Spray guns: special feature. The first version of this article was published on this website all the way back in 2002 and regularly pops up as a trending article. Thanks to Karl Isherwood of Anest Iwata for updating the article to include the latest spray gun technologies.
What sort of gun should you buy? Paint & Panel looks at the various types of spray gun on offer in the Australian market and examines the advantages of the latest 'technological breakthrough' - HTE or High Transfer Efficiency guns.
Conventional spray guns, those with high atomising pressures of 40psi or greater, have been around a long time. As technology evolves these are becoming less common in the professional refinish field and are more typically found in the DIY market place.
HVLP (High Volume Low Pressure) spray guns can improve transfer efficiency to around 65 per cent but there appears to be limitations with control of the finish either because the spray guns are very sensitive to small pressure fluctuations or they produce unacceptable levels of orange peel. Some manufacturers view HVLP as old, even superseded, technology having been in the market in excess of 30 years. As the name implies, the guns need large volumes of air to produce even a marginally satisfactory finish with air consumption of 16 cfm and higher common
HVLP is broadly defined as those spray guns that at the recommended air inlet pressure produce an air pressure inside the air cap of no greater than 10 psi.
Operators however, have a tendency to increase inlet pressures above recommended levels with the belief that this will increase application speeds and atomisation quality. The end result is the exact opposite in most cases - increased air consumption, greater power bills as the compressor struggles to keep up, reduced transfer efficiency resulting in increased paint usage and a poorer quality finish.
LVLP or Low Volume Low Pressure is the latest development in this area. Whilst maintaining the benefits of reduced air pressure and overspray these spray guns use much less air than those they replace. Anest Iwata LS400 Supernova consumes approx. 13 cfm and the LPH80 spot repair gun consumes as little as 3 cfm.
HTE (High Transfer Efficient) spray guns have become the main stay of the refinish industry.
As a broad average, spray guns of this technology consume between 9 and 12 cfm of air
Both fine atomisation and application speeds are maintained and transfer efficiencies greater than 65% are commonplace. Depending upon the paint type it is possible to achieve a transfer efficiency rating of more than 90%.
Transfer Efficiency is determined by independent laboratory testing under extremely strict protocols. Anest Iwata have for many years used Thatcham Laboratories in the UK for this purpose. In fact Anest Iwata was instrumental in developing the testing procedures which in turn became European Standard EN 13966.
Spray guns are determined to be Compliant at the point where they are proven to reach a transfer efficiency of 65% or greater. As such, a number of technologies can also be identified as Compliant technology.
All of the leading manufacturers of spray guns have models within their range that meet the specifications now generally associated with High Transfer Efficiency Spray guns. Anest Iwata for instance, now includes a QR code that allows the user to access both the instruction manual and the test certificate with each of its HTE and High TEC spray guns.
New technology paints rely more heavily on controlled minimum paint thickness or film build to achieve their characteristics, often using clear over base application to achieve the colour and gloss required. It is at this point that consistency of spray pattern becomes an important feature of the spray gun, allowing the lowest possible amount of paint to achieve the desired finished result. In most cases this is achieved more satisfactorily with the latest technology HTE High Transfer Efficient equipment, producing results with less mottle, which is difficult to control with heavy metallic basecoats particularly with high silver levels.
The results are that the newer technology High Transfer Efficient guns are producing superior results to both HVLP and conventional technologies not just with high solid and waterborne coatings but across the range.
Business owners and managers will also want to take advantage of the technology improvements to ensure that they remain competitive in this increasingly tough market. Benefits include a reduction of costs in the form of paint and energy usage and a minimising of the harmful effects that spray painting has on our environment can all be achieved.
In short, the better the transfer efficiency, the lower the waste.
Five tips to successful spraying
1. Take a test spray: Manufacturer's claims sound good on paper, but find out exactly how a gun feels, responds and performs by testing it yourself. Factor in consumables usage when considering the costs of different gun types.
2. Air: Clean, dry air is the foundation to a good spray application. With HVLP guns, you need high volumes of air, so make sure you match your spraying requirements to your compressor purchases. Remember to factor in other air tools such as sanders and frequency of use, when calculating the size of compressor required.
3. Preparation: It is tempting as a painter, on a payroll incentive scheme, to take short-cuts in the prep but as many have found to their cost, saving time is only worthwhile until your first rectification.
4. Follow instructions: There are a whole range of fluid tip combinations depending on type of gun (conventional, HVLP, HTE) and coating. Other variables include distance, psi, cfm and gun orientation. Always follow the manufacturer's guidelines for both the paint AND the spray gun.
5. Maintenance: Dirt particles are the enemy of the spray painter. Avoid them by regularly maintaining extraction, ventilation and air supply systems. Drain all moisture traps regularly and clean spraying equipment including guns after every use, preferably using a dedicated gun washer. When cleaning your spray do not soak or immerse the body in solvent. The basic rule is solvent goes where the paint goes, air goes where the air goes and the two shall never meet inside the gun.