GB2042699A

GB2042699A - Kiln with ceramic-fibre lining slabs

Info

Publication number: GB2042699A
Application number: GB8003403A
Authority: GB
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 1979-02-02
Filing date: 1980-02-01
Publication date: 1980-09-24
Also published as: DE3003459C2; GB2042699B; JPS5832136Y2; DE3003459A1; JPS55112698U

Abstract

A kiln provided with a plurality of layers of ceramic-fiber lining slabs 2 secured to the inner surfaces of a casing 1 and formed with a plurality of holes 3 extending in the direction of the thicknesses of the lining slabs. A support rod 4 is inserted in each of the holes 3 and secured at its forward end to the innermost layer of the lining slabs while its base portion extends through each wall of the casing to the outside, to secure the layers of lining slabs in position. A spring device 7 is mounted on the base portion of each support rod to urge by its biasing force the layers of lining slabs to move toward the inner surface of the casing at all times to avoid formation of gaps between the layers of the lining slabs which would otherwise be caused by shrinking of the ceramic fiber due to exposure to the heat of high temperature. <IMAGE>

Description

SPECIFICATION Kiln with ceramic-fiber lining slabs This invention relates to improvements in or relating to a kiln provided with ceramic-fiber lining slabs.

Ceramic fiber is refractory material in the form of cotton wool which may be produced by electrically melting a mixture comprising alumina and silica as its main constituents and by blowing the molten mixture by an air current of high speed. Ceramic fiber in the form of blanket, felt or board formed by adding some organic materials to ceramic fiber in the form of cotton wool is commercially available.

The ceramic fiber boards have characteristics such that they can resist heat of up to 1 6000 C, they are low in Young's modulus, bulk specific gravity and thermal capacity, and they are light in weight and high in heat insulating ability, so that they have in recent years been widely in use as lining slabs for various types of kilns for industrial production.

One exarnple of application of ceramic-fiber boards as lining slabs of a kiln is shown in Figs. 5 and 6 wherein, as is well known, ceramic-fiber lining slabs 22, 23, 24 and 25 are attached to the inner surfaces of a casing 21 of steel plate in a multiplicity of layers, and boits 26 mounted to the inner surface of the casing 21 and extending through the ceramic-fiber lining slabs 22,23,24 and 25 each have a nut threadably connected to the forward end portion of each bolt 26, so that the ceramic-fiber lining slabs 22, 23, 24 and 25 can be bolted in place as the nuts 27 are tightened. The layers of ceramic-fiber slabs located nearer to the inner surfaces of the casing 21 usually have lower refractoriness and their refractoriness increases in going away from the inner surfaces of the casing 21 toward the interior of the kiln.In the aforesaid constructional form, washers 29 each provided with a recessed portion 28 formed of refractory material and having refractory material 30 filled in the recessed portion 28 are fitted to the innermost layer of ceramic-fiber lining slabs in such a manner that the threaded portions of the bolts 26 and the nuts 27 in threadable engagement therewith are embedded in the refractory material 30 to prevent them from being damaged by heat. This constructional form of the prior art has some disadvantages.When in operation, the kiln is heated and the temperature in the interior rises to a high level in the range between 1250 and 1 5000C; and when the filing operation is over, the temperature in its interior drops to a low levei. As the rise and fall in temperature is repeated, the ceramic fiber undergoes expansion and coniraction. This repeated change in temperature gradually reduces the density of the ceramic fiber, and the thickness of the ceramic-fiber lining slabs is reduced.

With a reduction in the thickness of the ceramic fiber lining slabs, the clamping force exerted by the bolts 26 and nuts 27 on the ceramic-fiber lining slabs 22, 23, 24 and 25 is not sufficiently high to keep them close together. As a result, a gap is formed between the lining slabs 22 and 23 and 24 and 25, between the casing 21 and the outermost lining slabs 22, and between the innermost lining slabs 25 and washers 29. Gas of high pressure penetrates into these gaps to reduce the heat insulating effects achieved by the lining slabs 22, 23, 24 and 25 and to cause thermal damage to the bolts 26 and nuts 27.

This invention obviates the aforesaid disadvantages of the prior art. The invention has as its object the provision of a kiln provided with ceramic-fiber lining slabs wherein formation of gaps between the layers of ceramic-fiber lining slabs due to changes in the temperature in the interior of the kiln can be avoided, so that the ceramic-fiber lining slabs can have increased service life.

According to the invention, means for coping with a reduction in the thickness of ceramic-fiber lining slabs is provided to each support rod for securing the lining slabs in position, so that no gaps are formed between the lining slabs themselves and between the lining slabs and the casing.

Figs. 1 a, 1 b, 2, 3 and 4 are sectional views of different constructional forms of the invention; Fig. 5 is a fragmentary front view of a kiln provided with ceramic-fiber lining slabs of the prior art; and Fig. 6 is a sectional view of the essential portions of the kiln shown in Fig. 5.

Preferred embodiments will now be described by referring to the accompanying drawings. Fig. 1 a shows one constructional form of the invention wherein a multiplicity of layers of ceramic fiber lining slabs 2 are attached to the inner surface of a casing 1 of steel plate in such a manner that the layers of ceramic-fiber lining slabs 2 have increasingly higher refractoriness in going from the inner surface of the casing 1 toward the interior of the kiln. A plurality of holes 3 of a diameter in the range between 10 and 25 mm are formed in the plurality of layers of ceramic-fiber lining slabs 2 to extend in the direction of their thicknesses in positions suitably spaced apart from one another. A support rod 4 is inserted in each of the holes 3 through the wall of the casing 1 and has at its forward end a keep plate 13 for securing the lining slabs 2 in place.The support rod 4 has a coil spring device 5 mounted at a base portion 4' of the support rod 4 to urge by its biasing force the support rod 4 and hence the lining slabs 2 to move toward the inner surface of the casing 1 at all times. The coil spring device 5 includes a fixed plate 6 secured to a nut mounted on the base portion 4' of the support rod 4, and a compression coil spring 7 mounted between the fixed plate 6 and the wall of the casing 1 in a manner to surround the support rod 4. The spring device 5 is operative to urge by the biasing force of the compression coil spring 7 the lining slabs 2 to move toward the inner surface of the casing 1 through the support rod 4.

The spring of the spring device is not limited to the coil spring. Fig. 1 b shows a modification in which a plate spring 7' is used in place of the coil spring 7 shown in Fig. 1 a.

Fig. 2 shows another constructional form of the invention wherein the casing 1, lining slabs 2, holes 3 and support rods 4 are similar to those shown in Fig. la. However, the coil spring device 5 includes a tension coil spring 1 0 mounted between a fixed plate 8 secured to the base portion 4' of the support rod 4 and a fixed support 9 secured to the outer surface of the casing 1. The tension coil spring 10 urges by its biasing force the lining slabs 2 to move toward the inner surface of the casing 1 through the support rod 4 at all times.

Fig. 3 shows still another constructional form of the invention wherein the casing 1, lining slabs 2, support rod 4 and coil spring device 5 are similar to those shown in Fig. 1 a. However, the hole 3 shown in Fig. 3 is distinct from the hole 3 shown in Fig. 1 a in that a portion of the hole 3 extending through the lining slabs 2 disposed nearer to the inner wall surface of the casing 1 is replaced by a tube 11 extending through the lining slabs 2 and secured to the outer surface of the casing 1. The use of the tube 11 in one portion of the hole 3 has the effect of reducing the load applied to the support rod 4 because the tube 11 bears part of the load of the lining slabs 2 while allowing the support rod 4 in the hole 3 to move smoothly toward the inner surface of the casing 1.The reasons why the tube 11 is used only in a portion of the hole 3 disposed nearer to the inner surface of the casing 1 are because the movement of the lining slabs 2 disposed nearer to the interior of the kiln toward the inner surface of the casing 1 caused by the biasing force of the compression coil spring 7 can be facilitated and because the gap formed between the support rod 4 and the hole 3 is smaller than the gap formed between the support rod 4 and the tube 11 to make it possible to effectively avoid penetration of gas of elevated temperature.

The constructional form shown in Fig. 4 is similar to the constructional form shown in Fig. 2 in the casing 1, lining slabs 2, support rod 4 and spring device 5. However, the hole 3 is replaced, like the hole 3 of the constructional form shown in Fig. 3, in a portion thereof extending through the lining slabs 2 disposed nearer to the inner surface of the casing 1, by the tube 11 secured at its base to the casing 1.

The provision of the tube 11 achieves the same effects as is the case with the provision of the tube 11 in the constructional form shown in Fig. 3.

In the constructional forms shown in Figs. 1 a, 1 b, 2, 3 and 4, the keep plate 13 located at the forward end of the support rod 4 is shown as being a nut. However, the invention is not limited to this form of keep plate and the keep plate 13 may be of any other construction as desired. The support rod 4, keep plate 13 and tube 11 are formed of ceramic refractory material to minimize damage thereto caused by the heat of gas of elevated temperature. However, any other metallic heat-resisting material may be used to fabricate same.Preferably, ceramic refractory material is used when the temperature in the kiln rises above 10000C and steel or other metallic heat-resisting material is used when the temperature in the kiln remains under 10000 C. Also, in the aforesaid embodiments, the ceramic-fiber lining slabs 2 located nearer to the inner surface of the casing 1 have relatively lower refractoriness than the ceramic-fiber lining slabs 2 disposed nearer to the interior of the kiln which are exposed to the gas of elevated temperature. The lining slabs 2 disposed nearer to the inner surface of the casing 1 may be formed of calcium silicate or other heat insulating material suitable for coping with heat of lower temperature.

In all the embodiments described hereinabove, the ceramic-fiber lining slabs 2 supported by the support rods 4 fitted in the holes 3 extending in the direction of the thicknesses of the lining slabs 2 and attached to the inner surface of the casing 1 can exhibit excelient performance in resisting and insulating heat and they are light in weight. Thus the ceramic-fiber lining slabs 2 constructed as aforesaid can have particular utility for use with a kiln for ceramic industry and for heat treatment of metals wherein the interior is heated to elevated temperatures. As the kiln is repeatedly heated and cooled, the innermost layer of the ceramic-fiber lining slabs 2 heated to the highest temperature is first reduced in thickness and the adjacent layers become successively smaller in thickness.However, the provision of the coil spring device 5 mounted at the base portion 4' of the support rod 4 extending outwardly of the casing 1 for urging by its biasing force the support rod 4 and hence the lining slabs 2 to move toward the inner surface of the casing 1 has the effect of removing gaps which would otherwise be formed between the layers of lining slabs 2 due to a reduction in the thickness of the lining slabs 2.

Thus the layers of lining slabs 2 are free from the penetration of gas of high temperature and the casing 1 is impervious to the influence of the gas of high temperature by virtue of the superb heat insulating effect achieved by the lining slabs 2.

The use of the tube 11 in one portion of the hole 3 formed in the ceramic-fiber lining slabs 2 to extend in the direction of their thicknesses enables, as aforesaid, the load applied to the support rod 4 to.

be reduced and permits the support rod 4 to move smoothly toward the inner surface of the casing 1.

The coil spring device 5 may include either the compression coil spring 7 surrounding the support rod 4 between the fixed plate 6 secured to the base portion 4' of the support rod 4 and the outer surface of the casing 1 as shown in Fig. 3 or the tension coil spring 10 mounted between the fixed plate 8 secured to the base portion 4' of the support rod 4 and the fixed support 9 secured to the outer surface of the casing 1 as shown in Fig. 4. Although the coil spring devices 5 shown in Figs. 3 and 4 differ from each other in the direction in which the biasing forces of the coil springs act, they can achieve the same effect in operation.Both the compression coil spring 7 and tension coil spring 10 can have their resilience adjusted in such a manner that they can cope with the expansion of the ceramic-fiber lining slabs 2 due to their heating and the contraction thereof due to their cooling and with the expansion of casing 1 due to its heating.

When the ceramic-fiber lining slabs 2 are each square in shape and have a length of 1 m and a thickness of 20 to 30 mm, the lining slabs 2 can be used with excellent results in a kiln of high capacity for producing insulators of large size and special porcelain products by forming the holes 3 as follows: the holes 3 have a diameter of 10 to 25 mm, with one hole 3 being formed in the center of the square lining slab 2 and two holes 3 being formed at each of four sides in such a manner that they are also located at one side of each of the adjacent lining slab 2.

EXAMPLE A kiln provided with improved ceramic-fiber lining slabs according to the invention was compared with a kiln provided with ceramic-fiber lining slabs of the prior art. The specifications of the kilns, the conditions under which the kilns were operated and the results achieved ere shown in the following table:

Present Invention Prior Art 1 Specifications (Fig. la) (Fig. 6) Effective Dimen sions 1.45m (length) Ditto. 0.85m (width) 1.45m (height) Effective Volume 1.8m3 of Kiln 1.8m3 Ditto. Fumace Wall 7 Layers of Ceramic Structure Fiber Lining Slabs Ditto. Weight of Furnace Wall 33 kglm2 Ditto. Material of Ceramics Heat resisting Support Rods metal Firing Conditions Present Invention Prior Art Temperature 13000C Ditto Atmosphere. Reducing Flames Ditto Present Invention Prior Art Operation Time 50 (up to now) 15

Results Present Invention Prior Art Bending of None Metal support Support Rods rods bent. Deterioration None Backing material of Fiber deteriorated due to penetrating flames from the gaps. Casing None Penetrating flames Trouble from the gaps caused bending and oxidizing. Maintenance Support rod and Support rod re fiber replacements placements not readily effected, readily effected due to welding. Unscrewing of ceramic caps from support rod not readily effected. Service Life Over 250 operations 10 to 15 expected. operations

From the foregoing description, it will be appreciated that the present invention obviates the disadvantages of a kiln of the prior art provided with ceramic-fiber lining slabs. The kiln provided with ceramic-fiber lining slabs according to the invention has a high practical value because it has a long service life and attaching of the lining slabs in a large number to the walls of the casing and replacing thereof can be readily effected by virtue of the structural features of the invention.

Claims

1. A kiln provided with ceramic-fiber lining slabs comprising: a casing; a plurality of layers of the ceramic-fiber lining slabs attached to the inner surfaces of said casing; a plurality of holes formed in said plurality of layers of the ceramic-fiber lining slabs to extend in the direction of the thicknesses of the lining slabs; a plurality of support rods each inserted in one of said plurality of holes and secured at the base portion thereof to one of the outer surfaces of said casing; and means mounted at the base portion of each of said support rods for urging the ceramic-fiber lining slabs to move toward the inner surfaces of said casing through said support rod.

2. A kiln as claimed in claim 1 , wherein said means is a spring device.

3. A kiln as claimed in claim 2, wherein said spring device is a coil spring device.

4. A kiln as claimed in claim 3, wherein said coil spring device comprises a fixed plate secured to a base portion of each said support rods, and a compression coil spring mounted between said fixed plate and the outer surface of said casing and surrounding said support rod.

5. A kiln as claimed in claim 3, wherein said coil spring device comprises a fixed plate secured to a base portion of each of said support rod, a fixed support secured to the outer surface of said casing, and a tension coil spring mounted between said fixed plate and said fixed support.

6. A kiln as claimed in any one of claims 1 to 5, wherein each of said holes has in one portion thereof a tube penetrating the layers of the ceramic-fiber lining slabs located nearer to the inner surface of said casing and secured at its base to the casing.

7. A kiln as claimed in claim 1, substantially as described herein with reference to and as illustrated by any one of Figures 1 to 4 of the accompanying drawings.

8. An industrial plant comprising a kiln as claimed in any one of claims 1 to 7.