Design to avoid corrosion with powder coating

The Tri-Resin Powder Coat System has been successfully used since 2002. Initially developed to protect galvanized steel but was so reliable 95% of our work is now coated directly on to steel. Requested by Architects and main contractors the Tri-Resin System has proved itself to be a reliable powder coat system for steel, aluminium and galvanised steel.

Component must be suitable for powder coating

The component must be suitable for powder coating. Building in water traps and areas that inaccessible for painting will shorten the products life. Design to avoid corrosion.

This following is an extract from our terms and conditions and warranty and will act as a useful guide for avoiding problems with corrosion.

  • The component design must be suitable for powder coating.
  • The fabricator/designer must familiarise himself with appropriate and inappropriate methods of fabricating components, for painting in external environments.
  • It is not for Windridge Coatings Ltd to approve or reject the quality of fabrication and design, for it’s suitability for coating. Windridge Coatings will endeavour to bring to the fabricators’ attention any design or fabrication concerns prior to painting, but does not accept responsibility for anticipating every design or fabrication area vulnerable to rust.

Rusting or paint breakdown, which is the result of areas unsuitable for painting, will be excluded from the warranty.

Following are some, but not conclusive examples, of situations that should be avoided:

  • There must be no sharp edges either left from cutting or fabricating, particularly corners.
  • Welds must be smooth, ground if required. There must be no porosity within the weld fillet.
  • Folded returns must be avoided if it means that these areas cannot be painted.
  • Doors should be supplied separate, so there is good access for painting on the door and frame.
  • Water traps must be avoided.
  • Flat areas should not be secured together, where moisture or water can be ‘sandwiched’ and making these areas inaccessible for painting.
  • Components that have been laser cut must be bought to our attention, so that special procedures can take place to remove scale.
  • The use of resin fillers must not be used as many adversely react to high temperatures.
  • The use of cutting pastes and other contaminating substances should be avoided, or they must be removed from within or on the component prior to delivery.
  • Anti spatter or other solutions containing silicon must not be used as they can react with the powder coating.
  • Where folding is too sharp the metal can produce stress cracks, these can be difficult to seal with paint making them vulnerable to corrosion.
  • Protective polythene film should be removed from aluminium prior to welding, drilling and grinding, as it will melt into the scratches left by the machining.
  • We are happy to give more written or verbal explanations for the above if required.

Component preparation prior to painting

Self colour steel

Windridge Coatings will prepare the components for painting, but will not finish its manufacture. It is the responsibility of the fabricator to remove the fabrication marks i.e. creases left by break press, deep fabrication scratches, grinding smooth welds, rounding off sharp guillotine edges.

Galvanised material

Powder coating over galvanised steel is rarely as smooth and blemish free as painting over blasted steel. Windridge Coatings will fettle the galvanise and endeavour to remove the worst of the lumps, clinker, spikes and any other unsightly marks produced by the galvanising process. This does not include the build up over welded areas unless specifically requested.

Some of the components are large and complex in shape and have a galvanise pattern or grain covering the whole surface; it cannot be guaranteed that every blemish will be removed. If this is a requirement then the component should be fettled before it arrives for painting.

Galvanised material is frequently delivered damaged through transit or through rough handling. This can result in the zinc being removed by chipping. In such cases we will attempt to smoothen the jagged edges by grinding. During the heating of the paint process, these edges can reappear due to the different rates of expansion between steel and zinc. There may be visible signs of the original galvanise damage after painting.

It should be considered, that by removing all of the blemishes, and making the galvanise coating perfectly smooth; much of the zinc will also be removed. This will be detrimental for the galvanic protection of the steel. For this reason Windridge Coatings will not undertake to grind the galvanised surface totally smooth.