Design and Testing of Air-Separation-Type Tillage Layer Residual Film Recovery Machines

Abstract

Existing residual film recovery machines for the cultivated layer struggle to achieve an efficient separation of plastic film from impurities during operation. To address this challenge, a wind-separation-type residual film recovery machine equipped with a cross-flow fan was designed. Through theoretical analysis and field tests, the optimal operational parameters were determined. In this paper, with the recovery rate and impurity content of the residual film were taken as the test objectives, with the air inlet angle, fan speed, and the proportion of residual film quality as the test factors. The response surface diagram was drawn with design-expert software, and the optimal parameters of the fan device obtained by orthogonal test range analysis and variance analysis were that when the air inlet angle was 31°, the fan speed was 1277 r/min, and the residual film mass accounted for 62%. Under these parameters, the residual film recovery rate was 88.1%, and the impurity content was 3.7%, which met the operational requirements of residual film recovery, and the research results could provide a basis for the recovery of residual film in the tillage layer.

1. Introduction

Mulching cultivation technology originated in Europe and has gradually spread to the United States, Japan and the world at large due to its good economic benefits [1]. In China, plastic film mulching technology is widely used in agricultural production, significantly increasing crop yields, improving soil microenvironment, and enhancing water use efficiency [2]. Relevant data show that the use and coverage area of agricultural mulch film in China have gradually increased in recent years [3]. However, due to the failure of China to implement a policy on plastic film recycling in the process of promoting plastic film mulching technology, there has been a massive accumulation of plastic film residue in the agricultural soil [4]. With an increase in plastic film use, the amount of plastic film residue gradually increases, and the accumulation of residual film causes the deterioration of soil physical properties, resulting in soil compaction, which poses a great threat to the agricultural environment [5]. Since most foreign countries use plastic film with a thickness of more than 0.015 mm, the plastic film is relatively intact after use, and the recycling of the plastic film can be completed by means of retraction [6]. In contrast, the lack of unified standards and relatively poor mechanical properties of plastic film in China often renders it difficult to carry out simple mechanical recycling, which leads to the gradual downward migration of plastic film and the formation of persistent residual film in the topsoil or the tillage layer.

To address the challenge of residual plastic film recovery from cultivated layers, research institutions worldwide have developed various types of residual film recovery equipment [7,8,9,10,11,12,13,14]. One notable development is the 11MS-2.0 cultivated-layer residual film recovery machine, which employs a dual-stage reciprocating vibrating screen working in tandem with a centrifugal fan [5]. In this design, the centrifugal fan serves as the separation device, directly suctioning residual film at the end of the reciprocating vibrating screen. However, this approach presents significant limitations: direct suction of the film–impurity mixture by the centrifugal fan not only hinders the effective separation of residual film from straw and soil clods, but also leads to film entanglement around the fan impeller. Guo et al. [6] developed an alternative design featuring a comb-tooth loosening device coupled with a film-suction system. This machine utilizes rotating comb-tooth rollers to introduce soil into a gravity settling chamber, where the film mixture is then conveyed through a suction pipeline system powered by a centrifugal fan, ultimately collecting the residual film at the fan’s outlet. Nevertheless, this design suffers from inadequate airflow volume and pressure in the centrifugal fan, resulting in poor separation of the film from straw and soil clods, as well as significant film accumulation within the suction pipelines. The principle of the plastic film recovery machines in Japan, Europe and America is often relatively simple, such as in Chrysler, R.W. [15]. A machine capable of removing the plastic film covering layer was designed. The machine was driven forward by a tractor, and the film was directly pulled for recycling by a scraper and a film rolling roller device. Kanat M. Khazimov et al. [16] proposed a roller for a plastic covering recycler, which is used to directly pull and recycle plastic films during crop harvest. Due to the good quality of the plastic film, in regions outside China, the plastic film can be recycled simply by rolling it up. Therefore, the relevant experience from abroad has little reference significance for the issue of residual film recycling in China. Given the persistent issues of low recovery rates, high impurity content, and difficult film–impurity separation in current Chinese residual film recovery machines, our research team has identified that employing large cross-flow fans can effectively separate residual film from cotton stalks, soil clods, and other debris. Building on the distinct physical properties of various components in the film mixture [17], we have designed a novel cross-flow fan system that achieves rapid film–impurity separation and efficient residual film recovery. This development provides valuable insights for advancing cultivated-layer residual film recovery technology.

2. Materials and Methods

2.1. Structure and Working Principle

The membrane impurity separation device is mainly composed of a screen device, a cross-flow fan device, a walking wheel device, a conveyor pulley, etc. The mechanism structure is shown in Figure 1.

The residual film recycling machine is connected to a high-horsepower tractor through three-point suspension, and the residual film recycling machine adjusts the depth of its work through the depth-limiting wheel device during operation. During the excavation process, the shovel blade and screen will shear the soil, and the large pieces of soil and cotton stubble will be continuously broken into medium size, and when they fall into the roller pairing device, the soil and cotton stubble and other impurities will be further sheared. At the same time, the vibration of the machine will aggravate this process, a large number of broken soil clods and cotton stubble will fall back to the field in the process of conveyor chain transmission, and the unbroken part of the soil clods, cotton stubble, and residual film will be pushed by the conveyor chain to the membrane impurity separation device for further separation.

2.2. Working Principle

When the device is operating, the tractor transmits the power to the membrane impurity separation device through the suspension device, due to the difference in the suspension speed in the air medium. The speed of the fan is adjusted by the variable speed pulley to realize the adjustment of the size of the air flow, the high-speed rotation of the through-flow fan induces the air flow from the air inlet, and then through the blade disturbance, the air flows out of the fan laterally along the radial direction through the air outlet, producing a uniformly distributed flow field. Since the suspension speeds of the residual film, cotton stalk, and soil are different, their throwing distances in the horizontal direction also vary. The residual film suspension speed is small but the throwing distance is far, so it is blown into the film collection box device, while impurities such as cotton straw and soil have short throwing distances, so they fall to the ground, hence the separation of film impurities.

2.3. Motion Analysis and Key Devices of the Membrane Mixture

The membrane mixture is subject to gravity and airflow in the airflow field, and falls down through the secondary screen first, and the material is stressed as shown in Figure 2, due to the obvious difference in suspension speed, density, and quality of cotton straw, residual film, and soil. When subjected to the action of the airflow drag force of the cross-flow fan, the membrane mixture has different movement trajectories, as shown in Figure 2, where it is affected by the airflow drag force F_f and gravity G in the airflow field.

We performed a force analysis on the material in the flow field, and then

(1)$G=mg$

(2)$F_{\mathrm{f}}={\displaystyle \frac{1}{2}}{C}_d\rho S{\mathrm{v}}_{\mathrm{f}}^2$

where

m = Material mass kg;

g = Acceleration due to gravity 9.98 m/s²;

C_d = Drag coefficient, take 0.44

$\rho$ = Air density 1.29 kg/m³;

v_f = Wind speed of fan outlet m/s;

S = Windward area of the material m².

By consulting relevant literature, we can obtain the above-mentioned data [18]. Here, the drag force of the air flow is decomposed along the x-axis and y-axis to analyze the force of the membrane mixture, where a_x represents horizontal acceleration and a_y represents vertical directional acceleration.

(3)$G-F_f\sin \alpha =m{a}_y$

(4)$F_f\cos \alpha =m{a}_x$

(5)$a_y={\displaystyle \frac{G-F_f\sin \alpha }{m}}$

(6)$a_x={\displaystyle \frac{F_f\cos \alpha }{m}}$

S_y = Distance of the membrane mixture from the highest point of the screen, m;

S_x = Horizontal displacement of the membrane mixture during the separation process, m.

(7)$v_{1x}=v_1\sin \beta$

(8)$S_y={\displaystyle \frac{1}{2}}{a}_y{t}^2$

(9)$S_{\mathrm{x}}=v_{1x}t+{\displaystyle \frac{1}{2}}{a}_x{t}^2$

S_x = Horizontal displacement, m;

S_y = Vertical displacement, m;

v_1x = Horizontal component of initial velocity of material; m/s;

t = Material falling time, s;

v₁ = Initial velocity of the material, at an angle of β with the negative y-axis direction, m/s.

In order to achieve the effect of membrane impurity separation, it is necessary to ensure that the residual membrane can smoothly enter the collecting tank before it falls to the ground in the horizontal displacement direction. Therefore, we substitute Formulas (3)–(8) into Formula (9) to obtain the horizontal displacement S_x.

(10)$S_x=v_1\sin \beta \sqrt{{\displaystyle \frac{2S_{\mathrm{y}}}{G-F_f\sin \alpha }}}+{\displaystyle \frac{C_d\rho A{v}_f^2\cos \alpha }{2mg-C_d\rho S{v}_f^2\sin \alpha }}$

Formula (10) illustrates the relationship between the horizontal displacement of the residual film and impurities and various factors. In order to obtain the optimal working parameters for the subsequent field experiments, we need to know which parameters affect the horizontal displacement.

According to Formula (9), the horizontal displacement of the material can be deduced from the equation, and the horizontal displacement is related to the airflow velocity, the mass of the material, the angle of the airflow, the initial velocity of the material, the angle between the initial velocity of the material and the negative direction of the y-axis, the density of the material, and the windward area A of the material, so the airflow velocity and the airflow angle are important factors affecting the efficiency of the device.

2.4. Through-Flow Fan Device

During the process of picking up residual film, the screening mechanism will carry a large number of impurities, resulting in a large number of soil clods, cotton stalks and other impurities in the residual film after the operation of the recycling machine. In order to better reduce the impurity content of the recycled residual film, we plan to add a separation device. Since the cross-flow fan has the advantages of large air volume, compact structure and uniform axial distribution, it avoids the problems of impeller blockage and insufficient air volume encountered when the centrifugal fan is used as a separation device. Moreover, the transverse dimension of this residual film recycling machine is relatively large, and the axial length of the cross-flow fan is not restricted. Therefore, we chose the cross-flow fan as the separation device of the residual film recycling machine. By utilizing the suspension velocities of the residual film and cotton stalk soil clods in the air, a wind speed greater than the suspension velocity of the residual film and less than that of the cotton stalk soil clods is provided at the outlet of the cross-flow fan. In this way, the residual film will be blown into the film collection box under the action of the wind pressure generated by the cross-flow fan, while impurities such as straws and soil clods will fall to the ground, thus realizing the operation of separating the film from impurities. Referring to the design method given by Tao Nan [19], the structural parameters of the cross-flow fan are as follows: the total width of the fan is 1200 mm, the outer diameter of the impeller is 440 mm, the inner diameter of the impeller is 312.4 mm, the impeller inclination angle is 25°, and the number of blades is 32 (see Figure 3). Here, the bracket is used to fix the cross-flow fan and the residual film recycling machine, and the air volume adjustment plate is used to adjust the air volume.

3. Field Experiment

3.1. Test Conditions and Equipment

In April 2024, the actual machine test was carried out in Yuli county, Korla prefecture, Xinjiang, and the test site was a cotton field after harvest, with a soil moisture content of 19%, a soil firmness of 2.4 MPa, and a plastic film quality of 18.2 g/m². In accordance with the test method specified in the national standards “GB/T 25412-2021 [20] Residual Plastic Film Recycling Machine”, the membrane impurity separation device was tested on the ground, as shown in Figure 4. The test equipment mainly includes the following: ME204E electronic balance scale (range 0–220 g, accuracy 0.1 mg), tape measure, stopwatch, HD2 soil moisture meter (measurement range 0–100%, measurement accuracy ± 0.2%), 6234P non-contact tachometer (range 2.5–99,999 r/min, accuracy: ±0.05% + 1), effective wind speed tester (range 0–30 m/s, accuracy: ±5%, accuracy: ±0.1 m/s), DELIXI digital inclinometer (accuracy ± 0.2°) and other instruments and equipment.

3.2. Test Indicators

Based on the operation requirements, theoretical analysis and fan parameter limitations of the membrane separation device, the inlet angle A (20–40°), the fan speed B (1000–1400 r/min) and proportion of residual film quality C (40–80%) were selected as the test factors. The Residual Film Mass Ratio refers to the percentage of the residual film mass relative to the total mass of residual film and impurities. In addition, the recovery rate and impurity content of residual film were used as important indicators to evaluate the recovery effect, and they were selected as test indicators for field experiments. Referring to the provisions in “GB/T 25412-2010 [20] Residual Mulch Film Recycling Machine”, the calculation formulae are as follows.

(11)$Y_1=(1-{\displaystyle \frac{W}{W_0}})\times 100\%$

(12)$Y_2={\displaystyle \frac{\mathrm{m}}{M}}\times 100\%$

where

Y₁ = Residual film recovery rate (%);

Y2 = Impurity content (%);

W = Quality of the deep residual mulch film after operation (g);

W₀ = Quality of the deep residual mulch film before operation (g);

m = Mass of impurities in the film collection box (g);

M = Total mass of residual film and impurities in the film collection box (g).

3.3. Test Protocol

We carried out a three-factor three-level analysis test, using the Box–Behnken design in Design-Expert13 software. The response surface methodology (RSM) was implemented using the Box–Behnken design (BBD) module in Design-Expert 13 (Stat-Ease Inc., Minneapolis, MN, USA, https://www.statease.com/software/design-expert/), (accessed on 25 May 2024) [21] with the air inlet angle A, fan speed B, and proportion of residual film quality C as the test factors. Then, 17 groups of tests were conducted by selecting 5 points on the diagonal of the measurement area. At each point, the residual film was collected with a width area of 5 m× and depth of the surface and soil layer of 0–200 mm. Then, we removed the binders on the waste film, measured the quality of the residual film and the quality of the residual film impurities in the film collection box before and after operation at each point with an electronic balance scale, and used Formulas (10) and (11) to calculate the recovery rate and impurity content of the residual film. The test factors are shown in Table 1. After the completion of the field test, the results were recorded, and the test results are shown in Table 2.

4. Results and Discussion

4.1. Test Results

The experimental design protocol and results are shown in Table 3. The parameters of the influencing factors were analyzed according to the experimental results.

The analysis of variance of the regression equations for residual film recovery and impurity content derived from the experimental results is shown in Table 3. The residual film recovery test model p < 0.001 indicates that the model is extremely significant, which can reflect the relationship between the residual film recovery and the independent variables, among which A, B, C, A2, B2 and C2 are extremely significant for the residual film recovery Y1. For the impurity Y2, the parameters A, B, C, AB, AC, BC, A², B², and C² are extremely significant.

The optimal parameters of the residual film recycling machine were obtained by multiple regression fitting analysis with Design-Expert13 software. It can be seen from Table 3 that the p values of the terms were all less than 0.01, and the significance levels of the surface factors were extremely high, and the p values of the terms were all less than 0.05, indicating a high level of surface significance. However, the significance levels of other terms were not high. The regression coefficient equations for the residual film recovery rate Y₁ and the impurity content Y₂ are established as follows:

(13)$Y_1=87.06+0.71A+1.12B+0.98C-1.11A^2-0.89B^2-0.2775C^2$

(14)$R^2=4.13-0.15A+0.18B-0.64C+0.12ab+0.03AC-0.08BC+0.94A^2+0.99B^2+0.18C^2$

4.2. Analysis of Interactive Influencing Factors

Figure 5 shows the relationship between the residual film recovery rate and impurity content, as well as multiple factors during the operation of the factory. Figure 5a,d illustrate the response surface diagrams of the interaction between fan speed and fan inclination angle on the residual film recovery rate and impurity content when the quality ratio of the residual film is 60%. The residual film recovery rate shows a trend of increasing first and then decreasing with the increase in the inlet angle and fan speed, while the impurity content shows the opposite trend. This might be because a too-fast fan speed may cause the residual film and impurities to be recovered before they are separated, and an overly large or small inlet angle will lead to a significant decrease in the residual film recovery rate, and the fan speed has a greater impact on the residual film recovery rate. Figure 5b,e show the response surface of the interaction between the quality ratio of material film impurities and fan speed when the inlet angle is 30°. Under the influence of the overall interaction, the residual film recovery rate shows a trend of increasing first and then decreasing with the increase in the inlet angle and the quality ratio of residual film, while the impurity content shows the opposite trend. The reason might be that as the quality ratio of residual film increases, the residual film tends to adsorb more impurities, which may cause a mismatch between the airflow parameters and result in a decrease in the residual film recovery rate and an increase in the impurity content. As shown in the Figure, the quality ratio of film impurities has a greater impact on the residual film recovery rate. Figure 5c,f show the response surface of the interaction between the inlet angle and the quality ratio of residual film at 1200 revolutions per minute. Here, the residual film recovery rate increases first with the increase in the inlet angle and the quality ratio of residual film, and then decreases, while the impurity content shows the opposite trend. The quality ratio of residual film has a greater impact on the residual film recovery rate.

Based on the analysis of the above test results, in order to obtain the optimal working parameters of the membrane impurity separation device, Design-Expert13 software was used for multiple regression fitting analysis. When conducting data optimization, to ensure the rationality of the simulation and the reliability of the results, it is assumed that the soil parameters, residual film distribution, and machine performance for obtaining the optimal simulation solution remain consistent under field conditions. The optimal solution of the parameters is solved by taking the maximum value of the residual membrane recovery rate and the minimum value of the impurity content. The objective function is shown in Equation (14).

(15)$\left\{\begin{array}{l}\begin{array}{l}\left[\begin{array}{l}20°\le X_1\le 40°\\ 1000 \mathrm{r}/\min \le X_2\le 1400 \mathrm{r}/\min \\ 35 \mathrm{cm}\le X_3\le 55 \mathrm{cm}\end{array}\right]\\ \max \left(Y_1\right)\\ \min \left(Y_2\right)\end{array}\end{array}\right.$

The theoretical optimal working parameters were obtained by using the optimization function of Design-Expert software: the air inlet angle was 31°, the speed was 1277 r/min, the mass ratio of membrane impurities was 62%, the residual film recovery rate was 88.1%, and the impurity content was 3.58%.

4.3. Analysis and Discussion of Verification Results

Based on the operational requirements of the membrane separation device, theoretical analysis, and the limitations of fan parameters, the inlet angle A (20–40°), fan speed B (1000–1400 revolutions per minute), and the proportion of residual membrane mass C (40–80%) were selected as the test factors. Additionally, the recovery rate of residual membrane and the content of impurities were used as important indicators for evaluating the recovery effect and were selected as the test indicators for the field experiment. According to the regulations of “GB/T 25412-2010 Residual Plastic Film Recovery Machine”, the calculation formula is as follows.

To verify whether the theoretically optimal parameters meet the actual requirements, it can be seen from Table 4 that the average recovery rate of the residual membrane and the content of impurities are 86.7% and 3.4%, respectively, and compared with the theoretical optimized values, the relative errors are 1.4% and 1.58%, respectively, which indicates that the quadratic polynomial regression model has high accuracy. This study found that the theoretical optimal solution obtained using Design-Expert13 software conforms to the actual situation and has a relatively small relative error. Our data also confirmed that the wind-sorting-type tillage layer residual plastic film recovery machine can effectively achieve residual film recovery and separation of membrane impurities. This result contrasts with the comb teeth film separation pneumatic deflation-type tillage layer residual plastic film recovery machine designed by Guo et al. [6], indicating that the plastic film recovery rate increases with the increase in the air velocity at the suction port. Different from previous studies, our data show that the plastic film content rises first and then decreases with the increase in the fan air velocity. The possible reason is that when the air velocity of the cross-flow fan is too large, the impurities of the residual film cannot be separated in time and are blown into the collecting tank.

In addition, changes in moisture content will affect the effect of membrane impurity separation. Therefore, in future research, based on soil conditions with different moisture contents, verification experiments of machine operation conditions under different soil moisture contents should be developed, and mathematical models of soil moisture content and residual film recovery rate should be established, etc., to make this research more universally applicable.

5. Conclusions

Based on the above analysis, the following conclusions can be drawn:

(1). In order to solve the problem of low residual film recovery rate and high impurity content during the operation of the residual film recycling machine, a membrane impurity separation device was designed, and the whole structure and working principle of the membrane impurity separation device were expounded.

(2). The motion law of the membrane mixture was analyzed, and the kinematic equation of the membrane mixture separation zone was established. The main parameters affecting the separation effect of the membrane mixture were wind speed and wind inlet angle.

(3). The orthogonal simulation test was designed by using Design-Expert’s Box–Behnken, and the interaction of various factors on the recovery rate and impurity content of the residual film was tested based on the orthogonal test results.

(4). The proposed air-separation-type tillage layer residual film recovery machines achieved a 86.7% film recovery rate and a 3.4% impurity rate in the field test under the optimal parameter combination of 31° inlet angle, 1277 r/min fan speed, and 62% proportion of residual film quality. The relative error between the test results and the predicted values of Design-Expert 13 (88.1% recovery rate, 3.58% impurity rate) was less than 5%, and the relative error was smaller compared to the model’s predicted values, indicating that the parameter data is reliable. It significantly outperforms traditional mechanical screening-type recovery machines (such as the 82.6% film recovery rate reported by Shi et al. [11]).

(5). The successful recovery of this machine has significantly reduced the presence of crop residual film, directly enhanced agricultural production efficiency, indirectly increased the yield of related crops, achieved remarkable environmental protection, and brought about obvious economic benefits. However, due to the small scale of use of the residual film recovery machine, the fact that it does not bring direct economic benefits to farmers in developing countries, and the insufficient government support, there are challenges in practical application. If the government can increase publicity efforts and improve supportive policies in the future, it will be more conducive to the development of this machine and create greater economic value.

(6). Currently, most of the crop residue film recovery machines on the market are still at the stage of primary mechanical structure research. The mechanical recovery of crop residue films has strong randomness, which is also an important reason for the unstable recovery effect of crop residue film recovery machines. In the future development of crop residue film recovery machines, related technologies such as automation, vision, and sensors may be introduced to further improve the operation effect of the machine.

Author Contributions

Conceptualization, A.S., Z.X., and L.L.; Methodology, A.S., Z.X., M.Z., and L.D.; Software, Z.X. and L.D.; Validation, Z.Z. and M.Z.; Formal analysis, L.L. and Z.Z.; Investigation, Z.X. and Z.Z.; Resources, A.S. and L.D.; Data curation, Z.Z., M.Z., and L.D.; Writing—original draft preparation, Z.X. and L.L.; Writing—review and editing, A.S., Z.X., and M.Z.; Visualization, L.L. and Z.Z.; Supervision, A.S.; Project administration, A.S.; Funding acquisition, A.S. All authors have read and agreed to the published version of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

Figure 1 Schematic diagram of the structure of the tillage layer residual film recycling machine. 1. Suspension device. 2. Conveyor chain device. 3. Mesh filtration device. 4. Residual film collection box. 5. Depth limit wheel device. 6. Soil shovel device. 7. Frame. 8. Roller crushing device. 9. Cross-flow fan device. 10. Transmission device. 11. Walking wheel device.

Figure 2 Analysis of the movement of the membrane mixture in the blown film area.

Figure 3 Schematic diagram of the structure of a through-flow fan. 1. Fan spindle. 2. Fan shield. 3. Air volume adjustment plate. 4. Bracket. 5. Fan housing. 6. Impeller. 7. Side housing.

Figure 4 Field test of air-separation-type tillage layer residual film recovery machine. (The Chinese characters in the picture are the name of the manufacturer).

Figure 5 (a) The interactive effects of fan speed and angle of entry into the wind on the residual film recovery rate. (b) The interactive effects of the proportion of residual film quality film to impurities and the angle of entry into the wind on the residual film recovery rate. (c) The interactive effects of the proportion of residual film quality film to impurities and fan speed on the residual film recovery rate. (d) The interactive effects of fan speed and angle of entry into the wind on the impurity content. (e) The interactive effects of the proportion of residual film quality film to impurities and the angle of entry into the wind on the impurity content. (f) The interactive effects of the proportion of residual film quality film to impurities and fan speed on the impurity content.

Table 1

Experimental factors.

Serial	Angle of Entry Intothe Wind (/°)	Fan Speed/(r/min)	Proportion of Residual Film Quality (/%)
−1	20	1000	40
0	30	1200	60
1	40	1400	80

Table 2

Experimental design and results.

No.	Angle of Entry Intothe Wind (/°)	Fan Speed/(r/min)	Proportion of Residual Film QualityFilm to Impurities (/%)	Residual FilmRecovery Rate (%)	ImpurityContent (%)
1	1	−1	0	85.7	5.2
2	0	1	−1	86.6	5.7
3	0	0	0	87.9	3.6
4	−1	0	−1	84.8	5.6
5	0	1	1	87.1	5
6	−1	1	0	86.3	5.6
7	1	0	−1	86.1	5.3
8	0	−1	1	85.5	5.3
9	0	0	0	88.1	3.6
10	1	0	1	86.8	5.1
11	0	0	0	87.9	3.6
12	0	−1	−1	84.5	5.3
13	0	0	0	88.1	3.5
14	−1	−1	0	83.9	5.7
15	1	1	0	87.8	5.6
16	0	0	0	87.6	3.6
17	−1	0	1	85.1	5.1

Table 3

Analysis of variance of the regression equation.

Source	Residual Film Recovery Rate (%)					Impurity Content (%)
	SSQ	DF	MSE	F Value	p Value	SSQ	DF	MSE	F Value	F Value
ModelA	29.531.91	91	3.281.91	79.0646.05	<0.00010.0003	12.060.0919	91	1.340.0919	52.1.3035.74	<0.00010.0006
B	4.71	1	4.71	113.54	<0.0001	0.1237	1	0.1237	48.10	0.0002
C	5.93	1	5.93	142.91	<0.0001	2.55	1	2.55	990.99	<0.0001
AB	0.0225	1	0.0025	0.5422	0.4855	0.0625	1	0.0625	24.31	0.0017
AC	0.0400	1	0.0400	0.9639	0.3589	0.0225	1	0.0225	8.75	0.0212
BC	0.6250	1	0.0625	1.51	0.2594	0.1225	1	0.1225	47.64	0.0002
A2	5.19	1	5.19	125.01	<0.0001	3.78	1	3.78	1470.01	<0.0001
B2	3.30	1	3.30	79.46	<0.0001	4.19	1	4.19	1629.05	<0.0001
C2	5.19	1	5.19	125.01	<0.0001	2.35	1	2.35	914.92	<0.0001
Residuals	0.2905	7	0.0415			0.0180	7	0.0026
Lack of Fit	0.1225	3	0.0408	0.9722	0.4886	0.010	3	0.0033	1.67	0.3099
Pure error	0.1680	4	0.0420			0.0080	4	0.0020
Total sum	29.82	16				12.08	16

Note: p < 0.01 is the most significant impact; 0.01 < p < 0.05 was significant, p > 0.05 was not significant.

Table 4

Test verification results.

No.	Residual Film Recovery Rate	Impurity Content
1	85.5	3.26
2	87.6	3.43
3	86.3	3.62
4	87.3	3.29
average	86.7	3.4

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