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Environmentally friendly and cost-effective cleaning process for metal filter discs

SCHWING Technologies is an international specialist in thermal polymer removal

Neukirchen-Vlyun 21.07.2017 (NL) Metal filter discs for polymer filtration are becoming increasingly important in plastic-processing film extrusion (BOPET, PET, PA, etc.), and melt filtration processes are becoming increasingly complex. Metal filters ensure the highest quality standards in polymer production. At the same time, they offer answers to the requirements of the international market. The fact that these filters are becoming increasingly precise and costly to produce is obvious. While they used to be replaced and exchanged regularly, there is now an economically and ecologically motivated trend towards cleaning and re-use. A metal filter disc costs about 200 to 500 Euros today. It can easily be cleaned 50 to 60 times using SCHWING Technologies process solutions - and all without sacrificing filter quality.

Complete cleaning shops

As an international market leader, SCHWING is an expert in comprehensive thermal cleaning solutions. For 47 years, the German manufacturer has been a specialist in cleaning plastic-contaminated metal parts and the only worldwide expert for complete, tailor-made cleaning equipment. "So-called cleaning shops guarantee a deep-pore removal of polymers," says Managing Director Thomas Schwing, "without residue or damage, and with a guaranteed longer life." The long-term expertise of the well-known SCHWING specialists guarantees perfect cleaning results in this process.

Depending on customers' requirements, the company can set up individualized, targeted cleaning shops with a wide range of cleaning and post-treatment equipment. A tailor-made data sheet documents the entire process and offers reliable workflow support for customers. "We have had the positive experience," says Schwing, "that even new and inexperienced customers can easily and successfully learn to work with our hardware through appropriate training during commissioning." In this way, filter discs can be optimally freed from polymers in less than 48 hours.

Precise filter cleaning

Filter discs consist of a variety of ultra-thin braids and metal fleece fibers as fine as 1 or 2 μm. It is thus necessary to identify optimal cleaning processes for all layers and intermediate spaces, however fine. For this purpose, SCHWING offers the ideal cleaning methods for the removal of polymers. A workflow comprises a plurality of precisely matched process steps, in which the optimum interplay of individual factors and parameters is the key to perfectly successful cleaning. The thermal cleaning units are individually tailored to customer requirements using a vacuum pyrolysis unit, further post treatments, final checks, and detailed documentation. SCHWING distributes complete turn-key cleaning shops internationally, but also cleans in Germany as a service and invites customers to test its cleaning processes at the company's headquarters in Neukirchen-Vluyn. At the same time, the manufacturer is also constantly improving its equipment for optimum efficiency and adapting the cleaning processes to new material mixtures and metal filter designs.

Environmentally friendly vacuum pyrolysis

SCHWING's gentle VACUCLEAN vacuum pyrolysis system is ideal for cleaning filter bundles and filter discs - even those of the highest quality. Environmentally friendly, energy-efficient, and operated only with electricity and water, the system cleans through pyrolysis and oxidation, without additional chemicals or the use of triethylene glycol (TEG). "In the vacuum pyrolysis process, even degraded PET and gels are removed," explains SCHWING engineer Thomas Ceglarek. "This cleaning method achieves an even more impressive result than using TEG." In many countries, this chemical substance also creates environmental problems due to its high disposal costs, Ceglarek says.

Safe cleaning process

The entire cleaning process workflow starts either with a melting-down process or with the cleaning of complete filter bundles in a customized loading rack. SCHWING provides specific parameters in this regard, such as the positioning of the filters, the heating time, the temperatures and duration of the pyrolysis and oxidation, and the cooling times and opening temperatures. The goal is always a perfect cleaning result. In the next step, the filter bundles are disassembled, separated into individual discs, and again subjected to vacuum pyrolysis in order to achieve optimum cleaning, even at the deepest filter levels. In this process, customer-specific values for temperature and duration are again established and the optimum data is determined.

Individual post treatment

SCHWING also offers tailor-made solutions for post treatment. Although the thermal cleaning systems remove all organic impurities, inorganic residues can remain in the filter discs. Specially adapted post treatment methods remove these safely and without residue, and are always carefully adjusted to the individual filters and cleaning processes of the customer. A number of devices are used for this purpose, such as an ultrasonic bath and a high-pressure water purifier.

High-pressure manual or automatic post treatment processes that use hot water are suitable for removing further residues. The essential parameters in this regard are temperature, water volume, spray pattern, and water pressure. SCHWING recommends an optional industrial washing machine which performs this step in a semi-automated manner. The key points to be defined in this context are: temperature, pressure, spray pattern, and washing time.

The next cleaning step is provided by a sophisticated pulsating backflush system with wave- and pressure-like treatments. This removes inorganic residues from the interior and exterior. Important parameters here include: the tank filling liquid, the flush pressure, the disc adapter, and the number and length of the pulsating cycles.

In the ultrasonic system, sensitive filters are then freed from further remaining residual contamination in areas that are difficult to access. In this step, as well, SCHWING recommends a number of important specifications that should be considered: temperature, type of liquid, additives, position of the filters, ultrasonic frequency, and cleaning time and power. The filters need to be rinsed in an agitate rinse tank afterwards.

The filters are finally dried in a drying oven with an individual loading rack. Key parameters are: temperature, filter position, drying time, and ventilation System.

Verification and documentation

Checking the weight with a filter scale shows whether there are still contamination residues in the filter. A bubble test in turn documents whether the filter is faultless or mechanically damaged. The 10-liters-per-minute (LPM) flow test also verifies the result. Identifying variables are: liquid, test medium, test pressure, and disc adapter. For most filter media, SCHWING performs this test with water and does not use isopropanol .

Research innovation

In order to achieve perfect results, a team of experienced specialists and engineers continually improves and optimizes cleaning technologies at the Neukirchen-Vluyn site, while also bringing experience and expertise to research projects. This was the case recently with the pyrolysis research project performed for the Institute of Plastics Technology at the University of Paderborn, which focused on the contamination behavior and service life of polymer melt filters. In order to more thoroughly understand the processes, Thomas Ceglarek and the Paderborn Faculty of Mechanical Engineering examined cleaning results from 2015 to 2016. "This joint research effort has shown us," Ceglarek summarizes, "that our environmentally friendly vacuum pyrolysis achieves the equal or superior cleaning results when compared to hydrolysis. It is also inexpensive, and we can rule out the known disadvantages of hydrolysis systems, such as uncontrolled oxidation and damage of the filter fabric." .

Schwing Technologies

SCHWING Technologies has been operating since 1969 and is the worldwide market leader for high-temperature systems for thermal cleaning, thermo-chemical finishing and heat treatment of metal parts and tools. The owner-managed company constructs, manufactures and operates its systems at its headquarters in Neukirchen-Vluyn in Germany's Lower Rhine region. Built upon the achievements of German engineering, the medium-sized business is globally the best-known specialist in the removal of plastics. Among its around 2,500 international clients are companies from the plastics and fiber industries, as well as from the chemicals, metals and automobile sectors. With its 80-strong personnel, the company is equipped with the tools and systems for any cleaning need and delivers the best economy, ecology and quality. SCHWING is also a reliable service partner for contract cleaning by cleaning more than 250,000 tools and parts each year to the highest environmental and qualitative standards. In the words of Ewald and Thomas Schwing, the two managing directors at SCHWING Technologies, "So far, there has not been a single component that we have not been able to free from polymers and inorganic contaminants."For more information, please visit SCHWING's website at www.thermal-cleaning.com