Flatline Finishing Equipment
Mount Wachusett College and Wood Digest have teamed up to present a series of college-level wood technology courses. This is the 6th installment in the series of 12.
In March, one of the first statements in the article was: Sanding is the most critical step in finishing!
And it cannot be repeated enough.
The four critical components to a quality finish are:
- Sanding and surface preparation
- Equipment
- Finishing Materials
- Environmental Compliance
This month we continue with the "Equipment" section of the course, focusing on flatline finishing equipment. The May "Education In Print" article in Wood Digest will provide more in-depth information about flatline finishing.
A flatline finishing system is a long series of processing stations that may include sanding, staining, sealer and topcoat applications. As the name suggests, the primary part shapes include flat panel or part items. These items include case ends, plywood components, rails and other similar items. Items such as fully assembled chairs or cases would not work in a flatline system.
Parts travel on a horizontal conveyor belt through the flatline system application process. The number of processes it has, the type of finish applied, and drying time, governs the length of the system. Some flatline systems may be short, offering stain, sealer and topcoat operations only. The length of the system will increase if additional sanding, staining, washcoats, filler and a second topcoat are required. The drying time is directly related to the type of materials used.
Conventionally dried products (nitrocellulose lacquer, etc.) need air and/or heated ovens to dry the finish prior to subsequent operations. Catalyzed products are more durable and offer a much shorter curing time (catalyzed products cure chemically rather than by solvent evaporation with of air movement). Products cured by ultraviolet light (UV) offer the fastest drying times and the least amount of emissions. The transfer efficiency (TE) of these three product types increases as the drying times decrease. Catalyzed and UV products can offer 100 percent transfer efficiency. For these reasons, catalyzed and UV cured products are typically used in flatline systems.
ROLL OR CURTAIN COATERS
As the names suggest, the finishing material is applied to the substrate either with a roll or by conveying the part through a flowing "curtain" of material. Roll coating is accomplished using long cylinders or rolls, which transfer the material efficiently to the flat part. Curtain coaters will accomplish the same outcome as the part is conveyed through a waterfall curtain of finishing material.
AUTOMATED SPRAY GUNS
Automated spray guns, together with sensing devices, spray only the part in a controlled manner. The finishing material is uniformly applied to minimize defects and provide the "sprayed on" look to the part. Their benefits include minimum fluid use resulting in low overspray, extremely high speeds, safer working conditions for employees. Another important aspect for automatic spray guns is the quality achieved when repeatability is important. For example, consistency in coating thickness may be achieved easier with an automatic spray system than any other system. The spray guns can be adjusted to edge coat substrates, providing more coverage than roll or curtain coating machines. If the process remains uniform, the quality expectations are high. With any of the systems described above, material inconsistencies will wreak havoc. These inconsistencies include:
- Material temperature
- Material viscosity
- Speed of the production flow
- Dirt in the system
- Inconsistent compressed air
- Water in the lines
- Lack of a routine cleaning program
- Worn spray tips — lack of routine maintenance
- Insufficient liquid flow rates
- Humidity
- Moisture content in the wood
- Sanding and preparation
Try to maintain consistency and uniformity. Control as many factors as possible and your result will be a quality finish. Train your employees to troubleshoot every part of the system. Train them to understand the mechanics of a spray gun. Train them so they understand how finishing materials react with changes in temperature pressure.
TRY IT YOURSELF
To all readers and students: To explore the discussion topics above, you can follow along at home or at work. Due to the nature of information presented, it may be difficult to relate to the subject matter. Try surfing the net using the key words from this article. If you find technical information, please let the class know about them on Blackboards Discussion Board or e-mail to me.
For enrolled students: As part of your homework, chart the pros and cons of the finishing systems described above. Please take the April Wood Products Sanding and Finishing quiz, located on Blackboard. A password will be displayed to allow access. If you have any questions about Blackboard or the homework, contact me or ask a question on the Discussion section.