Coating Application Techniques Flashcards

Plural-component spray equipment is mainly used for which type of coating?

Answer: Fast-setting, short pot-life materials such as polyureas and some 100% solids epoxies

Plural-component rigs meter and mix the components at or near the gun, so materials with very short pot life can be applied.

During airless spraying, the fan pattern shows 'tails' (heavy stripes at the top and bottom edges). What is the most likely cause?

Answer: Fluid pressure too low or the material too viscous to atomize fully

Tails form when there is not enough pressure to atomize the material fully, which is usually low pressure or high viscosity.

What is the purpose of the induction (sweat-in) time listed for some two-component epoxies?

Answer: To let the components start reacting before application for better cure and film properties

Induction time lets the resin and curing agent pre-react, which improves compatibility and helps prevent problems such as amine blush.

What does using a mist coat (tack coat) before the full coat of a zinc-rich primer or over porous substrates help prevent?

Answer: Pinholing and bubbling from air displaced out of the porous surface

A thin mist coat lets air escape and seals the pores, so the following full coat does not pinhole or bubble.

What usually happens when you add more thinner than the manufacturer's maximum recommendation?

Answer: Lower DFT per coat, risk of sags, and possible VOC noncompliance

Over-thinning reduces the solids that are applied, encourages runs and sags, and can exceed regulatory VOC limits.

What is the main advantage of HVLP (high-volume, low-pressure) spray compared with conventional air spray?

Answer: Higher transfer efficiency and less overspray

HVLP atomizes at low air cap pressure, which reduces bounce-back and overspray and so raises transfer efficiency.

Inline heaters are sometimes used on airless or plural-component lines mainly to do what?

Answer: Lower viscosity without adding solvent so the material atomizes better

Heating lowers viscosity so high-solids materials spray well without thinners that raise VOC.