Why ceramic fiber modules are refractory and insulation

Update: 28-09-2020

As a new type of refractory and thermal insulation mate […]

As a new type of refractory and thermal insulation material, ceramic fiber modules have become popular since they were launched, and have now become one of the most popular materials. Many people can’t help but wonder, “The ceramic bowls we use for meals are very hot after serving hot rice. Why can ceramic fiber modules be fire-resistant and heat-preserving?” In fact, the fiber we use is not comparable to daily ceramics. Too much relationship refers to the general term for fibrous insulation materials with SiO2 and AL2O3 as the main components and with a refractoriness higher than 1580℃.

We can explain its fire resistance and heat preservation principle from the following two directions.

1. Poor heat transfer capacity of ceramic fiber modules

The ceramic fiber module does not have a clear directionality when it is interwoven. When heat is transferred, it is generally transferred along the fiber. Such non-directionality makes it impossible to transfer heat quickly. In addition, when the fiber is in contact with the hot surface, it is rarely in vertical contact, which makes it difficult for heat to transfer to the fiber. Third, the contact point of the fiber can reach 80%, which will further expand the thermal resistance of heat transfer. The fiber itself is opaque, heat rays cannot be transmitted in the fiber, and the area of ​​the fiber is small, and the received radiation is also less, so that the heat radiation is basically not transmitted on the fiber.

2. There is too much gas inside the ceramic fiber module and poor convective heat transfer

The individual fibers are intertwined to form many air cells, which are filled with still air. We all know that the heat transfer capacity of air is very poor, not to mention still air. These static gases have poor heat transfer effects on the one hand, and can also hinder the intrusion of hot air flow on the other hand.

The national standard density of ceramic fiber module is 220Kg/m3. As we all know, the good thermal insulation performance of ceramic fiber comes from its low thermal conductivity. The thermal conductivity of the ceramic fiber module decreases with the increase of the bulk density, but the extent of the decrease gradually decreases. When the density exceeds 400KG/M3, the thermal conductivity no longer decreases, and has a tendency to increase. However, the density limit of the ceramic fiber module is 260Kg/m3; this is because the ceramic fiber blanket is made of fiber cotton with a double-roll spinning process. The length of the fiber cotton is between 80-130 mm. Once it exceeds the limit of 260Kg/m3 Density, the fiber will break a lot, and the breakage rate is as high as 48%, which affects the product performance.

In practical applications, the density of the ceramic fiber module should be considered comprehensively according to the furnace type, temperature, combustion medium, and temperature rise requirements of the heat treatment furnace, but the reasonable density should be between 200-260Kg/m3, preferably 220Kg/m3 .


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