PSI - Issue 53

João Soeiro et al. / Procedia Structural Integrity 53 (2024) 367–375 Soeiro et al. / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 2. Design fixation plate for pull-out test of bi-material injection component (a); design plate with assembled component; technical scheme of the apparatus mounted on the testing machine (c).

R insert molding machine with 200 tons of clamping force was used. In an e ff ort to maintain reproducibility, every time the injection process had to be stopped, material discharges were performed (purging). This avoids the usage of degraded material, due to prolonged exposure to heat. Manual sanding was the selected method for the mechanically abrasive surface treatment. It involves the use of abrasive materials to roughen the surface of the metal insert. A P320 grit was used given its applicability towards the insert surface. The manual sanding passes were performed at a crossed 45° angle relative to the surface edges and crossed at a 90° angle with each other. The crossed passes were applied in the same direction (either up or down) across the surface of the metal insert. This technique was chosen for better control over the process, reducing the risk of over- and under-sanding. Also, maintaining the same direction of sanding passes, helped to prevent contamination of the sandpaper, as the abrasive particles were not being constantly reoriented. It is important to emphasize the repeatability of this method, which is crucial in this research setting, as multiple inserts were prepared. Additionally, flame treatment was employed, consisting of exposing the metal insert to a heat source (torch concentrated nozzle), modifying the surface properties of the metallic insert. The flame was generated by burning a mixture of air and a combustible gas (butane) with the goal of inducing physical and chemical changes, such as cleaning and oxidation, further activating its surface. Figure 3 shows the condition of a representative portion of the metallic insert surface after mechanical abrasive treatment (a) and flame treatment (b). Figure 3a illustrates the e ff ect of the abrasive process. Sanding has visibly increased the surface area of the metal insert, creating a rougher texture characterized by grooves and ridges. This increased surface area and roughness are key factors in enhancing mechanical interlocking, a crucial mechanism. Furthermore, the micrograph of the flame-treated insert, seen on figure 3b shows the presence of small bulges on the surface. These bubble shaped spots symbolize the separation of the silver coating from the metal surface, likely due to overexposure to the flame. The remaining surface does not show any apparent changes in the surface topography. However, upon increasing the magnification, micro-cracks appear, which could be the main cause of the increase in wettability.

Fig. 3. Optical microscope surface characterization of sanding treatment (a) and flame tratment (b) on the metallic insert.

The surfaces of the metallic inserts were subjected to surface tension testing, to evaluate the surface treatment impact on wettability (refer to figure 4). This was accomplished using the Arcotest Test Pens PINK, a pink-hued testing ink specifically designed for the measurement of surface tension. The highest available surface tension pen,