Bond Strength Between The Epoxy Resin Coating And Steel Structure Pretreated With Sand Blasting

Epoxy resin coatings have a lot of advantages, such as high bond strength, good corrosion resistance etc., and have been widely used in anti-corrosion coatings in all kinds steel structure. Sand blasting is an abrasive machining process, which is often used for the pretreatment of steel structure before coating. Sand blasting not only can be used to remove the surface contamination, but also can be used to make a rough surface so as to enhance the bond strength between the coating and the roughed substrate. In this paper, detailed studies were carried out on the formation of roughed surface by sand blasting, and its effect on the interface stress and bond strength between the coating and substrate.The state of abrasive particles in the nozzles during blasting was analyzed based on the gas-solid two-phase flow and fluid mechanics. The critical suspension speed and the steady speed of abrasive particles were obtained. The dynamic characteristics of the impact during sand blasting were analyzed based on the HZ quasi-static theory. Theoretical formula of the deformation area and the impact depth was obtained. Effect of the impact angle, abrasive size and air pressure on the surface roughness was investigated by sand blasting test. The change law of surface roughness with impact angle, abrasive size and air pressure was gained. The interface stress between coating and substrate was analyzed by finite element method. The change rules of the interface stress with the roughness profile were investigated. Results showed that the interface stress of sine model is the smallest (0.3577MPa), while the interface stress of line model is the largest (0.3975MPa). The extreme value of interface stress usually appears at the place of surface wave or trough (Rm and S). It is shown that reasonable surface roughness can reduce the interface stress between coating and substrate. The extreme value of interface stress showed the smallest value when S equals to 40μm, and Rm equals to 8μm.The bonding strength of the epoxy resin coating on the steel structure was measured by vertical stretching method, the effect of surface roughness and blasting parameters on the bonding strength of the coating was investigated. Results showed that: (1) pretreatment on the substrate has profound effect on the bond strength of the coating; the damage -resistant of the coating after sand blasting is 3 times higher than that of the sample without surface treatment; (2) bond strength between coating and substrate showed the highest value when with 9.6μm Rm; (3) the optimal roughness of the blasted surface and maximal bond strength between coating and substrate can be achieved with proper impact angle, particle size and air pressure. The highest bond strength between coating and substrate is 1.93 MPa under the test conditions: abrasive particle size 0.35-0.38μm, impact angle 40°, air pressure 0.75 MPa.