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Cause analysis of chamber crack in high temperature furnace

Release time:2020-06-11  Number of views:3813

In the field of ultra-high temperature, high-quality high temperature furnace refractory layer is made of alumina polycrystalline fiber products. In high-end and high-quality laboratory equipment, box type furnace and tube type furnace, most of them use this material.

Using the "colloidal method" process, the soluble aluminum, silicon salt made of colloidal with a certain viscosity, by spinning fiber preparation of high purity alumina fiber, and then through dehydration, drying and high temperature heat treatment crystallization process, into γ-Al2O3 alumina polycrystalline fiber, the main crystalline phase is mainly corundum phase and a small amount of mullite phase, Chemical composition is Al2O395%+ SiO25%, classification temperature up to 1700℃, the dissolution point up to 1840℃, fiber diameter of 3-5um, monofilm length of 10-150mm fiber, made of high temperature furnace by vacuum molding.

Alumina polycrystalline fiber products as Cenozoic refractories, is a kind of high performance inorganic fiber, compared with other refractory materials, its thermal conductivity is small, high chemical stability, easy to composite with ceramics, metals and other matrix, is widely used as insulation refractory materials. It has good chemical stability, can be used in weak acidic environment, oxidation atmosphere, reduction atmosphere and vacuum conditions, also has a certain corrosion resistance to weak alkaline environment, but easy to lead vapor and vanadium pentoxide and strong acid and base erosion.

Fiber products under the action of repeated high temperature rising and cooling stress, high temperature will lead to shrinkage of fiber diameter, fiber products surface will appear slight cracks, is a normal phenomenon. In the design process of high temperature furnace, the refractory part and the insulation part are made of composite material, and a small amount of cracks on the surface of the internal heat resistant layer will not affect its insulation performance. Large high temperature equipment generally do block installation or artificial sawing expansion joint, in order to reduce irregular cracks.

1. When there are cracks ≦1mm or so, it can be ignored;
2. When the crack of 1~3mm appears, the repair agent can be used to repair appropriately.
The method of using the repair agent
Stir the sediment of the repair mixture evenly
Wet the cracked part with a brush dipped in the repair agent.
Take proper amount of thickened repair agent, apply it into the cracked part and smooth it out.
Dry in the shade for 6 to 8 hours and heat up.
* When the repair agent becomes hard, it can be moistened and softened with water

3. When cracks occur after ≧5mm, the shrinkage of fiber in non-refractory layer is generally caused by the erosion of volatiles of sintered materials (strong acid and alkali, or lead vapor and vanadium pentaoxide). In actual use cases, some components added in zirconia products of sintered materials and volatiles of dyes of customers are easy to cause cracking of fiber products when caking. Customers are required to put similar materials in the oven before sintering at ≧170℃ to fully bake ≧40 minutes, so that corrosive volatile matter fully volatilized, which has extended the service life of the furnace and heating elements. Refractories should be replaced if the furnace cracks seriously.