HTE vs HVLP vs conventional

Spray guns: special feature

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 have been around a long time and are widely used in the market place. TyHVLP (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 Some manufacturers view HVLP as old, even superseded, technology having been in the market in excess of 30 years.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. Air usages of 16 cfm and higher are most common and the low air cap pressure of 10 psi can leads to average atomisation of today's high solid paints. Operators have a tendency to increase pressures above recommended levels to increase application speeds and atomisation quality and thus create even greater problems with air consumption whilst at the same time reducing transfer efficiency
HTE (High Transfer Efficient) spray guns have, more recently, been developed to overcome the problems associated with both of the preceding technologies. Using between 9 and 12 cfm of air for a standard refinish gun both fine atomisation and application speeds are maintained and transfer efficiencies of 75 per cent to 90+ per cent are being achieved depending on paint types. Many European businesses are adopting the new technology knowing that they can meet and even exceed the strict environmental laws that apply whilst at the same time saving paint and energy in the form of reduced air consumption. Independent tests can now be performed to a new Transfer Efficiency Standard to be adopted by a number of European countries, which will mean that more consistency in supply and quality of product will become the norm rather than the exception.
Many of the leading manufacturers of spray guns have now developed models within their range that meet the specifications now generally associated with High Transfer Efficiency Spray guns.
Anest Iwata for instance, now includes a copy of the independent test certificate with each of its HTE and High TEC spray guns.
Today's coatings require a lot more care to be taken with the selection of a spray gun so that the best possible finishes can be obtained from the equipment.
Business managers will also want to take advantage of the technology improvements to ensure that they remain competitive in this increasingly tough market whilst reducing costs in the form of paint and energy usage and reducing to a minimum the harmful effects that spray painting has on our environment. The better the transfer efficiency, the lower the waste.
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. Although some excellent results are being achieved with the older HVLP and conventional technologies.

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.

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.

What is transfer efficiency?
Transfer efficiency (TE) is the amount of paint that actually hits the panel as a proportion of the total paint used. So a typical HVLP gun might allow two thirds of the paint in the cup to hit the panel. That ratio is potentially even higher with the new generation of HTE guns. Why is a higher TE good? Because more paint hitting the metal means less paint wasted and less paint in the atmosphere.