Casting cleanliness has emerged as a critical aspect of casting quality and customer satisfaction, particularly for parts developed for advanced systems or machinery. To ensure the quality of subsequent process steps, avoid rejects, and guarantee the functionality of the end product, consistent parts cleanliness is an essential quality criterion. Ever-stricter or even modified cleanliness specifications must be met. In addition, demands on the speed, cost-effectiveness and sustainability of the cleaning process are constantly rising. How well, fast, and efficiently the cleaning work is carried out depends not only on the equipment, the process technology and the medium used, but also on specific details of the cleaning process.
So what do you do if parts suddenly come out of the system stained, if specifications for particulate or thin-film cleanliness are no longer met, the cleaned parts arrive at the customer’s corroded, or cleaning is too slow/too cost-intensive? A systematic process analysis – like those done at Ecoclean GmbH’s Ecoclean Academy, for example – can pinpoint the root cause of the error. The cleaning experts focus on the cleaning process and equipment, and also assess the overall manufacturing environment. The smallest change to the part, part spectrum or material, type of contamination, or modifications to upstream or downstream processes is enough to seriously impair cleaning results.
Stains and thin-film residues on parts. According to the cleaning experts, a poor cleaning result or one that does not meet new, higher requirements is a typical prompter for process analysis. The first step is to identify the exact problem – are thin-film cleanliness specifications not being fulfilled, or are there stains on the parts?
If staining is the problem, one question is whether the quantity and composition of the contaminants (processing media and other substances) have changed or whether the constituents and concentration of the cleaning medium are still appropriate. Other factors, such as rinsing water quality, bath treatment, process technology, and process sequence, as well as the drying step, are also examined closely. These are further influencing variables if thin-film cleanliness results are unsatisfactory.
Inability to meet particulate cleanliness requirements. If the cleanliness analysis after the cleaning cycle shows that too many or too large particles are still adhering to the parts, this also may be due to the cleaning program and process sequence. Possible causes include residual particles in the working chamber or on the part carriers, an unsuitable filtration system, or a clogged filter.
Sometimes, it is the wrong choice of cleaning containers, such as crates made of perforated galvanized sheet metal, which hinders efficient and reliable detachment and removal of particles. This type of crate blocks ultrasonic waves and prevents them from developing their full effect on the wash load. Likewise, the spray pressure does not reach the inside of the perforated crates. Compared to baskets made of round wire, a further problem is that the cleaning medium does not drip off these crates as effectively. This may result in the unwanted transfer of contaminants and/or cleaning chemicals. In any case, a much longer and more energy-intensive drying process is required.
Another cause of cleanliness inspection failure is burrs that detach when parts are handled during the residual contamination check, and then appear on the particle filter. If these particles are examined under a microscope, it can be determined whether they are chips or burrs. If the latter is the case, upstream processes must be evaluated to find out where the burrs occur and how their formation can be avoided.
Particulate cleanliness also can be impaired by magnetism that is introduced with raw materials, or arises during the manufacturing process. Magnetism binds chips to the parts and hinders or prevents their removal during the cleaning process.
Handling after cleaning. However, the cleaning process is not over when the parts come out of the machine with the required level of cleanliness. To prevent recontamination or corrosion, which can occur even with preserved or passivated parts, it is important to look at how parts are handled after the cleaning step.
These questions need to be answered: Where, how, and for how long are the parts stored? How are they transported to the next processing step? What kind of packaging is needed for this? In addition, high cleanliness requirements often make it necessary for processes like internal transport, assembly, or packaging to be performed in a clean environment or cleanroom.
Updating the cleaning process. Besides cleaning problems, modified cleaning programs can be a reason for carrying out a process analysis. Generally, the aim is to shorten process times or enhance the cleaning result. As always, the analysis starts by documenting the actual state, which includes verifying the process parameters, process sequence, and process times. Based on the analysis results, potential for improvement can be identified and appropriate measures can be defined. These may include modernizing the system, such as by retrofitting or upgrading ultrasonic equipment.
It is essential that the parts cleaning staff are involved in the process analysis and optimization measures. Raising awareness about cleanliness, as well as about the capabilities of the cleaning technology and the impact of parameter settings on the cleaning result, is critical. If there is a change of personnel, it is also important to pass on that knowledge of how the cleaning system works and how, for example, bath treatment measures or regular maintenance work is performed on the cleaning system. Otherwise, problems that had been eliminated in the past may occur again.
Investing in the training and continuing education of cleaning staff is therefore a cornerstone in order to achieve reliable cleanliness requirements in an economical and sustainable manner, and the Ecoclean Academy also combines process analyses with classic training courses.
Dieter Ortner is the director of Ecoclean Academy. Contact him at [email protected]