Rotary joints in high-speed machining centres The machine tool manufacturer takes the right turn to safely routing hose lines through the CNC machine. Three tool changes a minute are an everyday occurrence for Chiron-Werke machining centres. So in one year at the most, one million cycles are achieved; and they must be executed without a hitch. The solution was found with rotary joints. The technology of the so-called "simple turnable lead-in" is used by Chiron in all its machining centres having a work-piece changer table; this adds up to 500 machines leaving the factory each year, accounting for approximately 50 per cent of their sales turnover. The FZ 15 W high-performance centre is in this category. Above all, this masterpiece of a machine tool has outstanding chip-to-chip times of only 1.7 seconds and can rapid traverse at up to 75 m/min. The integrated work-piece changer table needs only 1.9 seconds to swing out through 180º. As with all other Chiron machine tools, here too the rapid tool changer assures the highest positioning accuracy, because the basket changer does not have to leave its position for changing tools. The simple turnable lead-in design also supports the "Seconds Ahead" concept, as Chiron calls it. "In the previous solution we could, in the truest sense of the words, swivel and orientate, just as we wished. The installation space in the middle of the rotary distributor was simply too small to install pneumatic and electrical lines too, in addition to the hydraulic ones", recalls Dipl.-Ing. Anton Schweizer, Design Chief and Product Group Manager for Compact Machines at Chiron. "Previously we used conventional rotating unions, a type of shaft with individual channels drilled from below, which were spaced out on a                                                                                                                                sleeve." Moving hose lines are the preferred application field for these rotary joints; for example, it is impossible to imagine mobile hydraulics without them. Proven in tough mobile installations, they have now found their way into stationary hydraulic systems such as machine tool applications. Wherever hose lines have to be connected to a rotating or swiveling machine part, rotary fittings prove their qualities for preventing torsion problems and allowing bigger line bend radii. These fittings can accommodate working pressures even up to 350 bar and can be used within a temperature range of -40 to 200°C. Applicable flow media are hydraulic oils, HETG and HEES-type hydraulic fluids, as well as mineral-based lubricants. The ball bearing and plain bearing versions of these rotary joints are available in straight and elbow types and with several axes. Before adopting them, as with all components used in its machines, Chiron subjected the rotary joints to a long duration test, which showed good results after half a year and paved the way towards design changes within the machine. Schweizer particularly mentions the high transverse forces that initially affected the exposed lines. With a test stand having a pneumatic swivel device, they were finally tested for more than a year. The new solution consists of a rotary table from which the connection lines in the area of the axis of rotation are routed under the machine and can then be bundled together. At the same time, Chiron decided to increase the passageway in the rotary distributor from 60mm to 120mm, so that all the lines could be brought together onto a connector plate. "Thanks to the new design, we can now install twelve hydraulic lines and, coaxially, a range of pneumatic and electrical lines too. During assembly, we only have to ensure that the various lines do not cross, because whilst the machine is operating, the work-piece changer turns through 180º. For this reason the electrical lines are protected by corrugated hose up to their connection to the control cabinet", Schweizer explains. The main advantage lies in the fact that now all moving lines can be bundled, because the hydraulic lines no longer require as much space as previously. Furthermore, torsion in the hydraulic hoses is prevented and they do not have to be assembled with narrow, critical bend radii. "Firstly, this gives us more flexible design configuration possibilities and secondly, increases the life of the hydraulic system and thereby the working availability of the complete machine." The Design Chief and Product Group Manager willingly concedes that the design changes make a positive, significant difference: "the conventional method of routing the lines was always the weak point in the system, which we had to abandon not least because of high O-ring wear. Now we have a real grip on the problem, guarantee one million cycles and in the future can tackle further automation questions without the risks from the hose lines." Speed Link InfoService Request more information by e-mail Reader Service No. Reader Number Email Address 00988    Tell a friend about this article:
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