Hydraulic and electrical engineering for testing machines

At its Nordhausen site, Poppe + Potthoff concentrates on test systems for burst tests, autofrettage, pulse tests and rotating bending fatigue and for supporting series production and prototype development. Machines include a burst pressure test stand that is suitable for both testing tube fittings and also hydraulic hose lines, and which also fully supports the new and further development of these components. Test sequences can be programmed flexibly, not only allowing testing with linear pressure increases and decreases, as well as holding times at a constant pressure and volume, but also burst pressure tests with a linear volume flow. In a large test chamber with a 10mm stainless steel safety cage, test objects can be burst tested in a controlled manner at pressures of up to 4000bar, for which data can be recorded in real-time with an accuracy of 100,000 measured values per second.

The development of the test stand described placed particular requirements on the design of the system, particularly because of the different properties of the test objects, fittings and hoses. In the past, Poppe + Potthoff Maschinenbau GmbH had the hydraulic power unit manufactured by an outside company; however, the machine builder decided to pursue a different approach with this test stand. In partnership with Eaton, an in-house hydraulic power unit was developed which is controlled by Eaton automation and switchgear technology.

Johannes Montag, who is responsible for Design Construction at Poppe + Potthoff Maschinenbau GmbH, explains: "In order to create the pressure in our plant, the hydraulic power unit first of all generates a pressure of up to 350bar. For the first time we have used two pressure amplifiers to create the high pressure. These have different piston diameters so that we can pre-fill quickly with the large pressure amplifier and then, particularly for position-controlled burst pressure testing, very finely regulate the pressure at high resolution using the small pressure amplifier." The key components for the precise control of the pressure amplifiers and thus the pressures in the test chamber are the proportional valves.

Seamless integration

Besides the proportional valves for the two pressure amplifiers, other important hydraulic components for the drive, control and connection are supplied by Eaton and integrate together seamlessly. The following components are used: Axial piston pumps and vane pumps, as well as valves from Eaton's Vickers product series, Aeroquip hoses, tube fittings from the Walterscheid product series, screw-in cartridge valves from the Integrated Hydraulics brand, as well as Internormen pressure filters and ventilation filters for the tank system. For the machine builders in Nordhausen, the service-oriented integration of Eaton's distribution arm also played an important role in the cooperation with Eaton. The Dsseldorf company Hyflexar Schlauch- und Armaturen GmbH was the Eaton service partner for Poppe + Potthoff, that not only kept all tubes, pumps and fittings in stock, but also configured and installed on site with its mobile workshop fluid conveyance systems to customer specifications, as well as providing a 24/7 spare parts service. Furthermore, the Eaton Store in the Rastatt Service Centre provides Eaton customers and partners with a point of contact for components and finishing services.

The proportional valves of this burst pressure stand are connected to the controller via CANopen. Poppe + Potthoff chose Eaton's modular XC200 for the PLC. Ren© Karwoth, who is responsible for software development at Poppe + Potthoff in Nordhausen, explains: "For us, the XC200 offers two major benefits for this test stand. Firstly, the integrated Ethernet interface allows us to connect the PLC directly to National Instruments LabVIEW and the network, without having to use MPI or PPI converters as was necessary before. Secondly, the CoDeSys-based software (SW-XSoft-CoDeSys-2) and the extensive range of functions of the closed-loop control toolbox enable us to complete programming and commissioning faster and more conveniently than before." Eaton's closed-loop control toolbox contains around 120 ready-to-use function blocks that make life easier for the developer by providing already implemented closed-loop control know-how, so that individual application options can be made simply and quickly by combining and cascading standard function blocks. A commissioning screen created with the XSoft-CoDeSys Target visualisation shows all important parameters at a glance, and thus not only noticeably simplifies commissioning, but also supports the end user with later optimisations.

Switchgear components

Poppe + Potthoff also sourced key components from Eaton in terms of switchgear. These include contactors, motor-protective circuit-breakers, soft starters, power supply units, miniature circuit-breakers and residual current circuit-breakers for this burst pressure test stand. In addition to this are the operating elements and safety technology products. The burst pressure test stand is thus provided with a two-hand control, an emergency-stop circuit and interlocking doors that are switched using Eaton safety relays.

Frank Baudler, head of engineering/R&D at Poppe + Potthoff Maschinenbau GmbH, notes: "Thanks to this project and the close cooperation with Eaton, we are now able to also offer our customers Eaton hydraulic power units in future for different test stands. The fact that we can source both the hydraulics and the electrical engineering from Eaton as a single supplier opens up new possibilities for us. By taking on our suppliers as partners, we can also increasingly give them greater responsibility." In future the specialist for high-pressure test stands will also use Eaton hydraulic power units in different performance classes. Thanks to the broad and comprehensive range of Eaton products a scaling of the unit is easy to implement.

To learn more about hydraulic and electrical components from Eaton Fluid Power, please go to www.eaton.com/hydraulics.