| Coal plays an important role in china's energy supply,coal are mainly transported by the mining transportation equipment.In a series of mine transportation equipment,belt conveyor is the most commonly used material conveying equipment.It has the advantages of large transport capacity and high reliability,tnerefore it has been widely used?With the development of economy,the progress of science and technology,the belt conveyor is moving towards the direction of high power,long distance and high capacity,the power of belt conveyor is closely related to the running resistance of the belt conveyor.On the other hand,the power value of the belt conveyor is directly related to the distance of the conveyor and the transportation of the material.In summary,the resistance of belt conveyor is in-depth study has a certain practical significance.The running resistance of belt conveyor is mainly composed of the following parts: the main resistance,additional resistance,special resistance and inclination resistance(also known as lifting resistance).The lifting resistance is directly related to the transport height of the material,which is usually a component of the gravity of the material,but the special resistance is not all the belt conveyors which are in running process will be produced,it is related to the specific structure of the conveyor.The additional resistance is mainly the frictional resistance between the discharge zone material blanking material and resistance and the guide groove side.The main resistance is the rotation resistance of the idler and the indentation rolling resistance of the conveyor belt.The rotation resistance of the idler is the running resistance which is produced by the load bearing part of the belt conveyor.Indentation rolling resistance is due to the contact between the idler and the conveyor belt and the relative movement between the two.According to the existing research literature,the rotation resistance of idler is about 9% in the running resistance of the conveyor,and the indentation rolling resistance of the conveyor is about 61% in the resistance of the conveyor.It shows that the indentation rolling resistance is the largest resistance of belt conveyor which is in running process,so the corresponding research work of indentation rolling resistance is very necessary.The number of research literature on the causes of the formation of the pressure resistance is high that has been published,The cause of indentation rolling resistance is mainly due to lower covering layer of conveyor belt has the characteristics of viscoelastic and the idler is a rigid body that contact with lower covering layer,When the belt conveyor is in the running state,due to the characteristics of lower covering layer and idler,the stress distribution in the contact area is not uniform,resulting in a force which is opposite to the running direction of the belt conveyor that this resistance is called the indentation rolling resistance.According to the research of the indentation rolling resistance,there are many researches in foreign countries,but the domestic research is relatively scarce,the related research abroad is not only theoretical research but also experimental research.On the theoretical research,the foreign countries mainly focus on two aspects,namely,the derivation of theoretical calculation formula and the distribution of stress distribution in contact area.The former is mainly from the Hertz contact theory to the Jonkers formula,and the latter is mainly based on the finite element method.The analysis of the main research focuses on the theoretical research,the selection of the viscoelastic model and the establishment of the mechanical model of the contact area.Therefore,the research results at home and abroad provide a useful reference for the research of this thesis.In this paper,based on the existing research results of indentation rolling resistance,it focuses on the working condition factors on the indentation rolling resistance,such as belt speed,load,idler radius,thickness of covering layer.On the basis of reference to the theoretical research results of the existing indentation rolling resistance,the theoretical mathematical method of the compressive resistance is completed on the three Maxwell model and one dimensional Winkler foundation.Using the iteration method,the relationship between the working condition factors and the indentation rolling resistance is analyzed theoretically.Subsequently,the computing method of indentation rolling resistance is also completed based on the three maxwell model and one dimensional Winkler foundation.Using this computing method with the help of iteration,the simulation analysis between the working condition factors and the indentation rolling resistance is analysed quantitatively,some valuable conclusions are obtained.Based on calculation method of this paper and after a series of derivation and simplification,the analytical formula of the indentation rolling resistance and simplified formula are obtained respectively.In especial,the simplified formula can directly reflect the influence of the working condition factors on the indentation rolling resistance.After completing the theoretical part of the paper,author puts forward two kinds of test scheme and selects one set of schemes as the test method of resistance,according to the test scheme,corresponding test device is designed.Finally,by means of the test device,author selects a number of test points to study the relationship between the speed,load and indentation rolling resistance.In the end,the error of the test data is analyzed qualitatively.The main research work of this paper is as follows:(1)In case of taking into account the practicality and accuracy,author considers three-parameter Maxwell viscoelastic model which can characterizate the viscoelastic property and derive a mathematical expression that can characterizate stress distribution of the contact area with the help of one-dimensional Winkler foundation.Finally,the relationship between the working condition factors and the indentation rolling resistance is analyzed theoretically.Due to the viscoelastic property of the conveyor belt and distribution of stress is not asymmetry in the contact zone between the conveyer belt and the idler.As a result,when the conveyor belt is running,indentation rolling resistance will be produced.However,now the viscoelastic model is almost two parameter viscoelastic model that has a low accuracy,when it is used to characterizate the viscoelastic property.Author takes into account the practicality and accuracy,as a result,paper uses three parameters Maxwell model substituting for two parameters viscoelastic model.On the other hand,indentation rolling resistance is closely related to the running energy consumption,Foreign's calculation formulas are also derived from the relationship between the energy consumption and the resistance,therefore,stress distribution in the contact area is neglected.This paper starts from the stress distribution on the contact area that is conducive to a deeper analysis of the relationship between resistance and the common working conditions.For this reason,author deduces the formula of the stress distribution on the contact area by means of one-dimensional Winkler foundation and three-element Maxwell model,firstly author makes a quantitative calculation of the stress distribution when the contact area is on static state at first,this result acts as initial value of the stress distribution when the contact area is on motion state,on the other hand,the indentation rolling resistance is caused by the asymmetric stress distribution in the contact area,therefore,this work has laid a necessary foundation for the derivation of the theoretical formula of the indentation rolling resistance.(2)Based on the three element Maxwell model and one dimensional Winkler foundation,the theoretical calculation formula of indentation rolling resistance is deduced and the simulation analysis between the working condition factors and the indentation rolling resistance is analysed quantitatively.As the first consideration of viscoelasticity on material,the Jonkers formula provides a useful reference for the derivation of the theoretical calculation formula of this paper.But the deficiency of Jonkers formula is that it is not able to directly reflect the influence of some important factors on the pressure resistance.In order to characterize the viscoelastic properties of the material,the corresponding viscoelastic model must be chosen,for the two parameter viscoelastic model is not able to characterize materials accurately,so this paper selects three parameter viscoelastic model is used to compensate for lack of two parameter model.In order to describe the stress distribution of contact area,author selects the one-dimensional Winkler foundation.For that the model is widely used for stress analysis of the foundation and this model can simplify the stress distribution of normal stress in the vertical direction.Finally,based on the above theory,author derives the theoretical calculation formula of indentation rolling resistance.The simulation analysis between the working condition factors and the indentation rolling resistance is useful to solve some problems in engineering,in this paper,the main factors are the belt speed;the load;the roller radius;the thickness of the covering layer,belt speed and load are the operating parameters of the belt conveyor,idler radius and the thickness of covering layer are the important parameters that influence the selection of parts in the design process of belt conveyor.Analysis of the relationship between the speed and resistance for solving the frequency conversion speed regulation on the impact of energy saving is a certain practical reference value,on the other hand,for the load is corresponding to the actual amount of coal transportation,therefore,the analysis of the relationship between the load and the resistance has guiding value for the real-time adjustment of traffic volume.A reasonable and correct analysis of the thickness and roller radius is not only beneficial to the energy saving and consumption reduction in the operation of the belt conveyor,but also is beneficial to the optimization of the design process of the belt conveyor.Finally,it is worth noting that the author completed the above work with the iterative method.(3)Based on theoretical calculation method of indentation rolling resistance,author deduces the analytical formula and simplified formula.As the calculation method which is obtained based on three-element Maxwell model and one dimensional Winkler foundation must be carried out the simulation of indentation rolling resistance by the iterative method,although it has a high precision but is very complicated,therefore,it is necessary to derive an analytical formula and simplified formula of the indentation rolling resistance based on this calculation method.On the other hand,although the calculation formula of the indentation rolling resistance which is derived based on Hertz contact theory not only is an analytic formula but also can directly reflects the common factors on the impact of indenation rolling resistance,Hertz contact theory is not suitable for the contact problem of viscoelastic materials.Jonkers' s formula is obtained based on the viscoelastic theory,nevertheless,the formula can not directly reflect the relationship between the speed and indentation rolling resistance.In this paper,the calculation method of the indentation rolling resistance can reflect the viscoelastic properties of the material,therefore,on the basis of this calculation method,the simplified formula of resistance can not only reflect the viscoelastic property of the material,but also directly reflect the relationship between the common factors and the resistance,the simplified formula can be used to make up the deficiency of the existing theoretical formula.Finally,author makes a qualitative and quantitative analysis of the error between the simplified formula of the indentation rolling resistance and the calculation method.(4)Based on the principle of the indirect test,a test device for indentation rolling resistance is designed which is prepared for the experiment analysis.After a series of theoretical derivation,a simplified formula of indentation rolling resistance is obtained.The simplified formula can not only reflect the viscoelastic properties of the material,but also can directly reflect the influence of the common working conditions on indentation rolling resistance,Such as belt speed,load,roller radius,thickness of the cover layer,viscoelastic parameters,and so on.In order to verify the correctness and rationality of theoretical study of resistance,it is necessary to carry out an experimental research on resistance.However,the premise of the experimental study is to design the corresponding test equipment,in order to achieve the above purpose,author designs two kinds of test program,namely,direct test method and indirect test method.The former uses the test device to test the experimental value of resistance on corresponding condition,the latter uses two sets of testing equipment to directly test main resistance and idler rotation resistance respectively under the same condition,subsequently,author obtains the indentation rolling resistance under the corresponding condition.For that laboratory has a certain research foundation for idler rotation resistance,as a result,after the comprehensive comparison,paper finally selects the indirect test method.Based on the principle of the indirect test method,author designs the corresponding test equipment,which can carry on an accurate test on the main resistance under certain condition,with the aid of the existing idler rotary resistance testing device,the test of indentation rolling resistance is completed.(5)By the way of test device,author makes an experiment on the influence of load and speed on indentation rolling resistance.With the help of test device,Focusing on the relationship between load,speed and indentation rolling resistnce,author carries out the corresponding experimental research.The reason for focusing on the belt speed and load is that they are the most important parameter in the running process of the belt conveyor,On the other hand,due to the inherent characteristics of the test device,it can not accurately acrry out on the the radius of the idler,the thickness of the cover.In order to carry out the analysis of the indentation resistance from the view of experimental point,author sets up a number of representative test points and analyses the experimental results obtained from the test points in each group.Finally,the experimental results are compared with the theoretical analysis and the similarities and differences between them are analysed to validate that simplified formula of indentation rolling resistance has a certain accuracy.Finally,through the above research work,the topic condenses the following innovation points.(1)Based on three-parameter Maxwell model and one Winkler foundation,a formula for calculating the stress distribution in contact region is deduced,anthor makes a quantitative analysis of the relationship between the common working conditions and the stress distribution.(2)Based on the stress distribution,author authors has deduced the calculation method of indentation rolling resistance.With the aid of iterative method,the relationship between various factors and resistance is theoretically analyzed.(3)Through a series of simplifications,a simplified formula for indentation rolling resistance is obtained by using the calculation method of the indentation rolling resistance,this formula can reflect not only the relation between the common working conditions and resistance,but also the viscoelasticity of the material.(4)a corresponding indentation rolling resistance test device is designed according to the indirect test method,an experimental analysis of the relationship between the belt speed,load and the resistance is carried out,finally,the experimental analysis and theoretical analysis are compared. |
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