Wear-scar diameter

Result A friction coefficient less than or equal to 0.175 indicates the fuel passes the lubricity evaluation. A friction coefficient greater than 0.175 indicates the fuel fails the lubricity evaluation. Wear scar diameter on the test ball is determined. A wear scar diameter of 440pm or less is considered acceptable for distillate fuel. 

Ball-on-Three-Disks (BOTD) This test method is utilized to measure the lubricity characteristics of distillate fuel. It involves rotating a ball against three disks lubricated by distillate fuel. After testing, the wear scar diameters on three disks are measured and averaged. Wear scar diameters of approximately 0.45 mm or less are presently considered acceptable. 

Appeldom and Tao (1968) and Goldblatt (1971) showed that boundary lubrication is not effective in dry argon under the steel ball-on-cylinder test. In the presence of methyl-naphthalene or indene, wear scar diameters (in mm) are 0.82 or 0.93. Remarkably, these diameters are 0.33 or 0.72 mm in dry air and 0.36 or 0.33 mm in wet air. 

In contrast with these unsaturated hydrocarbons, saturated hydrocarbons performed better in dry argon than in the presence of water or oxygen. For instance, decalin displays the following wear scar diameters (also in mm) 0.26 in dry argon, 0.35 in dry air, 0.42 in wet air (Appeldom Tao 1968). 

From this test, antiwear and extreme-pressure data were determined, such as welding load, load wear index and wear scar diameter under a load of 40 decanewtons (daN), 60 daN and 80 daN, respectively. First, evaluations were performed on the three original nonmodified hard-core RMs, then evaluations were performed on the sulfur-functionalized ones. Four-ball test data (results only for one concentration 10 wt% additive) are summarized in Table 3.9 (Delfort et al., 1995 and 1999) for ... 

Modified hard-core RMs by phosphosulfurized compound. Improved extreme-pressure and antiwear properties have also been obtained with the introduction of some chemical species, such as sulfur, phosphorus or boron derivatives, into the colloidal core (Delfort et al., 1998 Inoue, 1993 Inoue and Nose, 1987). Welding loads, load wear index and wear scar diameter at 5 wt% of a CaC03 core surrounded by a calcium alkylaryl-sulfonate surfactant shell, and modified by phosphosulfurized calcium carbonate core were evaluated for calcium dialkyl dithiophosphate (CaDTP) and calcium trithiophosphate (CaTTP) with the four-ball extreme-pressure test (ASTM D2783 standard method). Both modified products exhibit improved extreme-pressure performances (welding load and load wear index), while their antiwear properties (wear scar diameter) compared to those of the original micellar substrate remain at least at the same level. 

Welding loads and load wear index at 5 wt% concentration (as the extreme pressure performances) are improved compared to those of the original non-phosphosulfurized substrate (Delfort et al., 1998). The welding load (daN), wear load index (daN) and wear scar diameters (mm) under a load 60 daN behavior are... 

Medium Welding load (daN) Load wear index (daN) Wear scar diameter (mm)... 

Synthesis of oil soluble micellar calcium thiophosphate was performed in a one-step process involving the reaction of calcium oxide, tetraphosphorus decasulfide and water in the presence of an alkylaryl sulfonic acid. This product could be defined as a calcium thiophosphate hard-core surrounded by a calcium alkylarylsulphonate shell in accordance with a reverse micelle type association in oil. Three micellar products with the same chemical nature core were prepared, each with different core/shell ratio of 0.44, 0.92 and 1.54. Better performances are expected with products of higher core/shell ratios. The antiwear performance of micellar calcium carbonates is directly linked to the size of the mineral CaC03 colloidal particles. At a concentration of 2 % micellar cores, no antiwear effect is observed whatever the micellar size. At an intermediate concentration of 4 % of micellar cores, the wear scar diameter is clearly dependent on the micellar size, slipping from 1.70 mm to 1.10 mm, then to 0.79 mm when the core diameter moves from 4.37 nm to 6.07 nm, then to 6.78 nm. Size dependence is increased at a concentration of 5 % in colloidal cores. This clearly confirms the size dependence of the micellar cores on their antiwear performance (Delfort et al.,... 

Bartz carried out similar tests, and his results are shown in Figure 13.5. They show that 1 % of molybdenum disulphide gave a significant improvement in the initial seizure load compared with the base oil at the expense of higher wear scar diameters at low load. When 1 % of molybdenum disulphide was used in conjunction with a ZDDP there was little if any improvement. Bartz also used the standard... 

Four-Ball Machine later to study the interaction between molybdenum disulphide and several anti-wear and extreme-pressure additives and detergent/dispersant additives in a mineral oil. Unfortunately these results are difficult to compare directly with those of Thorp because he only reported wear scar diameters at two load levels. He found that at high load (lOOON) with 1 % of molybdenum disulphide, the combination with a ZDDP gave a wear scar diameter higher than either additive separately, and comparable to that of the base oil, and he described this as an antagonistic effect between the two additives. 

This is certainly contrary to Thorp s result (Figure 13.4) but unfortunately the 1000N (ca 100 kg) load is close to the transition load, and rapid changes in wear scar diameter with load occur at that point, which could be significantly affected by the use of a different mineral oil or a different ZDDP. It may be reasonable to sum up... 

Additive % P Wear scar diameter, mm Scuf f load, kg... 

Wear scar diameter was measured using Nikon and Leitz Laborlux Microscopes. 

A new spherical aluminum ball was used for each new experiment and the wear scar diameter on the balls was measured after each run. 

Coefficient of Friction at 200 mm/aec Wear Scar Diameter I Viacoaity... 

Figure 4. Correlation of coefficient of friction and wear scar diameter on aluminum/aluminum surfaces using 5% TRS 10-410 with 3% isobutyl alcohol in aqueous NaCl solutions.

The most interesting observation of the present study was a strong correlation of the coefficient of friction and wear-scar diameter. A lower coefficient of friction always corresponded to a smaller wear-scar diameter. 

The upper phase had high viscosity. When this phase was used for lubrication studies it gave low coefficient of friction. A strong correlation between coefficient of friction measurements and wear-scar diameter was seen and was observed previously. 

In summary the results indicate that the anisotropic phases at specific salt concentrations have strong affinity for the aluminum surfaces which reduce the friction and wear scar diameter. 

Table 1. Coefficient of friction, wear scar diameter, viscos and surface tension measurements of 5% TRS 10-410 + isobutyl alcohol system in aqueous NaCl solutions...

Table 2. Coefficient of friction, wear scar diameter, viscosi ...

NaCl cone, in the system (wt %) Phase Coefficient of Friction Wear Scar Diameter (mm) Viscosity at 26 C (cp) Surface Tension (Dyne/cm)... 

The tribological properties of Cu nanoparticles were determined on an MRS-lOA four-ball test machine at 1450 rpm in ambient conditions. The 12.7-mm-diame-ter balls used in the test were made of bearing steel (composition 0.95%-1.05% C, 0.15%-0.35% Si, 0.24%-0.40% Mn, <0.027% P, <0.020% S, 1.30%-1.67% Cr, <0.30% Ni, and <0.025% Cu) with a Rockwell hardness (Rc) of 61-64. The base oil was chemically pure liquid paraffin (LP), which has a distillation range of 180°C-250°C and density of 0.835-0.855 g/cm. Before each test, the balls and specimen holders were ultrasonically cleaned in petroleum ether (normal alkane with a boiling point of 60°C-90°C) and then dried in hot air. At the end of each test, the wear-scar diameters (WSD) of the three lower balls were measured on a digitalreading microscope to an accuracy of 0.01 mm. Then the average wear-scar diameter from the three balls was calculated. 

FIGURE 10.6 (See color insert following page XXX.) Effect of load on wear-scar diameter (four-ball test machine additive concentration in liquid paraffin (LP) 0.1% speed 1450 rpm test duration 30 min). 

The constant coefficient 222.47 results from the distribution of load P in the friction pair. The friction test was followed by measurements of wear-scar diameters of the three lower balls in two directions perpendicular to each other, and an arithmetic mean was calculated. The measurement error was determined on the basis of the Student s t distribution. (The results of the tests carried out at a constant load are discussed later, in section 17.4.2, and are shown in fig. 17.16 as coefficients of friction vs. time and in figs. 17.17 and 17.19, respectively, as coefficients of friction and wear-scar diameter vs. the chemistry of compound and its concentration in solution.)... 

The limiting pressure of seizure p represents the pressure present within a friction pair at the maximum seizure load (PqJ. It is a function of two variables seizure load P and wear-scar diameter (d) measured in a state of seizure on the stationary balls. It is less accurate than the other two quantities, and its interpretation can only be done with less confidence. Oxyethylated alcohol solutions display relatively high values of limiting pressure of seizure that, relative to water (200 N), increase from twofold to as much as fivefold. The dependence of the limiting pressure of seizure on the concentration and kind of ethoxylate is shown in fig. 17.14. 

The dependence of wear-scar diameter as a function of concentration and the type of additive is presented in fig. 17.19. The wear-scar diameter for the majority of solutions of oxyethylated alcohols and their concentrations decreases up to twofold relative to water (1.8 mm). Only for 0.1 wt% solutions are the wear-scar values greater than 1, with a maximum value of 1.6 (0.1 wt% solution of CJ2H25EO23). For concentrations equal to and above 0.5 wt%, the measured d values range from 0.9 to 1.1. Even oxyethylated oleyl alcohols do not exhibit any deviations from this. The effect of oxyethylation degree and the type of alkyl chain is analyzed on the basis of the results in fig. 17.20. There is no pronounced effect of the structure of the compound on wear under constant loading conditions. 

FIGURE 17.19 Changes in wear-scar diameter in the presence of aqueous solutions of oxy-ethylated alcohols as a function of concentration at a load of 2 kN. (Data obtained using tester T02.)... 

Tests at a constant load of 2 kN do not exhibit changes characteristic of seizure tests. Although both friction coefficient and wear-scar diameter decrease more than twofold relative to water, there is no pronounced effect of alkyl and ethylene oxide chains on the measured values. This is due to the relatively low temperature of the lubricant during these kinds of tests, in which surfactants do not undergo significant dehydration. 

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