US 3553010 A
Description (OCR text may contain errors)
CARBGN R GRAPHZTE FORMED BODY ttrnar Rubisch, Meitingen, near Augsburg, Germany, assignor to Sigri Elel-rtrographit Gescllschatt mit beschranltter lilaftung, Mcitingen, near Augsburg, Gerfective protection against oxidation of the aforementioned formed body of graphite or carbon. According to the 428 408e XR 395539010 SR 12 assault; a g Patented ,.laln. 5, 1971 invention, the primary layer is comprised of 90 to 100%, 3,553,010
preferably 95 to 98.9%, of silicon and 0 to 10%, preferably 1.1 to 5%, of sodium, magnesium, calcium, boron. aluminum, titanium, zirconium, manganese, iron, carbon, nitrogen, phosphorus and oxygen, separately or in com- 5 an bmatron, and the cover layer of 85 to 100%, preferably ia l lirgssi iig l il sd ifiiz? 719 08. Ser. No. 747,129 93 to 99.5%, of aluminum and 0 to 15%, preferably 0.5 Claims priority, application Germany, July 26, 1967, to 7%, of sodium, magnesium, boron, SlilCOl'l, phosphorus,
1,571,055 oxygen, copper, zinc, lead, titanium, zirconium chro- B443 1/20 mium manganese, iron, cobalt and nickel, separately or in 3 CL 117-217 5 Claims combination. All percentages used in this application are by weight. 1 b ff 5 The a lication of such a double ayer may e e ecte ABSTRACT OF THE DISCLOSURE in a kn ii'n manner by means of flame injection. It is This invention relates to a carbon or graphite formed particularly preferable to provide the primary layer with body, and m r p r y n rc el r ing a a layer thickness of 0.01 to 0.15 preferably p pg o protective layer which arrests oxidation, and which in- 0.1 rrrnm, and the comm a thickness 033i cludes a primary layer, applied. upon a carbon or graphite Winn, preferably ill to 0.3 mm. formed body, and a metallic cover layer comprised essen- Wen such a proEE'tiVlfiYE-"r" is applied by flame injectial y of aluminum r the P y y The p y -2 tion, it is only mechanically bound to the carbon or layer is comprised of 90 to 100%, preferably 95 to graphite formed body. It was found that when the thus 9 9%, of silicon and 0 to 10%, preferably 1.1 to 5.0%, coated bodies are heated above approximately 550 C., of Sodium, magnesium, Calcium, 13 aluminum, titathe components of the double layer react with each othernium, Zirconium, manganese, iron, carbon, nit ogen p to form a low melting, eutectic alloy which closes the phorus and oxygen, separately or in combination. The pores formed by the flame injection. Finally, I also found cover layer is'comprised of 85 to 100%, preferably 93 that silicon which is dissolved mainly in aluminum, reacts to 99.5%, aluminum and 0 to 15%, pref bly 0.5 to 7%, with the carbon of the fundamental body forming silicon sodium, magnesium, boron, silicon, phosphorus, oxygen, carbide when the operational temperature of the procopper, zinc, lead, titanium, zirconium, chromium, mantected parts exceeds about 550 C. which leads to a tearg fi, irOXl, Cobalt and nickel, lfi y in flflfree and solid bond between the protective layer to the tion. carbon part. This bond is resistant to temperature changes. Carbon or graphite bodies provided with such coatings have shown a long lasting excellent stability with respect My invention relates to a carbon or graphite formed to oxidation, at approximately 1700 C., due to the aforebody, and more particularly an arc electrode having a described alloying effect. During a particularly strong protective layer which arrests oxidation, and which inoxidation attack, the protective effect of the double layer "eludes a primary layer, applied upon a carbon or graphite upon the body can be increased by an additional melting formed. body, and a metallic cover layer, comprised essenof the already applied coating. This melting is carried out tially of aluminum, over the primary layer. in a known manner by an argon are or a direct plasma Carbon or graphite formed bodies are very widely used burner. The subsequent melting of the protective layers I in chemical and metallurgical arts because of their excelre ult in an elimination of the pores and in a chemical \X J lent mechanical and thermal qualities. Frequently, howanchoring, which leads to a considerable improvement of ,1 ,yever. the burning err, which occurs in these materials at the protection againstburning olf.
? temperatures above 550 C. in an oxidizing atmosphere, A similar additional increase of the protective action ;z is disturbing 5 may be obtained by sealing the metallic double layer with y ,f, It is kn wn that burning Off of the carbon and graphite a coating of an aqueous solution of -10 to 30% alkali bodies can be reduced by impregnation with phosphate. borate and/or phosphate and/0r silicate. ll This, b reduces ihe burning Off y p r The effect of the cover layer is also heightened through I tures up to approximately 1100 C. the fact that during operation of the arc furnace, the l t It is further known to reduce the burning Off through current load of the electrodes is so measured that the the utilization of clover layers on carbon or graphite cover layer is heatedio above its melting point or soften- 1,; bodies. It is preferred to produce said cover layers of ing point. This counteracts an otherwise possible tear transition metal silicides. The effect of such layers comformation in the cover layer caused by a. dilference in the prised of transition metal silicides is limited, though, to thermal expansion coefficients of the fundamental material high temperatures within a range of 1200 to 1700 C. and the cover layer, thus preventing increased oxidation Furthermore, the application of said layers is possible which is feasible inand near the tears. only by means of expensive techniques. It is also known In this type of operation, the coating layers in the to apply double layer coatings upon carbon or graphite total region between the electrode holder which serves as bodies. The base layer may be a carbide layer, e.g. a a current supply and the are, are in a fluid or even in a silicon carbide layer, while the cover layer may either plastic state, so that no voltages whatsoever can be proconstitute a layer of an oxide mixture or a metal or siliduced in the coating layer through the dilferent expan- .cide layer. But even these layers do not yet afford an adesions of the coating layer and the fundamental body. quate protection, since it was not possible, heretofore, to Previously formed tears are automatically sealed by the adjust the expansion coefficients of the body to be proplastic or fluid coating layer. Therefore a breaking off of tected and the applied layer, to each other. in the aforethe applied protective layer is not possible. mentioned double layers, the melting point is so high that I found it particularly advantageous to produce, using tears which form cannot be recovered by thellow of the aforementioned preferred method of operation, coatthe layer. As a result, the layer is undercut by oxidation ings of components which in a temperature range beand breaks off. tween 600 and 1200 (3., preferably 700 to i000" (3., The Present invention, lhefefofa, has 85 an j t rfform melting eutectics and to measure the current load such that the melting point of the eutectic is at least obtained on the electrode surface.
The atoredescrihed invention will now be disclosed with some embodiment examples.
EXAMPLE 1' A graphite electrode with a diameter of 450 mm. and a length of 2000 mm. is left to rotate at about 50 revolutions per minute, following the customary, accurately scaled turning oft", in a rotating lathe. Two tlame injection elec rodes, arranged in sequence at a distance of 200 mm., uniformly coat the electrode surface (injection dis tance 100 mm.), first with an 0.05 mm. thick. primary layer of 98.5% silicon+0.8% Fe+0.5% Al+0.2% Ca and thereafter with an 0.15 mm. thick cover layer of 99% Al+0.7% Mg+0.3% Si.
When used in an arc furnace, electrodes coated in this manner result in a graphite saving of 25 to 35% compared to untreated electrodes.
EXAMPLE 2 A graphite crucible 200 mm. in diameter, 500 mm. high and with 20 mm. wall thickness is slowly rotated on a turntable, e.g. at 30 rpm. An approximately 0.1 mm. thick primary layer of 95% Si+3% Ti+1.5% Fe+0.5% Al is applied by means of a powder fiame injection pistol. The coating which is still approximately 70 C. is injection coated with a cover layer of 0.2 mm. thickness, comprised of 98.2% Al+1.5% Mg+0.3% Mn, by Using a wire flame injection pistol, The coated crucible is subsequently dipped briefly into a 20% sodium phospiate solution (pH 5) and thereafter dried. at 120 When employed to operate in a copper casting installation, the above-described crucibles achieve a life span which is 4 to 6 times longer than in untreated crucibles.
1. Formed bodyof carbonor graphite having an oxidation arresting protective layer which encompasses a primary layer on the carbon or graphite formed body and a metallic cover layer on the primary layer, said primary layer being comprised of 90 to 100% silicon and 0 to 10% of sodium, magnesium, calcium, boron, aluminum, titanium, zirconium, manganese, iron, carbon, nitrogen, phosphorus and oxygen, separately or in combination, the cover layer being comprised of to 100% aluminum and 0 to 15% sodium, magnesium, boron, silicon, phosphorus, oxygen, copper, zinc, lead, titanium, zirconium, chromium, manganese, iron, cobalt and nickel, separately or in combination.
2. The body of claim 1 wherein the primary layer comprises to 98.9% silicon and 1.1 to 5.0% of a material selected from. sodium, magnesium, calcium, boron, aluminum, titanium, zirconium, manganese, iron, carbon, nitrogen, phosphorus, oxygen and mixtures thereof and the cover layer comprises 93 to 99.5% aluminum and 0.5 to 7% sodium, magnesium, boron, silicon, phosphorus, oxygen, copper, zinc, lead, titanium, zirconium, chromium, manganese, iron, cobalt and nickel and mixtures thereof.
3. The body of claim 1, wherein the primary. layer has a ltgglgnessmmgl tgfl 15 mrn and the cover layer has a thickness of 0.05150 M 4;"Fheh6dybf claim 1, wherein the primary layer has a thickness of 0.02 to 0.1 mm. and the cover layer has a thickness of 0.1 to 0.3 mm.
5. The body of claim 4, wherein a sealing layer consisting of alkali borate, phosphate, silicate or mixtures thereof is on the cover layer.
References Cited UNITED STATES PATENTS 2,295,379 9/1942 Beck et a1 117--223X 3,120,453 2/1964 Fitzer et a1. 117-217 3,348,929 10/1967 Valtschev et a1. 1172l7X 3,390,013 6/1968 Rubisch 117-221X 3,476,586 11/1969 Valtchev ct a1. 117-217X r ALFRED L. LEAVITT, Primary Examiner C. K. WEIFFENBACH, Assistant Examiner US. Cl. XJR-