Low cement castables are advanced refractories developed from conventional castables by applying rheology principles, dense packing theory and ultrafine powder technology.
They feature low porosity, small pore size, high bulk density, good volume stability, high strength and low water demand.
Unlike conventional castables which suffer strength loss at 800–1200°C, their strength rises with increasing temperature. This more than doubles the thermal shock resistance of furnace linings.
Application
Ironmaking: Suitable for blast furnace tapholes, capable of withstanding high temperature and impact of molten iron.
Steelmaking: Applicable to steel ladles, resisting high temperature and corrosion from molten steel and other chemicals.
Steel rolling: Used for relevant equipment in steel rolling production lines to resist high temperature and mechanical wear.
Building materials industry: Applied to kilns, sintering machines and other facilities. For instance, clay and high-alumina low-cement castables are used for linings of various heat treatment furnaces such as heating furnaces and soaking furnaces, as well as rotary kilns; low-cement castables are adopted for linings of high-temperature burners, wrapping linings for water-cooled tubes of heating furnaces, etc.
Other industrial kilns: Such as linings of electric furnace roofs, soaking furnaces, heating furnaces, annealing furnace linings, steel tapping troughs, tundish linings, etc. Corundum and chrome-bearing corundum low-cement castables are used for partial linings of steel secondary refining units, linings of power frequency induction furnaces, and high-temperature wear-resistant linings of petrochemical FCC reactors.
Physical And Chemical Properties
| Items | High aluminaBrand: ZF-16 | MulliteBrand:ZF-16K | CorundumBrand: ZF-17 | |
|---|---|---|---|---|
| Al2O3,% ≥ | 65 | 70 | 85 | |
| Bulk Density, g/cm3 BD≥ | 110∘C×24h | 2.5 | 2.5 | 2.8 |
| Cold Modulus of Rupture, MPa MOR≥ | 110∘C×24h | 10 | 12 | 12 |
| 1400∘C×3h | 14 | 16 | 18 | |
| Cold Crushing Strength, MPa CCS ≥ | 110∘C×24h | 80 | 90 | 100 |
| 1400∘C×3h | 120 | 150 | 180 | |
| Permanent Linear Change, % PLC | 1400∘C×3h | ±0.3 | ±0.3 | ±0.3 |
| Recommended Application Part | Rear entrance of cement kiln, kiln hood, rear end of cooler | Cement kiln grate cooler, kiln hood, tertiary air duct | Front kilneye of large cement kiln, coal burner | |
Main Features
1)Low Cement Content
Conventional refractory castables normally contain 15%–20% calcium aluminate cement. In contrast, low cement castables feature greatly reduced cement dosage, generally between 5% and 8% or even lower. This minimizes formation of low-melting eutectic phases within the material and raises refractoriness and high-temperature strength.
2)High Strength and Superior Refractoriness
With additives such as ultrafine powders and water reducers, low cement castables deliver excellent mechanical strength and refractory performance.
3)Low Porosity and High Bulk Density
Reduced cement content results in lower porosity and higher bulk density, which greatly improves thermal shock resistance and corrosion resistance.
4)Easy Construction
It requires less mixing water and shorter mixing time. Less cement hydrates form during curing, so spalling or cracking rarely occurs during heat-up.
5)Environmental Benefits
Lower cement consumption cuts CO₂ emissions, complying with green manufacturing requirements.
Differences between Low Cement Castable and Conventional Castable
Low Cement Castable
The main difference between low cement castables and conventional castables lies in their medium-temperature strength and final hot strength. Conventional castables have poor medium-temperature strength, while low cement castables outperform them by a wide margin. With lower cement and calcium content, low cement castables adopt ultrafine powder technology to achieve well-proportioned grain distribution, which greatly improves both medium-temperature strength and later-stage hot strength.
Conventional Castable
Conventional refractory castables are made of refractory aggregates, fine powders and high-alumina cement. Their aggregate grading is less precise than that of low cement castables. The cement particles are coarser and added in higher proportion, requiring more mixing water during construction. The high cement dosage and poor grain grading lead to incomplete cement hydration. Especially at around 800℃, almost no strength remains. For these reasons, conventional castables show inferior performance compared with low cement castables.
Factors Affecting Properties Of Low Cement Refractory Castables
Low cement castables are the most widely used unshaped refractory castables for industrial furnaces. Their properties are affected by many factors. The term "low cement" means the cement addition is much lower than that of conventional castables. This product series requires strict production control, and its performance directly determines furnace service life and safe operation.
Ultrafine Powder
Ultrafine powder acts as dispersing agent and densifier. It fills micro-pores effectively and improves density and strength of the material. Excessive SiO₂ ultrafine powder can increase strength yet reduce refractoriness. Insufficient dosage will lead to poor flowability and impair construction performance.
Aluminate Cement
Aluminate cement mainly serves as the setting component in low cement castables. Its type and dosage directly affect the strength development of castables.
Water Addition and Construction Technology
Too little mixing water results in inadequate mixing and poor densification. Too much water prolongs setting time and reduces final strength. Besides, the heat-up schedule is critical. The temperature must rise strictly in accordance with the heating curve to avoid spalling and peeling caused by rapid temperature increase.
Due to varying service requirements and physico-chemical specifications of castables, prices differ accordingly.
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