Press retrofit increases productivity, availability and safety

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Pilz has completed a project to upgrade the control system for an eccentric press from the 1980s, resulting in a modified press that is seemingly as good as a new press in terms of productivity, availability and safety.

Press retrofit increases productivity, availability and safetyIn the past, machines were designed to be robust and were often oversized to a greater degree than necessary – although this did increase the service life considerably. It is little wonder, then, that manufacturing operations often continue to use machines that are regarded as old iron' but still fulfil their function. To bring these machines up to the state-of-the-art, it often pays dividends to convert them to the latest generation of automation control system. This is what happened at the Lower Austrian Umdasch Group, who subjected an eccentric press to a fundamental retrofit at the end of 2015.

The Umdasch Group is one of Austria's largest, most traditional, family-owned woodworking companies, whose beginnings date back to 1868. The company's identity is particularly characterised by woodworking, but today it also processes metals and innovative new composites.

With its two divisions Doka Group and Umdasch Shopfitting Group, the Umdasch Group is mainly known for the ever-present yellow formwork boards used in the construction industry: these include formwork products for tunnel, civil engineering and building construction. Doka Group manufactures components such as ceiling props, heavy-duty supports, transverse load carriers and anchorage systems in-house.

The anchorage systems include waved anchors, which the Doku Group manufactures on an eccentric press dating back to the 1980s. This is used to convert a coarse-threaded steel rod into a Z-shape. Various tools for different lengths are available for reshaping. The waved anchors are cast into the concrete; the thread provides fixing points to attach climbing systems or supports, for example. The reshaping ensures that the waved, concrete-encased anchor withstands a defined tractive force and does not tear.

Upgrade required

As the press was otherwise in very good mechanical condition, it made sense for the company to invest in a retrofit in this case. Although the eccentric press was still functional, it was starting to show some shortcomings in terms of its availability: after maintenance it could no longer be guaranteed that the press would be ready for operation again within 10 days, should a component fail. The electrics in particular used very outdated technologies, for which spare parts were no longer available: they were implemented using obsolete contactor controls. Here in particular, a retrofit was required to guarantee that the press was upgraded to the latest standard, based on the most modern technology - and, above all, with components that are readily available.

The press originated from the former East Germany. The process at that time used special motor start-up systems to enable the motor to start up when the power supply was weak. Very many systems were installed for this reason, but are no longer necessary today with state-of-the-art technology.

Risk analysis

As the complete, safe automation supplier, Pilz was brought in to upgrade the press. In conjunction with Pilz, a risk analysis was conducted even before starting the project; this would determine the further course of action, such as which components needed renewing, for example.

Implementation guidelines from Doka formed the basis; these specified the manufacturers and components that were to be used. Pilz was responsible for completely planning the upgrade, acquiring all the relevant components, organising the control cabinet construction and performing the final, actual upgrade on-site. Doka could easily carry out the mechanical changes to the press in its own workshops.

Pilz has many years' experience in matters relating to press retrofits: numerous factors such as renewing the wiring or valves play an important role, in particular for press safety.

New control system

Ultimately the press was given a completely new motor as the main drive motor, which can be exchanged quickly at any time in the event of a failure. The press safety valves and all of the pneumatics were also exchanged. However, the upgrade mainly concerned the renewal of the complete control cabinet along with the wiring. The control system PSSuniversal PLC from the automation system PSS 4000 was installed as the higher-level control system. The automation system contains various hardware device classes. All control and I/O systems have a modular structure. As a result they can be used in various systems and are also expandable.

The 'old' mechanical rotary cam arrangement has been replaced by an electronic system from Pilz: a combination of control system, special software blocks and the PSENenco rotary encoder. Installation is very easy: the PSENenco safe rotary encoder is designed with complete redundancy and is fitted on the shaft and adjusted. It communicates the current encoder values to the PSSuniversal PLC via an SSI interface (synchronous serial interface). The software program uses these to calculate the respective operating angle of the press. This way it is possible to safely establish the angle calculation, number of strokes or direction of rotation for each movement.

There is no need for any complex mechanical re-adjustments on the safety system. As a result, press solutions can be implemented safely, flexibly and economically, from dynamisation of the overrun cam to internal broken shearpin monitoring. Only three parameters are required to set the run-up cam and overrun cam. The overrun cam can be calculated safely and dynamically for presses with a variable number of strokes. Each time the press stops the overrun is automatically recalculated, to guarantee that the resulting stopping point of the press is constantly exact. If the set limit values are exceeded, this will be signalled via the screen and the press will be stopped.

High productivity

Before the retrofit, although the slide stroke adjustment was electrical, it still had to be read via a scale. The current approach uses a distance measuring system, so now the operator can see the position directly on the operator terminal, a PMI (Pilz Machine Interface) 509 from Pilz. The display now shows plain text error messages; the previously mechanical piece counter is now incorporated via the software. Powerful 1GHz RISC processors guarantee speedy performance even with complex applications; and all data is transmitted quickly via an Ethernet interface. As such, the operator terminals guarantee high productivity of the plant or machine.

Following the retrofit, the states of all safety-related moving parts, such as the side protective guards for example, are polled by a total of three Pilz PSENmag magnetic safety switches. These are used to monitor the position of guards in accordance with EN 60947-5-3 (Low-voltage switchgear and controlgear - Part 5-3: Control circuit devices and switching elements - Requirements for proximity devices with defined behaviour under fault conditions (PDDB)) and also for general position monitoring. The safety switches can be connected in series and can easily be integrated into the system environment. Installation is concealed to prevent manipulation.

Following the press upgrade the operator has access to considerably more information and re-tooling is simpler. The final steps were to program the safety system and measuring system and implement the visualisation.

Manually operated presses have to be examined by a notified body following an upgrade, so the system was approved by TUV in the last instance. Training for the press operator marked the end of the project.

In all, 14 days were needed for the upgrade. A satisfied Markus Kaltenbrunner, maintenance engineer at Doka Metallbau, says: "In co-operation with Pilz we were able to retrofit our press quickly and smoothly. Pilz took care of the whole process and implemented it perfectly. Robustness was extremely important to us before – something like that is almost impossible to get hold of from new. By upgrading, not only could we save costs, we could also modify the press so that we can use it in full accordance with current considerations."

Thanks to the upgrade, the old press is seemingly as good as a new press in terms of productivity, availability and safety.

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