Determination of qualitative working indices of harrows with elastic fangs

In modern agriculture, grinding, levelling, loosening the soil surface layer and weed destruction, with application in the vegetable and technical crops sector, are carried out by a wide range of agricultural machines generically called harrows. These operations must be carried out by splitting on the natural lines of cohesion and not by hitting, cutting, compressing, breaking, when everything turns to dust. The paper presents the field tests for a harrow with elastic fangs in order to determine the following qualitative work indices: degree of soil grinding, degree of plant damage, degree of weed destruction, degree of levelling, working depth and operating energy indices for the maintenance of corn and sunflower crops.


Introduction
The mechanical processing of topsoil is one of the most important land preparation operations for the cultivation of future crops [1].
Equipment for the primary soil processing, such as ploughs, chisels, rippers, etc., are widely used, but don't produce adequate loosening and fragmentation of topsoil. Secondary processing tools are generally towed by agricultural tractors and can be divided into two main categories: passive and active equipment. Passive tools, such as harrows or vibratory cultivators, only fragment the soil by absorbing power from the tractor's drawbar, while the active equipment is additionally operated, by the tractor's power take-off [2,3]. Active and passive secondary processing equipment have been shown to have similar soil fragmentation efficiency [4,5,19].
The main objectives of the harrowing work are to achieve the control of weeds, the incorporation of vegetable residues and organic manure to improve soil moisture and fragmentation [6,7,8].
Harrowing work (tillage) has also been identified as one of the operations that requires high costs of resources and management, such as the need for high involve high fuel consumption [9].
In modern agriculture, aspects related to energy conversion and mechanical efficiency are very important, because most agricultural ma streamlining their products by designing new optimized shapes and materials to reduce wear and fuel consumption [10].
From an economic and environmental point of view, soil tillage operations in modern agriculture are also mandatory [11,12].
Thus, experimental researches were undertaken in order to highlight the importance of working stability for soil tillage aggregates, in terms of quality of work and fuel consumption [13,14].
Studies have been conducted on the automation of harrowing work [15]. Experimental researches have also been conducted, focus soil tillage aggregates in order to define what parameters influence the germination and emergence of future plants [16].
In order to obtain uniform and healthy crops with minimal impact on the environment, aggregates with homogeneous dimensions should be made for soil tillage [17 The paper presents the field tests for a harrow with elastic fangs in ord the qualitative working indices as well as the exploitation energy indices during the maintenance of corn and sunflower crops.

Material and method
The harrow with elastic fangs is a machine carried on the tractor (driven from the power take-off), being intended for the maintenance of crops of straw cereals, corn, sunflower, beets, peas, beans, potatoes, rapeseed, vegetables, sowing work. Figure 1 shows the diagram of the harrow with elastic fangs research. The machine consists of an 80 mm square pipe frame that the tractor's hydraulic lift.
The batteries with elastic fangs are attached to the rear cross member of the frame by means of three oscillating levers.
has also been identified as one of the operations that requires high costs of resources and management, such as the need for high-power tractors that In modern agriculture, aspects related to energy conversion and mechanical efficiency most agricultural machinery manufacturers focus on streamlining their products by designing new optimized shapes and using innovative materials to reduce wear and fuel consumption [10].
From an economic and environmental point of view, soil tillage operations in modern Thus, experimental researches were undertaken in order to highlight the importance of working stability for soil tillage aggregates, in terms of quality of work and fuel cted on the automation of harrowing work [15]. Experimental focusing on the physical and mechanical properties of to define what parameters influence the germination and In order to obtain uniform and healthy crops with minimal impact on the environment, aggregates with homogeneous dimensions should be made for soil tillage [17,18].
The paper presents the field tests for a harrow with elastic fangs in order to determine the qualitative working indices as well as the exploitation energy indices during the fangs is a machine carried on the tractor (driven from the power off), being intended for the maintenance of crops of straw cereals, corn, sunflower, beets, peas, beans, potatoes, rapeseed, vegetables, pastures, before and after conducting the The elastic fangs are springs that have the active part of 145 mm, and the spiral part inserted in a "U" profile provided with channels for the passage of the active part. The channels are long enough to move back the elastic fangs in case of meeting the plants, also allowing a strong lateral vibration.
The angle of attack of the elastic fangs can be adjusted in the range of 5-90° by an indexing system with bolts (in 6 positions).
The machine transmission includes the flywheel shaft, the elastic coupling, the oscillating washer, the oscillating swingarm that imprints the oscillating movement of the batteries with elastic fangs.
In the working position, the angle of attack of the elastic fangs is adjusted according to the stage of vegetation of the plants and the degree of soil moisture. Table 1 presents the conditions for conducting the experimental research. The experiments were performed using an aggregate consisting of an 80 HP tractor and a harrow with elastic fangs for the maintenance of corn and sunflower crops.

Results and discussion
The determination of the qualitative working indices of the harrow with elastic fangs required the following steps:

Determining the degree of soil grinding
The experimental researches were conducted in repetitions, on a 0.5 x 0.5 m 2 , with a maximum angle of attack of the elastic fangs. The results are presented in Table 2. From the analysis of Table 2 it results that the harrow with elastic fangs achieves, in appropriate moisture conditions, a good grinding of the soil.
Also, it was noticed that it achieves a good breaking of the crust formed after a torrential rain, if it is put to work about four days after the rain.

Determining the degree of plant damage
The experimental researches were conducted in three repetitions and at two working speeds (4 and 6 km/h).
The results are presented in Table 3. The results in Table 3 show that the degree of plant damage has values according to agrotechnical norms.
It should be noted that some of the plants recover in time if they are not uprooted.

Determining the degree of weed destruction
The experimental researches were conducted in three repetitions and at two working speeds. The results are presented in Table 4. The results presented in Table 4 show that the degree of weed destruction is relatively low, as the destruction of weeds that are at a high stage of development would increase the degree of plant damage.
It would be advisable to use the machine when the weeds are in an early stage and to repeat the work whenever necessary, but this has negative effects on fuel consumption, as well as on the degree of soil compaction.

Determination of the degree of levelling and
The experimental researches were conducted (in two repetitions) in order to determine the influence of the work performed by the harrow with elastic fangs.
The determination surface has the dimensions of 20 x 20 m. From the analysis of the data presented in Figure 2 it results that the harrow with elastic fangs achieves a degree of soil levelling between 90.6 appropriate and a degree of loosening between 4.1

Determining the working depth of the machine
The working depth was set at 10 points along the entire working width of the machine, in two positions of attack of the elastic fangs: maximum and minimum.
The results are presented in Table 5  From the results obtained in Table 5 it values between 19.8 -30.8 mm, the maximum values being between 38 Determination of the degree of levelling and the degree of loosening The experimental researches were conducted (in two repetitions) in order to determine the influence of the work performed by the harrow with elastic fangs.
The determination surface has the dimensions of 20 x 20 m.
Determination of the degree of levelling and the degree of loosening From the analysis of the data presented in Figure 2 it results that the harrow with elastic fangs achieves a degree of soil levelling between 90.6 -92.1%, being considered d a degree of loosening between 4.1 -5.0%.
Determining the working depth of the machine The working depth was set at 10 points along the entire working width of the machine, in two positions of attack of the elastic fangs: maximum and minimum. From the results obtained in Table 5 it results that the working depth has minimum 30.8 mm, the maximum values being between 38 -45.7 mm.

Determination of energetic indices
Energetic indices were determined on a flat terrain, sown with corn in the state of the second node. Experiments were conducted at three speed gears, in three repetitions, the result being presented in table 6. From the data presented in Table 6is observed that the values of hourly fuel consumption are situated between 5.49 l/h (1 st gear) and 7.7 l/h(3 rd gear).
Skidding has low values, situated around the value of 3.47%. The tensile strength of the machine also has small vales, between 212.5 and 231 daN. The maximum power necessary for driving the aggregate is 7.11 HP. The coefficient of using the engine's power is very small (maximum 16.5%), leading to the idea of using the harrow in aggregate with small power tractors (<65 HP).

Conclusions
The experimental field researches of the harrow with elastic fangs were performed in order to determine the qualitative work indices:  Degree of soil grinding,  Degree of plant damage,  Degree of weed destruction,  Degree of levelling,  Working depth,  Energetic indices. From the analysis of the data, it resulted that:  the degree of soil grinding had values between 83.7 and 87.3% for the 0-10 mm fraction and between 12.7 and 16.3 for the 10-50 mm fraction;  the degree of plant damage has a value of 0.76% for corn and 0.5% for sun flower at the speed of 4 km/h and of 1.3 % for corn and 1.0% for sun flower at the speed of 6 km/h;  the degree of weed destruction has value between 47.3 -51.4% at the speed of 4 km/h and between 55 -61.9 % at the speed of 6 km/h;  the degree of soil levelling has values between 90.6 -92.1 %, and the degree of loosening between 4.1 -5.2 %  the working depth was between 19.8 -30.8 mm at the minimum angle of attack of the elastic fangs and of 38 -45.7 mm at the maximum attack angle of the elastic fangs;  the hourly fuel consumption had the value of 7.71 l/h (3 rd gear);  the coefficient of using the engine's power was 14.9 % for the 2 nd gear and 16.5 % for the 3 rd gear. Through the mechanical control of weeds, the machine leads to the decrease of the quantity of herbicides introduced in the soil.