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Powder Finishing

CAUSE: Poor conductive hose material, causing friction and charging of hoses (sparking) at the injector due to insufficient grounding between object and hose due to bad grounding at the handgun due to too little grounding

CORRECTION: Use manufacturer’s original powder hoses, ground Injector, strip buckets and hoes of paint.

Do not wear rubber soles or gloves

CAUSE: Particle size distribution too fine

CORRECTION: Consult with powder suppliers

CAUSE: Moisture in the powder due to improper storage

CORRECTION: Powder must stored dry at processing temperature

CAUSE: Sintering at the baffle plate and the nozzle due to excessive conveying air pressure Damage to nozzles by too high an air pressure of the feed air

CORRECTION: Reduce conveying air

CORRECTION: Check for wear on the injector – collecting nozzle

CAUSE: Poor fluidization in the powder tank due to moist compressed air or blocked fluid plate, fluid tubes

CORRECTION: Check compressed air for contamination, replace fluid plate or fluid pipes

CAUSE: Poor conductive hose material, causing friction and charging of the hoses (sparking)

CORRECTION: Use manufacturer’s original powder hoses

CAUSE: Insufficient grounding at injector

CORRECTION: Ground injector

CAUSE: Between object and hoe due to bad grounding

CORRECTION: Strip buckets and hoes of paint

CAUSE: At the handgun due to too little ground

CORRECTION: Do not wear rubber soles or gloves

CAUSE: Workpieces insufficiently grounded

CORRECTION: Clean buckets

CAUSE: Powder with insufficient resistance

CORRECTION: Discuss with powder suppliers

CAUSE: Excessive field strength

CORRECTION: Change voltage and distance

CAUSE: Powder is blown out of the corners and recesses due to excessive air pressure

CORRECTION: Reduce air pressure, use proper nozzle

CAUSE: Too little penetration in the corners and niches due to excessive voltage or the use of an incorrect nozzle

CORRECTION: Reduce voltage and use appropriate nozzles, see also nozzles.

CAUSE: Poor pre-treatment

CORRECTION: Discuss with supplier

CAUSE: Poor oven setting (too high / too low temperature)

CORRECTION: Set oven temperature according to paint supplier

CAUSE: Inadequate powder quality

CORRECTION: Switch powder, change admixtures

CAUSE: Dirty base, oils etc.

CORRECTION: Check pretreatment

CAUSE: If powder escapes from a properly configured booth, and the pressure monitor of the exhaust system displays normal values, the fault can usually be found in the external vicinity of the booth.

CORRECTION: The most common cause is drafts in the system building, through open doors or windows.  Watch for cross drafts from auxiliary equipment such as air conditioners or general ventilation system in vicinity of the booth.

In order to obtain an optimum coating result, the choice of the nozzle must be adapted to specific coating needs. One size and type may not be applicable to all jobs.

The flat nozzle generates an elliptical cross-section and can be well-aligned with the object. It is used for more complex parts (profiles) with wells.

CAUSE: Sensor probe not adjusted properly

CORRECTION: Adjust immersion depth of probe to meet needs.

CAUSE: The ideal gun arrangement depends on the range of parts, booth configuration and exhaust system.

CORRECTION: A cabin with filter recovery is particularly suitable for the horizontal gun arrangement. Booths with central suction and quick color change systems should be built short as possible. In such cases, vertical arrangement is preferred.

CAUSE: Pulsation during powder supply results from incorrectly configured conveying air or an incorrect dosing ratio

CORRECTION: Check the conveying air setting and dosing ratio. For powder output of less than 80mg / min, a 10mm powder hose should be used.

CAUSE: Powder air speed too low

CORRECTION: The ideal amount of air should be in the range from 4-5 Nm3

CAUSE: Fine powder/powder with poor flow properties

CORRECTION: Use a powder container with fluid air and vibration

CAUSE: Short periods of high compressed air consumption can cause pressure fluctuations

CORRECTION: A compressed air reservoir before the powder plant solves this problem

CAUSE: Too small cross sections or too small radii in the powder hose routing

CORRECTION: The radii must be at minimum150-200mm

CAUSE: Incorrect ratio between fresh powder and recovered powder

CORRECTION: Use fresh powder

CAUSE: Excessively high/low emissions

CORRECTION: Adjusting the coating parameters

CAUSE: Contaminated injectors

CORRECTION: Injectors are often neglected during daily cleaning

CAUSE: Clogged return feed system


CAUSE: Clogged sieves

CORRECTION: Clean or Replace

CAUSE: Sieve clogs quickly

CORRECTION: Sieve with larger mesh size

CAUSE: Insufficient sieve mesh size

CORRECTION: Replace sieve

CAUSE: Surface impurities

CORRECTION: Use a sieve with a smaller mesh size or use an ultrasonic sieving system

CAUSE: White powder reacts by yellowing excessively when exposed to high curing temperatures or excessive time.

CORRECTION: If pure white powder is used, the curing specifications of the powder manufacturer must be strictly observed.

CAUSE: Inadequate sieve machine

CORRECTION: If a smaller mesh size is not sufficient, a sieve machine with ultrasound must be considered

CAUSE: If the conveyor is not cleaned regularly or inappropriate lubricants are used

CORRECTION: Clean regularly, attach a cover if necessary

CAUSE: If powder is blown-off in the curing oven

CORRECTION: Check the air currents in the building

CAUSE: Powder residue in the oven

CORRECTION: This can be prevented by regular cleaning

CAUSE: Poorly clean recovery

CORRECTION: Regular cleaning

CAUSE: Dirty air is sucked into the booth

CORRECTION: Here, the coating plant may need to be separated from production areas

CAUSE: If several booths are operated together, cleaning may cause an impairment may occur

CORRECTION: In this case, the booths must be separated from each other

  • Blow guns and check for sintering
  • Check the setting of the powder spray gun
  • Keep gun feed air low
  • Check the injectors (signs of caking or milling at collecting nozzle)
  • Blow injectors and hoses
  • Blow suction pipe and check out for leaks
  • Clean facility, recovery and surrounding area
  • Check suction resistance of recovery
  • Check fluidization
  • Check function of the level probe
  • Check function of the flowmeter
  • Check the setting of the air pistol
  • Check high-voltage and current display
  • Check and empty waste containers at the final filter
  • Check seal of filter/cyclone/piping

CAUSE: Check squeeze valve for material fatigue and check hose inserts for correct assembly, or replace

MEASURE: If new parts are integrated into the range, in most cases it is worth performing a review of the system parameters. If the objects are complex, a review of the gun assembly may also be worthwhile.

CAUSE: Too much powder accumulation in system components is often associated with leaks in the recovery system (absolute-filter, cyclone, hose connections, etc.)

CORRECTION: Check for leaks

CAUSE: In cyclone systems, peristaltic feed pumps or powder feed pumps can wear or clog

CORRECTION: Check powder recirculation system for function and leak-tightness

CAUSE: Clogged sieve mesh can substantially minimize separation

CORRECTION: Clean powder sieve regularly

CAUSE: When using structure powder in Corona guns, the so-called picture frame effect may occur

MEASURE: Effectively countered by the new MS controller with adjustable and variable amperage control.

CAUSE: Powder fluidizability has a major impact on coating quality

CORRECTION: For difficult powder, additional vibration of the powder tank is recommended. Retrofitting with a vibration table is simple.

CAUSE: If lumps occur in the the fluidized powder, the powder was stored for too long or exposed to temperatures above 35°

CORRECTION: Use new powder and check the storage of the powder, sift powder

CAUSE: Poor fluidization of the powder can result from a fluid air pressure setting that is too low

CORRECTION: Check the fluid air pressure settings

CAUSE: Excessive fluidization can also significantly reduce powder output

CORRECTION: Reduce air supply pressure

CAUSE: If powder emerges with dull / matt surface finish from the curing oven, specifications for powder curing have not been observed.

CORRECTION: The different curing temperatures of various powders must be observed.

CAUSE: Excessive powder cloud, distance between gun and workpiece too far.

CORRECTION: Minimize distance, use correct nozzles, or increase dosing air.

CAUSE: Excessive distances between the objects.

CORRECTION: Use automatic gap control, part recognition

The baffle plate produces a homogeneous powder cloud, which slowly approaches the grounded workpiece and therefore acts with good throwing power. The cloud can only be controlled under certain conditions and the penetration potential is small. It is used for flat parts, pipes and high surface services.

CAUSE: Often the use of silicone in the coating area is the reason for a dirty coating

MEASURE: Since all powder has an “allergic” reaction to silicone, it must never be used in the coating area

CAUSE: If powder layer on the object is too thick, this results in an uneven surface.

CORRECTION: Use the powder supplier’s settings for the powder coating, use less electricity (µA)

CAUSE: An active powder gun not only produces voltage, but also draws current.

CORRECTION: Power increases at the work piece as the gun approaches. Too much power causes back-ionization and orange peel finish. The current can be reduced by configuring µA settings.

CAUSE: Too much powder output quantity per gun resulting in inefficient powder separation

CORRECTION: Reduce powder output quantity and reduce chain speed

CAUSE: Powder propulsion generally too high

CORRECTION: Increase powder hose diameters

CAUSE: Excessively long powder hoses

CORRECTION: Shorten powder hoses or increase diameter

CAUSE: Incorrect powder nozzle

CORRECTION: See nozzle section

CAUSE: Humidity above 80% relative humidity

CORRECTION: Demarcation of the production area and air-conditioning

CAUSE: Too high proportion of of large particles in the powder

CORRECTION: Contact powder supplier

CAUSE: The fluid air pressure or the amount of air are too high

CORRECTION: The fluidized powder should “boil” only slightly but evenly. Prolonged use may lead to the partial closure of the fluid plates, which must be compensated for with a high amount of fluid air. In this case the bottom must be replaced.

CAUSE: “Back-ionization” occurs when the powder layer is too thick

CORRECTION: Reducing powder flow often prevents back-ionization, but results in a reduction of the transfer efficiency. Back-ionization also depends on the temperature and humidity. Very difficult powder materials may require air-conditioning of the coating zone. See also, orange peel effect.

CAUSE: There is a fundamental mathematical relationship between powder feed speed, gun motion velocity and number of moving guns to form and avoid banding on the workpiece.

MEASURE: Determine manufacturers recommendations. If the time of using a double stroke of the gun is less than the time it takes for the conveyor to pass through the width of the spray cloud, no banding or striping will occur.

CAUSE: Particle size distribution of the powder is too coarse.

CORRECTION: Contact powder suppliers.

CAUSE: Contamination

CORRECTION: Contamination by foreign powder can be avoided by careful cleaning of the plant. In addition, different powders should not be mixed.

CAUSE: Too high or too low film thicknesses

CORRECTION: Adjust powder output.

CAUSE: Too wet or too hot workpieces

CORRECTION: Check drying and temperature of the workpieces.

CAUSE: Powder deposits accumulate on nozzles

CORRECTION: Maintenance!

CAUSE: Drop formation occurs when the powder flow is too strong

CORRECTION: Verification of the voltage and the distance to the workpiece, or the addition of thixotroping agents can help.

CAUSE: Squeeze valve running too slow or too fast

CORRECTION: Set the time according to the manual

CAUSE: Squeeze valve not open completely

CORRECTION: Check squeeze valve for fatigue and hose inserts for correct assembly, or replace.

  • Check grounding inspection
  • Check whether the compressed air is clean, dry and free of oil
  • Check guns for voltage output
  • Check electrode for wear
  • Check fan nozzle / baffle plate for wear
  • Check powder hoses for sintering and kinks
  • Check lifting and display
  • Check filter systems

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