Ablación láser de recubrimientos de politetrafluoretileno (PTFE) aplicados sobre sustratos EN AW-5251

Abstract

RESUMEN:En la actualidad se utilizan diversos sistemas de eliminación de recubrimientos ricos en politetrafluoretileno (PTFE) sobre sustratos metálicos: granallado, pirólisis, procedimientos químicos y combinaciones de ellos, presentando todos ellos serias dificultades. En el presente trabajo se propone el uso de ablación láser para eliminar recubrimientos ricos en PTFE que previamente han sido aplicados en chapas de la aleación de aluminio magnesio EN AW-5251 H34. Para ello se han analizado los valores del límite elástico convencional, resistencia a la tracción, alargamiento porcentual, energía retenida por impacto y dureza. También se ha evaluado la distribución del tamaño de grano a nivel microestructural, el tamaño medio de grano ASTM y la distribución de partículas constituyentes. Los estudios se han efectuado en tres etapas sucesivas de aplicación y eliminación láser del recubrimiento. De forma paralela, se determinan y se comparan las propiedades con los mismos sustratos y etapas, pero eliminados por pirólisis. De la comparación de los resultados se concluye que la eliminación por ablación láser no produce un empobrecimiento añadido de las propiedades de los sustratos y que puede convertirse en una alternativa industrial a los procedimientos de eliminación tradicionales. ABSTRACT: Laser ablation of polytetrafluoroethylene (PTFE) coatings applied on EN AW-5251 substrates.Currently the most common used methods for removing PTFE rich coatings on metal substrates are: grinding, pyrolysis, chemical processes or a combination of these. While effective, all present serious difficulties. In this paper the use of laser ablation to remove PTFE rich coatings, which have previously been applied to sheets of aluminum magnesium alloy EN AW-5251 H34, is proposed. For this purpose the values of the yield strength, tensile strength, percent elongation, impact energy retained and hardness are analyzed. Equally, the grain size distribution at the microstructural level, the ASTM average grain size and distribution of constituent particles have been evaluated. Measurements were performed to three successive stages of application and laser coating removal. Moreover, the previous set of properties have been determined for the same substrates and stages but using pyrolysis to remove the coating. Comparison of the results shows that the removal by laser ablation does not cause any reduction in the properties of the substrates and may become an industrial alternative to traditional disposal procedures.

Experimental Study for the Stripping of PTFE Coatings on Al-Mg Substrates Using Dry Abrasive Materials

“…The best option to maximize the stripping rate in the proposed system are both white and brown corundum abrasives, applied at 0.6 MPa projection pressure showing stripping rate values between 0.6 and 0.7 cm 2 /s. These values are lower than those obtained by a two-step process (carbonization + sandblasting) in which rates of up to 1 to 1.2 cm 2 /s are reached [33].…”

“…Aluminium-magnesium substrates coated with PTFE suffer high thermal stress and their structure is recrystallized after the coating has cured. This recrystallized structure reduces hardness and mechanical properties [33]. It is, therefore, interesting to increase the hardness of the substrate to solve, at least partially, the loss of properties provoked by heat treatment.…”

Laser and pyrolysis removal of fluorinated ethylene propylene thin layers applied on EN AW-5251 aluminium substrates

“…However, the obtained removal rate has been low (150 cm 2 /min), compared with other processes and similar means [19,26,39]. Particularly, 4 times higher removal rates were achieved in a similar study carried out on PTFE [20], compared to the results obtained on FEP. Therefore, it is reasonable to think about a correlation between the thickness to eliminate and the removal rates, since, in the mentioned work, thickness was around 15-25 m for PTFE coatings, and for FEP coatings is among 50-60 m. Also, the incident laser radiation reflected by the coating surface is much lower for the PTFE coating of black colour (27-28%) than the corresponding value for the FEP coating of green colour (5%).…”

“…For example, a recent study has shown a comparison between laser and pyrolytic removal procedures of PTFE coatings on the EN-AW 5251 H34 alloy [20]. However, it is unknown if any of the cited advantages regarding the laser removal by ablation of other coatings may have the same level of success to the FEP-rich thin layers coatings.…”

Stripping of PFA Fluoropolymer Coatings Using a Nd:YAG Laser (Q-Switch) and an Yb Fiber Laser (CW)

“…As the temperature rises beyond certain limits in the coating, the fusion, sublimation, vaporization, combustion (carbonization), and decomposition occur by rupture of the joint. This is known as a photothermal or pyrolytic process [34]. On the other hand, the UV laser energy absorbed in the electronic excitation can be dissipated in the form of heat, leading to photothermal decomposition or causing the direct rupture of the coating’s molecular bond, which is classified as a photochemical or photolytic process.…”