For the Alphington Sewer Projekt in Melbourne, Australia, the responsible authority Melbourne Water ordered the replacement of masonry sewers more than 100 years old between Coate Park and the Latobe Golf Club in Alphington. A smaller section passing under the Yarra River and joining the main collector was also replaced.
The project was implemented over a period of eleven months. For two sections 580 and 270 m long, a microtunnelling machine “Unclemole Super TCS1500” from the Japanese manufacturer Iseki was employed. The cutterhead used was the result of a long collaboration between Iseki Microtunnelling and Kolk Maschinenbau GmbH, a German manufacturer of cutterheads and drilling tools.
After the bankruptcy of the company Maschinenbau Kolk GmbH, Mika Bohrtechnik took over the drilling technology division of the mining and tunnelling specialist on 1 March 2019. Under the technical management of Olaf Röhrig, the entire know-how could be preserved with the transfer of experienced employees and all the technical documentation.
Cutter Discs and Bearings
The cutterhead of the Alphington Sewer machine with a diameter of 1870 mm was fitted with 280 mm diameter cutter discs with HD bearing (full-roller bearings). The cutter discs can be variably fitted with steel or TCI (Tungsten Carbide Insert) rings. Basically, such rollers are suitable and can be delivered for any conceivable machine.
The construction of these cutter discs is comparable with standard cutter discs with taper roller bearings: cutter rings or cutter rims in various versions are mounted on the actual bearing – either as ring tooth of hardened steel, or with rings of highly annealed steel and hard metal pins. The cutter ring geometry is adapted to the conditions of the relevant project. They are available, depending on size, in single-, double- or triple-ring versions.
One advantage of the full roller bearing is increased strength and thus longer service life – presuming normal maintenance. Since they are reusable, the high costs of a complete bearing replacement can often be saved, as only the cutter rings are replaced. The type of cutter ring can also be adapted to suit changing geological conditions. This concept saves material and energy resources because only the worn components are changed, while intact parts can be reused after detailed testing and possible repair.
In addition to the HD bearings, versions with standard taper roller bearings are also offered. Also here, the concept of reusable bearing assemblies is followed. Through the modular design of the cutter roller bearings and cutting edge (ring tooth or cutter rims), the tools fitted to a cutterhead can be adapted to suit the prevailing geology.
In-House Design and Production
Mika GmbH not only designs and constructs the cutter discs in their own works but also cutterheads, tools and accessories for all types of machine. Essentially, cutterheads are available designed and made for soft, mixed or hard geologies. The emphasis is on diameters from 400–5000 mm. Since the takeover of the business of the former Kolk GmbH, the company Mika has used this technology tried and tested for decades in several national and international projects.