1/ Earthing of the object & equipment

The process of Powder coating application might generate a large quantity of negative charges being transfered to the object. Supposed these electrons could not be earthed efficiently, the coated subject surface rapidly develops a powerful negative charge which thus repel the negatively charged powder from the spraying gun. Thus, as a result of unsufficient earthing it becomes impossible to build up rapidly and efficiently a thick layer of powder with good flow and finish.

Inadequate earthing can easily be recognized by little or no powder accumulation around the hanging point of the object being coated.

2/ Air & Compress air quality

Relative humidity within the working environment is of great significant for spraying efficiency. Ideal relative humidity being 45~55%. A quicker build-up of the powder layer and more even coating thickness are two of the advantages achieved by controlled humidity. Relative humidity can be measured with simple and inexpensive equipment.

Only clean, dry compressed air should be supplied to powder coating equipment. The quality of the compressed air can change the electrostatic charging and transporting properties of the powder. Impure compressed air my also cause visul defects in the coating. Pressurized air must be free from oil, water and as dry as possible.

3/ Most frequent encountered problems shown in the table below





Poor charging

Inadequate powder build
Inadequate wrap on the part

Voltage too low

Poor earthing

Powder output is too high

Powder too fine

Check electrical continuity from voltage source to electrode, including cable, resistors and fuses.

Check earthing of the conveyer, hanger and substrate (<5 Ohm).

Replace broken or missing components.Clean electrode insulated by powder build.

All contact area must be free of powder build, heavy grease and other insulating material.

Turn down the powder feed until all material passing through corona field is adequately charged.

Reduce ratio of reclaim to virgin powder

Poor penetration, powder will not coat Faraday cage areas

Output of powder too low.

Poor ground.

Powder cloud too wide.

Poor gun placement.

Voltage too high

Check earthing.

Use a smaller deflector.

Adjust gun position so powder cloud has a direct path to recess area

Turn up powder delivery air setting. Use gun-barrel extension.

All contact area must be free of insulating material,

Turn voltage setting down so powder on part edges and leading surfaces do not repel powder from corner

Rotating valve of cyclone blocked

Temperature too high

Powder too fine

Sieve is collated

Vibration of valve

Content of hopper after sieve is too high

Optimize flow of powder in hopper

Cool valve.
Adjust rotating valve to avoid friction

Poor built-up (crater formation)

Voltage too high

Gun positioned too close to piece.

Poor earthing

Turn down voltage setting.

Change gun placement away from part

Check earthing of conveyer, hanging and substrate

Powder feet spurting or slugging, interrupted powder feed

Insufficient air pressure or volume

Hoses kinked, flattened or too long

Poor fluidization

Hoses, pump venturies or guns clogged with powder

Check air supply, enough air volume when other equipment make use of compressed air

Check supply-tubes

See "poor fluidization in fluidized bed"

Check filled tubes, venturies and guns on
Check free-flow properties of the powder
Check air suplly for moisture that caused powder compacting
Check air velocity: too low
Check feeding unit: too high
Plasticizer "swets" out of plastic material of the tube

Renew tubes if necessary

Clean or renew the tubes, venturies or guns
Clean the injectors
Install airdyer (dewpoint >40°C)
Increase air delivery
Use more guns
Renew the plastic material of the tube

Poor spray patterm, not a symmetrical powder cloud

Worn gun parts

Build up of agglomeration though friction

Delivery air too low

Replace worn parts

Clean gun parts, particularly the deflector

Increase delivery air

Poor fluidization in fluidized bed

Fluidization pressure is too low

Porous bottom clogged

Powder too fine

Moisture content of compressed air too high

Check particle size

(Dew point of atmospheric pressure -40°C)

Increase air pressure

Clean or replace porous bottom

Reduce the ratio of reclaimed powder
Contact powder supplier

Install an air dyer

Powder falls down from the substrate

Moisture content of powder too high

Bad chargeability of the powder

Powder output too high or the pressure for the transport air too high, which blows the powder from the object

Poor earthing

Powder is too old

Unsuitable particle size distribution

Check storage parameters (maximum humidity 75 %, max. temperature 25°C)

Adjust level of high tension unit

Reduce powder output and/or reduce pressure of transport air

Check earhing

Contact powder supplier

Reduce ratio of reclaim to virgin powder.
Contact the powder supplier