In the field of industrial metal cleaning machines, Quality control is focused to fulfill the surface cleaning specifications which are required for further processing and / or for the entire workflow. This is achieved by setting up control procedures and multiple instruments to perform the analysis.
From a practical point of view, the residues on the surfaces of the treated metals cannot be completely eliminated and not always, or not necessarily, can be considered harmful.
The residue limit values or residue quantities considered harmful must be determined on the basis of specific technical requirements and not on the basis of what is technically feasible in the cleaning process.
Excessive cleaning requirements often lead to excessive waste and a relative increase in costs linked to quality and subsequent rework.
The next processes indicate that the detergent, solvent or in any case the cleaning process, is or is not up to the required parameters.
In some cases a cleaning defect does not become evident immediately and can only be detected when the component is already mounted. This is the reason why cleaning requirements and analytical cleanliness checks have become more stringent over time.
VDA 19 and ISO 16232: the benchmarks for the quality of metal cleaning systems
In many applications, the quantity of residual particles on the surface of the components represents an aspect of the Quality and a parameter for evaluating the washing cycle.
VDA 19 and ISO 16232 standards provide guidelines in the field of the technical cleanliness of manufactured parts especially in the automotive industry.
VDA Volume 19 is the first comprehensive standardization document to deal with the approaches and procedures for characterizing the cleanliness of products within the automotive industry’s quality chain.
This document provides the guidelines on basic concepts of cleaning, to the ways in which the inspection methods should be chosen, to the methods of handling the samples under test, to the qualification and relief texts of the famous blank level, to the extraction methods. and filtration and, finally, to methods of analysis.
Next to the definitions you can find a series of examples and case studies to take as a reference.
In the second part of the document, however, we find all those aspects of cleaning that must be considered and respected within the production lines.
The standards defined in ISO 16232 instead describe how to perform the analyses and how the results must be reported: for each component the standard cleaning level to be respected is defined and the importance of test repeatability is emphasized.
There are no recognized institutional standards with a broad comparative basis for these residues, nor are there any corresponding technical measurement solutions other than controls for films and chemical residues such as those that remain on metal surfaces as a result of cooling lubricants or chemical cleaners. made with dyne testing pens that determine the surface tension.
Industries, associations and research institutes are working on recommendations, regulations, as well as the technology used.
Quality assurance of part cleanliness goes beyond the analysis of particulates, films and chemical residues.
Implement measures are included before, during and after the washing cycle of components.
The main aspects of Quality in metal cleaning systems
In the last part of this article we outline the most important aspects of Quality in metal washing processes, namely:
- Cleaning systems and procedures
- Upstream processes and sequences
- Protection against new part contamination and corrosion
- Potential optimizations of the washing environment
- Component design and assembly
CLEANING SYSTEMS AND PROCEDURES
An important aspect of Quality assurance is represented by the coordination of the washing process with the cleaning objectives from a chemical point of view .
The right process must be selected based on the cleaning requirements of the components: simple technological systems for preliminary and intermediate washing and more complex systems equipped with multiple washing chambers for more demanding cleaning targets.
Equally important is a correct and regular maintenance of the system by specialised personnel in order to identify and correct hidden failures.
UPSTREAM PROCESSES AND SEQUENCES
Anything that happens to the metal parts before they undergo the washing process can undermine the quality of the cleaning results.
We are referring to aspects such as the fluctuation in the degree of contamination of the parts: changes in the chemical composition of the fluids or the separation of agents could have negative consequences if the washing cycle was not designed for that particular type of compositions.
Compatibility should always be assured prior to any changes to ensure consistency of cleaning results.
PROTECTION AGAINST CONTAMINATION and CORROSION
At the end of the washing cycle the treated components have a very high degree of cleanliness.
All the precautions to be taken to avoid new contaminations of the components depend on the degree of cleanliness of the same.
Once the metal part meets the required cleanliness specifications after manufacture, this cleanliness must be maintained through later steps such as transport, inspection, storage and packing. To prevent particulate contamination from the environment, these subsequent steps must be carried out in a location removed from the manufacturing area, and personnel must be equipped with the necessary clothing and gloves.
Corrosion can also be avoided by moving components into suitable packages.
To learn more about this topic, the reading of our article on how to protect metal components and prevent corrosion in washing systems is highly suggested.
OPTIMIZATION OF THE WASHING ENVIRONMENT
The optimization of washing processes in order to improve cleaning results represents an ongoing challenge and a trend topic in the sector of metal cleaning systems.
It is difficult to give general guidelines and advice since everything that is done in this regard depends on the case.
COMPONENT DESIGN AND ASSEMBLY
From a Quality point of view it is important to :
- manufacture parts with easily manageable geometries and surfaces, avoiding an excessive number of points where dirt and residues accumulate and are difficult to eliminate;
- consider the tolerance and resistance level of certain contaminants;
- avoid materials and coatings that release particles or contaminants;
- opt for components with surfaces that are well suited for cleaning;
- avoid assembly processes that produce a high amount of residues and contaminants.
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