ORIGINAL ARTICLE

Design of an Implement to Remove Polyethylene Mulch in Strawberry Crops

MSc. María Victoria Gómez-Águila^{1  *} 
http://orcid.org/0000-0001-9603-2856

Ing. David Iván Sánchez-Chávez¹ 
http://orcid.org/0000-0001-7132-9741

Ing. Luis Tonatiuh Castellanos-Serrano¹ 
http://orcid.org/0000-0002-1071-3923

Ing. Luis Arturo Soriano-Avendaño¹ 
http://orcid.org/0000-0003-3299-9851

Ing. Marcelino Aurelio Pérez-Vivar¹ 
http://orcid.org/0000-0002-2746-8688

Ing. Ramiro Chávez-Mota¹ 
http://orcid.org/0000-0001-5354-4034

MC. Josué Vicente Cervantes-Bazán¹ 
http://orcid.org/0000-0003-4849-1518

¹Universidad Autónoma Chapingo, Centro de Investigaciones Interdisciplinarias y de Servicio en Ciencia, Naturaleza, Sociedad y Cultura, Texcoco de Mora. Estado de México, México.

ABSTRACT

In this work, the objective is to design an implement to collect the plastic used in strawberry mulch, cutting it at the ground level on each side of the agricultural bed on which the strawberry is planted, and winding it on a shaft that rotates so proportional to the advance of the tractor, driven by a chain power transmission system that relates the movement of the implement tires and the winding of plastic film. As a result, the design of an implement is obtained that works at a proposed speed of 7 km h-1 and that collects the plastic, cutting the soil of the agricultural bed 10 cm on each side, in order to ensure that it cuts the plastic of the mulch. It has a width of 1.3 m and a load capacity of 646 kg of plastic that can be kept in the collection shaft before having to deposit it in a warehouse.

Keywords: Mulching; Agricultural Bed; Chain Drive; Shafts

INTRODUCTION

In Mexico, the production of strawberries represents an important source of income, especially since a large part of the national production is destined for export, helping to generate jobs around all processes and activities from the preparation of the land to the arrival of the fruits on the shelves. This means that in this particular productive sector there is an important flow of economic resources. Strawberry cultivation has now increased. According to ^{Ortiz-Cañavate & Puig (1989)}, in recent years, national exports of the crop have tripled, from 52 thousand tons in 2003 to 152 thousand tons by 2020.

This crop uses particular techniques and practices that are necessary to allow the proper development of the fruits, some of these tasks can be mechanized or manual depending on the technological level of the crop and a great difference could exist between one form and the other, depending on the size and production volume. The speed to perform a labor can affect the dates set for production or represent an advantage to simplify the work, and in the end have an economic impact on the final profits.

One of these techniques used is the plastic mulch on agricultural beds, which provides protection benefits for the plants to obtain a better harvest, they act as follows:

On radiation, using as needed, the color (colored sheets) or the capacity obtained by metallization (use of aluminum or aluminum titanium oxides, etc.).

On soil temperature and humidity below the sheet

On the plants by eliminating weeds if black sheet is used; weed growth under clear sheets is normal if herbicides are not used.

On pests and certain microorganisms

On growth by ensuring that the carbon dioxide produced by soil fermentation remains in the area of ​​the stomata of growing seedlings (^{Dubois, 1980}).

These advantages are the reason why the practice of plastic mulch has been adopted so widely in recent years, to be applied not only to strawberries, but also to various crops, constantly, cycle after production cycle.

But this practice so beneficial for crop management has disadvantages, one of them is to generate contamination at the end of the useful life of plastics, despite the fact that it is appropriate for these wastes to be lifted and taken to a place where they are handled adequately and recycled or where advantage is taken of their energy recovery. In Mexico there is still no considerable progress in this.

Once the crops are finished, the plastic mulch is shown deteriorated and must be replaced. It must be removed from the field and properly disposed of for recycling or for a suitably enabled sanitary landfill. In no case should plastics be burned, the gases are toxic, especially due to the additives that are incorporated to the plastic during its production. Another incorrect practice is to track the batch and crumble the plastics, these will be carried by the breeze causing enormous distortions, the plastic with its additives has the capacity to last for years affecting the soil, flora and fauna. (^{Díaz, 2001}).

The alternatives for the management of agricultural plastic products are summarized in processes of mechanical recycling and their controlled dumping, while energy valuation is a practically wasted option (^{Díaz, 2001}).

In addition, the work of lifting the plastic films is usually left to the last moment and this can cause extra damage, for example, if it is left on the ground too long, the sun can degrade the plastic on the ground, which is affected. Due to the small waste that cannot be easily collected, this activity is also carried out manually and constitutes a complex job for field workers.

For this reason, the present work aims to design a simple machine that allows the collection of plastic mulches in strawberry agricultural beds.

MATERIALS AND METHODS

The parameters for the design of the implement are: implement width, 1.3 m (given by the dimensions of the cultivation beds), load capacity (646 kg) and operating speed (7 km·h^-1). The functions performed by the equipment in the field were defined, two solutions were proposed and the best alternative with the most appropriate components was selected.

The main components that make up the design of the implement are shown in Figure 1, made up of: the tires 1, which by friction with the ground transmit the movement to the chain transmission system 2, and in turn to the upper axis where the polyethylene film 3, the axles of the wheels 4, the guide roller 5, the frame 6 and the blades for cutting the polyethylene material 7 are accumulated.

FIGURE 1 Polyethylene padding collection implement. 

To select the implement tires, commercial catalogs of tires designed for agricultural work were consulted, taking into account the need for a small radius wheel, with a width of less than 33 cm and a load capacity of more than 700 kg.

Roller Chain Drive System Design

The angular speed of entry to the transmission system was calculated with a 1: 1 ratio, according to Equation (1), from the selected aggregate operating advance speed.

$\omega =V/r$ (1)

Where:

𝜔:	angular velocity of the tire, s^-1;
V:	operating advance speed of the tractor-implement unit, ms^-1;
r:	tire radius, m.

The power necessary to work up to 646 kg of accumulated plastic film is determined with Equation 2, according to ^{ASABE Standards (2006)}.

$P = F * V$ (2)

Where:

P:	power, W;
F:	load generated by the polyethylene material;
f:	service factor, 1.4.

The power obtained and the angular velocity were used to iterate standardized roller chain transmission designs in the catalogs, searching for the suitable pitch diameter (D1) for the machine, which was determined with Equation (3).

$D=\frac{P}{sen \left(\frac{180}{N}\right)}$ (3)

t:	chain pitch; mm,
Z:	number of teeth of the driving and moving stars,
D1y2:	primitive diameter of the stars; mm.

Distance between Centers and Number of Chain Links

The minimum distance between centers is determined by Equation 4, according to ^{Dobrovolski (1990)}.

Calculation of the minimum distance between axles (a _min ).

$a_{\mathrm{m}\mathrm{i}\mathrm{n}}=\mathrm{1,2}\cdot \left(\frac{D{e}_1+D{e}_2}{2}\right)+(30...50)$ (4)

Being:

$D_{e1}=t\cdot \left[\mathrm{0,5}+\frac{1}{\mathrm{t}\mathrm{a}\mathrm{n}\left(\frac{{180}^{\circ }}{z_1}\right)}\right]$ (5)

$D_{e2}=t\cdot \left[\mathrm{0,5}+\frac{1}{\mathrm{t}\mathrm{a}\mathrm{n}\left(\frac{{180}^{\circ }}{z_2}\right)}\right]$ (6)

Where:

De1 and De2 -	outer diameters of the driving star and of the moving star, mm;
Z1 and Z2 -	number of teeth of the driving and moving star.

Checking the minimum distance.

amin <	80 t
amin =	(30 ... 50) t, it is recommended for normal working conditions.

Calculation of the number of links. (Y).

$Y=\frac{Z_1+Z_2}{2}+\frac{2\cdot a_{mín}}{t}+{\left(\frac{Z_2-Z_1}{2}\right)}^2\cdot \frac{t}{a_{mín}}$ (7)

Note: The number of links calculated is approximated to the next even number.

Calculation of the final axial distance (a).

$a=\frac{t}{4}\cdot \left[Y-\frac{Z_1+Z_2}{2}+\sqrt{{\left(Y-\frac{Z_1+Z_2}{2}\right)}^2-8\cdot {\left(\frac{Z_2-Z_1}{2\pi }\right)}^2}\right]$ (8)

Pickup Shaft Design

For the shaft design, the fatigue failure theory according to ^{Dubois (1980)} & ^{ASABE Standards (2006)} is used, using Equation (9) to determine the adequate minimum diameter.

$D= 32\frac{f1}{\pi } \sqrt[3]{ {\left(kt M/Sn\right)}^{2 }+\mathrm{–}({T/Sy)}^2}$ (9)

where:

D:	minimum shaft diameter, mm;
f1:	design factor, measure of the relative safety of a component under the action of a load;
Kt:	coefficient for changes in the geometry of the shaft;
M:	bending moment, Nm;
𝑆y:	estimated fatigue strength of the shaft construction material, 1040 steel (^Deutschman et al., 1985), N/m^2;
T:	torsional moment in the shaft, Nm;
𝑆n:	yield strength of the shaft material, N/m^2.

To determine the critical bending moment, the forces acting on the shaft were obtained, and the torque was obtained with Equation (10).

$T=P/\omega$ (10)

Bearing Selection

A useful life of 20,000 hours was used for the selected bearings in both the upper axle and the tires, which was determined by Equation 11 (^{Mott, 2006}).

$Ld=h*n*60$ (11)

where:

Ld:	nominal longevity of a bearing, cycles;
h:	useful life, h;
n:	bearing rotation frequency; min^-1.

The reactions were determined and loads on the axis were obtained by applying the equations of static equilibrium, according to ^{ASABE Standards (2006)}. Static load is determined according to ^{Deutschman et al. (1985)}, and the dynamic load according to Equation 12 (^{Mott et al., 2009}).

$Cr=Pd {\left(\frac{Ld}{{10}^6}\right)}^{1/k}$ (12)

where:

Cr:	dynamic load; N;
Pd:	static load; N;
K =	3, for ball bearings (^ASABE Standards, 2006; ^Mott, 2006).

Implement Frame Design

For the design of the frame, the critical force was taken as the necessary to maintain the implement at a constant speed. That force applied by the tractor when dragging the implement was considered the resistance to rolling, according to the ^{ANSI/ASABE (2003)} and Equation (13).

$RR=W (\frac{1.2}{Cn }+0.04)$ (13)

where:

RR:	rolling resistance; N,
W:	normal load, N;
Cn:	dimensionless coefficient as a function of the cone index (Ci) for the soil.

The coefficient Cn was determined from equation (14).

$Cn= \frac{Ci b d}{W}$ (14)

where:

Ci:	soil cone index was determined by a standard penetrometer test, kPa;
b:	width of unloaded tires, m;
d:	height of unloaded tires, m.

Deflection was calculated according to ^{Deutschman et al. (1985}) from Equation (15), considering the model as a doubly supported beam, and it was compared with recommended limit values for machinery (^{Mott et al., 2009}).

$\nabla =\left(\frac{{Pl}^3}{48 EI} \right)$ (15)

where:

∇:	vertical deflection, m;
P:	external force, N;
E:	longitudinal modulus of elasticity, MPa;
I:	moment of inertia of the rectangular beam, m^4.

Wheel Axle Design

The power required to overcome rolling resistance (Pr) was calculated, guaranteeing that the tractor-implement aggregate advances at a constant speed, according to Equation 16.

$Pr=RR*V$ (16)

Design of Plastic Film Cutting Blades

The design of the blade was made according to ^{ANSI/ASABE (2003)} and serrated is recommended to facilitate cutting of the polyethylene material perpendicular to its thickness, with an angle of 180°.

For the calculation of the force that guarantees the penetration of the blades into the ground at 10 cm, necessary for cutting the polyethylene, Equation 17 was used, according to ^{Ortiz-Cañavate (1989)}; ^{ANSI/ASABE S (2003} & ^{Hibbeler (2010)}.

$Fr=a*p*\mu$ (17)

where:

Fr:	resistance force generated in the ground; N
a:	working width; cm,
p:	depth of work; cm,
μ-	specific soil resistance; N · cm^-2.

The specific resistance μ was determined by Equation 18, according to ^{ANSI/ASABE S (2003)}, for the most demanding conditions that correspond to a clay-silty soil.

$\mathrm{\mu }\mathrm{ }=\mathrm{ }7\mathrm{ }+\mathrm{ }0.049\mathrm{ } V^2$ (18)

Selection of Blades

The blades must withstand the work without failure. The area to be cut matched the cross-sectional area of the blade. It is determined considering the condition of mechanical resistance to shear, according to ^{Mott et al. (2009)}; ^{Hibbeler (2010)} and was calculated through Equation 19.

$\tau =\frac{Fc}{Ac} \le \tau p$ (19)

where:

Fc:	shear force; N
Ac:	cross-sectional area subjected to shear; 1.4 cm^2
$\tau$:	allowable shear stress; 375 MPa

For the blades, an AISI W1 steel was selected whose yield strength is 1500 MPa (^{GOST 4543 - 71, 1973} & ^{Deutschman et al., 1985}).

Three-Point Hitch

For the dimensions of the three-point hitch, the norm of ^{ASABE Standards (2006)} & ^{Sánchez (2015)} were followed, for a category II hitch.

RESULTS AND DISCUSSION

The design of an implement for the collection of polyethylene films used in strawberry cultivation beds was obtained, to work at 7 km h^-1 and with a load capacity of 646 kg of collected film, which could be operated by two people.

Tires

The tires selected for the implement had the following main characteristics: the tire contains an inner tube (TT- Tube type), ply rate (PR) of 8, width of the rim 13.97 cm, the weight (WT) is 10,886 kg, 72.136 cm outside diameter (OD), 20.066 cm section width, 32 cm static loaded radius (SLR), load capacity at 52 psi, specified pressure 948 kg, maximum recommended speed (SP) 48.27 km/h. These values ​​were obtained from the Alliance Tire Group brand catalog.

Power Transmission

A chain drive system was selected that transmits the power generated in the tire axle to the upper harvesting axle, the characteristics of the chain drive: Standard double row number 120 chain, with a pitch of 3.81 cm. The chain length L = 327.66 cm. The minimum distance between centers 30.5 cm. The final axial distance a = 116.205 cm. With two equal sprockets with 25 teeth (Z = 25), with diameters of D1 = 30.399 cm.

Upper Shaft

The upper shaft (Figure 2) of 1040 steel, a diameter of 85 mm and a total length of 1.4 m, in which the standard 6217 bearings were placed, in addition to the Catarina for power transmission.

FIGURE 2 Upper shaft. 

Wheel Axles

These axles with a diameter of 70 mm were attached to the tire rims, at the other end the two bearings of the standard type number 6914 were placed and they were attached to the lower columns of the frame, with a distance of 0.238 m from the joint with the rim to the end of the axle.

Plastic Cutting Blades

The blades were rectangular in shape and one of their sides was serrated to cut the polyethylene film, they were 7 cm wide, 17.62 cm long, of which 10 cm were serrated, and a thickness of 2 mm as can be seen in the Figure 3.

FIGURE 3 Blade. 

Figures 4a and 4b show the parts that make up the design made.

FIGURE 4a Machine components. 

1. Rotation axis of the plastic harvesting system, 2. Bars for plastic winding, 3. Discs to prevent the padding from coming off the bars, 4. Tires (implement traction), 5. Blade holder, 6. Blade, 7. Bar coupled to frame and blade holder, 8. 3-point hitch system, 9. Frame, 10. Guide roller for plastic.

FIGURA 4b Assemble of the final design in Solidworks. 

CONCLUSIONS

The design of the implement to remove the polyethylene mulch in strawberry crops was made up of: two wheels, two cutting bodies, bar or axles, supports for cutting bodies, double row chain-chain transmission, two 6217 ball bearings, 6914 and had a cutting capacity of 646 kg equivalent to an estimated area of 0.91 ha / h with advance of the machine equal to 7 km/h.

REFERENCES

ANSI/ASABE S: General Terminology for Traction of Agricultural Traction and Transport Devices and Vehicles, ANSI/ASABE S, 2003.

ASABE STANDARDS: Three Point Free Link Attachment for Hitching Implements to Agricultural Wheel Tractors, American Society of Agricultural and Biological Engineers, 2006.

DEUTSCHMAN, A.D.; MICHELS, W.J.; WILSON, C.E.; GARZA, C.J.A.: Machine design theory and practice. Diseño de máquinas: teoría y práctica, 1985, ISBN: 968-26-0600-4.

DÍAZ, S.T.: Los filmes plásticos en la producción agrícola, 2001, ISBN: 84-8476-004-9.

DOBROVOLSKI, V. Elementos de Máquinas. ENPES (Empresa Nacional de Producción de Educación Superior). Reimpresión de la edición de 1980 realizada por la Editorial Mir - Moscú. URSS. Pág. 584. 1990.

DUBOIS, P.: Los plásticos en la agricultura, Ed. MundiPrensa, Madrid, España, 209 p., 1980.

GOST 4543 - 71: Structural alloy steel bars Technical Specifications GOST 4543 - 71, [en línea], no. OKП 09 5040, Inst. State Standard of USSR, Russia, Russia, 24 p., 1973, Disponible en:http://www.swyaz.com, [Consulta: 10 de noviembre de 2019].

GUTIÉRREZ, V.C.; SERWATOWSKI, R.; CABRERA SIXTO, S.J.M.; SALDAÑA, R.N.; JUÁREZ-GUANÍ, G.J.A.: “Estudio de corte de películas plásticas sobre suelos acolchados”, Revista Ciencias Técnicas Agropecuarias, 19(4): 30-36, 2010, ISSN: 2071-0054.

HIBBELER, R.C.: Mecánica de materiales, Ed. Prentice Hall, decimosegunda ed., México, DF, 2010, ISBN: 978-607-442-560-4.

MOTT, R.L.: Diseo de Elementos de Maquinas-Con 1 CD, Ed. Pearson educación, 2006, ISBN: 970-26-0812-0.

MOTT, R.L.; SALAS, N.R.; FLORES, R.M.A.; MARTÍNEZ, B.E.: Resistencia de materiales, Ed. Pearson Educación, vol. 5, 2009.

ORTIZ-CAÑAVATE, J.: Técnica de la mecanización agrícola, Ed. Mundi-Prensa, tercera ed., Madrid, España, 643 p., 1989.

SÁNCHEZ, C.D.I.: Diseño de un implemento para retirar acolchados plásticos en cultivos de fresa, Universidad Autónoma Chapingo, Departamento de Ingeniería Mecánica Agrícola, Texcoco de Mora. Estado de México, 2015.

Received: February 10, 2021; Accepted: June 18, 2021

^*Author for correspondence: María Victoria Gómez-Águila, e-mail: [e-mail]

María Victoria Gómez-Águila, Profesora e Investigadora, Universidad Autónoma Chapingo, Centro de Investigaciones Interdisciplinarias y de Servicio en Ciencia, Naturaleza, Sociedad y Cultura, Texcoco de Mora. Estado de México, México, e-mail: [e-mail],[e-mail]

David Iván Sánchez-Chávez, Doctorante del Postgrado Ingeniería Agrícola y Uso Integral del Agua. Universidad Autónoma Chapingo, Texcoco de Mora. Estado de México, México, e-mail: [e-mail]

Luis Tonatiuh Castellanos-Serrano, Profesor e Investigador, Universidad Autónoma Chapingo, Centro de Investigaciones Interdisciplinarias y de Servicio en Ciencia, Naturaleza, Sociedad y Cultura, Texcoco de Mora. Estado de México, México, e-mail: [e-mail]

Luis Arturo Soriano-Avendaño, Profesor e Investigador, Universidad Autónoma Chapingo, Centro de Investigaciones Interdisciplinarias y de Servicio en Ciencia, Naturaleza, Sociedad y Cultura, Texcoco de Mora. Estado de México, México, e-mail: [e-mail]

Marcelino Aurelio Pérez-Vivar, Profesor e Investigador, Universidad Autónoma Chapingo, Centro de Investigaciones Interdisciplinarias y de Servicio en Ciencia, Naturaleza, Sociedad y Cultura, Texcoco de Mora. Estado de México, México, e-mail: [e-mail]

Ramiro Chávez-Mota, Profesor e Investigador, Universidad Autónoma Chapingo, Centro de Investigaciones Interdisciplinarias y de Servicio en Ciencia, Naturaleza, Sociedad y Cultura, Texcoco de Mora. Estado de México, México, e-mail: [e-mail]

Josué Vicente Cervantes-Bazán, Profesor e Investigador, Universidad Autónoma Chapingo, Centro de Investigaciones Interdisciplinarias y de Servicio en Ciencia, Naturaleza, Sociedad y Cultura, Texcoco de Mora. Estado de México, México, e-mail: [e-mail]

The authors of this work declare no conflict of interests.

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