Important warning: This is a historical archive text, not current guidance on spraying, equipment selection, ventilation or safe work with paints and varnishes. Pressures, equipment, booths, heating, materials and procedures must be checked against applicable regulations, safety data sheets, the manufacturer’s documentation and the rules for protection against fire, explosion and chemical exposure.
This text is not an offer of compressors, spray guns, booths or coatings from Savo Kusić. The current offer focuses on windows, doors and related solutions.
Pneumatic spraying system
Paints and varnishes are sprayed with compressed air supplied by a compressor station consisting of a compressor and receiver. Compressed air from the receiver enters the oil separator (Fig. 1), where water vapour and oil droplets introduced in the compressor cylinders are removed. From the oil separator, the purified air at a pressure of 2,5 to 3 atm. reaches the spray gun (Fig. 2) and the paint pressure tank, whose pressure is stated as 0,1 to 1,5 atm. (Fig. 2), depending on the consistency of the paint or varnish.
Figure 1: Longitudinal section of the oil separator
Figure 2: Spray gun
Figure 3: Paint pressure tank
Spray patterns and booths
The spray pattern depends on the position of the air cap on the spray-gun head. A horizontal air-cap position narrows the spray in the vertical plane (Fig. 4, a). An oblique (diagonal) position produces a round spray pattern (Fig. 4, b). When the air cap is vertical, a narrow pattern is formed as shown in Fig. 4, c. The spray pattern is selected according to the product’s construction. A flat pattern is used for large surfaces, while the text describes a conical pattern for latticework.
Figure 4: Air-cap positions on the spray-gun head and corresponding spray patterns
Spray painting and varnishing is performed in special chambers or booths (Fig. 5), described as comprising a semicircular enclosure, a rotating platform for the product or element, an overspray collector and a ventilation device. For mass spray coating, the text describes a conveyor line comprising a series of booths or chambers, intermittent or continuous conveying equipment and finned-tube heaters placed between the booths and along the conveyor to heat the air.
Figure 5: Spray-painting booth for smaller products
Hand tool for coating
Steel or wooden putty knives are used to apply filler (Fig. 6).
Figure 6: Putty knives
In most cases, paints and varnishes are applied with brushes (fig. 7).
Figure 7: Paint brushes
Historical coating structure
The finishing process for a joinery product is determined by its purpose, service conditions, the quality of the wood from which it is made and the coating material used. Figure 8 shows the structure of a nitro-paint coating. The text states that nitro paints form opaque coatings. Oil paints and enamel also form opaque coatings, so the stated structure is described as typical for them.
When finishing with oil and spirit varnishes, nitrocellulose lacquers and polishes, the text states that local or full-surface filling is unnecessary and that polishing and application of a finishing varnish may also be omitted.
Figure 8: Structure of paint coating