Hydrostatics make the difference


March 16 2012
Should one look for records and superlatives, the gas turbines factory of Siemens AG ...

Hydrostatics make the difference

Should one look for records and superlatives, the gas turbines factory of Siemens AG wouldn’t be the wrong address. There, work-pieces weighing a lot of tons and with a length of more than 6 meters are being machined with an accuracy of a few hundred millimetres. A task that a great part of machine tools producers simply had to refuse. But not the Italian machine tools specialist, the Company Innse Berardi.

With almost 13,000 co-operators, Siemens AG in Berlin is the biggest employer in town and inside the Siemens Group the biggest productive site worldwide. 3,000 people work for the gas turbine factory in Berlin-Moabit. Moreover, the biggest and most powerful gas turbine in the world is being built there. With a power of 375 Megawatt the model SGT5-8000H could for instance feed a metropolis like Hamburg and this – if compared with other conventional turbines – with an emission of CO2 reduced of about 43,000 tons a year. Connecting this turbine with a steam turbine one can reach an efficiency degree of the Energy plant of more than 60 percent, unique in the world, with a performance of more than 570 MW.

Just to be aware of the enormous size and weight of the new gas turbine, Markus Sprißler, Technology of Components and Gas Turbine Cases, (production of gas turbines Berlin), states that: „This turbine is 13 meters long and weighs about 440 tons and, despite this,  tolerances of few hundreds millimetres must be observed. Even the most little inaccuracy immediately affects the efficiency degree.“ This because also the working environment conditions play their role: the turbine works with a diameter of more than 5 meters with a nominal torque of 3,000 rev/min and this with temperatures of about 1.500 ° C.

It is anyway in the nature of things that, with a trend towards an even higher efficiency degree, one requires more and more high performances, particularly also in the machining technologies. At this point Dipl.-Ing. Oliver Beuchel, who is being consulted in his quality of processing advisor Lean Production for all the investments projects, states that: „The new generation of high power gas turbines has simply broken out the machining possibility on the current milling machines“. And this although in the machine shed, the so called Peter-Behrens-Halle, safeguarded by the Monuments Protection, milling machines with 6 meters of machining heights are already used.

These would also have been sufficient if, with the new generation of turbines, an (almost) insoluble problem did occur. Markus Sprißler: „Up to now the cases of the big turbines were composed normally of two segments: for several reasons with the new version the design provides for a single-case. First of all we defined which specifications would have been necessary for the machine so as to be able to realise the machining. Soon we had to consider that even on our biggest machine we would not be able to machine such huge pieces. Considering a work-piece height of 6,40 m, requiring anyhow also a machining of the front side, a height of more than 8 meters is soon reached.“

At this point, the sizes of the machines have been defined  and this has reduced the list of potential competitors up to a few specialists. Just during the first technical discussions it turned out that, at the end, only one supplier would be in a position to comply with all the requirements – and this was the Northern Italy manufacturer Innse Berardi. Hence, no surprise if considering the configuration requirement of  17,5 m in X, eight (!) meters in Y, and still 3,6 meters in W and Z, as well as a power of 150 KW with 28,000 (!) Nm and a rotary table with a load up to 250 t.

The planning did provide initially for a solution with a double machine (for which the building of a new shed would have been necessary) but when the economic crisis occurred, this concept had to  be changed in favour of two separated machines (one of 6 meters, the other one of 8 meters). Markus Sprißler: „ Just during the first discussions with Innse Berardi managers we noted that they had a great Know-How and competence and that they would be well-founded and honest in advising us. The reports of their reference customers did definitely convince us, as they were very satisfied of the quality of the machines installed by Innse.

Even if succeeding in fitting the new milling machine in the existing shed, big measures had to be taken for the realisation of the yard. Oliver Beuchel states that: „The depth of the foundation is of 13 meters, while the actual foundation starts at “only” eight meters depth. In the thickest point under the chips conveyer, the foundation measures some remarkable 3,50 meters. For the Innse machine area about 7.000 tons of concrete have been used  and hence, together  with the reinforced concrete, the same should weigh approximately 10,000 tons. Small detail: all activities concerning the foundation (for a period of about one year) were carried out during production, this means that at not even 10 meters distance from the yard, Siemens was engaged in the accurate removal of chips.

It is also stated: „Such an investment is a mere matter of confidence, as before having the machine in the yard, some remarkable investments turn out to be necessary in advance.“ The term “remarkable” can therefore be taken literally, considered that the sole foundation had involved an expense of more than 5 million Euros. Unfortunately there isn’t any way out possibility, as work-pieces being this big cannot be machined by outer companies. Markus Sprißler says: „We talk about a machine of utmost importance. This machine must be reliable and able to work with the required accuracy for a long period. There is no alternative to this system.“

At this point Mr Dipl.-Ing. Joachim Schuster, Machine Tools and Systems on site representative (WPK) Berlin, adds: „The required accuracies can only be achieved if the whole machine is supported hydrostatically along all linear and revolving axes. Considering the enormous weights of the pieces to be moved, the advantage is that there isn’t any metallic contact - which means at last no wear out -  and hence an extraordinary long lasting accuracy can be granted. There is also a peculiar technical feature, which in my opinion is an absolute novelty that no other manufacturer had never realised up to now: the use of screw nuts in axes X and Y."

But it’s not all, Angela Marzullo, Area Manager Germany in Innse Berardi, shows a list of further measures to grant the accuracy: „Besides having integrated a patented compensation system in order to keep the straightness during the output of the boring spindle, we have also introduced an electronically controlled  compensation system for the headstock and carriage weight during the axes movement.“ Joachim Schuster adds: „Also a thermal compensation of the machine, of the spindle line and of the boring spindle as well as a geometric compensation in the whole movement area  and an automatic self-diagnosis system have been realised too.“

Markus Sprißler states: „It was also important for us that all the basic components of the machine would be standard components, being already tested in routine procedures. Only some specific peculiarities, which were necessary for the complete machining of the case, would have been the topic of special solutions.“ These characteristics are for instance the automatic solution for the attachments change and special attachments for specific works (available are universal head, right angle head, special right angle head, multiplier, right angle head mounted in a universal head). Markus Sprißler explains another condition: „Since the beginning of the design there’s always been the requirement that we had to be able to prepare in secondary times (contemporarily with the machining) both the tools and the work-pieces.“ This is also be solved by the Innse Berardi designing.

As a conclusion, he describes the cooperation which started with the first meetings in 2008 up to the date of supply in April 2011 as follows: „During the whole planning period there has been a partnership cooperation. We have been knowing Innse Berardi for the whole designing period as a very innovative and pleasant partner, reliable and qualified.“ At this point there’s nothing more to say.

Innse Berardi

Innse Berardi is part of Camozzi Group, employing about 2,500 members worldwide.

The main firm Camozzi with seat in Brescia is one of the prime worldwide firms in the field of controlled pneumatics. Other crucial points are the sector of textile machines (Marzoli and Vouk), as well as the sector of big size machine tools of Ingersoll in the United States and Innse Berardi. The double name stands for the two former companies. Innse was one of the biggest Italian industrial poles and did already produce big machine tools. On the other hand, Berardi mainly dealt with transfer lines for the automotive sector.

 

Source : NC Fertigung , September 2011 , Helmut Angeli