Key technology and application of pre-stressed anchor to improve pre-tightening force

As one of the key parameters of bolt support, pre-tightening force plays a decisive role in active support. Domestic and foreign research shows that increasing the pre-tightening force of bolt can reduce the occurrence of roof fall accidents, so as to effectively improve the pre-tightening force of bolt and reduce the occurrence of broken anchor and lost anchor. The rolling anti-friction washer and tension-compression separation nut were developed. The torque-preload conversion relationship of the rolling anti-friction washer and tension-compression separation nut was studied by laboratory experiment, theoretical analysis and numerical calculation. The mechanical response characteristics of the common nut and tension-compression separation nut during pre-tightening process were studied. The research shows that about 60% of the torque is consumed by the friction between the bolt nut and the tray during the pre-tightening process of the ordinary bolt. The torque consumed by the friction can be reduced to 25% by using the rolling anti-friction gasket, and the torque-pretightening force conversion rate is increased by about 2 times. The stress of the internal thread pair of the ordinary bolt nut decreases exponentially along the axial direction away from the extrusion surface. The stress value of the first three rings in the nut is larger, and the stress concentration occurs obviously in this range, which is the dangerous surface of the bolt body fracture. The stress of the thread pair is evenly distributed after using the tension-compression separation nut, which eliminates the stress concentration phenomenon and the thread deformation is coordinated. The high pre-tightening force uniform bearing bolt was invented by integrating rolling friction reducing gasket, tension-compression separation nut, etc., which can increase the pre-tightening force to 2.5 times, eliminate the phenomenon that the bolt is easy to break from the thread section, and achieve good application effect in Zhuji Mine of Huainan Mining Area.