Correct selection of shield tunneling tools and forms of wear and failure

source：http://www.xrocktools.com/ Release Time：2015-01-03 15:35:12

The cutting tool of the shield machine is a key component for rock breaking and excavation, which is prone to damage during excavation and needs to be replaced frequently. In fact, the length of service life is not only related to the quality of tool manufacturing, but also to the correct selection and maintenance of tools. Therefore, the selection and maintenance of cutting tools directly affect the safety, reliability, and economy of shield tunneling construction. Proper selection and maintenance can often achieve twice the result with half the effort.

The classification of shield tunneling machine cutting tools is generally divided into two categories: scraping tools and rolling tools. Scraping tools (scrapers, cutters) refer to rock breaking tools that only rotate with the cutterhead without rotation There are many types of scraping tools, and currently the commonly used scraping tools on shield tunneling machines include edge scrapers, scrapers, toothed cutters, advance cutters, shell cutters, fish tail cutters, and other rolling tools (rolling cutters). Rolling tools refer to rock breaking tools that not only rotate with the cutterhead, but also rotate on their own. According to the shape of the blade, rolling cutters can be divided into toothed cutters (steel teeth and ball teeth), disc-shaped cutters (steel ring cutters and ball tooth ring cutters), and according to the installation position, rolling cutters can be divided into positive cutters, center cutters, edge cutters, and expansion cutters. The rolling cutters of shield tunneling machines are mainly disc-shaped cutters, which have single blade, double-edged, and multi blade types. According to the outer diameter of the blade, it is divided into specifications such as 13, 15, 17, 19, etc. Currently, the main one is the 17 series.

The main ways in which shield tunneling cutting tools fail are as follows: 1) Failure of scraper (toothed cutter): 1) Normal wear 2) Scraper blade cracking: In hard rock excavation, the wear of the cutter is too great, and the scraper directly cuts through hard rock that has not been crushed by the cutter; When excavating in hard rock, if the speed is too fast, encountering hard rock suddenly can cause the blade to crack due to impact; In hard rock excavation, the blade may crack due to reasons such as too deep cutting. 3) Scraper blade body fracture: The strength and toughness of the blade body itself are insufficient; The incision is too deep. 4) Scraper teeth falling off: The welding process of the alloy blade teeth is not up to standard; The scraper suddenly encountered hard rock. The main failure modes of rolling cutters are wear of the cutting ring, as well as early failure of bearings and seals, and breakage of the cutting ring. The normal wear of the cutter ring is non-uniform wear (eccentric wear and chord wear), and the wear degree of various parts around the cutter ring of the rolling cutter is inconsistent, with unilateral eccentric wear and multilateral eccentric wear. Unilateral eccentric wear is generally caused by the rolling cutter not rotating, while multilateral eccentric wear is caused by the rolling cutter not rotating when rotating. The reason why the rolling cutter cannot rotate continuously is mainly related to the formation, tool configuration, and shield operation, in addition to tool manufacturing. During the excavation process, the cutting edge of the cutter ring may break, crack, or even detach from the cutting body. This is related to the manufacturing technology of the cutting ring, geological conditions, and applications, and needs to be distinguished and analyzed. Bearing or seal damage: Bearings are an important component on cutting tools, which have a particularly significant impact on the reliability of tool excavation operation and tool consumption. Under normal use, the lifespan of most tool bearings can reach around 900 hours. However, during the construction process, due to various reasons, bearings may suffer early damage, mainly in the form of peeling: the surface of the raceway or rolling element peels off, presenting a concave convex shape. Damage to the retaining frame, etc. Mainly caused by improper assembly of cutting tools or inadequate performance and accuracy of components. The failure of the floating seal between the blade body and the blade cover causes oil leakage from the tool, and sediment enters the blade body, affecting the bearings. There are many reasons for the failure of tool sealing, usually related to the quality of the tool components themselves and assembly quality, the working conditions of the tool, and the rock conditions being excavated.

Cutting tools are vulnerable parts, so regular inspections, maintenance, and upkeep must be carried out to keep the cutterhead and cutting tools in good condition. When performing maintenance on the cutterhead, it is necessary to be careful and thorough, and damaged tools should be replaced in a timely manner. Due to the mutual protection of the arrangement of cutting tools, if a damaged tool is not detected and replaced in a timely manner, especially in hard rock formations or highly abrasive formations, continuing to excavate may result in widespread tool damage or even damage to the cutterhead, making it impossible to excavate. For uniform soft soil formations such as Shanghai, cutting tools can generally be used without significant wear from beginning to end. For uniform hard rock formations such as TBM tools, excavation inspection is also relatively convenient and easy to establish inspection systems for tools and cutterheads. For the composite formations in Guangzhou, Chengdu, and Shenzhen, they often do not have the conditions for opening warehouses, but it is precisely these formations that have poor tool adaptability, shorter tool life, or more frequent occurrence of abnormal tool damage. In this case, a strict and complete tool inspection and replacement system should be established. If measures such as tool wear detection devices, pressurized entry into the warehouse, and pre reinforcement are taken to ensure the implementation of the tool inspection and replacement system. It is not uncommon for the cutting tool to stop due to the lack of attention to tool inspection and failure to replace the tools in a timely manner, resulting in wear and tear of the cutting disc.

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