DE1902085A1 - Fireproof items and coatings - Google Patents

Description

concerning
Refractory articles uxid coatings

r -

The invention relates to refractory articles and coatings and to a method for their manufacture, in particular Rods made of metal oxides which, by flame spraying, produce refractory coatings on base materials allow.

It is flame spraying to produce stable Coatings made of metal oxides such as aluminum oxide or chromite known (U.S. Patent Specifications 2 70-691 and 2 227 752), where the ceramic starting material as a powder or in the form of sintered rods for use; got. The production The sintered rod is done by ruffling the fine oxides with a temporary binder, molding under pressure and Heating to achieve sintering of the objects and, at the same time, burning out of the temporary binder.

It is known to use rods made of pure zirconium oxide or aluminum oxide for flame spraying (USA patents 2,376 121 and 2,882 1? 4).

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In a publication by the applicant, namely "Bulletin Rl.l-la, EOKIDi; Ceramic St> ray Coatings", the use of various rods made of pure oxides for the production of coatings is described (ROKIDE A = aluminum oxide, ROKIDiC Z = zirxonium oxide, RCKIDE ZS = zirconium silicate, ROKIDK C = chromium oxide and ROKIDE M = magnesium aluminate). The coatings from these rods contain 98.55 % aluminum oxide. and 9 ^, 57% zirconia and 64, 12% of zirconia and 33.22% of silicon dioxide bzw..82,9 ^% chromium oxide or '6t, B; i> alumina and 29.5% ^v i iagnesiumoxid.

The application of the ceramic coatings is done on various base materials such as metal parts, e.g. made of steel, aluminum, magnesium, or on sheet metal.

The grain size of the refractory metal oxides, the shaping the oxide mixtures to the desired objects insoesonuere Rods, strips or rods for flame spraying and sintering or firing of the objects is done in a known manner Way. ■ '

Ceramic coatings made of chromium oxide, which was applied by flame spraying according to known methods, have heavy powers on. So they are air-permeable, have eii.e low density and are not particularly smooth, so there; 3 post-processing required are. Those used for flame spraying. Applied rods or rods have disadvantages, in particular since fusible binders are required and these binders result in a poor breaking modulus of the rod.

Starting from this prior art, according to which the coatings and articles are made of chromium oxide, which Vrfin ^ un "· now n ^ u ^ w ^ s ^ nnfl ntlicb brings better KeramikKeecenstände and flame sprayed coatings with a major proportion

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of chromium oxide Cr ₀ Q ,,. The coatings have a lower air permeability and better chemical resistance. They are denser and smoother on the surface. The chromium oxide articles according to the invention have a good breaking modulus.

The essential point of the objects and layers according to the invention is a solid solution of aluminum oxide in chromium oxide Cr ₂ O-. It was found namely, -da "3 is proper ceramic Gegexistände and vercesserte flanua can reach _b espritzte coatings when only chromium oxide and alumina are present in solid solution, in contrast to the known oxide ceramic products is no permanent binder is present. The mixture of aluminum oxide and chromium oxide in the production of the objects is shaped in a known manner, in particular into rods, strips or rods for flame spraying and then sintered. During this sintering process, the aluminum oxide diffuses into the chromium oxide and there forms a solid solution that hosts the bond.

For the preparation of erfindun ^ sgeraäiien articles and coatings using a mixture 2-30 / ° on alumina 98-70 -o chromium oxide Cr ₂ O, - .. i ^ awake the ormen is sintered at about 1400 C. These ο internal bodies can, if necessary, be used in a suitably constructed spray gun for flame spraying. In the sintered objects or the coatings there is 1 to 25 % aluminum oxide in 99 to 75 % chromium oxide, as can be determined by chemical analysis. Objects with 9.% wt. & Aluminum oxide, which in solid solution is 90.2; ^; 'Chromium oxide is located. The loss on ignition of the aluminum oxide is likely to lead to the different composition of the mixtures and the fired products.

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In the preparation of the mixture, 2 fractions are used ^: of molten chromium oxide and zx «jar with a grain size between 7 ^ and 177 / .u (SO to 200 mesh) and <? 4, u with burnt clay (" Alon C and E -lll-H ") mixed with fat and methyl cellulose as a temporary binder. By the aluminum oxide ^! 'Alon G' is a powder of colloidal alumina, the commercial product E-III-H is burnt alumina with a grain size of> 90 % < kh / rev .. The mixture is rolled in a drum with rubber balls for uniform mixing .

The discharged from the drum -Hasse is extruded, for example, 6.35 mm 0 at a pressure of about 6 to I ^ t and fired, the compacts in a tunnel oven at a temperature of about 1400 ⁰ ■ C (Orton cone 16).

The fired objects, especially rods for flame spraying, show only very little shrinkage, a density between about 3> O9 and 3.16 g / cm and a modulus of rupture of about 271 kg / cm ² to 600 kg / cm ² (. 3830 to ■ 84-50 psi). -

The flame spraying can be carried out in a known manner, for example at a distance of about 10 cm from the workpiece to be coated. Were determined density and gas permeability of the coating, namely by the time it has been found necessary to enable the atmospheric air to mm 0 to penetrate and enter into the pressure prevailing at the back of the sample vacuum through a sample of about 25th The gas permeability K results from the equation

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.where P is the initial pressure,.

P is the pressure at time t

t the required time in see

L is the specimen thickness in cm.

The lower the K value, the more impermeable it is Coating.

The invention is explained in more detail with the aid of the following examples.

example 1

A mixture of 2 % aluminum oxide and chromium oxide was prepared in which 19.6 kg of molten chromium oxide Cr _? 0o with a grain size between 74 and 177 / U and 4.9 kg of molten chromium oxide with a grain size <· 74 / U with 0.25 kg of very fine aluminum oxide powder (Alon C), 0.25 kg of aluminum oxide powder from the Bayer process and 0.3 kg of grease ("Texaco GB-2") and 2.5 kg of a 12 # aqueous solution of methyl cellulose (R1-12 Aiethocel HC 4000 poxvder) were ground in a drum with rubber balls for uniform mixing as a temporary binder . The output from the mill was extruded through an extruder with a mouth diameter of 6.247 mm at a pressure of 14 t. The rods obtained in this way showed good green strength, they were in a tunnel furnace at about 1460 G (Orton cone 16). burned. The fired rods had grown slightly (to 6.259), density 3.11 g / cnP, modulus of rupture 270 kg / cm ² (3830 psi). Based on chemical analysis, the bar contained 1.54 f ° Al _? 0o.

This rod was in a known manner at a distance of about 10 cm from the work piece to be withdrawn and a feed speed iR'keit of about 10 cm / min used for flame spraying. The coating had a density of 1.993 g / cm and a gas permeability of K = 1.24. · 10 ~.

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Example 2

An oxide mixture with 5% ^A1 2 ° 3 ^was prepared by mixing 19 kg molten chromium Grobfraktion.und ^, 75 kg Peinfraktion as defined in Example 1 with 0.25 kg of colloidal alumina and 1 kg of alumina from the Bayer process, with the binder · of Example 1 and was extruded at a pressure of 10 t. The bars had a high green strength. After the burning in the sense of the example, they were slightly dulled (6.2 mm) and had a

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Density of 3109 g / cnr and a modulus of rupture 505 kg / cm- (7180 psi). The chemical analysis showed an aluminum oxide content of 5> 08 %.

In the sense of Example 1, the rods were used for spraying lamb. The coatings had a density of J> 956 g / cm² and a gas permeability of ₈ 95 10 ″.

Example 3

A mixture with 10 % aluminum oxide from 18 kg chromium oxide coarse fraction and M-, 5 kg ^ single fraction with 0.5 kg colloidal clay and 2.5 '* g aluminum oxide from the Bayer process and 0.25 kg of the fat and 2, 5 μg of the methyl cellulose solution according to Example 1 were extruded under a pressure of 7 t and a mouth diameter of 6.3 nm and sintered according to Example 1.

The sixiter bars had the same dimensions: density 3.16 g / crP, modulus of rupture 595 kg / c; n ² (8450 psi), aluminum content 9.75 fr

In the sense of Example 1, these rods were used for flame spraying used with different feed speeds, namely 6.35 * 10.1, 15j24, 19/5 and 25 ^ cm / min. When spraying, a narrow-angled was seen

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Trötjfchenstrom. The surface of the coating was uniform smooth, the density was 4.84 g / cm2, gas permeability 0.7 x 10 ^.

Example 4

A mixture with 15 7 ° ^A1 2 ° ~ 3 was ⁽³ - ^e produced from 1. kg of chromium oxide coarse fraction and 4.25 kg of chromium oxide fine fraction, 0.5 kg of colloidal clay, 3 »25 kg of clay according to the Bayer Method and binder according to Example 1, but here 0.75 kg of fat. The whole was mixed as in Example 1 and extruded under a pressure of 6 tons. The pellets showed excellent green strength. They were fired and had a density according to Firing of 3> 12 g / cm2 and a modulus of rupture of 53 ° ^C; kf / cm (7660 psi) The proportion of alumina was 13. ^Q ji.

In a known way, these rods were used for flame spraying

3 used. The coatings showed a density of 4.74 g / cm3

—4 and a gas permeability of 0.69. 10

A graphite block was sprayed on all sides according to the invention and at a sufficient temperature. the graphite burned out. The layers were sufficiently strong because they were self-supporting and did not fall into one another after the graphite had burned out. While spraying, nan observed a flawless jet in sharp focus.

Example 3

In a modification of the above examples, masses with different aluminum oxide contents, namely in the form of burnt aluminum oxide from the Bayer process, were investigated, namely with 2, 5, 10, 15 and 25 %.

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The pellets were then fired at about 1550 g. The bars with 2 % alumina had a modulus of rupture of 530 kg / cm (7600 psi), with 5 % alumina of 630 kg / cm (9050 ¹ DSi) ₁ with 10 $ alumina. 605 kg / cm (% 4-C psi), with 15 % alumina of όθΰ ^: kg / cm (B565 psi) and finally 'with 25 % alumina only 4-4-5 kg / cm ² (636I psi). ■

Comparative experiment 1

In a known way, rods were made from molten chromium oxide granulate (standard AOKTDH C) with the usual ceramic bond and injected in the sense of example 1, namely with different feed rates in terms of example 3 - breaking modulus of the rod 314- kg / cm ² (44- 70 psi).

The coatings had a density of 4-, 34-3 g / cm and

Ll

a gas permeability of 1.4-2. 10. On a graphite block, which was sprayed with this material on all sides and then heated to burn out the graphite, no self-supporting coating was formed, the layer fell as a result of shrinkage cracks.

Comparative experiment 2 . ■

In a mill with rubber balls, 1080 g of molten chromium oxide coarse fraction and 270 g of fine fraction in the sense of Example 1 were added together with 150 t of ear oxide pigment GrOo (burned) and 14-0 g of methyl cellulose as a 10% aqueous solution and 70 g of lubricating grease " Texaco GB2 "dressed, extruded, and in an electric laboratory oven
soft and very bad.

see laboratory furnace fired at 1550 ° C. The bars were

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Comparative experiment 3

jStwa 10 - / ο aluminum oxide were 90 % chromium oxide Cr _? 0 ~ mixed in and the mixture melted at an elevated temperature. Analysis of the granules obtained showed a chromium oxide content of about 88.87 % with an aluminum oxide content of 10.96%. Finally 0.14 % i \ a ₉ 0 and 0.03; ^ _; Carbon present. The molten mass was sieved to a coarse fraction 7 ^ to 210 / U and fine fraction < kk / U, 450 g of the coarse fraction, 4-50 g medium fraction <210 / U and 100 & fine fraction < kk / U were mixed with the binder and approximately 125 g 12% methyl cellulose solution and 25 g grease. The whole thing was mixed, extruded under a pressure of more than 15 t and fired _{at BtWa 1} I ^ O ^{0 C.} The 3interköroer were very bad and sunbathed not to be used for flame spraying.

In contrast, when flame sprayed, the rods of Example 3 exhibited excellent jet with a dense narrow one Angle. The coating from the first comparative experiment was flaky.

Corrosion tests on with the flame spray coating, after

and

the prior art of the invention ^ steel articles provided revealed daiii only the erfinduxigsgemäiäe material, however, the known flaterial (1. Comparative Experiment) counter "over 5n at the hydroxide solution at 50 ⁰ C was not more than h stable 600th

Pat ent responses

909 832/1021

BAD ORSGINAL

Claims (3)

DR. ING. F. WTTESTHOFF 8 MtTNGSEN ΘΟ · ü ^ U £ U 8 5 DIPL ·. ING. G. PUI.S 'SCHWEIGEHSTHASSE 2 DR.E.V.PEOHMANN TILIrox 22 08 31 DR. ING. D. BEHRENS * MMO "iiot * DBias" i PATENTANWÄLTE. f 0 PHOTJCOXPATXKT hOkcbjcm 1A-35 631 Pate a ta a spruche 1. Refractory objects and coatings made of metal oxides / !, characterized by about 1 to 25 % by weight of aluminum oxide and about 99 to 75% by weight of chromium oxide in the form of a solid solution. 2. A method for producing the articles according to claim 1, characterized by ■ daiä one 2 to 30 Wt -.% Of alumina powder and 9 * ^Q feis 70 wt -.% Granular
Chromium oxide Cr ₀ O- together with a temporary binder
mixes and shapes and sinter the shaped bodies to remove the temporary binder and form the solid solution. 3. A method for producing the coatings according to claim 1, characterized in that rod-shaped bodies according to claim 2 are applied to the object to be coated
flame spray. ' BATH ORIGINAL 909832/10