Surface finishing better techniques and equipment
How to improve efficiency and reduce waste when using surface finishing techniques such as dipping and spraying.
You can reduce waste and the cost of surface finishing by using better application techniques and equipment. Coatings are applied either by dipping or spraying. Conventional spray guns are typically not more than 50 per cent efficient - for every two litres of paint you use, at least one litre is wasted.
If dipping, consider using electrophoretic and autophoretic dipping for priming and corrosion-resistant coating. Electrophoretic dipping involves the use of electrodes connected to the bath and the jigs to create the attraction between paint and substrate. Autophoretic dipping relies on a chemical reaction to create the attraction. Both techniques offer high material yield and high quality, and are water-based processes with no volatile organic chemical emissions.
If spraying, you should consider replacing conventional spray guns with high volume, low pressure (HVLP) spray guns. These give better control, better coverage of recesses and typically offer efficiencies of 65-85 per cent. HVLP guns typically pay for themselves within weeks.
When using viscous coatings, consider using hot-spray equipment that can produce the correct coating viscosity without the need for excessive use of thinners.
If your business uses higher value coatings, you should consider using electrostatic spraying. With wet paints, this allows the charged paint to be attracted to the earthed piece and gives high transfer efficiency. Combined with HVLP technology, electrostatics can achieve efficiency of 65-95 per cent.
You should consider using powder coating - using either a fluidised bed dip or spraying - as it is a very efficient, high-quality, dry electrostatic process. Unlike wet paints, you can readily collect and recirculate powder.
If using spray guns, you should pump mixed coatings directly or via a ring main to avoid decanting by individual operators. Some low-pressure pumping equipment can supply a number of spray guns directly from one paint container without the need for intermediate pressure pots. This reduces material wastage and the need for cleaning.
Robotic spraying often reduces coating use by 20-30 per cent compared with manual spraying. Although expensive, robotic spraying has advantages for large and complex shapes as it offers high efficiencies, high quality and reduced labour costs.
On robotic spraying equipment, dedicated paint lines often feed a colour changer that, in turn, supplies the gun down a feed line. The closer the colour changer is to the gun, the less waste of paint and cleaning materials on changeover. Alternatively, replace the feed lines with cartridges that can be loaded onto the paint atomiser.
On automatic cleaning systems, you can use pulsed air (in the direction of paint supply) with cleaning materials to improve cleaning and reduce material use. Reversing the direction of the compressed air can drive unused paint back down the supply line into the pressure pot, saving paint and cleaning solvents.
Consider line 'pigging' systems to improve paint recovery and reduce the amount of solvent used for cleaning.
Consider using enclosed gunwashing machines to avoid unnecessary emissions, recover the solvent used in spray-gun cleaning and allow its reuse within the machine.