Can Lasers Replace Thermal Spray Masking Tapes and Grits?

Masking tapes have long been used to prevent specific areas from being spray coated or grit blasted. But did you know that lasers provide a faster and more reliable alternative that’s easier to automate?  

Laser technology can drastically improve how you manage your thermal spray process when treating localized areas.  

• Instead of using thermal spray tapes, you can coat the entire surface and then use laser cleaning to remove the coating from specific areas.
• You can replace grit blasting with laser texturing to prepare localized areas that need to be coated, eliminating grits and tapes from your process while preventing damage to the substrate. 

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What Is Thermal Spray Coating? 

Thermal spray coating is a surface treatment that improves properties such as thermal resistance, wear resistance, environmental protection, and corrosion resistance. There are several types of thermal sprays, including high velocity oxygen fuel (HVOF), plasma spray, arc spray, and flame spray.  

The process uses a powder or a wire feedstock that is heated until it melts or almost melts. The melted feedstock is propelled onto the surface that needs coating using a hot gas stream. To prevent damage that could be caused by a heat buildup, the substrate is cooled during the coating process. 

Keeping Areas Coat Free: Thermal Masking or Laser Cleaning? 

During the thermal spray coating process, certain areas need to be maintained coat free because they need to be perfectly clean for other applications like welding or assembly. While masking tapes are widely used to protect these areas, laser cleaning is a new technology that simplifies the process. 

Let’s go over the thermal masking and laser cleaning approaches to understand the difference. 

What is Thermal Spray Masking? 

Thermal masking is the process of applying a tape on a metal surface to prevent a specific area from being coated or blasted. Thermal spray masking tapes offer high-temperature resistance and superior abrasion resistance, allowing them to withstand harsh treatments like thermal spraying and abrasive blasting. 

In the following video, masking tapes are first used to protect specific areas from blasting and then from thermal spray coating. 

Disadvantages of Thermal Masking Tapes 

Thermal masking is a process that is slow, prone to error, and labor intensive.  

• You need to wait a long time after applying the tape (typically 12 to 24 hours) to obtain a better adhesion. This delays the time you can begin the metal finishing process.
• Most tapes are pressure sensitive and can fail if improper pressure is applied.
• The surface on which the tape is applied needs to be clean and dry for the tape to adhere properly. Oil, skin, dirt, and dust all decrease adhesion and may cause the tape to fail.
• Tapes need to be stored in a temperature and humidity-controlled location to ensure a good shelf life. They must also be used before their quality degrades. 

Different spray applications require different types of tapes, and the choices can be overwhelming: foil tapes, vinyl tapes, duct tapes, fiberglass cloth tapes with silicone adhesives, silicone rubber-coated glass cloth tapes, aluminum foil tapes, and the list goes on. The tapes also need to have the right width and length, and they are available as single-layered or multi-layered depending on the resistance needed. 

How Can Laser Cleaning Replace Thermal Masking? 

Laser cleaning can remove coatings from localized areas. A pulsed laser beam is repeatedly sent onto the surface to transfer high amounts of energy that heat up and vaporize the coating. As a result, you can apply the coating to the entire part, then remove it from the desired areas. You no longer need to mask surfaces before coating. 

It’s important to note that a laser fume extractor is needed to manage dust and fumes generated in the process. 

In the following video, laser cleaning is used to remove phosphate coating from assembly areas on pinions. The laser process is the same when removing a thermal spray coating. 

Laser cleaning offers several benefits compared to thermal masking: 

• Easier to automate: While masking is typically performed manually, laser cleaning uses fiber lasers that are easy to automate. This allows you to integrate the whole process inline.
• Faster: Laser cleaning is ultra-fast and can keep up with high-volume production lines, making it possible to reach new levels in terms of production.
• Better precision and quality: While thermal masking has many pitfalls that can lead to quality issues, laser cleaning benefits from the accuracy and consistency of a computer-programmed laser beam backed up by high-precision optical components.
• Lower maintenance: Laser cleaning is a non-contact process and therefore suffers from no mechanical wear. Laserax also uses high-quality components to make sure our lasers operate with minimal maintenance in harsh conditions. This ensures that the production line is always running. 

Preparing Surfaces for Thermal Spraying: Grit Blasting or Laser Texturing? 

Before applying a thermal spray, the surface to be coated needs to be prepared to achieve a desirable texture and roughness. These properties will help obtain a strong bond between the coating and substrate. 

Grit Blasting 

This process is often used to prepare surfaces for the thermal spray. It is ideal to prepare large surfaces, as large areas can be covered quickly by the blasting media. Grit blasting is imprecise, however, and cannot be used to texture localized areas without resorting to high-abrasion-resistance masking tapes. This makes the whole process cumbersome: 

• It includes countless consumables, including grits and tapes
• The equipment breaks down quickly
• The substrate is potentially damaged in the process 

Laser Texturing 

When specific, localized areas need to be prepared for a thermal spray, laser texturing is a better solution. 

It uses a laser beam to etch specific patterns on the surface, generating a texture and roughness that create a stronger bond with the coating. Unlike grit blasting, laser texturing can be programmed to texture a precise area, which means masking tapes are no longer required. 

While the blasting media becomes worn down over time, which affects the consistency of the process, laser texturing creates a more consistent texture. Laser texturing can also follow curved shapes and generate a consistent texture over those shapes. 

In addition to eliminating the need for masking tapes, laser texturing is more cost effective in the long term for several reasons: 

• Reduced maintenance
• Fewer spare parts
• Longer operating life
• No damage to the surface (such as microcracks and inclusions) 

Laser Technology, A Valuable Alternative to Masking Applications 

Laser technology offers a valuable alternative to grit and thermal masking applications. With their high precision and control, lasers can make life simpler for manufacturers who can speed up their manufacturing process while diminishing the number of consumables, manual tasks, and manual errors. 

If you have a project that could benefit from laser cleaning or laser texturing, contact a Laserax expert today. 

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Alex Fraser

With a PhD in Laser Processing, Alex is one of the two laser experts who founded Laserax. He is now Vice President and Chief Technology Officer, overseeing the team that develops laser processes for laser marking, cleaning, texturing, and welding applications.

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