ASTM D6557 Standard Test Method for Evaluation of Rust Preventive Characteristics of Automotive Engine Oils
8. Preparation of Apparatus
8.1 Specimens:
8.1.1 Remove the appropriate number of specimens from vacuum-sealed packages into a 118 mL bottle (clear, medium-round with cap). Add sufficient heptane (see 7.1.3), approximately 59 mL, to cover specimens.
8.1.2 Cap the bottle loosely and place it in an ultrasonic cleaning bath. Sonicate for 30 min, and then decant the heptane.
8.1.3 Rinse two more times with heptane and follow with an acetone (see 7.1.2) rinse to ensure the specimens are free of contamination. Dry the specimens with nitrogen for (30 to 60) s.
NOTE 2 - The specimens can be prepared up to one week in advance and stored in heptane until needed for testing.
8.2 Test Tube Assembly, Tube Rack, and Shaker for Each Test Tube:
8.2.1 Cut 24 separate pieces of TFE-fluorocarbon FEP tubing, each piece to be 240 mm long.
8.2.1.1 Use compressed air (for technical use only), 345 kPa minimum, to remove most of the water/oil emulsion that can be trapped inside the short lengths of capillary tubing. Clean the tubing with heptane (see 7.1.3), followed by acetone (see 7.1.2), and dry with compressed air.
8.2.2 Check the flangeless fitting for the TFE-fluorocarbon tubing (O.D. 1.6 mm) for deterioration, and replace as necessary.
8.2.3 Remove and discard the plunger from a new 20 mL disposable plastic syringe (Luer-Lok), and securely fasten the syringe barrel to the short capillary tubing, using couplings, 1/4 -28 thread, and female Luer CTFE fittings, 1/4 -28 thread, and with a 1.5 mm bore.
8.2.3.1 Label the syringes (test tubes) from 1 to 24.
8.2.4 Place the assembled test tube in the tube rack with the capillary tubing facing upward in the adjacent small hole.
8.2.4.1 The test tube assembly rack is a specially designed aluminum fabrication. It holds 24 test tubes with easy snap-on lock, wing nuts, and hold-down bars (see Fig. 5).
8.2.5 Place one precleaned specimen into each test tube, using forceps that are 180 mm long, and have serrated tips to avoid contamination.
8.2.6 Insert 10 mL of test oil into each test tube, using a disposable syringe with a capacity of 10 mL.
8.2.7 Secure the test tubes to the tube holder with three hold-down bars and three wing nuts.
8.2.8 Fasten the test tube assembly rack to the shaker platform with four custom-made wing bolts.
8.3 Acid Delivery System:
8.3.1 Withdraw 6 mL of acid solution by hand from a wide-mouth beaker into an individual disposable plastic syringe (Luer-Lok) with a capacity of 5 mL.
8.3.1.1 Attach the syringe to an acid inlet port of one of the 24 three-way switching valves, with 1/4 -28 thread. (The other two ports are used for air inlet and mixed air/acid outlet.)
8.3.2 Turn the three-way valve to two-way open and eject, by hand, about 0.5 mL of acid solution into a waste beaker, while ensuring that no air bubbles remain in the syringe.
8.3.2.1 Place the syringe that now contains about 5.5 mL of acid solution on the holder of the multiple syringes pump.
8.3.3 Repeat the above procedure for the other 23 acid delivery syringes.
8.3.4 There are three multiple syringe pumps, and eight of the 5 mL syringes are attached to each of the pumps.
8.3.4.1 The pumps each have a ten-position rack and are required to satisfy a minimum flow rate range of 0.0001 µL/h to 220.82 mL/min. Required accuracy is +/- 1 %, and reproducibility is +/- 0.1 %.
8.3.5 Ensure that the syringe barrel flange and the plunger flange are firmly held by the six retaining clamps, which are 51 mm C-clamps that secure the ends of the hold-down bars of the multiple syringes pump.
8.3.5.1 Good alignment of all 24 acid delivery syringes against the retaining brackets is crucial to ensure repeatability. (See Fig. 3 for a photograph of the acid delivery system, and Fig. 4 for a schematic.)
8.3.6 Cut 24 pieces of TFE-fluorocarbon tubing; each piece to be (1295 +/- 25.4) mm in length.
8.3.6.1 Attach each of these tubes to the mixed air/acid outlet ports of the three-way switching valves.
8.4 Air Delivery System:
8.4.1 Clean, dry air, compressed to at least 345 kPa, is required.
8.4.2 A single stage, high-purity stainless steel pressure regulator is the first in the line; this is equipped with a (0 to 1100) kPa maximum pressure gauge.
8.4.3 Two compressed air filters capable of removing particles and mists are required, and are next in the line.
8.4.3.1 The first filter in the line is an A912-DX type, followed by an A912-BX type. These have polycarbonate bowls and should be equipped with aluminum shields. They have 1/4 -in. NPT (F) ports and will withstand 1034 kPa pressure maximum.
NOTE 3 - Alternatively, zero grade air cylinders can be used and will not require the extensive filtering outlined above.
8.4.4 A Drierite gas purifier, with a maximum working pressure of 690 kPa, is next in the line.
8.4.4.1 The first portion of the purifier (about 75 %) contains a molecular sieve, activated, Type 4A, 8 to 12 mesh.
8.4.4.2 The remaining portion of the purifier (about 25 %) contains Drierite absorbent, color indicating type, 8 mesh.
8.4.5 Next in the line is the downstream regulator, single stage high-purity stainless steel, that is equipped with a (0 to 415) kPa pressure gauge.
8.4.6 The next installation is a relief valve, in-line adjustable CA series, (345 to 1035) kPa cracking pressure range, set at 550 kPa (optional to control over pressure).
8.4.7 Lastly, install an air delivery manifold with 25 port outlets and 6.4 mm tube fittings. (See Figs. 1 and 2 for a photograph and schematic of the air system.)
8.4.8 Cut 25 pieces of the TFE-fluorocarbon tubing, each piece to be approximately 183 m in length.
8.4.8.1 These long tubes provide the necessary backpressure to allow good control of the very low airflow rate. The individual lengths may need to be adjusted slightly to ensure the same flow rates at a given delivery pressure. An equivalent multiport flow control system can be used.
8.4.8.2 Connect these tubes to the air delivery manifold.
(1) Connect one of these tubes to a calibrated flowmeter, capable of measuring up to 200 mL/min, and with a resolution of 0.1 mL/min (see Annex A1).
(2) Connect the other 24 tubes to the air inlet ports on the 24 three-way valves.
