One of the companies involved in the manufacturing of turbines not only for the Czech and Slovak markets but also for customers from Indonesia, Philippines, Armenia and Mexico is ČKD Blansko SMALL HYDRO, s.r.o.

Fot: Example of Kaplan turbine machining

In 2010 the company decided to extend the capacity and technological facilities of their own production in order to reduce the manufacturing cost, save the time and eliminate the need for external cooperation on certain more complex components. The main and essential idea was the implementation of the new technology of the progressive five-axis machining of complex components such as impeller wheels of Francis, Pelton and Kaplan turbines and their components.

The tender specifications included the requirement for machining of larger and heavier weldments - turbine spirals, forgings and castings of vane rings, chambers, stands, etc. As the technology of the plant is chosen according to the gradient and flow of the hydroelectric installation, the following machining pieces would come under consideration:

Kaplan turbines starting from impeller wheel diameter of 630 mm to 1,600 mm, Francis turbines with impeller wheel diameter from 640 mm to 1,080 mm and Pelton turbines with impeller wheel diameter 780 mm through 830 mm. There was also the requirement to extend the range of Francis´ and Pelton impeller wheel up to a theoretical diameter of 1,800 mm and the possibility of machining on clamping plate surface the turbine spirals, casings, frames and stands up to 3,000 mm in height and up to 6,000 mm in length.

Turbine casings, spirals and piping components are generally made of standard carbon steel with guaranteed weldability. Impeller wheels are by standard made of stainless steel or cast stainless steel. Recently the most frequently used material are semi-products forged from stainless steel.

The concept of the floor type machining centre FU 150 - V/8 made by TOS KUŘIM – OS, a.s. includes the rotary table type CES of dimensions 2,000 x 2,500 mm (table feed V = 1,250 mm) primarily for machining of rotary parts and the plate clamping field of dimensions 3,440 x 7,040 mm for clamping of larger components, have proven optimal for the specified needs of the customer. The machine is equipped with the Heidenhain iTNC 530 control system, vertical travel is 3,000 mm and its versatility in conjunction with high productivity is guaranteed by the use of automatic interchangeable milling heads VA1 (short roughing), VP2 (angular roughing) and VK (two axis universal) made by TOS KUŘIM - OS, a.s.

With respect to the machining operations of the above components, milling in combination with drilling is the prevailing operation. Very important is the 3D and 5D milling, with indexation or continuous control.

A set of tools from WALTER CZ, s.r.o. was used as the primary equipment, which was supplemented by tools from company A-tool. A specialty in this area are the extended mandrels for milling of deep shaped channels of the impeller wheel vanes, successfully were used mandrels up to 570 mm in length, milling cutters for high-speed milling, with diameter 42, 32 and 20 mm and ball cutter R8. There are also tools for intense stock removal during roughing and boring as well as for final surfacing of the shaped surface.
The duration of machining is in the order of days in case of simple weldments - frames and casings, in case of a more complex shapes, especially flanged vane rings and impeller wheels we are talking about weeks of intense machining in a three-shift operation.
In the future the turbine manufacturers from Blansko would like to become the elite in their field, especially by reducing the overall delivery time by one or two months (at present the average time of the manufacture is about 9-12 months depending on the complexity of the technical design of the turbine).
This effort should be significantly facilitated by the supplied FU-series machining center from TOS KUŘIM - OS, a.s. that - in addition to the expected machining quality - also addresses the issues of productivity and return on investments.

Machining of turbines for large hydroelectric plants

Another Czech company ŽĎAS, a.s. uses the gantry type machining centre made by TOS KUŘIM - OS, a.s. to machine monumental castings of Kaplan´s turbine vanes. Individual roughed castings weigh almost 20 tons, are made of stainless steel and are machined for the manufacturer of water turbines from Argentina.

Fot: Example of Francis turbine machining

The proposed gantry type machining centre FRF 300 - V/A6 with the output of 37 kW guarantees sufficient rigidity in combination with productivity and minimum re-clamping operations of the piece. The machine is equipped with the Siemens control system and the working area is 3,000 x 6,000 mm. The basic ranges of travel (X = 5,000 mm, Y = 3,800 mm and Z = 1,250 mm) were designed to increase the clearance under the gantry and the workstation was equipped with a special Pick-up tool magazine. The potential of the machine is significantly increased by the use of the automatic interchangeable milling heads VP2 (angular roughing) and VK (two axis universal) made by TOS KUŘIM - OS, a.s.

Based on the operating experience and with respect to the production start-up curve, the customer - in order to optimize the technological processes of machining - asked the standard head portfolio to be extended to include additional heads type VA1 (straight roughing) and VP1 (angular). The entire installation was completed in the course of 2009 as a turn-key project including the construction of the machine base.

The machined vanes are designed for a hydroelectric power plant that is being constructed on one of the many tributaries of the Orinoco River in Venezuela. The power plant will be equipped with ten turbines with rated output of 235 MW. At present this type of Kaplan´s turbine is the most powerful type of Kaplan turbine in the world. ŽĎAS, a.s. is preparing for this power plant the additional 120 units of completely machined castings and forgings to be used for inner equipment of the turbines.

In order to fulfill the deadlines set by the final customer, another machining center – type FRUF C , also by TOS KUŘIM- OS, a.s., was included in the process of machining of the turbines. This is the latest type of the milling machine with output of 71 kW, workplace 4,500 x 17,000 mm and clearance between table and cross-rail of 4,200 mm. The machine is equipped with 6 automatic interchangeable milling heads by TOS KUŘIM - OS, a.s. and all axes have hydrostatic guides, including adjustable cross-rail within 3,500 mm. Tools are exchanged by a fully automatic robot, the tools are stored in a rack tool magazine with 180 storage chambers, the workstation is equipped with a progressive tool adjustment system with state-of-the-art design.

Similar to the FRF machine, the entire system was a turn-key installation, including the construction of the machine base. The customer received significant support in the field of above-standard training of the operators and maintenance staff, including the fine tuning of individual machining operations in the presence of specialists of the machine manufacturer.

(Tos Kurim)