CA2032701A1 - Heat resistant alloy foil lining for kilns and method of lining kiln - Google Patents

Abstract

ABSTRACT

HEAT RESISTANT ALLOY FOIL LINING FOR KILNS
AND METHOD OF LINING KILN

There is disclosed herein a kiln for the heating and firing of ware, usually ceramic, which includes a preheat zone, a heat treatment or soaking zone operating above about 1400°F., and a post-heat zone. In the heat treatment zone the walls are fabri-cated of refractory wallboard or tile elements and includes an austenitic foil material applied to the hot face of the refractory in an interlocking or shiplap structure so as to wrap and surround the refractory board and prevent refractory spalling from entering the soaking zone and thereby contaminating the ware. It is important that in the entire process system including the preheat, soaking and post-heat zones, spalling and dust be minimized.

Description

~ 7 HEAT RESISTANT ALLOY FOIL LINING FOR KILNS
AND METHOD OF LINING KILN

DESCRIPTION
This invention relates to kilns for the heat treatment of objects, and more particularly, to a pro-tective construction for the walls of a kiln.
The heat treatment of objects such as the firing of chinaware is well known. In firing of china-ware, ware is loaded on a conveyer and moved through lo an elongated kiln in which there is a preheating area for raising the temperature of the china, a heat treat-ment area in which the appropriate heat treatment is conducted, and a cooling or post-heat treatment area.
Such kilns are often insulated with a fibrous refractory material (i.e., heat resistant ceramic material) which comes in the form of boards or large tile-like shapes. However, it has been found that these boards due to heat expansion and contraction across their cross-section and their frangible nature tend to spall and break off small particles which may land on the ware as dirt. In the situation of firing chinaware, the depositing of this dirt on a heated and soft glaze for the chinaware can produce imperfections in the end product which render the chinaware unsuit-able for sale.
It has therefore been an object to prevent material which is spalling or breaking off of refrac-tory material from being deposited on the chinaware or other objects within the kiln.
One technique which has been proposed for so protecting the objects has been to line the entire length of the furnace with plates or sheets of rela-tively thick stainless steel material. Thus the side walls would be lined, an artificial roof installed, and an artificial floor installed, all of stainless steel.
This has proved to be somewhat effective, but can be ~3^~ 70 costly and even the stainless steel exhibits a spalling and breaking due to its thickness and results in dirt contamination on the product.
One attempt to resolve this issue has been to line the kiln with a foil. Because of the thickness of the foil, it can preclude or capture any spalling or breaking by the refractory. In the heat treatment zone and in the cooling zone, the foil has been applied to the wall's heat face or surface in a flat overlapping fashion, which has been characterized as being applied in a "wallpaper" fashion. In the initial portions of the preheating zone, the foil has been applied in a wrapping fashion.
This system has worked satisfactorily in operation. It is an object of this invention to improve the function and use of that system.
These and other objects of this invention will become apparent from the following disclosure and appended claims.
There is provided by this invention a system for reducing the amount of dirt in a kiln. The system includes providing a foil of an austenitic-type, heat-resistant material in at least the high temperature or heat treatment zone of the kiln, which is above 1400F.
The material is applied to the walls of the heat treat-ment zone in a shiplap or interlocking fashion so as to wrap the particular refractory and prevent the refrac-tory material from entering the heat zone. Preferably this design is used throughout the kiln in the preheat, heat treatment, and post-heat areas.
The foil is designed to surround or wrap-around the refractory material and is provided in a shiplap or interlocking fashion. This is particularly suitable in the heat treatment area of the kiln where temperatures exceed 1400F. and spalling could be a 27~

significant problem.
FIGURE 1 is a diagrammatic view of a kiln;
FIGURE 2 is a cross-sectional view taken along line II-II of Fig. 1 showing the interior of a kiln in the heat treatment or soak area;
FIGURE 3 is a diagrammatic and perspective view of a kiln;
FIGURE 4 is a horizontal cross-sectional view of a wall of the kiln showing a method for wall attach-ment used in high temperature applications;
FIGURE 5 is an enlarged view taken from Fig.4 showing the interlocking foil connections;
FIGURE 6 is a view similar to Fig. 4 showing a method for wall attachment in lower temperature applications; and FIGURE 7 is a view similar to Fig. 4 showing a method for wall attachment in low temperature appli-cations.
ON THE DRAWINGS
Referring now to Fig. 1, there is shown a kiln 10 generally in stylized form. Product proceeds from left to right through the kiln on a conveyer. The fir t area or preheat zone is identified as 12, the intermediate soaking heat treatment zone is identified as 14, and the post-heat or cool-down zone is identi-fied as 16.
In the case of china, chinaware enters the kiln at the left edge and proceeds through the preheat zone 12 where its temperature is raised from about room temperature or ambient to about the heat treatment temperature in adjacent soak axea. In the heat treat-ment zone 14, the temperature is maintained above 1400F., for example, at 1450F. The ware proceeds through the heat treatment zone at a predetermined rate and then enters the post-heat or cool-down zone 16. In the cool-down zone, the ware is cooled from the heat treatment temperature down to about ambient or room temperature at which it can exit.
In the case of chinaware, the body has been already fired and glaze has been put on and the issue then is to place decorations on the glaze. In order to do that the glaze is softened during the preheat tem-perature and the decoration is fired into the glaze at the heat treatment temperature and then the body is cooled down. Since the glaze is soft so as to accept the decoration, it is essential that the operation be clean.
Referring now to Figs. 2 and 3, it is desir-able to have as little air circulation as possible so as to avoid dirt circulation within the kiln. One way to do that is to assure an even temperature between the floor and ceiling and to assure only exposure of the ware to a lined surface.
In Fig. 2 the kiln top or roof surface 18, bottom or floor surface 20, and side walls 22 and 24 are shown. Radiant tube heaters into which heated or flamed gas is introduced and which exits through the side walls are shown adjacent the top and bottom as 26 and 28. The floor of the kiln is formed by the inside surface of the bott:om 28. In the treatment or soak zone the floor may be refractory material or may be of stainless steel plate such as 30. A stainless steel roof 32 is hung from the refractory ceiling so as to be positioned above the ware but below the heating element 26. Such positioning protects the heated areas from spalling.
The side walls, such as 22 and 24, are fabricated from a steel shell outer wall 34, a series of fibrous ceramic (alumina-silica) tiles or boards, such as 36, 38 and 40, which are about 12"-18" x 18" x 7 ~

1" thick and a heat-resistant foil 42.
As can be seen from Fig. 2, the ware 44 is carried on a movable belt table or conveyer 46 through the kiln at a predetermined temperature. The ware 44 is shielded from the refractory. For example, the ceiling material 32 is stainless steel plate, the floor 30 may be stainless steel plate and the walls 22 and 24 may be lined with foil. Thus in any line of sight from the ware, there is no exposure to refractory material as dust from spalling, expansion, etc., depositing on the heated ware.
A diagrammatic and perspective view of a portion of the kiln 10 is shown in Fig. 3. In the pretreatment zone the roof and walls may be foilO In the post-treatment zone the ceiling, walls and floor may be foil.
Specifically, referring now to Fig. 4, a refractory wall is made up the steel shell 34, boards such as 36, 3~ and 40 and the foil 42. In the heat treatment zone the foil material, such as 42, is applied vertically and in sheets to cover the heat face of the refractory.
On one side the foil is folded around and behind the board it covers. On the other side it is folded around the board it covers and tucked behind the adjacent board. This produces an interlocking struc-ture which is sometimes referred to as a shiplap style.
This interlocking structure is used in the heat treat-ment zone and is shown in Fig. 5.
Referring to Fig. 5, the foil sheets 42 and 42' are shown. The sheet 42 is shown as being folded around a board. Sheet 42' covers the surface and side of one board and is fitted behind an adjacent board.
This depicts the interlocking or shiplap style.
The foil is generally between about 0.002 and - 6 ~

0.005 inch thick and is made of a material which is commercially known as 330 or Inconel 600 and 601. In terms of composition, the alloys have the following nominal composition:
330 (35% Ni)(19% Cr)(1.25% Si) Bal. Fe 601 (61% Ni)(23% Cr)(.2% Si)(1.4% Al) Bal. Fe 600 (76% Ni)(15% Cr~(.2% Si)(.08% C)(8% Fe) This material is a nickel-based material in an austen-itic phase so as to provide a stable surface for heating which avoids phase transformation, and thus dimensional changes.
The kiln shell, refractory and foil are secured together by a pin system. A pin system 50 for use at high temperature is shown in Fig. 4, a pin system 60 for low temperatures is shown in Fig. 6, and a pin system 70 for very low temperature is shown in Fig. 7.
Referring first to Fig. 4, the pin system 50 includes a metal stud 52, which is welded to the steel shell. A ceramic stud 54 is provided and extends from the steel stud through the front of the refractory wall or foil 42. The ceramic stud is held to the steel stud by a coupling sleeve 56, which is fabricated from an alloy-based material and utilizes a retaining wire system 57. The ceramic stud 54 is elongated and has a number of recesses~ A support washer 58 is supported against the foil by the stud and a lock washer 59 holds the entire assembly together and the foil and ceramic boards against the steel shell. This system would be used in the heat treatment zone.
Another and lower temperature embodiment 60 is seen in Fig. 6 where a ceramic cone and disc anchor assembly is used. In that assembly, a stud 61 is anchored to the exterior shell. A disc 62 engages the 3~ refractory and foil and the cone 64 holds the disc thereagainst and engage the stud. A plug 66 can be fitted into the cone.
In very low temperature situations a system 70 as in Fig. 7 is used. There a stainless steel stud, such as 72, is secured to the steel shell and extends through the boards. A metallic washer 74 is arranged to engage the stud and hold the ceramic and foil to the shell.
Although the invention has been described with respect to preferred embodiments, it is not to be so limited as changes and modifications can be made which are within the full intended scope of the inven-tion as defined b,v the appended claims.

Claims (8)

1. An elongated kiln having preheat, heat treatment and post-heat zones wherein the operating temperature in the heat treatment zone exceeds 1400°F., said kiln having refractory walls, ceiling and floor for each of said zones, said walls fabricated of adjacent board-like refractory elements, and in the heat treatment zone a plurality of sheets of foil material of the austenitic type each engaging the heat face of the refractory, constructed to surround said board-like elements, form an interlocking style pattern, and cooperate in protecting the interior of the kiln from spalling.

2. An apparatus as in claim 1, wherein the foil is held to the board-like element by a pin construction which extends through the foil and the refractory.

3. An apparatus as in claim 1, wherein the interlocking joint has a shiplap-style structure in which a foil sheet overlies the face of the refractory, extends along its vertical side toward the ambient and is fitted behind the surrounded board and adjacent board.

4. An apparatus as in claim 1, wherein the foil is applied to the walls and ceilings of the preheat and post-heat zones.

5. An apparatus as in claim 1, wherein the foil is between about 0.002 and 0.005 inch thick.

6. An apparatus as in claim 1, wherein the foil is a nickel-based material.

7. An apparatus as in claim 1, wherein there is further provided a plurality of heating elements, one extending through a side wall into an area adjacent the ceiling and another heating element extending through the side wall and into an area adjacent the floor.

8. An apparatus as in claim 1, wherein in the heat treatment zone the floor portion includes a stainless steel liner.