# Effectiveness of Bonding Steel Elements with Polyester-Coated Paint
## 2 Materials and Methods
### Process of Preparing and Applying Paint Coatings  
Three types of adherends were joined:  
* Reference samples;
* Samples with a paint coating in the form of polyester (powder) paint;
* Samples with a zinc primer and paint coating in the form of polyester paint.  
Polyester powder paint was used to make the painting surfaces. Coatings of this kind can be obtained via electrokinetic spraying followed by curing the powder. They are characterized by significant corrosion resistance and impact and abrasion resistance. Polyester pains can be used outdoors. They do not change their color under the influence of weather conditions or UV radiation. An advantage of using these powder coatings was that they provided coatings of desirable thicknesses (for a single application).  
Zinc primer is a protective layer that also protects against corrosion. It includes modified high-density epoxy resins as well as moisture resistance. In combination with metal, it also becomes a corrosion-resistant electrochemical. The structure of the zinc primer coating facilitates the adhesion of subsequent layers, including paint layers. The thickness of the zinc primer layer was 60-80 \(\upmu\)m, and its curing was carried out at 180 \({}^{\circ}\)C. After applying the zinc primer, it is possible to apply subsequent layers of paint coatings (i.e., in this case, polyester paint). A scheme of the process for preparing samples with a coating of polyester paint and with a primer and polyester paint is shown in Figure 1, and a description of the stages is given below.  
The first stage of the process of preparing paint coating samples with the applied primer and the paint coating was surface treatment. Two baths were carried out: a chemical bath and iron phosphating. The samples were then rinsed with demineralized water for 1 min. The samples were then dried in a warm drying oven at 120 \({}^{\circ}\)C for 10 min. Then, a zinc primer (thickness 60-80 \(\upmu\)m) was applied. The samples were cured in an oven at  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Properties** & **Description** & \\ \hline Type of paint coating & Paint coating & Primer and paint coating \\ Paint color & 9001 & 7024 \\  & (creamy white) & (grey graphite) \\ Paint surface & smooth mat & smooth mat \\ Resin & polyester & polyester \\ Paint curing temperature [\({}^{\circ}\)C] & 200 & 200 \\ Degree of paint gloss [\%] & 18–30 & 28–40 \\ Additionally applied primer layer & - & zinc primer layer \\ \hline \hline \end{tabular}
\end{table}
Table 1: Variants of paint coatings.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Properties** & **1.0503 Steel** \\ \hline Tensile strength Rm, MPa & 560–850 \\ Yield point Re, MPa & 275–490 \\ Elastic modulus E, GPa & 198–207 \\ Elongation A\({}_{5}\), \% & 14–17 \\ Percentage reduction of area, \% & 35–45 \\ Hardness in a softened state, HB & \(\leq\)229 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mechanical properties of steel adherends (PN-EN 10027-2).  
180 \({}^{\circ}\)C for 15 min. Such ovens are equipped with blowing devices at the entrance so that water does not enter the furnace while moving the elements from the wash tubs.  
The next step was the application of polyester paint using the Tribo method with a gun (Adal, Czosnow, Poland). In such a device, powder particles are charged by the electrokinetic method due to friction. After coating, the samples were cured at 160 \({}^{\circ}\)C for 15 min.  
The preparation process for the samples with the applied paint coating was carried out in a similar way. First, a chemical bath was prepared to decrease the surface, followed by iron phosphating. The samples were rinsed with demineralized water and then dried at 120 \({}^{\circ}\)C. The next stage was the application of a paint coating (polyester paint) with a gun. At the end, the sample was cured at 180 \({}^{\circ}\)C for 15 min.