|Title of Invention||
A METHOD OF MAKING MONOLITHIC REFRACTORIES
|Abstract||This invention relates to a method of producing monolithic refractories using improved flowable refractory composition, by casting setting and drying. The composition cons~sts of conventional refractory aggregates and setting agents bound together by an aqueous colloidal suspension of an inorganic compounds selected from silica, zirconia, alumina and mullite having a particle size of up to 5 microns. This inorganic gel bonding shows distinct advantage over conventional compositions for refractories.|
|Full Text||This invention relates to a method of making monolithic refractories and refractories made thereby. Refractories according to this invention are made from flowable refractory composition based on inorganic gel bond technology. These refractories have distinct advantages in physical and chemical properties such as penetration resistance to molten iron and slags and thermal shock resistance over the conventional and hitherto known refractories. Refractories of this invention are ideal for use in blast furnace, cast house, troughs, tunnels, and steel transfer ladles, continuous casting tundishes reheat furnace hearths and subhearths, waste incinerators and in preheat and cooler zones of cement kilns and other areas suitable for application.
Monolithic refractories are usually defined by their mode of application. For instance, a ramming refractory is installed by ramming either by mallets or by pneumatic rammers. Gunning refractories are installed by application through a gunning equipment and a castable refractory is installed by casting refractory compositions. During the past two decades, low oement castables have been developed which can be installed not only by casting but also under the force of vibration for moving the material. Water content in these compositions have been significantly reduced. These compositions behave in a pseudo-thixotropic fashion and the movement of the material takes place only under force of vibration. Preparation and
installation of refractory lining for metallurgical operations
has always been time and labour intensive. Known refractory
linings are cast against solid steel forms which can withstand
vibration during casting steps. Transportation of these steel
forms also poses problems.
987/rlAs/97 Our copending application No. / describes and claims
a refractory composition which is flowable without the
application of external force. This composition requires shorter
installation time than composition hitherto known in the art.
This refractory composition is obtained by combining refractory
aggregates with a colloidal solution of selected inorganic
compounds in aqueous medium or an aqueous suspension of selected
inorganic compounds of colloidal dimension. The particle size of
the selected inorganic compounds in the aqueous medium is a vital
factor that governs the flowability of the refractory
composition. Another advantage is that the dry refractory
aggregate may be prepared first and shipped to the installation
site where required quantity of the inorganic sol is added and
mixed prior to casting or lining operations. Since this
composition need not be vibrated during casting operations, it is
found possible to cast them on light removable form instead of
heavy steel forms, thus reducing the cost considerably.
According to this invention conventional refractory aggregates having 95 to 99% of refractory base material are mixed
with an aqueous solution containing 8 to 24% submicron sized inorganic binder material selected from silica, alumina, zirconia and mullite. The composition may include 1 to 10% of microsilica, 0 to 40% of silicon carbide, 5 to 15% calcined alumina, 0 to 5% of metallic powders such as aluminum, and/or silicon, antigassing agent such as pyridine, and 0.5 to 3% by weight of a setting agent based on the aqueous binder content. Refractory base materials may be calcined clay, mullite, calcined bauxite, sillimanite, kyanite, andalucite, brown fused alumina, or tabular alumina or other alumina materials. Setting agents such as calcium hydroxide, magnesium oxide or hydroxide, or calcium aluminate cement may also be added. Submicron size of the inorganic compounds selected from silica, alumina, zirconia or mullite which forms an aqueous colloidal binder may be of 10 microns or less than 5 microns.
By using the refractory composition of this invention, refractory linings may be installed even in remote areas where placement by conventional methods such as ramming and vibra casting would have been difficult.
The pump used for installation of this refractory can be a cement concrete pump with twin cylinders - one for drawing the material in and the other to push the material out into the pipe. The pump can be driven either by diesel or electric motors with suitable capacity. For transporting the high density large
grain and abrasive particles used for the blast furncace trough refractory, the exit cylinder should preferably have a minimum of 75 mm diameter connected to 75 mm pipes for installation. Larger diameter cylinders can also be used such as 100 or 125mm but the exit pipes need to be reduced to 100 or 75 mm otherwise the movement of the pipes becomes difficult for handling due to increased weight. The use of a 75 mm diameter cylinder with 75 mm exit pipe diameter provides a smooth operation and puts minimum strain on the motor. Any reduction in the diameter of the pipe line from the exit cylinder puts significant pressure on the pump.
The special monolithic refractory can also be installed by transporting by a mobile conveyor system whereby the wet mix from the mixer can be dumped onto the conveyor belt that can be shortened or elongated as needed for the specific distance of installation. The delivery of the wet mix from the mixer can be controlled by the pneumatic door on the mixer so that the material can have a steady flow to be delivered at the point of installation. The conveyer should be provided with wheels and also adjustable lengths. The method of installation by the conveyer belt is simpler and needs significantly less investment for the equipment.
A typical composition used for blast furnace cast house trough was prepared by mixing the following components in
weight percentages as follows :
Tabular alumina, particle size 6 mm to 200 microns 80
Reactive alumina, particle size 5 to 3 microns 10
Silicon Carbide, particle size 200 to 50 microns 35
Micro silica, particle size 0.5 to 0.1 microns 5
Metallic powder, particle size 200 to 75 microns 5
Graphite, particle size 200 to 100 microns 2.5
Setting agent 100 microns 0.5
Gas inhibitor 1.0
Aqueous colloidal suspension of micro silica 15
The above composition by mixing in place and installed by casting through a hopper without vibration, or by dumping into a pump and transporting into the site through steel and flexible pipes or by transporting the wet mix by dumping on to a flexible/movable conveyer belt as a trough lining in the blast furnace cast house. This composition will have excellent resistance to corrosion/erosion by the molten iron/slag and will provide good performance.
The use of the unique suspended binder system has distinct advantage over other conventionally used binders such as clay, phosphates and calcium aluminate cement systems. Since there is no chemically bonded water in this binder system, it is
much quicker for installation and also eliminates labor and avoids human error by avoiding the need of vibration. It is also easier to dry the installed lining since the moisture present is free and not chemically combined as in clay or calcium aluminate binder systems. The refractories with this binder system are better refractories with increased, thermal stability and thermal shock resistance. All these things contribute to longer life because of its overall superior properties resulting in lower cost in time and labor.
A typical composition for the iron runner in the blast furnace cast house will be as follows :
Calcined bauxite, particle size 5 mm to 200 microns 80
Calcined alumina, particle size 5 to 3 microns 5
Silicon Carbide, particle size 200 to 50 microns 30
Micro silica, particle size 0.5 to 0.1 microns 2.5
Graphite, particle size 200 to 75 microns 2.5
Setting agent 200 to 100 microns 0.5
Gas inhibitor 1-0
Aqueous colloidal suspension of sub micron silica 18
The above composition by mixing in place and installed either by casting through a hopper or by transporting by pumping
or by transferring the wet mix by a flexible and mobile conveyer belt as a lining for the iron runner will have rapid drying/heating characteristics, excellent resistance to erosion by molten iron and slag with good performance.
A typical example for application in the steel ladle barrel, reheat furnace hearth and sub hearths or tundish back-up lining will be as follows :
Calcined bauxite, avg. particle size 5 mm to 200 microns 85
Tabular alumina, particle size 75 to 50 microns 10
Silica fume, particle size 0.2 microns 5
Setting agent 200 to 100 microns 0.5
Aqueous colloidal suspension of micro silica 12
The above composition by mixing in place and installed either by casting through a hopper or by transporting by pumping or by transferring the wet mix by a flexible and mobile conveyer belt as a lining for applications like reheat furnace hearth, tundish back-up lining, steel ladle barrel and waste incinerator linings, will have excellent resistance to erosion and thermal shock with good performance.
RAW MATERIAL CHARACTERISTICS :
Calcined clay - the calcined clay may have a bulk density of 2.4-2.85 and the alumina content may vary from 40-75%. The grain size may vary from 6 mm to 200 microns.
Andalucite - the alumina may vary from 54-58%, the grain size may vary from 7 mm to 1 mm.
Sillimanite - the grain size of sillimanite may vary from 6 mm to 100 microns.
Calcined bauxite - this may be derived from either gibbsite, diaspore or boehmite base and the grain size may vary from 7 mm to 50 microns. The bulk density may be in the range of 3.10-3.50 and the alumina content may vary from 75-92% where the impurities should be Si02 (max. 2%), Ti02 (max. 4.5%) and Fe203 (max. 2.0%).
Brown fused alumina - The bulk density may be in the range of 3.80 - 3.95 and the alumina content may vary from 84-97%. The size range may vary from 7 mm to 100 microns.
Tabular alumina - The size range may vary from 7mm to 50 microns and the Na20 content should be in the range of 0.1-0.5% while the alumina content may be in the range of 97-99.5%.
Monolithic refractories according to this invention may be installed without any vibration against light removable forms. These forms are inexpensive and cost only a fraction of solid
steel forms conventionally used. As these forms are light, handling and transportation became easy. At the installation site, the refractory composition is allowed to set on the desired form or substrates for a period of 3 to 8 hours at ambient temperatures depending up on the thickness of the cast required. After setting the cast refractory is heated to 100 to 150°C for a period of 4 to 8 hours depending on the thickness of the refractory cast. Overall drying and heating time varies considerably depending on the thickness of the lining, and the conditions of the place of installation. The most critical time of heating is the period of driving free moisture out of the cast refractory. Since the flowable refractory composition used in casting do not have chemically combined water i.e. hydrated phase, conventional problems like cracking, spelling and the like are eliminated during this drying process. The refractory composition may also be cast under conventional vibration technique without affecting the properties of the cast refractory linings.
The method of making monolithic refractories according to this invention comprises the steps of casting a flowable refractory composition consisting of conventional refractory aggregates and setting agents bonded together by an aqueous colloidal suspension of an inorganic compound selected from silica, alumina, zirconia or mullite, the solid particles in the
said colloidal suspension having a particle size of up to 5 microns, setting and subsequently drying the cast refractory.
Casting step may be carried out with or without vibration and drying and sintering may be at a temperature ranging from 100 to 150°C for a period determined by the thickness of the cast refractory.
It will be obvious to persons skilled in the art that numerous modification and variations are possible without departing from the basic concept of this invention and all such modifications are to be considered within the scope of this invention and the appended claims.
1. A method for making monolithic refractories comprising the steps of casting a flowable refractory composition consisting of conventional refractory aggregates and setting agents bonded together by an aqueous colloidal suspension of an inorganic compound selected from silica, alumina, zirconia or mullite, the solid particles in the said colloidal suspension having a particle size of up to 10 microns, setting and subsequently drying the cast refractory.
2. The method as claimed in claim 1, wherein the refractory composition is cast against light weight removable frames.
3. The method as claimed in claim 1, wherein the refractory composition is cast against solid steel frames.
4. The method as claimed in claims 1 to 3, wherein the refractory composition is pumped through a conveyer to the casting site and cast with dynamic vibration.
5. The method as claimed in claims 1 to 4 wherein the cast refractory is allowed to set at ambient temperatures and is then dried at a temperature ranging from 100-150°C.
o. The method as claimed in claim 1, wherein the cast is allowed to set for 3 to 8 hours at room temperature and then heated to 100-150°C for a period of 4-8 hours.
7. The method as claimed in claims 1 to 6 wherein the refractory aggregates of the said composition has refractory base materials such as calcined clay, and alucite, sillimanite, calcined bauxite, brown fused alumina, tabular alumina or similar alumina material either alone or in combination with one another.
8. The method as claimed in claims 1 to 7 wherein the said refractory aggregate has 95 to 99% by weight of the said refractory base materials, 8 to 24% by weight of the said aqueous colloidal suspension, and 1 to 3% by weight of a known setting agent based on the colloidal binder.
9. The method as claimed in claim 8, wherein the setting agent is calcium hydroxide, magnesium oxide or hydroxide or calcium aluminate cement.
10. The method as claimed in claims 1 to 9 wherein the said refractory composition optionally contains upto 5% by weight of metallic powders such as silicon or aluminum.
11. The method as claimed in claims 1 to 10 wherein the said
refractory composition optionally contains upto 40% by weight of silicon
carbide, 1 to 10% by weight of micro silica and 1 to 5% by weight of any
known gas inhibiting agent.
12. The method as claimed in any one of the preceding claims
wherein the said refractory base material is calcined clay having a bulk
density of 2.4 - 2.85, an alumina contact ranging from 40 to 75% and grain
size ranging from 6mm to 100 microns.
14. The method as claimed in any one of the preceding claims
wherein the refractory base materials and alucite sillimanite, calcined
bauxite, brown fused alumina and tabular alumina or similar alumina
materials have a grain size ranging from 8mm to 100 microns.
15. A method for making monolithic refractories substantially as
herein described and exemplified.
|Indian Patent Application Number||1793/MAS/1997|
|PG Journal Number||27/2007|
|Date of Filing||12-Aug-1997|
|Name of Patentee||M/S. ANSWER TECHNOLOGY INCORPORATED|
|Applicant Address||P-104 TOLLA ROAD, KOLKATA 7000 008.|
|PCT International Classification Number||C 04 B 035/04|
|PCT International Application Number||N/A|
|PCT International Filing date|