Fixation and strip-shaping machines have been widely used to process the tea leaves in the tea industry. It is often required for the sufficient fixation at the upper part of the U-shaped trough, temperature uniformity, strip-forming rate, and strip quality during the fixation and strip-shaping. In this study, an upper-heating continuous fixation and strip-shaping machine was designed to improve the effect of the fixation process. An upper heating unit was also introduced into the fixation section of the U-shaped trough. A temperature field simulation was performed on the fixation section of the trough. A series of tests was then conducted to verify the simulation. The heating unit was regulated to significantly enhance the temperature uniformity of the trough. Meanwhile, the dynamic analysis was conducted on the strip-shaping movement of tea leaves in the trough. A tea-leaf-trough coupled dynamic model was established to reveal the movement and forming mechanism of the tea leaves during strip-shaping. A systematic investigation was made to explore the influence of the movement features and force distribution of tea leaves on tea forming under different stages. Initially, the influencing factors on the strip-shaping quality were determined, including the trough width, trough depth, feed quantity, and crank rotation speed. Furthermore, a strip-shaping model was established to simulate the entire process of tea leaves in the EDEM discrete element simulation software. A single-factor test was conducted to optimize the key influencing factors. The dynamic curves of average velocity and average force of tea particles with time during strip-shaping were obtained after simulation. Finally, trough width, feed quantity, and crank rotation speed were determined to regulate the strip-shaping quality. A three-factor three-level quadratic rotational orthogonal test was adopted to verify the optimal matching of key process parameters. Fresh leaves were selected as the test material from the Dushan small-leaf tea tree, a special raw material for making Lu'an Guapian tea. The key factors were taken as the test variables, while the strip-forming rate and sensory score were the evaluation indicators. Design Expert 13.0 statistical analysis software was used to conduct regression analysis and significance experiments on the test data. The iterative optimization was also performed on the upper heating test group. The optimal combination of the parameters was finally obtained: crank rotation speed 198 r/min, trough width 90 mm, and feed quantity 80 kg/h. The best effect of fixation and strip-shaping was achieved under the condition of these optimal parameters. A verification test was conducted using the test prototype. The strip-forming rate and sensory score reached 89.62% and 90.67 points, respectively. The relative error between the actual measured and the predicted values after optimization was within 5%, indicating the high accuracy and reliability of the parameter optimization. The fixation and strip-shaping machines can be expected for structural and parameter optimization. The findings can provide an important theoretical and practical reference for the structural design and parameter optimization of fixation and strip-shaping machines.

Lu'an Guapian Tea (also called melon seed) is one type of green tea from Liu'an County in Anhui Province, China. Among them, baking is one of the most important processes in tea processing. Its baking quality can dominate the quality of tea, due to its baking process being different from other famous green tea. It is still lacking in continuous baking equipment, specifically for the Lu'an Guapian Tea. The traditional drum baking machine cannot fully meet the requirements of large-scale production at present, such as the high broken tea rate, poor baking quality, and insufficient aroma. In this study, a drum-type tea baking machine was designed using EDEM software, according to the baking process of the Lu'an Guapian Tea. The crawler-type ceramic belt was used as the electric heating element and then installed close to the outer wall, in order to reduce the thermal resistance. The frequency conversion speed was regulated suitable for the tea products in different periods; Dynamic analysis was carried out to further clarify the motion state of tea in the drum during baking. The tea particles were also moved periodically in the drum. The periodic motion of the tea particles in the drum was composed of three stages: contact, take-up, and drop. The force analysis of the tea particles in the three stages was carried out to establish the dynamic equation. There were influencing factors on the broken tea rate and baking quality, such as the rotation speed of the drum, the helix angle of the guide vane, the number of the guide vane, and the width of the guide vane. The virtual prototype was constructed by SolidWorks software. The particle model of the tea material was established by EDEM software. A numerical simulation was performed on the baking process of the tea particles in the drum. There was a significant relationship between the rotation speed of the drum, the spiral angle of the guide vane plate, the number of the guide vane plate, the width of the guide vane plate, as well as the average speed and average force of the tea particles. The key influencing factors were determined by the movement of the tea particles, even the breaking rate and quality of the tea after baking. Taking the raw tea the Lu'an Guapian Tea as the experimental material, a three-factor and three-level quadratic rotation orthogonal test was carried out to optimize the key structural parameters. The broken tea rate and sensory score were taken as the evaluation objectives, while the drum speed, the spiral angle of the guide vane, and the number of the guide vane were the main factors. The results showed that the primary and secondary influencing factors on the baking were: the drum speed, the spiral angle of the guide vane, and the number of the guide vane. Design Expert 13.0 was used for the regression analysis of the experimental data. An optimal combination of the parameters was: the spiral angle of the guide vane plate was 6°, and the number of the guide vane plates was 5. The better quality of the tea baking was achieved at the drum speed of 24 r/min. The prototype test was carried out to verify before and after optimization. The broken tea rate and sensory score were changed from 5.86% and 86.4 points to 4.82% and 92.1 points, respectively. The relative error between the predicted and the test was less than 5%. The finding can also provide a theoretical reference to optimize the tea-baking machine.

A tea carding machine is one of the key equipment in the shaping process of needle-shaped green tea. However, the key parameters are the empirical values in the traditional tea carding equipment, leading to the low carding quality. This study aims to optimize the structural and operation parameters of a continuous tea carding machine using numerical simulation and analogy methods, in order to improve the performance. The kinematics analysis was implemented to express the velocity and acceleration of the pot trough. The motion and force of the pot trough were then determined to explore the relationship between the pot trough movement and the tea carding state. The dynamic model of the tea-U-shaped groove was then established at each stage of the collision motion of tea hitting the convex edge, the rubbing movement of tea at the bottom of the U-shaped groove, the collision motion of tea and the right plate of the U-shaped groove, as well as the collision motion between tea and the left arc inner wall of U-shaped groove. The force characteristics of tea were analyzed to evaluate the tea striping in each stage of the pot trough motion cycle. A single-factor test was carried out to simulate the tea carding using EDEM software. The key parameters were simulated, such as crank rotational speed, pot trough amplitude, pot trough inclination angle, number of convex ridges, and height of convex ridges. The relationship curves were obtained among the average speed, average force, and tea carding time of tea particles. After that, a three-factor and three-level quadratic rotation orthogonal test was designed, where the strip rate and broken tea rate were taken as the evaluation index. The data processing and regression analysis were carried out using Design-Expert software. The experiments were then performed to verify the optimal model. The simulation results show that the crank rotational speed, pot trough amplitude, and the number of convex ridges shared a great influence on the quality of tea carding, where the tea particles were gradually transited from the disordered state at the beginning of carding to the longitudinal ordered state. The longitudinal proportion of tea leaves increased with the increase of time, in order to promote the formation of strip shape in the axis direction of the main stem vein of tea leaves. The orthogonal test results were processed by data processing and regression analysis. The optimal combination of parameters was obtained with the crank rotational speed of 195 r/min, pot trough amplitude of 99 mm, and number of convex edges of 2. The strip rate was 87.39%, whereas, the broken tea rate was 1.85%. The relative error with the optimization was within 5%, indicating the reliability and accuracy after optimization. The findings can also provide a theoretical reference to optimize the continuous carding machine.

A tea vibrating-shifting machine is one of the most important equipment in the tea refining process. The low screening performance of traditional vibrating-shifting machines cannot fully meet the large-scale production in recent years, due to the low sieve net rate and high error screen rate. In this study, the virtual prototype was constructed to combine with the screening principle of the vibrating-shifting machine by Solidworks. A discrete element simulation model of tea particles was established by EDEM software. A systematic analysis was made to clarify the motion state of tea particles on the sifting surface. The dynamic simulation was carried out on the vibrating-shifting process of tea particles. A single-factor test was also conducted to obtain the average velocity and average interaction force curve of tea particles. The simulation results show that the connecting rod length, the crank radius, and the sift inclination of the surface were the main influencing factors in the screening performance of the tea vibrating-shifting machine. A three-factor three-level quadratic rotation orthogonal test was designed to perform the regression analysis on the test data using Design-Expert software, where the connecting rod length, the crank radius, and the sift inclination of the surface were taken as the influencing factors, while the sieve net rate and the error screen rate were as the evaluation indexes. The regression analysis showed that the best screening performance of the tea vibrating-shifting machine was achieved, where the sieving rate of the tea vibrating-shifting machine was 94.5%, and the false sifting rate was 4.61%. An optimal combination of parameters was the connecting rod length of the tea vibrating-shifting machine was 1 977 mm, the crank radius was 25 mm, and the sift inclination of the surface was 2.8°. The verification test was carried out with the optimal structural parameters of the tea vibrating-shifting machine. The false sifting rate of the tea vibrating-shifting machine before optimization was 90.7%, the false sifting rate was 5.12%, and the production efficiency was 293 kg/h. After optimization, the false sifting rate of the tea vibrating-shifting machine was 93.8%, and thefalse sifting rate was 4.73%. The verification test and regression analysis were basically the same agreement. At the same time, the production efficiency of the tea vibrating-shifting machine was 319 kg/h. The false sifting rate increased by 3.42%, the false sifting rate decreased by 7.62%, and the production efficiency increased by 8.87%, compared with before optimization. This finding can provide a theoretical basis for the optimization of tea screening equipment.