Seizure load

The more interesting results obtained were for the use of both additives together, all of which showed a further increase in load-carrying capacity, so that any interaction in these tests was beneficial. The greatest improvement was approximately 39 kg increase in Initial Seizure Load compared with the solution of ZDDP alone. Curiously, 1% of molybdenum disulphide gave only about 18 kg improvement over the ZDDP solution. There was virtually no increase in weld load compared with the ZDDP, and this again suggests that the concentrations of molybdenum disulphide were too low to be very effective. Thorp explained these results on the basis that molybdenum disulphide cannot compete with the base oil for adsorption on the steel surfaces, but can adsorb on top of an adsorbed ZDDP film, but there is no real proof of this explanation. 

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... 

When tested in the four-ball machine, solutions of sulfur in petroleum oils of moderate viscosity or in white oil raise the critical load for the onset of severe, destructive wear, which is designated as "antiseizure" action in the technological idiom of the four-ball test. Davey [54] found a significant increase in the critical initial seizure load from 834 N (85 kg) for a petroleum base oil to 1275 N (130 kg) for elemental sulfur dissolved in the oil. Sakurai and Sato [55] observed a 3.2-fold increase in the load-wear index (mean Hertz load) for a 0.5 weight-percent solution of elemental sulfur relative to that of the uncompounded white oil. The load-wear index is a specialized result of the four-ball test that can be taken as indicative of the average antiseizure behavior of the lubricant. Mould, Silver and Syrett [56] reported a load-wear index ratio of 3.08 for 0.48% sulfur in white oil relative to that of the solvent oil, and also an increase in the initial seizure load from 441 N to 637 N (45 kg to 65 kg) and in the 2.5-second seizure-delay load from 490 N to 833 N (50 kg to 90 kg). 

Ester Wear/load index, kg (a) Initial seizure load, kg Wear scar diameter, mm (b)... 

Forbes and Silver [40] published data directly comparing the alkyl ester tri-n-butyl phosphate and the aryl ester tricresyl phosphate. Table 11-13 shows the details of this comparison as well as wear data for the acid ester di-n-butyl phosphate. The wear/load index and the initial seizure load show substantially no discrimination between tributyl phosphate and tricresyl phosphate and very little advantage of the compounded oil over the base oil. The low-load wear test distinctly shows better performance with tricresyl phosphate. The data for di-n-butyl phosphate are at variance with the hypothesis that hydrolytic degradation to the acid ester is the first step in the antiwear action of neutral phosphate esters. On the other hand, Bieber, Klaus and Tewksbury [41] separated acidic constituents from commercial tricresyl phosphate by preparative chromatography, and on blending these constituents back into the original tricresyl phosphate at various concentrations they observed enhancement of antiwear action in the four-ball test, as shown in Fig. 11-7. It should be noted that Bieber et at. worked with only 0.051% phosphorus in the lubricant, which may explain the sensitivity they observed to acid impurities. 

The work of Forbes and Battersby [46] is an integrated study of the relations among the chemical structures of the dialkyl phosphites, their adsorption on and reaction with iron, and their behavior in four-ball bench testing of lubricant additive effectiveness. The four-ball data in Table 11-17 for solutions of additive in white oil show that both the wear/load index (mean Hertz load) and the initial seizure load are critically responsive to concentration, with a strong effect when the concentration increases from 0.01 to 0.04 molal (0.031% to 0.124% P). The initial seizure load is an uncomplicated criterion with a straightforward interpretation, whereas the wear/load index is contrived, both in concept and performance. The low-load 50 minute wear data show inconsistencies in the influence of additives that have not been explained. 

Figure 11-14 shows data obtained by Dorinson [38] in an investigation of the cooperative action of di-t-octyl disulfide and t-octyl chloride, two independently effective lubricant additives. The criteria for evaluation are the initial seizure load in the 10-second ASTM four-ball test and the magnitude and course of the post-seizure wear. With either 2% sulfur or 2% chlorine as the single active additive element in the lubricant, the post-seizure transition occurs in the load interval 80-100 kg, and the degree of seizure, as judged by the extent of wear, is not severe. With a combination of 1% sulfur and 1% chlorine in the... 

Additive (conc.S or Cl) (a) Wear/load index, kg Intitial seizure load, kg... 

Wear spot diameter under conditions of hydrodynamic friction and critical seizure load were determined on a four-ball friction testing machine with steel balls of 0.017 mm diameter and a rotation speed of 1 500 rev/min [2]. 

Lubricatliig Wear spot diameter (D ) [mm] Critical seizure loading [kg] ... 

However, the critical seizure load cannot be explained on the basis of thermophysical and conventional physical and chemical properties of siloxane fluids, as polymethylsiloxane fluids and oligodimethyldichlorophenylsiloxane which compare well with the proposed oils in terms of the... 

Drug analysis, either from seizure loads or biological-specimen extraction, is very difficult to describe in detail in this entry due to the different drug classes. Hereinafter, the main steps of the analysis of different drug classes are explained briefly. 

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 other factor that causes reduction in the cloud point is the increase of the alkyl chain length in oxyethylated alcohols. Following the assumed interpretation, one can expect a correlation between the seizure load and the increase in the hydro-phobic properties of oxyethylated alcohols. The dependences can be conveniently analyzed on the basis of the results shown in fig. 17.11b, which clearly point to a significant effect of the increase in hydrophiUcity of the compound. The differences... 

Seizure load is the highest value of the pressure at which the friction force moment exceeds 10 N m. In the four-ball machine used in the experiments, the loads range from zero to 7200 N. Several of the solutions tested reached the maximum load value without undergoing seizure. The 7200-N value is nearly two times higher than the seizure load for water (3700 N). The dependence of seizure load on concentration and type of compound is presented in fig. 17.12. 

For most of the solutions examined, an increase in the degree of oxyethylation results in an increase in seizure load. The P value for C12H25EO7 solutions, which... 

FIGURE 17.12 Changes in seizure load as a function of concentration and nature of oxyethylated alcohol as a component of aqueous solutions. (Data obtained using tester T02.)... 

FIGURE 17.13 Changes in seizure load for 1 wt% oxyethylated alcohol solutions as a function of (a) oxyethylation degree and (b) aUcyl chain length and type of compound. (Data... 

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 results of constant-load tests do not display regularities similar to the ones observed in seizure tests. The former were carried out under milder conditions than the seizure tests. There was no rapid increase in loading (409 N/s), and the constant load used (2 kN) was comparable to the seizure load. Under such conditions one may expect a stable lubricant film. The temperature in the friction node should... 

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... 

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. 

It was also interesting to observe that no seizure occurred in subsequent stages of the tests. Increasing the load of a friction pair resulted, admittedly, in an expected increase in friction torque, but after 2 or 3 s, resistance to motion decreased again. Seizure of the balls was not observed before the test ended (up to 8000 N). In such cases, according to the accepted methodology, the seizure load assumes the conventional value of 8000 N. 

Fluid Type Mol. weight V100°C, cSt V40°C cSt VI Pour point, °C Four ball wear scar, mm (a) Four ball seizure load, kg (a) Friction coefficient (b) Soluble in (C)... 

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