The following explanation can quickly help any contractor/applicator to understand the polyurea application process, the interplay between the various pieces of equipment, and the important design considerations of the pump, hoses, and spray gun. If you want to expand your business, this knowledge will help you to understand the market.
Coatings: The Next Frontier
Polyurea is becoming more popular in many areas that were previously dominated by acrylic, epoxy, and polyurethane. It is the aliphatic polyurea compound (an open-chain, organic compound) that is increasingly being used as a coating. This is due to its excellent mechanical properties (up to 3000-psi breaking strength and 250-to 500-psi burst force); low-temp flexibility (0 to -40 C); UV stability (100% color durability superior to polyurethanes); low volatility (due 100 percent solids formation).Polyureas can adhere to substrates such as cement, brick, and fiberglass. They are used in countless building applications, including encapsulating asbestos ceilings and coating floors. Polyureas can be used in high humidity and high moisture conditions, unlike polyurethanes.
Polyureas are used in manufacturing and process industries for everything, from lining storage tanks to covering shop floors to covering plant walls. Polyureas outperform paint which is often unable to withstand the rigorous cleaning processes in food and pharmaceutical processing plants. Polyurea systems' quick reaction time of three to 10 seconds is appealing to facility managers as it allows for fast installation and minimal disruption to existing process operations.
These performance benefits are part of the reason why polyurea systems will continue to be in high demand. Garry Froese, president and owner of ArmorThane Inc. in Springfield MO, says that based on what we have learned from his association and his interactions with the applicators and manufacturers of the systems and the raw material, He says he sees a 15-20 percent increase in this industry each year." Froese, one of the first people to implement polyurea systems is uniquely qualified to offer consulting advice to contractors who are interested in this field.
It pays to have some background knowledge.
Polyurea systems are made from the combination two components: an isocyanate resin and an amine. These components combine to form a urea linking system that is flexible and unlike the rigidity of polyurethanes. Froese was a chemist when he was told that polyureas could not be sprayed. Froese accepted the challenge.Froese loves to say, "I didn’t know any better." I set out to discover what was possible. To see if there were any formulations that could be created, I first needed equipment. I called Graco, one of the first equipment manufacturers I was able to locate. Graco has been a major supplier of plural-component proportioning equipment for decades.
Froese continues, "Once we got the equipment, it worked the first time." froese says that the equipment delivered the A and B components in a consistent, predictable manner. The equipment was working correctly, which gave Froese the opportunity to improve the resin formulations.
In 1989, the first commercial spray-polyurea coating was applied to a roofing system. This markedly changed the history of coatings systems. Froese says that polyureas are only effective when properly mixed. This is why it is important to choose the right equipment for this job.
Finding the right mix is the challenge
Although no chemical catalyst is necessary, it is highly recommended that special plural equipment be used due to the rapid reactivity of the compounds and their cure. To force the components to mix, high pressure is essential. To improve the mix and atomization, high temperatures are also required. Heating occurs at the pump and hoses. However, actual mixing occurs inside the gun where both components meet at high speed. This mechanical mixing is crucial for uniform concentration and better adhesion to the substrate. It is crucial to have equipment that can spray polyureas.Froese stresses that the quality and tolerances of the equipment's manufacturing have a significant impact on the product's output. While good equipment is more expensive, this is not the time to cut corners when spraying polyurea. The proportioning pump is the key to proper processing. This is the life support system that allows for proper installation and effective application.
It All Starts at the Pump
Spraying with polyureas requires special attention. This includes the choice of a high output pump. An increase in pressure will deliver more kinetic energy into the mixing zone. Pneumatic and hydraulic pumps can be operated in either a pneumatic or hydraulic manner. Both types require an air compressor as the air drives drum pumps that transport the material. You can choose from either a horizontal or vertical layout for your pumps.The traditional choice for paint contractors is the vertical pump. Vertical pumps are not suitable for high-solid coating systems such as polyureas because they cannot fill components with different viscosities at the same speed and time. A pressure imbalance between the up- and down strokes will always be noticed. This can cause a pulsating flow in the spray gun, which can affect the spray pattern and the coating consistency.
Polyureas should be mixed under steady pressure. The quality and consistency of the spray pattern can be affected if the pressure is too low or too high. Without sufficient volume, poor mixing, atomization, and application results.
Hoses
Heating the hoses carrying the components to the gun is essential. Otherwise, all of the benefits in viscosity reduction at the pump will be lost. Polyurethane-specific hoses are not designed to withstand the high temperatures and pressures needed for spraying polyureas. The initial heating occurs within the pump. However, the hoses must keep that temperature constant throughout their length, even if they are as long as a football pitch. These requirements require specially designed Hoses.Froese stated that hoses should have a step-down in their inside diameter (ID), depending on length to reduce pressure drop at the spray gun. The ID at the pump end is greater than the ID of the hose near the gun.
The Spray Gun
There are two main types of guns: mechanical or air. This is determined by how much material is removed from the chamber during detriggering. For applications that require a high level of precision or are difficult to mix, solvent purge guns can be used.The mechanical purge spray gun is the best spray gun to apply polyurea technology. The mechanical purge spray gun seals off the mixing chamber by returning the valving rod at the detriggering. All unwanted material is removed by the tight fitting of the valving rod and the high-pressure, kinetic force of its movements.
Froese says that the mechanical purge gun produces the best mix and properties partly due to the dynamics of the mixing chamber. Froese also stated that the purge of the mixing chamber is complete, eliminating any possibility of product buildup. Hold-up can cause problems with the mixture.
Air purge guns actually blow the material out when the trigger is released between sprays. The valving rod is moved back and forth to allow air into the mixing chamber.
Air purge guns have one problem: because air is used for purging, the pressure must remain high enough to flush the chamber completely. The tip can become blocked if it is not. Air can also enter the mixing chamber, causing additional problems. The air compressor could introduce contaminants such as oil or water onto the substrate. This could lead to blistering or delamination of polyurea coatings.
Additional Gun Considerations
Gun construction and gun geometry are also important considerations. When selecting polyurea spray system, maintenance and speed are important. Operator ergonomics must also be considered. Contractors new to polyurea spraying should look for an equipment manufacturer that offers good support and is committed to keeping a stock of spare parts.Get the job done right the first time
Contractors can reap the rewards of knowing the right equipment to use when entering the field of spray polyureas. Contractors can also be put out of business by ignorance.Froese explains, "When you work in the trenches using these applicators, you can see what the consequences of poor equipment right up top bam, there is!" I know of one instance where a man did a job for a customer but two things went wrong. The contractor failed to properly prepare the surface and the equipment wasn't suitable for field application of polyurea. The customer sued the contractor several times for the loss of revenue and the cost of the coating failure.
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