Abstract: Based on blocking issues of no-tillage planter for dry-land farming in two-crop-a-year region in North of China and shortcomings of anti-blocking mechanism developed, such as higher rotation speed (above 1500 r/min) and bigger power consumption (width power consumption per unit up to 16～41.74 kW/m, including traction power), a new sawing anti-blocking mechanism was developed and its cutting mechanism was investigated in this paper. Meanwhile stress distribution of the saw-tooth blade calculated by the ANSYS finity element software showed that the saw-tooth blade would be feasible to cut corn straws. Experimental results in the soil bin showed that: 1)The sawing anti-blocking mechanism with two cutting modes of sustaining and no-sustaining cut could realize an integrated function of cutting and directly throwing by reverse rotation, namely, it could throw straws directly to the rear of the opener by former angle of saw-tooth and thrower; 2)The cutting rate of straws would increase along with the rising of straw moisture and rotation speed, and higher moisture of straws would be of benefit to improving cutting quality; 3)The cutting rate of straws would decrease along with the rising of velocity of vehicle while interval of the moved and fixed blade was determined. And the sawing anti-blocking mechanism had higher cutting quality and lower power consumption without leaky cutting and tearing out with small interval of the moved and fixed blade. Compared with other driving anti-blocking mechanisms, theoretical analysis and experimental results showed that the sawing anti-blocking mechanism had fine cut capability and lower rotation speed (650 r/min) and lower power consumption (power consumption per unit width up to 2.95 kW/m) as well as stronger suitability to different stubbles mulch. Additionally, a new way was found out to improve anti-blocking performance of no-tillage planter.
Key words: no-tillage planter; sawing anti-blocking mechanism; cutting mechanism; cutting rate
1 Introduction
Anti-blocking issue of no-tillage planter had become one of the key factors affecting production efficiency and seeding quality of two-crop-a-year region in North of China. It was because there was a great deal of crop stubbles and crop seeding was started shortly after crop had been harvested, leaving no time for crop stubbles to decay. At present, there are two methods to solve anti-blocking issue of no-tillage: 1) Straws were chopped by the straw chopper before seeding, it would lead to adding working procedure and increase costs of production as well as delaying seeding time; 2) Stubbles were cleared out by driving chopping mechanism fixed on no-tillage planter, such as Strip Wheat Spinning and Furrow Planter made in Hebei Nonghaha Machinery Ltd Corporation and 2BMDF-Corn Strip Chopper made in China Agricultural University[1]and so on. In practice the driving chopping mechanism had significant effect on antiblocking, but also bigger vibration and noise as well as lower security because straws were chopped at high rotation speed.
It was reported that the blade base linear velocity of several main straw chopping mechanisms was between 37～56 m/s[2], mostly chopping mechanism combined with cutting and striking had higher striking velocity and higher power consumption[3], e.g. the blade base linear velocity up to 34 m/s could obtain fine cutting effect for corn straws[4], and 24 m/s on rice and wheat straws by supporting pole, respectively[5]. Even if corn straws were cut by sliding cut with vertical blade, its velocity of cutting one straw, two straws and three straws must be up to 10.3 m/s, 13.6 m/s, 15.8 m/s[6], respectively, and had higher power consumption. In a word, because the driving chopping mechanism developed presently had high rotation speed ( above 1500 r/min ) and higher power consumption (width power consumption per unit up to 16～41.74 kW/m, including traction power), to decrease rotation speed and power consumption would be urgent in practice.
Based on practical problems, the objective in this paper is to find a way to solve the shortcoming that it 64 is difficult for common smooth blade to seize straws and it must run at higher rotation speed, decrease power consumption and improve cutting effect as well as anti-blocking performance of no-tillage planter. Additionally some experiments were done by selecting saw-tooth as cutting blade of no-tillage planter and cutting mechanism of the sawing anti-blocking mechanism was investigated.
2 Structure and cutting rule of the sawing anti-blocking mechanism
2.1 Structure and characteristics
The sawing anti-blocking mechanism was made up of saw-tooth blade, throwing ban device, principal shaft, moved and fixed blade combination, covering shell, opener and working frame as well as transmission system. Sketch of the sawing anti-blocking mechanism is shown in Fig. 1. The main parts included saw-tooth blade, throwing ban device as well as fixed blade combinations. Diameter of saw-tooth with 60 teeth was 350 mm; throwing ban device with max 270 mm turning diameter was fixed on between adjacent saw-teeth; fixed blade combinations consisted of fixed blade with tooth and vertical type blade, and tooth type blade same to saw-tooth, Moreover, the vertical type blade would be used to obstruct straws without cutting from throwing area and participated in cutting straws. The sawing anti-blocking mechanism was fixed on the soil bin device, its width was 600 mm, the interval of adjacent openers was 200 mm. The sawing anti-blocking mechanism had many characteristics such as straws would be chopped by saw-tooth blade and fixed blade combinations, and had two cutting modes with susta-ining and no-sustaining cutting, the blade base line velocity of saw-tooth was lower to tossing blade type, namely, the sawing anti-blocking mechanism could change higher speed hewing into lower speed sawing.
2.2 Cutting principle
The sawing anti-blocking mechanism was driven to reverse rotation by power. First, straws were cut in no-sustaining mode by saw-tooth blades while saw-tooth blades touched straws, then after straws were completely cut down, they would be free and be thrown to the rear of opener by throwing ban device and inertial force. Second, straws not being completely cut down would be thrown to former upward and be cut in sustaining mode by fixed blade combinations until any of straws would be cut down, straws having been cut down were thrown to the rear of opener by throwing ban device and saw-tooth. In turn, time after time, straws would be carried out continuously to cut and throw by the sawing anti-blocking mechanism. The lowest point of the saw-tooth blades kept 15～30 mm interval from the soil. In terms of spreading status of straws in field existed perpendicularity or certain angle with marching direction, saw principal in landscape orientation had been determined for the sawing anti-blocking mechanism in order to decrease repeated cutting, leaky cutting and tearing out.
Working procedures of the sawing anti-blocking mechanism were as follows: 1) no-sustaining cut phase: static straws relative to ground were cut firstly atNpoint by saw-tooth blades, then, straws would be cut down completely or embedded in saw-tooth. Straws being cut down completely would be free and 65 Liao Qingxi et al: Design of anti-blocking mechanism for no-tillage planter dropped into adjacent saw-tooth; 2) dragging and delivering phase: after straws dropped into adjacent saw-tooth, they would be thrown to former upward by the throwing ban device, moreover, straws embedded in the saw-tooth would be thrown to former upward by the saw-tooth at higher speed rotation; 3) sustaining cut phase: straws not being cut down completely in no-sustaining cut phase would be cut in sustaining mode by fixed blade combinations atK point until any of straws would be cut down completely;
4)throwing phase: straws being cut down were thrown directly to the rear of opener by tooth former slanting angle of the saw-tooth and throwing ban device, time and again, straws would be carried out continuously to cut and throw. The working principle of the sawing anti-blocking mechanism is shown in Fig.2.
2.3 Analysis of mechanics characteristics of saw-tooth blade
Cutting properties of saw-tooth to cut straws belong to wriggly cut of no-metal materials, its ultimate objective is not only to improve surface cutting quality, but also to raise cutting efficiency, so it can decrease sawing force and power consumption[9]. Because the ratio of its diameter 350 mm to its thickness 1.8 mm is over 150, the saw-tooth blade belongs to exceed thin disc. It is as plane stress and no-axis symmetry problem according to elasticity theory. And because the saw-tooth blade was tighten by flange tray, six freedoms of its center hole were restricted, so its center parts could be regarded as restricted status completely not to bring any displacement and rotation. Saw-tooth blade belongs to excessive blade tools, it would bring to alternative sawing forces in cutting straws, The reasons lied in: 1) structure of straws with inner empty and outside hardness had determined micro-hardness un-uniformity distribution, so the single tooth force would be uncertain in cutting straws; 2) the total sawing forces of saw-tooth in horizontal direction would be uncertain because the tooth of saw-tooth blade is not continuous. These alternative characteristics would bring to transfiguration of the saw-tooth, moreover, the transfigured properties an size was relative to the stress properties and size of the saw-tooth in supporting outside loading. So, it was very essential to make clear stress distribution of the saw-tooth in order to ensure smooth cutting.
The stress distribution of the saw-tooth blade was calculated by the ANASYS finity element software. Number of the tooth participating in cutting straws was determined to 2～3 teeth while diameter of straws was in 20～45 mm[11]. The saw-tooth made in 65Mn ofEequal to 210 GPa[12]andμto 0.28 was separated into 1200 cells and 1260 nodes by trapezia gridding. Thus the stress distributions ofX,YandXYplane had been obtained by the ANASYS software according to the most average wring value 26.8 Nm[13]of the saw-tooth to cut straws by the wring sensor. The stress distributions are shown in Fig.3. Calculated results showed: 1 ) the saw-tooth blade had acted as alternative stress from the whole stress distribution of sawtooth, tooth and around center hole of the saw-tooth had been distributed primary stress, the biggest pressing stress was up to 70776 Pa, moreover, the biggest pulling stress up to 19945 Pa. Compared with yield fatigue intension 735 MPa[12]of the saw-tooth, the saw-tooth blade was difficult to be destroyed, so it would be feasible to cut corn straws; 2)Fig.3 showed, around stress distribution of the saw-tooth blade was in symmetry distribution, the area of relative bigger stress only occupied 3.33% of the saw-tooth whole area, the other 96.67%; 3)the former tooth of saw-tooth supported the biggest forces among the whole saw-tooth while the former tooth of the saw-tooth touched firstly straws, and its stress value was the smallest before cutting straws, but when saw-tooth started to cut straws, the stress value would increase 66 Vol.19, No.5 Transactions of the CSAE Sept.2003 sharply, its values would be over 105times comparing with the stress values before saw-tooth started to cut straws. However the stress would be down to the lowest point while saw-tooth had finished cutting straws. Thus, the saw-tooth was acted as alternative stress.
3 Results and discussion
3.1 Experiments and analysis of rotation direction of the saw-tooth blade for cutting quality
Some experiments were done by clockwise and counter-clockwise rotation of the saw-tooth blade in the soil bin device. The results are listed in Table 1.
Table 1 Experimental results of rotation direction of the saw-tooth blade
Table 1 showed that the way of cutting straws at counter-clockwise rotation would be of benefit to improve cutting quality and throwing effect, and boost up adaptability of weight of different stubble mulch. Therefore, counter-clockwise rotation direction of the saw-tooth blade had been determined.
3.2 Effect of the rotation speed on cutting quality
The experiments were done by selecting velocity 0.3 m/s of vehicle and interval 5 mm of the moved and fixed blade, and spacing 20 mm between the saw-tooth and ground as well as weight 11250 kg/hm2of the straws mulch, experimental results are shown in Fig.4. The results indicated that the power consump-tion and cutting rate would increase with rising of rotation speed of the saw-tooth blade. Because the wring values of cutting straws were equal basically on the same working condition, the cutting rate could be up to 100% while the rotation speed of the saw-tooth blade was above 650 r/min. It was because the probability rate of the saw-tooth blade to cut straws 67 Liao Qingxi et al: Design of anti-blocking mechanism for no-tillage planter would increase with rising of rotation speed whenweight of straws was fixed.
Fig.4 Relationships among rotation speed, cutting rate and power consumption
3.3 Effect of the straw moisture on cutting quality
The straw moisture of the same crops is different for different autumn and reaping time. The moisture were 20%, 40.5%, 64.4% and 80.16% respectively, after corn straws had been placed in field for different periods. Experiments were done by selecting velocity 0.3 m/s of vehicle and interval 5 mm between the moved and fixed blade and spacing 20 mm between sawtooth and ground, and rotation speed 650 r/min as well as mass 11250 kg/hm2of straws mulch, the results were shown in Fig.5. Fig.5 Results of straws moisture for cutting rate and power consumption
Experimental results show that power consumption decreased with increasing of straw moisture and cutting rate of straws increased with increasing of straws moisture on the same working condition, which had connected importantly with different moisture of straws. Straws would take on bigger hardness and best firmness and fine brittleness when straws moisture was in higher, which demonstrated that it had been easy to finish to cut straws. But straws would take on tired and soft status for fine flexible and toughness when straw moisture was lower, so it would be easy to bring to tearing and wrapping. The saw-tooth blade had fine cutting quality and higher cutting rate while straws moisture was up to 80.16% (Fig.6). However the saw-tooth blade had taken on
tearing while straw moisture was up to 20%(Fig.7).
4 Conclusions
1) A new type of sawing anti-blocking mechanism, which could get rid of some shortcoming that common smooth blade is difficult to seize straws as well as high rotation speed, was designed according to the anti-blocking requirements of no-tillage planter and need in practice. The sawing anti-blocking mechanism had strong capability to seize straws and lower rotation (650 r/min) speed and lower consumption (power consumption per unit width up to 2.95 kW/m) and higher cutting rate of straws, a new approach was provided for design and development of the anti-blocking mechanism of no-tillage planter.
2) The stress distribution of the saw-tooth blade was calculated by the ANASYS finity element software. The results showed that its intension would be difficult to be destroyed and the sawtooth blade was feasible to cut corn straws.
3) The sawing anti-blocking mechanism realized an integrated function of directly throwing and cutting straws by counter-clockwise. The straws could be cut down completely by two cutting modes of sustaining and no-sustaining cut. Meanwhile, the straws being cut down completely could be directly thrown to the rear of opener by the former tooth horn of sawtooth blade and throwing ban device.
4) Experimental results showed in the soil bin device that: (1) Cutting rate of straws increased with increasing of rotation speed of saw-tooth blade and moisture of straws, and higher moisture of straws would be of benefit to improve cutting quality; (2) Power consumption increases along with increasing of rotation speed, and that decreased with increasing of moisture of straws; ( 3 ) Cutting rate of straws decreased with increasing of velocity of the vehicle while interval between the fixed and moved blade had been determined, and to decrease the interval between the fixed and moved blade would be of benefit to improve cutting quality of straws without phenomena of rearing out and leaky cut, and could decrease power consumption.
Compared with the other driving anti-blocking mechanism, the theoretical analysis and experimental results showed that the sawing anti-blocking mechanism had better capability to cut and lower rotate speed and power consumption as well as stronger suitability for different stubbles mulch.
