ASTM D6200 Determination of Cooling Characteristics of Quench Oils
ASTM D6200 Standard Test Method for Determination of Cooling Characteristics of Quench Oils by Cooling Curve Analysis
9. Cleaning and Conditioning
9.1 Cleaning Used Probes - Wipe probe with a lintless cloth or absorbent paper after removal from the oil and prior to returning to the furnace. (Warning - see Note 4) A cleaning solvent may be used, but care should be taken that the probe is below 50°C (122°F).
NOTE 4 - Warning: The probe shall always be considered hot, as temperature below visual hot temperatures can still cause injury to the skin (Warning - see Note 5).
NOTE 5 - Warning: Do not use cleaning solvent near the furnace opening especially with automated transfer mechanisms.
9.2 Conditioning New Probes - Condition the probe prior to its initial use with any quenchant by carrying out a minimum of six trial quenches, or a greater number if required to achieve consistency, using a general purpose hydrocarbon oil. Consistency shall mean the last two tests shall have maximum cooling rates within 62 % in temperature and cooling rate. Clean the probe assembly between quenches as specified in 9.1. Quench the probe in the reference quenching fluid and check according to 12.3. If the probe does not meet the requirements of 12.3, recondition according to 9.3 and then recalibrate again according to 12.3. Do not use probes that do not meet these requirements.
9.3 Probe Reconditioning - The probe shall be reconditioned when the probe calibration according to 12.3 does not meet the calibration limits, +/-3 % at the maximum cooling rate, of the reference fluid. Recondition the probe by cleaning with emery paper. Although coarser 320-grit paper may be used for initial cleaning, the final finish shall be provided using 600-grit emery paper. Following this surface cleaning procedure, the probe shall be quenched until repeatable cooling curve results of a reference oil are obtained.
An alternative is to recondition the probe after every run. Before testing a set of heat treating oils, the probe is quenched into the reference fluid after surface conditioning. If the maximum cooling rate of the reference fluid is within +/-3 % of the calibration limit, the probe may be used for further testing. When testing, the probe is cleaned prior to each run. After testing of the set of fluids is completed, the probe is quenched into the reference fluid to ensure that it is still within calibration.
10. Sampling
10.1 Sampling shall be in accordance with 7.5. Ensure the sample is representative of the oil being tested. A clean and dry sample container shall be used.
11. Preparation of Apparatus
11.1 Preheat furnace to 815 to 857°C, (1500 to 1575°F).
11.2 Connect a dry, conditioned, calibrated probe to the transfer mechanism according to equipment manufacturer's instructions.
11.3 Heat fluid to the desired temperature, if production testing is being performed or to 40 +/- 2°C (104 +/- 3.6°F) if the reference quenching fluid is being tested. Continuously agitate the test sample when heating and remove stirring mechanism prior to start of test.
12. Calibration and Standardization
12.1 Probe:
12.1.1 Check the accuracy of the probe thermocouple by attaching a previously calibrated thermocouple to the outer surface of the probe. Locate the tip of the calibrated thermocouple 30 mm (1.181 in.) from the end of the probe. Heat the probe and calibrated thermocouple to the selected furnace temperature of 845 to 855°C, (1553 to 1571°F) and allow to equalize. Compare the outputs of both the furnace and probe thermocouples by any calibrated temperature measuring device capable of required accuracy as described in Specifications E 220 and E 230.
12.1.2 Frequency of Probe Calibration - Calibrate the probe against a reference quenching fluid before each set of test runs.
12.2 Equipment Calibration - Calibrate desired recording mechanism as described in Annex A1.
12.3 Total System Calibration - Calibrate the system with a reference quenching fluid (see 8.1) following the procedure described in Section 13. Calibrate the system prior to using a new probe for testing and before and after each new set of test runs. The limits of the results obtained on the reference fluid will be established for each reference fluid prior to use as described in 8.1. The limits shall include, as a minimum, the following values: maximum cooling rate (°C/s, °F/s), the temperature at the maximum cooling rate (°C, °F), cooling rate (°C/s, °F/s) at 300°C (572°F), and the time in seconds from immersion to three different temperatures such as: (a) 600°C (1112°F), (b) 400°C (752°F), and (c) 200°C (392°F). If the limits are greater than +/-3 % of those previously established for the reference fluid, the probe must be reconditioned (see 9.3).
