SPRAY UP TECHNIQUE:
Equipment: spray-up machine basically consists of:
1. Roving cutter: May be mounted remotely (far away, not closely) or directly on the spray head.
2. Two component resin catalyst delivery system: It has taken number of forms:
a. Pressure pot system
b. Air less system
c. Double nozzle guns which mix catalyst and resin in the air
d. Single mixing head guns.
3. Glass delivery system: It also varies with the remote system:
a. The chopped roving (A form of fibrous glass in which spun strands are woven into a tubular rope. The number of strands is variable but 60 is usual) is fed to the gun by hose instead of chopping at the point of delivery.
b. Some guns do not chop at all but deliver the roving as a continuous strand which is laid in a swirl pattern.
a. The unit (regardless of configuration) combines a catalyzed resin with an accelerated resin.
b. The glass fibers are wetted with this mixture which is sprayed on the mould surface.
c. Some spray guns are used to spray gel coats and some used to spray the resin, catalyst and a powered filler simultaneously.
Any large reinforced plastic structures can be build up simply and very rapidly.
The sprayed composite must be rolled by hand to remove the air and obtain sufficient density. Hence labour costs are equivalent to the hand lay-up techniques used to produce structures with good physical properties. The process will not yield consistently high properties.
Applications:The process was initially used to make studio sets. Now it is greatly accepted in the areas where physical properties are not of primary importance like large outdoor display signs, tank linings, shower and tub enclosures, roofing etc. Gel coating and spray-up are very compatible and their combination produces moulding with very fine single surface finishes.