DE1902085B2 - Process for flame spraying and a suitable sintered rod - Google Patents

Description

1 2

The invention relates to a method of manufacturing in the absence of a permanent binder. That

of ceramic coatings on objects by mixing aluminum oxide and chromium oxide in the

Flame spraying as well as a suitable sintering production of the rods and the like is carried out in a known manner

Rod. molded and then sintered. During this sintering process

It is the flame spraying to produce stable 5 diffuses the aluminum oxide into the chromium oxide

Coatings made of metal oxides such as aluminum oxide and there forms a solid solution that creates the bond

or chromite known (U.S. Pat. No. 2,707,691).

and 2 227 752), whereby the ceramic starting material used for the production of the material used according to the invention as a powder or in the form of sintered rods, a mixture of 2 to 30% is used. The manufacture of the sinter- io aluminum oxide to 98 to 70 ° / ₀ chromium oxide Cr ₂ O ₃ . rods are done by mixing the fine oxides with After molding, sintering takes place at about 1400 ⁰ C, a temporary binder, molding under pressure 'These sintered bodies can be used in a suitable construction and heating to sinter the objects and structured spray gun for flame spraying at the same time a burnout of the temporary connective tissue. To be achieved in the sintered rods or the conveyors. 15 puffs lie 1 to 25% aluminum oxide in 99 to 75%

It is known to make rods made from pure zirconia as shown by chemical analysis

or alumina let notice for flame spraying to comparable. Have particularly good properties

(U.S. Patents 2,876,121 and 2,882,174). Coatings with 9.8 percent by weight aluminum oxide,

In a publication by the patentee that is in solid solution in 90.2% chromium oxide

namely »Bulletin R-1.1-la, ROKFDE Ceramic Spray ao. The loss on ignition of the raw material

Coatings, “the use of various turned alumina rods is expected to lead to

from pure oxides for the production of coatings of different compositions of the mixtures

(ROKlDE A == aluminum oxide, ROKl- and the fired products.

DE Z = zirconium oxide, ROKJDE ZS = zirconium- When making the mixture, two silicate, ROKIDE C = chromium oxide and ROKIDE MA 35 fractions of molten chromium oxide, namely = Magncsium aluminate). The coatings from these with a grain size between 74 and 771 μ (80 to Bars contain 98.55% aluminum oxide or 94.57% 200 mesh) and <74μ with burnt clay Zirconium oxide or 64.12% zirconium oxide and ("Alon C and E-III-H") with fat and methyl cellulose 33.22% silicon dioxide or 82.94% chromium oxide mixed as a temporary binder. In the aluminum or 66.8% aluminum oxide and 29.5% magnesium oxide "Alon C" is a powder oxide. colloidal clay, in the case of the commercial product E-III-H

The application of the ceramic coatings to calcined alumina with a grain size of

applies to different base materials such as metal-> 90% < 44 µ. The mixture is in a drum

parts, e.g. B. made of steel, aluminum, magnesium, 'or' with rubber balls for even mixing

on sheets. 35 rolled.

The grain size of the refractory metal oxides that will be The mass discharged from the drum

Forming the oxide mixtures into the desired extruded ones, ζ. B. 6.35 mm diameter for a

Objects, especially rods, strips or pressing pressure of about 6 to 14 t and the compacts in

Rods for flame spraying and sintering or a tunnel furnace at a temperature of about

Firing the items is done in a known manner. 40 1400 ⁰ C (Ortong cone 16) fired.

Ceramic coatings made of chromium oxide, which through the fired objects, in particular rods

Flame spraying applied by known methods for flame spraying show only a very small amount

have serious disadvantages. So they're shrinking to a density between about 3.09 and

air-permeable, have a low density and are 3.16 g / cm ³ and a modulus of rupture of about 271 bis

not particularly smooth so reworks 45,600 kg / cm ^a (3830 to 8450 psi).

required are. The flame spraying used for flame spraying can be done in a known manner,

Bars or rods have disadvantages, especially e.g. B. at a distance of about 10 cm from the to

since fusible binders are required and these cover the workpiece. There were density

Binder determines a poor modulus of rupture of the rod and gas permeability of the coating,

result. 50 namely by determining the time that the

Based on this prior art, according to which atmospheric air is required to pass through a sample

Coatings and objects made of chromium oxide with a diameter of about 25 mm to penetrate and into the

are made, the invention now brings new and prevailing vacuum on the back of the sample

Much better ceramic objects and flame-retardant. The gas permeability K results

sprayed coatings with a major proportion of chromium-55 from the equation
oxide Cr ₂ O ₃ . The coatings have a lower air

permeability and better chemical resistance)

capability. They are denser and smoother on the surface. ? ~ Λ>>

The articles according to the invention made of chromium oxide wherein

have a good modulus of rupture. 60 ". _{Anfan (K} j _r "1,

The essential point of the invention? The pressure at the time /

Objects and layers is a solid solution of _{what you need to know}

Aluminum oxide in chromium oxide Cr ₂ O ₃ . hs showed _{L dje} p _robe * _{strength in} centimeters.
namheh that you can have flawless ceramic rods

for flame spraying and improved flame sprayed 65 The lower the K value, the more impermeable

Coatings can be achieved if only chromium oxide and is the coating.

Alumina are present in solid solution. In contrast, the invention is illustrated by the following examples

set of the well-known chromium oxide ceramic products explained in more detail.

example 1

A mixture of 2% aluminum oxide and chromium oxide was produced in which 19.6 kg of molten chromium oxide Cr ₂ O ₃ with a grain size between 74 and 177 μ and 4.9 kg of molten chromium oxide with a grain size of <74 μ with 0.25 kg very fine alumina powder (Alon C), 0.25 kg of alumina powder from the Bayer process and as a temporary binder kg 0.8 grease ( "Texaco GB-2") and 2.5 kg of a 12 ° / ₀ aqueous solution of methyl cellulose (M-12 Methocel MC 4000 powder) in a drum with rubber balls for uniform mixing. The mill discharge was extruded through an extruder with a mouthpiece diameter of 6.247 mm at a pressure of 141. The bars so obtained showed good green strength, they were fired in a tunnel furnace at about 1460 ⁰ C (Orton cone 16). . The fired rods had grown slightly (to 6.259), density 3.11 g / cm ³ , modulus of rupture 270 kg / cm ² (3830 psi). Based on the chemical analysis, the rod contained 1.54% Al ₂ O ₃ .

This rod was used for flame spraying in a known manner at a distance of about 10 cm from the workpiece to be coated and a feed rate of about 10 cm / min. The coating had a density of 4.993 g / cm ³ and a gas permeability K = 1.24 x 10 ^"4.

Example 2

An oxide mixture with 5% Al ₂ O ₃ was prepared by adding 19 kg of molten chromium oxide coarse fraction and 4.75 kg of fine fraction as in Example 1 with 0.25 kg of colloidal aluminum oxide and 1 kg of aluminum oxide from the Bayer process with the binder of the example 1 and extruded at 101 pressure. The bars had a high green strength. After firing as in Example 1, they had shrunk slightly (6.2 mm) and had a density of 3.09 g / cm ³ and a modulus of rupture of 505 kg / cm ² (7180 psi). The chemical analysis showed an aluminum oxide content of 5.08%

In the sense of Example 1, the rods were used for flame spraying. The coatings showed a density of 4.956 g / cm ³ and a gas permeability of 0.95 · 10. ⁴

Example 3

A mixture with 10% aluminum oxide from 18 kg chromium oxide coarse fraction and 4.5 kg fine fraction with 0.5 kg of colloidal clay and 2.5 kg of aluminum oxide from the Bayer process and 0.25 kg of des Fat and 2.5 kg of the methyl cellulose solution according to Example 1 were under a pressure of 71 Extruded urf your mouthpiece diameter of 6.3 mm and sintered according to Example 1.

The sintered bars had the same dimensions: density 3.16 g / cm ³ , modulus of rupture 595 kg / cm ² (8450 psi), aluminum content 9.75%.

In the sense of Example 1, these rods were used for flame spraying, specifically at different feed speeds, namely 6.35, 10.1, 15.24, 19.5 and 25.4 cm / min. A narrow-angled stream of droplets was seen during spraying. The surface of the coating was uniformly smooth, the density was 4.84 g / cm ^3, gas permeability 0.7 x 10 ~. ⁴

Example 4

A mixture with 15% Al ₂ O ₃ was prepared from 17 kg of chromium oxide coarse fraction and 4.25 kg of chromium oxide fine fraction, 0.5 kg of colloidal alumina, 3.25 kg of alumina according to the Bayer process and binding agent

ίο 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 compacts showed excellent green strength. They were fired and had a post-firing density of 3.12 g / cm ³ and a modulus of rupture of 538 kg / cm ² (7660 psi). The proportion of aluminum oxide was 13.8%. In a known manner, these rods were used for

Flame spray used. The coatings showed a density of 4.74 g / cm ³ and a gas-permeable

ao speed of 0.69 · 10 ~ ⁴ .

A graphite block was sprayed on all sides according to the invention and at a sufficient temperature of the Burnt out graphite. The layers were sufficiently strong that they were and were not self-supporting collapsed after the graphite burned out. A flawless one was observed when spraying Beam in sharp focus.

Example 5

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

The compacts were then fired for 10 hours at about 155o C ^0. The bars with 2% alumina had a modulus of rupture of 530 kg / cm ² (7600 psi), with 5% alumina of 630 kg / cm ² (9050 psi), with 10% alumina of 605 kg / cm ² (8640 psi), with 15% alumina at 600 kg / cm ² (8565 psi) and finally with 25% alumina only 445 kg / cm ² (6361 psi).

Comparative experiment 1

In a known manner, rods were produced from molten chromium oxide granulate (standard ROKIDE C) with the usual ceramic bond and injected in the sense of example 1, namely at different feed rates in terms of example 3, breaking modulus of the rod 314 kg / cm ² (4470 psi).

The coatings had a density of 4.343 g / cm ³ and a gas permeability of 1.42 x 10 ~. ⁴ No self-supporting coating was formed on a graphite block that was sprayed with this material on all sides and then heated to burn out the graphite; the layer collapsed 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 according to Example 1 together with 1501 of chromium oxide _{pigment CrO 3} (burned) and 140 g of methyl cellulose as a 10% aqueous solution and 70 g of lubricating grease »Texaco GB- 2 «

turned on, extruded and in an electric Laboratory furnace fired at 1550 ° C. The bars were soft and very bad.

Comparative experiment 3

About 10% aluminum oxide) 90 ° / ₀ chromium oxide Cr ₂ O _{3 were} mixed in and the mixture was melted at an elevated temperature. The 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% Na ₂ O and 0.03% carbon were still present. The molten mass was sieved to coarse fraction 74 to 210 μ and fine fraction <44 μ, 450 g of the coarse fraction, 450 g middle fraction <210 μ and 100 g fine fraction <44 μ were mixed with the binder, namely 126 g of 12% methyl cellulose solution and 25 g of grease. The whole was mixed, extruded under a pressure of the more than 15 t and fired at about 145 ° C ^0. The sintered bodies were very bad and could not be used for flame spraying.

In contrast, the rods of Example 3 exhibited an excellent jet with flame spraying a tight, narrow angle. The coating from the first comparative experiment was flaky.

Gave corrosion tests with the thermal spray coating according to the prior art and the invention steel articles provided that only material of the invention, but not the known material (first comparative test) compared with 5N sodium hydroxide solution at 5O ⁰ C was more stable than 600 hours.

Claims (2)

Patent claims: 1. Process for the production of ceramic coatings from metal oxides by flame spraying, characterized in that one sintered rod, band or rod from a solid solution of 2 to 30% aluminum oxide and 98 to 70% chromium oxide. 2. Rods, bands or rods for implementation of the method according to claim 1, characterized in that it is a sintered solid solution are comprised of 2 to 30% aluminum oxide and 98 to 70% chromium oxide.