Membrane filtration processes such as microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) have established themselves in numerous industrial processes as efficient solutions for bath maintenance, service life extension, and, in some cases, the recovery of valuable materials. Whether membrane filtration is suitable for a specific process bath depends primarily on the composition of the bath and the contaminants to be removed.
Basic principle of membrane filtration
In membrane filtration, undesirable substances are separated from the process medium based on their size. The membrane has a fixed pore size that clearly defines the separation limit. This allows contaminants to be continuously removed while desired bath components remain in the process (e.g., cleaners, surfactants, etc.).
Degreasing baths / cleaning baths
Degreasing baths are among the most common applications for membrane filtration at Atec.
During the cleaning process, oils, fats, and particles continuously enter the cleaning bath. These contaminants can be reliably removed from the bath using microfiltration or ultrafiltration. The cleaning solution remains largely in the process. The service life of the bath is often significantly extended, and the quality of the washing process improves.
Rinsing baths after degreasing
Rinse baths following degreasing baths are contaminated by pollutants and bath chemicals carried over from the degreasing stage via components, workpiece carriers, conveyor belts, or similar. This makes it clear: the best rinse bath maintenance often begins with the maintenance of the degreasing bath. A clean and well-maintained degreasing bath enormously reduces the carry-over of contamination into the rinse.
If the actual rinsing bath is to be treated, tighter membranes can often be used here. These can then separate carried-over surfactants in addition to the usual contaminants. In some cases, membrane filtration can be combined with further processes (e.g., to reduce conductivity).
Pickling baths
In acidic or alkaline pickling processes, membrane filtration can remove typical contaminants:
- Metal hydroxides
- Other reaction products
- Oils and other contaminants
Through the continuous removal of these undissolved substances, the activity of the pickle can be improved and its service life extended.
Pickling / etching of aluminum: Chemical milling and cleaning of extrusion dies
An application that is often technically and economically interesting is the treatment of highly contaminated alkaline aluminum pickling or etching baths. The most heavily contaminated pickling baths are typically chemical milling baths and pickling baths for the cleaning of extrusion dies / tools.
Rinsing baths after pickling / etching
The rinse after pickling is contaminated by the carried-over pickling medium (acidic or alkaline) and carried-over impurities. Therefore, a pickling baths well-maintained via membrane filtration reduces carry-over into the rinse bath.
Depending on the requirements of the specific application, the rinses can be treated purely by membrane filtration or using combined processes.
Sealing baths
After the anodizing of aluminum, the open pores of the material are closed in hot sealing baths. These baths often have a short service life (approx. 1 week), as precipitates lead to streaks and spots on the components. Occasional cooling of the bath (e.g., overnight) further exacerbates the problem.
Membrane filtration offers the ideal solution here. Precipitates are continuously and reliably removed from the medium. Occasional cooling even benefits the membrane filtration, because dissolved solids precipitate as the bath cools and can then be filtered out. With sealing baths, an enormous extension of service life is possible through membrane filtration (e.g., 6 weeks instead of 1 week).
Other baths
There are a variety of other process baths and process media that can also be effectively treated using membrane filtration. Examples include electrolytes from ECM processes, certain phosphating baths, and the process medium from vibratory finishing systems.