Evaluation of Substrates of Al-Mg and Aluminized Steel Coated With Non-Stick Fluoropolymers after the Removal of the Coating

Many trays and pieces of Al-Mg and aluminized steel are used in the food industry. Sometimes these elements have non-stick coatings to solve problems related to the adhesion of masses and food products. With use, the coatings deteriorate and lose efficiency and must be removed to apply a new coating. The thermal cycles suffered by these alloys during the removal process of the deteriorated coating (500 _C) and the polymerization of a new coating (400 _C) can affect the durability and efficiency of the metallic substrates. The evolution of the mechanical and microstructural properties of the Al-Mg and aluminized steel substrates after two thermal cycles was studied in this work. The following parameters were analyzed: tensile strength, elongation (%), hardness, ASTM grain size, and the nature and distribution of the constituent particles. The report concluded that the removal of the coating, after each cycle, produced a decrease in the mechanical properties of the substrates. The hardness and tensile strength in Al-Mg decreases between 20–27% and in aluminized steel between 10–11%. In both cases, the process does not compromise the reuse of the substrate for the application of a new coating layer. The final blasting stage does not affect the Al-Mg alloys but may affect the aluminized steel Al-Si protective layer if special precautions are not taken

Analysis, Validation and Optimization of the Multi-Stage Sequential Wiredrawing Process of EN AW-1370 Aluminium

For the wiredrawing of aluminium, the initial wire rod is obtained by continuous inverted casting. The raw geometry is industrially processed in a linear multi-step wiredrawing sequence to obtain a wire that is commonly used for the manufacture of electrical conductors. In the present work a complete study of the material has been made. The experimental procedure consisted in the realization of a sequence of section reduction stages in the laboratory, a sequence designed following the technological criteria recommended by the manufacturer of the drawing machine in which the industrial process will be implemented. From the specimens corresponding to each reduction step, it has been possible to know the evolution of the main mechanical properties when this pure aluminium is processed by wiredrawing. This information has led to establish the hardening law by which it is possible characterize the plastic behaviour of this pure metal when it is transformed by this specific sequential process of cold forming. The strain hardening law has been implemented in a numerical simulation software application and the experimental setup has been simulated for its validation. Finally, the classic analytical solution founded in the “slab method” has been applied for the design of a proposal for the optimization of the industrial wiredrawing process

Use of the support vector machine (SVM) algorithm to predict geometrical accuracy in the manufacture of molds via single point incremental forming (SPIF) using aluminized steel sheets

In the present work, the use of the support vector machine (SVM) algorithm is proposed to generate models that allow predicting the geometrical accuracy of molds manufactured via single point incremental forming (SPIF) using aluminized steel sheets DX51D AS120 B CO. For this purpose, 27 molds were manufactured, using the dummy technique, and employing different process parameters (tool diameter, spindle speed, feed rate, step size) and toolpath strategies (contour-parallel, spiral, radial). The molds manufactured were geometrically characterized by means of a coordinate measuring machine: the transverse profile of each mold was measured and compared with the expected theoretical profile. Three geometrical values were extracted from this comparison: the area between the two profiles, the moment of inertia of this area with respect to the Y-axis and the difference in height between the two profiles at the mid-point of the mold. The geometrical accuracy of the mold increases if these values decrease. The model that achieved the best results is the one associated with the area between the theoretical and real profiles (correctly classified instances = 90%; kappa statistic = 0.8). This model was generated using the LibSVM (linear kernel) algorithm and evaluating only three of the five parameters (strategy, tool diameter and step size). In addition, process maps were drawn up to show briefly which values generate higher geometrical accuracy in the molds: contour-parallel strategy, tool diameter equal to 12 mm and small step size values

Study on the Main Influencing Factors in the Removal Process of Non-Stick Fluoropolymer Coatings Using Nd:YAG Laser

The coatings with fluoropolymer resins rich in fluorinated ethylene propylene (FEP) and polytetrafluoroethylene (PTFE) are applied as anti-adherent coatings on aluminum–magnesium substrates for use in food containers. In many cases, due to wear, they must be stripped for the application of a new coating on the same substrate. There are several processes for this: blasting, plasma, pyrolysis, chemical processes, laser, high pressure water, and combinations of these. This work focuses on the characterization of the main factors that condition the FEP coating removal process by a continuous wave (CW) Nd:YAG laser, and on the determination of the efficiency of this type of technology used for this purpose. Stripping surface per unit of time and energy consumption per unit area has been determined among other efficiency indicators. Regarding the characterization of the coating object of study, its thickness, surface roughness, contact angle, microhardness and absorbance-reflectance responses have been determined, and the results have been compared with those obtained in the case of PTFE. In addition, to evaluate the mechanical damage caused in the substrate after coating removal by (CW) Nd:YAG laser, the tensile strength, Vickers hardness, Ra and Rz roughness, and the substrate thickness have been measured and analyzed

Experimental Study for the Stripping of PTFE Coatings on Al-Mg Substrates Using Dry Abrasive Materials

Polytetrafluoroethylene (PTFE) coatings are used in many applications and processing industries. With their use, they wear out and lose properties and must be replaced by new ones if the cost of the element so advises. There are different stripping techniques, but almost all of them are very difficult and require strict environmental controls. It is a challenge to approach the process through efficient and more sustainable techniques. In the present work, we have studied the stripping of PTFE coatings by projection with abrasives (1 step) as an alternative to carbonization + sandblasting procedures (2 steps). For this purpose, different types of abrasives have been selected: brown corundum, white corundum, glass microspheres, plastic particles, and a walnut shell. The tests were performed at pressures from 0.4 to 0.6 MPa on PTFE-coated aluminium substrates of EN AW-5182 H111 alloy. Stripping rates, surface roughness, and substrate hardness have been studied. Scanning electron microscopy (SEM) images of sandblasted specimens have also been obtained. All abrasives improved mechanical and surface properties in one-step vs. two-step processes. The abrasives of plastic and glass microspheres are the most appropriate for the one-step process, which increases the hardness and roughness level Ra in the substrate. Corundum abrasives enable the highest stripping rates

Use of Data Mining Techniques for the Prediction of Surface Roughness of Printed Parts in Polylactic Acid (PLA) by Fused Deposition Modeling (FDM): A Practical Application in Frame Glasses Manufacturing

In the present work, ten data mining algorithms have been used to generate models capable of predicting the surface roughness of parts printed on polylactic acid (PLA) by using fused deposition modeling (FDM). The models have been trained using experimental data measured on 27 horizontal (XY) and 27 vertical (XZ) specimens, printed using different values for the parameters studied (layer height, extrusion temperature, print speed, print acceleration and flow). The models generated by multilayer perceptron (MLP) and logistic model trees (LMT) have obtained the best results in a cross-validation. Although it does not obtain such optimal results, the J48 algorithm (C4.5) allows the generation of models in the form of a decision tree. These trees permit to determine which print parameters have an influence on the surface roughness. For XY specimens, the surface roughness measured in the direction parallel to the extrusion path (Ra,0,XY ) depends on the flow, the print temperature and the layer height; in the direction perpendicular to the extrusion path, the surface roughness (Ra,90,XY) depends only on the flow. For XZ specimens, the surface roughness measured in the direction parallel to the extrusion path (Ra,0,XZ) depends only on the print speed; in the direction perpendicular to the extrusion path (Ra,90,XZ), it depends on the layer height and the extrusion temperature. According to the study carried out, the most suitable set up provides values of Ra,0,XY, Ra,90,XY, Ra,0,XZ and Ra,90,XZ equal to 0.46, 1.18, 0.45 and 11.54, respectively. A practical application of this work is the manufacture of PLA frame glasses using FDM

Stripping of PFA Fluoropolymer Coatings Using a Nd:YAG Laser (Q-Switch) and an Yb Fiber Laser (CW)

Fluoropolymers such as PFA are used as coatings for the protection of metal substrates due to their high chemical inertia and non-stick properties. These are “wear and tear” coatings and they degrade, at which point they should be removed for a new application. The removal of these types of coating by laser is of interest due to the process’s flexibility, precision, ease of automation, and environmental sustainability. The efficiency of the procedure was shown with the use of a source in a pulsed Nd:YAG and a source in continuous mode of fiber (Yb). The rates of stripping (cm2/min) and fluence (J/cm2) were analyzed and related to the power of the laser sources. Variations of the substrate after stripping were studied: roughness and hardness. The properties of the coating, thickness, roughness, water sliding angle, and microhardness were also evaluated. It was concluded that the laser in continuous mode was more efficient than the pulsed laser; laser removal of fluoropolymers has a strong relationship with reflectivity, and the mechanical and surface properties of the substrate after stripping remained virtually unchanged

Transversal application on surface quality control in Manufacturing Engineering

Se ha fabricado y recubierto una serie de moldes físicos: chapas rectangulares de Al-Mg, con distintos materiales poliméricos que han permitido abarcar distintos puntos de vista de la ingeniería de superficies que se contemplan en las asignaturas implicadas en este proyecto. Sobre estos modelos se ha podido medir, verificar, proponer estudios, informes, etc., y se ha desarrollado actividades académicamente dirigidas y trabajos por competencias.A series of physical mouldings have been manufactured and coated: rectangular plates of Al-Mg, with different polymeric materials that have allowed including different points of view in the the engineering of surfaces that are contemplated in the subjects involved in this project. On these models it has been possible to measure, to verify, to propose studies, reports, etc., and has developed activities academically directed and works by competences

Non-Stick Coatings in Aluminium Molds for the Production of Polyurethane Foam

The manufacturing of polyurethane foam is a process of great industrial importance in the automotive and furniture sector. The operation of demolding is the most delicate, since the foam sticks firmly to the walls of the mold onto which it has spread. In order to avoid the use of demolding agents, the proposal is to coat the inside of the molds with non-stick coatings. In this work, three types of different coatings were studied: fluoropolymers, ceramics, and elastomers. After carrying out different tests in the laboratory, two fluoropolymer coatings (PFA (perfluoroalkoxy) and PTFE (polytetrafluoroethylene)) were selected for a test at the industrial level and, after 1500 cycles of demolding, it was experimentally proven that the PFA coating is the most adequate for the use studie

Water-Repellent Fluoropolymer-Based Coatings

We would like to thank to the company TECNIMACOR S.L. (Córdoba, Spain) for the preparation of the coatings studied in this work.Fluoropolymer-based coatings are widely used for release applications. However, these hydrophobic surfaces do not reveal a significantly low adhesion. Water repellency incorporated to fluoropolymer coatings might enhance their release performance. In this work, we focused on the surface texturing of a well-known polytetrafluoroethylene (PTFE)-based coating. We explored as texturing routes: sanding, sandblasting and laser ablation. We examined the surface roughness with white light confocal microscopy and the surface morphology with environmental scanning electron microscopy (ESEM). Water-repellent fluoropolymer coatings were reproduced in all cases, although with different degree, parametrized with bounces of water drops (4–5 μL). Laser ablation enabled the lowest adhesion of coatings with 24 ± 2 bounces. This result and the current development of laser patterning for industry assure the incipient use of laser ablation for release coatings.The research was funded by the projects MAT2014-60615-R and MAT2017-82182-R, funded by the Spanish Ministry of Economy and Competitiveness (MINECO-FEDER)