H. Gholami; D. Kalantari; M. Rajabi Vandechali
Abstract
Introduction One of the most important problems arising with operation of the conventional rototillers is severe vibration of the machine handle which is transmitted to the user’s hands, arms and shoulders. Long period exposure of the hand-transmitted vibration may cause various diseases such as ...
Read More
Introduction One of the most important problems arising with operation of the conventional rototillers is severe vibration of the machine handle which is transmitted to the user’s hands, arms and shoulders. Long period exposure of the hand-transmitted vibration may cause various diseases such as white finger syndrome. Therefore in this study, vibrations of a new type of rototiller with ridged blades were investigated at the position of handle/hand interface in different working conditions. Finally, the maximum allowable exposure time to the rototiller users in continuous tillage operation was obtained according to ISO 5349-1. Materials and Methods Experiments were carried out in one of the farms with silty clay soil texture, located in Sari city, Mazandaran province, Iran. Vibration measurements were performed according to ISO 5349-1 and ISO 5349-2 standards in two different modes, including in situ mode and tillage mode. Vibrational parameters were obtained in three blade rotational speeds, i.e., low speed (140-170 rpm), medium speed (170-200), and high speed (200-230). Blade rotational speed varied by changing engine speed using the throttle control lever. In each experiment, different vibrational values were individually recorded in three directions (x, y, and z). Experimental design and data analysis were performed in a Randomized Complete Block Design with three replications using the SPSS16 software. Results and Discussion Based on the obtained results in this study, the RMS of acceleration increased by increasing in rotational speed for all of the conducted experiments. The reason is that number of cutting per unit of time and consequently the frequency of changing in the dynamic forces exerting on the blades dramatically increases with increasing the rotational speed of the blades. Noteworthy is that in most cases the variation of acceleration in the tillage mode showed similar trend with vibrational values in the idling mode. This represents a significant contribution of the combustion engine in vibration of the examined rototiller. Meanwhile, contribution of the engine in the total measured vibration was more than 50% at different rotational speeds and different directions. The minimum engine contribution was measured equal to 56.39% in z-direction at 155 rpm, whereas the maximum engine contribution was observed equal to 79.5%, in x-direction and rotational speed of 215 rpm. These results indicate the importance of selecting a proper combustion engine for reducing the rototiller vibration. It should be noted that the contribution of the engine in total vibration reached its minimum value at the speed related to the maximum generated torque, i.e., 185 rpm of the rotor speed. This result indicates that using the combustion engine in its optimum speed reduces the entire device vibration in the vertical direction. By increasing the rotational speed of the blades in the y-direction, engine contribution in device vibration showed different trends in compare to the other directions. The most value was equal to 74.25% which was obtained at the rotation speed of 185 rpm. By increasing blade rotational speed from 155 rpm to 215 rpm, the engine contribution in device vibration in the z direction and the total acceleration steadily increased. Conclusion With growing mechanization and entering various types of machines to the farm, importance of considerations to human health is also increased, especially in working with rotational machines. Therefore, the current study was undertaken with the specific attention to the rototillers operational vibration at the handle/hand interface. Results of the conducted experiments showed that vibration of the examined rototiller depends more on the operation of the mounted combustion engine, rather than the soil working blades. Therefore, it is suggested to select a higher quality engine with less vibration or isolate the engine from chassis by a damper (such as a compressed rubber) to reduce the vibration transmitted to the operator’s hands and arms.
H. Gholami; D. Kalantari; M. Rajabi Vandechali
Abstract
Introduction Recently, employment of rotary tillers has been expanded in gardens and small farms, especially in the northern of Iran. However using the L-shaped blades in the conventional rotary tillers have some problems such as severe vibration problems, weeds stucking around the blades, forming the ...
Read More
Introduction Recently, employment of rotary tillers has been expanded in gardens and small farms, especially in the northern of Iran. However using the L-shaped blades in the conventional rotary tillers have some problems such as severe vibration problems, weeds stucking around the blades, forming the plow pan and lower performance due to the less powers of such small rototillers. Therefore in order to overcome the above mentioned problems, a rototiller with new ridged blades was designed, fabricated and tested in this research. Materials and Methods Experiments were carried out in one of the citrus orchards in Mazandaran, Sari. The experimental design was split plots based on randomized complete block design with three replications. The soil moisture as main plot varied in two levels of 13.5-21.9 and 21.9-30.3 percent based on dry weight and the rotational speed of blades as subplots varied in three levels of 140-170, 170-200 and 200-230 rpm. The measured parameters consist of soil particle mean weight diameter, soil bulk density, soil crumbling percentage, specific fuel consumption and machine efficiency. The diameter of soil particles was measured using a set of standard sieves with diameter ranging from 0.5 to 8 mm. Then a laboratory shaker was used to sift the samples. Each sample was shaken in 30 sec. The fuel consumption during the experiments was determined by the filled fuel tank method. Analysis of variance (ANOVA) and mean comparisons and interaction between the parameters were performed using the SPSS 16 software. Results and Discussion The results indicated that the soil particle mean weight diameter reduced by increasing blades rotational speed in both examined soil moisture contents. Results indicated that the soil crumbling percent increases with increasing the rotational speed. The main reason for this effect could be due to the more energy transferring to the soil at higher rotational speeds, which result in further crumbling of the soil slices. Regarding the results obtained in this study, the specific fuel consumption increased at first in a light slope, then in a steep rise with increasing the blades rotational speed. The reason can be the higher crumbling percent of the soil at higher rotational speeds and higher soil moisture contents (at the range of 21.9-30.3%), providing the more specific energy consumptions. The specific fuel consumption was the maximum at higher soil moisture content of 30 %. The results indicated that the blades rotational speed and soil moisture content had no significant effect on the field efficiency of the examined rototiller. The field efficiency varied in the range of 92 to 97% in all of the experiments, i.e., rotational speed between 140 to 230 rpm and moisture content ranging from 13.5 to 30.3%. The reason for that was due to the roughly similar turning times, minor adjustments, changing operators and some other parameters influencing the field efficiency. Reduction of the rotational speed of the rototiller from high-to-moderate speeds leads to decrease the fuel consumption to 17 liter ha-1, which could be significant in wide scale of soil tillage operations. As a general result, reduction of the rotational speed had some considerable advantages such as reducing power requirements, reducing blade wearing and maintaining soil structure. Conclusion Influence of soil moisture and rotational speed of blades on the soil particle mean weight diameter, soil crumbling percentage and specific fuel consumption were significant (P<0.01) for fabricated rototiller with new ridged blades. Statistical analysis indicated that the soil crumbling percentage and specific fuel consumptions increased linearly with increasing the rotational speed of blades. The determination coefficients of the crumbling percentage and specific fuel consumption as a function of rotational speed were 0.996 and 0.860, respectively. Meanwhile, clod mean weight diameter decreased linearly by increasing the rotational speed with a determination coefficient of 0.990. For achieving fine soil aggregates, combining high rotational speed and higher soil moisture (20 to 30%) is suggested, while to obtain a coarse soil gradation, low rotational speed and low soil moisture are more suitable compositions. The use of high rotational speed is not recommended due to increasing fuel consumption and consequently the soil erosion and environmental issues.