The mine “Kalksteingrube Auersmacher” is the last underground limestone mine in Germany. The owner of the mine is ROGESA which belongs to the Saarstahl group. In 1935 the mine started to excavate the limestone from underground by using the pillar mining method. The mine has 33 employees; there are 19 miners, seven craftsmen, three office clerks, one mine factory manager and three foremen. The limestone deposit has a dimension of 2.6 x 4.2 km. This limestone (CaCo3) was created in the Triasic Period about 235 million years ago. The deposit layer has a thickness of 4.8 – 7.5 m. The miners excavate the limestone by blasting using the room and pillar method. The pillars have the dimensions of 10 x 10 m and the excavated area between the pillars, i.e. the room is 6.5 – 6.7 metres wide. In the first section of the processing plat the limestone is fed through the primary crusher and then the secondary crusher where the end grain size is K50. After the material is screened out the oversize grains are directed to a hammer mill. Subsequently, the material is sieved again and the final product is directed to the exterior silos with the help of a conveyor belt. Single pieces are crushed afterwards by a smooth roll crusher. The plant has a quite high share of equipment failure due to wear. The cost of replacing main components due to wear is about 0.20 € per ton. The task of this project was to find out why certain tools (crushing segments, hammer heads) wear out and what improvement suggestions could increase the life span of these machines. What is wear out and why does it happen in these machines? The investigation showed that the design of the secondary crusher segments is not ideal. This has to be changed so that the loss of individual teeth will be avoided. Furthermore, the tooth tips (picks) made of hard metal must be more rounded and need more cobalt in order to make the unit more stable so that it resists the forces during the breaking process. The primary crusher does not show as many wear out difficulties, nevertheless, a solution was worked out which would increase the service life in many cases. Furthermore, examination was carried out in order to find out which protection materials against wear out are on the market. In this case some wear out materials or manufacturing procedures are listed which would increase the service life during the crushing process. The whole investigation was performed on a theoretical basis. The solution or better suggestions could not be demonstrated in such a short term project. For that reason the lifespan investigations are estimated ones. These results or a better solution could also be applied in other areas where wear out problems can be found. It could be indicated that TC in the right composition for critical components could improve their wear rate. The exact composition of TC and the bonding agent must be determined in a test. In the first step the share of TC should be 85% and the one of cobalt 15%. If this composition resists the crushing forces the share of TC can be increased. Other procedures against wear out, for example, the sinter cladding are currently very expensive and uneconomical but can certainly be used. In case of the hammer heads the lifespan would be improved as well, if TC picks were soldered in. A further improvement could be a share of the material XCC. Generally, good proposals for a prolongation of the service life were shown. These suggestions should be put into practice.
|Translated title of the contribution||Investigation of a crushing process in a limestone underground mine Kalksteingrube Auersmacher|
|Publication status||Published - 2015|