In many sectors of industry the cleanliness of component surfaces after pre-cleaning, intermediate cleaning or final cleaning processes is an important quality feature. Nevertheless, contamination can occur in manufacture despite the latest production techniques. This contamination must be lastingly removed before further process steps are taken.
We identify contaminating films quantitatively and qualitatively.
These are often manufacturing and cleaning residue such as oil, grease, cooling lubricants, cleaning agents, and also residue from corrosion inhibitors, coatings and other agents used in manufacture. Preservatives and adhesives as well as the sweat from hands and finger-marks also occur here. Further process steps such as bonding, welding, painting or assembly are made more difficult or prevented by them. The consequences include leaks or coating adhesion problems.
The methods we use depend on the requirements in the related subsequent processes. The measurement systems and methods cannot be compared with each other. Furthermore, for contaminating films there are no standards or standardised limits for the evaluation of the analysis results. Individual advice and the precise agreement of the goal of the analysis are therefore one of the basic prerequisites for success.
LOCAL AND INTEGRAL MEASUREMENT METHODS FOR CONTAMINATING FILMS:
To check whether a component is suitable for subsequent processes, we analyse it using chemical analytics with various methods and measured variables:
- Determination of the surface tension by means of test ink
- Detection of contaminating films by means of fluorescence measurement
- Quantification using gas chromatography (GC) with flame ionisation detector (FID)
- Identification and quantification using gas chromatography (GC) coupled to mass spectrometer (MS)
- Material identification using RAMAN and FT-IR spectroscopy
- Gravimetric assessment
Contaminated surfaces are more difficult to wet than clean surfaces. Good wettability is the basic prerequisite for coating with paints, printing inks or adhesives. A simple method for the measurement of the surface tension on a very wide range of materials is to use test inks. For this purpose, we apply test ink to the surface. If the lines remain stable, the surface is easy to wet. The surface of the substrate then corresponds as a minimum to the surface tension of the test ink. If the ink pulls together, the wettability of the substrate is lower than that of the test ink used. The procedure is then repeated with a test ink with a lower surface tension. The higher the value is for the surface tension, the cleaner the surface. The surface tension/surface energy is stated in mN/m.
Organic contaminating films such as greases, oils or wax fluoresce if they are excited using UV light. Materials that do not fluoresce can also be rendered visible by including fluorescing dyes as markers. In this way we can verify, quickly and without contact, the presence of organic substances on metallic surfaces. We only need an absolutely clean surface as a reference. The higher the fluorescence value measured, the thicker the filmic contamination. The measured value is stated in RFU (Relative Fluorescence Units).
VERIFICATION AND IDENTIFICATION USING RAMAN AND FT-IR SPECTROSCOPY
Chemical contaminating films such as oils, greases, cooling lubricants, cleaning agents, preservatives, solvents and more can be analysed directly on the surface of the component using the spectroscopic analysis methods RAMAN and FT-IR. These measurement and analysis methods provide qualitative measured values. This means we can verify the presence of contamination and identify it unambiguously. Reference databases are required for these near-surface analysis methods.
VERIFICATION AND QUANTIFICATION USING GAS CHROMATOGRAPHY (GC-FID)
For this purpose we extract the contamination from the component using a suitable solvent and analyse the organic residues released using gas chromatography coupled with a flame ionisation detector (GC-FID). As a result we obtain the sum of the soluble organic contamination in mg/component or in mg/m².
identification and quantification using gas chromatography (GC-MS)
For this purpose we extract the contamination from the component using a suitable solvent and analyse the organic residues released using gas chromatography coupled with a mass spectrometer (GC-MS). As a result we obtain the sum of the soluble organic contamination in mg/component or in mg/m² as well as the identification of the individual components.
Here we extract the contamination from the component using a suitable solvent and separate the solid residues using filtration. After the evaporation of the solvent, we determine the mass of the soluble residues gravimetrically using an analytical balance. The result is stated in mg/component or in mg/m².