Identification |
Possible cause |
Remedial action |
|---|---|---|
| Performance expectation of the coating is not achieved | Film thickness beyond nominal values | Comply with nominal values of film thickness |
| Insufficiently cross-linked powder | Check crosslinking/curing, comply with curing conditions | |
| Heating rate too low | Increase heating rate |
Checklist for a problem-free powder coating process
Problems on the coated object
Insufficient mechanical properties (adhesion, elongation, surface hardness); insufficient corrosion resistance and resistance to chemicals
Insufficient intercoat adhesion in two-coat procedures (peeling)
Identification |
Possible cause |
Remedial action |
|---|---|---|
| Insufficient mechanical properties | Insufficient pre-treatment of objects (phosphating, chromating) | Optimise pre-treatment |
| First coating overcured | Set up temperature of object and holding time optimally (temperature-time-diagram) | |
| Inappropriate powder type, film thicknesses extremely high | Coordinate assembly, use correct powder type | |
| Use of a directly heated gas oven | Use different heating method |
Levelling (orange peel) all areas or parts of the object
Identification |
Possible cause |
Remedial action |
|
|---|---|---|---|
| Performance expectation of the coating is not achieved (nominal value of levelling) | Film thickness of powder coating too high or low | Optimise powder output | |
| Temperature profile on the object not optimal | Optimise temperature on object | ||
| Usage of inappropriate powder (too reactive, too high-viscous) | Use appropriate powder | ||
| Particle size distribution of powder inappropriate | Use powder with changed particle size distribution | ||
| Incompatibility with other powders | Clean plant thoroughly, do not mix different powders | ||
| Back ionization effect (voltage too high, temperature and relative humidity at the plant location changed) | Reduce film thickness, reduce voltage; check air conditioning; divert “superfluous” charge by means of special spraying elements or additional equipment such as rings for diverting ions (e.g. Super Corona. Corona Star) | ||
| Powder stored too Iong/too warm | Check storage conditions | ||
| Relative humidity too low | Increase relative humidity |
Gloss variation
Identification |
Possible cause |
Remedial action |
|
|---|---|---|---|
| Performance expectation of the coating is not achieved (nominal value of gloss) | Curing conditions are not being adhered to | Set up temperature of object and holding time optimally (temperature-time-diagram) | |
| Special curing technology (heating with gas direct, infrared, near-infrared, inductive heating) | Use appropriate powders | ||
| Bad levelling (powder stored too long/too warm) | Optimise curing conditions, use new powder | ||
| Incompatibility with other powders | Clean plant thoroughly, do not mix different powders | ||
| Powder thermalIy unstable | Use thermalIy-stable powder | ||
| Film thickness too high/too low | Optimise film thicknesses | ||
| Emissions from the powder or the substrate in the course of the curing process | Use appropriate powders, check substrate/pre-treatment | ||
| Deposit or condensate (from the air inside the oven) | Clean oven, increase oven airflow if necessary |
Contaminated surface
Identification |
Possible cause |
Remedial action |
|---|---|---|
| Appearance of coated surface is not acceptable | Missing or too large mesh in reclaim sieve | Use sieve with correct mesh size in machine |
| Insufficient sieving | Use sieves with small mesh size | |
| Dirt from the air inside the application plant is deposited on the coated object due to air flow | Use screening machine with various sieves; use screening machine with automatic dirt and deposit discharge | |
| Dirt from the conveyor | Clean conveyor | |
| Dirt from the jig | Use conveyor with dirt trap | |
| Emissions from the powder inside the oven | Clean oven regularly; increase oven air flow if necessary | |
| Polluted air is being sucked into the booth or the oven | Provide for separation of coating plant from other factory floors; isolate coating plant with overpressure filtered air | |
| When operating two or more booths mutual suction of the powder-air mixture (especially during cleaning processes) | Provide for appropriate physical separation of the booths | |
| Check after filter regularly | ||
| Powder hose insuffiently cleaned after change of colour | Clean powder hose with compressed air and stopper | |
| Clothing fibres are being sucked in by the recovery unit | Use lint free clothing | |
| Fibres from the filter of the recovery unit | Use filters that will not leave fibres | |
| Adhering dirt particles on the object prior to the coating process | Provide for clean objects before the coating process | |
| Objects "cleaned" with fluffy cloth | Do not use fluffy cloths in application plant | |
| Powder contains contamination when delivered | Contact manufacturer of the powder |
Colour variation
Identification |
Possible cause |
Remedial action |
|---|---|---|
| Objects do not match in terms of colour | Curing conditions changed (oven temperature/time conditions, overcuring during breaks or downtimes, IR contribution) | Set up curing conditions correctly |
| Combustion products in directly gas-heated ovens | Use stabilised powders | |
| Film thickness beyond nominal values | Comply with nominal values of film thickness | |
| Object or operation mode changed (dimensions, mass) | Sort objects | |
| Insufficiently degreased or pre-treated objects | Optimise degreasing, pre-treatment | |
| Irregular film thickness of a priming coat | Apply primer with uniform film thickness in order to achieve even substrate in terms of colour | |
| Mixture of two powders | Separate powders carefully; clean plant thoroughly when changing powders | |
| Specification tolerances of the powder insufficiently defined | Check or specify tolerances together with the powder manufacturer |
Blisters (closed or burst), "pinholes"
Identification |
Possible cause |
Remedial action |
|---|---|---|
| Performance expectation of the coating is not achieved | Curing conditions not optimal (heating rate) | Optimise curing conditions |
| Weak spots when mechanically stressed | Surface of objects not cleaned sufficiently (grease residues, rust, water, emissions from the substrate) | Clean surface of objects perfectly; contact manufacturer of pre-treatment |
| High film thickness (air pockets, emissions from the powder, e.g. water) | Reduce film thickness | |
| Surface of the object has cavities (cracks, indentations, overlaps) | Improve surface of objects, change construction | |
| Blow holes on surfaces with hot-dip galvanized coat; porous surface, e.g. die casting | Degas objects appropriately, use appropriate primer | |
| Grade of the powder | Use powders for outgassing substrates | |
| Incompatible powders mixed together (contamination) | Separate powders carefully; clean plant thoroughly when changing powders |
Craters
Identification |
Possible cause |
Remedial action |
|---|---|---|
| Performance expectation of the coating is not achieved | Objects not sufficiently degreased, pre-treated | Optimise degreasing, pre-treatment |
| Weak spots when mechanically stressed | Incompatible powders mixed together (contamination) | Separate powders carefully; clean plant thoroughly when changing powders |
| Influences of products containing silicones | Avoid products containing silicones within the coating area (check air ducts of connected production units) | |
| Blow holes on surfaces of cast parts, hot-dip galvanized or zinc-sprayed coatings; porous substrates as e.g. die casting | Degas objects appropriately, use powders suitable for outgassing substrates, use appropriate primer | |
| Oily dirt from the conveyor chain | Clean conveyor chain | |
| Oil from the compressed air | Use and check oil separator, refrigerant type drier | |
| Condensates from the oven | Clean oven, increase oven airflow if necessary |
Beading, sagging and drop formation
Identification |
Possible cause |
Remedial action |
|---|---|---|
| Performance expectation of the coating is not achieved | Film thickness too high or variable | Optimise film thickness distribution |
| Fitting of components is compromised | Curing conditions not optimal (heating rate, object and oven temperature) | Optimise curing conditions |
| Geometry and surface profile of the objects (powder-drawing areas) | Introduce individual coating processes of objects | |
| Specification of the powder incorrect | Define specification profile of powder | |
| Wetting disturbance: "slipping" of the powder coating | Clean substrate residue-free (salts, oils, greases, residues of rust and separating agents) |
