Glass-fiber reinforced plastic pipes (GRP pipes) are used in many areas, especially if they involve water, waste water and process piping systems in the chemicals industry. Until now, most milling or cutting of pipes has been carried out under wet conditions, by adding water to keep tools cool and “absorb” GRP dust. But this produces huge volumes of “GRP mud” which has to be disposed of as special waste. To avoid this, experts at a company from Saxony joined forces with ALP, the Steinbeis Innovation Center for Automation in lightweight construction processes (ALP), as well as Chemnitz University of Technology. It was all part of an AiF-backed project to develop a dry processing system for GRP pipes.
GRP pipes are used for water, waste water and process piping systems in the chemicals industry. They are now used all over the world, mainly due to their excellent technical properties, corrosion resistance, the low specific weight and durability. They can be made with winding processes as well as centrifugal casting. One part of the pipe is slotted into place using special GRP couplings called “REKAs.” These couplings are made by cutting GRP connection pipes (larger diameters) into smaller sections and adding grooves and phases. The grooves are to hold rubber sealing rings. The cutting of the pipe and milling of the grooves takes place in one process with a multi-component set of tools on a machine which was specially designed for the process. Currently, processing involves adding water, but this results in significant volumes of GRP mud due to the size of the pipe – which can measure up to 4,000 mm in diameter. Gathering and disposing of the mud can be highly problematic. Precipitation and dehumidification is needed to dispose of the waste professionally. During the process, machines and the workplace can become heavily soiled, resulting in more severe wear and higher maintenance costs.
To avoid using water during the milling and cutting of the pipes, the team designed a fundamentally different process. Now, dust is no longer “absorbed” by water and flushed away. Instead it is removed the moment it is produced with a carefully directed jet of air. This also helps cool down the tools. The waste air containing dust particles is then cleaned by a filtering system and the dust is collated into a flour-like substance in suitable transportation containers. It can subsequently be disposed of without further treatment. Alternatively it can be reused as an aggregate in industrial processes. The new process was only possible thanks to special development work to adapt the machines and tool components. By pooling skills in the field of special machinery construction, tooling technology, ventilation systems and GRP technology, it was possible to design a system that goes way beyond the capabilities of existing machinery, not just for removing dust. The development of special diamond-coated tools and improvements in the kinematics of the tool drive made it possible to process pipe connectors measuring 300 mm in less than three minutes. Comparable systems already in operation need seven or eight minutes for the same task.
The AiF and ZIM-sponsored project involved collaboration between Huster Sonder- maschinen, DIT Diamanttechnik, ULT and the Steinbeis Innovation Center ALP as well as the professorship for lightweight construction processes at Chemnitz University of Technology, GRP Technique & Service and the engineering consultant Bernd Müller.
Dr.-Ing. Wolfgang Nendel
Mirko Spieler
Steinbeis Innovation Center Automation in lightweight construction processes (ALP, Chemnitz)
su1551@stw.de