ASTM D7097 Standard Test Method for Determination of Moderately High Temperature Piston Deposits by Thermo-Oxidation Engine Oil Simulation Test - TEOST MHT
8. Programming the Apparatus
8.1 PID (proportional, integral, and derivative) Settings for Temperature Control - In order for the thermocouple sensitivity and response values (PID settings) to have the minimum excursion from the temperature value desired during operation set them to the following settings: Pb 160 Re: 1.0 Ra 0.1. See Instrument Manual for more details on the adjustment technique.

8.2 Temperature Controller Setting - Set the temperature control program to maintain 285°C for 24-h according to the instructions in the Instrument Manual.

8.3 If using a strip chart recorder, turn on the strip chart, set the chart speed to 10 mm/h, but do not lower the pen(s) or turn on the chart drive at this time.

8.4 If using other means of continuously recording temperatures, prepare these for receiving information.

9. Calibration and Standardization
9.1 Calibration of Air Flow Rate (alternative procedures, follow 9.1.1 and 9.1.2):
9.1.1 Calibration of Air Flow Rate Using a Mass Flow Controller:
9.1.1.1 Use the bubble gauge or other primary calibration device before each test to check or calibrate a mass flow controller.
(1) The TEOST MHT protocol is sensitive to flow rate, therefore primary calibration of mass flow meters or other forms of air flow control such as analog or digital flow meters is desired to ensure proper flow rate.

NOTE 2 - Models of some mass flow meters may permit adjustment of the readout to the calibration value when the appropriate air flow is reached.

9.1.2 Calibration of Air Flow Rate Using an Air Flow Meter:
9.1.2.1 Use the bubble gauge or other primary calibration device before each test to calibrate analog or digital flow meters (see Note 3).

9.1.2.2 Set up the bubble gauge and flow meter equipped with a fine needle valve as shown schematically in Fig. 1a with a three-way stopcock or Fig. 1c with a ball valve.

NOTE 3 - A handheld flow meter may also be used.

9.1.2.3 Connect the dry air source to the flow meter and set the source's regulator to a pressure value no greater than allowed by the tolerances of the flow meter used.

9.1.2.4 Insert the end of the air inlet tube into the soft rubber tubing attached to the bubble gauge and check that the joint is leak tight with soap solution.

9.1.2.5 Adjust the flow meter rate and retest bubble rise rate to bring the flow rate to 10.0 +/- 0.2 mL/min.

9.2 Oil Pump Rate Calibration - Follow the technique in the manufacturer's Instrument Manual to set a test oil flow rate of 0.25 +/- 0.01 g/min.

9.3 Temperature Controller Setting - Follow the technique in the manufacturer's Instrument Manual to set a test temperature of 285°C on the temperature controller.

9.4 Calibration ofControl Thermocouple:
9.4.1 Calibrate the depositor rod temperature control thermocouple in a liquid or sand bath maintained at 285 +/- 50°C and, if necessary, adjust the temperature offset of the temperature controller to match the bath temperature for this thermocouple. In the absence of either a liquid, block or sand bath, boiling distilled water may be used to calibrate at 100°C. The temperature should be able to be calibrated within +/- 0.1°C.

9.4.2 Before each reuse of the thermocouple, clean any corrosion or other deposits from the thermocouple surface using a fine abrasive pad (500 grit or finer) or emery paper (800 grit). The resulting cleaned surface shall show bright metal, particularly in the temperature-sensitive area at the end of the thermocouple. Do not overclean the thermocouple surface or use coarse abrasives, as the thermocouple wall could be thinned and damaged.

9.5 Determination, Setting, and Use ofAppropriate Position for the Temperature Control Thermocouple - Follow the technique in the manufacturer's Instrument Manual to find the hottest point within the bore of the depositor rod.
9.5.1 Insert the thermocouple gently (see Note 5) into the bore of the depositor rod to bring the collar into contact with the emergent top of the rod when it is in position within the depositor rod casing assembly positioned in the busbars.

NOTE 4 - The locking collar may slip if the thermocouple is forced into the depositor rod thus resulting in a wrong position for the temperature sensing area of the thermocouple.

9.5.2 If desired, adjust the strip chart recorder or other temperature-recording device to record temperature sensed by the temperature control thermocouple.

NOTE 5 - Continuously record the temperature of the controlling thermocouple at maximum sensitivity setting to determine any aberration in temperature during a run that may be caused by temporary electrical failure or brownout of the local power supply.

9.6 Install the over-temperature thermocouple according to the manufacturer's Instrument Manual.

9.7 Standardize the TEOST MHT procedure using certified reference oils in accordance with Sections 10 and 15.

10. Instrument and Sample Preparation
10.1 Before testing unknown samples, confirm the functionality of the TEOST MHT instrument by testing one of the certified reference oils (see 7.6). Choosing one of the certified reference oils mentioned in 7.6, follow the directions in Section 10.

10.2 Make sure that the TEOST heat switch is in the off position to prevent any accidental startup of the test. Then turn on the main power switch and allow 30 min or more for the instrument electronics to warm up. Ensure that the pump switch is off.

10.3 Make sure that the thermocouples are clean (see 9.4.2).

10.4 Invert both the catalyst vial and the oil container at least three times to ensure homogeneity of both components prior to use.

10.5 Place a clean sample flask (see Fig. 2) on a precision balance and tare the balance (to bring the indicated mass of the container to zero).

10.6 Using a microlitre syringe that uses either a glass or PTFE plunger (do not use rubber plunger), add the precalculated mass of catalyst required to make 8.5 g of sample-catalyst mixture based on the certified value of the catalyst and record the mass to the nearest 0.0001 g. The range for the mass of catalyst to be added shall be +/- 0.0003 g of the mass required.

NOTE 6 - The mass of oil required for the appropriate mixture of catalyst-to-oil ratio is stated on the label of the vial of certified catalyst.

10.7 Again, tare the balance and add the required mass of oil to the sample flask to make the sample-catalyst mixture total 8.5 +/- 0.05 g. The range for the mass of the oil to be added shall be +/- 0.01 g of the mass required to obtain the catalyst/oil ratio shown on the catalyst bottle. If more oil than required is added, make a new sample.

NOTE 7 - An electronic file containing a generic calculation table to determine the appropriate catalyst/sample weights can be obtained from the ASTM Test Monitoring Center.

10.8 Add a TFE-fluorocarbon-coated magnetic stirring bar to the sample flask, and place the flask on the magnetic stirrer incorporated on the platform of the TEOST (or other appropriate magnetic stirrer) and stir for 30 to 60 min. Do not heat the mixture. Do not stir the mixture too vigorously, and particularly avoid creating a large vortex where the mixture may splash out. Be sure to load the sample and start the test within 20 min of the completion of the mixing process.

NOTE 8 - For planning purposes, the hardware setup and the finish of sample mixing can be arranged to coincide, so the test can be started in a shorter preparation time.

11. Hardware Setup
11.1 Install new end-cap O-rings in both end-caps.

NOTE 9 - At this point, any interest of the operator in determining the mass of volatiles, recovered end-of-test oil, and mantle deposits will require weighing and recording the initial mass of the volatiles collection vial, the recovered oil vial, and the cleaned and dried mantle.

11.2 Using a gentle twisting motion, insert the upper end of the glass mantle squarely into the upper end-cap. Avoid chipping the mantle glass, and make sure that the hole or window (see Fig. 5) in the upper mantle faces the corresponding oil feed tube opening in the upper end-cap. Set this assembly aside in a safe place until required to complete the depositor rod casing assembly.

11.3 Cleaning and Weighing a Depositor Rod; Use of Weighing Boat:
11.3.1 Select a weighing boat (see Fig. 3) for the depositor rod and obtain the boat's mass to +/- 0.0001 g. Keep covered when not in use to avoid contamination from particles falling from the air.

NOTE 10 - If fluctuations are seen on the balance, momentarily touch the boat to a grounding pad to eliminate static.

11.3.2 Once the depositor rod preparation has begun, handle the rod with care and do not set the rod down except on the weighing boat. Keep covered when not in use.

11.3.3 When handling and cleaning the wire-wound depositor rod, be careful not to distort the length and pitch of the wire coils.

NOTE 11 - The wire coils on the depositor rod are preset to a specified pitch by the manufacturer and are adjusted to a tension to just be able to slide up and down on the machined narrower section of the rod around which the wire coil is wrapped without being too loose.

11.3.4 Use hydrocarbon solvent, to rinse both the outside and inside of the rod. Use thin, solvent-resistant laboratory gloves or finger cots when handling the rod to keep natural skin oils from affecting the mass of the rod.

NOTE 12 - If the cots or gloves are chemically attacked by the hydrocarbon solvent, a film or residue will be left on the surface of the gloves.

11.3.5 Using a pipe cleaner soaked in acetone, swab the inside bore of the depositor rod by pushing the pipe-cleaner all the way through the bore in one direction, then repeat the cleaning of the inside bore in the opposite direction with a fresh pipe cleaner soaked in acetone. Exercise particular care in handling and cleaning the depositor rod during this stage, avoiding any distortion of the wire coil.

11.3.6 Rinse the outside and the inside bore of the depositor rod with acetone using appropriate solvent-resistant gloves.

11.3.7 Vacuum-dry or blow clean, dry air on the inside of the depositor rod while holding it between the thumb and index fingers. Dry the outside of the rod only by exposure to ambient air.

11.3.8 Set the depositor rod down in the pre-weighed weighing boat from 11.3.1 (see Fig. 3). Weigh the depositor rod and boat to a constant mass within +/- 0.0001 g. Record this value as the initial depositor rod and boat mass. Subtract the boat mass from the total mass for later determination of the depositor rod mass carrying deposits from the test.

11.3.9 After the boat and depositor rod masses have been obtained, put the covered boat aside for later use when the depositor rod has completed its exposure to deposits for 24-h.

11.4 Completing the Depositor Rod Casing Assembly (see Figs. 4-6):
11.4.1 Pick up the pre-assembled mantle and upper end-cap (see 11.2) and carefully slide the depositor rod up through the bottom of the glass mantle/upper-end-cap assembly until the end of the depositor rod emerges through the threaded stem of the upper end-cap.

11.4.2 Place two new small O-rings on the emergent depositor rod.

11.4.3 Place one of the ceramic isolators over the top of the depositor rod with the wider diameter of the isolator facing the O-rings. Pushing with the ceramic isolator, bring the O-rings in contact with the top of the threaded stem of the end-cap as shown in Fig. 4.

11.4.4 Place an end-cap nut on the emergent depositor rod and insert the narrower diameter of the isolator through the clearance hole in the nut. Finger-tighten the nut onto the threaded end-cap stem to compress the two-stacked O-rings around the depositor rod thus sealing and insulating the depositor rod from the end-cap.

11.4.5 Make sure that the bottom of the depositor rod helical wire winding is resting on the bottom shoulder of the narrower midsection of the rod.

11.4.6 Insert the bottom end of the depositor rod through the top of the lower end-cap and continue by inserting the lower end of the mantle into upper end of the lower end-cap (see Figs. 4 and 5). Again, use a careful twisting motion so as not to stress or fracture the glass mantle.

11.4.7 Repeat the same process for the bottom of the depositor rod and lower end-cap to complete the depositor rod casing assembly as shown in Fig. 5 with the exception of the introduction of the oil feed tube.

11.4.8 Make sure that the top and bottom emergent ends of the depositor rod in the depositor rod casing assembly are about the same length. If necessary, loosen the end-cap nuts and move the depositor rod as necessary to ensure this equivalence.

11.5 Connecting the Depositor Casing Assembly to the Bus Bars:
11.5.1 Make sure that both the upper and lower faces of the busbar assemblies are free of oil or other material that might interfere with electrical continuity when the depositor rod is in place and the busbar caps are screwed in place. If necessary, use a paper towel and moisten and wipe the busbar contacting area with hydrocarbon solvent (see 7.4) or a varnish removing solvent, rinse with water, and allow to dry.

11.5.2 Insert the depositor rod assembly into the bus bar assembly and tighten as described in the operations manual.

11.5.3 Slide the over-temperature thermocouple up into the depositor rod until its collar touches either the bottom of the depositor rod or the lower busbar.

11.5.4 Before every test, check to ensure that the temperature control thermocouple's lock collar is tight and correctly positioned for the proper insertion depth. This depth was previously established in 9.5.

11.5.5 Place the temperature control thermocouple down the top center bore of the depositor rod to the lock collar. During insertion of the thermocouple in either the depositor rod or thermocouple depth gauge, be careful not to bend the thermocouple.

11.6 Connecting the Rigid Oil Feed Tube and the Flexible Oil Flow Tubing:
11.6.1 Connecting a New Oil Feed Tube (see Fig. 5) for First-time Use:
11.6.1.1 Ensure that the depositor rod casing assembly has been completed before proceeding. Then do a first setting of the ferrule according to 11.6.1.2 to 11.6.1.7.
(1) It is a preferred technique to install and hold the depositor rod casing assembly fixed in the busbars when setting the ferrule.

11.6.1.2 Place the two-piece ferrule in position to clamp the outer diameter of the oil feed tube by inserting its beveled tip first through the oil feed tube inlet nut and then the two-piece ferrule with the ferrule's conical end facing the beveled end of the oil feed tube.

11.6.1.3 Lightly push the oil feed tube carrying the two-piece ferrule into the interior matching tapered socket of the oil feed tube inlet stem of the upper end-cap (see Fig. 7). Bring the beveled tip of the oil feed tube into light contact with the helically wound wire on the depositor rod (see Fig. 5) as viewed up through the mantle.

11.6.1.4 Using the oil feed tube inlet nut, push the two-part ferrule into the feed tube inlet stem and screw the nut onto the stem until resistance of the ferrule is felt.

11.6.1.5 Ensure that the beveled end of the oil feed tube is still in light contact with the depositor rod wire and that the opposite end of the oil feed tube is pointed downward when the depositor rod casing assembly is held upright (see Fig. 5), then tighten the nut about 1/2 -turn to set the conical ferrule onto the rigid tubing.

11.6.1.6 Test the effectiveness of the ferrule's contact with the oil feed tube by lightly trying to move the oil feed tube back from contact with the wire winding on the depositor rod while the oil feed tube inlet nut is still tightened.

11.6.1.7 If the oil feed tube can be moved back from contact with the depositor rod wire winding when the oil feed tube inlet nut is tight, once more bring the beveled tip in light contact with the rod wire and further tighten the inlet nut just enough to stop this back-and-forth motion of the oil feed tube.

NOTE 13 - This series of steps positions the ferrule on the plastic tube so that the beveled tip will always be in proper position in relation to the depositor rod when the non-beveled end is pointed downward. However, the ferrule has not been set firmly enough to prevent side-to-side motion of the non-beveled end. To set the ferrule so firmly as to prevent this side-to-side movement is not necessary in most installations but if it is desired to do so, contact the manufacturer for instruction.

11.6.2 Connecting a Previously Used Oil Feed Tube (see Fig. 5) to its Assigned Upper End Cap:
11.6.2.1 With the depositor rod casing assembled and connected to the bus bars, insert the beveled end of the oil feed tube into and through the oil feed tube inlet stem of the upper end-cap until the tip reaches and lightly touches the wire winding on the depositor rod. Tighten the oil feed tube inlet nut.

11.6.2.2 Position of Oil Feed Tube Tip:
(1) The oil feed tube tip shall either touch the wire or be within close proximity on the depositor rod to ensure that the test oil runs down the specially treated helical wire guide on the rod and does not bypass the rod by dripping straight to the bottom end-cap or run down the inside mantle wall.

(2) Through regular use, the beveled end of the oil feed tube will eventually degrade, becoming charred and less pliable. To ensure proper delivery of oil to the depositor rod, replace the oil feed tube after 25 tests or at any time the beveled tip becomes charred or the test oil bypasses the rod.

NOTE 14 - Occasionally, when the tip of the oil feed tube is sufficiently degraded, the test oil will move back up the outside of the tube and run down the inside of the mantle into the mantle trough and then into the volatiles vial, thus spoiling the test.

11.7 Connect the oil feed tube to the pump outlet with 3.2 mm (0.125 in.) outer diameter clear, oil-resistant, flexible plastic tubing.

11.8 Verification ofAirflow:
11.8.1 Adjust the air supply to the proper value of 10.0 mL/min and then check the airflow to the depositor rod casing assembly as directed in 9.1.

11.8.2 Connect the air inlet tubing to the air inlet stem on the upper end-cap and finger- tighten the nut (see Fig. 7). Place a rubber plug into the lower end-cap oil outlet to prevent any leakage of air from that opening.

11.8.3 To ensure that the air flow rate passing through the mantle is 10 +/- 0.2 mL/min, connect the bubble gauge or calibrated handheld digital flow-meter to the volatiles delivery tube so that all air exiting from that opening passes through the bubble gauge or handheld digital flow-meter.

11.8.4 Measure the air flow rate from the outlet of the volatiles delivery tube. Be sure that the pump switch is in the offposition before such measure of air flow.
11.8.4.1 If the flow rate is less than 10 +/- 0.2 mL/min, tighten the oil feed tube nut on the upper end-cap more firmly as well as the upper and lower end-cap nuts that press against the ceramic isolator and the two small O-rings holding the depositor rod (see Fig. 5 and Fig. 7).

11.8.4.2 If the flow rate remains less than 10 +/- 0.2 mL/min, check for air leakage around the upper and lower end-cap O-rings (see Fig. 5) with an eyedropper filled with detergent/water solution and check for bubbles. If bubbles are seen, first remove the mantle from the end-cap and check the mantle for cracks or chipping. If none are found, replace the end-cap O-ring and test again. If bubbles are still found, contact the manufacturer.

11.8.4.3 If the flow rate is still less than 10 +/- 0.2 mL/min, disconnect the air line from the upper end-cap and then check the flow rate at this point (see 9.1).

11.8.4.4 If the flow rate is correct at this point, replace the steel ferrule on the air inlet tubing with a plastic ferrule and firmly tighten the air supply connection to the air inlet stem top mantle end-cap (see Fig. 7).

11.8.4.5 Recheck the airflow rate from the volatiles delivery tube.

11.8.4.6 If the flow rate is more than 10 +/- 0.2 mL/min, recheck the flow rate from the air source using the bubble flow meter or handheld digital flow-meter.

11.8.4.7 If the flow rate cannot be set to 10 +/- 0.2 mL/min, contact the manufacturer.

11.8.4.8 If the airflow is acceptable, remove the connection from the volatiles delivery tube and the plug from the oil outlet of the lower end-cap.

11.8.4.9 The acceptable range of air flow fluctuation during the test is 10.0 +/- 1.0 mL/min.

12. Sample Installation
12.1 After the sample and catalyst have been well mixed (see 10.8) in the sample flask, inspect the mixture to determine if it appears homogeneous. If not, continue stirring and inspect the mixture occasionally until it has become homogeneous.

NOTE 15 - For higher viscosity or dark samples, such as SAE 20W-40 engine oils, achieving homogeneity is somewhat more difficult and may require viewing the mixture with a light to ensure thorough mixing.

12.2 Connect the pump inlet tubing to the sample flask's glass sidearm.

12.3 Remove the pump outlet tubing to the sample flask's glass sidearm.