thereof.

12. A pipe insulation according to Claim 11, wherein the members are as claimed in Claim 3 and the clamping brackets are at different distances from the end faces of the members so that adjacent brackets lie side by side and the U-shaped portions thereof cooperate to define a channel through which a metal rod is inserted to connect the members together circumferentially.

13. A pipe insulation as claimed in Claim 11, wherein the members are as claimed in Claim 6 and the ends of the rods which project beyond the metal end plates pass through holes provided therefor in the end plates of the circumferentially adjacent member and penetrate into the fibrous refractory material of such member.

14. A pipe insulation as claimed in any one of Claims 11 to 13, comprising additional said circumferentially adjacent members arranged in end to end longitudinal relationship, with longitudinally adjacent members being circumferentially staggered in relation to each other.

15. A pipe insulation according to any one of Claims 11 to 14, wherein the insulative members have a shape conforming to that of the surface of the pipe.

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.