Scuffing load

American Society for Testing and Materials. 1995. Standard test method for evaluating lubricity of diesel fuels by the scuffing load ball-on-cylinder lubricity evaluator (SLBOCLE). Draft of proposed method. Philadelphia. 

HFRR, The high-frequency reciprocating rig SLBOCLE, scuffing load ball-on-cylinder lubricity evaluator. 

These classes of compounds were the first used during the industrial revolution to improve the performance of machinery and were developed to improve the scuffing load of gear lubricants. Examples of typical structures of sulphur/nitrogen compounds which have found application are given in Fig. 3.12. 

Figure 10-15. Effect of fatty acid concentration on scuffing load, by Askwith, Cameron and Crouch [32].

Figure 14-11. Correlation of scuffing load limits obtained on different test machines. See Table 14-6 for identity of lubricants and Table 14-7 for operating parameters of the test machines. From data by G. H. Benedict [19].

TABLE 19-5. SCUFFING LOADS FOR A DYNAMICALLY MAINTAINED FILM OF MoS,... 

Tribological investigations were carried out by means of a four-ball tester and a T-11 tester with a ball-on-disk friction pair. Antiseizure properties (scuffing load— A. seizure load—and limiting pressure of seizure—as well as motion resistance and wear at a constant load were determined using a four-ball tester. It has been found that ethoxylates used as additives significantly modify tribological properties. The measured A. Az> Poz values increase by as much as several times compared with water. The coefficient of friction and wear measured at a constant load decrease considerably to about half relative to water. 

The error in the complex quantity (p ) was determined by the total differential method, whereas the errors in individual quantities p and d are represented by standard deviation. A set of three quantities—scuffing load seizure load (PJ), and the limiting pressure of seizure (p )—characterizes the antiseizure properties of lubricating substances. 

The individual curves represent 0.5 wt% solutions of alcohols of various oxyeth-ylation degrees. Studies were also carried out for water, which represents a reference system. The course of changes observed is relatively complicated, but it is possible to notice three intervals that differ in the rate of increase in the friction force moment. A slight increase can be observed at low loads, a moderate one at intermediate loads, and a rapid one ending with seizure at the friction force moment 10 N-m. Three quantities will be used to assess antiseizure properties scuffing load (P,), maximum seizure load (P ), and the limiting pressure of seizure (p. Seizure tests were carried out in the presence of oxyethylated lauryl alcohol solutions at concentrations of 0.1, 0.5, 1, 4, and 10 wt%, and for cetyl, oleyl, and stearyl alcohols at concentrations of 0.1,1, and 10 wt%. 

The scuffing load is the lowest load at which there occurs a pronounced increase in the friction force moment, which indicates breaking of a lubricant film. The value of scuffing load for water (200 N) is several times lower than that for oxyethylated alcohol solutions, which exceeds 1000 N. The highest value was observed for a 1 wt% solution of C12H25EO23 (ca. 1500 N). High antiseizure efficiency of compounds can be observed even at the lowest concentrations (0.1 wt%). The dependence of... 

FIGURE 17.11 Changes in scuffing load (PJ of 1 wt% oxyethylated alcohol solutions as a function of (a) oxyethylation degree and (h) length and nature of the alkyl chain. (Data obtained using tester T02.)... 

Antiseizure properties were characterized by scuffing load (P,), seizure load (P x). and the limiting pressure of seizure (p. The tendency of changes in these three quantities as a function of alkyl and ethylene oxide chain lengths was analogous for most compounds. The measured values show a good correlation with the activity of the compounds that results from the alkyl chain length. Its increase caused a reduction in the amount of adsorbed additive and unfavorably affected the stability of the lubricant film. Contrary to all expectations, an increase in hydrophilicity of a... 

Interesting results were also obtained with regard to antiseizure properties of the compositions tested. None of the 1 wt% aqueous solutions caused seizure of friction pair elements in the load range of up to 8 kN. The lowest values of scuffing loads... 

P. scuffing load, in N, at which the boundary layer is broken it can be characterized by a rapid increase in friction torque... 

Dependences of friction torque on time are presented in fig. 18.26, and the mean values of scuffing load, wear-scar diameters of the balls, and wear-scar profiles obtained after the tests in the presence of % aqueous solutions of SML/ESMIS mixtures are shown in figs. 18.27-18.29. 

It was observed in the case of water that, almost immediately after starting the test, there occnrred a sndden increase in friction torque (fig. 18.26). This resulted in a rapid seizure of friction-pair elements. The value of scuffing load F, was estimated to be at a level of 200 N, while seizure load (FqJ was about 3200 N. The wear-scar diameter of the balls after the tests was 2.6 mm. 

Aqueous solutions (1%) of SML/ESMIS mixtures exhibited entirely different antiseizure properties than water. For SML/ESMIS mixtures, the obtained dependences of friction torque on time (a change in time is equivalent to increasing load) had a similar course. No sudden increase in friction torque was observed within the first seconds of the test. This shows that a relatively stable adsorbed film that effectively reduced the motion resistance was produced on the mating elements. Scuffing load was estimated from the dependences obtained (fig. 18.26). The results obtained are presented in fig. 18.27. The highest values were found for 1% aqueous solutions of mixtures with the 5 5, 3 7, and 1 9 ratios. These equaled, respectively, 2500 N, 2350 N, and 2300 N. Lower P values were obtained for the other compositions. For a solution containing the 7 3 SML/ESMIS mixture, the P, value was 2000 N, while for the ESMIS solution (0 10) the value was 1900 N. 

Figure 6 Comparison of performance between the different configurations (defined in Table 2) for tests performed at 16 m/s sliding speed. Uncoated configurations added for comparison, (a) scuffing load (b) average mean bulk temperature at scuffing load (c) average traction coefficient at scuffing load.

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