The presented Safety couplings of the series ST R + W are available for torques of up 1000 160.000 Nm in four different sizes available. They are therefore particularly to reduce the high downtime costs for heavy machinery. It can shaft diameter 40 be adapted to 290 mm. The couplings are absolutely backlash-free and maintenance-free and have in comparison to other safety clutches an up to 23% smaller outer diameter.
State-of-the-art steel mills all over the world produce all the variations and alloys of the metal so that the enormous global demand can be met. In electronic arc furnaces, the basic or recycled material is melted down in batches of up to 100 t. The subsequent further processing of the steel in continuous casters for blooming or billets must be immediate. After a cooling time of several hours, the last step in modern steel production takes place in the rolling mill. In this part of the production, the shaping to bar steel (gas-heated Hubbalkenofen) or concrete cut (natural gas fired blast furnace) is carried out on different rolling mills. These large-scale systems in heavy machinery are or must usually be operated in 3 shift operation 7 days per week. Shutdown or shutdown of the systems for maintenance intervals of the individual components such as motors, gearboxes, bearings or couplings is avoided as much as possible because a so-called freezing of the system (eg slag bath) must be prevented. Consequently, as far as possible maintenance-free mechanical components are used. In total, the system is safe in normal operation. But what happens outside of normal operation:
- if in the single component a not previously detectable material fatigue takes place?
- if a billet wedges in the continuous casting plant?
- If a wrong pressure or a wrong stroke is set in the rolling mill?
In these points, the profitability of the plant is paramount. The large-scale plant in heavy machinery construction must be put back into operation as quickly as possible under all circumstances! At this point, a mechanical safety coupling from R + W Antriebselemente GmbH offers maximum protection against the destruction of the components in the drive train. The safety coupling is dimensioned in the design by the factor 1,3 to 2,0 on the example tilt or saddle torque of the motor. If a crash occurs during normal operation, the torque in the drive train increases disproportionately. The clutch separates the crash side of the still intact side in the millisecond range and prevents a total failure of all components. Due to the lightning-fast disconnection of the safety coupling, the installer only needs to replace or repair the blockage at best. The maintenance-free and above all re-engageable functional principle of the coupling finally allows the system to be restarted within minutes.
Comparison of mechanical safety clutches
The described topic has been known for decades in heavy machinery construction. In the event of a crash, the designer can choose from break bolt couplings or hydraulic couplings. The disadvantages compared to the mechanical safety coupling of R + W are clear. Although a break bolt coupling is cheaper in the purchase price, it requires a much higher installation time for recommissioning. The bolts (usually including sockets) must be completely disassembled. Then the clutch has to be readjusted before the new pins including sockets can be used with enormous installation effort. The initially advantageous purchase price is relativized at the latest at the first triggering process. Furthermore, the recommissioning of the clutch requires a high degree of experience of the installer, because in case of incorrect "repair" of the clutch this will lock in at other torques in the future! Which in sum causes extreme costs at standstill. An overload clutch that works on a hydraulic principle scores initially by an extremely compact design. If the clutch triggers due to overloading, the oil pressurized up to 1000 bar is ejected from the clutch by several shearing valves. The contamination of the machine components close to the coupling is extreme. After the system has stopped, the individual valves must be renewed and filled with a special pump (exact pressure display). At this point, the exact pressure must be maintained, otherwise the release torque changes. Although this hydraulic safety clutch separates the input and output side to the nominal torque in the event of overload. However, a free-running of the individual components takes place only after a certain time delay. This may result in further damage to components. In sum, the mechanical safety coupling combines the entire disadvantages and relativizes them. The mechanical operating principle can be put back into operation immediately (disc springs). It must be retrofitted no wearing parts such as bolts or valves. There is no contamination of the component components. The most important thing at this point is that the installer or the operator of the system has the 100% guaranteed safety that the clutch disengages exactly at the required torque in the event of a new damage. Improper restarting is excluded with the R + W principle.
Compared to other mechanical safety clutches, this clutch is up to 23% more compact in terms of outside diameter. The difference in the total weight of the clutch is in the most extreme case 1 t. As a result, much higher peripheral speed can be allowed for the respective clutch sizes. In total, the new development of the ST safety coupling improves the overall size, the total weight and the maximum permissible operating speed. The individual improvements, especially in size, were demanded directly by the market. A reduction (up to 73%) makes it easier to mount the coupling. This makes the entire powertrain lighter and can eventually be assembled in a pre-assembly. Finally, the lower total weight also reduces the moment of inertia due to the lower flywheel masses. In addition to the shortening in the acceleration and deceleration process, the system achieves a higher dynamics which ultimately means a higher productivity for the end customer.
Structure and functional principle
The safety coupling consists of two flanges, which are connected by means of so-called switching parts (ST). The switching parts are mounted in a defined circumference on the 1 flange. By disc springs, the ball sitting at the head end can be pressed with a defined force in the opposite latching segment. The clutch is adjusted via the physical relationship force x lever arm = torque. Each switching part can be adjusted in a predetermined force range. In contrast to the currently available switching segments, the R + W standard clearly indicates the setting range with a scale. It accounts for costly surveying the depth of the plunger or conclusions of the Ausrastdrehmoments graphics and adjustment diagrams. The time savings when setting the release torque at this point clearly. Finally, each switch part has a fixed stop in the adjusting nut. An incorrect operation (locking the clutch) is therefore also excluded. The safety coupling of the ST series extends up to a torque limitation of 160.000 Nm. When the coupling is delivered, it is fully functional and requires no additional maintenance or lubrication. Depending on the release torque, 3, 6 or 9 switch parts are distributed symmetrically around the circumference. The 9 pilot bores provided for all three versions allow the customer to retrofit individual switching parts at any time. In extreme cases (very compact mounting position with extremely high torques), the number of switching parts from 9 to 12 or the number of disc springs (higher force) can be increased. This results in a power increase of up to 25% of the entire clutch unit. The manufacturer was also able to present improvements at the Hannover Messe in the field of re-engagement. A circumferential groove allows a fulcrum for better and easier re-engagement of each ram. This advantage reduces downtime until the system is restarted.
Model series ST
The safety coupling of the ST series has been developed for indirect drives (model series ST1). Technical parameters such as radial lateral forces due to chain or belt wheels are compensated by special shoulder bearings. These bearings also allow a nearly unlimited time for braking the individual masses to a standstill. The main connection type for the ST1 series are cardan shafts or cardan shafts. These fasteners are mostly used for power transmission in heavy machinery. Due to the compact design of the outer diameter of the entire propeller shaft is only slightly larger. As a connection to the usually smaller DIN flanges of the cardan shaft, a simple solution with a connecting flange is offered.
In addition to the indirect drives, there are two further models for direct drives available on the market. In addition to the safety segment, the ST2 series has an elastic compensation element. This plastic in the form of natural or synthetic rubber balances the occurring offsets in the axial, lateral and angular direction. Furthermore, torque surges or vibrations are filtered. The second series for direct drives (model ST3) is offered as a torsionally rigid version. Features include an exact torque transfer, very high robustness and the compensation of all three types of offset occurring at very low restoring forces.