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Category: Friction Testing | Coefficient of Friction

 

Friction Evaluation at Extreme Low Speeds

Friction Evaluation at Extreme Low Speeds

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Importance of Friction Evaluation at Low Speeds

Friction is the force that resists the relative motion of solid surfaces sliding against each other. When the relative motion of these two contact surfaces takes place, the friction at the interface converts the kinetic energy into heat. Such a process can also lead to wear of the material and thus performance degradation of the parts in use.
With a large stretch ratio, high resilience, as well as great waterproof properties and wear resistance, rubber is extensively applied in a variety of applications and products in which friction plays an important role, such as automobile tires, windshield wiper blades. shoe soles and many others. Depending on the nature and requirement of these applications, either high or low friction against different material is desired. As a consequence, a controlled and reliable measurement of friction of rubber against various surfaces becomes critical.



Measurement Objective

The coefficient of friction (COF) of rubber against different materials is measured in a controlled and monitored manner using the Nanovea Tribometer. In this study, we would like to showcase the capacity of Nanovea Tribometer for measuring the COF of different materials at extremely low speeds.




Results and Discussion

The coefficient of friction (COF) of rubber balls (6 mm dia., RubberMill) on three materials (Stainless steel SS 316, Cu 110 and optional Acrylic) was evaluated by Nanovea Tribometer. The tested metal samples were mechanically polished to a mirror-like surface finish before the measurement. The slight deformation of the rubber ball under the applied normal load created an area contact, which also helps to reduce the impact of asperities or inhomogeneity of sample surface finish to the COF measurements. The test parameters are summarized in Table 1.


 

The COF of a rubber ball against different materials at four different speeds is shown in Figure. 2, and the average COFs calculated automatically by the software are summarized and compared in Figure 3. It is interesting that the metal samples (SS 316 and Cu 110) exhibit significantly increased COFs as the rotational speed increases from a very low value of 0.01 rpm to 5 rpm -the COF value of the rubber/SS 316 couple increases from 0.29 to 0.8, and from 0.65 to 1.1 for the rubber/Cu 110 couple. This finding is in agreement with the results reported from several laboratories. As proposed by Grosch4 the friction of rubber is mainly determined by two mechanisms: (1) the adhesion between rubber and the other material, and (2) the energy losses due to the deformation of the rubber caused by surface asperities. Schallamach5 observed waves of detachment of rubber from the counter material across the interface between soft rubber spheres and a hard surface. The force for rubber to peel from the substrate surface and rate of waves of detachment can explain the different friction at different speeds during the test.

In comparison, the rubber/acrylic material couple exhibits high COF at different rotational speeds. The COF value slightly increases from ~ 1.02 to ~ 1.09 as the rotational speed increases from 0.01 rpm to 5 rpm. Such high COF is possibly attributed to stronger local chemical bonding at the contact face formed during the tests.



 
 

 

 




Conclusion



In this study, we show that at extremely low speeds, the rubber exhibits a peculiar frictional behavior – its friction against a hard surface increases with the increased speed of the relative movement. Rubber shows different friction when it slides on different materials. Nanovea Tribometer can evaluate the frictional properties of materials in a controlled and monitored manner at different speeds, allowing users to improve fundamental understanding of the friction mechanism of the materials and select the best material couple for targeted tribological engineering applications.

Nanovea Tribometer offers precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high-temperature wear, lubrication and tribo-corrosion modules available in one pre-integrated system. It is capable of controlling the rotational stage at extremely low speeds down to 0.01 rpm and monitor the evolution of friction in situ. Nanovea’s unmatched range is an ideal solution for determining the full range of tribological properties of thin or thick, soft or hard coatings, films, and substrates.

Learn more about all the features our Nanovea Tribometer offers.

Mechanical Properties of Silicon Carbide Wafer Coatings

Understanding the mechanical properties of silicon carbide wafer coatings is critical. The fabrication process for microelectronic devices can have over 300 different processing steps and can take anywhere from six to eight weeks. During this process, the wafer substrate must be able to withstand the extreme conditions of manufacturing, since a failure at any step would result in the loss of time and money. The testing of hardness, adhesion/scratch resistance and COF/wear rate of the wafer must meet certain requirements in order to survive the conditions imposed during the manufacturing and application process to insure a failure will not occur.

Mechanical Properties of Silicon Carbide Wafer Coatings

Industrial Coating Scratch & Wear Evaluation

The wear process of the acrylic urethane floor paints with different topcoats is simulated in a controlled and monitored manner using the Nanovea Tribometer as shown in Fig. 1. Micro scratch testing is used to measure the load required to cause cohesive or adhesive failure to the paint. In this study, we would like to showcase that Nanovea Mechanical Tester and Tribometer are ideal tools for evaluation and quality control of commercial floor and automotive coatings.

Industrial Coating Scratch & Wear Evaluation

Self Cleaning Glass Coating Friction Measurement

Self cleaning glass coating possesses a low surface energy that repels both water and oils. Such a coating creates an easy-clean and non-stick glass surface that protects it against grime, dirt and staining.  The easy-clean coating substantially cuts the water and energy usage on glass cleaning. It does not require harsh and toxic chemical detergents, making it an eco-friendly choice for a wide variety of residential and commercial applications, such as mirrors, shower glasses, windows and windshields.

Self Cleaning Glass Coating Friction Measurement

Coating Inspection of TIN by Scratch Testing

Coating inspection of residual stress in protective PVD/CVD coatings plays a critical role in the performance and mechanical integrity of the coated component. The residual stress derives from several major sources, including growth stress, thermal gradients, geometric constraints and service stresses. The thermal expansion mismatch between the coating and the substrate created during coating deposition at elevated temperatures leads to high thermal residual stress. Moreover, the TiN coated tools are often used under very high concentrated stresses, e.g. drill bits and bearings. It is critical to develop a reliable quality control process to quantitatively inspect the cohesive and adhesive strength of the protective functional coatings.

Coating Inspection of TIN by Scratch Testing

Scratch Hardness Measurement Using Tribometer

In this study, the Nanovea Tribometer is used to measure the scratch hardness of different metals. The
capacity of performing scratch hardness measurement with high precision and reproducibility makes
Nanovea Tribometer a more complete system for tribological and mechanical evaluations.

Scratch Hardness Measurement Using Tribometer

Bio-Tribology of Endocardial Leads in Hanks’ Solution

In this study, we simulated and compared the nan friction and wear behaviors of endocardial pacing leads made of different materials, in Hanks Solution, using the Nanovea Mechanical and Tribometer, respectively.

Nano-Micro Bio-Tribology of Endocardial Leads in Hanks’ Solution

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