1. Misconceptions regarding the operating temperature of ceramic fibre paper:
The labelling of temperature parameters is highly confusing, with terms such as ‘operating temperature’, ‘maximum operating temperature’, ‘limit temperature’, ‘classification temperature’ and ‘long-term operating temperature’ being used interchangeably. In reality, the operating temperature of ceramic fibre paper is not only related to the chemical composition of the material, but is also closely linked to the operating atmosphere, fuel and environmental conditions. For example: if the maximum temperature at which a given material retains its basic properties in a standard atmosphere within a laboratory resistance furnace is 1260°C, the maximum operating temperature in a moderately to strongly reducing atmosphere will decrease by 100–180°C; in an environment where heavy fuel oil is burned, the operating temperature will be even lower due to the corrosive effects of elements such as sulphur and phosphorus on the ceramic fibre paper. The operating temperature should be determined by designers, users and technical personnel from the ceramic fibre paper manufacturer, taking into account the fuel used, the environment and the heating regime, in order to select the appropriate material.
2. Misconceptions regarding the chemical composition of ceramic fibre paper:
Over many years of ceramic fibre paper application, it has often been observed that, although the actual temperature did not exceed the material’s operating temperature range, the fibre material still underwent shrinkage and pulverisation. Upon testing the chemical composition, it was found that Al₂O₃ met product requirements, whilst SiO₂ was below specification; furthermore, the content of impurities such as Fe₂O₃, CaO, MgO, Na₂O and K₂O was significantly above the permissible limits. These impurities are low-melting-point oxides; an excess of such oxides will lower the eutectic point of the ceramic fibre paper. If the content of impurities other than Al₂O₃ and SiO₂ reaches 3.5% or more, compared to keeping it below 1%, the actual operating temperature of the ceramic fibre paper will be reduced by more than 100°C. Therefore, when selecting ceramic fibre paper, we must not only test the Al₂O₃ content but also strictly control the levels of other impurities.
3. Misconceptions regarding the bulk density of ceramic fibre paper:
The fibres themselves consist of Al₂O₃ and SiO₂, and their heat capacity is essentially the same as that of refractory brick products. However, ceramic fibre products such as ceramic fibre boards and ceramic fibre blankets, due to the interwoven fibre method used, form a loose cellular structure, which significantly reduces the product’s bulk density and alters its thermal conductivity. The thermal conductivity of fibre products with a bulk density of 150–250 kg/m³ is approximately 20% of that of heavy-duty bricks with a bulk density of 2070 kg/m³; it is approximately 37–40% of that of lightweight bricks with a bulk density of 1300 kg/m³. For fibre products with a bulk density ranging from 150 to 250 kg/m³, the thermal conductivity gradually decreases as the bulk density increases, and heat loss also gradually decreases. However, as the bulk density increases, the performance of the loose cellular structure also deteriorates; when the bulk density exceeds 400 kg/m³, the thermal conductivity actually increases, whilst heat storage loss also rises, resulting in a reduction in overall energy efficiency. Therefore, a one-sided pursuit of excessively low or high bulk density is not advisable.
4. The influence of slag ball content in ceramic fibre paper:
The slag ball content in ceramic fibre paper is a key factor affecting bulk density. As the bulk density of slag balls ranges from 2,800 to 3,200 kg/m³, an excessive amount of slag balls in the ceramic fibre paper will reduce overall energy-saving performance and simultaneously harm the interests of users. Overseas, the content of slag balls with a particle size >0.25 mm is controlled at ≤5%, whereas in China, due to limitations in fibre manufacturing technology, the content is controlled at ≤15%. This means that nearly one-eighth of the ceramic fibre paper may consist of slag balls, which is double the content found overseas. Mu Yi employs a new multi-stage slag removal process to ensure that the slag ball content is controlled at ≤10%, achieving a high standard within the industry. Therefore, when determining the bulk density of ceramic fibre paper, the content of slag balls must be fully taken into account.
