The influence of the surface roughness of the workpiece of the size of the size of the steel shot

1) The actual bonding area between the coating and the surface of the workpiece is increased, which is conducive to improving the bonding force of the coating. Steel shot size size and the ratio of actual surface area to theoretical surface area statistics.

 2) coating in the curing process will produce a lot of internal stress, the existence of surface roughness can effectively eliminate the stress concentration in the layer, to prevent cracking of the coating.

 3) The existence of surface roughness can support part of the quality of the coating, and is conducive to the elimination of the phenomenon of sagging, for the vertical coating of the surface, the role is particularly obvious.

Surface roughness is caused by the steel shot steel sand particles with high speed contact surface, impact, cutting and scouring of the joint action, therefore, the steel shot size particle size, hardness, particle shape, the hardness of the workpiece itself, the pressure of compressed air, the distance between the nozzle and the surface of the workpiece and the nozzle and the surface of the workpiece between the angle between the normal direction determines the size of the surface roughness and the shape of the contour.

Surface roughness, like surface cleanliness, is also determined by the corrosion engineer according to the coating requirements, and the main basis for determining the size of the surface roughness value is the type of coating and the thickness of the final coating.

In the absence of the development of the surface roughness value of the required conditions or technical information, the surface roughness value can be temporarily determined in the final coating thickness of 25% -30% of the value. For example, if the final coating thickness is 150µm, a surface roughness value in the range of 38-45µm is sufficient. Another method is to determine the surface roughness value according to the thickness of the primer, the surface roughness value can not be greater than the thickness of the primer, except for the second coat of paint immediately after spraying the primer.

Surface roughness value is low, to improve the adhesion of the coating is not favorable; surface roughness value is high, the coating thickness specified in the coating design may not be able to cover all the peaks in the surface roughness, pitting occurs within a short period of time, resulting in early failure of the coating.

Maintain the consistency of abrasive grain size throughout the blast cleaning process is to ensure that the surface roughness before and after the necessary precondition, different uses of abrasive can never be mixed or used instead. For example, a structural steel manufacturing company has undertaken a structural steel manufacturing project, the project's structural steel parts need to be painted, some need to be connected to the high-strength bolts on the bonding surface of the hair, in order to improve the friction factor between the bonding surface. The abrasive used for hair-beating is not only large in particle size, but also high in hardness, because the steel shot required for surface treatment before painting could not keep up for a while, the company put the abrasive used for hair-beating to use. Workpiece transported to the site soon, the problem was exposed, dense pitting surprised people, had to be re-sanded, and then brushed on a pass of paint. The root of the problem lies in the size of the steel shot, high hardness caused by the surface roughness with the design of the coating can not effectively cover, easy to rust.