Title of the article: Main bearing greases for TBM EPB by LAMANNA Luigi Franco (*) Premise Allow me to make an in-depth analysis, my previous article on the same topic, on the importance of sealing and lubricating the base bearings of the rotating cutting head of an EPB-TBM, which is the external part on which the tools (cutters) are placed [1], also equipped with special bearings, with the function of breaking up the rock [2] during the excavation of a tunnel.
Photo 01 - Implemented disc cutters The rotating cutting head of a TBM (Tunnel Boring Machines), is equipped with a rotary motion, controlled by electric motors, located in the rear area of the TBM, whose base and filling bearing lubrication system is made with a system of sealant, which is pumped, through a geometric configuration called a “labyrinth”, capable of guaranteeing high levels of reliability and availability without aggravating the extremely difficult working conditions associated with these types of excavation work by means of a mechanized cutter. This sealing system ensures that no other foreign material, such as water present in the ground or particular products of contaminating mineral aggregates, can penetrate inside the space, between the rotating and fixed part, and damage the bearings which, in case of failure, pointing out that they cannot be easily replaced, these can potentially cause long months of downtime of a TBM, as well as having accelerated wear of the bearings themselves, with large cost overruns that can easily reach several million dollars.
Photo 02 - TBM mechanized cutters manufactured by CREG, China (China Railway Engineering Equipment Group Co., Ltd) Tunneling specializes in research, design and manufacture of a full range of TBMs excavation Therefore, to protect these bearings from the hostile environment in which the TBM is located, during the tunneling phase, there is another fundamental component that deserves attention, which are the seals used for protection and sealing. Therefore, as already mentioned above, the seal of the base bearings is essential because they must achieve multiple objectives: to retain the sealing lubricant inside the bearing assembly, to prevent the entry of water, mud and debris and to absorb any e significant misalignment that can occur, due to the strong loads impressed, during the operation of the cutter.