Parameters Affecting the Process in Cataphoresis Plating Plants
Cataphoresis plating systems, although are initially used in the automobile industry; It is preferred in all sectors, especially for the primer or topcoat painting of metal parts with grift surfaces.
It is applied as a very strong method for the protection of products and surfaces from corrosion in many different alloys such as wheel manufacturers and white goods manufacturers.
It has very important advantages over Epoxy/ Acrylic wet or electrostatic powder paint systems or different electrolytic (Galvano) plating methods.
In addition to the homogeneous and aesthetic appearance of the film thickness, which is formed according to other different applications, it is also very ideal for sharp edges, grift and welded areas.
It also offers serious quality-cost advantages in terms of scratch and impact resistance.
In addition to its superior corrosion resistance limits, its high production capacity makes Cataphoresis plating an indisputable place to all manufacturers in terms of costs.
When considered together with the treatment costs; being an economical, low fire risk, and benefits in the field of occupational health and safety; gives it a serious advantage over different applications.
Today, if automobile manufacturers increased their corrosion warranty for more than10 years, this success would have been possible with the widespread use of cataphoresis systems (their use in automotive has reached a rate of 95%).
The electrolytic paint plating method treatments, which started with anaphoresis in the second half of the 1950s, were replaced by cathodic (cataphoresis) electrolytic coatings after the 1970s, and the anodic application was abandoned in many areas.
Cataphoresis Paint; To define its chemical nature roughly, it consists of a special dispersion fixed with a colloidal electrolyte. The Cataphoresis Paint System can be explained as simply as this.
After controlled pretreatment, metal parts that are given electrical direct current and required to be plated with paint; It is kept in the dip paint tank for 1 to 3 minutes.
The paint remaining on the surface of the parts removed from the paint tank, which can't adhere due to paint isolation, is removed from the surface by simple mechanical processes.
After the pre-evaporation period, the parts are dried in the curing oven.
The metal parts that will be painted are the electrodes, the paint tank forms the other electrode.
The metal parts to be painted; connecting the system to the anode part is called anaphoresis coating or anophoretic electrolytic plating or anodic electrolytic It can also be described as a plating. Conversely, when the metal parts to be painted are loaded on the cathode part, it is called cataphoresis coating or cathodic electroplating.
In other words; If it is a resin cation, it can be considered as anodic plating and if the resin is an anion, it can be considered as cataphoresis coating.
While plating, during the whole reaction process some chemical reactions may occur.
The stability of these reactions is only possible if the homogeneous solubility and dispersion of solvents, resins, pigments, and additives are fully ensured.
Although the formulation rates of the Cataphoresis Paints according to the manufacturer and the additive products used vary, they are approximate as follows.
75-90% Water
15-20% Resin
0-5% Pigment
0-5% Solvent
With ionization Cataphoresis Paint Resin selection; It is one of the most important parameters that determine the quality because the resin (Acrylic-Epoxy-Hybrid) used as raw material is the most basic product that also increases the resistance against corrosion and sunlight sensitivity.
Epoxy polymer resins have high corrosion and chemical resistance. UV resistance is the most prominent advantage of acrylic polymer resins.
Hybrid systems can be used for more complex expectations.
Pigment pastes add color, UV resistance, and shine.
Fillers increase the thickness and drying properties of the paint and also have reaction accelerating effects.
The main pigment elements are TiO2 and Carbon Black.
Fillers; silicate compounds can have different formulations, the purpose of which is to contribute to the formation of a homogeneous paint film.
The main solvent of the cataphoresis system is pure water, along with butyl glycol and phenoxypropanol.
Butyl glycol contributes to the dissolution, homogenization, and deep adhesion of the paint.
Phenoxypropanol and its derivatives help to obtain an aesthetic appearance by providing homogeneity of the surface distribution.
Since phenoxypropanol has very little solubility, it must be introduced into the system very slowly from the UF tank or resin/emulsion pump.
Deionized water is 75-90% of the paint component and is the common carrier of all chemical components.
The basic principle of Cataphoresis Plating
Electrical direct flow is given to the area where the metal parts and electrodes are immersed in the plating tank. With the voltage created, one of the electrodes will be anode positive (anodic) and the other metal piece will be negative (cathodic).
The plating process will slow down automatically with the first resistance of the paint in the tank to the direct current. If the Ionizing if it is paint, first goes quickly towards the areas closest to the electrode; Then, when these areas are coated with paint, the paint will insulate the metal, and the painting will be completed on these surfaces.
But then the plating reaction will continue until the paint ions move towards more intricate areas and the entire metal surface is isolated, that is, until a homogeneous paint layer is formed on the surface.
The electrical voltage applied to the metal part to be painted is a very important control parameter for the paint film thickness that will form on the surface of the part.
The covered paint film thickness will create a serious insulation and therefore resistance.
If this is the case, according to Ohm's law; As the electrical resistance increases, the electric current will decrease, inversely proportional to the coated regions.
The purpose of this system; It is possible to coat parts with intricate surfaces in a homogeneous thickness.
Time/ direct current relationship Parameters
By increasing the direct current, it is not an ideal or correct way to accelerate the coating and increase the paint thickness and therefore the capacity.
The high current that will occur will cause sudden hydrogen gas output and overheating on the part surface. This is the main reason for capillary or visible tears in the paint.
It is the high direct current application that causes this problem, also known as the rupture voltage. The disproportionately high current is also the source of the electrochemical dissolution of the metal.
This causes the formation of Fe2O3.H2O iron oxide, which reduces both appearance (yellow staining) and corrosion resistance.
Electrical direct flow; It basically creates three different resistance points between the anode and the cathode.
Anolyte resistance (Ra), paint resistance (Rb) and film resistance (Rf) of the coated paint, respectively.
If the point is to increase the paint film thickness, it is necessary to increase the anode surfaces parallel to the voltage, to decrease the distance between the anode and the cathode, or to reduce the electrical resistance that will occur.
Cost Efficiency in Cataphoresis Plating
Cataphoresis Overlay; It is the most efficient plating method in terms of operating costs.
Because being able to reach high capacities ensures the elimination of production based on retouching due to the low charge rate.
And its unique advantages such as transfer efficiency, standard paint film formation, 90-95% coating efficiency and low employment opportunity make Cataphoresis Coating unrivaled from all other paint systems in terms of paint consumption cost per area/unit.
It is very important for the intricate parts that the film thickness and homogeneity of the coated products can be controlled so that the consumption amounts are also manageable.
Theoretically, the film thickness of the Cataphoresis Coating is 2-5 microns.
A homogeneous plating cannot be achieved in different paint applications; This ratio is between 15-100 microns as droplets and surface depressions are formed.
With the adaptation of automation-based robotic solutions, it can be operated with much less personnel.
It is a quality plating system where there are no problems caused by the mental fatigue of the employees.
As it is a dipping system rather than spraying, parts can be hung much more frequently.
Cataphoresis Plating and Compliance with Environmental Regulations
Water-based, with minimum waste; The most outstanding ability is that heavy metal elements are not included in paint combinations../p>
The fact that it contains almost zero petroleum-derived organic solvents is proof that it is the most environmentally friendly paint system in terms of VOC values.
Unique advantages such as having a water-based chemical content, almost no paint waste, minimizing a possible fire hazard, and occupational health and safety are the dominant choices of Cataphoresis Platings.
Parameters affecting plating quality
Permeation; Although the chemical composition of cataphoresis paint varies according to the formulation properties: conductivity, physical properties of the surface and temperature are the most important parameters affecting the quality.
In metal workpieces subjected to the coating process, the first starting point of the coating is the nearest flat and outermost parts that see the anode cells. Then, the distance from the anode and the deep intricate areas continue the coating process. The reaction ends when the desired thickness is reached.
Another point to be paid attention is that thick paint film is not formed on flat surfaces and areas that see the anode (brittleness increases).
Cataphoresis Paint Controls and Analysis
05th April 2021
