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autodeposition products under the brand names Autophoretic® Coating Chemicals and Aquence® Coatings Chemicals. The autodeposition process has been. Autophoretic®, also known as autodepostion or A-coat, is a waterborne process Another characteristic of the Autophoretic® coating process is that is quite. Autophoretic® coating or autodeposition is a patented process which involves the chemical deposition of a PVDC polymer upon raw steel substrates providing a.
Presently, there are numerous installations in operation, both captive and job-shop, coating a variety of fabricated steel parts for the automotive and general industry markets. The bath viscosity is close to that of water with little or no organic solvents in the coating bath.
The mildly acid bath liberates a small amount of iron from the steel parts being immersed, causing an immediate surface reaction that releases iron ions. These ions interact with the latex in solution causing coating deposition on the surface of the steel parts. The newly deposited organic film is adherent yet quite porous.
This allows the chemical activators to diffuse rapidly in the film and etch the surface of the metal. The continuous formation of coating provides a film with a high degree of surface protection and corrosion resistance.
Introduction Painting a vehicle is one of the most expensive operations in automotive industry. This high cost is attributed to the need to have high quality coatings and the necessity of meeting strict environmental regulations. The coated surface must be finished in a way that provides an excellent surface quality [ 1 , 2 ]. Automotive paint has two main functions [ 2 , 3 ]: i to make the vehicle look good and ii to protect the underlying metal from the harsh environment to which it is exposed.
Despite the advances in surface coating technologies, priming remains the fundamental phase to prevent corrosion [ 3 ]. Protection against any form of corrosion and paint film durability is and will be of major importance. Many researchers have focused on the chemical-mechanical priming performances. They have found that the chemical composition of the formed rust depended on the nature of the anticorrosive pigment present in the primer coating.
Lonyuk et al. They have observed failure by delamination between the topcoat and primer for some coating systems and adhesive failures between the primer and substrate for others. Other authors [ 7 — 10 ] have demonstrated the great effect of the substrate type on the degradation of the painted metal. Suay et al. Miller [ 8 ] showed that the reactivity of a metal substrate and the type of corrosion product formed had an influence upon the reliability of a protective coating.
Kittelberger and Elm [ 9 ] concluded, in their work, that the type of the substrate was responsible for paint blistering susceptibility.
AUTOPHORETIC COATING PROCESS PDF
He concluded that the corrosion performance of these coatings, as measured by their delaminating time, was directly related to the corrosion resistance of the unpainted substrate. For the evaluation of coating systems performance, several tests have been used: mechanical testing using Persoz hardness, impact resistance, cupping, lattice method, and bending.
Experimental 2. Each set contained a series of 16 panels that had been painted with or without a topcoat.
Primer types, substrates, and their mechanical properties are summarized in Tables 1 , 2 , and 3. The electrogalvanizing and hot-dip galvanizing of steel panels were carried out under industrial subcontracting. Water rinsing was used after each step. Table 1: Chemical composition of the used substrates. Table 2: Mechanical properties of the used substrates.
Table 3: Characteristics of different primers. Primer coatings were applied using gravity pneumatic spray gun. Before application, viscosity and density of the different primers coatings were measured.
Testing Methods and Equipment 2. The stainless steel balls, 8 mm diameter, were of hardness HRC The total weight of the pendulum was g. The period of oscillation was 1 sec and the time for damping from a degree displacement to 4-degree displacement was taken.
Three tests were performed to each coated sample and the final result was the average of the three experiments. Impact Resistance Test Impact tests have been performed over coated samples by making the impact from the substrate side reverse impact according to ISO The impact tests consisted of checking the primer damage resistance to the collision of a ball g dropped from a fixed height of 0.
The weight was dropped through a guiding tube whose height was incrementally marked. Resistance of the Coating against Cupping in an Erichsen Cupping Test ISO The objective of this test was to identify the resistance of the paint film against the ongoing deformation of a coated substrate panel with a pressed-in 20 mm steel ball. Coating Resistance during Bending on a Cylindrical Mandrel This identified the resistance of the paint film against ongoing deformation of a coated substrate panel around a 2 cm diameter stainless steel mandrel, verifying the disruption of paint film cohesion during the bending of the painted substrate panel ISO Friction Test Friction tests were carried out in dry conditions using a pin-on-disc tribometer.
The applied normal load was 1 N. During tests, the variation of the friction coefficient versus time was recorded. A circular scratch surface 1 cm2 was made through the coating with a sharp instrument so as to expose the underlying metal to the aggressive environment. The panels were evaluated to assess failure at the scratch mark. Evaluation of specimens was performed after different exposure times 2, 7, and 15 days and consisted in the measurement of scratched surface increase.
Platinum sheet was used as a counter electrode and saturated calomel electrode SCE as a reference one. The tested coated samples were firstly allowed to reach a steady open circuit potential OCP.
Surface Morphology Surface profiles, using Surtronic 25 profiler from Taylor Hobson, were used to examine the surface topography of different paint coatings. The morphology of the corroded and delaminated paint coatings was studied using a LEICA optical microscope. Results and Discussion 3. Mechanical and Tribological Behaviors 3. In general, the hardness of a polymeric coating is an excellent probe of its chain stiffness [ 11 ]. For this reason, all coatings seem to have high adhesion on the painted panels.
It is to be noted that the presence of the zinc coating layer hot-dip galvanized or electrogalvanized has not shown a negative effect on the impact resistance of the painted systems. The Resistance of the Coating against Cupping During film formation and apart from the mechanism involved evaporation of solvent, coalescence, chemical reaction, or their combination , in almost all cases the coating tends to contract.
Standards require 4 mm as a minimum value of cupping for coating to be accepted. The cupping test is conducted with a relatively slow rate.
The cupping action is stopped when cracking in the coating is visually detected. As shown in Figure 1 a , the behaviors of PP and SP primers are conforming to the industrial regulations, for all substrates, whereas the other two primer coatings, AP and DP, are not.
If nonmetallic coated steel and aluminum substrates with PP and SP primers have comparative behaviors, zinc coated steels hot-dip galvanizing or electrogalvanizing show considerable differences.
Placing the primers in order from best to worst in terms of cupping, we obtain the sequence. The Degree of the Adhesion of Coatings by a Lattice Method This method is an adequate means for controlling the level of adhesion strength after the coating has been spread and cured on the substrate. Moreover, it allows the detection of any failure in the case of the dissolution of the bond between coating and substrate. After a lattice pattern is cut into the coating, the examination of the created grid area was conducted using an illuminated magnifier.
In the rather qualitative standardized tape-test the scales used to classify the specimens are from 0 to 5; that is, 0 corresponds to a very poor and 5 to a very good adhesion. Table 5 shows good adhesion strength of the whole coating systems.
Assessment of Automotive Coatings Used on Different Metallic Substrates
It magnification to find coating defects, observable corrosion, or coating erosion. After can also be easily reconditioned and recycled. However, due to consumer demands, this study was complete any defects would be further studied under a Field Emission- manufacturing companies are now looking beyond their four walls, far up the supply Scanning Electron Microscope FE-SEM.
Currently Standard Microscopy Results: The standard surface microscopy evaluation detected A-coat uses a Polyvinylchloride PVC coating base, which gives off chlorine gas, during multiple defects in the coating surface seen below. These defects appeared to be the materials manufacturing process. Due to this, a West Michigan manufacturing voids in the coating. These void locations were too big to be detected using the BET company is evaluating conventional autophoretic paint cost and performance against a experiment but too small to be observed by the naked eye.
When corroded specimens greener epoxy based A-coat, as well as a powder paint alternative. This company were examined these void locations were the localized points of failure.
The purpose of this study is to ascertain if powder paint or epoxy A-coat would be equivalent or superior to conventional A-coat while decreasing environmental impact.
Problem: Autophorectic Coating is used to coat a wide range of manufactured goods. However, it has been found that this coating will fail and corrosion will become evident over a relatively short period of time.
It is possible that this coating will not meet most manufacturers quality standards at the recommended coating thickness. Theoretically A-coating should out perform powder paint while requiring a fraction of the coating thickness. It is unknown if the coating is failing at its recommended thickness due to the coating material or from the coating process.Kittelberger and Elm [ 9 ] concluded, in their work, that the type of the substrate was responsible for paint blistering susceptibility.
This unusual feature strongly limits carryover of coating chemicals into the rinse tanks and greatly reduces the demand for waste treatment. I know that these two processes are not the same.
Sakata et al. Please contact your local PPG office for that paper.
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