By Sunish Vadakkeveetil, Mehran Shams Kondori, and Saied Taheri

Center for Tire Research (CenTiRe), Virginia Tech

 

 

 

 

 

 

 

 

Rubber, mainly because of its viscous nature, is a widely used material for most contact applications such as, seals, tyres, footwear, wiper blades, bushings etc. The material possesses the property of both a liquid (viscous) and a solid (elastic). Hence, rubber frictional losses at the contact interface is classified into three mechanisms as shown in Figure 1. Hysteresis  (μ_hys ) – Energy dissipated due to internal damping of rubber caused by undulation in the surface. Adhesion (μ_adh ) – Due to intermolecular or Vander Waals attraction at the contact interface. It vanishes in the presence of contaminants or lubricants on the surface. Viscous (μ_visc ) – Due to hydrodynamic resistance caused by the fluid in the contact interface. It mainly occurs under the presence of lubricant or fluid in between the contact interface.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Friction as a concept has evolved, as shown in Figure 2 from a simple empirical relation, developed by Amonton’s (1699) and Columb (1785) to more complex representations by considering these different mechanisms of friction. Initial experimental observations by Bowden and Tabor [1] observed the microscopic behaviour of the contact and obtained that the real area of contact is only a part of the nominal contact area. Grosch & Schallamach [2] performed experimental observation to determine the influential factors and obtain a relation between temperature and velocity-dependent friction to frequency-dependent viscoelastic behaviour. Savkoor[3] considers the frictional losses due to adhesive mechanism at the contact interface using a rudimentary theory where the interaction is considered as a series of processes from the growth of contact area in the initial stage to initiation and propagation of crack in the final stage.

Heinrich [4] developed an analytical representation to estimate the hysteretic component of friction by considering the energy losses at the contact interface to the internal damping of rubber from the undulations of the surface. The energy loss thus obtained is related to the frictional shear stress by the energy relation given by Eq. (2).

            ΔE=∫d^3 x dt u ̇ . σ (1)

           σ_f=ΔE/(A_0 v t)     (2)

Persson and Klüppel [5] extended the theory to consider the effect of the surface roughness by assuming the surface to behave as a fractal nature and obtaining the total energy loss being the sum over the different length scales. Klüppel considers the GW theory to consider the contact mechanics where Persson developed a stochastic based contact mechanics theory assuming the rubber deformations to follow the surface asperities, the results are as shown in Figure 3. To consider the actual deformation profile of rubber, an affine transformation approach [6] is considered to obtain the actual deformation of rubber contact. The results are as shown in Figure 4.

 

 

 

 

 

 

 

In addition to analytical methods, computational approaches are also considered to estimate deformation behaviour of a rubber block on a rough substrate (Figure 5). The numerical model [7] is validated using indentation experiment and compared against a single asperity model as shown in Figure 6. This is later being extended to obtain friction and wear characteristics of rubber at the contact interface by considering the deformations at the contact interface and obtaining the frictional force [5], [8].

 

 

 

 

 

 

 

 

 

 

Figure 6: FE Model Of Single Asperity Model & Comparison Of Results With Experimental & Analytical Approach

Wear is mainly due to the frictional shear stress generated at the contact interface leads to energy dissipation at the rubber – substrate contact interface that is either transformed into heat or responsible for crack initiation and propagation eventually leading to material removal. The major contribution of the wear occurs either due to the interaction of smooth asperity and rubber surface (adhesive wear), Figure 7 (a) instantaneous tearing of rubber by sharp asperities (abrasive wear), Figure 7 (b) or due to repeated cyclic contact stress (fatigue wear, Figure 7 (c)).

Due to the importance and complexity of the wear problem, it has been a vital topic of interest studied by many researchers [2]. Numerical techniques and empirical approaches have seen their light in the midst of the expensive and cumbersome experimental observations [9], [10]. Archard’s law states that “the volume rate of wear (W) is proportional to the work done by the frictional forces” as given by Eq. (3), where τ_f is the frictional shear stress and v is sliding velocity.

            W∝τ_f  v       (3)

 

 

 

 

 

 

 

 

 

 

 

In the case of road surfaces, the removal of rubber particles can be considered as a process of nucleation and propagation of crack like defects until it is detached to form a wear particle, as shown in Figure 8. Based on this mechanism of crack propagation, a physics-based theory assuming the crack propagates (Figure 9 & Figure 10) from already present defects or voids on the rubber surface was considered and then later compared with experimental methods performed using Dynamic Friction Tester (Figure 11) [6], [11], [12]. Future studies are being performed using analytical and computational approached to estimate the wear characteristics of a rubber material considering damage mechanics [8] and crack propagation theory considering the effect of surface roughness. An experimental technique is also being developed based on the Leonardo Da Vinci concept to experimental test the friction and wear characteristics of a rubber block under pure sliding.

 

References:

[1]       D. Bowden, F. P., & Tabor, The friction and lubrication of solids. Oxford university press., 2001.

[2]       A. Gent and J. Walter, The Pneumatic Tire, no. February. 2006.

[3]       A. R. Savkoor, “Dry adhesive friction of elastomers: a study of the fundamental mechanical aspects,” 1987.

[4]       H. Gert, “Hysteresis friction of sliding rubber on rough and fractal surfaces,” Pochvozn. i Agrokhimiya, vol. 25, no. 5, pp. 62–68, 1990.

[5]       S. Vadakkeveetil, “Analytical Modeling for Sliding Friction of Rubber-Road Contact,” Virginia Tech, 2017.

[6]       A. Emami and S. Taheri, “Investigation on Physics-based Multi-scale Modeling of Contact, Friction, and Wear in Viscoelastic Materials with Application in Rubber Compounds,” Virginia Tech, 2018.

[7]       S. Vadakkeveetil, A. Nouri, and S. Taheri, “Comparison of Analytical Model for Contact Mechanics Parameters with Numerical Analysis and Experimental Results,” Tire Sci. Technol., p. tire.19.180198, May 2019.

[8]       S. Vadakkeveetil and S. Taheri, “MULTI – LENGTH SCALE MODELING OF RUBBER TRIBOLOGY FOR TIRE APPLICATIONS,” Virginia Tech, 2019.

[9]       K. R. Smith, R. H. Kennedy, and S. B. Knisley, “Prediction of Tire Profile Wear by Steady-state FEM,” Tire Sci. Technol., vol. 36, no. 4, pp. 290–303, 2008.

[10]    B. W. and R. N. D. Stalnaker, J. Turner, D.Parekh, “Indoor Simulation of Tire Wear: Some Case Studies,” Tire Sci. Technol., vol. 24, no. 2, pp. 94–118, 1996.

[11]    A. Emami, S. Khaleghian, C. Su, and S. Taheri, “Comparison of multiscale analytical model of friction and wear of viscoelastic materials with experiments,” in ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE), 2017, vol. 9.

[12]    M. Motamedi, C. Su, M. Craft, S. Taheri, and C. Sandu, “Development of a Laboratory Based Dynamic Friction Tester,” in ISTVS 7th Americas Regional Conference, 2013.

 

Ecolomondo Corporation, a leading Canadian innovator in sustainable scrap tyre recycling technology, has announced that its new milling line at Hawkesbury facility has achieved a major milestone during recent testing by reaching a throughput of approximately 2,700 lbs per hour of recovered carbon black (rCB). This result surpasses the company’s projected target of 2,200 lbs per hour.

When the new milling line is completely operational, it should be able to process 2,200 pounds of rCB per hour and provide a particle size distribution of 96 percent between 10 and 15 microns. It is anticipated that the plant would process more than 1.5 million scrap tyres annually, recovering 1,350 MT of process gas while producing 4,500 MT of recovered carbon black, 5,400 MT of oil and 2,250 MT of steel.

The company expects the commercial production of rCB to start by the end of May 2025. After being contacted, offtake clients told the company that they were eagerly expecting a larger supply of steel, oil and rCB, said the company. Depending on end-product market pricing, the company's yearly income from the sale of these sustainable goods plus tipping fees of USD 145 per metric tonne is expected to reach USD 12.1 million, with an estimated EBITDA of 45 to 50 percent, added the company statement.

Jean-François Labbé, Interim CEO, Ecolomondo Corporation, said, “This is a major achievement that brings the Hawkesbury facility closer to full production and commercialisation.”

Global speciality chemicals company Orion S.A. has launched a new bio-circular carbon black called ECOLAR 50 POWDER to provide coatings manufacturers with a new solution for more sustainable coatings.

ECOLAR 50 POWDER, which is entirely based on bio-circular feedstock, has coloristic qualities that are on par with those of ordinary speciality carbon blacks and includes 100 percent biogenic raw material according to 14C analysis. The coloristic qualities of ECOLAR 50 POWDER, a low to medium colour furnace black, offer moderate tinting strength and medium jetness in mass tone applications. ECOLAR 50 POWDER offers equivalent coloristic performance for full-tone and tinting applications, as well as comparable wetting and dispersion characteristics to conventionally manufactured low-colour furnace blacks.

ECOLAR 50 POWDER outperformed other common specialist carbon blacks in achieving medium jetness in a solvent-borne alkyd/melamine stoving enamel system. It created a similar neutral undertone as well. When tested in a water-borne 1K PU coating system, ECOLAR 50 POWDER created a more neutral undertone and jetness that was on par with other regular speciality carbon blacks.

Tilo Lindner, Vice President Global Marketing – Speciality Carbon Black, Orion, said, “We’re leading the way in advancing carbon black to meet increasing industry demands for sustainable products. ECOLAR 50 POWDER enables coatings formulators to develop truly sustainable products in all kinds of coatings applications.”

LD Carbon has inaugurated Korea’s first and largest waste tyre pyrolysis plant in Dangjin, South Korea.

Located in the Dangjin Hapdeok General Industrial Complex, the plant is expected to begin full-scale operation next month. The plant is spread over 29,800 square metres and features two factory buildings and five silos. The plant has an annual capacity to process 50 kilotonnes per annum (ktpa) of tyre chips derived from end-of-life tyres (ELTs).

At the location, LD Carbon uses a two-step pyrolysis process, first turning ELTs into solid char and pyrolysis oil. After that, the business uses a secondary pyrolysis process to further compress the char and create recovered carbon black (rCB). It is anticipated that the Dangjin facility would generate 20 ktpa of rCB and 24 ktpa of pyrolysis oil, which is a substantial increase above the combined output of 7 ktpa at its current pilot plant in Gimcheon. When compared to traditional carbon black, the rCB generated by the technique is said to lower carbon emissions by up to 32 ktpa.

The company is planning to build plants overseas and intends to join the Asian market soon. It has also struck a 10-year offtake deal with SK Incheon Petrochem for its pyrolysis oil.

Speciality chemicals company LANXESS India organised its first exclusive Solutions Day event in Mumbai today to showcase its diversified and sustainable product portfolio to customers and other key stakeholders.

The event was organised to promote the idea of ‘One LANXESS’, where its business units – namely Advanced Industrial Intermediates, Flavors & Fragrances, Inorganic Pigments, Liquid Purification Technologies, Lubricant Additives Business, Material Protection Products, Polymer Additives, Rhein Chemie and Saltigo – displayed their distinctive products and solutions at the event. It provided an opportunity to highlight the cross-business synergies that characterise LANXESS' integrated approach and to present the company's cutting-edge solutions designed for a variety of industrial applications.

Three main business sectors, namely Advanced Industrial Intermediates, Speciality Additives and Consumer Protection Products, are currently the emphasis of LANXESS's strategy shift from a polymers to speciality chemicals company. In order to improve the value provided to clients, the event sought to promote cooperation and creativity across these various business divisions. In order to promote knowledge exchange, discover possible areas for collaboration and capitalise on the capabilities of each business unit to propel overall development and success, the day included interactive workshops, technical presentations and networking opportunities.

Namitesh Roy Choudhury, Vice Chairman & Managing Director, LANXESS India, said “Our goal with Solutions Day is to strengthen our existing partnerships and explore future collaborations that support sustainable industry growth. Through this event, we want to highlight LANXESS’ integrated offerings to all our stakeholders and address the global industrial challenges through the combined power of sustainable chemistry, innovation and responsible business.”