Simulation and Evaluation of the Performance of Pneumatic Residual Film Recycler Comb Teeth

Abstract

The interaction law between soil and tillage components is the basis for designing and selecting soil tillage components. This paper uses the discrete element method to explore the soil penetration performance of the comb teeth of a pneumatic film-stripping tillage residual film recycler under different structural and working state parameters. The soil particle contact model is set up, the virtual prototype of the comb roller is established, and EDEM (Version 2018, DEM Solutions Company, Edinburgh, UK) discrete element software is applied to simulate the interaction between the comb roller and the soil particles during the residual film recycler’s operation. Simulation and test results show that using a spiral arrangement of tooth comb knives (Alar, 843300, China, Zhongyuan Stainless Steel Bending Manufacturing Co.) can reduce the impact load on the machine, improving the soil disturbance and facilitating the penetration of soil mulch. The composite force on the combing roller increases with comb depth in the soil for a combing roller depth of 6–18 cm. Moreover, the rotational speed varies within the range of 60–120 r/min. The forward speed of the recycling machine significantly affects the soil penetration performance of the comb roller; the power it consumes increases with forward speed. This study can provide a reference for the structural design and optimization of working parameters of future deep tillage machines.

1. Introduction

Soil is a non-renewable resource for all humanity, as important as water and air. In China, especially in Xinjiang, mulching technology has brought great economic benefits to agricultural production. However, it has also caused serious “white pollution” to the agroecological environment [1]. Farmers are most worried about the high cost of recycling residual film and the low performance of recycling equipment, resulting in a large part of the film not being recycled; instead, it is buried in the soil with the cultivation of farmland [2]. Residual film materials in agricultural fields, primarily made of polyethylene, take almost a century to decompose under natural conditions. Hence, the movement of water, gases, and minerals in the soil is disturbed. Moreover, micro-organism activity, the germination and growth of seeds, and the efficacy of soil working machinery are also disturbed [3]. According to a survey conducted by the Department of Agriculture and Rural Development of the Xinjiang Uygur Autonomous Region, the amount of film residue on arable soil in Xinjiang, where cotton is grown all year round, has reached 17.91 kg/ha, or an area of 2460 m² [4]. Pollution from plastic sheeting has seriously threatened the safety of Xinjiang’s agricultural soil resources [5] (Figure 1 shows the contamination of residual film in arable soil).

Many domestic research institutes, universities, and enterprises have conducted significant research on agricultural residual film-recycling machinery and mechanisms in response to the issue of agricultural film pollution [6]. They have developed a wide range of residual film-recycling machines. The author’s team employed the “comb through hair” mimicry principle. Here, rotating comb teeth are employed to loosen soil and recycle film, including brush-type film separators, film separators with belts, and pneumatic film separators, i.e., three types of machines for tillage film recycling (Figure 2).

Researchers in agricultural engineering have prioritized drag reduction technologies for soil-contacting machinery parts, as soil–implement interactions critically influence resistance dynamics and energy utilization during field operations. Hence, the power consumption and efficiency of the machine are unstable. Investigating the interactions between the implements and the soil is conducive to the optimization of the structure of the implements and the work of parameters [7,8,9,10,11,12]. Aikins et al. described the application of the discrete element method to tillage and furrowing simulation, providing an overview of its application to tool optimization design [13]. Kesner et al. used a numerical model to simulate the stresses acting on the chisel shank during tillage [14]. Ucgul et al. utilized EDEM software to analyze the nonlinear contact model, hysteretic spring contact model (HSCM), and linear adhesion model. Their results demonstrate that the discrete element method can simulate tillage implements operating in soil [15].

Numerical simulation of agriculture machinery–soil interactions via a discrete element method is gaining popularity among researchers from different disciplines [16,17]. Wu numerically simulated the interaction process between the excavator shovel and soil based on DEM. The author investigated the dynamic performance of the cable shovel during the use of excavating robots [18]. Han used the discrete element simulation software EDEM to establish a contact mechanics model between manure particles and implements. Moreover, the author carried out an optimization of the structure and parameters of orchard fertilizer applicator devices [19]. Chong investigated the disturbance influence law of chisel-type plow shovels on soil based on EDEM simulation [20]. This software has become commercially used for discrete element analysis in soil modeling and machine–soil interaction simulation [21].

This paper investigates a pneumatic stripping-type deep plowing residual film recycler. A discrete element simulation test is carried out to investigate the performance of the key working part of the machine (the comb roller) in soil penetration. Lastly, a comparative analysis of the soil penetration performance of comb rollers under different structures and operating parameters is conducted to verify the power consumption of the recovery machine.

2. Materials and Methods

2.1. Structure and Working Principle

Many domestic research institutes, universities, and enterprises have conducted significant research on agricultural residual film-recycling machinery and mechanisms in response to the issue of agricultural film pollution. They have developed a wide range of residual film-recycling machines. The author’s team employed the “comb through hair” mimicry principle. Here, rotating comb teeth are employed to loosen soil and recycle film, including brush-type film separators, film separators with belts, and pneumatic film separators, i.e., three types of machines for tillage film recycling (Figure 2).

Figure 3 shows the research object in this paper, i.e., a comb film-lifting, pneumatic film-stripping tillage residual film-recycling machine. The working principle is as follows. The comb teeth are first used to pick out the residual film in the soil of the cultivated layer. Then, the negative-pressure air flow of the film suction mouth is used to suck out the residual film picked up by the comb teeth. The wind speed decreases due to the considerable cross-sectional area of the piping in the gravity deposition chamber. Impurities with high suspended velocities, such as stones and cotton rods, cannot be drawn into the suction duct. Hence, residual film sucked by the negative wind will be blown by the centrifugal blower outlet and the screen installation at the outlet. Lastly, the recycled residual film can be collected [22].

2.2. Simulation Test Method of Comb Roller Performance in Soil

2.2.1. Simulation Test Program

The main factors affecting the performance of comb teeth in the soil include the following [22]:

• The arrangement of comb teeth. Comb teeth in the roller have various arrangements, such as parallel or spiral. The spiral arrangement can be mainly divided into a one-way single-row spiral arrangement, a one-way multi-row spiral arrangement, and a two-way multi-row spiral arrangement.
• The structure of the comb teeth. The combing mechanism can be divided into flat and toothed knives.
• The depth of comb tooth penetration.
• The rotation speed of comb rollers.
• The forward speed of comb rollers.

The main purpose of the simulation test is to explore the influence of the above five factors on the working performance of the comb roller in the soil and determine the comb roller’s working parameters via simulation. The working performance of the comb roller in the soil mainly refers to the forward resistance, vertical force, resistance torque, and lateral force that the comb roller is subjected to when it enters the soil, as shown in Figure 4. Variable parameters of the simulation are shown in

Table 1. Main variables affecting the performance of combs in soil.

Item	Variable
Comb arrangement	Spiral	Parallel
Comb structure	Toothed	Flat
Depth of penetration of the comb in the soil (mm)	6	12	14	18
Speed of the roller (km/h)	60	80	100	120
Forward speed of the roller (km/h)	2	3	4	5

.

2.2.2. Contact Modeling of Soil Particles

This simulation of the soil penetration performance of the comb roller uses the discrete element method, which equates the soil as discrete spherical particles instead of a continuum. The execution of this simulation algorithm is achieved using the EDEM2018 software, which neglects the bonding between the soil and sets the contact model between the soil particles as the Hertz–Mindlin (no-slip) model. The model is efficient and accurate in calculating forces. The normal force component of the model is based on the Hertzian contact model [23]. In contrast, the tangential force component is based on the Middlin–Deresiewicz research theory [24].

The normal contact force $F_n$ is calculated via Equation (1) [24]:

$$F_n={\displaystyle \frac{4}{3}}{E}^{\mathrm{*}}\sqrt{R^{\mathrm{*}}}{\delta }_n^{{\displaystyle \frac{3}{2}}},$$

(1)

where $E^{\mathrm{*}}$ is the equivalent of Young’s modulus, $R^{\mathrm{*}}$ is the equivalent radius, and ${\delta }_n$ is the particle normal phase overlap. Parameters $E^{\mathrm{*}}$ and $R^{\mathrm{*}}$ are defined in Equations (2) and (3):

$${\displaystyle \frac{1}{E^{\ast }}}={\displaystyle \frac{\left(1-v_i^2\right)}{E_i}}+{\displaystyle \frac{\left(1-v_j^2\right)}{E_j}},$$

(2)

$${\displaystyle \frac{1}{R^{\ast }}}={\displaystyle \frac{1}{R_i}}+{\displaystyle \frac{1}{R_j}},$$

(3)

where Young’s modulus, Poisson’s ratio, and sphere radius of the spherical particles in contact are $E_i$, $v_i$, $R_i$ and $E_j$, $v_j$, $R_j$, respectively. The normal damping force $F_n^d$ is

$$F_n^d=-2\sqrt{{\displaystyle \frac{5}{6}}}\beta \sqrt{s_n{m}^{\ast }}{v}_n^{\overrightarrow{rel}},$$

(4)

where $m^{\mathrm{*}}$ is the equivalent mass, $v_n^{\overrightarrow{rel}}$ is the normal component of the relative velocity between particles, and $s_n$ is the normal stiffness. The expressions for the above parameters are shown in Equations (5)–(7).

$$m^{\ast }={\left({\displaystyle \frac{1}{m_i}}+{\displaystyle \frac{1}{m_j}}\right)}^{-1},$$

(5)

$$\beta ={\displaystyle \frac{\mathit{ln}e}{\sqrt{{\mathit{ln}}^{2}e+{\pi }^2}}},$$

(6)

$$s_n=2E^{\ast }\sqrt{R\ast {\delta }_n},$$

(7)

where e is the recovery coefficient. The tangential force $F_t$ is calculated as [25]

$$F_t=-S_t{\delta }_t,$$

(8)

where $S_t$ is the tangential stiffness coefficient, and ${\delta }_t$ is the tangential overlap of contacting particles. The tangential stiffness coefficient can be calculated as

$$S_t=8G^{\ast }\sqrt{R^{\ast }{\delta }_n},$$

(9)

where $G^{\mathrm{*}}$ is the equivalent shear modulus. The tangential damping $F_t^d$ can be expressed as

$$F_t^d=-2\sqrt{{\displaystyle \frac{5}{6}}}\beta \sqrt{s_t{m}^{\ast }}{v}_t^{\overrightarrow{rel}}.$$

(10)

2.2.3. Simulation Parameterization

This simulation test mainly includes the following parameters:

• Structural parameters of the soil film-recycling machine;
• Working parameters of the recycling machine;
• Soil parameters;
• Comb parameters;
• Soil and comb contact parameters.

The main technical parameters are also presented in

Table 2. The main technical parameters of the recycling machine.

Item	Description/Value
Length of the virtual comb roller (m)	1
Length of the combs	20
Thickness of the combs	10
Distance between the combs	10
Number of comb rows in the circumferential direction of the carding roller	7
Number of each column of combs	11
Materials of the roller	Steel 45
Helix angle of the roller (rad)	0.13–0.21
Diameter of the roller (mm)	120
Length of the roller (mm)	1000
Forward speed of the recycling machine (km/h)	1–7
Rotating speed of the comb roller (r/min)	40–140
Working range of the comb entry depth (cm)	0–20
Suction pressure (Pa)	5740

.

Since most of the soils in the southern Xinjiang region are sandy soils, the main operation object of the comb tooth film-lifting pneumatic film-stripping-type tillage residual film recycler investigated as the focus of this research is the recycling of the residual film in sandy soils. Therefore, the calibration of soil parameters, comb tooth parameters, and soil–comb tooth contact parameters is conducted according to [25]. The standard ball calibration was selected, the collision recovery factor was set to 0.15, the static friction factor was set to 0.8, and the rolling friction factor was set to 0.2. The specific simulation parameters were designed as shown in

Table 3. Virtual simulation parameters.

Parameters	Numerical Value
Dimensions of virtual soil tank (L × W × H), (mm × mm × mm)	1020 × 1020 × 832
Soil particle density (kg/m3)	2630
Poisson’s ratio of soil particles (v)	0.4
Soil particle shear modulus, G/Pa	1 × 106
65 M steel density (kg/m3)	7830
65 M steel Poisson’s ratio	0.35
65 M steel shear modulus	7.27 × 1010
Soil–soil recovery factor e1	0.3
Soil–soil dynamic friction factor e2	0.2
Soil–soil static friction factor e3	0.05
Coefficient of recovery between soil and 65 M steel f1	0.3
Dynamic friction factor between soil and 65 M steel f2	0.5
Static friction factor between soil and 65 M steel f3	0.05
Filling unit radius, r/mm	6
Number of soil particles, n	212,786
Gravitational acceleration, g/(m·s−2)	9.81
Simulation time, s	4

.

2.2.4. Comb Roller Virtual Prototype

The final comb roller virtual prototype is shown in Figure 5.

This virtual simulation sets the length of the soil groove in the forward direction of the comb to 1 m to simplify the numerical calculation, as shown in Figure 6. The comb entry process of this virtual simulation experiment is divided into three main processes [26]:

3. Results

3.1. Influence of Comb Arrangement on Soil Penetration Performance

3.1.1. Test Conditions

The arrangement of teeth on the roller is important in determining how it performs on the ground. Figure 7 shows parallel and spiral arrangements of the comb rollers. This experiment was conducted to simulate the comb teeth of these two structural modes and compare the results to analyze their soil penetration performance. Simulation conditions are as follows: forward speed is 3 km/h, rotation speed is 150 r/min, and soil penetration depth is 12 cm [27].

3.1.2. Simulation Results

The effect of comb arrangement on soil penetration performance is shown in Figure 8.

The following can be observed according to Figure 8. The lateral force suffered by the spiral arrangement of the comb roller is high when entering the ground. In contrast, the lateral force suffered by the parallel arrangement of the comb roller is relatively low and stable. The comb teeth are arranged in a spiral manner, resulting in a structure similar to that of a spiral conveyor. This structure generates a lateral force on the comb rollers. The comb teeth arranged in a spiral configuration underwent minor changes in vertical force, forward resistance, and resisting moment during soil penetration. The maximum difference value for force was 1700 N, and the corresponding moment was 1000 Nm.

In contrast, the comb teeth arranged in a parallel configuration underwent significant changes at these same forces and torques. The maximum force difference value was 6000 N, and the maximum torque difference value was 2500 Nm. One possible explanation is as follows. The comb roller’s parallel arrangement enters the soil at fixed intervals with a row of teeth. In contrast, the spiral arrangement continuously and uninterruptedly inserts numerous teeth into the soil, resulting in a smaller impact force during the insertion.

In the parallel arrangement of the comb roller structure, a large impact force and impact torque are not conducive to the structural stability and operational stability of the recycling machine. Consequently, the entire drive system is somewhat harmed. Therefore, this paper chooses the spiral arrangement to install the comb teeth on the roller.

3.2. Influence of Comb Structure in Soil on Soil Penetration Performance

3.2.1. Test Conditions

Combs that create a small, serrated structure on the working surface are known as toothed combs. On the other hand, combs with smooth working surfaces with no additional structural modifications are called flat combs. As indicated by Figure 9, the comb roller displays a flat knife spiral arrangement and a toothed knife spiral arrangement. In this section, a comparative simulation study is conducted to investigate the law that influences these two structures in the performance of soil penetration. The arrangement is a spiral arrangement, the forward speed is 3 km/h, the rotational speed is 150 r/min, and the depth of soil entry is 12 cm [28].

3.2.2. Simulation Results

A comparison and analysis of the lateral force, vertical force, forward resistance, and resistance moment curves of the flat knife and the toothed knife during soil penetration reveals that both knives similarly influence soil penetration performance. This observation is based on Figure 10.

A simulation test is conducted at standard depths of 6 cm, 10 cm, 12 cm, 14 cm, and 18 cm to examine the impact of the depth of the comb teeth on soil penetration efficiency. The simulation test includes a forward speed of 3 km/h, a rotational speed of 150 r/min, and toothed knife comb teeth. The comb teeth in the rollers follow a spiral arrangement. Figure 11 displays the simulation outcomes.

According to Figure 11, when the depth of the comb in the soil varies within the range of 6–18 cm, the lateral force, vertical force, forward resistance, and resistance moment values suffered by the comb roller increase with soil depth. Moreover, the power consumption of the recycling machine increases with soil depth. The deeper the comb teeth are sunk into the soil, the greater the contact area between the comb teeth and the soil. Consequently, the soil has a greater resistance to the comb teeth. When checking and designing the structural strength of the tillage residual film-recycling machine, the values of force and moment received at the maximum forward speed should be used to design and check the parameters of the frame, shaft, and power output.

3.3. Influence of Comb Speed in Soil on Soil Penetration Performance

The simulation test will be set to the rotational speed standard to investigate the effect of the rotational speed of the combing roller on the performance of soil penetration, i.e., 60 r/min, 80 r/min, 100 r/min, and 120 r/min. Simulation test conditions are as follows: the forward speed is 3 km/h, the depth of soil penetration is 12 cm, the shape of the comb teeth is a toothed knife, and the arrangement of the comb teeth in the roller is a spiral arrangement. The simulation results are shown in Figure 12.

According to Figure 12, when the speed of the comb roller varies within the range of 60–120 r/min, the lateral force, vertical force, forward resistance, and resisting torque acting on the comb roller barrel increase with the depth of the comb in the soil. However, the increase is relatively small. Moreover, the effect of the speed of the comb roller on its performance in the soil is relatively low. The optimal value of comb roller speed should be obtained by further tests and combined with the tillage layer’s residual film pick-up rate index.

3.4. Influence of Forward Speed on Soil Penetration Performance

The simulation test sets the forward speed standard as 2 km/h, 3 km/h, 4 km/h, and 5 km/h to explore the influence of the forward speed of the recycling machine on the performance of soil penetration [29]. The simulation test conditions are as follows: the rotational speed is 150 r/min, the depth of soil penetration is 12 cm, the shape of the comb teeth is a toothed knife, and the arrangement of the comb teeth in the roller is a spiral arrangement. The simulation results are shown in Figure 13.

According to Figure 13, the forward speed of the recycling machine significantly impacts the performance of the comb roller in the soil. The comb roller is subjected to lateral, vertical, and forward resistance. In contrast, the resistance torque is increased with forward speed. The faster the forward speed of the recycling machine, the higher the power consumption. The recycling machine should be combined with power consumption and residual film pick-up rate to choose the optimal value of forward speed.

3.5. Experimental Validation

A comb performance test rig was constructed to validate the simulation results in 2024, as illustrated in Figure 14. The validation test was conducted in the soil tank, with the entire machine’s traction force and the comb roller’s torque serving as the response indexes. The test conditions were as follows: forward speed of 3 km/h, comb roller speed of 150 r/min, soil humidity (RH) in the range of 19–23%, comb arrangement in a spiral arrangement, and comb depth in the soil of 100 mm.

The resistance torque and forward resistance were measured despite the technical limitations of the equipment. As demonstrated in

Table 4. Comparison of simulation test data with actual test data for torque.

	Simulation Results	Actual Result	Numeric Difference
Resistance torque (Nm)	836	910	74
Forward resistance (kN)	2.75	3.22	0.47

, the difference between the simulated and actual comb torque is 74 Nm, and the discrepancy between the simulated and actual traction force is 0.47 kN. The results of the field tests show that the discrete element method can be used to investigate the in-soil performance of the structure of the agricultural tillage machinery.

4. Conclusions

(1) The results of the comb arrangement on the performance of soil penetration are as follows. The lateral force suffered by the combing roller in the spiral arrangement increases. The vertical force, forward resistance, and resisting moment of the spirally arranged combs in soil penetration are relatively small. The comb teeth arranged in parallel are subjected to a large variation of the above forces and moments, with a maximum difference in the force of 6000 N and a maximum difference in the moment of 2500 Nm. The spiral arrangement of comb teeth is the most favorable for the combing roller to penetrate the soil.

(2) The results of the influence of the comb structure on the performance of soil penetration are as follows. The lateral force, vertical force, forward resistance, and resistance moment acting on the comb for flat and toothed knives during soil penetration are the same. However, the toothed knife is more conducive to separating the residual film from the soil. Therefore, this paper chooses the toothed knife structure.

(3) The results of the effect of comb entry depth on the entry performance are as follows. The values of lateral force, vertical force, forward resistance, and resisting moment suffered by the comb roller increase with the entry depth.

(4) The results of the effect of comb roller speed on the performance of soil penetration are as follows. The lateral force, vertical force, forward resistance, and resisting moment suffered by the comb roller increased with the soil penetration depth. However, the increase and the overall degree of influence were small.

(5) The effect of forward speed on the soil entry performance was as follows. The lateral force, vertical force, forward resistance, and the value of the resisting moment experienced by the comb rolls increased with forward speed.

(6) A comparison of the results of the field tests with those of the simulation tests shows that the errors are very small. Moreover, using the discrete element method to explore the in-soil performance of the structures of the agricultural tillage machinery is feasible. Lastly, the proposed method can help select the future structural parameters of agricultural machinery.