Research on the Structure of an Underground Irrigation Composite Pipe-Forming Device

Abstract

In order to promote the comprehensive utilization of corn straw and the development of field water-saving irrigation technologies, a kind of underground irrigation composite pipe-forming device mixed with soil extrusion molding was designed. The key extrusion-forming components affecting the forming rate of composite pipe were optimized by taking the diameter of the winch blade, the shaft diameter of the winch, and the winch pitch as variables and the forming rate and the output power of the winch shaft as test indices. The best structural parameters of the extrusion-forming components were obtained by using the weight normalization method; the diameter of the winch blade was 430 mm, the shaft diameter of the winch was 86 mm, the winch pitch was 387 mm, the forming rate was 1.37 kg/s, and the forming rate of the composite pipe was increased by 41%. Field tests were conducted to verify the simulation test results, and the relative error between the forming rate of composite pipe and the simulation test value was 5.88%, which verified the reliability of the simulation test. The average density of the extruded composite tube was 1.92 g/cm³, meeting the requirements for composite tube formation.

1. Introduction

As a by-product of agricultural production, corn straw has huge output potential but low economic value. Unreasonable disposal causes a series of problems for production and the environment [1,2,3]. Straw return is a common way to treat straw today, mainly through mechanical shredding, burial and return, surface mulching, or a combination of these procedures [4,5,6]. However, according to the survey, the amount of straw returned to the field only accounts for 43.2% of the amount of straw used, and it is difficult to calculate the full amount of corn directly returned to the field [7]. In order to adapt water-saving irrigation technology to modern agricultural production methods, underground irrigation is the main area of focus. However, there are still some application problems, such as the insufficient water supply in the seedling stage, increased risk of clogging, and difficulties in recycling capillary tubes after scrapping [8,9]. Therefore, in view of the advantages and problems of corn straw return to the field, as well as underground irrigation, the idea of underground straw irrigation was proposed, for which a supporting underground irrigation composite pipe-forming device was developed. The crop straw is crushed, then mixed with soil in different proportions to be extruded into a composite pipe with water permeability, followed by one-time burial and direct return to the field after a year or several seasons. This approach can solve the problems related to full amounts of corn straw being directly returned to the field, underground drip irrigation blockage, and pipe recovery. Through preliminary bench tests, the formation performance of the underground irrigation composite pipe basically met the return requirements, but the formation speed was slow and the production efficiency was lower [10]. In order to improve the forming speed of underground irrigation composite pipes and to increase production efficiency, the underground irrigation composite pipe-forming device needs to be optimized.

The discrete element method (DEM) is a numerical simulation method used to calculate the mechanical behavior of discontinuous problems in bulk media systems (dry bulk, wet bulk, or two-phase suspension). This method can reflect the different physical relationships between multiphase media, such as soil, by means of multiple connections between units. Thus, discontinuous phenomena such as cracking and the separation of the soil and the interaction forces between the working parts and the soil particle model can be simulated more effectively [11,12]. Zhang et al. [13] investigated the discrete element simulation parameters of a maize particle bonding model. Chen et al. [14] designed a straw strip picking and crushing deep burial device. The relationship between the operating speed and trenching depth with the movement of surface soil particles and the force on the trenching shovel was simulated using discrete-element full-factor simulation tests. Zhao et al. [15] designed an interactive, layered, deep loosening shovel based on the material characteristics (soil, straw, and root stubble), the slip-cutting principle, and discrete element (EDEM) simulations to analyze the action of a deep loosening shovel on soil. Ding et al. [16] established a discrete element model for deep loosening operations in clayey rice soils based on the actual physical parameters of the field soil. Fang et al. [17] established a discrete element model of the straw–soil–rotation knife interactions in order to explore the displacement of straw during the rototilling process. Hiroaki et al. [18] applied the discrete element method to establish a soil mechanics model and verified the applicability of the established model using soil infiltration tests and a simulation analysis. From the literature, it is known that the extrusion-forming components of the underground irrigation composite pipe-forming device, diameter of the winch blade, shaft diameter of the winch, and winch pitch have an important influence on the composite pipe-forming rate. At present, the research on straw-returning machinery mainly focuses on the design and testing of the whole machine, but there is less research on the mechanism of machine–soil–straw interactions, and the research on the influence of extrusion-forming parts on the forming rate of composite pipes is still unclear.

In this paper, the simulation model of an underground irrigation composite pipe-forming device is established by using the discrete element analysis method, and on the basis of the simulation and a theoretical analysis, a comprehensive performance index analysis is carried out using the weight normalization method. The key extrusion-forming parts affecting the forming rate of composite pipe are optimized and tested by taking the forming rate and the winch output power as the evaluation index of the forming device operation, and the optimum structural parameters of the extrusion-forming components are analyzed to achieve the optimization of the forming device.

2. Introduction to Forming Device for Underground Irrigation Composite Pipe

The forming device for the underground irrigation composite pipe mainly includes power parts, mixing parts, extrusion parts, and housing. The drive components mainly include the three-phase asynchronous motor, reducer, pulley, drive gear, stirring left-driven gear, and stirring right-driven gear. The mixing parts mainly include the left power shaft, the right power shaft, and four mixing plates. The extruded parts are mainly composed of the auger shaft and auger blade. The casing is not only a protective structure but also the main part of the shaping of straw composite pipes. The specific structure is shown in Figure 1. The diagram shows the structure of the forming unit for bench testing. The underground irrigation composite pipe-forming unit is connected to the tractor and moved onto the farm at a later stage, with the rear output shaft of the tractor providing power to the forming unit.

3. Design of Extrusion Parts

The diameter of the winch blade affects the shaft diameter of the winch; the shaft diameter of the winch and the winch pitch together affect the angle of rise of the reamer blade, which also determines the speed and direction of movement of the mixture in the auger conveyor. In order to improve the forming rate of the underground irrigation composite pipe, we mainly studied the extrusion-forming components of the underground irrigation composite pipe-forming device. We finally determined the suitable combination of parameters for the diameter of the winch blade, the shaft diameter of the winch, and the winch pitch.

Determination of Parameters of Extruded Parts

As an essential parameter of extrusion, the diameter of the winch blade directly affects the size and output of the device. To determine the diameter and size of spiral auger blades, factors such as the material conveying type, production capacity, and layout and structure of the extrusion-forming device components need to be considered.

The formula for the diameter of the winch blade is [19]:

$$D=K{\left(\frac{Q}{\varphi \lambda \epsilon }\right)}^{\frac{2}{5}}$$

(1)

where $K$ is the comprehensive characteristic coefficient of material, the value of which is 0.05; $Q$ is the displacement per unit time for the auger conveyor; $\varphi$ is the filling factor, the value of which is 0.3; $\lambda$ is the material density, the value of which is 0.15; $\epsilon$ is the inclined conveying coefficient, the value of which is 0.46.

In order to ensure the consistency of the mixed material feed rate of the extrusion molding device and the forming rate of the straw composite pipe, the displacement per unit time of the screw conveyor should be equal to the feed rate. According to the GB/T24675.6-2009 “Protective Tillage Machinery Straw Crushing and Returning Machine” field test. Before the test, a distance of 10 m is measured with a tape measure and a certain stable area is left before the 10 m measurement. After starting the equipment, the speed of the tractor will remain stable after running in the stability zone for a period of time. When entering the 10 m measurement area, the unit’s running time is measured with a stopwatch, and finally the tractor’s driving speed is obtained. The test showed that the amount of straw picked up by the straw returner with a width of 100 cm was 1394.72 g per 100 cm. Since the amount of straw picked up accounted for 5% of the total material, it can be calculated that the total mass of the mixed material was 27,894.40 g. According to the different driving speeds of the tractor, different material feeding quantities can be determined, i.e., $Q_1$ = 3.5 t/h, $Q_2$ = 4 t/h, and $Q_3$ = 4.5 t/h.

The above can be substituted into Formula (1) to get $D=0.05\times {\left(\frac{Q}{0.3\times 0.15\times 0.46}\right)}^{\frac{2}{5}}$, $D_1$ = 0.389 m = 389 mm, $D_2$ = 0.410 m = 410 mm, $D_3$ = 0.430 m = 430 mm. The diameters of the winch blades were $D_1$ = 390 mm, $D_2$ = 410 mm, and $D_3$ = 430 mm.

The screw diameter affects the size of the screw reamer shaft diameter, and the screw shaft diameter and the screw diameter together affect the lift angle of the reamer blade. These two aspects together determine the speed, size, and direction of movement of the mixture in the spiral winch conveyor. Thus, the reasonable numerical relationship between the spiral shaft diameter and the screw diameter should take into account the friction between the spiral surface of the winch blade and the extruded material being conveyed, as well as the velocity component of the mixture.

In general, the calculation formula for the shaft diameter of a winch is $d=\left(0.2~0.35\right)D$. The value is 0.2, so $d_1$ = 78 mm, $d_2$ = 82 mm, and $d_3$ = 86 mm.

The pitch of the screw not only affects the spiral lift angle but also affects the slip surface of the material transported under a certain filling factor; therefore, the size of the pitch directly affects the conveying state of the mixed material. When the discharge volume Q per unit time of the spiral winch conveyor and the diameter D of the diameter of winch blade are determined values, the winch pitch changes, the mixture conveying slip surface will also be changed, and the corresponding mixture conveying speed distribution occurs. Therefore, the determination of the spiral pitch should satisfy the following two relations: first, the distribution relation between the components of the material conveying the velocity; second, the friction relation between the surface of the spiral blade and the mixed material.

The calculation formula for the winch pitch is $S=K_{1}D$. For the spiral-stranded extruded parts, the $K_1$ values usually range from 0.8 to 1.0. Here, we take the value of 0.9 and substitute this into the formula to get $S_1$ = 351 mm, $S_2$ = 369 mm, and $S_3$ = 387 mm. The parameter values of extrusion-forming parts are shown in

Table 1. Parameter values of extrusion-forming parts.

Diameter of Winch Blade/mm	Shaft Diameter of Winch/mm	Winch Pitch/mm
390	78	351
410	82	369
430	86	387

.

4. Simulation Test of Extruded Parts

The extrusion-forming component is the key component of the underground irrigation composite pipe-forming device, and the combination of its structural parameters has an important influence on the forming effect of the composite pipe-forming device. A discrete element simulation model of the extruded forming parts was established for simulation tests. The structure and working parameters of the diameter of the winch blade, the shaft diameter of the winch, and the winch pitch on the discharge rate were assessed.

4.1. Determination of Parameters of Extruded Parts

According to the theoretical calculation used to obtain three sets of different values for the diameter of the winch blade, the strand blade pitch, and the shaft diameter of the winch, three-dimensional modeling is necessary to obtain three different simulation models of the extruded parts, as shown in Figure 2 (the following three components are represented by the diameter D of the winch blade; D₁ represents the parameter combination of the diameter of winch blade, which is 390 mm, the shaft diameter of the winch is 78 mm, and the winch pitch 351 mm, while D₂ and D₃ are equivalent to D₁).

4.2. Parameter Setting of Discrete Element Model

The particle model connects soil and straw using the Hertz–Mindlin function with JKR, and the particle model is bonded together through a certain size of the “bonding bond” [20]. When the particles begin to adhere, the normal force $F_n$, tangential force $F_t$, normal torque $T_n$, and tangential torque $T_t$ can be calculated between the particle models. The normal velocity and tangential velocity of the particle model are $V_n$ and $V_t$, respectively; the normal angular velocity of the particle model is n and the tangential angular velocity is $w_t$. When the time step t increases from 0, $F_n$, $F_t$, $T_n$, and $T_t$ also change accordingly. The calculation equation is as follows:

$$\delta F_n=\pi R_B^2{\nu }_n{S}_n\delta t$$

(2)

$$\delta F_t=\pi R_B^2{\nu }_t{S}_t\delta t$$

(3)

$$\delta T_n=2\pi R_B{\omega }_n{S}_t\delta t$$

(4)

$$\delta T_t=\pi R_B{\omega }_t{S}_n\delta t$$

(5)

where $R_B$ is the radius of the “bond key”; $\delta t$ is the time step; $S_n$ is the normal stiffness; $S_t$ is the tangential stiffness.

This “bonding bond” can withstand both tangential and normal motions, and when the maximum normal as well as the tangential shear stresses are reached, the bond breaks [21]. After this, the particles will be treated as rigid spheres for the contact solution; that is, in order to prevent bond rupture between particles, the critical values of normal and tangential shear stresses between particles need to satisfy the following formulae:

$${\sigma }_{\max }<\frac{-F_n}{\pi R_B^2}+\frac{4T_t}{\pi R_B^3}$$

(6)

$${\tau }_{\max }<\frac{-F_t}{\pi R_B^2}+\frac{2T_n}{\pi R_B^3}$$

(7)

where ${\sigma }_{\max }$ is the critical value of normal adhesion; ${\tau }_{\max }$ is the critical value of tangential adhesion.

These bonding forces and moments are not present in the standard Hertz–Mindlin model. This is because the bonding bonds in this model can still function when the particles are not in physical contact. In order to reflect the natural contact between the particle models, the model contact radius should be set larger than the actual radius of the particles.

Building the simulation model requires the basic particle model to be defined and corn and soil particle models to be created, where the particles are composed of one or more spherical surfaces; corn particles are composed of nine spherical surfaces and soil particles are represented by one spherical surface. We created a discrete element model of the underground irrigation composite pipe-forming device and assigned its material properties to steel. We specified the spiral strand shaft dynamics, and the geometry can be set to move partially during the simulation. In this model, corn straw particles and soil particles complete the extrusion-forming motion with the clockwise rotation of the spiral strand shaft. This spiral strand shaft rotation is set by the linear rotational power of the screw section, and the strand shaft speed is set to 470 rpm, followed by the setting of the rotation shaft direction and the starting and stopping points. The starting point along the direction of the curvature of the winch blade points to the end position. According to the right-hand rule, the direction of the starting point to the end point is the direction of rotation of the gibbet shaft, and the thumb’s point is the direction of discharge of the extruded underground irrigation composite pipe. The particle plant plate was created to define when, where, and how the corn and soil particle models would appear in the simulation. This is shown in Figure 3.

All particle plant plates had to be built on geometric sections. In order to simulate the working state of the underground irrigation composite pipe-forming unit as much as possible, a virtual plate was created at the top of the feed barrel, which defines the area in the particle model where the particles are generated. Next, the domain of the simulation area is defined. The domain is the area where the simulation process will take place, and the simulation simulator stops tracking any particles that move out of the domain during the simulation. The domain size has an impact on the simulation time, whereby the larger the domain, the longer the simulation takes to run. The size of the computational domain is based on the default size of the imported model of the underground irrigation composite pipe-forming device. The required parameters for the simulation are shown in

Table 2. Simulation parameters.

Parameter	Numerical Value	Parameter	Numerical Value
Device model density ${\rho }_1$	7850 kg/m3	Soil–Soil recovery coefficient e1	0.25
Device model shear modulus G1	7.90 × 1010 Pa	Soil–Steel recovery coefficient e2	0.5
Device model Poisson’s ratio ${\nu }_1$	0.3	Straw–steel recovery coefficient e3	0.6
Soil particle model bulk density ${\rho }_2$	1385 kg/m3	Soil–Soil static friction coefficient ${\mu }_{11}$	0.7
Shear modulus of soil particles G2	2.97 × 108 Pa	Soil–Steel static friction coefficient ${\mu }_{12}$	0.5
Poisson’s ratio of soil particles ${\nu }_2$	0.3	Straw–Steel static friction coefficient ${\mu }_{13}$	0.3
Straw particle model density ${\rho }_3$	100 kg/m3	Soil–Soil rolling friction coefficient ${\mu }_{21}$	0.03
Shear modulus of straw particles G3	1 × 106 Pa	Soil–Steel rolling friction coefficient ${\mu }_{22}$	0.01
Poisson’s ratio of straw particles ${\nu }_3$	0.4	Straw–steel rolling friction coefficient ${\mu }_{23}$	0.01

[22,23].

4.3. Simulation Test

From the analysis, it can be seen that the main factors affecting the extrusion rate of the mixture in the underground irrigation composite pipe-forming parts are the diameter of the winch blade, the winch pitch (387 mm), and the shaft diameter of the winch. Simulation experiments were performed on the extruded parts with three sets of parameters. With the amount of straw picked up accounting for 5% of the total mixed material, the generation rate of the straw particles was set to 0.1584 kg/s, the generation rate of the soil particles was set to 3 kg/s, the generation time was 3 s, and the total simulation time was 8 s. After the simulation was completed, the average forming rate at the discharge port and the output power of the winch shaft were recorded, as well as being calculated for the three sets of parameter combinations. The simulation process is shown in Figure 4.

In the simulation test, in order to ensure the reliability of the test results, the formed mass flow rate of the underground irrigation composite pipe at a certain time was used as the test index. Too little power in the working process will affect the operational efficiency of the equipment, while too much power will increase the energy consumption of the equipment. Therefore, a reasonably accurate assessment of the power is particularly important. The output power of the underground irrigation composite pipe-forming device under the combination of three parameters was obtained as a reference basis for the equipment evaluation.

4.4. Simulation Test Results and Analysis

4.4.1. Forming Rate of Composite Pipe

As shown in Figure 5, the horizontal coordinates represent the three different structural parameters, while the vertical coordinates represent the forming rate (kg/s). For the accuracy of the simulation results, the simulation time was selected as 5–8 s, while the forming rate was the average mass flow rate of the composite pipe formed from the 5th to the 8th second for three groups of different structural parameters. The final composite pipe-forming rates for the three groups of different parameters of an underground irrigation composite forming device were in the order of D₃ > D₁ > D₂.

4.4.2. Output Power of Auger Shaft of Extruded Parts

In the discrete element simulation software, the power data can be output. As shown in Figure 6, the output power data for the gibbet shaft of the device under a specific operating condition is shown. The output power does not include the power consumed by the device due to friction or inertia. Thus, we can understand the power required for mixing and extruding materials and can provide the design parameters for the motor selection and reducer design, which can provide an effective guarantee to improve the operation efficiency, reduce the equipment energy consumption, and extend the equipment life.

As shown in Figure 6, the horizontal coordinate represents the simulation time (s), while the vertical coordinate represents the output power of the winch shaft (kW). For the accuracy of the simulation results, the simulation time range is selected as 5–8 s, while the output power of the winch shaft is the average value of the time period. It can be seen that the output power of the winch shaft is positively correlated with the change in diameter of the winch blade, while the output power order for the winch shaft of the underground irrigation composite forming device with three different groups of parameters is D₃ > D₂ > D₁.

4.4.3. Analysis of Simulation Results

The above two indicators were normalized, and then a comprehensive performance analysis was carried out. The comprehensive performance index is a weighted average of the indexes of the composite tube forming rate and winch shaft output power according to a weight ratio of 6:4. This can reflect the performance of the molding test device in a comprehensive manner.

According to the calculation results of the comprehensive performance index, a visual analysis was carried out, and the corresponding extreme differences were finally obtained. The results of the visual analysis of the influence of each structural parameter on the comprehensive performance index are shown in Figure 7.

As shown in

Table 3. Comprehensive performance calculations of test indicators.

Combination of Structural Parameters of Underground Irrigation Composite Pipe-Forming Device	Measured Calculated Value		Normalized Value		Comprehensive Performance Indicators
	Q /kg⋅s−1	W /kW	q’	w’
D1	1.26	180.49008	0.307317073	−0.310766722	0.060083555
D2	1.2	193.51952	0.292682927	−0.333200732	0.042329463
D3	1.64	206.78	0.4	−0.356032546	0.097586982

Note: Q is the material output rate, Kg⋅s⁻¹; W is the power, kW; q’ is the normalized material output rate; w’ is the normalized power.

, through the weighted average of different weights for the two indicators of the forming rate and gibbet shaft output power, the comprehensive performance index values of the molding test device with different structural parameters shown in Figure 7 were obtained in the order of D₃ > D₁ > D₂. Therefore, the best combination of structural parameters for the extrusion molding parts was a winch blade diameter of 430 mm, winch shaft diameter of 86 mm, and winch pitch of 387 mm.

5. Experimental Validation and Comparison

In order to verify the validity of the simulation optimization results of the extrusion-forming parts and to compare and analyze the forming efficiency of the extruded composite pipe of the underground irrigation composite pipe-forming device before and after the optimization of the extrusion-forming parts, the test was carried out at the facilities of Moist Agricultural Equipment Co., Ltd., in Hebi City, Henan Province, China, using a constructed corn straw return machine. The main working parts of the corn straw return machine include straw collection, crushing, conveying, and trenching mechanisms, as well as an underground irrigation compound pipe-forming device. The parameters of the underground irrigation composite pipe-forming device were optimized; the diameter of the winch blade was 430 mm, the shaft diameter of the winch was 86 mm, and the winch pitch was 387 mm. The field operation of the test prototype is shown in Figure 8.

The test material was corn from the local test field, and the moisture content of the corn in the area was obtained at 25% by sampling the average values randomly for different areas. To ensure the effectiveness of the field test, a 2-m-wide and 10-m-long area was selected for the underground irrigation composite pipe-forming test. Before the test, the underground irrigation composite pipe-forming device was controlled at about 470 r/min by adjusting the tractor output shaft speed. With 1 m as the marker amount, a test distance of 6 m was chosen. The tractor works at a traction speed of 6.5 km/h. Under the tractor’s traction, the whole machine started to operate in the field. According to the preliminary test, we obtained a composite pipe with an outer diameter of 100 mm and an inner diameter of 30 mm, and the composite pipe’s forming density was not less than 1.30 g/cm³, as qualified in [10]. When the whole machine operating distance reaches 1 m, the stopwatch records the operating time and the composite pipe length of 100 cm is weighed. A total of six sets of forming weight and forming time values for the composite pipe measuring 100 cm in length were recorded, and the forming density and forming rate were calculated. The test six was performed times to obtain the average value; the test results are shown in

Table 4. Test results.

Test Number	Before Optimization		After Optimization
	Forming Density /(g/cm3)	Forming Rate /(kg/s)	Forming Density /(g/cm3)	Forming Rate /(kg/s)
1	1.99	2.21	1.87	3.12
2	2.07	2.20	1.91	3.11
3	1.87	2.22	1.93	3.13
4	1.91	2.36	1.94	3.28
5	1.94	2.49	1.94	3.41
6	1.93	2.40	1.94	3.32
Average test data	1.95	2.31	1.92	3.23

.

The composite pipe had an outer diameter of 100 mm and an inner diameter of 30 mm obtained. It was a hollow pipe made of a mixture of straw, water, and soil extruded by an underground irrigation composite pipe-forming device. It had a uniform texture and a smooth inner wall. There were uniform tiny cracks distributed on the wall of the pipe, which provided better water transmission and permeability conditions. This setup has the potential to become a different type of irrigation material.

The underground irrigation composite pipe with a length of 100 cm was weighed, and the formula was calculated to obtain the volumes of two different pipe diameters. Finally, the molding density values of two kinds of underground irrigation composite pipes were calculated. When the calculated density of the composite pipe reached at least 1.30 g/cm³, it was qualified; that is:

$$\rho =\frac{m}{v}$$

(8)

where $\rho$ is the density (g/cm³); $m$ is the composite tube mass (g); $v$ is the composite tube volume (cm³).

The mass of the underground irrigation composite pipe with a length of 100 cm was divided by the forming time to obtain the forming rate (kg/s).

The main data in Table 4 represent the composite tube’s forming density and forming rate before and after optimization, showing the average of six sets of test data for comparison. From Table 4, it can be seen that the relative error between the actual test value of the forming rate and the simulation-optimized value is 5.88%, which is less than 6%, verifying that the simulation-optimized test is reliable. The average value of the density of the extruded composite pipe is 1.92 g/cm³, which is greater than 1.30 g/cm³ and meets the requirements for composite pipe formation. The optimization of the extrusion molding parts effectively improved the working performance of the underground irrigation composite pipe molding device.

6. Conclusions

In this paper, theoretical analysis and design calculations were obtained to improve the forming rate of a composite pipe. The key lies in optimizing the structural parameters of the extrusion-forming parts of the underground irrigation composite pipe-forming device. By establishing the underground irrigation composite pipe-forming device (straw–soil discrete element model), the optimal structural parameters of the extrusion-forming parts of the underground irrigation composite pipe-forming device were determined using two indicators: the forming rate and winch shaft output power. The validity of the simulation results was verified using field tests, and the following conclusions were drawn:

(1)

According to the theoretical calculation, the structural parameters of the extrusion-forming part of the underground irrigation composite pipe-forming device were designed and optimized. The three-dimensional solid modeling of the underground irrigation composite pipe-forming device with three different structural parameters was completed, and the underground irrigation composite pipe-forming device–straw–soil discrete element model was established using discrete element software.

(2)

From the simulation results, we could see that a composite pipe with certain level of adhesion can be extruded and formed, which proved the rationality of the structural optimization and the correction of the simulation parameters. Through structural optimization, the forming rate of the composite tube was increased by 41%. The average flow rates from 5 s to 8 s were obtained from the composite tube forming rates in the order of D₃ > D₁ > D₂; the output power values of the strand shaft from 5 s to 8 s were in in the order D₃ > D₂ > D₁, and the output power of the strand shaft was positively correlated with the diameter of the strand blade.

(3)

The 2 indicators of the forming rate and winch shaft output power were normalized. According to the weight distribution of 6:4, the comprehensive performance index analysis was carried out, and the best combination was finally identified when the material moisture content was 23% and the spiral shaft speed was 470 r/min. The structural parameters of the extrusion-forming part of the underground irrigation composite pipe-forming device were as follows: the diameter of the winch blade was 430 mm, the shaft diameter of the winch was 86 mm, and the winch pitch was 387 mm. At this time, the best performance for the forming test device was achieved.

(4)

In order to verify the validity of the simulation results, a field test of the underground irrigation composite pipe-forming device was conducted. The relative error between the actual test value of the composite pipe-forming rate obtained from the field test and the simulation-optimized value was 5.88%, which was less than 6%, verifying the reliability of the simulated optimized test. The average value of the extruded composite pipe’s compactness after the optimization of extrusion-forming parts was 1.92 g/cm³, which met the requirements for composite pipe formation; meanwhile, the forming rate of the composite pipe increased by 39%. The optimized extrusion-forming parts effectively improved the working performance of the underground irrigation composite pipe-forming device and provide a technical reference for the combination of straw crushing and trenching and burying tools to form a combined operation machine.