CA1060189A

CA1060189A - Manufacture of resilient ceramic fiber seals

Info

Publication number: CA1060189A
Application number: CA260,612A
Authority: CA
Inventors: James A. Costick; Brian Hall
Original assignee: British Steel Corp
Current assignee: British Steel Corp
Priority date: 1975-09-08
Filing date: 1976-09-07
Publication date: 1979-08-14
Also published as: ZA765184B; DE2601276A1; SE7609863L; ES451305A1; JPS5256415A; MX145269A; NL7609980A; IT1071443B; FR2322701B1; BE845913A; DE2601276C3; FR2322701A1; BR7605896A; GB1531491A; DE2601276B2; AU1738276A; AU500962B2

Abstract

ABSTRACT OF THE DISCLOSURE:

A method of manufacturing an annular seal for a heat recuperator tube end is disclosed as comprising loosely wrapping without appreciable tension at least one layer of a compres-sible and resilient blanket of unbonded ceramic fibers about an annular forming mandrel, stabilizing the inner area of the fiber layer, thereafter compressing the fibers to decrease their volume while not destroying the recuperative ability of the fibers to resiliently expand back to a volume substantially greater than their compressed volume when the compression is released by wrapping a retainer exteriorly of the fibers to com-press them and to temporarily retain them in compressed condition, the retainer being destructable at operating temperatures of the tube ends of the recuperator in which the seal is to be used.
A specific wrapping process utilizing overlapping sheets of heat destructable wrapping material is disclosed.

Description

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This invention relates to recuperators, and in particuLar to recuperators of the type which incorporate ceramic refrac-tory tubes.
The advantages of recupera~ors incorporating ceramic re- i fractory tubes are that they can be used ar higher operating temperatures and give generally longer lives than metallic re-cuperators of similar construction. Their chief disadvantage -is that they are prone to high leakage rates which result from the breakdown of the tube seaLs under the differential thermaL
expansion forces. To try and overcome this problem a recupera- ~
- tor dèsign using flexible seals was developed, and this approach ~ `is described in British patent 1,244,911, published on 2nd ~ ~ ;
September 1971. One arrangement consists basically of a number of parallel ceramic tubes mounted either horlzontally or verti- ~
cally across the waste gas offtakes from a furnace; the tubes ;
being located at each end in holes in opposite monolithic re-fractory walls of the recuperator, with annular seaLs extending ~, between the outer circumferential surface at the end of each tube and ~he wall. The ends of the tubes open into a series ~ ~-of header boxes which are fitted on the outside of the mono-lithic walls. The tubes can be made of silicon carbide which is a heat conducting material. Air to be heated in the recup-erator is `passed through the tubes thereby enabling heat from the waste gas in the offtake to be transmitted to the air. The seals described comprise a plurality of rings of different overall diameter of compressed fibrous refractory material held in the compressed state by a locking ring which co-.': . _ 1 _ . :
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operates with the recuperator wall by means of a bayonet fitting within the wall block hole. A thrust washer may be positioned between the compressed rings and the means for :~
maintaining the rings in the compressed state, to minimize .1 any abrasive action on the rings themselves.
It is an object of the invention to provide a method of ~
sealing the tubes into the recuperator wall.s. !~ -More specifically, what is being claimed herein is a method of making an annular fibrous seal for high temperature ; ~
recuperator tube applications, which seal is capable of ~; :
radially expanding when first subjected to recuperator tube end ..
operating temperatures to establish and maintain a compressed seal between the peripheral tube end area and the adjacent cylindrical recuperator wall opening into which the tube ~ .
extends. The method comprises loosely wrapping, without appreciable tension, at least one layer of compressible and ! resilient.blanket of unbonded ceramic fibers about an annular ;~
.~ forming mandrel; providing means for stabilizing the form of the radially inner area of the fiber layer; after wrapping, compressing the ceramic fibers radially uniformly on the mandrel . to decrease their volume while not destroying the recuperative :
ability of the fibers to resiliently expand back to a volume substantially greater than their compressed volume when the com-' pression is released by wrapping a retainer means exteriorly `
of the fibers for compressing and temporarily retaining the ~;
fibers in raclially compressed condition. The retainer means is of the type which is destructable at operating temperatures of the tube ends of the recuperator in which the seal is to be used. Finally, the compressed fibers and the retainer means are to be removed from the mandrel.
In a preferred embodiment, the method inclucles the step of stabilizing the form-of the inner area of the fiber ,~

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1060~9 layer comprising impregnating the inner area only with a settable resin that is destructable at the tube end operating temperatures. This resin may be destructable by vaporization at the operating temperatures.
In another embodiment, the method includes the step of compressing the fibers by radially wrapping them after they have been wrapped on the mandrel, comprises circumferentially wrapping them with overlapping layers of sheet material applied under tension and securing the sheet ma-terial in place over the ;~
10 fibers to maintain the fibers compressed, the sheet material ~ `
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and the means used to secure such material in place being destructable at the tube end operating temperatures.
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Still according to another embodiment of the invention, the method comprises the step oE stabilizing the form of the inner area of the ibers comprising impregnating the inner area only with a settable resin, and the step of compressing the fibers after they are wrapped on the mandrel comprising cir~
1 cumferentially wrapping them with overlapping layers of sheet ` ;~
'~ material applied under tension after the fibers have been :j ' , , :
completely wrapped on the mandrel, and securing the sheet material :, to maintain the fibers in compression, the resin, the sheet .~ ; , , material and the sheet securing means being destructable at the tube end operating temperatures.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying ~ `
drawings in which~
;~ Figure 1 shows a side elevation in cross-section of `~
a recuperator wall with a recuperator tube end positioned in ` `

an opening in the wall, `~
Figure 2 shows a perspective view of one type of seal for insertion between the tube end and the wall opening f Figure 1, and Figures 3 to 9 illustrate schematically ~ 3 ~ -~'. ' )189 ~ ~
methods of making seals for insertion between th.e recuperator tube end and the wall opening of Fi~ure 1.
In Figure 1, a side wall 10 of a recuperator has a cylindrical opening 11 extending through it. The opening 11 is stepped inwardly towards the innermost side of wall 10. A
ceramic tube 12 is positioned in the opening 11 such that the tube end extends about two-thirds through the opening 11. In a typical recuperator installation, there will be a number of : ~ , tubes 12 extending parallel to one another and communicating with header boxes (not shown) on the respective outsides of the opposite recuperator walls 10.

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A ceramic fibre seal 13 fits between the outer cylindrical ~
surface of the tube 12 and the cylindrical opening ll so that :.
seal 13 abuts the stepped portion of opening 11. The seal 13 ' comprises an annular coil of ceramic fibre blanket, which blan~
ket has been radially compressed so that the coil has an outer diameter less than the diameter of the cylindrical wall opening ., 11, and has been impregnated with a heal: fugitive resin to hold the blanket in its compressed condition. The seal may have a ~.
number of laps of blanket as shown in FiLgure 2 or alternatively ~' it'comprises a single lap of relatively thick blanket. The seal' ;' 13 is held in place by an annular ceramic insert 14 which has a ,: ' bayonet fitting 15 cooperating with recesses 16 in the opening ', 11. A buffer ring 17 is provided between the ceramic insert 14 -~
', and, the end of tube 12, and a thrust washer 18 is itted between :~
the outer end of seal 13 and the ceramic lnsert 14 so as to mini-mize any abrasive actlon by the insert 14 on the seal 13.
The recuperator walls 10 heat up rapidly when the recuperator is put in line; the heat is transmitted to each seal 13 and the ,, heat fugitive binder thus degrades or evaporates so that the ~:
',, . 20 compressed seal expands to fill the annular space between the, ~' ~ end of tube 12 and the cylindrical opening 11, thereby providing ';, ' a substantially gas-tight seal at the pressures concerned. .~
'', The seal 13 may be manufactured by a number of alternative :
, methods. In Figure 3, the seal 13 is made by wrapping ~ibre :, 25 blanket. 20 around a former 21 in spiral manner, each lap of the ; , ' spiraL being compressed,radially as it is wound by a tensioned ,~

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10601~39 layer of adhesive plastic Eilm 22 supplied from reel 23 and in-terleaved between the laps of the spiral. The fibre blanket 2Q ,~
~, may have been prevlously soaked in water to make it more flexi-ble, or alternatively the blanket may be dry. '~he former 21, which is of combustible material, is mounted,on a collapsible mandrel 24 during the production of the spiral. After the seaL
' 13 ~as been formed, the seal 13 on its former 21 is removed from , ,'; the mandrel 24. me former 21 supports seal 13 during storage, ,~1 ; ~
~ and thus prevents distortion or collapse of the seal.
, In the method shown in Figure 4, the blanket is shown in a spirally'wound seal 13 which is being compressed radially as a whole by a tensioned plastic film 22 which may be adhesive~or . . :
non-adhesive. This method uses less film 22 than the method shown ln Figure'3 but may require a device (not shown) to assist ~;' , j . :
sl 15 in radially compressing the whole seal 13 prior to or during the I application of the fllm 22. '~
Il Figure 5 shows a fibre blanket 20 which has been impregnated , . . .
"~, with a heat fugitive resin (which acts as a reta~dant to the ~ fibre resil'iencej passing between a pair of pinch rolls 25 which : ,i , , ,l 20 compress the blanket 20. The resin is typically combustible or ! evaporates on the application of heat to the seal. The blanket ,, t~,', 20 is then wound under moderate tension in a spiral manner ohto ~' a former 21 mounted on a collapsible mandrel 24 and the completed ~ 1~ spiral is held for a time on the mandrel 24 to allow the resin to '~ ' 25 set. The seal '13 4~ its former is then removed from the mandrel.
,,~ A single lap coil is shown in Figure 6 being wound onto a ~ ~
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former 21. The blanket 20 has been previously cut to the correct ~' -, length for a slngle lap and is treated ln the apparatus of Figure 7 aEter impregnation with heat-fugitive resinO A squasher roll ' 26 runs on roll guides 27 mounted on a work-top ~not shown), the -; 5length of blanket 20 being fitted between the guldes 27. After squashing, the blanket 20 is wound around former 21 and held there until the resin has set. It is then removed from mandrel 24 and is suitable for use.
Figures 8 and 9 show another method of making a seal from a 10fibre blanket 20 previously cut to the required width and to a length sufficient to give the correct quantity of material. The seal 13 is made by loosely wrapping fibre bLanket 20 around a ;; ~' collapsible mandrel 24 with the innermost lap 28 impregnated with '~ !' ~i a hea~-fugitive resin. Three heat fugitive wraps 29 are attached "~
to restraining bars 30 and wrapped around the periphery of the coiled blanket'in such a way that each overlaps the preceding one.
The wraps 29 are rotated and tightened in a device not shown, such that the~ seal 13 is compressed radially as a whole. After'comp~e- `
ssion, as seen in Figure 9, a heat fugitive resLn 31 is applied~to~
each of the overLaps between the three wraps 29. The seal 13 is'~
held for a time on the mandrel 24 to allow the resin to set in ~ , both the innermost lap 28 and at the overlaps between the'wraps~
29. The'excess wraps are then cut off,restraining bars 30 are ~ slipped out parallel to the longitudlnal axis of the seal, and the ! 25 seal removed from the mandrel. ' ' ' '!
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of making an annular fibrous seal for high temperature recuperator tube applications, which seal is capable of radially expanding when first subjected to recuperator tube end operating temperatures to establish and maintain a compressed seal between the peripheral tube end area and the adjacent cylin-drical recuperator wall opening into which the tube extends compri-sing:
a) loosely wrapping without appreciable tension at least one layer of a compressible and resilient blanket of unbonded ceramic fibers about an annular forming mandrel;
b) providing means for stabilizing the form of the radially inner area of the fiber layer;
c) after wrapping, compressing the ceramic fibers radially uniformly on the mandrel to decrease their volume while not destroying the recuperative ability of the fibers to resiliently expand back to a volume substantially greater than their compressed volume when the compression is released by wrapping a retainer means exteriorly of the fibers for com-pressing and temporarily retaining the fibers in radially com-pressed condition, said retainer means being destructable at operating temperatures of the tube ends of the recuperator in which the seal is to be used; and d) removing the compressed fibers and the retainer means from the mandrel.

2. The method according to claim 1, the step of stabilizing the form of the inner area of the fiber layer com-prising impregnating said inner area only with a settable resin that is destructable at said tube end operating temperatures.

3. The method according to claim 2, said resin being destructable by vaporization at said operating temperatures.

4. The method according to claim 1, the step of radially compressing the fibers by wrapping them after they have been wrapped on the mandrel, comprising circumferentially wrap-ping them with overlapping layers of sheet material applied under tension and securing the sheet material in place over the fibers to maintain the fibers compressed, the sheet material and the means used to secure such material in place being destructable at said tube end operating temperatures.

5. The method according to claim 1, the step of stabilizing the form of the inner area of the fibers comprising impregnating said inner area only with a settable resin, and the step of compressing the fibers after they are wrapped on the mandrel comprising circumferentially wrapping them with over-lapping layers of sheet material applied under tension after the fibers have been completely wrapped on the mandrel, and securing the sheet material to maintain the fibers in compres-sion, the resin, the sheet material and the sheet securing means being destructable at said tube end operating temperatures.

6. The method according to claim 5, in which the step of securing the sheet material comprises bonding the over-lapping sheets together using an adhesive that is destructable at said tube end operating temperatures.

7. The method according to claim 1, the step of stabilizing the inner area of the fiber layer comprising wrapping the fibers about a temporary annular former element, said former element serving as the forming mandrel for the ceramic fibers, and being destructable at said tube end operating temperatures.

8. A method of making an annular fibrous seal for high temperature recuperator tube end applications, which seal is capable of radially expanding when first subjected to recuperator tube end operating temperatures to establish and maintain a compressed seal between the peripheral tube end area and the adjacent recuperator wall opening into which the tube end extends, comprising:
a) loosely wrapping in substantially tension free condition multiple layers of compressible and resilient unbonded ceramic fibers about a forming mandrel, the form of the inner most layer of the fibers being stabilized by impregnating only the innermost layer with a settable resin that is destructable at tube end operating temperatures;
b) compressing the fibers radially uniformly on the mandrel to decrease their volume while not destroying the ability of the fibers to resiliently expand back to a volume substantially greater than their compressed volume when the compression is released, the compression being carried out by circumferentially spirally winding overlapping layers of sheet material to the outer layer of the fibers and then tensioning the sheet material layers individually around the fibers, the sheet material being destructable at tube end operating temperatures;
c) securing the sheet material in place over the fibers by means that are destructable at tube end operating temperatures, and;
d) removing the compressed fibers and sheet material from the mandrel.

9. The method according to claim 8, the step of securing the sheet material in place comprising bonding the sheets together where they overlap using a settable resin, the sheet material and the resin being destructable at tube end operating temperatures.

10. The method according to claim 1, including the additional step of placing the compressed fibers with the temporary retaining means about a recuperator tube end between the tube end and adjacent cylindrical recuperator wall structure.