| The diamond frame saw has the advantages of large size,high efficiency,small saw gap,and high yield.Therefore,the frame saw is widely used in the sawing of marble and other soft stones.Large-format granite and other hard stone slabs are broadly used in industries such as building decoration.However,due to the high hardness and wear resistance of hard stone,sawing large-format slabs with the frame saw has many problems,such as large surface deviation,low efficiency,and serious segment wear.Aiming at this problem,a novel swing sawing process is proposed.Due to a lack of mechanical and mathematical tools,the sawing trajectory,segment wear,and process parameters fail to optimize.It is difficult to achieve high efficiency,high quality,and low loss for sawing granite.Therefore,revealing the removal mechanism of hard stone,establishing the theoretical model of swing sawing force,explaining the wear mechanism of segments,and optimizing the process parameters have become the key issues that need to be solved urgently to promote the efficient,high-quality,and low-loss technology of sawing large-format slabs.In this paper,such two granites as Tan Brown granite and Brazilian Golden granite are selected as the research objects to investigate the scratch morphology,debris characteristics,and segment wear mechanism.Research methods include fracture mechanics,rock mechanics,grinding theory,experimental tests,and microscopic observation are performed.This paper discusses the micromechanics and material properties of stone and reveals the material removal mechanism under the interaction of single scratch and multi-scratch.In addition,the rule of the influence of strain rate on the size of debris is clarified,and a prediction model is developed for the size of debris under the action of single scratch.Furthermore,a novel sawing force model is established comprehensively considering the elastic recovery of stone and segment morphology.Finally,the micro-fracture characteristics and segment wear mechanism of diamond grits have been revealed for sawing hard stone.The model of segment wear rate was developed and the process parameters were optimized.Through the study of this paper,the rationale is providing for the popularization of high-efficiency and high-quality technology of sawing hard stone.Firstly,the formation mechanism of cracks of hard stone and the size characteristics of debris are investigated.The mineral composition and content,hardness,fracture toughness,and elastic modulus of the stone are characterized by a polarizing microscope and indentation test.In addition,the elastic stress fields of the single scratch hard stone are analyzed by means of the analytical model.Afterward,the formation mechanism and propagation characteristics of the crack were discussed.Additionally,the mechanism of the influence of strain rate on the size of debris is revealed,and a prediction model for the size of debris under the action of single scratching is established.The results showed that the median crack nucleates in front of the diamond grit,the Hertz crack nucleates behind the diamond grit,and the radial crack nucleates behind the Hertz crack.Especially,the lateral crack,Hertz crack,and radial crack are interlaced and connected to shear the stone into detritus and remove it in the brittle pattern.In addition,the cracks of mode I produced under the action of tensile stress,the cleavage fracture on the cleavage surface of the quartz,mica,and feldspar crystals,and the shell-like fracture of complete grains.The size of the detritus decreases with the increase in strain rate,and the established model of detritus size is verified.Secondly,the crack propagation mechanism of hard stone under multi-scratch interaction is studied.The interference pattern between diamond grits during sawing is discussed,and the analytical model of the elastic stress fields for multi-scratch is developed.Furthermore,the distribution of the stress field for the multi-scratch is expounded,and the offset effect of the principal stress and the shielding effect of the median crack is revealed.Thereupon,the interaction of multi-scratch and the coupling effect of cracks are verified by several scratch experiments.The results showed that the change rate of Cl/Ch of Brazilian Golden granite is greater than that of Tan Brown granite with the increase of stress value.When the scratch spacing is small,the adjacent middle cracks restrain each other.Obviously,the scratch speed has little effect on the normal force.What is more,the coupling effect between lateral cracks has effectively reduced the scratch force under multiple scratch scenarios.For sawing hard stone,the length of the lateral crack corresponding to the driven stress σzr of the lateral crack provides important guidance for material removal.Next,the model of sawing force for the swing pattern is established considering the elastic recovery of stone and the segment morphology.Thus,the sawing trajectory and segment morphology are discussed.Then the sawing force model considering the elastic recovery and segment morphology of stone is established and verified by experiments.Additionally,the influence of friction coefficient,elastic recovery,and hardness of stone on the sawing force is clarified.Based on the EFAST method,the sensitivity of parameters affecting sawing force is analyzed.The results showed that the sawing force model has good prediction accuracy,and the maximum undeformed chip thickness is the main reason affecting the sawing force.Moreover,the global sensitivity indexes of normal force and tangential force are 0.7327 and 0.8565,respectively.Naturally,feed speed,flywheel speed,elastic recovery rate,and friction coefficient are successively influencing factors.It should be pointed out that the coupling interaction between the parameters has a great influence on the sawing force.Finally,the micro fracture characteristics of diamond grits and the wear mechanism of the segment for the swing sawing are revealed.The surface morphology of the segment matrix and diamond grits is characterized by SEM.Likewise,the contact form between diamond grits and stone is discussed.Then,the wear mechanism of different crystal planes of diamond grits and the matrix of segments is revealed.Additionally,the theoretical model for predicting the segment wear rate of swing sawing is established and the process parameters are optimized.The results showed that fracture,fracture step,cleavage,and river pattern are the main morphology of diamond grits.Obviously,the proportion of fracture along the {111}crystal plane that is flush with the matrix is approximately 90%.Moreover,the wear characteristics of the {100} crystal plane of diamond grits are different from the {111} crystal plane.There are more micro-cracks in the {111} crystal plane than in the {100} crystal plane.The primary wear style of the matrix is abrasive wear.The wear rate of the segment is the lowest under vf=63 mm/h and nf=80 r/min,and the productivity of the slabs is 13.608 m2/h.Summary,compared the swing sawing with the traditional horizontal sawing method,the flatness of the slabs is increased by 36%on average. |
