PRECISION ENGINEERING
Optimal cleaning processes for quality products They are critical in the manufacturing industries. Today, component cleanliness is just as much a quality criterion as dimensional accuracy. It is defined by given particulate and, increasingly, also thin-film cleanliness specifications. Meeting these reliably can be quite a task. For operations to be cost-effective, it is becoming ever-more important to design cleaning processes in line with user requirements and for reproducible cleaning results. Regardless of the industry sector, parts cleaning today has become one of the critical processes in manufacturing. For one, parts must be sufficiently clean for subsequent processing steps like coating, printing, heat treatment and assembly. For another, product quality and functionality are crucially dependent on clean components. In recent years, the focus has been on removing particulate contamination, including chips produced in machining and forming processes, but also burrs and particles generated from abrasion. Meanwhile, thin-film contamination has become a more serious issue. This is because the tiniest residues can impair the quality of the joints in joining processes such as laser welding, soldering and bonding. These residues are produced by machining oils and emulsions; cleaning media; and drawing, forming and release agents etc. When it comes to thin-film contamination, cleanliness specifications are often defined in terms of surface energy or surface tension (mN/m = milli-newtons per metre). Compliance can be checked comparatively, with ease, using test inks and by measuring contact angles.
Tailoring wet chemical cleaning processes to the task For the vast majority of parts, specifications regarding particulate 30
THE SINGAPORE ENGINEER June 2022
Component cleanliness is a quality criterion that contributes to customer satisfaction and thus to a high level of competitiveness.
and/or filmic cleanliness can be met using wet chemical cleaning processes. The parts are generally cleaned in batches, either in bulk or arranged in part carriers. However, stable and reproducible process quality and consistently good results can be obtained only if the cleaning chemicals as well as the system engineering and process technology are optimally tailored to the cleaning task.
Choosing the right cleaning medium for the contamination When selecting the cleaning medium, the chemical principle of ‘like solves like’ can serve as a guideline. This means that polar contaminants, such as cooling emulsions, polishing pastes, salts, particles from abrasion and other solids, are normally removed using water as a polar cleaning medium in conjunction with pH-neutral, acidic or alkaline cleaners. For mineral oil-based (organic, non-polar) contaminants, such as machining oils, greases and
waxes, solvents like non-halogenated hydrocarbons or chlorinated hydrocarbons are generally used. Modified alcohols (3-butoxy-2-propanols) have lipophilic and hydrophilic properties, and are therefore capable of removing both non-polar and polar contaminants to a certain extent. To determine exactly which cleaning medium is best for effectively removing the contaminants adhering to the respective parts, cleaning trials with original contaminated parts are recommended. In its technology centres around the world, Ecoclean GmbH has provided a variety of cleaning systems for all types of media. They are used to conduct tests on parts made of metallic materials, plastics, ceramic materials, glass and combinations thereof. In addition to the achievable cleaning result, the company also checks that the materials of the components to be cleaned are compatible with the cleaning media used.
