Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
1998-09-30
2001-01-09
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S080000, C501S081000, C501S082000, C501S130000, C428S702000
Reexamination Certificate
active
06171990
ABSTRACT:
INCORPORATION BY REFERENCE
U.S. Pat. No. 5,407,875, issued on Apr. 18, 1995, and U.S. Utility application, Ser. No. 08/742,669, filed on Nov. 4, 1996 are herein incorporated by reference.
FIELD OF THE INVENTION
The invention relates to a large-format fireclay refractory brick, in particular bottom block for a tin bath, consisting of brick-forming material of the system Al
2
O
3
—SiO
2
having a top surface for contacting a tin bath and showing an open porosity of about 20 to 25 percent by volume and a closed porosity. Furthermore, the invention is directed to a method for manufacturing large-format fireclay refractory bricks.
BACKGROUND OF THE INVENTION
Large format fireclay refractory bricks typically have a rectangular cross section and a top surface for contacting a tin bath and a bottom surface for not facing a tin bath. The bottom surface not facing the tin bath is supported by a steel construction in the form of a tub. Such large-format fireclay refractory bricks are manufactured in a known manner, and are formed of brick-forming material of the Al
2
O
3
—SiO
2
system, i.e. chamotte, silika, clay,etc.
The brick-forming material typically includes a mixture of chamotte with a grain size of up to 5mm; an incombustible clay which is rich in silic acid and having a quartz component of greater than 50% with respect to the clay component with the quartz having a grain size of up to 50 &mgr;m; a fine particle incombustible clay with an alkali component of up to 3%; an alkali-aluminosilicate, and; a binding agent. Additionally, one part of the chamotte can be replaced by a natural aluminosilicate, and fine particle C-glass with a particle size of less than 60 &mgr;m can be used as an alkali-aluminosilicate. The brick-forming material is processed in a known manner, whereby the material is mixed and then poured into a mould. The material in the mould is shaped, such as by pressing, stamping, etc., and then allowed to dry in an atmosphere having a humidity of between 4-7%, after which the material is subsequently fired for at least 5 hours at a temperature of between 1200-1350° C. After firing, the brick is cooled and then is typically ground with a grinder in order to finish the brick to a desired size and shape.
Such large-format fireclay refractory bricks used in a tub to be coated to receive the tin bath and consisting of a material of the Al
2
O
3
—SiO
2
system are known. The here interesting part of the glass producing facility has a steel construction being coated with the large-format refractory bricks. Thereby a production tub is formed being filled with liquid tin. The melted glass is poured out on the surface of the tin bath. The glass expands on the surface of the tin bath and is drawn as a thin band with a substantial width over the surface of the tin bath. This is the known way of manufacturing flat glass according to the float technique. Manufacturing flat glass temperatures of about 600° C. to 1200° C. occur above the surface of the tin bath. Manufacturing special kinds of glass even higher temperatures may occur. Due to these higher temperatures the large-format fireclay refractory bricks at all of its different points are subject to higher temperatures. It is known to cool the tub of the steel construction containing the bricks and the tin bath from outside in order to freeze the liquid tin in the gaps between the adjacent side surfaces of the bricks and thereby prevent the passage of liquid tin to the outside.
During the manufacturing of flat glass Na
2
O diffuses into the liquid tin so that sodium and atomic oxygen is solved in the tin bath. An exchange of sodium happens between the tin and the material of the fireclay refractory brick. This finally may lead to chipping off of layers of the top surface of the blocks facing the tin bath. In addition, there is the danger of penetration of liquid tin in the gaps between the side surfaces of adjacent bricks or of a passage of liquid tin through the gaps to the outside respectively. This is prevented by cooling as mentioned above. The cooling must be increased if above the tin bath higher temperatures occur than about 1000° C. Cooling the tub there is the danger that the cooling effect is not uniform at all points of the tub. This is especially the case if the cooling should fail. In both circumstances the temperature of the tin bath varies which results in a minor quality of the produced glass.
The known fireclay refractory bricks have an open porosity, i.e. a percent by volume of the open pores extending to the outside surface of the brick, which generally is in the amount of 20 to 25 percent by volume. These known blocks have a closed porosity also, i.e. a percent by volume of closed pores in the interior of the block. The percentage of the open porosity and the closed porosity are similar with respect to the known bricks.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a large-format fireclay refractory brick adapted to coat a tin bath and having a sufficient resistance to alkali attack and thereby substantially maintaining the air permeability, the H
2
diffusion, the elasticity, and the mechanical properties on the one hand and giving the possibility however to use higher temperatures above the surface of the tin bath and to reduce the danger of the passage of liquid tin to the outside on the other hand.
According to the invention, this object is realized with a large-format fireclay refractory brick of the type described above, wherein the material of the brick comprises such an amount of a lightweight filling material and/or such an amount of an opening material is added during the manufacture of the block so that the closed porosity is increased by about 10 to 15 percent by volume, while the open porosity is basically maintained in an unchanged condition.
REFERENCES:
patent: 4575439 (1986-03-01), Hintzen et al.
patent: 4687752 (1987-08-01), Peters
patent: 4833109 (1989-05-01), Macey et al.
patent: 5252526 (1993-10-01), Whittemore
patent: 5407875 (1995-04-01), Petschauer
Group Karl
Thomas Kayden Horstemeyer & Risley
VGT Industriekeramik GmbH
LandOfFree
Large-format fireclay refractory brick, in particular bottom... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Large-format fireclay refractory brick, in particular bottom..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Large-format fireclay refractory brick, in particular bottom... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2502713