ISO/DIS 8504-6

ISO/TC 35/SC 12

Secretariat: BSI

Date: 2025-12-08

Preparation of steel substrates before application of paints and related products — Surface preparation methods —

Part 6:
Laser cleaning

DIS stage

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Contents

Foreword

Introduction

Scope

Normative references

Terms and definitions

Health and Safety

Methods

General

Pulsed laser cleaning

continuous wavelaser cleaning

Procedure

Preparation before laser cleaning

During laser cleaning

After laser cleaning

(informative) Components

Bibliography

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

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This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee SC 12, Preparation of steel substrates before application of paints and related products.

A list of all parts in the ISO 8504 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

The performance of protective coatings of paint and related products applied to steel is significantly affected by the state of the steel surface immediately before painting. The principal factors that are known to influence this performance are:

• the presence of rust and mill scale;
• the presence of existing coating;
• the presence of surface contaminants, including salts, dust, oils and greases;
• the surface profile.

The ISO 8501 series, the ISO 8502 series and the ISO 8503 series provide methods for assessing these factors, while the ISO 8504 series provides guidance on the preparation methods that are available for cleaning steel substrates, indicating the capabilities of each in attaining the specified levels of cleanliness.

This document describes laser cleaning, which is an effective method for surface preparation.

laser cleaning technology is still developing, and the quality requirements for laser cleaning are relatively complex. In the future, some requirements will need to be individually agreed upon with the user, such as:

• Relevant requirements for laser protection in special application scenarios.
• Surface cleaning requirements proposed for typical products.
• Surface imperfections should be considered before surface preparation and coating application.

ISO 8504 series does not contain recommendations for the protective coating system to be applied to the steel surface. ISO 8504 series does not contain recommendations on surface quality requirements for specific situations even though surface quality can have a direct influence on the choice of protective coating and its performance. Such recommendations are found in other documents such as national standards and codes of practice.

Preparation of steel substrates before application of paints and related products — Surface preparation methods —

Part 6:
Laser cleaning

This document specifies laser cleaning methods for the preparation of steel surfaces before coating with paints and related products. It provides information on the effectiveness of the individual methods and their fields of application. It describes the equipment and the procedures to be followed.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 8502-3, Preparation of steel substrates before application of paints and related products — Tests for the assessment of surface cleanliness — Part 3: Assessment of dust on steel surfaces prepared for painting (pressure-sensitive tape method)

ISO 19818-1, Eye and face protection — Protection against laser radiation — Part 1: Requirements and test methods

IEC 60825-1:2014, Safety of laser products - Part 1: Equipment classification and requirements

EN 14387, Respiratory protective devices - Gas filter(s) and combined filter(s) - Requirements, testing, marking

ISO 11553 (all parts), Safety of machinery — Laser processing machines

For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

laser cleaning

removal of rust, paint, mill scale, contaminants and other unwanted materials from the substrates using a laser beam

pulsed laser

laser which emits radiation in the form of a single pulse or a train of pulses where the duration of a pulse is less than 0,25 s

[SOURCE: ISO 11145:2018, 3.19.3]

continuous wave

laser continuously emitting radiation over periods of time greater than or equal to 0,25 s

Note 1 to entry: This definition is consistent with the definition of "continuous wave (3.3)"in IEC 60825-1:2014 "safety of laser products - equipment classification, requirements, and user guide".

[SOURCE: ISO 11145:2018, 3.19.2]

laser power

power of the laser beam at each defined process operation

Note 1 to entry: laser power (3.4) is expressed in watts.

Note 2 to entry: The laser power (3.4) can be different when producing the contour (outline) of the test specimen and when hatching the part.

[SOURCE: ISO/ASTM 52936-1:2023, 3.2]

The procedures described in this document shall be carried out by suitably trained and/or supervised personnel. The procedures used in these methods can be injurious to health if adequate precautions are not taken. Attention is drawn in the text to certain specific hazards. This document refers only to the technical suitability of the methods and does not absolve the user from statutory obligations relating to health and safety.

WARNING — Equipment, materials and procedures for surface preparation can be hazardous. It is important to ensure that adequate instructions are given and that all precautions are exercised. Only trained or qualified operators should use the equipment.

Before activating the laser beam, all person in the work area shall wear appropriate personal protective equipment, consisting of specific laser safety eyewear at a minimum (ISO 19818-1), to provide protection against dust and fumes, laser cleaning equipment should be equipped with a dust removal unit, and operators should wear personal protective equipment respiratory masks as appropriate according EN 14387.

The extent of the work area shall be assessed to determine the minimal laser-controlled area and process safety requirements. The laser work area shall have laser safety curtains, or other suitable physical barriers, laser safety signage posted, and other controls as required to prevent exposure to the laser beam or vapours from the laser cleaning process to personnel or damage to property (ISO 11553 (all parts)).

The contract documents describe the final condition of the substrate. Depending on the initial condition of the area and the materials intended to be cleaned, the method to achieve the preparation can be pulsed laser cleaning and continuous wavelaser cleaning.The methods of laser cleaning are based on the capabilities of the equipment and its components. Laser type, laser power, cleaning speed, laser spot diameter, eetc.; all interact in determining what will be removed. laser cleaning can be used for paint and/or rust removal. The laser cleaning process shall be controlled to prevent metallurgical changes.

Multiple laser technologies as described below can be used in combination.

laser cleaning equipment can be handheld or non-handheld and operated with an open or closed beam. The general components of laser cleaning equipment can be found in Annex A.

Pulsed lasers deliver energy in short, intense pulses thereby generating very high energy densities in the range of up to several hundred MW/cm², even if their average power is similar to a CW laser.

Typical average laser power levels range from 10 W to 1 kW. 1 kW systems are commonly used for most industrial applications balancing precision and speed. For industrially common near infrared (NIR) systems, typical single pulse peak levels cover the range ~10 kW to ~10 MW depending on pulse energy (~10 mJ to ~100 mJ) and pulse duration (~10 ns to ~<200 ns).

The pulse duration is decisive for the ablation mechanism, as it defines the speed and duration of the energy input. Typically, the pulse duration is short, thus, heat accumulation and transfer into the substrate is limited.

The pulse repetition rate can be varying from several Hz up to several MHz. Q-switched lasers have pulse durations in nanosecond range. Mode locking lasers can achieve pulse duration in femtoseconds and even picoseconds. This requires high speed scanners to distribute the pulses to the surface.

In surface treatment of steel before painting, pulsed lasers are effective for removing contaminants, creating micro-textures, and modifying surface properties without significantly heating the bulk material, thus enhancing coating adhesion and durability.

continuous wave (CW) lasers deliver a continuous laser beam without complex pulsing mechanisms and can maintain very high average power outputs. For CW lasers, typically systems with laser power levels <1 kW are used for most applications and power levels up to 10 kW are common in situations where heat management is less crucial. Especially for handheld laser systems very long focal lengths are employed to avoid to high heat development. The size of the spot is often large and the intensity is mostly low, leading to higher degree of burning instead of vaporization. This can lead to higher amount of unburned gaseous emissions, as well as increased risk of ignition. A longer working distance to workpiece is often possible.

For the industrial flexible operation the fibre based sources with infrared wavelength are used, thus the laser beam can be guided through the fibre cable to the optic.

Typically, heat accumulation and transfer into the substrate are significantly higher than for pulsed lasers, which may be beneficial for contaminants that need sustained heat to be removed such as thick corrosion and scale layers.

Generally, for applications, where heat influx is less of a problem, CW lasers allow for fast processing of large areas by utilizing (preferably) automated scanning mechanisms. CW lasers are particularly useful for surface treatment of steel surfaces before painting, as the continuous energy delivery enables precise cleaning, oxidation removal, and microstructural modification, improving paint adhesion and corrosion resistance.

Check for the presence of oil, grease, salts or similar contaminants. Remove any deposits of these using a degreasing or washing procedure and check whether any other contaminants are still present. Mask off areas not to be laser-cleaned.

Suitable methods for removal of contaminants are described in ISO 12944-4.

laser cleaning parameters (power, scanning speed, overlap, etc.) shall be optimized to achieve the specified surface condition without altering the substrate integrity.

NOTE a previous present surface profile can be exposed if all coating or coating material is removed.

The degree of cleanliness to be achieved by laser cleaning shall be agreed upfront between the interested parties.

Select the appropriate laser cleaning method in Clause 5 which will produce the specified preparation level.

Select the appropriate laser cleaning equipment that fits the properties of the workplace and the productivity requirement.

After laser cleaning, remove loosely adhering dust and debris from the surface by vacuum cleaning, by brushing or by use of compressed air free of oil and moisture. The level of residual dust can be verified according to ISO 8502-3. Assess all cleaned surfaces to ensure they conform to the agreed degree of cleanliness.

Work performed under this document is subject to assessment by a representative of the party responsible for establishing the requirements. Work areas shall be accessible to the assessor. The procedure and time of the assessment shall be agreed by all parties involved.

Immediately prior to coating application, the entire substrate shall conform with the degree of cleaning as agreed by all parties involved. For testing methods, see the ISO 8502 (all parts).

1. 
   (informative)
   
   Components
   1. General

The laser cleaning equipment is typically composed of a laser source, beam delivery system, laser cleaning head, laser beam and vacuum system, as seen in Figure A.1.

Key

1 laser source

2 beam delivery system

3 laser cleaning head

4 laser beam

5 vacuum system

6 surface to be treated

Figure A.1 — Equipment composition

When selecting a laser cleaning equipment, the following factors are taken into account:

• The equipment can be a pulsed, or continuous wave laser
• The equipment can be either handheld or not
• The equipment can be either mobile or stationary
• The equipment can be remotely or manually controlled
• The equipment can be adaptable to the object to be cleaned
• The equipment can be open beam or closed beam
• The equipment should be used with a vacuum system, integrated or not
• Point extraction: Extraction of the vast majority of the fumes and dust caused by the laser removal action is required using the vacuum system. The efficiency of the laser and the safety of the operator is impacted by the presence of the particulates created by the laser cleaning. The point extraction shall be performed either by stand alone point extraction close to the laser beam impact area or by a attached integrated suction head mounted to a vacuum system.
• The vacuum system should be equipped with an adequate filtration set.
  1. Laser source

Radiation source that generates a coherent, monochromatic and very powerful beam of light in the range of ultraviolet, visible or infrared wavelengths. Whether it is a CO₂ laser, fibre laser, yttrium aluminium garnet (YAG) laser, or a hybrid of multiple laser types, the output power, beam mode, and scanning speed shall meet the technical requirements of laser cleaning.

• 1. Beam delivery system

The beam delivery can exist of several components. Typically it includes an optical fibre, cooling (depending on the system used this can be either liquid cooling or air cooling), other electrical components establishing the interface between the laser source and the laser cleaning head.

• 1. laser cleaning head

The laser cleaning head is an important component of the laser cleaning system, which is used to focus and direct the laser beam to the surface to be cleaned. The laser beam emerges through the laser cleaning head, which contains an optical assembly typically composed of lenses, mirrors and scanners. The lenses enable the focusing of the laser beam and allow control of the energy density at the surface to be cleaned. In some cases, an air knife can be added or integrated to the system to avoid dust and fumes settlement on the outer lens or protective glass.

• 1. Vacuum system

During laser cleaning, dust and fumes are removed or collected via a vacuum system which can extract dust and fumes and capture particulates.

Bibliography

[1] ISO 12944-4, Paints and varnishes — Corrosion protection of steel structures by protective paint systems — Part 4: Types of surface and surface preparation

[2] ISO 8502 (all parts), Preparation of steel substrates before application of paints and related products — Tests for the assessment of surface cleanliness