| Customization: | Available |
|---|---|
| After-sales Service: | on-Line Service |
| Warranty: | 1 Years |
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Purpose:
The furnace tube serves as the inner lining of various experimental electric furnaces, primarily isolating the heating elements from the test materials, enclosing the heating zone, and holding the test substances. It is widely used in high-temperature testing and analytical instruments across industries such as coal testing, metallurgical powder analysis, and chemical/glass laboratory equipment.
Material & Manufacturing:
Corundum furnace tubes are mainly made of fused alumina, available in two types:
Ultra-fine powder-bonded
Clay-bonded
The specifications are customized based on user requirements, including operating temperature, wear resistance, and chemical corrosion resistance.
Dimensions:
Outer diameter: 15-200 mm
Length: 100-2000 mm
Wall thickness: 3-15 mm
Usage Guidelines:
When using high-temperature testing equipment, ensure gradual heating and cooling to minimize internal stress caused by thermal expansion/contraction. This reduces the risk of cracking and extends the tube's service life.
Composition:
Made of porous fused alumina, offering high durability and heat resistance.
Applications:
Suitable for melting samples with weak alkaline fluxes (e.g., anhydrous NaCO).
Not suitable for strong alkaline fluxes (e.g., NaO, NaOH) or acidic fluxes (e.g., KSO).
99.70% Corundum
Max short-term temperature: 1800°C
mechanical strength in oxidizing/reducing atmospheres.
High thermal conductivity, low thermal expansion.
Operating range: 1650-1700°C
Excellent high-temperature insulation &
Chemically inert to air, steam, H, CO, etc., up to 1700°C.
99.35% Corundum
Max short-term temperature: 1750°C
Operating range: 1600-1650°C
Stable in oxidizing/reducing atmospheres.
85.00% High-Alumina
Max short-term temperature: 1400°C
Operating range: 1290°C
Good insulation & mechanical strength in oxidizing/reducing atmospheres.
High thermal conductivity, low thermal expansion.
Chemically inert to air, steam, H, CO, etc.
Suitable for long-term use under stable temperature conditions.
Quartz glass tubes are a specialized industrial technical glass made from silicon dioxide (SiO), serving as an exceptional fundamental material. Quartz glass exhibits a series of outstanding physical and chemical properties, including:
Softening point: ~1730°C
Long-term use: Up to 1100°C
Short-term maximum: 1450°C
Nearly inert to all acids except (HF).
Acid resistance:
30× that of ceramics
150× that of stainless steel
Superior high-temperature chemical stability, unmatched by other engineering materials.
Extremely low thermal expansion coefficient.
Withstands rapid temperature changes (e.g., heating to 1100°C and quenching in room-temperature water without cracking).
Excellent light transmission across UV to infrared spectra.
Visible light transmittance: >93%
UV spectrum transmittance: Up to 80%+
Resistivity: 10,000× higher than ordinary glass.
Maintains superb insulation even at high temperatures.
Usage & Properties
Can be used up to 1450°C, available in transparent and opaque variants.
Advantages: High purity, excellent temperature resistance, large size with high precision, good thermal insulation, energy-saving, and stable quality.
Chemical Compatibility
Not compatible with HF .
At high temperatures, reacts easily with caustic alkalis and alkali metal carbonates.
Suitable Fluxes
Ideal for melting samples using KSO (potassium pyrosulfate) or KHSO (potassium bisulfate).
Can also be used with NaSO (sodium pyrosulfate, pre-dried at 212°C) for sample processing.
Quartz Crucible Usage & Maintenance
Primary chemical composition: Silicon dioxide (SiO).
Chemically inert to most acids (except HF), but reacts with caustic alkalis and alkali metal carbonates.
Excellent thermal stability-can be heated directly over a flame.
Fragile like glassware-requires careful handling.
Permissible fluxes:
KHSO (potassium bisulfate), NaSO (sodium pyrosulfate, pre-dried at 212°C), etc.
Maximum melting temperature: 800°C.
Handling Precautions
Brittle and fragile-handle with care to avoid breakage.
Cleaning
Can be cleaned with dilute inorganic acids (except HF).
Material Characteristics: Hard and brittle, resistant to thermal shock, and not easily deformed at high temperatures. Other physical properties are as follows:
Density: 3.2 g/cm³
Mohs Hardness: 9.5
Specific Heat: 0.17 kcal/kg·°C
Thermal Conductivity: 20 kcal/m·h·°C
Linear Expansion Coefficient: 5×10 (m/°C)
Silicon carbide rods exhibit excellent chemical stability and strong resistance to acids. However, alkaline substances can corrode them at high temperatures.
When used long-term above 1000°C, silicon carbide rods react with oxygen and water vapor as follows:
SiC + 2O → SiO + CO
SiC + 4HO → SiO + 4H + CO
These reactions gradually increase the SiO content in the rod, leading to higher resistance and aging.
Excessive water vapor accelerates SiC oxidation, and the produced H reacts with O to form HO again, creating a harmful cycle that shortens the rod's lifespan.
Nitrogen (N) prevents SiC oxidation below 1200°C but reacts with SiC above 1350°C, decomposing it.
Chlorine (Cl) completely decomposes SiC.
Fragility: Silicon carbide rods are hard and brittle-avoid strong impacts or vibrations during transport and handling.
Heating Zone Length: The heating section should match the furnace chamber's width. Extending it into the furnace wall may damage the wall.
Cold End Length: The cold end should equal the furnace wall thickness plus 50-150 mm of extension outside the wall for cooling and clamping.
Furnace Hole Diameter: Should be 1.4-1.6× the cold end's outer diameter. Tight holes or filler materials can restrict thermal expansion, causing breakage. Install rods to allow 360° rotation.
Spacing Requirements:
Distance to heated materials/furnace wall: ≥ 3× heating zone diameter.
Center-to-center spacing between rods: ≥ 4× heating zone diameter.
Electrical Connectior, increasing contact resistance and risk of cracking.
Resistance Matching: Before use, group rods with similar resistance values.
ns: Use aluminum braids or foil to connect cold ends to the main circuit. Ensure clamps are tight.
Furnace Preheating: Preheat new or long-idle furnaces using old rods or other heat sources.
Storage: Keep rods dry. Moisture degrades the cold end's aluminum laye
Voltage Control: Use a voltage regulator. Start at 50% of operating voltage, then gradually increase to avoid thermal shock.
Operating Limits:
Surface load and temperature must be optimized.
Max temperature: ≤1650°C.
Avoid chemical reactions in corrosive gas environments.
Replacement: Replace rods with those of similar resistance or replace the entire set. Partially used rods can be reused later if resistance is suitable.
Avoid Molten Metal: Contact with molten metal causes breakage.
Avoid Alkalis: Alkali metals and oxides corrode the rods.
Regular Checks: Monitor amperage, voltage, and temperature. Inspect for:
Loose/oxidized clamps,
Rod fractures,
Uneven heating (red-hot zones).
| Property | Value |
|---|---|
| Bulk Density | 5.5 g/cm³ |
| Flexural Strength | 15-25 kg/cm² |
| Vickers Hardness | (HV) 570 kg/mm² |
| Porosity | 7.4% |
| Water Absorption | 1.2% |
| Thermal Elongation | 4% |
In high-temperature oxidizing atmospheres, silicon molybdenum rods form a protective quartz (SiO) layer on the surface that prevents further oxidation. When the element temperature exceeds 1700°C, this quartz layer melts. If continued use occurs in oxidizing atmospheres, the protective quartz layer regenerates.
Important Note: Silicon molybdenum rods should not be used long-term in the 400-700°C range, as low-temperature oxidation will cause the element to deteriorate into powder form.
| Atmosphere | Continuous Use Temp. | Short-term Max Temp. |
|---|---|---|
| NO, CO, O, Air | 1700°C | 1800°C |
| He, Ar, Ne | 1650°C | 1750°C |
| SO | 1600°C | 1700°C |
| CO, N | 1500°C | 1600°C |
| Moist H | 1400°C | 1500°C |
| Dry H | 1350°C | 1450°C |
Silicon molybdenum (Si-Mo) rods exhibit slight softening at high temperatures (above 1500°C) but become hard and brittle at low temperatures. To minimize thermal stress and accommodate thermal expansion/contraction, a free-hanging vertical installation is recommended. This method also facilitates hot replacement of rods without waiting for furnace cooling.
Furnace Lining Material
Use corundum bricks with FeO content <1%. Higher FeO reacts with the protective SiO layer, forming low-melting silicates that accelerate rod degradation.
Cold-End Sealing
Hot gas leakage from cold ends increases heat loss and may damage conductive clamps/leads. Asbestos clamps are preferred for insulation.
Handling Fragility
Si-Mo rods are brittle with low flexural strength. Avoid impacts during installation.
Secure asbestos/ceramic clamps before connecting conductive straps. Do not overtighten.
Mounting with Insulating Bricks
Use foamed corundum split bricks to house rods, minimizing mechanical stress during installation/removal.
Furnace Roof Installation
Insert rod-mounted bricks into pre-cut furnace roof slots. Extend bricks beyond the roof surface for easier disassembly.
Conductive Strap Connection
Connect straps to pre-installed brackets. Avoid tension or unnatural bends to prevent stress.
Anti-Sagging Measure
Apply refractory mortar (water glass-based) to joints, fixing asbestos clamps firmly to counter thermal expansion-induced drooping.
Positioning Clearances
Heating zone taper: Maintain 25-30 mm from furnace walls.
Cold ends: Extend 75 mm above the furnace roof.
Lower heating end: Keep ≥50 mm from the furnace floor.
Spacing Between Rods
Ensure center-to-center distance ≥ rod spacing specifications.
Gravity Balance
Balance weight distribution at both cold ends and wiring parts to prevent bending of the heating section.
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