Alternative Spray Equipment for Wood Finishing
One way for wood finishers to reduce waste and save money is by increasing transfer efficiency in their operations. Simply stated, transfer efficiency measures how much finish makes it from the finish can to the surface being finished. Overspray on the floor or booth filters is considered waste.
To achieve the best transfer efficiency, study the application equipment available, then evaluate the equipment’s performance using the coating material which meets your specifications. Because each application equipment combination has its own characteristics, the advantages and disadvantages must be weighed against the coating specifications for your product. Increasing transfer efficiency will help you to meet your specified coating film thickness while spraying less paint.
Conventional Spray
In use for over 40 years, conventional spray uses air at high pressure (40 to 70 pounds per square inch [psi]) to atomize a liquefied stream of finish. A high-energy air stream very finely atomizes the finish, making it easy to apply. This yields very good finishes with high-quality visual characteristics.
Conventional spray guns have a disadvantage because they are susceptible to overspray, resulting in more waste and less transfer efficiency. Overspray uses more paint, increasing VOC emissions from the solvents in the finish.
High Transfer Efficiency Technologies
High-volume/low-pressure (HVLP)
As the name suggests, a high volume of air at low pressure is used to atomize the finish. The defined air-pressure limit for HVLP is 10 psi at the spray gun. This reduced spray gun energy level reduces overspray and improves transfer efficiency. Generally, fluid-delivery rates up to 10 ounces per minute with low viscosities will work best with the HVLP gun. HVLP may not atomize well enough to achieve an acceptable finish for every application.
Airless
This is a method of atomizing finish without using compressed air. The paint is pumped at high pressure though a small opening at the spray tip to achieve atomization. Adjustments in airless spraying are done by adjusting the viscosity of the system pressure. Many high-viscosity coatings can be applied without costly solvent thinning. Also, this method allows a heavy finish coat to be applied rapidly—useful for keeping up with fast-moving painting lines.
Air-assisted
This spraying system helps or “assists” airless systems by using supplemental air jets to guide the finish spray and boost the level of atomization. Air-assisted airless technology combines the best characteristics of both air and airless spray. Benefits include substantial material savings and reduced overspray when compared to conventional air spray, and improved transfer efficiency and finishing appearance when compared to airless technology. Air-assisted has lower fluid pressure which increases finish quality. Operator technique is also enhanced as the application rate is reduced and the operator can more easily coat the product.
Considerations When Switching to Alternative Spray Equipment
Switching to a higher transfer efficiency spray gun will require employees to learn new techniques. For example, HVLP guns may spray more slowly than conventional guns. Proper training of employees is required to adjust to the new equipment.
Companies Testing and Using Alternative Spray Equipment
Many companies have begun testing and are switching to higher transfer efficiency spray equipment. This change results in cost savings and reduced emissions.
Viking
Viking switched to an HVLP spray gun for applying sealer coat. The estimated material savings are 1,300 gallons of sealer per year, translating into a savings of $10,530. Approximately four tons of VOC emissions and two tons of HAPS are prevented annually.
Viking also switched to an air-assisted airless spray gun to apply dark stain. Although cost savings and reduced emissions data have not been collected on this process, employees at Viking have noticed reduced overspray. Adjustments in spray techniques or gun spray tip size will need to be made to ensure correct wet film application or more stain will need to be wiped off, increasing rag use.
Foldcraft Company
A MnTAP intern worked with Foldcraft Company in Kenyon, a table and seating manufacturer for restaurants, fast food chains and cafeterias, to test alternative spray equipment. The intern found that by purchasing two air-assisted airless guns and an HVLP gun, transfer efficiency could increase 29%. He determined that the new equipment could save the company a total of $9,500 per year and reduce varnish use by 33%.