The frames of modern large-scale steel structure factories mostly use steel structures. Although the steel used as load-bearing components has the advantages of high strength, light weight, large load capacity, good seismic performance, easy construction, no pollution, and recyclability, its thermal conductivity is high. Once it encounters a fire, its temperature can rise to 700 ℃ within 10-15 minutes, far exceeding its critical temperature. At this time, the yield strength of the steel drops sharply to about 40% of the normal temperature state and loses its bearing capacity, which can cause building collapse. At present, China mostly uses steel structure fireproof coatings for coating protection. For the supporting columns of high-rise civil buildings, such as those supporting multiple floors in industrial and civil buildings, large-span steel structure factories, petrochemical engineering, etc., thick steel structure fireproof coatings with a fire resistance limit of more than 2 hours are often used for protection.
The thick coating fireproof coating for steel structure factory buildings is designed and produced specifically for the fire protection of load-bearing components of first-class fire-resistant steel structures. After spraying the coating on the surface of steel components, it forms a fire-resistant insulation protective layer by relying on the non flammability and low thermal conductivity of the coating itself when exposed to fire, which slows down the direct invasion of fire on load-bearing components and effectively improves the fire resistance limit of steel structures. This product has the characteristics of not corroding steel, not reacting chemically with any anti-corrosion primer, no irritating odor, light coating weight (relatively light structural load weight), large unit coating area, no smoke generation when exposed to fire, and no release of harmful gases.
Construction process and operation points of steel structure factory building
1.1 Construction process of thick coating fireproof coating for steel structure factory buildings
Homework preparation → Fireproof coating ingredients and mixing → Spraying → Inspection and acceptance.
1.2 Operation points
(1) Preparation of construction environment. ① Protection: The open floor protection can be equipped with external flame-retardant mesh, and the inner layer of the mesh should be covered with colored strips. The dense mesh and colored cloth are securely fixed. Local protection can be covered with colored strip cloth. Wrap the equipment, pipelines, and glass curtain wall keel with plastic film or colored strip cloth. ② Before applying fireproof coating, the rust removal and anti rust primer coating on the surface of steel components should comply with the design requirements and relevant national regulations. Dust, oil stains, and other debris on the surface of steel components should be thoroughly removed. ③ Fireproof coating should be applied before indoor decoration and under conditions that are not damaged by subsequent engineering. During construction, walls, doors, windows, mechanical equipment, and other components that do not require fire protection should be covered and protected.
(2) Material selection. ① The fireproof coating should be a thick coating type fireproof coating with an appearance of gray white granular lightweight powder. Before use, there must be a manufacturer’s production license, factory inspection report, and retest report issued by the manufacturer. ② High strength adhesive and steel anti adhesive are supplied by the manufacturer. Before use, there must be a factory inspection report and certificate of conformity issued by the manufacturer. ③ Before using water, its composition and corrosiveness need to be tested, and water that reacts with materials cannot be used.
(3) Fireproof coating ingredients and mixing
① Powdered coatings should be prepared as needed. Taking ST1-A type as an example, the preparation is shown in Table 1.
② Before coating, mix evenly according to the ratio of powder: lotion=1.0:. ③ Solid is advisable. For ultra wide and large steel materials, steel frame mesh should be added to prevent paint leakage or separation. ④ The slurry should be prepared as needed, and the prepared slurry should be used up within 1 hour to avoid waste due to curing caused by prolonged storage time. ⑤ When stirring, first pour the coating into the mixer and add water to stir for 2 minutes, then add adhesive and steel anti adhesive and stir thoroughly for 5 to 8 minutes to achieve a sprayable consistency.
(4) Spray painting. The spraying method can be a combination of spraying, wiping, scraping, or a combination of three methods for construction. When using spray painting, use a concave convex bucket spray gun with an air pressure of 0.6MPa to 0.8MPa and a nozzle diameter of 6mm to 10mm. The spray gun should be perpendicular to the surface of the coated component, preferably 40cm to 60cm. The first layer of spraying construction should not be too thick. After it dries, the next layer of construction should be carried out without flowing until the standard thickness is reached. According to the thickness requirements of the design, multiple construction steps are required, with each step having a thickness controlled within 5mm to 10mm and an interval of 24 hours between each step. The next step can be carried out after the previous step is basically dry. If a flat surface is required, it can be smoothed after the last step of construction. The construction environment temperature during spraying should be above 5 ℃, and the relative humidity should not exceed 85%. When the temperature is below 5 ℃, peripheral sealing and heating measures should be taken, and it is advisable to maintain a temperature of 5 ℃ or above for 48 hours before and after construction.
(5) Inspection and acceptance. Self inspection of fireproof coating: During the construction process, the operator should use a thickness gauge or gauge to timely detect the thickness of the coating until it meets the design requirements before stopping spraying. The thickness of the node should be 3mm to 5mm greater than the required thickness. Use a 0.75kg-1kg hammer to strike the coating and check for any paint hollowing. The crack width is measured directly with a ruler. During inspection and acceptance, use a steel needle with a scale to randomly check the thickness. If the thickness is found to be insufficient, re spray or remove it and re spray. Use a hammer to inspect the hollow drum, and if it is found, it should be re sprayed.
