| Nowadays,the multi-layer structure application field is wide and the cleaning demand is more and more: in the shipping hub project,the lock opening and closing machine rust removal;in the ship and other underwater device surface rust and pollutant removal;in industry,pipeline,paint and other cladding cleaning;in urban traffic,road stains,road markings cleaning or removal.In this paper,considering the actual situation of the experimental equipment and the limitation of the size of the jet pressure,the multi-layer structure with low material strength properties that are easy to destroy is chosen for the study.The application scenario of road stains and markings is selected,and the material is assumed to be three layers: road layer,marking layer and stain layer,thus constituting a multi-layer structure.The current removal methods for this application scenario include grinding elimination method,milling removal method,shot blasting removal method,sand blasting removal method,natural gas combustion method,soda jet removal method,and water jet removal method,among which the water jet marking cleaning method not only meets the requirements for environmental protection,but also improves the removal efficiency and effect,which is a green and efficient removal method.However,most studies focus on the action of water jets on a single layer of material,the lack of multi-layer structure under the surface material removal efficiency and the relationship between the destruction of the substrate material analysis and discussion,and therefore in the actual operation of the jet parameters need to be selected by the operator’s experience,resulting in poor cleaning effect and low efficiency.Therefore,it is necessary to study the water jet action on multilayer structure material.This paper investigates the optimal parameter interval for cleaning and erosion between multilayer structures by setting two working conditions.The first condition is to remove the surface layer but ensure that the middle layer is not damaged as much as possible;the second condition is to remove the middle layer but ensure that the bottom layer is not damaged as much as possible.The details of the study include:Firstly,this paper analyzes the basic structure of abrasive water jets and the mechanism of damage to materials,and theoretically describes the main forms of abrasive water jets acting on materials.Secondly,the effect of abrasive water jets at a pressure of 15 MPa was simulated by FLUENT software for mixing concentrations of 5,8,and 11%,and finally the best effect was obtained at an abrasive concentration of 5%,which was selected for the calculation in the next chapter.Thirdly,the process of water jet erosion of the material was simulated by LS-DYNA software,and the change process of the surface morphology of the material and the depth of the crater under the action of abrasive water jet diffusion was obtained;the change of the stress on the surface of the material with the erosion time was analyzed,and it was concluded that the maximum stress was not concentrated in the crater initially,but on the lower side of the crater,and then gradually moved to the inside of the crater,and finally the maximum stress in the crater became 0 with the deletion of the damage unit of the material,and the stress concentration area spread gradually with the expansion of the crater during the whole process.Fourth,the relationship between the erosion cleaning efficiency and the main parameters of the jet was calculated by LS-DYNA,and the relationship between the pressure and the traverse velocity was analyzed qualitatively,and it was concluded that the cleaning rate is proportional to 0.3 times of the cleaning pressure;the cleaning rate is proportional to-0.7 times of the traverse velocity;the existence of a critical target distance in the jet process makes the cleaning rate maximum.Fifth,considering that most of the studies on material removal by water jets involve single-layer materials,the removal rate can be directly derived from the surface damage area or damage depth,etc.,and a single amount determines the removal efficiency,while for multi-layer structures,there is a constraint relationship between whether the lower layer of material is damaged and the removal rate of the upper layer of material,and the removal rate of the upper layer of material can be improved by changing the parameters.At the same time to consider whether such a combination of parameters will produce damage to the substrate material,so for the removal efficiency of multi-layer material involves the combination of the removal rate of each layer,in order to visualize this relationship,by constructing an objective function to analyze the optimal jet erosion and cleaning parameters interval.The cleaning efficiency of the stained layer is best when the traverse speed is 30-40m/min and the pressure value is10-20 MPa,and the cleaning efficiency of the stained layer is lowest when the traverse speed is 20-30mm/min and the pressure value is 50-70 MPa,and the optimal combination of jet parameters can produce the maximum removal rate of the stained layer and as far as possible without damaging the marking layer.Remove the intermediate layer of material but ensure that the bottom layer of material is not damaged as far as possible when the best cleaning efficiency parameters are: traverse speed at 30-40m/min and pressure of 70-80 MPa range;traverse speed at 40-50m/min and pressure of 80-90 MPa range;traverse speed at 50-55m/min and pressure of95-100 MPa range In the range of 100-110 MPa for 60-70m/min traverse speed.In the traverse speed of 20-25m/min,the pressure is higher than 110 MPa,the combination of parameters at this time is more damaging to the pavement,so the cleaning efficiency is at a lower level.In addition,the effect on the variation of the optimal parameter interval was explored by changing the properties of the material parameters. |
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