CA1170283A

CA1170283A - Basic refractory cementitious materials and components thereof

Info

Publication number: CA1170283A
Application number: CA000401977A
Authority: CA
Inventors: Michael A. Roberts; Martin Copperthwaite
Original assignee: USS Engineers and Consultants Inc
Current assignee: USS Engineers and Consultants Inc
Priority date: 1981-04-29
Filing date: 1982-04-29
Publication date: 1984-07-03
Also published as: ES511772A0; NO159376C; NZ200451A; IN158132B; TR21823A; PL236200A1; FI821459L; GR75429B; LU84121A1; NL8201790A; SE8202675L; SE457794B; DE3215993A1; JPS57191256A; PT74748B; FI821459A0; AU8307182A; ZA822957B; IT1156464B; FI71718B

Abstract

ABSTRACT
BASIC REFRACTORY CEMENTITIOUS MATERIAL
AND COMPONENTS THEREOF
A cementitious formulation which is self-setting when mixed with water, and which can be cast into monolithic refractory components capable of resisting molten metal and repeated thermal shocks, has three main components: high purity magnesia (at least 94% by weight being MgO); high purity alumina (at least 98% by weight Al2O3) and high alumina cement (preferably 75% Al2O3 by weight, or greater). The magnesia may be 60 to 95% by weight of the three components and the alumina amounts to at least 1% by weight of the three components. Castings produced from the formulation can survive repeated flame testing even after exposure to firing at elevated temperatures.

Description

1 1~702~ -BASIC REFRACTORY CEMENTITIOUS ~ATERIAL

AND COMPONENTS THEREOF
-The present invention relates to basic refractory cementitious material and components thereof.
S ~he invention moreo~er rela~es to a method of makinq such cementitious components as are exposed to chemical attack, wear and erosion by molten metals such as steel ~.
Refractory components of valves, and refractory nozzles:fox various purposes in the metal pouring art, , :
~ ~ have conventionally been produced by pressing and firing .
; at high temperatures.~ Costly,~high purity mater:ials such as zirconia and 85 to 95% A12O3-base~:refractories have been considered nece~sary in view~:the extremely harsh lS ~e~vic~ conditions to which the~componenta are subjected.
Energy expended in~pxoduci~g c~mp~nents by pr~ssing and firing:ls ~ubstantial, sinoe ~iring;temperatures normally exceeding:l500~C must be~ created and main~ained:thrsughout .
~ the firing process. ~The~energy~expendit:ure c~ontributes ,, ~
.
..

~ . .

1 1 7û283 8ignifi~antly to the unit costs of c~mponents made from such fired refractory materials.
Despite the use of strong fired refractories in the metal p~uring art, items such as valve plates S commonly need frequent rep~acement at great cost.
Recently, chemically-bon~ed concretes have been proposed, for instance for sliding gate valve plates.
Like fired refractory plates, chemically bonded concrete plates are unlikely to withstand repeated thermal shocks.
Thus, their use in valves for ingot teeming is expec~ed to be beset by inconvenient stoppages for theix replace- -ments.
It has now been found that certain hydraulically-bonded basic cementitious ma~erials surprisingly possess the ability to withstand thermal shock extremely well, and the productîon of components from these materials is particularly straightforward.
Ac~ording to the present invention, ~here is provided an hydraulic refractory cementitious formulation for making cast refractory parts resistant to~molten metals, the formulation comprising an admixture of three component~ namely fused or sintered magnesia, alumina and high alumina hydraulic cement contalning at least 45%
A12O3, the~magnesia being present~in an amount of at least 60% by weight of the total weight of the three

2 -' . ~ , , ' ~ ~02~

components and the alumina component being present in an amount at least 1~ by weight of the total weight of the three components.
The invention also provides cast refractory parts made from the formulation and a method of making such cast refractory parts.
Formulations according to the invention essentially comprise three components~ namely magnesia, alumina and al~munous hydraulic cement~ Optionally, minor amounts of other components can be added for specific purposes, such as plasticizing compounds, wetting agents and carbon-containing materials such as tar or pitch. The latter are commonly used in valve plates and no2zles to prevent slags adheri~g to such members.
1~ The first two componen~s are preferably of high purity for best results. Thus, the magnesia component should have an MgO content o~ at least 94% by weight, and the alumina component should have an A1203 content of at least 98~ by weight. The alumina can ~e sintered, fused or preferably ~alcined~
The cement component could in principle be any high-alumina cement (A1203 con nt greater than 4S% by weight of the cemen ). Preferably, however, the alumin-ous cement component has an A1203~content of not less than 75~ ~y weight of the cement componentO

!

, I ' _ " ' ' ,j ' , 02~3 The magnesia components may be present in an amount of 60 to 95~ by weight of the total weight of the three components. On the ~ame percentage basis, the alumina component is present in an amount of at least 1~, such as 1 to 36%, and the cement component is in the range 4 to 15%.
Preferred ranges axe magnesia 70 to 86~, alumina 5 to 15~ and cement 9 t~ 12~.
The formula~ion should be prepared from graded particulate materials. The cement component should preferably ha~e a particle size of 75 microns or less. It is tolerable for some ~ment particles to be larger, but preferably at least 90% of the cement has : a particle size of 75 microns or less.
Formulations will desirably be selected from the data given in the following tabulation:

.

..

, , , ~.
: .
' _ - ~ P-~RC~TAGE ~ ~'GE
.. .. ,_ . . . __ _ ~ Overal1 Preferred erall Preferred I~agnesia (S{ntered ~ l~m -3m~ ~ lmm 20-40 20-30 or ~used) 5 I~gnesia (Sintered -lmm + 0.3 ~ 0.3 15-35 20-30 or Fused) mm mm I~gnesia (Sintered ~0.3mm C0.3mm 25-4~ 30-4 or Fused) Alu~na (sintered ~0.3mm ~003mm 0O20 O- 5 10 fused or calcined5 Alumina (calc~ed, <45 microns c45 microns 1~2~ ~-10 fused or sintered but preferaDly c~lcined) 15 Hydraulic cement I~n 9~ Min 9~a 4-15 9-~2 ~rith A120 csntent ~75 microns ~75 micron greater t~an 757~
_ _ The formulations are mixed with water in an amount adequate to yield a workable mix. Such a mix may, for instance, contain 7~ water ~y weight of the mix. The mix is self-setting at room temperature. Application of heat is unnecessary, althou~h moderate heating to accelerate curin~ of cast shapes may be permissible.
Without heating, however, curing to a ~tate allowing de-moulding ~an ~e achieved within one hour or so. Thus high produ tivity can be achieved~
The present hydraulically-~ondinq formulations possess significant advantages ~er chemically-bonded , 0~,~33 6ystems. A problem evPr present with chemically-bonded systems is that when they are in the process of heat setting and drying, the binder tends to migrate to exposed surfaces. Bond migration and resulting non-uniformity of the integrity of castings do not arise withthe formulations of the invention. Moreover, a rigid ~et occurs so that handling of castings is free from the risk of intro~ucing internal stress flaws. It is not impossible with chemically-bound castings to adversely affect them during handling.
The present formulations have surprisingly excellent resistnace to thermal shock. They are there-fore expected to find use in parts of ~lidin~ gate valves and associated pouring nozzles used in the inter-mittent teeming of molten metals.
A commonly used test for thermal shockresistance is the torch test developed by Vnited States Steel Corporationls Research Laboratories. In ~his test, an oxy-propane torch flame i~ slowly traversed over a refractory being tested at 1.7 mm per second, the torch being held 6.4 mm from the refractory surface.
Conventional pressed and f ired magnesia valve plates cannot ordinaxily withstand just one pass of the oxy-propane flame without significant surface and internal damage~ Known chemically-bonded ma~nesia ~alve .. :

.
~' , ' .
.
, ,:" .

:. . . .

~ ~ ~V2~3~

plates are better able to resist the flame, but tests have revealed moderate degradation following one pass.
By contrast, valve plates made from the present formulations have been found capable of withstanding repeated passes, for example twelve, without significant surface degradation. This implies their ability to cope with the temperature variations encountered during repeated valve throttling, and open/shut valve operations will show a marked improvement over fired or chemically bonded plates.
As indicated above, the present formuIatisns can be used for casting valve plates for sliding gate ~alves as well as nozzles such as co}lectors and extended pouring tubes associated therewith. Ladle wells and dis-pensing nozzIes can also be produced rom the formulationsand other applications w111 be apparent.
Articles cast from the present formulations will ordinarily be supplied in khe hydraulically set state. Nevertheless, it may sometimes be desired to supply the cast~axticles in a pre~fired condition, rather ; than allow them to fire in servlce. Pre-firing may be applicable for example to articles such as replaceable wear and erosion resistant sleeves cr liners for discharge nozzles.
7 ~

, EXAMPLE
This formulation had the $ollowing proportions.
The percentages given are again by weight of the total weight of the magnesia, alumina and cement components.

5 Magnesia, size range -3 to +1 mm 26%
Magnesia, size range -1 to +0.3 mm 25%
Magnesia, size less than or egual to 0.3 mm 34%
Calcined alumina, size less than or egual to 7~ microns 6~
10 ~igh alumina cement 9%

The cement had an A12O3 content greater than 75% by weight of the cement, and at least 90% by weight of the cement had a particle size less than 75 microns.
The magnesia and alumina re9pecti~ely had MgO and A12O3 contents of 94 and 98% by weight of these components.
- -The formulation yielded a workable an~ -adequately fluent concrete ~or casting when mixed with water am~unting to 7% of its weight. Mould filling oan be assisted by vibration, an exemplary vibration freguency 20~ ~eing 3000 8z.
Vlbration-cast~ concrete samples prepared as above,~a~tsr ~uring and drying~ posses~sed the following pxoperties at the Btated temperatures.

-.

: . - ., - , . , : -, .

. . ~, 1 ~ 7 ~ 3 PROPERTY FIRING TEMPERATURE ~C .
. _ I__110 _ , 1000 1500 _ 1700 Bulk Density g/cc ¦2.83 2.78 2.85 Apparent Porosity % 16.0 19.3 17.0 5 Permanent ~inear change Dry to Fired % +0.01 -1.24 -3.44 Cold Crushing Strength p.s.i. 7000 7350 12350 MNM_2_2 48.3 50.8 85.2 Kp.cm 492 517 868 10 Flame Test 1 Cycle Pass Pass Flame Test 12 Cycles Pass l The foregoing properties are considered entirely suitable for making case sliding gate valve components which, if desired, can be supplied in a subsequently fired condition.

:

_ g _ - .
,, ' ~

., , " ,, ,

Claims

The Embodiments of the Invention In Which An Exclusive Property or Privilege is Claimed Are As Follows:-l. An hydraulic refractory cementitious formulation for making cast refractory parts resistant to molten metals, the formulation comprising an admix-ture of three components namely fused or sintered magnesia, alumina and high alumina hydraulic cement containing at least 45% Al2O3, the magnesia being pre-sent in an amount of at least 60% by weight of the total weight of the three components and the alumina component being present in an amount at least 1% by weight of the total weight of the three components.
2. A formulation as claimed in claim 1, in which the magnesia component is present in an amount of 60 to 95% and the cement component is present in an amount of 4 to 15%.
3. A formulation according to claim 2 wherein said cement component contains at least 75% Al2O3.
4. A formulation according to claim 2 wherein said alumina component is selected from the group consisting of sintered alumina, fused alumina, calcined alumina, and mixtures thereof.
5. A formulation according to claim 2 wherein said alumina component is present in the amount of 5 to 15%.
6. A formulation according to claim 2 wherein said alumina component is present in the amount of 5 to 10%, and said alumina component has a particle size of 45 microns or less.
7. A formulation according to claim 2 wherein said component is present in an amount of 9 to 12%.
8. A formulation according to claim 2 or 7 wherein said cement component has a particle size of 75 microns or less.
9. The formulation of claim 2 wherein 20 to 40% of the formulation is said magnesia component having particle sizes within the range -5 mm to +1 mm, 15 to 35% on the same basis is said magnesia component having particle sizes in the range -1 mm to +0.3 mm, and 25 to 40% on the same basis is said magnesia component having particle sizes of 0.3 mm or less.
10. The formulation of claim 2 wherein 0 to 20%
of the formulation is said alumina component having particle sizes of 0.3 mm or less and 1 to 20% on the same basis is said alumina component having particle sizes of 45 microns or less.
11. The formulation of claim 2 wherein 20 to 30% of the formulation is said magnesia component having particle sizes within the range -3 mm to +1 mm, 20 to 30% on the same basis is said magnesia component having particle sizes within the range -1 mm to +0.3 mm, 30 to 40% on the same basis is said magnesia component having particle sizes less than or equal to 0.3 mm, 5 to 10% on the same basis is said alumina component in the form of calcined alumina and having particle sizes not less than 45 microns, and 9 to 12% on the same basis is said cement component 90% of which has particle sizes not less than 75 microns.
12. A cast refractory shape produced from an hydraulic refractory cementitious formulation consisting essentially of:
60 to 95% of a magnesia component contain-ing at least 94% MgO, 1 to 36% of an alumina component contain-ing at least 98% Al2O3, 4 to 15% of an aluminous cement component containing at least 45% Al2O3, said formulation after wetting being capable of hydraulically setting at room temperature, said cast refractory shape having a cold crushing strength after subjection to temperatures of 110°, 1000° and 1500°C of about 492, 517 and 868 Kp/Cm2 respectively and a bulk density after subjection to these temperatures of about 2.83, 2.78 and 2.85 g/cc.
13. The cast refractory shape of claim 12 wherein said shape has a linear dimensional stability characterised by an increase of 0.01% after subjection to a temperature of 1000°C and by a decrease of 1.24 after subjection to a temperature of 1500°C.
14. The cast refractory shape of claim 12 wherein the cement component of said formulation con-tains at least 75% Al2O3.
15. The cast refractory shape of claim 12 wherein the alumina component of said formulation is selected from the group consisting of sintered alumina, fused alumina, calcined alumina, and mixtures thereof.
16. The cast refractory shape of claim 12 wherein the alumina component of said formulation is present in the amount of 5 to 15%.
17. The cast refractory shape of claim 12 wherein the alumina component of said formulation is present in the amount of 5 to 10%, and said alumina component has a particle size of 45 microns or less.
18. The cast refractory shape of claim 12 wherein the cement component of said formulation is present in an amount of 9 to 12%.
19. The cast refractory shape of claim 12 wherein the cement component of said formulation has a particle size of 75 microns or less.
20. The cast refractory shape of claim 12 wherein 20 to 40% of the formulation is said magnesia component having particle sizes within the range -5 mm to +1 mm, 15 to 35% on the same basis is said magnesia component having particle sizes in the range -1 mm to +0.3 mm, and 25 to 40% on the same basis is said magnesia component having particle sizes of 0.3 mm to less.
21, The cast refractory shape of claim 12 wherein 0 to 20% of the formulation is said alumina component having particle sizes of 0.3 mm or less and 1 to 20% on the same basis is said alumina component having particle sizes of 45 microns or less.
22, The cast refractory shape of claim 12 wherein 20 to 30% of the formulation is said magnesia component having particle sizes within the range -3 mm to +1 mm, 20 to 30% on the same basis is said magnesia component having particle sizes within the range -1 mm to +0.3 mm, 30 to 40% on the same basis is said magnesia component having particle sizes less than or equal to 0.3 mm, 5 to 10% on the same basis is said alumina component in the form of calcined alumina and having particle sizes not less than 45 microns, and 9 to 12% on the same basis is said cement component 90%
of which has particle sizes not less than 75 microns.
23. A method of making a refractory part, comprising:
preparing a hydraulic refractory cementi-tious formulation consisting essentially of 60 to 95% of a magnesia component contain-ing at least 94% MgO, 1 to 36% of an alumina component contain-ing at least 98% Al2O3, 4 to 15% of an aluminous cement component containing at least 45% Al2O3, said formulation after wetting being capable of hydraulically setting at room temperature, adding water to the formulation so as to obtain a hydraulic concrete, forming the part in a mold by vibration casting said hydraulic concrete therein, and curing the casting and allowing it to dry.
24. The method of claim 23 wherein the amount of water added in said step to obtain a hydraulic con-crete is about 7% by weight of the weight of said formulation, and wherein said curing steps takes place at room temperature.
25. The method of claim 23 wherein the cement component in said formulation contains at least 75%
Al2O3.
26. The method of claim 23 wherein the alumina component in said formulation in selected from the group consisting of sintered alumina, fused alumina, calcined alumina, and mixtures thereof.
27. The method of claim 23 wherein the alumina component in said formulation is present in the amount of 5 to 15%.
28. The method of claim 23 wherein the alumina component in said formulation is present in the amount of 5 to 10%, and said alumina component has a particle size of 45 microns or less.
29. The method of claim 23 wherein the cement component in said formulation is present in an amount of 9 to 12%.
30. The method of claim 23 wherein the cement component in said formulation has a particle size of 75 microns or less.
31. The method of claim 23 wherein 20 to 40% of the formulation is said magnesia component having particle sizes within the range -5 mm to +1 mm, 15 to 35% on the same basis is said magnesia component having particle sizes in the range -1 mm to +0.3 mm, and 25 to 40% on the same basis is said magnesia component having particle sizes of 0.3 mm or less.
32. The method of claim 23 wherein 0 to 20% of the formulation is said alumina component having particle sizes of 0.3 mm or less and 1 to 20% on the same basis is said alumina component having particle sizes of 45 microns or less.
33. The method of claim 23 wherein 20 to 30%
of the formulation is said magnesia component having particle sizes within the range -3 mm to +1 mm, 20 to 30% on the same basis is said magnesia component having particle sizes within the range -1 mm to 0.3 mm, 30 to 40% on the same basis is said magnesia component having particle sizes less than or equal to 0.3 mm, 5 to 10%
on the same basis is said alumina component in the form of calcined alumina and having particle sizes not less than 45 microns, and 9 to 12% on the same basis is said cement component 90% of which has particle sizes not less than 75 microns.