Powder Coatings-1
- 5 April 2018
- Posted by: Stm Coatech
- Category: Educational Articles
Overview of Powder Paint
It is the generic name given to the dyes that are dyed during application. There are resins, pigments and modifying agents in the contents, but there is no solvent. The powdery paint is heat and often electrically connected to each other and forms a continuous film of paint film.
The most common way of applying the powder coating to metal objects is to spray the powder using an electrostatic gun, or corona gun. The gun imparts a negative electric charge to the powder, which is then sprayed towards the grounded object by mechanical or compressed air spraying and then accelerated toward the workpiece by the powerful electrostatic charge. There are a wide variety of spray nozzles available for use in electrostatic coating. The type of nozzle used will depend on the shape of the workpiece to be painted and the consistency of the paint. The object is then heated, and the powder melts into a uniform film, and is then cooled to form a hard coating. It is also common to heat the metal first and then spray the powder onto the hot substrate. Preheating can help to achieve a more uniform finish but can also create other problems, such as runs caused by excess powder. Another type of gun is called a tribo gun, which charges the powder by (triboelectric) friction. In this case, the powder picks up a positive charge while rubbing along the wall of a Teflon tube inside the barrel of the gun. These charged powder particles then adhere to the grounded substrate. Using a tribo gun requires a different formulation of powder than the more common corona guns. Tribo guns are not subject to some of the problems associated with corona guns, however, such as back ionization and the Faraday cage effect. Another method of applying powder coating, called the fluidized bed method, is by heating the substrate and then dipping it into an aerated, powder-filled bed. The powder sticks and melts to the hot object. Further heating is usually required to finish curing the coating. This method is generally used when the desired thickness of coating is to exceed 300 micrometres. This is how most dishwasher racks are coated.
Typical steps in a powder coating process for metal parts:
1. Cleaning (typically an alkaline cleaner, but substrate dependent)
2. Rinsing
3. Phosphating (optional step to improve corrosion protection and adhesion)
4. Drying
5. Powder Coating
6. Curing (typically energy intensive since relatively high temperatures are required to get the powder to liquefy and flow)
Curing
When a thermoset powder is exposed to elevated temperature, it begins to melt, flows out, and then chemically reacts to form a higher molecular weight polymer in a network-like structure. This cure process, called crosslinking, requires a certain temperature for a certain length of time in order to reach full cure and establish the full film properties for which the material was designed. Normally the powders cure at 200°C for 10 minutes. The curing schedule could vary according to the manufacturer’s specifications. The application of energy to the product to be cured can be accomplished by convection cure ovens or infrared cure ovens.
Advantages of Powder Coating:
Powder Coating Environmental friend. It does not produce any waste during production and consumption and it does not cause air and water pollution. In terms of protection of the environment, the organic volatile chemicals (VOC) that emerge in wet color are absolutely absent in powder.
The negative effect of powder paint on health is less than other paints.
Powder paint is ready to use. No mixing, no dilution with liquid.
Powder Paint usage technique is easy and user training can be done very short time. Manual and robotic systems are very suitable for use. Thus, the user can specialize with a short and practical training.
Any kind of decorative surface can be obtained with Powder Coating. (Smooth, glossy, rough, emery paper look, etc.)
Solvent usage during cleaning is lower.
A single floor can be thickened without current.
It quickly forms and cures in a controlled manner with high temperatures in the oven.
Application efficiency is higher (No losses can be applied with efficiency close to 100%)
Disadvantages of Powder Coating:
Thin films are more difficult to obtain.
Special chemistry may be required for repairs.
The initial investment cost is generally higher.
Color change is slower.
Powder paints can not be mixed with each other in any way.
Serious temperatures are required for curing (180-250 oC)
The wetted parts must be precisely handled.
The material to be painted in electrostatic applications must be sufficiently conductive. Otherwise, weakness may occur during application of paint.
Metal flake pigments are more difficult to form into paint.
For metal materials with complex and closed geometry, proper painting is very difficult (Faraday Cage Effect).
Special equipment and extractions are required for color changes.
Types Of Powder Coating
Epoxy: The formula contains epoxy type resin and suitable hardening agent. It is used when resistance against chemicals is needed. Particularly the fuel tanks can be given as an example. Such kind of coatings has less strength against temperature and light.
Epoxy-Polyester: It contains epoxy and polyester resin. It is the type of coating developed for providing physical and chemical strength properties together. It is particularly an inevitable solution for the white appliances industry. In addition to this, lighting fixtures, metal furniture, hospital equipment, armatures, and shower cabins can be coated with such kind of coatings. Although it is stronger than epoxy type coatings in terms of temperature and light resistance, it has less resistance than the outdoor polyester coatings. Its cost is lower than the other types of coatings.
Polyester/PRIMID: It is another exterior wall product made by using polyester resin and Primid hardening agent. It is developed as an alternative to Polyester/TGIC product. As is known, products containing TGIC have to receive some certain labeling marks according to the European Union norms, while Primid products do not contain any marking. They generally have the same characteristics with TGIC products. They are used for coating outdoor materials, particularly in the aluminum profile industry. These are Qualicoat certified products.
Polyurethane: It is made by hardening isocyanate with polyester resin. There are two types, including indoor and outdoor. The only handicap during the past years was the smoke it emitted during the curing process. The smoke problem has been solved in last versions of this kind of coatings, which allow very smooth surfaces.
Tests for Powder Coating
Surface Smoothness Test Gloss Test Color Test
Film Thickness Test Impact Resistance Test Flexibility Test
Hardness Test Density Test Moisture and Salt Test
Adhesion Test Conical Bend Test Particle Size Analysis
Accelerated Weathering Test Opasity Test Viscosity Test
Acid Resistance Test Detergent Resistance Test Yellowing Test
Gell Time Test Scratch Test Stone Impact Test
Cold Stone Impact Test DSC Test
Powder Coating Application Considerations
-Routine maintenances are important for ensuring that business quality is high, and business expenses are low.
-The ovens should be measured seasonally, and optimized when required.
-A good level of grounding is required for homogeneous coating and less recycling powder.
-Injectors of the guns should be replaced regularly, their loading capability should be measured regularly, and guns should be serviced when required.
Powder Coating Products Uses
Aluminum industry,
Steel door industry,
Machinery industry,
Lighting industry,
White goods industry,
Automotive supplier industry,
Metal furniture industry,
Steel shelf industry
Manufacture of agricultural tools and equipment,
Bicycle manufacturing,
Glass and wood industry,
Manufacture of kitchen tools and utensils (pots, pans, etc.),
Manufacture of electric panels,
Table, chair manufacture.
STM Coatech, SSPC PCI (International Coating Enspektörlüg), and Corroder (MPA Group England), Turkey, Romania, Ukraine, Georgia, Russia, Azerbaijan, Turkmenistan, Kazakhstan, Iraq, Qatar, Kuwait, Oman, the Sudan and Algeria official licensors.
It is also authorized examination center of the country we have already mentioned above, especially Turkey. Corrodere Training Courses are listed below.
1.Icorr Level 1
2.Icorr Level 2
3.Icorr Level 3
4.IMO PSPC
5.Corrodere Hot Galvanizing
6.Corrodere Insulation Inspector
7.Practical Workshop Icorr 1,2,3
8.Corrodere Marine & Offshore Inspector
9.Transition to Icorr
REFERENCES:
1. Rochester Institute of Technology, Powder Coating Process, Date of Access: 30 March 2018, https://www.rit.edu/affiliate/nysp2i/sites/rit.edu.affiliate.nysp2i/files/pdfs/powder_coating_process_final.pdf
2. Pulver, Electrostatic Powder Coating, Date of Access: 30 March 2018, http://www.pulver.com.tr/electrostatic-powder-coating
3. Element Boya, Powder Coating Application Process, Date of Access: 30 March 2018, http://www.elementboya.com/En/show/-powder-coating-application-process