When the coating is exposed to corrosion and oxidation (sometimes in high temperature), sealing is an important consideration for coating design.
This paper deals with the purpose and requirements of the sealing operation.
The types, properties, construction points, selection basis and application range of the sealant are introduced.
Any kind of thermal spraying method, especially the coating deposited by an oxygen flame spray (i.e. flame spraying), is a kind of porous structure.
Overall, the coating porosity range is considerable.
The gas one oxygen flame spray layer can sometimes reach up to 15%, while the high speed oxygen gas spraying (HVOF) layer is below 1%.
In practice, it is sometimes advantageous to have a hole structure.
The coating pores help to store oil, promote lubrication and reduce wear.
In some special applications, porous materials are made from thermal spraying for heat exchangers or other components.
In more cases, however, the coating pores are not desirable.
When exposed to air, steam, coating industry, chemical active substances, corrosion gas atmosphere and high temperature environment, corrosion pore is introduced into elements, chemical or electrochemical erosion in the coating and substrate, lead to coating failure, in this case, must to hole sealing coating.
As a kind of post-treatment process of thermal spraying, the main content of the sealing operation is the selection of sealing agent and construction method.
If some workpiece is needed for turning or grinding after spraying, the sealing hole should be applied before this, in order to prevent the coating pore pollution and ensure a better and cleaner grinding finish.
When the ceramic coating is used for insulation, the sealant can maintain the dielectric constant of the coating.
Otherwise, the coating pores will absorb moisture or be contaminated, forming undesirable conductive channels in the coating.
In addition, for the pump or hydraulic press equipment, sealing hole also prevents the liquid and pressure seal leakage.