Design of linkage type back reamer for large diameter drilling in coal mine

Aiming at the problems of multiple lifting, difficult control of drilling trajectory and low construction efficiency in large diameter drilling, an open and closed 300/153mm Linkage type Back Reamer was designed. By means of adjusting the flow rate of mud pump, the blade can be closed in the normal drilling process and opened in the target layer, so that the lifting operation and backexpanding operation can be carried out simultaneously.This paper introduces in detail the structure and principle of Linkage type Back Reaming Bit, analyzes the mechanical characteristics of the opening and closing mechanism of the Reamer, and obtains that the torque of the blade is related to the opening angle of the cutting blade, the length of the crank, the length of the connecting rod and the eccentricity. The eccentricity and the piston stroke were determined, and the optimal force transmission performance of the opening and closing mechanism of the drill bit was obtained by theoretical analysis Based on the free water jet model, the thrust calculation method of water flow on piston was proposed, and the thrust force of water flow on piston is obtained when the mud pump reaches the maximum flow rate, and the design calculation of the key component reset spring which affects the opening and reset of cutting blade wing is given. The Linkage type Back Reamer has been tested under the coal mine and the results showed that: the 300/153 mm rod type pull back reaming bit can achieve normal drilling, maintain the 153 mm drilling, and realize the 300 mm hole expansion when pulling back to expand the hole;the cutting blade is flexible in opening and closing, the drilling bit is stable and reliable, which verifies the feasibility of the structure design of the Linkage type Back Reamer and the construction technology suitable for large diameter drilling in common non-contact roadway.