19 Analytical Instrumentation
measured to the nearest 0.01 mm.[8] An average measurement is taken and used as the wear scar diameter.[8] Calculating the wear scar diameter concludes this test. Figure 3 visualizes typical wear scar formations after testing.
K94100/K94190 Automated BOCLE Tester
The Ball-on-Cylinder Lubricity Evaluator test is like the HFRR test; however, it is intended for jet fuel instead of diesel. The specifi c method is ASTM D5001, “Measurement of Lubricity of Aviation Turbine Fuels by the Ball-on-Cylinder Lubricity Evaluator (BOCLE)”.[2] An example shown in Figure 4 is the Koehler K94100 Automated BOCLE Tester which has built-in digital capabilities.
secure the holder (located bottom-right in Figure 4).
After the device is activated, the fuel will be conditioned through the air tubes for 15 minutes, followed by a 30-minute test. The 100x microscope is included with the unit and it is seamlessly integrated into the test software. Overall, this digital device has more features than the HFRR, but both units fulfi ll their niche within their respective ASTM specifi cations.
K93170-PN/K39179-PN Benchtop Four
Ball Wear and EP Tester The Four Ball Tester is a versatile unit designed for a range of test methods. The example pictured below is the Koehler K93170 Benchtop Four Ball Wear and EP Tester. It is a fully digital unit with the ASTM test methods pre-programmed into its software, and it offers a custom test functionality as well. It has graphing and data analysis capabilities, and test results can be exported using its USB port.
In summary, the unit tests lubricity, extreme-pressure properties, and frictional coeffi cients of oils and greases. Each test uses three stationary balls covered in lubricant and a rotating “top ball” pushed into them using a fi xed amount of pressure.[11],[12] Although they all create wear scars, only the wear test is specifi cally intended to measure the scar diameters, similar to the HFRR and BOCLE devices.[11] The extreme pressure test places increased loads on the top ball until failure, which is when the balls weld together.[12] The coeffi cient test is also performed until failure from increased loads, but the wear scar diameter is used in addition to the fi nal load force to calculate the coeffi cient of friction.[15] The signifi cance of the ASTM four-ball wear and friction methods is similar to that of the HFRR and BOCLE methods: they determine the ability of the tested products to minimize abrasion in the systems they interact with. This is especially important since the four-ball is specifi cally designed to test lubricants, unlike the other units that test fuels. The extreme pressure test is crucial for lubricants designed for high-load applications; such products are often used in universal joints and chassis joints, as those mechanisms experience constant pressure and wear.[16]
The setup for the K93170-PN/K93179-PN unit is similar for every test. The balls are assembled and tightened, and test lubricant is added to the chamber.
Figure 4. K94100 Automated BOCLE Tester
A similar result as from the HFRR test occurs: a ball is moved against a metal surface submerged in test fuel, and the result is a wear scar that is measured to determine the fuel lubricity. [2] The primary difference between the two methods is the test mechanism. While the HFRR moves the ball horizontally at a high frequency against the surface, the BOCLE keeps the ball stationary while a rotating ring creates the necessary friction.[2] The method is signifi cant to the aviation industry in the same way HFRR test methods are to diesel engines. Airplane fuel pumps and controls experience excessive friction and a shortened lifespan when the fuel lacks lubricity.[2] This is also the case for some fuel system hardware components,[2] making it vital for passenger safety and airline cost effi ciency.
The Koehler BOCLE unit requires installation and setup similar to the HFRR. The BOCLE has a built-in humidifi er to keep the test humidity standard; it must be fi lled with DI water. After the power is plugged in and the water is topped off, compressed air is added to the system through an inlet. The test ring is assembled using a spacer, adaptor, clamp, and screw; from there, the fuel bath is added and the thermocouple is inserted through a small hole. The fuel is added to the bath, air tubes are connected, and the test ball is positioned and tightened in the holder (located bottom-middle in Figure 4). A 500 g weight is added to the end of a lever arm to
Figure 6. K93170-PN Benchtop Four Ball Wear and EP Tester
Unlike the previous two devices that determine fuel lubricity, the Four Ball Tester is specifi cally designed for oils and greases. The ASTM methods are as follows:
ASTM D2266: “Standard Test Method for Wear Preventive Characteristics of Lubricating Grease (Four-Ball Method)”[11]
ASTM D2596: “Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Grease (Four-Ball Method)”[12]
ASTM D2783: “Standard Test Method for Measurement of Extreme-Pressure Properties of Lubricating Fluids (Four-Ball Method)”[13]
ASTM D4172: “Standard Test Method for Wear Preventive Characteristics of Lubricating Fluid (Four-Ball Method)”[14]
ASTM D5183: “Standard Test Method for Determination of the Coeffi cient of Friction of Lubricants Using the Four-Ball Wear Test Machine”[15]
Figure 7. Fully Assembled Test Chamber
The procedure for the wear test (D2266 and D4172) is as follows. The temperature is adjusted to 75±2 ℃, and the spindle attached to the top ball is spun at 1200±60 RPM; this is performed for approximately an hour.[11],[14] After completion, the balls are either removed from the holder or left in the ball cup assembly.[11],[14] The wear scars on each ball will be measured along two perpendicular axes using a microscope, and the average of the six values will be recorded as the wear scar diameter.[11],[14] This is similar to the HFRR and BOCLE methods but more reliable since three balls are used for a more precise average.
The D2596 and D2783 extreme-pressure methods involve a completely different procedure but use the same mechanical setup as D2266 and D4172. The temperature is set to
27±8 ℃, the initial pressure is set to 784 N, and the test is run for 10±1 seconds.[12],[13] The wear scars are examined and two factors are determined: the “last nonseizure load” and “weld point”.[12],[13] Table 1 below represents an adaptation from the ASTM D2596 manual used for these tests.
Figure 5. Fully Secured Holder with Lever Arm and Weight
WWW.PETRO-ONLINE.COM
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88
