As a plant manufacturer, many customers ask our advice when some problem concerning powder coating arises. Due to our long experience and profound expertise in the field of powder coating, we have the matching tips and tricks to make your coating process more efficient and to ensure outstanding coating results at any time.
On the below, you will find a collection of the most often asked questions, and the most often occurring problems in alphabetical order.
Please select the relevant topic and find the appropriate Gema solution.
- "Orange peel"
- "Pin pricks"
- Agglomeration formation
- Back Ionizer
- Edge build-up
- Gun arrangement
- Gun function
- Level sensor
- Maintenance work
- Picture frame effect
- Pit formation
- Powder container
- Powder depositing on an object
- Powder output irregular
- Powder separation degree of the cyclone
- Powder separation degree
- Sieve problems
- Stripe formation
- Uneven coating
Problem: "Orange peel"
Cause Remedies When the powder coating on the object is too thick, an uneven surface is created. If the coating thickness cannot be reduced, the use of a SuperCorona® ring will effectively prevent the formation of the “orange peel effect”. See also Back ionizer.
Problem: "Pin pricks"
Cause Remedies The use of silicon in the coating area is often the cause of a bad coating finish. Because all powders react “allergically” to silicon, it must never be used in the coating area.
Cause Remedies Workpieces grounded insufficiently. Clean the hangers and hooks. Powder resistance too low. Contact your powder manufacturer. Poor grain size distribution. Contact your powder manufacturer. Field strength too high. Change the current, and gun to object distance. Powder is blown out of the corners and cavities by too much air pressure. Reduce the Total air pressure. Too little penetration in the corners and cavities caused by too high current or using of the wrong nozzles.
Reduce the current and use more suitable nozzles. See also Nozzles.
Poor pre-treatment. Contact the supplier. Wrong oven settings (too high, too low, curing time too long). Improve the oven settings. Unsatisfactory powder quality. Contact the Powder supplier.
Change the powder.
A too rapid stroke movement can break up the powder cloud. The stroke speed should not exceed 0.6 m/s - values between 0.2 - 0.4 m/s are recommended.
Problem: Agglomeration formation
Cause Remedies Grain distribution too fine. Contact the powder manufacturer. Humidity in the powder due to incorrect storage. The powder must be dry and stored at the working temperature. Sintering in the nozzles caused by a too high Total air pressure. Reduce the Total air pressure to 4 – 5 Nm3/h. Poor fluidization in the powder container caused by humid compressed air or a clogged fluidizing plate. Check the compressed air for cleanliness, replace the fluidizing
Problem: Back Ionizer
Cause Remedies The so-called back ionization is created when the powder coating is too thick. Reducing the high-voltage prevents back ionization; this however, results in a reduction of the powder transfer rate. Back ionization formation is also dependent on the temperature, and relative humidity. With very difficult powders air-conditioning of the coating area may be necessary. See also “Orange peel”.
Cause Remedies When powder suddenly escapes from a well set up booth, and the pressure monitoring of the exhaust system displays normal values, then the fault is usually to be found in the booth surroundings. The most frequent cause is draughts from open doors or windows in the workshop (even far away from the booth).
Cause Remedies When a powder comes out of the oven mat, then the specifications of the curing temperature of the special powder have not been observed. Always take into consideration the different curing temperatures for the different powders
Cause Remedies Unsatisfactory sieve machine. When a smaller mesh is not sufficient, fitting a sieve machine with automatic contamination removal should be considered. When the chain conveyer is not cleaned regularly or unsuitable grease/oil is used. Clean regularly, and when necessary, fit a hood. When powder is blown into the oven. Check the workshop for air currents. Powder residue in the oven. This can be prevented by regular cleaning. Poorly cleaned recovery system. Clean regularly. When dirty air is sucked into the booth or the oven.
Under certain conditions the coating plant must be separated from the production areas.
When a number of booths are operated together, it can happen that cleaning is influenced.
In this case the booths must be separated further away from each another.
Cause Remedies In the hoses through charging the hoses by friction (spark generation) because the hose material has too little conductivity. Use original GEMA conductive powder hoses. On the injector because of poor grounding. Use original GEMA conductive pneumatic hoses. Between the object, and hook due to poor grounding. Strip the paint from the hangers and hooks. Too little grounding on the manual gun. Do not wear rubber soles and/or gloves. Using metallic powder. To avoid buildup of a conducting film, regular cleaning of the nozzles and powder hoses is recommended. Nozzles for the current generations of GEMA Guns GA02 / GA03 are suitable for metallic powders. For the older generation of GEMA guns: Use the especial metallic nozzles
Cause Remedies Next to the requirements in respect to chemical and mechanical resistance, color repetition, and surface structure, economical aspects also stand in the foreground for the end-user. If you are putting new parts into your product range it will pay, in most cases, to re-check the plant parameters. If the objects are complicated, it will also pay to re-check the arrangement of the guns.
Problem: Edge build-up
Cause Remedies Powder cloud too large. Operate with precisely aimed powder stream. Choose the right type of nozzle. Spacing between the objects too big. Use a gap control. Shape of Object Work with PCC Mode Use SuperCorona® ring
Cause Remedies Rough welded seams, and rust or water on the workpiece cause blisters on the coated surfaces, which can also flake off. A correctly pre-treated workpiece is a prerequisite for a high quality coating result.
Cause Remedies Fluidization of the powder has a great influence on the coating quality. In addition, with difficult powders we recommend to add a vibration of the powder hopper. Retrofitting a pneumatic or electric vibrating table is simple. Remark: GEMA OPTICENTERS ARE NOT PREPARED TO WORK WITH A VIBRATING TABLE. Lumps appear in the fluidized powder, if the powder is stored too long or came into contact with temperatures over 35° C (95° F). Use new powder and check the storage conditions of the powder. Poor fluidization of the powder can be caused by the fluidizing air being set too low. Check the fluidizing air setting.
Problem: Gun arrangement
Cause Remedies Definition of optimal gun arragement The ideal gun arrangement depends on the booth, and its exhaust air system. Booths with a CENTRAL EXHAUST AIR SYSTEM, and QUICK COLOUR CHANGE SYSTEMS should be short. A vertical gun arrangement is recommended here.
Problem: Gun function
Cause Remedies An active powder gun uses not only current, but also draws voltage. Voltage and Current can be set independently on the Gun controls. The adjusted setting is a limitation of the maximum values.
Problem: Level sensor
Cause Remedies Grounding of the powder hopper is achieved with help of electrically conducting fluidizing hose. The grounding of the injectors is achieved analogously through a conductive supplementary air hose. This serves not only the safety of the personnel, but is a prerequisite that the electronics of the level sensor do not get damaged. Always use the original conductive GEMA hose
Problem: Maintenance work
Cause Remedies The quality of your coating, and the length of the working life of the plant components depend greatly on the reliability of the maintenance of your plant. The following maintenance work must be carried out regularly: DAILY
- Blow out the guns, and check for sintering
- Check the setting of the spraying unit
- Keep the gun conveying air pressure low
- Check the injectors (caking / abrasion in the sleeve)
- Blow out the injectors, and hoses
- Clean the plant, recovery equipment, and surroundings
- Check the suction resistance of the powder recovery unit
- Check the grounding
- Check if the compressed air is clean, dry, and free from oil
- Check the current performance of the gun
- Check the powder hoses for sintering, and kinking
- Check the stroke movement, and display
- Check the filter system
Cause Remedies How can I choose the right type of nozzle for my application?
In order to obtain optimum coating results the choice of nozzle must be adapted to the coating requirements:
- A flat jet nozzle produces an elliptical cross-section, and can be well aligned to the object. It is used for a wide spectrum from flat to complex parts with cavities.
- The deflector plate creates a homogeneous powder cloud, which slowly approaches the grounded workpiece. The cloud can only be partially controlled and the penetration capability is poor. It is used for flat parts, and tube inside coating.
Problem: Picture frame effect
Cause Remedies The so-called “picture frame effect” can result when using structured powders with Corona guns. This is effectively countered with the SuperCorona® set. It is simple to fit to existing Gema powder guns. To achieve optimum results after conversion the setting parameters for high voltage, and powder output must be reset. The PCC mode is another effective way to avoid the picture frame effect.
Problem: Pit formation
Cause Remedies Pits form when gas escapes from the workpiece or contamination is not removed properly. Pitting is a pre-treatment fault, contact your supplier.
Problem: Powder container
Cause Remedies The fluidizing air pressure or air volume is set too high. The fluidized powder should only “boil” lightly, but evenly. In long term use, partial wear of the fluidizing plate can occur, which must be compensated for by increasing the air volume. In this case, the plate must be replaced. If the powder container does not stand close enough to the booth, the venting can become blocked, overpressure can form in the container and powder can escape. The powder hopper should be as close as possible to the booth, and connected to the booth with the shortest length of hose possible. This venting hose must be cleaned daily.
Problem: Powder depositing on an object
Cause Remedies Too large powder output volume per gun leads to a poor degree of powder separation. Reduce the powder output volume, and the conveyor speed. Total air setting too high. Adjust the air volume to 4 - 5 Nm3. Powder hoses too long. Shorten the powder hoses. Incorrect gun nozzle. See Nozzles. Relative Humidity over 80% The possible separation of the production area (with air-conditioning) and workshop. The proportion of large particles in the powder is too high. Contact your powder manufacturer.
Problem: Powder output irregular
Cause Remedies Total air setting too low. The ideal air volume should be in the region of 4 - 5 Nm3. Fine grain powder / powder with poor flow properties. Using a powder hopper with fluidizing air, and vibration will help. Short term, high compressed air consumption can cause pressure fluctuations. Fitting a larger compressed air reservoir directly before a high air consumption position will solve this problem. A too small cross-section or too small radius in the powder hose line up. Radius must be at least 150 - 200 mm. A poor ratio between fresh powder and recovered powder. Use an automatic fresh powder feed. Too high / low output Adapt to the coating parameters. Contaminated injectors Use an automatic fresh powder feed.
Problem: Powder separation degree of the cyclone
Cause Remedies Cyclone cone is filling up Check the recovery system.
Check function of level probe in the main powder hopper.
Insufficient exhaust air Adjust the exhaust air according to the fan curve.
Problem: Powder separation degree
Cause Remedies A poor degree of powder separation is often caused by leaks in seals in the recovery system (after filter, cyclone, day container, sieve, powder container venting, powder hose connections, etc.) Look out for leaks in the system.
Check the exhaust air volume.
Cause Remedies Pulsation in the powder feed is created through incorrect setting of the total air or an incorrect powder feed relationship. Check the settings of the Powder output, and Total air. Depending on the powder output, different Powder hose diameters are available.
- < 100gr/min = Ø 10/15 mm
- 100 – 200gr/min = 11/16mm
- 200 – 300gr/min = 12/18mm
Clogged after filter Clean Powder sintering in the side channel blower Clean Clogged Sieve Clean or replace
Problem: Sieve problems
Cause Remedies The powder hopper venting is too weak. Increase the air mover setting or if defective, replace. Mesh width of the sieve is too small. Replace the sieve. Waste bag The waste bag of the rotary sieve machine should be slightly under-pressure. When it is too inflated the Airmover must be set higher.
Problem: Stripe formation
Cause Remedies In principle a mathematical connection exists between the conveying speed, the stroke speed, and the number of moving guns for the formation and avoidance of stripes on the workpiece. Check the run of the sinus program. If the time of the double stroke of the gun is kept shorter than the time the reciprocator requires for the object to pass through the spray band, no stripes are formed.
Problem: Uneven coating
Cause Remedies Grain size distribution of the powder is too coarse. Contact the powder manufacturer. Contamination Contamination through “foreign” powder can be avoided by carefully cleaning the equipment. Different powders should not be mixed. Coating too thick or too thin. Adjust the powder output. Workpieces too humid or too warm. Check the drying, and temperature of the workpieces. Depositions on the nozzles. Maintenance! Teardrops form when the powder ‘runs’. Check the curing parameter / temperature.
Cause Remedies White powder reacts with too high curing temperatures or too long curing times with yellowing. If pure white powder is used the powder manufacturer’s curing instructions are to be followed exactly!