Squeezing Mechanical Analysis and Model Establishment of the Viscoelastic Rubber-Strip-Feeding Process of the Cold-Feed Rubber Extruder.

In the process of rubber extrusion, the feed structure directly affects the extrusion quality, extrusion uniformity, screw lateral force, and feed power consumption. Until now, the feed structure was mainly based on empirical designs, and there was no theoretical model for the optimal design of a feed structure. This paper focused on the squeezing mechanical analysis and model establishment of the feeding process in which viscoelastic rubber strips are passed through feed-wedge clearance in cold-feed extruders. The screw flight rotation squeezing process was simplified into a disc rotation squeezing process; the instantaneous squeezing velocity h˙(t) in the disc rotation squeezing model was derived according to feed wedge clearance geometry and the disc rotating speed. By transforming rotation squeezing into differential slab squeezing, mathematical expressions of the velocity distribution, pressure distribution, total squeezing force, and power consumption in the feeding process were derived in a rectangular coordinate system under isothermal and quasi-steady assumptions and certain boundary conditions by using balance equations and a Newtonian viscous constitutive relation. Theoretical calculations and experimental values showed the same trend. Through comparison, it was found that the power consumption (P3) caused by sliding friction is about 200-900 W according to theoretical calculations, while the experimental test results show it to be about 300-700 W. Additionally, the difference between theoretical pressure value and the experimental pressure value can be controlled within 5-15%. This could reflect the main factors that affect the feeding process, so could be used for analyses of actual feeding problems, and to contribute to rough quantitative descriptions of the feeding process, finite element simulation, and the optimization of the feeding structure.

Effect of Adding Pyrolysis Carbon Black (CBp) on Soft Friction and Metal Wear during Mixing.

In the cracking process of waste tires, pyrolysis carbon black (CBp), as a solid product, accounts for about 35% of the total tire rubber content. Here, the treated CBp has been gradually applied to the tire formula to improve the recycling efficiency of waste tires. This study elucidated the influence of adding CBp during the tire mixing process on soft friction and metal wear. Compared with industrial carbon black (I-CB), the friction coefficient of CBp was smaller at different mixing stages, and the ripple caused by adhesion friction was not evident. After the modified CBp (M-CBp) was obtained by implementing the surface activation of common CBp (C-CBp), the friction coefficient between M-CBp and metal increased by 10%, while the filler dispersion and comprehensive mechanical properties showed an upward trend. The wear rate of metal was higher than that observed after adding I-CB during the same mixing mode; thus, it was necessary to strengthen the wear resistance of the inner-wall surface of the mixing chamber. The -OH group on the M-CBp surface can also participate in the silane coupling reaction and aggravate the metal wear of the mixer chamber wall. Through a comparison of results, the mixing friction coefficient can reflect the strength of filler-rubber interaction, which in turn can preliminarily represent the dispersion effect and comprehensive properties, reveal the reason behind the poor performance of CBp, and highlight the need for modification from the perspective of tribology.

Effect of Interfacial Lubrication between Rubber and Metal on Reducing Mixer Chamber Wall Wear in Mixing Process.

This paper focused on adding a suitable lubrication effect at the interface between the rubber and mixer chamber wall on reducing the surface wear rate of the mixer chamber wall. In the research process, the contact model between the compound and internal mixer chamber wall was simplified to the pin-on-disc experimental model. The experimental results showed that the friction coefficient and the metal surface wear rate of the mixer chamber were reduced (by approximately 24%) by adding an appropriate amount of antifriction agent in the mixing process, while the comprehensive properties of the compound showed an improvement trend. By analyzing the surface elements of the rubber compound, the MoS2 with an anti-wear effect on the surface of the rubber compound can form a lubrication mechanism between the rubber, filler, and mixer chamber wall metal. Combined with the result of the comprehensive properties of rubber, which showed that although the appropriate amount of antifriction agent formed a lubrication protection mechanism between the rubber and the inner mixing chamber wall, the mechanism did not affect the friction behavior required for mixing. The study can effectively enhance the effective friction mixing and reduce the wear and power consumption of the mixing chamber caused by excess friction during the mixing process.

Study of Carbon Matrix Composite as Wear-Resistant Plate Material on Improving Wear Resistance and Mixing Effect in Mixing Process.

Silica and carbon black are the most important reinforcing systems in rubber formula. In the process of continuous optimization of the formula, silica gradually replaces carbon black by its characteristics. In view of the wear problem of the components of the mixer chamber caused by the increase in the proportion of silica in the formula, this research applied carbon matrix composite (CMC) materials to wear-resistant plate materials, and compared them with common wear-resistant (CWR) plate materials to explore the impact of replacing CWR plate with CMC on improving wear resistance and mixing effect. The results showed that compared with the CWR plate, CMC wear-resistant plate showed characteristics of a high friction coefficient and low wear rate (reduced by about 23%) in the mixing process of silica compound. However, the friction behavior of carbon black compound and carbon matrix composite wear-resistant plate showed an opposite trend, where the friction coefficient and wear rate increased simultaneously, especially the wear rate that increased by about 35%. The main reasons for the experimental results were related to the characteristics, elemental composition and surface morphology of carbon matrix composite, silica and carbon black. The experimental results also indicated that the carbon matrix composite wear-resistant plate is more suitable for a silica mixing process, and the increasing friction coefficient with decreasing wear rate of wear-resistant plate can further improve the importance of effective friction in mixing and prolonging the service life of wear-resistant plate.

Optimize Design of Run-Flat Tires by Simulation and Experimental Research.

In this study, the two key factors affecting the thermal performance of the insert rubber and stress distribution on the tire sidewall were analyzed extensively through various performance tests and simulations to promote the development of run-flat tires. Four compounds and two structures of insert rubber were designed to investigate the effects of heat accumulation and stress distribution on durability testing at zero pressure. It was concluded that the rigidity and tensile strength of the compound were negatively correlated with temperature. The deformation was a key factor that affects energy loss, which could not be judged solely by the loss factor. The stress distribution, however, should be considered in order to avoid early damage of the tire caused by stress concentration. On the whole, the careful balance of mechanical strength, energy loss, and structural rigidity was the key to the optimal development of run-flat tires. More importantly, the successful implementation of the simulations in the study provided important and useful guidance for run-flat tire development.

Effect of Adding MoDTC on the Properties of Carbon Black Rubber and the Friction and Wear of Metal during Mixing Process.

The gap between the rotor and the mixer chamber wall is an important factor in determining filler dispersion in rubber compounds. The inner wall of a mixer will wear after working for a long time, which will cause poor filler dispersion and affect the quality of rubber products. In this study, MoDTC was added to carbon black as a kind of filler, and the effect on filler dispersion, the properties of the rubber product, and the friction and wear of rubber and metal in the mixing process were examined. Experimental data showed that after adding 3 phr of MoDTC, carbon black dispersion was greatly improved, the curing time was shortened, and the performance remained stable. It was also found that the Mo element of the compound with 3 phr MoDTC dispersed better than that of the other compounds. Most importantly, adding 3 phr of MoDTC greatly reduced the amount of wear on the metal during the mixing process. However, the opposite effect occurred when the MoDTC content was high. The method proposed in this study can not only improve filler dispersion in rubber but also reduce metal wear to prolong the service life of the mixing chamber when applied to an actual mixing process.

Numerical Optimization Simulation of Synchronous Four-Wing Rotor.

The mixer is the most widely used batch mixing equipment in the rubber industry. The rotor is a core component and has a great impact on the mixing effect of the equipment. The current rotor structure design is done empirically, being tightly dependent on practical experience. This paper proposes a method for optimizing the rotor structure by using optimization algorithms combined with numerical simulation technology. Using MATLAB software, a parametric design program for synchronous rotors and a set of optimization programs for the particle swarm optimization (PSO) algorithm were written. The global distribution index was used as the fitness function to optimize the synchronous rotor configuration. A comparative analysis of the rotors before and after optimization shows that the optimization process is feasible, and the results are reliable. This provides new ideas for the design and development of mixer rotors.

Effect of Silane Coupling Agent on Modification of Areca Fiber/Natural Latex.

In this paper, the areca fiber was extracted by physical and chemical treatment, and then the areca fiber/natural latex composite was prepared by natural latex impregnation technology. In order to combine areca fiber and natural rubber latex better, three silane coupling agents with different action mechanism were selected: Si-69, KH550, and KH570 which were used to treat the areca fiber/natural latex compound. The results show that the silane coupling agent can change the surface of the fiber from hydrophilic surface to organophilic surface, making the bonding of areca fiber to natural latex more closely. At the same time, the mechanical properties, physical and mechanical properties, swelling properties, and dynamic viscoelastic properties of the tightly bonded areca fiber/nature latex composites were improved. After observing the micro-structure through a scanning electron microscope, it was found that the three silane coupling agents could effectively bind areca fiber and natural latex to enhance the performance of the composite material, of which Si-69 performed best, and the tensile strength and tear strength of the composite increased by 21.19% and 12.90% respectively.

Optimization of Serial Modular Continuous Mixing Process Parameters for Natural Rubber Composites Reinforced by Silica/Carbon Black.

In the tire industry, the combination of carbon black and silica is commonly utilized to improve the comprehensive performance of natural rubber so as to realize the best performance and cost-effectiveness. The corresponding mixing is divided into three processes (initial mixing, delivery, reactive mixing) by the serial modular continuous mixing method, thus achieving more accurate control of the mixing process, higher production efficiency and better performance. Moreover, the optimization of serial modular continuous mixing process parameters can not only improve the performance of composite materials, but help people understand the physical and chemical changes and the reinforcing mechanism of fillers in the mixing process. In this paper, the relationship among the parameters of eight processes and filler network structure, tensile strength, chemical reinforcing effect and tear resistance was explored through experiments. The deep causes of performance changes caused by parameters were analyzed. Consequently, the best process condition and the ranking of the influencing factors for a certain performance was obtained. Furthermore, the best preparation process of natural rubber (NR)/carbon black/silica composite was achieved through comprehensive analysis.

Friction and Wear between Polymer and Metal in the Mixing Process.

In order to obtain a longer mixing chamber life, a layer of hard alloy coating is generally welded on the surface. However, when the mixing chamber is used for a long time, the surface will be worn due to friction with small fillers and rubber. As a result, there will be a large gap between the mixing chamber and the rotor, which will further affect the quality of the mixed rubber. In this paper, the dispersion process of the reinforcing system is simulated at first, and the mixed rubber samples are obtained from different dispersion stages in preparation for experiments with the chamber material. On this basis, the friction experiment is carried out with the same material as the mixing chamber on the friction experiment machine employed in the improved test part. The experiment shows that the friction and wear between the mixture and metal produced in each mixing stage are different. The wear in the stage with high friction is not necessarily large. The wear will be intensified in the middle and later mixing periods, while the friction will tend to be stable. In this paper, besides the exploration on the friction of fillers and rubber on the mixing chamber in different mixing stages, the most important thing is to change the mixing process of rubber formula, so as to extend the service life of the mixing chamber without changing the comprehensive physical properties of the mixing rubber.

Continuous Preparation and Properties of Silica/Rubber Composite Using Serial Modular Mixing.

In order to efficiently prepare high-performance silica/rubber composites for use in the tread of semi-steel radial tires, a serial modular continuous mixer was designed according to the principle of modular functionalization. The modular structure and serial process helped control the accuracy of the silanization reaction. Synchronous four-wing serrated rotors and reverse meshing reaction mixing twin-rotors utilized shear flow and elongation flow to improve the dispersion. In this paper, the mechanism of serial modular continuous mixing was analyzed, and the influence of the core reaction mixing zone (various mixing elements) on silica-filled compounds was investigated by cooling visualization experiments, including dispersion, and the silanization reaction degree. Meanwhile, a comparative experiment between serial mixing and two-stage mixing was conducted, which showed that the serial process comprehensively improved the dispersion, mechanical properties, and dynamic mechanical properties of silica/rubber vulcanizate.

Application of Protein-Based Films and Coatings for Food Packaging: A Review.

As the IV generation of packaging, biopolymers, with the advantages of biodegradability, process ability, combination possibilities and no pollution to food, have become the leading food packaging materials. Biopolymers can be directly extracted from biomass, synthesized from bioderived monomers and produced directly by microorganisms which are all abundant and renewable. The raw materials used to produce biopolymers are low-cost, some even coming from agrion dustrial waste. This review summarized the advances in protein-based films and coatings for food packaging. The materials studied to develop protein-based packaging films and coatings can be divided into two classes: plant proteins and animal proteins. Parts of proteins are referred in this review, including plant proteins i.e., gluten, soy proteins and zein, and animal proteins i.e., casein, whey and gelatin. Films and coatings based on these proteins have excellent gas barrier properties and satisfactory mechanical properties. However, the hydrophilicity of proteins makes the protein-based films present poor water barrier characteristics. The application of plasticizers and the corresponding post-treatments can make the properties of the protein-based films and coatings improved. The addition of active compounds into protein-based films can effectively inhibit or delay the growth of microorganisms and the oxidation of lipids. The review also summarized the research about the storage requirements of various foods that can provide corresponding guidance for the preparation of food packaging materials. Numerous application examples of protein-based films and coatings in food packaging also confirm their important role in food packaging materials.