考虑塑性屈服的井下弹道式煤矸分离理论研究

Study on Underground Ballistic Separation for Coal and Gangue Considering Plastic Yielding

为完善井下弹道式煤矸分离方法的理论体系,对煤和矸石碰撞反弹过程中的弹塑性行为进行研究.以Hertz接触理论为基础,结合Drucker-Prager准则确定了煤和矸石碰撞过程中初始屈服点相对位置的表达式,指出该位置与泊松比近似呈线性关系,并得到初始屈服时相对变形量、接触力和相对速度的数学模型.基于线性强化弹塑性模型,得到接触力与变形量的函数关系,并依据能量守恒定律,确定碰撞分离时刻的相对速度,进而得到反弹距离的理论模型.在单颗粒冲撞实验台上对煤和矸石进行碰撞反弹试验,试验表明:反弹距离随初始速度的增加基本呈增大趋势,当初始速度较小、煤和矸石破碎较少时,采用材料参数平均值计算得到的反弹距离理论解与试验平均值的一致性较好,当煤和矸石有破碎产生时,由于能量的损失,试验平均值小于理论解.

Ballistic separation used in underground coal dressing is an option for green coal mining realization which can reduce the environmental pollution caused by gangue accumulation on the ground.This technique is proposed on the basis of elastic-plastic behavior differences between the coal and the gangue under impact load.The impact and rebound responses of coal and gangue are discussed in this work by taking into account the plastic yielding.To study the ballistic separation in theory,this work divides the impact process into three stages,which are the elastic compression stage,the elastic-plastic compression stage,and the elastic recovery stage.In the elastic compression stage,the contact force,the deformation and the contact stress conform to the Hertz contact theory.And the Drucker-Prager criterion is adopted to determine the initial yield.The relative deformation,the contact force and the relative velocity are obtained at the initial yield moment based on the expression of relative position determined at the initial yield point.In the elastic-plastic stage,the relationship between contact force and deformation is built based on the linear hardening model.In the elastic recovery stage,the relative velocity at the moment of separation and the rebound distance are deduced based on the energy conservation law.The theoretical study shows that there exists an approximate linear relationship between the relative position at the initial yield point and the Poisson＇s ratio.To verify the theoretical model,the impact and rebound experiments for coal and gangue are carried out on the experimental platform of single-particle impact.The theoretical values of rebound distance calculated using the average material parameters are in well agreement with the average experimental data of rebound distance at low initial impact velocity.The experimental results show that there are few breakages in both coal and gangue at low initial impact velocity,and the rebound distance increases with the initial impact velocity.The average rebound distances of coal and gangue in the experiments are both less than the theoretical values because of the energy loss in crushing.