The core process of refractory castable construction is: Construction Preparation → Mixing → Casting and Vibrating → Curing and Formwork Removal → Oven Drying. The water-to-material ratio and temperature must be strictly controlled throughout the process to avoid cracking and strength loss.
I. Pre-construction Preparation
1. Base Treatment
Remove oil stains, rust, dust and loose old linings from the metal/refractory base surface to ensure the base surface is rough and clean. Weld heat-resistant stainless steel anchor bolts (Y/V type, spacing 200–300mm, exposed length 50–100mm) on the metal base. After full welding, apply 1–2mm asphalt paint or wrap tape to prevent damage from expansion stress. The old lining area must be thoroughly chiseled to remove the loose layer; pre-wet the base surface (no standing water) before construction to avoid the base surface absorbing water, which would cause the castable to become loose and crack.
2. Formwork Installation
The formwork adopts steel plate/waterproof multi-layer board (thickness ≥10mm), and the inner surface is coated with release agent (engine oil/asphalt). The height of formwork support at one time shall not exceed 300mm, and pouring ports and expansion joints shall be reserved (set 2–3mm per 1.5m², filled with ceramic fiber paper). The formwork support shall be firm, with deformation ≤2mm.
3. Environment and Materials
The ambient temperature shall be 5–35℃; when the temperature is below 5℃ in winter, heating and heat preservation are required; when the temperature exceeds 30℃ in summer, ice water shall be used for mixing and sunshade measures shall be taken. Materials shall be free from caking and moisture, and different grades are strictly prohibited from being mixed; the materials shall match the service temperature (high alumina: 1200–1600℃, corundum: 1600–1800℃).
II. Mixing (Key to Water Control)
Equipment: Forced mixer, manual mixing is strictly prohibited.
Ratio: Control the water-to-material ratio according to the manufacturer's instructions (usually 5%–12%, preferably less rather than more). The water used shall be clean (pH 6–8, chloride ion < 300ppm).
Two-step mixing:
Dry mixing: Put the dry materials into the mixer and mix for 1–2 minutes (to disperse the fibers evenly).
Wet mixing: Add 80% of the water and mix for 3–5 minutes, then add the remaining water according to the consistency until the mixture is uniform without caking and has moderate fluidity.
Time limit: The mixed material shall be used up within 30 minutes; it shall be discarded if it exceeds the time limit.
III. Casting and Vibrating
Layered feeding: Each layer is 250–300mm thick, cast continuously, and the interval between layers is less than 30 minutes (before initial setting).
Vibrating to compact:
Use an inserted vibrator with quick insertion and slow extraction, spacing ≤250mm, and insert into the lower layer by 50–100mm.
Vibrate each point for 20–40 seconds until the surface exudes slurry and no bubbles; avoid touching the anchor bolts and formwork.
Finishing and expansion joints:
First finishing before initial setting (to eliminate pitting surface), second finishing before final setting (to ensure smoothness and compactness).
Divide large areas into blocks (≤1.5m²), and reserve 2–5mm expansion joints according to the design, filled with ceramic fiber rope/paper.
IV. Curing and Formwork Removal
Formwork-attached curing: ≥24 hours at normal temperature, ≥48 hours in winter; keep moist (spray water/cover with wet cotton), temperature 15–25℃, humidity ≥90%.
Formwork removal: Remove non-load-bearing formwork first, then load-bearing formwork; avoid prying hard to damage the edges and corners.
Subsequent curing: After formwork removal, perform natural curing for ≥3 days, spray water 2–3 times a day to keep the surface moist.
Defect repair: Chisel honeycombs and cavities to the compact layer, and repair and compact with castable of the same material; cut V-shaped grooves for cracks, and fill with special repair material after cleaning.
V. Oven Drying (Mandatory to Prevent Explosion and Cracking)
After curing, strictly heat up according to the oven drying curve. Heat up slowly in the low-temperature section (100–200℃) to remove free water; keep constant temperature in the medium-temperature section (300–600℃) to remove crystal water; gradually raise the temperature to the service temperature according to the working temperature in the high-temperature section.
Heating rate: 50–100℃/h, keep constant temperature for 2–4 hours at key temperature points (100℃, 300℃, 600℃).
VI. Common Problems and Taboos
Excessive water addition → high porosity, low strength, easy spalling.
Insufficient vibration → honeycombs, cavities and poor compactness.
Improper curing → surface cracking and failure to reach the required strength.
Too fast oven drying → rapid evaporation of water → explosion and cracking.
VII. Scenario-specific Points
Special-shaped structures (vaults/turning corners): The formwork pressure test deformation shall be ≤2mm; add stainless steel reinforcing ribs or polypropylene fibers (0.1%) at the turning corners to resist cracking.
Narrow spaces (pipe diameter < 500mm): Use self-flowing material guide pipes for material distribution, and manually compact dead corners; take ventilation and protection measures, and rotate operations every 30 minutes.
Zibo Shuangjian Refractory Materials Co., Ltd. provides one-stop supply of various refractory castables and wear-resistant refractory materials, supporting engineering construction services, spot direct delivery and customized on demand. Welcome to call for consultation and cooperation. Tel: +86018369999108, 0533-5780389
