RESEARCH ON THE RELIABILITY OF AGRICULTURAL MACHINERY USED FOR FIELD CROPS MECHANIZATION Summary of PhD. thesis PhD. thesis entitled "Research on the reliability of agricultural machinery used for field crops mechanization", coordinated by PhD professor Adrian Mitroi has, as purpose, to highlight the most important aspects of tractors and agricultural equipment reliability, by conducting a comprehensive study of their behavior during working process, in the country south. For this purpose, experimental research goals consisted of: studying of behavior in exploitation for different types of equipment used for agricultural mechanization at field crops (ploughs, seeders, combines, corn detasseling machines, disk harrows, etc.); monitoring of faults occurring in service; determination of the fault causes; normal wear identification; observations on failures and the establishment of its influence on the immobilization time; the determination of soil properties influence on ploughs wear; the determination of active pieces wear on specific energy consumption; the influence of maintenance on the safety of the agricultural machinery; the determination of the influence of some reliability parameters on reliability economic indicators; the development of scientific recommendations in order to improve the agricultural equipment maintenance. For research there were considered different exploitation conditions: mediumsized agricultural farms, located in the south of the country, endowed with both new, modern, tractors and farm machinery and older types agricultural machinery, modest condition type, but yet necessary in the working process, due to decreased renewal rate of the agricultural machinery fleet. PhD. thesis is divided into four sections, as follows: the first two chapters present the concept of reliability in the field of agricultural machinery, in terms of its basic indicators and necessary measures, for a good maintenance of agricultural equipment, taking into account the researches developed until present day; the following two chapters contain the researches on the reliability in service of the considered agricultural
machinery and a number of conclusions and recommendations that emerged from the study. For collection, processing and interpretation of the necessary data, there were observed and monitored a significant number of agricultural machinery and equipments in Braila, Calarasi, Ialomita, Buzau and Dâmbovia counties, during the work process, for an approximately four years period. The study-work consists of the following chapters: Introduction, Status of knowledge in agricultural machinery reliability, Researches on the reliability in exploitation of the agricultural machinery used for field crops mechanization, Conclusions, References. In the chapter entitled "Status of knowledge in agricultural machinery reliability" physical and mechanical aspects of agricultural equipment reliability and basic indicators of agricultural tractors and machinery are detailed; also, theoretical distribution laws used to determine reliability indicators are presented. Regarding physical and mechanical reliability aspects of agricultural machinery, the most important issue that contributes to loss of functional capacity of tractors and agricultural machinery parts is friction wear. Another aspect of agricultural machinery reliability is the limit condition of parts and joints; it represents the main element in assessing the potential of those parts and machinery, as well as the consuming rate for exchangeable pieces. Reliability can be considered through a series of key indicators, such as: good functioning time, maintenance capacity, repairing capacity, durability, pieces flop. The main index of reliability that gives a clear and eloquent image on the quality of execution and maintenance of agricultural machinery is good functioning time. In basic calculation of reliability indicators, theoretical distribution laws are used, but only for same technological and the same series equipments. Also, reliability can be regarded as a price indicator for agricultural equipment: thus, a high reliability is translated into lower costs of any equipment maintenance. In the second part of PhD thesis, "Researches on the reliability in exploitation of the agricultural machinery used for field crops mechanization" were examined issues such as: behavior of plough furrows in exploitation, reliability in service of agricultural
tractors, disc harrows, reliability and performance of pneumatic SK-8 PPS and Monosem sowing-machines, seed corn detasseling machines, harvesting machines and some equipment, such as baling presses. Plough furrows behavior in exploitation was studied on the following soil types: sandy soil, argic chernozem and alluvial soil. The results showed that the highest attrition (by subtracting the mass furrows) was recorded on sandy soil and the least pronounced attrition on alluvial soil. Also, soil moisture influenced the furrow wear, as follows: most wear occurred on very dry soil and the lowest wear on optimum moisturized soil. However, the wear degree of furrows has influenced the fuel consumption: when new plough furrows were used, specific fuel consumption was 20.2 l / ha and 25.7 l / ha at plough-work, when advanced wear furrows were used; the values were recorded in conditions of 22-24 cm depth plough-work, using U-650 tractor and PP 3-30 plough. Regarding agricultural tractors reliability in operation, researches on U-650 M, universal 683 DT tractor and S-1500 crawler tractor revealed failures, as follows: the hydraulic pump and injection pump (for U-650 tractor), gear damage and increased wear of clutch disc (for 683 DT universal tractor) and wear advanced power-trains (for S-1500 crawler tractor). Regarding the disc harrows reliability in exploitation, the analysis was performed for GD-3,4, respectively Kuhn Discover. On GD-3, 4 disc harrow it was established that sharpening of disks is required after 350-520 hectares; at Kuhn Discover harrow, after three years work, no failures were registrated but, for major maintenance, daily lubrication is required. To highlight the exploitation reliability of sowing-machines, the following types of drills work were analysed: SK, SPC-8, SUP-29, Monosem. Failures in this process were the following: rebuilding skates after 200 ha in case of SK machine, accidental falls (like a broken marker at hydrant impact), in case of SPC-8, frequent breakdowns caused by failure of the seed tube and breaking support, recorded at SUP-29 and an accidental fall, after 472 hours of work, consisting of cutting of tire, due to impact with a sharp metal object, in case of Monosem sowing-machine.
To determine the reliability in function of corn seed detasseling machines, an analysis was performed for a three machines in exploitation, manufactured in 2006: Hagie detasseling machine (U.S. production), Frema detasseling machine (production France), Castrix detasseling machine (Italian production). The analysis showed the following: - at Hagie, the failure occurred after 280 hours work at thermostat, as part of the engine cooling system and also, by a broken arm which supported cutting knives, leading to an 4 hours interruption in work; - at Frema, the following failures occurred: breaking of a high pressure hose, causing a 2-hour time restraint and injection pump failure (19 hours time restraint); - at Castrix, there was a restraint for 37 hours, caused by two knives damage as a result of an accidental fall; the machine was also 3 hours immobilized, due to the obstruction of the diesel filter. Research on agricultural harvesting machines focused, initially, on monitoring the occurrence of falls for 10 New Holland machines, TC 56 type, year 2003. If in the first year of exploitation failures were minor and accidental, in the second one, broken straps were found. In the subsequent phase, two C-14 combines have been observed during exploitation process; failures occurred consisted of oil leak and increased wear on bearings shields, appeared in first year of observation. Some research in the study-paper refers to nonspecific or apparently minor defects which led to reduced agricultural equipment reliability and have consisted primarily of sharp breaks or distortions in the machinery, failure of bearings and supports, failure of different connections, etc. The PhD. thesis also contains an analysis concerning costs determination, in order to maintain and repair equipments, such as: PP 3-30 ploughs, grain cereal harvesters, precision drills and detasseling machines. In order to estimate costs, the redemption has been calculated, considering the following elements: asset value of machine, the annual rate of redemption, hourly productivity of the machine on a work shift (ha / h), machine annual working time (h) and the value of maintenance and repairs costs.
Thus, considering the economical aspect, redemption highest values were registrated for corn detassseling machines, while the highest costs for maintenance and repairs were for combine harvesters. Conclusions that emerged from research showed that, in the current period, agricultural machinery equipment in small and medium-sized farms is mixed; that translates into fact that old local production equipment is maintained, as well as new imported equipment; in case of two machines existence, with the same destination - two tractors, two ploughs, two combines, etc. - they are often different brand, type, characteristics, making it impossible to joint planning of maintenance, repair pieces and insurance. Agricultural machinery reliability in case of experimental farm units is very different. The incidence of falls is increased for old equipment, with more modest performance. Most farms have minimum endowment of machine tools in their mechanical workshop, like: lathe, drill accessories and forging, welding machines, tools and devices. At farms with modern technical equipment, reliability indicators are much better: maintaining time is shorter and maintenance costs are lower. Failures produced in case of agricultural machinery focused more nonspecific components-framework, supports, joints, belts and chains. In farms where determinations were made, during several years research, little was used service and, if so, only for relatively new higher complexity equipment. A possible cause of this situation might be and that service system is yet not well in place and price for some interventions is relatively high. Some failures of agricultural machinery present ecological implications. Failures that lead to fuel oil flow cause soil and ground water pollution. Specific oil consumption growth, either indirectly caused, as mentioned above, or directly through the fuel system wear, with negative environmental impact due to increasing of carbon dioxide emission. All these assessments show the necessity of proper management in case of energy resources, in order to increase profitability in the agricultural process. It is also necessary to create a system that provides opportunities for raising the qualifications of individual farmers, as users of farm machinery. These systems, based on the Western
model, could develop the ability of farmer to use, to maintain and fix properly the damages of the agricultural equipment.