Safety Evaluation Of Metallurgical Crane Structure In Elevated Temperature Environment

Major mechanical equipment has long-term work in complex environments,and the mechanical properties of structures and components have gradually deteriorated.In the event of an accident,it is extremely likely to cause major economic losses and major casualties.As an important molten metal handling equipment,metallurgical cranes have the characteristics of harsh working environment,high price and high maintenance cost.With the demand for steel production continuing to increase,cranes that are overloaded with heavy loads are still in use,posing a significant safety hazard.The structural safety evaluation of metallurgical cranes has always been an engineering technical problem for a long time,and as the most complex weld index lacks objective and accurate fatigue assessment methods.This thesis focuses on the establishment of the most complex weld index fatigue life assessment problem in metallurgical crane metal structure safety evaluation system and evaluation system,and studies the metal structure safety evaluation of metallurgical cranes.The purpose of this thesis is to build the hierarchical structure safety evaluation system of metallurgical cranes,establish the identification method based on the indicator status value,compare the fatigue life evaluation methods of different welds,and evaluate the weld fatigue in the structure with dynamic load as the excitation.The main work and conclusions of this thesis are as follows:Through analyzing the maintenance records of metallurgical cranes,the factors affecting the structural safety of metallurgical cranes are explored.From the hierarchical structure of Analytic Hierarchy Process(AHP),a safety evaluation system based on strength,stiffness,deformation,corrosion and weld as a single factor index is established.The safety evaluation steps from the single factor index value to the overall structure of the metallurgical crane are studied,and the evaluation methods of each indicator status are given.In the established safety evaluation system for metal structures of Shuangliang metallurgical cranes,the state evaluation of weld indicators in the five indicators of each substructure is the most complicated.The life assessment of the weld requires the time-course stress at the dangerous point of the weld,and the calculation of the time-course stress at the dangerous point is studied.From the theory of vibration,the metallurgical crane structure,ladle,trolley and wire rope are simplified into a two-degree-of-freedom dynamic model.The Wilson-? method is used to solve the dynamic differential equations in the lifting phase,and the tension response of the wire rope under different lifting positions and different lifting speeds is obtained.It is found that the larger the lifting speed brings in larger dynamic load coefficient,and the norm estimated dynamic load coefficient has sufficient safety margin.The heat insulation effect of the heat insulation board is simulated by the method of reducing the surface emissivity of the ladle,and the temperature field analysis of the crane structure is carried out to obtain the structural temperature field under each lifting condition.The highest temperature part of the structure changes with the position of the lifting point.The temperature field is used as a predefined field to calculate the thermal coupling transient dynamics of the crane structure,and the dynamic stress spectrum of the dangerous points under each working condition is obtained,which paves the way for weld fatigue calculation.In the established safety evaluation system for metal structures of Shuangliang metallurgical cranes,the state evaluation of weld indicators in the five indicators of each substructure is the most complicated.Fatigue assessment of typical welds is performed in conjunction with calculated time-course stresses.The sub-model technology is used to establish the weld detail model of the main beam of the metallurgical crane.The weld fatigue calculation method(including surface extrapolation,thickness linearity and Dong method)is studied from different element types,different element sizes and different modeling methods.The residual life of the weld is calculated using the dynamic stress spectrum and the hot spot stress concentration factor.The results show that the calculated values of the weld toe hotspot stress by the high-order shell element are conservative.The element size sensitivity of the Dong method is better than the surface extrapolation method and the thickness linearization method.The hotspot stress calculation can be performed by the Dong method or the extrapolation method and the thickness linearization method with a relatively fine element size.It is found that the temperature field of the bridge structure has an effect on the remaining life of the weld,and the temperature influence increases with the increase of the service life.The calculation method of weights in the safety evaluation system of metal structure of Shuangliang metallurgical cranes and the evaluation and synthesis methods of evaluation index layer,subsystem layer and system layer are studied.The objective weighting of the entropy weight method and the subjective fixed power of the analytic hierarchy process are constructed using the empirical factor to construct a comprehensive weighting model,and the fuzzy comprehensive evaluation method is used to form a safety evaluation algorithm.And the value of the detection of the main beam of a metallurgical crane is used as an example.The research shows that under the balance of the comprehensive method,the weight can reflect the influence of the single factor state value and the relative importance of each factor attribute.The comprehensive evaluation and fuzzy comprehensive evaluation method constitute a safety evaluation algorithm which can reasonably reflect the overall structure state value.The algorithm can be used as the basic algorithm for structural safety evaluation of metallurgical cranes.