International Colloquium Tribology
ict
expert verlag Tübingen
125
2022
231
Accelerated compatibility test of sealing material - lubricant in a dynamic stress collective
125
2022
Ameneh Schneider
Josef Brenner
Felix Zak
The aim of this work was to develop a parameter set on the SRV® tribometer to simulate dynamic degradation of polymers in short measurement times and to enable a ranking of polymer/lubricant combinations based on residual mechanical properties after test and the coefficient of friction. For this purpose, the extent of the induced dynamic damage was compared with static insertion tests according to ISO 1817 as well as the original condition as a reference.
ict2310327
23rd International Colloquium Tribology - January 2022 327 Accelerated compatibility test of sealing material lubricant in a dynamic stress collective Ameneh Schneider Optimol Instruments Prüftechnik GmbH, D-81639 Munich, Germany Corresponding author: ameneh.schneider@optimol-instruments.de Josef Brenner AC2T Research GmbH, A-2700 Wiener Neustadt, Austria Felix Zak Optimol Instruments Prüftechnik GmbH, D-81639 Munich, Germany Summary The aim of this work was to develop a parameter set on the SRV ® tribometer to simulate dynamic degradation of polymers in short measurement times and to enable a ranking of polymer/ lubricant combinations based on residual mechanical properties after test and the coefficient of friction. For this purpose, the extent of the induced dynamic damage was compared with static insertion tests according to ISO 1817 as well as the original condition as a reference. Keywords: Tribological tests, dynamic load, elastomer compatibility, degradation, seal material, lubricant 1. Introduction The ISO 1817 standard (“Rubber, vulcanized or thermoplastic - Determination of the effect of liquids”) is a method by which the resistance of vulcanized or thermoplastic elastomers to liquids is tested [1]. Sealing’s damages caused by tribological-dynamic issues can often be observed in machineries. These damages result among others also from the counter surface, the lubrication and type of lubricant, the sliding speed as well as the temperature [2]. Braun described the challenges of static test very well [3]. This work represents added value to static compatibility test with conditions near to applications, the test setup is illustrated in figure 1. 2. Materials and method The following polymers (seal materials) and oils were selected for the feasibility of the tribological-dynamic investigation: Table 1: Investigated Materials Code Description Elastomers NBR Nitrile Butadiene Rubber NBR Semperit P 559 (70 Shore A, 2 mm) EPDM Ethylen-Propylen-Dien; M-group EPDM Semperit E 9566 (70 Shore A, 2 mm) Oils L32 Mineral base oil ISO VG 32 ES Ester oil Trioctyltrimellitat 99 % Figure 1: Clamped elastomeric tensile bar sample in the SRV®5 328 23rd International Colloquium Tribology - January 2022 Accelerated compatibility test of sealing material lubricant in a dynamic stress collective The test parameters were investigated as follows: • Normal force: 20 N à Pressing: → 1.6 MPa • Duration: 30 min • Temperature: 80 °C • Frequency: 40 Hz • Stroke: 4 mm 3. Results and discussions Figure 2 shows the comparison of coefficient of friction values after testing the different combinations of oils and elastomer with SRV ® 5 under the parameters mentioned above. Figure 2: COF from SRV ® 5 tests The EPDM/ mineral base oil L32 pairing had a significantly higher friction level (between 0.4 and 0.5) than the other (0.14 to 0.2). This combination shows a clear swelling of the elastomer (sample approx. 2 mm longer after testing, as can be seen in Figure 3). Figure 3: Samples after the dynamic tests The SRV ® 5 test confirms the incompatibility of EPDM with mineral base oil, as to be expected, in very short testing times, i.e., 30 min. Using HRA (High Resolution Analysis) of friction signal makes it possible to identify this incompatibility during the test online. Figure 4: COF hysteresis curves at 900 s of test In parallel to the dynamic investigations of the elastomers, static insertion tests were also carried out as a reference. Table 2 lists the chosen insertion times and temperatures: Table 2: Insertion parameters Sample code Temperature Insertion time 0,5 h 80 °C 80 °C 0.5 h 168 h 80 °C 80 °C 168 h 320 h RT RT 320 h original untreated The insertion test of 30 min at 80 °C served as a direct benchmark to the SRV ® tests. In this way, temperature influence and tribological-dynamic influence on the mechanical properties (e.g., tensile tests) of the elastomer samples were separated. Three samples of each elastomer type were insert in each oil under the chosen temperature and time. The following mechanical properties were evaluated after each insertion. • tensile strength • elongation at break 23rd International Colloquium Tribology - January 2022 329 Accelerated compatibility test of sealing material lubricant in a dynamic stress collective Figure 5 represents the results of tensile strength for NBR after treatment with oils L32 and ES. Figure 5: comparison of tensile strength after static and dynamic test condition Figure 6 shows the results of elongation break for NBR after treatment with oils L32 and ES Figure 6: comparison of elongation at break after static and dynamic test condition In this combination static thermal stress of 0.5 h at 80 °C hardly effected the NBR. SRV® tribo-tests of 0.5 h at 80 °C led to a light reduction in tensile strength but significant increase in elongation at break. Most changes are observed in the case of 168 h at 80 °C insertion time. The results of 320 h at RT static insertion and 0.5 h at 80 °C under dynamic insertion are in good agreement. Results of tensile tests for EPDM after treatment with oils L32 and ES show similar tendencies. 4. Summarized conclusions • As part of a feasibility study, a parameter set was developed on the SRV ® tribometer for dynamic polymer liquid compatibility testing • The method allows a ranking of elastomer/ lubricant combinations based on mechanical properties and the coefficient of friction • The elastomers from the SRV® tests (0.5 h at 80 °C), had significant different mechanical properties, when compared to the untested • The results indicate good agreement with the results of static insertion tests (320 h RT) 5. Outlook As these results are promising, this work will be extended and continued in new projects with variations in testing time and temperature (168 h 100 °C). The definition of criteria for elastomer compatibility based on mathematical calculation of hysteresis values of COF results will be further elaborated. This short dynamic test time and its defined criteria will save cost and time and give a quick ranking of polymer liquid compatibility. This method can be used for evaluation the fully formulated lubricants as well to screen, e.g., effects of additives. References [1] ISO 1817 standard “Rubber, vulcanized or thermoplastic - Determination of the effect of liquids” [2] M. Rinnbauer,“ Technische Elastomerwerkstoffe”, Verlag Moderne Industrie, Band 293, 2006 [3] Braun, „Elastomerverträglichkeitsuntersuchungen von Schmierstoffen - Reicht die bestehende Normung aus? “, Schmierstoffe und Schmierungstechnik, 2007
