1、Background

As a high-end equipment for diaphragm wall construction, the hydromill spends more than 70% of its time in rock breaking operations. At present, there are three main types of cutting wheels in hydromill, namely standard wheels, pick drum wheels and Spherical hobs. The standard wheel is mainly aimed at strata within 30MPa, the pick drum wheel is mainly aimed at strata above 30MPa, and the Spherical hobs can cope with strata above 100MPa. At present, Spherical hobs are used in many jobsites such as South Korea, Hong Kong and Singapore. However, due to the limitations of the hydromill structure, Spherical hobs have not exerted their due effect. Mainly reflected in the limited weight of the cutting module, which cannot provide sufficient downforce for the wheels. The hob cannot effectively crack the rock and can only break the rock in powder form. Not only is the efficiency low, but the ball tooth alloy wears quickly.

2、Spherical hob advantages

  • Significantly reduces the construction cost of hydromill cutting in hard rock layers, shortening the project duration.
  • No need for precutting holes, simplifying construction equipment.
  • The hob-tooth hydromill wheel enables long-term continuous operation (up to 100 hours), reducing the number of hydromill lifts, effectively extending construction time, and simplifying labor requirements.
  • Stable hydromill module operation with minimal gearbox impact, reducing maintenance time and costs.
  • Low ground disturbance, making it suitable for construction near buildings.
  • Enhances the deflection ability of hydromill cutting in hard rock layers.
  • The vertical accuracy of the trench can be controlled within 1‰.
  • Saves over 20% of fuel (currently averaging 73L/h with a CAT C18 engine), making it more energy-efficient and environmentally friendly.

3、Cutting wheels

If the Spherical hob is to be effective, it must exert sufficient downforce. A single hob requires at least 5 tons of downforce. Taking the 1200mm thickness wheel as an example, a set of wheels has a total of 54 hobs. , an average of 1/3, that is, 18 hobs, are involved in rock breaking, and the total pressure required is at least 90 tons. A single gearbox has to withstand 45 tons of pressure, which requires the gearbox to have sufficient radial load-bearing capacity. In addition, the hob is a rolling rock-breaker, which does not require much torque. For safety reasons, the gearbox torque is designed to be 150KNm; The output end adopts a tapered hexagonal structure, which allows quick installation and removal of the cutting wheel.

There are two main types of fixed cutting tools on the Spherical hob, one is the side hydromill and the other is the main cutting hydromill. There are three side hydromill designed, and two main cutting hydromill on each trajectory line. There is also a flapper tooth, which is designed in the form of a roller structure. The structure is simple and practical, and it has better force resistance than Bauer’s. The structure of Bauer flapper tooth is heavy and the force is poor, which will cause the wear block and guide ring to wear out quickly.