Production-work uses air or airless sprays in vacuum exhaust or water wash booths, etc. but small portable spray outfits are obtainable which will support one gun with pressures up to 60 lb per sq. in (4.218 kg/km2), and sufficient for all but the heaviest materials. These can be the compressor type or fully portable rotarv vane type (547), relatively inexpensive and efficient in use. Light pattern spray outfits for the handv-man are hardly suitable for serious work, as there must be sufficient pressure and feet cube (m3) air delivery per minute fully to atomize the spray or extensive spitting, blobbing, tear runs and orange-peel effect will result, and rubbing down will be as difficult and as tedious as with brush-work. Some form of moisture extractor should also be incorporated in the compressor, or as a separate unit installed in the pipeline, or 'blooming' will result. Even with fully efficient moisture extraction—and the very act of compressing air squeezes out the moisture always present—some blooming must be expected on humid days. This can be controlled by adding anti-chill thinners to the lacquer, which retard the evaporation and thus allow the suspended moisture to escape before it is trapped by the setting film, or by over-spraying the lacquered surface with thinners, but the gun must be good for this and the application skilful. Regulations regarding the storage and use of inflammable materials are fairly stringent, but nonregulation materials are available which are not subject to the legal requirements. Small outfits in which the air is delivered direct from the compressor unit to the gun do not need periodic testing, but air receivers, i.e. storage tanks for air under compression, require safety checks at regular intervals. In estimating for spray work it should not be forgotten that on average one-third of the material is lost.
Was this article helpful?