ASTM D4636 Standard Test Method for Corrosiveness and Oxidation Stability of Hydraulic Oils, Aircraft Turbine Engine Lubricants, and Other Highly Refined Oils
10. Procedure
10.1 Standard Test Procedure:
10.1.1 Determine acid number of the test oil in accordance with Test Method D664.
10.1.2 Determine the kinematic viscosity of the test oil at 40°C and 100°C in accordance with Test Method D445.
10.1.3 Turn on heating control to bring temperature of heating medium to a temperature that will maintain the oil sample within +/-0.5°C (+/-1°F) of the specified temperature (Warning - There are exposed hot surfaces on apparatus. Avoid contact with exposed skin by use of protective equipment as required.).
10.1.4 When assembling the clean sample tubes and accessories, use only the actual test oil to lubricate joints of each assembly.
10.1.5 Slide the prepared metal washer specimens onto the air tube in the following order: aluminum (bottom), silver, bronze, low carbon steel, M50 steel, magnesium, and titanium (top). Use one glass spacer only between each metal specimen.
10.1.6 Place the air tube with specimens into the sample tube.
10.1.7 Position the sample tube head on the sample tube with the air tube protruding through the center glass joint.
10.1.8 Seat the TFE-fluorocarbon adapter on the air tube with the air tube resting on the bottom of the sample tube and tighten the gland.
10.1.9 Insert the 70-cm (27.6-in.) long-sheathed thermocouple making sure the closed end of the sheath is at least 10 mm from the sample tube wall.
10.1.10 Weigh the entire apparatus to the nearest 0.1 g.
10.1.11 Add 200 +/- 2 mL of test oil in accordance with 8.3 to the sample tube, reweigh entire assembly to the nearest 0.1 g, and determine the mass of the sample added.
10.1.12 Position the sample tube in the heat medium at test temperature to an immersion depth of 250 +/- 20 mm.
10.1.13 Insert the condenser and start water flow. Maintain water temperature at 18 +/- 3°C (65 +/- 5°F).
10.1.14 Connect the thermocouple.
10.1.15 After the sample tube has been in a liquid heating medium for 15 min, connect the dry air supply, adjust the air flow rate to 10 +/- 1 L/h, and begin the test time. For an aluminum block heating medium without liquid heat transfer medium, allow 1 h between insertion of sample tube into heater and start of air flow and timing.
10.1.16 Adjust heat control to ensure oil sample temperature is held within +/-0.5°C (+/-1°F) of required value. Verify sample temperature and air flow occasionally during test specifically just prior to each sampling time.
10.1.17 Sample the test oil (10-mL sample) at the following times: 16, 24, 40, 48, 64, 72, 88, and 96 h.
10.1.18 Preweigh the sample flask, stopper, and tube to the nearest 0.1 g so that an accurate mass of sample withdrawn can be determined.
10.1.19 Perform sampling by withdrawing the thermocouple sheath and inserting the 4-mm tube attached to the sampling flask. Using a rubber bulb or similar source of slight suction on the flask tube, draw the required sample to a premarked level in the sampling flask. Do not interrupt air flow nor remove the same tube from the heat during sampling.
10.1.20 Determine and record mass of each sample removed during test.
10.1.21 Determine acid number in accordance with Test Method D664 of all samples.
NOTE 6 - If acid number is not determined on the same day of sampling, samples should be refrigerated up to a maximum of 1 week prior to determination.
10.1.22 Determine viscosity in accordance with Test Method D445 at 40°C on all samples and viscosity at 100°C on original and final sample only.
NOTE 7 - Due to the reduced sample volume availability, viscosity measurement is made using the semimicro viscometers listed in Test Method D445. In addition, it may be necessary to determine acid number using a titration sample size less than that required by Test Method D664. The semimicro Test Method D3339 may be used to determine acid number.
10.1.23 Shutdown:
10.1.23.1 After the final sample is taken, shut off the air flow and condenser water, remove the condenser, and disconnect the thermocouple. Note the presence of liquid or solid material on the inside of the condenser.
10.1.23.2 Remove the sample tube from the heat medium, wipe tube exterior, allow to cool, and, if necessary, clean the tube exterior by rinsing with n-heptane or toluene. Weigh the assembly to the nearest 0.1 g.
10.1.23.3 Remove the air tube, polytetrafluoroethylene adapter, and sample tube head.
10.1.23.4 Remove the air tube with metal specimens, rinse with n-heptane or toluene, and slide the specimens off the air tube carefully into a clean absorptive surface. Keep the specimens in order for identification, but if processing of specimens is to be delayed, store them under n-heptane.
10.1.23.5 Drain the test oil completely from the sample tube into a clean glass container and hold for sludge determination. Note the appearance of any deposits on the inside of the sample tube.
10.1.24 Sludge Determination - Take a representative portion, after well stirring the final test oil, and centrifuge a 25-mL aliquot for 1 h at a relative centrifugal force of 840 +/- 40 in accordance with Test Method D91. Record the volume of solid or semisolid sludge obtained to the nearest 0.1 mL.
10.1.25 Metal Specimens, Post-Test Processing:
10.1.25.1 Rinse the metal specimens individually with n-heptane or toluene. Wipe each metal specimen with n-heptane or toluene-wetted cotton pads until a fresh pad remains clean.
10.1.25.2 Rinse each specimen with clean n-heptane, then acetone, then air dry and weigh to the nearest 0.1 mg.
10.1.25.3 If there are visible carbon deposits remaining on the specimens, clean as indicated in Appendix X2.
10.2 Alternative Procedure 1:
10.2.1 Perform the standard test as in 10.1 except as follows:
10.2.2 Use 165 +/- 2 mL of the sample at the start.
10.2.3 Do no periodic sampling. Sample the oils only at completion of the test time. No sample tube head is needed. Use the condenser described in 5.1.5.
10.3 Alternative Procedure 2:
10.3.1 Perform the standard test as in 10.1 except as follows:
10.3.2 Use 100 +/- 1 mL of the sample at the start.
10.3.3 Use 5 +/- 0.5-L/h air flow rate.
10.3.4 Do no periodic sampling. Sample the oil only at completion of the test time. No sample tube head is needed. Use the condenser described in 5.1.4 or 5.1.5.
10.3.5 Instead of washer-shaped metal specimens, use square metal specimens as defined in 6.3.2.
10.3.5.1 Arrange metal squares in a wooden assembly fixture in the pattern shown in Fig. 6, making certain that the magnesium and copper squares do not touch each other.
10.3.5.2 Clean the cord or wire by boiling in distilled water for 10 min and allow to air dry.
10.3.5.3 Using forceps or cotton (linen) gloves, or both, to handle the cord or wire, tie the squares together as shown in Fig. 6. Due to potential contamination, use of latex gloves is not recommended.
10.3.5.4 Insert the tied metal squares into the sample tube, positioning the squares vertically (so that the air tube can be inserted to touch the bottom of the tube).
10.3.5.5 When the oil specification requires only two metal specimen squares, place the squares in the sample tube in such a manner as to form a "V" in the bottom of the tube. No tying is necessary.
10.3.6 Upon completion of 10.1.23.3, prepare square metal specimens for examination as follows:
10.3.6.1 Use forceps to withdraw the metal squares from the test tube and remove the cords holding them together.
10.3.6.2 Using forceps, wash each square individually in n-heptane or toluene.
10.3.6.3 Repeat the washing, using fresh n-heptane or toluene and scrubbing the squares with the short-bristled brush until the solvent shows no additional discoloration, and allow the squares to dry. Alternatively, scrubbing with n-heptane-moistened 100 % cotton balls until they look clean has also been found acceptable.
10.3.6.4 Weigh each square to the nearest 0.1 mg. Measure the face dimensions of each panel to the nearest 0.1 cm.
11. Calculation
11.1 Calculate the oil mass loss as follows:
where:
W1 = mass of tube assembly,
W2 = mass of tube assembly plus sample at start,
W3 = mass of tube assembly plus sample at end of test, and
W4 = accumulated mass of samples removed during test.
11.2 Calculate the viscosity change as follows:
where:
V1 = viscosity before test, cSt (mm2/s), and
V2 = viscosity after test, cSt (mm2/s).
11.3 Calculate the neutralization number change as follows:
Acid number change, mg KOH/g = T2 - T1
where:
T1 = acid number before test, mg KOH/g, and
T2 = acid number after test, mg KOH/g.
11.4 Calculate the metal specimen mass change as follows:
Metal mass change, mg/cm2 = M2 - M1/A
where:
M1 = mass of specimen before test, mg,
M2 = mass of specimen after test, mg, and
A= area of metal specimen based on the face surface without consideration for the edge area, cm2.
11.4.1 For washer specimens:
where:
D1 = initial diameter of hole, nearest 0.1 cm, and
D2 = initial diameter of specimen, nearest 0.1 cm.
11.4.2 For square specimens:
A = 2 LW
where L and W are the two face dimensions, nearest 0.1 cm.