DE1250331B - Process for the manufacture of refractory cast iron materials - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C04b

15-65?

German class: 80 b-8/17

Number: 1250331

File number: C 27970 VI b / 80 b

Registration date: September 19, 19.62

Opened on September 14, 1967

The present invention relates to the manufacture of fused cast alumina refractory materials with a crystalline structure consisting essentially of two phases, into which minor amounts of Alkaline earth metal oxide are included. As is well known, refractory fused-cast material is produced by that one melts a mass of refractory material of the desired composition and that poured molten refractory material and allowed to cool to a solidified refractory mass. ίο

The addition of alkaline earth metal oxides to an alumina melt in amounts of about 0.36 to 16.5 The mole percent, based on the oxide analysis, was found to be very useful in the refractory casting To prevent or greatly reduce the formation of a directed structure, which occurs in the case of only one phase from im essentially pure cast alumina occurs. This directional structure has a pattern of elongated corundum crystals oriented substantially perpendicular to each face of the refractory casting and in which have many elongated cavities between the mutually aligned crystals. This kind cast refractory materials does not have good thermal shock resistance and is easily cracked with certain Operating conditions. The alkaline earth metal oxide content causes during solidification and cooling a considerable formation of very small interlocking crystals of a second crystalline Phase and corundum instead of the directional structure of the refractory material with only one phase. These Refractory cast materials consisting essentially of two phases are characterized by a considerable Resistance to thermal shock.

In the manufacture of these two-phase melt cast refractories, difficulties are sometimes encountered in order to obtain a salable cast product. It has been found that these refractories tend to crack in the mold during solidification and cooling. This tendency is particularly evident in blocks of 43.5 kg and heavier, especially in the more common blocks of 130.5 to 522 kg. The cracks appear essentially as a network throughout the cast and in many cases radiate from the center of the cast to the edges and / or corners. These cracks in the cast are undesirable because they severely weaken the structural uniformity of the cast product. When the casting is exposed to mechanical and / or thermal loads, for example during shipping or in use, or even during the sawing of a block in the manufacturing process
refractory cast iron materials

Applicant:

Corhart Refractories Company,

Louisville, Ky. (V. St. A.)

Representative:

Dr. W. Beil, A. Hoeppener and Dr. H. J. Wolff,

Lawyers,

Frankfurt / M.-Höchst, Adelonstr. 58

Named as inventor:
Allen Myron Alper, Corning, NY;
Robert Nicholas McNaIIy, Horseheads, NY
(V. St. A.)

Claimed priority:

V. St. v. America September 26, 1961

(140775),

dated March 30, 1962 (183 770)

desired shapes, the cracks spread until they open and a piece pops off.

Attempts to prevent cracking in the two-phase cast refractories Avoiding the use of the usual regulated slow cooling has not been successful so far.

The object of the present invention is therefore a method for producing a thermal shock resistant Refractory fused-cast alkaline earth metal oxy-alumina material with a crystal structure of fine, interlocking Crystals of corundum and spinel and / or alkaline earth metal hexaluminate, which during the solidification and cooling shows practically no crack formation.

The process of the present invention is carried out by adding fluorine to a molten refractory Adds mass, which consists essentially of alkaline earth metal oxide and alumina, the Quantities of fluorine, alkaline earth metal oxide and alumina are measured in such a way that they form a molten,

709 647/507

3 4

Provide refractory mixture that essentially clog up in the furnace just prior to casting or

° / ° / introduce from 0.06 to 2.63 mol ₀ fluorine, 0.36 to 16.5 mol ₀ ground prior to pouring into the mold,

alkali metal oxide and, for the rest, essentially. Metal fluorides are generally used with

pure alumina and then the molten boiling point of at least about 1200 ⁰ C, since

zcnc refractory material to a solidified refractory 5 fluoride with too low a boiling point during

The mass cools down. the melting process excessively from the charge

The manufactured according to the present invention evaporate before they fuse with the other stock large and small castings which are visibly devoid of parts. Net-like cracks due to the low partial pressure. They also have the erwünsch- of fluorine in the feed due to the niedritcn properties of other refractory materials io Geren concentration of fluorine in melting down in _keincn> __Fluorzusiitz included, ie good heat melted refractory mass and the fact schock'beständigkeit and a crystal structure consisting of a balance between the partial pressure of the fine interlocking crystals of corundum fluorine in the mixture and above the bath in the and spinel and / or alkaline earth metal hexaluminate. The relatively short melting time before casting only does not occur in the microstructure of the 15 according to the invention, a considerable amount of fluorine refractory Schmclzgußstoffe occurring under- (e.g. over 70%) at the time of casting in the bath, the presence is very fine, accidentally retained .

scattered islands of a third crystal phase, which are usually used. Some examples of suitable ones follow

borrowed metal fluorides and their corresponding boiling points within the spinel and hexaluminate crystals:

appear. This third phase seems to be a fluoride 20

but their actual ZüläliTmeTis ^ rzuiigTTiciTr ^ Fluoride AlF ₃ MgF ₂ CaF ₂ BaF ₂ SrF ₂ NaF

secure. It should also be noted that the boiling point .. 1260 2239 2500 2137 2460 1705 The modulus of rupture in the melt-cast product according to the invention is significantly higher than in the corresponding. In addition, mixtures or metal materials can also be used without fluorine and in many cases even 25 fluoride complexes with sufficiently high boiling points increases to almost twice the strength. be used, e.g. B. cryolite.

A fused cast material is already known in the manufacture of the refractory fused cast material, in which the molten calcium fluoride tensile material of the present invention is used. There is, however, not a mixture of ingredients in granular form, crushing the addition of calcium oxide in molar excess to fluorine, if it does not have to be done in this form when the technical advantages of the trade are available. Thereafter, the mixture invention will be achieved. With the same molar percent of materials according to the desired composition of fluorine and calcium, no hexaluminate phase is formed for the refractory material to be cast, and the material consists solely of one and preferably before introduction into the enamel AljjOa phase, which the above in 35 oven premixed according to the description. Any of the known disadvantages of cracking during the melting furnace can be used, for example gas burning, cooling and solidification. The rupture modulus of the n unpsofen ( in which the heat from the combustion of new mass is significantly higher with very good a gaseous carbonaceous fuel and thermal shock resistance. Air is used) or an electric arc

To carry out the present invention 40 oven. The latter type is preferred. Thereafter, it is preferable to use relatively pure, melted, raw alumina, poured into suitable pre-alumina, alkaline earth oxides and fluorine, around damaged molds, and according to known effects on the properties of the invention, e.g. according to the US Pat. No. 1,615,750 cooled by appropriate refractory cast material to avoid GS Fu Icher described. In general. Certain impurities, such as alkali 45 common is the casting temperature of the geschmolmctalloxyde (eg., Na ₂ O, SiO _3, Fe ₂ O ₃ and TiO ₃₎ should Zenen refractory material is about 2030 to 2050 ⁰ C. because of its negative effect To explain the present invention, the following properties are now limited to a list of the commercially available ones used to explain the present invention: Resistance to granular mixture materials with the typiformungbci hot load, resistance to 50 see chemical analyzes in percent by weight: dem Cracking due to thermal shock and resistance- _T.
wedge against cracking due to an ^{oner e}

steady growth during repeated heating Al ₂ O ₃ 99.2

and cooling the refractory resulting Na, 0 0.45

weakened structure. In general, these should be 55 FeO 0 03

Total impurities 2 mole percent, based on <,. Jl ³ _η ' ₀ _

on the refractory material, do not exceed. ² '

Fluorine is preferred in the form of the metal fluoride Other substances plus ignition loss 0.3

used, but any quick lime can also be used

other suitable material can be used; e.g. 60

one can get fluorine gas through a molten mass of CaO 95.0

blow from clay and alkaline earth metal oxide. For SiO ₂ 1.3

Using a metal fluoride, this 0.85 MgO is mixed

preferably before melting with the other Al O 1

Constituents of the refractory mix; the fluoride 65 * ^s i 0.85

however, it can optionally also be any other stage ^ ^ε 2 ° 3 J ^

added to the melting or casting process; Other substances' 0.7

z. B. one can it of the molten refractory mass ignition loss 1.3

I.

Fluorospar

CaF ₂ 97.3

CaCO ₈ 1.2

SiO ₂ 1.1

Fe ₂ O ₃ 0.1

Ignition Loss · 0.3

AlF ₃ of high purity

AlF ₃ 99 +

These materials were measured appropriately, mixed prior to introduction into the furnace, and melted in the electric arc furnace. The molten material was poured into pre-formed graphite molds and annealed in the mold by slow cooling. In this way, a series of melts was produced in which the cast materials were free of cracks (see Table I).

r "

Table I.

331

melt
No. Mixture parts
in parts by weight
«-» 99.3
0.35
0.35 Melted
Mix
composition
in mole percent (b) 1 Clay ....
Quicklime
Fluorospar 98.7
0.8
0.5 98.48% Al ₂ O ₃
1.06% CaO
0.46% fluorine (b) 2 Clay ....
Quicklime
AlF ₃ by ho
her purity 99.06
0.74
0.2 97.67% Al ₂ O ₃
1.44% CaO
0.89% fluorine (b) 3 Clay
Quicklime
Eluorspar .... 98.81
0.52
0.67 98.15% Al ₂ O ₃
1.59% CaO
0.26% fluorine (b) 4th Clay
Quicklime
Fluorospar 97.8
1.53
0.67 97.36% Al ₂ O ₃
1.76% CaO
0.88% fluorine (b) 5 Alumina ¹ ....
Quicklime
Fluorospar .... 95.58% Al ₂ O ₃
3.55% CaO
0.87% fluorine

(a) Total Al and Ca content calculated as oxides.

(b) Maximum of 2 mole percent total impurities.

The data in Table II below illustrate the good thermal shock resistance of the cast refractory material of the present invention. This data is based on a rigorous test in which a 2.5 x 2.5 x 7.5 cm Gußprobe is introduced into a heated furnace at 1650 ⁰ C, held for 10 minutes in the heat and is then removed for cooling to room temperature . This represents a cycle and this process is repeated until a piece has jumped off the sample. At this point the number of cycles completed is noted. In order to show that the fluorine has no deleterious effect on the thermal shock resistance, the data are also given for two selected cast samples with essentially comparable compositions, but one of which does not contain fluorine.

6th Warmth-
shock-
circle-
runs Table II 11 melt
No. Melted mix together
settlement in mole percent 23 2 97.67% Al ₂ O ₃ , 1.44% CaO,
0.89% F ₂ 13th 4th 97.36% Al ₂ O ₃ , 1.76% CaO,
0.88% F ₂ 22nd A. 98.79% Al ₂ O ₃ , 1.21% CaO B. 96.42% Al ₂ O ₃ , 3.58% CaO

As already mentioned above, the addition of fluorine also increases the strength. This is shown in Table III by comparing the modulus of rupture values for cast samples of Melt No. 5 and B.

Table III

melt
No. Modulus of rupture
kg / cm ² 5
B. 490
266 "

Although the refractory melt casting material according to the invention can be made from a molten mixture of im essentially 0.06 to 2.63 mole percent fluorine, 0.36 to 16.5 mole percent alkaline earth metal oxide and the balance consist essentially entirely of clay, but the most favorable properties can be found in the preferred one achieve refractory melt mixture, which consists essentially of 0.06 to 2.63 mole percent fluorine, 0.36 to 11.8 mole percent alkaline earth metal oxide and the remainder consists essentially entirely of alumina. To achieve optimal thermal shock resistance, CaO in particular is used in the form of the alkaline earth metal oxide in the range of 0.36 to 10.5 mole percent preferred.

The cast refractory material of the present invention has many uses, but it is particularly useful for the use of vaults in steel furnaces, electric Arc furnace and glass melting furnace, furnace checkers and for metal annealing furnaces that operate with high temperatures work.

Claims (1)

Claim: Refractory cast material with a content of corundum and spinel and alkaline earth metal oxide, characterized by a content of essentially 0.06 to 2.63 mole percent fluorine and 0.36 to 16.5 mole percent alkaline earth metal oxide in addition to alumina, the mole percent of alkaline earth metal oxide being the mole percent of fluorine must exceed. References considered: U.S. Patent No. 2,154,318. 709 647/507 9.67 © Bundesdruckerei Berlin