What is technical cleanliness?
Basics of Component Cleanliness Inspection
Particle contamination refers to solid particles and filmic contaminants that remain on a component’s surface. Typically these are searched for after the component has undergone a cleaning process to ensure the desired standard gets attained during manufacture. Particle contamination can be generated during manufacture or may be introduced via vendor parts, packaging and logistics.
Technical cleanliness is defined by the number of residual contaminants on the surface of a component. To describe the state of cleanliness, residual contamination and the number, size and composition of the particles are determined.
In practice, the customer will define the threshold values for component contamination, sometimes referred to as the CCC or component cleanliness code. The supplier has to comply with these limits and is responsible for regular test measurements.
Hardness Classes of Impurities
The hardest residual contaminants are minerals like corundum, silicon carbide and sand. Most of these particles originate from surface treatment processes, such as grinding, tumbling or honing. Mineral particles are typically microscopic and light grey, thus resulting in weak contrasts, which is why they can not be reliably detected with a light microscope.
The hardness of a metallic particle strongly depends on its material. Steels are hard, non-ferrous metals are relatively soft. Residual metallic particles usually come directly from the manufacturing process. Low chromium steel particles are often oxidised by the time of analysis and lack a metallic gloss. These become classified as non-metallic in the light microscope, so we recommend SEM-EDX for the reliable detection of metals that readily oxidise.
Salts are a relatively soft residual contaminant, which is why they are classified as uncritical. These particles are typically residues of washing processes or additives of lubricants.
Organic Particles & Fibers
Organic particles, such as fibres and plastics, are soft. These particles are becoming increasingly relevant because of their typically larger size, which can clog fine holes and filters. Glass fibre reinforced plastics are also critical because they are highly abrasive due to their high glass content.
Oils and Fats
Hardness is not considered when it comes to oil and fat impurities. These contaminants occupy component surfaces in the form of a film. Liquids and films cause problems during subsequent processing stages, such as painting, anodising and coating. In addition, hermetically sealed assemblies such as ECU’s are dependent on liquid gasket seals, which will fail prematurely if the surface tension is not managed correctly through controlling filmic residues.