The fire protection methods of steel structure parts mainly include coating protection, fire board protection, concrete protection, flexible coil protection, inorganic fiber protection, water cooling protection in the structure, etc.Among them, the application of fireproof coating is convenient, light, low cost, not limited by the geometry of components, the most widely used and the highest efficiency.

In order to overcome the shortcomings of fire protection in practical application of steel structure materials, fire prevention treatment must be carried out, whose purpose is to increase the fire resistance limit of steel structure to the limit range specified in the design code.There are various measures to prevent deformation collapse of steel structure caused by rapid temperature rise in the fire. The key is to adopt different methods according to different situations, such as using heat insulation and refractory materials to block the flame to burn steel structure directly, reducing the speed of heat transfer and delaying the time of temperature rise and strength weakening of steel structure.But no matter what method is adopted, its principle is consistent.Fireproof coating is a kind of advanced fireproof technical measure in recent years.

The principle of steel structure fire protection is to use heat insulation or heat absorption materials to block the flame and burn steel structure directly, reduce the heat transfer speed to steel, and delay the time of steel structure temperature rise and strength reduction.Fire retardant coating for steel structure is defined as the coating applied on the surface of buildings and structures, which can form a fire-resistant and heat insulation protection layer to improve the fire resistance limit of steel structure.At present, the fireproof coatings for steel structure at home and abroad are mainly composed of matrix resin, catalyst, carbon forming agent, foaming agent, etc.

　　1. matrix resin

The compatibility of matrix resin with other components not only ensures that the coating has various functions under normal conditions, but also has flame retardancy and excellent expansion foaming performance under flame burning or high temperature conditions.Generally, the carbonized layer of acrylic fire retardant coating is of high quality, so acrylic resin is usually used as the main film-forming material and modified to improve the overall effect of the coating.

　　2.Catalyst

Catalyst is a kind of substance which can decompose phosphoric acid under certain conditions. The decomposed acid dehydrates the polyol, thus forming a non flammable three-dimensional carbonized layer.Generally, the water solubility of melamine phosphate is smaller than that of polyphosphate, and it has both catalytic and foaming functions. At present, melamine phosphate is mainly used as catalyst.

　　3. carbonaceous agent

The carbon forming agent is the material basis for the formation of a non flammable three-dimensional space structure of the foam carbonization layer at high temperature, and plays a skeleton role in the carbonization layer of the foam.The carbon forming agent should match the catalyst in decomposition temperature. When the polyphosphate amine is used as catalyst, the high carbon polyhydroxy compound with high thermal stability should be used as carbon forming agent, 

4. foaming agent

Only under the action of foaming agent, the intumescent coating can produce intumescent layer under high temperature flame.The foaming agent decomposes in case of fire and releases non combustible gases such as ammonia, water, carbon dioxide, hydrogen halide, etc., which makes the coating expand when it reaches the softening point, forming a sponge like structure