Material Type Matters when Selecting 2K Equipment
Plural component systems can be configured for a wide range of materials, including polyurethanes, epoxies, waterborne urethanes, conversion varnishes and fast-sets. For optimal results with your given material, you will need to select the right 2K equipment and configure it appropriately.
Polyurethanes are moisture sensitive and require a sealed system so that moisture from the atmosphere does not mix with the material. Sealed bellows pumps, diaphragm pumps, and other moisture resisting systems should be considered as well as nitrogen blankets on the supply tank. Failure to do this will cause undo wear on pump seals and can cause the catalyst to crystalize – plugging the system.
Epoxy materials are relatively easy to manage on their own but can be challenging when used in a 2K system with urethanes – for instance, an epoxy primer and a urethane topcoat. Epoxies and urethanes should never run in the same fluid path. There is no amount of flushing that will keep even the smallest amounts of residual material from reacting and plugging a system. Special 2K systems must be used and configured appropriately to ensure that these two materials never mix.
Waterborne urethanes present another challenge. The moisture-rich base material needs to be mixed with a moisture-sensitive catalyst. If this is done incorrectly, it can lead to poor performing coatings. Mixing needs to happen immediately after the two materials are combined or both materials will crystalize. To make sure the materials are mixed properly, a dynamic dosing system should be used. Additional care also needs to be taken with flushing. Side-A and Side-B must be able to clean independently of each other, since side-A should be flushed with water and side-B with solvent. Finally, it is critical that all of the moisture-sensitive catalyst is flushed from the system before it is shut down overnight.
Conversion varnishes are challenging as they use an acid-based catalyst. This acid-based catalyst will corrode standard 2K systems and so special ‘acid cat’ systems with high-grade stainless steel and PTFE seals are a must. A good system will also allow the acid to be flushed from the mixing system, including the meter, while it sits overnight to keep it in top condition.
Fast-set materials have a short pot life – oftentimes less than 15 minutes. With these materials, even brief interruptions in the painting process will very often require the mixed material line to be purged or dumped to waste – costing you money. The solution is to get a system that limits the amount of mixed material in the system to minimize costs associated with having to flush more frequently.
In some cases, standard fluid meters may need to be replaced with non-intrusive Coriolis meters. Coriolis meters measure fluid volume and flow rate without gears or other mechanical systems in the fluid path and are very accurate. Some materials may have fillers that prevent gears from moving over time. Others may be sensitive to the sheering a gear meter can introduce. Some acids can wear gear bearings and cause them to stick leading to less precision. In all of these cases, a Coriolis meter can be used to reduce maintenance and provide trouble free operation.
With the help of your Graco Distributor, you can save time and money while eliminating potential problems with you 2K materials.