Vpliv dinamične omočljivosti na trenje

Kus, Maja (author), Kalin, Mitjan (mentor)

V doktorskem delu smo preučevali vpliv različnih organskih modifikatorjev trenja na omočljivost z mazivom in posledično na trenje v elastohidrodinamičnih pogojih mazanja. Predstavljeno teoretično ozadje problema kaže, da trenutno vloga omočljivosti v triboloških aplikacijah še vedno ni povsem razjasnjena, predvsem kar se tiče omočljivosti z mazalnimi olji, ki v stiku z večino kovin izkazujejo razširjajoči tip omočljivosti. V delu smo zato vrednotili omočljivost z oljem s statičnimi in dinamičnimi parametri omočljivosti ter ugotovili, da so dinamični parametri bolj primerni za popis omočljivosti v realnih triboloških aplikacijah kot statični. Rezultati površinskih energij in ATR-FTIR spektroskopije (t.j. tehnika oslabljenega popolnega odboja IR spektroskopije s Fourierjevo transformacijo) kažejo, da se vsi testirani aditivi adsorbirajo na jekleno površino tako pri 25 °C kot pri 100 °C, adsorbirani film pa znatno poveča oleofobnost površine. Rezultati kvarčne mikrotehtnice z monitoringom disipacije (QCM-D) potrjujejo uspešno adsorpcijo aditivov iz olja na jeklo pri 25 °C in 100 °C, prav tako pa kažejo, da je adsorpcija aditiva odvisna od njegove polarnosti. Variiranje molekulske strukture aditiva (število polarnih skupin, dolžina alkilne verige, polarnost funkcionalne glave, nasičenost) prav tako vpliva na oleofobnost, trendi so enaki pri 25 °C in 100 °C, ta vpliv je najbolj očiten pri popisu omočljivosti z dinamičnimi parametri. Rezultati triboloških testov v elasto-hidrodinamičnem (EHD) režimu mazanja pri 25 °C in 100 °C kažejo, da testirani aditivi znižajo koeficient trenja tudi v pogojih popolnega mazalnega filma. Koeficient trenja se niža z naraščajočo oleofobnostjo adsorbiranega filma (večjimi napredujočimi in umikajočimi koti). Samo z dodatkom organskih modifikatorjev trenja baznemu olju, ki se adsorbirajo na jekleno površino, smo pri 25 °C dosegli do 12,4 % znižanje trenja, pri 100 °C pa do 22,2 % nižje trenje, kar predstavlja pomemben tehnološki doprinos.

• Language: Slovenian
• Keywords: dinamična omočljivost, koeficient trenja, aditivi, adsorpcija, olja, kot omočljivosti
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FS - Faculty of Mechanical Engineering
• Place of publishing: Ljubljana
• Publisher: [M. Kus]
• Year: 2019
• Number of pages: XXVI, 108 str.
• PID: 20.500.12556/RUL-113364
• UDC: 544.722.3:621.892:532.516(043.3)
• COBISS.SI-ID: 303385856
• Publication date in RUL: 22.12.2019

Secondary language

• Language: English
• Title: Influence of dynamic wetting on friction

Abstract

In the PhD thesis we have studied the effect of different organic friction modifiers on wetting with oil and consequently on elasto-hydrodynamic friction reduction. The theoretical background shows that, currently, the role of wettability in tribological applications is still not fully understood, especially with regard to wettability with lubricating oils, which exhibit the so-called spreading wetting behaviour in contact with most metals. In this work, we have evaluated the wettability of steel with oil at 25 °C and 100 °C using static and dynamic wetting parameters. The results show that the dynamic parameters are more suitable for wetting characterization in real tribological applications than the static ones. The results of surface energies and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy show that all tested additives adsorbed to the steel surface at both 25 °C and 100 °C, and that the adsorbed film significantly increases the oleophobicity of the surface. The Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) results confirm that the tested additives adsorbed from oil on steel at both 25 °C and 100 °C, and that the adsorption is governed by the polarity of the additive. Variations in the molecular structure of the additive (number of polar groups, alkyl chain length, polarity of the functional head-group, saturation) also affects oleophobicity, the trends are the same at 25 °C and 100 °C, this influence being most evident with dynamic wetting parameters. The results of tribological tests in the elasto-hydrodynamic (EHD) lubrication regime at 25 °C and 100 °C show that the tested additives reduce the friction coefficient even under when the surfaces are completely separated by the lubrication film. The coefficient of friction decreases with increasing oleophobicity of the adsorbed film (larger advancing and receding contact angles). Only with the addition of organic friction modifiers to the base oil that have the ability to adsorb to the steel surface, we have reduced the coefficient of friction up to 12.4 % at 25 °C and up to 22.2 % at 100 °C, which presents an important technological contribution.

• Keywords: dynamic wetting, coefficient of friction, additives, adsorption, oil, contact angle