General | 22. April 2021 Determination of the penetration behavior of sealers in thermally sprayed coatings (APS, HVOF, LDS, etc.)

Does the sealer work for your thermally sprayed coating? Have you ever asked yourself this question or do you still work according to the principle “no one has complained yet”?
We are not satisfied by selling sealers, we also want the sealers to work for you. For this reason, we offer our customers a functional proof of the penetration behavior of our sealers into their thermally sprayed coatings.

The sealer and thermal spray coating build a unit that ideally should be matched to each other. In practice attention is often paid to sealing as a “post-treatment method” (cf. DIN EN ISO 14924). Sealing is a comparatively simple process step which can have an huge impact on the service life of the entire coating system. The smallest pores or cracks in the thermal coatings can lead to premature failure even with extremely dense coatings such as HVOF (pore content < 1%). A good sealer is able to prevent such damage. The task for the sealer seems simple: penetrate into the pores and seal them permanently.

Unfortunately, the process is not so trivial in practice, and the large number of influencing parameters requires a much deeper understanding of the interaction between the sealer and the thermal spray layer. A decisive criterion for successful sealing is the penetration or sealing behavior of the sealer. In order to guarantee lasting protection in the event of layer erosion (machining, wear), the sealer must penetrate as deeply as possible into the layer. At the same time, however, it must also seal, which is often not conditional. Classical detection methods such as microscopy reach their limits here. If the penetration depth of the sealer can still be detected well, the optical evaluation does not provide any information about whether the sealer also seals.

But it is precisely this verification that is important when the function of the sealer-layer system is to be tested. In order to determine the functional penetration depth (depth to which the sealer-layer system is gas-tight), we carry out a specially developed test. Using the DIPERM measurement, we determine the functional penetration depth of the sealer in customer-specific layers and thus prove that the sealer works for the respective layer and provides real protection. We also use the DIPERM method to develop sealers and achieve optimizations for our customers. For example, for one customer we were able to develop a sealer for Al2O3 APS coatings that achieves a functional penetration depth of 80% and is applied to a hot component surface of +80°C. The sealer is also suitable for the application on a hot component surface. Compared to the previously used sealer, which had to be applied at room temperature, the production process could thus be shortened by approx. 12%. The result is an increase in efficiency combined with a proven protective effect. Quasi a double benefit for our customer. We would be pleased to support you in optimizing your “Siegler” post-treatment.

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