BS EN ISO 28763:2019 pdf download – Vitreous and porcelain enamels — Regenerative, enamelled and packed panels for air-gas and gas-gas heat exchangers — Specifications
5.6 Thermal-shock resistance
If required by the enameller, the thermal-shock resistance shall be determined in accordance with Annex A at a test temperature of 350 °C on at least three test specimens prepared in accordance with ISO 28764. After testing five times at the test temperature, the test specimens shall show no damage. 5.7 Adherence The adherence shall be determined in accordance with EN 10209:2013, Annex C, using test specimens with a known pickling speed (see 4.5) prepared in accordance with ISO 28764. The method of pre-treatment, application and firing of the enamel shall be described.
6 Characteristics of the enamel coating
6.1 Adherence Test specimens for the determination of adherence shall be prepared in accordance with ISO 28764 and shall be pre-treated and enamelled under the same conditions as for the production of the heat exchanger panels. When determined in accordance with EN 10209:2013, Annex C, the adherence of the enamel shall be at least level 2. Tests shall be carried out on every pre-treated batch of panels.
6.2 Thickness The thickness shall be determined in accordance with ISO 2178. Adjustment of the measurement equipment shall be carried out on the profile concerned. Select a pair of panels, one corrugated and one undulated, and carry out measurements from point A to point I (see Figure 1) on the front and reverse faces of each panel. The measurement points shall be situated at least 50 mm from the edge. The measurement points on the corrugated panel shall be as indicated by numbers 1 and 2, and on the undulated panel as indicated by 3. This will result in 54 measurements from each pair of panels tested, 36 from the corrugated panel and 18 from the undulated panel. The mean of the 54 measurements shall be 150 µm ± 30 µm, unless a different mean is agreed between customer and supplier at the time of ordering. Along the area bordering the edges of the panels, the total thickness may measure up to 600 µm (i.e. two faces of 300 µm) plus the thickness of the substrate. If a different mean has been agreed between customer and supplier, the total enamel thickness along the area bordering the edge of the panel may vary, but should preferably be kept to a minimum to avoid chipping and spalling, etc. With the exception of edges and suspension holes, the application thickness beside the measurement point (such as on both sides of the notches of the corrugation) shall nowhere fall below 80 µm. Measurements other than those at the points indicated shall be carried out on cross sections using microscopy. The test shall be carried out on a 2 h cycle.
6.3 Thermal-shock resistance Test specimens for the determination of thermal-shock resistance shall be prepared in accordance with ISO 28764 and shall be pre-treated and enamelled under the same conditions as for the production of the heat exchanger. They shall have an enamel layer thickness of 150 µm ± 20 µm. The thermal-shock resistance shall be determined in accordance with Annex A at a test temperature of 350 °C on at least three test specimens. After testing five times at the test temperature, the test specimens shall show no damage. The test shall be carried out on every 5 000 kg of enamel frit.
6.4 Fundamental defects A 100 % visual examination of the enamelled surface shall be carried out for fundamental defects. The enamelled surface shall be free of fundamental defects such as blisters, burn-off, chipping, copperheads, cracking, crazing, fish scaling, spalling and tearing. The enamelled surface shall be visually examined from a minimum distance of 1,5 m and a maximum distance of 2,5 m either in natural light or in D65 artificial daylight in accordance with ISO 105-J03.BS EN ISO 28763 pdf download.