SPRAY PAINTING EQUIPMENT

The following suggestions are intended only as a guide to the selection of spray painting equipment and are based on limited Plastiglas de Mexico laboratory experience. Consult the manufacturer of the equipment for recommendations for specific applications.

SPRAY GUN

The DeVilbiss Type MBC gun or equivalent can be used with suitable nozzles and air caps. An air cap with the maximum number of jets generally gives the best atomization. Consult the spray gun manufacturer or the paint supplier for the specific nozzle and air cap required.

If a siphon feed is used, it should be adjusted to give a wide pattern with a low feed rate. The siphon feed system should be equipped with a No. 30 air cap and an FF nozzle on the MBC spray gun.

A pressure feed system is best for spray painting. This will produce good atomization with half the volume of air required for a siphon feed system. Using less air means there will be less over-spray, and a larger pattern of spray will be developed, giving more uniform coverage. The MBC gun can be used with the DeVilbiss No. 765 air cap and an FX nozzle set to deliver a fluid flow of 3 to 4 oz./mint. Pressure tanks should be equipped with air operated stirrers for continuous operation during spraying. When the paint is mixed to the correct viscosity, the spray gun atomizing pressure should be in the range of 50 to 60 psi.

Regardless of the feed system used, the paint should be applied in light coats. When seen by reflected light, the paint should appear wet. For uniform light transmission, at least 8 mist coats should be applied. The Vical acrylic should be back lighted while spraying to judge the tube hiding ability of the paint coat. Only explosion proof lighting fixtures should be used in the spray booth. The spray gun should be cleaned after each day's use.

COMPRESSOR AND HOSE

The air compressor should have sufficient capacity to maintain the required air pressure for the type and number of guns used. A DeVilbiss Type UBP air compressor will maintain maximum pressure for two Type MBC spray guns with No. 30 air caps. The same spray guns with No. 765 air caps would require a DeVilbiss Type VBT compressor. The air hose should be about 25 feet long and at least 5/~6/' inside diameter to limit the amount of pressure drop.

STIRRERS

If pressure­feed tanks are used, they must be equipped with continuously operating air­driven stirrers. Constant stirring is necessary to prevent pigment settling. Hand stirrers are unsatisfactory because they offer only intermittent operation.

STRAINERS AND WATER TRAPS

Metal screen strainers should be used both at the pressure tank and at the spray gun. The DeVilbiss strainer Type VS­510 is suitable for attachment to the spray gun fluid inlet. Spray paint pots, filters, and strainers in the paint lines leading to the guns should be thoroughly cleaned at least once a week. The metal screens in the strainer should be cleaned at least once a day.

The air delivered to the spray gun must be free of moisture. Moisture can be removed from the air by a combination of condensers and transformers in the air line. Transformers of the DeVilbiss Types HL, HLC, or HLD are satisfactory. Auxiliary condensers should be installed in the line, and should be drained frequently to prevent accumulation of water. The frequency of draining will vary with atmospheric conditions. The air transformers should be equipped with automatic water drains to prevent contamination of the air supplied to the gun. DeVilbiss automatic drain Type DOD is available with adapters for attaching to Type HL or HLC transformers.

SPRAY BOOTH

Spray booths should be large enough to accommodate the largest size Vical acrylic panels to be painted. A floor type hood about 8 feet high by 12 feet wide is usually large enough. The ventilating system on the hood should be designed to remove vapors from the floor area as well as from the higher areas. The booth should also include an explosion­proof light box for back lighting.

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