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The technology of tires has been in the process of upgrading. In addition to the improvement of the ply, the improvement of the belt material makes the tires further divided into full steel tires and semi-steel tires; the use of an inner liner instead of the inner tube makes the tire gradually transition to a tubeless tire; the overall shape structure of the tire The improvement makes the tire show a trend of flattening.

Green tires refer to tires that have reduced rolling resistance by improving compound formulations, improving pattern design, and adding silica. The concept of “green tire” was proposed by the French Michelin company as early as 1992. It used a formula composed of solution-polymerized styrene-butadiene rubber (S-SBR rubber) and silica reinforcing agent to improve the pattern design of the tire and successfully produce it. An energy-saving and environmentally friendly tire with low rolling resistance, high wet grip, high wear resistance and low noise is developed. Michelin named it “green tires” in order to cater to the green economy concept emerging in Europe at that time.

At present, Europe is the most widely used area for green tires, and its consumption accounts for about half of the world. Compared with ordinary tires, green tires have obvious performance advantages and economic benefits by reducing rolling resistance, reducing tire weight, and saving fuel consumption of automobiles. Green tires have become an inevitable trend to fully replace existing tires.

Why green tires save energy

The rolling friction of tires generates energy consumption. Rolling friction refers to the resistance to rolling produced by an object rolling without sliding or having a tendency to roll on the surface of another object due to the deformation of the contact part under pressure. The following figure demonstrates the principle of rolling friction. When the wheel runs from right to left to ②, the red part of the rubber touches the ground, compresses and shears, and heats up. When the wheel continues to run to ③, the red part of the rubber touches the ground. Get off the ground, regain shape, and energy is wasted in the form of heat.

Rolling friction is fundamentally different from the familiar sliding friction. The magnitude of rolling friction is related to the molecular structure of the object material, while the sliding friction is related to the roughness of the contact surface. Assuming two perfectly smooth bodies, there is no sliding friction between them, but there may be rolling friction; if there are two rigid bodies that do not deform at all, there is no rolling friction between them, but there may be There is sliding friction. For example, a balloon filled with water and a steel ball roll freely on an inclined plane, and it will be much more difficult for the balloon to roll, because the deformation of the balloon is very serious.

It is difficult to unilaterally reduce the rolling friction of tires. In the tire industry, rolling friction is often referred to as rolling resistance. If the tires are made very stiff, they can reduce rolling resistance, but at the expense of cushioning. In car tires, it is sliding friction that provides traction, braking resistance and cornering centripetal force, while rolling resistance will only cause the tire to heat up during travel and waste energy. Therefore, tires pursue smaller rolling resistance and greater sliding friction, especially sliding friction on wet and snow, that is, wet grip.

Green tires break the limits of the “Devil’s Triangle”. In the tire industry, there is a saying of “devil’s triangle”. That is, it is difficult to simultaneously improve the three properties of rolling friction, wet grip, and tire wear resistance; often the improvement of one or two of them is at the expense of the performance of the other. The major breakthrough of green tires lies in breaking the limitation of “devil’s triangle” by improving the tread formula and tread pattern.

Process improvement of green tires

Compared with ordinary tires, green tires mainly have three process improvements: reinforcing filler, tread compound, and crown pattern design.

1. Reinforcing filler

Application and performance defects of carbon black. Carbon black is widely used as a reinforcing filler in the rubber industry, especially in the production of automobile tires. In the rubber industry, the consumption of carbon black is about half of that of rubber. Carbon black can significantly improve the wear resistance of tires, but traditional carbon black fillers have disadvantages such as difficulty in dispersion, high heat generation, and poor dynamic performance. In order to overcome these deficiencies, people have successively improved and developed products such as low-hysteresis carbon black and nanostructured carbon black. As a reinforcing filler, silica can significantly reduce the rolling resistance of tires. Silica, also known as hydrated silica, active silica, etc., is a highly dispersed amorphous powder or flocculent powder. It has been found that partial replacement of carbon black with silica can significantly reduce the rolling resistance of tires while maintaining or even improving wet grip.

The experimental data show that if white carbon black is simply used instead of carbon black in the tread rubber, the wear resistance will decrease by 20%~40%. The wet grip remained the same or even improved, the abrasion resistance dropped by only 5%, and the rolling resistance was reduced by 30%.

2. Tread compound

Classification of styrene-butadiene rubber. Styrene-butadiene rubber (SBR) is a general-purpose synthetic rubber and is the most productive variety of synthetic rubber. According to different polymerization methods, SBR can be divided into emulsion polystyrene butadiene rubber (E-SBR) and solution polystyrene butadiene rubber (S-SBR). E-SBR is an old variety of SBR, most of which is used for tread rubber, but it has the disadvantages of large hysteresis loss, large rolling resistance and small elasticity, which cannot meet the development needs of the tire industry; S-SBR is to overcome the above A kind of glue developed from defects.

Solution-polymerized styrene-butadiene rubber (S-SBR) is a new type of rubber with many advantages. S-SBR is a general-purpose rubber with comprehensive properties between E-SBR and BR (butadiene rubber). Due to the use of anionic living polymerization, the ratio of styrene to butadiene, the microstructure of butadiene units, the macrostructure of the polymer, the sequence distribution of unit composition, relative molecular mass and distribution, etc. can be arbitrarily controlled during the synthesis process. Therefore, rubber varieties with the advantages of wear resistance, flex resistance, low heat generation, and low rolling resistance can be produced. The production cost of S-SBR is slightly higher than that of E-SBR, but its performance is far better than that of E-SBR. In industrialized countries, E-SBR has passed its heyday, while S-SBR is growing steadily.

3. Tread pattern

The tread pattern design mainly optimizes two aspects of green tire performance: wet grip and tire noise. Improved wet grip. Tire pattern is also crucial to tire performance, and different patterns have different advantages and disadvantages. Green tires achieve balance in wet grip, corner grip, and wear resistance through the combination of different patterns. For example, a large number of longitudinal patterns will have a good drainage effect, but it sacrifices braking performance and wet stability, and is prone to cracking under high load; in order to make up for the lack of longitudinal patterns, some tires add a wide claw pattern, which increases the Braking force and drainage effect, but the problem is that there will be more rolling resistance and noise. Some tires are designed with sipes on the drainage grooves. This sharp pattern can puncture the water film between the wheel and the ground when driving, thereby enhancing wet grip; there are also asymmetric patterns that reduce resonance when touching the ground. Time and contact surface displacement, thereby reducing rolling resistance.

Improve tire noise. By changing the design of the tread pattern, the noise produced by the tire can be controlled. Half of the noise outside the car is caused by poor road conditions, and the other half is caused by improperly designed tire patterns. The tire tread noise is formed by the air column pipe sound generated by the tread drainage groove, the vibration sound of the grip, and the radiation sound of the multiple lateral blocks from the tread side end to the sidewall front end of the tire between the tires. Goodyear’s Royal Ride series is a typical quiet tire, which mainly achieves noise reduction by improving the pattern design. The closed shoulder design prevents the transmission of sound waves. The uniform block design makes the tire softer when it touches the ground to reduce the noise of hitting the ground. The vertical block edge design is to reduce the rigid deformation of the block and reduce the block size. It can also avoid the noise caused by uneven wear of the rear pattern.

To sum up

 In the driving process of the car, there is energy loss in each link, of which overcoming the rolling resistance accounts for 4% to 7% of the fuel energy, and the proportion of the vehicle energy consumption is very considerable. The tire’s rolling resistance consumption is dominated by the tread, sidewall and carcass, accounting for 74% of the rolling resistance fuel consumption. Therefore, by improving the rubber material of the tire, most of the rolling resistance can be effectively reduced.

Therefore, the energy saving effect of green tires is obvious. In view of the energy-saving effect of green tires, someone has done a test on Michelin tires: after turning off the engine, the vehicle is free to slide, and green tires can slide farther than ordinary tires. With the current production technology, the proportion of green tires reducing rolling resistance is between 20% and 35%. Based on the calculation of a car with a fuel consumption of 8 liters per 100 kilometers, the rolling resistance can be reduced by 25% after driving 10,000 kilometers per year, and the fuel consumption per 100 kilometers can be reduced by 5%, which can save 40 liters of fuel per year.

ICONVEY and HONG’S BELT jointly serve the tire manufacturing industry, and have reached confidential cooperation agreements with many advanced tire manufacturers, and together they have made significant optimization and innovation for the production process of green tires.

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