An Introduction To Paint Finishing

Spray Guns

What everyone thinks of when they think of paint spraying, is the manual paint spray gun. Even in this humble piece of equipment there are many variants:

Air Spray - Conventional – Traditional air spray gun. Using atomising air pressures in excess of 3 to 5 bar (45 to 75 psi). Still relevant for very small production volumes. Gives a very good paint finish but very wasteful of paint and solvent. Only rated at 35% efficient.

Air Spray – HVLP & Compliant – Virtually the same in appearance to conventional guns, but utilising much lower atomising air pressures: HVLP 0.7 bar (10 psi) and Compliant: 1 bar (15 psi). Both methods offer paint spraying efficiencies 65% or above on spraying flat surfaces, and offer compliance with existing EU solvent reduction legislation.

We supply the full range of Graco Air Pro Spray Guns which are available in the different variants mentioned above. Having varying sizes and paint outputs, with different air cap and fluid nozzle sizes to suit different paints and lacquers.

They also come with different paint supply methods: Siphon cup and gravity cup guns for small batch production. Pressure feed guns for large batches or continuous production from either Pressure Feed Containers (PFC’s) or paint supply pumps.

Pressure Feed Containers and Diaphragm Paint Pump Spray Packages

Until relatively recently if you used siphon or gravity type sprayguns and wanted to be able to spray for longer (without having to refill paint cups) you would normally graduate up to a Pressure Feed Container (PFC). Also known as a ‘Pressure Pot’.

This is a steel or aluminium paint vessel with a screw down lid assembly that is then pressurised with compressed air to force feed the paint out via paint hoses to the spray gun(s). The regulated air pressure then determines the paint output volume.

FTL supply a full range of P.F.C’s, though nowadays the move to small air driven diaphragm paint pumps have very much taken over from this older method.

Unlike P.F.C.’s these small pump units can be re-pleneshed with fresh paint without breaking production, offer very quick colour/material changes. Diaphragm pumps are also much faster to clean down and because they have a recirc valve they use much less cleaning solvent. They are also much safer to use than pressure vessels and do not require separate test certificates or insurance underwriting.

We offer a range of Aluminium & Stainless steel bodied 1:1 spray packages for solvent and water based paints and are available as complete spray packages with Air Spray and Electrostatic sprayguns.

For larger industrial applications requiring multiple take offs and paints/colours we can design a paint supply system utilising higher ratio 3:1 & 4:1 ratio paint pumps usually from a centralised paint mix room with steel supply pipe work, circulating or dead-leg whatever is most appropriate

Conversely, even if a company makes the best products in their class, if the final finish prematurely fails during its normal life-span, this can lead to a drop in reputation of that particular product and possibly the brand.

Companies should therefore be looking for a final finishing process that gives the best performance, highest efficiency and reliability.

In paint finishing the old adage ‘There are many ways to skin a cat’ can certainly apply. We list below different methods and types of paints spraying equipment. Each has its own merits and place in the production process. Fluid Technologies Limited supply all these various types of equipment and will be more than happy to discuss (and where necessary demonstrate) each type with you, to find what’s best for your application.

Air Assisted Airless Spraying

The name AAA is an almgamation of Air spray and Airless Spray. The technology was originally developed for the furniture industry, but has now progressed into most medium to high production finishing operations. It combines the high paint flow rates and therefore speed of airless spray (see under Protective Coatings section) with the high quality paint finish of Air spray.

Most medium to high volume production spraying applications will use Air Assisted airless as it offers the best combination of speed and performance with low initial purchase and running costs.

One of the most popular range of Air Assisted Airless sprayers in the world is Graco’s Merkur family of pumps outfits.

Pneumatically driven using Graco’s extremely reliable ‘poppet valve’ technology. Available in a full range of pump sizes and pressure ratios to cover all applications and scenarios. Made from stainless steel for all parts that come into contact with paint so is suitable for both solvent and water based paints.

For supplying moisture sensitive catalysts in a 2K mixings system we would recommend Graco’s fully enclosed bellows pump.

Electrostatic Spray Painting.

Applying to both wet paint and powder paints, then if your product is deemed suitable for electrostatic painting (we can help you determine this) and you choose to adopt this technology in your painting process, you will be using one of the most efficient methods known for paint spraying.

For both Paint & Powder, located at the tip of the paint spray gun is a small electrode, to which high voltage electricity is applied. As the paint particles travel at a slow speed through this corona of electricity, they become negatively charged.

The paint surface is the grounded, positively charged surface, which has a magnetic attraction to the negatively charged paint. As you spray the paint onto the substrate (product) generally the paint is pulled towards the surface. The paint or powder particles will stick to any surface that is conductive. Metal definitely. Even some wooden products have a moisture content that is high enough for electrostatic spraying to still be viable. The higher the moisture content of the wood, the greater the positive charge.

Non conductive surfaces such as plastics can also have a conductive adhesive promoter applied before painting. Particularly useful when applying a very expensive top coat.

The benefit of using an electrostatic paint sprayer is in the savings of paint and solvents. Expect to use 25 percent to 50 percent less paint. With Powder Coatings the benefits are even higher. What powder paint that does not make it onto the product, will usually be re-cycled in the spraybooth to be re-used again.

For wet paint spraying the technology is generally an addition to other methods of spraying, such as Air Spray, Air Assisted Airless. Where the atomisation is carried out by the first process and the electrostatic is applied thereafter as the paint exits the spray gun. All methods are available in manual and automatic versions.