Study On The Design And Property Of Hardfacing Layer For Shield Machine Cutters

There are plenty of grits and screes in stratum of Beijing area. Shield machine cutter suffers from high stress grain-abrasion and impact when it constructs subway by shield method. The import cutter's driving length is just about 250 meters. Cutter changing time increase caused bye cutter's short driving length induces more hidden troubles of tunnel collapse. In addition, cutters'import needs more cost and time which delays the schedule of subway construction badly.Based on the shield machine cutter's failure analyses, and launched on shield machine circumambient cutter's repairing, the anti-abrasion and anti-impact capability of shield machine cutter was realized. Design and capability study on hardfacing layer of cutter were done, and the main homemade work of shield machine cutter was done. The condition of repairing shield machine cutter is rigorous because of narrow hardfacing space, bad ventilation and unable to preheating and post heating to cutter body. Systemic research on developing hardfacing flux-cord wire (FCW) used on repairing shield machine cutter was done. Gas shield hardfacing FCW named DG7 and self-shield FCW named SDG7 which could be used on repairing and manufacturing shield machine cutter were developed through a series of components adjusting and processing property testing of FCW. The welding processing property and the hardfacing layer's capability of the two kinds of FCW talked in front are all right, and it can satisfy the request of cutter's capability and the conditions of the cutter's repairing and manufacturing. The microstructure of hardfacing layer is mainly low carbon martensite and partly discontinuous netlike austenite. The hardness of hardfacing layer is upwards HRC51. The hardfacing layer has a certain extent toughness and work hardening capability, and its hardness could achieve HRC55 to 60. The hardfacing layer puts up well abrasive wear resistance capability on MLS-225 wet sand/rubber wheel tester and MLD-10 type alterable load abrasive wear tester.Concerning shield machine cutter's hardfacing layer design, launched on circumambient cutter's repairing, and based on circumambient cutter's different parts'worn characteristics, the circumambient cutter's cutting edge, side face and working face were strengthened by hardfacing. Based on serrated knife's failure characteristics, its head, back and side face were strengthened by hardfacing. Furthermore, based on the status that the cutter disk's failure is earlier than the improved cutter's failure, cutter disk was strengthened by wear resistant composite plate, and then shield machine cutter's all-sided improving was achieved. In the eleventh segment of Beijing's subway line ten which is from Agriculture Exposition to Liang Ma Bridge and complete in February 2007, the improved cutter dug 780 meters one time which greatly exceeded the import cutter's service life. The cost of improved cutter is just three-quarter of import cutter, and it has good economic and social benefit.