Critical Temperature and Continuous Cooling Curve Analyzer: Principles, Specifications, and Operating Guide

Overview This transformation analyzer uses the dilatometry method to determine thermal expansion coefficients, critical (softening) temperatures, and phase transformations of metals, ceramics, refractories, and other solids. It is especially suitable for corundum (alumina), investment casting shells and cores, and other inorganic materials, supporting performance testing and research in industrial QA/QC and academic labs. Technical Specifications - Maximum furnace temperature: 1000 ℃; maximum temperature for cooling-curve measurements: 1000 ℃ - Heating rate: up to 5 ℃/min with manual or automatic control - Power supply: 220 V ±10%, 50 Hz - Maximum power consumption: ≤ 3.5 kW - Expansion measurement range and error: 0–5 mm, ±0.1% - Expansion indication: digital display - Expansion resolution: 1 µm System Composition and Working Principle The instrument consists of a displacement sensor assembly, a tube resistance furnace, a movable carriage, a base, and an electrical control cabinet. As the furnace heats, the specimen in the hot zone expands. A push rod in contact with the specimen transfers this displacement to an inductive displacement sensor. The indicated expansion equals specimen expansion if system thermal deformation is neglected; therefore, a temperature-dependent compensation Kt must be added in calculations to obtain the specimen’s true expansion. - Displacement assembly: One end of the push rod contacts the specimen; the other end connects to the sensor core. The opposite end of the specimen is fixed against a stop, so specimen expansion drives a corresponding sensor core displacement. The push rod slides within guide bushings. - Furnace: A tube resistance furnace using high-temperature resistance wire, SiC, or Mo heating elements. Water-cooled end caps protect sealing materials. Vertical and horizontal positioning adjustments are provided. - Motion: The specimen remains fixed within a specimen tube; the furnace moves on a carriage along base rails to insert or remove the hot zone, minimizing vibration effects on the specimen. - Electrical: Furnace temperature is measured with appropriate thermocouples and controlled by a temperature controller. Operation 1) Mechanical setup: Level the base. Align the furnace so the tube and specimen tube move without rubbing. Move slowly to prevent damage. Fix the furnace to the carriage and set a hard stop so that, when the carriage touches the stop, the distance from the furnace end face to the guide sleeve face is 30 mm. This positions the specimen within the furnace uniform temperature zone. 2) Lubrication: Add low-viscosity oil between guide bushings via two small holes at the push-rod end to ensure smooth following. 3) Zeroing: After the push rod contacts the specimen, the expansion display may not read zero. Use the fine adjustment to set the display to zero. 4) Electrical check: Verify all connections and instrument status. 5) Control cabinet: - Wire power, furnace, and thermocouple per the electrical schematic. - For heating control with the AI810 controller, use manual or automatic modes. For slower ramps, limit output power to about 30 to reduce overshoot; if ramp tracking lags, increase output appropriately. - Specimen expansion is indicated via the inductive displacement sensor on the display (or a micrometer dial). Measurement range is factory set and typically needs no user adjustment. - After use, return all switches to their original positions to avoid misoperation on next startup. Thermal Expansion Calculations After heating to temperature t (℃), compute linear expansion percentage δ and average linear expansion coefficient α: - δ = (ΔLt − Kt) / L × 100% - α = (ΔLt − Kt) / [L × (t − t0)] Where L is the specimen length at room temperature (mm); ΔLt is the measured linear change at t (mm) from the instrument (positive for expansion, negative for contraction); Kt is the system compensation at t (mm); t is the specimen temperature (℃); t0 is room temperature (℃). Determining Compensation Kt Users must pre-determine Kt. Use a quartz reference below 1000 ℃ and a high-purity alumina (corundum) reference above 1000 ℃. The instrument reading includes combined expansion of the reference, specimen tube, and push rod. Kt should represent only the specimen tube and push rod expansion at each temperature. Subtract the reference’s known expansion from the measured total to obtain Kt. If the reference expansion coefficient αref is known: Kt = ΔLt_ref − αref × Lref × (t − t0) Reference values: Quartz α ≈ 0.55 × 10−6/℃ (average). Alumina coefficients are provided in the appendix table. Example (Kt at 1400 ℃): Using an alumina reference with Lref = 50.1 mm, t0 = 20 ℃, measured ΔL1400_ref = 0.11 mm, and αref(1400 ℃) = 8.623 × 10−6/℃, K1400 = 0.11 − 8.623 × 10−6 × 50.1 × (1400 − 20) = −0.408 mm. Adjustment and Calibration - Expansion display: Use the AI501 digital indicator per its manual to set parameters and range. If the display is not at 0, adjust the zero knob to return to zero. Perform span calibration as required. - Heating program parameters: Factory-set and locked. If changes are necessary, refer to the AI810P controller manual. Parameters can be re-validated periodically. Specimen Standards and Preparation - Dimensions: Cylinders Φ(6–10) × 50 mm; Prisms (6–10) × (6–10) × 50 mm. - Shell materials: Press wax patterns, coat per shell process, dewax, then bake at 350–400 ℃ for 1 hour to remove residue; cool in furnace. If subsequent firing is planned, baking may be skipped. - Ceramic cores: Press cores and fire as follows: 300 ℃ for 2 h, 500 ℃ for 1 h, 900 ℃ for 1 h, then to 1150 ℃ for 2 h; cool in furnace. - Users may prepare specimens to meet their process requirements. Installation and Maintenance - Install on a stable foundation away from vibration. The main machine table height should be below 800 mm. - Provide argon and cooling water as required. Instruments rated for ≤1000 ℃ and applications not requiring protection may omit argon. - Clean the instrument promptly after tests. Alumina Reference Coefficients (Excerpt) High-purity alumina average linear expansion coefficients α (1/℃) at select temperatures: 20 ℃: 9.12 × 10−6; 100 ℃: 9.18 × 10−6; 200 ℃: 7.28 × 10−6; 300 ℃: 7.92 × 10−6; 400 ℃: 7.88 × 10−6; 500 ℃: 7.042 × 10−6; 600 ℃: 6.742 × 10−6; 700 ℃: 6.72 × 10−6; 800 ℃: 6.64 × 10−6; 900 ℃: 6.546 × 10−6; 1000 ℃: 6.508 × 10−6; 1100 ℃: 7.28 × 10−6; 1200 ℃: 7.352 × 10−6; 1300 ℃: 7.537 × 10−6; 1400 ℃: 7.607 × 10−6; 1500 ℃: 7.828 × 10−6; 1600 ℃: 8.253 × 10−6; 1700 ℃: 8.325 × 10−6. Software Installation and Key Functions - Installation: Insert the setup CD, run the installer (.EXE), and follow prompts. A desktop shortcut is created. Launch via the shortcut or Start menu. - Core modules: 1) System compensation test: Calibrate Kt by running a reference specimen (50 mm). End the run at 1000 ℃ or 1600 ℃ depending on range/reference. View compensation values by temperature. 2) Critical temperature by dilatometry: Enter specimen length, start the test, and stop at the target terminal temperature. Output results and review displacement–temperature curves. Save data before exit. 3) Continuous cooling transformation (CCT) by dilatometry: Enter specimen length, run the test, then output results, view curves, query detailed data, and generate CCT reports. Save data before exit. 4) Instrument parameter settings: Advanced function to edit controller internal parameters that affect temperature control quality. Use only after reading the controller manual; factory defaults are pre-set. 5) Results analysis: View, print, and query current or historical results in tables and curves. Adjust plotting “temperature interval” to refine curves, refresh, and print after filling variable fields (e.g., organization, ID, model, material, operator). - Data backup: After each test, use “Save test data” to store results. Back up the application database (.MDB) to another drive. Exit the software via the normal “Exit” workflow. Instrument Operation Essentials - Power-up: After cabling, close the main breaker and toggle the instrument power. Indicators light, and self-check runs. The temperature controller PV shows ambient temperature, SV shows setpoint; the displacement display shows current displacement. With no specimen installed, PV may show a fluctuating ORAL indication. - Heating program example: Program multi-step ramps on the AI810 series controller. Example: from room temperature to 300 ℃, hold 10 min, then to 400 ℃ and stop. For single-step ramps, omit the hold segment. Refer to the controller manual for parameter definitions and safe editing. - Loading specimens: Open the furnace to expose the specimen stage. Place a cylinder 50 mm long and 6–8 mm diameter on the stage, ensuring good contact with the push rod. Check the displacement reading; if it deviates significantly from about 2000 counts, remove the stage sleeve and adjust the zero screw until stable at ~2000, then re-install the sleeve. Move the furnace so the specimen is centered in the hot zone. - Cooling water and argon: If heating above 1000 ℃ (e.g., up to 1600 ℃ during compensation tests), connect circulating cooling water and argon protection as specified. Readiness Checklist Parameters are correctly set and stable; specimen is loaded; furnace is in position; the green “working” indicator is on; and communication between the instrument and the host computer is reliable. Common Issues and Precautions - Prepare specimens to standard dimensions: Cylinders Φ(6–8) mm × 50 mm, or prisms (6–8) mm × (6–8) mm × 50 mm. - Ensure full readiness before starting: furnace in place, specimen installed, comms cables connected, power on. If furnace temperatures will exceed 1400 ℃, connect cooling water. - If the software reports “port already open,” the previous session may not have exited normally. Terminate the process via Task Manager and relaunch. - Do not open the furnace immediately after tests. To avoid thermal shock damage to the specimen stage, open only when specimen temperature is below 100 ℃. If already opened hot, do not reinsert. - Handle specimens gently to protect sensor accuracy. Move the furnace slowly to avoid contact between the stage and furnace. Bill of Supply (Summary) - Mechanical main unit: 1 set - Control cabinet: 1 set - Accessories: Quartz reference Φ8 × 50 (1 pc); specimen stop plates (2 pcs); specimen shims (2 pcs) - Technical documents: Product manual (1), AI810P controller manual (1), Certificate of conformity (1) - For work above 1000 ℃, include one alumina reference; rubber tubing may be cut into six segments as needed. This guide consolidates principles, specifications, setup, operation, calculation methods, software workflow, and best practices for reliable determination of critical temperatures and CCT behavior via dilatometry.

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