How Is Calcium Silicate Insulation Manufactured?
Calcium silicate insulation is manufactured through a hydrothermal process that transforms raw lime and silica into xonotlite crystals under high-pressure steam. The process has four main stages, each critical to the final product properties.
Step 1: Raw Material Preparation
High-purity calcareous material (quicklime, CaO) and siliceous material (silica flour or diatomaceous earth, SiO&sub2;) are precisely weighed and mixed with water at a controlled CaO/SiO&sub2; molar ratio of 0.85 to 1.00. This ratio is critical -- it determines whether the final crystal phase is tobermorite or xonotlite. Synthetic reinforcing fibers (alkali-resistant glass fibers or carbon fibers) are dispersed into the slurry at this stage. No asbestos is used.
Step 2: Gel Reaction and Filter Pressing
The slurry is transferred to 30m³ reaction kettles where it is heated to 80-230°C under agitation. The lime and silica react to form a tobermorite-gel precursor. This gel slurry is then pumped to 400-ton vacuum filter presses where excess water is removed under pressure. The filter pressing pressure directly controls the final board density -- higher pressure removes more water and produces higher-density boards. The pressed cake is cut into the desired board or pipe section dimensions while still in a semi-plastic state.
Step 3: Autoclave Curing
The shaped products are loaded onto kiln cars and moved into industrial autoclaves. Here they are exposed to saturated steam at 190-220°C and 12-18 bar pressure for 5-8 hours. Under these hydrothermal conditions, the tobermorite-gel precursor dissolves and recrystallizes as interlocking needle-like xonotlite crystals (6CaO·6SiO&sub2;·H&sub2;O). This crystal transformation is the defining step that gives calcium silicate insulation its thermal stability, low thermal conductivity, and mechanical strength.
Step 4: Drying, Finishing, and Quality Control
After autoclave curing, the products contain residual moisture from the steam. They pass through 62m tunnel drying kilns at 150-200°C to remove free water. Dried boards are then CNC-sanded to achieve precise thickness tolerances (+/- 1mm). Every production batch undergoes density, compressive strength, thermal conductivity, and linear shrinkage testing. Products that pass are packaged on fumigated wooden pallets with waterproof PE film for export. For a more detailed look at Mingfa's production infrastructure, see our Company Overview page which includes the Manufacturing Process section.