Bearing Steel Surface Treatment Technology

Bearing steel usually loses its bearing capacity at a temperature of 450-650℃, undergoes a large deformation, and causes the steel column and steel beam to bend. As a result, it cannot continue to be used due to excessive deformation. The fire resistance limit of unprotected bearing steel is generally about 15 minutes. The length of this time is also related to the speed at which the component absorbs heat.

To overcome the shortcomings of fire prevention in practical applications of bearing steel materials, fire prevention treatment must be carried out, the purpose of which is to increase the fire resistance limit of bearing steel to the limit range specified in the design specifications. There are many measures to prevent bearing steel from rapidly heating up and deforming and collapsing in a fire. The key is to adopt different methods according to different situations, such as using insulation and refractory materials to block the flame from directly burning the bearing steel, reducing the speed of heat transfer, delaying the time when the bearing steel temperature rises and the strength weakens, etc. But no matter what method is adopted, the principle is the same. The following introduces several fire protection measures for different bearing steels.

1.Outer layer

It is to add an outer layer to the surface of the bearing steel, which can be cast in place or sprayed. The cast-in-place solid concrete outer layer is usually reinforced with wire mesh or steel bars to limit shrinkage cracks and ensure the strength of the shell. The spraying method can apply sand pumps to the surface of the bearing steel at the construction site to form a protective layer. The sand pumps can be lime cement or gypsum mortar, and can also be mixed with perlite or asbestos. At the same time, the outer layer can also be made of perlite, asbestos, gypsum or asbestos cement, light concrete to make prefabricated panels, and fixed to the bearing steel with adhesives, nails, and bolts.

2.Filling with water (water jacket)

Filling hollow bearing steel with water is the most effective protection against fire. This method can keep the bearing steel at a lower temperature during a fire. Water circulates inside the bearing steel and absorbs the heat of the material itself. The heated water can be recycled after cooling, or cold water can be introduced through pipes to replace the heated water.

3.Shielding

Bearing steel is set in the wall or ceiling made of refractory materials, or the components are hidden in the gap between two walls. The purpose of fire prevention can be achieved by adding a little refractory material or no refractory material. This is the most economical fire prevention method.

4.Expandable Materials

Bearing steel fire-retardant coating is used to protect components. This method has the advantages of good fireproofing and heat insulation performance, and the construction is not restricted by the geometric shape of bearing steel. Generally, no auxiliary facilities are required, and the coating is light in weight and has a certain aesthetic decorative effect. It is a modern advanced fire protection technical measure.