China environmental label product certification is aimed at the non asbestos fiber reinforced cement board industry. It shows that the product is not only qualified in quality, but also meets the specific environmental protection requirements in the process of production, use and disposal (it is strictly prohibited to use reinforced fiber harmful to human body, such as asbestos). At the same time, it saves resources in the production process. It is more beneficial to the ecological environment to reduce the waste of energy and the emission of waste gas. Therefore, the non-autoclaved non-asbestos fiber reinforced cement board (hereinafter referred to as the non-autoclaved pressure board) without using asbestos fiber and curing at room temperature is bound to become the development direction of non asbestos fiber reinforced cement board industry. This paper discusses the influence of raw materials, production equipment and process route on the production process of non steam non asbestos fiber reinforced cement board.
1.Raw material
Reinforced fiber: high strength and high modulus polyvinyl alcohol (PVA or vinylon) fiber, grade I, length of 4 mm and 6 mm (1:2 mixture recommended), tensile strength > 12 CN / dtex, modulus(0.1%~0.4%): ≥260 cN/dtex. According to the study on the durability of non asbestos fiber cement board made from vinylon at home and abroad, it is considered that the product has high strength even if exposed to the atmosphere. But its toughness decreases with the increase of time. This is mainly due to the continuous improvement of the interface between fiber and cement matrix.
Wood pulp fiber: heat resistant 230 ℃ (280 ℃ in a short time)The results showed that kappa number ≤ 35, average moisture ≤ 11%, moisture deviation ≤ 30%. Wood pulp fiber is an organic fiber obtained from natural coniferous wood after chemical treatment. It is divided into different length and thickness fibers by screening, splitting, high temperature treatment, chemical treatment, neutralization and screening, so as to meet the needs of different application materials. Due to the treatment temperature as high as 250 ℃, it is a chemical stable substance under normal conditions, which is not corroded by ordinary solvents, acids and alkalis. It has the excellent quality of non-toxic, tasteless, pollution-free and non radioactive. It does not affect the environment and is harmless to human body. It is a green environmental protection product, which is not possessed by other mineral fibers. The microstructure of the fiber is banded and curved, uneven and porous, flat at the intersection, good toughness, dispersion and chemical stability, strong water absorption, thickening and crack resistance.
Cellulose fiber: the main fiber length is 2 ~ 3 mm. The elastic modulus is 8 ~ 10 GPa. The diameter is 15 ~ 20 μ m. The specific surface area is 20 000 ~ 30 000 cm2 / g. The acid and alkali resistance retention rate is ≥ 95%. Cellulose fibers are mainly distributed vertically and horizontally in the green body, which can effectively reduce the stress concentration at the tip of microcracks, weaken or eliminate the tensile stress caused by internal dry shrinkage or wet expansion, and prevent the occurrence and expansion of microcracks. Due to the existence of cellulose fiber in the plate, the internal tensile stress concentration caused by multiple freeze-thaw cycles can be effectively reduced and the further expansion of micro cracks can be prevented. In addition, due to the improvement of the impermeability of the plate, of course, it is also conducive to improve its freeze-thaw resistance. Cellulose fiber is helpful to absorb the energy of the plate under impact, and because of the crack resistance effect of the fiber. The fiber can prevent the rapid expansion of internal cracks when the plate is under impact load. So it can effectively enhance the impact resistance and toughness of the board. Cellulose fiber can make cement hydration more complete, significantly reduce the gap in the plate structure, make the plate more dense, so as to improve the frost resistance and water permeability of the board, and give the board better durability.
Collagen fiber: the velvet like material made from collagen fiber cellulose. The main fiber length is 3 mm. Ash content is less than 5%. Volatile content is less than 8%. 149 μ m sieve residue is less than 5%. Collagen fiber strength is good, no environmental pollution. Fiber dendrite structure improves the mixing performance of mixture and promotes the dispersion of other raw materials. It has a good effect on improving the softness, compressibility and sealing performance of the material. It can reduce the amount of NBR and improve the impact toughness.
Alkali resistant glass fiber: the alkali resistance of ordinary glass fiber is poor. It is easy to lose its strength and rigidity in the alkaline environment of cement matrix. In the 1960s, although the research on glass fiber reinforced cement-based materials has been relatively in-depth, its products have not been widely applied. In the early 1970s, the British architectural research institute added zirconia to the ordinary glass fiber and developed alkali resistant glass fiber. Then the glass fiber reinforced cement products were made by Pilkington brothers of England Company mass production, promotion and application.
Polyolefin MULTI BRANCHED fiber: a kind of polyolefin spray formed fiber with multi branched structure. Melting point of 100 ~ 135 ℃, and can be evenly mixed with various particles and cellulose fibers in water, with good hydrophilicity. Compared with the general resin fiber, the diameter distribution with branch structure (branch part 2 μ m, trunk part 30 μ m) has larger specific surface area. Micron level multi branched fiber can physically capture cement particles and various fillers, so as to inhibit the settlement of water dispersion, which is very conducive to the improvement of production efficiency of papermaking method, making the surface of products both beautiful and firm, and preventing cracking.
Cementitious material: P · Ⅱ 42.5R cement. 74 μ m sieve residue ≤ 8%. Loss on ignition ≤ 3.5%. The stability meets the standard requirements. Internal irradiation index (IRA) ≤ 0.4, external exposure index (IR) ≤ 0.4.
Filling material: heavy calcium carbonate, white powder, odorless and tasteless, stable in air. Relative density: 2.6 ~ 2.7 g / cm3, 25 / 4 ℃. Melting point: 1 339 ℃. 74 μ m sieve residue ≤ 3%. Calcium carbonate content > 90%.
2.The auxiliary materials are as follows:
Mica powder: Sand content ≤ 1.5%. Loss on ignition ≤ 5.5%. Loose density ≤ 350 kg / m3. Particle size distribution: 0.45 mm. Sieve residue ≤ 5%. 149 μ m sieve residue ≥ 85%. Water content ≤ 1%. Radioactive level: internal radiation index (IRA) ≤ 0.4. External radiation index (IR) ≤ 0.4.
Wollastonite powder: Wollastonite content ≥ 80%. Loss on ignition ≤ 3.5%. Sedimentation value ≥ 55 ml / 30 g. Loose density ≤ 550 kg / m3. Moisture content ≤ 1%. Particle size distribution: 0.25 mm sieve residue ≤ 10%. 8 mm sieve residue ≥ 40%. Radioactive level: internal radiation index (IRA) ≤ 0.4. External radiation index (IR) ≤ 0.4.
Micro silica powder: SiO2 content ≥ 92%. Loss on ignition ≤ 6%. Specific surface area ≥ 15 m2 / g. The average particle size is 0.15 μ m. Micro silica fume is an ideal admixture to improve the mechanical properties and durability of non autoclaved platens. Micro silica fume has a good effect on improving and improving the performance of non evaporated board. In terms of hydration mechanism, the micro silica powder has high volcano ash activity, that is, react with Ca (OH) 2 produced by hydration of cement to generate more calcium silicate gel, resulting in increased strength. In terms of fiber reinforcement effect, it is explained that after adding micro silica fume. The bonding force between the fiber and the cement substrate is significantly improved. Thus the fiber reinforcement effect of the final product is significantly improved. At the same time, the micro silicon powder can effectively improve the lamination problem in the production of non autoclaved pressing board by the method of papermaking.
Inorganic pigment: it is required that the water-soluble matter should not have obvious stratification, the residue of 44 μ m sieve should be less than 5%. And the volatile matter at 105 ℃ should be less than or equal to 1%.
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Post time: Aug-18-2020