Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D5/00—Supports, screens, or the like for the charge within the furnace
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D3/00—Charging; Discharging; Manipulation of charge
  • F27D3/02—Skids or tracks for heavy objects

Definitions

• the invention relates to support bodies in the form of rollers, Beams, plates, positioning supports or the like as a piece of equipment in heat treatment furnaces for heat treatment of metals consisting of SiC and are coated with a corrosion protection layer and a method for the heat treatment of metals with such a support body.
• high-temperature-resistant ceramic carrier components offers the advantage over metals that they maintain their shape stability under (static or dynamic) mechanical stress at high operating temperatures and show no distortion after or during cooling.
• the surface defects ("pittings") described above also disappear when using ceramic supports.
• These ceramics are oxide-ceramic materials that are characterized by good creep resistance and resistance to temperature changes even at temperatures above 1,000 ° C. Nevertheless, the durability of oxide ceramic supports in the high temperature range is limited, since their typical compositions are not corrosion-resistant to the constituents of the metal material, in particular Fe.
• oxide-ceramic supports Due to this corrosion reaction, the usability of oxide-ceramic supports is only possible to a limited extent. In the case of very high mechanical loads, such as those that can occur during the transport of steel blocks through roller hardening furnaces, or in the case of very abrupt temperature changes, such as those that occur during quenching in a discontinuously operating hardening furnace, the use of the above-mentioned oxide ceramic materials is additionally restricted at all, since they have the required strength and cannot provide resistance to temperature changes.
• the invention is characterized by the characteristic features of claim 1 solved.
• the subclaims show advantageous further training.
• SiC carrier bodies according to the invention are now compared more resilient to oxidic ceramics and are also extremely resistant to temperature changes. So they can disadvantages known for the oxide-ceramic idlers, as described above, overcome will.
• the support body according to the invention are shown also clearly superior to the metallic ones, there now the typical appearance that glides on each other two hot metal surfaces ("pitting") arises, no longer occur.
• SiC materials come in particular recrystallized SiC (RSiC) that infiltrated silicon SiC (SiSiC), the nitridic or oxynitridic bonded SiC and the sintered SiC (SSiC) in Consideration.
• the inventive coating of the SiC material with a thermally sprayed corrosion protection layer prevents the elements contained in the steels, in particular iron, from reacting with the SiC.
• SiC materials are not chemically resistant to the elements present in steel (in particular Fe or Ni), since these elements (Me) reduce the SiC at high temperatures under reducing or vacuum conditions according to the reaction equation SiC + Me SiMe + C decompose.
• Analogous silicide formation reactions eg Cr, Mn, Co, Mo, Nb
• Alloy elements such as V, Ti, Ta, W can, depending on the thermodynamic equilibrium conditions, after silicide formation or after carbide formation SiC + Me MeC + Si come in. For this reason, SiC grain is used, for example, in the processing of cast iron for carburizing and siliciding, and is used as a deoxidizer in the steel casting process.
• Nitridic binding phases react similarly Si3N4 + Me SiMe + xN such as Si3N4 + Me MeN + Si or excess metallic Si in the SiC material to form an alloy formation that may lower the melting point and thus increase the vapor pressure, which may result in an increase in the porosity at operating temperatures from approx. 1200 ° C: Si + Me SiMe
• Si + Me SiMe These reactions lead to a weakening of the SiC material structure, which means that it cannot be used in contact with the above-mentioned metallic elements at high temperatures. For this reason, no support rollers made of SiC have previously been used in the prior art for the heat treatment of metals in heat treatment furnaces.
• the coating of SiC idlers with oxides is however from another area of application, namely known for the heat treatment of oxidic ceramics (silicate and oxide ceramics). It is proposed to avoid sticking in high temperature applications for oxidic materials, a Apply suspension to the SiC carrier.
• the Compositions of the suspensions (engobes) is predominantly based on Al2O3 and is preferred on Plates made of recrystallized SiC, which as a base for fired goods in porcelain smooth firing serve at temperatures around 1,400 ° C.
• the consolidation the engobe layer is caused by fire in the area the operating temperature reached, liability to that SiC base is based on toothing with the open porous Surface of the RSiC.
• stick Engobes on dense SiC surfaces like them SSiC or SiSiC are generally worse, because the necessary mechanical interlocking of the There is no engobe with the SiC.
• the Al2O3 layer applied to the SiC has the function of a separating layer in this application in order to prevent the adhesion between the roll and the plate which frequently occurs in temperature ranges from 1,200 to 1,300 ° C.
• idlers made of high-purity sintered quartz and alumina-containing ceramic are used by means of thermal spraying processes, adhesive layers made of Si, Cr, Ni or their mixtures and the subsequent functional layer made of MgAl2O4, 3Al2O3, 2SiO2, Al2TiO5, ZrO2, Y2O3, TiO2, BaO, MgO, SnO2 or the rare earth oxides described.
• the function of the oxide layers here is to prevent caking and adhesion reactions between the rollers and the firing material during transport in the furnace.
• SiC support body with a thermally sprayed corrosion protection layer also for heat treatment of metals in heat treatment furnaces at temperatures > 1000 ° C can be used.
• the supporting body showed even in temperature ranges above 1,300 ° C an excellent resistance. That too treating metal did not react in any case with the SiC carrier.
• disadvantages namely the ability to react the SiC with metals contained in the alloys, it was not to be expected that only through the thermally sprayed protective layer of this SiC support body compared to the known metallic or oxide ceramic have such superior properties.
• the corrosion protection layers according to the invention serve thus for chemical bonding and / or diffusion hindrance the diffusing into the layer structure Metal ions and / or for rejection or slowdown penetration of metallic (partial) Melting in the layer structure.
• the different compositions of the corrosion protection layers characterize their different Individual functions. These individual functions can through appropriate graded or graded Complete mixed compositions with each other, whereby the total thickness of the corrosion protection layer (s) Do not exceed 300 ⁇ m.
• The is preferably 200 ⁇ m thick.
• Characteristic of the composition of the corrosion protection layer is on the one hand that this in reduced or protective gas atmosphere or vacuum low wettability of metallic melting phases exhibit. This is due to corrosion protection coating compositions achieved that proportionately or completely from spinels of the general formula AB2O4, Proportionately or entirely of chromium oxides, in particular Cr2O3 aluminum oxide, titanium oxide or zirconium oxide or consist of their mixtures.
• A are divalent metals from the group Mg, Fe, Zn, Mn, Co, Ni, Cu or Cd and for B the metals Al, Fe, V, Cr or Ti.
• Mg / Al spinels are particularly preferred.
• a particularly preferred embodiment now proposes to apply a so-called compensation layer with a layer thickness of up to 300 ⁇ m, preferably 200 ⁇ m, between the SiC support body and the corrosion protection layer.
• These compensation layers are composed in such a way that they bring about an adjustment or compensation of the different coefficients of thermal expansion and / or different elastic constants between the corrosion protection layers and the SiC carrier body.
• the compensation or equalization of the different coefficients of thermal expansion is achieved according to the invention in that the thermal expansion coefficients of the compensating layers are equalized or less than that of the SiC.
• the invention includes all of these connections.
• Al2TiO5 for example, has a coefficient of thermal expansion of ⁇ 20-1,000 ° C ⁇ 1.5 ⁇ 10 ⁇ 6 1 / K .
• the compensation layers can be graded or staged based on, for example, 3Al2O3 ⁇ 2SiO2, ZrO2 ⁇ SiO2 or Al2TiO5.
• 10 individual layers of approx. 20 ⁇ m each with the mixing ratios 3Al2O3 ⁇ 2SiO2: Cr2O3 from 5:95, 10: 90, 20:80 etc. to 90:10 can be passed over and thus directly adapted to the outer corrosion protection layer.
• the leveling layers are characterized by certain crack or lamella structures in their structure.
• Compensating layers with 3Al2O3 ⁇ 2SiO3 and / or ZrO2 ⁇ SiO2 as a layer component are advantageously characterized in that they can form a crack structure or lamella structure parallel to the surface of the base body through the use of thermal spraying technology.
• These lamellar cracks with a lamellar structure within a typically approx. 200 ⁇ m thick compensation layer lead to a delayed or completely prevented progress of radially aligned cracks, which in turn have their origin due to thermally induced stresses within the corrosion protection layers.
• Compensating layers that consist partly or completely of Al2 TiO5 have, due to the pronounced anisotropic thermal expansion behavior of the Al2TiO5 single crystal, a material structure typically interspersed with the finest microcracks with a comparatively low modulus of elasticity of approx. 1.5 GPA (elastic modulus of SiSiC is approx .360 GPa). It is therefore characteristic of these compensation layers that thermally or mechanically induced stresses in the layer structure can be reduced or reduced within the compensation layer interspersed with microcracks, the structure giving in to the applied stresses relatively easily.
• the use of a partial or complete Al2TiO5 compensating layer is the corrosion-inhibiting effect already described above.
• an adhesive layer is primarily required for dense SiC materials, i.e. Materials without open porosity or smooth surface. These include the sintered SSiC and the silicium-filtered SiSiC.
• Adhesive layers are in a total thickness of max. 50 ⁇ m, preferably 20 ⁇ m, directly on the previously cleaned and roughened, i.e. with e.g. Corundum grains blasted surface, sprayed on.
• the function of the adhesive layers is one, fixed adhesive transition between compensation or corrosion protection layer under the SiC material surface to guarantee. This is typically done by metallic Adhesive layer compositions of Si, Ti, Ni, Cr or mixtures or alloys of these elements or also by NiCrAlY, CoCrAlY or NiCoCrAlY alloys reached. Depending on the composition of the adhesive layer can be a vacuum or protective gas atmosphere have a positive influence on the adhesion properties of the layer.
• metallic adhesive layers are capable mechanical stresses caused by reduce their ductility.
• the adhesive coating is more open-porous SiC ceramics such as recrystallized SiC (RSiC) or nitridically or oxynitridically bound SiC also supports firm liability in this case the leveling layer and / or anti-corrosion layer to get on the SiC underground, though adhesion without mechanical layer due to mechanical Interlocking is given.
• RSiC recrystallized SiC
• nitridically or oxynitridically bound SiC also supports firm liability in this case the leveling layer and / or anti-corrosion layer to get on the SiC underground, though adhesion without mechanical layer due to mechanical Interlocking is given.
• the invention Discrete layer structure provided from individual layers. But it is also possible that either in individual Layers, e.g. in a corrosion protection layer there is a graded structure or that just one layer in the form of a changing material composition is used.
• the invention encompasses thus all layer variants, starting from one Corrosion protection layer with a uniform composition, one or more layers with graded Structure, like multiple layers with uniform compositions.
• Figure 1 shows schematically a layer structure on the SiC support body 1.
• an adhesive layer 2 with a layer thickness of 20 ⁇ m applied.
• the leveling layer deposited on it 3 has a thickness of 200 microns.
• 2 corrosion protection layers 4, 5 provided, each having a thickness of Have 50 microns.
• the layer compositions can now be chosen so that the individual layers only materials of the respective layer type contain or have a graded structure. In this case the composition changes in one shift.
• Example II shows one partial formation of new phases in the corrosion protection layer from Al2O3 to FeO Al2O3 (Hercynit) connected with a near-surface compaction of the layer for closed porosity.
• Example III Base body: nitride-bonded SiC
• Example No. IV Base: nitride-bonded SiC
• Example No. V Base body: silicon infiltrated SiC (SiSiC)
• Example No. VI Base body: silicon-infiltrated SiC (SiSiC)
• Example No. VII Base: sintered SiC (SSiC)
• Example No. VIII Base: sintered SiC (SSiC)
• Examples VII and VIII illustrate one Three-layer structure. Analogous to example V. and VI. were the Si adhesive layers atmospheric in an air atmosphere upset. By increasing the compensation layer thickness on the Anosovite to about 250 ⁇ m an approximately 70 ⁇ m thick ZrO2 layer is sprayed on directly will. Radial crack formation after outsourcing or Thermal shock could occur with this layer thickness ratio be restricted. Possibly. Cracks appear on the Anosovite layer prevented from further progress. Corrosion tests showed a dark discoloration of the ZrO2 protective layer, a new phase formation could cannot be proven. The Cr2O3 protective layer variant also showed no new phase formation. A crack progress from the Cr2O3 layer after outsourcing or after thermal shock tests could from a leveling layer thickness of around 100 ⁇ m can already be prevented.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Coating By Spraying Or Casting (AREA)
• Ceramic Products (AREA)
• Heat Treatments In General, Especially Conveying And Cooling (AREA)

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• 1994
  • 1994-10-14 DE DE4436823A patent/DE4436823C1/de not_active Expired - Fee Related
• 1995
  • 1995-10-12 DE DE59509964T patent/DE59509964D1/de not_active Expired - Fee Related
  • 1995-10-12 AT AT95116102T patent/ATE211252T1/de not_active IP Right Cessation
  • 1995-10-12 EP EP95116102A patent/EP0707188B1/fr not_active Expired - Lifetime

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