# An Analysis of the Process of Applying Technical Lubricating Coatings
## 2 Materials and Methods
### Methods  
The first step was to set process assumptions. One of the most important was to achieve the greatest uniformity of the sprayed material layer. In addition, an important aspect was the smallest amount of material dust outside the intended spray path.  
To make the process repeatable, it was necessary to use a constant linear valve speed of 120 mm/s in each measurement series, as well as a constant distance of the nozzle from the sprayed surface, equal to 10 mm. An important parameter was the amount of sprayed material, or the dose applied to the substrate each time. It was 7.5 g/min, and to obtain the required flow in the valve at this level, calibration was performed, which was carried out in the following steps:  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristics** & **Lubricant No. 1** & **Lubricant No. 2** \\ \hline Base oil & PFPE & PFPE \\ Viscosity of oil at 40 \({}^{\circ}\)C (mm\({}^{2}\)/s) & 8 & 8 \\ Thickener & PTFE & PTFE \\ Density (kg/dm\({}^{3}\)) & 1.93 & 1.93 \\ Penetration \(\times\) 0.1 mm & 265–295 & 355–385 \\ NLGI class & 2 & 0 \\ Vapor pressure at 70\({}^{\circ}\) C (Torr) & 10\({}^{-3}\) & \(<\)10\({}^{-2}\) \\ Operating temperature range (\({}^{\circ}\)C) & –70–200 & –70–200 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The characteristics of lubricants used[35].  
Figure 2: Shape of the obtained sprays[34]: (**a**) solid cone when using Nordson EFD 7856-46 SS 0.046” nozzle; (**b**) fan-flat when using Nordson EFD 7856F-46 SS 0.046” nozzle; (**c**) exemplary measurements of the spray angle.  
Setting constant process parameters;
* Modifying the material flow as needed by adjusting the degree of valve opening, i.e., needle lift, by adjusting (microadjust);
* Re-regulating the material flow by changing the material pressure from 4 bar to 4.4 bar;
* Dosing material into a controlled vessel for 10 s;
* Measuring the weight of the dosed material;
* Performing calculations to check the flow in 60 s.  
Two nozzles with different designs were used in the study to compare how their geometry affects the obtained spray, with the outlet hole diameter always the same. It was 0.046 in. In addition, the impact of lubricants classified into different NLGI classes was compared, as well as the impact of variable atomization pressure in the range of 20 to 80 psi. Four measurement series were performed: two series for the full cone spray nozzle, and two series for the fan-flat spray nozzle for both lubricants (Table 3).  
The photographic method was used to analyze the obtained spray path as well as the angle of the lubricant spray. This method is a basis for applying computer image analysis, which can be helpful in controlling plastic lubricants [36]. To take photos of the applied paths, a Canon digital SLR camera, Canon EOS-100D, was used. It was mounted on a compatible tripod to maintain identical operational conditions during photography. Standard camera settings were applied. The spray was applied to a black substrate to facilitate computer analysis. To digitally register the sprayed lubricant in order to measure the spray angle (\(\alpha\)), a USB Dino Lite AM3113T digital microscope was used. With its use, the spray was registered each time. As with photography, a black background was placed behind the measurement station to facilitate further analysis. After converting the obtained frame-by-frame film, a series of photos was obtained. Next, the computer analysis of the photographs began using the Image-Pro Plus program by Media Cybernetics (Rockville, MD, USA).