Chemical paint removal or laser ablation: which secondary processes arise?

Wet chemical processes can also treat geometries that are difficult to reach and still have a firm place in many industries. Laser-based ablation, by contrast, works dry and can be controlled locally. Each of them creates different requirements for handling, post-processing, occupational safety, disposal and system integration.

This article therefore does not judge in general terms which process is “better”. It shows which secondary processes companies should take into account in a realistic comparison.

Why paint removal is more than the actual removal step

Processing a coating is often reduced to a single working step:

Paint gone.

For a production operation the task is more complex.

Before processing, the workpiece has to be made ready. After removal, a defined condition has to be reached so that the next process can start.

In between, different steps may be necessary depending on the process.

A comparison should therefore consider the complete route:

coated component → released surface for the next production step.

The technical basics of laser-based material removal are described in the article already published, How does laser ablation work when cleaning metal?, and are not derived again here.

Which process steps a wet chemical route can involve

Wet chemical surface treatment is not a single process.

Fraunhofer IFAM describes various applications such as cleaning, pickling, etching, activating and building up functional surfaces.

Depending on the specific chemical process, several stages may be required.

An industrial sequence can include, for example:

• Application or immersion
• a defined contact time
• Detaching the coating
• Rinsing
• Neutralising
• rinsing again
• Drying
• Inspection

Not every process has every one of these stages.

The decisive point is this: the actual chemical action can be only one part of a longer chain of equipment.

Fraunhofer FEP, for example, operates a system for wet chemical surface treatment with several cleaning baths, triple rinsing and hot-air drying. That is not a universal template for paint removal, but it shows very clearly that wet chemical processes can consist of several consecutive stages.

These times and systems have to be taken into account in a cost-effectiveness calculation.

What the laser process adds

Laser-based ablation is dry.

Fraunhofer IFAM names as an advantage of laser-based surface treatment that no chemical additives or abrasive media are required for the process itself.

That does not eliminate all secondary processes, however.

The following can be necessary or relevant:

• Positioning the component
• safe set-up of the laser area
• Process extraction
• Filter technology
• Inspection of the surface
• Replacing protective components
• possibly several passes

The removed material has to be captured with the laser as well.

A professional assessment should therefore not claim:

Chemistry has secondary processes, the laser does not.

The more accurate comparison is:

Both have secondary processes – but different ones.

Complex geometries as a strength of wet chemistry

A key advantage of wet chemical processes is that liquid can also reach areas that are difficult to access for an optical process.

Fraunhofer IFAM expressly points out that wet chemical pre-treatment can also treat internal cavities and complex or hard-to-reach structures that are not readily accessible to laser or plasma processes.

That is an important technical point.

A laser needs an optical line of sight to the point being processed.

A concealed internal surface behind a geometry cannot simply be reached through the material.

With complicated internal spaces, an immersion or flushing process can therefore have clear advantages.

When selecting a process, it should therefore be checked early on:

Is the entire surface to be treated optically accessible?

If not, this question can already be more important than the later speed.

Local ablation as a strength of the laser

The opposite case arises when it is precisely not the whole component that is to be treated.

Fraunhofer IFAM expressly describes laser-based coating removal as a locally and selectively controllable process.

For example:

• Contact surfaces
• Earthing points
• Welding zones
• Bonding areas
• local repair areas

A laser can be used for these.

This means the rest of the coating does not necessarily have to be treated as well.

With a chemical immersion process, such local limitation is considerably more difficult, or requires masking or other additional steps.

That can change the process chain considerably.

If only five per cent of the component surface has to be exposed, treating the whole surface may be unnecessary.

Rinsing and drying

In many wet chemical processes, the after-treatment with rinsing and drying stages plays an important part.

Residues of the chemicals used should not be left on the workpiece in an uncontrolled way.

In addition, the surface has to be dry before certain downstream processes.

In its automated wet chemical cleaning system, Fraunhofer FEP names several rinsing stages and hot-air drying, for example.

With a dry laser-based process, such water-related rinsing and drying steps are dispensed with in principle.

That can be of particular interest for inline applications.

Fraunhofer IFAM highlights exactly this aspect for laser and plasma processes: because the processing is dry, rinsing and drying phases can be dispensed with.

That does not automatically mean, however, that every laser-based process chain is shorter.

If the actual processing takes longer over a large area, the advantage can be used up again.

The whole cycle time therefore has to be compared.

Chemical logistics and storage

Chemical processes need suitable operating materials.

Depending on the chemical, this involves questions about:

• Procurement
• Storage
• Dosing
• Labelling
• personal protective equipment
• Changing baths
• Monitoring the concentration
• Disposal

Which requirements apply depends entirely on the substances used.

It would therefore be wrong to describe chemical paint removal in general terms as particularly dangerous or problematic.

Many industrial wet chemical processes have been safely established for decades.

The additional logistics nevertheless remain a real part of operations.

Fraunhofer IFAM also points out that regulatory requirements and the substitution of certain substances in various industries play a part in the further development of wet chemical processes.

For a long-term investment comparison, the availability of the intended chemical system can therefore also become relevant.

Extraction instead of blasting media

No chemical paint removal media are used in the laser process.

Instead, the removal produces particles and, where applicable, gaseous constituents from the coating being processed.

Suitable process extraction is therefore part of a professional system.

The DGUV guidance document FBHM-139 covers both optical hazards and the hazardous substances produced when cleaning and removing coatings with hand-held class 4 laser systems.

The extraction should be effective as close as possible to the point where they arise.

That in turn brings its own operating costs:

• Filters
• Maintenance
• Energy
• Checking the capture

A comparison must therefore not assess only the chemical handling that has been eliminated.

The necessary air-handling technology belongs on the other side of the calculation.

Waste water, residues and disposal

In wet chemical processes, spent media, rinsing liquids and dissolved or detached coating constituents can become part of the disposal question.

Which treatment is necessary depends on the chemicals used and the material removed.

With the laser, no rinsing water arises from the process itself.

The removed material nevertheless has to be captured and, depending on its composition, treated.

With old or unknown paints in particular, it should not simply be assumed that the residue is harmless.

The following therefore applies to both processes:

Before considering disposal, it must be known which coating is being removed.

A comparison of “waste versus no waste” is technically wrong.

What makes sense is:

Which waste streams arise, and in what quantity?

Series process or repair area?

The optimum technology can change completely with the quantity.

A permanently installed wet chemical process can work very efficiently with high quantities and recurring components.

Workpieces run through defined stages, and the secondary processes are spread over large quantities.

For a single local repair, the same outlay on equipment would hardly make sense.

Here a process that can be used locally can have advantages.

Conversely, complete large-area paint removal on a complicated three-dimensional component can be considerably more efficient by wet chemical means than optical processing of every single area.

The comparison should therefore always contain at least four variables:

• Quantity
• Geometry
• the proportion of the surface to be treated
• the required cycle time

Only from this does a sensible process architecture emerge.

Comparing occupational safety properly

No simplified comparison should be made for occupational safety either.

Chemical processes bring substance-specific hazards with them that arise from the particular product.

Laser processes bring hazards from optical radiation and from the material removed during processing.

With class 4 systems, suitable technical, organisational and personal protective measures are required.

That means:

A process is not automatically “safe” simply because no chemical is used.

The character of the hazard changes.

The operational decision should therefore be based on the risk assessment for the specific process.

How a process matrix is built

A simple process matrix can be helpful for the selection.

On one side are the requirements:

Geometry, surface area, quantity, cycle time, coating and the desired final condition.

On the other side are the process sequences.

For wet chemical paint removal, the following are assessed, for example:

• Contact time
• Rinsing
• Drying
• Chemical consumption
• System floor area
• Waste water or media treatment

For the laser:

• Processing time
• Extraction
• Safeguarding the workplace
• Filters
• Process control
• Accessibility

This makes it visible which technology actually causes fewer secondary processes for the specific operation.

When a combination can make sense

Industrial processes do not necessarily have to be either entirely wet chemical or entirely laser-based.

Fraunhofer IFAM works expressly on different surface processes and their combination.

A company could, for example, keep an established full-surface process for certain components and use a laser only where local functional areas have to be exposed afterwards.

Conversely, a laser-based process can prepare a surface locally while a subsequent wet chemical process fulfils a different function.

The optimum production chain therefore does not have to consist of only one technology.

Conclusion: secondary processes decide the real cost-effectiveness

Chemical paint removal or laser ablation: which secondary processes arise?

With the wet chemical process, contact time, rinsing, drying, media handling and disposal can be relevant.

With the laser process, safeguarding the workplace, extraction, filters and the actual optical processing time are added.

Wet chemical processes have clear advantages with complicated and internal geometries.

Laser-based ablation can play to its strength when a surface is to be processed locally and within sharp limits.

For a B2B decision, two theoretical removal speeds should therefore not be compared.

Whether chemical stripping or laser ablation is the cheaper solution is therefore not decided by the individual working step, but by the entire process chain from the coated component through to the surface that can be released for the next working step.

Sources

• Fraunhofer IFAM – Wet chemical surface treatment for better bonds and coatings — information on wet chemical cleaning, etching, pickling and hard-to-reach geometries.
• Fraunhofer IFAM – Surface decoating by laser — information on the selective and local removal of coatings.
• Fraunhofer FEP – CLAIRE — example of an automated wet chemical process chain with cleaning, rinsing and drying stages.
• DGUV – FBHM-139 “Strahlarbeiten – Reinigen und Entschichten mit Laserstrahlung” — edition 06/2024.

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