Study On Rock Breaking Mechanism Using Conical Picks And Cutting Performance Of Roadheaders

Drilling and blasting method is the main way of rock excavation,the method is even widely applied to break medium hard rock.However,with the development of coal industry and the increase of the quantity of urban underground excavation works,roadheaders have been popularized in rock breaking.Meanwhile,higher requirements for their performanceare also proposed.Rock cutting mechansim using dray-typed picks is the base for designing high performance work units of roadheaders and for predicting their performance.Therefore,it is necessary to further deeply study the rock cutting mechanism,which would be further used for optimizing the design of cutting headers,and reasonably guiding the roadheaders selection.It has an important significance for improving the performance of roahdeaders,and for reducing costs of rock excavations.Based on the linear rock cutting machine,effects of cutting parameters on rock cutting performance of conical picks were deeply discussed,and the prediction models of tool forces and specific energy were developed as well.Design and research approaches of cutting head were discussed based on the results of rock cutting mechanism,and the model of production rate of roadheaders was also developed.All models and results can provide theoretical and experimental basis for improving the performance of roadheaders and applying them in rock excavation.Firsly,domination mechanical properties of the rock affecting the performance of rock cutting and their test methods were briefly discussed,and relevant empirical relationships among the properties were developed based on experimental data.These will provide basis parameters for rock cutting mechanism study by theoy and experiment,and for developing prediction models of tool forces and specific energy.Based on the linear rock cutting machine,lots of rock cutting tests were carried out under different levels of cutting parameters on five common sandstones with different strength.The effects of cutting parameters on force parameters and specific energy were deeply researched and discussed.Experimental results indicate that the effects of attack angle on the performance of rock cutting couple with the effects of rake angle and clearance angle on it.Small attack angles along with small clearance angels will cause serious friction between rock and the pick,and further lead to high tool forces and specific energy,expecially when it is close with zero degree.Under the circumstances,the clearance angle plays a leading role in the influence on the performance of rock cutting.With increase of attack angle,the effects of rake angle and cone angle of the pick on the tool forces become manifest and play leading roles replacing the clearance angle.Depth of cut and line spacing are the key parameters affecting the performance of rock cutting as well.Tool forces increase with increase of depth of cut and line spacing.Based on test data of this study,some empirical relationships between tool forces and cutting parameters and geometrical parameter of the pick were developed using regression analysis method.The results will provide experimental evidence for development of prediction models of tool forces considering relevant cutting parameters,the geometrical parameter of the pick and rock strength.Based on fracture mechanics,theoretical model of specific energy was estabilished.Result indicates that depth of cut is the most important cutting parameter affecting the specific energy,and the result can provide theoretical guidance for linear rock cutting.The results of linear rock cutting indicate that the cone angle of the conical pick,attack angle and rake angle have no obvious influences on specific energy when the clearance angle is greater.The depth of cut and line spacing have significant influences on specific energy.Specific energy decreases with increase of depth of cut in power function.There is an optimum value of the ratio of line spacing to depth of cut to obtain the smallest specific energy,and the optimum value of the ratio is not influenced by depth of cut and line spacing.Based on regression analysis method,the relationship between specific energy and depth of cut was established,it can provide a basis for developing the prediction model of specific energy.The rock chips formed in the linear cutting were processed using sieve method.The results show that the rock chips conform to the distribution law of Rosin-Rammler function and fractal distribution.There are statistically significant associations among the characteristic indexes,between cutting parameters and characteristic parameters,and between specific energy and characterstic parameters.These will provide more methods for specific energy study and prediction.General models of cutting and normal forces and specific energy were firstly proposed.Cutting force models were then developed based on theoretical models and test data considering the attack angle,cone angle of the pick,the friction angle between rock and the pick,depth of cut and rock strength using principle component regression method.The normal force models were developed using the ratio of normal to cutting force.The specific energy models were developed using multiple non-linear regression method and principle component regression method considering the depth of cut and rock strength.The performance of prediction models were discussed and compared using statistical methods.The proposed models can provide basic parameters for calculating the loads acting on cutting heads and for performace evaluation of roadheaders.Based on the results of rock cutting mechanism,the design method of cutting head was discussed in detail.A cutting head was designed for EBZ200 roadheader,and the loads were simulated acting on the cutting head used for performance evaluation of the cutting head.The feasibility and advantages using the specific energy as the rock cuttability index were briefly discussed.The production rate models of roahdeaders were developed using specific energy,and its performance was also discussed based on statistical methods.These can provide basises for machine selection and performance evaluation of roadheaders.