Powder Coating Problems and Solutions

All the powder coating companies have problems with their coating. Here you can find some useful information about powder coating problems and solutions.

Powder coating is increasingly accepted as the preferred finishing process for many applications. Increasingly stringent environmental regulations, rising costs in all areas, and demands by consumers for better quality and more durable products are among the challenges facing today’s finishers. Powder coatings provide a solution to these challenges and others. Powder coating is the technique of applying dry paint to the component.

The powdered paint is normally applied by using a powder feed system and gun to electrostatically charge and spray the powder onto the part. For some applications, the part being coated is dipped into a fluidized bed of powder. The coated part is then heated in an oven, or via infrared panels, to melt and cure the paint. During the curing process, a chemical cross-linking reaction is triggered and it is this chemical reaction that gives the powder coatings many of their desirable properties.

Powder Coating

Powder coating is a dry finishing process that uses finely ground dry particles of pigment and resin to create a durable, hard, protective finish on a wide variety of surfaces. The powder is electrostatically charged and applied to the surface of the object to be coated, where it adheres and then cures under heat to form a hard, durable finish.

Powder application can be a challenging process, and there are a number of problems that can occur. Some of the most common problems include:

Faraday cage effect: This occurs when the object being coated is surrounded by a metal cage, such as a Faraday cage. The cage blocks the electrostatic charge from reaching the object, and the powder does not adhere properly.
Poor adhesion: This can be caused by a number of factors, including improper surface preparation, incorrect curing parameters, or using the wrong type of powder.
Uneven coating: This can be caused by a number of factors, including incorrect gun settings, improper distance between the gun and the object, or using the wrong type of powder.
Orange peel: This is a defect that causes the surface of the coating to look like an orange peel. It is caused by a variety of factors, including incorrect gun settings, improper curing parameters, or using the wrong type of powder.
Fish eyes: These are small, round defects that appear on the surface of the coating. They are caused by bubbles of air or solvent that are trapped in the coating.

There are a number of solutions to these problems. Some of the most common solutions include:

Faraday cage effect: This can be solved by grounding the object being coated.
Poor adhesion: This can be solved by properly preparing the surface of the object, using the correct curing parameters, and using the right type of powder.
Uneven coating: This can be solved by using the correct gun settings, using the correct distance between the gun and the object, and using the right type of powder.
Orange peel: This can be solved by using the correct gun settings, using the correct curing parameters, and using the right type of powder.
Fish eyes: This can be solved by using the correct gun settings, using a cleaner gun, and using a better quality air supply. <br>

Here are some additional tips for preventing powder coating problems:

Use a high-quality powder: A high-quality powder will have a more uniform particle size and shape, which will improve transfer efficiency and reduce the risk of defects.
Use a properly maintained gun: A properly maintained gun will help to ensure that the powder is applied evenly and that the correct amount of powder is used.
Pretreat the substrate: Pretreating the substrate will help to improve surface adhesion and reduce the risk of defects.
Use the correct application parameters: Using the correct application parameters will help to ensure that the powder is applied evenly and that the correct amount of powder is used.
Monitor your results: Regularly monitor your results to identify areas for improvement.

By following these tips, you can prevent powder coating problems and improve the quality of your finishes.

Poor fluidization in powder hopper:

The powder is supposed to flow like water in the fluid container (boil). Poor fluidization is recognizable in the slow and non-continuous transportation of the powder coating from the fluid container to the guns. No homogenous powder cloud is achieved.

Possible Causes	Explanation
Powder level too low	Add powder to the normal level
Fluidizing air low or too high	Change pressure use larger hose diameter
Oil remnants in compressed air	Check the filter in front of the coating booth
Compact or damp powder	1. Manually loosen powder in hopper 2. Check compressed air for quality
Oil remnants in compressed air	Check the filter in front of the coating booth
Fluidizing plate chugged / defective	Clean plate or exchange the plate

Clogging of the powder feed houses

Deposits (agglomerates) form in the powder feed hoses, which sporadically are freed by delivery air and appear as powder puffs on the workpieces. After curing these powder puffs appear as faulty surface elevations.

Possible Causes	Explanation
Feed air pressure too high/too low	Reduce/increase pressure
Delivery of air moist or oil in pressurized air	Check in-line filters and moisture traps
The material choice of hoses	Check hoses for material quality
Worn venture or pump	Replace worn parts
Too fine powder	Decrease amount of reclaim to hopper Optimize virgin powder plus reclaim ration
Feed hose too long	Minimize feed hose length

Poor Attraction of the Powder to the Component

Possible Causes	Explanation
Incorrect Voltage at the gun	Check voltage, clean or replace the gun
Insufficient Grounding	Clean grounding points and hangers
Excessive build-up of cured powder coating	Clean hanger
Worn venture or pump	Replace worn parts
Too much powder out put	Reduce air flow/powder flow
Gun distance to part too close, blast effect	Adjust the distance
Gun air pressure too high	Reduce forward air pressure
Film build too high	Reduce powder flow
Insufficient wetting	Check pre-treatment

Poor Wrapping

With one-sided gun positioning, only minimal film thickness can be achieved on the opposite side.

Possible Cause	Explanation
Powder flow too low or too high	Optimize system parameters, adjust air flow
Insufficient grounding	Use clean hooks
Supplemental air flow is too high or too low	Adjust air speed and powder cloud
Gun voltage too high	Adjust voltage to suit parts
Insufficient charging of the powder	Adjust high voltage; consult powder manufacturer
Poor or wrong positioning of the parts	Adjust hanging configuration

Poor Penetration into Recesses

Possible Causes	Explanation
Too low powder delivery	Increase powder flow
Airspeed too high	Adjust equipment controls
Poor grounding	Adjust equipment controls to suit the parts
Insufficient charging of powder/defective	Check and improved grounding
Incorrect spray pattern/spray to wide	Adjust voltage, contact equipment
Too high voltage	Try different spray nozzle
Poor gun placement	Reduce voltage so that surface closest to the gun does not repel powder
Powder too fine	Adjust gun position to enter directly into the recessed area
	Reduce ration to reclaim to the hopper, contact powder manufacturer

Film Thickness on Component Too High

The powder coat layer shows an uneven surface prior to curing after curing shows orange peel or pinholes

Possible Causes	Explanation
Excessive powder delivery	1. Reduce powder feed to gun 2. Increase distance between gun and component
Coating time too long	Lower the coating time
Unfavorable geometry of parts	Change hanging or gun configuration
Gun voltage too high	Reset gun voltage
Too much pre-heat (if used)	Reduce pre-heat cycle

Film Thickness on Component Too Low

Possible Causes	Explanation
Powder delivery is too low	1. Set correct powder feed pressure 2. Check if powder venture is the correct size, clean and set correctly
Insufficient coating time	Increase the time component by
Insufficient charging of the powder	Test and adjust the voltage
Faraday cage effect	Adjust the voltage and forward airflow
The surface area of the hanger is too large compared to the surface area of the workpiece	Reduce the size of hangers
Damp powder	Remover powder and replace, ensure all powder coatings are kept sealed until required in the use
Insufficient grounding	Use clean hooks, avoid thin hooks
The lower level of powder in fluid hoper	Check minimum indicator

Appearance looks uneven and broken before curing

Possible Causes	Explanation
Back ionization	1. Reduce voltage 2. Check if grounding points are clean 3. Reduce deposition rate and film thickness 4. Ensure no moisture is entering the system 5. Move the gun further away from the component

Powder dusting out of hoper

Possible Causes	Explanation
Too high air pressure	Reduce air pressure to fluid bed
Too fine powder	1. Decrease amount of reclaiming ho hopper 2. Check ration of virgin powder

Surface Defects in the powder coating problems and solutions

Powder Puffs on the workpiece

Powder puffs are powder clusters that in an improperly fused condition are visible as powder hills in the powder film. After curing these powder puffs appear as disturbing elevations on the surface

Possible Causes	Explanation
Powder Large	hose too long or diameter to	Change hose diameter, shorten hose
Powder too fine (reclaim)	Add virgin powder
Powder falls off booth ceiling	Adjust/increase cleaning intervals	frequency	of	booth
Powder fails off the workpiece	Test grounding, check the diameter of hoses
Gun nozzle defective	Check nozzle, replace
powder moist	Use dry powder, check air filter and moisture traps in the compressed air system

Crater

Defect – blank area in the powder coat, which extends all the way to the substrate (diameter up to 2mm)

Possible Causes	Explanation
Insufficient pre-treatment (e.g. oil and grease residues)	Test pre-treatment if necessary, contact pre-treatment supplier
Rust, white rust on parts	Assure clean surface, apply recommended
Incompatibility with powder coating from other manufacturers	Cleaning of coating and application equipment, contact powder coating supplier
Surrounding air contaminated	Balance air flows in the plant, avoid cross drafts
Workpiece moist/wet	Increase drying time/temperature
Liquid and powder paint in the same plant	Definitely avoid – reconfigure the plant
The base coat was cleaned with solvents	Preheat the workpiece or avoid solvents

Pinholes in the film

Development of fine pores on the surface also leads to change in gloss level

Possible Causes	Explanation
Silicone contamination	Locate and remove the source
Oil contamination	Check degreasing plant
The moisture content of powder is too high	Testing through drying of powder/test storage conditions
Oil/water in the air supply	Check oil/water separators on the air supply
Film build too high	Note recommendations of powder manufacturer to minimize film thickness
Very porous workpieces	Check for satisfactory work pieces, possible surface is too rough from sandblasting.

Picture Framing Effect in powder coating problems and solutions

Higher film build of coating on the edges of the part due to wrap, therefore uneven flow

Possible Causes	Explanation
Powder particles too rough/unsuitable for	Strain powder to optimize particle
particular application	distribution consult powder coating
	manufacturer
Voltage too high	Adjust voltage to suit part
Distance from gun to workpiece too low	Adjust/increase the distance
Feed air/powder flow too high	Adjust powder flow

Contamination of Color

Possible Causes	Explanation
Poor housekeeping, when color changing	Totally clean plant, gun, and recycling equipment and recharge with new powder
Cross-contamination at the manufacture	Contact powder supplier
Contamination from equipment cleaning	Vacuuming is more effective than 8air
Deposits from dust and particles in the oven	1. Do not care about another color at the same time 2. Reduce airspeed
Deposits of dust and powder on cured object	Dust-free cooling zones, avoid drafts

Blistering

Elevation of differing size in the powder coat no adhesion due to enclosures at the part surface

Possible Causes	Explanation
Water on work piece	Check dryer and hanging configuration
Corrosion, oil and grease residues	Optimize pre-treatment
Over coating	Assure flawless first coat
Film thickness too high, powder accumulations	Check system parameters, reduce film thickness
Salt residues or chemical remnants on	Check pre-treatment, final rinse stage

Poor Adhesion

Possible Causes	Explanation
Under cure film	1. Increase over temperature 2. Decrease line speed
Poor pre-treatment	Check pre-treatment adjusting tanks to suppliers recommendations

Orange peel in powder coating problems and solutions

Poor flow (orange peel look) short or long waviness of powder coat layer, noticeable only after curing

Possible Causes	Explanation
Heat up cycle of parts too slow	Determine heat up curve and increase
Substrate temperature exceeds the melt temperature of the powder, causing	Check substrate temperature, increase cool down phase
Powder coating material too reactive	Consult powder manufacturer
Film thickness too high or too low	Check system parameters
Incompatibility with other powder	Clean booth, check compatibility
Voltage too high	Optimize voltage
Textured work piece surface	Optimize texture, check work piece surface
Unsuitable particle size distribution	Optimize particle size distribution consult manufacturer

Insufficient wet out of the substrate

Poor or no adhesion of powder coat to the parts surface, large area lifting of cured powder coat

Possible Causes	Explanation
Per-treatment residues	Final rinse de-ionised water
Displaced oils or greases in Per-treatment excessive film build	Per-treatment, check oil separator
Gummed oils, greases or separating compounds, insoluble extrusion oils	Check Pretreatment or change, use different extrusion oils or separating

Gloss too High

Possible Causes	Explanation
Cure temperature too low	1. Increase air temp and metal temperature 2. Decrease line speed
Oven cycle too short	1. Decrease line speed 2. Increase oven temperature

Gloss too low

Oven temperature too high	1. Reduce air temp. and check metal temp. 2. Increase line speed
Time in oven too long	1. Increase line speed 2. Decrease oven temperature
Contamination with a powder which is incompatible	Clean all equipment including gun, booth and recovery system and re-charge with virgin powder

Surface Variations in the Powder Coating Problems and Solutions

Surface variations in powder coating are imperfections on the surface of a finished product that can affect the appearance and performance of the coating. These variations can be caused by a number of factors, including:

Improper surface preparation: The surface of the object to be coated must be clean and free of contaminants before the powder is applied. If the surface is not properly prepared, the powder may not adhere properly and can cause a number of defects, such as peeling, cracking, and bubbling.
Incorrect gun settings: The gun settings, such as the air pressure, voltage, and spray distance, must be set correctly to ensure that the powder is applied evenly and that the correct amount of powder is used. If the gun settings are incorrect, the powder may not be applied evenly, which can cause a number of defects, such as orange peel and fish eyes.
Incorrect curing parameters: The curing parameters, such as the temperature and time, must be set correctly to ensure that the powder cures properly. If the curing parameters are incorrect, the powder may not cure properly, which can cause a number of defects, such as poor adhesion and chalking.
Using the wrong type of powder: There are different types of powder available, and each type is designed for a specific application. If the wrong type of powder is used, it may not adhere properly or may not cure properly, which can cause a number of defects.
Ambient conditions: The ambient conditions, such as the temperature and humidity, can also affect the surface finish of a powder coating. If the ambient conditions are not ideal, the powder may not flow properly or may not cure properly, which can cause a number of defects.

There are a number of solutions to surface variations in powder coating. Some of the most common solutions include:

Proper surface preparation: The surface of the object to be coated must be clean and free of contaminants before the powder is applied. This can be done by degreasing, sanding, and blasting the surface.
Correct gun settings: The gun settings must be set correctly to ensure that the powder is applied evenly and that the correct amount of powder is used. This can be done by consulting the powder manufacturer’s recommendations.
Correct curing parameters: The curing parameters must be set correctly to ensure that the powder cures properly. This can be done by consulting the powder manufacturer’s recommendations.
Using the right type of powder: The right type of powder must be used for the specific application. This can be done by consulting with a powder coating expert.
Controlling ambient conditions: The ambient conditions should be controlled to ensure that the powder flows properly and cures properly. This can be done by using a climate-controlled booth.

By following these solutions, you can prevent surface variations in powder coating and improve the quality of your finishes.

Color difference

Continues or suddenly appearing changes in color at effect compared to original sample part or compared to first parts coated

Possible causes	Explanation
Film thickness varies greatly	Assure constant film thickness
Differing substrates and substrate color	Use substrates of same type for comparisons
Film thickness too him	Apply higher film thickness
Not sufficient or wrong pigmentation in the formulation	Consult powder coating manufacturer
Over curing of powder coating (especially with organic pigments	Observe curing parameters of powder manufacturer
Varying film thickness with over coating	Assure even film thickness
Color deviation due to curing technique or oven atmosphere	Use suitable powder coating, control oven use outside air supply for burner

Cloud Formation: Uneven light to dark or matte to glossy effect of the coating on the work pieces.
Possible Causes	Explanation
Gun distance from part too great or small	Test distance
Uneven powder transport	Introduce sufficient virgin powder
Manual touch-up	If possible pre-coat
Uneven charging	Test application
Uneven grounding of parts	Test grounding
Strongly varying film thickness	Optimize film thickness

Insufficient coverage:
Possible causes	Explanation
Film thickness to low	Assure appropriate film thickness
Film thickness varies greatly from part to	Optimize system parameters
Differing materials and metal colors	Use same materials for comparison

Loss of Mechanical & Chemical Properties in Powder Coating Problems and Solutions

Poor Mechanical properties and chemical resistance: Insufficient compliance with the necessary technical properties of the powder coating
Possible causes	Explanation
Too/high too low heat up temperature or time	Observed curing parameter of powder Coating manufacture
Oil, grease ,Extrusion oils, dust on the surface	Optimize pre-treatment
Differing materials and material color	Insufficient pre-treatment
Incompatible pre-treatment and powder coating	Adjust pre-treatment method Consult chemical and powder supplier

Greasy surface in powder coating problems and solutions

Possible Causes	Explanation
Blooming effect- which film on the powder coating surface, which can be wiped off	Change powder coating formula Increase curing temperature
Insufficient air circulation in the oven	Increase air circulation
Contamination on the surface because of incompatible powder coating from different manufactures	Use only powder coating from one Manufacture at the same time in an oven Consult powder the manufacturer
Powder coating not sufficiently cured	Observe curing parameters

Lifting of the powder coat layer:
Possible causes	Explanation
Under or over coating of the powder coating film	Observe curing parameters
Insufficient/inappropriate parameter	Adjust pre-treatment to job at hand
Scale, surface rust on the work pieces	use “fresh” work piece or stone in dry environment; mechanical pre-treatment
Oxide layer on the work pieces, white rust on zinc plating	Use suitable pre-treatment materials Use mechanical pre-treatment
Film thickness too high	Reduce film thickness or use more

Poor impact Resistance / poor flexibility:
Possible causes	Explanation
Under curing of the powder coating film	Optimize curing parameters
Poor cleaning or pre-treatment	Check pre-treatment chemical and process
Film thickness too high	Optimize the thickness of film
Poor properties of powder coating material/resin	Consult with the powder supplier