(Abstracts from “Bauteilreinigung“) The classification of cleaning processes as subcategory of manufacturing processes can be done according to the draft German standard 8592. In this draft a hierarchical structure of the cleaning processes alongside the impact principle is proposed. Hierarchical levels are represented by a multi digit number. Initially “cleaning” is integrated into the structure of DIN 8580 as a subcategory of the manufacturing process “separating” receiving the order number 3.6. The next hierarchical level of the classification scheme states the physical impact principle of the cleaning processes. Whereby the blasting processes turn out to be problematic, as these processes combine the “mechanical” and the “jet” technique. Therefore the blasting processes were put into a special subgroup.

Draft DIN 8592 neither considers processes which combine several physical impact principles nor can newly developed special processes be integrated into the scheme. Also the proposed gradation is not detailed enough to clearly differentiate single processes from one another. E.g. diluting under 3641 covers the processes: steam degreasing, immersion cleaning, wiping, brushing, drum cleaning, spray cleaning, flooding, boiling and ultrasound supported solvent cleaning.

Standards providing clear guidance for the actual cleaning exist only for a limited number of processes. Only processes which have been applied for a long time have been standardized like: high pressure water blasting (DIN EN 1829), cleaning with alkaline agents (DIN 65079), solvent cleaning (DIN 65078, LN 29740), blasting (DIN 65468), electrolytic cleaning (DIN 65473) and flame blasting (DIN 32539). In recent years mainly in USA newly developed processes have not been introduced into European standards.

Degrees of cleanliness, which can be achieved by the single cleaning processes have only be standardized in very limited cases, e.g. photographic pattern for comparison of surface preparation degrees preceding coating in steel construction (DIN 55928, ISO 8501-8504) In addition some standards recommend different analytical methods, like e.g. the water break test, for the determination of a sufficient removal of fats. However these approaches cannot as such be applied to other cases.

As concerns the area of cleaning equipment mainly the safety aspects of this machinery shall be standardized without referring to utilization and application limits of the described equipment (pr EN 12921).

Summarizing it has to be noted, that the German and European standardization only give limited assistance when trying to select a specific cleaning process according to the actual workshop requirements.

Overview over the main standards regarding parts cleaning (2001):

DIN EN 1829 (1995, 2008)
Title: High pressure cleaner, high pressure water blast equipment, safety requirements
Content: Contains definitions and safety requirements for high pressure cleaning equipment
VDI/VDE 2420 (1981)
Title: Metal surface treatment in precision engineering – overview
Content: Uncomplete overview over the most common cleaning methods and solvents.
ISO 8501-8504 (1988 – 2000)
Title: Preparation of steel surfaces bfore applying coatings
Content: Describes procedures for corrosion protection of steel structures and lays down surface preparation degrees by comparable photo samples.
DIN 8592 (2003)
Title: Manufacturing procedure cleaning: Ranking, classification, terms
Content: Relates cleaning to manufacturing procedure “cutting” per DIN 8580 and states further subgroups.
DIN EN 12921 (2005)
Title: Machines for surface cleaning and preparation of industrial products
Content: Contains definitions of terms and safety requirements for cleaning plants using aqueous, flammable and halogenated cleaners.
LN 29740 (1966)
Title: Manufacturing guidelines for the metal parts steam degreasing with perchloroethylen.
Content: Gives a rough overview over steam degreasing and the necessary procedure parameters.
DIN 32539 (1998)
Title: Flame blasting of steel and concrete surfaces
Content: Contains a detailed description of the procedure, the applicable plants and of the flow of work.
DIN 55928 (1991)
Title: Corrosion protection of steel structures by coating and plating.
Content: Gives surface preparation degrees for corrosion protection of steel structures by comparable photo samples.
DIN 58747 (1982)
Title: Manufacturing of optical products: Ultrasound plants, area measurements for cleaning racks and containers
Content: Lays down the size of containers and the measurements of cleaning racks for the ultrasound cleaning of optical components.
DIN 65078 (1988)
Title: Aerospace: Cleaning with organic surfactants
Content: Gives a rough overview over cleaning procedures and related legal requirements.
DIN 65079 (1987)
Title: Aerospace: Cleaning of metal surface with alkaline agents
Content: Gives a rough overview over work flow realted to alkaline cleaning.
DIN 65468 (1991)
Title: Aerospace: Blasting abrasive, non-abrasive
Content: Gives a rough overview over blasting methods and related work flow.
DIN 65473 (1991)
Title: Aerospace: Electrolytic degreasing and cleaning
Content: Gives an overview over work flow and procedure parameter for electrolytic cleaning.
New: VDA 19, ISO 16232
Title: Automobile industry: Cleanliness specifications for function relevant automobilte components
Content: Description of procedures to check the compliance with the cleanliness specifications

Definition of degrees of cleanliness

A classification of the degree of soiling or cleanliness is not provided by the German or European standards. Only for surface preparation degrees for steel structures there is an existing standard (DIN 55928). But this definition cannot be applied in general to the cleaning of components. The US American standards give at least approaches to the definition of degrees of cleanliness and related cleaning methods.
The American ASTM (American Society for Testing and Materials) lays down compulsory test methods in many areas, which are meant to probe the fitness of a cleaning procedure for a given purpose. In most cases not the cleanliness of a component is tested but rather as to whether the subsequent process (e.g. coating, painting or gluing) can be successfully fulfilled. A quantitative cleanliness standard is applied at the US military: The American military standard MIL-STD 1246C contains an approach relating to the amount of soiling of a given type on a defined surface area or in a defined volume. The units depend on the type of dirts (e.g. number of particles, mass or covered area) and are given as follows:


X: Numerical particle cleanliness degree according to a table, gives the number of inorganic particles per surface unit
Y: Cleanliness description for NVR (non volatile residue) according to a table in mass per area unit, resp. mass per volume unit
Z: Alternative or additional degrees of cleanliness according to one or more elements of the following list in the given units
PAC: Covered area of component by dirt in percent
PC: Number of particles independed of the table for particle cleanliness
CVCM: Gathered volatile substances according to ASTM E595
VCM: Volatile substances, determined different from ASTM E595, with statement of test method
NTU: Nephelometric cloudiness, units as per table, for liquids
TML: Total loss of mass according to ASTM E595

The test methods for the determination of the degree of cleanliness are compulsory. This standard and the related degrees of cleanliness are based on very high requirements as they are needed for, among others, aeronautics. To apply these standards in ordinary manufacturing cannot be recommended because of the necessary expensive test methods.

Test- and analytical methods:

Fast test for visible dirt

Procedure Principle Kind of information
Visual Test Assessment of cleanliness/spots on surface subjective decision: spot free or not

Fast tests for grease/oil

Water Break Test Makes changes in the wetting ability of metal surfaces visible Shows hydrophobic dirts (oil/grease)
Atomizer Mist Test Makes changes in the wetting ability of metal surfaces visible Shows hydrophobic dirts (oil/grease)
Nigrosin Test Makes changes in the wetting ability of metal surfaces visible Shows hydrophobic dirts (oil/grease)
Solvent Red Test Makes changes in the wetting ability of metal surfaces visible Shows hydrophobic dirts (oil/grease)
Test Inks Makes changes in the wetting ability of metal surfaces visible Surface tension
Contact Angle Test Makes changes in the wetting ability of metal surfaces visible Surface energy
UV-Test Makes oils visible via fluorescence in UV radiation fluoresz. residue

Fast test for pigmented dirt

Wipe test Makes particles visible Grey blur on white cloth
Tape-Test Makes particles visible Number and size of particles
Removal method (Ablöseverfahren) Makes particles visible Number and size of particles

Detection of passive layers

Copper SulfateTest Passive layers prevent a copper coating in copper sulphate solution Reactivity
Berlin-Blue-Test Passive layers prevent blue spots in Hexacyanoferrate(3)- solution (K3Fe(CN)6) Reactivity
Anodic Polarisation Applying a voltage or a current allows conclusions concerning cleanliness Reactivity

Quantitative test methods

Gravimetric Test Determination of weight difference or removal of dirt and weighing of the added dirt to a solvent Mass of dirt
Optical Particle Counter Counting of dissolved particles in a shining through light test cell Number and size of particles
Determination of carbon by oxidation Incineration of hydro carbon chains and measuring of C-content Mass of C- containing dirt

Surface analytic using instruments

Infrared Spektroscopy (IR,IR-RA) Detection of mineral oil hydrocarbons on surfaces Amount of hydro carbons
Removal method according to DIN 38409 Detection of hydro carbons in removed medium Amount of hydro carbons
Glow Discharge Spektroscopy (GDS) Element-analysis in depth of thick layers Composition
Energy Dispersive X-Ray Analyzer (EDXA) Element-analysis in depth of thick layers Composition
Scanning Electron Microscopy (XPS, SIMS, REM, AES) qualitative and quantitative analysis of thin (nm-range) layers Amount and composition
Atomic Force Microscopy (AFM) Surface topography Coarseness indication