Heat generation is inevitable for any rubber product or material that experiences cyclic loading while in service. This includes tires, industrial belts, and countless other examples. Heat generation under cyclic loading is the product of friction between fillers and polymer chains. The technical term of this type of heat generation is hysteresis loss, and it is quantified by measuring dissipated energy during deformation.
Heat generation can be harmless below a certain threshold, but too much friction between polymer chains and fillers leads to faster material degradation. Excess heat buildup can have serious consequences, including:
- Premature wear. Higher temperatures are correlated with reduced abrasion resistance, which can lead to premature wear and shorten the service life of the product.
- Reduced safety. Overheated tires are more vulnerable to rapid losses of inflation pressure, often called blowouts or bursts.
- Energy inefficiency. Heat buildup in tires leads to higher rolling resistance, which decreases the fuel economy of the vehicle. Businesses and consumers alike are becoming increasingly conscious of sustainability when making purchasing decisions, which makes rolling resistance an especially relevant parameter.
How does bound rubber affect heat generation?
A study by Alpha Technologies demonstrated a strong correlation between heat generation and bound rubber content. Bound rubber is the product of microscopic interactions between fillers and polymer chains, which creates a 3D network throughout the compound. Learn more about bound rubber >
These strengthened filler-rubber interactions enhance the mechanical properties of the rubber compound while also increasing friction—and, thus, heat—under cyclic loading.
As is often the case with rubber compounding, chemists and engineers are faced with the challenge of striking a balance between different attributes. For example, higher bound rubber content is correlated with improved tear strength and hardness and decreased tensile strength and elongation. Achieving the desired harmony between competing parameters requires deep understanding of the bound rubber content in a given compound and its impact on filler-polymer interactions.
An established method for measuring heat build-up in the Goodrich Flexometer. The Goodrich Flexometer is known to be accurate, but the testing process takes several hours.
A valuable—and faster—alternative for testing bound rubber is a rubber process analyzer (RPA). The Premier RPA from Alpha Technologies delivers exceptional precision and efficiency when quantifying bound rubber and its impact on heat generation.
The Premier RPA measures hysteresis loss directly from shear stress-strain curves, resulting in accurate prediction of heat buildup. Strain sweeps reveal the breakdown of filler networks under strain, as well as the greater Payne effect associated with strong filler-rubber bonds. Temperature sweeps link tan δ values to rolling resistance and wet grip performance. Additionally, with Sub-Zero Technology, the Premier RPA can evaluate low-temperature behavior of a given compound without liquid nitrogen or additional equipment.
Solving real-world challenges with the Premier RPA
The real-world implications of the RPA’s value as a heat buildup prediction tool are considerable, with possible applications in multiple industries.
For example, automotive seal and mount manufacturers can leverage the RPA to achieve better heat resistance without compromising flexibility by optimizing bound rubber content. Similarly, it is possible to minimize thermal degradation of industrial belts and dampers in high-load applications by lowering hysteresis loss.
Perhaps the greatest potential for bound rubber optimization lies in the tire industry, where sustainability is becoming increasingly important to manufacturers and consumers alike. Understanding bound rubber content may offer deeper insight into the ongoing challenge of striking the appropriate balance between competing parameters. Alpha Technologies observed that moderate bound rubber content in the tread compound could lower the tire’s rolling resistance without sacrificing its wet grip characteristics. Additionally, limiting heat generation, which is correlated with bound rubber content, can extend the lifespan of the tire. Over time further optimization of these parameters through deeper study of bound rubber content could yield valuable intel.
Alpha Technologies published a paper detailing the results of a bound rubber study, with extensive graphics and in-depth data from the Premier RPA. Download the paper >