Introduction to mechanical engineering: safety risk analysis of agricultural machinery
1 safety risk assessment process of agricultural machinery
Agricultural machinery safety risk assessment is to identify and analyze the causes of agricultural machinery safety accidents by using scientific methods and procedures, take measures to eliminate or reduce all kinds of safety hazards in the installation, use and maintenance of agricultural machinery, prevent safety accidents and improve the safety of agricultural machinery. This process includes risk analysis (determining product restrictions, hazard identification and safety risk assessment), safety risk assessment and risk reduction. Security risk assessment is an iterative process. Through safety risk assessment, take measures to eliminate or reduce unacceptable safety risks, and analyze and evaluate risks (including regeneration risks) again until the safety risks are reduced to an acceptable level.
2 agricultural machinery hazard identification
Before identifying the danger, we should first determine the mechanical limit. That is, it describes the working function, expected use range, foreseeable misuse, use and maintenance environment of the product to determine the scope of hazard identification. Generally, it can be described according to the function and operation of the product. Such as refueling, adding water, getting on the bus, starting, moving forward, turning, reversing, braking, parking, getting off, hanging, traction, lifting, maintenance, etc. Danger refers to the potential source of injury. The main hazards of agricultural machinery products include: mechanical hazards (such as extrusion, shearing, impact, winding, inhalation or winding, cutting, high-pressure fluid injection, etc. ), electrical hazards (such as contact with live parts), thermal hazards (such as contact with high-temperature objects, thermal radiation, etc. ), noise hazards, vibration hazards (such as seat and handle vibration), hazards caused by materials and substances (such as human contact with pesticides). Different agricultural machinery products may produce different forms and quantities of dangers. The purpose of hazard identification is to determine and form a list of hazards, hazardous states and hazardous events within mechanical limits. Hazard identification shall systematically identify the foreseeable hazards in all relevant tasks at all stages (such as transportation, installation, use, shutdown, maintenance, etc.). ) during the life of agricultural machinery. Hazard identification generally adopts top-down and bottom-up methods. The top-down method is to determine the risk of injury according to the list of potential consequences (such as crushing and burns). The bottom-up method is based on checking all the dangers, and considering all possible ways of making mistakes (such as braking function failure and human error) and ways of causing injuries under certain dangerous conditions. Comparatively speaking, the bottom-up method is more comprehensive and thorough, but the process is more complicated.
3 Agricultural machinery safety risk assessment
Safety risk is the combination of injury probability and injury severity. Agricultural machinery safety risk assessment is a process to determine the probability and severity of various injuries according to the risk identification results of agricultural machinery products. The purpose is to determine the highest safety risk of each dangerous state or accident. Usually, a level, index or score is used to indicate the size of a security risk. The injury probability should be determined after considering the personnel exposed to the dangerous area, the possibility of dangerous events (product characteristics, product maturity, production enterprise scale, production mode), avoiding or limiting injuries and other factors. The severity of injury can be determined after considering the degree of injury or health impact (such as minor injury, serious injury and death) and the scope of injury (such as the number of people). Safety risk assessment methods are divided into qualitative assessment methods and quantitative assessment methods. Common methods include risk matrix method, risk map method, numerical scoring method, quantitative risk assessment method and comprehensive assessment method. Among them, risk matrix method and risk diagram method are simple and commonly used.
3. 1 risk matrix method
For each identified danger, the risk matrix method divides the two factors that determine the risk of dangerous events, that is, the severity of injury and the probability of causing injury, into corresponding grades to form a risk matrix, and uses cross units to qualitatively measure the risk. This method includes four steps: risk matrix selection, injury severity evaluation, injury occurrence probability evaluation and risk grade evaluation.
3.2 Risk Diagram Method
Risk map is developed on the basis of decision tree, which is characterized by visualizing the assessed risks for easy analysis and comparison. In the risk graph, each node represents a risk parameter (severity, exposure, probability of occurrence of dangerous events and possibility of avoidance), and the branches of each node respectively represent the levels of corresponding risk parameters (such as minor and severe). In risk assessment, starting from the starting point, at each node, we move forward along the branch with a certain level, and the end point is the risk level.
4 agricultural machinery safety risk reduction
The purpose of security risk assessment is to reduce or eliminate unacceptable security risks. Security risk consists of security risk factors. To reduce or eliminate safety risks, it is necessary to reduce or eliminate risk factors (hazard source, occurrence probability or injury degree) that affect the risk level. Reducing or eliminating the risk factors that affect the risk level can be achieved by taking corresponding measures in the product design stage and use stage.
4. 1 Take measures to eliminate or reduce safety risks during product design and manufacturing.
1) intrinsically safe design and manufacture. That is, eliminate or reduce the danger through product design and manufacturing. For example, the risk of scraping or squeezing can be eliminated by removing acute angles on the covers of agricultural machinery such as harvesters and tractors and increasing the gap between the operating handle of tractors and adjacent components. Not all hazards can be completely eliminated through product design and manufacturing. When there are dangers that cannot be eliminated by design, the risks should be reduced by design and manufacture. For example, reduce the running speed and the height of the center of mass of the self-propelled sprayer with high clearance to improve the stability; Damping mechanism is used to reduce the vibration of tractor seat. Intrinsic safety design and manufacturing are the most effective measures to reduce safety risks and should be given priority. 2) Safety protection measures. When safety risks cannot be eliminated or completely reduced through product design and manufacturing, safety measures should be taken to limit exposure to danger, reduce the probability of dangerous events or eliminate or reduce the possibility of injury. For example, the exposed rotating parts of harvesters and tractors should be equipped with protective covers, and power sprayers should be equipped with safety valves to limit pressure. 3) Use information. The usage information is used to warn the remaining safety risks after taking intrinsic safety design and protection measures, so as to reduce the possibility of injury. Such as sticking safety warning signs and labels on dangerous parts of agricultural machinery; Install signal devices such as speakers and rearview mirrors; Explain the safe use rules in the product instruction manual; Limit the scope of use and so on.
4.2 Take measures to reduce the risks in the product use stage.
After taking safety risk reduction measures in the product design and manufacturing stage, most agricultural machinery products will still leave safety risks due to the inherent characteristics of products and the differences in production design. In this regard, targeted measures should be taken against the remaining security risks in the use stage. The main measures include: first, the implementation of administrative licensing management, that is, through the implementation of licensing system to reduce the possibility of injury. For example, the tractor driver's license system implemented in China; Safety inspection system for tractors and harvesters; Plant protection machinery implements CCC certification system. The second is to formulate safety operation procedures. The third is to cultivate users. Fourth, use personal protective devices, such as wearing gas masks, protective gloves, safety helmets, etc. Conclusion Using scientific methods and procedures can effectively identify, evaluate and reduce the safety risks of agricultural machinery products and improve the safety of agricultural machinery products. The results of safety risk identification and assessment are the basis for scientific formulation of safety standards and safety supervision measures for agricultural machinery products.
Introduction to Mechanical Engineering Paper Mode 2: Technical Transformation and Maintenance of Agricultural Machinery
1. the changing law of technical state of agricultural machinery
After agricultural machinery is put into use, with the increase of time, its main technical performance indicators will gradually deviate from the initial standard values. When the technical performance index does not exceed the allowable limit value, the machine meets the basic requirements and works normally, so it can be considered that the technical state at this time is normal. When the allowable limit value is exceeded, the machinery can not meet the basic requirements of normal work, such as poor working quality, low working efficiency, sharp decline in economic benefits and sharp increase in mechanical failures. This phenomenon is called technological degradation. At this time, it should be stopped for maintenance or scrapped. Although the specific change process of the technical state of agricultural machinery is complex, it has certain regularity. For example, the basic deterioration form of moving parts such as crankshaft and bearing, piston and cylinder liner is the increase of fit clearance, and its law is that the increase rate of fit clearance is large at the initial stage of work, and when the workpieces run in with each other, the clearance increases and the speed decreases, and it remains relatively stable for a long period of time. When the clearance between mating parts increases to the limit value, there will be impact between mating parts and the lubrication conditions will deteriorate. If the work continues, the machine will be damaged
Another example is the filter oil filter, the basic deterioration form of which is the dirty plug of the filter screen. Its change law is that at the initial stage of work, the impurities on the surface of the filter screen have a stronger filtering effect on the oil, and the accumulation speed of impurities is faster. With the extension of working time, the scaling degree on the surface of the filter screen increases, the oil throughput decreases, the effect of filtering impurities weakens and the accumulation speed of impurities slows down. Once the surface of the filter screen is completely blocked, it will completely lose the function of filtering impurities. Other parts of machinery also have their own technical state change rules. Because of the different materials, working conditions and functions of each part, the changing forms and laws of the technical state in the working process are also different, which have an impact on the changing laws of the technical state of the whole machine. Among them, the influence of the main part plays a decisive role. Therefore, a thorough understanding of the changing law of the technical state of the main parts can predict the changing trend of the technical state of the whole machine, so as to actively take various effective technical measures. More complex and expensive agricultural machinery is not scrapped immediately after one-time use, but continues to be used after repeated repairs. When the main performance index of the machine is close to the limit, it should be repaired in time to restore the main performance index to the standard value, and then the machine can be put into use again. If the technical indicators permit, the service life of the machinery should be extended as much as possible, and various technical measures should be taken to maintain and restore the technical state of the machinery.
2. Agricultural machinery maintenance system
The technical maintenance system of agricultural machinery refers to the technical maintenance system to maintain and restore the normal technical state of machinery during use, including the contents, methods and standards of various technical measures to be taken. Although most agricultural machinery is operated by agricultural machinery users at present, a scientific maintenance system is very necessary, because only by prolonging the service life of agricultural machinery can we bring direct economic benefits to farmers and generate huge social benefits. At present, there are three main maintenance systems:
The first is the fault maintenance system. The machine has been used until it breaks down or is damaged, and then it is forced to stop maintenance. At present, this compulsory maintenance system is widely adopted by agricultural machinery households, which can not only save daily maintenance costs, but also make full use of some parts. However, due to the premature deterioration of the technical state of machinery, not only can the technical life of all machine parts not be fully utilized, but it often causes serious damage, making it impossible for machinery to be repaired and scrapped as soon as possible.
The second is regular maintenance system. Carry out compulsory technical maintenance on the machine regularly. Its cycle is determined according to the changing law of mechanical technical state, and technical maintenance measures can be taken to prevent mechanical failure and damage and maintain the reliability of mechanical work in a planned way. This is a scientific maintenance system, but it has not attracted the general attention of agricultural machinery households.
The third is to maintain the system on demand. Check the machinery regularly without disassembly, and maintain the machinery according to the needs of technical status. This is also a planned preventive maintenance system, which can not only maintain the high reliability of machinery, but also make full use of the technical life of mechanical parts. It is more advanced than the conventional maintenance system. It is suggested that farmers widely use it.