PhD position: Rheology, Flow, Phase-separation and Leakage of Lubricating Grease from Rolling Bearings
The Chair Tribology-Based Maintenance, Faculty of Engineering Technology of the University of Twente has an opening for a PhD candidate in the research area …
- Drienerlolaan, Enschede, Overijssel
- Tijdelijk contract / Tijdelijke opdracht
- Uren per week:
- 38 - 38 uur
- € 2325 - € 2972 per maand
The Chair Tribology-Based Maintenance, Faculty of Engineering Technology of the University of Twente has an opening for a PhD candidate in the research area of Grease Lubrication. This project operates at the interface of fluid dynamics, rheology, complex fluids and tribology. The expected outcome of this 4-year project will be a model that can predict the (very slow) leakage of base-oil and thickener from rolling bearings. This requires a thorough understanding of the flow and rheology, phase separation and degradation of lubricating greases in rolling bearings. The project is executed in close collaboration with SKF, a leading global bearing manufacturer.THE CHALLENGE
Lubricating grease is a visco-elastic material, consisting of a thickener matrix (usually a soap, 5-15%), base oil (mineral or synthetic) and additives (anti-corrosion, anti-wear, 1-5%). At small strains, lubricating grease is apparently solid. This quantity makes grease easy to use: it does not easily leak out of a bearing and acts as a seal, preventing contamination to enter the bearing. Only creep flow may occur. This is ascribed to the thickener matrix that forms a network filled with oil. At larger shear rates the viscous properties dominate. At very high shear rates the viscosity approaches that of the base oil.
After start-up of the bearing, macroscopic flow takes place (churning phase): the balls push the grease to the size of the bearing and some out of the bearing through the seals. This continues for about 12 hours, after which a semi-steady state occurs (bleeding phase). The oil is slowly released from the grease (“grease bleed”) into the tribological contacts (ball-ring contacts) providing a feed mechanisms for the lubricant film (with thickness up to typically 0.2 microns). In the case of non-contacting seals or defects in contacting seals, the grease/bled-oil slowly leaks out of the bearing. The causes a loss mechanism for the film thickness. The film thickness is now determined by the feed and loss balance. The end of the functional life of the grease is given by the point in time when there is no longer enough oil to provide a sufficiently thick film. The goal in this project is to develop a model for the prediction of the loss of grease in the initial (churning) phase and loss of base oil in the second phase (bleeding phase). This loss will be a function of time, grease type and bearing temperature/speed.
- You will study the rheological behavior of some model greases.
- You will study how this behavior changes in a rolling bearing by “mechanical load” on the grease matrix (the matrix deteriorates due to large shear and pressure).
- You will study the oil separation behavior in a ball bearing.
- You will perform bearing tests and analyze grease and oil leakage from bearings.
- You will study the change in micro-structure of grease taken from the bearing tests using Atomic Force Microscopy (AFM) or other techniques.
- You will develop an analytical model for grease and (thin film) oil flow that can be used to predict leakage from rolling bearings.
- You will closely collaborate with your research-team colleagues at the University of Twente. If needed, part of the research may be executed at SKF Research and Development, Nieuwegein, The Netherlands.
- You will mentor BSc and MSc students, who do graduation projects in support of your research.
- You will finish your research with a PhD thesis and publish your work in academic journals and at conferences.
- You hold an MSc degree in Physics or Mechanical Engineering or a closely related discipline.
- You have good knowledge/demonstrated awareness of modelling using Python, C++ and/or MatLab.
- You have good experimental skills.
- You have a strong analytical mind and an eye for detail, as well as a critical attitude towards assessment of experimental results;
- You like to present your results to colleagues, the industrial partner and at international conferences;
- You are fluent in English and express yourself easily both in speech and in writing. (A TOEFL (>score 90) or IELTS test results (>score 6.5) or Cambridge CAE or CPE is required).
For information, please contact Prof.dr.ir. Piet M. Lugt (firstname.lastname@example.org)
The start of the project is May 1st. We also invite applications from candidates, who expect to graduate soon. Your application should be submitted before 28th February 2019.
Please send the following documents through the link below:
- Letter of motivation
- Curriculum vitae
- List with grades of courses attended from both Bachelor and Master degrees
- References and, if applicable, a list of publications.
- We provide excellent mentorship and a stimulating research environment with excellent facilities;
- You are offered a professional and personal development program within Graduate School Twente;
- A starting salary of € 2.325 gross per month in the first year and a salary of € 2.972 in the fourth year gross per month;
- A holiday allowance of 8% of the gross annual salary and a year-end bonus of 8.3%;
- A solid pension scheme;
- Minimum of 29 holidays per year in case of fulltime employment.