3 Construction plans

3.1 Surface treatment

Figure 3 Substrate surface treatment process

3.2 Thermal insulation coating

The repair process of thermal insulation coating is shown in Figure 4. The mesh cloth is rolled up and down to apply the first thermal insulation coating, so that the thermal insulation coating covers the surface of the material, and the thickness should not be too thick, just cover the glass fiber mesh completely; after the first thermal insulation coating is dry, scrape the second coating The thermal insulation coating is flush with the old thermal insulation layer; after the second thermal insulation coating dries, it will shrink relative to the surface of the old coating. Repaint and apply self-leveling thermal insulation coating on the outer surface to make the surface smooth and beautiful.

Figure 4 The construction process of thermal insulation coating repair

3.3 Protective surface coating

The construction process of the thermal insulation coating supporting the protective surface layer is shown in Figure 5. After the thermal insulation coating is completely dry, brush the surface with two layers of interface agent; after the interface agent is dried for 1 hour, apply a single layer of acrylic polyurethane topcoat with a dry film thickness of 30~50μm.

Figure 5 Construction process of the supporting protective surface layer of the thermal insulation coating

3.4 Repair effect detection

After the repair of the heating furnace insulation coating is completed, the surface is smooth and there is no obvious quality defect. The thickness of the thermal insulation coating was measured to be about 6 mm. Surface contact thermometer (TES-1310, Taiwan Taishi), bond strength tester (ZP-ZDLB10S, Shijiazhuang Zhuopu Technology Co., Ltd.) and thermal conductivity tester (TC3200, Xi'an Xiaxi Electronic Technology Co., Ltd.) were used to measure the coating. The outer surface temperature, bonding strength and thermal conductivity of the coating are shown in Table 6.

Table 6 Test results of thermal insulation effect of repaired thermal insulation coating

From the results in Table 6, it can be seen that compared with the original thermal insulation coating, the surface temperature after repair is reduced by 4 °C, the thermal conductivity of the self-developed aerogel thermal insulation coating is better, and the bonding strength of the coating is greatly improved (the test data are all 2 brand products have just been put into use, i.e. performance data at the beginning of service). It can improve the overall mechanical strength while ensuring the thermal insulation effect. The heat inside the heating furnace is transferred in three forms: solid heat conduction, air heat transfer and heat radiation, of which solid heat conduction and heat radiation account for a larger proportion. After the thermal insulation coating is applied on the furnace wall of the heating furnace, the SiO2 aerogel forms a nano-scale open-pore network structure with a high porosity and a pore size of <70nm (mean free path of molecular motion), thus blocking air heat convection conduction. In addition, the solid framework with very little content in the aerogel is also composed of nanoparticles, and its contact area is very small, so that the aerogel also has a very small solid-state thermal conductivity. The thermal radiation conduction of aerogel is mainly infrared thermal radiation in the region of 3-5 μm, which can effectively block infrared thermal radiation at room temperature. In order to further reduce the high-temperature infrared heat radiation, metal oxides with reflection or scattering effects are added, and the absorbed heat energy is converted into far-infrared electromagnetic waves with its higher reflectivity or scattering rate, so that the heat of the furnace wall is rapidly radiated to the furnace, and at the same time The heat loss to the outside of the furnace wall is reduced, and the thermal efficiency is improved. During the film-forming process, the fibers can form an overlapping network structure with the polymer chains. This network structure can reduce the film-forming shrinkage and the expansion and contraction caused by the temperature difference, so that the coating has good stability. and bond strength to ensure that the coating will not crack when applied to a certain thickness each time.

4 Conclusion

The self-developed silica aerogel thermal insulation coating is suitable for the thermal insulation repair of the surface of the heating furnace, which can significantly reduce the temperature of the furnace wall, effectively reduce the heat dissipation loss of the outer wall, and improve the thermal efficiency of the heating furnace. The thermal insulation effect of aerogel thermal insulation coating is better, and the mechanical strength of thermal insulation coating is improved while ensuring thermal insulation effect; the surface of thermal insulation coating is designed with interface agent and protective surface layer protection scheme, which can improve the water resistance and salt spray resistance of the supporting system performance, reducing the risk of corrosion under insulation.